目的探讨采用Ribbed股骨柄假体行人工全髋关节置换术(total hip arthroplasty,THA)的中远期疗效。方法回顾分析2006年10月—2016年5月采用Ribbed股骨柄假体行THA且获完整随访的354例(384髋)髋关节疾病患者临床资料。男171例,女183例;年...目的探讨采用Ribbed股骨柄假体行人工全髋关节置换术(total hip arthroplasty,THA)的中远期疗效。方法回顾分析2006年10月—2016年5月采用Ribbed股骨柄假体行THA且获完整随访的354例(384髋)髋关节疾病患者临床资料。男171例,女183例;年龄20~82岁,平均53.4岁。单髋324例,双髋30例。关节置换原因:股骨头缺血性坏死151例(159髋),髋关节骨关节炎134例(136髋),类风湿性关节炎43例(43髋),强直性脊柱炎20例(40髋),创伤6例(6髋)。术前患者Harris评分为(42.34±8.89)分。术后采用Harris评分评价髋关节功能;摄X线片判断双下肢是否等长、股骨侧有无透亮带、假体稳定性以及应力遮挡发生情况。结果术后切口均Ⅰ期愈合。354例患者均获随访,随访时间2~11年,平均7.4年。末次随访时Harris评分为(80.52±7.61)分,与术前比较差异有统计学意义(t=134.804,P=0.000)。术后发生2例(2髋)假体感染,3例(3髋)假体松动,4例(4髋)假体周围骨折,48例(48髋)存在轻到中度大腿疼痛。X线片示76例(78髋)股骨侧存在透亮线以及不同程度应力遮挡。按照Engh等的方法评价假体稳定性,骨长入性稳定364髋,纤维长入性稳定15髋,假体不稳定5髋。25例(25髋)发生股骨柄假体下沉,其中5例患者双下肢长度差异>10 mm。结论采用Ribbed股骨柄假体行THA具有初始稳定性好、骨长入好等优点,术后应力遮挡发生率相对较高,但对假体中远期生存率和疗效无明显影响。展开更多
Stiffening-ribbed-hollow-pipe cast-in place reinforced concrete girderless floor is a new-style hollow girderless floor system. Model experimental researches of simply-supported floor and four-corners bearing floor ha...Stiffening-ribbed-hollow-pipe cast-in place reinforced concrete girderless floor is a new-style hollow girderless floor system. Model experimental researches of simply-supported floor and four-corners bearing floor have been done on this new kind of floor system in this paper. The experiment results show that the floor system has good mechanical property such as high bearing capacity, big rigidity and good tensility. A theoretical method is presented in this paper that the stiffening-ribbed-hollow-pipe girderless floor can be analyzed by being converted equivalently to orthotropic solid slab. It is indicated that the method is correct and reasonable according to the contrast between theoretical calculated results and experimental measured results. The theoretical results coincide with the measured results well.展开更多
Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch an...Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.展开更多
In current numerical study,forced flow and heat transfer of water/NDG(Nitrogen-doped graphene)nanofluid in nanoparticles mass fractions(φ)of 0,2%and 4%at Reynolds numbers(Re)of 10,50,100 and 150 are simulated in stea...In current numerical study,forced flow and heat transfer of water/NDG(Nitrogen-doped graphene)nanofluid in nanoparticles mass fractions(φ)of 0,2%and 4%at Reynolds numbers(Re)of 10,50,100 and 150 are simulated in steady states.Studied geometry is a two-dimensional microchannel under the influence of nanofluid jet injection.Temperature of inlet fluid equals with Tc=293 K and hot source of microchannel is under the influence of oscillating heat flux.Also,in this research,the effect of the variations of attack angle of triangular rib(15°,30°,45°and 60°)on laminar nanofluid flow behavior inside the studied rectangular geometry with the ratio of L/H=28 and nanofluid jet injection is investigated.Obtained results indicate that the increase of Reynolds number,nanoparticles mass fraction and attack angle of rib leads to the increase of pressure drop.By increasing fluid viscosity,momentum depreciation of fluid in collusion with microchannel surfaces enhances.Also,the increase of attack angle of rib at higher Reynolds numbers has a great effect on this coefficient.At low Reynolds numbers,due to slow motion of fluid,variations of attack angle of rib,especially in angles of 30°,45°and 60°are almost similar.By increasing fluid velocity,the effect of the variations of attack angle on pressure drop becomes significant and pressure drop figures act differently.In general,by using heat transfer enhancement methods in studied geometry,heat transfer increases almost 25%.展开更多
A new type of cooling stave with internal ribbed tube was proposed,and the heat transfer performance of the stave was studied by means of thermal test and numerical simulation.The temperature of cooling stave was moni...A new type of cooling stave with internal ribbed tube was proposed,and the heat transfer performance of the stave was studied by means of thermal test and numerical simulation.The temperature of cooling stave was monitored in the conditions of furnace gas temperature of 200-700 C and cooling water velocity of 0.2-1.0 m/s.The thermal test results show that the internal rib structure can form swirl in the water pipe and improve the cooling capacity of the cooling stave.The higher the furnace temperature or the lower the cooling water flow rate,the more obvious the advantage of the cooling stave with internal ribbed tube.The mathematical model of the cooling stave with internal ribbed tube was established by FLUENT software,and the influence of the internal rib structure parameters on the heat transfer performance of the cooling stave was discussed.It is suggested that the parameters of the internal ribbed tube should be 4 ribs,1 mm in height,5-7 mm in width,and 20-30 mm in lead.In the same common working conditions of the cooling stave,the maximum temperature of the newly designed cooling stave with internal ribbed tube is reduced by 5.6%compared with that of common cooling stave with round tube.The water flow rate in the internal ribbed tube only needs 0.9 m/s to reach the cooling effect of 2 m/s in the common tube cooling stave,which can save 55%of water.In case of water shortage accident of cooling stave,the maximum temperature of the cooling stave with internal ribbed tube is decreased by 22.4%compared with that of common round tube,which can effectively reduce the harm of water shortage and protect the cooling stave.展开更多
For the simplified model of the internal cooling passage in the turbine blade of an aero-engine,the present study applies a newly developed turbulence modeling method,very-large eddy simulation(VLES),for analyzing rot...For the simplified model of the internal cooling passage in the turbine blade of an aero-engine,the present study applies a newly developed turbulence modeling method,very-large eddy simulation(VLES),for analyzing rotational effects on the characteristics of complex turbulent flow.For comparison,not only are the delayed detached eddy simulation(DDES)method(recognized as one of the most popular hybrid Reynolds-averaged Navier-Stokes–large eddy simulation(RANS-LES)methods)and the LES method used with the same numerical setup,but also three RANS turbulence models,including the k-ωshear stress transport(SST),standard k-ε,and Reynolds stress models,are applied to analyze the flow structure in the ribbed channel(whether rotating or stationary).Complex turbulent flows in a square ribbed channel at high Reynolds number of 100000 in the stationary state and different rotational numbers(Ro)between 0.1 and 0.4 are simulated and analyzed in detail.The comparisons show that when compared with the experimental data the VLES method works best in both the stationary and rotating states.It can capture unsteady flow characteristics such as wall shear layer separation and the vortex structure resulting from the rib disturbance.The DDES method can only capture the larger-scale vortex structures,and its predictions of the time-averaged velocity differ considerably from experiments,especially in the stationary state.With a relatively coarse grid,satisfactory prediction cannot be achieved in either rotating or stationary state by the LES method with wall-adapting local eddy-viscosity(WALE)and dynamic Smagorinsky models.The three RANS models perform poorly in both the stationary and rotating states.The results demonstrate the advantages of the VLES method in analyzing the unsteady flow characteristics in the ribbed channel at high Reynolds numbers for both stationary and rotating conditions.On that basis,the study uses the VLES method to analyze the flow evolution under different rotational numbers,and the rotational effects on the fluid mechanisms are analyzed.展开更多
