Near Critical Heat Flux From Small Substrates Under Controlled Spray Cooling

2009 ◽  
Author(s):  
Sergio Escobar-Vargas ◽  
Jorge E. Gonzalez ◽  
Orlando Ruiz ◽  
Cullen Bash ◽  
Ratnesh Sharma ◽  
...  
Keyword(s):  
Heat Flux ◽  
Mass Flow Rate ◽  
Critical Heat Flux ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Dissipation ◽  
High Heat ◽  
Heat Fluxes ◽  
Experimental Results ◽  
High Heat Flux

The increasing power density on electronic components has resulted in temperature problems related to the generation of hot spots and the need to remove high heat flux in small areas. This work is aimed at the cooling of small surfaces (1 mm × 1.2 mm) by using a monodisperse spray from thermal ink jet (TIJ) atomizers. Heat fluxes near the critical heat flux (CHF) are obtained for different conditions of cooling mass flow rate, droplet deposition, and number of active droplet jets. Experimental results at quasiequilibrium show the heat flux scales to the cooling mass flow rate. It is observed that two simultaneously activated jets result in slightly smaller heat flux compared to a single jet of droplets for the same mass flow rate. Droplet momentum and spreading or splashing, as determined by a combination of Weber number and Reynolds number effect via K = We1/2Re1/4, may impact the efficiency of the delivery of the cooling mass flow. Current experimental results at K = 24.5 and K = 52.2 for the copper surface temperatures ranging 110 – 120 °C indicate there is little influence of the splashing on the heat dissipation. System heat losses are measured experimentally and compared to a numerical and analytical solution to estimate the actual heat dissipated by the droplet change of phase.

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.

High Heat Flux With Small Scale Monodisperse Sprays

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Sergio Escobar-Vargas ◽  
Jorge E. Gonzalez ◽  
Drazen Fabris ◽  
Ratnesh Sharma ◽  
Cullen Bash
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Film Thickness ◽  
Liquid Film ◽  
Heat Dissipation ◽  
High Heat ◽  
Heat Fluxes ◽  
Liquid Film Thickness ◽  
Small Scale ◽  
High Heat Flux

This work is aimed at cooling small surfaces (1.3 mm × 2 mm and 3 mm × 5 mm) using spray from thermal ink jet (TIJ) atomizers. Particular interests in this work include obtaining heat fluxes near the critical heat flux (CHF), understanding the correlation between the heat dissipation efficiency (η) and the liquid film thickness (δ) through experimental data, and understanding the primary mode of heat transfer on spray cooling at different liquid film thickness. Current experimental results indicate that high heat fluxes (∼4 × 107 W/m2) are obtained for controlled conditions of cooling mass flow rate, higher efficiencies are achieved at smaller liquid film thickness (δ ≈ 5 μm → η ≈ 0.9), and the heat transfer by conduction through the film becomes dominant as δ decreases.

Radiation and Convection Heat Flux Sensor for High Temperature Gas Environment

1998 ◽  
Author(s):  
Nelson Martins ◽  
Maria da Graça Carvalho ◽  
Naim Afgan ◽  
Alexander Ivanovich Leontiev
Keyword(s):  
Heat Flux ◽  
High Temperature ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Critical Mass ◽  
Flux Measurement ◽  
Heat Fluxes ◽  
Sensing Element ◽  
Porous Element

The heat flux measurement is one of the essential parameter for the diagnostic of thermal systems. In the high temperature environment there are difficulties in differentiating between the convective and radiation component of heat flux on the heat transfer surface. A new method for heat flux measurement is being developed using a porous sensing element. The gas stream flowing through the porous element is used to measure the heat received by the sensor surface exposed to the hot gas environment and to control whether or not the sensing element receives the convection component of the total heat flux. It is possible to define a critical mass flow rate corresponding to the destruction of the boundary layer over the sensing element. With subcritical mass flow rate the porous sensing element will receive both the convective and radiative heat fluxes. A supercritical mass flow rate will eliminate the convective component of the total heat flux. Two consecutive measurements considering respectively a critical and a sub-critical mass flow rate can be used to determine separately the convection and radiation heat fluxes. A numerical model of sensor with appropriate boundary condition has been developed in order to perform analysis of possible options in the design of the sensor. The analysis includes: geometry of element, physical parameters of gas and solid and gas flow rate through the porous element. For the optimal selection of the relevant parameters an experimental set-up was designed, including the sensor element with corresponding cooling and monitoring system and high temperature radiation source. Applying the respective measuring procedure the calibration curve of the sensor was obtained. The linear dependency of the heat flux and respective temperature difference of the gas was verified. The accuracy analysis of the sensor reading has proved high linearity of the calibration curve and accuracy of ± 5%.

