Researches On The Distribution Of Liquid Film And The Condensation Heat Transfer Characteristics Of The Horizontal Finned Tubes

The condensation heat transfer is widely exists in the refrigeration and air conditioning industry, chemical industry, nuclear power and other fields, In the process of condensation, the liquid film is the main thermal resistance, the fins, reducing the thickness of the thin liquid films to intensify the performance of the condensation heat transfer outside tube, organic working fluid as an energy carrier, the relatively stable performance can be used as refrigerants. Then study of the organic working medium condensation heat transfer characteristics on finned tube provide theoretical reference to design efficient condensing equipment, and of great significance to improve energy efficiency and economic benefit.The liquid film thermal resistance depends on the size of the liquid film thickness and distribution outside finned tubes, and related with finned structure size(fin height, density of fin, fin thickness),the type of tube, the arrangement of tubes, fluid velocity and physical parameters and so on. Then using theoretical analysis and numerical calculation method to studied condensing liquid film thickness and heat transfer characteristics of horizontal finned tube.Based on the Nusselt theory, using modified film theory, this paper established the mathematical model of organic working fluid condensation outside finned tube, the model depended on elemental calculation by dividing the tube wall into finite elements, through the working medium of R134 a and TFE verifies the superiority of the model, getting the condensed liquid film distribution on the fin wall and the channel between fins. Analysis the influence of the fin geometry size and the tube type on the condensation heat transfer. The results show that,(1) the thickness of film on fin flank constantly thickening follow the angle of circumference and constantly thinning follow the direction of rib height, the local heat transfer coefficient on fin flank decreases in the circumferential direction and increases in the direction of the rib height; on the channel between fins the thickness of film increase and the Heat transfer coefficient decrease from the angle 0 to ?f of circumference,arrived at the flooded region the thickness sharply increase and the heat transfer coefficient sharply decrease.(2) The fin height is 1.19 mm, the average heat transfer coefficient along with the increase of density of fin first increases then decreases, the optimal density of fin is 25 fpi; the fin height have less effect on the condensation heat transfer.(3) Elliptic finned tube,the thermal resistance on the channel between fins is greater than the fin wall, in the upper tube, liquid film thermal resistance decreases with the increase of inscribed angle, in the second half, liquid film thermal resistance increases with the increase of inscribed angle.(4) Drop type finned tube, the liquid film thermal resistance and local condensation heat transfer coefficient of the upper pipe the same with the circular finned tube, in the second half it is the same with elliptical finned tube.(5) The average heat transfer coefficient of the different rib tube with different curvature and the average condensation heat transfer coefficient of the same diameter of circular finned tube the strengthen rate greater than 1, elliptic finned tube is superior to the drop type finned tube.(6) The condensation heat transfer performance of the elliptic finned tube greater with the curvature increasing.