Physics Help Forum How to design a CSP receiver pipe (acting as a generator for Vapor absorption system)

 Mar 15th 2016, 12:15 PM #1 Junior Member   Join Date: Mar 2016 Posts: 2 How to design a CSP receiver pipe (acting as a generator for Vapor absorption system) Hello everyone, I am an Engineering student currently working on a project. The project is to design and fabricate CSP (concentrated solar power) based vapor absorption refrigeration system. I hope everyone here knows about vapor absorption system and its components. The problem that led me to post here is that, I am using concentrated solar power from a parabolic trough as a heat source for my generator. The generator is actually a pipe which contains the refrigerant and absorbent solution(LiBr-Water),the generator is directly exposed to the concentrated solar light. Now I am all set with other components of the system, the only problem is: "I have T1 as temperature at pipe(generator) inlet and T2 as the temperature at exit and the 'Qg' is the heat transfer per second to the pipe through radiation, now how can I calculate the length of the pipe so that I get T2 as my exit temperature". It is easy to find the length of the pipe for me if the heat transfer is between two fluids but here as the source is solar light, so I am confused what I should do now? Thanks in advance.
 Mar 16th 2016, 03:19 PM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,354 You can calculate the the power in watts per unit area of the solar radiation impinging on the pipe from the reflector. Then a rough estimate of the temp rise of the fluid is the solar power times the time it takes for the fluid to travel the length of the pipe divided by the specific heat of the fluid. This will overstate the temp rise, as it assumes 100% efficiency of heat transfer into the fluid, so ignores cooling due to the convection with the air. But it should give a reasonable ballpark estimate.
 Mar 17th 2016, 10:56 AM #3 Junior Member   Join Date: Mar 2016 Posts: 2 I understood your point, varying the mass flow rate of the fluid can vary the temperature rise of the fluid but what if there is the restriction on changing the mass flow rate? and the only alternative is to vary the pipe length, then how I can choose the length. I can not assume any the length. am I right?
 Mar 17th 2016, 02:26 PM #4 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,354 The calculation I suggested is this: L/v = time, in seconds, that a particle of fluid is in the pipe. Multiply by solar power (in watts) acting on the pipe and you get the energy (in Joules) that is put into the fluid in the pipe during the time that particle is in the pipe. The amount of solar power is equal to the power flux of sunlight (watts/sq meter) times the area of the collector. Now divide the energy by the mass of fluid in the pipe and you get Joule/Kg. Then divide by the specific heat of the fluid and you get temp rise. So in sum: Delta T = LP/(vmC) You can put this in terms of mass flow rate (m dot) and you get: Delta T = P/(m dot C) At first glance it may seem that L is not a factor, but recall that P equals power flux fro the sun times the collector's area, so this means making the collector twice as long doubles the temp rise.

 Tags absorption, acting, csp, design, generator, pipe, receiver, system, vapor