This study develops an analytical model to evaluate the cooling performance of a porous terracotta tubular direct evaporative heat and mass exchanger. By combining energy and mass balance equations with heat and mass ...This study develops an analytical model to evaluate the cooling performance of a porous terracotta tubular direct evaporative heat and mass exchanger. By combining energy and mass balance equations with heat and mass transfer coefficients and air psychrometric correlations, the model provides insights into the impact of design and operational parameters on the exchanger cooling performance. Validated against an established numerical model, it accurately simulates cooling behavior with a Root Mean Square Deviation of 0.43 - 1.18˚C under varying inlet air conditions. The results show that tube geometry, including equivalent diameter, flatness ratio, and length significantly influences cooling outcomes. Smaller diameters enhance wet-bulb effectiveness but reduce cooling capacity, while increased flatness and length improve both. For example, extending the flatness ratio of a 15 mm diameter, 0.6 m long tube from 1 (circular) to 4 raises the exchange surface area from 0.028 to 0.037 m2, increasing wet-bulb effectiveness from 60% to 71%. Recommended diameters range from 5 mm for tubes under 0.5 m to 1 cm for tubes 0.5 to 1 m in length. Optimal air velocities depend on tube length: 1 m/s for tubes under 0.8 m, 1.5 m/s for lengths of 0.8 to 1.2 m, and up to 2 m/s for longer tubes. This model offers a practical alternative to complex numerical and CFD methods, with potential applications in cooling tower optimization for thermal and nuclear power plants and geothermal heat exchangers.展开更多
The objective of the present study is to investigate the efficiency of indirect adiabatic chiller-based cooling system efficiency dependence of outdoor air humidity. The system is located in historical building, in te...The objective of the present study is to investigate the efficiency of indirect adiabatic chiller-based cooling system efficiency dependence of outdoor air humidity. The system is located in historical building, in temperate climate of Latvia. The data about electricity consumption, water consumption, chiller operation stages, cooling average temperatures and outdoor air parameters have been acquired for the period of 2.5 month, during the cooling season. Using data collected by BACnet based BMS controllers and adiabatic chiller control system, we have analyzed operation efficiency of the chiller and its dependence of outdoor air humidity. Data range for the period from August 1st till October 13th, 2011 was taken for deeper analysis, which showed that in temperature range 22.0 ± 0.5 ℃ for the studied period of time chiller＇s COP is slightly dependent on the outdoor air moisture.展开更多
An overview of the development and current status of the directional solidification process assisted by liquid metal cooling （LMC） has been presented in this paper. The driving force of the rapid development of the ...An overview of the development and current status of the directional solidification process assisted by liquid metal cooling （LMC） has been presented in this paper. The driving force of the rapid development of the LMC process has been analyzed by considering the demands of （1） newer technologies that can provide higher thermal gradients for alleviated segregation in advanced alloy systems, and （2） better production yield of the large directionally solidified superalloy components. The brief history of the industrialization of the LMC process has been reviewed, followed by the discussion on the LMC parameters including selection of the cooling media, using of the dynamic baffle, and the influence of withdrawal rates and so on. The microstructure and mechanical properties of the traditional superalloys processed by LMC, as well as the new alloys particularly developed for LMC process were then described. Finally, future aspects concerning the LMC process have been summarized.展开更多
The dendrite morphologies and spacings of directionally solidified DZ125 superalloy were investigated under high thermal gradient about 500 K/cm. The results reveal that, with increasing cooling rate, both the spacing...The dendrite morphologies and spacings of directionally solidified DZ125 superalloy were investigated under high thermal gradient about 500 K/cm. The results reveal that, with increasing cooling rate, both the spacings of primary and secondary dendrite arms decrease, and the dendrite morphologies transit from coarse to superfme dendrite. The secondary dendrite arms trend to be refined and be well developed, and the tertiary dendrite will occur. The predictions of the Kurz/Fisher model and the Hunt/Lu model accord basically with the experimental data for primary dendrite arm spacing. The regression equation of the primary dendrite arm spacings 21 and the cooling rate Vc is λ1 = 0.013 Vc^-0.32. The regression equation of the secondary dendrite arm spacing λ2 and the cooling rate Vc is λ2 = 0.00258 Vc^-0.31, which gives good agreement with the Feurer/Wunderlin model.展开更多
In this work, some important factors such as ceramic shell strength, heat preservation temperature, standing time and withdrawal rate, which influence the formability of directionally solidified large-size blades of h...In this work, some important factors such as ceramic shell strength, heat preservation temperature, standing time and withdrawal rate, which influence the formability of directionally solidified large-size blades of heavy-duty gas turbine with the liquid metal cooling(LMC) process, were studied through the method of microstructure analysis combining. The results show that the ceramic shell with medium strength(the high temperature flexural strength is 8 MPa, the flexural strength after thermal shock resistance is 12 MPa and the residual flexural strength is 20 MPa) can prevent the rupture and runout of the blade. The appropriate temperature(1,520 ℃ for upper region and 1,500 ℃ for lower region) of the heating furnace can eliminate the wide-angle grain boundary, the deviation of grain and the run-out caused by the shell crack. The holding time after pouring(3-5 min) can promote the growth of competitive grains and avoid a great deviation of columnar grains along the crystal orientation <001>, resulting in a straight and uniform grain structure. In addition, to avoid the formation of wrinkles and to ensure a smooth blade surface, the withdrawal rate should be no greater than the growth rate of grain. It is also found that the dendritic space of the blade decreases with the rise of solidification rate, and increases with the enlarging distance between the solidification position and the chill plate.展开更多
