Analysis of Transient Conjugate Heat Transfer From a Hemispherical Plate During Liquid Jet Impingement

2010 ◽  
Author(s):  
Muhammad M. Rahman ◽  
Cesar F. Hernandez
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Steady State ◽  
Finite Thickness ◽  
Jet Impingement ◽  
Constant Heat Flux ◽  
State Condition ◽  
Liquid Jet ◽  
Transient Heating ◽  
Steady State Condition

Transient heating of a hemispherical solid plate of finite thickness during impingement of a free liquid jet is studied. A constant heat flux is imposed at the inner surface of the hemispherical plate at t = 0 and heat transfer is monitored for the entire duration of the transient until a steady state condition is reached. Calculations are done for Re = 500–1500 and b/dn = 0.083–1.5 using water (H2O) as the coolant and various solid materials such as silicon, Constantan, and copper. It was found that the time for the plate to achieve the steady-state condition decreases and Nusselt number increases with Reynolds number. A plate material with higher thickness provides higher average Nusselt number and longer transient period.

Numerical Simulation of Transient Thermal Transport on a Rotating Disk Under Partially Confined Laminar Liquid Jet Impingement

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Jorge C. Lallave ◽  
Muhammad M. Rahman
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Finite Thickness ◽  
Jet Impingement ◽  
Rotating Disk ◽  
State Condition ◽  
Bottom Surface ◽  
Liquid Jet ◽  
Steady State Condition ◽  
Solid Disk

Abstract This paper considers the transient conjugate heat transfer characterization of a partially confined liquid jet impinging on a rotating and uniformly heated solid disk of finite thickness and radius. A constant heat flux was imposed at the bottom surface of the solid disk at t=0, and heat transfer was monitored for the entire duration of the transient until the steady state condition was reached. Calculations were done for a number of disk materials using water as the coolant, covering a range of Reynolds numbers (225–900), Ekman numbers (7.08×10−5−∞), nozzle-to-target spacing (β=0.25–1.0), confinement ratios (rp/rd=0.2–0.75), disk thicknesses to nozzle diameter ratios (b/dn=0.25–1.67), and solid to fluid thermal conductivity ratios (36.91–697.56). It was found that a higher Reynolds number decreases the time to achieve the steady state condition and increases the local and average Nusselt number. The duration of the transient increases with the increment of the Ekman number and disk thickness, and the reduction in the thermal diffusivity of the disk material.

Multilayer Insulation Venting During Payload Depressurization

2005 ◽  
Author(s):  
Ingrid Cotoros ◽  
Ab Hashemi
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Thermal Control ◽  
Pressure Differential ◽  
State Condition ◽  
Space Application ◽  
Steady State Condition ◽  
Satellite Systems ◽  
Multilayer Insulation

Multilayer Insulation (MLI) blankets consist of closely spaced aluminum coated shields that are spaced apart to reduce heat transfer between the payload and the environment, particularly in vacuum. In space application, satellite systems and sub-systems are wrapped in MLI blankets to thermally isolate them from the environment and achieve thermal control requirements. During spacecraft launch, the payload undergoes a rapid depressurization before reaching steady state condition. The MLI blankets are usually perforated and/or connected at the boundaries with Velcro strips to allow out-gassing. The blankets can lose their integrity and functionality if the depressurization process is too rapid: the out-gassing flow can tear the perforations, and the pressure differential built-up across the blanket can pull the Velcro strips apart. This paper describes the design and modeling of depressurization through X-slits cut into the blanket and Velcro strips taped along the sides. A methodology is developed, and a model for quantifying the pressure differential build-up is described and applied to a payload enclosure aboard a Delta II rocket.

Transient Thermal Management Using a Confined Jet Impingement of Liquid Ammonia

2003 ◽  
Author(s):  
Ryan M. Mead ◽  
Muhammad M. Rahman
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Average Nusselt Number ◽  
Liquid Ammonia ◽  
Plate Thickness ◽  
Average Heat Transfer Coefficient ◽  
Steady State Condition ◽  
Average Heat

This paper introduces the results of transient heat transfer involving a jet of liquid ammonia perpendicularly on a solid substrate of finite thickness containing discrete electronic sources on the opposite surface. The jet was confined by using a cover plate to prevent any evaporation or loss of ammonia during the heat transfer process. The numerical simulation considered both the solid and fluid regions as a conjugate problem. The equations solved in the liquid region included the conservation of mass, conservation of energy, and conservation of momentum. For the solid region, only the heat conduction equation was solved. Computed results included the temperature distribution, local and average heat transfer coefficient, and local and average Nusselt number at the solid-fluid interface. Some of the parameters such as the jet velocity, plate thickness, and plate material were altered to examine the effect that they had on the problem. It was found that the average heat transfer coefficient and a average Nusselt number were high at the initial stages of the transient process and decreased steadily with time until it reached the steady condition. As the plate thickness decreased, and as the jet velocity increased, it was observed that the time it took to reach the steady state condition declined. The time it took to reach steady state condition did not change significantly for different plate materials. However, it did change noticeably for different plate thickness and different Reynolds number.

