Experimental investigation of convective heat transfer in an inserted coiled tube type three fluid heat exchanger

In the present study, an experimental investigation of a three fluid heat exchanger (TFHE) has been performed. The TFHE presented here is an improved version of double pipe heat exchanger, where a helical tube is inserted between two concentric straight tubes. The curvature ratio, δ = 0.1315, pitch to inside diameter, p/dci = 2.88 of the helical tube are taken constant during the test while range of coil side Reynolds number are varied between 9000 and 54,000 during this investigation. Coil side Nusselt numbers are calculated using traditional Wilson plot technique and compared with the Nusselt numbers reported from literature for both parallel and counterflow configurations. Temperature distribution data has been obtained using analytical approach and experimental approach for three fluids. The effect of variation in volume flow rate on performance of the TFHE is assessed as well. Overall heat transfer co-efficient found to be increased in each case when flow rate of different fluids in TFHE increased. The effectiveness decreases or increases, which are the combined effect of residence time, capacity ratio, R and NTU. TFHE provides optimized performance, when flow rate of normal water increases in counter flow configuration. Simultaneous space heating and water heating is the novelty of the proposed TFHE.