Heat Transfer Mechanism and Flow Pattern During Flow Boiling of Water in a Vertical Narrow Channel: Experimental Results

2006 ◽  
Author(s):  
Ewelina Sobierska ◽  
Rudi Kulenovic ◽  
Rainer Mertz
Keyword(s):  
Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Transfer Mechanism ◽  
Phase Flow ◽  
Fluid Temperature ◽  
Heat Transfer Mechanism ◽  
Two Phase ◽  
Mass Fluxes

Experimental investigations on flow boiling phenomena in a vertical narrow rectangular microchannel with the hydraulic diameter dh = 0.48 mm were carried out. The experiments were performed under fluid-inlet subcooling conditions with deionised and degassed water for different mass fluxes. Investigations on pressure drop and heat transfer during single-and two-phase flow have been carried out. Moreover, flow visualisation of the two-phase flow patterns along the channel was performed using a digital high-speed video camera. The present work outlines local heat transfer coefficients for three mass fluxes (200, 700 and 1500 kg/m2s) and heat fluxes (30–110, 35–150 and 65–200 kW/m2, respectively) during two-phase flow. The fluid temperature at the inlet was about 50 °C what corresponds to inlet subcooling, depending on flow pressure conditions, from 34 °C to 57 °C. The visual observations were used to obtain a better insight about the heat transfer mechanism.

Experimental Study of Heat Transfer, Pressure Drop, and Dryout for Flow Boiling of Water in an Oil Heated Minichannel

2004 ◽  
Author(s):  
Levi A. Campbell ◽  
Satish Kandlikar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Test Section ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Small Diameter ◽  
Constant Heat Flux ◽  
Phase Flow ◽  
Two Phase ◽  
Mass Fluxes

Heat transfer and pressure drop, are experimentally recorded for flow boiling water in a single 706 μm circular copper channel 158.75 mm long. Heat is supplied by heat transfer oil at specified temperatures to a helical channel in the test section. In contrast to other current experimental techniques for flow boiling in small diameter tubes, a uniform temperature boundary condition is employed rather than a constant heat flux condition. The principal results of these experiments are two-phase flow boiling heat transfer rates and an analysis of the time-dependent pressure drop signature during two-phase flow in a minichannel. The range of experiments includes mass fluxes of 43.8–3070 kg/m2s and wall temperatures of 100°C–171.2°C. In all cases the test section water inlet is subcooled to between 72.9°C and 99.6°C. The inlet pressures used are 1.1–230.5 kPa (gage).

Experimental Investigation of Flow Boiling in a Vertical Narrow Channel

2005 ◽  
Author(s):  
Ewelina Sobierska ◽  
Klaudia Chmiel ◽  
Rudi Kulenovic ◽  
Rainer Mertz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Experimental Investigations ◽  
Flow Visualisation ◽  
Phase Flow ◽  
Two Phase

Experimental investigations on thermofluid-dynamic phenomena in a vertical narrow rectangular microchannel with the hydraulic diameter dh = 0.27 mm were carried out. The experiments are performed under fluid-inlet subcooling conditions with de-ionised and degassed water for different mass fluxes (50–2000 kg/m2s) and heat fluxes (2–150 kW/m2). Moreover, flow visualisation of the two-phase flow patterns along the channel is performed using a digital high-speed video camera. Investigations on pressure drop during single- and two-phase flow have been carried out. The present work is concentrated on two-phase heat transfer. The mean heat transfer coefficient and the local heat transfer coefficient at saturated conditions were calculated and the latter ones was compared with available correlations.

scholarly journals Evaluation of Pressure Drop of Two-Phase Flow Boiling with R290 in Horizontal Mini Channel

2021 ◽  
Vol 89 (2) ◽  
pp. 160-166
Author(s):  
Fajriocta Umar ◽  
Jong Taek Oh ◽  
Agus Sunjarianto Pamitran
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Two Phase ◽  
Mass Fluxes ◽  
Channel Tube ◽  
Inner Diameter

Various experiments on the pressure drop of a two-phase flow boiling in a mini channel tube have been carried out. This study is aimed at characteristics of the pressure drop of a two-phase flow boiling using a refrigerant R290. The experiment uses a horizontal, stainless steel, 2-m-long mini-channel tube with a 3-mm inner diameter. The experiment has been carried out using various data with the vapor qualities ranging from 0.1 to 0.9, the mass fluxes ranging 50 kg/m2s to 180 kg/m2s, and the heat fluxes ranging from 5 kW/m2 to 20 kW/m2. Furthermore, several homogeneous and separated methods were used to predict the experimental data. Li and Hibiki’s correlation give the best overall deviation pressure drop value is the most accurate with its deviation amounting 19.47%.

