Validation and Analysis of Numerical Results for a Varying Aspect Ratio Two-Pass Internal Cooling Channel

Abstract

Numerical results for an internal ribbed cooling channel including a 180° bend with a 2:1 inlet and 1:1 aspect ratio outlet channel were validated against experimental results in terms of spatially resolved heat transfer distributions, pressure losses, and velocity distributions. The numerical domain consisted of one rib segment in the inlet channel and three ribs segments in the outlet channel to reduce the overall numerical effort and allow for an extensive parametric study. The results showed good agreement for both heat transfer magnitudes and spatial distributions and the numerical results captured the predominate flow physics resulting from the 180° bend. The production of Dean vortices and acceleration of the flow in the bend produced strongly increased heat transfer on both the ribbed and unribbed walls in the outlet channel in addition to increases due to the ribs. Numerical simulations were performed for a wide range of divider wall-to-tip wall distances, which influenced the position of the highest heat transfer levels on the outlet walls and changed the shape of the heat transfer distribution on the tip wall. Analysis of section averages of heat transfer in the bend and outlet channel showed a strong influence of the tip wall distance while no effect was seen upstream of the bend. A similarly large effect on pressure losses in the bend was observed with varying tip wall position. Trends in averaged heat transfer varied linearly with tip wall distance while pressure losses followed a non-linear trend, resulting in an optimum tip wall distance with respect to heat transfer efficiency.

Heat transfer modeling of a parabolic trough solar collector with working fluid of Fe3O4 and CuO/Therminol 66 nanofluids under magnetic field

“…in which , y, and are defined as friction velocity at the nearest wall, distance to the nearest wall, and local * kinematic viscosity of the fluid, respectively. A value close to 1 can be considered as a good output for the y+, and hence, the discretized model can capture near wall boundary layer adequately [42]- [44]. A mesh sensitivity analysis was made for the receiver tube and thermal efficiency of solar collector as well as y+ of receiver tube were calculated for different meshes.…”

Effect of rotation on forced convection in wavy wall channels

“…The friction coefficient is employed to evaluate the hydrodynamic performance of the fluid flow inside the wavy channel and is defined as [28], [29] :…”

“…It is obvious that rotation has a substantial impact on the heat transfer enhancement because it can cause flow spreading in the spanwise direction and hence enhancing the spanwise heat transfer. The normalized Nusselt number ( ) is used to evaluate the performance of heat transfer from a surface [28], [29], [33].…”

“…In order to evaluate the performance of the heat transfer enhancement of the wavy surface, it is helpful to introduce the aerothermal efficiency . It is a compromise between the heat ( ) transfer enhancement performance and friction loss when the heat transfer and associated pressure loss are both high [28], [29]. It can be defined as:…”

Effect of divider wall-to-end wall distance on the vortical structures and heat transfer characteristics of two-pass channel using topological analysis

“…A number of studies inspect the influence of a divider wall on the serpentine channel flow and HT, i.e. location (Shevchuk et al, 2011), thickness (Prabhu and Vedula, 2000;Liou et al, 1999), inclined divider wall (Hirota et al, 2002), and turn clearance (Hirota et al, 1997), etc. Hirota et al (1999 experimental measured local HT characteristics inside and downstream the sharp turn in a rectangular two-pass passage with different turn clearances and Re numbers.…”