Experimental investigation of heat transfer enhancement in straight and U-bend double-pipe heat exchanger with wire insert

In this paper, the possibility of heat transfer enhancement in the U-bend exchanger was presented. Experimental research has been carried out for four individual heat exchanger constructions i.e. plain tube in tube, turbulized tube in tube, plain U-bend and U-bend with turbulator. Also, heat transfer experiments for various boundary conditions were performed to obtain reference values. In case of U-bend exchanger with and without turbulator, tests were conducted based on the water-water system. The study covered a wide measuring range, i.e. Re = 800-9000 - on the jacket side, P-el = 500-1400 W (for reference) cold water temperature of 9 degrees C and hot water of 50 degrees C. The exchangers were made from a copper pipe with an external diameter of 10 mm and 18 mm and wall thickness of 1 mm. The helicoidal vortex generator was made from brass wire with a diameter of 2.4 mm, coil diameter 13 mm and pitch 11 mm. For these geometries, the values of pressure drop and rate of heat transfer were determined. The comparison of heat transfer efficiency was performed based on NTU-epsilon method. For the same thermal-flow parameters, wire inserts provide up to 280% heat transfer enhancement and 85% higher heat transfer rate.