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This study proposes a heat transfer augmentation technique using a brazed helix tube (BHT) fabricated from a helical tube with precision brazing between coil turns in a novel multi-fluid heat exchanger (NMFHE) for simultaneous heating of water and air using solar energy. The thermo-hydraulic performance of the present NMFHE for residential heating of water (CW) and air (CA) using hot water (HW) is tested experimentally. Nusselt number and friction factor for fluid flow inside the NMFHE are calculated as the thermo-hydraulic measure relating to variations in flow rate, inlet temperature, and flow configuration. Optimal flow parameters for overall optimized performances that is, maximum heat transfer and minimum pressure drop in NMFHE are determined using the Taguchi Grey relational approach. NMFHE performs efficiently in the Counterflow (cold water reverse) flow configuration with HW flow rate of 100 LPH, CW flow rate of 200 LPH, and HW inlet temperature of 70°C. The CW flow rate has the greatest impact on both the Nusselt number and friction factor, with a contribution of 82.37% and 93.42%, respectively. A confirmation test has been conducted to validate the findings, revealing a significant performance improvement of 32.19% when using the Grey relational grade model.
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