Considering the special walking behavior of astronauts on the lunar surface,to reduce the impact on their bones and improve safety during extravehicular operations and walking,a magnetorheological(MR)damping mechanism...Considering the special walking behavior of astronauts on the lunar surface,to reduce the impact on their bones and improve safety during extravehicular operations and walking,a magnetorheological(MR)damping mechanism of power assisted transmission joint used in a new type spacesuit is proposed.In order to improve the damping performance of the MR damper,the influence of the damper s structural parameters on both the output and dynamic adjustable range of the damping torque is examined.According to the theoretical mechanical model,the output damping torque is calculated,the finite element method is used to conduct numerical tests.At the same time,the structural parameters of the damper are optimized by the response surface methods.The results indicate that the simulated torque aligns with the theoretically designed torque,and the damping characteristics of the optimized structure are effectively improved by the response surface method.Compared with the initial structure,the damping torque is increased by 10.8%,and the dynamic adjustable range is expanded by 52.9%.展开更多
Approximately 40% of pheochromocytoma and paraganglioma(PPGL) cases are familial, typically presenting earlier with more complex symptoms. This paper synthesizes literature and guidelines to inform on clinical charact...Approximately 40% of pheochromocytoma and paraganglioma(PPGL) cases are familial, typically presenting earlier with more complex symptoms. This paper synthesizes literature and guidelines to inform on clinical characteristics and perioperative care for PPGL. Pheochromocytoma in von Hippel-Lindau(VHL) disease exhibits heightened secretion activity without significant perioperative hemodynamic changes. Tumors in multiple endocrine neoplasia type 2(MEN2) have a stronger endocrine function, which may induce hemodynamic fluctuations during surgery. Therefore, pheochromocytoma screening is essential at all stages of MEN2. Neurofibromatosis type 1(NF1) often presents multisystem lesions and can result in difficult airway. Pheochromocytoma should be evaluated when NF1 patients present hypertension. Pheochromocytoma and paraganglioma type 5 may present multiple lesions of pheochromocytoma or paraganglioma. In summary, hereditary PPGLs may present with severe lesions in other systems, beyond tumor function. A multi-disciplinary team(MDT) approach is often invaluable in perioperative management.展开更多
Migraine is a complex and heterogeneous disorder. Although several genetic models has been proposed including autosomal-dominant/autosomal recessive, sex-linked, sex-limited, mitochondrial, and multi-gene, none of the...Migraine is a complex and heterogeneous disorder. Although several genetic models has been proposed including autosomal-dominant/autosomal recessive, sex-linked, sex-limited, mitochondrial, and multi-gene, none of these models can well-explain the transmission of the disease. We hypothesied that migraine is a sex-conditioned inherited disorder (autosomal dominant in females and autosomal recessive in males). This hypothesis is supported by the evidence such as the locations of genes associated with familial hemiplegic migraine, possibly "typical" migraine as well (dominantly on chromosome 19p, lq, and 2q), male:female ratio of prevalence (1:2-1:4), the mostly youth-onset, the provocation by the contraceptives, the induction by menstruation, and the self-limitation after menopause. Female sex-hormones appear to be the key contributor to a higher prevalence of migraine in female. Socio-environmental factors may also play an important role.展开更多
[ Objective ] The aim of this study was to investigate the epidemic status of porcine pleuropneumonia in western Shandong and establish the PCR method of actinobacillus pleuropneumoniae (APP). [ Method] The epidemic...[ Objective ] The aim of this study was to investigate the epidemic status of porcine pleuropneumonia in western Shandong and establish the PCR method of actinobacillus pleuropneumoniae (APP). [ Method] The epidemic status of APP in lesion tissues of 186 death pigs and 545 health pigs without clinical symptoms was analyzed by PCR method. [ Result] APP positive rate in 186 samples accounted for 43.0% (80/186), while that in 545 porcine serums accounted for 9.4% (51/545). [ Conclusion] This PCR method can be used as one of the important means for APP clinical diagnosis.展开更多
Objective: To evaluate the effects of dietary factors on cancer and non-communicable diseases. Methods: A correlation analysis between the consumption of various indicator food and mortality rates of cancer or non-com...Objective: To evaluate the effects of dietary factors on cancer and non-communicable diseases. Methods: A correlation analysis between the consumption of various indicator food and mortality rates of cancer or non-communicable diseases was conducted by collecting secondary data from national nutrition surveys in Japan. Results: The consumption of cereal foods, plant energy and plant protein showed a significant negative correlation with mortality of cancer, heart diseases and diabetes; negatively related to the lung cancer and colon cancer in both sexes; a strong negative correlation with mortality of rectum cancer, liver cancer and prostate cancer in males, and of breast cancer in females; and a significant positive correlation with the stomach