A New Analysis of Heat Transfer Deterioration on Basis of Turbulent Viscosity Variations of Supercritical Fluids

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Mahdi Mohseni ◽  
Majid Bazargan
Keyword(s):  
Heat Transfer ◽  
Turbulent Flows ◽  
Supercritical Fluids ◽  
Turbulent Viscosity ◽  
Convection Heat Transfer ◽  
Two Dimensional ◽  
Convection Heat ◽  
Heat Transfer Deterioration ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Turbulence

A two-dimensional computational fluid dynamics (CFD) code has been used to study the anomalies encountered in convection heat transfer to upward turbulent flows of supercritical fluids in tubes. In this study, the effect of turbulent viscosity variations on heat transfer deterioration (HTD) and the mechanisms involved have been investigated. The results show that the suppression of the flow turbulence which leads to the deterioration of heat transfer can be partially due to the decrease in the turbulent viscosity as a result of density decrease along a heated flow. Before this study the buoyancy and the thermal acceleration effects were called as the main two known mechanisms for the heat transfer deterioration.

Numerical Study of Deteriorated Convection Heat Transfer of Supercritical Fluid Flowing Through Vertical Mini Tube at Relatively Low Reynolds Numbers

2018 ◽  
Author(s):  
Chen-Ru Zhao ◽  
Zhen Zhang ◽  
Qian-Feng Liu ◽  
Han-Liang Bo ◽  
Pei-Xue Jiang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Convection Heat Transfer ◽  
Turbulence Models ◽  
Convection Heat ◽  
Flow Acceleration ◽  
Heat Transfer Deterioration ◽  
Low Reynolds

Numerical investigations are performed on the convection heat transfer of supercritical pressure fluid flowing through vertical mini tube with inner diameter of 0.27 mm and inlet Reynolds number of 1900 under various heat fluxes conditions using low Reynolds number k-ε turbulence models due to LB (Lam and Bremhorst), LS (Launder and Sharma) and V2F (v2-f). The predictions are compared with the corresponding experimentally measured values. The prediction ability of various low Reynolds number k-ε turbulence models under deteriorated heat transfer conditions induced by combinations of buoyancy and flow acceleration effects are evaluated. Results show that all the three models give fairly good predictions of local wall temperature variations in conditions with relatively high inlet Reynolds number. For cases with relatively low inlet Reynolds number, V2F model is able to capture the general trends of deteriorated heat transfer when the heat flux is relatively low. However, the LS and V2F models exaggerate the flow acceleration effect when the heat flux increases, while the LB model produces qualitative predictions, but further improvements are still needed for quantitative prediction. Based on the detailed flow and heat transfer information generated by simulation, a better understanding of the mechanism of heat transfer deterioration is obtained. Results show that the redistribution of flow field induced by the buoyancy and flow acceleration effects are main factors leading to the heat transfer deterioration.

Modifying a meshless method to solving κ−ε turbulent natural convection heat transfer

2019 ◽  
Vol 31 (01) ◽  
pp. 2050014
Author(s):  
Nasrin Sheikhi ◽  
Mohammad Najafi ◽  
Vali Enjilela
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Numerical Methods ◽  
Turbulent Flow ◽  
Turbulent Viscosity ◽  
Convection Heat Transfer ◽  
New Technique ◽  
Test Cases ◽  
Convection Heat ◽  
Transfer Problems

The conventional meshless local Petrov–Galerkin method is modified to enable the method to solve turbulent convection heat transfer problems. The modifications include developing a new computer code which empowers the method to adopt nonlinear equations. A source term expressed in terms of turbulent viscosity gradients is appended to the code to optimize the accuracy for turbulent flow domains. The standard [Formula: see text] transport equations, one of the most applicable two equation turbulent viscosity models, is incorporated, appropriately, into the developed code to bring about both versibility and stability for turbulent natural heat transfer applications. The amenability of the new developed technique is tested by applying the modified method to two conventional turbulent fluid flow test cases. Upon the obtained acceptable results, the modified technique is, next, applied to two conventional natural heat transfer test cases for their turbulent domain. Based on comparing the results of the new technique with those of the available experimental or conventional numerical methods, the proposed method shows good adaptability and accuracy for both the fluid flow and convection heat transfer applications in turbulent domains. The new technique, now, furthers the applicability of the mesh-free local Petrov-Galerkin (MLPG) method to turbulent flow and heat transfer problems and provides much closer results to those of the available experimental or conventional numerical methods.

scholarly journals Simulation and Optimization of Air-Cooled PEMFC Stack for Lightweight Hybrid Vehicle Application

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Jingming Liang ◽  
Zefeng Wu
Keyword(s):  
Heat Transfer ◽  
Proton Exchange Membrane ◽  
Convection Heat Transfer ◽  
Hybrid Vehicle ◽  
Proton Exchange ◽  
Convection Heat ◽  
Simulation Data ◽  
Simulation And Optimization ◽  
Computational Fluid Dynamics Cfd ◽  
Exchange Membrane

A model of 2 kW air-cooled proton exchange membrane fuel cell (PEMFC) stack has been built based upon the application of lightweight hybrid vehicle after analyzing the characteristics of heat transfer of the air-cooled stack. Different dissipating models of the air-cooled stack have been simulated and an optimal simulation model for air-cooled stack called convection heat transfer (CHT) model has been figured out by applying the computational fluid dynamics (CFD) software, based on which, the structure of the air-cooled stack has been optimized by adding irregular cooling fins at the end of the stack. According to the simulation result, the temperature of the stack has been equally distributed, reducing the cooling density and saving energy. Finally, the 2 kW hydrogen-air air-cooled PEMFC stack is manufactured and tested by comparing the simulation data which is to find out its operating regulations in order to further optimize its structure.

Heat Transfer of Springs in Oblique Crossflows

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Daniel B. Biggs ◽  
Christopher B. Churchill ◽  
John A. Shaw
Keyword(s):  
Heat Transfer ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Experimental Program ◽  
Convection Heat ◽  
Computational Tool ◽  
Cfd Simulations ◽  
Nonmonotonic Dependence ◽  
Computational Fluid Dynamics Cfd ◽  
Good Agreement

An experimental program is presented of heated tension springs in an external crossflow over a range of laminar Reynolds numbers, spring stretch ratios, and angles of attack. Extensive measurements of the forced convection heat transfer of helical wire within a wind tunnel reveal an interesting nonmonotonic dependence on angle of attack. Computational fluid dynamics (CFD) simulations, showing good agreement with the experimental data, are used to explore the behavior and gain a better understanding of the observed trends. A dimensionless correlation is developed that well captures the experimental and CFD data and can be used as an efficient computational tool in broader applications.

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