Introduction
In this experiment(Creating sound with heat), we will be demonstrating the thermoacoustic phenomenon, in which heat is used for oscillating gasses without moving parts. We will also be characterising the properties of a thermoacoustic engine and using solar energy by powering the engine and testing different engine designs.
We hypothesised that the sound onset, pitch, and sound intensity depend on the applied power and size of the resonant cavity.
Aim
Our aim is to;
1. Demonstrate thermoacoustic phenomenon.
2. Characterize the properties of a thermoacoustic engine.
3. Using a solar engine, power the engine.
4. Test different engine designs.
Theory
The phenomenon in which sound is produced just by using heat without moving any of its parts is termed the thermoacoustic phenomenon.
Requirements
1. Engine,
2. Three designs of the thermoacoustic stack (aceramic cube with flow channels, a wire mesh of random flow paths, and rolled metal foils with parallel channels),
3. Parabolic solar concentrator,
4. Notebook,
Procedure
Step 1: Using a thermoacoustic stack inside a Pyrex tube, make an engine.
Step 2: A solid matrix that has a flow channel is called a stack.
Step 3: To create a steep temperature gradient along the length of the engine, apply electrical power at one end of the stack.
Step 4: Noise is created when the temperature gradient exceeds the critical value of temperature.
Step 5: Repeat the same process with three other designs of stacks which are, an aceramic cube with flow channels, a wire mesh of random flow paths, and a rolled metal foil with parallel channels.
Step 6: For creating the temperature gradient across the stack, use a parabolic solar concentrator.
Step 7: Change the power levels and the stacking energy to determine the generated sound.
Step 8: Collect the data that includes the applied power, temperature of the hot end, time of sound onset, and the intensity and frequency of the sound.
Observation
1. We observed that the thermoacoustic engine can produce sound without moving parts i.e by using only heat.
2. It uses inert gasses as working fluid and also is powered using solar energy. Therefore, it is environmentally friendly.
3. The intensity of generated sound increases with increasing power.
4. The position of the stack for obtaining the maximum result was near the middle of the test tube.
Result
We have divided our results into two parts.
First parts:-
1. After fixing the stack position, we plotted the intensity of sound, the time of onset, and the hot end temperature as a function of the power applied.
2. As we increased the power, the intensity of sound increased while the time of sound onset and temperature at the hot end decreased.
Second parts:-
1. We plotted the hot temperature, the time of sound onset, and the hot end temperature as a function of the position of the stack.
2. When the position of the stack was in the middle of the test tube; the hot end temperature, the onset time, and the applied energy was minimized.
3. The standing wave was produced by the engine with a wavelength four times the length of the test tube. Therefore, the generated sound frequency depends on the test tube length.
Precaution
1. Use Pyrex Tube only for placing the thermoacoustic stack.
2. Record your observation carefully.
3. Use inert gas.
Viva Questions with Answers
Q.1 What was the aim of your experiment?
ANS. Our aim was divided into three parts;
1. Demonstrate thermoacoustic phenomenon.
2. Characterize the properties of a thermoacoustic engine.
3. Using a solar engine, power the engine.
4. Test different engine designs.
Q.2 Is it possible to demonstrate thermoacoustic phenomena?
ANS. Yes, it is possible. As we have seen in our experiment, the thermoacoustic stack generated a sound without moving its part, just by using the gasses.
Q.3 Does the frequency of the generated sound of the thermoacoustic stack depend on any physical quantity?
ANS. Yes, the frequency of generated sound depends on the length of the test tube.
Q.4 What is the relation between power and the intensity of sound?
ANS. As we increase the power, the intensity of the sound increases.
Q.5 What is the relation between power and the hot end temperature, and the time of sound onset?
ANS The hot end temperature and the time of sound onset decreases with increasing power.
Q.6 What kind of wave was produced by the engine?
ANS. The engine produced a standing wave that had a wavelength four times the length of the test tube.
Q.7 Where did you place the stack for minimizing the onset time, the hot end temperature, and the applied energy?
ANS. At the middle of the test tube.
Saquib Siddiqui is a Mechanical Engineer and a content creator. He has special interest in science experiments and teaches the same to school and college students. He is also a technical lead at RUDE LABS PVT. LTD.
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