• Energy Research

This study experimentally investigates the performance of a helical coil integrated chilled water system (HCCWS) used for simultaneous cooling of hot air (HA) and water (HW). The current HCCWS operates with three fluids in which chilled water (CW) flows inside the shell while hot water and air pass through the helical coil and innermost tube. Nusselt number, friction factor, and JF factor are measured as performance of the HCCWS corresponding to variations in inlet temperature, flow rate, and velocity of different fluids respectively. Temperature distribution of different fluids along the length of the HCCWS test section was determined. From results, it is observed that Nusselt number increases considerably as the flow rate of CW increases, reaching a maximum of 150.01 at a flow rate of 200 liter per hour (LPH) and an inlet temperature of 13°C. As the flow rate of chilled water increases, the friction factor drops. The lowest friction factor measured was 0.016 with a flow rate of 200 LPH and an inlet temperature of 13°C. The chilled water inlet temperature and hot water flow rate significantly affect the JF factor of CW, HW, and HA with a contribution of 33.47%, 33.7%, and 32.69%, respectively. The Taguchi-Grey technique was used to optimize the overall JF factor corresponding to input parameters. The optimal HCCWS performance was achieved at 13°C inlet temperature, 100 LPH chilled and hot water flow rates, and 4 m/s hot air velocity, raising the grey relation grade to 1.

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.

Abstract A novel multi-fluid heat exchanger deployed for simultaneous heating of water and space is experimentally investigated to predict its thermo-hydraulic, exergetic, and sustainability performance for distinct Al2O3, TiO2, and CuO nanofluid (NF) flow of 50 ppm concentration of each through the inserted brazed helix tube (BHT). The input parameters such as flowrates, helix tube diameters, and nanofluid types are varied throughout the experiments to evaluate their effect on output performance parameters i.e., Nusselt number (Nu), friction factor ( f), entropy generation number (Ns), JF factor (JF), exergy efficiency (ƐE), and sustainability index (SI). The NF flowing through the BHT is the heating fluid that simultaneously heated the cold water, and cold air flowing through the outer shell and inner conduit of the BHT respectively. A distinct Nusselt number correlation for turbulent nanofluid flow inside BHT was developed, compared, and validated reasonably with the current result. For Al2O3 NF at a Reynolds number of 5698 with a 1/2-in. diameter helix tube, the best results for JF, ƐE, and SI are found to be 0.009, 0.72, and 3.53, respectively. Furthermore, for Al2O3 and TiO2 NF at a Reynolds number of 14,250 and a helix tube diameter of 3/8 in. and 1/2 in., f, and Ns are found to be 0.0047 and 0.043, respectively are minimum. It is observed that the use of Al2O3 NF, higher helix tube diameters, and lower flowrates all make the proposed heating application more sustainable.