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The flow of hybrid alumina–copper/water nanofluid with mixed convection heat transfer from multiple square cylinders arranged in three different types of arrays, namely equilateral triangle (ET), rotated square (RS), and rotated rhombus (RR) in a heat exchanger, has never been studied before the present study. Navier–Stokes and energy equations with a periodic boundary condition in the transverse direction for all three array types having the same porosity are solved with the finite volume methodology. The combined effect of aiding buoyancy (Richardson number 0–2), the configuration of square cylinders, and hybrid nanoparticle volume fraction (0-0.06) on the flow dynamics and their impact on the overall heat transfer phenomenon through three different array configurations is thoroughly elucidated. The arrays’ overall drag and friction coefficient increases with an increase in the strength of aiding buoyancy and nanoparticle volume fraction. An increment in Richardson number, and nanoparticle volume fraction, causes thermal boundary layer thinning and results in higher heat transfer rates across all three arrays. With an increase in Ri from 0 to 2 at a nanoparticle volume fraction of 0.06, the mean Nusselt number of ET, RS, and RR arrays is increased by 161%, 5%, and 32%, respectively. While, with an increase in nanoparticle volume fraction from 0 to 0.06 at Ri = 2, the mean Nusselt number of ET, RS, and RR arrays is augmented by 17%, 6%, and 9%, respectively. Finally, the efficient array configuration in terms of fluid-thermal behavior is proposed to design various heat-exchange systems under differing operating conditions.

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.

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.

The flow of alumina–water nanofluid across heated circular tubes arranged in inline and staggered arrays in a heat exchanger has been studied numerically using the finite volume method (FVM). For calculating the nanofluid’s thermophysical properties such as effective thermal conductivity and effective viscosity, Corcione’s correlations are utilized. Corcione’s correlations consider nanoparticles size, their Brownian motion, and operating temperature while calculating these effective properties of nanofluids. The impact of three parameters on heat transfer characteristics across inline and staggered arrays of heated circular cylinders has been examined. These parameters are nanoparticle diameter dp, which is varied between 10 nm and 50 nm, nanoparticle volume fraction ɸ varying from 0.01 to 0.05, and Reynolds number Re ranging from 10 to 200. It is observed that heat transfer augmentation across both inline and staggered arrays occurs when nanoparticle concentration is increased and smaller diameter nanoparticles are used. Mean Nusselt number NuM is increased by 31% when ɸ is increased from 0.01 to 0.05 at Re = 200 and dp = 10 nm in an inline array and by 25% in a staggered array. NuM is enhanced by 20% for the inline array and 16% for the staggering array when dp decreases from 50 nm to 10 nm at Re = 200 and ɸ = 0.05. At any given value of dp, ɸ, and Re, the mean Nusselt number is always higher for staggered array in comparison with the inline array. The results reported in the present study can be utilized for the optimal design of various heat exchange systems under the given operating conditions. The present results are extensively validated with the available experimental/numerical studies.

Flow around an isolated generic sharp-edged object with varying height ratio (β = 0–1) i.e. height from the rear end of the object to the front end ( β = H 2 / H 1 ) has been investigated in cross-flow configuration covering steady and periodic regimes at Reynolds number (Re) from 1 to 150 using air as a working fluid. Flow separation is delayed with a decrease in β. Wake formed is the highest for β = 1 (square object) and progressively decreases with the decrease in β. The vortex shedding effect has been demonstrated on the heat transfer phenomena around the objects. For all the cases of height ratios, as Re increases the flow undergoes supercritical Hopf bifurcation to periodic state as steady-state condition loses its stability. Stuart-Landau theory has been used to determine the value of critical Re or the onset of vortex shedding for all the cases of height ratios. As β increases from 0 to 0.7, the value of critical Re increases. Influence of surface vorticity and surface pressure on the overall drag coefficient ( C D ) has been explored. Effect of β on the Strouhal number (St) has been investigated and the findings are in agreement with previous results. Finally, correlations relating Lr, C D , Nu ‾ and St with Re and β have been developed.

Numerical computations were brought up to study the effect of opposing buoyancy mixed convection (Ri = 0 to − 1) flow of power law shear-thinning fluids past a confined cooled square bluff body at ...

