scholarly journals An Interferometric Study of Free Convective Heat Transfer in a Double Glazed Window With a Between-Panes Venetian Blind

2021 ◽  
Author(s):  
Bertha Lai
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Test Fluid ◽  
Flat Plates ◽  
Set Up ◽  
Free Convective Heat Transfer

The free convective heat transfer in a double-glazed window with between-panes Venetian blinds was measured using a Mach-Zehnder interferometer. A vertical cavity with differentially heated/cooled flat plates was set up with an internal blind at slat angles of ø=0⁰, ø=45⁰, and ø=90⁰ from the horizontal and tip-to-plate spacings of s=2mm, s=4mm, and s=8mm. Heat transfer measurements were taken with air as the test fluid and at Rayleigh numbers of Ra~4.5x10(4), RA~6.7X10(4), and Ra~13.1x10(4), based on cavity widths of W=28.7mm, W=32.7mm, and W=40.7mm, respectively. Finite fringe interferograms were used to obtain local and average heat transfer data. Infinite fringe interferograms were taken to visualize the temperature field within the cavity. A preliminary numerical study of the experimental geometry was also conducted. The results show that there was substantial variation in local heat transfer rates caused by the presence of the between-panes blind inside the window cavity. In general, experimental average Nusselt numbers were found to be lower than those of a cavity without blinds.

scholarly journals An Interferometric Study of Free Convective Heat Transfer in a Double Glazed Window With a Between-Panes Venetian Blind

2021 ◽  
Author(s):  
Bertha Lai
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Test Fluid ◽  
Flat Plates ◽  
Set Up ◽  
Free Convective Heat Transfer

The free convective heat transfer in a double-glazed window with between-panes Venetian blinds was measured using a Mach-Zehnder interferometer. A vertical cavity with differentially heated/cooled flat plates was set up with an internal blind at slat angles of ø=0⁰, ø=45⁰, and ø=90⁰ from the horizontal and tip-to-plate spacings of s=2mm, s=4mm, and s=8mm. Heat transfer measurements were taken with air as the test fluid and at Rayleigh numbers of Ra~4.5x10(4), RA~6.7X10(4), and Ra~13.1x10(4), based on cavity widths of W=28.7mm, W=32.7mm, and W=40.7mm, respectively. Finite fringe interferograms were used to obtain local and average heat transfer data. Infinite fringe interferograms were taken to visualize the temperature field within the cavity. A preliminary numerical study of the experimental geometry was also conducted. The results show that there was substantial variation in local heat transfer rates caused by the presence of the between-panes blind inside the window cavity. In general, experimental average Nusselt numbers were found to be lower than those of a cavity without blinds.

scholarly journals A numerical study of free convective heat transfer in a double-glazed window with a between-pane Venetian blind

2021 ◽  
Author(s):  
Tony Avedissian
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
Numerical Study ◽  
Thermal Conductivity Ratio ◽  
Number Range ◽  
Free Convective Heat Transfer ◽  
Venetian Blind

The free convective heat transfer in a double-glazed window with a between-pane Venetian blind has been studied numerically. The model geometry consists of a two-dimensional vertical cavity with a set of internal slats, centred between the glazings. Approximately 700 computational fluid dynamic solutions were conducted, including a grid sensitivity study. A wide set of geometrical and thermo-physical conditions was considered. Blind width to cavity width ratios of 0.5, 0.65, 0.8, and 0.9 were studied, along with three slat angles, 0º (fully open, +/- 45º (partially open), and 75º (closed). The blind to fluid thermal conductivity ratio was set to 15 and 4600. Cavity aspects of 20, 40, and 60, were examined over a Rayleigh number range of 10 to 10⁵, with the Prandtl number equal to 0.71. The resulting convective heat transfer data are presented in terms of average Nusselt numbers. Depending on the specific window/blind geometry, the solutions indicate that the blind can either reduce or enhance the convective heat transfer rate across the glazings. The present study does not consider radiation effects in the numerical solution. Therefore, a post-processing algorithm is presented that incorporates the convective and radiative influences, in order to determine the overall heat transfer rate across the window/blind system.

Convective Heat Transfer in a Triple-Cavity Structure Near Turbine Blade Trailing Edge

2002 ◽  
Author(s):  
Minking K. Chyu ◽  
Unal Uysal ◽  
Pei-Wen Lee
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Turbine Blade ◽  
Convective Heat ◽  
Internal Heat ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Trailing Edge ◽  
Cavity Structure ◽  
Exit Slot

The present study explores the internal heat transfer in a triple-cavity cooling structure with a ribbed lip for a turbine blade trailing edge. The design consists of two impingement cavities, two sets of crossover holes, a third cavity and an exit slot with eleven ribs attached to it. Local heat transfer in each subregion is determined. Results indicate that the highest heat transfer occurs in the second impingement cavity. The exit slot area between the ribs is identified as a region of low heat transfer in the overall design. A comparison with enhancement induced by arrays of pin fins and fins of other geometries reveals that the triple-cavity design represents a lesser quality cooling scheme in the range of Reynolds numbers tested. Further improvement of the convective heat transfer at the exit slot with either film cooling, or different rib geometries appears to be essential to make the triple-cavity strategy superior to those of the traditional approaches for cooling of blade trailing edge.

