Flow pattern, pressure drop and heat transfer coefficient during two-phase flow boiling of R134a in pump-assisted separate heat pipe

2017 ◽  
Vol 85 ◽  
pp. 240-247 ◽  
Author(s):  
Jie Shao ◽  
Xiaohua Li ◽  
Zhenjiang Guo ◽  
Tengfei Ma ◽  
Ruijing Liu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Pipe ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase

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 Flow Conjugate Heat Transfer in Wavy Microchannel

2018 ◽  
Author(s):  
Nishant Tiwari ◽  
Manoj Kumar Moharana
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Bubble Nucleation ◽  
Bottom Surface ◽  
Substrate Thickness ◽  
Phase Flow ◽  
Two Phase

Flow boiling in microchannel heat sink offers an effective cooling solution for high power density micro devices. A three-dimensional numerical study based on volume of fraction model (VOF) coupled with evaporation condensation model accounting for the liquid-vapor phase change is undertaken to recreate vapor bubble formation in saturated flow boiling in wavy microchannel. Constant wall heat flux imposed at the bottom surface of the substrate while other faces are insulated. To understand the conjugate effects, simulations has been carried out for substrate thickness to channel depth ratio (δsf ∼ 1–5), substrate wall to fluid thermal conductivity ratio (ksf ∼ 22–300) and waviness (γ ∼ 0.008–0.04). Bubble nucleation, growth, and departure of bubble plays a significant role in heat transfer and pressure drop characteristics in two-phase flow in wavy microchannel. The coolant (water) temperature at the inlet is taken to be 373 K while flow was at atmospheric pressure. This makes shorter waiting period of bubble nucleation, and the number density of bubbles on the solid surface increases. This results in enhancement of the boiling effect, and thus with the presence of bubbles, the mixing of laminar boundary layers improves and enhances the overall heat transfer coefficient. Channel amplitude play an important factor that can suitably reduce the friction factor and enhances the heat transfer coefficient.

scholarly journals Evaluation of Heat Transfer Coefficient of Two-Phase Flow Boiling with R290 in Horizontal Mini Channel

2021 ◽  
Vol 88 (3) ◽  
pp. 88-95
Author(s):  
Ronald Akbar ◽  
Jong Taek Oh ◽  
Agus Sunjarianto Pamitran
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
The Heat Transfer Coefficient

Various experiments have been conducted on the heat transfer coefficient of two-phase flow boiling in mini channel tubes. In addition to obtaining data on the heat transfer coefficients through experiments, many researchers have also compared their experimental data using existing correlations. This research aims to determine the characteristics of the heat transfer coefficient of refrigerant R290 from the data used by processing and knowing the best heat transfer coefficient correlation in predicting the experimental data so that the results are expected to be a reference for designing a heat exchanger or for further research. The experimental data predicted is the two-phase flow boiling in a horizontal tube 3 mm diameter, with the mass flux of 50-180 kg/m2s, heat flux of 5-20 kW/m2, saturation temperature of 0-11 °C, and vapor quality of 0-1. The correlation used in this research is based on the asymptotic flow model, where the model is a combination of the nucleate and convective flow boiling mechanisms. The results show an effect of mass flux and heat flux on the experimental heat transfer coefficient and the predicted R290 heat transfer coefficient with asymptotic correlations had a good and similar result to the experimental data.

scholarly journals Flow Pattern of Two-phase Flow Boiling with Heat Transfer and Pressure Drop Using Natural Refrigerant (Propane) in Microchannel

Evergreen ◽  
2020 ◽  
Vol 7 (4) ◽  
pp. 544-548
Author(s):  
A.S. Pamitran ◽  
S. Novianto ◽  
N. Mohd-Ghazali ◽  
R.A Koestoer
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
Natural Refrigerant

scholarly journals Research on flow boiling heat transfer for vertical upward and downward flows along a minichannel with a smooth heated surface

2018 ◽  
Vol 70 ◽  
pp. 02014 ◽  
Author(s):  
Kinga Strąk ◽  
Magdalena Piasecka
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Flow Structures ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

