The water in a 40-L tank is to be heated from 15°C to 45°C by a25-cm-diameter spherical heater whose surface temperature ismaintained at 85°C. Determine how long the heater should be kepton.
Given: The properties of air at 1 atm and the film temperatureof 57.5°C.
Fluid temperature = Average temperature for water(15+45)/2=30°C
k = 0.6515 W/m.°C, v = 0.493 x 10-6 m2/s,Pr = 3.12, and ? = 0.501 x 10-3 K-1
The properties of water at 30°C.
? = 996 kg/m3 and cp = 4178 J/kg.°C, andvolume, V = 0.040 m3