The influence of different conditions on ribbed towel gourd seed germination was tested in this paper. Results showed that the seeds germinating energy and germination percentage were increased evidently under the tre...The influence of different conditions on ribbed towel gourd seed germination was tested in this paper. Results showed that the seeds germinating energy and germination percentage were increased evidently under the treatment of dipping in normal water temperature for 4 hours and drying out for 1 hour at 30℃.展开更多
The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments.Reynolds numbers studied in the channel r...The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments.Reynolds numbers studied in the channel range from 1 400 to 8 000.The ratios of rib height to hydraulic diameter (e/D) are 0.2and 0.33,respectively.The ratio of rib spacing to height (P/e) ranges from 5to 15.The rib orientations in the opposite surfaces are symmetrical and staggered arrangements.The results show that the heat transfer coefficients are increased with the increase of rib height and Reynolds number,though at the cost of higher pressure losses.When the rib spacing to height ratio is 10,it keeps the highest heat transfer coefficient in three kinds of rib spacing to height ratios 5,10 and 15.The heat transfer coefficient of symmetrical arrangement ribs is higher than that of the staggered arrangement ribs,but the pressure loss of the symmetrical arrangement ribs is larger than that of the staggered arrangement ribs.展开更多
To completely solve the problem of fatigue cracking issue of orthotropic steel bridge decks(OSDs),the authors proposed a steel–ultra-high performance concrete(UHPC)lightweight composite deck(LWCD)with closed ribs in ...To completely solve the problem of fatigue cracking issue of orthotropic steel bridge decks(OSDs),the authors proposed a steel–ultra-high performance concrete(UHPC)lightweight composite deck(LWCD)with closed ribs in 2010.Based on the successful application of that LWCD,an adaptation incorporating an innovative composite deck structure,i.e.,the hot-rolled section steel–UHPC composite deck with open ribs(SSD)is proposed in this paper,aiming to simplify the fabrication process as well as to reduce the cost of LWCD.Based on a long-span cable-stayed bridge,a design scheme is proposed and is compared with the conventional OSD scheme.Further,a finite element(FE)calculation is conducted to reflect both the global and local behavior of the SSD scheme,and it is found that the peaked stresses in the SSD components are less than the corresponding allowable values.A static test is performed for an SSD strip specimen to understand the anti-cracking behavior of the UHPC layer under negative bending moments.The static test results indicate that the UHPC layer exhibited a satisfactory tensile toughness,the UHPC tensile strength obtained from the test is 1.8 times the calculated stress by the FE model of the real bridge.In addition,the fatigue stresses of typical fatigue-prone details in the SSD are calculated and evaluated,and the influences of key design parameters on the fatigue performance of the SSD are analyzed.According to the fatigue results,the peaked stress ranges for all of the 10 fatigue-prone details are within the corresponding constant amplitude fatigue limits.Then a fatigue test is carried out for another SSD strip specimen to explore the fatigue behavior of the fillet weld between the longitudinal and transverse ribs.The specimen failed at the fillet weld after equivalent 47.5 million cycles of loading under the design fatigue stress range,indicating that the fatigue performance of the SSD could meet the fatigue design requirement.Theoretical calculations and experiments provide a basis for the promotion and application of this structure in bridge engineering.展开更多
BACKGROUND Slipping rib syndrome(SRS)is caused by abnormal subluxation of floating ribs,resulting in chronic pain and possible tissue damage.Its prevalence is often overlooked,as it shares symptoms with other musculos...BACKGROUND Slipping rib syndrome(SRS)is caused by abnormal subluxation of floating ribs,resulting in chronic pain and possible tissue damage.Its prevalence is often overlooked,as it shares symptoms with other musculoskeletal conditions,and is more common in young females and athletes.Symptoms include pain along the lower rib margin,aggravated by trunk movements,deep breathing and coughing.Treatment usually starts conservatively with physiotherapy and analgesics.In severe cases,extrapleural rib resection may be required.CASE SUMMARY In April 2023,a 24-year-old woman presented with persistent right hemithorax pain in the eleventh rib for one year.Instrumental examinations,including ultrasonography and magnetic resonance imaging,were negative for abdominal and osteochondral abnormalities.The pain intensity,rated 8/10 on the numeric rating scale(NRS),remained unresponsive to pain therapy.After a careful literature review and discussion with the patient,we opted for a minimally invasive surgical approach.Under general anesthesia,a mini-thoracotomy was performed along the anterior course of the eleventh rib.After exposure,abnormal rib mobility was detected,which led to resection of the medial margin and anchoring to the overlying rib with nonabsorbable sutures.Histological examination revealed no abnormalities.The patient was discharged on the first postoperative day.Pain decreased significantly,reaching 1/10 on the NRS at one month.At 3 months,the patient had mild fluctuating pain(2/10)requiring occasional analgesics but did not interfere with daily activities.CONCLUSION Minimally invasive rib-preserving surgery effectively reduces pain and hospitalization time,offering a valid alternative to conventional rib resection for refractory SRS.展开更多
