The pivotal role microchannels play in the thermal management of electronic components has,in recent decades,prompted extensive research into methods for enhancing their heat transfer performance.Among these methods,s...The pivotal role microchannels play in the thermal management of electronic components has,in recent decades,prompted extensive research into methods for enhancing their heat transfer performance.Among these methods,surface wettability modification was found to be highly effective owing to its significant influence on boiling dynamics and heat transfer mechanisms.In this study,we modified surface wettability using a nanocomposite coating composed of graphene nano plate(GNPs)and multi-walled carbon nanotubes(MWCNT)and then examined how the modification affected the transfer of boiling heat in microchannels.The resultant heat transfer coefficients for hydrophilic and hydrophilic composite(GNPs+MWCNT)microchannels were,respectively,42.8%and 33.95%higher compared with that of the uncoated surface.These results verify that hydrophilic GNP-based coating significantly improves boiling heat transfer performance.It was observed that a minor increase in contact angle,θfrom 73.142°to 75.73°,resulted in a noticeable decrease in thermal performance.This is attributed to diminished liquid film stability,reduced nucleation site activity,and weakened capillary-driven liquid replenishment.These findings underscore the crucial role of optimized surface wettability in maintaining efficient microchannel boiling.At high mass flux,the GNPS microchannels exhibited maximum pressure drop values,with a pressure drop ratio as high as 36%compared to 29%for the GNPs+MWCNT composite samples.Nevertheless,when a composite hydrophilic–hydrophobic coating was deposited through electrodeposition,the enhancement in heat transfer was less significant.This was probably due to decreased surface uniformity,diminished liquid film stability,and the disruption of effective nucleation behavior,all associated with the slight increase in surface contact angle.The obtained results can be used as guidance for designing advanced cooling surfaces in high-performance microelectronic and energy systems,where precise control of surface characteristics is critical.展开更多
This research explores the characteristics of boiling in inclined pipes,a domain of great importance in engineering.Employing an experimental visualization technique,the boiling dynamics of deionizedwater are examined...This research explores the characteristics of boiling in inclined pipes,a domain of great importance in engineering.Employing an experimental visualization technique,the boiling dynamics of deionizedwater are examined at varying inclination angles,paying special attention to the emerging flow patterns.The findings demonstrate that the inclination angle significantly impacts flow pattern transitions within the 0°to 90°range.As the heat flux rises,bubbles form in the liquid.The liquid’s inertia extends the bubble-wall contact time,thereby delaying the onset of bulk bubble flow.Beyond a 90°inclination,however,the patterning behavior is more influenced by the fluid velocity.At low speeds,incomplete pipe filling results in a large liquid plug hindering flow,while high speeds lead to full pipe filling.In general,gravity,inertia,buoyancy forces,and capillary forces are themain influential factors in the considered problem.However,an analysis of the heat transfer coefficient and boiling curve for different inclination angles reveals that the observed variations are essentially due to corresponding changes in the flow pattern.Finally,an optimal mass flux and inclination angle,able to minimize total entropy generation and improve heat transfer efficiency,are determined by means of an entropy generation analysis.展开更多
This study investigates the flow boiling heat transfer coefficient and pressure gradient of refrigerant R410A inmicro-channel flat tubes.Experiments were conducted at saturation temperatures ranging from 25℃ to 30℃,...This study investigates the flow boiling heat transfer coefficient and pressure gradient of refrigerant R410A inmicro-channel flat tubes.Experiments were conducted at saturation temperatures ranging from 25℃ to 30℃,mass fluxes between 198 and 305 kg/m^(2)s,and heat fluxes from 9.77 to 20.18 kW/m^(2),yielding 99 sets of local heat transfer coefficient data.The results show that increasing heat flux and mass flux enhances the heat transfer coefficient,although the rate of enhancement decreases with increasing vapor quality.Conversely,higher saturation temperatures slightly reduce the heat transfer coefficient.Additionally,the experimental findings reveal discrepancies in the accuracy of existing pressure drop and heat transfer coefficient prediction models under the studied conditions.This study recommends using the Kimand Mudawar correlation to predict pressure gradients within the tested range,with aMean Error(ME)of−5.24%observed in this study.For heat transfer coefficients,the Cooper and Kandlikar correlations are recommended,achieving a Mean Absolute Error(MAE)of approximately 22%.This research provides value for performance prediction and parameter selection of micro-channel technology in broader application scenarios within heating,ventilation and air-conditioning fields.展开更多
In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 k...In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 kg/(m2 s),saturation temperatures of 293,298,and 303 K,and inlet sub-cooling of 5,10,and 15 K.The analysis of the experimental results provides the following conclusions:a reduced mass flux and lower subcooling correspond to a diminished degree of superheat at the boiling inception wall;conversely,an elevated saturation temperature results in a reduced amount of superheat at the boiling inception wall.Furthermore,an increase in sub-cooling and saturation temperature will enhance heat transfer efficiency.The wall temperature is mostly influenced by variations in saturation temperature and is minimally related to changes in mass flux and subcooling degree.An increase in mass flux results in a greater pressure drop attributed to heightened frictional pressure loss.The variation in pressure drop with respect to sub-cooling is minimal,while an increased saturation temperature correlates with a reduced pressure drop due to the formation of smaller bubbles and lowered frictional pressure loss at high saturation pressures.This study thoroughly examines and summarizes the effects of mass flow rate,saturation temperature,and subcooling on the flow-boiling heat transfer and pressure drop characteristics of R1234yf.Furthermore,the new correlation has 93.42%of the predicted values fall within a 15%mean absolute error,exhibiting a mean absolute error of 5.75%.It provides a superior method for predicting the flow-boiling heat transfer coefficients of R1234yf in the heat sink of parallel microchannels compared to existing correlations.展开更多
