Comparative study of the thermal performance of four different parallel flow shell and tube heat exchangers with different performance indicators

Round rod baffle (RRB), plain plate baffle (PPB), wavy-shaped plate baffle (WSB) and polygonal-shaped plate baffle (PSB) are four commonly used baffles in parallel flow shell and tube heat exchangers (STHXs). Comparative study of these four different baffles are numerically carried out using different performance indicators including Nusselt number, friction factor, performance evaluation criterion, entropy generation ratio, and entransy dissipation ratio for flow in full turbulent regime. Heat transfer mechanism has also been discussed. Correlations for Nusselt number and friction factor are fitted and the cost estimation using Hall’s method is compared. It is found that the Nusselt number of STHX-PPB, STHX-WSB, and STHX-PSB increased by 20.9%, 15.2%, and 23.9% averagely compared with STHX-RRB, respectively. The friction factor can be increased on average by 142.0%, 154.5%, and 242.4%, respectively. However, the overall performance of them is only 90.1%, 84.4%, and 82.3% that of STHX-RRB, respectively. The sequence of entropy generation and entransy dissipation is STHX-RRB > STHX-WSB > STHX-PPB > STHX-PSB. The inlet Re and baffle distance have significant effects on different performance indicators while the baffle width does not. Finally, the results show that the STHX-PSB can reduce the total cost as it has better ability on heat enhancement.

Constructal Equivalent Thermal Resistance Minimization for Tau-Shaped Fin

With the aid of constructal theory and entransy theory, a Tau-shaped fin (TAUSF) is investigated in this paper, and the widths of the bend end and elemental fins are assumed to be different. The construct of the TAUSF is optimized by the minimum equivalent thermal resistance (ETR) obtained by entransy dissipation rate. The constraints of total enveloping volume and fin material volume are considered. The results show that in the specified range of width ratio, the twice minimum ETR of the TAUSF can be yielded by an optimal width ratio and an optimal length ratio. In addition, comparing the optimal performance of the TAUSF with the counterpart of a T-shaped fin, the former sacrifices a small amount of heat transfer performance and its stiffness increases due to its structure with the bend end. The optimal structure of the TAUSF yielded from ETR minimization is conspicuously different with the counterpart yielded from maximum thermal resistance minimization. Comparing the thermal performances of the two optimal constructs, the ETR of the former optimal construct is declined by 10.58%, whereas the maximum thermal resistance is augmented by 5.22%. The former optimal construct can lead to the uniformity of temperature gradient and the reduction in thermal stress, and can guide the engineering designs of practical fins.

Numerical Study on Heat Transfer Performance in Packed Bed

Packed beds are widely used in industries and it is of great significance to enhance the heat transfer between gas and solid states inside the bed. In this paper, numerical simulation method is adopted to investigate the heat transfer principle in the bed at particle scale, and to develop the direct enhanced heat transfer methods in packed beds. The gas is treated as continuous phase and solved by Computational Fluid Dynamics (CFD), while the particles are treated as discrete phase and solved by the Discrete Element Method (DEM); taking entransy dissipation to evaluate the heat transfer process. Considering the overall performance and entransy dissipation, the results show that, compared with the uniform particle size distribution, radial distribution of multiparticle size can effectively improve the heat transfer performance because it optimizes the velocity and temperature field, reduces the equivalent thermal resistance of convection heat transfer process, and the temperature of outlet gas increases significantly, which indicates the heat quality of the gas has been greatly improved. The increase in distribution thickness obviously enhances heat transfer performance without reducing the equivalent thermal resistance in the bed. The result is of great importance for guiding practical engineering applications.