A long tube with a uniform heat source is insulated at its outer radius r_o and cooled at its inner radius r_i, and the one-dimensional, radial, steady-state heat transfer is calculated. Use buttons to view a cross section of the tube or plot the temperature as a function of the radius. The heat transfer rate, temperature at position r and the outer surface temperature T_o are shown on the cross section diagram. Use sliders to set the coolant temperature, tube thickness r_o – r_i, radial position, heat generation, convection coefficient and thermal conductivity.