Central region coarse grains and centerline segregation are common defects in aluminum ingots fabricated by direct chill(DC)casting.A double cooling field was introduced into the DC casting process to reduce these def...Central region coarse grains and centerline segregation are common defects in aluminum ingots fabricated by direct chill(DC)casting.A double cooling field was introduced into the DC casting process to reduce these defects,whereby the external cooling was supplied by the mold and water jets,and intercooling was achieved by inserting a rod of the same alloy into the molten pool along the central axis of the ingot.Rather than forming a good metallurgical interface during solid-liquid compound casting,in the present work,the purpose of inserting the rod is to enforce internal cooling and consequently decrease the sump depth.Moreover,the insertion provides more nucleation sites with the unmoltenα-Al particles.The structure and the macrosegregation of 2024 Al alloy ingots prepared by DC casting with and without the inserts were investigated.Results show that when the inserting position is 50 mm above the upper edge of the graphite ring,significant grain refinement in the central region of the ingot and a reduced centerline segregation are achieved.展开更多
A series of directional solidification experiments have been performed to study the effect of cooling rate on the precipitation behavior of MC carbide in nickel-based superalloy under the temperature gradient of 500 K...A series of directional solidification experiments have been performed to study the effect of cooling rate on the precipitation behavior of MC carbide in nickel-based superalloy under the temperature gradient of 500 K-s^-1. Results reveal that the morphology of MC carbide changes from coarse block to fine strip, then to Chinese-script, and their sizes reduce gradually with the increasing of cooling rate from 2.53 K.s^-1 to 36.4 K.s^-1. At low cooling rates, most of these carbides are found to be located at the grain boundary and interdendritic regions, while the coupled growth of some carbides and 7 matrix in the center of 7 grains is occurred at high cooling rate. The main elements forming MC carbide are Ta, W, and Hf.展开更多
We conducted a transient experimental investigation of steam–water direct contact condensation in the absence of noncondensible gas in a laboratory-scale column with the inner diameter of 325 mm and the height of 104...We conducted a transient experimental investigation of steam–water direct contact condensation in the absence of noncondensible gas in a laboratory-scale column with the inner diameter of 325 mm and the height of 1045 mm. We applied a new analysis method for the steam state equation to analyze the molar quantity change in steam over the course of the experiment and determined the transient steam variation. We also investigated the influence of flow rates and temperatures ofcooling water on the efficiency ofsteam condensation. Our experimental results show that appropriate increasing of the cooling water flow rate can significantly accelerate the steam condensation. We achieved a rapid increase in the total volumetric heat transfer coefficient by increasing the flow rate of cooling water, which indicated a higher thermal convection between the steam and the cooling water with higher flow rates. We found that the temperature ofcooling water did not play an important role on steam condensation. This method was confirmed to be effective for rapid recovering ofsteam.展开更多
In order to investigate the relationship between microstructure and MnS inclusion in non-quenched and tempered steel, and cooling rate during horizontal directional solidification, 49MnVS steel was used to conduct the...In order to investigate the relationship between microstructure and MnS inclusion in non-quenched and tempered steel, and cooling rate during horizontal directional solidification, 49MnVS steel was used to conduct the experiments with a selfdesigned device. The mathematical effect of cooling rate on dendritic arm spacing and mean diameter of MnS particles (dMnS) were determined by using linear regression method. The results show that the length of dendrite from solid–liquid interface to end-solidification decreased with increasing the withdrawal velocity (#). dMnS has a similar value in the area of the steady directional solidification;the value of dMnS was 4.1, 3.6, 3.3, 2.8 and 2.3 lm at withdrawal velocity of 50, 75, 100, 150 and 200 lm/s, respectively. dMnS increased with reducing # or RC (interface cooling rate). MnS precipitated in the gaps between dendrites and was influenced by secondary dendritic arm spacing. Besides, a new concept of the ‘Precipitation Unit Space’(PUS) was proposed and the relationships between dMnS, VPUS (volume of PUS) and RC were obtained.展开更多
The Al^＋ ion optical clock is a very promising optical frequency standard candidate due to its extremely small black-body radiation shift. It has been successfully demonstrated with the indirect cooled, quantum-logic...The Al^＋ ion optical clock is a very promising optical frequency standard candidate due to its extremely small black-body radiation shift. It has been successfully demonstrated with the indirect cooled, quantum-logic-based spectroscopy technique. Its accuracy is limited by second-order Doppler shift, and its stability is limited by the number of ions that can be probed in quantum logic processing. We propose a direct laser cooling scheme of AI＋ ion optical clocks where both the stability and accuracy of the clocks are greatly improved. In the proposed scheme, two Al^＋ traps are utilized. The first trap is used to trap a large number of Al^＋ ions to improve the stability of the clock laser, while the second trap is used to trap a single Al^＋ ion to provide the ultimate accuracy. Both traps are cooled with a continuous wave 167nm laser. The expected clock laser stability can reach 9.0 × 10^-17/√τ. For the second trap, in addition to 167nm laser Doppler cooling, a second stage pulsed 234nm two-photon cooling laser is utilized to further improve the accuracy of the clock laser. The total systematic uncertainty can be reduced to about 1 × 10^-18. The proposed Al^＋ ion optical clock has the potential to become the most accurate and stable optical clock.展开更多
