Automotive radiator is an affordable and available alternative to hot water room heating radiators. It is also lightweight, enabling women, elders and the physically challenged to carry and install. They have matching fan and shroud to blow air through.
How to estimate the BTU/h for a certain automotive radiator for 75F ambient air and a certain CFM of the fan?
I know they are not rated for the maximum power of car. Can we use car's highway MPG as a ball park estimate?
For example, assume highway speed is 60mph, a 30mpg car use 2 gallons of gasoline per hour, or 230K BTU per hour. If engine has 10% thermal power carried away by coolant, it's 23K btu/h through the radiator with coolant temperature 195F, so we can use this radiator instead of a 23K heating BTU PTAC unit.
However, the above have not considered the 60mph airflow while car is going 60mph. Radiator fans typically only blow air by 5mph. How much BTUs should be discounted from the air speed difference?
so let's further estimate the numbers:
Radiator size = 400 square inch, at 60mph there is 2.14 million mol of air passing through it per hour, air's thermal capacity is 30J/mol*K, put 23K BTU in, in this condition, temperature rise of air is 0.37K.
If we blow it 5mph instead, the temperature rise will be 0.37*(60/5) = 4.44K, right? Seems not a significant rise of outlet temperature, or thermal conduct rate. Point out my mistake if I am wrong.