Wall Heat Flux Ratio Research Articles

Analytical Solution for Fully Developed Mixed Convection Between Parallel Vertical Plates With Heat and Mass Transfer

Exact analytical solutions for fully-developed, steady-state laminar mixed convection with heat and mass transfer between vertical parallel plates are presented. The thermal boundary conditions are UWT or UHF while the concentration at each wall is assumed to be uniform but not necessarily the same. The solution for the UWT case depends on a single parameter which combines the effects of thermal and solutal buoyancy. In the UHF case it depends on three independent parameters, the ratio of the thermal Grashof number to the Reynolds number, the ratio of the solutal Grashof number to the Reynolds number, and the wall heat flux ratio.

Direct numerical simulation of turbulent concentric annular pipe flow: Part 2: Heat transfer

A direct numerical simulation is performed for turbulent heat transfer in a concentric annulus at Re D h =8900 and Pr=0.71 for two radius ratios ( R 1/ R 2=0.1 and 0.5) and wall heat flux ratio q ∗=1.0 . Main emphasis is placed on the transverse curvature effect on near-wall turbulent thermal structures. Near-wall turbulent thermal structures close to the inner and outer walls are scrutinized by computing the lower-order statistics. The fluctuating temperature variance and turbulent heat flux budgets are illustrated to confirm the results of the lower-order statistics. Probability density functions of the splat/anti-splat process are investigated to analyze the transverse curvature effect on the strong relationship between sweep and splat events. The present numerical results show that the turbulent thermal structures near the outer wall are more activated than those near the inner wall, which may be attributed to the different vortex regeneration processes between the inner and outer walls.

Spray Cooling with Formation of Liquid Film. Film-Boiling Heat Transfer of Liquid Film Flow.

In this report, subcooled film-boiling heat transfer of liquid film flow formed by liquid spray on a hot surface was simulated by film-boiling heat transfer of a subcooled liquid film flow supplied from a nozzle along the hot surface. Experimental data indicated that the effects of film thickness, wall superheat and distance from the leading edge on the film-boiling heat transfer were weak. The main parameters controlling the film-boiling heat transfer were liquid velocity and subcooling. The modified heat transfer coefficient was defined as the ratio of wall heat flux to liquid subcooling and a heat transfer correlation between the Nusselt number based on the modified heat transfer coefficient and the Reynolds number was obtained. The correlating equation was very similar to that of turbulent heat transfer of single phase flow, and it was found that most of the heat flux was dissipated to increase the liquid temperature.

DISPERSED FLOW HEAT TRANSFER IN CIRCULAR BENDS

Abstract This paper presents an experimental study of dispersed flow heat transfer in 90-degree circular bends. From extensive measurements, two different heat transfer patterns are identified, i.e. heat transfer without and with rewetting. Their intrinsic mechanisms are analysed, based on the present experimental evidence and our previous theoretical studies. Effects of mass flow rate, wall heat flux, system pressure and curvature ratio on heat transfer are also investigated. An empirical criterion is developed to identify the heat transfer pattern in the bend.

Influence of Surface Heat Flux Ratio on Heat Transfer Augmentation in Square Channels With Parallel, Crossed, and V-Shaped Angled Ribs

The effect of wall heat flux ratio on the local heat transfer augmentation in a square channel with two opposite in-line ribbed walls was investigated for Reynolds numbers from 15,000 to 80,000. The square channel composed of ten isolated copper sections has a length-to-hydraulic diameter ratio (L/D) of 20. The rib height-to-hydraulic diameter ratio (e/D) is 0.0625 and the rib pitch-to-height ratio (P/e) equals 10. Six ribbed side to smooth side wall heat flux ratios (Case 1—q″r1/q″s = q″r2/q″s = 1; Case 2—q″r1/q″s = q″r2/q″s = 3; Case 3—q″r1/q″s = q″r2/q″s = 6; Case 4—q″r1/q″s = 6 and q″r2/q″s = 4; Case 5—q″r1/q″s = q″r2/q″s = ∞; Case 6—q″r1/q″s = ∞ and q″r2/q″s = 0) were studied for four rib orientations (90 deg rib, 60 deg parallel rib, 60 deg crossed rib, and 60 deg V-shaped rib). The results show that the ribbed side wall heat transfer augmentation increases with increasing ribbed side to smooth side wall heat flux ratios, but the reverse is true for the smooth side wall heat transfer augmentation. The average heat transfer augmentation of the ribbed side and smooth side wall decreases slightly with increasing wall heat flux ratios. Two ribbed side wall heating (Case 5—q″r1/q″s = q″r2/q″s = ∞) provides a higher ribbed side wall heat transfer augmentation than the four-wall uniform heating (Case 1—q″r1/q″s = q″r2/q″s = 1). The effect of wall heat flux ratio reduces with increasing Reynolds numbers. The results also indicate that the 60 deg V-shaped rib and 60 deg parallel rib perform better than the 60 deg crossed rib and 90 deg rib, regardless of wall heat flux ratio and Reynolds number.