Heat transfer and entropy generation in air jet impingement on a model rough surface

2016 ◽  
Vol 72 ◽  
pp. 48-56 ◽  
Author(s):  
Peng Xu ◽  
Agus P. Sasmito ◽  
Shuxia Qiu ◽  
Arun S. Mujumdar ◽  
Long Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Rough Surface ◽  
Entropy Generation ◽  
Jet Impingement ◽  
Air Jet

Heat transfer of multi-slot nozzle air jet impingement with different Reynolds number

2020 ◽  
pp. 116470
Author(s):  
Jinqi Zhu ◽  
Ruifeng Dou ◽  
Ye Hu ◽  
Shixing Zhang ◽  
Xuyun Wang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Jet Impingement ◽  
Slot Nozzle ◽  
Air Jet

Experimental Measurements of the Flow and Heat Transfer of a Square Jet Impinging on an Array of Square Pin Fins

2002 ◽  
Author(s):  
Johnny S. Issa ◽  
Alfonso Ortega
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Flow Behavior ◽  
Jet Impingement ◽  
Tip Clearance ◽  
Heat Sinks ◽  
Clearance Ratio ◽  
Cross Sectional ◽  
Pressure Loss Coefficient ◽  
Air Jet

An experimental investigation was conducted to explore the flow behavior, pressure drop, and heat transfer due to free air jet impingement on square in-line pin fin heat sinks (PFHS) mounted on a plane horizontal surface. A parametrically consistent set of aluminum heat sinks with fixed base dimension of 25 × 25 mm was used, with pin heights varying between 12.5 mm and 22.5 mm, and fin thickness between 1.5 mm and 2.5 mm. A 6:1 contracting nozzle having a square outlet cross sectional area of 25 × 25 mm was used to blow air at ambient temperature on the top of the heat sinks with velocities varying from 2 to 20 m/s. The ratio of the gap between the jet exit and the pin tips to the pin height, the so-called tip clearance ratio, was varied from 0 (no tip clearance) to 1. The stagnation pressure recovered at the center of the heat sink was higher for tall pins than short pins. The pressure loss coefficient showed a little dependence on Re, increased with increasing pin density, and pin diameter, and decreased with increasing pin height and clearance ratio. The overall base-to-ambient thermal resistance decreased with increasing Re number, pin density and pin diameter. Surprisingly, the dependence of the thermal resistance on the pin height and clearance ratio was shown to be mild at low Re, and to vanish at high Re number.

scholarly journals Enhanced heat transfer characteristics of conjugated air jet impingement on a finned heat sink

2017 ◽  
Vol 21 (1 Part A) ◽  
pp. 279-288 ◽  
Author(s):  
Shuxia Qiu ◽  
Peng Xu ◽  
Liping Geng ◽  
Arun Mujumdar ◽  
Zhouting Jiang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Cooling System ◽  
Flow Characteristics ◽  
Jet Impingement ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Air Jet

Air jet impingement is one of the effective cooling techniques employed in micro-electronic industry. To enhance the heat transfer performance, a cooling system with air jet impingement on a finned heat sink is evaluated via the computational fluid dynamics method. A two-dimensional confined slot air impinging on a finned flat plate is modeled. The numerical model is validated by comparison of the computed Nusselt number distribution on the impingement target with published experimental results. The flow characteristics and heat transfer performance of jet impingement on both of smooth and finned heat sinks are compared. It is observed that jet impingement over finned target plate improves the cooling performance significantly. A dimensionless heat transfer enhancement factor is introduced to quantify the effect of jet flow Reynolds number on the finned surface. The effect of rectangular fin dimensions on impingement heat transfer rate is discussed in order to optimize the cooling system. Also, the computed flow and thermal fields of the air impingement system are examined to explore the physical mechanisms for heat transfer enhancement.

