In this paper we present a thermodynamic and economic comparison of a recently proposed two-phase
thermofluidic oscillator known as the Up-THERM heat converter and the more established organic Rankine cycle
(ORC) engine, when converting heat at temperatures below 150 °C using the refrigerant R-227ea as the working
fluid. The Up-THERM heat converter is being considered as a possible prime mover for small- to medium-scale
combined heat and power (CHP) applications. Using suitable thermodynamic models of both systems, it is found
that the power output and thermal efficiencies of a pre-specified Up-THERM design are generally lower than
those of an equivalent ORC engine. The Up-THERM, however, also demonstrates higher exergy efficiencies and
is associated with lower capital costs, as expected owing to its simple construction and use of fewer and more
basic components. Interestingly, the specific costs (per rated kW) of the ORC engine are lower than those of the
Up-THERM converter at lower heat source temperatures, specifically below 130 °C, whereas the Up-THERM
becomes a more cost effective alternative (in terms of the specific cost) to the ORC engine at higher temperatures.