Two-Phase Flow and Heat Transfer in Pin-Fin Enhanced Micro-Gaps With Non-Uniform Heating

2013 ◽  
Author(s):  
Steven A. Isaacs ◽  
Yogendra Joshi ◽  
Yue Zhang ◽  
Muhannad S. Bakir ◽  
Yoon Jo Kim
Keyword(s):  
Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Pin Fin ◽  
Flow And Heat Transfer ◽  
Imaging Results

In modern microprocessors, thermal management has become one of the main hurdles in continued performance enhancement. Cooling schemes utilizing single phase microfluidics have been investigated extensively for enhanced heat dissipation from microprocessors. However, two-phase fluidic cooling devices are becoming a promising approach, and are less understood. This study aims to examine two-phase flow and heat transfer within a pin-fin enhanced micro-gap. The pin-fin array covered an area of 1cm × 1cm and had a pin diameter, height and pitch of 150μm, 200μm and 225μm, respectively, (aspect ratio of 1.33). Heating from two upstream heaters was considered. The working fluid used was R245fa. The average heat transfer coefficient was evaluated for a range of heat fluxes and flow rates. Flow regime visualization was performed using high-speed imaging. Results indicate a sharp transition to convective flow boiling mechanism. Unique, conically-shaped two-phase wakes are recorded, demonstrating 2D spreading capability of the device. Surface roughness features are also discussed.

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.

Numerical Simulation of Subcooled Flow Boiling Heat Transfer in Helical Tubes

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Jong Chull Jo ◽  
Woong Sik Kim ◽  
Chang-Yong Choi ◽  
Yong Kab Lee
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Steam Generator ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Transfer Analysis ◽  
Normal Operation ◽  
Phase Flow ◽  
Two Phase ◽  
Side Flow

This paper addresses the numerical simulation of two-phase flow heat transfer in the helically coiled tubes of an integral type pressurized water reactor steam generator under normal operation using a computational fluid dynamics code. The shell-side flow field where a single-phase fluid flows in the downward direction is also calculated in conjunction with the tube-side two-phase flow characteristics. For the calculation of tube-side two-phase flow, the inhomogeneous two-fluid model is used. Both the Rensselaer Polytechnic Institute wall boiling model and the bulk boiling model are implemented for the numerical simulations of boiling-induced two-phase flow in a vertical straight pipe and channel, and the computed results are compared with the available measured data. The conjugate heat transfer analysis method is employed to calculate the conduction in the tube wall with finite thickness and the convections in the internal and external fluids simultaneously so as to match the fluid-wall-fluid interface conditions properly. Both the internal and external turbulent flows are simulated using the standard k-ε model. From the results of the present numerical simulation, it is shown that the bulk boiling model can be applied to the simulation of two-phase flow in the helically coiled steam generator tubes. In addition, the present simulation method is considered to be physically plausible in the light of discussions on the computed results.

Numerical Simulation of Forced Convective Boiling in a Microchannel

2018 ◽  
Vol 10 (4) ◽  
Author(s):  
Yun Whan Na ◽  
J. N. Chung
Keyword(s):  
Numerical Simulation ◽  
Two Phase Flow ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Simulation Method ◽  
Flow Patterns ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Two Phase ◽  
Convective Boiling

Forced convective flow boiling in a single microchannel with different channel heights was studied through a numerical simulation method to investigate bubble dynamics, two-phase flow patterns, and boiling heat transfer. The momentum and energy equations were solved using a finite volume (FV) numerical method, while the liquid–vapor interface of a bubble is captured using the volume of fluid (VOF) technique. The effects of different constant wall heat fluxes and different channel heights on the boiling mechanisms were investigated. The effects of liquid velocity on the bubble departure diameter were also analyzed. The predicted bubble shapes and distribution profiles together with two-phase flow patterns are also provided.

Flow Boiling Heat Transfer and Two-Phase Flow Instability of Nanofluids in a Minichannel

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Leyuan Yu ◽  
Aritra Sur ◽  
Dong Liu
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Flow Instabilities ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Boiling Heat Transfer

Single-phase convective heat transfer of nanofluids has been studied extensively, and different degrees of enhancement were observed over the base fluids, whereas there is still debate on the improvement in overall thermal performance when both heat transfer and hydrodynamic characteristics are considered. Meanwhile, very few studies have been devoted to investigating two-phase heat transfer of nanofluids, and it remains inconclusive whether the same pessimistic outlook should be expected. In this work, an experimental study of forced convective flow boiling and two-phase flow was conducted for Al2O3–water nanofluids through a minichannel. General flow boiling heat transfer characteristics were measured, and the effects of nanofluids on the onset of nucleate boiling (ONB) were studied. Two-phase flow instabilities were also explored with an emphasis on the transition boundaries of onset of flow instabilities (OFI). It was found that the presence of nanoparticles delays ONB and suppresses OFI, and the extent is correlated to the nanoparticle volume concentration. These effects were attributed to the changes in available nucleation sites and surface wettability as well as thinning of thermal boundary layers in nanofluid flow. Additionally, it was observed that the pressure-drop type flow instability prevails in two-phase flow of nanofluids, but with reduced amplitude in pressure, temperature, and mass flux oscillations.

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