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The present experimental work deals with the effect of partial blockage in the exit of the mixing channel on thermo-hydraulic performance of multi-pass jet plate solar air heater. This investigation is performed at IIT(ISM) Dhanbad campus (India) to obtain the results in terms of outlet temperature, collector efficiency, Temperature rise parameter (TRP), thermo - hydraulic performance parameter (THPP) and Nusselt number for double–pass cross and non–cross flow inline holes Jet Plate Solar Air Heater (JPSAH). Results for different ranges of operating and geometrical parameters such as, mass flow rate = 0.10–0.14 kg/s, Reynolds number, Re = 4741–10632, daily average solar flux incident on glass cover, I tavg. = 611–1113 W / m 2 and blockage ratio (H/Z 2) = 0, 0.33, 0.66 are presented. This work also compares the present results with simple double – pass solar air heater. It is found that the maximum percentage increments in THPP and Nu are 37 % and 79 % respectively at Re = 10247 and 9500 for BR = 0 compared to non-cross flow and simple double pass solar air heater. Based on the experimental data, correlations for the Nusselt number, friction factor and THPP have been developed. [ABSTRACT FROM AUTHOR]

• Fluid yield-stress suppresses flow field in severely confined flows. • Confinement of cylinder can lead to augmentation in heat transfer rate. • Shape of the cylinder significantly affects the momentum and thermal transport in channel confined flow. • Strong aiding buoyancy causes flow reversal at the walls at low Reynolds numbers. The aiding-buoyancy mixed convection heat transfer in Bingham plastic fluids from an isothermal cylinder of elliptical and circular shape in a vertical adiabatic channel is numerically investigated. For a fixed shape of the elliptical cylinder E = 2 (ratio of major to minor axes), the effect of confinement is studied for three values of blockage ratio, B , defined as the ratio of the channel width to the circumference of the cylinder/π, as 6.5, 2.17 and 1.3. In order to delineate the role of cross-section of the cylinder, results are also presented here for a circular cylinder of the same heat transfer area as the elliptical cylinder. The results presented herein span the range of conditions as: Bingham number, 0 ≤ Bn ≤ 100, Reynolds number, 1 ≤ Re ≤ 40, and Prandtl number, 1 ≤ Pr ≤ 100 over the range of Richardson number Ri = 0 (pure forced convection) to Ri = 10. Extensive results on drag coefficient, local and surface averaged values of the Nusselt number and yield surfaces are presented herein to elucidate the combined effects of buoyancy, blockage ratio and fluid yield stress. The morphology of the yield surfaces shows that the unyielded plug regions formed upstream and downstream of the cylinder grow faster at low Reynolds numbers with the increasing yield stress effects under the weak buoyancy forces, i.e., small values of Grashof or Richardson number. The heat transfer enhancement is observed with the increasing channel-confinement due to the sharpening of the temperature gradients near the surface of the cylinder. The average Nusselt number shows a positive dependence on the Reynolds number, Prandtl number and Richardson number irrespective of the shape of the cylinder or the type of fluid. By employing the modified definitions of the dimensionless parameters (based on the two choices of the overall effective fluid velocity), predictive correlations have been established for estimating the value of the average Nusselt number in a new application. [ABSTRACT FROM AUTHOR]

Abstract Transient laminar opposing mixed convection heat transfer from a circular cylinder confined inside a vertical closed-loop downward rectangular water channel has been studied experimentally. The cylinder is subjected to a constant wall heat flux boundary condition while the other bounding walls are insulated and adiabatic. The cylinder is placed horizontally at the mid-plane with a 40% blockage ratio (B R , ratio between the cylinder diameter and the thickness of the rectangular section) and a cylinder aspect ratio (A R , ratio between the length and diameter of the cylinder) of 6. Experiments are performed for flow conditions with Reynolds number based on cylinder diameter in the range 170 ≤ R e ≤ 260 , Prandtl number of P r = 7, and for values of the modified Richardson number, R i ∗ = G r ∗ / R e 2 , from 3.6 to 142.5. From experimental measurements, the variation in time-averaged local temperature distributions with angular position are obtained at nondimensional distances of 0.25, 0.5 and 0.75 of the cylinder span. Also, space-averaged surface temperatures and overall Nusselt number are obtained for a wide range in the parametric space. It is observed that for all values of R e and R i ∗ up to 40.1, a steep increase in the overall Nusselt number is observed with increasing buoyancy. However, because of the channel blockage, for values of R i ∗ > 40.1 and up to R i ∗ = 142.5, the overall Nusselt number reaches a plateau and its value remains practically fixed. Results indicate that for relatively large values of R i ∗ , because of the buoyancy-induced secondary flow resulting from the proximity of the cylinder to the channel walls, the three-dimensional (3D) configuration of the flow is no longer symmetric with respect to the channel centerline and the heat transfer rates vary along the span. The analysis brings out the significance of the end conditions and the buoyancy-induced secondary flow on the local and overall heat transfer characteristics of the bounded flow. [ABSTRACT FROM AUTHOR]

