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An investigation of the laminar flow and enhanced heat transfer rate through a triangular array of cylinders embedded in a fluid-saturated porous media is considered. Mixed convection covering forced convection cases has been studied using a finite-volume approach considering the local thermal equilibrium model. Darcy–Brinkman–Forchheimer momentum equations are used to characterize the porous media in question. The study is constrained to the low and intermediate Peclet number (Re = 5 to 40, Pr = 50) and high range of Darcy number (Da = 10−3 to 10−1) for different cylinder spacings (0.7 ≤ φ ≤ 0.99). It is anticipated that porous media would enhance heat transfer, but it derives a multiple order in pressure drop indubitably not desirable in many heat applications. Investigation reveals that both mean drag coefficient (CD) and Nusselt number (Nu) are strong functions of Da and φ; however, the influence of the buoyancy parameter is mainly witnessed in higher permeability levels and high Peclet numbers. The study also details the effect of governing parameters on mean gap velocities and pressure coefficients. Surprisingly, recirculation wakes exist for the lowest cylinder spacing (φ = 0.7) in high fluid momentum. Low φ and high permeability are desirable in a forced convection regime, whereas both φ and Da should be high in the case of mixed convection. This article also quantifies the combined effect of the Darcy number and buoyancy parameter on the heat-transfer enhancement ratio. A maximum of 112% increase in Nu for φ = 0.7 and 452% for φ = 0.99 are reported at Da = 10−1, but at the cost of higher pressure drop in the latter case. [ABSTRACT FROM AUTHOR]

An analysis has been carried out to understand the consequences of side-by-side gap-ratio on thermal buoyancy-assisted two-dimensional flow past a pair of heated circular cylinders for a dominant viscous flow field. This is implemented through studies at Reynolds number (Re) ranging from 5 to 40, Prandtl number (Pr) 0.7, gap-ratio (T/D) 1.5 to 4 and Richardson number (Ri) 0 to 1. An ANSYS-based incompressible flow solver is used with Boussinesq approximation to account for density variations in the momentum equation. One can realize features like the steady-separated and steady-unseparated flow on varying flow and thermal parameters. Unlike streamlines, non-interacting isotherms are non-existent in the current numerical framework. The influence of gap-ratio on enhancement in Nusselt number (Nu) is the best realized at T/D = 1.5 and buoyancy-aided effects play a dominant role for enhancement in Nu at diffusion and/or viscous-dominant conditions occurring at Re = 5. Correlations are developed to quantify the impact of T/D, Re, and Richardson number Ri on Nu. For the first time, Nu 's correlation based on varying side-by-side gap-ratio has been stated in a single expression. Finally, a comparison for the heat transfer enhancement/reduction in Nu under a similar numerical framework is provided with cases of high-Pr flow and/or different relatable flow arrangements for circular and square cylinders. [ABSTRACT FROM AUTHOR]

The dynamics of a shear-thinning fluid flowing past a pair of mildly heated side-by-side square cylinders, in a confined horizontal flow channel at low Reynolds number (Re), has been investigated. A detailed probe for flow physics in terms of vortex shedding patterns, near-wake streamlines and stretch of isotherms are carried out at Re = 1 and 100 (signifying two-dimensional unseparated steady flow and transient flow). The power-law index (n) is varied from 0.4 to 1 and the side-by-side transverse gap ratio (s/d) ranges from 1 (pressure-driven flow regime) to 5 (momentum-driven flow regime) at a constant value of Prandtl number (Pr) = 50. When the shear-thinning effects in the flow are increased (in the present numerical framework) at Re = 100, the time-averaged streamlines depict an early onset of leading edge flow separations from the pair of side-by-side square cylinders. One can infer from the phase space plots that the flow becomes chaotic with the increase in shear-thinning effect from n = 0.8 to 0.4 and decrease in s/d from 5 to 1. An anti-phase vortex shedding can be characterized by the occurrences of symmetrical structures of negative ζ (where ζ quantifies the accumulation and propagation of the vortices) contours in the downstream and this is realized at Re = 100, n = 0.8 and s/d ≥ 1.7. An in-phase vortex shedding (which occurs at Re = 100, n = 0.4 and all values of s/d) is characterized by asymmetrical occurrences of negative ζ contours which have a tendency of dying down early in the downstream with the increase in the nearness of the side-by-side square cylinders. This is more clearly realized at enhanced shear-thinning effects in the flow. Finally, the variation of time and space-averaged drag flow parameter (CD) and Nusselt number (Nu) with respect to shear-thinning effects in the flow has been extensively determined. [ABSTRACT FROM AUTHOR]

