应用不同混合工质的自复叠制冷机组性能的理论分析

混合工质的不同直接影响到自复叠制冷机组的各项性能。在给定的工况下分析了R744/R600 a、R744/R290、R744/R134 a、R23/R134 a、R23/R22与R32/R600等混合工质的配比、蒸发器出口温度对机组的冷凝压力、制冷量、压缩机耗功和COP的影响。结果表明:R744/R600 a、R744/R290、R744/R134 a与R32/R600 a的最佳配比为35∶65,R23/R134 a的最佳配比为40∶60,R23/R22的最佳配比为30∶70,其中R744/R290系统的COP值为最大;低沸点组分增大情况下,R744/R290、R744/R134 a与R23/R22机组的制冷量和压缩机耗功随着先增加后减小,但R23/R134 a、R32/R600与R744/R600 a机组的制冷量和压缩机耗功一直增加;在最佳配比情况下,随着蒸发温度的升高,其机组的COP值不断增加,而冷凝压力几乎不变。     

Asymmetric first‐order transition and interlocked particle state in magnetocaloric La(Fe,Si)13

In‐situ synchrotron XRD measurements of the magnetocaloric material LaFe_11.8Si_1.2 are used to understand virgin effects and asymmetry of the underlying first order magnetovolume transition. A remarkable change of the transition kinetics occurs after the first cycle, which we attribute to the formation of cracks originating from the volume change. Tomographic imaging revealed that the bulk material disintegrates via an interlocked state where fragments are loosely connected. Though cracks have opened between the fragments, the transition is sharp, which we attribute to magnetostatic interactions. In the cycled sample we find a strong asymmetry between the transition interval upon heating and cooling, which we explain by isostatic pressure acting on parts of the sample during the cooling transition. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Investigation of Boiling of Refrigeration Medium Under Periodic Disturbance Conditions

Abstract

Experimental investigations of boiling in flow of a refrigeration medium under disturbances typically occurring in refrigeration units are conducted. The development and decay of boiling is stimulated by periodic changes of mass flux density in the coil tube. It is confirmed that the two-phase systems exhibit wave properties and the disturbances generated in the system propagate with finite velocities. An experiment-based correlation to describe the disturbance propagation velocity during the development and decay of boiling in the coil tube is elaborated. The investigations are carried out for an environment-friendly refrigerant R404A supplied under pressure to the heat exchanger.     

活性炭-甲醇吸附制冰机的循环特性分析

所研究的吸附式制冰机以块状活性炭和甲醇为工质对,采用烟气加热。研究表明,对于本系统,双床循环较为合 适;双床循环中回热回质过程可以有效的改善吸附床的工作性能以及系统的热力完善度,并能将系统的制冷功率提高7％ 到11％。在循环时间为50 min时,回热回质条件下制冷功率为2 kw左右,可以实现每小时制冰15 kg左右。     

Full Analysis of Internal Adsorbate Redistribution in Regenerative Adsorption Cycles

Adsorption cycles with heat regeneration are a promising CFC-free alternative to compression cycles, for refrigeration or heat pumping purposes. However, the process is complex and therefore requires efficient analysis tools to understand correctly. These tools are now developed and used here for studying the phenomenon of internal adsorbate redistribution. This phenomenon takes place during the periods when the adsorber is pressurised, or depressurised, under globally isosteric conditions. It can be easily thought that internal adsorbate redistribution reduces the cycle performance. In order to avoid this reduction, the adsorbate redistribution can be reduced by implementing separate vapour compartments inside the adsorbers, which also requires the installation of additive check valves between the adsorber, condenser and evaporator.The present study shows that, in fact, this phenomenon does not affect performance. In addition, thanks to the different analysis tools, a physical explanation of this result, based on first and second laws of thermodynamics is developed. This result is then valid for any heat regenerative cycle using an adsorption pair.     

Bolometers operated at 0.1 K and 0.2 K cooled by adiabatic demagnetization

We have constructed bolometers operating at temperatures of 0.1 K and 0.2 K cooled by adiabatic demagnetization. The electrical noise equivalent power (NEP) of the bolometers was found to be 1.8×10^–16 W/Hz^1/2 and 6.6×10^–16 W/Hz^1/2 respectively. These values are within a factor of two of the expected performance based upon bolometer theory. The thermistor material used was gallium doped single crystal germanium, for which we find a resistivity temperature dependence of the form = ^o exp (AT^–1/2).     

Performance of an irreversible quantum refrigeration cycle

A new model of a quantum refrigeration cycle composed of two adiabatic and two isomagnetic field processes is established. The working substance in the cycle consists of many non-interacting spin-1/2 systems. The performance of the cycle is investigated, based on the quantum master equation and semi-group approach. The general expressions of several important performance parameters, such as the coefficient of performance, cooling rate, and power input, are given. It is found that the coefficient of performance of this cycle is in the closest analogy to that of the classical Carnot cycle. Furthermore, at high temperatures the optimal relations of the cooling rate and the maximum cooling rate are analysed in detail. Some performance characteristic curves of the cycle are plotted, such as the cooling rate versus the maximum ratio between high and low ``temperatures' of the working substances, the maximum cooling rate versus the ratio between high and low ``magnetic fields' and the ``temperature' ratio between high and low reservoirs. The obtained results are further generalized and discussed, so that they may be directly applied to describing the performance of the quantum refrigerator using spin-$J$ systems as the working substance. Finally, the optimum characteristics of the quantum Carnot and Ericsson refrigeration cycles are derived by analogy.     

具有非平衡吸附特征的吸附床传热特性研究

吸附床是固体吸附制冷系统的关键部件,对于连续回热等快速进行的吸附制冷循环,吸附床内温度的变化及其压力交变对吸附特性的影响不可忽视。本文对吸附床在吸附、解吸过程中的温度场和吸附率分布进行了模拟计算,并将其与采用平衡吸附模型的计算结果进行了比较,文中比较及结论有助于深入认识吸附床在制冷循环中工作特性,并为吸附床的设计提供参考依据。