Advantages Of Immersion Cooling

Contents

List of Figures iii

Introduction 1

Theory 1

Advantages of Immersion Cooling: 2

System types 2

Open loop 2

Closed loop 4

External vs internal condenser 4

Immersed condenser 7

Heat transfer coefficients of dielectric fluids 10

Other considerations 11

Bibliography 11

List of Figures

Figure 1 Heat transfer coefficients of dielectric liquids 1

Figure 2 External reservoir open loop immersion cooling system 3

Figure 3 Pressure/temperature graph 4

Figure 4 External condenser (pool boiling cooling) 5

Figure 5 Internal condenser 5

Figure 6 Rapid cooling unit 6

Figure 7 Immersed condenser 7

Figure 8 Convection in a liquid 8

Figure 9 Electronic box immersed in cooling fluid (air in this case) 9

Figure 10 finned heat tube exchanger 10

A dielectric liquid is a liquid which is a poor conductor of electricity but a good supporter of an electrostatic field. At specified pressure a fluid boils isothermally (no change in temperature due to the energy supplied going into converting the state of the liquid to a vapour). A large amount of heat is absorbed during this process which is essentially isothermal. This process is taking advantage of the high heat transfer coefficient associated with boiling. Another advantage is that by immersing the electronic component in a liquid medium, the temperature throughout is uniform. Any spot where there is a large build-up of heat will have its temperature distributed throughout the liquid. Below is a graph of heat transfer coefficients of dielectric fluids as well as mentions of heat

Saturation point being the temperature which has a liquid/vapour equilibrium. Equilibrium means that the rate at which vapour is being condensed is the same as the rate as liquid is being vaporized. Figure 8 Convection in a liquid

(Heating and cooling, 2006)

The above figure shows the movement of a hot, less dense liquid to the top while the cooler, denser liquid moves to the bottom. This creates the circulation process which is present in the immersed condenser. This process may be classified as forced convection.

The immersed condenser system still takes advantage of the high heat transfer coefficient associated with boiling. Therefore this system can remove heat from the surface of electronics at a high rate. However, there are a few limitations to this system. The capacity of this system is limited to the rate at which external cooling liquid can remove heat in a liquid to liquid heat exchanger. Condensation has a much higher heat transfer coefficient than the forced convection used in this system.

Due to the above reasons, this system would be inappropriate for electronic enclosures which have high power dissipation per unit