Parametric analysis and design of a power plant to recover low-grade heat from data center electronics by using liquid nitrogen

The purpose of this paper is to expound the recovery of low-grade heat deriving from cooling data center electronics, in order to sustain a thermodynamic cycle of the Rankine type, using cryogenic nitrogen as the working fluid. A novel conception of energy plant is proposed and considered where these resources are available. The evaporator, built in a closed and thermally insulated vessel, is the key component. Liquid nitrogen is evaporated by means of an immersed serpentine which provides for the thermal power and produces the pressurized gas. A supplementary reservoir acts as super-heater, as well as buffer. The plant is completed with a turboexpander that generates power and a pump to recirculate the fluid. A thermodynamic model is developed. A dimensioning procedure for all the subsystems is reported, while a verification analysis is made to detect the maximum pressure that can be exerted. Hence, an in-depth parametric analysis is made for two plant layout scenarios, based on the presence (1) and absence (2) of the supplementary tank. The simulations are aimed at determining all the operating parameters of the plant, as well as the performance. The results show that pressure is beneficial for performance, presenting scenario 1 as better than 2. The maximum nitrogen pressurization is 12-bar, which corresponds to an electric efficiency of 31.5 %, under a thermal supply of 2.79 kW per 1 kW of net electric power produced.