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Liammaloney
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Homework Statement
Hi everyone,
I'm working on an assignment and am totally stumped by this question:
A horizontal cylinder is heated electrically. The cylinder is supplied with a current at a DC Voltage. Using the data supplied and allowing for both natural convection and radiation, estimate the steady state temperature of the cylinder surface.
Hint- You may have to solve the heat balance equation numerically.
A fan is used to blow air over the heated cylinder in a cross flow at an average velocity of 50m/s. Estimate the surface temperature now.
The heating is stopped and the cylinder is left in the airflow of 50m/x velocity. Estimate the time for the cylinder temperature to drop by 10K.
You will need to find the relevant fluid properties, but may assume a surface emissivity of ε=0.9.
Homework Equations
Cylinder Diameter = 87mm
Cylinder Length = 254mm
Surrounding air temperature = 20°C
Current = 1.032A
Voltage = 20V
Specific heat of cylinder = 450J/kgK
Density of Cylinder = 7850km/m^3
The Attempt at a Solution
I'm not sure where to start but I have had a go trying to find out where I'm meant to be going.
I first went about finding the resistance in the cylinder using:
R = V/I (20/1.03=19.42Ω)
With this I could then find the heat generated per unit volume in the cylinder using:
q(dot)g = I^2*R/AL ((1.03^2*19.42)/(5.9*10^-3*0.254) = 13.64kW
After this though I'm not sure where I'm meant to be going, and would really appreciate any help!