Natural Convective Heat Transfer From an Array of Square Vertical Plates Mounted on a Large Plane Vertical Adiabatic Surface and With One High Heat Flux Element

2009 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Jane T. Paul
Keyword(s):  
Heat Flux ◽  
High Heat ◽  
Heat Fluxes ◽  
The Other ◽  
Uniform Heat Flux ◽  
High Heat Flux ◽  
Wide Range ◽  
The Mean ◽  
Adiabatic Surface ◽  
Flux Element

An array of nine square heated elements mounted in a square three-by-three pattern with no gap between the elements on a large vertical adiabatic surface with natural convective flow over the elements has been considered. Each of the elements has a uniform heat flux over its surface, the heat fluxes over eight of the elements being the same and the heat flux over the ninth element being higher than that over the other eight elements. The basic aim of the study was to determine the effect the position of the higher heat flux element on the mean temperatures of the other eight elements. The situation considered is an approximate model of situations that can arise in electronic cooling. The flow has been assumed to be steady and laminar and it has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. The solution has been obtained by numerically solving the full three-dimensional form of the governing equations, these equations being written in terms of dimensionless variables using the commercial cfd code FLUENT. The solution has the heat flux Rayleigh number, the Prandtl number, the ratio of the heat flux over the high heat flux element to the heat flux over the other eight elements, and the position of the high heat flux element as parameters. Because of the application that motivated this work results have only been obtained for Pr = 0.7. Results have been obtained for a wide range of values of the other input parameters and the effect of these parameter values on the mean surface temperatures of each of the elements has been studied.

Heat Transfer Enhancement in Compact Phase Change Microchannel Heat Exchangers for High Flux Laser Diodes

2018 ◽  
Author(s):  
Jensen Hoke ◽  
Todd Bandhauer ◽  
Jack Kotovsky ◽  
Julie Hamilton ◽  
Paul Fontejon
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Flow Boiling ◽  
Laser Diodes ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Maximum Heat ◽  
Average Maximum

Liquid-vapor phase change heat transfer in microchannels offers a number of significant advantages for thermal management of high heat flux laser diodes, including reduced flow rates and near constant temperature heat rejection. Modern laser diode bars can produce waste heat loads >1 kW cm−2, and prior studies show that microchannel flow boiling heat transfer at these heat fluxes is possible in very compact heat exchanger geometries. This paper describes further performance improvements through area enhancement of microchannels using a pyramid etching scheme that increases heat transfer area by ∼40% over straight walled channels, which works to promote heat spreading and suppress dry-out phenomenon when exposed to high heat fluxes. The device is constructed from a reactive ion etched silicon wafer bonded to borosilicate to allow flow visualization. The silicon layer is etched to contain an inlet and outlet manifold and a plurality of 40μm wide, 200μm deep, 2mm long channels separated by 40μm wide fins. 15μm wide 150μm long restrictions are placed at the inlet of each channel to promote uniform flow rate in each channel as well as flow stability in each channel. In the area enhanced parts either a 3μm or 6μm sawtooth pattern was etched vertically into the walls, which were also scalloped along the flow path with the a 3μm periodicity. The experimental results showed that the 6μm area-enhanced device increased the average maximum heat flux at the heater to 1.26 kW cm2 using R134a, which compares favorably to a maximum of 0.95 kw cm2 dissipated by the plain walled test section. The 3μm area enhanced test sections, which dissipated a maximum of 1.02 kW cm2 showed only a modest increase in performance over the plain walled test sections. Both area enhancement schemes delayed the onset of critical heat flux to higher heat inputs.

