太阳能无泵溴化锂制冷机性能优化分析

为了改善吸收器的吸收性能和提高系统的整体运行性能,在搭建小型太阳能无泵溴化锂吸收式制冷系统的基础上,采用温控装置控制太阳能模拟集热器的温度（80～93℃）与实际集热器的工作温度范围相一致,增加弦月形热虹吸管的数量,将二次发生装置引入气液分离器,吸收器和蒸发器封装同体并左右布置,采用蛇形叉排式横管降膜吸收和蒸发,并增设布液器和溢流式喷淋装置。结构优化后系统启动温度平均降低5℃,提高了太阳能的利用率;溶液可在较低的初始质量分数（46％～53％）下被提升,扩大了放气范围;吸收器降膜表面持液率增大,浓溶液进口浓度平均提高4％,吸收率也相应增大为原来的3．575倍。通过变工况试验,得到吸收性能与各种影响因素之间的应变规律,为研制高效吸收器和推进系统小型化提供依据。     

板式膜反转降膜吸收器设计与性能研究

板式膜反转降膜吸收器是一种将板式降膜吸收和膜反转技术相结合而开发的新型吸收器,合理设计与掌握其吸收性能对今后这种吸收器的工程应用十分重要.为此,通过建立、求解板式膜反转降膜吸收过程的数学模型,确立了设计条件下最佳吸收器结构;对于所设计的板式膜反转吸收器进行了不同吸收压力、溶液流量、进口浓度、进口温度及冷却条件下传热传质性能的计算,并与竖板降膜吸收器进行了比较.     

绝热喷雾吸收器在扩散吸收制冷中的应用分析

研究了一种带绝热喷雾吸收器的低温扩散吸收式制冷系统.探讨了绝热喷雾吸收器应用在扩散吸收式制冷系统中的特性,建立了系统各容器的数学模型并进行了模拟,尤其是对喷雾吸收器进行了模拟分析和计算.分析结果表明:在其它条件一定的情况下,吸收器的喷淋浓度越高,系统的cop值越小,且吸收器喷淋溶液温度对系统性能有很大影响;而在吸收器喷淋温度一定的情况下,随着发生温度的提高或蒸发温度的降低,或溶液换热器和气体换热器效率的提高,所要求的吸收器喷淋浓度就越高.在不同工况下,吸收器喷淋浓度的大小直接影响着整个系统性能的好坏,对能否正常运行起到关键性作用.     

模糊控制理论在舰船制冷装置中的应用研究

以蒸发器和冷库作为被控对象，利用计算机进行了制冷系统模糊控制的研究．针对蒸发器过热度和库温控制问题设计了模糊控制器．在理论研究的同时，建立了制冷装置计算机控制和数据采集系统．在Visual Basic环境下开发了蒸发器过热度模糊控制程序．对比实验运行表明：利用模糊控制器和电子膨胀阀对蒸发器过热度和库温进行控制较之用热力膨胀阀控制，制冷剂流量调节范围大、过热度小、蒸发器面积利用率高、装置节能效果好．     

太阳能溴化锂吸收式制冷系统溶液降膜吸收流动分析

溴化锂降膜式吸收器能在较小液流量和较小温差下获得较高的热流密度和传热传质系数,尤其是当液膜沿着水平管外作降膜流动时,传热传质效果更佳。为此建立溴化锂降膜吸收器溶液吸收过程流动的物理模型,通过对模型假设简化,对其进行数值求解,从而进行流动分析。与实验结果分析相结合,使得对吸收式制冷系统的分析更加全面。     

小型太阳能无泵溴化锂制冷机的试验研究

在前人工作的基础上对太阳能无泵溴化锂制冷机的结构进行改进，试验取得了突破性进展。弦月形的热虹吸提升管由原来的1根增加到3根，增大了溶液提升量，降低了热源启动温度。蒸发器和吸收器采用叉排蛇形管的结构，应用垂直降膜蒸发和吸收的原理，分别在铜管上包一层铜丝网和不锈钢丝网，实现一次蒸发，完全吸收，从而提高了系统性能。系统可持续稳定运行，并对数据进行了分析。     

铜翅片换热器开发应用的分析Ⅱ--铜翅片换热器对空调器性能影响分析

在Part Ⅰ中对铜翅片效率、铜换热单元传热系数以及整个铜换热器换热特性分析的基础上，理论分析了空调换热器采用铜翅片后，换热器单体性能以及空调系统性能的变化。结果显示：采用铜片铜管换热器后(不论是蒸发器，还是冷凝器)，制冷系统的制冷系数较之铝翅片换热器均有提高。蒸发器换热性能的变化比冷凝器换热性能的变化对系统性能的影响要大。当同时采用铜片蒸发器和铜片冷凝器时，传热强化系数按照通常所能达到的1．1计算时，COP随着工况变化而变化的范围可以达到3．0％-10．0％；如果单独设计换热器使换热强化系数达到1．3时，则COP的提高可达4．0％～25．0％。以上对铜翅片换热器开发应用的分析，为空调换热器的高性能化、小型化提供一条可行的发展方向。     