In modern engineering,enhancing boiling heat transfer efficiency is crucial for optimizing energy use and several industrial processes involving different types of materials.This study explores the enhancement of pool...In modern engineering,enhancing boiling heat transfer efficiency is crucial for optimizing energy use and several industrial processes involving different types of materials.This study explores the enhancement of pool boiling heat transfer potentially induced by combining perforated copper particles on a heated surface with a sodium dodecyl sulfate(SDS)surfactant in saturated deionized water.Experiments were conducted at standard atmospheric pressure,with heat flux ranging from 20 to 100 kW/m2.The heating surface,positioned below the layer of freely moving copper beads,allowed the particle layer to shift due to liquid convection and steam nucleation.The study reports on the influence of copper bead diameter(2,3,4,and 5 mm),particle quantity,arrangement,and SDS concentration(20,200,and 500 ppm).It is shown that the combination of 5 mm particles and a 500 ppm SDS concentration can yield a remarkable 139%improvement in heat transfer efficiency.As demonstrated by direct flow visualization,bubble formation occurs primarily in the gaps between the particles and the heated surface,with the presence of SDS reducing bubble size and accelerating bubble detachment.展开更多
This experimental investigation was conducted on the flow boiling performance of refrigerant R134a in two types of parallel microchannels:sintered porous microchannels(PP-MCs)and smooth parallel microchannels(SP-MCs)....This experimental investigation was conducted on the flow boiling performance of refrigerant R134a in two types of parallel microchannels:sintered porous microchannels(PP-MCs)and smooth parallel microchannels(SP-MCs).The tests were performed under controlled conditions including an inlet subcooling of 5±0.2℃,saturation temperature of 33℃,mass fluxes of 346 and 485 kg/m2·s,and a range of heat fluxes.Key findings reveal that the sintered porous microstructure significantly enhances bubble nucleation,reducing the wall superheat required for the onset of nucleate boiling(ONB)to only 0.13℃ compared to 2.2℃ in smooth channels.The porous structure also improves heat transfer coefficients at low and medium heat fluxes(<20–30 W/cm^(2))and low vapor quality(x<0.2–0.4)due to augmented thin-film evaporation and intensified nucleate boiling.However,smooth microchannels exhibit superior performance under high heat flux and high vapor quality conditions,as the porous structure is prone to early dry-out and flow blockage.Notably,the porous microchannels demonstrate lower flow resistance and enhanced stability,with pressure drop fluctuations reduced by up to 46.4%in amplitude and 44.8%in standard deviation,attributed to improved capillary-assisted liquid replenishment and suppressed flow oscillations.The results underscore the potential of PP-MCs as a high-performance cooling solution for high-heat-flux applications.展开更多
Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.Ho...Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.However,the continuous rise in power density of electronic components imposesmore stringent requirements on the heat transfer capability of microchannel flow boiling.HFE-7100,a dielectric coolant with favorable thermophysical properties,has become a focal point of research for enhancing flow boiling performance in open microchannels.The flow boiling heat transfer performance ofHFE-7100 was investigated in this study by fabricating micro-nano composite structures on the bottom surface of open microchannels using laser ablation technology.Based on visualization results,a comparative analysis was conducted on the bubble dynamics and flow pattern characteristics of HFE-7100 flow boiling in micronano structured open microchannels(MNSOMC)and smooth-surface open microchannels(SSOMC),to elucidate the enhancement mechanism of micro-nano structures on flow boiling heat transfer in open microchannels.The results indicate that the surface structures and strong wettability of MNSOMC accelerated bubble nucleation and departure.Moreover,bubbles in the channel tended to coalesce along the flow direction,forming elongated slug bubbles with high aspect ratios,which enabled efficient thin film evaporation in conjunction with intense nucleate boiling,thereby significantly enhancing flow boiling heat transfer.Under the experimental conditions of this study,the maximum enhancements in the heat transfer coefficient(HTC)and critical heat flux(CHF)of HFE-7100 inMNSOMC were 33.4%and 133.1%,respectively,with the CHF reaching up to 1542.3 kW⋅m^(−2).Furthermore,due to the superior wettability and capillary wicking capability of the micro-nano composite structures,the significant enhancement in flow boiling heat transfer was achieved without incurring a noticeable pressure drop penalty.展开更多
Based on the superposition principle of the nucleate boiling and convective heat transfer terms,a new correlation is developed for flow boiling heat transfer characteristics in helically coiled tubes.The effects of th...Based on the superposition principle of the nucleate boiling and convective heat transfer terms,a new correlation is developed for flow boiling heat transfer characteristics in helically coiled tubes.The effects of the geometric and system parameters on heat transfer characteristics in helically coiled tubes are investigated by collecting large amounts of experimental data and analyzing the heat transfer mechanisms. The existing correlations are divided into two categories,and they are calculated with the experimental data.The Dn factor is introduced to take into account the effect of a complex geometrical structure on flow boiling heat transfer.A new correlation is developed for predicting the flow boiling heat transfer coefficients in the helically coiled tubes,which is validated by the experimental data of R134a flow boiling heat transfer in them;and the average relative error and root mean square error of the new correlation are calculated.The results show that the new correlation agrees well with the experimental data,indicating that the new correlation can be used for predicting flow boiling heat transfer characteristics in the helically coiled tubes.展开更多
Two types of tube bundles are designed,which are,respectively,composed of six tubes arranged in the boiling chamber.The nucleate pool boiling performance of smooth tube bundles and sintered porous surface tube bundles...Two types of tube bundles are designed,which are,respectively,composed of six tubes arranged in the boiling chamber.The nucleate pool boiling performance of smooth tube bundles and sintered porous surface tube bundles with deionized water as a medium are experimentally studied at atmospheric and sub-atmospheric pressures,respectively.The experimental results indicate that the boiling heat transfer coefficients of the two types of tube bundles increase with the increase in pressure under vacuum conditions as they behave under ordinary pressure.As the pressure varies from 10 to 100 kPa,it also can be seen that the heat transfer coefficient of the sintered porous surface tube is increased by 0.2 to 4 times compared with the smooth one under the same operating parameters.In addition,the experimental data show that a definite bundle effect exists in both sintered porous surface tubes and smooth tubes under vacuum conditions.展开更多
