## 2 System Description
### Experimental Setup for the Absorption Cooling System  
The absorption cooling unit operated with the ammonia-lithium nitrate mixture and was built using five plate heat exchangers (PHE) as a generator, absorber, condenser, evaporator, and economizer, the system also utilized a solution pump, an expansion valve, and two low-capacity storage tanks. The PHE had a vertical orientation. The experimental absorption cooling system was conceived in several stages: the first one involves the development of a first-law thermodynamic model that included mass, matter and thermal balances as well as equations for the thermophysical properties for the ammonia-lithium nitrate mixture. During the second stage, the type of plate heat exchangers to use was defined, considering the affinity between the components commercially available and the desired characteristics for the heat exchangers, for instance, the maximum permissible dimensions and the heat load to be transferred as well as the properties of the working mixture. In the last stage, it was utilized a computational code to obtain the theoretical heat transfer area for each component of the ACS, this code employs the main geometric characteristics of the selected plate heat exchangers. The plate heat exchangers utilized were manufactured by Alfa Laval(tm). The model Alfanova 52(r) was used in the components acting as generator, economizer, and absorber, the number of plates in these components was 40. The condenser and evaporator utilized the model Alfanova 27(r) with \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Unit** \\ \hline Length & 2.44 & m \\ Width & 1.05 & m \\ Aperture area & 2.56 & m\({}^{2}\) \\ Rim angle & 90 & \({}^{\circ}\) \\ Exterior diameter & 0.0254 & m \\ Inner diameter & 0.019 & m \\ Focal length & 0.26 & m \\ Number of PTC & 15 & \\ Orientation & North-South & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of parabolic trough collector. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Concentration ratio C & 13.158 \\ Reflectivity \(\rho\) & 0.92 \\ Transmisvisityn \(\tau\) & 1.0 \\ Abpsortance \(\alpha s\) & 0.9 \\ Intercept factor \(\gamma\) & 0.84 \\ Geometric factor \(A_{f}\) & 0.22 \\ Optical efficiency \(\eta_{o}\) & 0.705 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Optical parameters for the Parabolic Trough Collector (PTC). 20 plates in each heat exchanger. A [PERSON](r) diaphragm pump was used to send the solution from the absorber to the generator. The expansion valve used was a stainless steel needle valve with a maximum flow coefficient equal to 0.004. A couple of small capacity (2 L) storage tanks were included in the system. One of them was installed in the line at the exit of the generator, whose porpoise was to allow the phase separation, facilitating the ammonia vapor to flow to the condenser, and the solution liquid-phase to flow to the absorber. The other tank was useful to keep the liquid solution at an adequate level, in order to avoid the undesirable flow of the solution to the evaporator. The ACS measurements are 1 \(\times\) 1 \(\times\) 0.8 m (width-height-depth), resulting in a system with an overall volume of around 0.7 m\({}^{3}\). All of the components in the system (including the piping and valves) are made out of stainless steel to avoid corrosion problems caused by ammonia. The thermal energy required to desorb the refrigerant from the solution in the generator, before the integration of the solar system was supplied by an auxiliary heating system whose function is to simulate the heat power that would be supplied by the parabolic trough collector field. This auxiliary system uses an electric resistance to heat a mass flow rate of water and keep its temperature at the desired conditions. The hot water is supplied to the generator at a gauge pressure near to 200 kPa (2 bar), avoiding the boiling of the water inside the heating system.