Pro/Forums - View Single Post - Maximizing Surface area where it is needed.

8-Ball · 05-25-2003, 04:24 AM

The way am beginning to see waterblock design is as follows.

It isn't sufficient to think just about surface area or "turbulence". You need to consider the two together, and in fact, an understanding of the conductivity through the copper would help as well.

OK, so how does this work.

For a given surface, and a given "flow" of coolant, the heat exchanger will have convective heat transfer coefficient (CHTC).

What is this?

In a heat exchanger, you are often considering the transfer of thermal energy from a solid surface, (in this case, the surface of the fins/pins) to a coolant fluid (water in this case, but air is also a "fluid").

Why convective heat transfer?

There is a layer of slow/sationary moving fluid adjacent to the surface of the heat exchanger, through which the thermal energy must travel, in order to reach the fast moving stream of coolant, where it can be transported to the radiator.

For a given coolant, the CHTC will be determined by the flow velocity and the geometry of the heat exchanger.

What does the CHTC mean?

Essentially, this is an efficiency, (the inverse of a resistance) so W/C. So for a higher CHTC, the temperature difference required between the SURFACE of the heat exchanger, and the flowing coolant fluid can be lower for a given heat load.

However, we also need to consider the surface area fo the "furniture".

If the CHTC were constant, then it would be simple to say that you want the maximum surface area possible. However, it is never simple.

The "trick", is to maximise the surface area, with the best possible convective heat transfer coefficient (normalised, per unit area of surface), and do this just above the core.

BUT, you also want to do it in such a way, that the thermal energy does not have to conduct very far to the convection surface. It's all very well designing a waterblock with furniture all across the base plate, but if there is insufficient thermal gradient to get the thermal energy out there, then it was a wasted effort.

I hope this makes sense.

8-ball

05-25-2003, 04:24 AM	#2
8-Ball Cooling Savant Join Date: Feb 2002 Location: Oxford University, UK Posts: 452	The way am beginning to see waterblock design is as follows. It isn't sufficient to think just about surface area or "turbulence". You need to consider the two together, and in fact, an understanding of the conductivity through the copper would help as well. OK, so how does this work. For a given surface, and a given "flow" of coolant, the heat exchanger will have convective heat transfer coefficient (CHTC). What is this? In a heat exchanger, you are often considering the transfer of thermal energy from a solid surface, (in this case, the surface of the fins/pins) to a coolant fluid (water in this case, but air is also a "fluid"). Why convective heat transfer? There is a layer of slow/sationary moving fluid adjacent to the surface of the heat exchanger, through which the thermal energy must travel, in order to reach the fast moving stream of coolant, where it can be transported to the radiator. For a given coolant, the CHTC will be determined by the flow velocity and the geometry of the heat exchanger. What does the CHTC mean? Essentially, this is an efficiency, (the inverse of a resistance) so W/C. So for a higher CHTC, the temperature difference required between the SURFACE of the heat exchanger, and the flowing coolant fluid can be lower for a given heat load. However, we also need to consider the surface area fo the "furniture". If the CHTC were constant, then it would be simple to say that you want the maximum surface area possible. However, it is never simple. The "trick", is to maximise the surface area, with the best possible convective heat transfer coefficient (normalised, per unit area of surface), and do this just above the core. BUT, you also want to do it in such a way, that the thermal energy does not have to conduct very far to the convection surface. It's all very well designing a waterblock with furniture all across the base plate, but if there is insufficient thermal gradient to get the thermal energy out there, then it was a wasted effort. I hope this makes sense. 8-ball __________________ For those who believe that water needs to travel slowly through the radiator for optimum performance, read the following thread. READ ALL OF THIS!!!!