12 oct
12/10/2017 10:15


Soutenance de thèse : Arnaud LANDELLE

Experimental and numerical study of transcritical Organic Rankine Cycles for low-grade heat conversion into electricity from various sources

Doctorant : Arnaud LANDELLE 

Laboratoire INSA : CETHIL
Ecole doctorale : ED162 : Mécanique, Energétique, Génie civil et acoustique (MEGA)

The Organic Rankine Cycle (ORC) is a technology used for low-grade thermal energy conversion into electricity. Transcritical ORC has been identified as a solution for efficient waste heat recovery. However, few experimental tests have been conducted to confirm the interest of transcritical ORC and investigate its operational behaviors.  The work presented focuses on the operation and the optimization of subcritical and transcritical Organic Rankine Cycles for low-grade heat conversion into electricity from various heat sources (solar, industrial waste heat). First, the thermodynamic framework of the ORC technology is presented. Energetic and exergetic performance criteria, appropriate to each type of input source, are introduced and selected. The criteria are later applied to a database of ORC prototypes, in order to objectively analyze the state-of-the-art. In a second step, the experimental and numerical tools, specifically developed or used in the present thesis, are presented. Three subcritical and transcritical ORC test benches (hosted by CEA and AUA) provided experimental data. Numerical models were developed under different environments: Matlab for steady-state modeling, data processing and energy/exergy analysis. The Modelica/Dymola environment for system dynamics and transient operations. Lastly, the different tools are exploited to investigate four different topics: - The ORC pump operation is investigated, both under an energetic and volumetric standpoint, while semi-empirical models and correlations are exposed. - Supercritical heat transfers are explored. Global and local heat transfer coefficients are  estimated  and  analyzed  under  supercritical  conditions,  while  literature  correlations  are introduced for comparison. - Working fluid charge influence over the ORC performance and behavior is investigated. Optimal fluid charge is estimated under various operating conditions and mechanisms for charge active regulation are exposed. - ORC system performances and behavior are discussed. Through both an energetic and exergetic standpoint, performance are compared with the state-of-the-art,  while optimization opportunities are identified through an exergetic analysis.