汽车空调换热器性能试验台的研制及实验分析

根据换热器性能测试的空气焓差法和制冷剂流量剂法,设计了汽车空调换热器性能测试试验台的制冷剂工况系统和焓差室测试系统。该试验装置不仅可以对汽车空调换热器在实际运行状态下的换热量和阻力特性进行试验研究,还可以进行整机性能试验。为验证试验台的稳定性和可靠性,分别进行了环境室工况条件试验以及冷凝器和蒸发器的样件的单体性能测试试验。通过对试验数据的计算分析,得出实验台的主测空气侧和辅测制冷剂侧换热量偏差均在3%的范围内,满足国标和企业技术要求。     

双蒸发器户式热湿分控机组变工况运行实验研究

使用双蒸发器空调机组作为户式冷热源,在长沙进行安装,并对不同工况下机组的运行性能进行研究。结果表明:双蒸发器空调机组可实现户式热湿分控;不同蒸发器间制冷量的合理有效分配是机组得以稳定运行并达到良好节能效果的重要因素。     

太阳能固体吸附式制冷系统部件的实物设计

对太阳能固体吸附式制冰机系统的关键零部件吸附床、冷凝器、蒸发器加以分析,并进行了实物设计。实验结果表明,所设计的系统零部件在太阳能固体吸附式制冰机装置实际运行工况下具有较好的传热、传质特性,系统各子部件间运行时能够很好地匹配,为太阳能制冷空调的实用化奠定了良好的基础。     

光伏直驱变频离心式冷水机组的实验研究

基于光伏直驱变频离心式冷水机组系统特性,设计并搭建一座全天候整机、逆变器性能测试平台。结合机组特有的数种工作模式满足对光伏侧、电网侧、机组水侧各参数的监控,并计算转换效率及制冷量。试验结果表明:纯光伏模式的转换效率达98.25%,用电模式额定功率转换效率为96.3%,名义工况下的性能系数(coefficient of performance,COP)为6.79,光伏空调的COPsg为6.89。在光伏功率5%～100%波动的情况下,机组功率保持在480 kW,制冷量保持在3180～3200 kW,未引起机组加卸载。平台可满足全天光伏空调并网性能、整机性能、可靠性测试需求。     

临界喷嘴式分流器改善冷库用翅片蒸发器性能的实验研究

对采用临界喷嘴式分流器的冷库用翅片蒸发器性能进行实验研究,在0、-4、-8、-12、-16、-18及-20℃七种不同环境工况下进行传热性能测试,并将测试结果与采用气液分离式分流器、CAL分流器和文丘里式分流器进行对比分析。研究结果表明:库温为0℃时,对应的翅片式蒸发器的制冷量和传热系数分别为8.5 kW和37.9 W/(m~2·℃),相比气液分离式分流器、德国CAL分流器、文丘里分流器其对应冷风机的制冷量分别提高了8.1%、17.4%和21.7%,传热系数提高了4.5%、13.9%和18.6%。库温为-18℃时,对应的翅片式蒸发器的制冷量和传热系数分别为5.5 kW和30.9 W/(m~2·℃),其对应的蒸发器的制冷量分别提高了7.2%、14.3%和18.7%。库温为-18℃时,对应的传热系数分别提高了0.9%、10.1%和13.2%。实验结论为有效提高翅片蒸发器性能提供了一种解决方案。     

蓄冷型LNG重卡冷能利用空调系统性能研究

提出了一种具有蓄冷功能的LNG重卡冷能利用空调系统,阐述了LNG重卡冷能利用空调系统的设计原理,基于Aspen plus软件模拟了系统流程,并对系统性能进行了分析。研究结果表明,在设定工况参数下,循环风量为520.00m~3/h时,蒸发器侧送风温度为19.85℃,空调制冷量为3.704kW,满足重卡3.500kW的制冷需求,同时,蓄冷器蓄存冷量0.410kW,可适应重卡多工况下空调系统的正常运行。此外,搭建静态实验台验证系统可行性,并将实验结果与同工况下模拟结果对比,二者曲线趋势一致,系统运行效果良好,制冷能力能够满足实际需要。     

小型太阳能驱动单效溴化锂吸收式制冷机组的模拟研究

对太阳能驱动的单效溴化锂吸收式制冷机组的性能进行数值模拟研究,通过TRNSYS建立太阳集热器仿真系统,分析太阳能辐射强度及太阳能驱动温度对机组制冷性能的影响;利用EES(engineering equation solver)编程建立小型单效溴化锂吸收式制冷机组(12 kW)模型,采用动态数值模拟的方法,研究小型制冷机在设计工况以及变工况下的热力性能和机组运行状态。并采用耦合研究的方式,系统分析驱动热源温度、热源流量、冷媒水进出口温度、冷却水进口温度等因素对机组制冷性能的影响。研究结果表明:低温集热器的工作温度区间和单效溴化锂制冷机匹配性较好,既可避免能源品位的浪费,又不会使热源驱动温度过高,造成溴化锂溶液结晶的出现。太阳有效辐射强度对机组制冷性能影响显著,辐射强度从550 W/m2增至990 W/m2时,制冷量由5 kW增至16 kW,在设计参数下,小型太阳能吸收式制冷机的性能系数可达到0.70。     