This study deals with the buoyancy induced flow and heat transfer in a parallel plate channel with a heat source array, which simulates an electronic package. The heat source array consists of four discrete protruding heat sources made of copper. The focus of this study is concentrated on the effect of heat source blockage ratio ( b r ) on recirculating flow and cooling performance of the system. Studies are conducted both for flush mounted or protruding heat source cases. Four different values of the blockage ratio of the protruding heat sources ( b r  = 0.125, 0.25, 0.375 and 0.5) are considered. The range of the modified Grashof number covers the values between 9.6 × 10 5 and 1.53 × 10 7 . In the experiments, flow visualization and temperature measurements are conducted. Numerical studies are performed via ANSYS Fluent software. From the experimental results and numerical studies, it is found that buoyancy induced flow and cooling performance is significantly affected by the blockage ratio of the heat source array. [ABSTRACT FROM AUTHOR]

The impact of double-sided delta-winglet tape (DWTs) inserts on convective heat transfer and friction behaviors in a tube was experimentally investigated. Three DWTs with ratios of winglet-height (b) to inner tube diameter (di) called blockage ratio (Rb) of 0.28, 0.35 and 0.42 were tested and their performance was compared to that of a longitudinal strip and plain tube under similar test flow conditions. Experiments were conducted over a wide range of flow rates, 3.35 × 10-5-8.33 × 10-5 m³/s, which correspond to 5500 ≤ Reynolds number (Re) ≤ 14,500 in the 14.3 mm i.d. tube. The results revealed that using DWTs dramatically increased the Nusselt number (Nu) by as much as 364.3% and the friction factor (f ) by 15.5 times compared with those of a plain tube. Thermal performance (η) increased with a corresponding increase in Rb. The highest thermal performance (η) obtained was 1.4. Showing a notable improvement on the thermal performance of the system, DWTs are proposed as a favorable insert device. [ABSTRACT FROM AUTHOR]

The present paper deals with entropy generation study of CuO/water nanofluid flow over a spherical heat source that is installed inside a cylindrical channel with sudden expansion and contraction. To estimate the entropy generation rate; first, the governing equations are solved numerically to find the velocity and temperature fields in the domain where the flow is steady and laminar. Next, using the simulation data, the entropy generation number is calculated theoretically. The effects of nanofluid concentration, nanoparticle size, blockage ratio, and Reynolds number on the entropy generation have been investigated. The outcomes of this research elucidate that entropy generation number rises with an increase in the nanoparticle volume fraction and surface temperature of the heat source. On the other hand, it was found that the entropy generation is diminished by implementing finer nanoparticles and lowering the blockage ratio. In this study, a new correlation has also been presented to calculate the Nusselt number that is a function of Reynolds number, Prandtl number, and blockage ratio. [ABSTRACT FROM AUTHOR]

Experimental investigations in fluid flow and heat transfer have been carried out to study the effect of wall proximity due to flow separation around rectangular prisms. Experiments have been carried out for the Reynolds number 2.6 × 104, blockage ratios are 0.1, 0.2, 0.3, and 0.4, aspect ratios ( d/ c) are 1.5, 1.33, 0.667, and 0.333, with different height-ratios and various angles of attack. The static pressure distribution has been measured on all faces of the rectangular prisms. The results have been presented in the form of pressure coefficient, drag coefficient for various height-ratios and blockage ratios. The pressure distribution shows positive values on the front face whereas on the rear face negative values of the pressure coefficient have been observed. The drag coefficient decreases with the increase in angle of attack as the height-ratio decreases. The heat transfer experiments have been carried out under constant heat flux conditions. Heat transfer coefficients are determined from the measured wall temperature and ambient temperature and presented in the form of a Nusselt number. Both local and average Nusselt numbers have been presented for various height-ratios. The variation of the local Nusselt number has been shown with nondimensional distance for different angles of attack and blockage ratios. The variation of the average Nusselt number has also been shown with different angles of attack for blockage ratios. The local as well as average Nusselt number decreases as the height-ratio decreases for all nondimensional distances and angles of attack, respectively, for rectangular prisms. Empirical correlations for the average Nusselt number have been presented for a rectangular prism as a function of the Reynolds number, Prandtl number and relevant nondimensional parameters. [ABSTRACT FROM AUTHOR]

