TAILIEUCHUNG - Heat Transfer Handbook part 58

Heat Transfer Handbook part 58. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | 562 NATURAL CONVECTION Here NuL q represents the Nusselt number at x L and Gr gpq L4 kv2. In a later study Vliet and Ross 1975 obtained a closer corroboration for data in air with the following relationships f Gr Pr 0-2 NUx 4 I Gr Pr 0-25 for laminar flow for turbulent flow Nuq can be obtained by computing the mean temperature difference and using the overall heat transfer rate provided by Vliet and Ross 1975 . Inclined and Horizontal Flat Surfaces As discussed earlier the results obtained for vertical surfaces may be employed for surfaces inclined at an angle y up to about 45 with the vertical by replacing g with g cos y in the Grashof number. For inclined surfaces with constant heat flux Vliet and Ross 1975 have suggested the use of eq. for laminar flow with the replacement of Gr by GrX cos y for both upward- and downward-facing heated inclined surfaces. In the turbulent region also eq. is suggested with Gr replaced by Gr cos y for an upward-facing heated surface and with GrX replaced by Gr cos2 y for a downward-facing surface. Several correlations for inclined surfaces under various thermal conditions were given by Fujii and Imura 1972 . For an inclined plate with heated surface facing upward with approximately constant heat flux the correlation obtained is of the form Nuq Gr Pr 1 3 - Grcr Pr 1 3 Grcr Prcos y 1 4 for 105 Gr Pr cos y 1011 and 15 y 75 where Grcr is the critical Grashof number at which the Nusselt number starts deviating from the laminar relationship which is the second expression on the right-hand side of eq. . This correlation applies for Gr Grcr. The value of Grcr is also given for various inclination angles. For y 15 30 60 and 70 Grcr is given as 5 x 109 2 x 109 108 and 106 respectively. For inclined heated surfaces facing downward the expression given is Nuq Gr Prcosy 1 4 for 105 Gr Prcosy 1011 y 88 The fluid properties are evaluated at Tw -T and P at T Tw -T .

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