Orientation Effects on Critical Heat Flux From Discrete, In-Line Heat Sources in a Flow Channel

1993 ◽  
Vol 115 (4) ◽  
pp. 973-985 ◽  
Author(s):  
C. O. Gersey ◽  
I. Mudawar
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Liquid Velocity ◽  
Heat Fluxes ◽  
Heat Sources ◽  
Low Velocity ◽  
Two Phase ◽  
Chip Surface ◽  
Horizontal Orientation ◽  
Limited Success

The effects of flow orientation on critical heat flux (CHF) were investigated on a series of nine in-line simulated microelectronic chips in Fluorinert FC-72. The chips were subjected to coolant in upflow, downflow, or horizontal flow with the chips on the top or bottom walls of the channel with respect to gravity. Changes in angle of orientation affected CHF for velocities below 200 cm/s, with some chips reaching CHF at heat fluxes below the pool boiling and flooding-induced CHF values. Increased subcooling was found to dampen this adverse effect of orientation slightly. Critical heat flux was overwhelmingly caused by localized dryout of the chip surface. However, during the low velocity downflow tests, low CHF values were measured because of liquid blockage by vapor counterflow and vapor stagnation in the channel. At the horizontal orientation with downward-facing chips, vapor/liquid stratification also yielded low CHF values. Previously derived correlations for water and long, continuous heaters had limited success in predicting CHF for the present discontinuous heater configuration. Because orientation has a profound effect on the hydrodynamics of two-phase flow and, consequently, on CHF for small inlet velocities, downflow angles should be avoided, or when other constraints force the usage of downflow angles, the inlet liquid velocity should be sufficiently large.

scholarly journals Heat transfer and critical heat flux for two-phase immersion cooling of an inverter power module

2021 ◽  
Vol 2116 (1) ◽  
pp. 012007
Author(s):  
I T’ Jollyn ◽  
J Nonneman ◽  
M De Paepe
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Flux Measurement ◽  
Base Plate ◽  
Heat Fluxes ◽  
Power Module ◽  
Two Phase ◽  
Heat Flux Measurement

Abstract Heat transfer and critical heat flux measurement are reported for pool boiling cooling of the base plate of an inverter power module. Novec 649 is used as refrigerant. Heat fluxes up to 14.6 W/cm2 were applied with refrigerant saturation temperatures of 36 °C, 41 °C and 46 °C. The measured boiling curves are comparable to those reported for similar refrigerants. The critical heat fluxes range from 12.1 W/cm2 to 14.6 W/cm2, which corresponds within 10% to the correlation of Zuber. The critical heat flux is significantly lower than the highest heat fluxes expected from the power module, indicating that methods to increase the critical heat flux are needed to enable two-phase power module cooling.

Critical Heat Flux on a Horizontal Cylinder in an Upward Subcooled and Low-Quality Two-Phase Crossflow

1986 ◽  
Vol 108 (2) ◽  
pp. 441-447 ◽  
Author(s):  
M. K. Jensen ◽  
M. Pourdashti
Keyword(s):  
Heat Flux ◽  
Experimental Investigation ◽  
Flow Regime ◽  
Critical Heat Flux ◽  
Horizontal Tube ◽  
Horizontal Cylinder ◽  
Regime Transition ◽  
Low Velocity ◽  
Two Phase ◽  
Flow Regime Transition

An experimental investigation has been conducted to determine the low-velocity critical heat flux (CHF) behavior on a single horizontal tube in a subcooled and low-quality two-phase crossflow of R-113. Data were obtained over a range of velocities (up to 0.3 m/s), subcooling (0 to 14 K), and qualities (0 < x < +30 percent) at two pressures. There was a linear decrease in the CHF with increasing quality up to about 10 percent quality; then, due to a flow regime transition, the CHF remained relatively constant. A correlation has been developed which predicted well the subcooled and low-quality region CHF condition in the linearly decreasing portion of the curve. Data from the literature are also predicted well.

scholarly journals CFD parametric investigation for two-phase flow of ammonia-water mixing in bubble pump tube

2019 ◽  
pp. 324-324
Author(s):  
Ali Benhmidene ◽  
Kozhikkatil Arjun ◽  
Bechir Chaouachi
Keyword(s):  
Heat Flux ◽  
Flow Regime ◽  
Liquid Velocity ◽  
Turbulent Viscosity ◽  
Heat Fluxes ◽  
Two Phase ◽  
Ansys Fluent ◽  
Ammonia Water ◽  
Hydrodynamic Parameters ◽  
Bubble Pump