The microstructures and mechanical properties of a series of direct-quenched steels containing,in weight percent,from 0.05 to 0.20 carbon,0.20 to 0.40 silicon,1.10 to 1.70 manganese and at least one microalloying elem...The microstructures and mechanical properties of a series of direct-quenched steels containing,in weight percent,from 0.05 to 0.20 carbon,0.20 to 0.40 silicon,1.10 to 1.70 manganese and at least one microalloying element of vanadium,niobium,titanium and boron have been investigated.After controlled rolling,these steels were cooled in spray water to 400,300 and 200℃,respectively and then cooled in still air.Comparison of the Charpy V-notch impact toughness of direct-quenched steels without subsequent tempering was made with that of direct-quenched steels tempered at 600℃.It is found that an attractive combination of strength and toughness is achived by means of direct-quenching.There exists two types of microstructures in accordance with carbon equivalent.Lath martensitic microstructure is obtained for C>0.4%,granular bainitic microstructures for C.< 0.35%and mixtures of martensite and bainite for C,.in the range of 0.35— 0.40%.The effect of interrupted quenching temperature on microstructure is not significant for low C.steel,but interrupted quenching temperature has a strong effect on microstructure for high C,.steel.展开更多
1|Introduction Conventional cooling systems exhibit substantial electricity consumption and environmental detriments through contin-uous greenhouse gas emissions.Thermal management accounts for approximately 50%of glo...1|Introduction Conventional cooling systems exhibit substantial electricity consumption and environmental detriments through contin-uous greenhouse gas emissions.Thermal management accounts for approximately 50%of global energy expenditure[1,2],necessitating urgent development of sustainable cooling alter-natives.Radiative cooling emerges as a passive thermal regu-lation strategy,operating without external energy input via direct infrared emission from materials to the environment[3].展开更多
Titanium slag in this study was produced by subjecting titanomagnetite concentrate to direct reductionelectric furnace smelting. Processing mineralogy and mineral phase reconstruction behavior at high temperature and ...Titanium slag in this study was produced by subjecting titanomagnetite concentrate to direct reductionelectric furnace smelting. Processing mineralogy and mineral phase reconstruction behavior at high temperature and slow cooling treatment were examined by chemical analysis, X-ray diffraction （XRD）, optical microscopy （OM）, scanning electron microscopy （SEM）, and energydispersive spectroscopy （EDS）. Anosovite solid solution is the main titanium product by the direct reduction and smelting process. Results of slow-cooling experiments show that crystal volume and size increase as cooling rate decreases. Anosovite and gangue mineral crystals develop fully with large crystal volume and size at a cooling rate of 2 K.min-1. Moreover, the growth of anosovite crystal was characterized by crystal nucleation and growth theory. These results provide further insights into the separation of anosovite from gangue by mineral processing.展开更多
The performance of a patented water pumping model with steam-air power was presented,which operates automatically by direct contact cooling method.The main objective was to study feasibility of a pumping model for und...The performance of a patented water pumping model with steam-air power was presented,which operates automatically by direct contact cooling method.The main objective was to study feasibility of a pumping model for underground water.In this model,a heater installed within the heat tank represented sources of waste heat as energy input for finding appropriate conditions of the 10 L pump model.The system operation had five stages:heating,pumping,vapor flow,cooling,and water suction.The overall water heads of 3,4.5,6 and 7.5 m were tested.At the same time,it was found that the pump with 50%air volume is sufficient for pumping water to a desired level.In the experiment,the temperatures in the heating and pumping stages were 100-103℃and 80-90℃,respectively.The pressure in the pumping stage was 12-18 kPa,and the pressure in the suction stage was about-80 kPa,sufficient for the best performance.It could pump 170 L of water at a 2 m suction head,120 L at a 3.5 m suction head,100 L at a 5 m suction head,and 65 L at a 6.5 m suction head in 2 h.A mathematical model for larger pumps was also presented,which operates nearly the same as the present system.Economic analysis of the 10 L pump was also included.展开更多
Efficient Air Conditioning (A/C) system is the key to reducing energy consumption in building operation. In order to decrease the energy consumption in an A/C system, a method to calculate the optimal tube row number ...Efficient Air Conditioning (A/C) system is the key to reducing energy consumption in building operation. In order to decrease the energy consumption in an A/C system, a method to calculate the optimal tube row number of a direct expansion (DX) cooling coil for minimizing the entropy generation in the DX cooling which functioned as evaporator in the A/C system was developed. The optimal tube row numbers were determined based on the entropy generation minimization (EGM) approach. Parametric studies were conducted to demonstrate the application of the analytical calculation method. Optimal tube row number for different air mass flow rates, inlet air temperatures and sensible cooling loads were investigated. It was found that the optimal tube row number of a DX cooling coil was in the range of 5 - 9 under normal operating conditions. The optimal tube row number was less when the mass flow rate and inlet air temperature were increased. The tube row number increased when the sensible cooling load was increased. The exergy loss when using a non-optimal and optimal tube row numbers was compared to show the advantage of using the optimal tube row number. The decrease of exery loss ranged from around 24% to 70%. Therefore the new analytical method developed in this paper offers a good practice guide for the design of DX cooling coils for energy conservation.展开更多
