In order to improve the corrosion resistance of refrigeration evaporator in lithium bromide central air-conditioning system, titanium tube is used instead of a copper tube, and the elliptical tube is proposed to replace the circular tube to improve the evaporation efficiency of refrigerant outside the titanium tube.
In the lithium bromide absorption refrigeration system, LiBr-H2O solution is highly corrosive to stainless steel, copper, and copper alloys, which directly affects the service life of the refrigeration system and degrades the system performance. Titanium alloy has become a good choice to replace copper alloy in manufacturing heat exchange tubes due to its excellent corrosion resistance, low density, and high hardness. However, the thermal conductivity of titanium is only 18.7 W · m-2 · K-1, which is much lower than that of copper 401 W · m-2 · K-1. Therefore, it is of great significance to study the flow behavior and related heat transfer characteristics of the liquid film outside the titanium tube and develop high-performance titanium heat exchanger tubes in terms of anti-corrosion of heat exchanger tubes.
Compared with the round tube, the non-circular tube has better liquid film flow and heat transfer characteristics, and the elliptical tube has greater advantages. The theoretical analysis of the liquid film heat transfer process shows that increasing the elliptical coefficient of the horizontal tube can improve the overall heat transfer coefficient. In the range of ellipticity coefficient E=1.0~1.7, with the increase of E, the average thickness of liquid film outside the tube decreases, the velocity of the liquid film increases, the drywall area decreases, and the heat transfer boundary layer is thinner, so the heat transfer effect is significantly improved. Elliptical tubes have a better heat transfer effect.
