Numerical Modeling of Jet Impingement and Validation of Convection: Conduction Decoupling in Thermal Design

2005 ◽  
Author(s):  
Madhusudan Iyengar ◽  
Michael J. Ellsworth ◽  
Robert E. Simons ◽  
Levi A. Campbell
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
High Performance ◽  
Jet Impingement ◽  
Thermal Design ◽  
Liquid Jet ◽  
Average Heat Transfer Coefficient ◽  
Average Heat

The steady rise in cooling requirements of commercial computer products mandates the development of aggressive thermal management techniques, as well as accurate design and analysis methodologies. Single phase direct liquid jet impingement, offers a controlled high performance alternative, by eliminating the need for a thermal interface, and by delivering the coolant directly to the surface of the chip. This paper characterizes the thermal performance of a specific direct liquid jet impingement scheme in which the hot fluid exhausts via return vents located in the immediate vicinity of the jet. The study also quantifies the error associated with using the average heat transfer coefficient as a thermal performance metric for the non-uniform cooling boundary condition that occurs in such jet impingement solutions. The thermal performance of the direct liquid jet impingement designs are characterized and studied, via CFD (Computational Fluid Dynamics) models constructed using a commercial numerical solver. The hydraulic performance is analytically estimated using a simple loss coefficient based model. A square 10×10×0.75 mm3 chip, dissipating 400W, and cooled by water at 32°C, is considered as the representative example for the analysis. The effect of jet density on thermal performance is characterized for 1–400 jets/cm2, and for several feasible flow parameters, i.e. inlet jet velocities (5–10 m/s) and volumetric flow rates (946–1893 liters/minute). For the configurations explored, the optimal jet density was found to be 100 jets/cm2. An engineering cut-off point for the use of the 1-D average heat transfer coefficient metric, was identified as 10 jets/cm2. The error associated with use of a 1-D average heat transfer coefficient was shown to be in excess of 5% when the jet density is less than 10 jets/cm2, as high as 20% for the single jet case, and less than 0.7% for jet densities greater than 36 jets/cm2.

Confined Liquid Jet Impingement on a Plate With Discrete Heating Elements

2005 ◽  
Author(s):  
Muhammad M. Rahman ◽  
Santosh K. Mukka
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Liquid Jet ◽  
Heat Sources ◽  
Average Heat Transfer Coefficient ◽  
Average Heat ◽  
Discrete Heat Sources ◽  
Solid Region

The primary focus of this paper is the conjugate heat transfer during vertical impingement of a two-dimensional (slot) submerged confined liquid jet using liquid ammonia as the working fluid. Numerical model for the heat transfer process has been developed. The solid region has been modeled along with the fluid region as a conjugate problem. Discrete heat sources have been used to study the overall effect on convective heat transfer. Simulation of discrete heat sources was done by introducing localized heat fluxes at various locations and their magnitudes being varied. Simulations are performed for two different substrate materials namely silicon and stainless steel. The equations solved in the liquid region included the conservation of mass, conservation of momentum, and conservation of energy. In the solid region, only the energy equation, which reduced to the heat conduction equation, had to be solved. The solid-fluid interface temperature showed a strong dependence on several geometric, fluid flow, and heat transfer parameters. The Nusselt number increased with Reynolds number. For a given flow rate, a higher heat transfer coefficient was obtained with smaller slot width and lower impingement height. For a constant Reynolds number, jet impingement height and plate thickness, a wider opening of the slot provided higher average heat transfer coefficient and higher average Nusselt number. A higher average heat transfer coefficient was seen at a smaller thickness, whereas a thicker plate provided a more uniform distribution of heat transfer coefficient. Higher thermal conductivity substrates also provided a more uniform heat distribution.

Rib Heat Transfer Coefficient Measurements in a Rib-Roughened Square Passage

1998 ◽  
Vol 120 (2) ◽  
pp. 376-385 ◽  
Author(s):  
G. J. Korotky ◽  
M. E. Taslim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Blockage Ratio ◽  
Average Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Average Heat ◽  
Heat Transfer Coefficients