太阳能热泵供热系统的模拟研究

为研究太阳能热泵系统供热性能,使用Visual C#语言编制了各部件模型,运用各部件间耦合关系,建立了太阳能热泵仿真模型。通过仿真程序的运算,分析了太阳辐射强度、集热板面积、蒸发器进口水温、冷凝器进口水温对吸热量、制热量、系统COP的影响,并与试验结果进行对比,验证了仿真模型的准确性,为热泵系统的选型与匹配提供一定的数据参考。     

传热传质分离式太阳能吸收式制冷机实验研究

设计研究了小型太阳能溴化锂吸收式制冷机组,对吸收器、蒸发器、发生器均采用传热传质分离设计,通过高效板式换热器的预先冷却或加热的方法,实现了对发生过程、吸收过程、蒸发过程的传热和传质分离,达到了制冷机小型化的目的.实验研究结果显示:制冷量和COP值随太阳能热水温度升高而升高;在某个全天的测试过程中,制冷量最大为3.7kw,COP最大为0.5,日平均制冷量为2.34kW,平均COP为0.34;实验机组的电制冷系数要高于普通的电制冷空调,其平均EER达到了3.25.     

变工况污水源热泵系统性能优化研究

在污水源热泵系统仿真模型的基础上,权衡了各阶段不同工况性能系数对全年总能耗的影响,提出了污水源热泵系统全年性能优化理念,定义了全年性能系数ACOP,并以此作为优化目标函数,以机组蒸发器、冷凝器和污水-中介水换热器的换热面积作为优化变量,研究系统通过机组压缩机启停控制方式下系统的面积优化匹配,并分别与系统初始设计参数、以供热性能系数HSPF、制冷性能系数SEER和EER为优化目标的优化计算结果进行对照,结果表明,采用ACOP作为优化目标具有更加客观的节能效果。     

A simplified model for shell-and-tubes heat exchangers: Practical application

In this paper, a simplified model for the study of shell-and-tubes heat exchangers (HXs) is proposed. The model aims to agree with the HXs when they are working as condensers or evaporators. Despite its simplicity, the model proves to be useful to the pre-designment and correct selection of shell-and-tubes HXs working at full and complex refrigeration systems. The heat transfer coefficient and pressure drop correlations are specially selected and treated to implement them into the shell-and-tubes HXs presented. The model is implemented and tested in the modellization of a general refrigeration cycle and the results are compared with data obtained from a specific test bench for the analysis of shell-and-tubes HXs.     

A novel household refrigerator with shape-stabilized PCM (Phase Change Material) heat storage condensers: An experimental investigation

In this study, a kind of shape-stabilized phase change material (PCM) was adopted for constructing heat storage condensers. And a novel household refrigerator equipped with the heat storage condensers was setup based on an ordinary double-door three-star compartment refrigerator. The experimental investigation on the characteristics of the novel refrigerator and an ordinary refrigerator was carried out under the ISO standard test conditions. For the novel refrigerator, part of the condensation heat was stored in the shape-stabilized PCM during the on-time and discharged to the environment while the compressor was off. Therefore, the heat dissipation of the novel refrigerator was continuous during a complete cycle (including a successive on-time and off-time period), different from the intermittent heat dissipation of the ordinary setup. Thus, the overall heat-transfer performances of the condensers could be significantly improved, which resulted in a lower condensation temperature, a higher evaporation temperature and a much larger subcooling degree at the condenser outlet. Compared to the ordinary refrigerator, the total cycle time and the ratio of on-time to the total cycle time of the novel refrigerator were much smaller, which led to more frequent starts of the compressor but lower energy consumption. Experiments demonstrated that the novel refrigerator could increase the energy efficiency by about 12% with only little increase of the cost.     

不同管径组合的冷凝器换热数值研究

基于对传统空调用铜管翅片式冷凝器的研究分析，提出了一种新型的冷凝器形式，其迎风侧和背风侧采用不同直径的铜管和不同宽度的翅片，通过对两种形式的冷凝器的流动和换热进行的数值分析，新设计的冷凝器具有比传统冷凝器高的换热能力和低的空气流动阻力，适合于空调器的使用，而且该设计思路可以推广到空调用蒸发器的优化设计中。     

Frictional Pressure Drop for Gas/Liquid Two-Phase Flow in Plate Heat Exchangers

Two-phase flow occurs in plate heat exchangers used as evaporators or condensers. The frictional pressure drop for two-phase flow can be considerably higher than for single-phase flow, because of the interaction between the phases. In this article, measurements of air-water flow in two different plate-and-frame exchangers are presented. Correlations developed for tubular flow are compared with the experimental results. Recommendations for a calculation procedure are given.     

Thermoeconomic considerations in the design and rating of two-phase heat exchangers

We discuss a closed-form model for thermoeconomic design and analysis of two-phase heat exchangers used as condensers and evaporators. The results are presented in terms of the optimum number of heat-transfer units (NTUs) as a function of the dimensionless unit-cost ratio and the exit-to-inlet absolute temperature ratio of the single-phase fluid. The sensitivities of various unit-cost parameters (UCPs) are presented. It is demonstrated that the selection of UCPs play a significant role in sizing heat exchangers.     

