Hitachi Ltd. started manufacturing water cooling system modules for PCs and some other applications in January 2007. The company currently supplies its water cooling systems for Hewlett-Packard Japan Ltd.'s "HP xw9400/CT Workstation" and NEC Corp.'s "ValueStar W" desktop PC. Hitachi is further advancing the development of a water cooling system for notebook PCs as well.
Nikkei Electronics interviewed Hideaki Gemma, general manager at Hitachi's IT Thermal Solution Center, Solution Business Division, Consumer Business Group, about the water cooling system for notebook PCs that Hitachi is developing. (Interviewer: Mayuko Uno, Nikkei Electronics)
Q: What kind of a water cooling system is Hitachi pursuing now?
Gemma: Although we have not finished the development yet, a concept model has already been completed. The concept model consists of (1) a pump-embedded water-cooled jacket for a microprocessor, (2) a thermo radiator integrating fans and reserve tanks, (3) a water-cooled jacket for other components such as graphics LSIs and chipsets and (4) coolant tubes, which also connect these components.
This water cooling system was developed for so-called desktop PC substitute notebooks, which are not generally taken outside of the building where they are used. We expect the system to be employed for notebook PCs with a 17- to 20-inch display with a focus on gaming and AV capabilities. It is our estimate such notebook PCs will emerge in significant numbers around 2008.
Such notebook PCs are anticipated to incorporate 70 to 200 W high power LSIs, which will make it difficult to sufficiently radiate heat. To cool a 110 W or higher power LSI while lowering noise from fan rotation at the same time, a cooling system that uses the back surface of an LCD is said to be necessary. Water cooling system is indispensable to transport heat from the LSI under the keyboard to the LCD's back surface.
Q: What are the differences between water cooling systems for desktop PCs and those for notebook PCs?
Gemma: Compared with desktop PCs, notebooks don't have much room in component mounting areas. Moreover, targeted characteristics such as slimness and superior functionality vary greatly depending on the product. As a result, requirements for components significantly vary by product as well.
As for radiators, for example, some clients may say, "If it's slim, a large radiator will do," with a view to mounting it on the LCD's back surface, while others may say, "A thick radiator is acceptable, but make it smaller instead" to package it under the keyboard.
We could expect to standardize certain components in water cooling systems for desktop PCs, but we consider it will be difficult to standardize components in those for notebook PCs since such components need to be customized as described above.
However, we want to standardize as many components as possible to lower costs. We are, therefore, considering preparing several kinds of water-cooled jackets, radiators and some other components and optimizing the combination of desired components for each product.
For example, we will offer two kinds of radiators with two fans and three fans, which have cooling performances of 90 W and 130 W. If the product's power exceeds 200 W, these two kinds of radiators will be used in combination.
When cooling a 90 W or lower power microprocessor, the radiator with two embedded fans can be applied. That is the minimum composition system using our latest concept model. Using the same components seen in the photo below, we can easily assemble them into the minimum system.
Q: To optimize the system for notebook PCs, what technical efforts did you make for each component?
Gemma: Basically, we reduced the thickness of each component. The most significant achievement is the slim pump integrated with the water-cooled jacket for a microprocessor. It uses a certain manufacturer's 8.3-mm slim pump. Although we cannot reveal the details, the pump boasts about double the pumping pressure of standard centrifugal pumps, a flow rate of 400 mL per minute and power consumption of less than 2 W.
The copper plate, on which micro-channels for coolant are formed, is 1.6 mm thick across the plate, including the part of a 0.09 mm-pitch fin. Even the height of the water-cooled jacket with a built-in pump is only 11 mm. Considering most of other components including optical disc drives are around 9.5 mm high, we see the 11 mm is slim enough to be adopted to notebook PCs, but will discuss more details with clients.
When actually commercializing the system, drop tests and life tests for the hinge parts are likely to be bottlenecks. This concept model is just a standalone water cooling system, so we haven't introduced any measures against drop test and other challenges. We consider that we need to develop such measures in accordance with a whole PC unit.
Concerning size- and weight-reduction, this system has achieved sufficient levels as long as assuming 17- to 20-inch notebook PCs as application, hasn't it? If it is the 90 W minimal system, it is even lighter than an air cooling system using heat pipes.
I think the system is even adoptable to 15-inch notebook PCs as well. In some instances, demand is likely to rise from desktop PC manufacturers in pursuit of lower noise. Even slim type desktop PCs can house such a small system, and the fan rotational frequency can be also reduced compared with air cooling systems.
Q: Don't you include handheld small notebook PCs in application targets?
Gemma: There is significant sustainable demand for fanless systems in the market for such small notebook PCs. In that sense, we consider there may be demand for water cooling systems that use the LCD's whole back surface for heat liberation. However, our current water cooling system cannot be housed in a B5-sized notebook PC. We can't realize the lightness and slimness that the market requires at present.
The slim pump used in this concept model is still too large for handheld notebook PCs. We can downsize the system if we use a piezoelectric-based pump, but a flow rate will be insufficient since it is as small as less than 100 mL per minute. We will need further research and development for that application.