二级回热低温空气制冷系统性能实验研究

在低温空气循环制冷系统中增加二级回热器及水分离器,除去涡轮进口空气中的水分,以提高系统效率和可靠性。在不同的工况条件下,对3种回热流程的空气制冷系统性能进行实验研究,结果表明,压气机进口压力的升高,增大了涡轮膨胀比,降低了涡轮出口温度,提高了系统制冷量和制冷系数;在系统中增加回热器及相应的水分离器,可显著提高系统的制冷效率和除水性能,且二级回热流程的系统性能最优,与无回热流程相比,系统制冷量和制冷系数分别增加了47%和41%,涡轮进口含湿量下降了约36%;不同的制冷温度下,系统制冷系数较低。     

Water—lithium bromide—lithium nitrate三元工双效吸收式制冷循环的研究质

比较了水-溴化锂-硝酸锂三元工质与传统的水一溴化锂工质的双效吸收式制冷循环,分析了直燃型双效制冷系统。结果表明：采用新工质后,系统的热力系数COP有了明显的提高,其它表征系统热力性能的经济指标也均有不同程度的改善,尤其在直燃型双效冷热水机组中有明显的优势,热力系数COP提高约30％,溶液循环倍率降低12％。因此,该新工质与传统的水-溴化锂工质相比,具有较好的热力性能。     

Water-lithium bromide-lithium nitrate三元工质双效吸收式制冷循环的研究

比较了水-溴化锂-硝酸锂三元工质与传统的水-溴化锂工质的双效吸收式制冷循环,分析了直燃型双效制冷系统.结果表明:采用新工质后,系统的热力系数COP有了明显的提高,其它表征系统热力性能的经济指标也均有不同程度的改善,尤其在商燃型双效冷热水机组中有明显的优势,热力系数COP提高约30%,溶液循环倍率降低12%.因此,该新工质与传统的水-溴化锂工质相比,具有较好的热力性能.     

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。     

双制冷温度双工质吸收制冷系统Ⅱ的模拟

为克服在较高温度的热源下只用氨作为制冷剂时采用二级再生流程系统操作压力高的弊病,提出了一种新的吸收制冷系统.将水-溴化锂和氨-硝酸锂二系统耦合,在后者所组成的系统2中设置二个不同蒸发温度的蒸发器.对该系统的操作性能进行了热力学模拟,分析讨论了热源温度、冷却水温度和低温蒸发温度的影响及系统适宜的操作条件.在较高的热源温度和较宽的操作条件下,系统操作性能稳定,其制冷性能系数COP可以稳定在0.95以上,稍低于类似条件下只用水-溴化锂作为工质的二级再生系统,但相应的制冷温度分别为1℃和-5℃,是一种很有实用价值的吸收制冷系统.     

小型无泵溴化锂吸收式制冷系统的实验研究

建立了小型太阳能热水型无泵溴化锂吸收式制冷系统,系统主要采用降膜吸收器、降膜蒸发器、弦月型通道热虹吸提升管等新型设计。为了提高制冷系统的整体运行效果,首次设计了一套二次发生装置,使系统能在较低的初始溶液浓度范围（46％～54％）下运行,并保持较高的放气范围和吸收率,有助于提高吸收器性能;并使冷剂水产量较之不使用二次发生器的情况增大1．68倍,明显改善了蒸发效果;对冷凝器与蒸发器间压差的建立也起到一定的作用,改善了制冷系统的整体运行性能,平均制冷系数可达0．725。     

一种双制冷温度双工质吸收制冷系统的模拟

在较高的热源温度下,吸收制冷系统需采用双效再生流程提高制冷性能系数COP,从而却使只用氨作为制冷剂的系统再生操作压力大幅度增高.为克服这种缺陷,提出了一种新的吸收制冷系统,分别以水-溴化锂和氨-硝酸锂作为二个系统的工质,将二系统耦合组成双制冷温度双工质系统.对该系统的操作性能进行了热力学模拟,分析讨论了热源温度、冷却水温度和蒸发器2蒸发温度对系统操作性能的影响及系统适宜的操作条件.该系统操作稳定,在较宽的操作条件下,COP可以稳定在1.10以上,与类似条件下只用水-溴化锂作为工质的系统相当,但相应的制冷温度可低至-13℃以下,是一种很有开发应用前景的吸收制冷系统.     

