6 replies to this topic

[nav3057]

Well you all know how a refrigerator works...
IN simple words,
It extract heat from the inside of refrigerator and it is dissipated outside through fins.
So what i was thinking to use this heat in useful manner so as to make food warm.so that it has a good heat retaining capacity to keep the food warm for longer periods.
Any suggestions how to extract heat in this case OR a similar case of A.C. ..

[Wit Knien]

My first thoughts are that the temperature of the backside (condensor) of a refrigerator only needs to be around 15oC higher than ambient temperature to function. Which would mean that the food, at best only warms up to those 15 degrees above ambient temperatures.

I actually once discussed a similar idea with a former teacher of mine and we concluded that the difference in temperature is too small to put it to effective use of heating things.

[nav3057]

what if use the fins directly into a container in which the food can be stored.

[Wit Knien]

I'm not a 100% sure about the statements I'll mention below, but these are the difficulties I see, in regard to your idea.

Well you have to take a few things into account,

- The increased temperatures at the condensor side of the refrigerator (as you seem to be willing to put the food warmer directly behind it) will mean the condensor will have to perform more duty to be able to cool the stuff inside. Which, in regard to heat losses of the food container may not even be worth the effort if you look at energy savings.

- Heat transfer follows the equation phi W = U (overall heat transfer) * A (surface area) * deltaT (condensor temperature - ambient temperature) . Your temperature difference is relatively small so you'd need a large surface area to compensate. But that also may come with a larger heat loss (since the same formula applies to the heat loss in the food warmer).

I'm not sure if you're trying to do this for a refrigerator for domestic use or on a somewhat more industrial scale, but domestic use may not be worthwhile. As I said earlier, I'm not a 100%.

[nav3057]

well there are plenty of problem..
yeah the heat rejection in case of home refrigerators are quite low noting fruitful can be done, but cases where large heat is wasted in
bigger refrigerators and a.c. over bigger places this can be used to recover lots of heat..

[nav3057]

dear wit,
yeah the efficiency will surely go down if condenser is not able to reject the inside heat properly...
we've to consider that also...
one thing came to my mind that what if we use one more compressor in series which will surely increase the heat content of the refrigerant..
what say...

[Wit Knien]

I'm by no means an expert on this case, so I cannot help you in regard to multistage compressors. Have you tried sketching out the system you have in mind so it will be easier to follow? Since I am going out on a limb here with any statements.