Abstract
The Up-THERM heat converter is an unsteady, two-phase thermofluidic oscillator that employs an organic working fluid, which is currently being considered as a prime-mover in small- to medium-scale combined heat and power (CHP) applications. In this paper, the Up-THERM heat converter is compared to a basic (sub-critical, non-regenerative) organic Rankine cycle (ORC) heat engine with respect to their power outputs, thermal efficiencies and exergy efficiencies, as well as their capital and specific costs. The study focuses on a pre-specified Up-THERM design in a selected application, a heat-source temperature range from 210 °C to 500 °C and five different working fluids (three n-alkanes and two refrigerants). A modeling methodology is developed that allows the above thermo-economic performance indicators to be estimated for the two power-generation systems. For the chosen applications, the power output of the ORC engine is generally higher than that of the Up-THERM heat converter. However, the capital costs of the Up-THERM heat converter are lower than those of the ORC engine. Although the specific costs (£/kW) of the ORC engine are lower than those of the Up-THERM converter at low heat-source temperatures, the two systems become progressively comparable at higher temperatures, with the Up-THERM heat converter attaining a considerably lower specific cost at the highest heat-source temperatures considered.
Highlights
Ensuring long-term energy and environmental security by reducing the current rates of consumption of finite fossil-fuel reserves and the release of related emissions to the environment have been increasingly desirable goals in recent years
The displacer cylinder represents the thermofluidic oscillator part of the engine. It consists of the hot heat-exchanger (HHX) and cold heat-exchanger (CHX), the solid piston that forms together with the inner wall of the displacer cylinder the piston valve, a slide bearing where piston and liquid working fluid are separated, and two mechanical springs that are fixed to the top and bottom of the lower part of the displacer cylinder and are loosely attached to the piston
The marker of the organic Rankine cycle (ORC) power output shows the cycle with an isentropic efficiency of the expander of 70%, while the error bars indicate the results for 65% and 75% isentropic efficiency, respectively
Summary
Ensuring long-term energy and environmental security by reducing the current rates of consumption of finite fossil-fuel reserves and the release of related emissions to the environment have been increasingly desirable goals in recent years. The interest in the utilization of sustainable energy resources such as geothermal and solar heat, which are abundantly available, is attracting increasing attention, as is the recovery and utilization of low- and medium-grade (i.e., temperature) waste heat, significant quantities of which are being rejected in the industrial, transport and residential sectors [1,2]. These goals can be met to an extent by collecting or recovering thermal energy from the above mentioned sources and converting this heat to useful work such as electricity, shaft work, or pumping (hydraulic) work. This allows more affordable materials and manufacturing techniques to be used, leading to lower capital costs and longer maintenance cycles and lower operating costs than conventional power-generation systems
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