Extensive Parametric Study of Heat Transfer to Arrays of Oblique Impinging Jets With Phase Change

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Robert A. Buchanan ◽  
Timothy A. Shedd
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Parametric Study ◽  
Single Phase ◽  
Flow Behavior ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Phase Correlation ◽  
Two Phase

This work presents the single- and two-phase results of a parametric study investigating the performance of oblique jet arrays impinging at 45 deg on a 3.63 cm2 square copper heater surface using R-245fa. It was found that the parameters that most impact heat transfer changed as the system progressed from single- to two-phase flow behavior. The single-phase performance was governed by the jet geometry and the volumetric flow rate, while in the two-phase region, heat transfer performance was primarily affected by the fluid conditions and the heat flux applied. A single-phase correlation was developed to capture the low heat flux response, and the two-phase results were well-correlated by a pool boiling correlation. A new general correlation for jet impingement heat transfer with phase change is presented combining these correlations. Critical heat flux (CHF) data were compared with literature correlations and a new correlation was developed for arrays of boiling jets.

Single-Phase and Boiling Cooling of Small Pin Fin Arrays by Multiple Nozzle Jet Impingement

1996 ◽  
Vol 118 (1) ◽  
pp. 21-26 ◽  
Author(s):  
David Copeland
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Single Phase ◽  
Jet Impingement ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Aspect Ratios ◽  
Pin Fin Arrays

Experimental measurements of multiple nozzle submerged jet array impingement single-phase and boiling heat transfer were made using FC-72 and 1 cm square copper pin fin arrays, having equal width and spacing of 0.1 and 0.2 mm, with aspect ratios from 1 to 5. Arrays of 25 and 100 nozzles were used, with diameters of 0.25 to 1.0 mm providing nozzle area from 5 to 20 mm2 (5 to 20% of the heat source base area). Flow rates of 2.5 to 10 cm3/s (0.15 to 0.6 l/min) were studied, with nozzle velocities from 0.125 to 2 m/s. Single nozzles and smooth surfaces were also evaluated for comparison. Single-phase heat transfer coefficients (based on planform area) from 2.4 to 49.3 kW/m2 K were measured, while critical heat flux varied from 45 to 395 W/cm2. Correlations of the single-phase heat transfer coefficient and critical heat flux as functions of pin fin dimensions, number of nozzles, nozzle area and liquid flow rate are provided.

Phase-Change Heat Transfer of Ethanol-Water Mixtures: Towards Development of a Distributed Hydrogen Generator

2013 ◽  
Author(s):  
Manoj Kumar Moharana ◽  
Rohan M. Nemade ◽  
Sameer Khandekar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Single Phase ◽  
Flow Boiling ◽  
Phase Region ◽  
Design Flow ◽  
Two Phase ◽  
Vapor Region

Hydrogen fuel from renewable bio-ethanol is a potentially strong contender as an energy carrier. Its distributed production by steam reforming of ethanol on microscale platforms is an efficient upcoming method. Such systems require (a) a pre-heater for liquid to vapor conversion of ethanol water mixtures (b) a gas-phase catalytic reactor. We focus on the fundamental experimental heat transfer studies (pool and flow boiling of ethanol-water mixtures) required for the primary pre-heater boiler design. Flow boiling results (in a 256 μm square channel) clearly show the influence of mixture composition. Heat transfer coefficient remains almost constant in the single-phase region and rapidly increases as the two-phase region starts. On further increasing the wall superheat, heat transfer starts to decrease. At higher applied heat flux, the channel is subjected to axial back conduction from the single-phase vapor region to the two-phase liquid-vapor region, thus raising local wall temperatures. Simultaneously, to gain understanding of phase-change mechanisms in binary mixtures and to generate data for the modeling of flow boiling process, pool-boiling of ethanol-water mixtures has also been initiated. After benchmarking the setup against pure fluids, variation of heat transfer coefficient, bubble growth, contact angles, are compared at different operating conditions. Results show strong degradation in heat transfer in mixtures, which increases with operating temperature.

Analysis on Heat Transfer and Phase Change for Two-Phase Boiling Flow in Quenching Process

2019 ◽  
Author(s):  
Lu Wang ◽  
Nobuyuki Oshima ◽  
Sangwon Kim
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Wall Temperature ◽  
Computational Domain ◽  
Heating Wall ◽  
Two Phase ◽  
Phase Form ◽  
Quenching Process ◽  
Boiling Flow

Abstract A series of numerical simulations using “interThermalPhaseChangeFOAM” solver with improved VOF multiphase flow model in OpenFOAM were conducted to investigate the heat transfer and phase change characteristics for liquid-vapor boiling flow in quenching process. The computational domain is a cuboid with the heating wall at the bottom for both the variable and fixed wall temperature cases. The results for the variable wall temperature case with the heating wall temperature Twall = 150K show that the boiling phenomenon can be divided into the vapor film stage, the boiling stage and the convection stage. Then the fixed wall temperature cases with Twall = 110K, 120K and 140K are analyzed. It is found that 140K case is the most stable one, in which bubble formation is regular such as the bubble at the corner, resulting in the steady variation of heat flux. 120K case is the most unstable one, since the liquid phase and gas phase form the cross-interface shape and maintain this for a long time, leading to the fluctuations in heat flux. Finally, the influence of computational sizes on predicting the properties of boiling phenomenon is investigated. Although the variations of heat flux are not exactly same, the whole tendency is similar.

