Introduction

Alphacool is a German manufacturer and provider of complete water cooling kits.  Their products are fairly well known to Europeans but they are not currently sold in the US.  Their flagship waterblock, the NexXxoS XP, is currently regarded as the #1 waterblock by Watercoolplanet (a large German water cooling review site whose test results are highly regarded).  Procooling was fortunate to receive a sample block for review from Alphacool by way of Cathar (Little River Waterblocks).

The NexXxos XP has a copper baseplate with small pins cut into its center (presumably with a slit saw) .  It also has a center plate that features 20 small holes over the center of the block that act as accelerator jets.  The result is is similar to the #5 nozzle of the Danger Den RBX/TDX.  A rather interesting design choice was to use an offset inlet rather than an inlet barb directly over the accelerator plate holes. This was done to facilitate the Alphacool mounting hardware, but it undoubtedly has an adverse effect on pressure drop to have the inlet water meet such an abrupt restriction.  The top and middle plates are nickel-plated for a nice shiny appearance. This effect is somewhat hindered by the fact that the mounting hardware basically obscures the block..   

The NexXxoS XP looks to be very well constructed and is certainly a different design from the common US waterblocks. I contacted Alphacool for more information on the design and any additional comments but they did not respond.  So I'll just leave it at that.

Test Results and Observations

I finally got around to putting together a summary of my testing methods and equipment, so if you want to get the full lowdown on the Procooling test bench then just give that a read.  All tests were done with a TBred B 1700+ at 175x12.5 and 1.825V in BIOS (estimated to be 71W given the dT across wb).  Here is a bit more information on the "delta T" numbers that are used in all the graphs that follow:

 I measure CPU diode temperatures, the temperature of the water at the waterblock's inlet, and the water flow rate.  By plotting the difference between CPU temperature and water temperature, we can normalize all testing.  This is required because water temperatures may vary from day to day in my testing room.  The closer that this delta T (engineering-speak for temperature differential) is to 0, the better the waterblock is performing.

The first test I conduct is the variation of waterblock performance over many mounting replicates at 1.42GPM flow rate (the maximum I could achieve). 

Over five mountings the average temperature difference between CPU diode and water inlet was 8.64C, and the standard deviation was 0.13. This is a good place to talk about the mounting of the block though. It's straight out of 1990s; effective but crude.  You can see the mounting hardware in the above picture. A cage surrounds the block and locks onto the 6 socket lugs.  An allen bolt is tightened through the crosspiece to apply pressure on the CPU core.  This works reasonably well provided you have the right metric attachment and can use a hex driver.  But there is virtually no way to determine how much force is being applied to the core.  I tightened the hex bolt down tightly in all cases and could achieve a reproducible mount.  I might somewhat be favoring the NexXxoS by doing this, however. I REALLY wish that they had used a top plate designed for the 4 AMD mounting holes and that had the inlet barb directly over the inlet jets.

The next test conducted is the relationship between waterblock performance and flow rate:

For comparison the best commercial waterblocks I have tested, the Little River Cascade and Storm G4 waterblocks are also shown.  The NexXxoS XP fares extremely well in this dT vs. flow graph, although it is extremely restrictive. The maximum flow rate I could achieve was 1.42 GPM with the Alphacool waterblock, which makes it the most restrictive waterblock I have tested.  Conventional wisdom is that this doesn't matter because the Alphacool (and other European waterblocks for that matter) are "designed for low flow". If one looks at the above graph, these comments don't seem to be valid.  One can see that the performance curve of the NexXxoS XP is similar to the Cascade and Storm G4 and that progressing from a flow rate of  0.5GPM to 1.4GPM yields about 3C of additional cooling.  Compare that with the Swiftech MCW6000; which benefits around 1C for the same flow rate increase.  In fact the relatively thin baseplate and accelerator nozzle make the NexXxoS block perform extremely well at higher flow rates, but it is not especially well-suited to flow rates below 0.5-0.75 GPM.

Of interest to most readers is the performance of the NexXxoS XP waterblock plotted versus other commercial blocks I have tested:

It should be clear from this graph that the Alphacool offering is obviously competitive with the best commonly available commercial waterblocks. The silver waterblocks I have tested (Cascade SS and Storm G5) were omitted from this graph because I view them as rather "niche" products. This figure is getting pretty busy (though not so much in the Storm G4 and NexXxoS XP region of the graph), and I recommend either clicking on the graph or following this link to use Procooling's interactive waterblock comparison page.  The Storm G5 is the clear performance leader over all other commercial blocks at all flow rates shown but as I said it is silver, very expensive, and not available at this moment. 

This graph really only tells half of the story though because flow rates in a real cooling loop will be determined by the resistance of all the components.  We have been discussing more reasonable ways to present a real world picture of waterblock performance in the Pro/forums, and Lolito_fr and Cathar have been extremely helpful in putting together a model of what performance of different waterblocks would look like with a Thermochill 120.2 radiator, 2 Papst 4312L fans, 2m 1/2" ID tubing, and a variety of waterblocks and pumps. Take a look at the graph below (click to enlarge):

I shall issue a large caveat that this is just a theoretical model and is NOT, as of now, fully validated. However, one can see that contrary to conventional wisdom the Alphacool is NOT OPTIMIZED for loops with low flow rates (such as the Eheim 1046 can provide).  In such a loop the Swiftech MCW6000-A would actually be a better choice. As flow rates increase with larger pumps, however, the NexXxoS XP becomes extremely competitive. In essence what this graph is showing is that the decreased flow rates caused by the Alphacool block being extremely restrictive (and has lower flow rates) more or less negates the fact it performs much better as a function of flow rate than other blocks I have tested.  Hopefully this provides a more clear picture of how cooling performance, flow rate, and flow resistance are related in a real system.  Also note that the MCP600 pump appears to be the best choice for all these blocks, and that it is currently sold by Cooltechnica (a Procooling sponsor) as the AquaXtreme 50Z-12DC.

The bottom line for the Alphacool NexXxoS XP is that it combines excellent performance with a reasonable price (for Europeans anyway).  Its mounting hardware is a bit clunky and it is very restrictive, but it is nonetheless one of the best commercially available waterblocks when combined with a moderately powerful pump and a good radiator. 

I would like to thank Alphacool for providing this block for review and Cathar and lolito_fr for their comments, assistance, and modeling work in our forums.

If you have any comments or Questions please contact pHaestus@ProCooling.com