cancer in both sexes. The consumption of animal foods, animal energy, animal protein and fat showed a strong positive correlation with cancer, heart diseases and diabetes; a positive relations to lung cancer and colon cancer in both sexes, and rectum cancer, liver cancer and prostate cancer in males and breast cancer in females. On the contrary, a strong negative correlation was found in stomach cancer in both sexes; and esophagus cancer, liver cancer and uterus cancer in females. The consumption of vegetables and fruits showed a weak negative correlation with stomach cancer. Conclusion : The results suggest that diet not only plays a significant role in increasing the risks of some kinds of cancer or non-communicable diseases but also has a preventive effect. It is very important that dietary balance should be emphasized to prevent cancer and non-com-municable diseases.展开更多
Analysis is carried out to study the existence, uniqueness and behavior of exact solutions of the fourth order nonlinear coupled ordinary differential equations arising in the flow and heat transfer of a viscoelastic,...Analysis is carried out to study the existence, uniqueness and behavior of exact solutions of the fourth order nonlinear coupled ordinary differential equations arising in the flow and heat transfer of a viscoelastic, electrically conducting fluid past a continuously stretching sheet. The ranges of the parametric values are obtained for which the system has a unique pair of solutions, a double pair of solutions and infinitely many solutions.展开更多
The mechanically stirred internal loop airlift reactors equipped with or without static mixers are devised for intensification of gas-liquid mass transfer rate. The influences of superficial gas velocity, agitation o...The mechanically stirred internal loop airlift reactors equipped with or without static mixers are devised for intensification of gas-liquid mass transfer rate. The influences of superficial gas velocity, agitation or static mixers on gas hold-up, mixing time, liquid circulating velocity and volumetric mass transfer coefficient have been investigated with tap water and carboxymethyl cellulose (CMC) aqueous solution. The experimental results indicate that mechanical agitation is more efficacious than static mixer in highly viscous media for improving mass transfer in airlift reactors. The empirical correlation of volumetric mass transfer coefficient with apparent viscosity, and energy consumption for mechanical agitation and aeration is developed.展开更多
Almost without exception literature data and modeling effort are understandably devoted to water as the sprayed liquid since it constitutes the most common liquid used in spray drying applications. In selected applica...Almost without exception literature data and modeling effort are understandably devoted to water as the sprayed liquid since it constitutes the most common liquid used in spray drying applications. In selected applications, however, the liquid making up the solution or suspension may not be water. The objective of this work is to examine the differences in flow patterns, thermal behavior and drying rates caused by different liquids having different thermo-physical properties spray into a spray dryer using a computational fluid dynamic model.Numerical experiments were carried out for water (base case), ethyl alcohol and isopropyl alcohol-the latter two as model non-aqueous liquids. The chamber geometry was cylinder type with a co-current axial pressure nozzle and also an axial central exit so that the configuration is two dimensional and axi-symmetric. It is shown that the liquid properties can have major influence on the thermal field, droplet trajectories, residence times and overall evaporation capacity when all parameters of the problem are held fixed. Deviations from the single phase turbulent airflow in the same chamber without spray are different for the three liquids examined.展开更多
Shape and quantity of helical baffles have great impact on the shell-side performance of helical baffled heat exchangers (HBHE). In this work, three physical models of HBHE with baffles of different shape (trisecti...Shape and quantity of helical baffles have great impact on the shell-side performance of helical baffled heat exchangers (HBHE). In this work, three physical models of HBHE with baffles of different shape (trisection, quadrant and sextant sector) were investigated. Numerical simulations were performed on HBHE at three helix an- gles (10°, 25° and 40°) by the software ANSYS CFX. Analyses of numerical results indicate that the sextant HBHE shows relatively better fluid flow performance because the leakage flow in the triangle area is evidently reduced and the fluid streamline appears much closer to an ideal spiral flow, while the trisection and quadrant HBHE show more scattered and disordered streamline distributions. The convective heat transfer coefficient and pressure drop in three types of HBHE were presented. Further investigations on the shell side performance with different helical baf- fles were implemented by the field synergy theory. Both theoretical and numerical analyses gave support on the re- lations between helical baffle shape and shell-side performance. This paper may provide useful reference for the selection of baffle shade and auantitv in HBHE.展开更多