Spray Cooling Heat Transfer Enhancement and Degradation Using Fractal-Like Micro-Structured Surfaces

2011 ◽  
Author(s):  
Alex Tulchinsky ◽  
Deborah V. Pence ◽  
James A. Liburdy
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Smooth Surface ◽  
Single Phase ◽  
High Volume ◽  
Spray Cooling ◽  
Volume Flux ◽  
Two Phase ◽  
Structured Surfaces

In the present study, spray cooling curves are presented for two micro-structured surfaces and are compared to smooth surface results. The micro-structured surfaces consisted of bio-inspired fractal-like geometries, denoted as grooves or fins, extending in a radial direction from the center to the periphery of a 37.8 mm circular disc. Depending on the location on the surface, dimensions of groove widths and heights varied from 100 to 500 μm, and 30 to 60 μm, respectively. Fin width and height dimensions remained constant over the surface at 127 and 60 μm, respectively. Results are presented as heat flux versus the surface-to-exit spray temperature difference at each of five volume flux conditions ranging from 0.54 to 2.04 × 10−3 m3/m2-s. Convection heat transfer coefficients are also presented for each case as a function of heat flux. Results indicate that at low and high volume fluxes, an improvement in heat transfer occurs in the single phase regime for the fin geometry. Enhancement in the single phase regime does not occur at the intermediate volume flux condition. In the two phase regime for the fin structure significant enhancements, up to 50%, are observed. Whereas the groove structure performs similarly to the smooth surface in the single phase regime and exhibits large degradation in the two phase and critical heat flux regimes, up to 50%. Critical heat flux for the fin surface compares well to that of the flat surface, with a slightly increase at high volume flux conditions.

Performance Evaluation of Liquid Flow With PCM Particles in Microchannels

2005 ◽  
Vol 127 (8) ◽  
pp. 931-940 ◽  
Author(s):  
K. Q. Xing ◽  
Y.-X. Tao ◽  
Y. L. Hao
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Laminar Flow ◽  
Phase Change ◽  
Performance Index ◽  
Single Phase ◽  
Suspension Flow ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase

A two-phase, non thermal equilibrium-based model is applied to the numerical simulation of laminar flow and heat transfer characteristics of suspension with microsize phase-change material (PCM) particles in a microchannel. The model solves the conservation of mass, momentum, and thermal energy equations for liquid and particle phases separately. The study focuses on the parametric study of optimal conditions where heat transfer is enhanced with an increase in fluid power necessary for pumping the two-phase flow. The main contribution of PCM particles to the enhancement of heat transfer in a microsize tube is to increase the effective thermal capacity and utilize the latent heat effect under the laminar flow condition. An effectiveness factor εeff is defined to evaluate the heat transfer enhancement compared to the single-phase flow heat transfer and is calculated under different wall heat fluxes and different Reynolds numbers. The comparison is also made to evaluate the performance index, i.e., the ratio of total heat transfer rate to fluid flow power (pressure drop multiplied by volume flow rate) between PCM suspension flow and pure water single-phase flow. The results show that for a given Reynolds number, there exists an optimal heat flux under which the εeff value is the greatest. In general, the PCM suspension flow with phase change has a significantly higher performance index than the pure-fluid flow. The comparison of the model simulation with the limited experimental results for a MCPCM suspension flow in a 3mmdia tube reveals the sensitivity of wall temperature distribution to the PCM supply temperature and the importance of characterizing the phase change region for a given tube length.

scholarly journals Visualization Study on Thermo-Hydrodynamic Behaviors of a Flat Two-Phase Thermosyphon

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2295 ◽  
Author(s):  
Chao Wang ◽  
Feng Yao ◽  
Juan Shi ◽  
Liangyu Wu ◽  
Mengchen Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Thermal Performance ◽  
Flow Behavior ◽  
Heat Transfer Process ◽  
Liquid Pool ◽  
Two Phase ◽  
Convective Boiling ◽  
Wick Structure ◽  
Vapor Liquid

The coupled effect of boiling and condensation inside a flat two-phase thermosyphon has a non-negligible influence on the two-phase fluid flow behavior and heat transfer process. Therefore, a flat two-phase thermosyphon with transparent wall was manufactured. Based on this device, a visualization experiment system was developed to study the vapor–liquid two-phase behaviors and thermal performance of the flat two-phase thermosyphon. A cross-shaped wick using copper mesh was embedded into the cavity of two-phase thermosyphon to improve the heat transfer performance. The effects of heat flux density, working medium, and wick structure on the thermal performance are examined and analyzed. The results indicated that a strong liquid disturbance is caused by the bubble motions, leading to the enhancement of both convective boiling and condensation heat transfer. More bubbles are generated as the heat flux increases; therefore, the disturbance of bubble motion on liquid pool and condensation film becomes stronger, resulting in better thermal performance of the flat two-phase thermosyphon. The addition of the wick inside the cavity effectively reduces the temperature oscillation of the evaporator wall. In addition, the wick structure provides backflow paths for the condensate owing to the effect of capillary force and enhances the vapor–liquid phase change heat transfer, resulting in the improvement of thermal performance for the flat two-phase thermosyphon.

