Numerical Optimisation of Heat Transfer using Combined Steady and Pulsating Jet Array (original) (raw)
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Numerical Optimisation of Heat Transfer using Pulsating Jet Array with Phase Shift
The advancement in science had led to highly complicated electronic devices and at the same time the size of such devices is getting reduced day by day. The amount of heat generated by these devices is increasing in par with its complexity. The efficiency of electronics devices decreases with increase in temperature. The cooling of these devices to their normal working temperature is a great challenge since the area available for heat transfer will be very less and there is restricted movement of air. This paper deals with jet impingement cooling, in which high velocity jets are used for removal of heat from a surface. The jets are arranged in the form of a staggered array and are pulsating in nature. To increase the turbulence in the flow domain the jets are pulsated at a phase shift. The study is carried out at different frequencies. The objective of this study is to compare the heat transfer at different combinations of frequencies and angles of phase shift and find the combination at which the heat transfer is maximum. The study is done using computational fluid dynamics software tool ANSYS Fluent version 14.
Thermal Management Using Pulsating Jet Cooling Technology
Journal of Physics: Conference Series, 2014
The existing methods of heat removal from compact electronic devises are known to be deficient as the evolving technology demands more power density and accordingly better cooling techniques. Impinging jets can be used as a satisfactory method for thermal management of electronic devices with limited space and volume. Pulsating flows can produce an additional enhancement in heat transfer rate compared to steady flows. This article is part of a comprehensive experimental and numerical study performed on pulsating jet cooling technology. The experimental approach explores heat transfer performance of a pulsating air jet impinging onto a flat surface for nozzle-to-surface distances 1 ≤ H/D ≤ 6, Reynolds numbers 1,300 ≤ Re ≤ 2,800 pulsation frequency 2Hz ≤ f ≤ 65Hz, and Strouhal number 0.0012 ≤ Sr = fD/U m ≤ 0.084. The time-resolved velocity at the nozzle exit is measured to quantify the turbulence intensity profile. The numerical methodology is firstly validated using the experimental local Nusselt number distribution for the steady jet with the same geometry and boundary conditions. For a time-averaged Reynolds number of 6,000, the heat transfer enhancement using the pulsating jet for 9Hz ≤ f ≤ 55Hz and 0.017 ≤ Sr ≤ 0.102 and 1 ≤ H/D ≤ 6 are calculated. For the same range of Sr number, the numerical and experimental methods show consistent results.
2010
The problem of cooling of electronic components has become a subject of special interest in recent years due to the increasing capacity and rapidly decreasing size of electronic components. Direct contact cooling using multiple jet impingement is considered as the most effective method. The heat transfer problem is complex and better understanding of the jet impingement method is essential for proper application of this method for electronic cooling. Investigations were carried out using electrically heated test plate. Heat flux in the range of 25 to 200 W/cm2, which is a typical requirement for cooling high power electronic components was dissipated using 0.25 mm and 0.5 mm diameter air jets arranged in 7 x 7 array with a pitch of 3 mm. Tests were performed in the Reynolds number range of 1200 to 4500. Results show significant increase in heat transfer co-efficient with increase in heat flux.
Impingement Heat Transfer with array of Multiple air Jets Dr
2016
The use of impinging air jets in electronic thermal management is attracting some consideration due to their very high heat transfer coefficients. Direct contact cooling using multiple jet impingements is considered as the most effective method. The heat transfer problem is complex and better understanding of the jet impingement method is essential for proper application of this method for electronic cooling. In this investigation an experimental study of cooling capabilities of impinging air jet array is presented. Investigations were carried out using electrically heated test plate. Heat flux in the range of 25 to 200W/cm, which is a typical requirement for cooling high power electronic components was dissipated using 0.25mm and 0.5mm diameter air jets arranged in 7X7 array with a pitch of 3mm. Tests were performed in the Reynolds number range of 1200 to 4500. Results shows higher values of heat transfer coefficient are obtained with the lower diameter jets.
2013
This paper describes the experimental results on heat transfer characteristics of array of jet impingement cooling of a steel plate. The experiments were conducted on a stationary electrically heated steel plate. A commercially available shower was used to generate array of jets. The Time dependent temperature profiles were recorded by NI-cRIO DAS at the desired locations of the bottom surface of the plate embedded with K-type thermocouples. The controlling parameters considered in the experiments were water pressure, mass impingement density, mass flow rate, shower exit to surface distance respectively. Effects of these parameters on cooling rate were analysed through plots in the MS-EXCEL environments. The experimental results showed a dramatic improvement of heat transfer rate from the surface and the results established good optimal cooling strategies.
