Ah where to being.
I have a degree in mechanical engineer. As part of this degree I have lectures on turbulence. I did Reynolds number in first year. In my locker at the moment I have 3 books on turbulence, ones 500 pages long and looks mean. I also gotta see a man about some turbulence tomorrow as well.
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Originally Posted by bobo5195
Turbulence and boundary layers dont work like that what so ever and in fact the entire sentence makes no sense.
No, do a little research on the reynolds formula and you will realize that besides the velocity, the channel diameter is the most important factor of Turbulence. When two channels have water with the same middle velocity flowing through them, the channel with the smaller width will have the more turbulence.
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Reynolds number. It’s a non-dimensional number not a formula. You change the formula if you so wish. It can all get a bit random.
So I will ask you this question what does the Reynolds number actually mean and where does it come from?
Hint it is only partially to do with turbulence. You will from that answer that the Reynolds number only tells a bit of the story about turbulence. A flow with a Re=50000 is not necessarily turbulent.
It might take you a few thousand words to answer that. Probably by the non-dimenisonal navier-stokes equation (hint hint).
Second question what is a boundary layer?
I’ll answer this one. Its when a flow is 99% (okay so it doesn’t need to be 99% could be 90% or whatever, a large percentage) of the mean flow velocity. Actually there is the fluid boundary layer (velocity boundary) and the thermal boundary layer (temperature). You haven’t defined which one you are talking about. Common engineering language would say that boundary layer is fluid boundary layer. Now I’m going to bet that your actually talking about thermal boundary layer here instead. Shrinking the thermal boundary layer could be a good thing it would imply lower thermal resistance but its undoubtedly complicated. Arguments saying that the thermal gradient is equal to conductivity etc maybe (k * dT/dx). I’m not convinced entirely. Could also argue that jets have their fluid boundary layer and I would accept that too. But in between the pins possibly not.
Pin block jets only for water distribution?
Hmm, a lot of fluid mechanics for people are trying to do other stuff and use them for cooling. Jet impingement cooling is mainly used in these situations. Get a normal heatsink that is not doing its job and add jets to make it better.
You can do an awful lot with maze blocks and a fluid mech block. Using some boundary layer stuff you could work out heat transfer rate. You may even find out that for you average maze block the thermal boundary layer would cover 10% max of the flow.
I was talking about blind hole (as you call it) blocks. They most definitely are connected to the baseplate. Jet hit fin, fin touches base plate.
Recirculation zones are not good ever (well actually there are some cases, storm blocks might get 50% of their heat transfer from). They are generally not advantageous.
I think you should go and read a good book on heat transfer then you might see that turbulence is only a marginally good enhancer of performance. Velocity has everything to do with it. I was doing some CFD today on fins the correlations I came up with were heat transfer was Nu = Cl x Ra^(1/3) for lamina and Nu = Ct x Ra^(3/8) for turbulent. Not a lot of difference there. Ra = Rayliegh number its like Reynolds number for convection.
There’s much more I could post but I’m going to bed. I might add some more in the morning when this post isn't brought to you by beer
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