Secondary flow intensity determines Nusselt number on the fin surfaces of circle tube bank fin heat exchanger

2013 ◽  
Vol 62 ◽  
pp. 620-631 ◽  
Author(s):  
Wan-Ling Hu ◽  
Ke-Wei Song ◽  
Yong Guan ◽  
Li-Min Chang ◽  
Song Liu ◽  
...  
Keyword(s):  
Nusselt Number ◽  
Heat Exchanger ◽  
Secondary Flow ◽  
Tube Bank ◽  
Flow Intensity ◽  
Circle Tube

The Effectiveness of Secondary Flow Produced by Vortex Generators Mounted on Both Surfaces of the Fin to Enhance Heat Transfer in a Flat Tube Bank Fin Heat Exchanger

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Ke-Wei Song ◽  
Liang-Bi Wang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Convective Heat Transfer ◽  
Secondary Flow ◽  
Average Nusselt Number ◽  
Vortex Generators ◽  
Tube Bank ◽  
Flat Tube ◽  
Flow Intensity

Secondary flow is the flow in the cross section normal to the main flow. It plays an important role on the enhanced heat transfer and in the applications in other fields. Secondary flow can greatly enhance the convective heat transfer. In order to find the effectiveness of secondary flow for heat transfer enhancement, a nondimensional parameter, Se, based on the absolute vorticity flux is reported to specify the intensity of secondary flow. Its physical meaning is the ratio of inertial force to viscous force induced by secondary flow. As an example, the effectiveness of secondary flow was numerically studied for a flat tube bank fin heat exchanger with vortex generators (VGs) mounted on both surfaces of the fin. The contributions of VGs are investigated for the enhancements of secondary flow intensity, convective heat transfer, and pressure drop. The method is demonstrated using Se to find out the optimum configurations of VGs. The results reveal that close relationships exist not only between the span-average nondimensional intensity of secondary flow and the span-average Nusselt number but also between the volume average nondimensional intensity of secondary flow and the overall average Nusselt number. For the configuration studied, a ratio of Nusselt number enhancement to the friction factor enhancement increases with increasing the enhancement of secondary flow intensity. As a supplement to traditional criteria on a good performance heat transfer surface, the nondimensional intensity of secondary flow can be used clearly for an optimum value of VG parameter.

Performance enhancement for tube bank staggered configuration heat exchanger – CFD Study

2021 ◽  
pp. 108392
Author(s):  
Ahmed M. Nagib Elmekawy ◽  
Alaa A. Ibrahim ◽  
Abdalrahman M. Shahin ◽  
Sara Al-Ali ◽  
Gasser E. Hassan
Keyword(s):  
Heat Exchanger ◽  
Performance Enhancement ◽  
Tube Bank

Non-Axisymmetric Turbine Endwall Aerodynamic Optimization Design: Part I — Turbine Cascade Design and Experimental Validations

2014 ◽  
Author(s):  
Hao Sun ◽  
Jun Li ◽  
Liming Song ◽  
Zhenping Feng
Keyword(s):  
Secondary Flow ◽  
Evaluation Method ◽  
Pressure Coefficient ◽  
Optimization Method ◽  
Experimental Measurements ◽  
Turbine Cascade ◽  
Aerodynamic Optimization ◽  
Flow Losses ◽  
Flow Intensity ◽  
Performance Evaluation Method

The non-axisymmetric endwall profiling has been proven to be an effective tool to reduce the secondary flow loss in turbomachinery. In this work, the aerodynamic optimization for the non-axisymmetric endwall profile of the turbine cascade and stage was presented and the design results were validated by annular cascade experimental measurements and numerical simulations. The parametric method of the non-axisymmetric endwall profile was proposed based on the relation between the pressure field variation and the secondary flow intensity. The optimization system combines with the non-axisymmetric endwall parameterization method, global optimization method of the adaptive range differential evolution algorithm and the aerodynamic performance evaluation method using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and k–ω SST turbulent with transition model solutions. In the part I, the optimization method is used to design the optimum non-axisymmetric endwall profile of the typical high loaded turbine stator. The design objective was selected for the maximum total pressure coefficient with constrains on the mass flow rate and outlet flow angle. Only five design variables are needed for one endwall to search the optimum non-axisymmetric endwall profile. The optimized non-axisymmetric endwall profile of turbine cascade demonstrated an improvement of total pressure coefficient of 0.21% absolutely, comparing with the referenced axisymmetric endwall design case. The reliability of the numerical calculation used in the aerodynamic performance evaluation method and the optimization result were validated by the annular vane experimental measurements. The static pressure distribution at midspan was measured while the cascade flow field was measured with the five-hole probe for both the referenced axisymmetric and optimized non-axisymmetric endwall profile cascades. Both the experimental measurements and numerical simulations demonstrated that both the secondary flow losses and the profile loss of the optimized non-axisymmetric endwall profile cascade were significantly reduced by comparison of the referenced axisymmetric case. The weakening of the secondary flow of the optimized non-axisymmetric endwall profile design was also proven by the secondary flow vector results in the experiment. The detailed flow mechanism of the secondary flow losses reduction in the non-axisymmetric endwall profile cascade was analyzed by investigating the relation between the change of the pressure gradient and the variation of the secondary flow intensity.

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