This paper introduces the traditional heat exchange methods in data centers and the three liquid cooling methods commonly used at present, and describes the composition forms of the three liquid cooling methods, compares the advantages and disadvantages of each of the three liquid cooling methods, and introduces them in a targeted manner in terms of energy saving, noise, land occupation, arrangement methods, environmental requirements, server reliability, maintenance expenditures and customer acceptance, respectively.

Keywords: data center; liquid cooling; cold plate; spraying; submersion

1 Introduction of liquid cooling system

    The traditional data center cooling method is air cooling, i.e., using air as the refrigerant to transfer heat to the heat-generating parts of the server and take away the heat. The IDC liquid cooling system is a technology that uses liquid instead of air as the refrigerant to heat the heated parts and take away the heat. When using liquid cooling method, it is necessary to use liquid cooling server. This server refers to a server that injects liquid into the server to take away heat from the server through cold and heat exchange.

    The composition of the liquid cooling system mainly contains the primary side heat exchange part and the secondary side heat exchange part. The primary side refers to the loop that takes away heat from the server and carries out the loop medium for heat dissipation on the secondary side, and the secondary side refers to the loop that discharges heat from the primary side to the outdoor environment or other heat recovery units.

2 The main forms of liquid cooling methods

    Liquid cooling forms are mainly divided into spray type, cold plate type and submerged type, the main difference between the three is reflected in the different ways of heat dissipation to the server. Spray liquid cooling is the coolant through the spray on the server cooling components to take away the heat generated by the server; cold plate liquid cooling is in the server CPU and other large power consumption components using liquid cooling plate cooling, other small number of heat generating devices (such as hard disk, interface cards, etc.) still using air cooling cooling system; submerged liquid cooling refers to the server's heat generating components completely submerged in the coolant, through the coolant of the convection or phase change of the coolant to remove the heat of the server cooling system. Secondly, spray submerged servers do not have fans, while fans exist in cold plate servers. The details are described as follows.

  2.1 Sprayed liquid cooling system

    Spray direct liquid cooling is a precise spraying, direct contact liquid cooling technology for electronic equipment devices. Coolant can be sprayed directly onto the heat-generating devices of IT equipment or the solid heat-conducting materials connected to them through gravity or system pressure, and heat exchange with them to achieve thermal management of IT equipment. In the process of heat exchange, the free liquid level of the coolant in the IT equipment is lower than the heat generating device or the solid heat-conducting material connected to it, and the system can exchange heat to the coolant through the heat exchange unit outside the IT equipment to meet the requirement of recycling.

  2.2 Cold plate type liquid cooling system

    The basic working principle of cold plate type liquid cooling cabinet is described as follows: using cold plate assembly and high heat flow density components contact, heat generation through the cooling media in the cold plate assembly export, and then through one or more cooling circuit heat exchange transfer, and finally the equipment heat will be distributed to the external environment or recycling a liquid cooling realization method.

  2.3 Submerged liquid cooling system

    The basic working principle of submerged liquid cooling cabinet is described as follows: a form of heat dissipation by submerging the electronic information equipment in the coolant and taking away the heat by the coolant. According to the different forms of coolant heat dissipation process, it is divided into phase change and and single-phase liquid cooling.