吸收式冰箱发展的若干问题

在主要由热能来驱动的吸收式制冷系统中,目前普遍使用的有氨—水、水—溴化锂双组分吸收式制冷及氨—水—氢三组分连续扩散吸收制冷。前两者已广泛用于大型的制冷和空调系统;扩散吸收制冷循环在三十、四十年代,则以煤气冰箱型式得到过广泛的应用。这种制冷方式的特点是在系统中采用氨为致冷剂,水为吸收剂,并加入一定压力的惰性气体—氢。在装置中,氨、水蒸汽和氢的总压力在各个部分都相等。而在蒸发器     

新型太阳能降压吸收式制冷空调系统特性的理论分析

在两级溴化锂吸收式制冷的基础上提出了一种新型高效的降压吸收式制冷循环,能够有效利用太阳能实现制冷,解决传统吸收式太阳能空调系统存在的弊端。其特点是在传统的两级吸收式循环的基础上,将高压发生器发生出的LiBr溶液与低压吸收器的吸收后的溶液混合,在发生温度与压力允许的范围内,使高压吸收器的吸收剂浓度较两级吸收式循环高,从而在相同的冷凝条件下减小了其压力。分析了新型空调系统的性能特性,理论计算结果表明影响新型系统整体效率的主要因素是LiBr溶液的浓度及驱动热源的可利用温差。新型吸收式循环热源可利用温差最高可达33.5℃,整体效率比两级吸收式系统有较大提高,最大提高46.4%,其集热面积单耗最大减小47.1%,热源单耗是两级系统的0.21,效果较明显。     

两级溴化锂吸收式制冷机的变工况性能实验

介绍了自主研制的350 kW两级溴化锂吸收式制冷机,并对该机组进行了4种变工况条件下的性能测试.分别通过改变冷媒水出口温度,冷却水进口温度,热水进口温度和热水流量来测试该制冷设备在以上4种常见变工况的外界条件下,其制冷量和热力系数(COP)的变化趋势.该实验结果显示,在设计值上下20％的变化范围内,随着冷媒水出口温度和热水进口温度的升高,热水流量的加大以及冷却水进口温度的降低,机组制冷量和热力系数(COP)均会得到提高.     

1-D transient numerical model of a regenerator in a novel sub Kelvin Active Magnetic Regenerative Refrigerator

A sub Kelvin Active Magnetic Regenerative Refrigerator (AMRR) is being developed at the University of Wisconsin – Madison. This AMRR consists of two circulators, two regenerators, one superleak, one cold heat exchanger, and two warm heat exchangers. The circulators are novel non-moving part pumps that reciprocate a superfluid mixture of ⁴He–³He in the system. Heat from the mixture is removed within the two regenerators of this tandem system. An accurate model of the regenerators in this AMRR is necessary in order to predict the performance of these components, which in turn helps predicting the overall performance of the AMRR system. This work presents modeling methodology along with results from a 1-D transient numerical model of the regenerators of an AMRR capable of removing 2.5 mW at 850 mK at cyclic steady state.     

磁制冷核心问题及高效利用新方式

旋转式磁制冷机是目前室温磁制冷机的主流技术方案,本文针对制约现有磁制冷机的关键因素,综述了磁回热器的高效传热、多组磁回热器的流路控制、多层磁工质复叠制冷及磁体、系统集成等核心问题的最新研究进展并提出了发展方向,深入总结了通过复合制冷的方式拓展磁制冷应用范围及制冷性能的途径及潜力,以助于明确未来磁制冷的研究方向,为研发高性能磁制冷机提供思路。     

Heat exchanger versus regenerator: A fundamental comparison

Irreversible processes in regenerators and heat exchangers limit the performance of cryocoolers. In this paper we compare the performance of cryocoolers, operating with regenerators and heat exchangers from a fundamental point of view. The losses in the two systems are calculated from the entropy productions due to the various irreversible processes. Whether an optimized regenerator or heat exchanger performs better depends on the system parameters (molar flux, temperature, and pressure). At temperatures below 200 K the losses due to heat conduction in the axial direction are dominant.     