Three staggered 90 deg rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested for pitch-to-height ratios of 5, 8.5, and 10, and for two distinct thermal boundary conditions of heated and unheated channel walls. Comparisons were made between the surface-averaged heat transfer coefficients and friction factors for ribs with rounded corners and those with sharp corners, reported previously. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared. It was concluded that: (a) For the geometries tested, the rib average heat transfer coefficient was much higher than that for the area between the ribs. For the sharp-corner ribs, the rib average heat transfer coefficient increased with blockage ratio. However, when the corners were rounded, the trend depended on the level of roundness. (b) High-blockage-ratio (e/Dh = 0.25) ribs were insensitive to the pitch-to-height ratio. For the other two blockage ratios, the pitch-to-height ratio of 5 produced the lowest heat transfer coefficient. Results of the other two pitch-to-height ratios were very close, with the results of S/e = 10 slightly higher than those of S/e = 8.5. (c) Under otherwise identical conditions, ribs in the furthest upstream position produced lower heat transfer coefficients for all cases except that of the smallest blockage ratio with S/e of 5. In that position, for the rib geometries tested, while the sharp-corner rib average heat transfer coefficients increased with the blockage ratio, the trend of the round-corner ribs depended on the level of roundness, r/e. (d) Thermal performance decreased with the blockage ratio. While the smallest rib geometry at a pitch-to-height ratio of 10 had the highest thermal performance, thermal performance of high blockage ribs at a pitch-to-height ratio of 5 was the lowest. (e) The general effects of rounding were a decrease in heat transfer coefficient for the midstream ribs and an increase in heat transfer coefficient for ribs in the furthest upstream position.

Rib Heat Transfer Coefficient Measurements in a Rib-Roughened Square Passage

1996 ◽  
Author(s):  
G. J. Korotky ◽  
M. E. Taslim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Blockage Ratio ◽  
Average Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Average Heat ◽  
Heat Transfer Coefficients

Three staggered 90° rib geometries corresponding to blockage ratios of 0.133, 0.167 and 0.25 were tested for pitch-to-height ratios of 5, 8.5 and 10, and for two distinct thermal boundary conditions of heated and unheated channel walls. Comparisons were made between the surface averaged heat transfer coefficients and friction factors for ribs with rounded corners and those with sharp comers, reported previously. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared. It was concluded that: a) For the geometries tested, the rib average heat transfer coefficient was much higher than that for the area between the ribs. For the sharp-corner ribs, the rib average heat transfer coefficient increased with blockage ratio. However, when the corners were rounded, the trend depended on the level of roundness. b) High blockage ratio (e/Dh=0.25) ribs were insensitive to the pitch-to-height ratio. For the other two blockage ratios, the pitch-to-height ratio of 5 produced the lowest heat transfer coefficient. Results of the other two pitch-to-height ratios were very close, with the results of S/e = 10 slightly higher than those of S/e=8.5. c) Under otherwise identical conditions, ribs in the furthest upstream position produced lower heat transfer coefficients for all cases except that of the smallest blockage ratio with S/e of 5. In that position, for the rib geometries tested, while the sharp-comer rib average heat transfer coefficients increased with the blockage ratio, the trend of the round-corner ribs depended on the level of roundness, r/e. d) Thermal performance decreased with the blockage ratio. While the smallest rib geometry at a pitch-to-height ratio of 10 had the highest thermal performance, thermal performance of high blockage ribs at a pitch-to-height ratio of 5 was the lowest. e) The general effects of rounding were a decrease in heat transfer coefficient for the midstream ribs and an increase in heat transfer coefficient for ribs in the furthest upstream position.

ANALYSIS OF METHODS FOR CALCULATING HEAT TRANSFER IN THERMOELECTRIC COOLING SYSTEMS FOR HEAT-STRESSED ELEMENTS

2021 ◽  
pp. 21-31
Author(s):  
С.В. Бородкин ◽  
А.В. Иванов ◽  
И.Л. Батаронов ◽  
А.В. Кретинин
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cooling System ◽  
Average Heat Transfer Coefficient ◽  
The Finite Element Method ◽  
Differential Heat ◽  
Average Heat ◽  
Principal Possibility

