Theres a more thorough exploration of using a black holes in a reversible Carnot Cycle here: http://dx.doi.org/10.1088/1674-1056/18/3/015 http://dx.doi.org/10.1

Theres a more thorough exploration of using a black holes in a reversible Carnot Cycle here: http://dx.doi.org/10.1088/1674-1056/18/3/015 http://dx.doi.org/10.1088/1674-1056/18/3/015 unfortunately behind a paywall.