Rice husk high boiling solvent lignin （RHL） was prepared by high boiling solvent method, and its characteristics was analyzed by using chemical composition analysis, infrared spectroscopy, and ^1H-NMR and ^13C-NMR s...Rice husk high boiling solvent lignin （RHL） was prepared by high boiling solvent method, and its characteristics was analyzed by using chemical composition analysis, infrared spectroscopy, and ^1H-NMR and ^13C-NMR spectroscopy. The optimum prepared condition was that the rice husk with 70%-90% aqueous solution of 1, 4-butanediol was mixed with autoclave, under a certain weight ratio of solid raw material and solvent, heated to 200-220℃ for 1.0-3.0 h, then water-insoluble RHL was separated from the liquor reaction mixture by water precipitation. Results suggested that the lower digestion temperature and concentration of 1,4-butanediol were both unfavorable for extracting lignin. Chemical weight-average molecular weight of RHL was 1939 g·mol^-1, and the residual polysaccharide content was 5.12%. The ^1H-NMR spectra of RHL showed the relative intensity ratio, aliphatic over aromatic methoxyl groups, situated at 3.5-3.8 and 3.8-4.0 ppm, respectively. The results from ^13C-NMR spectra showed that β-O-4 bond and β-5 carbon-carbon linkage were the major linkages between RHL units. The C9-formula of RHL was calculated by the experiment data.展开更多
The molecular transformations of carboxylic acids in heavy acidic SL crude before and after true boiling point distillation were examined by ultra-high resolution negative-ion electrospray ionization(ESI) Fourier tran...The molecular transformations of carboxylic acids in heavy acidic SL crude before and after true boiling point distillation were examined by ultra-high resolution negative-ion electrospray ionization(ESI) Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS). The acid class(heteroatom number), type(z numbers) and carbon number distributions were positively characterized. It was found out that the total acid number(TAN) of SL crude decreased after true boiling point distillation, and the abundance of O2 class in mass spectra was also found to be reduced from 67.6% to 34.5% in SL TBP mixed crude as measured by MS spectra, indicating to a potential carboxylic acid decomposition. However, it was interesting that the carboxylic acids type distribution in both oils was almost the same although their relative abundance in SL TBP mixed crude turned to be much lower, suggesting that various petroleum carboxylic acid types have the similar thermal decomposition reaction behavior. Furthermore, for each O2 type of acids in SL TBP mixed crude, the abundance of carboxylic acids with carbon number higher than 35 was reduced greatly, especially for those with carbon number higher than 60, the mass peaks of which were nearly totally removed, indicating that the large carboxylic acid molecules in heavy fractions decomposed more significantly because of longer heating time during the true boiling point distillation process. As a result, the reduction of TAN may be caused by the thermal decomposition of carboxylic acids especially those with high carbon number, suggesting that quick distillation or much lower pressure is required to avoid the thermal decomposition.展开更多
Experiments were carried out to investigate the boiling heat transfer characteristics of Al_2O_3-water nanofluids in swirl microchannels under terrestrial gravity and acceleration fields. A centrifuge with a two-meter...Experiments were carried out to investigate the boiling heat transfer characteristics of Al_2O_3-water nanofluids in swirl microchannels under terrestrial gravity and acceleration fields. A centrifuge with a two-meter long rotational arm was used to simulate the acceleration magnitude up to 9 g and three various acceleration directions. Three test sections with different geometric parameters were applied. The volume concentration of Al_2O_3 nanoparticles with an average diameter of 13 nm was varied from 0.07% to 0.1%. The mass flow rate and vapor quality were in ranges of 3–6 kg/h and 0.4–1.0%, respectively. The effects of the mass flow rate, microchannel aspect ratio,vapor quality, nanoparticle volume concentration, and acceleration direction and magnitude were analyzed in a systematic manner. Experimental results showed that the acceleration direction and magnitude had significant influences on the boiling heat transfer. The heat transfer under configuration C was found to be superior to that under configurations A and B. Moreover, the heat transfer coefficient increased with increases of the mass flow rate and the volume concentration and decreased with the aspect ratio.展开更多
In order to solve the fouling problems in boiling processes,a boiling system was designedby adding solid particles to the boiling liquid In this paper.both theoretical analyses andexperimental studies on the boiling h...In order to solve the fouling problems in boiling processes,a boiling system was designedby adding solid particles to the boiling liquid In this paper.both theoretical analyses andexperimental studies on the boiling heat transfer in such a three-phase flow boiling were carried out.Based on the analysis of heat transfer characters of this three-phase flow boiling,a mathematical mod-el for the heat transfer coefficient of flow boiling was developed.The experiments show that,in thepresence of particles the boiling heat transfer is enhanced and is about 2 times that of the vaporliquid two phase one with better flow stability.The fluidized particles rub the heat transfer wall toprevent and to clean the fouling.展开更多
A new position group contribution model is proposed for the estimation of normal boiling data of organic compounds involving a carbon chain from C2 to C18.The characteristic of this method is the use of position distr...A new position group contribution model is proposed for the estimation of normal boiling data of organic compounds involving a carbon chain from C2 to C18.The characteristic of this method is the use of position distribution function.It could distinguish most of isomers that include cis-or trans-structure from organic compounds.Contributions for hydrocarbons and hydrocarbon derivatives containing oxygen,nitrogen,chlorine,bromine and sulfur,are given.Compared with the predictions,results made use of the most common existing group contribution methods,the overall average absolute difference of boiling point predictions of 417 organic compounds is 4.2 K;and the average absolute percent derivation is 1.0%,which is compared with 12.3 K and 3.2% with the method of Joback,12.1 K and 3.1% with the method of Constantinou-Gani.This new position contribution groups method is not only much more accurate but also has the advantages of simplicity and stability.展开更多
