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.

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.

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.

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.

scholarly journals Steady-State Fluid-Solid Mixing Plane to Replace Transient Conjugate Heat Transfer Computations during Design Phase

2021 ◽  
Vol 6 (2) ◽  
pp. 6
Author(s):  
Lucian Hanimann ◽  
Luca Mangani ◽  
Ernesto Casartelli ◽  
Elmar Gröschel ◽  
Magnus Fischer
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Conjugate Heat Transfer ◽  
Pressure Ratio ◽  
Jet Impingement ◽  
Rotating Disk ◽  
Propagation Time ◽  
Back Side ◽  
Thermal Loads ◽  
Physical Point

The demand for increased turbomachinery performance, both, towards higher pressures and temperatures, leads to high thermal-loads of specific components and can critically affect mechanical integrity. In the particular case of rotating-disk configurations, like the back-side of wheels or in cavities, a very efficient way for cooling is jet impingement. An example for this situation are high pressure-ratio turbochargers, where cooling of the impeller disk (back wall) is introduced to achieve tolerable thermal loads. From the physical point of view, jet impingement on a rotating wall generates an unsteady heat transfer situation. On the other end, accurate values of time-averaged temperatures would be sufficient for design purposes. In general, obtaining circumferentially time-averaged solutions requires transient analysis of the conjugate heat transfer (CHT) process to account for the mean effect of jet cooling on solids. Such analysis is computationally expensive, due to the difference in information propagation time-scale for the solid and the fluid. In this paper, a new approach to directly compute circumferentially time-averaged (i.e., steady-state) temperature distributions for rotating-disk CHT problems is presented based on an adaption of the well known fluid-fluid mixing plane approach.

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.

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