Based on the steady state distributed parameters model of the condensers which was put forward in the previous related reference the heat transfer and flow characteristics of four different two-rows condensers which used the refrigerant replacement(R407C,R410A,R134A)of R22 were studied.In the three groups of numerical results,all the researches indicate that the counter-flow condensers have a better performance than other arrangement condensers.Among the characteristic comparison of four refrigerants condensers.The heat transfer rate of R410A condensers is better than the other refrigerant condensers,but its condense pressure is much higher than that of R22,the pressure drop of R134A condensers is more high,both of the above two refrigerant replacements are not the perfect replacements.The heat transfer rate of R407C condensers is 3%～5% higher than that of R22,therefore condensers and the pressure drop of R407C condensers is 5%～10% lower than that of R22,therefore.R407C is the ideal refrigerant replacement of R22.

Based on the steady state distributed parameters model of the condensers which was put forward in the previous related reference. The effect of different non-uniform air distribution,different flow rate of the refrigerant,different refrigerant layout and different rows on the performance of the condensers are studied and some useful results are obtained. All the non-uniform air distribution make the performance of the condensers worse. The non-uniform degree can be measured by the non-uniform factor. When the non-uniform factor increase,the performance of the condensers become worse. All these research results can be applied to predict the influence on the performance of condensers when the inlet air distribution is non-uniform.

Based on the ε-NTU method,numerically simulates the refrigerant circuitry of the condensers with 2 to 4 rows of tubing and analyses the characteristics of the heat transfer and flow.The research results show that the counter-flow condensers have a better performance than that of other arrangements in single-circuit condensers,and that branch flow should be adopted in multi-rows condensers to decrease the pressure drop and increase the heat transfer capacity,and that the influence of gravity force can not be ignored,and that there must be an optimum refrigerant mass flow which can make the condenser perform best when the air velocity is constant while there must be an optimum air flow which can make the condenser perform best when the refrigerant mass flow is constant.

基于传热单元数法,建立了冷凝器的数学模型,模拟了两种不同流路冷凝器的换热性能和阻力特性.对比结果表明,冷凝器沿管长的壁温分布与前人的实验结果较为一致,阻力计算结果与实验结果最大偏差为7%,该模型可以用来比较不同形式流路对冷凝器性能的影响.

Based on the,a steady state distributed parameters model was established in the numerical simulation of refrigerant circuitry in condensers.The calculation results are in agreement with the experiments in the previous literature.The heat transfer and flow characteristics of six different two-rows condensers were studied with the present model.The research results show that the counter-flow condensers have a better performance than other arrangements condensers. When the front velocity is constant,there must be an optimum refrigerant mass velocity,leading to the best performance for the condensers.Similarly,when the refrigerant mass velocity is constant,there must be an optimum front velocity.In addition,the influence of gravity force cannot be ignored.Some practical refrigerant circuitry branching and joining principals were proposed and extensively studied,considering the pressure,heat resistance,and heat transfer coefficient distribution along the heat tubes.

Based on the e_c-BF,a steady state distributed parameters model is put forward in the numerical simulation of refrigerant circuitry in evaporators.Applying this model,the heat transfer and flow characteristics of four different two-rows evaporators are studied.The research indicates that the counter-flow evaporators have a better performance than other arrangements.Gravity effects should not be ignored in the arrangement of refrigerants circuitry.When the refrigerants are in the phase of liquid or in the two phase,they should be arranged to flow from up-portion to down-portion,so as to decrease the drop pressure in the tube and increase the heat transfer rate of the evaporators.The total capacity,sensible capacity and latent capacity of R407C evaporators is 3%～5% higher than that of R22 evaporators and the pressure drop of R407C evaporators is 5%～10% lower than that of R22 evaporators.R407C is the perfect refrigerant replacement of R22.

基于湿球温度效率法,建立了蒸发器的稳态分布参数模型,分析了三种不同流路布置蒸发器的换热性能,并与前人的实验研究结果进行对比,计算所得的换热量与试验值的最大偏差为9.44%,说明该模型切实可行.运用该模型计算并分析了六种不同流路布置蒸发器的流动和换热特性,结果表明:逆流布置蒸发器换热最好,错流其次,顺流最差.各种流路布置方案管外迎风面风速不变时,随着管内冷媒流量的增大,管内压降、总换热量、显热换热量、潜热换热量均增大,但潜热所占比重增大.管内冷媒流量保持不变,蒸发器迎风面风速增大时,总换热量、显热换热量均增大,潜热换热量、压降、吸湿系数均减小;当风速增大到一定程度时,蒸发器换热量、压降的变化都趋于平缓.同时,在蒸发器流路布置中,重力的影响不可忽略.研究结论为蒸发器流程布置的优化设计提供了理论基础和指导方向.

Based on theε-NTV,a steady state distributed parameters model was put forward in the numerical simulation of refrigerant circuitry in condensers in this paper.The heat transfer and flow characteristics of four different refrigerant circuitry two-rows condensers with R410A.The research results indicate that the counter-flow condensers have a better performance than other arrangements.The heat transfer rate of counter-flow condensers is 5～15% higher than that of parallel-flow condensers and the pressure drop of counter-flow condensers is 3～20% higher than that of parallel-flow condensers.Between the characteristic comparison of the two refrigerant condensers(R410A and R22),the heat transfer rate of R410A condensers is 6～15% higher than that of R22 condensers and the pressure drop of R410A condensers is 30～50% lower than that of R.22 condensers.All these results supply the theory basis and guide direction for the optimized design of refrigerant circuitry in condensers.

