scholarly journals OPTIMALLY STAGGERED FINNED CIRCULAR AND ELLIPTIC TUBES IN FORCED CONVECTION

2003 ◽  
Vol 2 (2) ◽  
pp. 65 ◽  
Author(s):  
R. S. Matos ◽  
T. A. Laursen ◽  
J. V. C. Vargas ◽  
A. Bejan
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Optimization Procedure ◽  
Total Heat ◽  
Cross Sectional ◽  
Maximum Heat ◽  
Pressure Drops ◽  
Tube Cross Section ◽  
Fixed Volume ◽  
Maximum Heat Transfer

This work presents a three-dimensional (3-D) numerical and experimental geometric optimization study to maximize the total heat transfer rate between a bundle of finned tubes in a given volume and a given external flow both for circular and elliptic arrangements, for general staggered configurations. The optimization procedure started by recognizing the design limited space availability as a fixed volume constraint. The experimental results were obtained for circular and elliptic configurations with a fixed number of tubes (12), starting with an equilateral triangle configuration, which fitted uniformly into the fixed volume with a resulting maximum dimensionless tube-to-tube spacing S/2b = 1.5, where S is the actual spacing and b is the smaller ellipse semi-axis. Several experimental configurations were built by reducing the tube-to-tube spacings, identifying the optimal spacing for maximum heat transfer. Similarly, it was possible to investigate the existence of optima with respect to other two geometric degrees of freedom, i.e., tube eccentricity and fin-to-fin spacing. The results are reported for air as the external fluid in the laminar regime, for 125 and 100 Re 2b , where 2b is the ellipses smaller axis length. Circular and elliptic arrangements with the same flow obstruction cross-sectional area were compared on the basis of maximum total heat transfer. This criterion allows one to quantify the heat transfer gain in the most isolated way possible, by studying arrangements with equivalent total pressure drops independently of the tube cross section shape. This paper reports three-dimensional (3- D) numerical optimization results for finned circular and elliptic tubes arrangements, which are validated by direct comparison with experimental measurements with good agreement. Global optima with respect to tube-to-tube spacing, eccentricity and fin-tofin spacing ( 0.5 e 0.5, S/2b and 06 . 0 f for 125 and 100 Re 2b , respectively) were found and reported in general dimensionless variables. A relative heat transfer gain of up to 19% is observed in the optimal elliptic arrangement, as compared to the optimal circular one. The heat transfer gain, combined with the relative material mass reduction of up to 32% observed in the optimal elliptic arrangement in comparison to the circular one, show the elliptical arrangement has the potential for a considerably better overall performance and lower cost than the traditional circular geometry.

scholarly journals OPTIMALLY STAGGERED FINNED CIRCULAR AND ELLIPTIC TUBES IN FORCED CONVECTION

2003 ◽  
Vol 2 (2) ◽  
Author(s):  
R. S. Matos ◽  
T. A. Laursen ◽  
J. V. C. Vargas ◽  
A. Bejan
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Fixed Number ◽  
Geometric Optimization ◽  
Total Heat ◽  
Total Heat Transfer ◽  
Cross Sectional ◽  
Maximum Heat ◽  
Fixed Volume ◽  
Maximum Heat Transfer

This work presents a three-dimensional (3-D) numerical and experimental geometric optimization study to maximize the total heat transfer rate between a bundle of finned tubes in a given volume and a given external flow both for circular and elliptic arrangements, for general staggered configurations. The optimization procedure started by recognizing the design limited space availability as a fixed volume constraint. The experimental results were obtained for circular and elliptic configurations with a fixed number of tubes (12), starting with an equilateral triangle configuration, which fitted uniformly into the fixed volume with a resulting maximum dimensionless tube-to-tube spacing S/2b = 1.5, where S is the actual spacing and b is the smaller ellipse semi-axis. Several experimental configurations were built by reducing the tube-to-tube spacings, identifying the optimal spacing for maximum heat transfer. Similarly, it was possible to investigate the existence of optima with respect to other two geometric degrees of freedom, i.e., tube eccentricity and fin-to-fin spacing. The results are reported for air as the external fluid in the laminar regime, for 125 and 100 Re 2b , where 2b is the ellipses smaller axis length. Circular and elliptic arrangements with the same flow obstruction cross-sectional area were compared on the basis of maximum total heat transfer. This criterion allows one to quantify the heat transfer gain in the most isolated way possible, by studying arrangements with equivalent total pressure drops independently of the tube cross section shape. This paper reports three-dimensional (3- D) numerical optimization results for finned circular and elliptic tubes arrangements, which are validated by direct comparison with experimental measurements with good agreement. Global optima with respect to tube-to-tube spacing, eccentricity and fin-tofin spacing ( 0.5 e 0.5, S/2b and 06 . 0 f for 125 and 100 Re 2b , respectively) were found and reported in general dimensionless variables. A relative heat transfer gain of up to 19% is observed in the optimal elliptic arrangement, as compared to the optimal circular one. The heat transfer gain, combined with the relative material mass reduction of up to 32% observed in the optimal elliptic arrangement in comparison to the circular one, show the elliptical arrangement has the potential for a considerably better overall performance and lower cost than the traditional circular geometry.

