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The present study performs a three-dimensional CFD analysis to investigate the hydrodynamic and thermal properties of annular finned tubes in a heat exchange system. All computations are performed in the turbulent flow regime (4330 ≤ Re ≤ 8790), and the Transition SST model is applied for turbulence modelling. The impact of Prandtl number (0.7 ≤ Pr ≤ 50) on the various parameters, such as the heat transfer coefficient, heat transfer rate, and pressure drop, are considered. The results indicate that the thermo-hydraulic behaviour is significantly affected by incrementing both Reynolds and Prandtl numbers. The fin's surface temperature distribution is examined to get a better insight into its thermal performance, and it is observed that the rear portion of the fin contributes the least to heat transfer. Other important parameters like the fin efficiency and Colburn heat transfer factor are found to significantly impact the performance of the heat exchange system for the above range of settings. The velocity contours show the horseshoe vortex formation near the fin-tube junction, and the channelling effect is observed between consecutive tubes. Different fluids are compared based on the j/f factor for enhanced heat transfer at the minimum possible flow resistance. [ABSTRACT FROM AUTHOR]

The effect of aiding and opposing buoyancy (−1 ≤ Ri ≤ 1) on flow and heat transfer across cylinders specifically arranged in an equilateral triangular array in a heat exchanger has not previously been studied. Periodic boundary condition in the transverse direction is imposed where porosity of the array ranges from 0.7 to 0.99. The influence of buoyancy and Prandtl number (1 and 50) on the flow structure and its effect on the overall heat transfer is thoroughly elucidated in the present work. The impact of aiding/opposing buoyancy on the thermal performance of the array is predominant at higher porosities. The average drag of the array of cylinders increases with an increase in the aiding buoyancy and decreases with an increase in opposing buoyancy with respect to forced convection. The porosity of the triangular array has an inverse relation with the average drag coefficient, barring few exceptions which are explained in detail in the present work. The heat exchange is assertively higher at opposing‐buoyancy cases for all values of porosity and Prandtl number. The present results are in agreement with the available experimental/numerical studies. [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]

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. [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]

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]

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 allS/Bandn. Augmentation in heat transfer for the two tandem triangular cylinders is calculated with respect to bothS/Bandn. [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]

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]

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: 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]