Modeling of mixed convection for double-pipe heat exchanger in a partially cooled enclosure

Abstract

In this thesis, mixed convection heat transfer for double-pipe heat exchanger in a partially cooled-enclosure has been investigated numerically. The upper lid of the cavity is considered to be moving and a hollow cylinder is used at the middle of the enclosure. Physical problems are governed by the equations of continuity, momentum and energy along with the boundary conditions. The governing equations along with the boundary conditions are transformed into non-dimensional form and solved by employing a finite-element scheme based on the Galerkin weighted residuals method. The investigations are conducted for different governing parameters namely thermal conductivity ratio (Kr), Prandtl number (Pr), heat generation parameter (Q), cooling length (Lc), Richardson number (Ri), Reynolds number (Re). The results are presented in terms of streamlines, isotherms and average heat transfer rate. Computations are done for different values of thermal conductivity ratio 1.1 ≤ Kr ≤30, Prandtl number 1 ≤ Pr ≤10, heat generation parameter ratio 0.0 ≤ Q ≤ 0.75, cooling length 0.2≤ Lc ≤0.8, Richardson number 0.01 ≤ Ri ≤ 10, Reynolds number 50 ≤ Re ≤ 500 for different values of dimensionless time (τ) 0.1, 0.5 and 1. The average Nusselt number (Nuh) of the heated surface for different thermal conductivity ratio (Kr) shows an oscillatory phenomenon with increasing values of τ. But Prandtl number (Pr) increases and heat generation parameter decreases sharply for increasing values of dimensionless time (τ). The other parameters such as cooling length (Lc), Richardson number (Ri), Reynolds number (Re) are not that significant pattern for different values of dimensionless time (τ).