摘要
本文针对有热敏性物料的蒸发浓缩和有机溶剂回收问题,建立了一套间歇操作的热泵低温蒸发实验系统。以水为料液,R22为工质进行实验,考察了系统的制热性能系数COP、制热量、蒸发量、蒸发温度、制冷量及热媒流量以及压缩机实际输入功率之间的关系。实验结果表明,系统热负荷、物料蒸发量和冷凝量、系统制热系数COP、压缩机理论耗功量和理论热媒流量均随着料液蒸发温度的升高而增大。蒸发温度在40℃以下,COP在2.8-5.4之间,压缩机的等熵效率在0.53-0.61之间。冷凝器传热阻力随蒸发温度的增大而减小,蒸发器传热阻力在34-35℃存在最小值。蒸发量为4-8.1kg/h二次蒸汽回收率在71%-91%之间,效果较好,能够完成热敏性物料在低温下蒸发的要求。以葡萄糖水溶液为料液的实验结果表明随着压缩机频率的增大,压缩机输入功率、系统制热量和制冷量、料液蒸发量和冷凝量、压缩机有效功率、压缩机效率也呈现相同的增大趋势。蒸发量在4.5-9kg/h,冷凝量为3.4-8kg/h,回收效果较好。同时压缩机效率为70%-90%,系统COPR在3.2-4.9,节能性能较好。
为了进一步研究热泵低温蒸发器的系统性能,本文为以R134a为工质,对系统进行热力学分析,研究了蒸发温度在20-40℃范围内、传热温差分别为5℃、7℃、10℃时系统的热力学性质。计算发现系统COP、制热量、料液蒸发量和工质流量随料液蒸发温度的升高而增大,随传热温差的增大而减小,压缩机功耗增大。在相同蒸发温度下,随着吸气过热度的增大,系统COPH在所选范围内变化不明显,而料液蒸发量缓慢增大,工质流量减小。对于R134a,过热度增大对系统有利。当料液蒸发温度相同时,冷凝器出口过冷度越高,系统COPH越高,料液蒸发量增大,工质流量不变。
The evaporation of heat-sensitive materials is a severe problem in operations. To solve the question, an experiment of low-temperature heat pump evaporator was conducted in this paper. Water and R22were used as material fluid and working medium respectively to study the relationships between the system coefficient of performance COP, heating capacity, evaporation capacity, evaporation temperature, cooling capacity, working medium flow rate and actual compressor input power. The results showed that, when the evaporation temperature increase, the heat load, the material evaporation and condensation capacity, the system heating coefficient of performance COP, compressor theoretical power consumption and the theoretical heating medium flow rate all increased. The evaporation temperature was under40℃, and the COPR was from2.8to5.4, the compressor isentropic efficiency was between0.53-0.61, condenser heat transfer resistance decreased by increasing evaporation temperature, the minimum evaporator heat transfer resistance was at the34-35℃. The system can achieve an evaporation of4-8.1kg/h and the steam recovery was71%-91%, which can efficiently deal with heat-sensitive materials at low temperature evaporation. With glucose solution as the material fluid, the experimental results show that with the increase of compressor frequency and input power, system heating and cooling capacities, evaporation and condensation capacities, compressor effective input power and efficiency all have the same trend of increase. And can achieve an evaporation of4.5-9kg/h and condensation of3.4-8kg/h. With fine energy-saving performance, the efficiency of the compressor is70%-90%, COPR was3.2-4.9.
In order to further study on the system performance of the low-temperature heat pump evaporator, R134a was used as the working fluid to analysis the system thermodynamic characteristics. System thermodynamic properties was studied in the condition of20-40℃ranged evaporation temperature with3specific temperature differences,5℃,7℃,10℃. It was found that the system COP, heating capacity, evaporation capacity and the working fluid flow rate increases along with the evaporation temperature, but decreases when the temperature difference increases, however, the compressor power consumption increases. With the increase of suction superheat at the same evaporation temperature, the system COPH did not change significantly within the selected range, while the evaporation capacity slowly increases and the working fluid flow rate decreases. For R134a, the increases of superheat benefit the system. And when the evaporation temperature is fixed, higher the degree of subcooling can achieve higher system COPH and higher evaporation capacity while working fluid flow rate remains unchanged.
引文
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