An Experimental Study of a Single-Device Jet Impingement Cooler With Phase Change Using HFE-7100 and a Vapor Extraction Manifold

2013 ◽  
Author(s):  
Shailesh N. Joshi ◽  
Matthew J. Rau ◽  
Ercan M. Dede
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Device Design ◽  
Vapor Extraction ◽  
Heat Spreader ◽  
Two Phase ◽  
Effective Heat Transfer Coefficient

There is substantial ongoing research into jet impingement cooling with phase change for high heat flux electronics applications. Higher heat transfer coefficients can be achieved through coolant phase change, although the proper evacuation of the resulting two-phase flow is important as it can affect the overall heat transfer performance of the cooler. In prior work, the accumulation of vapor in a multi-device cooler during the two-phase heat transfer process was shown to cause a build-up of pressure inside the cooler. This increase in pressure is logically related to the position of the cooler inlet and outlet ports with respect to the internal cooling geometry. Such pressure increases lead to an increase in the saturation temperature of the coolant and additional concerns regarding fluid containment. The present study describes a novel two-phase single-device cooler with HFE-7100 as the coolant, where the design allows for efficient removal of vapor from the test-section via a sloped outlet manifold. The performance of the cooler was evaluated using smooth and finned copper heat spreaders. To assess the effectiveness of the vapor extraction manifold, a comparison is made with the performance of a related multi-device cooler. Experimental results show that the single-device design reduces pressure build-up inside the cooler by an order of magnitude from 59 kPa to 7 kPa. A 36% increase in the effective heat transfer coefficient (∼19,000 W/m2K) at 50 W/cm2) was also achieved using the new single-device design with the smooth heat spreader when compared to the multi-device cooler. Additionally, by enhancing the heat spreader surface area with fins, the effective heat transfer coefficient was further boosted to 23,000 W/m2K.

Numerical Analysis of a Multiple Jet Impingement System

2009 ◽  
Author(s):  
G. Arvind Rao ◽  
Myra Kitron-Belinkov ◽  
Yeshayahou Levy
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Turbulent Regime ◽  
Transfer Coefficients ◽  
Complex Flow

Jet impingement is known to provide higher heat transfer coefficients as compared to other conventional modes of single phase heat transfer. Jet impingement has been a subject of research for a long time. Single jets have been studied extensively for their heat transfer and flow characteristics. However, for practical usage, multiple jets (in the form of arrays) have to be used for increasing the total heat transfer over a given area. Most of the research on multiple impinging jets have focused on evaluating heat transfer correlations for such arrays in the turbulent regime (Re >2500). The focus of the present paper is on experimental investigation of a large array of impinging jets in the low Reynolds number regime (<1000) and subsequently numerically modeling the same array by using existing Computational Fluid Dynamics tools in order to study the physical phenomena within such a complex system. Different turbulence models were used for modeling the fluid flow within these impinging jets and it was found that the SST k-ω model is the most suitable. Results obtained from CFD analysis are in reasonable agreement with experimental values. It was observed that CFD simulations over predicted the Nusselt number and pressure drop when compared to the experimentally obtained values. It was also observed that the decrease in Nusselt number along the streamwise direction of the array was not monotonic. This could be due to the complex flow field resulting from interaction between the crossflow and the impinging jets in the wall jet region. It is anticipated that results obtained from the present work will provide greater insight into the flow behavior and the heat transfer mechanism occurring in multiple impinging jets.

scholarly journals Experimental Achievements in Mini- and Micro- Channel Cooling

2021 ◽  
Vol 2119 (1) ◽  
pp. 012131
Author(s):  
M. V. Pukhovoy ◽  
E. F. Bykovskaya ◽  
O. A. Kabov
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Single Phase ◽  
Micro Channel ◽  
Two Phase ◽  
Channel One ◽  
Mini Channels ◽  
Small Set ◽  
Two Phase Cooling ◽  
The Heat Transfer Coefficient

Abstract There are a significant number of cooling techniques for micro- and mini-sized devices. One of them is mini-channel cooling. In this review, a large amount of experimental work on mini-channel cooling by various liquids is conceptually considered, in which the threshold in the removal of specific heat flux of >1 MW/m2 has been reached. A comparison of mini-channel cooling with other cooling techniques is performed. It was established that 1) micro-channel cooling has practically no thermophysical advantages over macro- or mini-channel one; 2) single-phase cooling in mini-channels gives comparable results compared to two-phase cooling; 3) only a small set of conceptual techniques allows the mini-channel heat exchanger to overcome the limit of 10 MW/m2 or to reach the heat transfer coefficient larger than 0.2 MW/(m2*K).

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