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W A T L O W

Application Guide catalog - 7347 Application Guide

Reference Data

c.Bottom losses
• • •

Examples of Applications

Q
L4 = A F
SL C
F t
e Continued = (1385 in
2 )
• (0.95 W/in
2 )
• (0.63)
• (1 hr)= 829 Whwhere:A= 1385 in
2 (previously calculated)F
SL = surface loss factor for a surface at 250°F=(bottom temperature = 250°F; assume hotter than top or sides due to pedestal and poured ceramic hearth)= 0.95 W/in
2 Reference Data C
F = bottom surface correction factor of 0.63t
e = exposure time for losses = 1 hr d.Open furnace cover losses Opening and closing of the furnace cover to add additional ingots, causessignificant power losses. The 22 inch diameter skin of the molten aluminum in a full crucible, the upper edges of the exposed crucible and other surfacesare all sources of heat losses when the cover is open. Assuming the cover is opened and closed several times per hour, we can say that the cover is openfor 10 minutes during a one hour period. From Equation 3D, (Page18).Q
L4 = A
• F
SL • t
e = (380 in
2 )
• (13 W/in
2 )
• (0.167 hr)= 825 Whwhere:A= molten aluminum surface area= (22 in. dia/2)
2 • Ï€ = 380 in
2 F
SL = surface loss factor from Reference 13 (Page28) at 1080°F= 13 in
2 t
e = 10 minutes = 0.167 hr e.Total losses Sides=4486
• WhTop=715
• WhBottom=829
• WhOpen Lid=825
• WhTotal Q
L =6855
• Wh 169