## 2 Thermodynamic Analysis of the Solar ORC System with Zeotropic Mixtures
### Model Validation  
Available experimental data in the literature for an ORC system utilising mixtures of R245 fa/R123 as the working fluid with four mass fractions of R245 fa mass fractions, i.e., 0, 0.33, 0.66, and 1 at the same operating conditions, i.e., hot source temperature of 120 \({}^{\circ}\)C and mass flowrate of 0.15 kg/s, by [PERSON] et al. [34] have been utilised to validate the thermodynamic model in this work, as shown in  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Input Description** & **Parameter** & **System Unit** \\ \hline Evaporation pressure & \(p_{3}\) & MPa \\ Evaporation bubble-point temperature & \(t_{3}\) & \({}^{\circ}\)C \\ Evaporation temperature glide & \(t_{4}-t_{5}\) & \({}^{\circ}\)C \\ Condensation pressure & \(p_{1}\) & MPa \\ Condensation dew-point temperature & \(t_{7}\) & \({}^{\circ}\)C \\ Condensation temperature glide & \(t_{7}-t_{1}\) & \({}^{\circ}\)C \\ Pump inlet enthalpy at low pressure & \(h_{1}\) & kJ/kg \\ Evaporator inlet temperature & \(t_{2}\) & \({}^{\circ}\)C \\ Evaporator inlet enthalpy & \(h_{2}\) & kJ/kg \\ Enthaly at liquid phase at high pressure & \(h_{3}\) & kJ/kg \\ Enthaly at vapour phase at high pressure & \(h_{4}\) & kJ/kg \\ Expanded inlet enthalpy & \(h_{5}\) & kJ/kg \\ Expanded outlet enthalpy & \(h_{6}\) & kJ/kg \\ Expander outlet temperature & \(t_{6}\) & \({}^{\circ}\)C \\ Enthaly at vapour phase at low pressure & \(h_{7}\) & kJ/kg \\ Entropy at vapour phase at high pressure & \(s_{4}\) & ((J/kg)/K \\ Entropy at vapour phase at low pressure & \(s_{7}\) & (J/kg)/K \\ Specific volume at expander inlet & \(p_{5}\) & m\({}^{3}\)/kg \\ Specific volume at expander outlet & \(p_{6}\) & m\({}^{3}\)/kg \\ Volume ratio & \(v_{5}/v_{5}\) & \\ Cold source inlet temperature at regenerator & \(h_{4}\) & \({}^{\circ}\)C \\ Cold source inlet enthalpy at regenerator & \(h_{4}=k_{4}/k_{2}-h_{24}\) & kJ/kg \\ Hot source outlet enthalpy at regenerator & \(h_{6}=k_{6}+k_{2}-h_{24}\) & kJ/kg \\ Expansion work output & \(W_{1}\) & kW \\ Pump work input & \(W_{2}\) & kW \\ Net power output & \(W_{1}-W_{2}\) & kW \\ Solar collector heat input-evaporator (without regenerator) & \(\dot{m}(h_{8}-h_{2})\) & kW \\ Solar collector heat input-evaporator (with regenerator) & \(\dot{m}(h_{8}-h_{24})\) & kW \\ Rankine cycle efficiency (without regenerator) & \(\dot{\eta}_{1}\) & \% \\ Rankine cycle efficiency (with regenerator) & \(\dot{\eta}_{1}\) & \% \\ Carnot efficiency & \(\dot{\eta}_{C}\) & \% \\ Thermodynamics perfection (without regenerator) & \(\dot{\eta}_{1}/\dot{\eta}_{C}\) & \% \\ Thermodynamics perfection (with regenerator) & \(\dot{\eta}_{1}/\dot{\eta}_{C}\) & \% \\ Thermodynamic mean temperature of the evaporator & \(T_{\rm wk,free}\) & \({}^{\circ}\)C \\ Exergy of the absorbed heat & \(\dot{E}_{0}\) & kW \\ Second law efficiency & \(\dot{\eta}_{2}\) & \% \\ \hline \hline \end{tabular}
\end{table}
Table 2: Outputs of the ORC system.  
Figure 3: Flow diagram of the solar-driven ORC system.  
Figure 4. The assumptions of the thermodynamic model are listed in Section 2.2. Kinetic energy and potential energies of operating modes are neglected. Pressure drops and heat losses are disregarded in the heat exchangers, condenser, evaporator, and pipes. Comparison of cycle efficiency simulation results by means of the present model and the available experimental data at different R245 fa mass fractions shows an uncertainty range of 3.4% to 6.6%, which can reasonably be considered as a good agreement in the context where the measurements uncertainty range is somewhat similar. As a result, the current model can be utilised for further analysis with supporting reliability of the calculations.