Effect of compressibility and nozzle configuration on heat transfer by impinging air jet over a smooth plate

2016 ◽  
Vol 101 ◽  
pp. 293-307 ◽  
Author(s):  
Ravish Vinze ◽  
S. Chandel ◽  
M.D. Limaye ◽  
S.V. Prabhu
Author(s):  
Jinqi Zhu ◽  
Ruifeng Dou ◽  
Ye Hu ◽  
Shixing Zhang ◽  
Xuyun Wang

2014 ◽  
Vol 663 ◽  
pp. 322-328 ◽  
Author(s):  
Ali Ahmed Gitan ◽  
Rozli Zulkifli ◽  
Kamaruzaman Sopian ◽  
Shahrir Abdullah

The problem of environmental pollution and depletion of fossil fuel can be reduced in automotives by using an alternative bio-fuel and improve the ignition process in engine. Both solutions need to use the fuel preheating technique. This work presents the idea of fuel preheating by using exhaust impingement on the fuel tank. Heat transfer between twin pulsating hot air jets and flat copper target was investigated as an application for preheating of automotive fuel to improve ignition process in the engine. The nozzle of 20 mm was used to produce air jet of Reynolds number, Re ≃ 5500 and a temperature of 54°C. The impinged target was imposed to still air surrounding at temperature of 24°C. Pulsating frequencies of 10-50 Hz were applied on air jets by using twin pulsating jet mechanism. The effect of pulsation frequency on heat transfer was measured using IR camera and heat flux-temperature micro foil sensor. The results obtained by both of these methods showed well agreement. Also, the results revealed significant influence of flow rate difference between steady and pulsating jet cases. In addition, the highest Nusselt number, Nu ≃ 7.2, was obtained at pulsation frequency of 20 Hz.


Author(s):  
Johnny S. Issa ◽  
Alfonso Ortega

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.


1991 ◽  
Vol 113 (4) ◽  
pp. 858-864 ◽  
Author(s):  
C. Gau ◽  
C. M. Chung

Experiments are performed to study surface curvature effects on the impingement cooling flow and the heat transfer processes over a concave and a convex surface. A single air jet issuing from different size slots continuously impinges normally on the concave side or the convexside of a heated semicylindrical surface. An electrical resistance wire is used to generate smoke, which allows us to visualize the impinging flow structure. The local heat transfer Nusselt number along the surfaces is measured. For impingement on a convex surface, three-dimensional counterrotating vortices on the stagnation point are initiated, which result in the enhancement of the heat transfer process. For impingement on a concave surface, the heat transfer Nusselt number increases with increasing surface curvature, which suggests the initiation of Taylor–Go¨rtler vortices along the surface. In the experiment, the Reynolds number ranges from 6000 to 350,000, the slot-to-plate spacing from 2 to 16, and the diameter-to-slot-width ratio D/b from 8 to 45.7. Correlations of both the stagnation point and the average Nusselt number over the curved surface, which account for the surface curvature effect, are presented.


2017 ◽  
Vol 21 (1 Part A) ◽  
pp. 279-288 ◽  
Author(s):  
Shuxia Qiu ◽  
Peng Xu ◽  
Liping Geng ◽  
Arun Mujumdar ◽  
Zhouting Jiang ◽  
...  

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.


Author(s):  
Patricia Streufert ◽  
Terry X. Yan ◽  
Mahdi G. Baygloo

Local turbulent convective heat transfer from a flat plate to a circular impinging air jet is numerically investigated. The jet-to-plate distance (L/D) effect on local heat transfer is the main focus of this study. The eddy viscosity V2F turbulence model is used with a nonuniform structured mesh. Reynolds-Averaged Navier-Stokes equations (RANS) and the energy equation are solved for axisymmetric, three-dimensional flow. The numerical solutions obtained are compared with published experimental data. Four jet-to-plate distances, (L/D = 2, 4, 6 and 10) and seven Reynolds numbers (Re = 7,000, 15,000, 23,000, 50,000, 70,000, 100,000 and 120,000) were parametrically studied. Local and average heat transfer results are analyzed and correlated with Reynolds number and the jet-to-plate distance. Results show that the numerical solutions matched experimental data best at low jet-to-plate distances and lower Reynolds numbers, decreasing in ability to accurately predict the heat transfer as jet-to-plate distance and Reynolds number was increased.


1990 ◽  
Vol 112 (1) ◽  
pp. 97-104 ◽  
Author(s):  
A. Demir

A thorough investigation of the existing texturing nozzles will, no doubt, lead to the design of improved nozzles. This paper reports the experimental research carried on the scaled-up versions of the T100 HemaJet with varying geometrical configurations, being the exit shape, situation, and inclination of the inlet holes, and the ratio of the incoming holes area to the nozzle’s main duct area. It has been found that the exit shape has virtually no effect on the airflow whilst other parameters contribute to the formation of the emerging jet which performs the texturing.


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