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myv65 · 05-23-2002, 10:04 PM

To redleader, radiator efficiency is much like block efficiency. However, the relationship tends to be reciprocal. Imagine a radiator in which the water exited a mere second after it entered. There would be insufficient time for the water to approach the temperature of the air blowing over the radiator. On the other extreme, imagine a radiator where the water required ten minutes to get from entrance to exit. Upon exiting, the water would essentially match the air temperature. Each of these extremes would not exist in a computer cooling setup, but illustrates the concept involved.

This is the catch-22 of water cooling. Blocks perform better with high water velocity, yet radiators perform better with longer dwell time.

In pHaestus' graph, you see the effect in a block. As flow approaches zero, the differential between the CPU and fluid grows as 1/flow. As flow increases, the differential follows this same 1/flow trend. If a similar graph was plotted for radiators showing the differential between fluid and air, you'd find a relationship that is the reciprocal of that for the block. ie 1 over 1/flow = flow. As flow rate in a radiator drops, delta T drops. As flow rate through the radiator increases, delta T increases.

There is no magic in stating that blocks do well with high velocity while radiators do well with low (water) velocity. What more folks need to recognize is that velocity is not simply a function of volumetric flow rate. Velocity is volumetric flow rate divided by flow area. Blocks that utilize (properly defined) small flow paths can meet or exceed the performance of blocks using substantially larger flow paths (and correspondingly higher flow requirements). The kicker here is that a block with small flow pathways and low volumetric flow rate yields better radiator performance that a high flow block with all other components held constant. It does this simply because the lower flow of the former block creates more dwell time for the water in the radiator.

A corollary to this concept is that you can get equal performance from a smaller radiator using a low flow block when compared against a big radiator and big block. Make no mistake, to realize such a result requires proper design of the block and proper selection of the pump, radiator, radiator fans, and tubing. Unfortunately, the majority of water cooling users seem to blindly follow the "bigger is better" theory without regard for the interactions that take place between the block and radiator.

05-23-2002, 10:04 PM	#18
myv65 Cooling Savant Join Date: May 2002 Location: home Posts: 365	To redleader, radiator efficiency is much like block efficiency. However, the relationship tends to be reciprocal. Imagine a radiator in which the water exited a mere second after it entered. There would be insufficient time for the water to approach the temperature of the air blowing over the radiator. On the other extreme, imagine a radiator where the water required ten minutes to get from entrance to exit. Upon exiting, the water would essentially match the air temperature. Each of these extremes would not exist in a computer cooling setup, but illustrates the concept involved. This is the catch-22 of water cooling. Blocks perform better with high water velocity, yet radiators perform better with longer dwell time. In pHaestus' graph, you see the effect in a block. As flow approaches zero, the differential between the CPU and fluid grows as 1/flow. As flow increases, the differential follows this same 1/flow trend. If a similar graph was plotted for radiators showing the differential between fluid and air, you'd find a relationship that is the reciprocal of that for the block. ie 1 over 1/flow = flow. As flow rate in a radiator drops, delta T drops. As flow rate through the radiator increases, delta T increases. There is no magic in stating that blocks do well with high velocity while radiators do well with low (water) velocity. What more folks need to recognize is that velocity is not simply a function of volumetric flow rate. Velocity is volumetric flow rate divided by flow area. Blocks that utilize (properly defined) small flow paths can meet or exceed the performance of blocks using substantially larger flow paths (and correspondingly higher flow requirements). The kicker here is that a block with small flow pathways and low volumetric flow rate yields better radiator performance that a high flow block with all other components held constant. It does this simply because the lower flow of the former block creates more dwell time for the water in the radiator. A corollary to this concept is that you can get equal performance from a smaller radiator using a low flow block when compared against a big radiator and big block. Make no mistake, to realize such a result requires proper design of the block and proper selection of the pump, radiator, radiator fans, and tubing. Unfortunately, the majority of water cooling users seem to blindly follow the "bigger is better" theory without regard for the interactions that take place between the block and radiator.