How Liquid-Cooled PCs Operate

Key Insights

Whether you're on a desktop or a laptop, if you take a moment to pause and listen closely, you're likely to hear the hum of a fan. With a high-end video card and powerful processing capabilities, your computer may even have more than one fan operating.

In most computers, fans are effective at maintaining the temperature of electronic components. However, for users pushing high-performance hardware or trying to get their PCs to run faster, a fan may not provide enough cooling. If a computer produces too much heat, liquid cooling — or water cooling — can offer a more efficient solution.

Although it may seem unusual to introduce liquids near delicate electronics, cooling with water is much more efficient than using air.

A liquid-cooling system for a PC functions similarly to a car’s cooling system. Both systems are based on a fundamental thermodynamic principle — heat naturally flows from warmer objects to cooler ones. As the cooler object warms up, the warmer object cools down. You can observe this by placing your hand on a cool spot on your desk for a few moments. After lifting your hand, you’ll feel your palm cooler, while the spot where your hand rested will have warmed up slightly.

Liquid cooling is a widely used process. A car’s cooling system circulates water, usually mixed with antifreeze, throughout the engine. The engine's hot surfaces warm the water, which then cools down as it circulates.

The water flows from the engine to the radiator, a system of fans and tubes designed to maximize surface area. Heat transfers from the hot water to the radiator, cooling it down. The cooled water then returns to the engine. Simultaneously, a fan circulates air around the radiator's exterior. The radiator warms the air, which helps it cool itself. In this process, the engine's heat moves from the cooling system into the surrounding air. Without the radiator's surfaces interacting with the air to release heat, the system would simply circulate the heat without eliminating it.

A car engine produces heat as a result of burning fuel, whereas computer components generate heat from the movement of electrons. A computer’s microchips are packed with electrical transistors, which act as on/off switches. When transistors switch between these states, electricity moves within the microchip. The more transistors a chip has, and the faster they switch states, the hotter the microchip becomes. Just like a car engine, if the chip overheats, it will fail.

Heat Sinks vs. Liquid Cooling

Most computers manage heat with heat sinks and fans. Heat sinks are essentially metal components designed to provide ample surface area for air contact. The microchip heats up the heat sink, which then warms the air, and the fan expels the warm air from the PC case.

This method works for the majority of systems, but sometimes electronic components generate more heat than simple air circulation can manage. High-performance chips with numerous transistors can overpower an air-cooling setup. Overclocked chips, which are manually adjusted to run faster than their default settings, can also strain an air cooling system.

This is where water cooling becomes beneficial. Water has better thermal conductivity than air, meaning it can transfer heat more efficiently. Additionally, water has a higher specific heat capacity, allowing it to absorb more heat before reaching high temperatures.

There are two main reasons a computer may require the enhanced thermal conductivity and heat absorption of water:

In other words, there are two main reasons you might opt to cool your computer with liquid rather than air:

Many users upgrade their cooling systems to intentionally overclock their CPUs or GPUs, but be cautious. Pushing components beyond the manufacturer’s specifications can void warranties and create long-term reliability issues, even with enhanced cooling.

Next, let’s explore the components of a liquid-cooling system and understand how they function together.

Cooling With Liquid: System Parts

A liquid-cooling system for a PC operates similarly to a car’s cooling system. Coolant circulates through channels in the car's engine block, and the rest of the cooling system includes:

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

While many CPU water blocks are universal, some GPU water blocks are designed for specific chips. Additionally, water blocks can be found to cool other high-temperature chipsets, such as the northbridge heatsink, which links the CPU to your memory. Typically, small bolts and washers are used to secure the water block to the necessary printed circuit board (PCB), like the motherboard or video card.

Liquid Cooling Pump and Radiator

A liquid cooling pump for a PC is typically a centrifugal pump, similar to those found in car cooling systems. Some PC liquid-cooling pumps are submersible and can be placed directly in the PC's coolant reservoir, while others must remain dry. If you plan to use a submersible pump, ensure that its exterior doesn’t heat up the fluid in the reservoir too much.

The pump is a critical component in the PC's cooling system. Its flow rate determines how fast coolant circulates through the tubes and blocks. If the water flows too quickly, it doesn’t have enough time to absorb heat, while if it moves too slowly, heat can accumulate around sensitive parts. The complexity of the system affects the overall flow rate — the more resistance the fluid faces in the blocks and radiator, the slower the flow.

The pump must also have enough strength to push the liquid from the lowest point to the highest in the system. This is referred to as head pressure or vertical pressure, and it’s particularly crucial when liquid cooling large server towers.

The PC's radiator can be custom-designed for liquid-cooling systems, or it might be a heater core from a car. Heater cores are highly efficient at dissipating heat as they provide the warm air for a car's heating system during winter. However, they often lack the aesthetic appeal of radiators specifically designed for liquid-cooling applications.

Liquid Cooling System Reservoirs and Tubing

Not all liquid-cooled PC systems use a fan, though most do to assist the radiator in dissipating heat more efficiently. Similarly, not every system has a separate reservoir. Those that don’t usually include a fill/bleed line, which allows for the addition of coolant and removal of excess air. This line typically leads to a filling port at the top of the computer case.

In a liquid-cooled PC, tubing presents a unique challenge. It must be flexible enough to connect components that may be positioned at odd angles, yet it can't be susceptible to kinking, as a kinked hose can significantly restrict fluid flow.

In a basic liquid-cooled PC setup, a tube connects the pump to the inlet of a water block. Additional tubes run from the water block’s outlet to the radiator, and from the radiator to the reservoir, which is often placed in one of the computer's CD-ROM bays. The final tube connects the reservoir back to the pump. In systems with multiple water blocks, tubes link each block’s outlet to the next block’s inlet, creating a series connection like a daisy chain.

PC Liquid Cooling Liquid

The final element in a PC liquid-cooling system is the coolant itself. Distilled water is a common choice, as tap water can contain impurities that may cloud the system or block the channels in the water blocks and radiator.

Special additives can be mixed into the coolant to give it color, enhancing the visual appeal, especially in clear cases. These additives can also lower the freezing point or surface tension of the water, making it more efficient at cooling. Additionally, some additives contain antimicrobial or anti-corrosion agents, which can extend the system's lifespan.

If you choose to install a liquid-cooling system, it's advisable to let the pump circulate the coolant for a while to check for leaks. Ensure your computer is turned off during this testing phase to minimize the risk of damaging your hardware if a leak occurs.

Once you are confident everything is sealed properly, you can power up your computer. To monitor the temperature of your components, access your computer’s BIOS menu or use third-party software designed to track temperature. If needed, you can apply smaller heat sinks to components such as RAM chips and other high-heat parts in your system.

If you're interested in liquid cooling but don't want to dive into the details of individual components, you can purchase a ready-to-use unit or kit. These self-contained systems can be plugged directly into your computer's expansion slots or power supply, providing cooling for a specific chip. Kits come with all necessary parts and assembly instructions; just be sure the components are compatible with your computer's hardware. Some companies even sell high-performance PCs with liquid cooling pre-installed.

Explore the following links to deepen your understanding of PCs, thermodynamics, liquid-cooled computers, and other related topics.