Enhancement of Heat Transfer From Hot Metal Surface by Impingement of Array of Jets
The jet impingement cooling process was experimented at different parametric conditions. Experiments were carried out on a stationary hot steel plate under an array of free jets to determine the heat transfer characteristics. Array of jets was allowed to fall freely on the upper surface of the hot plate after achieving the desired initial temperature. K-type thermocouples were embedded at the bottom surface of the plate at different locations. With the help of NI-cRIO DAS the time dependent transient temperature data were acquired. Influence of several experimental conditions such as water pressure, impingement density, water flow rate, shower exit to target distance on heat transfer mechanism were observed by analyzing the generated plots in MS EXCEL environments. Experimental results revealed that the array jet cooling system is one of the promising techniques to achieve very higher cooling rate from the steel surface. The maximum cooling rate achieved was of 4.52 in its non-dimen...
Experimental Study of Heat Transfer Coefficients on the Plate with Confined Impinging Jet Array
Advanced Science Letters, 2012
Experiments were conducted to investigate the cooling manner of an ultra-thick hot aluminum alloy plate during multistage quenching. Cooling curves and heat flux curves of different rapid quenching flux varied from 23 to 40 L min −1 and were analyzed in detail. In this investigation, cooling process was divided into the following four steps: (I) starting step, (II) rapid cooling step, (III) slow cooling step, and (IV) stopping step. Based on the curves, the calculation method for surface transfer coefficient was provided, and the effects of coefficient on surface temperature and quenching flux were discussed. Results showed that the transfer coefficient disagreed with heat flux and that it is a nonlinear function of surface temperature. The highest coefficient was observed not in the rapid cooling step with the largest heat flux but in the slow cooling step with lower heat flux. The coefficient increased with surface temperature ranging from 480 to 150°C, and a coefficient peak appeared in the temperature range of 150-100°C. The coefficient also increased with quenching flux. Finally, a simulation was performed using the finite element method to verify the reliability of the coefficient results, which showed good agreement with the measurement values.
Effect of Cross-Shaped Circular Jet Array on Impingement Heat Transfer
Volume 4: Heat Transfer, Parts A and B, 2012
The purpose of this study is to clarify heat transfer characteristics for the high cooling performance with multiple jet impingement. In the present study, the influence of the interaction among adjacent impinging jets on heat transfer of target surface is experimentally investigated. The study is focused on the effect of jet injection shape on the heat transfer. 3×3 square array of cross-shaped circular jet is tested. Injection distances L are 2 and 4 jet hole diameters, and jet-to-jet spacing S are 4, 6 and 8 jet hole diameters. Experiments are conducted for a constant Reynolds number Re=4,680 based on the jet hole diameter. Steady state thermochromic liquid crystal technique is employed to measure local and area averaged Nusselt numbers. The flow field is visualized by smoke-wire and oil flow techniques. It is found that the cross-shaped circular jet array improves heat transfer at the intermediate area enclosed by four impinging jets compared to that of circular jet array at the narrow injection distance. In the case of cross-shaped circular jet array, the wall jet produces a stronger turbulence than that of circular jet, which makes the heat transfer push up toward the apex of square detachment line at injection distance L/D=2 and jet-to-jet spacing S/D=6 and 8.
Journal of Heat Transfer, 2016
In this paper, an optimization was performed to achieve uniform distribution of convective heat transfer coefficient over a target plate using two impinging slot (air) jets. The objective function is the root mean square error (Erms) of the local Nusselt distribution computed by computational fluid dynamic (CFD) simulations from desired Nusselt numbers. This pattern search minimized this objective function. Design variables are nozzle widths, jet-to-jet distance, jet-to-target plate distance, frequency of pulsations (for pulsating jets), and the flow rate. First, an inverse design is performed for two steady jets for simplicity and the obtained errors for three different desired Nusselt numbers, NuD = 7, 10, and 13, were 20.73%, 20.08%, and 22.92%, respectively. Uniform distribution of heat transfer coefficient for two steady jets was not achieved. Thus, two pulsating jets are considered. The range of design variables for pulsating state is as same as steady-state and heat transfer ...
Study of heat transfer charecterstics of a multiple jet cooling
INTERNATIONAL JOURNAL OF RECENT TRENDS IN ENGINEERING & RESEARCH, 2020
In this work an experimental study of cooling capabilities of impinging water and air jet array is presented. Investigations were carried out using electrically heated test plate. Heat flux in the range of 25 to 200W/cm 2 , which is a typical requirement for cooling high power electronic components was dissipated using 0.25mm and 0.5mm diameter water and air jets arranged in 7X7 array with a pitch of 3mm. Tests were performed in the Reynolds number range of 1200 to 4500. Results shows higher values of heat transfer coefficient are obtained.Theeffect of positioning of jets are insignificant.