scholarly journals Outcomes of the “steady-state crisis” experiment in the MIR reactor channel

2019 ◽  
Vol 5 (3) ◽  
pp. 207-212
Author(s):  
Aleksandr V. Alekseev ◽  
Oleg I. Dreganov ◽  
Aleksey L. Izhutov ◽  
Irina V. Kiseleva ◽  
Vitaly N. Shulimov
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Mass Flow Rate ◽  
Critical Heat Flux ◽  
Mass Flow ◽  
Flow Rate ◽  
Experimental Parameter ◽  
Reactor Channel ◽  
Dry Heat ◽  
Fuel Elements

To license nuclear fuel for nuclear power plants, data on the behavior of fuel elements (FE) under design-basis accidents are required. These data are obtained during tests of fuel assemblies (FA) and single fuel elements in research reactor channels followed by post-test studies in protective chambers. A reactivity-initiated accident (RIA) with an unauthorized release of CPS rods from the reactor core leads to a pulsed channel power increase. This accident can proceed according to two scenarios: without a critical heat flux (CHF) on the fuel element jacket at the final stage and with a dry heat flux. To date, a series of experiments have been carried out according to the first scenario in the MIR reactor channel and the corresponding data on the behavior of fuel elements have been obtained. An urgent task for today is to prepare and conduct reactor experiments according to the second scenario. The main experimental parameter that determines the behavior and final state of the studied fuel elements is their temperature. No experimental data were found on the critical heat flux for the rod bundles in the low coolant mass flow rate region (experiments in the MIR reactor channel can be conducted in the range of 200–250 kg/(m2s)). The available data are in the extrapolation range. The “steady-state crisis” experiment was conducted to obtain data on the critical heat flux value within the specified coolant mass flow rate range in the MIR reactor channel. The test object was a jacket fuel assembly composed of three shortened VVER-1000 fuel rods with a length of 1230 mm (the fuel part length = 1000 mm) installed in a triangular grid at a pitch of 12.75 mm, which is a cell of the VVER-1000 core. This assembly configuration is used for in-pile tests to study the behavior of fuel elements under emergency conditions. The in-pile testing results are presented. The paper shows the possibility of detecting the start and development of a dry heat flux based on the readings of thermocouples located inside the FE kernel. As a result, the directly measured test parameters were used to determine the critical heat flux value.

Experimental results from a high heat flux solar furnace with a molten metal-cooled receiver SOMMER

Solar Energy ◽  
2021 ◽  
Vol 221 ◽  
pp. 176-184
Author(s):  
F. Müller-Trefzer ◽  
K. Niedermeier ◽  
F. Fellmoser ◽  
J. Flesch ◽  
J. Pacio ◽  
...  
Keyword(s):  
Heat Flux ◽  
Molten Metal ◽  
High Heat ◽  
Experimental Results ◽  
Solar Furnace ◽  
High Heat Flux

Development of Cooling System for a Large Area at High Heat Flux by Using Flow Boiling in Narrow Channels

2009 ◽  
Author(s):  
Shinichi Miura ◽  
Yukihiro Inada ◽  
Yasuhisa Shinmoto ◽  
Haruhiko Ohta
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Mass Velocity ◽  
Cooling System ◽  
Volumetric Flow Rate ◽  
High Heat ◽  
High Heat Flux ◽  
Gap Size ◽  
Heated Channel

Advance of an electronic technology has caused the increase of heat generation density for semiconductors densely integrated. Thermal management becomes more important, and a cooling system for high heat flux is required. It is extremely effective to such a demand using flow boiling heat transfer because of its high heat removal ability. To develop the cooling system for a large area at high heat flux, the cold plate structure of narrow channels with auxiliary unheated channel for additional liquid supply was devised and confirmed its validity by experiments. A large surface of 150mm in heated length and 30mm in width with grooves of an apex angle of 90 deg, 0.5mm depth and 1mm in pitch was employed. A structure of narrow rectangular heated channel between parallel plates with an unheated auxiliary channel was employed and the heat transfer characteristics were examined by using water for different combinations of gap sizes and volumetric flow rates. Five different liquid distribution modes were tested and their data were compared. The values of CHF larger than 1.9×106W/m2 for gap size of 2mm under mass velocity based on total volumetric flow rate and on the cross section area of main heated channel 720kg/m2s or 1.7×106W/m2 for gap size of 5mm under 290kg/m2s were obtained under total volumetric flow rate 4.5×10−5m3/s regardless of the liquid distribution modes. Under several conditions, the extensions of dry-patches were observed at the upstream location of the main heated channel resulting burnout not at the downstream but at the upstream. High values of CHF larger than 2×106W/m2 were obtained only for gap size of 2mm. The result indicates that higher mass velocity in the main heated channel is more effective for the increase in CHF. It was clarified that there is optimum flow rate distribution to obtain the highest values of CHF. For gap size of 2mm, high heat transfer coefficient as much as 7.4×104W/m2K were obtained at heat flux 1.5×106W/m2 under mass velocity 720kg/m2s based on total volumetric flow rate and on the cross section area of main heated channel. Also to obtain high heat transfer coefficient, it is more useful to supply the cooling liquid from the auxiliary unheated channel for additional liquid supply in the transverse direction perpendicular to the flow in the main heated channel.