Experiments were carried out to study the heat transfer performance of an impinging jet in a cross flow.Several parameters including the jet-to-cross-flow mass ratio(X=2%-8%), the Reynolds number(Red=1434-5735)and the...Experiments were carried out to study the heat transfer performance of an impinging jet in a cross flow.Several parameters including the jet-to-cross-flow mass ratio(X=2%-8%), the Reynolds number(Red=1434-5735)and the jet diameter(d=2-4 mm) were explored. The heat transfer enhancement factor was found to increase with the jet-to-cross-flow mass ratio and the Reynolds number, but decrease with the jet diameter when other parameters maintain fixed. The presence of a cross flow was observed to degrade the heat transfer performance in respect to the effect of impinging jet to the target surface only. In addition, an impinging jet was confirmed to be capable of enhancing the heat transfer process in considerable amplitude even though the jet was not designed to impinge on the target surface.展开更多
A new kind of hydraulic transformer, called variable hydraulic transformer(VHT), is proposed to control its load flow rate. The hydraulic transformer evolves from a pressure transducer to a power transducer. The flow ...A new kind of hydraulic transformer, called variable hydraulic transformer(VHT), is proposed to control its load flow rate. The hydraulic transformer evolves from a pressure transducer to a power transducer. The flow characteristics of VHT, such as its instantaneous flow rates, average flow rates, and flow pulsations in the ports, are investigated. Matlab software is used to simulate and calculate. There are five controlled angles of the port plate that can help to define the flow characteristics of VHT. The relationships between the flow characteristics and the structure in VHT are shown. Also, the plus-minus change of the average flow rates and the continuity of the instantaneous flow rates in the ports are presented. The results demonstrate the performance laws of VHT when the controlled angles of the port plate and of the swash plate change. The results also reveal that the special principle of the flow pulsation in the ports and the jump points of the instantaneous curves are the two basic causes of its loud noise, and that the control angles of the port plate and the swash plate and the pressures in the ports are the three key factors of the noise.展开更多
The physical models of the outer and inner half coil jackets were simplified to two types of coiled ducts.The mathematic models of incompressible fluid at the condition of laminar flow and heat transfer in the two typ...The physical models of the outer and inner half coil jackets were simplified to two types of coiled ducts.The mathematic models of incompressible fluid at the condition of laminar flow and heat transfer in the two types of jackets for cooling process reactor were set up and solved by the semi-implicit method for pressure linked equa-tions consistent (SIMPLEC) algorithm based on a control volume method.The flow and temperature fields were given and the effects of Dean and Prandtl numbers on flow and heat transfer were studied.The results show that flow in the inner half coil jacket is found to exhibit transition of secondary flow pattern from two vortices to four vortices when the Dean number increases,but that in the outer half coil jacket is not found.The critical Dean num-ber is about 96.The inner half coil jacket has stronger heat transfer ability than the outer half coil jacket and this superiority is more evident with larger Prandtl number.However,as the Dean number is greater than 105,the flow resistance enhances more severely in the inner jacket than the outer jacket.For both jackets,the centers of the heated wall are the poorest for heat transfer.展开更多
The main objective of this work is to investigate analytically the steady nanofluid flow and heat transfer characteristics between nonparallel plane walls. Using appropriate transformations for the velocity and temper...The main objective of this work is to investigate analytically the steady nanofluid flow and heat transfer characteristics between nonparallel plane walls. Using appropriate transformations for the velocity and temperature, the basic nonlinear partial differential equations are reduced to the ordinary differential equations. Then, these equations have been solved analytically and numerically for some values of the governing parameters, Reynolds number, Re, channel half angle, α, Prandtl number, Pr, and Eckert number, Ec, using Adomian decomposition method and the Runge-Kutta method with mathematic package. Analytical and numerical results are searched for the skin friction coefficient, Nusselt number and the velocity and temperature profiles. It is found on one hand that the Nusselt number increases as Eckert number or channel half-angle increases, but it decreases as Reynolds number increases. On the other hand, it is also found that the presence of Cu nanoparticles in a water base fluid enhances heat transfer between nonparallel plane walls and in consequence the Nusselt number increases with the increase of nanoparticles volume fraction. Finally, an excellent agreement between analytical results and those obtained by numerical Runge-Kutta method is highly noticed.展开更多
