scholarly journals Microlayer dynamics during the growth process of a single vapour bubble under subcooled flow boiling conditions

2021 ◽  
Vol 931 ◽  
Author(s):  
Gulshan Kumar Sinha ◽  
Surya Narayan ◽  
Atul Srivastava
Keyword(s):  
Bubble Growth ◽  
High Speed ◽  
Growth Process ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Working Fluid ◽  
Vapour Bubble ◽  
Subcooled Flow Boiling ◽  
High Speed Cinematography ◽  
Fringe Patterns

The phenomena of microlayer formation and its dynamic characteristics during the nucleate pool boiling regime have been widely investigated in the past. However, experimental works on real-time microlayer dynamics during nucleate flow boiling conditions are highly scarce. The present work is an attempt to address this lacuna and is concerned with developing a fundamental understanding of microlayer dynamics during the growth process of a single vapour bubble under nucleate flow boiling conditions. Boiling experiments have been conducted under subcooled conditions in a vertical rectangular channel with water as the working fluid. Thin-film interferometry combined with high-speed cinematography have been adopted to simultaneously capture the dynamic behaviour of the microlayer along with the bubble growth process. Transients associated with the microlayer have been recorded in the form of interferometric fringe patterns, which clearly reveal the evolution of the microlayer beneath the growing vapour bubble, the movement of the triple contact line and the growth of the dryspot region during the bubble growth process. While symmetric growth of the microlayer was confirmed in the early growth phase, the bulk flow-induced bubble deformation rendered asymmetry to its profile during the later stages of the bubble growth process. The recorded fringe patterns have been quantitatively analysed to obtain microlayer thickness profiles at different stages of the bubble growth process. For Re = 3600, the maximum thickness of the almost wedge-shaped microlayer was obtained as δ ~ 3.5 μm for a vapour bubble of diameter 1.6 mm. Similarly, for Re = 6000, a maximum microlayer thickness of δ ~ 2.5 μm was obtained for a bubble of diameter 1.1 mm.

scholarly journals Enhancement of Subcooled Flow Boiling Heat Transfer with High Porosity Sintered Fiber Metal

2021 ◽  
Vol 11 (3) ◽  
pp. 1237
Author(s):  
Yusuke Otomo ◽  
Edgar Santiago Galicia ◽  
Koji Enoki
Keyword(s):  
Heat Flux ◽  
Mass Flux ◽  
High Speed ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Working Fluid ◽  
High Porosity ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Porous Surfaces

We conducted experimental research using high-porosity sintered fiber attached on the surface, as a passive method to increase the heat flux for subcooled flow boiling. Two different porous thicknesses (1 and 0.5 mm) and one bare surface (0 mm) were compared under three different inlet subcooling temperatures (30, 50 and 70 K) and low mass flux (150–600 kg·m−2·s−1) using deionized water as the working fluid under atmospheric pressure. The test section was a rectangular channel, and the hydraulic diameter was 10 mm. The results showed that the heat flux on porous surfaces with a thickness of 1 and 0.5 mm increased by 60% and 40%, respectively, compared to bare surfaces at ΔTsat = 40 K at a subcooled temperature of 50 K and mass flux of 300 kg·m−2·s−1. An abrupt increase in the wall superheat was avoided, and critical heat flux (CHF) was not reached on the porous surfaces. The flow pattern and bubble were recorded with a high-speed camera, and the bubble dynamics are discussed.

BUBBLE BEHAVIOR AND BUBBLE GROWTH MODEL OF HIGHLY SUBCOOLED FLOW BOILING IN A VERTICAL RECTANGULAR CHANNEL

2018 ◽  
Vol 49 (12) ◽  
pp. 1199-1218
Author(s):  
Dewen Yuan ◽  
Xiao Yan ◽  
Deqi Chen ◽  
Yunke Zhong ◽  
Yanping Huang ◽  
...  
Keyword(s):  
Growth Model ◽  
Bubble Growth ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Bubble Behavior ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Experiment Research of Vapor Bubble Stochastic Characteristics in a Narrow Rectangular Channel

2016 ◽  
Author(s):  
Shaodan Li ◽  
Yong Li ◽  
Yuansheng Lin ◽  
Zhiguo Wei ◽  
Bangming Li ◽  
...  
Keyword(s):  
Vapor Bubble ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Nucleation Site ◽  
Bubble Nucleation ◽  
Maximum Diameter ◽  
Working Fluid ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Stochastic Characteristics

