Originally Posted by pedro2000uk  Have you forgotten what it is we is supposed to b doin .... and your previous post... ... we is freezing an LNB... you said .. the extra heat produced (through the freezing process wot always produces heat as a by product I presumed you meant.. correct?) will help with condensation**.. . |
No - the idea is to keep the heat components (the radiator or low pressure side of the fridge) away from the LNB, which is why the use of a refrigeration plant has so many advantages over the Peltier units.
The heat transfer components are kept well away from the LNB, best place is strapped to the back of the reflector, but in front of the mount/motor, and then the pipes carrying the freon/halide can be of rigid construction.
Originally Posted by pedro2000uk but I said... we don't want that heat near it.. that would be counter productive (OWTTE).. we want the heat exchanger etc.. that gets rid of the by product heat.. some distance away... and the LNB as cold as possible. (but see below re feed horn cover face defrosting**).. |
As above
Originally Posted by pedro2000uk feed? by this you mean the feed horn/ (& wave guide etc)? .. it's sealed or it should be.. |
The feed is not sealed in the systems I have used for testing (are you talking about integral feed/LNBs , if so then the methods of cooling would have to be modified)
Originally Posted by pedro2000uk Lagging does not reduce condensation...... hmmm.
Yes it does/ or can ...
not in a house though ...
if a house ...snip ..... all produce litres of water that have to be..... vented away***.
but a sealed LNB doesn't produce any moisture . |
It is not sealed, the air around it is able to permeate through the feed/cooling pipes, or lack of sealing between the feed and LNB.
Originally Posted by pedro2000uk if you super cool it without any lagging, passing moisture in open air will condensate on it like crazy and freeze...
lag it and use the lagging to also seal it in and the lagging will drastically reduce the extreme cold coming in contact with the outside air... on the outer surface of the lagging it will be cold but nothing like the -30c inside... so condensation will be drastically reduced and limited to the outer surface of the lagging and if it (the lagging) is also sealed, then this will limit normal moist air getting in and giving up it's moisture to the -30c surfaces inside.
So lagging can drastically reduce condensation... in this case.. |
But the refrigeration part is also inside any potential lagging, and moisture will be present either side of the lagging, ready to freeze once the temperature is reduced.
Originally Posted by pedro2000uk Absolute sealing is a problem.. I thought of sealing the LNB in a lagging block in a super dry environment and including a dry pack in a place that wouldn't cause a problem to at least limit it.... It's the feed horn cover face that is the most vulnerable- can't lag it and most plastic is x% porous. You can only limit it as you say... but most engineering process battle against the laws of physics and rarely win 100% - you just limit it, accept it.. and move on.. |
You cannot leave dessicated silica gel on its own, it will spoil within a week of freezing and then you will need to dismatle all your work
Originally Posted by pedro2000uk **Now... if you used some of the excess heat just on the face of the feed horn cover to keep ice from building up there... that might be a worth while compromise.... which is in part what you said.. (I think).
. |
No need if you vent it
Originally Posted by pedro2000uk ***- the building regs got that one really wrong in the eighties. |
We know
