## 3 Experimental Results
### Data Reduction  
The performance of the ORC system and its main components is expressed in common and relevant parameters of such systems. The theoretical mass flow rate of the volumetric pumps was calculated using Equation (1). This equation was used to calculate the theoretical mass flow rate of the diathermic oil and the refrigerant in the evaporator.  
\[\dot{m}_{th,i}=\frac{N_{i}\cdot SV_{i}\cdot\rho_{su,i}}{60} \tag{1}\]  
where \(N\) is the pump speed (rpm), \(SV\) is the pump swept volume (m\({}^{3}\)/rev) and \(\rho_{i}\) is the fluid density (kg/m\({}^{3}\)).  
However, the real flow rate of the volumetric pumps is always less than their theoretical flow rates due to internal leakage. Hence, the volumetric efficiency of a pump depends on the working conditions of the pump, especially its rotational speed and operating temperature. The latter affects the fluid viscosity and the physical condition of the internal  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \(\dot{m}_{ref}\) [kg/h] & \(N_{exp}\) [rpm] & \(P_{su,exp}\) [bar] & \(P_{su,p}\) [bar] & \(T_{in,HF,eq}\) [\({}^{\circ}\)C] & \(T_{in,CF,eq}\) [\({}^{\circ}\)C] & **SH [K]** & **SC [K]** \\ \hline
195–176 & 753–1416 & 11.2–15.4 & 4.7–7.1 & 119.7–150.7 & 8.7–19.6 & 2–24 & 3.7–7.9 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Range of working conditions during the experimental tests campaign.  
sealings. The ratio of the pump measured mass flow rate over the theoretical mass flow rate is the pump volumetric efficiency.  
\[\eta_{vol,p}=\frac{\dot{m}_{meas}}{\dot{m}_{th}} \tag{2}\]  
Expander isentropic and mechanical efficiencies are presented in Equations (3) and (4), respectively.  
\[\eta_{is,exp}=\frac{\dot{W}_{th,act}}{\dot{W}_{th,is}}\times 100=\frac{h_{su, exp}-h_{dis,exp}}{h_{su,exp}-h_{dis,s,exp}}\times 100 \tag{3}\]  
\[\eta_{mech,exp}=\frac{\dot{W}_{sh}}{\dot{W}_{th,act}}\times 100=\frac{\dot{W}_{ sh}}{\dot{m}\left(h_{su,exp}-h_{dis,exp}\right)}\times 100 \tag{4}\]  
The expander produced shaft power was calculated using Equation (5).  
\[\dot{W}_{sh}=2\pi\tau\cdot N_{exp}/60 \tag{5}\]  
The scroll expander volumetric efficiency also called the filling factor, is the ratio of the measured volumetric flow rate over the theoretical volumetric flow rate. Unlike the pump efficiency, its value is usually above unity indicating internal leakage.  
\[FF_{exp}=\frac{\dot{V}_{meas}}{\dot{V}_{th}}=\frac{\dot{m}_{ref}/\rho_{su, exp}}{N_{exp}\cdot SV_{comp}/(60 BVR)} \tag{6}\]  
where \(BVR\) is the expander built-in volume ratio adopted from the manufacturer datasheet to calculate the expander swept volume using the scroll compressor suction displacement (\(SV_{comp}\)). Finally, the system performance is expressed using the net and gross electric efficiencies:  
\[\eta_{el,net}=\frac{\dot{W}_{el,net}}{\dot{Q}_{ev}}\times 100=\frac{\dot{W}_{el, exp}-\dot{W}_{el,p}}{\dot{m}(h_{ex,ev,HF}-h_{in,ev,HF})}\times 100 \tag{7}\]  
\[\eta_{el, gross}=\frac{\dot{W}_{el,exp}}{\dot{Q}_{ev}}\times 100=\frac{\dot{W}_{el,exp}}{\dot{m}(h_{ex,ev,HF}-h_{in,ev,HF})}\times 100 \tag{8}\]  
The gross efficiency is also used here since the refrigerant pump selected for the tests operates in off-design conditions resulting in low isentropic efficiencies, which leads to negative net electric efficiency for some points. To better understand the impact of the pump, the back-work ratio (BWR) is presented as follows:  
\[BWR=\frac{\dot{W}_{el,p}}{\dot{W}_{el,exp}} \tag{9}\]