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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 engine cooling curves and factors affecting heat transfer based on Newton's Law of Cooling.

Identifier  ExFiles\Box 24\4\  Scan279
Date  21th November 1924 guessed
  
-2-
circulation in this way being maintained normally by the pump.
Top and bottom water temperatures and atmospheric readings were
taken at fixed intervals throughout the run until the mean
radiator temperature fell to 40°C. Both way readings were
taken in each case and the tests carried out on a straight
stretch of road to eliminate the effect of wind.
In order to discover whether these cooling curves
followed Newtons Law θ1 = θ2 e -at.
where θ2 = starting temp
θ1 = temp. after any time t
a = heat transfer co-efficient log θ, where θ1 is
the difference between the mean radiator temp. and atmospheric,
was plotted against the time taken to reach this temp. t. The
result was almost a straight line at the higher radiator temps.
but a curve with a definitely increasing slope after the mean
radiator temp. fell below 70°C. The reason for this was
found to be -
(a) That the crankcase estracted heat from the system
at the beginning of each run, due to its not following
the water temperature when this was rapidly brought
up to 90°C.
(b) That turning the engine over to circulate the water
generated heat which was imparted thereto in a constant
quantity throughout the test.
Tests were actually made to discover the behaviour
of the crankcase and the mechanical efficiency of the engine
being the factor 'B' was established. These two factors tend
to compensate each other at the higher temperatures. contd :-
  
  


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