Investing On Heat And Mass Transfer Of Horizontal Spiral Finned Tube Falling Film Evaporation

The scarcity of freshwater resources and shortages of energy lead to the utilization of desalination in renewable energy technology is getting more and more attention. Inner Mongolia is lack of water resource, the main usable water resource is groundwater which is generally salinity and higher fluorine water. So connecting with the characteristic of local abundant solar energy resource, the new system which combines the solar distillation with falling film evaporation on horizontal tubes is designed, and it provides a new way for desalination in the region.Small temperature differences, high heat transfer coefficient and utilizing of low-grade energy can be achieved by falling film evaporation on horizontal tubes which has become an energy-saving technology for desalination and distillation. A horizontal tubes evaporation table for experimental study is setup, the process of falling film evaporation on horizontal tubes is researched. Different spray density 、 evaporation temperature and heat flux which have influence on evaporation capacity and heat transfer coefficient of falling film evaporation are studied. The results show that:(1)evaporation capacity: within the experimental parameter region, evaporation capacity per unit time of helical finned tube bundles and smooth tube bundles is respectively augmented with the increase of evaporation temperature and spray density; for the former, it is large with the evaporation heat transfer coefficient of 0.060kg/(m·s) and evaporation temperature of 40℃or 50 ℃, and with the evaporation heat transfer coefficient of 0.072kg/(m·s) and the evaporation temperatures of 60℃ or 70℃; for the latter, evaporation capacity per unit time is large with the heat flux of 3.91kw/m2~7.69 kw/m2, spray density of 0.072kg/(m·s),and with the heat flux of 10.11kw/m2~16.05 kw/m2, spray density of 0.060kg/(m·s).(2)evaporation heat transfer coefficient: within the experimental parameter region, heat transfer coefficient of helical finned tube bundles and smooth tube bundles is all augmented with the increase of evaporation temperature. For the helical finned tube bundles, heat transfer coefficient augments with increasing heat flux, but it is not significantly affected by spray density. For the smooth tube bundles, heat flux has little effect on heat transfer coefficient; it increases at first then decreases with evaporation temperature of 40 ℃ and the increasing of spray density; it decreases slightly with evaporation temperature of 70 ℃ and the increasing of spray density. Heat transfer coefficient of helical finned tube bundles is approximately 2 times that of smooth tube bundles with spray density of 0.064kg/(m·s), evaporation temperature of 50℃ and heat flux of 193.2W~394W.This paper studies three-dimensional numerical simulation for distribution of liquid membrane outside tubes using Fluent soft ware, longitudinal opening distance of liquid arrangement has influence on the distribution of liquid film outside tube, it is the mostuniform with s=8mm, two ends of it should decrease properly with s=10mm. Liquid film thickness increases firstly and then decreases along circumferential angle of tube wall, it reaches the minimum at about 120°.Velocity ’ s magnitude is basically identical in X and Y direction of the upper and bottom heat exchange tube, viscous sublayer exists in the tube wall.