Operational Optimisation of a Non-Recuperative 1-kWe Organic Rankine Cycle Engine Prototype

Abstract

Several heat-to-power conversion technologies are being proposed as suitable for waste-heat recovery (WHR) applications, including thermoelectric generators, hot-air (e.g., Ericsson or Stirling) engines and vapour-cycle engines such as steam or organic Rankine cycle (ORC) power systems. The latter technology has demonstrated the highest efficiencies at small and intermediate scales and low to medium heat-source temperatures and is considered a suitable option for WHR in relevant applications. However, ORC systems experience variations in performance at part-load or off-design conditions, which need to be predicted accurately by empirical or physics-based models if one is to assess accurately the techno-economic potential of such ORC-WHR solutions. This paper presents results from an experimental investigation of the part-load performance of a 1-kWe ORC engine, operated with R245fa as a working fluid, with the aim of producing high-fidelity steady-state and transient data relating to the operational performance of this system. The experimental apparatus is composed of a rotary-vane pump, brazed-plate evaporator and condenser units and a scroll expander magnetically coupled to a generator with an adjustable resistive load. An electric heater is used to provide a hot oil-stream to the evaporator, supplied at three different temperatures in the current study: 100, 120 and 140 ∘ C. The optimal operating conditions, that is, pump speed and expander load, are determined at various heat-source conditions, thus resulting in a total of 124 steady-state data points used to analyse the part-load performance of the engine. A maximum thermal efficiency of 4.2 ± 0.1% is reported for a heat-source temperature of 120 ∘ C, while a maximum net power output of 508 ± 2 W is obtained for a heat-source temperature at 140 ∘ C. For a 100- ∘ C heat source, a maximum exergy efficiency of 18.7 ± 0.3% is achieved. A detailed exergy analysis allows us to quantify the contribution of each component to the overall exergy destruction. The share of the evaporator, condenser and expander components are all significant for the three heat-source conditions, while the exergy destroyed in the pump is negligible by comparison (below 4%). The data can be used for the development and validation of advanced models capable of steady-state part-load and off-design performance predictions, as well as predictions of the transient/dynamic operation of ORC systems.

Integrated Geothermal Energy Systems for Small-Scale Combined Heat and Power Production: Energy and Economic Investigation

“…The main components of an ORC are a pump, an evaporator, a turbine, and a condenser (Figure 2a) [85,86]. The pump increases the pressure of the organic working fluid to the maximum value (1-2 process) then the evaporator is adopted to obtain the superheated vapour (2-3) that expands in the turbine (3)(4) to provide the mechanical work that is converted into electricity by an alternator.…”

Heat exchanger network design of an organic Rankine cycle integrated waste heat recovery system of a marine vessel using pinch point analysis

“…In this comparison, the performance parameters of η th and the net power output ( net ) are analyzed for the given parameters of T evap , P evap , T cond , P cond , and for the three heat source temperatures as shown in Figure 4. The maximum deviation of 5.56% can be observed between the measured 36 and calculated data, which might be caused by the assumptions of constant pump and turbine efficiencies. As a result, the numerical solutions obtained from the ORC simulation in this study show consistency with the results obtained from the studies carried out by Yang and Yeh 35 and Unamba et al 36 for similar input parameters.…”

“…The maximum deviation of 5.56% can be observed between the measured 36 and calculated data, which might be caused by the assumptions of constant pump and turbine efficiencies. As a result, the numerical solutions obtained from the ORC simulation in this study show consistency with the results obtained from the studies carried out by Yang and Yeh 35 and Unamba et al 36 for similar input parameters.…”

“…Table 4 shows the comparison of the thermal efficiency ( η th ) and the turbine power output ( turbine ) results of the presented model with the validated study of Yang and Yeh 35 for isobutane as the working fluid. In addition, for the working fluid as R245fa, the results of this study are compared with the experimental results of a 1‐kW ORC system from the study of Unamba et al 36 Results were given at the heat source temperatures of 100°C, 120°C, and 140°C in their study. In this comparison, the performance parameters of η th and the net power output ( net ) are analyzed for the given parameters of T evap , P evap , T cond , P cond , and for the three heat source temperatures as shown in Figure 4.…”

“…Validation of the organic Rankine cycle (ORC) model with the experimental results of a reference study 36 for a 1‐kW organic Rankine cycle (ORC) system operating with R245fa for (A) the net power output and (B) the thermal efficiency [Colour figure can be viewed at wileyonlinelibrary.com]…”