The impact of double-sided delta-winglet tape (DWTs) inserts on convective heat transfer and friction behaviors in a tube was experimentally investigated. Three DWTs with ratios of winglet-height (b) to inner tube diameter (di) called blockage ratio (Rb) of 0.28, 0.35 and 0.42 were tested and their performance was compared to that of a longitudinal strip and plain tube under similar test flow conditions. Experiments were conducted over a wide range of flow rates, 3.35 × 10−5–8.33 × 10−5 m3/s, which correspond to 5500 ≤ Reynolds number (Re) ≤ 14,500 in the 14.3 mm i.d. tube. The results revealed that using DWTs dramatically increased the Nusselt number (Nu) by as much as 364.3% and the friction factor (f) by 15.5 times compared with those of a plain tube. Thermal performance (η) increased with a corresponding increase in Rb. The highest thermal performance (η) obtained was 1.4. Showing a notable improvement on the thermal performance of the system, DWTs are proposed as a favorable insert device.

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]

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]

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]

In this work, a numerical study is performed to predict the solution of two – dimensional, steady and laminar mixed convection flow over a square cylinder placed symmetrically in a vertical parallel plate. A finite difference method is employed to solve the governing differential equations, continuity, momentum, and energy equation balances. The solution is obtained for stream function, vorticity and temperature as dependent variables by iterative technique known as successive over relaxation. The flow and temperature patterns are obtained for Reynolds number and Grashof number at (Re= -50,50,100,-100) (positive or negative value refers to aidding or opposing buoyancy , +1 assisting flow, -1 opposing flow) and (102 to 105) , respectively. The results displaced that the recirculation length above the cylinder increases with the increase in Gr number and the average Nu number is the highest at the lower surface of the cylinder, while is the lowest at the top of the cylinder surface. A comparison between the obtained results and the published computational studies has been made and it showed a good agreement.

In aseptic food processing, a hot carrier fluid, usually non-Newtonian, is used to thermally sterilize the food particles suspended in a holding tube. The effects of a spherical food particle's diameter relative to the holding tube diameter on the heat transfer rates are investigated using Computational Fluid Dynamics (CFDs) simulations. As the particle to holding tube diameter ratio (blockage-ratio) increases, higher particle heating rates were usually observed when compared to the heating rates of an unconfined particle. Variations in the non-Newtonian fluid viscosities with shear rate and temperature played important roles in affecting the local Nusselt numbers. Significant effect of the blockage ratio was found on the integrated lethality of the thermal treatment at low particle Reynolds numbers (Rep). For such cases, conventional steady state fluid-particle heat transfer coefficient correlations, applicable when the particle is immersed in an unbounded stream of fluid, may lead to erroneous predictions of integrated lethality of treatment inside the holding tube. The thermal processing of the food particle was compared using two approaches. In the first rigorous approach, the transient and spatial fluid-particle heat flux variations around the sphere were accounted while in the second approach, a constant heat transfer coefficient value was specified as the boundary condition. Even at intermediate Biot number values (4-17), considerable differences between the two approaches could be observed in the conductive heating patterns inside the sphere as well as in the integrated lethalities. [ABSTRACT FROM AUTHOR]

Experimental investigations of fluid flow and heat transfer have been carried out to study the effect of wall proximity due to flow separation around square prisms. Experiments have been carried for Reynolds number equal to 2.6∙104. The results are presented in the form of pressure coefficient, drag coefficient, and Nusselt numbers for various height ratios, blockage ratios, and angles of attack. The pressure coefficient distribution shows positive values on the front face, whereas on the rear face negative values are observed. The drag coefficient decreases with increase in angle of attack as the height ratio decreases, and its maximum value takes place at an angle of about 50°. Both the local and average Nusselt numbers decrease as the height ratio decreases. [ABSTRACT FROM AUTHOR]