The so-called indirect evaporative cooling technology is widely used in air conditioning applications.The thermal characterization of tube-type indirect evaporative coolers,however,still presents challenges which need...The so-called indirect evaporative cooling technology is widely used in air conditioning applications.The thermal characterization of tube-type indirect evaporative coolers,however,still presents challenges which need to be addressed to make this technology more reliable and easy to implement.This experimental study deals with the performances of a tube-type indirect evaporative cooler based on an aluminum tube with a 10 mm diameter.In particular,the required tests were carried out considering a range of dry-bulb temperatures between 16℃ and 18℃ and a temperature difference between the wet-bulb and dry-bulb temperature of 2℃∼4℃.The integrated convective heat transfer coefficient inside the tube in the drenching condition has been found to lie in the range between 36.10 and 437.4(W/(m^(2)⋅K)).展开更多
Given the distribution feature of resources such as coal and water, the requirements for the development of Chinese power industry, and the fact of monopoly by foreign companies, it is very necessary and significant t...Given the distribution feature of resources such as coal and water, the requirements for the development of Chinese power industry, and the fact of monopoly by foreign companies, it is very necessary and significant to independently research and develop air-cooling technologies. Through experimental research, simulative calculation, process and equipment development, field tests and a demonstration project, the design and operation technologies for air-cooling system are grasped and relevant key equipment is developed. The results of the demonstration project show that the technical indicators for the air-cooling system have met or exceeded the design requirements. Part of the research results have been incorporated into the relevant national design standards. The technologies developed have been applied to more than 23 sets of thermal power units of or above 600 MW in China.展开更多
To assess the curative effects of different reduction techniques on the dislocation of cricoarytenoid joint caused by intubation,indirect laryngoscope (IL ) and direct laryngoscope (DL ) were utilized for the closed...To assess the curative effects of different reduction techniques on the dislocation of cricoarytenoid joint caused by intubation,indirect laryngoscope (IL ) and direct laryngoscope (DL ) were utilized for the closed reduction of the displaced arytenoid under local anesthesia.2 3patients who underwent the reduction for dislocated arytenoid under IL or DL from January1991to June 2 0 0 1were reviewed.The data were collected on the duration of the laryngeal injury,tim es of re- ceiving reduction,side- effects after the treatment and the period for voice to return to normal. The relationship between the duration of the laryngeal lesion and the period of the voice rehabilita- tion was examined.13patients received the reduction under IL and 10 patients under DL .Except the tim es of the reduction,which showed significant difference,no differences were found between IL group and DL group in the course and the period of voice rehabilitation,as well as sore throat after the manipulation.The patients'voice recovery was positively related to their course of dis- ease in both IL and DL group.Itis concluded thatthe recovery of normal voice is obviously affect- ed by the duration of arytenoid dislocation.The reduction under IL is as effective as under DL in the treatment of arytenoid dislocation.Reduction by DL is better suit the patients with long tim e course of disease.展开更多
A novel control method for a general class of nonlinear systems using fuzzy logic systems （FLSs） is presertted. Indirect and direct methods are combined to design the adaptive fuzzy output feedback controller and a ...A novel control method for a general class of nonlinear systems using fuzzy logic systems （FLSs） is presertted. Indirect and direct methods are combined to design the adaptive fuzzy output feedback controller and a high-gain observer is used to estimate the derivatives of the system output. The closed-loop system is proven to be semiglobally uniformly ultimately bounded. In addition, it is shown that if the approximation accuracy of the fuzzy logic system is high enough and the observer gain is chosen sufficiently large, an arbitrarily small tracking error can be achieved. Simulation results verify the effectiveness of the newly designed scheme and the theoretical discussion.展开更多
A review is conducted about the application of the evaporative cooling technology in thermal power plants.Different case studies are considered,namely,evaporative air conditioners,evaporative cooling in direct air-coo...A review is conducted about the application of the evaporative cooling technology in thermal power plants.Different case studies are considered,namely,evaporative air conditioners,evaporative cooling in direct air-cooled systems,gas turbine inlet cooling,wet cooling towers,and hybrid cooling towers with a crosswind effect.Some effort is provided to describe the advantages related to direct evaporative cooling when it is applied in thermal power plants and illustrate the research gaps,which have not been filled yet.In particular,typical case studies are intentionally used to compare the cooling performances when direct evaporative cooling is implemented in different types of cooling towers,including the natural draft wet cooling tower(NDWCT)and the pre-cooled natural draft dry cooling tower(NDDCT).It is shown that the NDWCT provides the best cooling performance in terms of power station cooling,followed by the pre-cooled NDDCT,and the NDDCT;moreover,the evaporative pre-cooling is able to enhance the cooling performance of NDDCT.Besides,on a yearly basis,better NDDCT cooling performances can be obtained by means of a spray-based pre-cooling approach with respect to wet media pre-cooling.Therefore,the use of nozzle spray is suggested for improvement in the performance of indirect/direct air-cooling systems with controlled water consumption.展开更多
