From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The efficiency of direct versus indirect radiator cooling systems with an accompanying graph.
| Identifier | ExFiles\Box 24\5\ Scan332 | |
| Date | 24th September 1930 | |
| -2- Hs{Lord Ernest Hives - Chair}/Hn.{F. C. Honeyman - Retail orders}1/Wl.24.9.30.Contd. of 150 miles per hour. These results rather confirm what we have been thinking recently, that is that for low air velocities through the core, indirect cooling surface is almost as efficient as direct cooling. The advantage of using indirect cooling is, of course, that a much larger radiating surface can be contained in the matrix for a given weight and frontal area. The Bureau of Standards tests show, as will be seen from the attached graph, that a core with only 25% direct cooling can, up to 75 M.P.H., be more efficient weight for weight than a round tube core of the type we use having over 90% direct cooling. Above 75 M.P.H. air speed through the core the matrix with the greater percentage of direct cooling becomes the more efficient, as one would expect. However we are not concerned with air speeds through our radiators of more than about 55 M.P.H. as far as we can estimate and therefore it is improbable that we can overdo the amount of indirect cooling we are projecting on the new square tube radiator. The attached curve shows the measured air velocity through a car radiator obtained by Dalby and given in a paper before I.C.E. plotted against the car speed through the air. Actually we think these figures are about the same as those we get on the Phantom II for the following reason. From the figures obtained on Brooklands at 60 M.P.H. Graph Text: Y-axis: MEAN AIR SPEED THROUGH RADIATOR M.P.H X-axis: CAR SPEED M.P.H | ||