Two-dimensional numerical simulation of two-phase ammonia/water flowing under uniformly heated tube is used. ANSYS Fluent is used to predict the time evolution of thermal and hydrodynamic parameters of the bubble pump. Phase-dependent turbulent models are used to calculate the turbulent viscosity of each phase. Through User-Defined Functions, different interfacial force models and the wall boiling model are implemented in the code. The simulation results show a slow oscillation of hydrodynamic parameters such as pressure, mass flux, vapour velocity and liquid velocity during the initial stage of operation; however, a vigorous oscillation is detected for the temperature behaviour. The amplitude and period of oscillation decrease with the heat input increasing. By using the void fraction contour, it is possible to predict the flow regime along the bubble pump at different times of the operation. The domination of flow regime is the function of heat flux too. It is bubbly to slug for heat fluxes less than 5kW/m? and transits from churn to annular for 15 and 50kW/m? of heat flux.

Study on Critical Heat Flux in Rectangular Channels Heated From One or Both Sides at Pressures Ranging From 0.1 to 14 MPa

1996 ◽  
Vol 118 (3) ◽  
pp. 680-688 ◽  
Author(s):  
Y. Sudo
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Model ◽  
High Water ◽  
Experimental Results ◽  
Low Velocity ◽  
Two Phase ◽  
Flow Models ◽  
Rectangular Channels ◽  
Boiling Flow

In this study, a quantitative analysis of critical heat flux (CHF) in rectangular heated channels was carried out based on new flow models and the analytical results were compared with existing experimental results at pressures of about 0.1 to 14 MPa with a water mass flux of 3.9 to 28,000 kg/m2s and inlet water subcooling ranging from 0 to 328 K. The flow models proposed for CHF were a completely separated two-phase flow model with a macroliquid sublayer under conditions of comparatively low velocity and zero water subcooling at outlet of the channel and a subcooled boiling flow model with a macroliquid sublayer under the conditions of high water subcooling and high velocity, respectively. It could be shown that the analytical CHF results gave good predictions for over 800 existing experimental results, identifying the effects of predominant parameters as regards CHF.

scholarly journals Determination of Pool Boiling Critical Heat Flux Enhancement in Nanofluids

2007 ◽  
Author(s):  
Bao H. Truong
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Porous Coating ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Sem Images ◽  
Heat Transfer Coefficients ◽  
Nucleate Boiling Heat Transfer

Nanofluids are engineered colloids composed of nano-size particles dispersed in common fluids such as water or refrigerants. Using an electrically controlled wire heater, pool boiling Critical Heat Flux (CHF) of Alumina and Silica water-based nanofluids of concentration less than or equal to 0.1 percent by volume were measured. Silica nanofluids showed a CHF enhancement up to 68% and there seems to be a monotonic relationship between the nanoparticle concentration and the magnitude of enhancement. Alumina nanofluids had a CHF enhancement up to 56% but the peak occurred at the intermediate concentration. The boiling curves in nanofluid were found to shift to the left of that of water and correspond to higher nucleate boiling heat transfer coefficients in the two-phase flow regime. Scanning Electron Microscopy (SEM) images show a porous coating layer of nanoparticles on wires subjected to nanofluid CHF tests. These coating layers change the morphology of the heater’s surface, and are responsible for the CHF enhancement. The thickness of the coating was estimated using SEM and was found ranging from 3.0 to 6.0 micrometers for Alumina, and 3.0 to 15.0 micrometers for Silica.

Experimental Measurements and CFD Evaluation of the Onset Flow Boiling at Low Pressure and High Subcooling Flow of R-11 Within Vertical Annulus

2014 ◽  
Author(s):  
Y. Bouaichaoui ◽  
R. Kibboua ◽  
M. Matkovič
Keyword(s):  
Heat Flux ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Fluid Model ◽  
Computer Code ◽  
Computational Method ◽  
Subcooled Boiling ◽  
Two Phase ◽  
Local Flow ◽  
Wide Range

The knowledge of the onset of subcooled boiling in forced convective flow at high liquid velocity and subcooling is of importance in thermal hydraulic studies. Measurements were performed under various conditions of mass flux, heat flux, and inlet subcooling, which enabled to study the influence of different boundary conditions on the development of local flow parameters. Also, some measurements have been compared to the predictions by the three-dimensional two-fluid model of subcooled boiling flow carried out with the computer code ANSYS-CFX-13. A computational method based on theoretical studies of steady state two phase forced convection along a test section loop was released. The calculation model covers a wide range of two phase flow conditions. It predicts the heat transfer rates and transitions points such as the Onset of Critical Heat Flux.

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