This work illustrates the steady state, two dimensional natural convective flow and heat transfer features in square enclosure containing heated hexagonal block maintained either at constant wall temperature(CWT) or u...This work illustrates the steady state, two dimensional natural convective flow and heat transfer features in square enclosure containing heated hexagonal block maintained either at constant wall temperature(CWT) or uniform heat flux(UHF) thermal conditions. Governing equations(mass, momentum and energy) are solved by using finite volume method(FVM) with 3rd order accurate QUICK discretization scheme and SIMPLE algorithm for range of field pertinent parameters such as, Grashof number(10~3≤ Gr ≤ 10~6), Prandtl number(1 ≤ Pr ≤ 100) and power law index(0.5 ≤ n ≤ 1.5). The analysis of momentum and heat transfer characteristics are delineated by evolution of streamlines, isotherms, variation of average Nusselt number value and Colburn factor for natural convection(j_(nH)). A remarkable change is observed on fluid flow and thermal distribution pattern in cavity for both thermal conditions. Nusselt number shows linear variation with Grashof and Prandtl numbers; while rate of heat transfer by convection decreases for power law index value. Higher heat transfer rate can be achieved by using uniform heat flux condition. A Nusselt number correlation is developed for possible utilization in engineering/scientific design purpose.展开更多
New models for describing hydrodynamics and mass transfer performance in supercritical fluid extraction columns were proposed. Those models were proved by experimental data, which were obtained in supercritical fluid ...New models for describing hydrodynamics and mass transfer performance in supercritical fluid extraction columns were proposed. Those models were proved by experimental data, which were obtained in supercritical fluid extraction packed column, spray column and sieve tray column respectively. The inner diameter of those columns areФ25 mm. These experimental systems include supercritical carbon diox-ide-isopropanol-water and supercritical carbon dioxide-ethanol-water, in which supercritical carbon dioxide was dispersed phase, and another was continuous phase. The extraction processes were operated with continuous countercurrent flow. The predicted values are agreed well with experimental data.展开更多
Nano fluid is considered to be a class of high efficient heat transfer fluid created by dispersing some special solid nanoparticles (normally less than 100 nm) in traditional heat transfer fluid. The present experimen...Nano fluid is considered to be a class of high efficient heat transfer fluid created by dispersing some special solid nanoparticles (normally less than 100 nm) in traditional heat transfer fluid. The present experiment was conducted aiming at investigating the forced heat transfer characteristics of aqueous copper (Cu) nanofluid at varying concentration of Cu nano-particles in different flow regimes (300<Re≤16 000). The forced convective heat transfer enhancement is available both in the laminar and turbulent flow with increasing the concentration. Especially, the enhancement rate increases dramatically in laminar flow regime, for instance, the heat transfer coefficient of Cu/water nanofluid increases by two times at around Re=2 000 compared with that of base fluid water, and averagely increases by 62% at 1% volume fraction. However, the heat transfer coefficient of Cu/water decreases sharply in the transition flow regime. Furthermore, it has the trend that the heat transfer coefficient displays worse with increasing the concentration.展开更多
An experimental study was conducted to investigate the fouling process of calcium carbonate on the heat transfer surface, during forced convective heat transfer. The dynamic monitoring apparatus of fouling resistance ...An experimental study was conducted to investigate the fouling process of calcium carbonate on the heat transfer surface, during forced convective heat transfer. The dynamic monitoring apparatus of fouling resistance was set up for the present experiments. The fouling behavio(s were examined under different factors including fluid velocity, hardness,alkalinity, solution temperature, and wall temperature. Asymptotic fouling curves varying with time were obtained. The fouling rate and asymptotic fouling resistance increased and the induction periods were shortened with the fluid velocity decreasing, hardness andalkalinity increasing, and solution temperature and heat transfer surface temperature increasing. Thecomponents of fouling that formed on the heat transfer surface included crystallization fouling and particulate fouling. The thermal performance parameter of fouling,ρfhf, varied from 380 to 2600 kg·W·(m^4·K)^-1, increasing with growing velocity and decreasing solution temperature, hardness or alkalinity. Furthermore, the thermal conductivity of fouling, λf, varied from 1.7 to 2.2 W·(m·K)^-1 .展开更多
This paper investigates the maximal achievable multi-rate throughput problem of a multicast ses-sion at the presence of network coding. Deviating from previous works which focus on single-rate network coding, our work...This paper investigates the maximal achievable multi-rate throughput problem of a multicast ses-sion at the presence of network coding. Deviating from previous works which focus on single-rate network coding, our work takes the heterogeneity of sinks into account and provides multiple data layers to address the problem. Firstly formulated is the maximal achievable throughput problem with the assumption that the data layers are independent and layer rates are static. It is proved that the problem in this case is, unfortunately, Non-deterministic Polynomial-time (NP)-hard. In addition, our formulation is extended to the problems with dependent layers and dynamic layers. Furthermore, the approximation algorithm which satisfies certain fair-ness is proposed.展开更多
基金The Natural Science Foundation of Shanghai(No.20ZR1401300).
