Analytical Model Quantifying the Net Coolant Flow Rate to a Microstructured Copper Surface validated with Two-Phase PIV Measurements

2021 ◽  
Author(s):  
Matt Harrison ◽  
Joshua Gess
Keyword(s):  
Heat Transfer ◽  
Analytical Model ◽  
Flow Rate ◽  
Circular Disk ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Coolant Flow ◽  
Coolant Flow Rate ◽  
Two Phase

Abstract Using Particle Image Velocimetry (PIV), the amount of fluid required to sustain nucleate boiling was quantified to a microstructured copper circular disk. Having prepared the disk with preferential nucleation sites, an analytical model of the net coolant flow rate requirements to a single site has been produced and validated against experimental data. The model assumes that there are three primary phenomena contributing to the coolant flow rate requirements at the boiling surface; radial growth of vapor throughout incipience to departure, bubble rise, and natural convection around the periphery. The total mass flowrate is the sum of these contributing portions. The model accurately predicts the quenching fluid flow rate at low and high heat fluxes with 4% and 30% error of the measured value respectively. For the microstructured surface examined in this study, coolant flow rate requirements ranged from 0.1 to 0.16 kg/sec for a range of heat fluxes from 5.5 to 11.0 W/cm2. Under subcooled conditions, the coolant flow rate requirements plummeted to a nearly negligible value due to domination of transient conduction as the primary heat transfer mechanism at the liquid/vapor/surface interface. PIV and the validated analytical model could be used as a test standard where the amount of coolant the surface needs in relation to its heat transfer coefficient or thermal resistance is a benchmark for the efficacy of a standard surface or boiling enhancement coating/surface structure.

Experimental Investigation of Porous Micro Heat Sink for Electronics Cooling Application

2011 ◽  
Vol 204-210 ◽  
pp. 2023-2026
Author(s):  
Ka Lin Su ◽  
Jing Liu ◽  
Jun Rong ◽  
Jun Hua Wan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Thermal Resistance ◽  
Flow Rate ◽  
Heat Sink ◽  
Heat Load ◽  
High Heat ◽  
Heat Fluxes ◽  
Coolant Flow ◽  
Coolant Flow Rate

A novel porous micro heat sink system was presented for dissipating high heat fluxes of electronic device. The flow and heat transfer of porous micro heat sink was investigated by experiment at the condition of high heat fluxes, and the results showed that the heat load of up to 280W was removed by the heat sink, and the heater junction temperature was 63.8°C at the coolant flow rate of 5.1cm3/s. The whole heat transfer coefficient of heat sink increased with the increases of coolant flow rate and heat load, and the maximal heat transfer coefficient was 33kW(m2.°C)-1 in the experiment. The minimum value of 0.19°C/W for whole thermal resistance of heat sink was achieved at flow rate of 5.1cm3/s, and increasing of coolant flow rate and heat fluxes could decrease the thermal resistance.

Dryout Avoidance Control for Multi-Evaporator Vapor Compression Cycles With Transient Heat Flux

2014 ◽  
Author(s):  
Daniel T. Pollock ◽  
Zehao Yang ◽  
John T. Wen
Keyword(s):  
Heat Flux ◽  
Flow Rate ◽  
Coolant Flow ◽  
Coolant Flow Rate ◽  
High Heat Flux ◽  
Vapor Compression ◽  
Transient Heating ◽  
Outer Loop ◽  
Two Phase ◽  
Loop Control

Multiple-evaporator vapor compression cycles may be used for distributed cooling of high heat-flux systems, such as arrays of high-power electronics. Under transient heating conditions, these systems must be carefully controlled to avoid critical heat flux (CHF) due to evaporator dryout. An active control strategy is presented that regulates two-phase flow quality in multiple evaporators in order to avoid critical quality under transient heating conditions. A two-loop control system is used, in which an outer loop uses model-based feedforward combined with evaporator wall temperature feedback to determine the necessary coolant flow rate to avoid CHF, while an inner loop uses system actuators (variable speed compressor, electronic expansion valves) to track to the desired flow rate. An advantage of this approach is that the inner-loop control handles the system complexity arising from pressure coupling and actuator nonlinearity. Additionally, the outer-loop quality control may be applied to other two-phase cooling schemes, for instance pumped systems, by providing coolant flow rate setpoints. Simulations and corresponding experimental controller validation were conducted using a three-evaporator vapor compression testbed with transient imposed heat-flux.

