How Liquid-cooled PCs Work

Most computers dispel heat with heat sinks and fans. Heat sinks are basically pieces of metal that provide lots of surface area for the air to touch. The microchip warms the heat sink, the heat sink warms the air, and the fan moves the warm air out of the PC case.

This system works most of the time, but sometimes, electronic components produce more heat than simple air circulation can dispel. High-end chips with lots of transistors can overwhelm an air-cooling system. So can chips that have been overclocked, or manually set to work faster than their default speeds.

That's where water cooling comes in. Water has a higher thermal conductivity than air — it can move heat faster than air can. Water also has a higher specific heat capacity. It can absorb more heat before it starts to feel hot.

There are two reasons why a computer might need the increased thermal conductivity and heat capacity of water:

In other words, there are two reasons why you might need to cool a computer with a liquid instead of air:

Many users upgrade their cooling systems as a means to intentionally overclock their CPUs or GPUs, but beware. Continuously exceeding manufacturer specs can void component warranties and lead to long-term reliability issues, even with extra cooling.

Next, we'll look at the components of a liquid-cooled system and how they work together.

A liquid-cooling system for a PC is a lot like a cooling system for a car. Coolant flows through channels in a car's engine block, and the rest of the cooling system incorporates:

Many electronic components do not tolerate direct contact with liquid. So instead of using channels to pump liquid directly through microchips as in a car engine, a liquid-cooled PC uses water blocks. A water block is a piece of heat-conductive metal, like copper or aluminum, that's filled with hollow tubes and channels. The bottom of the water block is a flat piece of metal that sits directly on top of the chip being cooled. Thermal paste between the chip and the block improves the heat transfer between the two surfaces. The chip heats the block, and the water absorbs the heat as it flows through all the channels.

Many central processing unit (CPU) water blocks are universal, but some graphics processing unit (GPU) water blocks only work with specific chips. You can also find water blocks designed to cool other high-temperature chipsets, like the northbridge heatsink, which connects your CPU to your memory. Usually, small bolts and washers attach the water block to the necessary printed circuit board (PCB), such as the motherboard or video card.

A liquid cooling pump for a PC is usually a centrifugal pump, much like you'd find in a car's cooling system. Some PC liquid-cooling pumps are submersible, and you can place them directly inside the PC's coolant reservoir. Others need to be kept dry. If you're thinking about using a submersible pump, make sure its exterior doesn't get hot enough to heat all the fluid in the reservoir.

The pump is one of the most important parts of the PC's cooling system. Its flow rate determines how quickly the coolant moves through the tubes and blocks. If the water moves too quickly, it doesn't have time to absorb heat before moving on. If it moves too slowly, too much heat can build up around sensitive components. The complexity of the system affects the overall flow rate — the more resistance the fluid encounters within the blocks and radiator, the slower the overall flow rate.

The pump also has to be strong enough to move the liquid from the lowest point in the system to the highest. This is known as head pressure or vertical pressure, and it's especially important when liquid cooling tall server towers.

The PC's radiator can be designed specifically for liquid-cooling systems, or it can be the heater core from a car. Heater cores dispel lots of heat — they provide the warm air for a car's heating system in the winter. However, they're not usually as attractive as radiators that are designed for use with a liquid-cooling system.

Not every liquid-cooled system PC has a fan, but most use one to help the radiator dispel heat faster. Similarly, not every system has a separate reservoir. Those that don't generally have a fill/bleed line for adding coolant and removing extra air from the system. Usually, the fill/bleed line leads to a filling port at the top of the computer's case.

In a liquid-cooled PC, the tubing presents a special challenge. It has to be flexible enough to connect components that may be at odd angles to one another. But it can't be prone to kinking — a kinked hose can severely restrict the flow of fluid through the system.

In a simple liquid-cooled system PC, a tube connects the pump to the inlet of a water block. Separate tubes run from the water block's outlet to the radiator and the radiator to the reservoir, which often sits in one of the computer's CD-ROM bays. The final tube connects the reservoir back to the pump. For systems with multiple water blocks, tubes connect one block's outlet to the next block's inlet, connecting the blocks in series like a daisy chain.

The final component of a PC liquid-cooling system is the liquid itself. Many people use distilled water, since tap water contains contaminants that can cloud the system or clog the channels in the water blocks and radiator.

Specialized additives can add color to the fluid, making it more visually appealing when used in a clear case. They can also lower the freezing point or surface tension of the water, making it a more effective coolant. Finally, some additives have antimicrobial or anti-corrosion ingredients, which can increase the life of the system.

If you decide to install a liquid-cooling system in your computer, it's a good idea to let the pump circulate the fluid for a while so you can check for leaks. Keep your computer turned off during this test period so you'll be less likely to damage your hardware if a leak does occur.

Once you're sure that everything is watertight, boot up the computer. You can check the temperature of your components in your computer's BIOS menu or by using a third-party application that monitors temperature. If necessary, you can also apply smaller heat sinks to RAM chips and other higher-temperature components in your system.

If you like the idea of liquid cooling but don't want to research individual components, you can buy a ready-to-use unit or kit. Self-contained units can plug directly into a computer's expansion slots or power supply and provide liquid cooling to one specific chip. Kits include all the parts you need and instructions for assembling them; just make sure the parts included are compatible with your computer's hardware. Some companies also sell high-end PCs with liquid cooling factory-installed.

Check out the links that follow to learn more about PCs, thermodynamics, liquid-cooled computers and related topics.