Cascade & some equations
 

It is raining :cry: here and I had some time to play with some equations:

Click here

Maybe in the future I will do a real fluid/solid thermal coupling analysis in ANSYS.
(I'm having a little trouble with convergence & solid fuid coupling right now).

hrmm interesting.
Not too sure about the jet bore, I thought it was closer to 0.8mm. Also can you redo the sim for different flow rates? (if its still raining:) )
1000l/min (even l/hour) might be a wee bit unrealistic... AFAIK 600l/h is about the max?

That's a pretty darn cool analysis. I'm not enough of a :geek: to understand all the theory behind it, but I am a math geek so I can follow the equations. The sim software is some very cool stuff!

Sorry my mistake -> 1000l/min is a typing mistake, 1000l/h is the right number.

Something amiss with the projected value for h.

Testing shows that h, in practise, is estimated to be about 10x higher than what you have determined.

Somewhat hard to follow without some dialogue, but I think what you've done is apply basic flow-across-a-surface convection calculations as if the cups were essentially a pipe with water running over the walls, which really isn't what's going on here.

The difficulty here is that for constrained submersed jet impingement is that there is limited applicable theory available with which to work from.

Edit:

Just read through the calcs more carefully and realised you mean thermal conductivity instead of heat transfer coefficient

just out of interest what is the film coefficient. Sorry I'm being dim I just haven't heard of it before (probably due to being asleep in the lecture :))

To Cathar

1. What do you mean by h ?
2. If the cup is long enough (i'd say if cup heigth > diameter) than the cascade is just heat transfer in a tube (i will give you an example of the velocitiy of water flowing trough a jet in a cup later), except of course for the base of the cup, for which I just assumed that the film coefficient is the same as in the tube (I could be way wrong here).

To WAJ_UK

1. The film coefficient (type this in GOOGLE) is about the same as the heat transfer coefficient (W/m*K)only this time in the join between two different mediums (copper/water, copper/air) and is measured in W/m^2*K.

lets say for heat transfering in the same medium (= heat conduction)
Q=heat transfer coefficient *medium length*temperature difference

lets say for heat transfering between copper/air (= heat convection, forced convection)
Q=film coefficient *area*temperature difference

Examples for different block base thickness (Q=1000l/h, block dimensions the same as before).

1mm
http://members.lycos.co.uk/mfs905/base/001base_thk.gif
2.5mm
http://members.lycos.co.uk/mfs905/base/025base_thk.gif
5mm
http://members.lycos.co.uk/mfs905/base/050base_thk.gif
7.5mm
http://members.lycos.co.uk/mfs905/base/075base_thk.gif
10mm
http://members.lycos.co.uk/mfs905/base/100base_thk.gif

And different flow rates:

1000l/h
http://members.lycos.co.uk/mfs905/flow/1000lpm.gif

900l/h
http://members.lycos.co.uk/mfs905/flow/0900lpm.gif

800l/h
http://members.lycos.co.uk/mfs905/flow/0800lpm.gif

700l/h
http://members.lycos.co.uk/mfs905/flow/0700lpm.gif

600l/h (the flow gets laminar, film coefficient only 730W/m^2K, something stinks here I know)
http://members.lycos.co.uk/mfs905/flow/0600lpm.gif

RKB2 I think you are getting heat transfer coefficient confused with thermal conductivity

>> RKB2 I think you are getting heat transfer coefficient confused with thermal conductivity

You are right, sorry english is not my mother language.

And for Cathar:

Water velocity trough the cup (warning the solution did not converge after 5000
iterations, so results may be wrong).

http://members.lycos.co.uk/mfs905/cascade/cfd1000.gif

http://members.lycos.co.uk/mfs905/cascade/cfd1001.gif

Some very good work here rkb2. I think with some tuning of your parameters you could start generating some really good data. The base thickness behaviour is particularly interesting, some higher resolution modelling when the jet dimensions are established more accurately, please?

Good stuff.

Cheers

Incoherent