Quote:
Originally posted by BrianH
Not sure whay you mean here. If you are talking about the MCW50-T block, then direct TEC cooling would eliminate the heat transfers between the hot side/AS3/Copper base. Should be much more efficient overall???
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The mechanism by which heat is tranferrd from a solid body into an adjacent fluid, whether stationary or flowing, is by convective heat transfer.
It is "possible" to work out the convective heat transfer coefficient for a heat exchanger, though not really necessary. It is however beneficial to understand the factors which come into play.
The Nusselt number (non-dimensional convective heat transfer coefficient) is as follows.
Nu = C x Re^m x Pr^n
Pr is the Prandtl number, which is the the kinematic viscosity divided by the thermal diffusivity of the fluid, and is dependent on properties of the coolant fluid alone, so does not change with the design of the block.
Re is the reynolds number, and is a measure of the flow characteristic of the coolant. The higher the Reynolds number, the more turbulent the flow. There is a geometric factor in here, which depends on the furniture of the block as well as the flow rate and dynamic viscosity of the fluid and it's density.
C, m and n are constants which are dependent on the geometry of the heat exchanger and the range of the reynolds number, ie the characteristic of the flow.
Ultimately, we want to maximise this, which means changing the geometry and the reynolds number to suit.
The point I am getting at is that the convective heat transfer coefficient of the flat surface of a TEC is not likely to be very high unless the flow can be made extremely turbulent, ie by having very high flow, or with the addition of "turbulators". So would the increased convective heat transfer coefficient of an elaborately machined hot plate be sufficiently high to more than compensate for the additional heat transfer "stage" introduced, ie, getting from the surface of the TEC to the fins/pins or whatever has been machined into the hotplate.
Quote:
Originally posted by BrianH
With diect TEC cooling, the clamping pressure on the hot side is no longer needed. The cold plate and the TEC with still need a large clamping force. Since the hot side would only be clamped along the edges (I assume??), then great clamping force on the cold side may be difficault to achieve.
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I agree that high clamping pressure is required to reduce the thermal resistance of an interface, but I was wondering if there was anything else whic would very with pressure.
Would the operational efficiency of the TEC ITSELF, not the interfaces, vary if depending on how much it is being clamped.
ie; might the semiconductor jucntions behave slightly differently if they are clamped.
Also note that the thermal resistance between each of the little "pellets" in the TEC and the white ceramic sides will also change with clamping pressure.
So it may not be just the interface between the hot side and the hot plate or the cold side and the cold plate which is affected by clamping pressure.
I don't know the answer to these questions, though I suspect the junction properties will probably not change, but there are still interfaces between the individual peltier elements and the ceramic mounting plates. Could this interface be affected by removing the clamping pressure.
8-ball