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Air source heat pumps (ASHPs) have been widely used for space heating in cold winter. When it operates in frosting environment, defrosting is necessary to maintain the system performance resulting in a discontinuous space heating. The defrosting time is an important parameter to evaluate the performance of different defrosting methods. At present, the widely applied ways for defrosting are the standard reverse-cycle defrosting and hot-gas bypass defrosting methods. For the two defrosting methods, the biggest problem is that no heat source is available for the defrosting cycle which leads to a long defrosting time. For the past few years, study on the use of heat exchangers with phase change material (PCM-HE) to storage heat for the defrosting receives lots interest. This paper presents a review of these reported defrosting methods using PCM-HE. The ASHPs with PCM-HE and their defrosting principles are introduced. Furthermore, the frequently-used phase change materials together with structure of PCM-HE are also summarized. Finally, the further research direction to realize effective defrosting and continuous heating of air-source heat pump products is discussed.

During the storage and transportation of crude oil, volatile organic vapors (VOCs) are generated. International organizations and relevant countries have formulated relevant regulations for VOCs emissions. This article introduces four kinds of oil and gas recovery technologies and their combined processes: absorption method, adsorption method, membrane separation method and condensation method. The advantages and disadvantages of different oil and gas recovery technologies are analyzed and the process performance is compared. It lists examples of the application of oil and gas recovery technology in ships, points out its shortcomings, and puts forward relevant suggestions for the research of marine VOCs recovery technology.

The mechanical vapor compression (MVC) system is a promising way for energy saving among energy intensive industries such as desalination, food and beverage, chemistry and waste water concentration etc. In practical its application is limited by the vapor compressor technology which is demanded to have high pressure ratio for large saturation temperature difference and low discharge steam temperature. Due to the ability of wet compression, twin screw compressor can overcome the technical limitation above by the injection of liquid water into the working chamber. In this paper a test rig of a MVC system with water injected twin screw compressor has been designed and built. Compressor performance of flow rate, power consumption and discharge temperature was measured. Moreover, operation characteristics of the water injected twin screw compressor were studied by the measurement of its working process p-V diagram. Volumetric efficiency and adiabatic efficiency of the compressor variation under different operation conditions were calculated. The mass flow rate and temperature of injected water was also measured and adjusted for optimization. The results of the experiment study can provide some design guidances of water injected twin screw compressor for mechanical vapor compression system.

The heat pump system of mechanical vapor compression/recompression (MVC/MVR) combined with evaporation is a high efficiency, energy-saving solution for energy intensive processes. However, a suitable compressor with high pressure ratio and low discharge temperature is not available in engineering practice. In this paper a water-injected twin screw compressor recognized as a promising type for water vapor compression is presented by detailed descriptions of the rotor profile development and structure design. Then the calculation of water quantity and its influence on the steam flow rate are presented. Moreover, the effects of injected water on the working process and performance of the compressor are discussed. Finally, it is found that the volume flow rate increases a lot because of the water evaporation during the compressing process which is originally aims to guarantee saturate discharge temperature. And the temperature difference of the MVC system is a main parameter that affects the performance of the compressor.

Semi-hermetic screw refrigeration compressor is mostly driven by a three phase asynchronous induction motor with its squirrel cage rotor attached to the shaft of the compressor helical male rotor. The motor is cooled by low temperature refrigerant coming from evaporator before it is inspired into compressor suction port. In order to investigate cooling effects of the motor and performance of the compressor under part-load conditions, a lumped parameter model describing heat transfer characteristics inside the motor and a part-load model of screw refrigeration compressor are developed. Heating effects at compressor suction end are taken into account and nodes representing refrigerant inside the motor cooling passages are modeled separately. Due to the decreasing refrigerant mass flow rate and motor efficiency, temperature rise of refrigerant through the motor increases and stator winding temperature curve goes up when the compressor load drops by suction volume variation.