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.

Performance of a variety of low Reynolds number turbulence models applied to mixed convection heat transfer to air flowing upwards in a vertical tube

2004 ◽  
Vol 218 (11) ◽  
pp. 1361-1372 ◽  
Author(s):  
W S Kim ◽  
J D Jackson ◽  
S He ◽  
J Li
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Low Reynolds Number ◽  
Convection Heat Transfer ◽  
Turbulence Models ◽  
Vertical Tube ◽  
Convection Heat ◽  
Mixed Convection Heat Transfer ◽  
Low Reynolds

The study reported here is concerned with mixed convection heat transfer to air flowing upwards in a vertical tube. Computational simulations of experiments from a recent investigation have been performed using an ‘in-house’ code which was written specifically for variable-property, developing, buoyancy-influenced flow and heat transfer in a vertical passage. The code incorporates a selection of two-equation, low Reynolds number turbulence models. The objective of the study was to evaluate the models in terms of their capability of reproducing the effects on turbulent heat transfer of non-uniformity of fluid properties and buoyancy. Direct comparisons have been made between results from the experimental investigation and those obtained by computational modelling for a range of conditions. The trends of impairment and enhancement of heat transfer owing to the influence of buoyancy found in the experiments were captured to some extent in the simulations using each of the models. However, none reproduced observed behaviour correctly over the entire range of buoyancy influence.

Numerical Simulation of Turbine Blade Boundary Layer and Heat Transfer and Assessment of Turbulence Models

1997 ◽  
Vol 119 (4) ◽  
pp. 794-801 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Bypass Transition ◽  
Boundary Layer Development ◽  
Low Reynolds ◽  
Layer Development

The boundary layer development and convective heat transfer on transonic turbine nozzle vanes are investigated using a compressible Navier–Stokes code with three low-Reynolds-number k–ε models. The mean-flow and turbulence transport equations are integrated by a four-stage Runge–Kutta scheme. Numerical predictions are compared with the experimental data acquired at Allison Engine Company. An assessment of the performance of various turbulence models is carried out. The two modes of transition, bypass transition and separation-induced transition, are studied comparatively. Effects of blade surface pressure gradients, free-stream turbulence level, and Reynolds number on the blade boundary layer development, particularly transition onset, are examined. Predictions from a parabolic boundary layer code are included for comparison with those from the elliptic Navier–Stokes code. The present study indicates that the turbine external heat transfer, under real engine conditions, can be predicted well by the Navier–Stokes procedure with the low-Reynolds-number k–ε models employed.

A Comparative Study of Performance of Low Reynolds Number Turbulence Models for Various Heat Transfer Enhancement Simulations

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Ankit Tiwari ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Fluid Dynamic ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Transfer Enhancement ◽  
Low Reynolds

The goal of this study is to evaluate the computational fluid dynamic (CFD) predictions of friction factor and Nusselt number from six different low Reynolds number k–ε (LRKE) models namely Chang–Hsieh–Chen (CHC), Launder–Sharma (LS), Abid, Lam–Bremhorst (LB), Yang–Shih (YS), and Abe–Kondoh–Nagano (AKN) for various heat transfer enhancement applications. Standard and realizable k–ε (RKE) models with enhanced wall treatment (EWT) were also studied. CFD predictions of Nusselt number, Stanton number, and friction factor were compared with experimental data from literature. Various parameters such as effect of type of mesh element and grid resolution were also studied. It is recommended that a model, which predicts reasonably accurate values for both friction factor and Nusselt number, should be chosen over disparate models, which may predict either of these quantities more accurately. This is based on the performance evaluation criterion developed by Webb and Kim (2006, Principles of Enhanced Heat Transfer, 2nd ed., Taylor and Francis Group, pp. 1–72) for heat transfer enhancement. It was found that all LRKE models failed to predict friction factor and Nusselt number accurately (within 30%) for transverse rectangular ribs, whereas standard and RKE with EWT predicted friction factor and Nusselt number within 25%. Conversely, for transverse grooves, AKN, AKN/CHC, and LS (with modified constants) models accurately predicted (within 30%) both friction factor and Nusselt number for rectangular, circular, and trapezoidal grooves, respectively. In these cases, standard and RKE predictions were inaccurate and inconsistent. For longitudinal fins, Standard/RKE model, AKN, LS and Abid LRKE models gave the friction factor and Nusselt number predictions within 25%, with the AKN model being the most accurate.