This article elaborates on the numerical simulation of forced convective incompressible flow in a horizontal plane channel and heat transfer over two isothermal tandem square cylinders. Finite-volume method was applied to discretize the momentum and energy equations. This study details the effects of S/H (gap between two squares), Reynolds number, and blockage ratio on the characteristics of flow field and heat transfer. The blockage ratios and Reynolds numbers were chosen between 12.5 to 50 per cent and 100 ⩽ Re ⩽ 300, respectively. Results are presented in the form of time-averaged streamlines, instantaneous contours of temperature and vorticity, and some characteristics of fluid flow and heat transfer such as time-averaged of the local and total Nusselt number, drag coefficient, and Strouhal number. The present results show that the gap spacing between squares at high blockage ratios does not have an obvious effect on heat transfer. On the other hand, this parameter plays a main role on the drag coefficient at a high value (S/H = 4), which is because of the formation of the vortex cores in gap spacing and downstream of the second square. The heat transfer rate of the second square increases with the increase of S/H. Increasing the blockage ratio has a negative effect on convective heat transfer of the second square. With the vortex shedding in the gap spacing, the drag coefficient. [ABSTRACT FROM AUTHOR]

Abstract: Experimental investigations in fluid flow and heat transfer have been carried out to study the effect of wall proximity due to flow separation around rectangular prisms. Experiments have been carried out for the Reynolds number 4.9×104, blockage ratios are 0.1, 0.2, 0.3 and 0.4, aspect ratio are 1.5, 1.33, 0.667 and 0.333, different height-ratios and various angles of attack. The static pressure distribution has been measured on all faces of the rectangular prisms. The results have been presented in the form of pressure coefficient, drag coefficient for various height-ratios and blockage ratios. The pressure distribution shows positive values on the front face whereas on the rear face negative values of the pressure coefficient have been observed. The positive pressure coefficient for different height-ratios does not vary too much but the negative values of pressure coefficient are higher for all points on the surface as the bluff body approaches the upper wall of the wind tunnel. The drag coefficient decreases with the increase in angle of attack as the height-ratio decreases. There is no definite angle of attack for all blockage ratios and Reynolds numbers at which the value of drag coefficient is either maximum or minimum. The heat transfer experiments have been carried out under constant heat flux condition. Heat transfer coefficient are determined from the measured wall temperature and ambient temperature and presented in the form of Nusselt number. Both local and average Nusselt numbers have been presented for various height-ratios. The variation of local Nusselt number has been shown with non-dimensional distance for different angles of attack and blockage ratios. The variation of average Nusselt number has also been shown with different angles of attack for blockage ratios. The local as well as average Nusselt number decreases as the height-ratio decreases for all non-dimensional distance and angle of attack, respectively, for rectangular prisms. The average Nusselt number for rectangular prisms of different blockage ratio varies with the angle of attack. But there is no definite angle of attack at different blockage ratio at which the value of average Nusselt number is either maximum or minimum. Empirical correlations for average Nusselt number have been presented for rectangular prism as a function of Reynolds number, Prandtl number and relevant non-dimensional parameters. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

