On the throttling process of the Kerr--Newman--anti-de Sitter black holes in the extended phase space

The throttling process of the Kerr--Newman--anti-de Sitter (KN--AdS) black holes is systematically studied in the extended phase space. In this framework, the cosmological constant is interpreted as a varying thermodynamic pressure, and the black hole mass is identified with enthalpy. The throttling process is essentially an isenthalpic (i.e., constant-mass) process for the KN--AdS black holes. The Joule--Thomson coefficient, inversion temperature, inversion curve, and isenthalpic curve are investigated in detail, with both analytical and numerical methods. It is found that there are no maximum inversion temperatures, but only minimum ones that are around one half of the critical temperatures of the KN--AdS black holes.