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Papers by Pratibha Biswal

International Journal of Heat and Mass Transfer, 2017

Journal of the Taiwan Institute of Chemical Engineers, 2016

International Journal of Mechanical Sciences, 2016

International Communications in Heat and Mass Transfer, 2016

International Journal of Heat and Mass Transfer, 2016

Proceedings of the 15th International Heat Transfer Conference, 2014

International Journal of Heat and Mass Transfer, 2012

ABSTRACT Entropy generation due to natural convection in right-angled triangular enclosures fille... more ABSTRACT Entropy generation due to natural convection in right-angled triangular enclosures filled with porous media with top angles 15° and 45° for various thermal boundary conditions (cases 1–4) has been studied numerically using Galerkin finite element method. Simulations are carried out for Pr = 0.025 and 1000 in the range of Darcy numbers 10−5–10−3. Note that, Sθ,max is observed at vertex of the cavity for cases 1 and 3, near corner between left wall and bottom wall for case 2 and near lower portion of the right wall for case 4. It is found that, Sψ,max is observed near middle portions of the side walls for all cases and the location of Sψ,max mainly depends on the presence of high velocity gradients. The total entropy generation, Stotal, is found to be an increasing function of Da. It is observed that decrease in Beav with Da for both φs is due to increase in fluid friction irreversibility. Analysis of the variation of Beav with Da for various fluids indicates that, higher Beav values are observed for Pr = 0.025 due to low frictional irreversibility. It is observed that Θcup decreases with Da for all Pr due to decrease in thermal mixing. It is found that, the maximum heat transfer rate (Nul¯ or Nur¯) occurs for φ = 15° cavities compared to φ = 45° cavities at Da = 10−3 in both isothermal and linear heating cases for all Pr due to larger thermal gradients at φ = 15°. Overall, triangular cavities with φ = 15° may be the optimal top angle for right angled triangular enclosure for thermal processing of all types of fluids (Pr = 0.025 and 1000) due to its high heat transfer rate (Nul¯ or Nur¯), high thermal mixing (high Θcup) and less total entropy generation (Stotal) for all heating strategies (cases 1–4) especially at Da = 10−4.

Current work attempts to study the heatline patterns during natural convection for different type... more Current work attempts to study the heatline patterns during natural convection for different types of Dirichlet heatfunction boundary conditions. The enclosures with various shapes (square, curved, trapezoidal, tilted square and parallelogrammic) are considered with various thermal boundary conditions such as (a) case 1: hot left wall, cold right wall and adiabatic horizontal walls, (b) case 2: hot bottom wall, cold left and right walls and adiabatic top wall and (c) case 3: hot bottom wall with other cold walls. Traditionally, the reference of heatfunction (P ¼ 0) is assumed at the adiabatic wall and the implementation of reference (P ¼ 0) may be non-trivial for the case with zero or multiple adiabatic wall(s). Various heatfunction boundary conditions have been formulated based on locations of P ¼ 0 for systems with more than one adiabatic walls (case 1) or no adiabatic wall (case 3). As test problems, P ¼ 0 is considered at the junctions of isothermal walls (cases 2 and 3) or on the isothermal wall (case 3). The governing equations are solved via the Galerkin finite element method at various Rayleigh numbers (10 3 and 10 5 ) and Prandtl numbers (Pr ¼ 0:015 and 7.2). The magnitudes of the heatfunctions change drastically with the location of the datum of P (P ¼ 0) whereas, the heat flow patterns remain same irrespective of the heatfunction boundary conditions. The gradients of heatfunctions or the heat flux along the active walls (hot/cold) are invariant of the choice of the reference (P ¼ 0). The local and average Nusselt numbers are also independent of the choice of P ¼ 0 and the Nusselt numbers are found to be identical with heatfunction gradients obtained with various locations of P ¼ 0. Current work may be useful for heat flow visualization in various thermal systems involving complex thermal boundary conditions.

Computational study of natural convection within differentially heated enclosures with curved (co... more Computational study of natural convection within differentially heated enclosures with curved (concave/ convex) side walls is carried out via entropy generation analysis. Numerical simulation has been carried out for various Prandtl numbers (Pr ¼ 0:015 and 1000) and Rayleigh numbers ð10 3 6 Ra 6 10 5 Þ with different wall curvatures. Results are presented in terms of isotherms ðhÞ, streamlines ðwÞ, entropy generation due to heat transfer ðS h Þ and fluid friction ðS w Þ. The effects of Rayleigh number on the total entropy generation ðS total Þ, average Bejan number ðBe av Þ and global heat transfer rate ðNu r Þ are examined for all the cases. Maximum values of S h (S h;max ) are found at the middle portion of the side walls for concave cases, whereas, S h;max is observed near the top right and bottom left corner of the cavity for convex cases. On the other hand, S w;max is seen near the solid walls of the cavity for all concave and convex cases. At all Ra and low Pr, largest heat transfer rate and lesser entropy generation is found for case 3 (highly concave case). Overall, for convex case, case 1 or case 2 (lesser convex cases) are efficient for all Ra and Pr. On the other hand, case 3 of concave case (highly concave) offers larger heat transfer rate and lesser entropy generation compared to less concave and all convex cases at low Ra and all Pr. At high Ra and low Pr, case 3 (concave) may be the optimal case whereas, at high Ra and high Pr, case 1 (less concave) may be recommended based on higher heat transfer rate. A comparative study of the concave and convex cases also revealed that the concave cases with high concavity (case 3) may be chosen as the energy efficient case at high Ra and high Pr.

Numerical Heat Transfer, Part A: Applications, 2013

Analysis of natural convection in porous right angled triangular enclosures with a concave/ conve... more Analysis of natural convection in porous right angled triangular enclosures with a concave/ convex hypotenuse has been carried out using the Bejan's heatlines approach. A generalized non-Darcy model without Forchheimer term is employed for fluid flow in a porous matrix and the governing equations are solved by the Galerkin finite element method. The cavity is subjected to a thermal boundary condition of an isothermal cold left wall, isothermal hot curved right wall, and adiabatic bottom wall. Due to intense closed loop heatlines, thermal mixing is higher in convex cases compared to the concave case for all parameters. Average heat transfer rate is found to be largest in the concave hypotenuse case.

Energy, 2014

Numerical simulation for natural convection flow in fluid filled enclosures with curved side wall... more Numerical simulation for natural convection flow in fluid filled enclosures with curved side walls is carried out for various fluids with several Prandtl numbers (Pr ¼ 0.015, 0.7 and 1000) in the range of Rayleigh numbers (Ra ¼ 10 3 e10 6 ) for various cases based on convexity/concavity of the curved side walls using the Galerkin finite element method. Results show that patterns of streamlines and heatlines are largely influenced by wall curvature in concave cases. At low Ra, the enclosure with highest wall concavity offers largest heat transfer rate. On the other hand, at high Ra, heatline cells are segregated and thus heat transfer rate was observed to be least for highest concavity case. In convex cases, no significant variations in heat and flow distributions are observed with increase in convexity of side walls. At high Ra and Pr, heat transfer rate is observed to be enhanced greatly with increase in wall convexity. Results indicate that enhanced thermal mixing is observed in convex cases compared to concave cases. Comparative study of average Nusselt number of a standard square enclosure with concave and convex cases is also carried out. In conduction dominant regime (low Ra), concave cases exhibit higher heat transfer rates compared to square enclosure. At high Ra, low Pr, concave cases with P 1 P 0 1 ¼ 0:4 is advantageous based on flow separation and enhanced local heat transfer rates.