Integrating Bayesian Optimization with Volume of Fluid (VOF) simulations, this work aims to optimize the operational conditions and geometric parameters of T-junction microchannels for target droplet sizes. Bayesian O...Integrating Bayesian Optimization with Volume of Fluid (VOF) simulations, this work aims to optimize the operational conditions and geometric parameters of T-junction microchannels for target droplet sizes. Bayesian Optimization utilizes Gaussian Process (GP) as its core model and employs an adaptive search strategy to efficiently explore and identify optimal combinations of operational parameters within a limited parameter space, thereby enabling rapid optimization of the required parameters to achieve the target droplet size. Traditional methods typically rely on manually selecting a series of operational parameters and conducting multiple simulations to gradually approach the target droplet size. This process is time-consuming and prone to getting trapped in local optima. In contrast, Bayesian Optimization adaptively adjusts its search strategy, significantly reducing computational costs and effectively exploring global optima, thus greatly improving optimization efficiency. Additionally, the study investigates the impact of rectangular rib structures within the T-junction microchannel on droplet generation, revealing how the channel geometry influences droplet formation and size. After determining the target droplet size, we further applied Bayesian Optimization to refine the rib geometry. The integration of Bayesian Optimization with computational fluid dynamics (CFD) offers a promising tool and provides new insights into the optimal design of microfluidic devices.展开更多
Squeezing phenomena can lead to severe loads in deep tunnels,especially in the presence of a low ratio of surrounding rock strength to overburden pressure.For this reason,it is highly imperative to analyze and identif...Squeezing phenomena can lead to severe loads in deep tunnels,especially in the presence of a low ratio of surrounding rock strength to overburden pressure.For this reason,it is highly imperative to analyze and identify a suitable methodology to estimate the squeezing potential and select a proper support system of rock mass.This study aims to reveal the causes of failure of Tishreen tunnel in the west of Syria and develop remediation measures accordingly so as to bring the tunnel back into service.The tunnel in question was subjected to successive failures such as buckling and spalling of side walls,floor heave,and extremely large convergence reaching the failure state of the tunnel lining.In this study,an effective way was demonstrated to evaluate the squeezing potential of the tunnel lining and appropriate modeling of the long-term response of a tunnel excavated in weak rock.Specifically,the causes of failure of Tishreen tunnel were first evaluated by empirical approaches.Then,a numerical model was developed using a timedependent constitutive model to investigate the time-dependent response of the tunnel lining.On this basis,this study proposed an effective reinforcement schemes including steel ribs,grout injection,ground anchors,and new lining of reinforced concrete.The results show that the Burger viscoplastic model simulates effectively the resulting deformation and creep behavior of squeezing ground.It is also observed that using a combined heavy support system can provide efficient control over squeezing deformation and maintain the serviceability of the tunnel under study.展开更多
Rib spalling is a highly severe issue during mining in deep-buried large-mining-height working faces.This study takes Zhaogu No.2 Coal Mine in Jiaozuo Coalfield,China,as the research background and carries out three f...Rib spalling is a highly severe issue during mining in deep-buried large-mining-height working faces.This study takes Zhaogu No.2 Coal Mine in Jiaozuo Coalfield,China,as the research background and carries out three focused works to address this problem.Firstly,field measurements were conducted to clarify rib spalling characteristics:the coal wall is dominated by shear failure,internal cracks are mainly distributed 3–6 m above the coal wall surface,and the maximum depth of crack development reaches 3 m.Secondly,Universal Distinct Element Code(UDEC)numerical simulation software was used to build a rib spalling model,with the Trigon model adopted to divide the coal wall into blocks.Analysis of four key factors shows that increased buried depth and mining height significantly raise the total length of coal wall internal cracks,increasing rib spalling risk,while higher coal body strength and support strength effectively alleviate this phenomenon.Finally,an orthogonal experiment was designed to quantitatively determine the influence degree of the four factors on rib spalling.Results show that coal body strength has the greatest impact,followed by support strength,mining height,and mining depth in order of influence.This study provides valuable theoretical guidance for on-site prevention and control of coal wall rib spalling.展开更多
Background: Reconstruction of Nasal Tip Columella (NTC) subunits is one of the most challenging aspects in functional aesthetic rhinoplasty. Moreover, racial variation for Asian nose rhinoplasty could even demand soph...Background: Reconstruction of Nasal Tip Columella (NTC) subunits is one of the most challenging aspects in functional aesthetic rhinoplasty. Moreover, racial variation for Asian nose rhinoplasty could even demand sophistication of tip and columella strut graft infrastructure enhancement. Various autogenous graft options such as 6th costal cartilage, septal cartilage and conchal cartilage are very commonly considered whilst the 10th costal cartilage is scarcely reported. Objective and Method: The purpose of this manuscript is to illustrate the detailed operative steps to harvest the 10th costal cartilage for infrastructural grafting at NTC subunits by a case illustration. The pros and cons of different cartilage options will be discussed, particularly its application in cleft nose rhinoplasty in Chinese patient. We have adopted the 10th rib as the key option for NTC reconstruction in 11 cases of Chinese cleft secondary rhinoplasty since 2019 and have achieved good and stable results without complications. Conclusion: The 10th costal cartilage is one of the best options in Nasal Tip Columella subunits reconstruction, particularly in complex cleft nose or failure revision aesthetic rhinoplasty cases, due to its safety of harvesting, and the sufficient quality and quantity of grafting materials it provides for simultaneous adjunctive augmentation purpose.展开更多