文摘Considering the special walking behavior of astronauts on the lunar surface,to reduce the impact on their bones and improve safety during extravehicular operations and walking,a magnetorheological(MR)damping mechanism of power assisted transmission joint used in a new type spacesuit is proposed.In order to improve the damping performance of the MR damper,the influence of the damper s structural parameters on both the output and dynamic adjustable range of the damping torque is examined.According to the theoretical mechanical model,the output damping torque is calculated,the finite element method is used to conduct numerical tests.At the same time,the structural parameters of the damper are optimized by the response surface methods.The results indicate that the simulated torque aligns with the theoretically designed torque,and the damping characteristics of the optimized structure are effectively improved by the response surface method.Compared with the initial structure,the damping torque is increased by 10.8%,and the dynamic adjustable range is expanded by 52.9%.
文摘Approximately 40% of pheochromocytoma and paraganglioma(PPGL) cases are familial, typically presenting earlier with more complex symptoms. This paper synthesizes literature and guidelines to inform on clinical characteristics and perioperative care for PPGL. Pheochromocytoma in von Hippel-Lindau(VHL) disease exhibits heightened secretion activity without significant perioperative hemodynamic changes. Tumors in multiple endocrine neoplasia type 2(MEN2) have a stronger endocrine function, which may induce hemodynamic fluctuations during surgery. Therefore, pheochromocytoma screening is essential at all stages of MEN2. Neurofibromatosis type 1(NF1) often presents multisystem lesions and can result in difficult airway. Pheochromocytoma should be evaluated when NF1 patients present hypertension. Pheochromocytoma and paraganglioma type 5 may present multiple lesions of pheochromocytoma or paraganglioma. In summary, hereditary PPGLs may present with severe lesions in other systems, beyond tumor function. A multi-disciplinary team(MDT) approach is often invaluable in perioperative management.
文摘Migraine is a complex and heterogeneous disorder. Although several genetic models has been proposed including autosomal-dominant/autosomal recessive, sex-linked, sex-limited, mitochondrial, and multi-gene, none of these models can well-explain the transmission of the disease. We hypothesied that migraine is a sex-conditioned inherited disorder (autosomal dominant in females and autosomal recessive in males). This hypothesis is supported by the evidence such as the locations of genes associated with familial hemiplegic migraine, possibly "typical" migraine as well (dominantly on chromosome 19p, lq, and 2q), male:female ratio of prevalence (1:2-1:4), the mostly youth-onset, the provocation by the contraceptives, the induction by menstruation, and the self-limitation after menopause. Female sex-hormones appear to be the key contributor to a higher prevalence of migraine in female. Socio-environmental factors may also play an important role.
基金Supported by Visiting Scholar Fund for Outstanding Young Teachersin colleges and Universities of Shandong~~
文摘[ Objective ] The aim of this study was to investigate the epidemic status of porcine pleuropneumonia in western Shandong and establish the PCR method of actinobacillus pleuropneumoniae (APP). [ Method] The epidemic status of APP in lesion tissues of 186 death pigs and 545 health pigs without clinical symptoms was analyzed by PCR method. [ Result] APP positive rate in 186 samples accounted for 43.0% (80/186), while that in 545 porcine serums accounted for 9.4% (51/545). [ Conclusion] This PCR method can be used as one of the important means for APP clinical diagnosis.