Assessment of heat release rate in a compartment fires is a major concern for fire investigators to predict the fire behavior. The fire experiment was conducted in a cubical compartment of 64 m−3 with a door opening provided at one of the wall. Using the fundamental energy balance equation, an attempt has been made to determine the heat release rate for various interval of time. Instrumentations were made to measure several parameters which include the compartment gas temperature, the velocity and temperature of outgoing gas, heat flux to the compartment boundaries and the heat release rate of the burning crib. Analyzing the results, it was determined that major portion of the energy release during fire went to heat the compartment boundaries followed by energy loss through compartment door opening and energy goes to heat up the gases in the compartment. Nearly 54% of the energy went to heat compartment boundaries, 25% of the energy loss due to outflow of hot gases through door opening, 16% of energy went to heat the compartment gases and 5% of energy dissipated from the door in for of radiation.

Flow and heat transfer characteristics around a semi-circular cylinder placed in a confined channel are investigated in the unsteady regime. The two-dimensional simulations are carried out for varying values of control parameters: Reynolds number (Re) = 50–200 and Prandtl number (Pr) = 0.7, 10 and 100 at a fixed blockage ratio of 25% for Newtonian constant-property fluid. Continuity, Navier–Stokes and energy equations with appropriate boundary conditions are solved using the commercial computational fluid dynamics solver Ansys Fluent. The transition from steady to time-periodic flow occurs between Re = 69 and 70. The effect of Prandtl number on Nusselt number is pronounced; the ratio of Nusselt number values belonging to Pr = 100 and those belonging to Pr = 0.7 ranges from 6.3 to 6.5 over the Reynolds number domain investigated. Finally, the present numerical results are used to develop drag coefficient, Strouhal number and Nusselt number correlations.

The effects of cross-buoyancy mixed convection from a square cylinder in the proximity of a plane wall are studied for Reynolds number (Re) = 1–100, Richardson number (Ri) = 0–2, and gap ratio (G) = 0.25–1 at Prandtl number (Pr) = 0.7. The flow observed is steady for G = 0.25 and 0.5. The transition from a steady to a time-periodic system is observed for G = 1, and it is found at Re = 56, 60, and 74 for Ri = 0, 1, and 2, respectively. With increasing G and/or Ri, the drag coefficient and average Nusselt number increase for all Re values studied and the lift coefficient decreases with increasing Ri except at Re = 1. Maximum heat transfer augmentation is found about 89% at G = 0.5 (Re = 20, Pr = 0.7, Ri = 0) with respect to the corresponding value at G = 0.25 (Re = 20, Pr = 0.7, Ri = 0). Lastly, the correlations of drag coefficient and heat transfer have been obtained.

The influence of opposing-buoyancy mixed convection from a square cylinder in a vertical channel has been studied at Reynolds numbers (Re) = 1–100, Richardson numbers (Ri) = 0 to −1, and blockage ratios (β) = 10–50% for air as a working fluid. The onset of a steady to a time-periodic regime is found for Ri = 0 (at Re = 35, 65, 74, and 62), Ri = −0.5 (at Re = 12, 39, 48, and 54), and Ri = −1 (at Re = 9, 30, 39, and 50) for β = 10%, 25%, 30%, and 50%, respectively. The initiation of flow separation is also determined. Finally, the correlations of Strouhal number, drag coefficient, and the Colburn heat transfer factor were obtained.

In this article, investigations have been carried out to decipher the effect of thermal buoyancy in a viscosity stratified flow field for a shear-thinning fluid flowing past a pair of heated side-by-side square cylinders, which is an extension part of our recent study [Sanyal, A. and Dhiman, A., “Wake interactions in a fluid flow past a pair of side-by-side square cylinders in presence of mixed convection,” Phys. Fluids 29, 103602 (2017)]. It is found that the leading-edge flow-separations from the square cylinders influence the near-wake structures and vortex shedding patterns in the presence of shear-thinning effects, which is otherwise missing for Newtonian fluid flow at Reynolds number Re = 40 and Richardson number Ri = 1. The distribution of wall-viscosity η along the inner surfaces of the side-by-side square cylinders, at different values of transverse spacings s/d and flow-behavior indices n, hints at large dependency on the inflections in the velocity profile within the gap-flow region. Under thermal buoyancy-driven mild shear-thinning flow conditions (n = 0.6 and 0.8), the gap-flow characteristics have been classified into “pressure-driven” and “momentum-driven” flow regimes, which provides a good explanation for the aberrations noted in the distribution pattern of η. The root-mean-square fluctuations of the velocity-magnitude and vortex shedding phenomenon are found to reciprocate a consistent flow physics associated with a shear-thinning flow at near and far-field downstream. The single body deflected type flow is primarily seen under predominant shear-thinning flow conditions (n = 0.4), compared to chaotic or quasi-periodic flow under mild shear-thinning conditions. Besides, the evolution of non-linear dynamics-based flow regimes (classified with respect to s/d using power spectrum density analysis) at different values of n and s/d is thoroughly summarized. The time-variant fluctuations of lift and drag force parameters are also found to be unified through cause and effects.