In most of the previous studies, the vapor bubble parameters were averaging processed in order to establish the empirical-based correlations or mechanism-based models. While it should be noted that the thermal hydraulic parameters around a bubble in a subcooled flow boiling channel are unsteady, that means the vapor bubbles behaves some stochastic characteristics. In the present research, a high speed visualization experiment was conducted in a subcooled flow boiling narrow rectangular channel to investigate the vapor bubble behavior. The working fluid in the experiment was deionized water. The obtained bubble images were processed by a digital image processing program in order to acquire the bubble parameters. The stochastic features of the bubbles were analyzed based on the experimental results. Two types of bubble behaviors were observed under different working conditions, which results in two types of bubble stochastic features. The results shown that the distribution function of the bubble maximum diameter in a specific nucleation site can be expressed by the normal distribution, while in the whole range of the observation window the distribution of the bubble maximum diameter was expressed by the lognormal distribution. The distribution of the second type bubble diameter depends on the local bubble nucleation site and the upstream bubble behaviors.

Bubble Growth During Subcooled Forced Convective Flow Boiling

2013 ◽  
Author(s):  
Qiang Zheng ◽  
Puzhen Gao ◽  
Jian Hu
Keyword(s):  
High Speed ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Average Diameter ◽  
Working Fluid ◽  
Absolute Pressure ◽  
Subcooled Flow ◽  
Single Side ◽  
Long Lifetime ◽  
Forced Convective Flow

The inception, growth and collapse of vapor bubbles were observed and measured by using visual method under subcooled flow nucleation. The test section was a single-side heated rectangular channel by the scale of 2×40×700mm and the working fluid was clean water. The working condition was set as: the inlet subcooling Δ Tin = 330 °C, the mass flux m = 694kg/(m2s), the heat flux q = 210kW/m2 and the absolute pressure p = 0.22MPa. A high speed camera was used to record the bubble behaviors at the speed of 5000fps (frame per second). The results showed that the bubble lifetime was from 0.4ms to 2.2ms and the fraction of bubble with short lifetime was bigger than that of long lifetime. The bubble’s average diameter showed a linear relationship with the lifetime and it was also found that the sliding bubble would enhance heat transfer.

Heat Transfer Characteristics and Flow Pattern Visualization for Flow Boiling in a Vertical Narrow Microchannel

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Kan Zhou ◽  
Hua Zhu ◽  
Wei Li ◽  
Junye Li ◽  
Kuang Sheng ◽  
...  
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Heat Dissipation ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Rectangular Microchannel ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Recently, microchannel heat sinks have been emerged as a kind of high performance cooling scheme to meet the heat dissipation requirement of electronics packaging and integration. In this study, an experimental investigation of subcooled flow boiling in a high-aspect-ratio rectangular microchannel was conducted with de-ionized water as the working fluid. In the experimental operations, the mass flux was varied from 200 to 400 kg/m2s and the imposed heat flux from 3 to 20 W/cm2 while the fluid inlet temperature was regulated constantly at 90 °C. The boiling curves, onset of nucleate boiling (ONB), and flow patterns of subcooled flow boiling were investigated with the aid of instrumental measurements and a high-speed camera. The slope of the boiling curves increased sharply once the superheat needed to initiate the onset of nucleate boiling was attained, with lower superheat required of boiling incipience for lower mass fluxes. Meanwhile, the initiative superheat and heat flux of onset of nucleate boiling were compared with the existing correlations in the literature with good agreement. As for the flow visualization images, slug flow and reverse backflow were observed, where transient local dryout as well as rewetting occurred. A facile image processing tool was developed to profile the transient development and progression of the liquid–vapor interface and partial dryout patches in microchannels, which proved that the physical quantities of bubble dynamics for the elongation period during subcooled boiling could be well detected and calculated.

Boiling Curves and Visual Observations of Subcooled Flow Boiling of Water Over a Horizontal Plate Heater in a Rectangular Channel

2005 ◽  
Author(s):  
Ho Sung Lee ◽  
Andrew T. O’Neill
Keyword(s):  
Forced Convection ◽  
High Speed ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Convection Flow ◽  
Cross Sectional ◽  
Subcooled Flow Boiling ◽  
Engine Cooling ◽  
Subcooled Flow ◽  
Forced Convection Flow

A 20-mm-width × 30-mm-length flat copper heater in a 30-mm-width × 20-mm-height cross-sectional rectangular channel was used to simulate the forced convection flow and subcooled flow boiling in standard engine cooling systems. To visualize the effects of velocity, subcooling, and pressure, a high-speed camera was used. The subcooling ranged from 10°C to 50°C, the velocity from 0.5 m/s to 4 m/s, the pressure from 1 atm to 2.6 atm, and the heat flux from 0 W/cm2 to 80 W/cm2. The measured forced convection and boiling curves of water were presented along with high-speed photographs.

