Question 1: Figure below shows a scale drawing of the temperature profile through a composite plane wall.
a) Identify the layer with the largest thermal conductivity,
b) Identify the layer that provides the greatest resistance to the flow of heat.
State any suppositions made and describe your answers.
Figure: Temperature profile via a composite plane wall
Question 2: A 3kW electric water heater is a cylindrical element containing outside diameter 10mm. The heat transfer between the heater and the surrounding water is 980W/m2K.
Find out the length of the heater if the surface temperature must not surpass 95oC when the water is at 65oC.
The element includes an electric resistance heater, diameter 2mm in the centre of the 10mm diameter stainless steel tube that has a wall thickness of 1mm. The gap between the resistance heater and within of the tube is packed with a ceramic material, Thermal conductivity 2W/mK.
Find out the temperature of the electric heater element. You might supppose that the heater element is at uniform temperature and the thermal resistance between the element and the ceramic is negligible. The thermal conductivity of the stainless steel is 16W/mK