Influences of wall superheat and channel width ratio on bubble behaviors and heat transfer within a heated microchannel T-junction

2021 ◽  
Vol 126 ◽  
pp. 105481
Author(s):  
Zhe Yan ◽  
Haoxiang Huang ◽  
Wentao Pan ◽  
Bili Deng ◽  
Zhenhai Pan
Keyword(s):  
Heat Transfer ◽  
Channel Width ◽  
Width Ratio ◽  
Wall Superheat

Boiling Heat Transfer and Critical Heat Flux Enhancement of Upward- and Downward-Facing Heater in Nanofluids

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Muhamad Zuhairi Sulaiman ◽  
Masahiro Takamura ◽  
Kazuki Nakahashi ◽  
Tomio Okawa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Flux Enhancement ◽  
Optimum Configuration ◽  
Wall Superheat ◽  
Nucleate Boiling Heat Transfer

Boiling heat transfer (BHT) and critical heat flux (CHF) performance were experimentally studied for saturated pool boiling of water-based nanofluids. In present experimental works, copper heaters of 20 mm diameter with titanium-oxide (TiO2) nanocoated surface were produced in pool boiling of nanofluid. Experiments were performed in both upward and downward facing nanofluid coated heater surface. TiO2 nanoparticle was used with concentration ranging from 0.004 until 0.4 kg/m3 and boiling time of tb = 1, 3, 10, 20, 40, and 60 mins. Distilled water was used to observed BHT and CHF performance of different nanofluids boiling time and concentration configurations. Nucleate boiling heat transfer observed to deteriorate in upward facing heater, however; in contrast effect of enhancement for downward. Maximum enhancements of CHF for upward- and downward-facing heater are 2.1 and 1.9 times, respectively. Reduction of mean contact angle demonstrate enhancement on the critical heat flux for both upward-facing and downward-facing heater configuration. However, nucleate boiling heat transfer shows inconsistency in similar concentration with sequence of boiling time. For both downward- and upward-facing nanocoated heater's BHT and CHF, the optimum configuration denotes by C = 400 kg/m3 with tb = 1 min which shows the best increment of boiling curve trend with lowest wall superheat ΔT = 25 K and critical heat flux enhancement of 2.02 times.

HEAT TRANSFER TO DISPERSED SWIRL FLOW OF HIGH-PRESSURE WATER WITH LOW WALL SUPERHEAT

1991 ◽  
Vol 4 (2) ◽  
pp. 153-169 ◽  
Author(s):  
P. Papadopoulos ◽  
D. M. France ◽  
W. J. Minkowycz
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Swirl Flow ◽  
Wall Superheat ◽  
Pressure Water

Effect of the Bottom and Top Configurations on Pool Film Boiling Around a Vertical Finite-Length Cylinder

2011 ◽  
Author(s):  
Satoru Momoki ◽  
Kenichi Araki ◽  
Toru Shigechi ◽  
Takashi Yamada ◽  
Kaoru Toyoda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Finite Length ◽  
Lateral Surface ◽  
Film Boiling ◽  
Bottom Surface ◽  
Flat Bottom ◽  
Surface Area Ratio ◽  
Test Cylinder ◽  
Saturated Water ◽  
Wall Superheat

The bottom configuration of a vertical finite-length cylinder is an important factor to examine the convective heat transfer by film boiling around a vertical finite-length cylinder, as the vapor generated under the bottom surface grows thicker during flowing upward along the vertical lateral surface and finally leaves the top surface as bubbles. In this study, four types of silver cylinder with a vertical lateral length equal to the diameter of 32mm were prepared for the possible combinations of bottom and top configurations: with a flat bottom and a flat top, with a flat bottom and a curved top, with a curved bottom and a flat top, and with a curved bottom and a curved top, where “flat” refers to “horizontal” and “curved” to “convex hemispherical”. Quenching experiments have been carried out for the test cylinders for saturated and subcooled water at atmospheric pressure. The initial temperature in the measurement is 600 °C. Boiling curves were obtained from the cooling curves measured using a K-type thermocouple inserted near the center on the axis of the test cylinder and the film boiling process was observed by still and high speed video cameras. The following results were obtained from the experiments using four types of test cylinder. 1. For saturated water, the test cylinders are entirely covered with a thick continuous vapor film, however, the effect of bottom configuration on film boiling heat transfer is appeared within 18% in terms of the wall heat flux averaged over the entire surface depending on the vapor fluid flow on the bottom and vertical lateral surfaces. 2. For the cylinders with a flat bottom surface, the wall heat flux averaged over the entire surface increases significantly with an increase in liquid sub cooling. This is attributed to that the convective heat transfer and the surface area ratio on the vertical lateral surface are predominant and govern the total heat transfer. 3. The effects of the cylinder top configurations on the film boiling heat transfer are small as the heat transfer on the top surface is small compared with that on the vertical lateral surface. 4. The differences between film boiling characteristics due to the bottom and top configurations are explained by examining the average heat transfer coefficient composed of the heat transfer coefficient and the surface area ratio on each surface. 5. The minimum wall superheat corresponding to the vapor-film-collapse is almost constant at 133K for four types of test cylinder in saturated water. In subcooled water, the minimum wall superheat for the cylinders with a flat bottom surface is larger than that for the cases with a convex hemispherical bottom surface.