Significance of Delta Winglets on the Air Side Performance of Flat Finned Versus Wavy Finned-Tube Heat Exchangers

2020 ◽  
Author(s):  
Tariq Amin Khan ◽  
Nasir Mehdi Gardezi ◽  
Wei Li ◽  
Yang Zhou ◽  
Zahid Ayub
Keyword(s):  
Heat Transfer ◽  
Genetic Algorithm ◽  
Heat Exchangers ◽  
Three Dimensional ◽  
Finned Tube ◽  
Maximum Heat ◽  
Multi Objective ◽  
Multi Objective Genetic Algorithm ◽  
Maximum Heat Transfer ◽  
Side Flow

Abstract The performance on the air side flow is often limited due to its lower heat transfer coefficient. This work is related to numerical simulation to study the significance of employing delta winglets in flat finned and wavy finned-tube heat exchangers. For this purpose, three-dimensional simulation data and a multi-objective genetic algorithm are employed. The angle of attack (α) of delta winglets and Reynolds number varied from 15° to 75° and 500 to 1300, respectively. Employing delta winglets has increased the heat transfer per unit temperature and per unit volume (Z) and the fan power per unit core volume (E) for both flat finned and wavy finned-tube heat exchangers. To achieve a maximum heat transfer enhancement and a minimum friction factor, the optimal values of these parameters (Re and α) are calculated using the Pareto optimal strategy. For this purpose, CFD data, a surrogate model (neural network) and a multi-objective optimization genetic algorithm are combined. Results show that the performance of wavy finned-tube heat exchangers is higher than flat-finned tube heat exchangers which signify the importance of delta winglets in the wavy finned-tube heat exchangers.

Optimum Geometry of Plate Fins

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
R. Karvinen ◽  
T. Karvinen
Keyword(s):  
Heat Transfer ◽  
Convection Heat Transfer ◽  
Transfer Coefficients ◽  
Maximum Heat ◽  
Geometrical Properties ◽  
Heat Transfer Coefficients ◽  
Fixed Volume ◽  
Maximum Heat Transfer ◽  
Heat Transfer Theory ◽  
Approximate Analytical Solutions

A method and practical results are presented for finding the geometries of fixed volume plate fins for maximizing dissipated heat flux. The heat transfer theory used in optimization is based on approximate analytical solutions of conjugated heat transfer, which couple conduction in the fin and convection from the fluid. Nondimensional variables have been found that contain thermal and geometrical properties of the fins and the flow, and these variables have a fixed value at the optimum point. The values are given for rectangular, convex parabolic, triangular, and concave parabolic fin shapes for natural and forced convection including laminar and turbulent boundary layers. An essential conclusion is that it is not necessary to evaluate the convection heat transfer coefficients because convection is already included in these variables when the flow type is specified. Easy-to-use design rules are presented for finding the geometries of fixed volume fins that give the maximum heat transfer. A comparison between the heat transfer capacities of different fins is also discussed.

Computational Development of a Gas to Liquid Heat Exchanger With a Breathing Operation

2010 ◽  
Author(s):  
Richard N. Jorgenson ◽  
James D. Van de Ven
Keyword(s):  
Heat Transfer ◽  
Surface Area ◽  
Fitness Function ◽  
Liquid Bath ◽  
Nsga Ii ◽  
Maximum Heat ◽  
Pressure Drops ◽  
Maximum Heat Transfer ◽  
Compression And Expansion ◽  
3D Elements

