Quote:
Originally posted by myv65
if your system is truly sealed, the suction line may be at less than atmospheric pressure. Usually it will be, but if your system was filled with relatively cool water and heated, the expansion of the water will create a static pressure higher than atmospheric. Whether or not you get a vacuum at the suction then depends on elasticity of the tubing and the overall temperature rise of the fluid as well as flow rate and velocity in the lines.
|
Thanx ! That was exactly the kind of answer i wanted to read.
Actually my system is:
* closed loop, no res, no airtrap
* sealed
and tubes / pipes are rigid.
Given :
* the quite high flow restriction of a waterblock and our small tubes,
* the way our centrifugal pumps work (they are not volumetric, they only work by applying a pressure), the pressure differential in a working pump between inlet and outlet should always be around it's head pressure,
* the quite low temperature differential accors the circuit (1°C or less). Is 1°C enough to produce a noticeable static pressure ?
i've been wondering what was the *real* pressure distribution around a closed loop of water. Maybe CFD would answer that..
You seem to say that in every case the pressure is positive around the whole circuit, which i doubt by experience. (say, i only "doubt", ie i may be quite wrong on this).
What i'm considering here is the dynamic effects.
In a turning flow; the radial kinetic forces tend to create a pressure on the outer side, and an underpressure in the underside (Bernouilli, if my memories serve me right). This effect is mostly noticeable in rads ans waterblocks, under CFD or other flow analysis tool scrutiny. The question is, whats the difference when "ambient" or "static" pressure of the flow at this point is "high" or "low" ?
Notes:
* I doubt that with rigid tubing the pressure "suddenly" drops at pump inlet. Correct me here if i'm wrong.
* i've got a rather powerful pump (rated at 27W), but i doubt it dumps all its 27W in water. Actually it's quite hot to the touch, and since it has fins i suspect it dumps a good part of its heat in the air. Besides the engine (hot part) is totally insulated from the water chamber, since it's a mag drive. The percentage of heat dumped by the pump into water has been a hot topic but until now i've seen no convincing answer.
gone_fishing: you got it right.