scholarly journals An interferometric study of free convection in a window with a heated between-panes blind

2021 ◽  
Author(s):  
Fabio Almeida
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Temperature Field ◽  
Free Convection ◽  
Unique Feature ◽  
Heat Fluxes ◽  
Simplified Model ◽  
Plate Temperature ◽  
Interferometric Study ◽  
Lateral Heat

An experimental study has been conducted to examine free convection in a window with an enclosed aluminum Venetian blind. The unique feature of this experiment was that the blind slats were heated electrically to simulate absorbed solar radiation. Centre-glass convective heat transfer measurements and temperature field visualization were obtained using a laser Mach-Zehnder interferometer. Measurements were made for three plate (glazing) spacings, three blind slat angles, three blind heat fluxes, and two plate temperature differences. It was found that a recently proposed simplified model, called the Reduced Slat Length (RSL) model, closely predicted the experimental results when the flow appeared to be laminar and steady. Under these conditions, the temperature field and lateral heat transfer was dominated by conduction. Under some conditions, evidence of highly unsteady/turbulent flow was observed. As expected, the RSL model performed poorly under these conditions.

scholarly journals An interferometric study of free convection in a window with a heated between-panes blind

2021 ◽  
Author(s):  
Fabio Almeida
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Temperature Field ◽  
Free Convection ◽  
Unique Feature ◽  
Heat Fluxes ◽  
Simplified Model ◽  
Plate Temperature ◽  
Interferometric Study ◽  
Lateral Heat

An experimental study has been conducted to examine free convection in a window with an enclosed aluminum Venetian blind. The unique feature of this experiment was that the blind slats were heated electrically to simulate absorbed solar radiation. Centre-glass convective heat transfer measurements and temperature field visualization were obtained using a laser Mach-Zehnder interferometer. Measurements were made for three plate (glazing) spacings, three blind slat angles, three blind heat fluxes, and two plate temperature differences. It was found that a recently proposed simplified model, called the Reduced Slat Length (RSL) model, closely predicted the experimental results when the flow appeared to be laminar and steady. Under these conditions, the temperature field and lateral heat transfer was dominated by conduction. Under some conditions, evidence of highly unsteady/turbulent flow was observed. As expected, the RSL model performed poorly under these conditions.

Improvement Of Free Convection From Three horizontal Finned Cylinders Fixed Between Two Walls

2018 ◽  
Vol 6 (2) ◽  
pp. 98-114 ◽  
Author(s):  
Hassan K. Abdullah ◽  
Haneen H. Rahman
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Prandtl Number ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Heat Fluxes ◽  
Head Orientation ◽  
Outer Diameter ◽  
Gravitational Acceleration ◽  
Convection Heat

Improvement of  free convection heat transfer from three finned cylinders arranged at a triangle shape fixed between two walls has been investigated in this study. Three mild steel finned cylinders fixed between two walls from Pyrex glass have been used as a test rig. It has been changed the spacing between the cylinders (X/D=1,2,3 & S/D=2,4,6) and the head orientation of a triangle to the top under constant heat flux values (38, 254, 660, 1268) W/m2 and compare with case of three finned cylinders arranged in vertical array in line fixed between two wall. The experiments are carried for Rayleigh number (Ra) from (15x103 to 14 x104 ) and Prandtl  number from (0.706-0.714 ). The results indicated an increase in Nu with increasing Ra for all cylinders. Furthermore,hx and Nu increased proportionally with the increasing of cylinder spacings for all heat fluxes. Also the experimental results show the case of triangle arrangement is improvement the heat transfer more than case of vertical arrangement. Heat transfer dimensionless correlating equation is also proposed.              Nomeclature: Ax: surface area(m2), T∞: surrounding temperature(k), D: the outer diameter of fin (m), Kf: the thermal conductivity for air at film temperature(W/m.k), hx: Local convection heat transfer(W/m2.k),  Gravitational acceleration(m/s2), I: Electric current (Amp), Nu: Nusselt number, Pr: Prandtl number

Incipient Flow Boiling in a Vertical Channel With a Wavy Wall

2010 ◽  
Author(s):  
T. Netz ◽  
R. Shalem ◽  
J. Aharon ◽  
G. Ziskind ◽  
R. Letan
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
High Speed ◽  
Flow Boiling ◽  
Heated Surface ◽  
Vertical Channel ◽  
Infrared Camera ◽  
Heat Fluxes ◽  
Heated Wall ◽  
Boiling Incipience

In the present study, incipient flow boiling of water is studied experimentally in a square-cross-section vertical channel. Water, preheated to 60–80 degrees Celsius, flows upwards. The channel has an electrically heated wall, where the heat fluxes can be as high as above one megawatt per square meter. The experiment is repeated for different water flow rates, and the maximum Reynolds number reached in the present study is 27,300. Boiling is observed and recorded using a high-speed digital video camera. The temperature field on the heated surface is measured with an infrared camera and a software is used to obtain quantitative temperature data. Thus, the recorded boiling images are analyzed in conjunction with the detailed temperature field. The dependence of incipient boiling on the flow and heat transfer parameters is established. For a flat wall, the results for various velocities and subcooling conditions agree well with the existing literature. Furthermore, three different wavy heated surfaces are explored, having the same pitch of 4mm but different amplitudes of 0.25mm, 0.5mm and 0.75mm. The effect of surface waviness on single-phase heat transfer and boiling incipience is shown. The differences in boiling incipience on various surfaces are elucidated, and the effect of wave amplitude on the results is discussed.