Extensive numerical computations for the confined flow and heat transfer of shear-thinning fluids over two long tandem triangular bluff bodies are performed for Reynolds number (Re) = 1–40, power-law index (n) = 0.2–1, and gap ratio (S/B) = 1–4 for a fixed blockage ratio and Prandtl number of 25% and 50, respectively. The values of critical Re are obtained for each of the two triangular cylinders for all S/B and n. Augmentation in heat transfer for the two tandem triangular cylinders is calculated with respect to both S/B and n.

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 proje...

A numerical analysis using Ansys Fluent was carried out to investigate the forced convection of power-law fluids (power-law index varying from 0.2 to 1.8) around a heated semi-circular cylinder with wall confinement (or blockage ratio) of 25%, Prandtl number of 50, and Reynolds numbers 1–40. Flow and thermal fields were found to be steady for Re up to 40. The shear-thickening behavior was found to have a higher value of drag coefficient, whereas the shear-thinning behavior had a smaller value of drag coefficient when compared with Newtonian fluids in the steady regime. The wake size was found shorter in shear-thickening fluids than Newtonian and shear-thinning fluids. An overall heat transfer rate was calculated and found to increase with the rise in Reynolds number. The average Nusselt numbers were observed higher for shear-thinning fluids than Newtonian and shear-thickening fluids; and the maximum enhancement in the heat transfer was achieved approximately 47% as compared to Newtonian fluids. The present results have also been correlated in terms of wake length, drag coefficient and average Nusselt number expressions for various Reynolds numbers and power-law indices studied. In addition, the effects of blockage ratios ranging from 16.67% to 50% on the engineering output parameters with varying power-law index at Re = 40 were reported.

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 jh 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 jh factor. The jh factor is found higher for the symmetric case as compared to the asymmetric case.

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.

Two-dimensional numerical simulations are carried out to understand the effects of cross-buoyancy on the confined flow and heat transfer characteristics over an equilateral triangular bluff body at low and intermediate Reynolds numbers (Re). For a fixed Richardson number (Ri), an average cylinder Nusselt number increases with increasing Re. However, the average Nusselt number shows a soft response toward increasing Ri. The critical Re for the onset of periodic unsteady flow increases with increasing cross-buoyancy (Ri). A simple heat transfer correlation is also obtained to relate the values of average cylinder Nusselt number, Re, and Ri.

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 .

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 jh factor have been established in the steady regime.

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.

The present study focuses on momentum and heat transfer characteristics of the laminar flow of power-law fluids in a vertical channel with a built-in square cylinder under the influence of aiding buoyancy. The simulations are carried out at low Reynolds numbers (1–40) for the range of settings as power-law index = 0.4–1, Richardson number = 0–1, blockage ratio = 25%–50%, and Prandtl number = 50. It is found that the drag coefficient and the Nusselt number increase with the aiding buoyancy, while the shear-thinning behavior reduces the drag coefficient and increases the heat transfer rate.

A numerical investigation is conducted to analyze the steady and unsteady laminar flow and heat transfer in a channel with two square bars (of equal diameters) arranged side-by-side. The analysis is carried out for Reynolds number = 10–100, Prandtl number = 0.7–50, for transverse separation distance between the bars (i.e., gap ratio) of 1.5, 2, 2.5, 5, and 10 at the blockage ratio of 1/18. The results found here are in good agreement with previously published data. The effects of gap ratio, Reynolds number, and Prandtl number on the detailed kinematics of the flow and the heat transfer are presented. The engineering parameters such as total drag coefficient, average Nusselt number, and Strouhal number are calculated for the preceding range of conditions. It is observed that the overall drag coefficient decreases with increasing Reynolds number, whereas the average Nusselt number for the square cylinders increases with increasing Reynolds number and/or Prandtl number for all the values of gap ratios studie...

