Forced convection from an isolated heat source in a channel with porous medium

A numerical study is made of flow and heat transfer characteristics of forced convection in a channel that is partially filled with a porous medium. The flow geometry models convective cooling process in a printed circuit board system with a porous insert.The channel walls are assumed to be adiabatic. Comprehensive numerical solutions are acquired to the governing Navier-Stokes equations, using the Brinkman-Forchheimer-extended Darcy model for the regions of porous media. Details of flow and thermal fields are examined over ranges of the principal parameters; i.e., the Reynolds number Re, the Darcy number Da (≡K/H²), the thickness of the porous substrate S, and the ratio of thermal conductivities R_k (≡k_eff/k). Two types of the location of the porous block are considered. The maximum temperature at the heat source and the associated pressure drop are presented for varying Re, Da, S, and R_k. The results illustrate that as S increases or Da decreases, the fluid flow rate increases. Also, as R_k increases for fixed Da, heat transfer rates are augmented. Explicit influences of Re on the flow and heat transport characteristics are also scrutinized. Assessment is made of the utility of using a porous insert by cross comparing the gain in heat transport against the increase in pressure drop.     

Investigation of a heat transfer augmenter as a fouling cleaner and its optimum geometry in the tube side of a condenser

A spiral wire was used to augment the heat transfer inside the tubes of surface condensers or shell-and-tube heat exchangers. A spiral wire with a reinforcing component in the direction of the spiral axis has been investigated as a fouling cleaner on the internal surface of a tube, when it is driven in a reciprocating motion with the help of reinforcing wires. When it stays in the tube, it augments the convective heat transfer. Based on the an experimental investigation, the relationships among the heat transfer, drag, cleaning effectiveness, fouling rates, and geometric variables of the cleaner-augmenter performance were found. The results of the experimental investigations on the cleaner-augmenter and the comprehensive evaluation criterion for the device as a fouling cleaner are presented along with the dimensions of tube diameter, wire diameter, and pitch.     

Role of the inclination of an inverted‐V upper plate on the heat and flow behavior of trapped gases in a modified Rayleigh–Bénard cavity

Thermal buoyant air inside a modified Rayleigh–Bénard (RB) cavity bounded by a lower flat plate and an inverted‐V upper plate has been investigated numerically using the finite‐volume method. The second‐order‐accurate QUICK and SIMPLE schemes were used for the discretization of the convective terms and the pressure–velocity coupling in the set of conservation equations, respectively. The problem under study is controlled by two parameters: (1) the Rayleigh number ranging from 10³ to 10⁶ and (2) the relative height of the vertical sidewalls d. In reference to the latter, it varies from one limiting case corresponding to the standard RB cavity (a rectangle with d = 1) to another limiting case represented by an isosceles triangular cavity where d = 0. The numerical results for the velocity and temperature fields are presented in terms of streamlines, isotherms, local and mean heat fluxes. An additional effort was devoted to determine the critical Ra values characterizing the transition from symmetrical to asymmetrical buoyant airflow responsive to incremental changes in Ra. For purposes of engineering design, a general correlation equation for the Nusselt number in terms of the pertinent Ra and d was constructed using nonlinear multiple regression theory. Copyright © 2007 John Wiley & Sons, Ltd.     

On the existence of a threshold value of the plate bluntness in the interference of an oblique shock with boundary and entropy layers

The heat transfer to sharp and slightly blunted flat plates in the zone of oblique shock incidence has been experimentally investigated. The experiments were performed at the Mach numbers M = 6, 8, and 10 and Reynolds numbers ranging from 0.2 × 10⁶ to 1.3 × 10⁶ corresponding to transitional (laminar-turbulent) flow in the shock-induced separation zone. Emphasis is placed on small values of the bluntness radius r. It is established that there exists a threshold value r _th of the radius that bounds the range of its influence on the heat transfer, namely, an increase in r to r _th leads to a sharp reduction in the maximum heat transfer coefficient in the interference zone, whereas a further increase (beyond r _th) has only a slight effect on the maximum heat transfer coefficient. The dependence of r _th on the main hypersonic flow parameters is analyzed. an explanation of the observable phenomena is given.