降膜和泡式等不同吸收模式的分析研究

本文的目的是针对降膜和泡式两种吸收模式,分析氨水吸收过程的复合传热传质,并企图对传热传质面积等重要参数对吸收量的影响进行参数分析。用在冷却剂侧有偏置肋片（OSF）的板式热交换器来设计降膜和泡式吸收器。已经发现,泡式吸收器的局部吸收量总是大于降膜式,使此种吸收器的尺寸比降膜式约小48．7％。对降膜式吸收器、液体侧的传质阻力是决定性的,而气体侧的热热和传质阻力的也很大。对泡式吸收器,液体侧传质阻力是决定性的,而比泡式吸收器大,而对泡式吸收器,传质系数的影响比降膜式更大。     

溴化锂风冷垂直降膜吸收过程数值模拟

通过对溴化锂溶液在降膜吸收过程中传热、传质特性的分析,建立了垂直降膜吸收过程的数学模型。在这个模型中,考虑了对流及变膜厚等因素对传热、传质性能的影响。并对风冷垂直管降膜吸收过程进行了数值模拟。得出的结论对垂直降膜吸收器的设计和优化具有指导意义。     

添加剂和纳米粒子强化溴化锂水溶液／氨水吸收特性研究进展

吸收式制冷以其节能、环保等诸多优点得到了越来越广泛的应用。本文总结与分析添加剂和纳米粒子强化溴化锂水溶液及氨水吸收特性的机制和相关实验研究的发展现状。针对吸收式制冷系统中吸收器传质系数和换热系数小而导致的制冷效率低的问题,很多学者进行了添加剂和纳米粒子对吸收过程影响的实验研究,并据此采取措施增大传质传热效率。实验主要包括以下几个方面：表面张力实验、静态池吸收实验、降膜吸收实验和氨水鼓泡吸收实验。实验结果均表明添加剂和纳米粒子可以提高吸收器中溴化锂水溶液及氨水的传热传质性能。该研究对于提高吸收式制冷系统的制冷效率有很大帮助,同时为该技术在实际系统中的应用奠定基础。     

Comparative study of irreversibilities in an aqua-ammonia absorption refrigeration system

Irreversibilities in components of an aqua-ammonia absorption refrigeratio system (ARS) have been determined by second law analysis. The components of the ARS are as follows: condenser, evaporator, absorber, generator, pump, expansion valves, mixture heat exchanger and refrigerant heat exchanger. It is assumed that the ammonia concentration at the generator exit is, independent of the other parameters, equal to 0.999 and at the evaporator exit the gas is saturated vapour. Pressrre losses between the generator and condenser, and the evaporator and absorber are taken into consideration. In the results the dimensionless exergy loss of each component, the exergetic coefficient of performance, the coefficient of performance and the circulation ratio are given graphically for each different generator, evaporator, condenser and absorber temperature.     

Effect of pressure and concentration on performance of a vertical falling-film type of absorber and generator using lithium bromide aqueous solutions

Experiments on an absorber and generator in an absorption refrigerating machine were made using a vertical falling-film type of stainless steel column. Three lithium bromid e aqueous solutions (40, 55 and 60wt% LiBr) were used as working fluid. The experimental apparatus was operated at 1.3 kPa (the pressure for a practical absorber) and 5.3 kPa (the intermediate pressure between absorber and generator). The measured absorption (evaporation) rate decreased with reducing pressure an d increasing concentration of LiBr in the falling liquid. The rate agreed with the values obtained from the analysis of heat and mass transfer in a falling film. Therefore, a falling-film type of absorber and generator can be designed and operated by a consistent method.     

Optimization of generator temperatures in two-stage dual-fluid absorption cycles operated by biogas

Generator temperatures in ammonia absorption systems at subfreezing evaporator conditions have been optimized to use the minimum volume of biogas required to operate two-stage dual-fluid cycles. In this dual-fluid cycle, a LiBr---H₂O absorption system is used at the first stage with ammonia absorption systems at the second stage. Three different refrigerant-absorbent combinations (NH₃---H₂O, NH₃---NaSCN, NH₃---LiNO₃) were selected for this study. The absorber at the second stage is cooled by the low temperature water-refrigerant from the evaporator at the first stage. Lowering the absorber temperature reduces the heat input to the generator, which lowers the generating temperature and improves the performance of the absorption systems at the second stage. The optimum generator temperatures and performance coefficients of the systems at the first and second stages and the overall two-stage dual-fluid cycles are presented graphically. A comparative study between the three ammonia systems used in the two-stage dual-fluid cycle has been carried out.     