文摘This study develops an analytical model to evaluate the cooling performance of a porous terracotta tubular direct evaporative heat and mass exchanger. By combining energy and mass balance equations with heat and mass transfer coefficients and air psychrometric correlations, the model provides insights into the impact of design and operational parameters on the exchanger cooling performance. Validated against an established numerical model, it accurately simulates cooling behavior with a Root Mean Square Deviation of 0.43 - 1.18˚C under varying inlet air conditions. The results show that tube geometry, including equivalent diameter, flatness ratio, and length significantly influences cooling outcomes. Smaller diameters enhance wet-bulb effectiveness but reduce cooling capacity, while increased flatness and length improve both. For example, extending the flatness ratio of a 15 mm diameter, 0.6 m long tube from 1 (circular) to 4 raises the exchange surface area from 0.028 to 0.037 m2, increasing wet-bulb effectiveness from 60% to 71%. Recommended diameters range from 5 mm for tubes under 0.5 m to 1 cm for tubes 0.5 to 1 m in length. Optimal air velocities depend on tube length: 1 m/s for tubes under 0.8 m, 1.5 m/s for lengths of 0.8 to 1.2 m, and up to 2 m/s for longer tubes. This model offers a practical alternative to complex numerical and CFD methods, with potential applications in cooling tower optimization for thermal and nuclear power plants and geothermal heat exchangers.
文摘The objective of the present study is to investigate the efficiency of indirect adiabatic chiller-based cooling system efficiency dependence of outdoor air humidity. The system is located in historical building, in temperate climate of Latvia. The data about electricity consumption, water consumption, chiller operation stages, cooling average temperatures and outdoor air parameters have been acquired for the period of 2.5 month, during the cooling season. Using data collected by BACnet based BMS controllers and adiabatic chiller control system, we have analyzed operation efficiency of the chiller and its dependence of outdoor air humidity. Data range for the period from August 1st till October 13th, 2011 was taken for deeper analysis, which showed that in temperature range 22.0 ± 0.5 ℃ for the studied period of time chiller＇s COP is slightly dependent on the outdoor air moisture.
文摘An overview of the development and current status of the directional solidification process assisted by liquid metal cooling （LMC） has been presented in this paper. The driving force of the rapid development of the LMC process has been analyzed by considering the demands of （1） newer technologies that can provide higher thermal gradients for alleviated segregation in advanced alloy systems, and （2） better production yield of the large directionally solidified superalloy components. The brief history of the industrialization of the LMC process has been reviewed, followed by the discussion on the LMC parameters including selection of the cooling media, using of the dynamic baffle, and the influence of withdrawal rates and so on. The microstructure and mechanical properties of the traditional superalloys processed by LMC, as well as the new alloys particularly developed for LMC process were then described. Finally, future aspects concerning the LMC process have been summarized.
基金supported by the National Natural Science Foundation of China (Nos.50771081,50827102)the National Basic Research Program of China (No.2006CB605202)
文摘The dendrite morphologies and spacings of directionally solidified DZ125 superalloy were investigated under high thermal gradient about 500 K/cm. The results reveal that, with increasing cooling rate, both the spacings of primary and secondary dendrite arms decrease, and the dendrite morphologies transit from coarse to superfme dendrite. The secondary dendrite arms trend to be refined and be well developed, and the tertiary dendrite will occur. The predictions of the Kurz/Fisher model and the Hunt/Lu model accord basically with the experimental data for primary dendrite arm spacing. The regression equation of the primary dendrite arm spacings 21 and the cooling rate Vc is λ1 = 0.013 Vc^-0.32. The regression equation of the secondary dendrite arm spacing λ2 and the cooling rate Vc is λ2 = 0.00258 Vc^-0.31, which gives good agreement with the Feurer/Wunderlin model.
基金financially supported by the National Science and Technology Major Project of High-end CNC Machine Tools and Basic Manufacturing Equipment(No.2017ZX04014001)
文摘In this work, some important factors such as ceramic shell strength, heat preservation temperature, standing time and withdrawal rate, which influence the formability of directionally solidified large-size blades of heavy-duty gas turbine with the liquid metal cooling(LMC) process, were studied through the method of microstructure analysis combining. The results show that the ceramic shell with medium strength(the high temperature flexural strength is 8 MPa, the flexural strength after thermal shock resistance is 12 MPa and the residual flexural strength is 20 MPa) can prevent the rupture and runout of the blade. The appropriate temperature(1,520 ℃ for upper region and 1,500 ℃ for lower region) of the heating furnace can eliminate the wide-angle grain boundary, the deviation of grain and the run-out caused by the shell crack. The holding time after pouring(3-5 min) can promote the growth of competitive grains and avoid a great deviation of columnar grains along the crystal orientation <001>, resulting in a straight and uniform grain structure. In addition, to avoid the formation of wrinkles and to ensure a smooth blade surface, the withdrawal rate should be no greater than the growth rate of grain. It is also found that the dendritic space of the blade decreases with the rise of solidification rate, and increases with the enlarging distance between the solidification position and the chill plate.
