"Waterblock Bench Testing Results"
Bill Adams - 11/22/02
page 1 of 4
This is a review of waterblock (wb) bench testing results utilizing equipment and procedures previously described in this article.
The focus will be on those performance parameters of significance to WCers in the selection of wbs and understanding the significance of these attributes with respect to the WCing system's performance. The principal wb characteristics are:
- Pressure Drop as a consequence of the coolant flow rate,
- Thermal Impedance (or "C/W") in relation to the coolant flow rate,
- Thermal Impedance (or "C/W") in relation to the heat load, and
- Thermal Impedance (or "C/W") in relation to the coolant input temperature
The following graphs are from a variety of wbs and illustrate the data that can be developed. As they may also be from somewhat different test equipment setups, the values should not be considered as being directly comparable, unless of course the data appears on the same graph.
The wbs are treated as a 'black box' having a certain effect; no appraisal is made of the wb's internals as to why it may have those performance
attributes. Waterblock design is a completely different topic.
Pressure Drop
A wb's flow characteristics affect its specific performance and constitute a significant part of the total WCing system's flow resistance (together with the radiator, hoses, and any fittings, reservoir, etc.) The pressure drop is not difficult to measure and easily understood by even neophytes to WCing.
But while it is tempting to think that 'lower is better', such may not be the case as different wbs' cooling capability is often inversely related to their pressure drop.
Better cooling due to increased turbulence or surface area
for example, will always increase the pressure drop - one has to 'dig
deeper'. The comparative pressure drops of some current wbs are shown
below.
Chart 1
Thermal Impedance - "C/W"
When the wb's thermal impedance is expressed as "C/W" and measured at different coolant flow rates, a curve will result with the "C/W"
decreasing as the flow increases. Due to the improved convection resulting from higher flow rates (actually the resultant increased velocity),
Higher flow will always improve a wb's performance.
The
"C/W"s of the same wb's as in the Pressure Drop graph (above) are
shown in Chart 2. Noteworthy is that the wb with the
lowest pressure drop (the Swiftech 462-UH), also has the highest "C/W" (poorest cooling expressed as a function of the coolant flow rate). The three mid-range wbs, in terms of their pressure drop are now seen to have the lowest "C/W" (thermal impedance).
From this, it can be seen that it is not simply flow that does the cooling:
A higher flowing wb is not necessarily better than a lower flowing one.
A WCing myth is shot down.
Bill Adams
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