Objective:To compare the diagnostic value of 99mTc-MDP SPECT/CT and MSCT in detecting thoracic wall and rib involvement in lung adenocarcinoma.Methods:A retrospective analysis was conducted on the imaging data of 78 t...Objective:To compare the diagnostic value of 99mTc-MDP SPECT/CT and MSCT in detecting thoracic wall and rib involvement in lung adenocarcinoma.Methods:A retrospective analysis was conducted on the imaging data of 78 thoracic wall and rib lesions from 66 patients,a total of 32 males and 34 females,aged(53.2±5.6)years old with pathologically confirmed lung adenocarcinoma who underwent both 99mTc-MDP SPECT/CT and MSCT examinations from March 2017 to September 2023.The diagnostic efficacy of the two imaging modalities was compared using pathological confirmation or clinical follow-up as the gold standard.Results:Pathological confirmation or clinical follow-up revealed 74 lesions with thoracic wall bone involvement in lung adenocarcinoma(20 lesions confirmed by surgical pathology and 54 lesions confirmed by clinical follow-up)and 4 lesions without thoracic wall or rib involvement(2 lesions confirmed by surgical pathology and 2 lesions confirmed by clinical follow-up).The diagnostic sensitivity,specificity,and accuracy of 99mTc-MDP SPECT/CT were 97.3%,50.0%,and 94.9%,respectively.Its diagnostic sensitivity and accuracy were higher than those of MSCT(72.3%and 74.4%,respectively),with statistically significant differences(P<0.05).The specificity of 99mTc-MDP SPECT/CT was lower than that of MSCT(100.0%),but the difference was not statistically significant(P<0.05).There were no statistically significant differences in the positive predictive value and negative predictive value between 99mTc-MDP SPECT/CT and MSCT(P>0.05).99mTc-MDP SPECT/CT examination revised the MSCT tumor staging in 14 patients[21.2%(14/66)]with lung adenocarcinoma.Conclusion:99mTc-MDP SPECT/CT imaging demonstrates superior diagnostic efficacy compared to MSCT in detecting thoracic wall and rib involvement in lung adenocarcinoma.It offers more accurate tumor staging than MSCT,and an accurate diagnosis aids in clinical treatment decision-making.展开更多
The mass transport and ohmic losses in proton exchange membrane fuel cells(PEMFCs)is significantly influenced by the channel to rib width ratio(CRWR),particularly when accounting for the interfacial contact resistance...The mass transport and ohmic losses in proton exchange membrane fuel cells(PEMFCs)is significantly influenced by the channel to rib width ratio(CRWR),particularly when accounting for the interfacial contact resistance between bipolar plates(BPs)and gas diffusion layers(GDLs)(ICRBP-GDL).Both the determination of the optimal CRWR value and the development of an efficient flow field structure are significantly influenced by ICRBP-GDLs.To investigate this,three-dimensional numerical models were developed,revealing that selecting an optimal CRWR tailored to specific ICRBP-GDL values can effectively balance mass transport and ohmic losses.Building on this insight,a novel island two-dimensional flow field design is proposed,demonstrating the ability to enhance oxygen transport to the catalyst layer(CL)and achieve a more uniform oxygen distribution without increasing ohmic losses.Compared to conventional straight and serpentine flow fields,the island flow field improves output power density by 4.5%and 3.5%,respectively,while reducing the liquid water coverage ratio by 30%.Additionally,the study identifies optimal CRWR values for conventional flow fields corresponding to ICRBP-GDLs of 2.5,5,10,20,and 40 mΩ·cm^(2) as 1.5,1.5,1.0,0.67,and 0.43,respectively.For the island flow field,the optimal CRWRs are consistently smaller-1.5,1.0,0.67,0.43,and 0.43-due to its superior mass transfer capability.This work provides a valuable framework for optimizing flow field designs to achieve improved PEMFC performance.展开更多
The admittance features representing the physical attributes are used as the in termediates to extract the materialattributesrelated impact sound features of ribbed plates. Firstly, the admittance feature representati...The admittance features representing the physical attributes are used as the in termediates to extract the materialattributesrelated impact sound features of ribbed plates. Firstly, the admittance feature representations of metal ribbed plates attributes are obtained and the relationship between the admittance features and the impact sound features are established via correlation analysis method. Then, materialattributesrelated impact sound features are obtained indirectly. Finally, the performances of different sound features for the material recognition of ribbedmetal plates are verified through the Support Vector Machine classifier. The results indicate that the obtained four sets of features can effectively identify the materials of the metal ribbed plates, while the accuracy of a single feature depends on the separable degree of the corresponding material attribute. And the features extracted based on admittance functions have higher average accuracy than that of timbre features. Therefore, the proposed sound feature extraction method based on admittance features is valid, and the extracted sound features can effectively reflect the physical attributes.展开更多
Heat transfer and turbulent flow characteristics between the ribbed plates have been numerically studied in the present paper.The ribs with the rectangular cross-section have been placed on the top and the bottom plat...Heat transfer and turbulent flow characteristics between the ribbed plates have been numerically studied in the present paper.The ribs with the rectangular cross-section have been placed on the top and the bottom plates of the duct,symmetrically.It is assumed that the fluid at 300 K has entered the system while the walls kept at 400 K.All numerical analyses have been performed by k-ωShear Stress Transport(SST)turbulence model for Re=10000,15000 and 20000.For the fixed rib width,the dimensionless height and the dimensionless spacing have been respectively varied as 0.1≤h’≤0.3 and 0.5≤S’≤1,and the results have been compared with the ones of the smooth plate.Even though there are twenty-seven cases obtained as a result of parametric combinations,the number of various cases has been reduced from twenty-seven to only nine different variations by applying the Taguchi method.Furthermore,the effects of all the considered parameters on the heat transfer and flow characteristics have been determined in terms of the influence degree.The optimum parameters for Nusselt number and pressure loss have been ascertained individually.What is more,the almost exact values for Nusselt number and pressure loss have also been attained by the confirmation test having an error percentage of 6%.The most dominant factor has been determined as the rib height due to its effect on both heat transfer and flow characteristics.Similarly,with respect to the numerical results,increasing the rib height,the rib spacing and Reynolds number has separately increased Nusselt number.Nevertheless,symmetrical flow structure has been disturbed as a result of ascending the rib height as clearly seen for h’=0.3 from the charts.In the meantime,pressure loss has been augmented owing to the increment of the geometrical parameters and also Reynolds number.h’=0.1 with S’=0.5 at Re=10000,h’=0.2 with S’=0.5 at Re=15000 and h’=0.1 with S’=0.75 at Re=15000 can be suggested for the heat transfer enhancement since the pressure loss of the system is tolerated.展开更多
