Recent Advances in Thermal Modeling of Micro-Evaporators for Cooling of Microprocessors

2007 ◽  
Author(s):  
John R. Thome ◽  
Re´mi Revellin ◽  
Bruno Agostini ◽  
Jung Eung Park
Keyword(s):  
Flow Pattern ◽  
Hot Spots ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Base Temperature ◽  
Two Phase ◽  
Pressure Drops ◽  
Flow Boiling Heat Transfer ◽  
Recent Experimental Work

Cooling of microprocessors using flow boiling of low pressure refrigerants in multi-microchannel evaporator cooling elements is a promising technique for dissipation of footprint heat fluxes of over 300 W/cm2 while maintaining the chip safely below its maximum working temperature, providing a nearly uniform chip base temperature and minimizing energy consumption. The present invited lecture focuses on our recent experimental work and modeling of two-phase flow and boiling in single and multi-microchannels, covering: bubble dynamics, bubble coalescence, flow pattern recognition, diabatic flow pattern map, critical heat flux, hot spots, flow boiling heat transfer and two-phase pressure drops.

Flow Boiling Characteristics for R1234ze(E) in 1.0 and 2.2 mm Circular Channels

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Cristiano Bigonha Tibiriçá ◽  
Gherhardt Ribatski ◽  
John Richard Thome
Keyword(s):  
Heat Transfer ◽  
Flow Pattern ◽  
High Speed ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Internal Diameter ◽  
Steel Tubes ◽  
Experimental Campaign ◽  
Microscale Flow ◽  
Flow Boiling Heat Transfer

Experimental flow boiling heat transfer results are presented for horizontal 1.0 and 2.2 mm I.D. (internal diameter) stainless steel tubes for tests with R1234ze(E), a new refrigerant developed as a substitute for R134a with a much lower global warming potential (GWP). The experiments were performed for these two tube diameters in order to investigate a possible transition between macro and microscale flow boiling behavior. The experimental campaign includes mass velocities ranging from 50 to 1500 kg/m2 s, heat fluxes from 10 to 300 kW/m2, exit saturation temperatures of 25, 31 and 35 °C, vapor qualities from 0.05 to 0.99 and heated lengths of 180 mm and 361 mm. Flow pattern characterization was performed using high speed videos. Heat transfer coefficient, critical heat flux and flow pattern data were obtained. R1234ze(E) demonstrated similar thermal performance to R134a data when running at similar conditions.

Local Measurements of Flow Boiling Heat Transfer on Hot Spots in 3D Compatible Radial Microchannels

2015 ◽  
Author(s):  
Fanghao Yang ◽  
Mark Schultz ◽  
Pritish Parida ◽  
Evan Colgan ◽  
Robert Polastre ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Power Density ◽  
High Power ◽  
Hot Spots ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Hot Spot ◽  
Uniform Heat Flux ◽  
Two Phase ◽  
Flow Boiling Heat Transfer

Hot spots and temperature non-uniformities are critical thermal characteristics of current high power electronics and future three dimensional (3D) integrated circuits (ICs). Experimental investigation to understand flow boiling heat transfer on hot spots is required for any two-phase cooling configuration targeting these applications. This work investigates hot spot cooling utilizing novel radial microchannels with embedded pin arrays representing through-silicon-via (TSV) interconnects. Inlet orifices were designed to distribute flow in radial channels in a manner that supplies appropriate amounts of coolant to high-power-density cores. Specially designed test vehicles and systems were used to produce non-uniform heat flux profiles with nominally 20 W/cm2 background heating, 200 W/cm2 core heating and up to 21 W/mm2 hot spot (0.2 mm × 0.2 mm) heating to mimic a stackable eight core processor die (20 mm × 20 mm) with two hot spots on each core. The temperatures associated with flow boiling heat transfer at the hot spots were locally measured by resistance temperature detectors (RTDs) integrated between the heat source and sink. At nominal pressure and flow conditions, use of R1234ze in these devices resulted in a maximum hot spot temperature (Ths) of under 63 °C and average Ths of 57 °C at a hot spot power density of 21 W/mm2. A semi-empirical model was used to calculate the equivalent heat transfer rate around the hot spots which can provide a baseline for future studies on local thermal management of hot spots.

