Study Of Ammonia-Water Vertical Falling Film Absorption And Its Application

Vertical falling-film absorber plays an important role in absorption refrigeration. The ammonia-water absorption unit with air-cooled vertical falling-film absorber can utilize the solar energy as driving heat resources, get rid of water-cooling tower, cooling water pump and so on, reduce the power consumption, lower the investment, it can be minimized to be solar air conditioner.Ammonia-water vertical falling-film absorption is a complex and coupled heat and mass transfer process. The research about falling film ammonia-water absorption in vertical tube is few, there are no enough design resources for air-cooled vertical falling-film absorber.A vertical ammonia-water falling-film absorption experiment set-up has been established to investigate the absorption performance on inner tube surface and measure the heat and mass transfer effectiveness.According to the double-film theory, the ammonia-water falling-film adiabatic absorption was simulated and the result was compared with the experiment result. An air-cooled two-stage ammonia water absorption experimental prototype has been built based on the analysis of the falling-film absorber. It also has been tested. The main conclusions are obtained as follows:(1) the falling-film absorption experiment shows that the absorption heat and mass transfer rate will be increased with higher film Re and absorption pressure. With lower cooling water temperature and weak solution concentration, the absorption performance is better. In the experiment, the vapor flow direction relative to the solution has no effect on the absorption.(2) With the falling-film absorption experiment result, the heat and mass transfer effectiveness is fitted as follows: Nu =3. 47×10?3 Re0.27023(P/Pr)0.74596, Sh = 2 .11×10?3 Re0.51224Sc0.42415(P/Pr)0.99996, P r=200 kPa, Re is between 70~350,Sc is between 250~400,the absorption pressure is between 300~550kPa。(3) The adiabatic absorption simulation shows that the absorption mass transfer is main at the top section under the subcooling condition, subcooling can promote the absorption mass transfer. The simulated result agreed with the experiment result within 20%.(4) Air-cooled two-stage ammonia water absorption experimental prototype with air-cooled vertical absorber works steady. TCOP is 0.21,ECOP is 5.1 when the heat resources is 85℃,ambient temperature is 29℃, evaporation temperature is 8℃.