• Drag coefficient is found to decrease and wake size increase with Re. • 25% higher maximum heat transfer is found for n < 1 liquid than for n = 1. • Average Nusselt number is smaller for trapezoidal cylinder than for square cylinder. • We established correlation for average Nusselt number as a function of Re and n. Hydrodynamic and thermal features of two-dimensional, incompressible shear-thinning and shear-thickening non-Newtonian power-law liquids under forced convection across a trapezoidal cylinder are the focus of this study, carried out at Reynolds number Re = 1–40, power-law index n = 0.4–1.8 and Prandtl number Pr = 50 using ANSYS Fluent. In this steady system, the drag coefficient is found to decrease, whereas the wake size and the average Nusselt number increase with the increase in Re. However, with the increase in n value, the average Nusselt number decreases. Similar to a square cylinder, compared to Newtonian liquids, shear-thinning liquids increases heat transfer and shear-thickening reduces it. The maximum increase in heat transfer for shear-thinning liquids compared to Newtonian liquids for a trapezoidal cylinder is approximately 25%, while the average heat transfer is somewhat lower for shear-thickening liquids than for Newtonian. The average Nusselt number is smaller for the trapezoidal cylinder than for a square cylinder in the parameter domain investigated; the largest difference is around 25%. A simple relationship for the average Nusselt number as a function of Re and n has been determined. [ABSTRACT FROM AUTHOR]

Highlights • Mixed convection characteristics were explored across a periodic array of cylinders. • The dense and curved streamlines and isotherms were obtained. • Drag coefficients were diminished with rise in Reynolds number and fluid volume fractions. • Statistical correlations were developed for drag coefficient and Nusselt number. • The present results displayed an excellent agreement with the available literature. Abstract Aiding buoyancy mixed convection features of Newtonian fluids across a periodic array of heated cylinders have been studied numerically using a commercial CFD solver ANSYS FLUENT. The governing equations have been solved for the following ranges of physical parameters: Reynolds (1 ≤ Re ≤ 40), Prandtl (0.70 ≤ Pr ≤ 50) and Richardson (0 ≤ Ri ≤ 2) numbers and fluid volume fractions of 0.70–0.99. Qualitatively, the dense and curved streamlines and isotherms were seen with the increasing inertial (Re), viscous diffusion (Pr) and buoyancy parameter (Ri) across all the fluid volume fractions. The drag coefficients were observed to be diminished with an upturn in Re and fluid volume fractions, whereas an opposite behavior was noticed with rising in Pr and buoyancy parameter. The Nusselt numbers were found to be enhanced with Re and Pr numbers and moreover with fluid volume fractions also as in contrast to forced convection (Ri = 0) cases. Aiding buoyancy enhances flow as well as heat transfer features and yields unsteady behavior also at the higher fluid volume fractions and Re for all the values of Pr and Ri numbers. Moreover, statistical correlations have been developed for the total drag coefficient and average Nusselt number to gain the more physical insight of the results. Lastly, the findings have been compared with the literature which displayed the good agreement within the ranges of parameters studied herein. [ABSTRACT FROM AUTHOR]

This paper focuses on the effects of wall confinements (or blockage ratios) on the flow and heat transfer characteristics around a long equilateral triangular bluff body placed in a horizontal channel for Reynolds number (Re) range 1 to 80 and blockage ratio range 0.1 to 0.5 for air as the working fluid. The governing continuity, Navier-Stokes and energy equations along with appropriate boundary conditions are solved by using a finite volume method-based commercial solver Ansys Fluent. The total drag coefficient decreases with an increasing value of Re for a fixed value of the blockage ratio; however, it increases with an increasing value of the blockage ratio for a fixed value of Re due to the fact that the channel walls exert an extra retardation force on the obstacle. The onset of flow separation is delayed as the value of the blockage ratio increases. The critical Re (i.e., the transition to a time-periodic regime) exists between 45 and 46, 46 and 47, 58 and 59, and 79 and 80 for the blockage ratios of 0.1, 0.125, 0.25, and 0.5, respectively. The simple correlations for wake length, total drag coefficient, and average obstacle Nusselt number are obtained for the range of conditions covered. [ABSTRACT FROM AUTHOR]

