Session: 30-08 Heat Pumps

Paper Number: 127501

127501 - CO2 Transcritical Turbines Stator Optimization for Refrigeration Applications 

The global temperature increase as well as the increasingly frequent heat waves will result in the increasing use of air conditioning. Improving the efficiency of refrigeration systems is therefore a crucial issue for limiting constraints on the management and supply of electricity in the future. In addition, current regulatory developments leave room, among other fluids, for natural refrigeration fluids. In this context, the use of CO2 has many advantages. However, its thermodynamic efficiency is relatively low and its use is currently limited to countries with a temperate climate. Several improvement ways exist.  One of the major items of losses is the expansion valve. A two-phase turbine would make it possible to recover these losses by producing work and would also increase the refrigeration capacity of the system. However, there is currently no general method for designing such turbines. Moreover, the literature on the topic is very poor compared to that on single-phase turbines.

The main objective of the work presented in the paper is to perform an optimization of the stator nozzle. This is done using a 1D two-phase metastable model. This model includes a transitional interface area formulation, the Aleksandrov interface heat transfer coefficient and Schiller-Naumann interface drag model. The optimization is based on the research of an optimal pressure profile defined by Bezier curves leading to an optimal cross-sectional area profile. Various types of linear constrained optimization algorithms were explored. The results show that for inlet operating conditions close to critical point of CO2, the maximum efficiency that can be attained is always higher than at lower inlet temperature conditions.

The obtained optimal nozzle profiles should be tested in subsequent experimental work in order to evaluate the performance of the method. Eventually nozzle machining constraints should be included in the optimization process in order reduce the stator cost.

Presenting Author: Saugnac Renaud Mines Paris

Presenting Author Biography: Phd Student

Authors:

Saugnac Renaud Mines Paris
Ortego Sampedro Egoï Mines Paris
Bouallou Chakib Mines Paris