基金financially supported by the Natural Science Foundation of Liaoning Province(Nos.2019-ZD-0002,2019KF-0503)the Fundamental Research Funds for the Central Universities(Nos.N2002025,N2109006)the National Natural Science Foundation of China(No.51674078)。
文摘Central region coarse grains and centerline segregation are common defects in aluminum ingots fabricated by direct chill(DC)casting.A double cooling field was introduced into the DC casting process to reduce these defects,whereby the external cooling was supplied by the mold and water jets,and intercooling was achieved by inserting a rod of the same alloy into the molten pool along the central axis of the ingot.Rather than forming a good metallurgical interface during solid-liquid compound casting,in the present work,the purpose of inserting the rod is to enforce internal cooling and consequently decrease the sump depth.Moreover,the insertion provides more nucleation sites with the unmoltenα-Al particles.The structure and the macrosegregation of 2024 Al alloy ingots prepared by DC casting with and without the inserts were investigated.Results show that when the inserting position is 50 mm above the upper edge of the graphite ring,significant grain refinement in the central region of the ingot and a reduced centerline segregation are achieved.
基金financially supported by the Scientific Research Foundation for Ph.D.,Northwest A & F University (No.Z109021103)the Special Fund for Basic Scientific Research of Central Colleges,Northwest A & F University No.Z109021114)the fund of the State Key Laboratory of Solidification Processing in NWPU (SKLSP201220)
文摘A series of directional solidification experiments have been performed to study the effect of cooling rate on the precipitation behavior of MC carbide in nickel-based superalloy under the temperature gradient of 500 K-s^-1. Results reveal that the morphology of MC carbide changes from coarse block to fine strip, then to Chinese-script, and their sizes reduce gradually with the increasing of cooling rate from 2.53 K.s^-1 to 36.4 K.s^-1. At low cooling rates, most of these carbides are found to be located at the grain boundary and interdendritic regions, while the coupled growth of some carbides and 7 matrix in the center of 7 grains is occurred at high cooling rate. The main elements forming MC carbide are Ta, W, and Hf.
文摘We conducted a transient experimental investigation of steam–water direct contact condensation in the absence of noncondensible gas in a laboratory-scale column with the inner diameter of 325 mm and the height of 1045 mm. We applied a new analysis method for the steam state equation to analyze the molar quantity change in steam over the course of the experiment and determined the transient steam variation. We also investigated the influence of flow rates and temperatures ofcooling water on the efficiency ofsteam condensation. Our experimental results show that appropriate increasing of the cooling water flow rate can significantly accelerate the steam condensation. We achieved a rapid increase in the total volumetric heat transfer coefficient by increasing the flow rate of cooling water, which indicated a higher thermal convection between the steam and the cooling water with higher flow rates. We found that the temperature ofcooling water did not play an important role on steam condensation. This method was confirmed to be effective for rapid recovering ofsteam.
基金This work is supported by National Key Research and Development Program of China (2018YFB0704400)the National Natural Science Foundation of China (Grant Nos. 51671124 and 51474142)the support of State Key Laboratory of Development and Application Technology of Automotive Steels (Baosteel Group).
文摘In order to investigate the relationship between microstructure and MnS inclusion in non-quenched and tempered steel, and cooling rate during horizontal directional solidification, 49MnVS steel was used to conduct the experiments with a selfdesigned device. The mathematical effect of cooling rate on dendritic arm spacing and mean diameter of MnS particles (dMnS) were determined by using linear regression method. The results show that the length of dendrite from solid–liquid interface to end-solidification decreased with increasing the withdrawal velocity (#). dMnS has a similar value in the area of the steady directional solidification;the value of dMnS was 4.1, 3.6, 3.3, 2.8 and 2.3 lm at withdrawal velocity of 50, 75, 100, 150 and 200 lm/s, respectively. dMnS increased with reducing # or RC (interface cooling rate). MnS precipitated in the gaps between dendrites and was influenced by secondary dendritic arm spacing. Besides, a new concept of the ‘Precipitation Unit Space’(PUS) was proposed and the relationships between dMnS, VPUS (volume of PUS) and RC were obtained.
基金Supported by the National Basic Research Program of China under Grant No 2012CB821300the National Natural Science Foundation of China under Grant Nos 91336213,11304109,91536116 and 11174095the Program for New Century Excellent Talents by the Ministry of Education under Grant No NCET-11-0176
文摘The Al^＋ ion optical clock is a very promising optical frequency standard candidate due to its extremely small black-body radiation shift. It has been successfully demonstrated with the indirect cooled, quantum-logic-based spectroscopy technique. Its accuracy is limited by second-order Doppler shift, and its stability is limited by the number of ions that can be probed in quantum logic processing. We propose a direct laser cooling scheme of AI＋ ion optical clocks where both the stability and accuracy of the clocks are greatly improved. In the proposed scheme, two Al^＋ traps are utilized. The first trap is used to trap a large number of Al^＋ ions to improve the stability of the clock laser, while the second trap is used to trap a single Al^＋ ion to provide the ultimate accuracy. Both traps are cooled with a continuous wave 167nm laser. The expected clock laser stability can reach 9.0 × 10^-17/√τ. For the second trap, in addition to 167nm laser Doppler cooling, a second stage pulsed 234nm two-photon cooling laser is utilized to further improve the accuracy of the clock laser. The total systematic uncertainty can be reduced to about 1 × 10^-18. The proposed Al^＋ ion optical clock has the potential to become the most accurate and stable optical clock.