Development of Advanced High Heat Flux Cooling System for Power Electronics

2009 ◽  
Author(s):  
Yasuhisa Shinmoto ◽  
Shinichi Miura ◽  
Koichi Suzuki ◽  
Yoshiyuki Abe ◽  
Haruhiko Ohta
Keyword(s):  
Heat Flux ◽  
Power Electronics ◽  
Critical Heat Flux ◽  
Heating Surface ◽  
Narrow Channel ◽  
High Heat ◽  
High Heat Flux ◽  
Gap Size ◽  
Narrow Channels ◽  
Very High

Recent development in electronic devices with increased heat dissipation requires severe cooling conditions and an efficient method for heat removal is needed for the cooling under high heat flux conditions. Most researches are concentrated on small semiconductors with high heat flux density, while almost no existing researches concerning the cooling of a large semiconductor, i.e. power electronics, with high heat generation density from a large cooling area. A narrow channel between parallel plates is one of ideal structures for the application of boiling phenomena which uses the cooling for such large semiconductors. To develop high-performance cooling systems for power electronics, experiments on increase in critical heat flux (CHF) for flow boiling in narrow channels by improved liquid supply was conducted. To realize the cooling of large areas at extremely high heat flux under the conditions for a minimum gap size and a minimum flow rate of liquid supplied, the structure with auxiliary liquid supply was devised to prevent the extension of dry-patches underneath flattened bubbles generated in a narrow channel. The heating surface was experimented in two channels with different dimensions. The heating surfaces have the width of 30mm and the lengths of 50mm and 150mm in the flow direction. A large width of actual power electronics is realizable by the parallel installation of the same channel structure in the transverse direction. The cooling liquid is additionally supplied via sintered metal plates from the auxiliary unheated channels located at sides or behind the main heated channel. To supply the liquid to the entire heating surface, fine grooves are machined on the heating surface for enhance the spontaneous liquid supply by the aid of capillary force. The gap size of narrow channels are varied as 0.7mm, 2mm and 5mm. Distribution of liquid flow rate to the main heated channel and the auxiliary unheated channels were varied to investigate its effect on the critical heat flux. Test liquids employed are R113, FC72 and water. The systematic experiments by using water as a test liquid were conducted. Critical heat flux values larger than 2×106W/m2 were obtained at both gap sizes of 2mm and 5mm for a heated length of 150mm. A very high heat transfer coefficient as much as 1×105W/m2K was obtained at very high heat flux near CHF for the gap size of 2mm. This paper is a summary of experimental results obtained in the past by the present authors.

Thermal and Fluid Dynamic Behavior of a Horizontal Channel With Adiabatic Moving Lower Plate

2005 ◽  
Author(s):  
Assunta Andreozzi ◽  
Vincenzo Naso ◽  
Oronzio Manca
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Horizontal Channel ◽  
Lower Plate ◽  
Stationary Condition ◽  
Moving Plate ◽  
Plate Velocity

In this study a numerical investigation of mixed convection in air in horizontal parallel walled channels with moving lower plate is carried out. The moving lower plate has a constant velocity and it is adiabatic, whereas the upper one is heated at uniform heat flux. The effects of horizontal channel height, heat flux and moving plate velocity are analyzed. Results in terms of temperature and stream function fields are given and the mass flow rate per unit of length and divided by the dynamic viscosity is reported as a function of Reynolds number based on the moving plate velocity. For stationary condition of lower plate, a typical C–loop inside the horizontal channel is detected. Different flow motions are observed in the channel and the two reservoirs, depending on the heat flux values and the distance between the heated upper stationary plate and lower adiabatic moving plate. The dimensionless induced mass flow rate presents different increase between the Reynolds number lower or greater than 1000.

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.

Sign in / Sign up

Export Citation Format

Share Document