Spatial and Temporal Wall Temperature Fluctuations in Two-Phase Flow in Microgap Coolers

2010 ◽  
Author(s):  
Jessica Sheehan ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Volumetric Cooling ◽  
Very High

Heat transfer to an evaporating refrigerant and/or dielectric liquid in a microgap channel can provide very high heat transfer coefficients and volumetric cooling rates. Recent studies at Maryland have established the dominance of the annular flow regime in such microgap channels and related the observed high-quality peak of an M-shaped heat transfer coefficient curve to the onset of local dryout. The present study utilizes infrared thermography to locate such nascent dryout regions and operating conditions. Data obtained with a 210 micron microgap channel, operated with a mass flux of 195.2 kg/m2-s and heat fluxes of 10.3 to 26 W/cm2 are presented and discussed.

Effect of Rotation and Coolant Throughflow on the Heat Transfer and Temperature Field in an Enclosure

1976 ◽  
Vol 98 (3) ◽  
pp. 387-394 ◽  
Author(s):  
E. M. Sparrow ◽  
Leonardo Goldstein
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Flow Rate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Coolant Flow ◽  
Coolant Flow Rate ◽  
Transfer Coefficients ◽  
Disk System ◽  
Heat Transfer Coefficients

Measurements were performed to determine the local heat transfer coefficients along the heated shroud of a shrouded parallel disk system. The temperature field within the enclosure formed by the shroud and the disks was also measured. One of the disks was rotating, whereas the other disk and the shroud were stationary. Coolant air was introduced into the enclosure through an aperture at the center of the stationary disk and exited through a slot at the rim of the rotating disk. The coolant entrance-exit arrangement differed from that of previous studies, with the additional difference that the incoming coolant stream was free of rotation. The coolant flow rate, the disk rotational speed, and the aspect ratio of the enclosure were varied during the experiments. The heat transfer coefficients were found to be increasingly insensitive to the absence or presence of rotation as the coolant flow rate increased. There was a general increase of the transfer coefficients with increasing coolant flow rate, especially for low rotational speeds. The temperature field in the enclosure differed markedly depending on the relative importance of rotation and of coolant throughflow. When the latter dominates, the temperature in the core is relatively uniform, but in the presence of strong rotation there are significant nonuniformities. A comparison was made between the present Nusselt number results and those of prior experiments characterized by different coolant entrance—exit arrangements. The positioning of the coolant exit slot relative to the direction of the boundary layer flow on the shroud emerged as an important factor in the comparison.

Heat Transfer Correlations for Liquid Film in the Evaporator of Enclosed, Gravity-Assisted Thermosyphons

1998 ◽  
Vol 120 (2) ◽  
pp. 477-484 ◽  
Author(s):  
M. S. El-Genk ◽  
H. H. Saber
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Smooth Transition ◽  
Working Fluid ◽  
Two Phase ◽  
Data Set ◽  
Evaporator Section ◽  
Heat Transfer Correlations

Heat transfer correlations were developed for the liquid film region, in the evaporator section of closed, two-phase, gravity-assisted thermosyphons in the following regimes: (a) laminar convection, at low heat fluxes, (b) combined convection, at intermediate heat fluxes, and (c) nucleate boiling, at high heat fluxes. These correlations were based on a data set consisting of a total of 305 points for ethanol, acetone, R-11, and R-113 working fluids, wall heat fluxes of 0.99–52.62 kW/m2, working fluid filling ratios of 0.01–0.62, inner diameters of 6–37 mm, evaporator section lengths of 50–609.6 mm, and vapor temperatures of 261–352 K. The combined convention data were correlated by superimposing the correlations of laminar convention and nucleate boiling using a power law approach, to ensure smooth transition among the three heat transfer regimes. The three heat transfer correlations developed in this work are within ±15 percent of experimental data.