An experimental study of passive regenerator geometries

Active magnetic regenerative (AMR) systems are being investigated because they represent a potentially attractive alternative to vapor compression technology. The performance of these systems is dependent on the heat transfer and pressure drop performance of the regenerator geometry. Therefore this article studies the effects of regenerator geometry on performance for flat plate regenerators. This paper investigates methods of improving the performance of flat plate regenerators for use in AMR systems and studies how manufacturing variation affects regenerator performance. In order to eliminate experimental uncertainty associated with magnetocaloric material properties, all regenerators are made of aluminum. The performance of corrugated plates and dimpled plates are compared to traditional flat plate regenerators for a range of cycle times and utilizations. Each regenerator is built using 18 aluminum plates with a 0.4 mm thickness, which allows their performance to be compared directly.     

回热式低温制冷机用回热器结构研究综述

回热器是回热式低温制冷机中的关键部件,对制冷机性能有重要影响.文章阐述了回热式低温制冷机用回热器结构在近几年的研究进展,根据填料填充方式的不同,将回热器分为层叠金属丝网式、平行金属丝式、堆叠金属珠式、平行金属片式、随机丝式、金属丝网和金属珠混合填充式等六类,并总结对比了不同填充方式回热器的优缺点,提出采用回热器回热效率η比表面积a、流动不均匀性指数Fm、流动阻力系数f、填料几何因数ГT、填料轴向导热指数Ck、长径比/D等七个评价指标对回热器性能进行较为全面的评价,展望了回热器结构研究发展急需解决的难题及所面临的挑战.     

热声制冷机回热器的现状及展望

概括介绍了目前热声热机常用热声研究理论及常见类型的热声回热器。重点综述了目前常用回热器研究理论及实验研究进展,针对不同种类回热器进行简单分析对比。基于热声回热器发展的现状对回热器今后研究发展趋势进行了展望。     

Novel flow analysis of regenerator under oscillating flow with pulsating pressure

A new model for the oscillating flow combined with pulsating pressure in cryocooler regenerators is developed to overcome inaccuracy of the conventional flow model based on steady flow friction factor. The new model is based on two non-dimensional parameters and one-dimensional governing equations. One of the parameters is the oscillating flow friction factor represented by the amplitudes of the pressure drop and the flow rate. The idea of the other important parameter originates from a volume averaged continuity equation, which includes the characteristic of randomly oriented matrix geometry. This parameter is named as Breathing factor, which implies that the regenerator breathes against the main oscillating flow. Empirical correlations of the parameters are obtained for screen regenerators. It is revealed that the phase angles of the pressure drop and the mass flow rate in regenerators are well predicted by introduction of the Breathing factor.     

室温磁制冷回热器数值模拟

介绍了一种磁制冷回热器的数值计算模型,不仅适用于匀速流,也适用于正弦流.该模型是基于控制容积法计算的一维周期流动模型,并对常规回热器内填料能量控制方程进行了修正,考虑了磁性材料磁热效应的影响,相当于添加内热源.计算分析了某些特征参数变化对制冷性能的影响,给出的部分模拟结果为后续实验台的改造提供参考.     

The effect of tapering on a magnetocaloric regenerator bed

To design a high efficiency magnetocaloric heat pump for the residential sector, we focused on the improvement of the performance of the regenerator bed. In particular, placing the regenerators circumferentially on a plane, we decided to use tapered regenerators instead of the straight channel ones. Therefore, this paper investigates the effect of the tapering of the regenerators, which exhibit better air-gap utilization. Several simulations using a 1D AMR model were run to study the performance of the tapered regenerator, and the results were compared to the case of the straight regenerator bed. Moreover, the temperature span was held fixed at 25 K, and the working temperature of the regenerator was shifted to study the sensitivity to the variation of the working conditions. This paper considers a 10-layer regenerator, with Curie temperature (T_C) spacing of 2.5 K.     

Performance modeling of AMR refrigerators

A system modeling approach for predicting the performance of active magnetic regenerators using a one-phase approximation is presented. The approach is described for an arbitrary AMR device independent of the magnetic refrigerant, thermal losses or magnetic waveform. A general expression for magnetic work is derived which can be used for cycles where the low-field intensity is not zero. Additionally, a means of treating the varying magnetic field waveform as a single high and low field is described. The model is applied to a permanent magnet magnetic refrigerator using water–glycol as the heat transfer fluid. Simulated results are compared to experimental data which vary by heat load, frequency and utilization. A sensitivity analysis is performed using utilization, adiabatic temperature change, effective conductivity and particle size as independent variables. Comparisons to experimental data show that reducing the calculated magnetocaloric effect by 25% provides good agreement between simulations and experimental results.