Heat transfer characteristics of a composite radiant wall under cooling/heating conditions

2019 ◽  
Vol 29 (8) ◽  
pp. 1155-1168
Author(s):  
S. Y. Qin ◽  
Y. A. Wang ◽  
S. Gao ◽  
D. G. Xu ◽  
X. Cui ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
State Condition ◽  
Ratio Model ◽  
Steady State Condition ◽  
Proposed Model ◽  
Heat Transfer Capacity ◽  
Large Heat ◽  
Temperature Heating ◽  
Indoor And Outdoor

The radiant wall composited with capillary tubes has been widely applied in heating or cooling systems due to its large heat transfer area, low-temperature heating and high-temperature cooling. In this study, a ratio model of heat transfer in steady-state condition was established, which explores heat transfer capacity from the capillary layer (active layer) towards the indoor and outdoor sides. The experimental data including the radiant surface temperature, the capillary layer temperature and the heat flux distribution were collected in cooling and heating conditions. The proposed ratio model was validated. The results show that the fluctuation of indoor air temperature is relatively small, suggesting that the radiant system possesses higher stability. Results showed that thermal resistances of the composite radiant wall in summer and winter conditions vary greatly due to different moisture contents. With the continuation of the system operation, the calculated values from the ratio model under the steady-state condition were more consistent with average values obtained from experiments under unsteady-state conditions, indicating that the overall heat transfer performance of the composite radiant wall could be properly evaluated by the proposed model in engineering applications.

Experimental Study of Air Slot Jet Impingement Cooling From Cylinder Placed on a Flat Plate

2019 ◽  
Vol 12 (4) ◽  
Author(s):  
Ketan Atulkumar Ganatra ◽  
Dushyant Singh
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Nusselt Number ◽  
Flat Plate ◽  
Local Nusselt Number ◽  
Jet Impingement ◽  
Maximum Error ◽  
Constant Heat Flux ◽  
Impingement Cooling ◽  
Heated Cylinder

Abstract The experimental study for air slot jet impingement cooling from the heated cylinder is carried out. The heated cylinder is placed on a flat plate. The flat plate has an effective dimension as plate length (P) from heat transfer point of view. The heating of the cylindrical surface is done by providing a constant heat flux. The various parameters which affect the heat transfer from the cylinder are ReD, h/S, S/D, and P/D. The range of the parameters considered are ReD = 10,000–25,000, h/S = 4–12, S/D = 0.072–0.108, and P/D = 0–2. The effect of various parameters on heat transfer distribution (stagnation and local Nusselt number) from the cylinder is investigated. The local Nusselt number has a maximum value at θ = 0 deg and then it decreases upto θ = 180 deg. This trend is observed for all the parametric variations. The stagnation Nusselt number (Nustag) and local Nusselt number increases with the change of parameters as increase in ReD and S/D and decrease in h/S. However, Nustag remains independent with the change in P/D. The correlation for stagnation and mean Nusselt number is developed using regression analysis as a function of ReD, h/S, S/D, and P/D. The maximum error associated with the correlated value of Nustag and Num as compared with the experimental data is observed as ±13% and ±25%.

Confined and Submerged Liquid Jet Impingement Heat Transfer

1995 ◽  
Vol 117 (4) ◽  
pp. 871-877 ◽  
Author(s):  
S. V. Garimella ◽  
R. A. Rice
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Source ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Liquid Jet ◽  
Local Surface Temperature ◽  
Radial Outflow

The local heat transfer from a small heat source to a normally impinging, axisymmetric, and submerged liquid jet, in confined and unconfined configurations, was experimentally investigated. A single jet of FC-77 issuing from a round nozzle impinged onto a square foil heater, which dissipated a constant heat flux. The nozzle and the heat source were both mounted in large round plates to ensure axisymmetric radial outflow of the spent fluid. The local surface temperature of the heat source was measured at different radial locations (r/d) from the center of the jet in fine increments. Results for the local heat transfer coefficient distribution at the heat source are presented as functions of nozzle diameter (0.79 ≤ d ≤ 6.35 mm), Reynolds number (4000 to 23,000), and nozzle-to-heat source spacing (1 ≤ Z/d ≤ 14). Secondary peaks in the local heat transfer observed at r/d ≈ 2 were more pronounced at the smaller (confined) spacings and larger nozzle diameters for a given Reynolds number, and shifted radially outward from the stagnation point as the spacing increased. The secondary-peak magnitude increased with Reynolds number, and was higher than the stagnation value in some instances. Correlations are proposed for the stagnation and average Nusselt numbers as functions of these parameters.