A two-dimensional numerical study has been conducted to analyze forced convective confined flow and heat transfer from a pair of side-by-side square cylinders with a transverse gap ratio (defined as the ratio of the distance between the obstacles to the size of an obstacle) of 1.5. The flow is steady Newtonian in a viscous dominant flow field, investigated at Reynolds numbers (Re) ranging from 10 to 40 for Prandtl numbers (Pr)= 0.7 and 50. The present results are found to be in the excellent agreement with the literature, with a maximum deviation of 1.5%. It is observed from the streamlines that the wake formation increases with Re. The onset of ow separation was observed at Re= 7 and further a correlation connecting wake length with Re is stated. [ABSTRACT FROM AUTHOR]

The common engineering problem of flow across an in-line bank of circular cylinders was studied using CFD to investigate the nature of flow and heat transfer of a Newtonian incompressible fluid under a two-dimensional laminar forced convection regime. The problem was modelled as a unit cell with symmetric and periodic boundary conditions, and the forced convection flow-governing equations were solved numerically using a finite volume-based solver (ANSYS Fluent). The study examined the dependence of local and global characteristics (streamlines, pressure and isotherm contours, individual and total drag coefficients, and average Nusselt number) on the following parameters: free-volume fraction (0.7 ≤ ϕf ≤ 0.99), Reynolds number (1 ≤ Re ≤ 40), and Prandtl number (0.7 ≤ Pr ≤ 100). The results reveal that, as the cylinder diameter becomes large relative to the pitch (i.e. as ϕf decreases), friction drag across the cylinder surface increases, as well as pressure drag in the wake. Analogously, heat transfer improves and the Nusselt number increases as cylinder diameter-to-pitch ratio increases. The results were used to develop simple correlations for the drag coefficients and average Nusselt number. [ABSTRACT FROM AUTHOR]

This study involves the numerical solution of the laminar heat transfer in a separating and reattaching flow by simulating the flow and heat transfer downstream of a backward-facing step. The in-house finite volume code has been implemented employing a hybrid differencing scheme and the SIMPLE algorithm for the pressure-velocity coupling. Three principal parameters governing heat transfer in this geometry, that is channel expansion ratio (ER), Reynolds number (Re), and Prandtl number (Pr), are systematically varied in the range ER = 1.111 to 2, Re = 1 to 200, and Pr = 0.71 to 100, and the simple correlations between these parameters have been elucidated. A series of important findings have been established by analyzing the results some of which are: (1) there is an associated shifting of the point of maximum heat transfer with respect to the flow-reattachment point with gradually decreasing the values of ER and (2) the heat transfer enhancement increases with the increase in Pr number as a result of the compression of the thermal boundary layer and the maximum Nusselt number varies as [ABSTRACT FROM AUTHOR]

The present study is concerned with the simulation of incompressible Newtonian fluid flow and heat transfer over a long semicircular bluff body in a channel at low Reynolds numbers. In particular, wall effects on the forced convection from a (heated) semicircular cylinder confined in a horizontal channel are investigated for Reynolds number = 1–40 and blockage ratio = 16.67–50% for air as the working fluid. Flow and thermal fields are found steady for the preceding range of settings. The onset of flow separation increases as the wall confinement increases. The size of the recirculation zone downstream of a semicircular cylinder is seen to increase almost linearly with Reynolds number for a fixed blockage ratio, but it decreases with increasing blockage ratio for a fixed Reynolds number. As expected, total drag coefficient and its components decrease with increasing value of Reynolds number. However, with increasing blockage ratio, the values of these drag coefficients increase. On the basis of equal projected area, the total drag coefficient for the present flow system is found to be greater than the corresponding drag in the case of the unconfined semicircular cylinder. Similarly, the overall drag in the case of a confined semicircular cylinder is found to be greater than that of a confined circular cylinder for the appropriate range of dimensionless control parameters. The maximum augmentation in heat transfer for blockage ratios of 25% and 50% is found to be approximately 16% and 51% with respect to the corresponding value at the blockage ratio of 16.67% at Reynolds number = 1. Finally, the correlations of wake length, drag coefficient, and average Nusselt number are obtained. [ABSTRACT FROM AUTHOR]