This paper proposed a new experimental rig of testing flow boiling heat transfer of refrigerant and lubricant oil mixture. The quantity of oil in the test section can be controlled and regulated conveniently and accur...This paper proposed a new experimental rig of testing flow boiling heat transfer of refrigerant and lubricant oil mixture. The quantity of oil in the test section can be controlled and regulated conveniently and accurately by connecting separate lubricant oil circuit with test section in parallel. It was built up by retrofitting a multiple air-conditioner and installing three oil-separators in serials at the compressor outlet. And so the lubricant oil in the discharged refrigerant gas of compressor can be removed completely.The refrigerant flow rate through test section can be bypassed by the by-path circuit of indoor unit.This experimental rig has advantages such as on-line and continuous oil injection, short time of obtaining stability, flexible operation, simple control, which lead to high efficiency in the research of flow boiling heat transfer of refrigerant and lubricant oil mixture.展开更多
Boiling processing is commonly used in post-harvest handling of White Paeony Root （WPR）, in order to whiten the herbal materials and preserve the bright color, since such WPR is empirically considered to possess a h...Boiling processing is commonly used in post-harvest handling of White Paeony Root （WPR）, in order to whiten the herbal materials and preserve the bright color, since such WPR is empirically considered to possess a higher quality. The present study was designed to investigate whether and how the boiling processing affects overall quality of WPR. First, an ultra-high performance liquid chromatography quadrupole/time-of-flight mass spectrometry-based metabolomics approach coupled with multivariate statistical analysis was developed to compare the holistic quality of boiled and un-boiled WPR samples. Second, ten major components in WPR samples boiled for different durations were quantitatively determined using high performance liquid chromatography to further explore the effects of boiling time on the holistic quality of WPR, meanwhile the appearance of the processed herbal materials was observed. The results suggested that the boiling processing conspicuously affected the holistic quality of WPR by simultaneously and inconsistently altering the chemical compositions and that short-time boiling processing between 2 and 10 rain could both make the WPR bright-colored and improve tile contents of major bioactive components, which were not achieved either without boiling or with prolonged boiling. In conclusion, short-term boiling （2-10 min） is recommended for post-harvest handling of WPR.展开更多
Fouling of heat transfer surfaces during subcooled flow boiling is a frequent engineering problem in process industries. It has been generally observed that the deposits in such industrial systems consist mainly of ca...Fouling of heat transfer surfaces during subcooled flow boiling is a frequent engineering problem in process industries. It has been generally observed that the deposits in such industrial systems consist mainly of calcium carbonate （CaCO3）, which has inverse solubility characteristics. This investigation focused on the mechanism to control deposition and the morphology of crystalline deposits. A series of experiments were carried out at different surface and bulk temperatures, fluid velocities and salt ion concentrations. It is shown that the deposition rate is controlled by different mechanism in the range of experimental parameters, depending on salt ion concentration. At higher ion concentration, the fouling rate increases linearly with surface temperature and the effect of flow velocity on deposition rate is quite strong, suggesting that mass diffusion controls the fouling process. On the contrary, at lower ion concentration, the fouling rate increases exponentially with surface temperature and is independent of the velocity, illustrating that surface reaction controls the fouling process. By analysis of the morphology of scale, two types of crystal （calcite and aragonite） are formed. The lower the temperature and ion concentration, the longer the induction period and the higher the percentage of calcite nreciDitated.展开更多
The surfactant additive octadecylamine (ODA) was used to enhance the flow boiling heat transfer of water in vertical copper tube, and the effects of the aqueous solution properties, mass fraction of ODA, mass flux and...The surfactant additive octadecylamine (ODA) was used to enhance the flow boiling heat transfer of water in vertical copper tube, and the effects of the aqueous solution properties, mass fraction of ODA, mass flux and heat flux etc. on flow boiling heat transfer were investigated. In order to analyze the mechanism of enhancement on boiling heat transfer with ODA, the copper surface was detected by XPS, and the diagram of binding energy was obtained. The results show that ODA can be adsorbed on the surface of the copper wall, and affects the properties of the heating surfaces and enhances the flow boiling heat transfer of water. Only in low heat flux and in a suitable range of concentration, can ODA aqueous solution enhance flow boiling heat transfer, and the suitable mass fraction of ODA is in the range of 1×10 -5 5×10 -5 . In addition, compared with water, ODA aqueous solution does not increase the flow drag under the same experimental conditions.展开更多
Heat transfer coefficients in nucleate pool boiling were measured on a horizontal copper surface for refrigerants, HFC-134a, HFC-32, and HFC-125, their binary and ternary mixtures under saturated conditions at 0.9MPa....Heat transfer coefficients in nucleate pool boiling were measured on a horizontal copper surface for refrigerants, HFC-134a, HFC-32, and HFC-125, their binary and ternary mixtures under saturated conditions at 0.9MPa. Compared to pure components, both binary and ternary mixtures showed lower heat transfer coefficients.This deterioration was more pronounced as heat flux was increased. Experimental data were compared with some empirical and semi-empirical correlations available in literature. For binary mixture, the accuracy of the correlations varied considerably with mixtures and the heat flux. Experimental data for HFC-32/134a/125 were also compared with available correlated equation obtained by Thome. For ternary mixture, the boiling range of binary mixture composed by the pure fluids with the lowest and the medium boiling points, and their concentration difference had important effects on boiling heat transfer coefficients.展开更多