Two-phase pressure drop due to friction in micro-channel

2013 ◽  
Vol 228 (5) ◽  
pp. 921-931 ◽  
Author(s):  
Tae-Woo Lim ◽  
Sam-Sang You ◽  
Jong-Su Kim ◽  
Serng-Bae Moon ◽  
Dong-Hoan Seo
Keyword(s):  
Pressure Drop ◽  
Flow Boiling ◽  
Homogeneous Model ◽  
Absolute Error ◽  
Heat Fluxes ◽  
Micro Channel ◽  
Two Phase ◽  
Pressure Drops ◽  
Frictional Pressure Drop ◽  
New Correlation

This paper deals with an experimental investigation to measure the frictional pressure drops for two-phase flow boiling in a micro-channel with a hydraulic diameter of 500 µm. First, the experimental study is performed under the test conditions: heat fluxes ranging from 100 to 400 kW/m2, vapor qualities from 0 to 0.2, and mass fluxes of 200, 400 and 600 kg/m2s. Then, the frictional pressure drop during flow boiling is estimated using two models: the homogeneous model and the separated flow model. The experimental results show that the two-phase multiplier decreases with the increase of mass flux. In addition, the measured pressure drops are compared with those from a few correlation models available for macro-scales and mini/micro-scales. Finally, the present paper proposes a new correlation for two-phase frictional pressure drops in mini/micro-scales. This correlation model is developed based on the Chisholm constant C as a function of two-phase Reynolds and Weber numbers. It is found that the new correlation satisfactorily predicts the experimental data within mean absolute error (MAE) of 3.9%.

scholarly journals Experimental Investigation and Prediction on Pressure Drop during Flow Boiling in Horizontal Microchannels

Micromachines ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 510
Author(s):  
Yan Huang ◽  
Bifen Shu ◽  
Shengnan Zhou ◽  
Qi Shi
Keyword(s):  
Pressure Drop ◽  
Flow Model ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Separated Flow ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Vapor Quality ◽  
Two Phase ◽  
Gas Flux

In this paper, two-phase pressure drop data were obtained for boiling in horizontal rectangular microchannels with a hydraulic diameter of 0.55 mm for R-134a over mass velocities from 790 to 1122, heat fluxes from 0 to 31.08 kW/m2 and vapor qualities from 0 to 0.25. The experimental results show that the Chisholm parameter in the separated flow model relies heavily on the vapor quality, especially in the low vapor quality region (from 0 to 0.1), where the two-phase flow pattern is mainly bubbly and slug flow. Then, the measured pressure drop data are compared with those from six separated flow models. Based on the comparison result, the superficial gas flux is introduced in this paper to consider the comprehensive influence of mass velocity and vapor quality on two-phase flow pressure drop, and a new equation for the Chisholm parameter in the separated flow model is proposed as a function of the superficial gas flux . The mean absolute error (MAE ) of the new flow correlation is 16.82%, which is significantly lower than the other correlations. Moreover, the applicability of the new expression has been verified by the experimental data in other literatures.

Flow Boiling Heat Transfer, Pressure Drop, and Flow Pattern for CO2 in a 3.5mm Horizontal Smooth Tube

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Chang Yong Park ◽  
Pega Hrnjak
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

Abstract C O 2 flow boiling heat transfer coefficients and pressure drop in a 3.5mm horizontal smooth tube are presented. Also, flow patterns were visualized and studied at adiabatic conditions in a 3mm glass tube located immediately after a heat transfer section. Heat was applied by a secondary fluid through two brass half cylinders to the test section tubes. This research was performed at evaporation temperatures of −15°C and −30°C, mass fluxes of 200kg∕m2s and 400kg∕m2s, and heat flux from 5kW∕m2 to 15kW∕m2 for vapor qualities ranging from 0.1 to 0.8. The CO2 heat transfer coefficients indicated the nucleate boiling dominant heat transfer characteristics such as the strong dependence on heat fluxes at a mass flux of 200kg∕m2s. However, enhanced convective boiling contribution was observed at 400kg∕m2s. Surface conditions for two different tubes were investigated with a profilometer, atomic force microscope, and scanning electron microscope images, and their possible effects on heat transfer are discussed. Pressure drop, measured at adiabatic conditions, increased with the increase of mass flux and quality, and with the decrease of evaporation temperature. The measured heat transfer coefficients and pressure drop were compared with general correlations. Some of these correlations showed relatively good agreements with measured values. Visualized flow patterns were compared with two flow pattern maps and the comparison showed that the flow pattern maps need improvement in the transition regions from intermittent to annular flow.

scholarly journals Supercapillary Architecture‐Activated Two‐Phase Boundary Layer Structures for Highly Stable and Efficient Flow Boiling Heat Transfer

2019 ◽  
Vol 32 (2) ◽  
pp. 1905117 ◽  
Author(s):  
Wenming Li ◽  
Zuankai Wang ◽  
Fanghao Yang ◽  
Tamanna Alam ◽  
Mengnan Jiang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Phase Boundary ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Two Phase ◽  
Layer Structures ◽  
Flow Boiling Heat Transfer
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