Assumeing a constant pump speed, when the=20= thermostat closes and head pressure goes up, power required to drive t= he=20 waterpump does NOT go up=2E It actually goes DOWN=2E Reason:&nbs= p; There=20 is less mass being accelerated (energy) at lower flow rates=2E In the=20= extream example (zero flow) the same water in the pump housing is bein= g=20 spun around at a constant velocity which requires no energy=2E Of cour= se=20 there are losses in the pump so the energy consumed is not zero=2E

This argument applies ONLY to centrifugal p= umps (of=20 which automotive waterpumps are an example) and not positive displaceme= nt=20 types (like oil pumps)=2E

-----------------------------

Tracy, I agree with you with respect to the= amount=20 of energy being used to pump water, however the frictional losses in the pum= p=20 increase with rpm and decreasing flow=2E The point I was trying to mak= e=20 (apparently poorly) is that the power dissipated in the pump can rise rapidl= y=20 with RPM=2E The energy into the pump is turned into heat energy, and althoug= h this=20 effect is small at lower RPM, it rises rather quickly with RPM=2E

A water brake dynomometer is just a pump th= at is=20 dumping its energy into raising the temperature of the water=2E

Bill Schertz

------=_NextPart_84815C5ABAF209EF376268C8 Content-type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Tracy wrote Assumeing a constant pump speed, when the thermostat closes and= head pressure goes up, power required to drive the waterpump does NOT go up=2E = It actually goes DOWN=2E Reason: There is less mass being accelerated (energy) at lowe= r flow rates=2E In the extream example (zero flow) the same water in the pump hou= sing is being spun around at a constant velocity which requires no energy=2E Of cou= rse there are losses in the pump so the energy consumed is not zero=2E This argument = applies ONLY to centrifugal pumps (of which automotive waterpumps are an example) an= d not positive displacement types (like oil pumps)=2E ---------------------------= -- Tracy, I agree with you with respect to the amount of energy being used to pump wat= er, however the frictional losses in the pump increase with rpm and decreasing f= low=2E=20 The point I was trying to make (apparently poorly) is that the power dissipa= ted in the pump can rise rapidly with RPM=2E The energy into the pump is turned = into heat energy, and although this effect is small at lower RPM, it rises rather quic= kly with RPM=2E A water brake dynomometer is just a pump that is dumping its en= ergy into raising the temperature of the water=2E Bill Schertz=20 ------=_NextPart_84815C5ABAF209EF376268C8--