Heat Transfer for the Blade of a Cooled Stage and One-Half High-Pressure Turbine—Part II: Independent Influences of Vane Trailing Edge and Purge Cooling

2011 ◽  
Vol 134 (3) ◽  
Author(s):  
R. M. Mathison ◽  
C. W. Haldeman ◽  
M. G. Dunn
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Flow Rate ◽  
Pressure Field ◽  
Its Region ◽  
Coolant Flow ◽  
Coolant Flow Rate ◽  
High Pressure Turbine ◽  
Suction Surface ◽  
Trailing Edge

The independent influences of vane trailing edge and purge cooling are studied in detail for a one-and-one-half stage transonic high-pressure turbine operating at design-corrected conditions. This paper builds on the conclusions of Part I, which investigated the combined influence of all cooling circuits. Heat-flux measurements for the airfoil, platform, tip, and root of the turbine blade, as well as the shroud and the vane side of the purge cavity, are used to track the influence of cooling flow. By independently varying the coolant flow rate through the vane trailing edge or purge circuit, the region of influence of each circuit can be isolated. Vane trailing edge cooling is found to create the largest reductions in blade heat transfer. However, much of the coolant accumulates on the blade suction surface and little influence is observed for the pressure surface. In contrast, the purge cooling is able to cause small reductions in heat transfer on both the suction and pressure surfaces of the airfoil. Its region of influence is limited to near the hub, but given that the purge coolant mass flow rate is 1/8 that of the vane trailing edge, it is impressive that any impact is observed at all. The cooling contributions of these two circuits account for nearly all of the cooling reductions observed for all three circuits in Part I, indicating that the vane inner cooling circuit that feeds most of the vane film-cooling holes has little impact on the downstream blade heat transfer. Time-accurate pressure measurements provide further insight into the complex interactions in the purge region that govern purge coolant injection. While the pressures supplying the purge coolant and the overall coolant flow rate remain fairly constant, the interactions of the vane pressure field and the rotor pressure field create moving regions of high pressure and low pressure at the exit of the cavity. This results in pulsing regions of injection and ingestion.

Statistical Modelling of Bubble Nucleation and Heat Transfer Using Interface Tracking in TransAT CMFD Code

2010 ◽  
Author(s):  
Chidambaram Narayanan ◽  
Siju Thomas ◽  
Djamel Lakehal
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Statistical Modelling ◽  
Nucleate Boiling ◽  
High Heat ◽  
Bubble Nucleation ◽  
Heat Fluxes ◽  
Conductive Heat Transfer ◽  
Transfer Model ◽  
Conductive Heat

This paper presents results of numerical simulations of various processes that demonstrate phase change heat transfer at high heat fluxes using the level-set method. The model used for the purpose has been first validated for the growth of an evaporating bubble in infinite medium, and fim boiling in 2D and 3D. It has then been applied to simulate the nucleation and departure of a single bubble from a solid body subject to conductive heat transfer. Unlike our previous investigations where phase change induced evaporation rate was incorporated like a sub-grid scale heat transfer model applied to the triple contact line, the present work reports simulations with direct phase change modelling by integrating energy fluxes at the interface. The effect of the conductive heat transfer in the solid from which the bubble departs is also taken into account. Comparison with visual images suggests that accounting for conjugate heat transfer is important to capturing micro-hydrodynamics in nucleate boiling, at least qualitatively.

scholarly journals ANALYSIS ON THE PERFORMANCE OF THE BANDUNG CONVERSION FUEL-PLATE TRIGA REACTOR IN STEADY STATE WITH CONSTANT COOLANT FLOW RATE

2020 ◽  
Vol 22 (2) ◽  
pp. 41
Author(s):  
Endiah Puji Hastuti ◽  
Sudjatmi K. Alfa ◽  
Sudarmono Sudarmono
Keyword(s):  
Steady State ◽  
Fuel Element ◽  
Flow Rate ◽  
Flow Instability ◽  
Safety Margin ◽  
Nucleate Boiling ◽  
Coolant Flow ◽  
Coolant Flow Rate ◽  
Steady State Condition ◽  
Triga Reactor