Thermal conditioning of a gas during compression and expansion processes requires rapid transfer of heat. Proposed is a thin flexible membrane with a biologically-inspired, lung-like structure characterized by branching tubes, massive surface area, and low overall pressure drops. By forcing the working gas into contact with the large surface area of a thin membrane, rapid heat transfer may be achieved across the membrane and into a liquid bath. Inspiration and expiration of the gas is driven by volume changes in the liquid bath. A computational approach is taken to the design of the lung-like structure. First, Non-dominated Sorting Genetic Algorithm II (NSGA-II) is run to optimize elemental geometries for minimum pressure drop and maximum heat transfer. In the initial case, 2D elements are passed through Gambit and Fluent to evaluate the fitness function. Here, we present the results of the elemental optimization. In the future, 3D elements will be analyzed and connected in an optimal way to generate a 3D lung-like structure.

Optimal Configuration of Vortex Generator for Heat Transfer Enhancement in a Plate-Fin Channel

2017 ◽  
Vol 10 (2) ◽  
Author(s):  
Tariq Amin Khan ◽  
Wei Li
Keyword(s):  
Heat Transfer ◽  
Numerical Simulations ◽  
Three Dimensional ◽  
Vortex Generator ◽  
Design Parameters ◽  
Heat Transfer Characteristics ◽  
Maximum Heat ◽  
Transfer Characteristics ◽  
Maximum Heat Transfer ◽  
Independent Design

Heat transfer is a naturally occurring phenomenon and its augmentation is a vital research topic for many years. Although, vortex generators (VGs) are widely used to enhance the heat transfer of plate-fin type heat exchangers, few researches deal with its thermal optimization. This work is dedicated to the numerical investigation and optimization of VGs configuration in a plate-fin channel. Three-dimensional (3D) numerical simulations are performed to study the effect of angle of attack and attach angle (angle between VG and wall) and shape of VG on the fluid flow and heat transfer characteristics. The flow is assumed as steady-state, incompressible, and laminar within the range of studied Reynolds numbers (Re = 380–1140). Results are presented in the form average and local Nusselt number and friction factor. The effect of attach angle is highlighted and the results show that the attach angle of 90 deg may not be necessary for enhancing the heat transfer. The flow structure and heat transfer characteristics of certain cases are examined in detail. The parameters of VG are then optimized for maximum heat transfer and minimum pressure drop. The three independent design parameters are considered for the two objective functions. For this purpose, computation fluid dynamics (CFD) data, response surface methodology (RSM) and a multi-objective optimization algorithm (MOA) are combined. The data obtained from numerical simulations are used to train a Bayesian-regularized artificial neural network (BRANN). This in turn is used to drive a MOA to find the optimal parameters of VGs in the form of Pareto front. The optimal values of these parameters are finally presented.

scholarly journals Heat Transfer and Hydrodynamic Properties Using Different Metal-Oxide Nanostructures in Horizontal Concentric Annular Tube: An Optimization Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1979
Author(s):  
Omer A. Alawi ◽  
Ali H. Abdelrazek ◽  
Mohammed Suleman Aldlemy ◽  
Waqar Ahmed ◽  
Omar A. Hussein ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Flux Ratio ◽  
Hydrodynamic Properties ◽  
Maximum Heat ◽  
Aspect Ratios ◽  
Maximum Heat Transfer ◽  
Optimization Study ◽  
Wide Range ◽  
Metal Oxide Nanostructures

Numerical studies were performed to estimate the heat transfer and hydrodynamic properties of a forced convection turbulent flow using three-dimensional horizontal concentric annuli. This paper applied the standard k–ε turbulence model for the flow range 1 × 104 ≤ Re ≥ 24 × 103. A wide range of parameters like different nanomaterials (Al2O3, CuO, SiO2 and ZnO), different particle nanoshapes (spherical, cylindrical, blades, platelets and bricks), different heat flux ratio (HFR) (0, 0.5, 1 and 2) and different aspect ratios (AR) (1.5, 2, 2.5 and 3) were examined. Also, the effect of inner cylinder rotation was discussed. An experiment was conducted out using a field-emission scanning electron microscope (FE-SEM) to characterize metallic oxides in spherical morphologies. Nano-platelet particles showed the best enhancements in heat transfer properties, followed by nano-cylinders, nano-bricks, nano-blades, and nano-spheres. The maximum heat transfer enhancement was found in SiO2, followed by ZnO, CuO, and Al2O3, in that order. Meanwhile, the effect of the HFR parameter was insignificant. At Re = 24,000, the inner wall rotation enhanced the heat transfer about 47.94%, 43.03%, 42.06% and 39.79% for SiO2, ZnO, CuO and Al2O3, respectively. Moreover, the AR of 2.5 presented the higher heat transfer improvement followed by 3, 2, and 1.5.