Based on the e_c-BF, a steady state distributed parameters model is put forward in the numerical simulation of refrigerant circuitry in evaporators in this paper. Applying this model, the heat transfers and flow characteristics of two-rows counter-flow evaporators which used the refrigerant replacement of R22 (R407C, R410A, R134A) are studied. When the frontal velocity is constant, with the refrigerant mass velocity increasing, the total capacity, sensible capacity , and the latent capacity of all evaporators which apply different refrigerants increase, the pressure drop in tubes decrease. When the refrigerant mass velocity is constant, with the frontal velocity increasing, the total capacity, sensible capacity of all evaporators which apply different refrigerants increase and the latent capacity, pressure drop in tubes decrease. Among the characteristic comparison of four refrigerants evaporators, the heat transfer rate of R134A evaporators is better than the other refrigerants evaporators, but its pressure drop is the highest. The heat transfer rate of R410A evaporators is better than R22 evaporator, but the evaporate pressure much higher than that of R22; both of the two refrigerant replacement are not the perfect replacements. The heat transfer rate of R407C evaporators is 3%～5% higher than R22 evaporators and the pressure drop of R407C evaporators is 5%～10% lower than R22. R407C is the ideal refrigerant replacement of R22.

本文提出了运用多孔介质模型、分布阻力模型和k-ε湍流模型对壳侧为翅片管束的壳管式换热器壳侧速度场与温度场进行三维数值模拟的方法,并对一相应类型换热器壳侧的流动与换热进行了数值模拟,得出了壳侧流场参数的图示以及壳侧进出口压降,温差,换热量随壳侧Re变化的特性曲线.

The research status and development of refrigerant circuitry in fin-and-tube heat exchangers is presented in this paper.The flow characteristics of refrigerant in the tube is analyzed.The suggestions that research in refrigerant circuitry should be paid attention to is put forward.

A three-dimensional, staggered grid, full-implicit consistent control-volume numerical model was presented for the analysis of turbulence fluid flow and heat transfer in the shell side of shell-and-tube heat exchanger.The numerical model used the distributed resistance method along with the concept of volumetric porosities, surface permeabilities to account for the presence of tubes in the heat exchangers. A modified k-e model was used to account for the effects of tubes on turbulence generation and dissipation. Shell and baffle walls were modeled by using the wall function approach. The three-dimensional model was validated by comparison of the computed pressure drop distribution with experiment data obtained on an E shell type heat exchanger model and the previous research results. Good agreement between the simulation results and experimental data is obtained. It showed that the three-dimensional numerical model could more effectively simulate the flow characteristics in the shell-side of heat exchanger than the previous numerical simulation models.

Three-dimensional numerical simulation was performed for the fluid flow and heat transfer in the shell side of shell-and-tube heat exchangers with helical baffles on the basis of porous medium and distributed resistance assumptions. The improved κ-ε turbulence model in conjunction with wall function and the step-wise approximation technique were adopted. It is found that for the same inner diameter and shell-side flow rate the pressure drop in the shell with helical baffles is appreciably lower than those of shell with vertical baffles, and with the increase of the helical angle, the pressure drop tends downwards. Compared with the test data obtained for small flow rate, the numerical results coincide satisfactorily with an average deviation below 14% and the maximum deviation of 18%.

The optimal design for multi-stream plate-fin heat exchanger with differential model was investigated. An effective method for the passage arrangement was presented, together with the corresponding calculation program. With this program, many conditions with different initial lengths and slice thicknesses were calculated. The calculation results show that the initial length almost has no effect on the final divergent length, but the slice thickness has great influence on the final result. A numerical example shows the feasibility and effectiveness of the proposed method.

The effect of tube juncture on heat loss in viscous oil extraction is numerically investigated. On the basis of calculation, a method is presented that proposes how to use a simple configuration of tube juncture to replace the complex one in the process of heat loss calculation in viscous oil extraction, and is called as 1/3 equivalence method. The method has been applied to the practical steam inject tube's heat loss calculation in viscous oil extraction, and the result shows its feasibility in practical application.

A three-dimensional, staggered grid, full-implicit consistent control-volume numerical model was presented for the analysis of turbulent fluid flow in shell side of shell-and-tube heat exchangers. The numerical model used the distributed resistance method along with the concept of volumetric porosities, anisotropic surface permeabilities to account for the presence of tubes in the heat exchangers. A modified k-e model was applied and the near wall region was modeled using the wall function approach. The three-dimensional model was validated by comparison with the computed pressure drop distribution of the experimental data obtained from an TEMA-E shell type heat exchanger model. The maximum error between experimental results and numerical simulation results is about 20%. The anisotropic porosities model can simulate the flow characteristics in the shell-side of heat exchangers more effectively than the existing isotropic porosities model.

Within the Reynolds number range from 5000 to 40000, experiments were performed by using cross-ribs (three angles: 45, 60, 75 degrees; two heights: 4 mm, 5 mm) roughened ducts to determine the effect of building repeated turbulators in the inner surface of rectangular duct on forced convection and fluid friction. The experimental results show that for the cross rib arrangements, the rib height and cross angle have positive effect on heat transfer; the larger the cross angles and the rib height, the higher the heat transfer coefficients. At the meantime, the friction factor also increases significantly. Compared with the parallel rib configuration, the cross-rib arrangement can enhance heat transfer with greater penalty in pressure drop.