A temperature gradient is established along the stack soon after the heat is supplied. This temperature difference induced
across the stack indicates that thermoacoustic effects have occurred. The temperature difference for the 3-cm stack seems to
stabilize at approximately 20 minutes after the torch was fired, at T = 430°C, which is slightly lower than the maximum
temperature difference achieved. Since the celcor ceramic stack in this study was taken from a used catalytic converter of a
Proton Perdana V6, a local car, the temperature gradient could have been higher if a new celcor stack had been used. The
maximum temperature difference for the 2-cm stack achieved after 10 minutes is 50% lower than that from the 3 cm stack,
dropping soon after, shown here in Fig 4. The higher temperature observed at the cold side of the 2-cm stack can be
attributed to the axial conduction heat transfer from the hot side thus causing a lower temperature difference across the
stack. Although thermoacoustic analysis always assume a short stack approximation such that its presence does not interfere
with the acoustic oscillations, an optimum length comparable to the resonator length is required for a stable temperature
gradient as seen here.
The pressure measured by the microphone for the 3-cm stack is shown in Figure 5, the increase from ambient fluctuating
after 20 minutes. The sound pressure level observed without the background noise is equivalent to 53 dB. Further
experiments need to be done to identify if the fluctuating behavior repeats itself to indicate a standing wave profile. No
significant sound level was recorded, however, for the 2-cm stack