Experimental Investigations and Performance Optimization of Multifluid Heat Exchangers for Sustainable Residential Heating Applications

Abstract

vi newlineABSTRACT newlineThis thesis presents a thorough experimental analysis of a Novel Multi-Fluid Heat Exchanger (NMFHE), suggested for simultaneous heating of air and water in a domestic heating system. The current NMFHE is an improved version of Three fluid Heat Exchanger (TFHE) presented by Mohapatra et al., where the helical coil tube was replaced by a Brazed Helix Tube (BHT) for enhanced heat transfer. The current BHT is novel and made from a helical tube with precision brazing between coil turns to provide two flow passages. Primarily, the experimental investigation of the NMFHE is conducted to predicts its thermo-hydraulic, exergetic, and sustainability performance corresponding to variation in flow rates, inlet temperatures, flow configurations, and geometrical parameters and compared with the results of TFHE presented by Mohapatra et al. Afterward, overall performance of the NMFHE is optimized using Taguchi-Gray and RSM techniques. newlineExperimental investigation was carried out for Reynolds numbers ranging from 7,300 to 27,000, flow rates from 100 to 300 liters per hour, inlet temperatures between 60 to 80°C, and helical tube diameters from 1/4 to 1/2 inches. The overall heat transfer coefficient (Uo), effectiveness (and#949;), Colburn factor (j), JF factor (JF), sustainability index (SI), and exergy efficiency were calculated as thermos-hydraulic, exergetic, and sustainability measures of the present study. 276.1 W/m2.K and 22.03 W/m2.K are determined as the maximum values of overall heat transfer coefficients at 300 LPH flow rate and 80°C inlet temperature of HF1 in CF1 flow configurations for energy transfer from HF1 to HF2 and HF3 respectively. 0.497 and 0.27 are determined as the maximum effectiveness for energy transfer from HF1 to HF2 and HF3 respectively at flow rates of 100 LPH and 300 LPH with HF1 inlet temperatures of 80°C and 60°C, respectively, in CF1 configuration. 0.006 and 0.08 are determined as the maximum Colburn factor and the JF factor, respectively, observed at 100 LPH flow rate and 60°C inlet temperature of HF1 in CF1 flow configurations for the Colburn factor and PF configurations for the JF factor. The maximum exergy efficiency and sustainability index, 0.7855 and 4.06 respectively, are observed at the flow rate of 100 LPH and an inlet temperature of 60°C for HF1 in CF1 flow configurations. The present results prove the enhanced performance of the NMFHE as compared to TFHE for heat transfer from HF1 to HF3. newlinePerformance optimization of the NMFHE was conducted using the Taguchi GRA method. The CF2 flow configuration, 150 LPH of HF1 flow rate, 150 LPH of HF2 flow rate, and 80°C of HF1 inlet temperature were found as the optimum input parameters for this study. Similarly using RSM, with a composite desirability, D of 0.931, the optimum value of newlinevii newlineNusselt number for HF1, HF2, and HF3 of 47.997, 58.077, and 100.164, respectively, and lowest value of entropy generation number of 0.024 are predicted. These optimized performances for the NMFHE are evaluated for the optimal value of input parameters of 150 LPH flow rate of HF1, 200 LPH flow rate of HF2, and 60°C inlet temperature of HF1. newlineThis thesis highlights the significant potential of the NMFHE in sustainable energy systems. It offers valuable insights into the design and operational strategies for multi-fluid heat exchangers, particularly when used for conventional water and air heating. Future scope of this thesis works also elaborated. The effect of coil diameter and shell diameter on the optimum performance of the NMFHE may be tested. Transient behavior of temperature variations of heat transfer fluids may be tested analytically and numerically. The performance of the NMFHE in waste heat recovery and cooling applications may be tested. newlineKeywords: Three fluid heat exchanger; Helical coil; Nanofluid; Taguchi technique, Correlation development; Nusselt number; friction factor; Entropy generation number; Thermohydraulic behaviour; JF factor, Response surface methodology; artificial neural network; multi-response optimization. newline