Experimental and numerical investigation of natural convection heat transfer in inclined rectangular enclosures are carried out .The effect of Rayleigh number ,angle of inclination and enclosure aspect ratio on the Nusselt number are evaluated .The use of rectangular and tubular honeycomb structure to reduce the heat losses from the enclosure is also studied .Closed enclosure with low vacuum condition as a low molecular density space for reducing the heat losses is also investigated. Experiments are conducted for a rectangular enclosure with a base area of 0.2mx0.4m employing five aspect ratio of 8,10,13.3,20,and 40 . The Rayleigh number is varied from 3.6x103 to 3.6x105 ,and the tilt angle is changed from 0 deg . ( horizontal position) to 90 deg .(vertical position) in astep of 15 deg .The results showed that there is an inverse relation between the average Nusselt number and the enclosure tilt angle until a certain value lies in an interval that starts at 60 deg. .Increasing the enclosure tilt angle until a certain value lies in an interval that starts at 60 deg .Increasing the tilt angle any more slightly affect the average Nusselt number by about 2-3 times .The experimental results showed also that ,using of compound honeycomb structure is helpful for natural convection suppression in the enclosure .It reduces the average Nusselt number by a factor of about 25 % compared with the enclosure without honeycomb. Finally the experimental results showed that keeping low vacuum condition inside the enclosure reduces the surface temperature due to the absence of macro-convection currents and thus minimizing the heat losses.
A mathematical model is developed and ANSYS-CFD software is used in solving Equations . Comparisons between numerical and experimental results are conducted and fair agreement is noticed.
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