Free Convective Heat Transfer in a Closed Gap between Concentric Semi-Hemispheres

Free convective heat transfer in the closed gap between concentric semi-hemispheres is quantified by means of a numerical approach based on the volume control method using the SIMPLE algorithm. The average Nusselt number is determined for several configurations obtained by varying the cavity’s aspect ratio between 0.15 and 1.5, while the Rayleigh number varies within the 5.33 × 103–4.50 × 108 range. The results show that the correlations available in the literature dealing with concentric whole spheres cannot be used for the configuration treated here. The new correlation between the Nusselt and Rayleigh numbers proposed in this work can be applied in various engineering sectors, such as in the electronic packaging considered in this present work, buildings, and architecture.

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

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.

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

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.

A numerical study of free convective heat transfer in a double-glazed window with a between-pane 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.

A numerical study of free convective heat transfer in a double-glazed window with a between-pane 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.

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

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.

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

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.