1. Water is heated in a tube that is placed at a focal point of a parabolic mirror. The optical gain of this mirror is 2 so the heat flux reaching the surface of the tube is twice as much as solar irradiance.

a) Assuming that the solar irradiance in the geographical location of this setup is 1000 W/m^2, the tube is well insulated and absorbs all the thermal energy it receives (how?); under the stated assumptions, find out how long a tube is needed to raise the water temperature from 20 to 80 C.

b) Estimate the wall temperature at the outlet

c) Do you expect any boiling, discuss?

d) If the optical gain was 3, what would be the surface (tube wall) temperature of the tube at the outlet?

e) Due to space requirements, you have been asked to do this without using the parabolic mirror, as you expect the required length will increase. what is the new length?

f) Compare the energy efficiency in part e part a and discuss what you would do if you were about to choose between these two configurations on the basis of the energy cost (ignore the capital cost)?

hint: added work for the pumping of the fluid should be considered.

Assumptions: Fluid Water Flow rate 0.6 L/min

pipe diameter 0.6 cm

State any other assumptions you made