文摘Objective: To evaluate the effects of dietary factors on cancer and non-communicable diseases. Methods: A correlation analysis between the consumption of various indicator food and mortality rates of cancer or non-communicable diseases was conducted by collecting secondary data from national nutrition surveys in Japan. Results: The consumption of cereal foods, plant energy and plant protein showed a significant negative correlation with mortality of cancer, heart diseases and diabetes; negatively related to the lung cancer and colon cancer in both sexes; a strong negative correlation with mortality of rectum cancer, liver cancer and prostate cancer in males, and of breast cancer in females; and a significant positive correlation with the stomach cancer in both sexes. The consumption of animal foods, animal energy, animal protein and fat showed a strong positive correlation with cancer, heart diseases and diabetes; a positive relations to lung cancer and colon cancer in both sexes, and rectum cancer, liver cancer and prostate cancer in males and breast cancer in females. On the contrary, a strong negative correlation was found in stomach cancer in both sexes; and esophagus cancer, liver cancer and uterus cancer in females. The consumption of vegetables and fruits showed a weak negative correlation with stomach cancer. Conclusion : The results suggest that diet not only plays a significant role in increasing the risks of some kinds of cancer or non-communicable diseases but also has a preventive effect. It is very important that dietary balance should be emphasized to prevent cancer and non-com-municable diseases.
文摘Analysis is carried out to study the existence, uniqueness and behavior of exact solutions of the fourth order nonlinear coupled ordinary differential equations arising in the flow and heat transfer of a viscoelastic, electrically conducting fluid past a continuously stretching sheet. The ranges of the parametric values are obtained for which the system has a unique pair of solutions, a double pair of solutions and infinitely many solutions.
文摘The mechanically stirred internal loop airlift reactors equipped with or without static mixers are devised for intensification of gas-liquid mass transfer rate. The influences of superficial gas velocity, agitation or static mixers on gas hold-up, mixing time, liquid circulating velocity and volumetric mass transfer coefficient have been investigated with tap water and carboxymethyl cellulose (CMC) aqueous solution. The experimental results indicate that mechanical agitation is more efficacious than static mixer in highly viscous media for improving mass transfer in airlift reactors. The empirical correlation of volumetric mass transfer coefficient with apparent viscosity, and energy consumption for mechanical agitation and aeration is developed.
文摘Almost without exception literature data and modeling effort are understandably devoted to water as the sprayed liquid since it constitutes the most common liquid used in spray drying applications. In selected applications, however, the liquid making up the solution or suspension may not be water. The objective of this work is to examine the differences in flow patterns, thermal behavior and drying rates caused by different liquids having different thermo-physical properties spray into a spray dryer using a computational fluid dynamic model.Numerical experiments were carried out for water (base case), ethyl alcohol and isopropyl alcohol-the latter two as model non-aqueous liquids. The chamber geometry was cylinder type with a co-current axial pressure nozzle and also an axial central exit so that the configuration is two dimensional and axi-symmetric. It is shown that the liquid properties can have major influence on the thermal field, droplet trajectories, residence times and overall evaporation capacity when all parameters of the problem are held fixed. Deviations from the single phase turbulent airflow in the same chamber without spray are different for the three liquids examined.
基金Supported by the National Natural Science Foundation of China(51106090)the National Key Basic Research Program of China(2013CB228305)the Independent Innovation Foundation of Shandong University(2012TS190)
文摘Shape and quantity of helical baffles have great impact on the shell-side performance of helical baffled heat exchangers (HBHE). In this work, three physical models of HBHE with baffles of different shape (trisection, quadrant and sextant sector) were investigated. Numerical simulations were performed on HBHE at three helix an- gles (10°, 25° and 40°) by the software ANSYS CFX. Analyses of numerical results indicate that the sextant HBHE shows relatively better fluid flow performance because the leakage flow in the triangle area is evidently reduced and the fluid streamline appears much closer to an ideal spiral flow, while the trisection and quadrant HBHE show more scattered and disordered streamline distributions. The convective heat transfer coefficient and pressure drop in three types of HBHE were presented. Further investigations on the shell side performance with different helical baf- fles were implemented by the field synergy theory. Both theoretical and numerical analyses gave support on the re- lations between helical baffle shape and shell-side performance. This paper may provide useful reference for the selection of baffle shade and auantitv in HBHE.