• Tendency of appearing velocity overshoot decreases as Reynolds number increases. • Wake size increases with Weissenberg number at low polymer extensibility parameter, whereas it increases at high values of it. • Drag coefficient decreases with Weissenberg and Reynolds numbers, but increases with blockage ratio. • There is a critical Weissenberg number up to which average number increases and beyond that it remains constant or decreases. • Simple correlations for drag coefficient and average Nusselt number are presented. An extensive numerical investigation of the flow and heat transfer phenomena of a solid sphere translating in a cylindrical tube filled with FENE-P viscoelastic fluids is reported herein. The governing equations, namely, mass, momentum, energy, and viscoelastic constitutive equations, have been solved over the following ranges of conditions: Reynolds number, 1 ≤ R e ≤ 100 , Weissenberg number, 0 ≤ W i ≤ 10 , polymer extensibility parameter, 10 ≤ L 2 ≤ 500 and blockage ratio, 0 ≤ B R ≤ 0.7 for a fixed value of the polymer viscosity ratio β = 0.5 and Prandtl number Pr = 10. Limited simulations with the FENE-CR viscoelastic fluid model have also been carried out to make a comparison between the two viscoelastic models. At low Reynolds numbers, the velocity overshoot and/or negative wake downstream the sphere has been observed under appropriate conditions. This tendency of their appearing decreases with the increasing Reynolds number, and decreasing blockage ratio, polymer extensibility parameter and Weissenberg number. The size of the recirculation region (wake length) increases with the Weissenberg number at low values of the polymer extensibility parameter, whereas a reverse trend is seen at high values of L 2. The drag coefficient decreases with the Reynolds and Weissenberg numbers, whereas it increases with the blockage ratio. On the other hand, the average Nusselt number always increases with the Reynolds number irrespective of the values of Wi, L 2 and BR. However, the corresponding effect of the blockage ratio and polymer extensibility parameter is seen to be more complex, modulated by the values of Re and Wi. For instance, at high Reynolds numbers, the average Nusselt number always increases with the blockage ratio; however, at low values of it, there is a critical value of the blockage ratio present up to which the average Nusselt number increases, and beyond that, it decreases. Furthermore, the average Nusselt number always initially increases up to a certain value of the Weissenberg number, and after that, it remains almost constant or decreases depending upon the values of L 2, BR and Re. Finally, simple correlations for the average Nusselt number and drag ratio are presented, which not only capture the functional dependence of the governing parameters, but also can be used for the interpolation of the present results for the intermediate values of the governing parameters in a new application. [ABSTRACT FROM AUTHOR]

This work analyses the effects of three different Prandtl number fluids (Pr = 0.025, 5.83 and 151) on convective heat transfer inside a closed square cavity with an adiabatic left wall and three other cold walls. A centrally positioned square hot block with respective blockage ratios of 0.25 and 0.5 heats the cavity, which induces natural convection inside it for Grashof numbers Gr = 104, 105 and 106. Besides, two different cases of mixed convection based on the direction of moving right wall are investigated for varying Richardson numbers (0.01 ≤ Ri ≤ 100) at Gr = 104. We implement multiple-relaxation-time based thermal lattice Boltzmann model to study these flow configurations. The comprehensive analysis of the results suggests that the block size and Pr have a considerable influence on the flow and heat transfer behaviour. The average Nusselt number over the block surface N u h ‾ and total entropy generation throughout the cavity S t o t ‾ increase with an increase in Pr and Gr due to the augmentation of convective heat transfer. For all three cases, N u h ‾ at BR = 0.25 is higher compared to BR = 0.5. In mixed convection, the heat transfer irreversibility mostly dominates the entropy generation at all Pr irrespective of Ri values as indicated by large average Bejan number. The present code is carefully validated with the well-established results obtained through conventional numerical techniques. • MRT-LBM is exploited to stimulate convection in a hot-block-inserted square cavity. • Natural and mixed convection occur based on three different boundary conditions. • Three different fluids with Prandtl numbers (Pr) = 0.025, 5.83 and 151 are considered. • Block size and Pr have a strong influence on heat transfer rate and entropy generation. • Average Nusselt number at blockage ratio BR = 0.25 is higher compared to BR = 0.5. [ABSTRACT FROM AUTHOR]

The Poiseuille flow of power-law fluids past a heated sphere in a tapered tube is studied over the following ranges: Blockage ratio, BR (0.1 to 0.5), Separation ratio, SR (0.1 to 0.7), taper angle, α (1o to 20o), Reynolds number, Re (1 to 100), Prandtl number, Pr (10 to 100), and the power law index, n (0.2 to 1). The hydrodynamic force exerted on the sphere is expressed using the total drag coefficient and its pressure component. Both exhibit the expected inverse dependence on Re while it bears a positive dependence on n , SR and BR. The normalized drag for a confined sphere also exhibits a complex functional relationship with each of these parameters. The normalized drag is significantly influenced by the taper angle. In general, SR , BR and α delay the boundary layer separation and hence, stabilize the flow. Similarly, the heat transfer characteristics are described in terms of isotherms, local and surface average Nusselt number. The Nusselt number shows a positive relationship both with SR and BR. The taper angle exerts only a weak effect on the Nusselt number. The heat transfer coefficient is augmented up to 59% in shear-thinning fluids above that in a Newtonian fluid. [ABSTRACT FROM AUTHOR]

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 (). DOI 10.1002/htj.21071 [ABSTRACT FROM AUTHOR]