A rod of diameter D=25mm and thermal conductivity k=60W/(m*K) protrudes normally from a furnace wall that is at Tw=200°C and is covered by insulation of thickness Lins=200mm. The rod is welded to the furnace wall and is used as a hanger to support instrumentation cables. To avoid damaging the cables, the temperature of the rod at its exposed surface, To, must be maintained below a specified operating limit of Tmax=100°C. The ambient air temperature is 30°C, and the convection coefficient is 17.0 W/(m2*K). a) Derive an expression for the exposed surface

Respuesta :

Answer:

The expression for the exposed surface temperature is [tex] T_{0}=T_{\infty}+\dfrac{R_{fin}}{R_{ins}+R_{fin}}(T_{w}-T_{\infty})[/tex]

Explanation:

Given that,

Diameter = 25 mm

Conductivity = 60 W/mK

Temperature of wall = 200°C

Thickness = 200 mm

maximum temperature = 100°C

Temperature of ambient air = 30°C

Convection coefficient = 17.0 W/m²K

We need to calculate the heat transfer equation

Using diagram of thermal circuit

[tex]q_{f}=\dfrac{T_{0}-T_{\infty}}{R_{fin}}[/tex]

[tex]\dfrac{T_{0}-T_{\infty}}{R_{fin}}=\dfrac{T_{w}-T_{\infty}}{R_{ins}+R_{fin}}[/tex]

[tex]T_{0}-T_{\infty}=\dfrac{R_{fin}}{R_{ins}+R_{fin}}(T_{w}-T_{\infty})[/tex]

[tex]T_{0}=T_{\infty}+\dfrac{R_{fin}}{R_{ins}+R_{fin}}(T_{w}-T_{\infty})[/tex]

Hence, The expression for the exposed surface temperature is [tex] T_{0}=T_{\infty}+\dfrac{R_{fin}}{R_{ins}+R_{fin}}(T_{w}-T_{\infty})[/tex]

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