scholarly journals Convection Heat Transfer Analysis with Flow Resistance for Mini-Helically Coiled Tubes at Supercritical Pressures Experimentally

2021 ◽  
Vol 39 (3) ◽  
pp. 817-824
Author(s):  
Ameer Abed Jaddoa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Mass Flux ◽  
Flow Resistance ◽  
Convection Heat Transfer ◽  
Heat Fluxes ◽  
Exergy Destruction ◽  
Convection Heat

This paper analyzes the effect of fluid flow characteristics on the convection heat transfer for mini-helically coiled tubes (HCT) using supercritical carbon dioxide (CO2) as a natural refrigerant. Two experimental cases have studied in this work for mini-helically coiled tubes at different diameters with different coil pitches for analyzing the convection heat transfer with flow resistance. In the first case, the inner tube diameter, coil diameter and coil pitch were 5 mm, 200 mm and 10 mm respectively, while 10 mm, 100 mm and 5 mm were for the second case. Moreover, this work has also investigated the influence of frictional pressure drop, heat flux, friction factor and mass flux on dimensionless exergy destruction. The work environments were 300-500 K as an inlet temperatures range, 200-2000 Kg / (m2. s) as a mass heat fluxes range, 50,000-500,000 as a Reynolds number (Re) range and 50-200 Kw/m2 as an inner heat fluxes range. As a result, a large effect has been observed for dimensionless exergy destruction compared with the flow friction of CO2 which induced by heat transfer irreversibility. On the other point of view, a good sensitivity of optimal Re with the tube dimeter and mass flux also noticed compared with the heat flux. At a suitable range for Re, smallest and best exergy destruction also noticed for the tube diameters. A correlation has for the optimal Reynolds number as function of main dimensionless parameters related to wall heat flux, mass flux, fluid properties and geometric dimensions is proposed. Characteristics of the fluid flow had influenced significantly by mass and heat fluxes. In the future, the collected experimental data can be employed in order to design and improve the refrigeration conditioning performance for exchangers and other systems such as heat pumps.

scholarly journals THE EFFECT OF VIBRATION ON NATURAL CONVECTION HEAT TRANSFER IN AN ENCLOSED SQUARE CAVITY

2020 ◽  
Vol 20 (4) ◽  
pp. 282-307
Author(s):  
Baydaa Khalil Khudhair ◽  
Adel Mahmood Salh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Natural Convection ◽  
Thermal Convection ◽  
Low Reynolds Number ◽  
Differential Forms ◽  
Convection Heat Transfer ◽  
Simple Algorithm ◽  
Square Enclosure ◽  
Low Reynolds

  A numerical investigation has been implemented to elucidate the effect of vertical and horizontal vibration at normal gravity on natural convection in a square enclosure filled with air at Rayleigh number 7×107 and 4× 108. The enclosure was comprised of two vertical and opposed surfaces (the right hot and the left cold) while the two other surfaces are adiabatic. The two-dimensional, low-Reynolds number k ? ???? turbulence model is applied to enable it to cope with low Reynolds number flows. By transforming the equation of (continuity, Navier-Stokes and energy) using finite volume method from differential forms to algebraic forms using SIMPLE algorithm with hybrid scheme dealing with the time term are adopted to solve the governing equations. A computer program in Fortran 90 was built to carry on the numerical solution. Three cases were studied in this work, case I(reaches to steady state and then begins the effect of vibration at each frequency), caseII and caseIII(begin the effect of vibration from the transient at ascending and descending frequencies respectively).After the validity of the present code by comparing results with these of previous study for similar conditions, solutions have been obtained for Prandtle number of 0.7, aspect ratio (A=1). In the high Rayleih number case (Ra=4×108), the gravitional thermal convection dominates, and the vibration motion does not enhances the heat transfer remarkably. In contrast, in low Rayleigh (Ra=7×107), the vibration thermal convection is dominant, and the vibration enhaces the heat transfer rate significantly. The effect of vertical directional vibration is more powerful in caseII(ascending frequency), when the horizontal directional vibration more effective in case III(descending frequency).  

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