On the Nature of Critical Heat Flux in Microchannels

2005 ◽  
Vol 127 (1) ◽  
pp. 101-107 ◽  
Author(s):  
A. E. Bergles ◽  
S. G. Kandlikar
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Flow Distribution ◽  
High Heat ◽  
Operating Conditions ◽  
High Heat Flux ◽  
Clear Understanding ◽  
Wide Range ◽  
Parallel Microchannels

The critical heat flux (CHF) limit is an important consideration in the design of most flow boiling systems. Before the use of microchannels under saturated flow boiling conditions becomes widely accepted in cooling of high-heat-flux devices, such as electronics and laser diodes, it is essential to have a clear understanding of the CHF mechanism. This must be coupled with an extensive database covering a wide range of fluids, channel configurations, and operating conditions. The experiments required to obtain this information pose unique challenges. Among other issues, flow distribution among parallel channels, conjugate effects, and instrumentation need to be considered. An examination of the limited CHF data indicates that CHF in parallel microchannels seems to be the result of either an upstream compressible volume instability or an excursive instability rather than the conventional dryout mechanism. It is expected that the CHF in parallel microchannels would be higher if the flow is stabilized by an orifice at the entrance of each channel. The nature of CHF in microchannels is thus different than anticipated, but recent advances in microelectronic fabrication may make it possible to realize the higher power levels.

Optimization of Refrigeration Systems for High-Heat-Flux Microelectronics

2008 ◽  
Author(s):  
P. E. Phelan ◽  
Y. Gupta ◽  
H. Tyagi ◽  
R. Prasher ◽  
J. Cattano ◽  
...  
Keyword(s):  
Heat Flux ◽  
Energy Consumption ◽  
System Design ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
High Heat Flux ◽  
Vapor Compression ◽  
Refrigeration System ◽  
Compressor Inlet

Increasingly, military and civilian applications of electronics require extremely high heat fluxes, on the order of 1000 W/cm2. Thermal management solutions for these severe operating conditions are subject to a number of constraints, including energy consumption, controllability, and the volume or size of the package. Calculations indicate that the only possible approach to meeting this heat flux condition, while maintaining the chip temperature below 50 °C, is to utilize refrigeration. Here we report an initial optimization of the refrigeration system design. Because the outlet quality of the fluid leaving the evaporator must be held to approximately less than 20%, in order to avoid reaching critical heat flux, the refrigeration system design is dramatically different from typical configurations for household applications. In short, a simple vapor-compression cycle will require excessive energy consumption, largely because of the superheat required to return the refrigerant to its vapor state before the compressor inlet. A better design is determined to be a “two-loop” cycle, in which the vapor-compression loop is coupled thermally to a primary loop that directly cools the high-heat-flux chip.

scholarly journals Annual, Seasonal, and Interannual Variability of Air–Sea Heat Fluxes in the Indian Ocean

2007 ◽  
Vol 20 (13) ◽  
pp. 3190-3209 ◽  
Author(s):  
Lisan Yu ◽  
Xiangze Jin ◽  
Robert A. Weller
Keyword(s):  
Heat Flux ◽  
Indian Ocean ◽  
Interannual Variability ◽  
Seasonal Cycle ◽  
Arabian Sea ◽  
Heat Fluxes ◽  
The Other ◽  
Net Heat Flux ◽  
The Indian Ocean ◽  
The Mean

