Quasi-steady and transient study of heat transfer during sub-cooled flow boiling in a small aspect ratio microchannel

2020 ◽  
Vol 133 ◽  
pp. 103446
Author(s):  
Mrinal Jagirdar ◽  
Poh Seng Lee
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Flow Boiling ◽  
Small Aspect Ratio ◽  
Transient Study

Confined Bubble and Heat Transfer during Flow Boiling in a High Aspect Ratio Mini-Channel

2011 ◽  
Vol 312-315 ◽  
pp. 548-553 ◽  
Author(s):  
Yuan Wang ◽  
Khellil Sefiane
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Bubble Growth ◽  
Flow Boiling ◽  
Critical Time ◽  
Heat Fluxes ◽  
Equivalent Radius ◽  
Mass Fluxes ◽  
Transfer Mechanisms ◽  
Working Liquid

Single vapour bubble growth and heat transfer mechanism during flow boiling in a rectangular horizontal mini-channel were experimentally investigated. The hydraulic diameter of the channel was 1454 μm, with an aspect ratio (Win/din) of 10. Degassed FC-72 was used as the working liquid. In this paper, bubble equivalent radius was found to increase linearly till a critical time, beyond which the growth turned into exponential. Bubble growth rate increases with increasing heat flux. Heat transfer mechanisms of the bubble growth at different heat fluxes and mass fluxes were discussed. In addition, the relation between thermal and flow conditions with bubble temporal geometry was explored.

Experimental Comparison of Flow Boiling Heat Transfer in High Aspect Ratio Microchannels With Plain and Grooved Walls

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Xiao Cheng ◽  
Huiying Wu
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Liquid Film ◽  
High Aspect Ratio ◽  
Heat Sink ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Experimental Comparison ◽  
Dry Out

Abstract The dry-out easily occurs on high-aspect ratio microchannel sidewalls due to the decreasing of liquid film thickness. In this paper, the triangular microgrooves possessing the characteristic of evaporating meniscus were designed on the microchannel sidewalls. The heat sink consisted of 33 parallel microchannels, having a hydraulic diameter of 100 μm and an aspect ratio of 4. A platinum film heater and platinum resistance temperature detectors (RTDs) were integrated on the backside of the heat sink to realize uniform heating and precise temperature measurement, respectively. Flow boiling visualization experiments were carried out by high-speed camera in triangular groove-wall and plain-wall microchannels at mass fluxes of 148–490 kg/m2·s and inlet temperatures of 42 °C and 60 °C. The boiling curve, heat transfer coefficient (HTC), pressure drop, and two-phase flow boiling instability were systematically investigated to assess the flow boiling performances. Thin liquid film was observed in the triangular grooves during the dry-out process, compared to the dry-out in plain-wall microchannels. The oscillations of wall temperature, inlet temperature, and pressure drop were significantly suppressed in triangular groove-wall microchannels. Moreover, the earlier onset of nucleate boiling, improved heat flux, and HTC were realized in triangular groove-wall microchannels compared to plain-wall microchannels. Therefore, triangular groove design on the sidewalls is a promising solution to enhance boiling heat transfer and suppress flow boiling instabilities for high-aspect ratio microchannels.

scholarly journals Effect of Functional Surfaces with Gradient Mixed Wettability on Flow Boiling in a High Aspect Ratio Microchannel

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 239
Author(s):  
Vahid Ebrahimpour Ahmadi ◽  
Akam Aboubakri ◽  
Abdolali Khalili Sadaghiani ◽  
Khellil Sefiane ◽  
Ali Koşar
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Bubbly Flow ◽  
Reference Sample ◽  
Hydrophobic Surface ◽  
Heat Fluxes ◽  
Mixed Wettability

Flow boiling is one of the most effective phase-change heat transfer mechanisms and is strongly dependent on surface properties. The surface wettability is a crucial parameter, which has a considerable effect on the heat transfer performance, particularly in flow boiling. The contact angle determines the number of nucleation sites as well as bubble dynamics and flow patterns. This study introduces three new generation mixed wettability surfaces and compares them with a wholly hydrophobic surface reference sample, in flow boiling in a high aspect ratio microchannel. The mixed wettability substrates have five regions as fully Al2O3, (hydrophobic zone) region, three different patterned configurations with various A* values, and fully SiO2 (hydrophilic zone) region, where A* is defined as A Al2O3/A total (hydrophobicity ratio). Boiling heat transfer results were obtained for each surface at various wall heat fluxes and three different mass fluxes. According to the obtained results, significant enhancements in heat transfer (by up to 56.7%) could be obtained with biphilic surfaces compared to the reference sample (hydrophobic surface). Performed flow visualization proves that the tested biphilic surfaces enhance heat transfer by reducing the bubbly flow regime and extending the slug regime.

scholarly journals The Thermal Charging Performance of Finned Conical Thermal Storage System Filled with Nano-Enhanced Phase Change Material

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1605
Author(s):  
Mohammad Ghalambaz ◽  
Hassan Shirivand ◽  
Kasra Ayoubi Ayoubloo ◽  
S.A.M. Mehryan ◽  
Obai Younis ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Phase Change ◽  
Inclination Angle ◽  
Conical Shell ◽  
Volume Fraction ◽  
Small Radius ◽  
Design Parameters ◽  
Small Aspect Ratio ◽  
Charging Time

A latent heat thermal energy storage (LHTES) unit can store a notable amount of heat in a compact volume. However, the charging time could be tediously long due to weak heat transfer. Thus, an improvement of heat transfer and a reduction in charging time is an essential task. The present research aims to improve the thermal charging of a conical shell-tube LHTES unit by optimizing the shell-shape and fin-inclination angle in the presence of nanoadditives. The governing equations for the natural convection heat transfer and phase change heat transfer are written as partial differential equations. The finite element method is applied to solve the equations numerically. The Taguchi optimization approach is then invoked to optimize the fin-inclination angle, shell aspect ratio, and the type and volume fraction of nanoparticles. The results showed that the shell-aspect ratio and fin inclination angle are the most important design parameters influencing the charging time. The charging time could be changed by 40% by variation of design parameters. Interestingly a conical shell with a small radius at the bottom and a large radius at the top (small aspect ratio) is the best shell design. However, a too-small aspect ratio could entrap the liquid-PCM between fins and increase the charging time. An optimum volume fraction of 4% is found for nanoparticle concentration.

815 Heat Transfer Characteristics on the Surfaces of a Turbine Blade with Small Aspect Ratio

2001 ◽  
Vol 2001.38 (0) ◽  
pp. 263-264
Author(s):  
Katsuichi UCHIDA ◽  
Masakazu OBATA ◽  
Kohei SHOJI
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Turbine Blade ◽  
Small Aspect Ratio ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics
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