Flow and Heat Transfer Phenomena Across Two Confined Tandem Heated Triangular Bluff Bodies

International Journal of Heat and Mass Transfer

Baranyi

2015

Self Cite

a b s t r a c tA numerical analysis using Ansys Fluent was carried out to investigate the forced convection of powerlaw 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 powerlaw index at Re = 40 were reported.

Section: Resultsmentioning

confidence: 98%

Section: Problem Descriptionmentioning

confidence: 99%

CFD analysis of power-law fluid flow and heat transfer around a confined semi-circular cylinder

Kumar

International Journal of Heat and Mass Transfer

Baranyi

2015

Self Cite

“…The semi-circular cylindrical obstruction is mounted at the center-line at an upstream distance equal to L u from the inlet or at a downstream distance equal to L d from the outlet. The channel confinement or the blockage ratio is chosen to be D/H = 25% (in concurrence to the relevant confined domain studies such as Kumar et al [5,6]; Al-Sumaily and Thompson [8]; Zdravkovich [18]; Bijjam and Dhiman [19]; Abbassi et al [20]; Srikanth et al [21]; Agarwal and Dhiman [22]; and Rasool et al [23]), D being the unit scale length cylinder diameter, and H the height of channel. The time period of sinusoidal oscillations τ , while the amplitude is A.…”

Section: Mathematical Formulation 21 Problem Statementmentioning

confidence: 99%

Pulsating flow and heat transfer analysis around a heated semi-circular cylinder at low and moderate Reynolds numbers

Bhalla

J Braz. Soc. Mech. Sci. Eng.

2017

List of symbols A Amplitude of oscillation for axial inlet velocity, dimensionless Cp Heat capacity, J kg −1 K −1 C D Total drag coefficient, C D = F D /(ρU 2 D/2), dimensionless D Diameter, m f Pulsating frequency, s −1 (or Hz) F D Drag force, N/m G Gap ratio, dimensionless Gr Grashof number, dimensionless h Average heat transfer coefficient, W m −2 K −1 H Channel height, m k Thermal conductivity of the fluid, W m −1 K −1 K C Keulegan-Carpenter number, dimensionless L Channel length, m L d Downstream length, m L u Upstream length, m n Power-law index, dimensionless Nu Average Nusselt number, Nu = hD/k, dimensionless p Pressure, N m −2 Pr Prandtl number, Pr = μCp/k, dimensionless q s Heat flux on the surface of the cylinder, W m −2 Re Reynolds number, Re = ρDU/μ, dimensionless Ri Richardson number, dimensionless N S Stokes number, dimensionless St Strouhal number, St = fD/U, dimensionless t Time, s T Temperature, K U Average velocity, m/s U x , U y x-and y-components of the velocity, m/s x, y Horizontal and vertical coordinates, m Abstract A numerical analysis was carried out to examine the effect of pulsating flows around a semi-circular (heated) cylinder placed in a horizontal confined empty channel. The heat transfer induced as an outcome of non-zero mean sinusoidally varying flow past a semi-circular cylinder was investigated. For this purpose, computations are carried out for the following range of parameters: wall confinement (or blockage ratio, β) = 25%; Prandtl number (Pr) = 7 (water as a working fluid); Reynolds number (Re) = 10-100; Strouhal number (St) = 0-2; and amplitude of oscillation (A) = 0-0.6. The current situation is numerically investigated by solving the continuity, momentum and energy equations using the finite volume method-based solver Ansys Fluent. Results in terms of total drag coefficient and Nusselt number have been presented and discussed. The nature of flow for each considered case is reported. The flow (streamlines) and thermal (isothermal contours) patterns have been analyzed. The maximum augmentations of about 22 and 10% were obtained in drag coefficient and Nusselt number, respectively. It is noteworthy that amongst all the cases studied, an appreciable amount of augmentation is observed when St = 1 and A = 0.6 (with respect to the case of non-pulsating flow i.e. St = 0).

“…The choices of these values were consistent with the literature [37]. Based on the literature [37][38][39][40][41], the blockage ratio (β = D/H) of the domain was taken as 25%. Both cylinders were kept at a fixed temperature of T w and unveiled to a fully developed velocity profile with average velocity U avg and temperature T ∞ .…”

Section: No Slip Conditionmentioning

confidence: 99%

Flow and heat transfer analysis around tandem cylinders: critical gap ratio and thermal cross-buoyancy

Dwivedi

J Braz. Soc. Mech. Sci. Eng.

2019

The focus of the current numerical investigation is to study the fluid flow and mixed convective (thermal cross-buoyancy) heat transfer of incompressible fluid across identical cylinders organized in a confined tandem configuration because of their enormous engineering and industrial applications such as heat exchange tubes, electronic cooling, twin chimney stacks, cooling tower, etc. The involved flow and energy equations are solved for different gap ratios (S/D = 2.5, 3, 3.5, 4, 5, and 5.5) with varying Richardson number (Ri = 0, 0.5, and 1) at Reynolds number Re = 100, Prandtl number Pr = 0.7 and wall confinement β = 25% by using a finite volume method-based commercial solver ANSYS Fluent. It is found that after a certain gap ratio there is a drastic change in the physical parameters and after that gap ratio the change is gradual; this gap ratio is termed as a critical gap ratio. The introduction of thermal cross-buoyancy (Ri > 0) plays a deep impact on the physical parameters, and it is to be noted that the critical spacing shifts towards a lower value with increasing Ri. The analysis of lift coefficients shows that the fluctuations in lift signal shift from zero average value at Ri = 0 towards the nonzero negative average value for the tandem cylinders at Ri > 0. The local Nusselt number shows the shift in the front stagnation point on both cylinders with increasing thermal cross-buoyancy. The drag coefficient and Nusselt number of the downstream cylinder are always less than the upstream cylinder, but the percentage increment in the physical parameters of the downstream cylinder after critical spacing is much more than its upstream counterpart. KeywordsConfined cylinders • Tandem configuration • Cross-buoyancy mixed convection • Gap ratio • Strouhal number and power spectrum density List of symbols C D Drag coefficient C L Lift coefficient C P Fluid specific heat (J/kg K) D Cylinder diameter (m) f Vortex shedding frequency (Hz) g Acceleration due to gravity (m/s 2 ) Gr Grashof number g v( T w −T ∞) D 3 2 h Φ Local coefficient of heat transfer (W/m 2 K) H Vertical length of channel (m) k Thermal conductivity of fluid (W/mK) L Horizontal length of channel (m) n Direction normal to cylinder surface Nu Φ Local Nusselt number