Experimental Investigation of Air–Water Mist Jet Impingement Cooling Over a Heated Cylinder

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Chunkyraj Khangembam ◽  
Dushyant Singh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stagnation Point ◽  
Jet Impingement ◽  
Water Mist ◽  
Heated Cylinder ◽  
Air Jet ◽  
The Heat Transfer Coefficient

Experimental investigation on heat transfer mechanism of air–water mist jet impingement cooling on a heated cylinder is presented. The target cylinder was electrically heated and was maintained under the boiling temperature of water. Parametric studies were carried out for four different values of mist loading fractions, Reynolds numbers, and nozzle-to-surface spacings. Reynolds number, Rehyd, defined based on the hydraulic diameter, was varied from 8820 to 17,106; mist loading fraction, f ranges from 0.25% to 1.0%; and nozzle-to-surface spacing, H/d was varied from 30 to 60. The increment in the heat transfer coefficient with respect to air-jet impingement is presented along with variation in the heat transfer coefficient along the axial and circumferential direction. It is observed that the increase in mist loading greatly increases the heat transfer rate. Increment in the heat transfer coefficient at the stagnation point is found to be 185%, 234%, 272%, and 312% for mist loading fraction 0.25%, 0.50%, 0.75%, and 1.0%, respectively. Experimental study shows identical increment in stagnation point heat transfer coefficient with increasing Reynolds number, with lowest Reynolds number yielding highest increment. Stagnation point heat transfer coefficient increased 263%, 259%, 241%, and 241% as compared to air-jet impingement for Reynolds number 8820, 11,493, 14,166, and 17,106, respectively. The increment in the heat transfer coefficient is observed with a decrease in nozzle-to-surface spacing. Stagnation point heat transfer coefficient increased 282%, 248%, 239%, and 232% as compared to air-jet impingement for nozzle-to-surface spacing of 30, 40, 50, and 60, respectively, is obtained from the experimental analysis. Based on the experimental results, a correlation for stagnation point heat transfer coefficient increment is also proposed.

Heat Transfer Characteristic Analysis of Confined Impinging Jet Cooling System with Micro-Scale Round Nozzles

2010 ◽  
Vol 171-172 ◽  
pp. 799-803
Author(s):  
Chang Hong Wang ◽  
Ying Chen ◽  
Juan Tu
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Transfer Characteristic ◽  
Characteristic Analysis ◽  
Chip Cooling ◽  
Jet Cooling ◽  
Air Jet ◽  
Nozzle Type

In order to investigate the heat transfer of confined impinging jet with tiny size round nozzle, a bakelite laminate was used as the heat transfer surface of simulated chip. The thermocouples were mounted symmetrically along the diagonal of the laminate to measure the temperature distribution of the surface. The parameters such as Reynolds number (Re) and ratio of height-to-diameter were changed to investigate the radial distribution of Nu and the characteristics of heat transfer in stagnant section. The results show that hear transfer coefficient at stagnation point is maximal. It is decreased with the increases of the radial jet distance, but increased with Re and impinging height. Moreover, the effect of single-nozzle type is stronger than that of multi-nozzle type in the cases of same air flow. These studies will give a way for the application of air jet impingement in the electronics chip cooling.

scholarly journals Heat Transfer From a Finned Surface in Ducted Air Jet Suction and Impingement

1999 ◽  
Vol 122 (3) ◽  
pp. 282-285 ◽  
Author(s):  
Luis A. Brignoni ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Jet Impingement ◽  
Target Distance ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Air Jet ◽  
Finned Surface ◽  
Different Diameters

Experimental measurements were obtained to characterize the thermal performance of ducted air suction in conjunction with a pin-fin heat sink. Four single nozzles of different diameters and two multiple-nozzle arrays were studied at a fixed nozzle-to-target distance, for different turbulent Reynolds numbers 5000⩽Re⩽20,000. Variations of nozzle-to-target distance, i.e., open area, in ducted suction were found to have a strong effect on heat transfer especially with the larger diameter single nozzle and both multiple-nozzle arrays. Enhancement factors were computed with the heat sink in suction flow, relative to a bare surface, and were in the range of 8.3 to 17.7, with the largest value being obtained for the nine-nozzle array. Results from the present study on air jet suction are compared with previous experiments with air jet impingement on the pin-fin heat sink. Average heat transfer coefficients and thermal resistance values are reported for the heat sink as a function of Reynolds number, air flow rate, and pumping power. [S1043-7398(00)00903-8]

scholarly journals Experimental investigation of heat transfer of flowing liquid film with inserted metal foam layer subjected to air jet impingement

