Energy and exergy analyses on the off-design performance of an absorption heat transformer

Absorption heat transformers (AHTs) have great potential in utilization of low-level heat sources, such as industrial waste heat. However, the operation of an AHT is limited by heat sources, customer load, and cooling water. However, such conditions may change in practical applications. Thus, research on the off-design performance of an AHT is important and necessary. In this paper, mathematical models for the cycle and components of a vertical falling film AHT operating with water/lithium bromide solution were developed. The coefficient of performance, output heat capacity, and exergy efficiency were used to evaluate the performance of the AHT. Furthermore, the exergy loss distribution diagrams under off-design conditions were carried out, and the exergy loss ratio was decomposed into several factors to determine why exergy loss ratio varies under off-design conditions. Finally, exergy loss ratio in the solution heat exchanger plays an important role under off-design conditions, which is analyzed thoroughly. A kind of effective adjustment is studied and proven to be effective in improving the performance of the AHT. The present work provides a tool for thoroughly understanding the mechanism of performance change in the AHT under off-design conditions.

► Mathematical models for cycle and key components of an AHT were developed.
► We studied exergy efficiency, COP and exergy distribution under off-design conditions.
► The solution heat exchanger played an important role under off-design conditions.
► The exergy loss ratio was decomposed into several factors to study it better.
► Circulation ratio control strategy was proposed and proven to be efficient.