hi all, i am working on a solar thermal power generation unit on a very small scale for a final year project. the heat exchanger is part of this project. the water will be heated in a pipe that is placed at the focus of a almost parabolic reflector, however i want to turn this water to steam as well, to be able to run a small steam engine that can run a 500watt generator. less than 500watt will also do. but i have limited space available, and water having high cp will take longer to attain high temperature. or i would have to use a very small flow rate. i was thinking, if the water was to flow in a multipass heat exchanger, with the external fluid being oil of low cp, would i be able to heat up water to a higher temperature in a shorter space? also can the oil be in a sealed pipe and not need to flow in a circuit? that is the oil just stays in the heat exchanger and heats up due to solar radiation. also this heat exchanger will be a tube type that can be placed at the focus of the reflector. the oil should reach a much higher temp than water due to low cp in the same time. and if heat transfer is to be on the basis of temperature difference than the water should have a greater amount of heat transfered to it.. am i thinking right? rougly the parabolic collector will have and area of 4.25 square meters. also i am not using a true mirror reflector.. rather strips of mirrors focused on the same point please help !