I just want to chime in on the “Try googling heat transfer and flow rate for automotive radiators” comment.
In a car, the radiator is not a real radiator, because it does not radiate, but instead uses forced convection. There are two circuits involved in this system
1. The coolant water taking heat from the engine and delivering to the “radiator”
2. Forced air passing over the cooling fins of the “radiator”
Both of these circuits used forced convection and hence are not suited to a comparison with solar water heating.
More importantly however is the fact that there are two interconnected “systems”. One which can have variable water flow rate (depending on engine speed and design of the water pump impeller) and one which will have a fixed air flow rate (at a given vehicle speed). To achieve maximum efficiency in an interconnected system where one sub-system has a fixed flow rate can easily be determined. The difficulty come in when both sub-systems do not have fixed rates (like the automotive radiator analogy). That is when the PhD comes in handy (except mine doesn’t come from MIT).
In solar pool heating, there aren’t multiple sub-systems, so yes, in this scenario it can follow “immutable laws of physics” as previously mentioned
There will come a point where the work required to move the water results in either:
a. So much pressure (and hence Temperature), which by PV=T, that the temperature gain is greater than that which can be extracted from the collector.
b. So much pressure that the collectors can fail.
We are typically well below either of those limits.
I would like to add one though which may support “greatest efficiency at lower flow rate”.
If your return jets create larger water surface disturbance at higher flow rates, then surface evaporation as a result of this could lead to greater heat loss out of the system, and so a lower apparent net heat gain.
And this could also be a result of the layout of your plumbing, since if the “solar” water is merged back to the “non-solar” flow then the above point is moot.
In conclusion, the greatest thermal conduction (up to limits we cannot reach in pool heating) will occur at the greatest temperature gradient, and that occurs when the panels are at their coldest, and that occurs when the water flow is at its maximum achievable.
In a car, the radiator is not a real radiator, because it does not radiate, but instead uses forced convection. There are two circuits involved in this system
1. The coolant water taking heat from the engine and delivering to the “radiator”
2. Forced air passing over the cooling fins of the “radiator”
Both of these circuits used forced convection and hence are not suited to a comparison with solar water heating.
More importantly however is the fact that there are two interconnected “systems”. One which can have variable water flow rate (depending on engine speed and design of the water pump impeller) and one which will have a fixed air flow rate (at a given vehicle speed). To achieve maximum efficiency in an interconnected system where one sub-system has a fixed flow rate can easily be determined. The difficulty come in when both sub-systems do not have fixed rates (like the automotive radiator analogy). That is when the PhD comes in handy (except mine doesn’t come from MIT).
In solar pool heating, there aren’t multiple sub-systems, so yes, in this scenario it can follow “immutable laws of physics” as previously mentioned
There will come a point where the work required to move the water results in either:
a. So much pressure (and hence Temperature), which by PV=T, that the temperature gain is greater than that which can be extracted from the collector.
b. So much pressure that the collectors can fail.
We are typically well below either of those limits.
I would like to add one though which may support “greatest efficiency at lower flow rate”.
If your return jets create larger water surface disturbance at higher flow rates, then surface evaporation as a result of this could lead to greater heat loss out of the system, and so a lower apparent net heat gain.
And this could also be a result of the layout of your plumbing, since if the “solar” water is merged back to the “non-solar” flow then the above point is moot.
In conclusion, the greatest thermal conduction (up to limits we cannot reach in pool heating) will occur at the greatest temperature gradient, and that occurs when the panels are at their coldest, and that occurs when the water flow is at its maximum achievable.
