I hope it's clearer.
Not so much for me, forgive me.
According to you, to the final, what will the temperature rise induced by the use of PVC instead of copper?
I put the wikipedia diffusivity
http://fr.wikipedia.org/wiki/Diffusivit%C3%A9_thermique because it gives
all thermal basic values in table used to calculate the diffusivity by the report: thermal conductivity of heat capacity, etc .., to hold minimum.
The thermal conductivity is dynamic, heat flow, falsely static but basic in diffusivity, which is similar to the penetration of a radio frequency or sudden magnetic field in a metal, with penetration depth as the square root of time, or the inverse of the square root of the frequency. This is not an impedance, since there is no wave propagation constant speed, but
broadcast, random walk, with advance slowing as the square root of time.
We are at zero frequency, we are interested in a passive heat resistance problem in steady state. w = 0, the diffusivity has no influence here in our problem.
By putting a contact thermometer (thermocouple or infrared) on the surface of 14x16 pipe with cold water circulating in the sun, we verify my claim.
It also checks the putting hands on a similar hose with cold water flowing in, it is not hot at all, unlike the same burning sun without water pipe
This is not the issue, to me it seems. A hose without water, sunlight, eventually heat (for broadcast in its thickness) heat (energy) received from the sun. The cold water will cool the flow. Then, every second, the sun transfer to the pipe surface energy E, a power P which will cause heating of the surface of the pipe. This energy can not easily or through the thickness of the pipe and deliver every second heat. If so (if it is copper, very good heat conductor), joules easily cross and are removed by the water flowing through the pipe. So the pipe surface temperature is close to that of water, low thermal resistance creates a low temperature drop. If now the pipe wall lets evil go the received energy (PVC for example) the temperature gradient is much greater. At the extreme, however, if the material is a perfect insulator, no energy can pass through, and it accumulates on the receiving surface, its temperature increases and less able to evacuate this energy by convection or IR radiation it is ensured cast. The temperature gradient is therefore proportional to the thermal resistance of the pipe. In our case it prevents breakage because the exchange surface of the pipe is large enough and air enough (relatively) cold. So there convection and IR radiation. But the performance suffers. Diffusivity has nothing to do with our problem. It is used only transient or sinusoidal mode or in response to a level or temperature Dirac, or permanent periodic solicitation. Here we are in steady state, with solicitation (the sun), constant, zero pulse, in materials to finished thickness.
Amortization A induced diffusivity is: exp (z / delta (omega))
Here the delta quantity (omega) is + infinity as delta (omega) = sqrt {2. D \ omega} and omega = 0 (pulse).
Therefore A = 1 which means: no damping: the temperature is the same at all points of the thickness of the material, we are steady, dissemination was made. The energy flows into the thickness constant density. Diffusivity do not play. A does not depend on z, the depth, it is 1.
Falcon.
