scholarly journals Microscale heat transfer in a free jet against a plane surface

2004 ◽  
Vol 35 (3-6) ◽  
pp. 645-656 ◽  
Author(s):  
Jian-Jun Shu
Keyword(s):  
Heat Transfer ◽  
Plane Surface ◽  
Free Jet ◽  
Microscale Heat Transfer

THE COEFFICIENT OF HEAT TRANSFER FOR VERTICAL SURFACES IN STILL AIR

1937 ◽  
Vol 15a (7) ◽  
pp. 109-117
Author(s):  
R. Ruedy
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Loss ◽  
Temperature Difference ◽  
Plane Surface ◽  
Vertical Plane ◽  
Black Body ◽  
Average Temperature ◽  
Fourth Root

For a vertical plane surface in still air the coefficient of heat transfer, valid within the range of temperatures occurring in buildings, depends on the temperature and the height of the surface. If black body conditions are assumed for the heat lost by radiation, the coefficient is equal to 1.39, 1.50, 1.62, and 1.73 B.t.u. per sq. ft. per ° F. at 32°, 50°, 68°, and 86° F. respectively, the height of the heated surfaces being 100 cm. Convection is responsible for about one-third, and radiation, mainly in the region of 10 microns, for about two-thirds of the heat loss. Convection currents depend on the temperature difference, while radiation depends on the average temperature. When attempts are made to stop convection currents by placing obstacles across the surface, the loss of heat due to natural convection varies inversely as the fourth root of the height, providing that the nature of the flow of air remains unchanged.

Research on Heat Transfer Performance of Water Film for Outside the Tubes of the Microscale Evaporative Condenser

2009 ◽  
Author(s):  
Minghui Hu ◽  
Dongsheng Zhu ◽  
Jialong Shen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Performance ◽  
Water Film ◽  
Transfer Performance ◽  
Air Velocity ◽  
Microscale Heat Transfer ◽  
High Heat Transfer ◽  
Spray Density

It is requested to develop a microscale and high performance heat exchanger for small size energy equipments. The heat transfer performance of the water film on the condensing coils of the microscale evaporative condenser was studied for a single-stage compressed refrigeration cycle system. Under various operation conditions, the effects of the spray density and the head-on air velocity on the heat transfer performance of the water film were investigated. The results show that the microscale heat transfer coefficient of the water film αw increases with the increase of spray density and decreases with the increase of head-on air velocity. The results indicate that the key factor affecting the microscale heat transfer of the water film is the spray density. As the results, it is measured that the present device attained high heat transfer quantity despite the weight is light. In addition, via regression analysis of the experimental data, the correlation equation for calculating the microscale heat transfer coefficient of the water film was obtained, its regression correlation coefficient R is 0.98 and the standard deviation is 7.5%. Finally, the correlations from other works were compared. The results presented that the experimental correlation had better consistency with the correlations from other works. In general, the obtained experimental results of the water film heat transfer are helpful to the design and practical operation of the microscale evaporative condensers.

Large Eddy Simulation of the Heat Transfer Due to Swirling and Non-Swirling Jet Impingement

2008 ◽  
Author(s):  
Naseem Uddin ◽  
S. O. Neumann ◽  
B. Weigand
Keyword(s):  
Heat Transfer ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Test Case ◽  
Complex Flow ◽  
Free Jet ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Target Wall

Turbulent impinging jet is a complex flow phenomenon involving free jet, impingement and subsequent wall jet development zones; this makes it a difficult test case for the evaluation of new turbulence models. The complexity of the jet impingement can be further amplified by the addition of the swirl. In this paper, results of Large Eddy Simulations (LES) of swirling and non-swirling impinging jet are presented. The Reynolds number of the jet based on bulk axial velocity is 23000 and target-to-wall distance (H/D) is two. The Swirl numbers (S) of the jet are 0,0.2, 0.47. In swirling jets, the heat transfer at the geometric stagnation zone deteriorates due to the formation of conical recirculation zone. It is found numerically that the addition of swirl does not give any improvement for the over all heat transfer at the target wall. The LES predictions are validated by available experimental data.

Heat Transfer in Compartment Fires Near Regions of Ceiling-Jet Impingement on a Wall

1989 ◽  
Vol 111 (2) ◽  
pp. 455-460 ◽  
Author(s):  
L. Y. Cooper
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Problem Formulation ◽  
Jet Flows ◽  
Fire Plume ◽  
Compartment Fires ◽  
Free Jet ◽  
Wall Impingement ◽  
Energy Release Rates ◽  
Scale Experiment

The problem of heat transfer to walls from fire-plume-driven ceiling jets during compartment fires is introduced. Estimates are obtained for the mass, momentum, and enthalpy flux of the ceiling jet immediately upstream of the ceiling–wall junction. An analogy is drawn between the flow dynamics and heat transfer at ceiling-jet/wall impingement and at the line impingement of a wall and a two-dimensional, plane, free jet. Using the analogy, results from the literature on plane, free-jet flows and corresponding wall-stagnation heat transfer rates are recast into a ceiling-jet/wall-impingement-problem formulation. This leads to a readily usable estimate for the heat transfer from the ceiling jet as it turns downward and begins its initial descent as a negatively buoyant flow along the compartment walls. Available data from a reduced-scale experiment provide some limited verification of the heat transfer estimate. Depending on the proximity of a wall to the point of plume–ceiling impingement, the result indicates that for typical full-scale compartment fires with energy release rates in the range 200–2000 kW and fire-to-ceiling distances of 2–3 m, the rate of heat transfer to walls can be enhanced by a factor of 1.1–2.3 over the heat transfer to ceilings immediately upstream of ceiling-jet impingement.

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