Thermal and economic investigation of straight and U-bend double tube heat exchanger with coiled wire turbulator

Experimental research has been carried out for four individual heat exchanger constructions, i.e., plain double tube, turbulized double tube, plain U-bend and U-bend with turbulator. Tests were made for the water-water system. The study covered a wide measuring range, i.e., Re = 800–9000 – on the shell side, for a constant cold water temperature of 9°C and hot water of 50°C. The heat exchangers were made from copper tubes with external diameter of 10 mm and 18 mm respectively and wall thickness of 1 mm. The helicoidal vortex generator was made from brass wire with a diameter of 2.4 mm, coil diameter of 13 mm and pitch of 11 mm. For these geometries, the values of pressure drop, heat flux and heat transfer coefficient were determined. Wire coil turbulator increased the heat transfer coefficient (HTC) over 100% and pressure drop up by 100%. The comparison of heat transfer efficiency was performed based on the number of transfer units-effectivenes (NTU-ε) method. The modified construction achieved a similar efficiency. Economic analysis of wire coil turbulator was made to validate its use in the system. It showed that a coiled wire turbulator can greatly decrease the investment cost of the double tube heat exchanger while maintaining transferred heat at a constant level.