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.
Highlights
As one of the passive heat transfer improvements, helically coiled tube heat exchangers have been widely researched and have applications in diverse industries: pharmaceutical, biological, petrochemical, mechanical and biomedical [1]
In the heat transfer forming field, the results showed that the coil pitch is important
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 on the hot outlet temperature and temperature distributed along coil surface (T-1, T-2, T-3 and T-4) has studied
Summary
As one of the passive heat transfer improvements, helically coiled tube heat exchangers have been widely researched and have applications in diverse industries: pharmaceutical, biological, petrochemical, mechanical and biomedical [1]. Dean [8] has given the first approximation of the laminar flow into an infinitely long curved pipe with a circular cross-section with a mathematical analysis used to investigate the fluid motion through a coil pipe. It laid the basis for further studies [9,10] and greatly contributed to the understanding of the flow through curved pipe
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