Forced Convective Heat Transfer in Cross-Corrugated Solar Air Heaters

1994 ◽  
Vol 116 (4) ◽  
pp. 212-214 ◽  
Author(s):  
Y. Piao ◽  
E. G. Hauptmann ◽  
M. Iqbal
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Fluid Velocity ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Working Fluid ◽  
Solar Air Heater ◽  
Forced Convective Heat Transfer ◽  
Radiant Heater

Forced convective heat transfer in a cross-corrugated channel solar air heater has been studied experimentally using air as a working fluid. The channel was formed by two transversely positioned corrugated sheets and two flat thermally insulated side walls. One corrugated sheet was heated by a radiant heater, while the other was thermally insulated. The fluid velocity and temperature, and the wall temperature and the local heat flux across the heated corrugated sheet were measured for a variety of operating flow rates. Experimental results for the channel geometry have yielded the correlation Nu=0.0743(Re)0.76. This heat-transfer coefficient is about 2.8 times that of a smooth flat channel. The experiments showed that local heat transfer rate was smaller on the valley of the corrugation than that on the peak. The ratio of the local heat transfer rates on the two locations was related to the Reynolds number.

Convective Heat Transfer of Alumina Nanofluids in a Microchannel

2010 ◽  
Author(s):  
Saeid Vafaei ◽  
Dongsheng Wen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Axial Distance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

This work reports an experimental study of convective heat transfer of aqueous alumina nanofluids in a horizontal microchannel under laminar flow condition. The variation of local heat transfer coefficients, in both entrance and developed flow regime, is obtained as a function of axial distance. The heat transfer coefficient of nanofluids is found to be dependent upon not only nanoparticle concentration but also mass flow rate. Different to the behavior in conventional-sized channels, the major heat transfer coefficient enhancement is observed in fully developed region in microchannels. Discussions of the results suggest that the heterogeneous nature of nanoparticle flow should be considered.

Convective Heat Transfer Enhancement Due to Intermittency in an Impinging Jet

1993 ◽  
Vol 115 (1) ◽  
pp. 91-98 ◽  
Author(s):  
D. A. Zumbrunnen ◽  
M. Aziz
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Stagnation Line ◽  
High Heat Transfer ◽  
Short Period

An experimental investigation has been performed to study the effect of flow intermittency on convective heat transfer to a planar water jet impinging on a constant heat flux surface. Enhanced heat transfer was achieved by periodically restarting an impinging flow and thereby forcing renewal of the hydrodynamic and thermal boundary layers. Although convective heat transfer was less effective during a short period when flow was interrupted, high heat transfer rates, which immediately follow initial wetting, prevailed above a threshold frequency, and a net enhancement occurred. Experiments with intermittent flows yielded enhancements in convective heat transfer coefficients of nearly a factor of two, and theoretical considerations suggest that higher enhancements can be achieved by increasing the frequency of the intermittency. Enhancements need not result in an increased pressure drop within a flow system, since flow interruptions can be induced beyond a nozzle exit. Experimental results are presented for both the steady and intermittent impinging jets at distances up to seven jet widths from the stagnation line. A theoretical model of the transient boundary layer response is used to reveal parameters that govern the measured enhancements. A useful correlation is also provided of local heat transfer results for steadily impinging jets.

scholarly journals An interferometric study of free convective heat transfer at an indoor glazing with an insect screen attachment

2021 ◽  
Author(s):  
Daniel Zalcman
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Flow Simulation ◽  
Cfd Models ◽  
Interferometric Study ◽  
Set Up ◽  
Screen Temperature ◽  
Good Agreement ◽  
Free Convective Heat Transfer

Free convective heat transfer from an idealized window with an insect screen attachment was studied using a Mach-Zehnder interferometer. An experimental model was set up with an isothermal plate, two commercially available screens (KHP=8.74×10-9 m2, tHP=0.29 mm and KLP=3.40×10-9 m2, tLP=0.65 mm) and window to screen spacings of b=2 cm and b=1 cm. Heat transfer measurements using finite fringe interferograms were taken at a Rayleigh number of Ra=5.30×107 based on window height. Infinite fringe interferograms were taken for temperature field visualization. Screen temperature was also measured. Experimental results were compared to a preliminary CFD model developed with SolidWorks Flow Simulation and show good agreement. The results show that an insect screen produces a reduction in the convective heat transfer from the indoor glazing. The current measurements show that the effect of window to screen spacing is small. Results from this study are expected to be used for the validation of CFD models and for the development of correlations.

The Influence of Flexible Strip Height on Convective Heat Transfer Enhancement

2019 ◽  
Author(s):  
Yang Yang ◽  
David S.-K. Ting ◽  
Steve Ray
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Vortical Flow ◽  
Transfer Enhancement ◽  
Local Flow ◽  
Convective Heat Transfer Enhancement

Abstract A 12.7 mm wide flexible rectangular strip, made from 0.1 mm-thick aluminum sheet, is experimentally explored as a vortical flow generator for promoting heat convection from a flat plate in a wind tunnel. The strip is positioned normal to the freestream with an incoming velocity of 10 m/s, resulting in a Reynolds number, based on the strip width, of 8,500. The influence of the height of the flexible strip on the convective heat transfer enhancement is of interest. Three strip heights, 25.4 mm, 38.1 mm and 50.8 mm, were investigated. The heat transfer results are expressed in terms of Nusselt number, Nu, normalized by the unperturbed reference Nu0. The shortest, 25.4 mm high flexible strip resulted in the highest peak and overall heat transfer enhancement. The distribution of the local heat transfer enhancement is found to correlate well with the turbulent flow motion detailed using a triple-sensor hot-wire anemometer. Pointedly, the heat transfer rate is most elevated when the local flow is moving toward the hot plate, sweeping across a stretch of the surface before moving away from it. These effective convective motions are most effectively generated by the vortices produced by the shortest strip.

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