Convective Heat Transfer From Confined Heated Surfaces With Slot Jet Impingement

2005 ◽  
Author(s):  
L. K. Liu ◽  
C. J. Fang ◽  
M. C. Wu ◽  
C. H. Peng ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Steady State ◽  
Convective Heat ◽  
Local Nusselt Number ◽  
Jet Impingement ◽  
Experimental Investigations ◽  
Surface Center ◽  
Nusselt Numbers ◽  
Extended Surface

A series of experimental investigations with a stringent measurement method on the transient-/steady-state heat transfer behavior for confined smooth surfaces with slot jet impingement have been successfully conducted. From the results, a generalized correlation is proposed to represent the distributions of normalized transient convective heat flux. The highest heat transfer during the transient period occurs at the surface center of confined heated smooth or extended surface. The transient local Nusselt number decreases along the distance from the surface center toward the surface edge. The transient-/steady-state local and average Nusselt numbers are almost independent of Grs, and they are more significantly affected by ReD as compared with H/W. They will increase with increasing ReD. Maximum local and average Nusselt numbers can be found between H/W = 3 and H/W = 5. The effects of Grs and H/W on the dimensionless local Nusselt number distribution are insignificant; and the distribution can be expressed as a generalized bell-shaped profile, which is only dependent of ReD. Finally, a new composite correlation of steady-state average Nusselt number for mixed convection from confined smooth due to slot jet impingement and buoyancy are presented.

Transient Thermal Management of Microelectronics Using Free Liquid Jet Impingement

2004 ◽  
Author(s):  
Antonio J. Bula ◽  
Muhammad M. Rahman
Keyword(s):  
Heat Transfer ◽  
Finite Thickness ◽  
Jet Impingement ◽  
Transport Processes ◽  
Uniform Grid ◽  
Liquid Region ◽  
Fluid Interface ◽  
Transfer Coefficients ◽  
Steady State Condition ◽  
Average Heat

The results of numerical simulation of a transient heat transfer process when a free jet of high Prandtl number fluid impinges perpendicularly on a solid substrate of finite thickness containing discrete electronics on the opposite surface are presented. The numerical model was developed considering both solid and fluid regions and solved as a conjugate problem. Equations for the conservation of mass, momentum, and energy were solved in the liquid region taking into account the transport processes at the inlet and exit boundaries as well as at the solid-liquid and liquid-gas interfaces. In the solid region, only heat conduction equation was solved. The shape and location of the free surface (liquid-gas interface) was determined iteratively as a part of the solution process by satisfying the kinematic condition as well as the balance of normal and shear forces at this interface. The number of elements in the fluid and solid regions were determined from a systematic grid-independence study. A non-uniform grid distribution was used to adequately capture large variations near the solid-fluid interface. Computed results included the local and average heat transfer coefficients at the solid-fluid interface. Computations were carried out to investigate the influence of different operating parameters such as jet velocity and plate material. It was found that the average heat transfer coefficient is maximum at early stages of the transient process and decreases gradually with time to the final steady state condition.

scholarly journals Design and Optimization of a Radial Flow Heat Sink under Free Convection at Steady State Condition

2017 ◽  
Vol 13 (2) ◽  
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Free Convection ◽  
Heat Sink ◽  
Radial Flow ◽  
Numerical Models ◽  
State Condition ◽  
Design Parameters ◽  
Steady State Condition ◽  
Flow Heat

Three dimensional numerical models were developed to make prediction free convection heat transfer at steady state condition from radial flow heat sink. The air was considered as the medium of heat transfer. In radial flow heat sink, heat conducts through base in radial pattern and is uniformly transported to the fins. The Tagucy method was used to investigate the effect of several design parameters such as fin length, fin height, number of fins and heat sink base radius on heat transfer. There are five factors and four levels on each factor were chosen. Sixteen types of model were analyzed to obtain total heat transfer for each model. The result was used to estimate the optimum designed values of the parameters affecting the heat sink efficiency. The reproducibility of the optimum design value was verified. The average rate of heat transfer of optimum model was increased by more than 50 % than the reference model. Finally, the heat transfer data of radial flow heat sink were correlated of several outer radius by an equation.

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