Evaluation Analysis of Double Coil Heat Exchanger for Heat Transfer Enhancement

Abstract

In order to maximize the thermal efficiency of shell and coil heat exchangers, substantial research has been done and geometrical modification is one way to improve the exchange of thermal energy between two or more fluids. One of the peculiar features of coiled geometry is that the temperature distribution is highly variable along the circumferential section due to the centrifugal force induced in the fluid. Moreover, most researchers are concentrated on using a shell and single helical coil heat exchanger to enhance the heat transfer rate and thermal efficiency at different operating parameters. Therefore, the aim of this study is to investigate temperature variation ((T-1, T-2, T-3 and T-4) across a shell and single/double coil heat exchanger at different coil pitches, hot water flow rate, and cold-water flow rate along the outer surface of the coil using experimental and numerical analysis. For single and double coil heat exchangers, Computational Fluid Dynamics (CFD) is carried out using pure water with a hot water flow rate ranging between 1-2 l/min for the coil side heat exchanger. For single coil heat exchangers, the numerical analysis findings showed a good agreement with experimental four-temperature measurement results (T-1, T-2, T-3 and T-4) with an error rate of 1.80%, 3.05%, 5.34% and 2.17% respectively. Moreover, in the current double coil analysis, the hot outlet temperature decreased by 3.07% compared to a single coil (baseline case) at a 2.5L/min hot water flow rate. In addition, increasing the coil pitch will increase the contact between the hot fluid and the coil at a constant hot water flow rate and thereby decrease the hot fluid outlet temperature. Finally, a computational analysis was carried out to examine the flow structure inside single and double coil heat exchangers, and the findings indicated that the effect of centrifugal forces in double coil heat exchangers at various coil pitches caused the secondary flow to be substantially reduced. Conclusions An experimental validation and numerical investigation are provided in the present study for a shell and single/double coil heat exchanger and the effect of operating parameters (hot and cold flow rate) on the hot outlet temperature and temperature distributed along coil surface (T-1, T-2, T-3 and T-4) has studied. The experimental and numerical findings showed that the four temperatures (T-1, T-2, T-3, and T-4) were in good agreement. According to the findings of this study, when a single coil is converted into a double coil, the hot outlet temperature and the temperature distributed along the coil surface decreases at high hot water flow rate (2.5 L/min). Also, the results showed that the influence of coil pitch 30, 60 and 90 mm on a double coil heat exchanger was found to have a minimum temperature of 4.80% at p= 90 mm compared to the other two pitch numbers. In addition, the coil parameters (coil pitch and curvature diameter) have a significant impact on secondary flow within the coil. Future research can quantify LMTD and NTU to evaluate shell and double coil heat exchangers.

Keywords

• Double coil
• Flow rate
• Coil pitch
• Secondary flow