STUDIES OF FLOW BOILING HEAT TRANSFER ENHANCEMENT INSIDE A HORIZONTAL TUBE USING TURBULENCE PROMOTERS

Abstract

In the present work an experimental investigation of flow boiling heat transfer augmentation of R- 1 34a inside a horizontal tube using a `spring insert' has been carried out and significant enhancement observed. The plain tube data were also obtained to establish the integrity of the test set-up and to judge the insert performance. An experimental set-up was designed and fabricated in the laboratory to study the flow boiling augmentation. Tests were conducted using a single tube evaporator test facility. The test section used was kept horizontally of 1000 mm long with 12.2 mm inside diameter of hard drawn Copper tube with `spring insert' also be made of Copper. A full length spring of 12.2mm outside diameter is inserted inside horizontal tube with the help of a rod and a wire. The present study covers the range of two parameters likes, Mass flux, G, 91.3-629 kg/m2-sec, and Heat flux, q, 4.0-12.7 kW/m2. The refrigerant vapor quality, X, was varied from the range of 0.0-0.30. Two phase pressure drop data were obtained for evaporation in two horizontal test section and these data have been compared against few of two phase frictional pressure drop prediction methods (Muller-Stein Hagen & Heck [38]) It was found that a spring insert could enhance the heat transfer by 1.2 to 2.0 based on the mass flux and heat flux. The highest heat transfer was observed at mass flux of 628.76 kg/m2-sec and heat flux of 6.455 kW/m2. The wire coil insert provides enhancement by flow separation at the wire, causing fluid mixing in the down stream boundary layer. Augmentation of heat transfer and augmented length are found to be dependent on mass flux, G, and heat flux, q. Pressure drop is also observed for plain and augmented flow. Pressure drop is higher for augmented flow. iii