На основе уравнений теплопереноса в движущейся среде и соотношений теплопередачи в термоэлектрическом охладителе приведен сравнительный анализ методик расчета поля температуры в теплонапряженном элементе. Рассмотрены методики на основе: 1) теплового баланса, 2) среднего коэффициента теплоотдачи, 3) дифференциального коэффициента теплоотдачи, 4) прямого расчета в рамках метода конечных элементов. Установлено, что первые две методики не дают адекватного распределения поля температур, но могут быть полезны для определения принципиальной возможности заданного охлаждения с использованием термоэлектрических элементов. Последние две методики позволяют корректно рассчитать температурное поле, но для использования третьей методики необходим дифференциальный коэффициент теплоотдачи, который может быть найден из расчета по четвертой методике. Сделан вывод о необходимости комбинированного использования методик в общем случае. Методы теплового баланса и среднего коэффициента теплоотдачи позволяют определить принципиальную возможность использования термоэлектрического охлаждения конкретного теплонапряженного элемента (ТЭ). Реальные параметры системы охлаждения должны определяться в рамках комбинации методов дифференциального коэффициента теплоотдачи и конечных элементов (МКЭ). Первый из них позволяет определить теплонапряженные области и рассчитать параметры системы охлаждения, которые обеспечивают тепловую разгрузку этих областей. Второй метод используется для проведения численных экспериментов по определению коэффициента теплоотдачи реальной конструкции The article presents on the basis of the equations of heat transfer in a moving medium and the relations of heat transfer in a thermoelectric cooler, a comparative analysis of methods for calculating the temperature field in a heat-stressed element. We considered methods based on: 1) heat balance, 2) average heat transfer coefficient, 3) differential heat transfer coefficient, 4) direct calculation using the finite element method. We established that the first two methods do not provide an adequate distribution of the temperature field but can be useful for determining the principal possibility of a given cooling using thermoelectric elements. The last two methods allow us to correctly calculate the temperature field; but to use the third method, we need a differential heat transfer coefficient, which can be found from the calculation using the fourth method. We made a conclusion about the need for combined use of methods in a general case. The methods of thermal balance and average heat transfer coefficient allow us to determine the principal possibility of using thermoelectric cooling of a specific heat-stressed element. The actual parameters of the cooling system should be determined using a combination of the differential heat transfer coefficient and the finite element method. The first of them allows us to determine the heat-stressed areas and calculate the parameters of the cooling system that provide thermal discharge of these areas. The second method is used to perform numerical experiments to determine the heat transfer coefficient of a real structure

An Experimental Investigation of the Rib Surface-Averaged Heat Transfer Coefficient in a Rib-Roughened Square Passage

1997 ◽  
Vol 119 (2) ◽  
pp. 381-389 ◽  
Author(s):  
M. E. Taslim ◽  
C. M. Wadsworth
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Blockage Ratio ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient

Turbine blade cooling, a common practice in modern aircraft engines, is accomplished, among other methods, by passing the cooling air through an often serpentine passage in the core of the blade. Furthermore, to enhance the heat transfer coefficient, these passages are roughened with rib-shaped turbulence promoters (turbulators). Considerable data are available on the heat transfer coefficient on the passage surface between the ribs. However, the heat transfer coefficients on the surface of the ribs themselves have not been investigated to the same extent. In small aircraft engines with small cooling passages and relatively large ribs, the rib surfaces comprise a large portion of the passage heat transfer area. Therefore, an accurate account of the heat transfer coefficient on the rib surfaces is critical in the overall design of the blade cooling system. The objective of this experimental investigation was to conduct a series of 13 tests to measure the rib surface-averaged heat transfer coefficient, hrib, in a square duct roughened with staggered 90 deg ribs. To investigate the effects that blockage ratio, e/Dh and pitch-to-height ratio, S/e, have on hrib and passage friction factor, three rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested for pitch-to-height ratios of 5, 7, 8.5, and 10. Comparisons were made between the rib average heat transfer coefficient and that on the wall surface between two ribs, hfloor, reported previously. Heat transfer coefficients of the upstream-most rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared. It is concluded that: 1 The rib average heat transfer coefficient is much higher than that for the area between the ribs; 2 similar to the heat transfer coefficient on the surface between the ribs, the average rib heat transfer coefficient increases with the blockage ratio; 3 a pitch-to-height ratios of 8.5 consistently produced the highest rib average heat transfer coefficients amongst all tested; 4 under otherwise identical conditions, ribs in upstream-most position produced lower heat transfer coefficients than the midchannel positions, 5 the upstream-most rib average heat transfer coefficients decreased with the blockage ratio; and 6 thermal performance decreased with increased blockage ratio. While a pitch-to-height ratio of 8.5 and 10 had the highest thermal performance for the smallest rib geometry, thermal performance of high blockage ribs did not change significantly with the pitch-to-height ratio.