文摘The microstructures and mechanical properties of a series of direct-quenched steels containing,in weight percent,from 0.05 to 0.20 carbon,0.20 to 0.40 silicon,1.10 to 1.70 manganese and at least one microalloying element of vanadium,niobium,titanium and boron have been investigated.After controlled rolling,these steels were cooled in spray water to 400,300 and 200℃,respectively and then cooled in still air.Comparison of the Charpy V-notch impact toughness of direct-quenched steels without subsequent tempering was made with that of direct-quenched steels tempered at 600℃.It is found that an attractive combination of strength and toughness is achived by means of direct-quenching.There exists two types of microstructures in accordance with carbon equivalent.Lath martensitic microstructure is obtained for C>0.4%,granular bainitic microstructures for C.< 0.35%and mixtures of martensite and bainite for C,.in the range of 0.35— 0.40%.The effect of interrupted quenching temperature on microstructure is not significant for low C.steel,but interrupted quenching temperature has a strong effect on microstructure for high C,.steel.
基金the financial support from the National Key R&D Program of China(No.2020YFA0711500)the National Natural Science Foundation of China(Nos.52473215 and 52273248).
文摘1|Introduction Conventional cooling systems exhibit substantial electricity consumption and environmental detriments through contin-uous greenhouse gas emissions.Thermal management accounts for approximately 50%of global energy expenditure[1,2],necessitating urgent development of sustainable cooling alter-natives.Radiative cooling emerges as a passive thermal regu-lation strategy,operating without external energy input via direct infrared emission from materials to the environment[3].
基金financially supported by the Major Program of the National Natural Science Foundation of China(No.51090385)
文摘Titanium slag in this study was produced by subjecting titanomagnetite concentrate to direct reductionelectric furnace smelting. Processing mineralogy and mineral phase reconstruction behavior at high temperature and slow cooling treatment were examined by chemical analysis, X-ray diffraction （XRD）, optical microscopy （OM）, scanning electron microscopy （SEM）, and energydispersive spectroscopy （EDS）. Anosovite solid solution is the main titanium product by the direct reduction and smelting process. Results of slow-cooling experiments show that crystal volume and size increase as cooling rate decreases. Anosovite and gangue mineral crystals develop fully with large crystal volume and size at a cooling rate of 2 K.min-1. Moreover, the growth of anosovite crystal was characterized by crystal nucleation and growth theory. These results provide further insights into the separation of anosovite from gangue by mineral processing.
基金the financial support provided by National Research Council of Thailand and the Energy Technology Division,School of Energy Environment and Materials,King Mongkut’s University of Technology Thonburisupported by the Higher Education Research Promotion and National Research University Project of Thailand,Office of the Higher Education Commission
文摘The performance of a patented water pumping model with steam-air power was presented,which operates automatically by direct contact cooling method.The main objective was to study feasibility of a pumping model for underground water.In this model,a heater installed within the heat tank represented sources of waste heat as energy input for finding appropriate conditions of the 10 L pump model.The system operation had five stages:heating,pumping,vapor flow,cooling,and water suction.The overall water heads of 3,4.5,6 and 7.5 m were tested.At the same time,it was found that the pump with 50%air volume is sufficient for pumping water to a desired level.In the experiment,the temperatures in the heating and pumping stages were 100-103℃and 80-90℃,respectively.The pressure in the pumping stage was 12-18 kPa,and the pressure in the suction stage was about-80 kPa,sufficient for the best performance.It could pump 170 L of water at a 2 m suction head,120 L at a 3.5 m suction head,100 L at a 5 m suction head,and 65 L at a 6.5 m suction head in 2 h.A mathematical model for larger pumps was also presented,which operates nearly the same as the present system.Economic analysis of the 10 L pump was also included.
文摘Efficient Air Conditioning (A/C) system is the key to reducing energy consumption in building operation. In order to decrease the energy consumption in an A/C system, a method to calculate the optimal tube row number of a direct expansion (DX) cooling coil for minimizing the entropy generation in the DX cooling which functioned as evaporator in the A/C system was developed. The optimal tube row numbers were determined based on the entropy generation minimization (EGM) approach. Parametric studies were conducted to demonstrate the application of the analytical calculation method. Optimal tube row number for different air mass flow rates, inlet air temperatures and sensible cooling loads were investigated. It was found that the optimal tube row number of a DX cooling coil was in the range of 5 - 9 under normal operating conditions. The optimal tube row number was less when the mass flow rate and inlet air temperature were increased. The tube row number increased when the sensible cooling load was increased. The exergy loss when using a non-optimal and optimal tube row numbers was compared to show the advantage of using the optimal tube row number. The decrease of exery loss ranged from around 24% to 70%. Therefore the new analytical method developed in this paper offers a good practice guide for the design of DX cooling coils for energy conservation.