Abstract This study investigated the accuracy and physical representation of air–sea surface heat flux estimates for the Indian Ocean on annual, seasonal, and interannual time scales. Six heat flux products were analyzed, including the newly developed latent and sensible heat fluxes from the Objectively Analyzed Air–Sea Heat Fluxes (OAFlux) project and net shortwave and longwave radiation results from the International Satellite Cloud Climatology Project (ISCCP), the heat flux analysis from the Southampton Oceanography Centre (SOC), the National Centers for Environmental Prediction reanalysis 1 (NCEP1) and reanalysis-2 (NCEP2) datasets, and the European Centre for Medium-Range Weather Forecasts operational (ECMWF-OP) and 40-yr Re-Analysis (ERA-40) products. This paper presents the analysis of the six products in depicting the mean, the seasonal cycle, and the interannual variability of the net heat flux into the ocean. Two time series of in situ flux measurements, one taken from a 1-yr Arabian Sea Experiment field program and the other from a 1-month Joint Air–Sea Monsoon Interaction Experiment (JASMINE) field program in the Bay of Bengal were used to evaluate the statistical properties of the flux products over the measurement periods. The consistency between the six products on seasonal and interannual time scales was investigated using a standard deviation analysis and a physically based correlation analysis. The study has three findings. First of all, large differences exist in the mean value of the six heat flux products. Part of the differences may be attributable to the bias in the numerical weather prediction (NWP) models that underestimates the net heat flux into the Indian Ocean. Along the JASMINE ship tracks, the four NWP modeled mean fluxes all have a sign opposite to the observations, with NCEP1 being underestimated by 53 W m−2 (the least biased) and ECMWF-OP by 108 W m−2 (the most biased). At the Arabian Sea buoy site, the NWP mean fluxes also have an underestimation bias, with the smallest bias of 26 W m−2 (ERA-40) and the largest bias of 69 W m−2 (NCEP1). On the other hand, the OAFlux+ISCCP has the best comparison at both measurement sites. Second, the bias effect changes with the time scale. Despite the fact that the mean is biased significantly, there is no major bias in the seasonal cycle of all the products except for ECMWF-OP. The latter does not have a fixed mean due to the frequent updates of the model platform. Finally, among the four products (OAFlux+ISCCP, ERA-40, NCEP1, and NCEP2) that can be used for studying interannual variability, OAFlux+ISCCP and ERA-40 Qnet have good consistency as judged from both statistical and physical measures. NCEP1 shows broad agreement with the two products, with varying details. By comparison, NCEP2 is the least representative of the Qnet variabilities over the basin scale.

Integrated Vapor Chamber Heat Spreader for Power Module Applications

2017 ◽  
Author(s):  
Clayton L. Hose ◽  
Dimeji Ibitayo ◽  
Lauren M. Boteler ◽  
Jens Weyant ◽  
Bradley Richard
Keyword(s):  
Heat Flux ◽  
Thermal Resistance ◽  
Power Electronics ◽  
Coefficient Of Thermal Expansion ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Vapor Chamber ◽  
Power Module ◽  
Heat Spreader

This work presents a demonstration of a coefficient of thermal expansion (CTE) matched, high heat flux vapor chamber directly integrated onto the backside of a direct bond copper (DBC) substrate to improve heat spreading and reduce thermal resistance of power electronics modules. Typical vapor chambers are designed to operate at heat fluxes > 25 W/cm2 with overall thermal resistances < 0.20 °C/W. Due to the rising demands for increased thermal performance in high power electronics modules, this vapor chamber has been designed as a passive, drop-in replacement for a standard heat spreader. In order to operate with device heat fluxes >500 W/cm2 while maintaining low thermal resistance, a planar vapor chamber is positioned onto the backside of the power substrate, which incorporates a specially designed wick directly beneath the active heat dissipating components to balance liquid return and vapor mass flow. In addition to the high heat flux capability, the vapor chamber is designed to be CTE matched to reduce thermally induced stresses. Modeling results showed effective thermal conductivities of up to 950 W/m-K, which is 5 times better than standard copper-molybdenum (CuMo) heat spreaders. Experimental results show a 43°C reduction in device temperature compared to a standard solid CuMo heat spreader at a heat flux of 520 W/cm2.

A Review of Two-Phase Forced Cooling in Three-Dimensional Stacked Electronics: Technology Integration

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Craig Green ◽  
Peter Kottke ◽  
Xuefei Han ◽  
Casey Woodrum ◽  
Thomas Sarvey ◽  
...  
Keyword(s):  
Heat Flux ◽  
Heat Sink ◽  
Three Dimensional ◽  
High Heat ◽  
Heat Fluxes ◽  
Thermal Design ◽  
High Heat Flux ◽  
Two Phase ◽  
Forced Cooling ◽  
Fluidic Routing