scholarly journals Numerical prediction of heat transfer phenomena from a chip assembly for low Reynolds number

2011 ◽  
Vol 15 (2) ◽  
pp. 379-388
Author(s):  
Srinivas Bhatta ◽  
Seetharam Ramarao ◽  
Kankanhalli Seetharamuω
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Three Dimensional ◽  
Circuit Board ◽  
Bottom Plate ◽  
Moderate Pressure ◽  
Maximum Heat ◽  
Square Channel ◽  
Maximum Heat Transfer

A three dimensional study of heat transfer from three heated blocks in a square channel at a Reynolds number of 108 with height of the chip assembly as the characteristic length is presented. Heated blocks affixed to the bottom plate represent electronic chips mounted on horizontal circuit board. A hexahedron block is affixed on to the top shrouding wall over the heated section. Thickness of this block is varied to study the effect on heat transfer from the chip assembly. A block of thickness equal to the passage between substrates produces maximum heat transfer enhancement. A block over the first passage enhances heat transfer from both immediate upstream and downstream chips considerably. A block over each recirculation zone produces moderate heat transfer from all the chips for a moderate pressure-drop. It is also observed that addition of blocks in the top plate does not add much to the pressure-drop in the duct.

Heat Transfer in a Rotating Rib-Roughened Wedge-Shaped U-Duct

2017 ◽  
Author(s):  
Liang Ding ◽  
Shuqing Tian ◽  
Hongwu Deng
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Copper Plate ◽  
Enhancement Effect ◽  
Transfer Coefficients ◽  
Maximum Heat ◽  
Pressure Drops ◽  
Maximum Heat Transfer ◽  
Rotation Numbers ◽  
First Pass

Heat transfer in a rotating two-pass trapezium-shaped channel, with staggered 90-deg ribs on both leading and trailing surfaces is experimentally investigated. The hydraulic diameter of the first and second pass is 24.5 mm and 16.9 mm, respectively. The inlet Reynolds number and rotational speed range from 10000 to 50000 and zero to 1000 rpm, respectively, which results in the inlet rotation number varying from zero to 1.0. The heated copper plate technique is employed to measure the regional averaged heater transfer coefficients. Pressure drops are measured by newly designed rotating pressure measurements module. Both ribbed cases and smooth cases are compared to present rib enhancement effect. For non-rotating result, the results show that the trailing surface presents much higher heat transfer than other cases due to the special wedge-shaped geometry. The ribbed wedge-shaped achieves enhanced regional heat transfer performances than the smooth case at all locations. Compared with the non-rotating results in the first pass, heat transfer on both trailing and leading surfaces is enhanced except for the position near the turn region, but weakened on outer surface in stream-wise direction. And at high rotation numbers, the highest maximum heat transfer on railing surface happens at a location of approximately X/D = 10. In the first pass, rotation always enhances heat transfer on the trailing surface as rotation number increases and the rotation-to-stationary Nusselt number ratio reaches to 2.0 at the rotation number of 0.5. The leading and outer surfaces both have a critical rotation number located at Roc = 0.05.

Unsteady Incompressible Three-Dimensional Asymmetric Stagnation-Point Boundary Layers

1980 ◽  
Vol 47 (2) ◽  
pp. 241-246 ◽  
Author(s):  
M. Kumari ◽  
G. Nath
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Mass Transfer ◽  
Stagnation Point ◽  
Wall Temperature ◽  
Three Dimensional ◽  
Stream Velocity ◽  
Symmetric Flow ◽  
Maximum Heat ◽  
Maximum Heat Transfer

The unsteady laminar incompressible boundary-layer flow near the three-dimensional asymmetric stagnation point has been studied under the assumptions that the free-stream velocity, wall temperature, and surface mass transfer vary arbitrarily with time. The partial differential equations governing the flow have been solved numerically using an implicit finite-difference scheme. It is found that in contrast with the symmetric flow, the maximum heat transfer occurs away from the stagnation point due to the decrease in the boundary-layer thickness. The effect of the variation of the wall temperature with time on heat transfer is strong. The skin friction and heat transfer due to asymmetric flow only are comparatively less affected by the mass transfer as compared to those of symmetric flow.

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