# Hydrogen Production in Methane Decomposition Reactor Using Solar Thermal Energy
## 5 Experimental Results
### Indirect Heating Reactor 3  
Figure 16 shows the experimental results for reactor 3 in Figure 13. To increase the reaction time, heating was started before sunrise using a heater inside the cavity. After sunrise, solar thermal energy was supplied together with the heater to the reactor. When the temperature at the center and bottom of the catalyst reached 1000 \({}^{\circ}\)C, 40 L/min of methane was supplied instead of nitrogen. Afterwards, the heater was used only to supply heat as a result of insufficient heat owing to fluctuations in insolation.  
Figure 16: Experimental results using the reactor 3.  
At the beginning of the supply of methane, the catalyst temperature dropped by approximately 100 \({}^{\circ}\)C due to an endothermic reaction that occurs when methane is decomposed and the specific heat of methane is twice that of nitrogen. Accordingly, to increase the temperature, the blind opening ratio was increased from 60% to 90%. After 30 min of methane supply, it was confirmed that there was no nitrogen in the reactor system, and the conversion rate was measured using a gas analyzer. The initial conversion rate was in the range of 45-52%, as the entire catalyst temperature was lower than 1000 \({}^{\circ}\)C. However, as the catalyst temperature increased steadily to an average of 1081 \({}^{\circ}\)C, and a maximum of 1158 \({}^{\circ}\)C, a maximum conversion rate of 82.6% was achieved at 40 L/min of methane. Subsequently, to confirm the conversion rate at higher flow rates, it was increased to 50 L/min; however, the experiment was suspended due to cloudy weather. Furthermore, the sun's altitude angle was lowered after the meridian transit time.  
In Figure 16, at 40 L/min of methane, the conversion rate was 71.5% when the average temperature of the catalyst's top, center, and bottom was 1041 \({}^{\circ}\)C, but increased to 82.6% at 1071 \({}^{\circ}\)C. This implies that when the temperature rises by 2.8% on average, the conversion rate increases by 11.1%, which shows that the conversion rate by catalyst activation has high temperature sensitivity.  
Reactor 2 was used in the experiment for 4.5 h; however, reactor 3 with applied thermal barrier coating was used for approximately 50 h, which is estimated to be eleven times longer operation than that of Reactor 2. Therefore, it is established that thermal barrier coating increases the durability of the reactor. Nonetheless, increasing the catalyst temperature above 1200 \({}^{\circ}\)C may cause thermal damage to the reactor; hence, the catalyst temperature must be controlled during the experiment.  
In addition, when the methane flow rate and conversion rate were 40 L/min and 82.6%, respectively, the system efficiency was calculated as in Equation (5), and 65.6% was achieved. Two servo motors with power consumption of 800 W and a 150 W control PC were driven for 2-axis control of the heliostat. The calorific value of hydrogen and methane is based on the lower heating value.  
\[\eta_{system}=\frac{q_{produced\ hydrogen}(W)+q_{remaining\ methane}(W)}{q_{ heliostat\ control}(W)+q_{supplied\ methane}(W)} \tag{5}\]