In this study, the thermal characteristics of three cases of Air-type PVT collectors designed with different shapes of perforated baffles were evaluated based on NX 10.0 CFD fluid analysis simulation program. In addition, the actual collector was fabricated, and the thermal and electrical performance of the collector was evaluated through outdoor experiments, and the experimental and simulation results were compared for the thermal performance.
The main results of the simulation are as follows. Firstly, the Air-type PVT collector with a perforated baffle has a phenomenon in which the internal fluid is stagnant in the part where the baffle is applied, and when a square perforated baffle is applied, the temperature of the part with baffle was confirmed to be higher than the temperature of the part without baffle. When the V-shaped perforated baffle was applied, it was found that the temperature increased due to friction at the peak of the baffle. The collector to which the bent perforated baffle was applied showed the most uniform temperature distribution, and the collector outlet temperature was found to be about 4℃ higher than that of other cases.
The average flow velocity inside the collector was 0.9m/s for Case 1 and Case 2, but the maximum flow velocity in the former case was about 2.1m/s, which was about 0.5m/s higher than the latter. A higher flow velocity was measured for Case 1 collector where the perforated portions were arranged alternately, compared to Case 2, where the perforations of the collector were on the same line with respect to the y-axis. The Nusselt Number related to the heat transfer coefficient of fluid was about 10% higher in Case 3 than in the rest of the cases. This means that the heat transfer rate of the fluid was relatively high in Case 3. Consequently, results confirmed that the average flow rate inside the collector and the outlet temperature increased.
The Air-type PVT collector with bent perforated baffle was found to have a higher outlet temperature of about 4℃ than the other two cases, and accordingly, the thermal efficiency of the collector increased by about 7%. The Case 3 collector, which had a fast flow velocity inside the collector and a relatively high Nusselt Number, showed the highest thermal efficiency.
Through outdoor experiments, the thermal and electrical efficiencies of the Air-type PVT collector with the bent perforated baffle were found to be about 32% and 16%, respectively. Compared to the simulation results, the thermal efficiency of the collector varied by about 6%.
As a result, there was an error between the results derived through the CFD simulation and the results of the actual experiment. The reason for this error is that it is difficult to implement the exact same conditions as the actual experiment in the simulation. However, an error of 6% is a reliable result considering that an average error of 5% occurred in other studies previously conducted. Even though it was numerically confirmed that an error occurs between the simulation and experimental results, it is very important that the thermal performance of the collector, which varies depending on the shape of the perforated baffle, can be estimated by simulation rather than experiment. Therefore, based on the previous research, when the shape of the perforated baffle is changed in the same condition in the future, a study to confirm the performance of the collector should be conducted.