The Use of New Refrigerants in Compact Heat Exchangers for the Refrigeration Industry

The present article reports on the results of experimental research carried out on compact plate heat exchangers, currently used as evaporators and condensers in refrigeration loops. The research was aimed at getting information on the thermal efficiency of the heat exchangers, under reference commercial conditions, when using new ozone-friendly refrigerants to replace CFCs and HCFCs. Specifically, the influence of some thermal-hydraulic parameters on the heat flux and the overall heat transfer coefficient are investigated for evaporators, using R134a, R407C, and R410A, three fluids proposed to replace R22, and HCFC, currently the most common refrigerant used in residential and commercial air conditioning equipment. Moreover, in this article a new thermodynamic method has been applied with the purpose of defining the saturation temperature and investigating the other main parameters for mixtures in the two-phase region for the fluids R407C and R410A, which are blends of, respectively, three and two pure refrigerants.     

Heat and mass transfer during adsorption of ammonia in a cylindrical adsorbent bed: thermal performance study of a combined parabolic solar collector, water heat pipe and adsorber generator assembly

In this paper we present the study of adsorption refrigerator which use an activated carbon-pair ammonia. The ability of activated carbons to adsorb large mass of ammonia makes them ideal for use in adsorption refrigeration and pump systems. These systems have not reasonable efficiency. In order to make these systems economically viable, their size must be reduced. This implies a need for a rapid heating and cooling the adsorbent/refrigerant pair. However, the main problems to be overcome is related to the poor heat transfer in the adsorbent bed. So, it is necessary to study and understand the heat and mass transfer within the bed and to improve it. A detailed model of heat and mass transfer into the generator has been developed. For a given heat flux, temperature and adsorbed mass have been computed in every point at each step time along the adsorbed bed (generator). Experimental installation simulating an adsorption machine working within a temperature ranging from 20 to 250 °C and pressure ranging from 0 to 2.5 × 10⁶ Pa, allows for identification of the generator's equivalent thermal conductivity and internal heat transfer coefficient. These two parameters are then used to simulate thermal performance of a design whose features include the insertion of stainless steel water heat pipe (HP's) condensers into the generator. The HP's evaporator heat input is of solar origin using a compound parabolic collector (CPC). Nominal Solar coefficient of performance, COPs =14.37% obtained through both Adimensional Exergy Loss (AEL), and COP study, shows the competitiveness of the proposed design.     

翅片管式蒸发器结霜性能的仿真与实验研究

建立了结霜条件下翅片管蒸发器空气侧流动和换热的分布参数仿真模型,模型考虑了蒸发器结构、霜层厚度以及湿空气状态等参数在气流方向的沿程变化.对冰箱冷冻室蒸发器结霜条件下的动态性能进行了试验研究和数值模拟.结果表明,蒸发器结霜过程中的结霜量、能量传递系数和空气侧压降的计算值和试验值吻合良好,证明模型可以应用于翅片管蒸发器结霜性能的正确预测和优化设计分析.     

A New Numerical Approach for Predicting the Two-Phase Flow of Refrigerants during Evaporation and Condensation

This article reports on four finite-volume–based numerical methods developed for predicting the one-dimensional two-phase flow of pure refrigerants in evaporators and condensers during change-of-phase processes. The methods differ in the physical assumptions considered at the interface separating the liquid and vapor phases and in the equation used to predict the variation of the refrigerant flow quality during change of phase. In all methods, numerical predictions are obtained via a locally iterative marching-type solution algorithm. Therefore, the models permit the prediction of the size of the pipe needed to achieve full evaporation/condensation of the saturated refrigerant. The effectiveness and robustness of the numerical procedures in predicting the flow and heat transfer characteristics are assessed by comparing results with published experimental data. Good agreement is obtained. The new approach is used to perform a parametric study analyzing the effect of refrigerant type, pipe diameter, and mass flow rate on the flow and heat transfer characteristics in evaporators.     

Conflation of ε-Ntu and EGM design methods for heat exchangers with uniform wall temperature

This paper conflates two heat exchanger design approaches – the ε-N_tu (effectiveness–number of transfer units) and the EGM (entropy generation minimization) – focusing on heat exchangers with uniform wall temperature, i.e. condensers and evaporators. An algebraic formulation which expresses the dimensionless rate of entropy generation as a function of the heat exchanger geometry (number of transfer units), the thermal-hydraulic characteristics (friction factor and Colburn j-factor), and the operating conditions (heat transfer duty, core velocity, surface temperature, and fluid properties) is derived. It is shown that there does exist a particular number of transfer units which minimizes the dimensionless rate of entropy generation. An algebraic expression for the optimum heat exchanger effectiveness, based on the working conditions, heat exchanger geometry and fluid properties, is also presented. The theoretical analysis led to the conclusion that a high effectiveness heat exchanger design does not necessarily provide the best thermal-hydraulic performance.