Consider a short cylinder of radius \(r_{o}\) and height \(H\) in which heat is generated at a constant rate of \(\dot{e}_{\text {gen. }}\). Heat is lost from the cylindrical surface at \(r=r_{o}\) by convection to the surrounding medium at temperature \(T_{\infty}\) with a heat transfer coefficient of \(h\). The bottom surface of the cylinder at \(z=0\) is insulated, while the top surface at \(z=H\) is subjected to uniform heat flux \(\dot{q}_{H}\). Assuming constant thermal conductivity and steady two-dimensional heat transfer, express the mathematical formulation (the differential equation and the boundary conditions) of this heat conduction problem. Do not solve.

Short Answer

Expert verified
Based on the given information, the mathematical formulation for the heat conduction problem in a short cylinder can be derived as the following: 1. Governing equation in cylindrical coordinates (steady state, 2D, constant thermal conductivity, and heat generation): \(\frac{1}{r}\frac{\partial}{\partial r}\left(r\frac{\partial T}{\partial r}\right) + \frac{\partial^2 T}{\partial z^2} = \frac{\dot{e}_{\text{gen}}}{k}\) 2. Boundary conditions: a. Heat loss from the cylindrical surface: \(\left.-k\frac{\partial T}{\partial r}\right|_{r=r_o} = h(T(r_o, z) - T_\infty)\) b. Insulated bottom surface: \(\left.\frac{\partial T}{\partial z}\right|_{z=0} = 0\) c. Uniform heat flux from the top surface: \(\left.-k\frac{\partial T}{\partial z}\right|_{z=H} = \dot{q}_H\) d. Symmetry condition at the centerline: \(\left.\frac{\partial T}{\partial r}\right|_{r=0} = 0\) These equations and boundary conditions together define the mathematical model for the heat transfer problem in the short cylinder.

Step by step solution

01

Write down the equation governing heat transfer in cylindrical coordinates

Since the problem is related to heat transfer in a cylindrical body, we should use the heat conduction equation in cylindrical coordinates. For a steady state, two-dimensional problem with constant thermal conductivity \(k\) and heat generation \(\dot{e}_{\text{gen}}\), the equation is: \(\frac{1}{r}\frac{\partial}{\partial r}\left(r\frac{\partial T}{\partial r}\right) + \frac{\partial^2 T}{\partial z^2} = \frac{\dot{e}_{\text{gen}}}{k}\)
02

Write down the boundary conditions

We have four boundary conditions for this problem: 1. Heat is lost from the cylindrical surface at \(r=r_o\) by convection. We can write the boundary condition for this as: \(\left.-k\frac{\partial T}{\partial r}\right|_{r=r_o} = h(T(r_o, z) - T_\infty)\) 2. The bottom surface at \(z=0\) is insulated, which means no heat is conducted through it. The boundary condition for this is: \(\left.\frac{\partial T}{\partial z}\right|_{z=0} = 0\) 3. The top surface at \(z=H\) has a uniform heat flux \(\dot{q}_H\). The boundary condition for this is: \(\left.-k\frac{\partial T}{\partial z}\right|_{z=H} = \dot{q}_H\) 4. Symmetry condition: Since the problem is axisymmetric, there should be no heat flux along the radial direction at the centerline \(r=0\). The boundary condition for this is: \(\left.\frac{\partial T}{\partial r}\right|_{r=0} = 0\) Now we have the mathematical formulation of the problem, consisting of the heat conduction equation and the boundary conditions.

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