Bandung TRIGA2000 Reactor, a General Atomic (GA)-made research reactor used for training, research andiIsotope production, has been upgraded to operate at power of 2000 kW using TRIGA fuel rod type. Recently, the TRIGA reactor fuel element producers are going to discontinue the production of TRIGA fuel element. To overcome the unavailability of TRIGA fuel element, BATAN planned to modify TRIGA2000 fuel type from rod-type to U3Si2-Al plate-type fuel with 19.75% enrichment, similar to the domestically fabricated one used in RSG-GAS. The carried out design emphasized on the determination of operation condition limits for setting the reactor protection system in accordance to the reactor safety calculation results. The conceptual design of the innovative fuel plate TRIGA reactor cooling system is expected to remove heat generated by fuels with nominal power of 1 MW up to 2 MW. The design is developed through modelling and safety analysis using COOLOD-N2 validated code. The safety margin is set to its flow instability at transient condition of the fuel plate, which is ≥ 2.38; departure from nucleate boiling ratio ≥1.50; and no onset of nucleate boiling, ΔTONB ≥ 0oC. The primary coolant flow rate accommodating the existing Bandung TRIGA reactor capability is as high as 50 kg/s. The analysis results show that at power of 1 MW, the reactor can safely operate, while at power of 2 MW the safety margin is exceeded. In other words, the plate TRIGA reactor that employs forced convection mode operates safely at 1 MW with excess power 120% of its nominal power.Keywords: 1 MW, Thermalhydraulic design, Steady state condition, TRIGA plate, Constant flowrate

scholarly journals Modelling of Boiling Flows for Nuclear Thermal Hydraulics Applications—A Brief Review

Inventions ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 47
Author(s):  
Giovanni Giustini
Keyword(s):  
Heat Transfer ◽  
Liquid Water ◽  
Cfd Simulation ◽  
High Surface ◽  
Computational Modelling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Thermal Hydraulics ◽  
Two Phase ◽  
Water Reactors

The boiling process is utterly fundamental to the design and safety of water-cooled fission reactors. Both boiling water reactors and pressurised water reactors use boiling under high-pressure subcooled liquid flow conditions to achieve high surface heat fluxes required for their operation. Liquid water is an excellent coolant, which is why water-cooled reactors can have such small sizes and high-power densities, yet also have relatively low component temperatures. Steam is in contrast a very poor coolant. A good understanding of how liquid water coolant turns into steam is correspondingly vital. This need is particularly pressing because heat transfer by water when it is only partially steam (‘nucleate boiling’ regime) is particularly effective, providing a great incentive to operate a plant in this regime. Computational modelling of boiling, using computational fluid dynamics (CFD) simulation at the ‘component scale’ typical of nuclear subchannel analysis and at the scale of the single bubbles, is a core activity of current nuclear thermal hydraulics research. This paper gives an overview of recent literature on computational modelling of boiling. The knowledge and capabilities embodied in the surveyed literature entail theoretical, experimental and modelling work, and enabled the scientific community to improve its current understanding of the fundamental heat transfer phenomena in boiling fluids and to develop more accurate tools for the prediction of two-phase cooling in nuclear systems. Data and insights gathered on the fundamental heat transfer processes associated with the behaviour of single bubbles enabled us to develop and apply more capable modelling tools for engineering simulation and to obtain reliable estimates of the heat transfer rates associated with the growth and departure of steam bubbles from heated surfaces. While results so far are promising, much work is still needed in terms of development of fundamental understanding of the physical processes and application of improved modelling capabilities to industrially relevant flows.

Guidelines for Designing Micropillar Structures for Enhanced Evaporative Heat Transfer

2021 ◽  
Author(s):  
Kidus Guye ◽  
De Dong ◽  
Yunseo Kim ◽  
Hyoungsoon Lee ◽  
Baris Dogruoz ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Interfacial Area ◽  
High Heat ◽  
Heat Fluxes ◽  
Air Cooling ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Evaporation Heat

Abstract Over the last several decades, cooling technologies have been developed to address the growing thermal challenges associated with high-powered electronics. However, within the next several years, the heat generated by these devices is predicted to exceed 1 kW/cm2, and traditional methods, such as air cooling, are limited in their capacities to dissipate such high heat fluxes. In contrast, two-phase cooling methods, such as microdroplet evaporation, are very promising due to the large latent heat of vaporization associated with the phase change process. Previous studies have shown non-axisymmetric droplets exhibit different evaporation characteristics than spherical droplets. For a droplet pinned atop a micropillar, the solid-liquid and liquid-vapor interfacial area, the volume, and thickness of the droplet are the major factors that govern the evaporation heat transport process. In this work, we develop a shape optimization tool using the particle swarm optimization algorithm to maximize evaporation from a droplet confined atop a micropillar. The tool is used to optimize the shape of a nonaxisymmetric droplet. Compared to droplets atop circular and regular equilateral triangular micropillar structures, we find that droplets confined on pseudo-triangular micropillar structures have 23.7% and 5.7% higher heat transfer coefficients, respectively. The results of this work will advance the design of microstructures that support droplets with maximum heat transfer performance.

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