Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Multi-disciplinary Studies | en_US |
| dc.contributor | Department of Mechanical Engineering | en_US |
| dc.creator | Lam, Tak-wah | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/1993 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | - |
| dc.rights | All rights reserved | en_US |
| dc.title | The feedback control of thermal noise from a Rijke tube | en_US |
| dcterms.abstract | A simple feedback control mechanism has been developed to actively control the thermal noise generated from a Rijke tube. The feedback control mechanism consists of a microphone mounted near the upper end of the Rijke tube, a loudspeaker at the lower end of the Rijke tube to produce a counter control pressure field. A phase shifter and an amplifier are made to modify the pressure picked up by the microphone and feedback to the loudspeaker. The pressure field produced by the loudspeaker changes the boundary conditions at the lower end of the Rijke tube and the Rijke tube is silenced. This experiment used a glass tube installed with a hot gauze made of nichrome wire at the lower half of a vertical glass tube. This leads to a very loud booming noise at about 380Hz, the fundamental frequency of the tube. The noise level is about 80dBA. It demonstrated standing sound waves excited by the convection currents. The effect on the booming noise caused by the following modifications are also investigated in this study. . providing a backward air current into the glass tube by a ventilation fan. . covering the downstream section of glass tube by heat insulation. . making a small hole on the tube wall. and the results confirm our understanding of the Rijke tube. The pressure field produced by the loudspeaker can be controlled by adjusting the phase shifter and amplifier. It changes the boundary conditions at the end of Rijke tube. The booming noise is cancelled when the phase angle of the controlled pressure field from 180o to 240o behind the primary field. | en_US |
| dcterms.extent | iv, 49, [34] leaves : ill. (some col.) ; 30 cm | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 1999 | en_US |
| dcterms.educationalLevel | All Master | en_US |
| dcterms.educationalLevel | M.Sc. | en_US |
| dcterms.LCSH | Noise control | en_US |
| dcterms.LCSH | Combustion | en_US |
| dcterms.LCSH | Oscillations | en_US |
| dcterms.LCSH | Acoustical engineering | en_US |
| dcterms.LCSH | Hong Kong Polytechnic University -- Dissertations | en_US |
| dcterms.accessRights | restricted access | en_US |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| b14792424.pdf | For All Users (off-campus access for PolyU Staff & Students only) | 4.48 MB | Adobe PDF | View/Open |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/1993