This paper presents results of a numerical investigation of heat transfer and flow pattern characteristics of a channel with repeated ribs on one broad wall. Numerical computations are performed for seven ribs placed ...This paper presents results of a numerical investigation of heat transfer and flow pattern characteristics of a channel with repeated ribs on one broad wall. Numerical computations are performed for seven ribs placed on the bottom wall of a channel for Reynolds numbers ranging from 10,000 to 30,000. The newly modified ribs (the ones with convex pointing upstream/downstream rib, wedge pointing upstream/downstream rib, concave pointing upstream/downstream rib and also concave-concave rib as well as convex-concave rib), are proposed for simulation with prospect to reduce flow separation and extend reattachment area compared to the unmodified square rib. The numerical results are reported in forms of flow structure, temperature field, turbulent kinetic energy, Nusselt number, friction factor and thermal enhancement factor. The results indicate the rib with concave-concave surfaces efficiently suppresses flow separation bubble in the corner of the rib and induces large recirculation zone over those of the others, hence giving the highest Nusselt number and friction factor. On the other hand, the one with convex-concave surface provides the lowest friction factor with moderate Nusselt number. Due to the prominent effect of its low friction factor, the rib with convex-concave surface offers the highest thermal enhancement factor of 1.19.展开更多
文摘目的探讨采用Ribbed股骨柄假体行人工全髋关节置换术(total hip arthroplasty,THA)的中远期疗效。方法回顾分析2006年10月—2016年5月采用Ribbed股骨柄假体行THA且获完整随访的354例(384髋)髋关节疾病患者临床资料。男171例,女183例;年龄20~82岁,平均53.4岁。单髋324例,双髋30例。关节置换原因:股骨头缺血性坏死151例(159髋),髋关节骨关节炎134例(136髋),类风湿性关节炎43例(43髋),强直性脊柱炎20例(40髋),创伤6例(6髋)。术前患者Harris评分为(42.34±8.89)分。术后采用Harris评分评价髋关节功能;摄X线片判断双下肢是否等长、股骨侧有无透亮带、假体稳定性以及应力遮挡发生情况。结果术后切口均Ⅰ期愈合。354例患者均获随访,随访时间2~11年,平均7.4年。末次随访时Harris评分为(80.52±7.61)分,与术前比较差异有统计学意义(t=134.804,P=0.000)。术后发生2例(2髋)假体感染,3例(3髋)假体松动,4例(4髋)假体周围骨折,48例(48髋)存在轻到中度大腿疼痛。X线片示76例(78髋)股骨侧存在透亮线以及不同程度应力遮挡。按照Engh等的方法评价假体稳定性,骨长入性稳定364髋,纤维长入性稳定15髋,假体不稳定5髋。25例(25髋)发生股骨柄假体下沉,其中5例患者双下肢长度差异>10 mm。结论采用Ribbed股骨柄假体行THA具有初始稳定性好、骨长入好等优点,术后应力遮挡发生率相对较高,但对假体中远期生存率和疗效无明显影响。
文摘Stiffening-ribbed-hollow-pipe cast-in place reinforced concrete girderless floor is a new-style hollow girderless floor system. Model experimental researches of simply-supported floor and four-corners bearing floor have been done on this new kind of floor system in this paper. The experiment results show that the floor system has good mechanical property such as high bearing capacity, big rigidity and good tensility. A theoretical method is presented in this paper that the stiffening-ribbed-hollow-pipe girderless floor can be analyzed by being converted equivalently to orthotropic solid slab. It is indicated that the method is correct and reasonable according to the contrast between theoretical calculated results and experimental measured results. The theoretical results coincide with the measured results well.
基金Supported by the National Natural Science Foundation of China(11472093 and21276056)
文摘Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.
文摘In current numerical study,forced flow and heat transfer of water/NDG(Nitrogen-doped graphene)nanofluid in nanoparticles mass fractions(φ)of 0,2%and 4%at Reynolds numbers(Re)of 10,50,100 and 150 are simulated in steady states.Studied geometry is a two-dimensional microchannel under the influence of nanofluid jet injection.Temperature of inlet fluid equals with Tc=293 K and hot source of microchannel is under the influence of oscillating heat flux.Also,in this research,the effect of the variations of attack angle of triangular rib(15°,30°,45°and 60°)on laminar nanofluid flow behavior inside the studied rectangular geometry with the ratio of L/H=28 and nanofluid jet injection is investigated.Obtained results indicate that the increase of Reynolds number,nanoparticles mass fraction and attack angle of rib leads to the increase of pressure drop.By increasing fluid viscosity,momentum depreciation of fluid in collusion with microchannel surfaces enhances.Also,the increase of attack angle of rib at higher Reynolds numbers has a great effect on this coefficient.At low Reynolds numbers,due to slow motion of fluid,variations of attack angle of rib,especially in angles of 30°,45°and 60°are almost similar.By increasing fluid velocity,the effect of the variations of attack angle on pressure drop becomes significant and pressure drop figures act differently.In general,by using heat transfer enhancement methods in studied geometry,heat transfer increases almost 25%.
基金funded by the National Natural Science Foundation of China(51574179)Nantong Science and Technology Project(JC2019154).
文摘A new type of cooling stave with internal ribbed tube was proposed,and the heat transfer performance of the stave was studied by means of thermal test and numerical simulation.The temperature of cooling stave was monitored in the conditions of furnace gas temperature of 200-700 C and cooling water velocity of 0.2-1.0 m/s.The thermal test results show that the internal rib structure can form swirl in the water pipe and improve the cooling capacity of the cooling stave.The higher the furnace temperature or the lower the cooling water flow rate,the more obvious the advantage of the cooling stave with internal ribbed tube.The mathematical model of the cooling stave with internal ribbed tube was established by FLUENT software,and the influence of the internal rib structure parameters on the heat transfer performance of the cooling stave was discussed.It is suggested that the parameters of the internal ribbed tube should be 4 ribs,1 mm in height,5-7 mm in width,and 20-30 mm in lead.In the same common working conditions of the cooling stave,the maximum temperature of the newly designed cooling stave with internal ribbed tube is reduced by 5.6%compared with that of common cooling stave with round tube.The water flow rate in the internal ribbed tube only needs 0.9 m/s to reach the cooling effect of 2 m/s in the common tube cooling stave,which can save 55%of water.In case of water shortage accident of cooling stave,the maximum temperature of the cooling stave with internal ribbed tube is decreased by 22.4%compared with that of common round tube,which can effectively reduce the harm of water shortage and protect the cooling stave.
