Water Block Design
Outer block design
From the top down view of the blocks, you can see that they all share a similar "X" style hold-down layout, matching that of the standard Intel socket design parameters. The big differences come with the block top materials, the thickness of the top hold-down plate, and how the entire block assembly is held together. With the exception of the Koolance CPU-360 block, all blocks are of a mixed metal / acrylic construction. The Koolance CPU-360 block is an all metal construction. The all-metal construction of the CPU-360 makes for a more durable design, especially when inserting and removing barbs from the block. The acrylic tops have more give to them, but their barb holes can become worn over time and lead to cross-threaded holds which don't hold the barbs as securely.
The XSPC Raystorm block is equipped with the thickest hold-down plate, measuring a full 0.25 (1/4) inches thick. Both Koolance blocks come in at a close second with their plates measuring 0.1875 (3/16) inches thick. The two Swiftech block are equipped with a hold-down plate measuring a thickness of 0.625 (1/16) inches. While all hold-down plates are more than up to the task of holding the water block firmly seating to the CPU, the thicker plates are less likely to warp or bend under pressure over time. Hold-down plate warping could lead to non-optimal interface between the block and CPU surface over time, translating to escalating CPU temperatures and instability in overclocking situation.
The hold-down plates for all blocks with the exception of the XSPC Raystorm block are bolted to the bottom plate, intrinsic to the integrity of the block and internal fluid channels. The XSPC Raystorm block's hold down plate is removable, sitting atop a groove along the outside edge of the block's top. The removable hold-down plate of the Raystorm block is a mixed blessing, positive in that it can be easily replaced without taking apart the block if it breaks. In its default configuration, the Raystorm block comes with an acrylic hold-down plate with a metal liner. After repeated mounts and dismounts of the block, the hold-down plate can crack (as happened to me). The metal version of the hold-down plate is much more durable and was easily replaced without much effort because the plate is not bolted into place. However, the hold-down plate can shift much more easily during block board mounting (again, because it is not bolted to the block), making for a trickier CPU block installation process.
Inner block design
When the blocks are taken apart, the design differences between them become more apparent. The internal block design approaches differ in through distinct areas: number of fluid inlets/outlets, positioning of fluid inlets/outlets, and fluid delivery into the block's base plate. With the exception of the Swiftech Apogee HD block, all the blocks have a single inlet port into the block and single outlet port leaving the block. This single inlet/outlet design promotes more directional flow through the block's base plate channels. Swiftech took a different approach with the Apogee HD block, designing it with a single inlet port and up to three outlet ports. The block can be used in the traditional single outlet port configuration. However, it can be used to split the outlet flow between three outlet sources, increasing the fluid flow rate through the block by reducing the block's internal resistance. However, flow rate through the side outlet ports may be reduced in comparison to the port in line with the inlet port because coolant will more naturally flow towards the in line outlet port.
Out of the tested blocks, only a single block has its outlet port offset from its inlet port – the Koolance CPU-360 block. The Koolance CPU-360 outlet port is positioned to the right of the inlet port, forcing the fluid to split through the micro-channels to either side of the inlet port and come together via the outlet port. This splitting and reforming action forces the coolant to more optimally flow through the entire surface of the block's base plate but reduces the coolant flow rate through the block. All the other blocks were designed with their outlet ports in line with the inlet ports. The in line port design increases flow rate through the block, but can lead to non-uniform flow rate through the block and base plate channels.
Three of the blocks (the two Koolance blocks and the XSPC Raystorm block) use a jet impingement plate and micro-channel design while the two Swiftech blocks use a straight-thru micro-pin design for fluid heat absorption. The jet impingement plate and micro-channel design affects fluid flow rate through the block adversely, but makes for more even distribute of the coolant medium over the base plate's cooling channels. The straight-thru micro-pin approach preferred by Swiftech allows for high fluid flow through the block, but can lead to "hot zones" within the base plate. These "hot zones" are caused by the fluid tendency to take the shortest path through the base plate if not directed (as in the jet impingement / micro-channel design).
Block fluid channel design
The block's base plate design is critical to the cooling potential of the block. The base plate design criteria include base plate material and cooling channel layout. All of the blocks use copper-based base plates, a material that absorb transfers heat very well between the CPU surface and the coolant flowing through the base plate channels. The two Koolance blocks are nickel-plated copper with the other three blocks being naked copper. The nickel-plating gives the base plate corrosion and scratch resistance, but can lower the heat absorption capabilities of the copper. Untreated copper can become discolored and corrode over time as the top layer of the copy interacts with the atmosphere or liquid coolant.
The tested blocks have two types of channel layout – micro-channel and micro-pin. The micro-channel layout consists of small vertical channels running from to back along the base plate's surface, normally fed liquid via a jet impingement plate to force the coolant evenly across all channels. The micro-pin layout consists of rectangular pins oriented in a front to back uniform layout, resembling a copper forest. The micro-channel design leads to more even distribution of the coolant across the base plate, while the micro-pin design passes the liquid straight through the copper pin forest leading to the formation of "hot zones" on the base plate. These "hot zones" are caused by the tendency of liquid take the shortest route possible when flowing between the inlet and outlet ports. The micro-pin design alleviates this "hot zone" effect to some extent be causing flow turbulence as the liquid passes through the pin "forest".
The Koolance and XSPC water blocks use a jet impingement-fed micro-channel design with the two Swiftech blocks using a micro-pin-based design. The Apogee HD block uses a hybrid approach with micro-channels feeding coolant into the micro-pin forest, as well as micro-channels leading from the forest to the main and auxiliary outlet ports. Both Swiftech blocks as well as the Koolance CPU-380i block have coolant collection channels at the top and bottom of their channels. These collection areas sit over the inlet and main outlet ports for the Swiftech coolers, assisting with the coolant flow through the block. On the Koolance CPU-380i block, the upper collection area sits over the outlet port, forcing the liquid from the lower collection point to flow back to the upper one. This could cause further restrictions to coolant flow through the block as well as dissuade the coolant from traveling to the lower collection point. The Koolance CPU-360 and XSPC Raystorm blocks do not have any defined coolant collection areas, relying on the channels cut into the block top as well as the positioning of the outlet port to define coolant flow through the base plate channels.