Expert: Paul Soderman - 3/31/2009

Question
QUESTION: Respected Sir,
I am an final year mechanical engineering student planning to do project on passive solar tracking mechanism. I planned to use freon to make the design but now i am intersted in portasol tracker which uses rapeseed oil to drive piston and cylinder. I would like to know that do ineed to compress oil so that it gets heated progressively by ambient air & sunlight

ANSWER: Some passive solar trackers use oil as the hydraulic fluid. See:

http://www.solartracking.com.au/index-tess1.php?ItemNo=1002

I am not familiar with the details of the design, but you can find the expansion of a fluid at:

http://www.mhtl.uwaterloo.ca/old/onlinetools/airprop/airprop.html

I assume you need to compute the force delivered by a piston given an expansion due to thermal change.  Then you design a mechanical system that moves when driven by that force and gravity.
Paul

---------- FOLLOW-UP ----------

QUESTION: Dear Sir,

Herewith I would like to inform you that Iam doing passive solar tracker using Pongenia Oil.

The oil in the reservoir (Aluminum Cylinder) get heated by ambient temperature and solar racliation and flows to another reservoir (Hydraulic Cylinder) which is under shade due to the temperature resevon.

First I used 70% of oil in cylinder and 30% of air, the response was quite good but if I fill 100% oil the movement becomes difficult and also it needs some opening in hydraulic cylinder to escape the inside air.

Kindly help as I need to rotate the shaft 15 degree per hour. The extension needed is quite small. Also let me know can I use the completely enclosed system without any air passage or do I need to provide any air passage to drive the mechanism.

Thanking you for your kind help.

With warm regards,
Ramesh

Answer
Sorry Ramesh - I don't know enough about your system to answer your question.  Your attempts at trial and error seem to be the best approach.  I would have thought that air in the system would compress somewhat and reduce the piston motion.  But if you find out differently you should proceed.
Paul