Three-dimensional (3D) stacked electronics present significant advantages from an electrical design perspective, ranging from shorter interconnect lengths to enabling heterogeneous integration. However, multitier stacking exacerbates an already difficult thermal problem. Localized hotspots within individual tiers can provide an additional challenge when the high heat flux region is buried within the stack. Numerous investigations have been launched in the previous decade seeking to develop cooling solutions that can be integrated within the 3D stack, allowing the cooling to scale with the number of tiers in the system. Two-phase cooling is of particular interest, because the associated reduced flow rates may allow reduction in pumping power, and the saturated temperature condition of the coolant may offer enhanced device temperature uniformity. This paper presents a review of the advances in two-phase forced cooling in the past decade, with a focus on the challenges of integrating the technology in high heat flux 3D systems. A holistic approach is applied, considering not only the thermal performance of standalone cooling strategies but also coolant selection, fluidic routing, packaging, and system reliability. Finally, a cohesive approach to thermal design of an evaporative cooling based heat sink developed by the authors is presented, taking into account all of the integration considerations discussed previously. The thermal design seeks to achieve the dissipation of very large (in excess of 500 W/cm2) background heat fluxes over a large 1 cm × 1 cm chip area, as well as extreme (in excess of 2 kW/cm2) hotspot heat fluxes over small 200 μm × 200 μm areas, employing a hybrid design strategy that combines a micropin–fin heat sink for background cooling as well as localized, ultrathin microgaps for hotspot cooling.

scholarly journals Experimental characterization of the hypersonic flow around a cuboid

2020 ◽  
Vol 61 (7) ◽  
Author(s):  
Thomas W. Rees ◽  
Tom B. Fisher ◽  
Paul J. K. Bruce ◽  
Jim A. Merrifield ◽  
Mark K. Quinn
Keyword(s):  
Heat Flux ◽  
Hypersonic Flow ◽  
Stagnation Point ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Simple Method ◽  
High Reynolds

Abstract Understanding the hypersonic flow around faceted shapes is important in the context of the fragmentation and demise of satellites undergoing uncontrolled atmospheric entry. To better understand the physics of such flows, as well as the satellite demise process, we perform an experimental study of the Mach 5 flow around a cuboid geometry in the University of Manchester High SuperSonic Tunnel. Heat fluxes are measured using infrared thermography and a 3D inverse heat conduction solution, and flow features are imaged using schlieren photography. Measurements are taken at a range of Reynolds numbers from $${40.0 \times 10^3}$$ 40.0 × 10 3 to $${549 \times 10^3}$$ 549 × 10 3 . The schlieren results suggest the presence of a separation bubble at the windward edge of the cube at high Reynolds numbers. High heat fluxes are observed near corners and edges, which are caused by boundary-layer thinning. Additionally, on the side (off-stagnation) faces of the cube, we observe wedge-shaped regions of high heat flux emanating from the windward corners of the cube. We attribute these to vortical structures being generated by the strong expansion around the cube’s corners. We also observe that the stagnation point of the cube is off-centre of the windward face, which we propose is due to sting flex under aerodynamic loading. Finally, we propose a simple method of calculating the stagnation point heat flux to a cube, as well as relations which can be used to predict hypersonic heat fluxes to cuboid geometries such as satellites during atmospheric re-entry. Graphic abstract

Experimental Characterization of Two-Phase Cooling of Power Electronics in Thermosiphon and Forced Convection Modes

2021 ◽  
Vol 143 (3) ◽  
Author(s):  
Fabio Battaglia ◽  
Farah Singer ◽  
David C. Deisenroth ◽  
Michael M. Ohadi
Keyword(s):  
Heat Flux ◽  
Thermal Resistance ◽  
Power Electronics ◽  
Forced Convection ◽  
Heat Removal ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Two Phase ◽  
Total Thermal Resistance

Abstract In this paper, we present the results of an experimental study involving low thermal resistance cooling of high heat flux power electronics in a forced convection mode, as well as in a thermosiphon (buoyancy-driven) mode. The force-fed manifold microchannel cooling concept was utilized to substantially improve the cooling performance. In our design, the heat sink was integrated with the simulated heat source, through a single solder layer and substrate, thus reducing the total thermal resistance. The system was characterized and tested experimentally in two different configurations: the passive (buoyancy-driven) loop and the forced convection loop. Parametric studies were conducted to examine the role of different controlling parameters. It was demonstrated that the thermosiphon loop can handle heat fluxes in excess of 200 W/cm2 with a cooling thermal resistance of 0.225 (K cm2)/W for the novel cooling concept and moderate fluctuations in temperature. In the forced convection mode, a more uniform temperature distribution was achieved, while the heat removal performance was also substantially enhanced, with a corresponding heat flux capacity of up to 500 W/cm2 and a thermal resistance of 0.125 (K cm2)/W. A detailed characterization leading to these significant results, a comparison between the performance between the two configurations, and a flow visualization in both configurations are discussed in this paper.