基金the National Natural Science Foundation of China(No.91841302)the Jiangsu Provincial Natural Science Foundation of China(No.BK20200069)+1 种基金the Shanghai Academy of Spaceflight Technology(SAST)Innovation Fundthe Fundamental Research Funds for the Central Universities,China。
文摘For the simplified model of the internal cooling passage in the turbine blade of an aero-engine,the present study applies a newly developed turbulence modeling method,very-large eddy simulation(VLES),for analyzing rotational effects on the characteristics of complex turbulent flow.For comparison,not only are the delayed detached eddy simulation(DDES)method(recognized as one of the most popular hybrid Reynolds-averaged Navier-Stokes–large eddy simulation(RANS-LES)methods)and the LES method used with the same numerical setup,but also three RANS turbulence models,including the k-ωshear stress transport(SST),standard k-ε,and Reynolds stress models,are applied to analyze the flow structure in the ribbed channel(whether rotating or stationary).Complex turbulent flows in a square ribbed channel at high Reynolds number of 100000 in the stationary state and different rotational numbers(Ro)between 0.1 and 0.4 are simulated and analyzed in detail.The comparisons show that when compared with the experimental data the VLES method works best in both the stationary and rotating states.It can capture unsteady flow characteristics such as wall shear layer separation and the vortex structure resulting from the rib disturbance.The DDES method can only capture the larger-scale vortex structures,and its predictions of the time-averaged velocity differ considerably from experiments,especially in the stationary state.With a relatively coarse grid,satisfactory prediction cannot be achieved in either rotating or stationary state by the LES method with wall-adapting local eddy-viscosity(WALE)and dynamic Smagorinsky models.The three RANS models perform poorly in both the stationary and rotating states.The results demonstrate the advantages of the VLES method in analyzing the unsteady flow characteristics in the ribbed channel at high Reynolds numbers for both stationary and rotating conditions.On that basis,the study uses the VLES method to analyze the flow evolution under different rotational numbers,and the rotational effects on the fluid mechanisms are analyzed.
文摘The influence of different conditions on ribbed towel gourd seed germination was tested in this paper. Results showed that the seeds germinating energy and germination percentage were increased evidently under the treatment of dipping in normal water temperature for 4 hours and drying out for 1 hour at 30℃.
基金supported by the National Natural Science Foundation of China(No.51276088)
文摘The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments.Reynolds numbers studied in the channel range from 1 400 to 8 000.The ratios of rib height to hydraulic diameter (e/D) are 0.2and 0.33,respectively.The ratio of rib spacing to height (P/e) ranges from 5to 15.The rib orientations in the opposite surfaces are symmetrical and staggered arrangements.The results show that the heat transfer coefficients are increased with the increase of rib height and Reynolds number,though at the cost of higher pressure losses.When the rib spacing to height ratio is 10,it keeps the highest heat transfer coefficient in three kinds of rib spacing to height ratios 5,10 and 15.The heat transfer coefficient of symmetrical arrangement ribs is higher than that of the staggered arrangement ribs,but the pressure loss of the symmetrical arrangement ribs is larger than that of the staggered arrangement ribs.
基金The authors gratefully thank the National Natural Science Foundation of China(Grant Nos.52038003 and 51778223)Technology R&D Plan of China Construction Fifth Engineering Division Co.,Ltd.(No.CSCES5b-2022-12)for their financial support.
文摘To completely solve the problem of fatigue cracking issue of orthotropic steel bridge decks(OSDs),the authors proposed a steel–ultra-high performance concrete(UHPC)lightweight composite deck(LWCD)with closed ribs in 2010.Based on the successful application of that LWCD,an adaptation incorporating an innovative composite deck structure,i.e.,the hot-rolled section steel–UHPC composite deck with open ribs(SSD)is proposed in this paper,aiming to simplify the fabrication process as well as to reduce the cost of LWCD.Based on a long-span cable-stayed bridge,a design scheme is proposed and is compared with the conventional OSD scheme.Further,a finite element(FE)calculation is conducted to reflect both the global and local behavior of the SSD scheme,and it is found that the peaked stresses in the SSD components are less than the corresponding allowable values.A static test is performed for an SSD strip specimen to understand the anti-cracking behavior of the UHPC layer under negative bending moments.The static test results indicate that the UHPC layer exhibited a satisfactory tensile toughness,the UHPC tensile strength obtained from the test is 1.8 times the calculated stress by the FE model of the real bridge.In addition,the fatigue stresses of typical fatigue-prone details in the SSD are calculated and evaluated,and the influences of key design parameters on the fatigue performance of the SSD are analyzed.According to the fatigue results,the peaked stress ranges for all of the 10 fatigue-prone details are within the corresponding constant amplitude fatigue limits.Then a fatigue test is carried out for another SSD strip specimen to explore the fatigue behavior of the fillet weld between the longitudinal and transverse ribs.The specimen failed at the fillet weld after equivalent 47.5 million cycles of loading under the design fatigue stress range,indicating that the fatigue performance of the SSD could meet the fatigue design requirement.Theoretical calculations and experiments provide a basis for the promotion and application of this structure in bridge engineering.
文摘BACKGROUND Slipping rib syndrome(SRS)is caused by abnormal subluxation of floating ribs,resulting in chronic pain and possible tissue damage.Its prevalence is often overlooked,as it shares symptoms with other musculoskeletal conditions,and is more common in young females and athletes.Symptoms include pain along the lower rib margin,aggravated by trunk movements,deep breathing and coughing.Treatment usually starts conservatively with physiotherapy and analgesics.In severe cases,extrapleural rib resection may be required.CASE SUMMARY In April 2023,a 24-year-old woman presented with persistent right hemithorax pain in the eleventh rib for one year.Instrumental examinations,including ultrasonography and magnetic resonance imaging,were negative for abdominal and osteochondral abnormalities.The pain intensity,rated 8/10 on the numeric rating scale(NRS),remained unresponsive to pain therapy.After a careful literature review and discussion with the patient,we opted for a minimally invasive surgical approach.Under general anesthesia,a mini-thoracotomy was performed along the anterior course of the eleventh rib.After exposure,abnormal rib mobility was detected,which led to resection of the medial margin and anchoring to the overlying rib with nonabsorbable sutures.Histological examination revealed no abnormalities.The patient was discharged on the first postoperative day.Pain decreased significantly,reaching 1/10 on the NRS at one month.At 3 months,the patient had mild fluctuating pain(2/10)requiring occasional analgesics but did not interfere with daily activities.CONCLUSION Minimally invasive rib-preserving surgery effectively reduces pain and hospitalization time,offering a valid alternative to conventional rib resection for refractory SRS.
