Heat and mass transfer in the vertical twin‐parallel‐tube absorber‐evaporator unit

Abstract

A vertical twin‐parallel‐tube absorber‐evaporator unit was built for the present study to investigate the overall heat transfer and mass absorption rates at various operation conditions. In order to establish the optimal surface wetting condition for the thin absorbent film during operation process, an annular‐slot type solution distributor with declining surface was adopted for the present system. The main objective of the present study is to perform an experimental investigation of the controlling parameters associated with absorption by falling film, including the operation pressure, the inlet temperature of the cooling water, and the Reynolds number, temperature, and concentration of the inlet absorbent solution. An analogy between heat and mass transfer near the film surface is then applied to calculate the interfacial concentration and temperature of the absorbent film, and thus the heat and mass transfer coefficients of the absorbent film is determined. The present results show that, the higher the inlet Reynolds number of the absorbent solution is, the lower the total heat transfer rate is. Increasing operation pressure will increase the concentration difference of the absorbent solution. The concentration difference of absorbent solution film between inlet and outlet increases sharply as the Reynolds number of the inlet absorbent film decreases below 200. When the Reynolds number of the inlet absorbent film is around 200, optimal absorption‐evaporation exists and will provide appropriate conditions for a high efficiency absorption air conditioning system.

Key words:

• surface wetting
• falling film
• analogy between heat and mass transfer
• operation pressure

Notes

Correspondence addressee