Many companies offer heatsinks that are configured for two-way or three-way designs, and the name may be a bit misleading. On the surface, the two-channel heat sink sounds like a fluid passing through the heat sink twice, which is not the case.
The dual channel design is nothing more than a baffle welded in the end can. This is done by cutting the heat sink in half and flowing the fluid through each half in series. Since each part is half the size of the entire core, the fluid is twice as fast and the pressure drop is now doubled. Many people think this design is superior because the fluid stays in the heat sink for a longer period of time. The reality is that the fluid has twice the distance, but it travels twice as fast. Finally, the fluid flows through each tube only once, and a more suitable description is the U flow. The design requires the inlet and outlet to be on the same tank.
A triple-pass has two baffles, one in each end tank. Now the core is divided into three small sections and flows through each one in series. This creates very high flow rates and high pressure drops though the system.