溴化锂制冷蒸发器中钛椭圆管外降膜流动及传热特性

Flow and heat transfer characteristics of falling film outside titanium elliptical tube in LiBr refrigeration evaporator

为了提高溴化锂中央空调系统中制冷蒸发器的耐腐蚀性,采用钛管代替铜管,并提出椭圆管代替圆管方式提高钛管外制冷剂蒸发效率,数值模拟研究椭圆系数E对椭圆钛管外制冷剂流动过程、液膜厚度分布及传热系数影响规律。结果表明:在椭圆系数E=1.0~1.7范围内,随着E增大,管外液膜平均厚度减薄、液膜速度增大、干壁面积减少、传热边界层也更薄,传热效果显著提升;相比于圆管,E=1.7的椭圆管外液膜平均厚度减少26.21%,平均液膜速度增大20.81%,干壁面积减少86.00%,管外平均传热系数提高8.67%;E=1.8~2.0范围内,随着E增大,管外液膜平均厚度增大、液膜干壁面积增大,均不利于强化传热。

In order to improve the corrosion resistance of refrigeration evaporator in LiBr(lithium bromide) central air conditioning system, titanium tube is used instead of copper tube. In addition, an elliptical tube instead of a circular tube is proposed to improve the evaporation efficiency of refrigerant outside the titanium tube. Effect of elliptic coefficient E on flow process, film thickness distribution and heat transfer coefficient of refrigerant outside the titanium tube was studied by numerical simulation. The results show that in the E(elliptic coefficient) range of 1.0—1.7, the average thickness of the liquid film is thinner, the flow velocity of the liquid film is increased, the area of the dry wall is reduced, the heat transfer boundary layer is thinner and the heat transfer effect is improved significantly with the increase of E. Compared with circular tube, when E=1.7, the average thickness of the liquid film is reduced by 26.21%, the flow velocity of the liquid film is increased by 20.81%, the area of the dry wall is reduced by 86.00% and the average heat transfer coefficient outside tube is increased by 8.67%. However, in the E range of 1.8—2.0, the average thickness of the liquid film and the area of dry wall are increased. Therefore, too large elliptic coefficient is not conducive to heat transfer enhancement.