2019 ◽  
Vol 23 (5 Part B) ◽  
pp. 3093-3104
Author(s):  
Yunsong Zhang ◽  
Wei Chen ◽  
Wei Li ◽  
Xiao Zhu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Porous Layer ◽  
Metal Foam ◽  
Jet Impingement ◽  
Heated Wall ◽  
Flowing Liquid ◽  
Air Jet

In this paper, coupling the air jet impingement and the copper metal foam above flowing liquid film were employed to enhance the heat transfer. The thickness of flowing liquid film can be controlled owing to the application of the metal foam above the film, and its solid matrix extends the air-liquid-solid interface of heating surface. The evaporated water can be supplied by the capillary force in the porous layer. The experiments were conducted to investigate the performances of the flowing liquid film with inserted porous layer subjected to impinging jet air. The air jet velocity, the flow rate and thicknesses of the liquid film as well as the porosity of metal foam influence the surface temperature of heated wall and the corresponding local heat transfer coefficient greatly. The change ratios of heat transfer coefficient due to the above factors were presented. More cooling can be obtained on the heated wall in the flowing liquid film with inserted porous layer subjected to impinging jet air while the higher liquid film velocity and air jet velocity, the thinner liquid film and the lower porosity of metal foam occur.

An Experimental Setup for Multiple Air Jet Impingement Over a Surface

2018 ◽  
Author(s):  
Flávia V. Barbosa ◽  
João P. V. Silva ◽  
Pedro E. A. Ribeiro ◽  
Senhorinha F. C. F. Teixeira ◽  
Delfim F. Soares ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Thermal Design ◽  
Test Facility ◽  
Experimental Setup ◽  
Optimized Design ◽  
Transfer Coefficients ◽  
Reflow Soldering ◽  
Air Jet ◽  
High Heat Transfer

Air jet impingement technology receives considerable attention due to its high performance for heat transfer enhancement in thermal equipment, providing high heat transfer rates. Due to its inherent characteristics of high average heat transfer coefficients and uniformity of the heat transfer over the impinging surface, this technology is implemented in a variety of engineering applications and industrial processes, such as reflow soldering, drying of textile, cooling of turbojet engine blades and fusion reactors. Multiple jet impingement involves several variables such as: jets arrangement, jet diameter, nozzle-to-surface distance, nozzle shape, jet-to-jet spacing, jet velocity and Reynolds number, among others. However, the total control of all these parameters is still one of the remarkable issues of the thermal design of jet impingement systems. In some industries that have implemented this technology in their processes, such as reflow soldering, the range of values of these variables are established through empiricism and “trial and error” techniques. To improve the process and to reduce time and costs, it is fundamental to define accurately all the process parameters in order to obtain an optimized design with a high degree of control of the heat transfer over the target surface. To perform an accurate and complete study of the multiple jet impingement variables for a specific application, the development of both experimental and numerical studies is fundamental in order to obtain reliable results. In that sense, this work reports the project and construction of a purpose-built test facility which has been commissioned, using a PIV system. This experimental setup is based on the oven used in the reflow soldering process. The optimization of the multiple jets geometry which is integrated in the experimental setup is herein described and discussed both experimentally and numerically. The numerical simulation of the jet impingement inside the oven was conducted using the ANSYS software, specially designed to predict the fluid behavior. Regarding the relevance of the multiple jet impingement, this work intends to improve the knowledge in this field and to give reliable and scientifically proved answers to the industries that apply this technology in their processes.

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