基金support from National Key Research and Development Program of China(2023YFC3905400)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA0490102)National Natural Science Foundation of China(22178354,2242100322408374).
文摘Integrating Bayesian Optimization with Volume of Fluid (VOF) simulations, this work aims to optimize the operational conditions and geometric parameters of T-junction microchannels for target droplet sizes. Bayesian Optimization utilizes Gaussian Process (GP) as its core model and employs an adaptive search strategy to efficiently explore and identify optimal combinations of operational parameters within a limited parameter space, thereby enabling rapid optimization of the required parameters to achieve the target droplet size. Traditional methods typically rely on manually selecting a series of operational parameters and conducting multiple simulations to gradually approach the target droplet size. This process is time-consuming and prone to getting trapped in local optima. In contrast, Bayesian Optimization adaptively adjusts its search strategy, significantly reducing computational costs and effectively exploring global optima, thus greatly improving optimization efficiency. Additionally, the study investigates the impact of rectangular rib structures within the T-junction microchannel on droplet generation, revealing how the channel geometry influences droplet formation and size. After determining the target droplet size, we further applied Bayesian Optimization to refine the rib geometry. The integration of Bayesian Optimization with computational fluid dynamics (CFD) offers a promising tool and provides new insights into the optimal design of microfluidic devices.
文摘Squeezing phenomena can lead to severe loads in deep tunnels,especially in the presence of a low ratio of surrounding rock strength to overburden pressure.For this reason,it is highly imperative to analyze and identify a suitable methodology to estimate the squeezing potential and select a proper support system of rock mass.This study aims to reveal the causes of failure of Tishreen tunnel in the west of Syria and develop remediation measures accordingly so as to bring the tunnel back into service.The tunnel in question was subjected to successive failures such as buckling and spalling of side walls,floor heave,and extremely large convergence reaching the failure state of the tunnel lining.In this study,an effective way was demonstrated to evaluate the squeezing potential of the tunnel lining and appropriate modeling of the long-term response of a tunnel excavated in weak rock.Specifically,the causes of failure of Tishreen tunnel were first evaluated by empirical approaches.Then,a numerical model was developed using a timedependent constitutive model to investigate the time-dependent response of the tunnel lining.On this basis,this study proposed an effective reinforcement schemes including steel ribs,grout injection,ground anchors,and new lining of reinforced concrete.The results show that the Burger viscoplastic model simulates effectively the resulting deformation and creep behavior of squeezing ground.It is also observed that using a combined heavy support system can provide efficient control over squeezing deformation and maintain the serviceability of the tunnel under study.
基金supported by the National Key Research and Development Program of China(No.2023YFC2907501)the National Natural Science Foundation of China(No.52374106)+1 种基金the China Postdoctoral Science Foundation(Grant no.2024T171006)the National Natural Science Foundation of China(Grant no.52204163).
文摘Rib spalling is a highly severe issue during mining in deep-buried large-mining-height working faces.This study takes Zhaogu No.2 Coal Mine in Jiaozuo Coalfield,China,as the research background and carries out three focused works to address this problem.Firstly,field measurements were conducted to clarify rib spalling characteristics:the coal wall is dominated by shear failure,internal cracks are mainly distributed 3–6 m above the coal wall surface,and the maximum depth of crack development reaches 3 m.Secondly,Universal Distinct Element Code(UDEC)numerical simulation software was used to build a rib spalling model,with the Trigon model adopted to divide the coal wall into blocks.Analysis of four key factors shows that increased buried depth and mining height significantly raise the total length of coal wall internal cracks,increasing rib spalling risk,while higher coal body strength and support strength effectively alleviate this phenomenon.Finally,an orthogonal experiment was designed to quantitatively determine the influence degree of the four factors on rib spalling.Results show that coal body strength has the greatest impact,followed by support strength,mining height,and mining depth in order of influence.This study provides valuable theoretical guidance for on-site prevention and control of coal wall rib spalling.
文摘Background: Reconstruction of Nasal Tip Columella (NTC) subunits is one of the most challenging aspects in functional aesthetic rhinoplasty. Moreover, racial variation for Asian nose rhinoplasty could even demand sophistication of tip and columella strut graft infrastructure enhancement. Various autogenous graft options such as 6th costal cartilage, septal cartilage and conchal cartilage are very commonly considered whilst the 10th costal cartilage is scarcely reported. Objective and Method: The purpose of this manuscript is to illustrate the detailed operative steps to harvest the 10th costal cartilage for infrastructural grafting at NTC subunits by a case illustration. The pros and cons of different cartilage options will be discussed, particularly its application in cleft nose rhinoplasty in Chinese patient. We have adopted the 10th rib as the key option for NTC reconstruction in 11 cases of Chinese cleft secondary rhinoplasty since 2019 and have achieved good and stable results without complications. Conclusion: The 10th costal cartilage is one of the best options in Nasal Tip Columella subunits reconstruction, particularly in complex cleft nose or failure revision aesthetic rhinoplasty cases, due to its safety of harvesting, and the sufficient quality and quantity of grafting materials it provides for simultaneous adjunctive augmentation purpose.
文摘Objective:To compare the diagnostic value of 99mTc-MDP SPECT/CT and MSCT in detecting thoracic wall and rib involvement in lung adenocarcinoma.Methods:A retrospective analysis was conducted on the imaging data of 78 thoracic wall and rib lesions from 66 patients,a total of 32 males and 34 females,aged(53.2±5.6)years old with pathologically confirmed lung adenocarcinoma who underwent both 99mTc-MDP SPECT/CT and MSCT examinations from March 2017 to September 2023.The diagnostic efficacy of the two imaging modalities was compared using pathological confirmation or clinical follow-up as the gold standard.Results:Pathological confirmation or clinical follow-up revealed 74 lesions with thoracic wall bone involvement in lung adenocarcinoma(20 lesions confirmed by surgical pathology and 54 lesions confirmed by clinical follow-up)and 4 lesions without thoracic wall or rib involvement(2 lesions confirmed by surgical pathology and 2 lesions confirmed by clinical follow-up).The diagnostic sensitivity,specificity,and accuracy of 99mTc-MDP SPECT/CT were 97.3%,50.0%,and 94.9%,respectively.Its diagnostic sensitivity and accuracy were higher than those of MSCT(72.3%and 74.4%,respectively),with statistically significant differences(P<0.05).The specificity of 99mTc-MDP SPECT/CT was lower than that of MSCT(100.0%),but the difference was not statistically significant(P<0.05).There were no statistically significant differences in the positive predictive value and negative predictive value between 99mTc-MDP SPECT/CT and MSCT(P>0.05).99mTc-MDP SPECT/CT examination revised the MSCT tumor staging in 14 patients[21.2%(14/66)]with lung adenocarcinoma.Conclusion:99mTc-MDP SPECT/CT imaging demonstrates superior diagnostic efficacy compared to MSCT in detecting thoracic wall and rib involvement in lung adenocarcinoma.It offers more accurate tumor staging than MSCT,and an accurate diagnosis aids in clinical treatment decision-making.
