HEAT TRANSFER AUGMENTATION IN HORIZONTAL R-22 EVAPORATOR WITH COILED WIRE INSERTS

Abstract

Experiments were carried out to study the :effect of turbulence promoters on the heat transfer rate and pressure drop. Test section consisted of a stainless steel tube, 10 mm internal diameter, 12.94 mm outer diameter and 2.1 metre heated length. Tube was heated externally by passing regulated electric curry?nt through it. Coiled wires obtained from 18 SWG (1.24 mm) stainless steel wire were employed as turbulence promoters. Copper-constanton thermocouples were spot welded along the top, side and bottom of the test tube at ten different locations to measure the outside wall temperatures. Data were collected for following values of heat flux, vapour quality and twist ratio.: i) Heat flux : 12, 15,18,E 20, 22, 25 KW/m2 ii) Vapour Quality .: 0.15 to 0.75 iii) Twist Ratio : 0.5, 1.0, 1.5, 2.0 iv) Mass flow rate : 60 kg/hr. Results indicate that considerable enhancement in heat transfer rates may be achieved by using turbulence promoters. The insertion of coiled wire tends to establish annular flow at quite low vapour quality when compared to plain flow. It is also observed that increase in heat transfer rats: is accompanied by the increase in pressure drops. For —iii— those applications, where enhancement in heat transfer rate is of greater importance, twist ratio 1.0 was found to perform better but for those, situations where pressure; drop plays a significant role, twist ratio 2.0 may be preferred.