scholarly journals Average Heat Transfer Coefficient in the Circular Model Airway Having Ring Type Roughness Elements with Semicircular Cross-section

1971 ◽  
Vol 87 (994) ◽  
pp. 11-16
Author(s):  
Yukio YOSHIZAWA ◽  
Toshio KAWASHIMA ◽  
Hiroshi KIYOHASHI
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cross Section ◽  
Average Heat Transfer Coefficient ◽  
Average Heat ◽  
Ring Type ◽  
Circular Model ◽  
Roughness Elements ◽  
Semicircular Cross Section

Experimental Thermal Characterization of Pin Fin Heat Sinks With Top and Side Bypass

2005 ◽  
Author(s):  
Ning Lei ◽  
Alfonso Ortega
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Thermal Resistance ◽  
Transfer Coefficient ◽  
Cross Section ◽  
Heat Sinks ◽  
Average Heat Transfer Coefficient ◽  
Average Heat ◽  
Pin Fin

Extensive tests were conducted to obtain thermal characteristics of pin fin heat sinks with pins of square cross-section under different top and side bypass conditions. A consistent set of aluminum heat sinks with constant planform area and variable pitch were utilized. The heat sinks were tested in an adjustable cross-section wind tunnel, which provides 0 to 1 top and 0 to 10 side clearance ratios. The base temperature of the heat sinks was measured under constant heat flux. The overall thermal resistance and average heat transfer coefficient of the heat sinks were calculated and the influence of top and side bypass was explored. The thermal experimental data were consistent with the previous hydraulic experimental data. With the increase of flow velocity, flow transition from laminar to turbulent flow was revealed by the thermal resistance data. It was found that the average heat transfer coefficient depends strongly on the flow velocity through the heat sinks. Heat sinks with side clearance only result in smaller overall thermal resistance compared to top clearance only at the same clearance ratio. In some cases, the heat sinks with a small side clearance had better thermal performance than the same heat sinks without clearance. The empirical equation for infinitely long tube bundles of circular cross-section was used to correlate the thermal experimental data.

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

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.

Study on Free Convection Heat Transfer in a Finned Tube Array

2015 ◽  
Vol 23 (01) ◽  
pp. 1550007 ◽  
Author(s):  
Ryoji Katsuki ◽  
Tsutomu Shioyama ◽  
Chikako Iwaki ◽  
Tadamichi Yanazawa
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Finned Tube ◽  
Average Heat Transfer Coefficient ◽  
Average Heat ◽  
Finned Tubes ◽  
Air Cooled Heat Exchanger ◽  
The Heat Transfer Coefficient

We have been developing a free convection air cooled heat exchanger without power supply to improve economic efficiency and mechanical reliability. However, this heat exchanger requires a larger installation area than the forced draft type air cooled heat exchanger since a large heating surface is needed to compensate for the small heat transfer by natural convection. Therefore, we have been investigating a heat exchanger consisting of an array of finned tubes and chimney to increase the heat transfer coefficient. Since the heat transfer characteristics of finned tube arrays have not been clarified, we conducted experiments with a finned tube array to determine the relation between the configuration of finned tubes and the heat transfer coefficient of a tube array. The results showed that the average heat transfer coefficient increased with pitch in the vertical direction, and became constant when the pitch was over five times the fin diameter. The average heat transfer coefficient was about 1.4 times higher than that of a single finned tube in free space. The ratio of the average heat transfer coefficient of the finned tube array with chimney to that of a single finned tube was found to be independent of the difference in temperature between the tube surface and air.

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.

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