Effects of wall confinements on the laminar flow and heat transfer around a heated tapered trapezoidal bluff body are investigated numerically in the confined domain (Reynolds number, Re = 1 to 40; blockage ratio = 0.125 to 0.5; and Prandtl number, Pr = 0.71). The onset of flow separation is found between Re = 4 and 5 for the blockage ratio of 0.125 and between Re = 5 and 6 for the blockage ratios of 0.25 and 0.5. If compared with a long circular obstacle on the basis of equal projected area, the total drag coefficient of the trapezoidal cylinder is found to be larger than the circular one, but an opposite trend is observed for the heat transfer. The augmentation in heat transfer for trapezoidal and circular cylinders is found to be approximately 46, 72, 74, and 65 percent for Re = 1, 5, 10, and 40, respectively for the blockage ratio of 0.25. The maximum enhancement in heat transfer for a tapered trapezoidal bluff body with respect to a square bluff body is found to be approximately 104 percent and 101 percent for blockage ratios of 0.25 and 0.5, respectively. Finally, simple correlations of wake length, drag, and average cylinder Nusselt number are established. [ABSTRACT FROM AUTHOR]

The present study focuses on the flow across an asymmetrically confined (heated) cylinder in a channel for fluids obeying Ostwald-de Wale (power-law) equation for the settings: Reynolds number ( Re ) = 1–40, power-law index ( n ) = 1–1.8, gap ratio ( γ ) = 0.375–1, blockage ratio ( β ) = 0.2–0.5 and Prandtl number ( Pr ) = 1–50. Total drag coefficient and its individual components have been analyzed as a function of Re , β , γ and n . The overall drag coefficient was found to increase with blockage and behavior of fluid, while it drops gradually for increasing Re . The asymmetrical configuration is seen to mitigate the overall as well as individual drag coefficients. The surface heat transfer coefficient in the form of average Nusselt number and the Colburn heat transfer j h factor has been thoroughly discussed. Heat transfer rate is found to increase with increasing Reynolds number and wall confinement, while increasing dilatant behavior impedes the same. As expected, heat transfer results have been reconciled in a single curve by way of the Colburn j h factor. The j h factor is found higher for the symmetric case as compared to the asymmetric case. [ABSTRACT FROM AUTHOR]

Confined flow and heat transfer phenomena across two long triangular bars in tandem arrangement in a horizontal channel have been studied for the range of Reynolds number (Re) = 1–40, Prandtl number (Pr) = 0.71–50 and gap ratio (S/B) = 1–4 for a fixed blockage ratio of 25%. The average Nusselt number of the first triangular cylinder is found to be larger than the corresponding value for the second triangular cylinder in the tandem configuration. Heat transfer correlations in terms of the Colburn jhfactor have been established in the steady regime. [ABSTRACT FROM PUBLISHER]

Effects of cross-buoyancy mixed convection on flow and heat transfer characteristics of a long semi-circular cylinder (long in neutral direction) in a confined channel have been investigated in the laminar regime. The numerical results have been presented and discussed for the range of conditions as Reynolds number (Re) = 1–40, Richardson number (Ri) = 0–4, Prandtl number (Pr) = 0.71–50 and blockage ratio (β) = 16.67%–50%. The drag coefficient increases with increasing Richardson number and/or blockage ratio. The average Nusselt number is showing a maximum relative enhancement of approximately 45% for Ri = 4 with respect to corresponding forced convection value (Ri = 0). The average Nusselt number increases with increase in Prandtl number and shows a maximum relative enhancement of approximately 1136% for Pr = 50 with respect to corresponding value at Pr = 0.71. On the other hand, the maximum relative variation of the total drag coefficient is found to be approximately 55% for Ri = 4 with respect to corresponding value at Ri = 0. Finally, the simple heat transfer correlation is obtained for the proceeding range of control parameters. [ABSTRACT FROM AUTHOR]

This study focuses on the confined upward flow and heat transfer around a square cylinder under the effect of aiding buoyancy (Richardson number,Ri=0–1) in the vertical channel for Reynolds number (Re)=1–40 and blockage ratio (BR)=25–50% for the air as working fluid. Flow is found to be steady and symmetric for the range of settings. ForRe≤2, no separation zone occurs for BR=25% and 30%. However, for BR=50%, no wakes are observed forRe≤3. The onset of flow separation takes place betweenRe=2 and 3 for BR=25% and 30%; whereas, for BR=50%, it exists betweenRe=3 and 4, irrespective of the value ofRi. Heat transfer correlations have also been obtained at different values ofRe, BR andRi. [ABSTRACT FROM PUBLISHER]

