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Aleck · 12-11-2003, 11:49 AM

[quote]Originally posted by Cathar
[b]Again, I am struggling to find the exact link to the paper that I read, but basically it was showing that the effect of extra turbulence in the jet stream by standing it off from the base and having it shear against the water around it was actually more effective at stripping the boundary layers despite the force of the jet's effect being slightly reduced. I believe that I've been able to mimic and observe the paper's statements through experimentation myself. The paper was talking about simple submerged jet behavior and not really talking about jet-in-a-cup behavior which is something else that I had to explore.

[quote]

Yup, it has been proven that the collision between the the boundary layer of two side by side jets hiting the base will create turbulance and enhance heat transfer provided the jets are close enough and the boundary layer has not lost much of its momentum.

But this research is done using a flat base as the heat transfer wall. In the case of a base with cavities (cascade design), the boundary layer at the botom of the cavity created by the jet will hit the sides of the cavity creating a 2nd impingement effect. As the fluid rises out of the cavity, the fluid has not much energy in it due to the double impingement previously. Even if there is still enough momentum, the fluids momentum will be directed upwards to the centre plate.
Then only will it react with the boundary layer that came from the fluid of the neighbouring jet.

But im still not sure which of the cases above (flat base & dimpled base) gives beter heat transfer.

Double impingement with reduced crossflow effect

or

Single impingement with enhanced turbulance with slightly higher crossflow effect

which is beter ?

12-11-2003, 11:49 AM	#26
Aleck Cooling Neophyte Join Date: Nov 2003 Location: Malaysia Posts: 29	[quote]Originally posted by Cathar [b]Again, I am struggling to find the exact link to the paper that I read, but basically it was showing that the effect of extra turbulence in the jet stream by standing it off from the base and having it shear against the water around it was actually more effective at stripping the boundary layers despite the force of the jet's effect being slightly reduced. I believe that I've been able to mimic and observe the paper's statements through experimentation myself. The paper was talking about simple submerged jet behavior and not really talking about jet-in-a-cup behavior which is something else that I had to explore. [quote] Yup, it has been proven that the collision between the the boundary layer of two side by side jets hiting the base will create turbulance and enhance heat transfer provided the jets are close enough and the boundary layer has not lost much of its momentum. But this research is done using a flat base as the heat transfer wall. In the case of a base with cavities (cascade design), the boundary layer at the botom of the cavity created by the jet will hit the sides of the cavity creating a 2nd impingement effect. As the fluid rises out of the cavity, the fluid has not much energy in it due to the double impingement previously. Even if there is still enough momentum, the fluids momentum will be directed upwards to the centre plate. Then only will it react with the boundary layer that came from the fluid of the neighbouring jet. But im still not sure which of the cases above (flat base & dimpled base) gives beter heat transfer. Double impingement with reduced crossflow effect or Single impingement with enhanced turbulance with slightly higher crossflow effect which is beter ? Last edited by Aleck; 12-11-2003 at 11:58 AM.