文摘The pivotal role microchannels play in the thermal management of electronic components has,in recent decades,prompted extensive research into methods for enhancing their heat transfer performance.Among these methods,surface wettability modification was found to be highly effective owing to its significant influence on boiling dynamics and heat transfer mechanisms.In this study,we modified surface wettability using a nanocomposite coating composed of graphene nano plate(GNPs)and multi-walled carbon nanotubes(MWCNT)and then examined how the modification affected the transfer of boiling heat in microchannels.The resultant heat transfer coefficients for hydrophilic and hydrophilic composite(GNPs+MWCNT)microchannels were,respectively,42.8%and 33.95%higher compared with that of the uncoated surface.These results verify that hydrophilic GNP-based coating significantly improves boiling heat transfer performance.It was observed that a minor increase in contact angle,θfrom 73.142°to 75.73°,resulted in a noticeable decrease in thermal performance.This is attributed to diminished liquid film stability,reduced nucleation site activity,and weakened capillary-driven liquid replenishment.These findings underscore the crucial role of optimized surface wettability in maintaining efficient microchannel boiling.At high mass flux,the GNPS microchannels exhibited maximum pressure drop values,with a pressure drop ratio as high as 36%compared to 29%for the GNPs+MWCNT composite samples.Nevertheless,when a composite hydrophilic–hydrophobic coating was deposited through electrodeposition,the enhancement in heat transfer was less significant.This was probably due to decreased surface uniformity,diminished liquid film stability,and the disruption of effective nucleation behavior,all associated with the slight increase in surface contact angle.The obtained results can be used as guidance for designing advanced cooling surfaces in high-performance microelectronic and energy systems,where precise control of surface characteristics is critical.
基金supported by the National Natural Science Foundation of China(Project No.52166004)the National Key Research and Development Program of China(Project No.2022YFC3902000)the Major Science and Technology Special Project of Yunnan Province(Project Nos.202202AG050007,202202AG050002).
文摘This research explores the characteristics of boiling in inclined pipes,a domain of great importance in engineering.Employing an experimental visualization technique,the boiling dynamics of deionizedwater are examined at varying inclination angles,paying special attention to the emerging flow patterns.The findings demonstrate that the inclination angle significantly impacts flow pattern transitions within the 0°to 90°range.As the heat flux rises,bubbles form in the liquid.The liquid’s inertia extends the bubble-wall contact time,thereby delaying the onset of bulk bubble flow.Beyond a 90°inclination,however,the patterning behavior is more influenced by the fluid velocity.At low speeds,incomplete pipe filling results in a large liquid plug hindering flow,while high speeds lead to full pipe filling.In general,gravity,inertia,buoyancy forces,and capillary forces are themain influential factors in the considered problem.However,an analysis of the heat transfer coefficient and boiling curve for different inclination angles reveals that the observed variations are essentially due to corresponding changes in the flow pattern.Finally,an optimal mass flux and inclination angle,able to minimize total entropy generation and improve heat transfer efficiency,are determined by means of an entropy generation analysis.
基金supported by the National Natural Science Foundation of China(Grant No.52306026)the State Key Laboratory of Air-Conditioning Equipment and System Energy Conservation Open Project(Project No.ACSKL2021KT01)The APC was covered by the Special Innovation Project Fund of the the State Key Laboratory of Air-Conditioning Equipment and System Energy Conservation Open Project(Project No.ACSKL2021KT01).
文摘This study investigates the flow boiling heat transfer coefficient and pressure gradient of refrigerant R410A inmicro-channel flat tubes.Experiments were conducted at saturation temperatures ranging from 25℃ to 30℃,mass fluxes between 198 and 305 kg/m^(2)s,and heat fluxes from 9.77 to 20.18 kW/m^(2),yielding 99 sets of local heat transfer coefficient data.The results show that increasing heat flux and mass flux enhances the heat transfer coefficient,although the rate of enhancement decreases with increasing vapor quality.Conversely,higher saturation temperatures slightly reduce the heat transfer coefficient.Additionally,the experimental findings reveal discrepancies in the accuracy of existing pressure drop and heat transfer coefficient prediction models under the studied conditions.This study recommends using the Kimand Mudawar correlation to predict pressure gradients within the tested range,with aMean Error(ME)of−5.24%observed in this study.For heat transfer coefficients,the Cooper and Kandlikar correlations are recommended,achieving a Mean Absolute Error(MAE)of approximately 22%.This research provides value for performance prediction and parameter selection of micro-channel technology in broader application scenarios within heating,ventilation and air-conditioning fields.
基金supported by the Beijing Municipal Science&Technology Commission(Z231100006123010).
文摘In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 kg/(m2 s),saturation temperatures of 293,298,and 303 K,and inlet sub-cooling of 5,10,and 15 K.The analysis of the experimental results provides the following conclusions:a reduced mass flux and lower subcooling correspond to a diminished degree of superheat at the boiling inception wall;conversely,an elevated saturation temperature results in a reduced amount of superheat at the boiling inception wall.Furthermore,an increase in sub-cooling and saturation temperature will enhance heat transfer efficiency.The wall temperature is mostly influenced by variations in saturation temperature and is minimally related to changes in mass flux and subcooling degree.An increase in mass flux results in a greater pressure drop attributed to heightened frictional pressure loss.The variation in pressure drop with respect to sub-cooling is minimal,while an increased saturation temperature correlates with a reduced pressure drop due to the formation of smaller bubbles and lowered frictional pressure loss at high saturation pressures.This study thoroughly examines and summarizes the effects of mass flow rate,saturation temperature,and subcooling on the flow-boiling heat transfer and pressure drop characteristics of R1234yf.Furthermore,the new correlation has 93.42%of the predicted values fall within a 15%mean absolute error,exhibiting a mean absolute error of 5.75%.It provides a superior method for predicting the flow-boiling heat transfer coefficients of R1234yf in the heat sink of parallel microchannels compared to existing correlations.
