# Thermodynamics -- Comparing Materials with large differences in Heat Conduction

Steven Bolgiano
Hi Folks,
I'm 70, so I often confuse myself! Ha !

My question is: Do materials both absorb and release heat equally?
So when I evaluate different materials for thermo efficiency, does a copper pipe's surface absorb solar heat at the same rate it gives off heat?

My question is specific to a solar water heated, anaerobic digester project already under construction. The digester itself is a soft tank, tightly sitting inside a frame and acrylic panels, ... heated from underneath with solar heated water.
The plan for the sake of economy, is to use 3/4" cPVC pipe in a clear sealed "cabinet", for collecting the solar rays, that connects adjacently, to another pattern of 3/4" type N copper under the tank to heat the tank.
Attached are some slightly obsolete images, I just used to grab quickly, ... but they may help to visualize

So if there is a large disparity between the Collector (cpvc) and the Radiators'(copper) conduction rates, ... am I wasting time using copper for the radiator, because of that disparity?

I was hoping using copper as the Radiator, would use the heat from the cPVC with the optimum efficiency.

As I understand the three methods of heat transfer, any comments, corrections:
Conduction - Heat transfer by molecular contact
Convection - Heat Transfer through density differences
Radiation - Heat transfer by wave motion (no material required)
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Conduction operates by contact
Convection operates by density
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Mentor
My question is: Do materials both absorb and release heat equally?
So when I evaluate different materials for thermo efficiency, does a copper pipe's surface absorb solar heat at the same rate it gives off heat?

My question is specific to a solar water heated, anaerobic digester project already under construction. The digester itself is a soft tank, tightly sitting inside a frame and acrylic panels, ...
Welcome to PF.

No; the conditions of absorbing and releasing heat tend to be very different from each other, so the rate is typically different.
So if there is a large disparity between the Collector (cpvc) and the Radiators'(copper) conduction rates, ... am I wasting time using copper for the radiator, because of that disparity?
Maybe, but it is really difficult to determine something like that ahead of time. Ultimately the system will reach an equilibrium where the rate of absorption of heat from the sun and release of heat from the copper will equalize. So each component of the system affects the total heat transfer rate.

I assume you are using water as a heat transfer fluid? What sort of temperatures are you looking for? (both the temperature in the digester and ambient). Do you know how much heat you need?

Steven Bolgiano
Apologies for delaying responding!