压缩式制冷空调机组壳管式换热器的传热强化研究进展

冷凝器和蒸发器是压缩式制冷空调机组中的重要设备,其传热系数的高低直接影响机组的效率和成本。采用强化传热技术是提高冷凝器与蒸发器传热性能的关键。对于管外冷凝传热强化,在Turbo-C管的基础上,将翅片从翅顶到翅根完全割裂,形成断裂的三维翅片管,以减少表面张力作用下冷凝液在传热管表面粘滞特性对传热的影响。采用螺旋隔板替代冷凝器和干式蒸发器的弓型隔板,能改善壳程流体的流动与传热性能;针对降膜蒸发器的降膜蒸发区与满液蒸发区的不同特点,应分别采用不同类型的强化管,以提高蒸发器传热系数。     

Energy and exergy analysis of single effect and series flow double effect water–lithium bromide absorption refrigeration systems

In this paper, the energy and exergy analysis of single effect and series flow double effect water–lithium bromide absorption systems is presented. A computational model has been developed for the parametric investigation of these systems. Newly developed computationally efficient property equations of water–lithium bromide solution have been used in the computer code. The analysis involves the determination of effects of generator, absorber and evaporator temperatures on the energetic and exergetic performance of these systems. The effects of pressure drop between evaporator and absorber, and effectiveness of heat exchangers are also investigated. The performance parameters computed are coefficient of performance, exergy destruction, efficiency defects and exergetic efficiency. The results indicate that coefficient of performance of the single effect system lies in range of 0.6–0.75 and the corresponding value of coefficient of performance for the series flow double effect system lies in the range of 1–1.28. The effect of parameters such as temperature difference between heat source and generator and evaporator and cold room have also been investigated. Irreversibility is highest in the absorber in both systems when compared to other system components.     

Experimental study on LiCl solution falling-film generation process outside a vertical tube

For the purpose of the development of a generator with higher performance utilizing LiCl/H₂O as the working pair in a two-stage absorption refrigeration system, an experimental investigation of LiCl solution falling film generation outside a vertical tube as the high-pressure stage solution cycle was conducted. An experimental setup was established to study heat and mass transfer process in a falling-film generator for LiCl/H₂O using low-temperature heat source. The experiments showed effect of the flow rates of hot water and falling film solution, temperature of heat source, concentration of the solution and generation pressure on the LiCl/H₂O generation process. To compare with conventional LiBr/H₂O solution, some comparative experiments of falling film generation were tested in order to discuss the mass transfer performance of two different working pairs in a high-pressure generator. The results showed that the two working pairs had similar mass transfer rate. The LiCl/H₂O solution had a similar mass transfer rate to that of the LiBr/H₂O solution, while the concentration of LiCl/H₂O solution was much lower with smaller circulation ratio of the solution, and it could make for possible improvement in the thermal performance of the absorption refrigeration system.     

制冷用水平降膜式蒸发器研究进展

降膜式蒸发器目前在牛奶、制药、化工、海水淡化等行业取得了较为广泛的商业应用,它从上世纪90年代以后开始应用于制冷空调系统。目前针对制冷用水平降膜式蒸发器的研究目的主要是明确各个参数对蒸发器传热性能的影响以及他们之间的联系,由于降膜式蒸发器的独特结构和内部传热传质的复杂性,这些研究尚处于初步阶段。在介绍其工作原理的基础上,针对水平降膜式蒸发器,着重讨论了布液器的结构与高度、管束(包括管径、管排数、管道表面形状)、制冷剂(流型、流量)等参数对其性能的影响。由于经验关联式在实际应用中的巨大优势,还总结了前人提出的关联式及其适用的范围,文章将为制冷用降膜式蒸发器的进一步研究和应用提供参考。     

Experimental studies on air-cooled NH3-H2O based modified gax absorption cooling system

An experimental investigation on the performance of an air-cooled modified generator absorber heat exchange (GAX) absorption cooling system has been carried out and presented in this paper. The conventional system is modified by incorporating high pressure GAX, low pressure GAX, a solution cooler and an additional solution heat exchanger to reduce the heat input to the system. The system is designed for a cooling capacity of 10.5 kW using ammonia-water (NH₃-H₂O) as the working fluid. The performance of the system in terms of the circulation ratio, internal heat recovery and coefficient of performance (COP) has been obtained. The system is capable of producing a low evaporator temperature of −5 °C, at a sink temperature of 35 °C, under no load conditions. The results indicate that at a generator and evaporator temperature of 120 °C and 2 °C respectively, the system delivers a maximum cooling capacity of about 9.5 kW with a fuel and total COP of 0.61 and 0.57 respectively.