Pressure Drop Characteristics of Flow Boiling in Narrow Rectangular Channel

2013 ◽  
Author(s):  
Shu-ping Lv ◽  
Liang-ming Pan ◽  
De-qi Chen
Keyword(s):  
Pressure Drop ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Working Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Experimental Conditions ◽  
Subcooled Flow Boiling ◽  
Flow Pressure

Pressure drop is the earliest and the most extensive issue in the research of two phase flow. Due to the influence of various factors on two phase flow pressure drop, there is no accurate and general correlation on this issue yet. In this paper, pressure drop characteristics of flow boiling were studied in a single vertical narrow rectangular channel with cross-section of 47 mm by 1.8 mm using water as working fluid. Subcooled flow boiling was experimentally investigated. The experimental conditions included inlet subcooling (2°C∼18°C), mass flow rate (222.3∼457.4 kg.m2s−1) and heat flux (113.6∼270.5 kW/m2). The influence of these parameters on the characteristics of flow boiling pressure drop has been investigated. The experimental results show that the conventional correlations failed to predict the two-phase flow pressure drop in this narrow rectangular channel. According to experiment results, a modified Chisholm correlation was proposed, and the new correlation gave more accurate predictions of the pressure drop.

High Speed Imaging and Two-Phase Flow Patterns During Flow Boiling in a Single Microchannel

2008 ◽  
Author(s):  
Jacqueline Barber ◽  
Khellil Sefiane ◽  
David Brutin ◽  
Lounes Tadrist
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Pressure Sensors ◽  
Flow Patterns ◽  
Bubble Nucleation ◽  
Phase Flow ◽  
Vapour Bubble ◽  
Two Phase ◽  
Over Time

Boiling in microchannels remains elusive due to the lack of full understanding of the mechanisms involved. A powerful tool in achieving better comprehension of the mechanisms is detailed imaging and analysis of the two phase flow at a fundamental level. We induced boiling in a single microchannel geometry (hydraulic diameter 727 μm), using a refrigerant FC-72, to investigate several flow patterns. A transparent, metallic, conductive deposit has been developed on the exterior of rectangular microchannels, allowing simultaneous uniform heating and visualisation to be conducted. The data presented in this paper is for a particular case with a uniform heat flux of 4.26 kW/m2 applied to the microchannel and inlet liquid mass flowrate, held constant at 1.33×10−5 kg/s. In conjunction with obtaining high-speed images and videos, sensitive pressure sensors are used to record the pressure drop profiles across the microchannel over time. Bubble nucleation, growth and coalescence, as well as periodic slug flow, are observed in the test section. Phenomena are noted, such as the aspect ratio and Reynolds number of a vapour bubble, which are in turn correlated to the associated pressure drops over time. From analysis of our results, images and video sequences with the corresponding physical data obtained, it is possible to follow visually the nucleation and subsequent both ‘free’ and ‘confined’ growth of a vapour bubble over time.

Two-Phase Flow in Microchannels

2001 ◽  
Author(s):  
G. Hetsroni ◽  
A. Mosyak ◽  
Z. Segal
Keyword(s):  
Heat Sink ◽  
High Speed ◽  
Single Phase ◽  
Flow Boiling ◽  
Electronics Cooling ◽  
Working Fluid ◽  
Microchannel Heat Sink ◽  
Two Phase ◽  
Infrared Radiometry ◽  
Phase Water

Abstract Experimental investigation of a heat sink for electronics cooling is performed. The objective is to keep the operating temperature at a relatively low level of about 323–333K, while reducing the undesired temperature variation in both the streamwise and transverse directions. The experimental study is based on systematic temperature, flow and pressure measurements, infrared radiometry and high-speed digital video imaging. The heat sink has parallel triangular microchannels with a base of 250μm. According to the objectives of the present study, Vertrel XF is chosen as the working fluid. Experiments on flow boiling of Vertrel XF in the microchannel heat sink are performed to study the effect of mass velocity and vapor quality on the heat transfer, as well as to compare the two-phase results to a single-phase water flow.

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