How Does a CPU Liquid Cooler Work? A Beginner's Guide

To understand how liquid cooling works in a CPU, consider how an engine is cooled in a car. Liquids have a higher specific heat, which means they can remove heat better than air. The car uses water to take heat from the engine and release it into the air using a radiator. CPU liquid coolers work the same way. 

Every CPU generates heat as it’s an electronic component, and this heat is absorbed by a water block where liquid coolant is circulating. This liquid is pumped from the water block to the radiator, similar to how it works in cars. The radiator's function is to extract heat from the liquid flowing inside and transfer it to the radiator's fins. A fan then moves cool air over the fins. This setup, as shown in the picture, is particularly noteworthy because liquid cooling has made it more efficient to remove heat from modern CPUs with high TDPs that are overclocked and generate significant heat.  

Understanding CPU Heat: Why Cooling Matters

Electricity is the flow of electrons through a conductor. When electricity passes through any conductor, it generates heat due to the resistance to the flow of electrons. Similarly, when electricity passes through the CPU, it will also generate heat.

A microprocessor or CPU is made with billions of transistors. Whenever we use a CPU, it will use these transistors in a computational logic. These transistors charge and discharge, producing an electrical resistance that affects electron flow and generates heat. The more intense operations on the CPU, like gaming or video rendering, will create more heat and require a cooling system for such demanding workloads.

In such cases, a CPU closed-loop liquid system is preferred to keep the temperature within limits. Otherwise, the CPU will start thermal throttling, affecting its performance. In some cases, if cooling is very poor, it may even damage the CPU or other internal components, such as RAM and GPU.

Key Components of a Liquid Cooling System

Basic components of liquid components include

• Water block
• The pump
• The radiator
• Tubing, Reservoir, and Coolant

The Water Block

It's the heart of the liquid cooling system that extracts heat from the CPU. The most premium type of water blocks is made from oxygen-free copper that has high thermal conductivity. If the water block is used with aluminum parts, these water blocks are made with nickel plating (mostly the base of the water block is nickel-plated to avoid oxidation).

These blocks feature 0.5 to 1 mm micro channels in their base, allowing liquid to flow and absorb heat generated by the CPU.  To minimize the air gap between the block and CPU, a thermal paste with a thermal conductivity of more than 8-12W/mK is used. To increase conductivity, the gap between the water block and the CPU is minimized to 0.1mm, facilitated by a robust mounting mechanism for the water block. The thermal efficiency of the cooling system largely depends on flow and the design of the fin array. When liquid enters the block, it starts convective cooling with a heat transfer coefficient of 500-5000W/m2.

The Pump

The pump in the cooling system makes the coolant flow through the water block and radiator, providing the pressure to the fluid to overcome the resistance of the tubing. Without a suitable flow, even the most efficient system would not work correctly. In most cooling systems, these pumps operate on 12 volts at 2000-4000 rpm, providing enough flow of 0.5-1 l/min and head to perform the cooling. In modern cooling systems for CPUs, these pumps are made with precision to have low noise and vibration, coupled with ceramic bearings to provide frictionless operation. These pumps can change their speed as required by the heat load.

The Radiator

The heat taken from the CPU by the liquid is rejected to the atmosphere with the help of a device called a radiator and a fan mounted to it. Radiators are made with an aluminum core with copper fins and coolant channels. Fins are provided to have better conductive heat transfer with an efficiency of 0.8-0.9. Fin spacing is a very important factor. If the fin density FPI (Fins per Inch) is high, the effective area would increase. However, a higher flow of air is required due to increased resistance to air flow.

Lower FPI reduces air flow resistance, but also decreases the effective surface area. Typically, the liquid from the CPU has a temperature 10-20 °C higher than the ambient air. It enters the radiator, where it transfers heat to the fins. A fan (1000-2000rpm) then provides airflow to remove heat from the fins.

Tubing, Reservoir, and Coolant

Tubing in a liquid system provides a path for the liquid to transfer from one component to another, made from PVC having an ID of 10mm and an OD of 13mm. It is also provided with braided support to avoid deformation and bursting under extreme working conditions. Tubing must not have sharp bends, as it will increase flow resistance and reduce overall performance.

A reservoir manages air and fluid volume. It is made from PVC and provides a mechanism for filling with liquid and venting air bubbles to the atmosphere. In some cases, the reservoir is an integral part of the pump, especially in an AIO (All-in-One) system. In most cases, the liquid inside is distilled water and 30% glycol. Some biocides are also added to prevent bacterial growth, and glycol is added to lower the freezing point to as low as -10 °C. The purpose of the coolant is to take heat from the CPU and release it in the radiator.

