Rack Mount Liquid Cooling System

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With the advent of the 5G Internet of Everything era, the demand for high-performance and high-density computing is accelerating, and the problem of energy consumption in data centers has become increasingly prominent. How much do you know about liquid cooling? Which liquid cooling method should you choose? How to choose the refrigerant?

1. Trend of liquid cooling technology

As we all know, if the heat dissipation is not good, high temperature will not only reduce the working stability of the chip, but also cause excessive thermal stress due to the temperature difference between the inside of the module and the external environment, affecting the electrical performance, operating frequency, mechanical strength and reliability of the chip. The failure rate of electronic components increases exponentially with the increase of operating temperature. For every 10°C increase in the temperature of a single semiconductor component, the reliability of the system will decrease by 50%. The use of liquid coolant instead of air to cool computer equipment is a technological revolution in future data centers.

Compared with traditional air cooling technology, liquid cooling technology has the following obvious advantages:

– Take away more heat: The same volume of liquid takes away nearly 3000 times more heat than the same volume of air.

– Faster temperature transfer: The thermal conductivity of liquid is 25 times that of air.

– Lower noise: With the same heat dissipation level, the noise level of liquid cooling is 20-35 decibels lower than that of air cooling.

– More power consumption and energy saving: the liquid cooling system saves about 30%-50% of electricity than the air cooling system.

2. Classification of liquid cooling

The so-called liquid cooling does not simply refer to water. It refers to the use of liquid with high specific heat capacity as a transmission medium to take away the heat generated by IT equipment or servers to cool them down. At present, there are three main deployment methods of liquid cooling technology, namely immersion, cold plate, and spray.

Cold plate type: The liquid-cooled cold plate is fixed on the main heat-generating device of the server, and the heat is taken away by the liquid flowing through the cold plate to achieve the purpose of heat dissipation. The liquid cooling of the cold plate solves the heat dissipation of the components with high heat generation in the server, and other heat dissipation components have to rely on air cooling. Therefore, servers using cold plate liquid cooling are also called gas-liquid dual-channel servers. The liquid in the cold plate does not touch the cooled device, and the heat conduction plate is used in the middle to transfer heat, which has high safety.

Spray type: store liquid and open holes on the top of the chassis, and let the cooling liquid spray the heating body according to the position of the heating body and the amount of heat generation, so as to achieve the purpose of cooling the equipment. The sprayed liquid is in direct contact with the cooled device, and the cooling efficiency is high; however, when the liquid encounters a high-temperature object during the spraying process, it will flow and evaporate, and the mist and gas will spread out of the case along the holes and gaps of the case, causing the environment in the computer room to be damaged. Decreased cleanliness or impact on other equipment.

Immersion type: The heating element is directly immersed in the cooling liquid, and the heat generated by the operation of the server and other equipment is taken away by the flow cycle of the liquid. Immersion liquid cooling is a typical direct contact liquid cooling. Since the heating element is in direct contact with the coolant, the heat dissipation efficiency is higher and the noise is lower, which can solve the problem of preventing high heat. Immersion liquid cooling is divided into two-phase liquid cooling and single-phase liquid cooling, and the heat dissipation methods can be in the form of dry coolers and cooling towers.

– Two-phase liquid cooling: The cooling liquid undergoes a phase change in the circulation heat dissipation. The heat transfer efficiency of two-phase liquid cooling is higher, but the control is relatively complicated. The pressure will change during the phase change, which requires high requirements on the container, and the coolant is easily polluted during use.

– Single-phase liquid cooling: The cooling liquid always maintains a liquid state in the process of circulating heat dissipation without phase change, so the boiling point of the cooling liquid is required to be high, so that the control of cooling liquid volatilization and loss is relatively simple, and the compatibility with IT equipment components is relatively good , but its efficiency is lower than that of two-phase liquid cooling. According to the actual application scenario, a dry cooler or a cooling tower can be used to dissipate heat.

3. Coolant

Water

Liquid cooling is the most direct and cheapest. Water is not an insulator and can only be used for indirect contact liquid cooling. Once a leak occurs, the damage to IT equipment such as servers will be very fatal.

Mineral oil

Mineral oil is also an excellent and inexpensive coolant. Single-phase mineral oil is non-toxic, odorless and non-volatile. High viscosity, easy to form residues on the surface of equipment. Although the ignition point is high, it is still possible to burn under certain conditions.

Fluorinated solution

The biggest feature is insulation and non-combustibility. It is the safest one in data center liquid cooling technology. Currently the most widely used. But the price is high.

Liquid cooling technology is mainly used in the field of high-performance computing. With the development of high-density and high-power data centers, traditional air-cooling technologies can no longer fully meet their heat dissipation needs. These are the main factors that promote the sinking of liquid cooling technology. Liquid cooling technology can significantly reduce energy consumption in data centers. For example, the PUE of many immersion liquid cooling data centers can even reach an astonishing 1.03 ~ 1.05. However, the PUE value of an air-cooled system data center of the same size is still between 1.03 and 1.05.

In addition to traditional large-scale data centers, with the advent of the edge computing era, about 20% of edge data centers will use liquid cooling technology. The data center using the liquid cooling system can recover the investment invested in the cooling system within two to three years after completion, and the electricity cost saved in the later period can be regarded as its income. And the larger the data center, the better the effect.

4. Rack-mounted liquid cooling solution

Rack-mounted GPU liquid-cooled servers can accommodate as many GPU graphics cards as possible in a small space. By customizing the high-quality liquid cooling system of Blue Ocean Brain, the graphics card and processor can obtain a higher boost clock rate. The hardware packing density per server rack can be maximized, and even under continuous load, the best performance of the hardware can be tuned without any cooling concerns. Supports up to 9 GPU graphics cards and 2 CPU processors. All components can maintain the maximum possible circulation without throttling due to high temperature. Compared with air cooling, liquid cooling system has higher density, more energy saving and anti-noise effect better.

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