基金supported by the National Natural Science Foundation of China(Project No.52166004)the National Key Research and Development Program of China(Project No.2022YFC3902000)+2 种基金the Major Science and Technology Special Project of Yunnan Province(Project Nos.202202AG050007202202AG050002)the Research on the Development of Complete Sets of Technology for Extraction of Aromatic Substances from Tobacco Waste and Its Application,Applied Research-Pyrolysis Process Technology Research(2023QT01).
文摘In modern engineering,enhancing boiling heat transfer efficiency is crucial for optimizing energy use and several industrial processes involving different types of materials.This study explores the enhancement of pool boiling heat transfer potentially induced by combining perforated copper particles on a heated surface with a sodium dodecyl sulfate(SDS)surfactant in saturated deionized water.Experiments were conducted at standard atmospheric pressure,with heat flux ranging from 20 to 100 kW/m2.The heating surface,positioned below the layer of freely moving copper beads,allowed the particle layer to shift due to liquid convection and steam nucleation.The study reports on the influence of copper bead diameter(2,3,4,and 5 mm),particle quantity,arrangement,and SDS concentration(20,200,and 500 ppm).It is shown that the combination of 5 mm particles and a 500 ppm SDS concentration can yield a remarkable 139%improvement in heat transfer efficiency.As demonstrated by direct flow visualization,bubble formation occurs primarily in the gaps between the particles and the heated surface,with the presence of SDS reducing bubble size and accelerating bubble detachment.
基金ported by the Beijing Municipal Science&Technology Commission(Z231100006123010)Guizhou Provincial Major Scientific and Technological Program(XKBF(2025)031)a grant from Tianjin Key Laboratory of Refrigeration Technology(2025TKLRT002).
文摘This experimental investigation was conducted on the flow boiling performance of refrigerant R134a in two types of parallel microchannels:sintered porous microchannels(PP-MCs)and smooth parallel microchannels(SP-MCs).The tests were performed under controlled conditions including an inlet subcooling of 5±0.2℃,saturation temperature of 33℃,mass fluxes of 346 and 485 kg/m2·s,and a range of heat fluxes.Key findings reveal that the sintered porous microstructure significantly enhances bubble nucleation,reducing the wall superheat required for the onset of nucleate boiling(ONB)to only 0.13℃ compared to 2.2℃ in smooth channels.The porous structure also improves heat transfer coefficients at low and medium heat fluxes(<20–30 W/cm^(2))and low vapor quality(x<0.2–0.4)due to augmented thin-film evaporation and intensified nucleate boiling.However,smooth microchannels exhibit superior performance under high heat flux and high vapor quality conditions,as the porous structure is prone to early dry-out and flow blockage.Notably,the porous microchannels demonstrate lower flow resistance and enhanced stability,with pressure drop fluctuations reduced by up to 46.4%in amplitude and 44.8%in standard deviation,attributed to improved capillary-assisted liquid replenishment and suppressed flow oscillations.The results underscore the potential of PP-MCs as a high-performance cooling solution for high-heat-flux applications.
基金funded by the National Natural Science Foundation of China(Grant No.52276047)the Open Fund of NationalKey Laboratory of SpacecraftThermal Control(Grant No.NKLST-JJ-202401011)the Beijing Municipal Science&Technology Commission(Grant No.Z231100006123010).
文摘Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.However,the continuous rise in power density of electronic components imposesmore stringent requirements on the heat transfer capability of microchannel flow boiling.HFE-7100,a dielectric coolant with favorable thermophysical properties,has become a focal point of research for enhancing flow boiling performance in open microchannels.The flow boiling heat transfer performance ofHFE-7100 was investigated in this study by fabricating micro-nano composite structures on the bottom surface of open microchannels using laser ablation technology.Based on visualization results,a comparative analysis was conducted on the bubble dynamics and flow pattern characteristics of HFE-7100 flow boiling in micronano structured open microchannels(MNSOMC)and smooth-surface open microchannels(SSOMC),to elucidate the enhancement mechanism of micro-nano structures on flow boiling heat transfer in open microchannels.The results indicate that the surface structures and strong wettability of MNSOMC accelerated bubble nucleation and departure.Moreover,bubbles in the channel tended to coalesce along the flow direction,forming elongated slug bubbles with high aspect ratios,which enabled efficient thin film evaporation in conjunction with intense nucleate boiling,thereby significantly enhancing flow boiling heat transfer.Under the experimental conditions of this study,the maximum enhancements in the heat transfer coefficient(HTC)and critical heat flux(CHF)of HFE-7100 inMNSOMC were 33.4%and 133.1%,respectively,with the CHF reaching up to 1542.3 kW⋅m^(−2).Furthermore,due to the superior wettability and capillary wicking capability of the micro-nano composite structures,the significant enhancement in flow boiling heat transfer was achieved without incurring a noticeable pressure drop penalty.
基金The National Natural Science Foundation of China(No.50776055,51076084)
文摘Based on the superposition principle of the nucleate boiling and convective heat transfer terms,a new correlation is developed for flow boiling heat transfer characteristics in helically coiled tubes.The effects of the geometric and system parameters on heat transfer characteristics in helically coiled tubes are investigated by collecting large amounts of experimental data and analyzing the heat transfer mechanisms. The existing correlations are divided into two categories,and they are calculated with the experimental data.The Dn factor is introduced to take into account the effect of a complex geometrical structure on flow boiling heat transfer.A new correlation is developed for predicting the flow boiling heat transfer coefficients in the helically coiled tubes,which is validated by the experimental data of R134a flow boiling heat transfer in them;and the average relative error and root mean square error of the new correlation are calculated.The results show that the new correlation agrees well with the experimental data,indicating that the new correlation can be used for predicting flow boiling heat transfer characteristics in the helically coiled tubes.