Flow and heat transfer of non-Newtonian power-law fluids over an inclined square cylinder placed inside a channel are studied numerically at low Reynolds numbers. In particular, calculations are carried out for Reynolds number (Re) = 1–40; power-law index (n) = 0.4–1 and blockage ratio (β) = 12.5–50% at a Prandtl number (Pr) = 50. An increase in blockage ratio results in an increase in the total drag coefficient and decrease in the wake length. The Strouhal number and the root mean square value of the lift coefficient increase with the increasing Reynolds number for the fixed values of blockage ratio and power-law index. The average Nusselt number increases with power-law index and/or blockage ratio. The maximum enhancement in heat transfer is approximately 49, 41, and 35% for the values of blockages of 50, 25, and 12.5%, respectively, as compared to the corresponding Newtonian value. The average Nusselt number for the inclined square cylinder (at α = 45°) is always greater than the average Nusselt number for the regular square cylinder (at α = 0). Finally, simple expressions of drag and Nusselt number have been established for the above range of settings. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res 43(2): 167-196, 2014; Published online 20 June 2013 in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21071

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.

Flow and heat transfer of non-Newtonian power-law fluids across a pair of identical circular cylinders in side-by-side arrangement are investigated numerically by solving the continuity, momentum and energy equations along with the appropriate boundary conditions. The numerical calculations are performed in an unconfined computational domain for the following range of physical parameters: Reynolds number, Re = 1–40 and power-law index, n = 0.4–1.8 (covering shear-thinning, n n = 1 and shear-thickening, n > 1 behaviors) for gap ratio, T / D = 1.5–4.0 at a constant Prandtl number of 50. The global characteristics such as drag coefficients and average Nusselt number, etc. are calculated and the representative streamline and isotherm contours are presented for the above range of conditions. It has been found that the individual and overall drag coefficients decrease and the average Nusselt number increases with Reynolds number for all T / D and n considered here. The heat transfer is found higher in shear-thinning fluids than Newtonian fluids and followed by shear-thickening fluids for 1.5 ⩽ T / D ⩽ 4.0 and 1 ⩽ Re ⩽ 40.

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.

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.

In this paper, fluid flow and heat transfer across a long equilateral triangular cylinder placed in a horizontal channel is studied for Reynolds number range 1–80 (in the steps of 5) and Prandtl number of 0.71 for a fixed blockage ratio of 0.25. The governing Navier-Stokes and energy equations along with appropriate boundary conditions are solved by using a commercial CFD solver FLUENT (6.3). The computational grid is created in a commercial grid generator GAMBIT. The flow and temperature fields are presented by stream-line and isotherm profiles, respectively. The wake/recirculation length, mean drag coefficient and average Nusselt number, etc. are calculated for the above range of conditions studied here. The critical value of the Reynolds number (i.e., transition to transient) is found to lie between Re = 58 and Re = 59. The average Nusselt number and the wake length increase with increasing value of the Reynolds number; however, the mean drag coefficient decreases with increasing value of the Reynolds number. Finally, simple correlations for wake length, mean drag coefficient and average Nusselt number are obtained for the range of conditions studied here.

In this research article, we have analyzed the effect of thermal stratification of shear layers due to mixed convection heat transfer past a pair of side-by-side square cylinders in a confined domain, an extended part of our recent study [A. Sanyal and A. Dhiman, “Wake interactions in a fluid flow past a pair of side-by-side square cylinders in presence of mixed convection,” Phys. Fluids 29, 103602 (2017)]. Investigations from the studies of instantaneous and time-averaged isotherms revealed the actual stretches of the temperature gradient in streamwise and transverse extents at Re = 1–40, Ri = 0–1, s/d = 0.7–10, and Pr = 50. The effects of “baroclinic production,” embedded in the transport of vorticity, were rigorously analyzed through the determination of local period-averaged vorticity flux at a certain cross section in the near-field downstream. The study also revealed the underlying flow physics pertaining to the variations in period-averaged wall vorticity and the local Nusselt number. The transport of vorticity has been explained in terms of the vortex structure formulations, and because of the absence of any such similar studies for multiple bluff-body arrangements, the study has been thoroughly correlated from the cases of single bluff-body flow. In an attempt to control several flow regimes by slightly changing the flow and thermal parameters, it is found that chaotic flow cannot exist beyond a certain value of s/d. However, an abnormality was noted in terms of the flow bifurcations at s/d = 1.5 at the juncture of flow transition from unseparated to a separated steady flow for the first time and this is solely attributed to the effect of thermal buoyancy in the flow field.

