The Onset of Nucleate Boiling in a Micro-Channel Subjected to a Pulsed Heat Flux

A numerical study of subcooled onset of nucleate boiling (ONB) in a micro-channel under pulsed heating using the volume of fluids (VOF) model was conducted. The ONB time was determined when the void fraction at the microheater surface starts to exist. A smooth thin Pt heater was located between the water in the channel and the solid material. The theoretical superheat for homogeneous nucleation did not predict the transient ONB results of convective flow of water. Once heat load increases at the heater, transient flow boiling starts to occur. From a parametric study, it was found that the time constant increases with large substrate thermal diffusivity, low Reynolds number, and large channel diameter.

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Two-Phase Electronic Cooling Using Mini-Channel and Micro-Channel Heat Sinks: Part 1—Design Criteria and Heat Diffusion Constraints

Journal of Electronic Packaging ◽

10.1115/1.2905700 ◽

1994 ◽

Vol 116 (4) ◽

pp. 290-297 ◽

Cited By ~ 65

Author(s):

Morris B. Bowers ◽

Issam Mudawar

Keyword(s):

Heat Flux ◽

Heat Sink ◽

Structural Integrity ◽

Flow Boiling ◽

Heated Surface ◽

Heat Sinks ◽

Heat Diffusion ◽

High Heat Flux ◽

Micro Channel ◽

Channel Diameter

Mini-channel (D = 2.54 mm) and micro-channel (D = 510 μm) heat sinks with a 1-cm2 heated surface were tested for their high heat flux performance with flow boiling of R-113. Experimental results yielded CHF values in excess of 200 W cm−2 for flow rates less than 95 ml min−1 (0.025 gpm) over a range of inlet subcooling from 10 to 32°C. Heat diffusion within the heat sink was analyzed to ascertain the optimum heat sink geometry in terms of channel spacing and overall thickness. A heat sink thickness to channel diameter ratio of 1.2 provided a good compromise between minimizing overall thermal resistance and structural integrity. A ratio of channel pitch to diameter of less than two produced negligible surface temperature gradients even with a surface heat flux of 200 W cm−2. To further aid in determining channel diameter for a specific cooling application, a pressure drop model was developed, which is presented in the second part of the study.

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Transient flow boiling in a semi-annular duct: From the Onset of Nucleate Boiling to the Fully Developed Nucleate Boiling

International Journal of Heat and Mass Transfer ◽

10.1016/j.ijheatmasstransfer.2019.04.069 ◽

2019 ◽

Vol 138 ◽

pp. 699-712 ◽

Cited By ~ 1

Author(s):

V. Scheiff ◽

N. Baudin ◽

P. Ruyer ◽

J. Sebilleau ◽

C. Colin

Keyword(s):

Transient Flow ◽

Flow Boiling ◽

Nucleate Boiling ◽

Annular Duct

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A Numerical Study of Flow Boiling Heat Transfer of Nanoemulsion in Mini-Channel Heat Exchanger

Volume 2: Development and Applications in Computational Fluid Dynamics; Industrial and Environmental Applications of Fluid Mechanics; Fluid Measurement and Instrumentation; Cavitation and Phase Change ◽

10.1115/fedsm2018-83396 ◽

2018 ◽

Author(s):

Jiajun Xu ◽

Musa Acar ◽

Naresh Poudel ◽

Jaime Rios ◽

Thanh N. Tran

Keyword(s):

Heat Transfer ◽

Heat Exchanger ◽

Boiling Heat Transfer ◽

Single Phase ◽

Numerical Study ◽

Flow Boiling ◽

Heat Transfer Fluid ◽

Working Fluid ◽

Vof Model ◽

Flow Boiling Heat Transfer

In this study, a numerical study has been performed on the two-phase heat transfer of a new nanostructured heat transfer fluid: Water-in-Polyalphaolefin (PAO) Nanoemulsion Fluid inside a mini-channel heat exchanger using ANSYS FLUENT. Nanoemulsion fluids are liquid suspensions of nanosized droplets, which are part of a broad class of colloidal dispersions. The nanoemulsion fluid can be formed spontaneously by self-assembly, in which these nanodroplets are in fact swollen micelles. To simplify the complexity of the numerical model, the nanoemulsion fluid was then treated as a homogenous fluid during single-phase and only the water vaporizes during the phase change. The volume of fraction (VOF) model with Pressure-Velocity coupling based Semi Implicit Method for Pressure Linked Equations (SIMPLE) iterative algorithm is employed to solve the continuity, momentum, energy equations in two dimensional domains. The thermophysical properties of the nanoemulsion fluid were measured and used for the current simulation. The results were verified using the experimental results and has shown good agreement. This study has demonstrated the feasibility of simplyig the simulation of flow boiling heat transfer of this new heat transfer fluid through treating it as a homogenous fluid during single-phase convective heat transfer and separating the vapor phase of the nano-micelles during flow boiling. This study has also shown that this Water-in-PAO nanoemulsion could function as a good and alternative conventional working fluid in heat transfer applications.

