Experimental Study On Fluid Flow, Heat And Mass Transfer Of Falling Film Absorption On Coated Tube

As the energy consumption becomes larger and the request for environment protection, the cascade utilization of waste heat generated in industrial processes attracts more and more attention. AHT (absorption heat transformer) has a promising prospect for its benefits both on economy and environment. As the most vital component, absorber takes the charge of absorbing process, which includes fluid dynamics, heat and mass transfer.Teflon coated tubes are prepared, the contact angle of coated region is about120°and the SEM images show that there are defects existing in the coated region, leading to the contact angle decrease of the coated region after experiments. Experimental observation shows that the flow pattern changes from drop flow, rivulet flow to twisted rope flow and film flow as the spray density increasing. The square type coating can redistribute the flowing liquid.High precision capacitance micrometer is used to measure the liquid film thickness. The wave chart shows that film thickness fluctuates approximate periodically, and the front end of wave crest is gentle while the backend is sheer. Under the specified experimental condition, the effect distance of single staggered coatings is about8cm.Surface temperature distribution of liquid film is studied by the thermal infrared imager. Effects of liquid film Re, flowing distance, inlet temperature and heat flux on the temperature field are considered. Results show that surface temperature decreases as the distance and Re increasing. The highest temperature is captured in coated region. Temperature lift on coated tube is2℃higher than that without coating.The platform for high temperature LiBr/H2O absorption heat transformer is built and the heat and mass transfer properties of the coated tubes are tested. Experimental results show that the heat transfer coefficient becomes higher when the temperature and concentration of LiBr increase. In the heat transfer process, effect of mixing triggered by coatings is more powerful than the effect of film thickness, which leads to the increase of the heat transfer coefficient. While in the’process of mass transfer, film thickness becomes the prime factor, resulting in the decrease of mass transfer coefficient. The heat and mass transfer of square type coated tube both are higher than the helix type coated tube. Heat transfer coefficients of coated tube are higher than non-coated tube, and the heat transfer coefficient of square type coated tube is10～15%higher than non-coated tube.