Flow Response - Time
One of the experiments was to investigate the behaviour of the flow as time progressed, and the results of this are shown here. The graphs below have been simplified by removing all of the temperature readings other than the controlling temperature and sensor 5 (from the centre of our grid). Both of these recorded a high number of samples, so moving average trend lines have been used to cut down the erratic nature of the measurements. The full flow response - time results can be found within the excel document linked here.
The first graph of the response, from a high-speed air flow at 22°C, shows us that after a certain period of time the measured temperature in the room (i.e. at the user of the PV system) will stabilise, and start to oscillate slightly with the controlling temperature. While this still is not ideal - no oscillation would be preferable - this is simply a problem with the control system, and should be possible to eliminate in the future.
The second thing that can be seen is that the air speed directly influences the rate of the temperature change. Comparing the graph above with the one below (the only difference is in the flow rate parameter) it can be clearly seen that the air heats from approximately 19°C to 21°C over 150 seconds in the first case, and in the second case from 20°C to 21°C over the same timeframe - so the first case is heating twice as quickly.
The final conclusion that can be drawn from this experiment is that the losses to the room air increase dramatically as the controlling temperature is increased. The third graph is of high speed air and 24°C, but we can see that the measured temperature is still only in the region of 21-22°C - the same as the first two cases. This suggests that the PV system is only possible of heating the air to 2°C above the ambient room temperature, and to attempt increasing it further simply wastes heating power. It is thought that the design of the diffuser head contributes to this fact, and if it were to be redesigned it should be possible to have less 'spread' in the flow, thus losing less energy to the ambient room air.