The paper reports results for flow boiling heat transfer in a 1.7 mm deep minichannel vertically-oriented with upward and downward flow. The heated element for HFE-649 flowing upward or downward in a channel was a smooth plate. Infrared thermography allowed determining changes in temperature on the outer plate side. Two-phase flow structures were recorded through a glass pane at the other side of the channel being in contact with the fluid. Analysis of the results was performed on the basis of experimental series obtained for the same heat flux for upward and downward flows and two mass flow velocities. The results are presented as relationships between the heat transfer coefficient or the plate temperature and the channel length, boiling curves, and between the heat flux and the heat transfer coefficient and two-phase flow structure images. The impact of mass flow velocity on the heat transfer coefficient and two-phase flow structures for vertical upward and downward flows were discussed.

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.

Flow Boiling Heat Transfer and Pressure Drops of R1234ze(E) in a Silicon Micro-pin Fin Evaporator

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
C. Falsetti ◽  
M. Magnini ◽  
J. R. Thome
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
Pressure Drops ◽  
Pin Fin ◽  
The Heat Transfer Coefficient

The development of newer and more efficient cooling techniques to sustain the increasing power density of high-performance computing systems is becoming one of the major challenges in the development of microelectronics. In this framework, two-phase cooling is a promising solution for dissipating the greater amount of generated heat. In the present study, an experimental investigation of two-phase flow boiling in a micro-pin fin evaporator is performed. The micro-evaporator has a heated area of 1 cm2 containing 66 rows of cylindrical in-line micro-pin fins with diameter, height, and pitch of, respectively, 50 μm, 100 μm, and 91.7 μm. The working fluid is R1234ze(E) tested over a wide range of conditions: mass fluxes varying from 750 kg/m2 s to 1750 kg/m2 s and heat fluxes ranging from 20 W/cm2 to 44 W/cm2. The effects of saturation temperature on the heat transfer are investigated by testing three different outlet saturation temperatures: 25 °C, 30 °C, and 35 °C. In order to assess the thermal–hydraulic performance of the current heat sink, the total pressure drops are directly measured, while local values of heat transfer coefficient are evaluated by coupling high-speed flow visualization with infrared temperature measurements. According to the experimental results, the mass flux has the most significant impact on the heat transfer coefficient while heat flux is a less influential parameter. The vapor quality varies in a range between 0 and 0.45. The heat transfer coefficient in the subcooled region reaches a maximum value of about 12 kW/m2 K, whilst in two-phase flow it goes up to 30 kW/m2 K.

scholarly journals Peripheral Heat Transfer Coefficient during Flow Boiling: Comparison between 2-D and 1-D Data Reduction and Discussion about Their Applicability

Energies ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 4483 ◽  
Author(s):  
Rita Mastrullo ◽  
Alfonso William Mauro
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Data Reduction ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Operating Conditions ◽  
Phase Flow ◽  
Two Phase

This paper presents a critical analysis of possible data reduction procedures for the evaluation of local heat transfer coefficient during flow boiling experiments. The benchmark method using one-dimensional (1-D) heat transfer in a heated tube was compared to a new data reduction method in which both radial and circumferential contributions to the conductive heat transfer inside a metal tube are considered. Using published experimental flow boiling data, the circumferential profiles of the wall superheat, inner wall heat flux, and heat transfer coefficients were independently calculated with the two data reduction procedures. The differences between the two methods were then examined according to the different heat transfer behavior observed (symmetric or asymmetric), which in turn was related to the two-phase flow regimes occurring in a channel during evaporation. A statistical analysis using the mean absolute percentage error (MAPE) index was then performed for a database of 417 collected flow boiling data taken under different operating conditions in terms of working fluid, saturation temperature, mass velocity, vapor quality, and imposed heat flux. Results showed that the maximum deviations between the two methods could reach up to 130% in the case of asymmetric heat transfer. Finally, the possible uses of the two data reduction methods are discussed, pointing out that the two-dimensional (2-D) model is the most reliable method to be employed in the case of high-level modeling of two-phase flow or advanced design of heat exchangers and heat spreader systems.

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