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).
Analysis of heat dissipation from plain and ribbed engine oil sumps at various speeds.
| Identifier | ExFiles\Box 179b\3\ img310 | |
| Date | 13th March 1933 | |
| -3- find that at 70 M.P.H. between .6 and .7 B.Th.U's can be dissipated per sq. ft. of surface per °C difference in temperature between the air and the surface. The plain bottom half has an area of about 3.2 sq.ft. At 70 M.P.H. the heat dissipated balances the heat imparted to the oil (Curve 1 - He.954) when the difference of temperature between the oil and air is approx. 100°C. Assuming, therefore, that the heat gets from the oil to the sump as rapidly as the air carries it away, and taking a midway factor of .65 for dissipation, the best we should expect the bottom half to be able to do is to eliminate 3.2 X 100 X .65 B.Th.U's/min. or 210 B.Th.U's/min. From He.Pr.39, however, we note that with reduced oil pressure the heat to the oil at 70 M.P.H. is 310 B.Th.U's. Therefore the bottom half can only deal with about 60% of the heat to the oil in the case of the plain sump, the top half presumably accounting for the remainder. We confirmed this on the test bench by blowing a 70 M.P.H. blast over the bottom half, when it was observed that 20 - 30% less heat was dissipated than on the road where the top half gets a draught also. It is evident from the road results already obtained that with the allowable 55°C difference in temperature between the oil and air to give a maximum oil temperature not exceeding 85°C with an oil pressure of 20 lbs/sq.in. the plain bottom half will only dissipate 115 B.Th.U's, and the top half 55 B.Th.U's, leaving 140 B.Th.U's to be dealt with in some other way at 70 M.P.H. At 75 M.P.H. the position will be worse by an additional 70 B.Th.U's/min. We hope that the car finally will hold 75 M.P.H. and therefore with the plain sump we have 210 B.Th.U's to dissipate to be safe. RIBBED SUMP. The ribbed sump has an area exposed to the air of 7½ sq.ft., or more than double that of the plain sump. The increase in weight is 4 lbs. 1 oz. On the road, however, as is shown by the curve (1) He. 954 the actual drop in temperature of the oil at 70 M.P.H. is only 7°C. which is equivalent to an increase in heat dissipated from the bottom half of about 21 B.Th.U's/min. or 18% Therefore by over 100% increase in air surface, the cooling capacity of the bottom half has only increased 18% | ||