# Experimental and Numerical Study of Thermal Performance of an Innovative Waste Heat Recovery System
## 3 Results  
### Experimental Results  
The temperature of the primary agent was kept constant for one hour. Since the temperature of the secondary agents is rising very slowly after about 50 min, and the variations are small, we considered that after 1 h of constant temperature in the condenser the temperature of the evaporator reaches a quasi-constant state.  
The sensors CH1, CH2, and CH3 are responsible for tracking the temperature variation in time. CH1 is placed at the inlet of the condenser, CH2 at the outlet of the condenser and CH3 at the inlet of the evaporator. The electronic thermometer was set to record the temperature every 60 s.  
The temperature recorded after 60 min for the test no. 1 was 40.7 \({}^{\circ}\)C, for the test no. 2 the results showed 35.7 \({}^{\circ}\)C, while for the test no. 3 the temperature was 32.1 \({}^{\circ}\)C. As we can observe in Figure 4, the most significant temperature variation takes place in the first 10 min. After this period of time, the rising of temperature is slower.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **T\({}_{\text{E}v,1}\)** [\({}^{\circ}\)C] & **T\({}_{\text{C}0,1}\)** [\({}^{\circ}\)C] & **q\({}_{1}\)** [L/min] & **q\({}_{2}\)** [L/min] \\ \hline Test no. 1 & 60 & 10 & 1 & 24 \\ Test no. 2 & 60 & 10 & 2 & 24 \\ Test no. 3 & 60 & 10 & 3 & 24 \\ Test no. 4 & 65 & 10 & 1 & 24 \\ Test no. 5 & 65 & 10 & 2 & 24 \\ Test no. 6 & 65 & 10 & 3 & 24 \\ Test no. 7 & 70 & 10 & 1 & 24 \\ Test no. 8 & 70 & 10 & 2 & 24 \\ Test no. 9 & 70 & 10 & 3 & 24 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Testing parameters.  
To visualize the external temperature of the heat recovery system, we took some photos with a FLIR thermal vision camera during test no. 1. In Figure 5 we can observe that most of the heat recovered is first absorbed by the water in the middle of the condenser during the first 15 min of the test, but after that, the temperature tends to become uniform inside the condenser.  
For the next 3 tests we used a temperature of 65 \({}^{\circ}\)C at the inlet of the evaporator and the sensors revealed a temperature of 47.4 \({}^{\circ}\)C for test no. 4, 41.8 \({}^{\circ}\)C for test no. 5 and 36.3 \({}^{\circ}\)C for test no. 6. In the first 10 min, the volume flow rate of the secondary agent does not have a significant impact on the heat recovery rate. After about 20 min, the temperature rise in the condenser is slow, with about 0.1 \({}^{\circ}\)C/min for all of the three cases (Figure 6).  
Figure 4: The variation of temperature at the outlet of the condenser for tests no. 1, 2, 3.  
Figure 5: Photos with FLIR thermal camera during test no. 1.  
The tests were repeated for the same volume flow rates but this time with the temperature of the primary agent of 70 \({}^{\circ}\)C. As we can observe in Figure 7, the temperature of the secondary agent after 60 min was 56.1 \({}^{\circ}\)C for case no. 7, 46.7 \({}^{\circ}\)C for case no. 8 and 41.1 \({}^{\circ}\)C for case no. 9. Again, the amount of heat recovered in the first 10 min does not depend on the volume flow rate of the secondary agent. After 10 min, the \(\Delta\)T between the inlet and the outlet of the condenser is about 18.5 \({}^{\circ}\)C for all three cases (Figure 7).