Research On Optimization Of Refrigerant Distribution Structure And Performance In Dry Type Shell-tube Evaporator

Dry type shell-tube evaporator occupies an important position in the refrigeration and air conditioning system.The heat transfer performance of the evaporator plays a central role in the entire refrigeration system.The uniformity of the refrigerant distribution is an important factor in determining the heat transfer performance of the evaporator,so the refrigerant distribution uniformity is studied.It is of great significance to improve the uniformity of refrigerant distribution in the tubes.In the thesis,the distribution uniformity of refrigerant in different inlet structures of dryexpansion shell and tube evaporators and its effect on shell performance are studied quantitatively,and the influence of the distributor plate under different opening structure on refrigerant distribution uniformity is analyzed.In this thesis,the following contents are studied:1.The uniformities of refrigerant flow distributions under four different inlet structures of the evaporators are investigated,and the factors affecting the uniformity of refrigerant distribution are analyzed.To improve the even distribution of refrigerant under the tube sheet inlet structure,the optimized inlet structure is presented.Three new inlet structures are single-stage flared,convex 5mm,convex 10 mm,.The optimized three inlet structures have greatly improved the uniformity of the distribution of the refrigerant.The convex 10 mm refrigerant distribution performance is optimal,and closely followed is the convex 5mm structure.The inlet mass flow of the refrigerant and the pressure at the entrance of the heat exchange tube are the main factors affecting the distribution uniformity of the refrigerant.With the inlet mass flow increases,the refrigerant distribution uniformity slightly decreases,but when the refrigerant increases to 0.5~0.6kg/s,the refrigerant distribution uniformity no longer undergoes a large change.Except for the heat exchange tubes that are extremely close to the center,pressure changes of other heat exchange tubes are proportional to the flow rate of the refrigerant,and the distribution of the refrigerant is more uniform in the area where the pressure is high.2.A comparative analysis of the advantages of installing the splitter plate in the inlet was conducted,and the opening structure of the splitter plate is optimized by analyzing the effect of three different open structure splitter plate on refrigerant distribution uniformity.With the inlet device added to the splitter plate,the refrigerant passes through the secondary splitter of the splitter plate and flows into each heat exchange tube more evenly.Compared with the non-splitter plate,the refrigerant distribution uniformity is greatly improved.The effects of structures of center of circular hole,cross hole,hole splitter plate structure on the influence of the refrigerant distribution uniformity are analyzed quantitatively.It is found that the center hole diverter plate has the best distribution uniformity of the refrigerant,followed by the cross hole,and the equal circle hole structure is the worst.Compared with the equal circle splitter plate,the distribution uniformity of refrigerant in the cross hole structure is improved by 26.45%~35.76%.For the splitter plate with the center hole structure,the distribution uniformity of the refrigerant in the cross-head orifice manifold is increased by 11.54%~12.36%.The change in the opening structure of the splitter plate can effectively improve the distribution of refrigerant distribution.3.When the shell-side flow rate ranges from 4.043kg/s to 12.13kg/s,the heat transfer performance of the convex 10 mm entrance structure is the best,and followed by the is convex 5mm structure.The heat transfer performance of the shell-and-tube structure is minimal.The numerical simulation calculation of the continuous spiral baffle heat exchanger in the literature proves the credibility of the numerical calculation results in this paper.The uniformity of refrigerant distribution in the heat exchange tubes affects the heat transfer performance of the evaporator shell.The refrigerant distributes more uniformly,the heat transfer performance of the evaporator shell side is higher.And the refrigerant distributing uniformity has less impact on the shell-side pressure drop of evaporator.There is a corresponding relationship between the heat transfer coefficient of the heat transfer tube wall of the evaporator and the flow rate of the refrigerant in the corresponding heat exchange tube,the heat transfer coefficient of evaporator increases with the increase of refrigerant distributing rate in the heat exchange tubes,and the heat transfer coefficient of evaporator decreases with the decrease of refrigerant distributing rate in the heat exchange tubes.