Cooling Reviews Watercooling

Volume flow, pressure loss and cooling performance using the example of a CPU and GPU water block | Practical knowledge

Reduction of volume flow through the coolers

Each component in the circuit causes a drop in the current volume flow via a more or less large resistance, which is colloquially referred to as pressure loss. Even the walls of pipes or hoses provide this resistance, in addition to cross-sectional changes, bends, vertebrae, air pockets and much more. the whole of the whole then adds up to a noticeable and unfortunately also measurable total value.

But let's look at another big post next to the radiators, namely a graphics card cooler. I take the measurements on an Alphacool ice block ES Acetal, which was in quite grateful test object. First, I vary the reference volume flow by activating the bypass B and precisely adjusting the desired value by means of bypass A and the pressure control valve and waiting until the value has stabilized or as long as necessary (blue curve). Then I switch over to the cooler and now read off the volume flow resulting from the series-switched cooler (red curve).

The pressure loss can also be described as a reduction in the volume flow and the difference can be calculated. The orange curve shows the result very clearly. this difference is almost constant from a certain limit. If at 0.5 l/m (30 l/h) it is still 0.03 l/m at 1.5 l/m (90 l/h) already 0.12 l/m and at 3 l/m (180 l/h) then 0.15 l/m. So you can see that the value from approx. 1.5 l/m (90 l/h) hardly rises significantly. This is important to know if you really venture into a real low-flow system, because it is then essential to find components that have the lowest possible resistance even at low volume flows. Unfortunately, such information about the coolers is rarely or not at all found.

By the way, the X-axis of the diagram refers to the blue curve as a 1:60 conversion to l/h and serves only for better orientation. Next, let's look at the CPU cooler. Here I have hung a rather large Alphacool ice block XPX Pro Aurora into the circuit, which produces a very defined, but also over wide ranges much more constant pressure drop than just the GPU cooling block. I pinned the part to an Aorus X299 Master and enjoyed an Intel Core i9-7980 XE.

The maximum pressure loss was between 0.16 l/m (9.6 l/h) and 0.13 l/m (7.8 l/h) for the smallest volume flow. So we see that the CPU water block with jetplate and a cold plate shaped by microchannels acts almost linearly, because here all chambers, circuits and alternating flow speeds are eliminated.

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About the author

Igor Wallossek

Editor-in-chief and name-giver of igor'sLAB as the content successor of Tom's Hardware Germany, whose license was returned in June 2019 in order to better meet the qualitative demands of web content and challenges of new media such as YouTube with its own channel.

Computer nerd since 1983, audio freak since 1979 and pretty much open to anything with a plug or battery for over 50 years.

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