The heat exchanger/boiler is where energy is transferred from the hot oil into the water to create steam. In the 2x4ft mirror test unit copper double walled heat exchanger will be tested.
From the data of this test we will be able to calculated the size of the heat exchanger required for the solar thermal car. It is import at the heat exchanger is vertical so the steam can boil out the top. In the solar thermal car there will only be enough vertical space for a 4ft long heat exchanger. Different diameters will be tested and if needed several smaller heat exchangers maybe used.
The centre pipe of the heat exchanger will be thick copper pipe. Copper is required because it has very good heat conduction. A thinker pipe is required because of the high pressures in this boiler pipe. The outer pipe can be made of thinner M copper pipe or a lower cost material. This outer pipe is not pressurized or used for heat transfer.
It is difficult to build a heat exchanger without leaks. The enter pipe expanses with pressure and the two pipe expand differently based on temperature. High heat brazing is required to have a strong leak free heat exchanger.
The centre boiler pipe also contains an internal pipe required for temperature and water level control. This pipe must be also installed using brazing because this joint is under pressure.