Convective Heat Transfer Distribution on the Surface of an Electronic Package

1994 ◽  
Vol 116 (1) ◽  
pp. 49-54 ◽  
Author(s):  
R. A. Wirtz ◽  
Ashok Mathur
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Average Heat Transfer Coefficient ◽  
Number Range ◽  
Electronic Package ◽  
Average Heat

Measurements of the distribution of convective heat transfer over the five exposed faces of a low profile electronic package are described. The package, of square planform and length-to-height ratio, L/a = 6, is part of a regular array of such elements attached to one wall of a low aspect ratio channel. The coolant is air, and experiments are described for the Reynolds number range, 3000<Re<7000. The average heat transfer coefficient for the top face is found to be nearly equal to the overall average heat transfer coefficient for the element. The average heat transfer coefficient for the upstream face and two side faces are higher than the overall average by approximately 30–40 percent and 20–30 percent, respectively while that for the downstream face is 20–30 percent less than the overall average. Furthermore, the distribution in local heat transfer coefficient over the five surfaces of the element is approximately independent of variations in Reynolds number.

Non-Intrusive Heat Transfer Coefficient Determination in a Packed Bed of Spheres

2010 ◽  
Author(s):  
David J. Geb ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Generation ◽  
Packed Bed ◽  
Computational Procedure ◽  
Spherical Particles ◽  
Average Heat Transfer Coefficient ◽  
Heat Generation Rate ◽  
Average Heat

Non-intrusive measurements of the internal average heat transfer coefficient [1] in a randomly packed bed of spherical particles are made. It is desired to establish accurate results for this simple geometry so that the method used can then be extended to determine the heat transfer characteristics in any porous medium, such as a compact heat exchanger. Under steady, one-dimensional flow the spherical particles are subjected to a step change in volumetric heat generation rate via induction heating. The fluid temperature response is measured. The average heat transfer coefficient is determined by comparing the results of a numerical simulation based on volume averaging theory with the experimental results. More specifically, the average heat transfer coefficient is adjusted within the computational procedure until the predicted values of the fluid outlet temperature match the experimental values. The only information needed is the basic material properties, the flow rate, and the experimental data. The computational procedure alleviates the need for solid and fluid phase temperature measurements, which are difficult to make and can disturb the solid-fluid interaction. Moreover, a simple analysis allows us to proceed without knowledge of the heat generation rate, which is difficult to determine due to challenges associated with calibrating an inductively-coupled, sample specific, heat generation system. The average heat transfer coefficient was determined, and expressed in terms of the Nusselt number, over a Reynolds number range of 20–600. The results compared favorably to the work of Whitaker [2] and Kays and London [3]. The success of this method, in determining the average heat transfer coefficient in a randomly packed bed of spheres, suggests that it can be used to determine the average heat transfer coefficient in other porous media.

On the Scalability of Liquid Microjet Array Impingement Cooling for Large Area Systems

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Avijit Bhunia ◽  
C. L. Chen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Heat Source ◽  
Transfer Coefficient ◽  
High Heat Flux ◽  
Average Heat Transfer Coefficient ◽  
Large Area ◽  
Impingement Cooling ◽  
Average Heat

The necessity for an efficient thermal management system covering large areas is growing rapidly with the push toward more electric systems. A significant amount of research over the past 2 decades has conclusively proved the suitability of jet, droplet, or spray impingement for high heat flux cooling. However, all these research consider small heat source areas, typically about a few cm2. Can a large array of impingement pattern, covering a much wider area, achieve similar heat flux levels? This article presents liquid microjet array impingement cooling of a heat source that is about two orders of magnitude larger than studied in the previous works. Experiments are carried out with 441 jets of de-ionized water and a dielectric liquid HFE7200, each 200 μm diameter. The jets impinge on a 189 cm2 area surface, in free surface and confined jet configurations. The average heat transfer coefficient values of the present experiment are compared with correlations from the literature. While some correlations show excellent agreement, others deviate significantly. The ensuing discussion suggests that the post-impingement liquid dynamics, particularly the collision between the liquid fronts on the surface created from surrounding jets, is the most important criterion dictating the average heat transfer coefficient. Thus, similar thermal performance can be achieved, irrespective of the length scale, as long as the flow dynamics are similar. These results prove the scalability of the liquid microjet array impingement technique for cooling a few cm2 area to a few hundred cm2 area.

Sign in / Sign up

Export Citation Format

Share Document