return line to gas tank

[Tom Sharpe]

Greg Hermann wrote:

> >>If the pump draws 8 amps (@ 12 volts), and all of the heat from that winds
> >>up in the fuel (which it basically does , sooner or later), that is 96
> >>watts. Which converts to 327 BTU/hour. which is enough heat to raise the
> >>temperature of 10 gallons of gasoline about 7 degrees over the course of
> >>one hour if none of that heat is dissipated anywhere.
> >
> >The power which goes into heat is significantly less than the power the
> >pump uses
> >to push fuel. The way to determine how much electrical input power is
> >converted to
> >heat is to convert the output flow of the pump to work. Then, calculate the
> >efficiency of the pump based on input power (96 Watts). The amount of
> >energy not
> >directly used for pumping should be a fair approximation of  how much heat is
> >added to the fuel by the pump.
> >
> >It is not simple to do, but I would guess that the pump must be 75-80%
> >efficient.
> >Any thoughts on this?
>
> Hey--give an A+ to the guy who caught the trick question!! But note that I
> said "sooner or later", and was running a quick, worst case calc to
> disprove Tom's theory. What I meant by sooner or later was that some of the
> work put into flow energy (and static pressure potential energy)  in the
> fuel by the pump comes back as fuel heating where the throttled flow
> through the pressure regulator occurs. More heating happens (but does not
> stay in the system) with the throttled flow through the injectors.  More
> heating of the fuel occurs from typical frictional flow losses in the
> supply and return fuel lines. The IR losses in the pump motor windings go
> straight into the fuel, and I would guess to be about 25% of the input.
> mechanical (friction) losses in the pump (analogous to the heating of lube
> oil) I would guess to be about another 15-25 % of input. But no matter--it
> ain't the pump which is heating up a tank full of gas!!
>
> Regards, Greg

I disagree with only one point--- all others are perfect.

An oil pump at 40-50 PSI will easily warm the oil 30 degrees all by itself. They
are some of the most inefficient pumps made. Tech-Line claims that their anti
friction coatings will drop oil temp by 30 degrees - mine is down at least
25...... I'm a believer.

Regards  Tom