Performance characteristics of new enhanced heat transfer tubes for evaporator/absorber in absorption chiller

초록

This study addresses the low heat transfer efficiency of evaporators and absorbers in single-effect LiBr-H2O absorption chillers, a key limitation in utilizing low-temperature waste heat. A novel micro end cross tube was developed to enhance wettability, reduce film thickness, and improve overall performance compared to existing end cross dimple (evaporator) and floral (absorber) tubes. Experiments were conducted using a full-cycle singleeffect absorption chiller to evaluate the heat transfer rate, overall heat transfer coefficient, and convective heat transfer coefficient under varying chilled water inlet temperatures, surfactant concentrations, and Reynolds numbers inside heat transfer tube. Results show that increasing the evaporator inlet temperature from 8 degrees C to 12 degrees C improved the overall heat transfer coefficient by 21 %, while adding 2000 ppm octyl alcohol in the absorber enhanced it by 40 %. Doubling the internal Reynolds number increased internal convective heat transfer coefficients by 84 % (evaporator) and 88 % (absorber). The newly developed micro end cross tube achieved a 27 % improvement in the evaporator and 13 % in the absorber over conventional tubes. These findings demonstrate that microstructure tube designs can significantly improve absorption chiller efficiency, reducing size and cost while enabling broader utilization of low-grade heat sources.

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