The Numerical Simulation Research on Heat Transfer Enhancement of the Interpolation-Tubular Air Pre-Heater with Semi-Elliptic Cylinder Shell Vortex Generator

2013 ◽  
Vol 397-400 ◽  
pp. 230-234
Author(s):  
De Fan Qing ◽  
Qing Feng Ai
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Vortex Generator ◽  
Elliptic Cylinder ◽  
Attack Angle ◽  
Width Ratio ◽  
Transfer Enhancement ◽  
Simulation Research ◽  
Number Range ◽  
Dip Angle

The semi-elliptic cylinder shell vortex generator set in the interpolation-tubular air pre-heater was studied. And by changing the high-width Ratiov, dip angleα, attack angleβ, spacingsof vortex generator to research the heat transfer and resistance properties under different working conditions, and the optimization structure of vortex generator was determined. The heating medium of the air pre-heater is the flue gas that passes across tube outside, and the cooling air as the cooling medium in the tube longitudinal scoured. The Reynolds number range is 25000 ~ 40000. The research shows that: semi-elliptic cylinder vortex generator can obviously improve the heat transfer performance, the optimization structure of the semi-elliptic cylinder vortex generator: high-width ratiov= 0.45, attack angleβ= 65 °, dip angleα= 15 °, spans= 90 mm, the heat transfer enhancement comprehensive effect raised about 43.2%~72.6%.

An Experimental Investigation of Microchannel Size Effects on Flow Boiling With De-Ionized Water

2009 ◽  
Author(s):  
Bradley T. Holcomb ◽  
Tannaz Harirchian ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Flow Boiling ◽  
Dielectric Liquid ◽  
Channel Width ◽  
Boiling Curve ◽  
Test Pieces ◽  
Parallel Microchannels

The heat transfer characteristics during flow boiling of deionized water in parallel microchannels are investigated. The silicon heat sinks contain an array of integrated heaters and diodes for localized heat-flux control and temperature measurement. The channel widths for the three different test pieces range from 250 μm to 2200 μm, with a nominal depth for all channels of 400 μm. The present study investigates the effects of the channel width and mass flux on the boiling performance. This study follows a previous study using a wetting dielectric liquid, and aims to understand the role of wetting since water is relatively non-wetting. From the results of the present study, a weak dependence of the boiling curve and heat transfer coefficient on mass flux was observed. Varying the channel width also does not have a strong effect on either the boiling curve or the heat transfer coefficient. The experimental results are compared to those obtained previously for a dielectric liquid. They are also compared with predictions from several correlations from the literature.

Liquid-Solid Contact During Flow Film Boiling of Subcooled Freon-11

1990 ◽  
Vol 112 (2) ◽  
pp. 465-471 ◽  
Author(s):  
K. H. Chang ◽  
L. C. Witte
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Heat Fluxes ◽  
Film Boiling ◽  
Small Scale ◽  
Solid Contact ◽  
Heated Cylinder ◽  
Experimental Heat ◽  
Wall Superheat ◽  
Flow Film Boiling

Liquid-solid contacts were measured for flow film boiling of subcooled Freon-11 over an electrically heated cylinder equipped with a surface microthermocouple probe. No systematic variation of the extent of liquid-solid contact with wall superheat, liquid subcooling, or velocity was detected. Only random small-scale contacts that contribute negligibly to overall heat transfer were detected when the surface was above the homogeneous nucleation temperature of the Freon-11. When large-scale contacts were detected, they led to an unexpected intermediate transition from local film boiling to local transition boiling. An explanation is proposed for these unexpected transitions. A comparison of analytical results that used experimentally determined liquid-solid contact parameters to experimental heat fluxes did not show good agreement. It was concluded that the available model for heat transfer accounting for liquid-solid contact is not adequate for flow film boiling.

Experimental Study of Flow and Heat Transfer Characteristics in Silicon-Based Corrugated Microchannels

2009 ◽  
Author(s):  
Huimin Tang ◽  
Huiying Wu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
High Efficiency ◽  
Cooling System ◽  
Width Ratio ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Total Thermal Resistance ◽  
Transfer Characteristics ◽  
Silicon Based

In this paper, the silicon-based corrugated microchannels used for the heat transfer enhancement were fabricated by MEMS technology for the first time. Both the flow and convective heat transfer characteristics of the deionized water through these corrugated microchannels were investigated experimentally, and comparisons were performed between corrugated microchannels and straight microchannels with the same cross-sectional aspect ratio (height-to-width ratio) and same hydraulic diameter. Experimental results showed that both the flow friction and Nusselt number in corrugated microchannels increased considerably compared with those in straight microchannels, and this increase became enlarged with the increase in the Reynolds number. With the same pumping power, using corrugated microchannels instead of straight microchannels caused the reduction in the total thermal resistance. The heat transfer enhancement mechanism of the corrugated microchannels was discussed. The results presented in this paper help to design the high efficiency integrated chip cooling system.