Experimental Study of the Temperature Field Equation in the Leeward Tunnel during Mine Fire Period

2012 ◽  
Vol 588-589 ◽  
pp. 1842-1848
Author(s):  
Wen Cai Wang ◽  
Yu Hong Jiang ◽  
Tao Hou ◽  
Wei Liu ◽  
Yang Lu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Temperature Field ◽  
Field Equation ◽  
Wind Speed ◽  
Stable Phase ◽  
Measuring Point ◽  
Mine Fire ◽  
Mine Roadway ◽  
Set Up

According to the principle of heat transfer, the temperature field equation in the leeward tunnel was set up and the experimental device with a ratio of 1:20 was built. When it happened to fire in roadway, the correctness of the temperature field equation can be verified by the experiment. In experiments, the armored thermocouple and color paperless recorder were used to record the temperature of each measuring point. The S-3-300 pitot tube and YJB-2500 compensation micro-manometer were used to determine the wind speed. When the mine roadway fired, the experiment determined the temperature field equation experiment coefficient of Kc. It showed that in the developing phase of the fire Kc= 15 ~ 20, in the stable phase of the fire Kc= 10 ~ 15, in the failing phase of the fire Kc= 20 ~ 25.

Experimental Study of Enhanced Pool Boiling Heat Transfer Using Graphite Foam Inserts

2011 ◽  
Vol 312-315 ◽  
pp. 352-357 ◽  
Author(s):  
K.C. Leong ◽  
L.W. Jin ◽  
I. Pranoto ◽  
H.Y Li ◽  
J.C. Chai
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Bubble Formation ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Copper Block ◽  
Different Types ◽  
Graphite Foam

This paper presents the results of an experimental study of heat transfer in a pool boiling evaporator with porous insert. Different types of graphite foams were tested with the phase change coolant FC-72 in a designed thermosyphon. Comparisons between the graphite foams and a solid copper block show that the porous structure enhances pool boiling significantly. The boiling thermal resistance of the tested graphite foams was found to be about 2 times lower than that of the copper block. The bubble formation recorded by a high speed camera indicates that boiling from a graphite foam is more vigorous than from a copper block. The designed thermosyphon with graphite foam insert can remove heat fluxes of up to 112 W/cm2 with the maximum heater temperature maintained below 100°C.

An Experimental Study of Miniature-Scale Pool Boiling

2003 ◽  
Vol 125 (6) ◽  
pp. 1074-1086 ◽  
Author(s):  
Tailian Chen ◽  
Jacob N. Chung
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Boiling Curve ◽  
Feedback Control System ◽  
Electronic Feedback ◽  
Fundamental Understanding ◽  
Peak Heat Flux ◽  
Different Temperatures

By generating single bubbles on a micro-heater at different wall superheats, an experimental study of miniature-scale pool boiling heat transfer has been performed to provide a fundamental understanding of the heater size effect. In this study, the constant-temperature microheater is set at different temperatures by an electronic feedback control system. The heat transfer history during the lifetime of a single bubble which includes nucleation, growth, detachment and departure has been measured. The boiling curve obtained from the microheater is composed of two regimes which are separated by a peak heat flux. It is suggested that in the lower superheat regime, the boiling is dominated by liquid rewetting and micro-layer evaporation, while in the higher superheat regime, conduction through the vapor film and micro-convection plays the key heat transfer role as the heater is covered by vapor all the time. In general, boiling on microheaters is characterized by larger bubble departure sizes, smaller bubble growth rates due to the dryout of microlayer as the bubble grows, and higher bubble incipience superheat. As the heater size decreases, the boiling curve shifts towards higher heat fluxes with corresponding higher superheats.

A Study of the Heat Transfer Mechanisms in Horizontal Flame Propagation

1980 ◽  
Vol 102 (2) ◽  
pp. 357-363 ◽  
Author(s):  
S. R. Ray ◽  
A. C. Fernandez-Pello ◽  
I. Glassman
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Conduction ◽  
Flux Distribution ◽  
Heat Transfer Process ◽  
Heat Fluxes ◽  
Temperature Fields ◽  
Gas Velocity ◽  
Field Temperature ◽  
Transfer Mechanisms

An experimental study is performed on the magnitude of the different mechanisms by which heat is transferred from the flaming region to the unburnt fuel ahead of the flame for flames propagating horizontally over the surface of a solid fuel. Measurements of the gas velocity field, temperature fields and radiant flux distribution in a particular case of laboratory scale flame spread over a thick fuel are used to determine the magnitude of the heat fluxes ahead of the flame. The results show that, for this particular case, although heat conduction through the solid is dominant, radiation from the flame contributes significantly to the heat transfer process. An analysis of the development of the fire indicates that there is a transition in the mechanisms of heat transfer as the fire grows. While in the early stages of the fire, heat conduction through the solid is dominant, radiation from the flame becomes of increased importance as the size of the fire increases.

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