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 1 ⩽ Re ⩽ 45 , 1 ⩽ n ⩽ 2.0 and 1 ⩽ Pr ⩽ 100 (the maximum Peclet number being 4000) for a fixed blockage ratio, β = 1 / 8 . 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 ( j h ) 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.

The effect of blockage ratio on the flow characteristics of power-law fluids across a square cylinder confined in a channel has been investigated for the range of conditions 1 ≤ Re ≤ 45, 0.5 ≤n ≤ 2.0 and β = 1/8, 1/6 and 1/4. Extensive numerical results on the individual and total drag coefficients, wake length, stream function, vorticity and power-law viscosity on the surface of the square cylinder are reported to determine the combined effects of the flow behavior index, blockage ratio and Reynolds number. The size of the wake region is influenced more by blockage than by power-law index. Similarly, drag is also seen to be more influenced by blockage ratio and the Reynolds number than that by the power-law index.

The effects of cross-buoyancy and of Prandtl number on the flow and heat transfer characteristics of an isothermal square cylinder confined in a channel has been investigated here. The numerical results have been presented for the range of conditions as: 1 ≤ Re ≤ 30, 0.7 ≤ Pr ≤ 100 (the maximum value of Peclet number being 3000) and 0 ≤ Ri ≤ 1for a fixed blockage ratio of 0.125. The overall drag and lift coefficients, local and average Nusselt numbers and the representative streamline and isotherm plots are presented to elucidate the role of Reynolds number, Prandtl number and Richardson number. The drag coefficient is found to be less sensitive to the Richardson number than the lift coefficient.

Forced-convection heat transfer to power-law fluids from a heated square cylinder has been investigated numerically for the range of conditions 1 ≤ Re ≤ 45, 0.5 ≤ n ≤ 2.0 and 1 ≤ Pr ≤ 100 (the maximum Peclet number being 4,000). In this range of Reynolds number, the flow is known to be steady and two-dimensional. The variation of the local Nusselt number on the individual surfaces of the square cylinder and the representative isotherm plots, for both the constant-temperature and uniform-heat-flux boundary conditions prescribed on the surface of the square obstacle, are presented to elucidate the role of Reynolds number, Prandtl number, and power-law index on the heat transfer characteristics. Using the present numerical data, appropriate predictive correlations are obtained for estimating the value of the mean heat transfer coefficient in a new application.

The effects of Reynolds and Prandtl numbers on the heat transfer characteristics of an isolated square cylinder have been investigated for the range of conditions 1 ≤ Re ≤ 45 and 0.7 ≤ Pr ≤ 4,000 (the maximum value of Peclet number being 4,000) in crossflow. Heat transfer correlations are obtained for the constant cylinder temperature and constant heat flux boundary conditions on a solid square cylinder in the steady flow regime. In addition, the variation of local Nusselt number on each face of the obstacle and representative isotherm plots are presented to elucidate the role of Prandtl number on heat transfer in the steady flow regime.

The flow and heat transfer characteristics of an isolated square cylinder in crossflow placed symmetrically in a planar slit have been investigated for the range of conditions as 1 ⩽ Re ⩽ 45, 0.7 ⩽ Pr ⩽ 4000 (Pe ⩽ 4000) and β = 1/8, 1/6 and 1/4. Heat transfer correlations have been obtained in the steady flow regime for the constant temperature and constant heat flux boundary conditions on the solid square cylinder in crossflow. In addition, variation of the local Nusselt number on each face of the obstacle and representative isotherm plots are presented to elucidate the role of Prandtl number and blockage ratio on drag coefficient and heat transfer.

In this research article, we investigated the phenomena of a buoyancy-driven cross-flow impinging on a bulk flow from the inlet for a flow past a pair of side-by-side square cylinders in a confined channel wall (which are kept in an adiabatic condition), a special case of an “internal flow” type problem. The density difference in the flow was achieved through a subtle temperature difference between the ambient fluid and the solid walls present in the domain. The study has been carried out at the Reynolds number Re = 1–40 for a transverse gap ratio s/d = 0.7–10 and the Richardson number Ri = 0–1 at a constant value of the Prandtl number Pr = 50. During a rigorous parametric study, we found that the mixed convection not only brings an early unsteadiness in the flow but also fetches an early formation of different flow regimes at Re = 40. An effort has been made to identify the precise near-wake formations leading to the vortex shedding processes in a mixed convection flow for a various range of s/d values. ...