The Effect of Turning Vanes on Pressure Loss and Heat Transfer of a Ribbed Rectangular Two-Pass Internal Cooling Channel

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Marco Schüler ◽  
Frank Zehnder ◽  
Bernhard Weigand ◽  
Jens von Wolfersdorf ◽  
Sven Olaf Neumann
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Stokes Equations ◽  
Turbine Blades ◽  
Local Heat Transfer ◽  
Width Ratio ◽  
Channel Height ◽  
Internal Cooling ◽  
Thermochromic Liquid Crystal ◽  
Sharp Turn

Gas turbine blades are usually cooled by using ribbed serpentine internal cooling passages, which are fed by extracted compressor air. The individual straight ducts are connected by sharp 180 deg bends. The integration of turning vanes in the bend region lets one expect a significant reduction in pressure loss while keeping the heat transfer levels high. Therefore, the objective of the present study was to investigate the influence of different turning vane configurations on pressure loss and local heat transfer distribution. The investigations were conducted in a rectangular two-pass channel connected by a 180 deg sharp turn with a channel height-to-width ratio of H/W=2. The channel was equipped with 45 deg skewed ribs in a parallel arrangement with e/dh=0.1 and P/e=10. The tip-to-web distance was kept constant at Wel/W=1. Spatially resolved heat transfer distributions were obtained using the transient thermochromic liquid crystal technique. Furthermore static pressure measurements were conducted in order to determine the influence of turning vane configurations on pressure loss. Additionally, the configurations were investigated numerically by solving the Reynolds-averaged Navier–Stokes equations using the finite-volume solver FLUENT. The numerical grids were generated by the hybrid grid generator CENTAUR. Three different turbulence models were considered: the realizable k-ε model with two-layer wall treatment, the k-ω-SST model, and the v2-f turbulence model. The results showed a significant influence of the turning vane configuration on pressure loss and heat transfer in the bend region and the outlet pass. While using an appropriate turning vane configuration, pressure loss was reduced by about 25%, keeping the heat transfer at nearly the same level in the bend region. An inappropriate configuration led to an increase in pressure loss while the heat transfer was reduced in the bend region and outlet pass.

Pool Boiling Heat Transfer Characteristics on Twisted Tube Bundles in a Flooded Evaporator

2013 ◽  
Vol 416-417 ◽  
pp. 1049-1055
Author(s):  
Ji Cheng Zhou ◽  
Dong Sheng Zhu ◽  
Zheng Qi Huo ◽  
Jun Li ◽  
Yan Li
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Heat Transfer Characteristics ◽  
Pool Boiling Heat Transfer ◽  
Twisted Tube ◽  
Wall Superheat ◽  
Twisted Tubes

The objectives of this paper are to study the pool boiling heat transfer characteristics of twisted tubes in the flooded evaporator. The twisted tubes are processed from common circular evaporating tubes with an outer diameter of 15.88mm. The outer major axis diameter, minor axis diameter, wall thickness and length of the twisted tube are 19.50mm, 11.28mm, 1.09mm, and 3310mm, respectively. The outside tube pool boiling heat transfer coefficients, tube side Reynolds numbers, the wall superheat, the saturation temperature of refrigerant and the heat flux are considered as the key parameters. The results show that pool boiling heat transfer coefficient data increase with , and , respectively, and decrease as the wall superheat increases. It can be found in the case study that the overall heat transfer coefficient of twisted tube flooded evaporator (TFE) is about 1.15 times as high as the one of common flooded evaporator (FE) with a same heat capacity. It is proved that an application of the TFE in the water-cooled screw chiller can be feasible.

Numerical Analysis of Vapor Bubble Growth and Wall Heat Transfer During Flow Boiling of Water in a Microchannel

2005 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Vapor Bubble ◽  
Bubble Growth ◽  
Stokes Equations ◽  
Flow Boiling ◽  
Navier Stokes ◽  
Channel Cross Section ◽  
Wall Heat Transfer ◽  
Wall Superheat

The present study is performed to analyze the wall heat transfer mechanisms during growth of a vapor bubble inside a microchannel. The microchannel is of 200 μm square cross section and a vapor bubble begins to grow at one of the walls, with liquid coming in through the channel inlet. The complete Navier-Stokes equations along with continuity and energy equations are solved using the SIMPLER method. The liquid vapor interface is captured using the level set technique. The bubble grows rapidly due to heat transfer from the walls and soon turns into a plug filling the entire channel cross section. The average wall heat transfer at the channel walls is studied for different values of wall superheat and incoming liquid mass flux. The results show that the wall heat transfer increases with wall superheat but is almost unaffected by the liquid flow rate. The bubble growth is found to be the primary mechanism of increasing wall heat transfer as it pushes the liquid against the walls thereby influencing the thermal boundary layer development.

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