基金the financial support of Natural Science Foundation of Hunan Province(2023JJ40261).
文摘The mass transport and ohmic losses in proton exchange membrane fuel cells(PEMFCs)is significantly influenced by the channel to rib width ratio(CRWR),particularly when accounting for the interfacial contact resistance between bipolar plates(BPs)and gas diffusion layers(GDLs)(ICRBP-GDL).Both the determination of the optimal CRWR value and the development of an efficient flow field structure are significantly influenced by ICRBP-GDLs.To investigate this,three-dimensional numerical models were developed,revealing that selecting an optimal CRWR tailored to specific ICRBP-GDL values can effectively balance mass transport and ohmic losses.Building on this insight,a novel island two-dimensional flow field design is proposed,demonstrating the ability to enhance oxygen transport to the catalyst layer(CL)and achieve a more uniform oxygen distribution without increasing ohmic losses.Compared to conventional straight and serpentine flow fields,the island flow field improves output power density by 4.5%and 3.5%,respectively,while reducing the liquid water coverage ratio by 30%.Additionally,the study identifies optimal CRWR values for conventional flow fields corresponding to ICRBP-GDLs of 2.5,5,10,20,and 40 mΩ·cm^(2) as 1.5,1.5,1.0,0.67,and 0.43,respectively.For the island flow field,the optimal CRWRs are consistently smaller-1.5,1.0,0.67,0.43,and 0.43-due to its superior mass transfer capability.This work provides a valuable framework for optimizing flow field designs to achieve improved PEMFC performance.
基金supported by the National Natural Science Foundation of China(11574249)the Aeronautical Science Foundation of China(20131553018)
文摘The admittance features representing the physical attributes are used as the in termediates to extract the materialattributesrelated impact sound features of ribbed plates. Firstly, the admittance feature representations of metal ribbed plates attributes are obtained and the relationship between the admittance features and the impact sound features are established via correlation analysis method. Then, materialattributesrelated impact sound features are obtained indirectly. Finally, the performances of different sound features for the material recognition of ribbedmetal plates are verified through the Support Vector Machine classifier. The results indicate that the obtained four sets of features can effectively identify the materials of the metal ribbed plates, while the accuracy of a single feature depends on the separable degree of the corresponding material attribute. And the features extracted based on admittance functions have higher average accuracy than that of timbre features. Therefore, the proposed sound feature extraction method based on admittance features is valid, and the extracted sound features can effectively reflect the physical attributes.
基金2015-OYP-007 of Selcuk University Academic Staff Training Program(OYP)。
文摘Heat transfer and turbulent flow characteristics between the ribbed plates have been numerically studied in the present paper.The ribs with the rectangular cross-section have been placed on the top and the bottom plates of the duct,symmetrically.It is assumed that the fluid at 300 K has entered the system while the walls kept at 400 K.All numerical analyses have been performed by k-ωShear Stress Transport(SST)turbulence model for Re=10000,15000 and 20000.For the fixed rib width,the dimensionless height and the dimensionless spacing have been respectively varied as 0.1≤h’≤0.3 and 0.5≤S’≤1,and the results have been compared with the ones of the smooth plate.Even though there are twenty-seven cases obtained as a result of parametric combinations,the number of various cases has been reduced from twenty-seven to only nine different variations by applying the Taguchi method.Furthermore,the effects of all the considered parameters on the heat transfer and flow characteristics have been determined in terms of the influence degree.The optimum parameters for Nusselt number and pressure loss have been ascertained individually.What is more,the almost exact values for Nusselt number and pressure loss have also been attained by the confirmation test having an error percentage of 6%.The most dominant factor has been determined as the rib height due to its effect on both heat transfer and flow characteristics.Similarly,with respect to the numerical results,increasing the rib height,the rib spacing and Reynolds number has separately increased Nusselt number.Nevertheless,symmetrical flow structure has been disturbed as a result of ascending the rib height as clearly seen for h’=0.3 from the charts.In the meantime,pressure loss has been augmented owing to the increment of the geometrical parameters and also Reynolds number.h’=0.1 with S’=0.5 at Re=10000,h’=0.2 with S’=0.5 at Re=15000 and h’=0.1 with S’=0.75 at Re=15000 can be suggested for the heat transfer enhancement since the pressure loss of the system is tolerated.
文摘This paper presents results of a numerical investigation of heat transfer and flow pattern characteristics of a channel with repeated ribs on one broad wall. Numerical computations are performed for seven ribs placed on the bottom wall of a channel for Reynolds numbers ranging from 10,000 to 30,000. The newly modified ribs (the ones with convex pointing upstream/downstream rib, wedge pointing upstream/downstream rib, concave pointing upstream/downstream rib and also concave-concave rib as well as convex-concave rib), are proposed for simulation with prospect to reduce flow separation and extend reattachment area compared to the unmodified square rib. The numerical results are reported in forms of flow structure, temperature field, turbulent kinetic energy, Nusselt number, friction factor and thermal enhancement factor. The results indicate the rib with concave-concave surfaces efficiently suppresses flow separation bubble in the corner of the rib and induces large recirculation zone over those of the others, hence giving the highest Nusselt number and friction factor. On the other hand, the one with convex-concave surface provides the lowest friction factor with moderate Nusselt number. Due to the prominent effect of its low friction factor, the rib with convex-concave surface offers the highest thermal enhancement factor of 1.19.