Micro Heat Changers and Surface-Micro-Coolers for High Heat Flux

2008 ◽  
Author(s):  
Ulrich Schygulla ◽  
Ju¨rgen J. Brandner ◽  
Eugen Anurjew ◽  
Edgar Hansjosten ◽  
Klaus Schubert
Keyword(s):  
Heat Flux ◽  
Heat Exchanger ◽  
Mass Flow ◽  
Pressure Loss ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Micro Heat Exchanger ◽  
Micro Channels ◽  
Higher Temperature

This publication describes the development of a new microstructure to transfer high heat fluxes. With a simple mathematical model based on heat conduction theory for the heat transfer in a micro channel at laminar flow conditions it was deduced that for the transmission of high heat fluxes only the initial part at the beginning of the micro channels is of importance, i.e. the micro channels should be short. Based on this principle a micro structure was designed with a large number of short micro channels taken in parallel. With this newly developed microstructure a prototype of a micro heat exchanger and a surface micro cooler was manufactured and tested. Using the prototype of the micro heat exchanger, manufactured of plastic, heat fluxes up to 500 W/cm2 were achieved at a pressure loss of 0.16 MPa and a mass flow of the water of 200 kg/h per passage. Due to the use of materials with a higher temperature resistance and higher stability like aluminum or ceramic, higher water throughputs and higher flow velocities could be realized in the micro channels. Thus it was possible to increase the heat flux up to approx. 800 W/cm2 at a pressure loss of approx. 0.35 MPa and a mass flow of 350 kg/h per passage. The important focus of investigation of the surface micro cooler was set on the examination of the surface temperatures for different heat fluxes and different velocities of the water in the micro channels. The experimental results of these surface micro coolers are summarized to characteristic maps. With this characteristic maps it is possible to determine whether a micro surface cooler can be used for a specific application.

Design of Thermoelectric Modules for High Heat Flux Cooling

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Ram Ranjan ◽  
Joseph E. Turney ◽  
Charles E. Lents ◽  
Virginia H. Faustino
Keyword(s):  
Heat Flux ◽  
Electrical Current ◽  
High Heat ◽  
Packing Fraction ◽  
Heat Fluxes ◽  
Coefficient Of Performance ◽  
Shear Stresses ◽  
High Heat Flux ◽  
Thermoelectric Coolers ◽  
Active Elements

Thermoelectric (TE) coolers work on the Seebeck effect, where an electrical current is used to drive a heat flux against a temperature gradient. They have applications for active cooling of electronic devices but have low coefficients of performance (COP < 1) at high heat fluxes (>10 W/cm2, dT = 15 K). While the active elements (TE material) in a TE cooling module lead to cooling, the nonactive elements, such as the electrical leads and headers, cause joule heating and decrease the coefficient of performance. A conventional module design uses purely horizontal leads and vertical active elements. In this work, we numerically investigate trapezoidal leads with angled active elements as a method to improve cooler performance in terms of lower parasitic resistance, higher packing fraction and higher reliability, for both supperlattice thin-film and bulk TE materials. For source and sink side temperatures of 30 °C and 45 °C, we show that, for a constant packing fraction, defined as the ratio of active element area to the couple base area, trapezoidal leads decrease electrical losses but also increase thermal resistance. We also demonstrate that trapezoidal leads can be used to increase the packing fraction to values greater than one, leading to a two times increase in heat pumping capacity. Structural analysis shows a significant reduction in both tensile and shear stresses in the TE modules with trapezoidal leads. Thus, the present work provides a pathway to engineer more reliable thermoelectric coolers (TECs) and improve their efficiency by >30% at a two times higher heat flux as compared to the state-of-the-art.

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