Quote:
Originally posted by bigben2k
As Alchemy so importantly pointed out, turbulent flow may not be achieved. I was under the impression that it could be achieved in one of two ways: turbulators or plain high speed. Can you tell me more? What about Utabintarbo's suggestion?
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Well, turbulence is determined by a dimensionless value called a "Reynolds number." The exact range between turbulent and laminar flow is disagreed upon in some circles.
According to McCabe, Smith, and Harriott, turbulent flow will occur at Reynolds numbers above Re~24,000. Turbulence can be forced by obstructions in the flow as long as the Reynolds number is well above Re=2,100. Below that, there's no way to avoid laminar flow.
Sieder and Tate define turbulent flow for significant heat transfer to be abover Re=100,000.
In the inner channels, you're going to have Re=2600. In the outer channels, Re=1300.
This makes for an extremely inefficient design - the increase in surface area these channels create won't make up for this.
My *rough estimate* of the heat transfer coefficient between the copper channels and the the fluid is h~4 kW/m^2 C.
Under the very best of conditions, you could get perhaps a 3 degree C difference between the copper walls and the fluid. This might still be acceptable, but I don't think this is going to outperform most WB's on the market.
Alchemy