Before reviewing the individual radiator results the effect of the air to coolant temperature differential must be well understood.

From the above graph it is clear that as the air to coolant temperature difference is increased, likewise is the dissipation. The comparison being based on (T_fluid – T_air) = C versus W, where T_fluid = (T_out + T_in) ÷ 2. The calculated C/W was 0.015 for each of these three tests. (This is a seriously large radiator.)

Conclusion #1:

Any description of radiator capacity MUST define the coolant to air temperature difference for that ‘rating’.

The performance of the three radiators tested comprehensively is shown below.

And to repeat, while the heat dissipation values may seem small, note that the temperature differential is small as well.

HE 80.1 Test Results:

The four curves each show the radiator’s heat dissipation at a specific backpressure, which is also a specific air flow rate for that individual radiator. Of note is the changing relationship between the liquid and air sides; at low to moderate air flow rates the dissipation increases only slightly with the flow rate, while at a high air flow rate there is also a marked increase in cooling capability.

“For the common respective flow rates, the convection heat transfer for air is the limiting parameter for a liquid to air heat exchanger. This is why there are fins (to increase convection heat transfer) on the air side and not on the liquid side for these heat exchangers. For low air flow rates, the thermal resistance of the air side is much more important than the fluid side (except for low fluid flow rates). Increasing the fluid flow rate leads to an improvement for the convection heat transfer, thus a lower thermal resistance, of the fluid side but this is negligible as compared to the air side thermal resistance. Improving the air side convection heat transfer, in other words the air flow rate, leads to a better global improvement.” *

For the HE 80.1 the fan tests were done only at 3.8 lpm (1.0 gpm) and it can be seen that all ‘normal’ air flow rates can be achieved by means of fan selection. From an application perspective it can be understood that using this small a radiator will result in somewhat higher coolant temperatures (to increase the air/coolant differential) and that a higher air flow rate will be needed.

Several fans were tested at 12 and 7V, both singly and in a push-pull configuration. Running the single Delta FFB0812EHE at 7V instead of 12V reduced the radiator capacity by 18%. Running two Panaflo FBA08A12 fans at 12V instead of one increased the heat dissipation by 17%, while running the two Panaflo fans at 7V produced no gain at all compared to the single fan at the same voltage.

It can also be seen that the highest backpressure / air flow rate cannot be attained with any ‘normal’ fan – or reasonable noise level. This is true for all the radiators tested, and may be considered a characteristic of this type of radiator core construction. Likewise, the lowest backpressure air flow rate yielded very poor performance. Fan selection should be based on achieving an air flow rate between the two middle curves, at the upper (37.4 Pa) for maximum performance and towards the lower (12.5 Pa) for low noise.

*Corrections and explanatory comments graciously provided by Antoine Dechaume.

Bill Adams