基于理论的相变储能换热器传热性能分析

在理论成功应用于常规换热器的基础上,将传递效率、耗散数及基于耗散的换热器热阻应用于相变储能换热器的传热性能分析中。定义广义耗散率并由此推导出相变储能换热器蓄热、放热及总过程的传递效率及其瞬时值。确定耗散数及基于耗散的换热器热阻计算中换热量的取法。选取一种相变储能装置作为分析对象,通过理论分析绘制各主要部分温度变化趋势,进一步简化得到硅油、水的出口温度表达式,作为算例分析基础。结果表明, 传递效率的应用范围最广,可用于计算相变储能换热器蓄热、放热及总过程的(瞬时)不可逆热损失,且评价结果与传热性能相符,瞬时传递效率随蓄热时间的增加先增大后不变再增大,随放热时间的增加先减小后不变再减小; 耗散数在蓄热过程和总过程中的评价结果与传递效率一致,瞬时耗散数随蓄热时间的增加先减小后不变再减小,然而在放热过程中的应用受限。基于耗散的换热器热阻的部分评价结果与实际不符,应用限制较大。蓄热过程及总过程中,当蓄热量、取热量与蓄、放热阶段时长同步变化时, 传递效率、耗散数与基于耗散的换热器热阻几乎无变化;当装置传热性能提高时, 传递效率增大, 耗散数减小,基于耗散的换热器热阻减小;放热过程中,设置参数的变化不影响装置传热性能, 传递效率基本无变化。

Heat transfer performance analysis of phase change energy storage heat exchanger based on entransy theory

Entransy transfer efficiency, entransy dissipation number and thermal resistance of heat exchanger based on entransy dissipation were applied to heat transfer performance analysis of phase change energy storage heat exchanger on the basis of successful application of entransy theory on conventional heat exchanger. The generalized entransy dissipation rate was defined to derive (instantaneous) entransy transfer efficiency of phase change energy storage heat exchanger in heat storage, heat release and total process, and heat transfer rate was determined to calculate entransy dissipation number and thermal resistance of heat exchanger based on entransy dissipation. A kind of phase change energy storage heat exchanger was selected as the object, and the temperature variation of main parts were described by theoretical analyses. The temperature variation of outlet of silicon oil and water were further simplified to derive their expression, as the basis of calculation and analyses. The results showed that the application range of entransy transfer efficiency was the widest, which was used to calculate the (instantaneous) irreversible heat loss of phase change energy storage heat exchanger in heat storage, heat release and total process. The evaluation results of entransy transfer efficiency were consistent with heat transfer performance and its instantaneous values were increased first, then unchanged, finally increased, with increasing heat storage time, and were decreased first, then unchanged, finally decreased, with increasing heat release time. The evaluation results of entransy dissipation number in heat storage and total process were consistent with that of entransy transfer efficiency. With increasing heat storage time, its instantaneous values were decreased first, then unchanged, finally decreased, while its application was limited in heat release process. The application of thermal resistance of heat exchanger based on entransy dissipation was the most limited since parts of its evaluation results were inconsistent with actual state. In heat storage and total process, the entransy transfer efficiency, entransy dissipation number and thermal resistance of heat exchanger based on entransy dissipation were nearly unchangeable when the heat storage quantity, heat release quantity and stage time in the process of heat storage and release were synchronous. The entransy transfer efficiency was increased, while the entransy dissipation number and the thermal resistance of heat exchanger based on entransy dissipation were decreased when the heat transfer efficiency was improved. In the heat release process, entransy transfer efficiency was unchangeable since the heat transfer performance of system was not influenced by the change of parameters setted.