Pro/Forums - View Single Post - Thoughts on water pressure & flow rate...

Graystar · 04-17-2003, 01:58 PM

You're opening a can of worms with this one!

First off, what do you mean by "efficient"? Higher pressure increases flow, and that affects the system performance. But people have different concepts of what is "efficient", usually confusing efficiency with performance.

If you are considering the power consumed for a given amount of work, you are talking about efficiency. If you are considering the max amount of work that can be done, you are talking about performance. Generally, we talk about performance and not really worry too much about efficiency (although I personally give efficiency a lot of thought.)

So, back to your question. There is a basic physics-based answer, and then there is the more complex application of the physics to our WC systems. Watch the bouncing ball...

Faster flow always transfers more heat. That will always be true. So if you increase the flow rate through your waterblock, you will remove more heat from the CPU. Also, if you increase the flow through your radiator, you will transfer more heat from the water to the radiator. That's the basic physics part.

Now, lets step into reality. Reality tosses in three factors that may kill any benefit from increased flow. First is the difference in performance gain between the waterblock and the radiator.

When you increase flow, the waterblock performs better. That performance increase is attributed solely to increased flow, because we assume that the temperature of the water going into the waterblock remains the same. That's fine. However, the temperature of the water coming *out* of the waterblock has dropped (just happens to be a function of increased flow.) So our radiator will have two factors affecting its performance; increased flow and lower inlet temperature. A lower inlet temperature counters the gain from increased flow.

So when you increase flow the radiator works better, but it doesn't get the same boost as the waterblock. What this means is that the radiator will have to work harder to get rid of all the heat that the waterblock is sending its way.

The second factor is air. In the end, a watercooling system turns into an air cooling system. The amount of heat that you can ultimately remove is based on the relationship between your fans and radiator. So while you may make your waterblock work better with increased flow, you may simply be stuck with that extra heat if you can't get rid of it fast enough.

The last factor is the pump. Increasing pressure is the most costly operation for a pump in terms of watts consumed. The centrifugal pumps that we use are so inefficient for this task that they end up adding heat to the water. Usually, we increase pressure by getting a bigger pump. However, that means more heat added. So the benefits realized from increased flow may be wiped out by the additional heat.

So...not so simple.

04-17-2003, 01:58 PM	#3
Graystar Registered User Join Date: Mar 2003 Location: Brooklyn, NY Posts: 112	You're opening a can of worms with this one! First off, what do you mean by "efficient"? Higher pressure increases flow, and that affects the system performance. But people have different concepts of what is "efficient", usually confusing efficiency with performance. If you are considering the power consumed for a given amount of work, you are talking about efficiency. If you are considering the max amount of work that can be done, you are talking about performance. Generally, we talk about performance and not really worry too much about efficiency (although I personally give efficiency a lot of thought.) So, back to your question. There is a basic physics-based answer, and then there is the more complex application of the physics to our WC systems. Watch the bouncing ball... Faster flow always transfers more heat. That will always be true. So if you increase the flow rate through your waterblock, you will remove more heat from the CPU. Also, if you increase the flow through your radiator, you will transfer more heat from the water to the radiator. That's the basic physics part. Now, lets step into reality. Reality tosses in three factors that may kill any benefit from increased flow. First is the difference in performance gain between the waterblock and the radiator. When you increase flow, the waterblock performs better. That performance increase is attributed solely to increased flow, because we assume that the temperature of the water going into the waterblock remains the same. That's fine. However, the temperature of the water coming out of the waterblock has dropped (just happens to be a function of increased flow.) So our radiator will have two factors affecting its performance; increased flow and lower inlet temperature. A lower inlet temperature counters the gain from increased flow. So when you increase flow the radiator works better, but it doesn't get the same boost as the waterblock. What this means is that the radiator will have to work harder to get rid of all the heat that the waterblock is sending its way. The second factor is air. In the end, a watercooling system turns into an air cooling system. The amount of heat that you can ultimately remove is based on the relationship between your fans and radiator. So while you may make your waterblock work better with increased flow, you may simply be stuck with that extra heat if you can't get rid of it fast enough. The last factor is the pump. Increasing pressure is the most costly operation for a pump in terms of watts consumed. The centrifugal pumps that we use are so inefficient for this task that they end up adding heat to the water. Usually, we increase pressure by getting a bigger pump. However, that means more heat added. So the benefits realized from increased flow may be wiped out by the additional heat. So...not so simple.