基金The National Natural Science Foundation of China(No.50706012)
文摘Two types of tube bundles are designed,which are,respectively,composed of six tubes arranged in the boiling chamber.The nucleate pool boiling performance of smooth tube bundles and sintered porous surface tube bundles with deionized water as a medium are experimentally studied at atmospheric and sub-atmospheric pressures,respectively.The experimental results indicate that the boiling heat transfer coefficients of the two types of tube bundles increase with the increase in pressure under vacuum conditions as they behave under ordinary pressure.As the pressure varies from 10 to 100 kPa,it also can be seen that the heat transfer coefficient of the sintered porous surface tube is increased by 0.2 to 4 times compared with the smooth one under the same operating parameters.In addition,the experimental data show that a definite bundle effect exists in both sintered porous surface tubes and smooth tubes under vacuum conditions.
基金This study was sponsored by the Research Funding for Key Laboratory of Cellulose and Ligno cellulosics Chemistry, Guangzhou Institute of Chemistry, Chinese Academy of Sciences (No. LCLC-2004-158)the National Natural Science Foundation of Fujian(No. Z0513015)
文摘Rice husk high boiling solvent lignin （RHL） was prepared by high boiling solvent method, and its characteristics was analyzed by using chemical composition analysis, infrared spectroscopy, and ^1H-NMR and ^13C-NMR spectroscopy. The optimum prepared condition was that the rice husk with 70%-90% aqueous solution of 1, 4-butanediol was mixed with autoclave, under a certain weight ratio of solid raw material and solvent, heated to 200-220℃ for 1.0-3.0 h, then water-insoluble RHL was separated from the liquor reaction mixture by water precipitation. Results suggested that the lower digestion temperature and concentration of 1,4-butanediol were both unfavorable for extracting lignin. Chemical weight-average molecular weight of RHL was 1939 g·mol^-1, and the residual polysaccharide content was 5.12%. The ^1H-NMR spectra of RHL showed the relative intensity ratio, aliphatic over aromatic methoxyl groups, situated at 3.5-3.8 and 3.8-4.0 ppm, respectively. The results from ^13C-NMR spectra showed that β-O-4 bond and β-5 carbon-carbon linkage were the major linkages between RHL units. The C9-formula of RHL was calculated by the experiment data.
基金financially supported by the National Key Basic Research Development Program "973" Project (2006CB202501)
文摘The molecular transformations of carboxylic acids in heavy acidic SL crude before and after true boiling point distillation were examined by ultra-high resolution negative-ion electrospray ionization(ESI) Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS). The acid class(heteroatom number), type(z numbers) and carbon number distributions were positively characterized. It was found out that the total acid number(TAN) of SL crude decreased after true boiling point distillation, and the abundance of O2 class in mass spectra was also found to be reduced from 67.6% to 34.5% in SL TBP mixed crude as measured by MS spectra, indicating to a potential carboxylic acid decomposition. However, it was interesting that the carboxylic acids type distribution in both oils was almost the same although their relative abundance in SL TBP mixed crude turned to be much lower, suggesting that various petroleum carboxylic acid types have the similar thermal decomposition reaction behavior. Furthermore, for each O2 type of acids in SL TBP mixed crude, the abundance of carboxylic acids with carbon number higher than 35 was reduced greatly, especially for those with carbon number higher than 60, the mass peaks of which were nearly totally removed, indicating that the large carboxylic acid molecules in heavy fractions decomposed more significantly because of longer heating time during the true boiling point distillation process. As a result, the reduction of TAN may be caused by the thermal decomposition of carboxylic acids especially those with high carbon number, suggesting that quick distillation or much lower pressure is required to avoid the thermal decomposition.
基金the financial support from the Youth Talent Plan of Beijing of China (No. YETP 1087)
文摘Experiments were carried out to investigate the boiling heat transfer characteristics of Al_2O_3-water nanofluids in swirl microchannels under terrestrial gravity and acceleration fields. A centrifuge with a two-meter long rotational arm was used to simulate the acceleration magnitude up to 9 g and three various acceleration directions. Three test sections with different geometric parameters were applied. The volume concentration of Al_2O_3 nanoparticles with an average diameter of 13 nm was varied from 0.07% to 0.1%. The mass flow rate and vapor quality were in ranges of 3–6 kg/h and 0.4–1.0%, respectively. The effects of the mass flow rate, microchannel aspect ratio,vapor quality, nanoparticle volume concentration, and acceleration direction and magnitude were analyzed in a systematic manner. Experimental results showed that the acceleration direction and magnitude had significant influences on the boiling heat transfer. The heat transfer under configuration C was found to be superior to that under configurations A and B. Moreover, the heat transfer coefficient increased with increases of the mass flow rate and the volume concentration and decreased with the aspect ratio.
文摘In order to solve the fouling problems in boiling processes,a boiling system was designedby adding solid particles to the boiling liquid In this paper.both theoretical analyses andexperimental studies on the boiling heat transfer in such a three-phase flow boiling were carried out.Based on the analysis of heat transfer characters of this three-phase flow boiling,a mathematical mod-el for the heat transfer coefficient of flow boiling was developed.The experiments show that,in thepresence of particles the boiling heat transfer is enhanced and is about 2 times that of the vaporliquid two phase one with better flow stability.The fluidized particles rub the heat transfer wall toprevent and to clean the fouling.