Mixed-convectionflow and heat transfer of non-Newtonian power-law fluids over a pairof side-by-side circular cylinders in aiding buoyancy are investigatednumerically. The calculations are performed in an unconfined domainfor the following range of physical control parameters: Reynolds number(Re) = 1–40, Richardson number (Ri) = 0–1, and power-law index (n) = 0.2–1for a transverse gap ratio of 1.5 at a constant Prandtl number (Pr) of 50. Extensive numerical results are presented, suchas viscous, pressure, and total drag coefficients, average Nusseltnumber, and transition from a steady to a time-periodic regime. Theoverall drag coefficient and its components decrease with the Reynoldsnumber and increase with the Richardson number for all values of thepower-law index considered. The average Nusselt number increases withan increase in both the Reynolds and Richardson numbers but decreaseswith an increase in the power-law index. It is observed that aidingbuoyancy and shear-thinning tendency augment heat-transfer characteristics.The maximum enhancement in heat transfer is found to be approximately85% for Re= 40, n= 0.2, and Ri= 1. However, the maximum enhancement in the value ofthe average Nusselt number for Ri= 0 and 0.5 isfound to be approximately 70% and 81%, respectively. Finally, a simpleheat-transfer correlation is obtained for the values of Re, n, and Ricovered in this study. [ABSTRACT FROM AUTHOR]

ABSTRACT Two-dimensional unconfined flow and heat transfer across a long tapered trapezoidal bluff body are investigated for the range Re = 1 to 150 (thereby covering both steady and unsteady periodic regimes) and Pr = 0.7 (air). A number of engineering parameters, e.g. drag and lift coefficients, Strouhal and Nusselt numbers, and others, is calculated for the above range of conditions. No flow separation occurs from the surface of the trapezoidal cylinder for the range Re ≤ 5; however, flow starts to separate from the rear surface of the cylinder at Re = 6. Therefore, the onset of flow separation exits between Re = 5 and 6. The critical value of the Reynolds number (i.e. transition from steady to unsteady) exists between Re = 46 and 47. The drag coefficient decreases with increasing Reynolds number in the steady regime; however, the drag increases with Reynolds number in the unsteady regime. The Strouhal number and the average Nusselt number increase with increasing value of the Reynolds number. Finally, the simple correlation for the average Nusselt number is obtained in the steady flow regime. © 2012 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Steady and unsteady forced convection flow and heat transfer past a long expanded trapezoidal bluff body are investigated for the air as working fluid for Re=1–150. The wake length increases as the Reynolds number increases in the steady flow regime (1⩽Re⩽47). The transition from steady regime to unsteady regime occurs between Re=47 and 48. The total drag coefficient decreases with the increasing value of the Reynolds number up to Re=90 and thereafter it increases with Reynolds number. However, heat transfer as well as Strouhal number increase with the increasing value of the Reynolds number. The maximum augmentation in heat transfer for the expanded trapezoidal cylinder with respect to the tapered trapezoidal cylinder is found to be approximately 146%. On the other hand, pressure drop shows an enhancement of approximately 97% for the expanded trapezoidal cylinder when compared with the tapered one. Simple correlations of wake length, drag, average Nusselt number and Strouhal number with Reynolds number have also been established. [Copyright &y& Elsevier]

Abstract: In this paper, mixed convection flow and heat transfer around a long cylinder of square cross-section under the influence of aiding buoyancy are investigated in the vertical unconfined configuration (Reynolds number, Re =1–40 and Richardson number, Ri =0–1). The semi-explicit finite volume method implemented on the collocated grid arrangement is used to solve the governing equations along with the appropriate boundary conditions. The onset of flow separation occurs between Re =1–2, between Re =2–3 and between Re =3–4 for Ri =0, 0.5 and 1, respectively. The flow is found to be steady for the range of conditions studied here. The friction, pressure and total drag coefficients are found to increase with Richardson number, i.e., as the influence of aiding buoyancy increases drag coefficients increase at the constant value of the Reynolds number. The temperature field around the obstacle is presented by isotherm contours at the Prandtl number of 0.7 (air). The local and average Nusselt numbers are calculated to give a detailed study of heat transfer over each surface of the square cylinder and an overall heat transfer rate and it is found that heat transfer increases with increase in Reynolds number and/or Richardson number. The simple expressions for the wake length and average cylinder Nusselt number are obtained for the range of conditions covered in this work. [Copyright &y& Elsevier]