基金This work was supported by Natural Science Basic Research Program of Shaanxi(2021JQ-689).
文摘The so-called indirect evaporative cooling technology is widely used in air conditioning applications.The thermal characterization of tube-type indirect evaporative coolers,however,still presents challenges which need to be addressed to make this technology more reliable and easy to implement.This experimental study deals with the performances of a tube-type indirect evaporative cooler based on an aluminum tube with a 10 mm diameter.In particular,the required tests were carried out considering a range of dry-bulb temperatures between 16℃ and 18℃ and a temperature difference between the wet-bulb and dry-bulb temperature of 2℃∼4℃.The integrated convective heat transfer coefficient inside the tube in the drenching condition has been found to lie in the range between 36.10 and 437.4(W/(m^(2)⋅K)).
文摘Given the distribution feature of resources such as coal and water, the requirements for the development of Chinese power industry, and the fact of monopoly by foreign companies, it is very necessary and significant to independently research and develop air-cooling technologies. Through experimental research, simulative calculation, process and equipment development, field tests and a demonstration project, the design and operation technologies for air-cooling system are grasped and relevant key equipment is developed. The results of the demonstration project show that the technical indicators for the air-cooling system have met or exceeded the design requirements. Part of the research results have been incorporated into the relevant national design standards. The technologies developed have been applied to more than 23 sets of thermal power units of or above 600 MW in China.
文摘To assess the curative effects of different reduction techniques on the dislocation of cricoarytenoid joint caused by intubation,indirect laryngoscope (IL ) and direct laryngoscope (DL ) were utilized for the closed reduction of the displaced arytenoid under local anesthesia.2 3patients who underwent the reduction for dislocated arytenoid under IL or DL from January1991to June 2 0 0 1were reviewed.The data were collected on the duration of the laryngeal injury,tim es of re- ceiving reduction,side- effects after the treatment and the period for voice to return to normal. The relationship between the duration of the laryngeal lesion and the period of the voice rehabilita- tion was examined.13patients received the reduction under IL and 10 patients under DL .Except the tim es of the reduction,which showed significant difference,no differences were found between IL group and DL group in the course and the period of voice rehabilitation,as well as sore throat after the manipulation.The patients'voice recovery was positively related to their course of dis- ease in both IL and DL group.Itis concluded thatthe recovery of normal voice is obviously affect- ed by the duration of arytenoid dislocation.The reduction under IL is as effective as under DL in the treatment of arytenoid dislocation.Reduction by DL is better suit the patients with long tim e course of disease.
基金This project was supported by the National Natural Science Foundation of China (90405011).
文摘A novel control method for a general class of nonlinear systems using fuzzy logic systems （FLSs） is presertted. Indirect and direct methods are combined to design the adaptive fuzzy output feedback controller and a high-gain observer is used to estimate the derivatives of the system output. The closed-loop system is proven to be semiglobally uniformly ultimately bounded. In addition, it is shown that if the approximation accuracy of the fuzzy logic system is high enough and the observer gain is chosen sufficiently large, an arbitrarily small tracking error can be achieved. Simulation results verify the effectiveness of the newly designed scheme and the theoretical discussion.
基金supported by the Shandong Natural Science Foundation(Grant No.ZR2022ME008)the Shandong Provincial Science and Technology SMEs Innovation Capacity Improvement Project(2022TSGC2018)+3 种基金the Shenzhen Science and Technology Program(KCXFZ20201221173409026)The financial supports from the“Young Scholars Program of Shandong University”(YSPSDU,No.2018WLJH73)the Open Project of State Key Laboratory of Clean Energy Utilization,Zhejiang University(Program Number ZJUCEU2020011)the Shandong Natural Science Foundation(Grant No.ZR2021ME118)are gratefully acknowledged。
文摘A review is conducted about the application of the evaporative cooling technology in thermal power plants.Different case studies are considered,namely,evaporative air conditioners,evaporative cooling in direct air-cooled systems,gas turbine inlet cooling,wet cooling towers,and hybrid cooling towers with a crosswind effect.Some effort is provided to describe the advantages related to direct evaporative cooling when it is applied in thermal power plants and illustrate the research gaps,which have not been filled yet.In particular,typical case studies are intentionally used to compare the cooling performances when direct evaporative cooling is implemented in different types of cooling towers,including the natural draft wet cooling tower(NDWCT)and the pre-cooled natural draft dry cooling tower(NDDCT).It is shown that the NDWCT provides the best cooling performance in terms of power station cooling,followed by the pre-cooled NDDCT,and the NDDCT;moreover,the evaporative pre-cooling is able to enhance the cooling performance of NDDCT.Besides,on a yearly basis,better NDDCT cooling performances can be obtained by means of a spray-based pre-cooling approach with respect to wet media pre-cooling.Therefore,the use of nozzle spray is suggested for improvement in the performance of indirect/direct air-cooling systems with controlled water consumption.
