At 10:38 PM 6/20/2011, Stephen A. Lawrence wrote:
On 11-06-20 10:11 PM, Abd ul-Rahman Lomax wrote:
At 04:10 PM 6/20/2011, Stephen A. Lawrence wrote:
Aw, these reports drive me nuts. I'd not read this one, I think.
They have a pump for cooling water, it seems. So when they start
up, they are pumping an estimated 6.47 kg per hour of water. They
assume that this flow rate remains the same. Why?
It's a constant displacement pump. That's what it does.
Sure. But does it pump the same regardless of back pressure?
YES -- That's exactly what it does! That's the whole point -- you
can use it for calorimetry because its flow rate is unchanged! You
can't do that with pumps that don't have a predictable flow rate.
That "predictable flow rate" assumes back pressure below a certain
value, which will be one of the specifications of the pump. What
happens if you, say, close a valve on the outlet of the pump? If it
is truly constant rate, the pressure would increase without limit
until it blows the measly valve off the pipe....
In fact, the internal valves that are part of the pump will fail, and
if it is a good design, they fail gracefully. They simply fail to
close all the way, or they blow open, releasing the pressure. With a
good design, this doesn't harm the pump at all.
It's like the thing found in the basement of East Campus, labeled "1
Amp -- No Matter What".
Hey, it's just got a big honkin' inductor. Do not open the switch in
this line except with a long pole. And hope that "no matter what" is
still limited by some physical constraints, or else you will have an
arc that won't quit.... the voltage will increase without limit, and
at 1 amp.... you don't want to be anywhere near this thing.
Did they record the number of pump cycles per minute more than at
initiation? Imagine that the pump has a leak in its internal
mechanism, say a leaky flap valve.
Oh, for goodness sake. And every time they run the test they
happen to use a defective pump, eh?
Actually, these pumps are, my guess, designed to leak. All of them.
When the pressure exceeds their rating. Otherwise they will break.
(another possibility, the actuating mechanism must be limited in the
force it can apply. So it simply fails to operate the pump. In this
case, the sound of the pump would definitely change. It would
probably be stuck.
Suppose the reservoir has a leak, too, while you're at it, and
nobody noticed the wet floor.
No, that was one of the observers who, hearing some sound, thought
the thing was about to blow.
They also weighed the reservoir before & after, as a double
check. You can forget about varying flow rates -- there is no
evidence to support the idea.
Stephen has raised an interesting point about it, about how it comes
to be that the pump setting and the steam generation are so perfectly
matched. I pointed out that the match doesn't have to be perfect,
but, sooner or later, it would create a problem!
I don't know how they address the problem.