文摘A new position group contribution model is proposed for the estimation of normal boiling data of organic compounds involving a carbon chain from C2 to C18.The characteristic of this method is the use of position distribution function.It could distinguish most of isomers that include cis-or trans-structure from organic compounds.Contributions for hydrocarbons and hydrocarbon derivatives containing oxygen,nitrogen,chlorine,bromine and sulfur,are given.Compared with the predictions,results made use of the most common existing group contribution methods,the overall average absolute difference of boiling point predictions of 417 organic compounds is 4.2 K;and the average absolute percent derivation is 1.0%,which is compared with 12.3 K and 3.2% with the method of Joback,12.1 K and 3.1% with the method of Constantinou-Gani.This new position contribution groups method is not only much more accurate but also has the advantages of simplicity and stability.
文摘This paper proposed a new experimental rig of testing flow boiling heat transfer of refrigerant and lubricant oil mixture. The quantity of oil in the test section can be controlled and regulated conveniently and accurately by connecting separate lubricant oil circuit with test section in parallel. It was built up by retrofitting a multiple air-conditioner and installing three oil-separators in serials at the compressor outlet. And so the lubricant oil in the discharged refrigerant gas of compressor can be removed completely.The refrigerant flow rate through test section can be bypassed by the by-path circuit of indoor unit.This experimental rig has advantages such as on-line and continuous oil injection, short time of obtaining stability, flexible operation, simple control, which lead to high efficiency in the research of flow boiling heat transfer of refrigerant and lubricant oil mixture.
基金supported by a special fund of China State Administration of Traditional Chinese Medicine(No.201307008-2)National High Technology Research and Development Plan of China(863 Plain)(No.2014AA022204)+1 种基金Jiangsu Province Six Talent Project(YY-007)Jiangsu Branch of China Academy of Chinese Medical Science(No.JSBN1301)
文摘Boiling processing is commonly used in post-harvest handling of White Paeony Root （WPR）, in order to whiten the herbal materials and preserve the bright color, since such WPR is empirically considered to possess a higher quality. The present study was designed to investigate whether and how the boiling processing affects overall quality of WPR. First, an ultra-high performance liquid chromatography quadrupole/time-of-flight mass spectrometry-based metabolomics approach coupled with multivariate statistical analysis was developed to compare the holistic quality of boiled and un-boiled WPR samples. Second, ten major components in WPR samples boiled for different durations were quantitatively determined using high performance liquid chromatography to further explore the effects of boiling time on the holistic quality of WPR, meanwhile the appearance of the processed herbal materials was observed. The results suggested that the boiling processing conspicuously affected the holistic quality of WPR by simultaneously and inconsistently altering the chemical compositions and that short-time boiling processing between 2 and 10 rain could both make the WPR bright-colored and improve tile contents of major bioactive components, which were not achieved either without boiling or with prolonged boiling. In conclusion, short-term boiling （2-10 min） is recommended for post-harvest handling of WPR.
基金Supported by the Special Funds for Major State Basic Research Projects of China (G2000026304)
文摘Fouling of heat transfer surfaces during subcooled flow boiling is a frequent engineering problem in process industries. It has been generally observed that the deposits in such industrial systems consist mainly of calcium carbonate （CaCO3）, which has inverse solubility characteristics. This investigation focused on the mechanism to control deposition and the morphology of crystalline deposits. A series of experiments were carried out at different surface and bulk temperatures, fluid velocities and salt ion concentrations. It is shown that the deposition rate is controlled by different mechanism in the range of experimental parameters, depending on salt ion concentration. At higher ion concentration, the fouling rate increases linearly with surface temperature and the effect of flow velocity on deposition rate is quite strong, suggesting that mass diffusion controls the fouling process. On the contrary, at lower ion concentration, the fouling rate increases exponentially with surface temperature and is independent of the velocity, illustrating that surface reaction controls the fouling process. By analysis of the morphology of scale, two types of crystal （calcite and aragonite） are formed. The lower the temperature and ion concentration, the longer the induction period and the higher the percentage of calcite nreciDitated.
基金The Natural Science Foundation of Tianjin(No.94220)
文摘The surfactant additive octadecylamine (ODA) was used to enhance the flow boiling heat transfer of water in vertical copper tube, and the effects of the aqueous solution properties, mass fraction of ODA, mass flux and heat flux etc. on flow boiling heat transfer were investigated. In order to analyze the mechanism of enhancement on boiling heat transfer with ODA, the copper surface was detected by XPS, and the diagram of binding energy was obtained. The results show that ODA can be adsorbed on the surface of the copper wall, and affects the properties of the heating surfaces and enhances the flow boiling heat transfer of water. Only in low heat flux and in a suitable range of concentration, can ODA aqueous solution enhance flow boiling heat transfer, and the suitable mass fraction of ODA is in the range of 1×10 -5 5×10 -5 . In addition, compared with water, ODA aqueous solution does not increase the flow drag under the same experimental conditions.
基金Century Programme of Chinese Academy of Sciences.
文摘Heat transfer coefficients in nucleate pool boiling were measured on a horizontal copper surface for refrigerants, HFC-134a, HFC-32, and HFC-125, their binary and ternary mixtures under saturated conditions at 0.9MPa. Compared to pure components, both binary and ternary mixtures showed lower heat transfer coefficients.This deterioration was more pronounced as heat flux was increased. Experimental data were compared with some empirical and semi-empirical correlations available in literature. For binary mixture, the accuracy of the correlations varied considerably with mixtures and the heat flux. Experimental data for HFC-32/134a/125 were also compared with available correlated equation obtained by Thome. For ternary mixture, the boiling range of binary mixture composed by the pure fluids with the lowest and the medium boiling points, and their concentration difference had important effects on boiling heat transfer coefficients.