基金Supported by the National Natural Science Foundation of China(51106140)the Natural Science Foundation of Zhejiang Province(Z1110695)
文摘Experiments were carried out to study the heat transfer performance of an impinging jet in a cross flow.Several parameters including the jet-to-cross-flow mass ratio(X=2%-8%), the Reynolds number(Red=1434-5735)and the jet diameter(d=2-4 mm) were explored. The heat transfer enhancement factor was found to increase with the jet-to-cross-flow mass ratio and the Reynolds number, but decrease with the jet diameter when other parameters maintain fixed. The presence of a cross flow was observed to degrade the heat transfer performance in respect to the effect of impinging jet to the target surface only. In addition, an impinging jet was confirmed to be capable of enhancing the heat transfer process in considerable amplitude even though the jet was not designed to impinge on the target surface.
基金Projects(50875054,51275123)supported by the National Natural Science Foundation of ChinaProject(GZKF-2008003)supported by the Open Foundation of State Key Laboratory of Fluid Transmission and Control,China
文摘A new kind of hydraulic transformer, called variable hydraulic transformer(VHT), is proposed to control its load flow rate. The hydraulic transformer evolves from a pressure transducer to a power transducer. The flow characteristics of VHT, such as its instantaneous flow rates, average flow rates, and flow pulsations in the ports, are investigated. Matlab software is used to simulate and calculate. There are five controlled angles of the port plate that can help to define the flow characteristics of VHT. The relationships between the flow characteristics and the structure in VHT are shown. Also, the plus-minus change of the average flow rates and the continuity of the instantaneous flow rates in the ports are presented. The results demonstrate the performance laws of VHT when the controlled angles of the port plate and of the swash plate change. The results also reveal that the special principle of the flow pulsation in the ports and the jump points of the instantaneous curves are the two basic causes of its loud noise, and that the control angles of the port plate and the swash plate and the pressures in the ports are the three key factors of the noise.
基金Supported by the National Key Technologies Research and Development Program during the 10th Five-year Plan Period(2004BA319B1)the Educational Commission of Liaoning Province of China(2008S117)
文摘The physical models of the outer and inner half coil jackets were simplified to two types of coiled ducts.The mathematic models of incompressible fluid at the condition of laminar flow and heat transfer in the two types of jackets for cooling process reactor were set up and solved by the semi-implicit method for pressure linked equa-tions consistent (SIMPLEC) algorithm based on a control volume method.The flow and temperature fields were given and the effects of Dean and Prandtl numbers on flow and heat transfer were studied.The results show that flow in the inner half coil jacket is found to exhibit transition of secondary flow pattern from two vortices to four vortices when the Dean number increases,but that in the outer half coil jacket is not found.The critical Dean num-ber is about 96.The inner half coil jacket has stronger heat transfer ability than the outer half coil jacket and this superiority is more evident with larger Prandtl number.However,as the Dean number is greater than 105,the flow resistance enhances more severely in the inner jacket than the outer jacket.For both jackets,the centers of the heated wall are the poorest for heat transfer.
文摘The main objective of this work is to investigate analytically the steady nanofluid flow and heat transfer characteristics between nonparallel plane walls. Using appropriate transformations for the velocity and temperature, the basic nonlinear partial differential equations are reduced to the ordinary differential equations. Then, these equations have been solved analytically and numerically for some values of the governing parameters, Reynolds number, Re, channel half angle, α, Prandtl number, Pr, and Eckert number, Ec, using Adomian decomposition method and the Runge-Kutta method with mathematic package. Analytical and numerical results are searched for the skin friction coefficient, Nusselt number and the velocity and temperature profiles. It is found on one hand that the Nusselt number increases as Eckert number or channel half-angle increases, but it decreases as Reynolds number increases. On the other hand, it is also found that the presence of Cu nanoparticles in a water base fluid enhances heat transfer between nonparallel plane walls and in consequence the Nusselt number increases with the increase of nanoparticles volume fraction. Finally, an excellent agreement between analytical results and those obtained by numerical Runge-Kutta method is highly noticed.
