2D computational investigation into transport phenomena of subcooled and saturated flow boiling in large length to diameter ratio micro-channel heat sinks

2022 ◽  
Vol 183 ◽  
pp. 122128
Author(s):  
Ilhwan Yeo ◽  
Seunghyun Lee
Keyword(s):  
Flow Boiling ◽  
Transport Phenomena ◽  
Diameter Ratio ◽  
Heat Sinks ◽  
Micro Channel ◽  
Computational Investigation ◽  
Saturated Flow ◽  
Large Length ◽  
Length To Diameter Ratio

Two-Phase Flow and Heat Transfer in Rectangular Micro-Channels

2004 ◽  
Vol 126 (3) ◽  
pp. 288-300 ◽  
Author(s):  
Weilin Qu ◽  
Seok-Mann Yoon ◽  
Issam Mudawar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Heat Sinks ◽  
Phase Flow ◽  
Micro Channel ◽  
Two Phase

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406×2.032mm2 cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Features unique to two-phase micro-channel flow were identified and employed to validate key assumptions of an annular flow boiling model that was previously developed to predict pressure drop and heat transfer in two-phase micro-channel heat sinks. This earlier model was modified based on new findings from the adiabatic two-phase flow study. The modified model shows good agreement with experimental data for water-cooled heat sinks.

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

1994 ◽  
Vol 116 (4) ◽  
pp. 290-297 ◽  
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.

Optimal Parameters Analysis of Dynamical Vibration Absorption Lathe Tool with Large Length to Diameter Ratio

2011 ◽  
Vol 121-126 ◽  
pp. 2146-2150
Author(s):  
Bai Qin ◽  
Bo Zhang ◽  
Xiao Dong Yu ◽  
Yan Qin Zhang ◽  
Gui Hua Han ◽  
...  
Keyword(s):  
Frequency Response ◽  
Diameter Ratio ◽  
Flexible Body ◽  
Equivalent Viscous Damping ◽  
Vibration Absorption ◽  
Large Length ◽  
Relationship Of ◽  
System Frequency ◽  
Lathe Tool ◽  
Length To Diameter Ratio

The multi flexible body dynamical simulation model of dynamical vibration absorption lathe tool with large length to diameter ratio is built up according to the actual experiment lathe tool by using the software ADAMS and ANSYS. The experiment data which are consistent with the simulation result verify the correctness of the multi flexible body dynamical model. Aiming at reducing the peak value of system frequency response, the dynamical vibration absorption system is optimized. The optimized frequency curve shows that the system frequency response is improved obviously. On this basis the influence of the mass of heavy turning body on the vibration system is discussed. Also, the relationship of the mass of heavy turning body and the optimal system parameters including equivalent stiffness coefficient and equivalent viscous damping coefficient is studied. This offers the design considerations about the structure of the dynamical vibration absorption lathe tool with large length to diameter ratio.

Experimental Investigation On the Change in Flow Boiling Characteristics Due to Boiling-Induced Copper Ageing

2021 ◽  
Author(s):  
Prasanna Jayaramu ◽  
Shashwat Jain ◽  
Sateesh Gedupudi ◽  
Sarit Kumar Das
Keyword(s):  
Surface Morphology ◽  
Surface Characterization ◽  
Flow Boiling ◽  
Surface Oxidation ◽  
Surface Characteristics ◽  
Heat Sinks ◽  
Micro Channel ◽  
Fresh Sample ◽  
Characterization Study ◽  
Micro Channels

Abstract Heat sinks and heat exchangers based on flow boiling in mini/micro-channels are expected to be more compact and efficient. One of the major challenges while using copper material for phase-change heat transfer application is the change in surface characteristics after prolonged usage due to the thermal oxidation of surface over time. The present study involves the repeated experimental runs of flow boiling of water in a 1 mm hydraulic diameter end-milled copper channel to verify the influence of ageing on the thermal and hydraulic performance. As it is difficult to measure the surface wettability in a mini/micro-channel, the present work makes use of the ageing and surface characterization study conducted on the dummy copper samples to infer the influence of ageing on mini/micro-channel surface characteristics and consequently its boiling performance. The test involves measuring over a period of time the wetting behaviors of the end-milled copper samples left in water at three different conditions, one in a constant temperature bath maintained at 60 oC and 1 atm and the remaining two in a pool of boiling water at 110 oC and 120 oC. The study compares the fresh sample and the aged sample for the surface oxidation, surface chemical composition and surface morphology, and discusses the changes in contact angle and surface morphology caused by copper ageing.

Transport Phenomena in Two-Phase Micro-Channel Heat Sinks

2002 ◽  
Author(s):  
Weilin Qu ◽  
Issam Mudawar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Hydrodynamic Instability ◽  
Transport Phenomena ◽  
Flow Patterns ◽  
Heat Sinks ◽  
Micro Channel ◽  
Two Phase ◽  
Convective Boiling ◽  
Micro Channels

The design and reliable operation of a two-phase micro-channel heat sink require a fundamental understanding of the complex transport phenomena associated with convective boiling in small, parallel coolant passages. This understanding is the primary goal of this paper. This goal is realized by exploring the following aspects of boiling in micro-channels: hydrodynamic instability, two-phase flow patterns, pressure drop, and convective boiling heat transfer. High-speed photographic methods were used to determine dominant flow patterns and explore as well as characterize hydrodynamic instabilities. Two types of dynamic instability were identified, a severe pressure drop oscillation and a mild parallel channel instability, and a simple method is recommended to completely suppress the former. Predictions of three popular two-phase pressure drop models and correlations were compared to micro-channel water data, and only a separated flow (Lockhart-Martinelli) correlation based on the assumption of laminar flow in both phases gave acceptable predictions. Several popular heat transfer correlations were also examined and deemed unsuitable for micro-channel heat sinks because all these correlations are based on turbulent flow assumptions, and do not capture the unique features of micro-channel flow such as abrupt transition to slug flow, hydrodynamic instability, and high droplet entrainment in the annular regime. These findings point to the need for further study of boiling behavior and new predictive tools specifically tailored to micro-channel heat sinks.

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