The Cooling Cycle

Heat Generation

During operation, especially while performing intense tasks like gaming or video rendering, or any graphical or computational work, the CPU generates heat of more than 300 watts. This heat generation starts at the transistor built inside the CPU  and ultimately moves to the integrated heat spreader, where a water block is installed to take the heat from the CPU with the help of liquid flowing inside it. A conduction process removes this heat because the water block is at a higher temperature than the liquid.

Absorption

The liquid inside the water block absorbs the heat generated by the CPU as it flows through the channels made inside the water block. The liquid, while flowing through the block, ensures that turbulence and conduction of heat are designed to have maximum efficiency in terms of thermal conductivity. When fluid flows out of the water block, its temperature has risen.

Circulation

A pump is installed in the liquid cooling system for the CPU to transmit heated liquid, ensuring the temperature does not exceed a specific limit. The pump provides a constant flow of liquid from the water block to the radiator, keeping the CPU cool and performing its tasks effectively. In a modern system, pumps are selected for their very low noise and minimal wear on components, thanks to their high flow rate.

Dissipation

The heated liquid finally enters the radiator, where it will be cooled by air from a fan installed in the radiator. Radiators are made of aluminum with copper fins. These fins increase the surface area as the fan blows air, cooling them in the process. When these fins are cooled, the coolant that passes through the tubes is cooled.

Return

The liquid then returns to the water block after being cooled by the radiator. Another piece of equipment, known as a reservoir, is installed in the liquid cooling system. It allows water to return if there's an excess quantity and helps the system refill when the liquid level is reduced.

Engineering Innovations That Make Liquid Cooling Fascinating

With the advancement of technology, we have high-speed CPUs of 7nm that produce more heat. To address this, we utilize a liquid cooling system, as air cooling is insufficient for CPUs that generate high heat.  Engineering is now evolving the liquid cooling system and its manufacturing process.

Now, water blocks are made with a narrow passage of 0.2mm for liquid flow, which creates turbulence to increase heat transfer up to 50%. Modern liquid also comes with a PID controller that monitors and controls the temperature within 2 °C of the set point with varying fan and pump speed, and provides real-time temperature monitoring. Additionally, liquids injected with copper oxide are tested to increase thermal conductivity, which shows 20% better performance.

Wait, there is more! Liquid cooling is continuously evolving with the help of engineering using CFD simulations to optimize fin construction, flow speed, and turbulence, cooling, and thermal design. If this technology upgrade continues, we could have a cooling system that utilizes a phase change of liquid at the hot interface to cool the CPU, which would then condense at the radiator.

Installation and Maintenance Tips

The installation of liquid requires expert skills because it involves very sensitive components, including water, which can damage the CPU if leaked. Before starting installation, clean all the elements and apply thermal paste to the CPU. Mount the water block and tighten the screws with even torque that can range from 0.6-1Nm, and note that the screws are to be tightened in a cross pattern. The tubing through which liquid will flow is also an important component. When installing it, ensure that the tubing is routed according to the manual and that every hose is secured with a clamp. Before starting, ensure the system is adequately primed and has no trapped air.

For maintenance, consider either seeking guidance from an expert or having the work done by one. Some of the tips we can share include using a UV-reactive die that glows under UV lighting to detect leakage, performing purge cycles annually or as needed, which will remove 95% of air to improve efficiency. Also, make sure to flush the system annually with a vinegar solution. Circulate the solution for 30 minutes to dissolve the scaling inside the tubes and components, and then rinse it.

Advantages Over Traditional Air Cooling

The specific heat of water is much better than that of air, and it naturally gives an edge to the cooling system that uses liquid. If a sustained load is applied to a CPU, liquid cooling will keep the temperature 40% lower than if the same CPU is cooled with an air-cooled system. Liquid systems provide better cooling and are quieter because pumps produce less noise, water acts as a natural damper for noise, and the fans in radiators are quieter. Liquid cooling systems are smaller in size, and they can be easily adjusted in a compact ITX build computer, making the computer eye-catching with better aesthetics.  

Conclusion

Thermodynamics and engineering have transformed liquid cooling, providing better CPU performance with precisely machined flow paths. Steady flow patterns using pumps and efficient radiators that traders use to heat the surroundings, making it a reliable cooling solution for modern high computing computers. They offer better thermal conductivity, a sleeker design, improved aesthetics, and quieter operation, making them a superior choice over air cooling solutions and rendering heat management an art.

For a practical implementation of CPU liquid coolers, consider visiting the ESGAMING liquid cooler page. You will find various designs and capacities for these coolers made with the highest quality material.