In this work, effects of Prandtl number on the heat transfer characteristics of an unconfined rotating circular cylinder are investigated for varying rotation rate (α = 0-5) in the Reynolds number range of 1-35 and Prandtl numbers range of 0.7- 100 in the steady flow regime. The numerical calculations are carried out by using a finite volume method based commercial computational fluid dynamics solver FLUENT. The isotherm patterns are presented for varying values of Prandtl number and rotation rate in the steady regime. The variation of the local and the average Nusselt numbers with Reynolds number, Prandtl number, and rotation rate are presented for the range of conditions. The average Nusselt number is found to decrease with increasing value of the rotation rate for the fixed value of the Reynolds and Prandtl numbers. With increasing value of the Prandtl number, the average Nusselt number increases for the fixed value of the rotation rate and the Reynolds number; however, the larger values of the Prandtl numbers show a large reduction in the value of the average Nusselt number with increasing rotation rate. [ABSTRACT FROM AUTHOR]

Abstract: The current study investigates the augmentation in the laminar forced convection characteristics of the backward-facing step flow in a two-dimensional channel by means of introducing an adiabatic circular cylinder in the domain. The effects of various cross-stream positions (i.e., yc  = 0–1.5) of the circular cylinder on the flow and heat transfer characteristics of the backward-facing step flow has been numerically explored for the Reynolds number range 1–200 and Prandtl number of 0.71 (air). The governing continuity, Navier–Stokes and energy equations along with appropriate boundary conditions are solved by using FLUENT. The flow and thermal fields have been explained by streamline and isotherm profiles, respectively; however, no temperature dependency effects are considered for the flow viscosity and thermal conductivity. The engineering parameters like wake/recirculation length, total drag coefficient and average Nusselt number, etc. are calculated for the above range of conditions. The present results show an enhancement in the peak Nusselt value of up to 155% using a circular cylinder as compared to the unobstructed case (i.e., without cylinder). Finally, simple correlations for total drag coefficient and peak Nusselt number are obtained for the above range of conditions. [Copyright &y& Elsevier]

Abstract: In this study, heat transfer to power-law dilatant fluids from a long square cylinder (heated) confined in a channel in the steady flow regime is investigated. The effects of Reynolds number, Prandtl number and flow behavior index on the heat transfer characteristics of a cylinder is examined for the range of conditions , and (the maximum Peclet number being 4000) for a fixed blockage ratio, . The variation of the local Nusselt number on the individual surfaces of the square obstacle for the constant wall temperature (CWT) and uniform heat flux (UHF) boundary conditions prescribed on the surface of the square obstacle are presented. Likewise, the representative isotherm plots for the two classical thermal boundary conditions are shown. The average Nusselt number and the heat transfer factor () have also been calculated. Irrespective of the value of the flow behavior index, the value of the local Nusselt number at each corner of the square cylinder increases with an increase in the Reynolds and/or Prandtl number. The average Nusselt number increases monotonically with an increase in the Reynolds and/or the Prandtl number. Finally, simple heat transfer correlations have been provided for the range of conditions covered here. [Copyright &y& Elsevier]

Numerical computations have been carried out to explore the influence of mixed convection heat transfer from heated trapezoidal geometries of two different configurations namely converging and diverging cylinders in a vertical domain. The recirculation length of the diverging cylinder is found to be more than that of the converging cylinder for all values of Re (5 to 40) considered in this study and this length decreases after introducing buoyancy effect. Drag coefficients decrease with increase in Re for a fixed Ri. However, drag increases for the increasing values of Ri (values considered up to 1). The drag coefficient is found to be the smaller for diverging cylinder than that of converging one. Local Nusselt number shows significant increase as Re and Ri values increase, which results in enhanced heat transfer. Keeping Ri fixed and increasing the value of Re results in the augmentation of heat transfer and is around 15% at Re = 5 and 23% at Re = 40 for Ri = 0 for a square cylinder with respect to diverging cylinder. Under the influence of aiding buoyancy, the values of average Nusselt number (Nu¯) for the diverging cylinder are higher compared to that of converging cylinder. A correlation expressing functional relationship of Nu¯ with Re and Ri has also been generated. [ABSTRACT FROM AUTHOR]