文摘This work illustrates the steady state, two dimensional natural convective flow and heat transfer features in square enclosure containing heated hexagonal block maintained either at constant wall temperature(CWT) or uniform heat flux(UHF) thermal conditions. Governing equations(mass, momentum and energy) are solved by using finite volume method(FVM) with 3rd order accurate QUICK discretization scheme and SIMPLE algorithm for range of field pertinent parameters such as, Grashof number(10~3≤ Gr ≤ 10~6), Prandtl number(1 ≤ Pr ≤ 100) and power law index(0.5 ≤ n ≤ 1.5). The analysis of momentum and heat transfer characteristics are delineated by evolution of streamlines, isotherms, variation of average Nusselt number value and Colburn factor for natural convection(j_(nH)). A remarkable change is observed on fluid flow and thermal distribution pattern in cavity for both thermal conditions. Nusselt number shows linear variation with Grashof and Prandtl numbers; while rate of heat transfer by convection decreases for power law index value. Higher heat transfer rate can be achieved by using uniform heat flux condition. A Nusselt number correlation is developed for possible utilization in engineering/scientific design purpose.
基金Supported by the National Natural Science Foundation of China (No.29976001) and Ministry of Education of China (No.00017).
文摘New models for describing hydrodynamics and mass transfer performance in supercritical fluid extraction columns were proposed. Those models were proved by experimental data, which were obtained in supercritical fluid extraction packed column, spray column and sieve tray column respectively. The inner diameter of those columns areФ25 mm. These experimental systems include supercritical carbon diox-ide-isopropanol-water and supercritical carbon dioxide-ethanol-water, in which supercritical carbon dioxide was dispersed phase, and another was continuous phase. The extraction processes were operated with continuous countercurrent flow. The predicted values are agreed well with experimental data.
基金supported by Basic Science Research Program through the National Research Foundation of Korea (NRF)funded by the Ministry of Education, Science and Technology (No.2012-0004544)
文摘Nano fluid is considered to be a class of high efficient heat transfer fluid created by dispersing some special solid nanoparticles (normally less than 100 nm) in traditional heat transfer fluid. The present experiment was conducted aiming at investigating the forced heat transfer characteristics of aqueous copper (Cu) nanofluid at varying concentration of Cu nano-particles in different flow regimes (300<Re≤16 000). The forced convective heat transfer enhancement is available both in the laminar and turbulent flow with increasing the concentration. Especially, the enhancement rate increases dramatically in laminar flow regime, for instance, the heat transfer coefficient of Cu/water nanofluid increases by two times at around Re=2 000 compared with that of base fluid water, and averagely increases by 62% at 1% volume fraction. However, the heat transfer coefficient of Cu/water decreases sharply in the transition flow regime. Furthermore, it has the trend that the heat transfer coefficient displays worse with increasing the concentration.
基金the State Key Development Program for Basic Research of China(G2007CB206904)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,Ministry of Education of China(00084)the Doctoral Fund of Beijing University of Technology(X004016200801)
文摘An experimental study was conducted to investigate the fouling process of calcium carbonate on the heat transfer surface, during forced convective heat transfer. The dynamic monitoring apparatus of fouling resistance was set up for the present experiments. The fouling behavio(s were examined under different factors including fluid velocity, hardness,alkalinity, solution temperature, and wall temperature. Asymptotic fouling curves varying with time were obtained. The fouling rate and asymptotic fouling resistance increased and the induction periods were shortened with the fluid velocity decreasing, hardness andalkalinity increasing, and solution temperature and heat transfer surface temperature increasing. Thecomponents of fouling that formed on the heat transfer surface included crystallization fouling and particulate fouling. The thermal performance parameter of fouling,ρfhf, varied from 380 to 2600 kg·W·(m^4·K)^-1, increasing with growing velocity and decreasing solution temperature, hardness or alkalinity. Furthermore, the thermal conductivity of fouling, λf, varied from 1.7 to 2.2 W·(m·K)^-1 .
基金Supported by the National 863 High-tech Program of China (No.2003AA121560) and High-tech Project of Jiangsu Province (No.BG2003001).
文摘This paper investigates the maximal achievable multi-rate throughput problem of a multicast ses-sion at the presence of network coding. Deviating from previous works which focus on single-rate network coding, our work takes the heterogeneity of sinks into account and provides multiple data layers to address the problem. Firstly formulated is the maximal achievable throughput problem with the assumption that the data layers are independent and layer rates are static. It is proved that the problem in this case is, unfortunately, Non-deterministic Polynomial-time (NP)-hard. In addition, our formulation is extended to the problems with dependent layers and dynamic layers. Furthermore, the approximation algorithm which satisfies certain fair-ness is proposed.