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    Numerical and experimental study on thermal performance of a novel shell and helically coiled tube heat exchanger design with integrated rings and discs
    (Elsevier France-Editions Scientifiques Medicales Elsevier, 2022) Gungor, Alper; Khanlari, Ataollah; Sozen, Adnan; Variyenli, Halil Ibrahim
    Shell and Helically Coiled Tube Heat Exchangers (SHCTHEXs) are utilized in energy conversion applications in industry and in various engineering systems. They are generally composed of a helically coiled tube and a shell covering it. This coiled structure of tubes, provides better heat transfer and takes less space. There is an ongoing interest in research on this type of heat exchangers. In this study, a new design was created modifying a simple type of conventional shell and helically coiled heat exchanger, by integrating discs and rings. These rings and discs were attached to the helically coiled tubes with the aim of performing as baffles restricting the shell side flow and creating turbulence. The thermal performance of a conventional heat exchanger was improved by this modification. The study was carried out both numerically and experimentally. At first step, two SHCTHEXs, one conventional; one modified, were designed with same overall geometric dimensions. Then created solid models were numerically simulated with same boundary conditions using ANSYS Fluent. Simulations were performed with various flow rates and the results were reported. According to the simulations, compared to the conventional one, with the modified heat exchanger 7.1% increase in average amount of heat transfer rate and around 20% increase in overall heat transfer coefficient were obtained. With the promising results taken by simulations, the modified heat exchanger was fabricated with the same dimensions and it was experimentally tested with same conditions in laboratory to verify the simulation results. Experimental results were in harmony with the simulations with little differences. The average differences between simulation and experimental values in terms of average amount of heat transfer rate were obtained as 2.4% for 3 l/min hot fluid flow rate and 3.5% for 4 l/ min hot fluid flow rate. Overall heat transfer coefficient of modified SHCTHEX with circular baffles achieved in the range of 1050-1400 W/m2K. General outcomes of this study exhibited successful design of baffled SHCTHEX.
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    NUMERICAL INVESTIGATION OF THERMAL PERFORMANCE ENHANCEMENT POTENTIAL OF USING Al2O3-TiO2/WATER HYBRID NANOFLUID IN SHELL AND HELICALLY COILED HEAT EXCHANGERS
    (Begell House Inc, 2022) Gungor, Alper; Sozen, Adnan; Khanlari, Ataollah
    Shell and helically coiled tube heat exchangers (SHCTHEXs) are a special type of shell-and-tube heat exchangers and they are widely used in industry in many processes. The tubes inside the shell are curved to form a helical coil which has a positive impact on heat transfer. The main purpose of this study is to investigate thermal performance enhancement potential of using a new type of hybrid nanofluid in SHCTHEXs. In this study, two types of SHCTHEXs - one vertically oriented and the other horizontally oriented - have been designed with the same geometrical dimensions. These designs have been simulated with two types of fluid on the shell side: water and Al2O3-TiO2/water hybrid-type nanofluid at various shell-side flow rates in order to reveal the heat transfer improvement potential of using this hybrid nanofluid in SHCTHEXs. The simulations indicated that utilizing Al2O3-TiO2/water hybrid-type nanofluid on the shell side resulted in 7.7% increase in the average heat transfer rate for vertically oriented SHCTHEX and 9% increase for the horizontally oriented SHCTHEX. Calculated heat transfer rate values ranged between 3337 and 5136 W. Among the simulated designs the best performing combination has been horizontally oriented SHCTHEX with Al2O3-TiO2/water hybrid-type nanofluid on the shell side. This combination provided 2.5 degrees C better cooling at the hot fluid outlet compared to poorest performing combination: vertically oriented SHCTHEX with water (both streams at 3 lpm). Using nanofluid increased the overall heat transfer coefficient parameter in horizontally and vertically oriented heat exchangers as 17.2% and 13.7%, respectively. The achieved outcomes of this work indicate that utilizing an Al2O3-TiO2/water hybrid nanofluid provides a notable amount of increase in heat transfer rate. In addition, overall results of the study showed that horizontally oriented SHCTHEX had better performance in comparison with vertically oriented one.