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

A vertical twin-parallel-tube absorber-evaporator unit was built for the pr esent study to investigate the overall heat transfer and mass absorption ra tes at various operation conditions. In order to establish the optimal surf ace wetting condition for the thin absorbent film during operation process, an annular-slot type solution distributor with declining surface was adopt ed for the present system. The main objective of the present study is to pe rform an experimental investigation of the controlling parameters associate d with absorption by falling film, including the operation pressure, the in let 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 i nterfacial concentration and temperature of the absorbent film, and thus th e 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. Increasin g operation pressure will increase the concentration difference of the abso rbent solution. The concentration difference of absorbent solution film bet ween 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 wil l provide appropriate conditions for a high efficiency absorption air condi tioning system.