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The Effect of Hydraulic Diameter on Flow Boiling within Single Rectangular Microchannels and Comparison of Heat Sink Configuration of a Single and Multiple Microchannels

Energies ◽

10.3390/en14206641 ◽

2021 ◽

Vol 14 (20) ◽

pp. 6641

Author(s):

Konstantinos Vontas ◽

Manolia Andredaki ◽

Anastasios Georgoulas ◽

Nicolas Miché ◽

Marco Marengo

Keyword(s):

Heat Transfer ◽

Thermal Resistance ◽

Single Phase ◽

Transient Flow ◽

Numerical Study ◽

Flow Boiling ◽

Hydraulic Diameter ◽

Rectangular Microchannel ◽

Rectangular Microchannels ◽

Parallel Microchannels

Phase change heat transfer within microchannels is considered one of the most promising cooling methods for the efficient cooling of high-performance electronic devices. However, there are still fundamental parameters, such as the effect of channel hydraulic diameter Dh, whose effects on fluid flow and heat transfer characteristics are not clearly defined yet. The objective of the present work is to numerically investigate the first transient flow boiling characteristics from the bubble inception up to the first stages of the flow boiling regime development, in rectangular microchannels of varying hydraulic diameters, utilising an enhanced custom VOF-based solver. The solver accounts for conjugate heat transfer effects, implemented in OpenFOAM and validated in the literature through experimental results and analytical solutions. The numerical study was conducted through two different sets of simulations. In the first set, flow boiling characteristics in four single microchannels of Dh = 50, 100, 150, and 200 μm with constant channel aspect ratio of 0.5 and length of 2.4 mm were examined. Due to the different Dh, the applied heat and mass flux values varied between 20 to 200 kW/m2 and 150 to 2400 kg/m2s, respectively. The results of the two-phase simulations were compared with the corresponding initial single-phase stage of the simulations, and an increase of up to 37.4% on the global Nu number Nuglob was revealed. In the second set of simulations, the effectiveness of having microchannel evaporators of single versus multiple parallel microchannels was investigated by performing and comparing simulations of a single rectangular microchannel with Dh of 200 μm and four-parallel rectangular microchannels, each having a hydraulic diameter Dh of 50 μm. By comparing the local time-averaged thermal resistance along the channels, it is found that the parallel microchannels configuration resulted in a 23.3% decrease in the average thermal resistance R¯l compared to the corresponding single-phase simulation stage, while the flow boiling process reduced the R¯l by only 5.4% for the single microchannel case. As for the developed flow regimes, churn and slug flow dominated, whereas liquid film evaporation and, for some cases, contact line evaporation were the main contributing flow boiling mechanisms.

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Three-Dimensional Numerical Study of R134a Flow Boiling Characteristics in a Circular Tube under Overload

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4042909 ◽

2019 ◽

pp. 1-11

Author(s):

Yu Xu ◽

Yafeng Chen ◽

Guohua Li

Keyword(s):

Heat Transfer ◽

Circular Tube ◽

Numerical Study ◽

Flow Boiling ◽

Saturation Pressure ◽

Three Dimensional ◽

Potential Method ◽

Momentum Equation ◽

Frictional Pressure Drop ◽

Vof Model

Three-dimensional numerical study of R134a flow boiling under overload was conducted based on the VOF model. A series of simulations were implemented with a 1.002 mm circular tube under six gravity levels ranging from 1 to 15 g and three directions (θ) ranging from 0° to 180° with mass fluxes of 200, 350, and 500 kg/m2 s, outlet vapor qualities of 0.041, 0.082, and 0.164, and saturation pressure of 0.71MPa. The gravity conditions were introduced into the momentum equation during the simulations. Comparisons among flow boiling characteristics under different gravity levels and directions are made, and significant effects of overload are found. With the increasing overload, the vapor phase distributions of flow boiling gradually turn into forms similar to ellipsoids/spheres, stratified flow, and elongated slugs, at θ = 0°, 90°, and 180°, respectively. Accordingly, the heat transfer coefficient keeps almost stable at θ = 0° and 180°, but decreases obviously at θ = 90°; the frictional pressure drop decreases at θ = 0°, decreases slightly at θ = 90°, but increases at θ = 180°. Making θ away from 90° is a potential method to avoid the flow boiling heat transfer deterioration under overload.

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