The Library
Development and characterisation of MWCNT filled HDPE foams for acoustic transducer applications
Tools
Amoroso, Lorena (2021) Development and characterisation of MWCNT filled HDPE foams for acoustic transducer applications. EngD thesis, University of Warwick.
|
PDF
WRAP_Theses_Amorosa_2021.pdf - Submitted Version - Requires a PDF viewer. Download (16Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b3765787
Abstract
The determination of the flow rate of fluids pumped through pipelines is an engineering problem of considerable practical interest. Over other more traditional flow measurement techniques (e.g. orifice, turbine or vortex meters), UFM technology is widely used in large diameter pipelines for measuring flow. Ultrasonic signals are transmitted through the medium of interest by means of electromechanical conversion, with the resultant backscattered energy being detected and converted into an electrical format (transmission and detection of ultrasonic energy). Air-coupled ultrasonic transducers sent and received the ultrasound, determining the performance of the flowmeter. For the purpose of custody transfer of natural gas, one of the most important applications of measurements of gas flow rate in large gas pipelines, a high degree of reliability and accuracy are of paramount importance. Both researchers and manufacturers of measuring equipment must reduce measurement errors. It is essential to optimise the sensor device. The use of new materials for passive MLs within the sensor assembly together with the study/implementation of advanced manufacturing methods for their manufacture is a route to optimizing ultrasonic transducers and their efficiency for enhancing energy transfer and so reducing measurement errors in UFM applications. In the present work, the concept of using lightweight composite foams based on HDPE and non-functionalised MWCNTs for sound absorption in ultrasonic flow metering (UFM) applications is described for the first time. Materials with suitable acoustic properties (i.e. very low acoustic impedance and attenuation) are not readily available for ML fabrication. The study of new acoustic materials as alternatives to conventional materials for the ML within the sensor assembly has been addressed and is the scope of this EngD project. A number of methodologies were here employed for the foaming of HDPE, with and without inclusion of MWCNTs using chemical and physical BAs. The key objective was to assess whether foamed HDPE and HDPE-MWCNT composite parts had the required properties to function as passive layers within acoustic sensors. For this purpose, a number of foamed samples with different cellular structures were produced by varying the processing conditions, concentration of BAs and MWCNT content during foaming, using industrially relevant polymer processing methods such as extrusion and IM. Controlling the cellular structure and thus, the resulting properties of the parts is challenging, especially when foaming a semi-crystalline polymer, such as HDPE which also has a very high melt viscosity and rapid crystallisation kinetics. On one hand, the composite foams produced by chemical foaming had acoustic properties comparable to those of syntactic foams commonly used in the target application, i.e. acoustic impedances of the order of 1 MRayl. On the other hand, the use of physical foaming allowed for even lower acoustic impedance by a further order of magnitude, ≤0.4 MRayl for unfilled HDPE foams and to a minimum of 0.57 MRayl for the 1 ii HDPE-MWCNT composite foams, for a MWCNT content of 0.5 wt%. Physical foaming produced highly foamed parts capable of achieving lower acoustic impedances than materials currently used as commercial layers in the sensor industry (e.g. ML-Trelleborg and Commercial ML). Foams of HDPE and HDPE-MWCNT composites are suitable for use as matching layers (MLs) in ultrasonic transducers. The low values of the speed of sound, acoustic impedance and acoustic attenuation, low cost and the possibility of manufacturing these lightweight layers at scale and in high volumes make them a viable alternative to the benchmarking materials.
Item Type: | Thesis (EngD) | ||||
---|---|---|---|---|---|
Subjects: | T Technology > TA Engineering (General). Civil engineering (General) T Technology > TC Hydraulic engineering. Ocean engineering T Technology > TJ Mechanical engineering and machinery T Technology > TK Electrical engineering. Electronics Nuclear engineering |
||||
Library of Congress Subject Headings (LCSH): | Flow meters, Tubes -- Fluid dynamics, Ultrasonic transducers, High-density polyethylene, Carbon nanotubes | ||||
Official Date: | May 2021 | ||||
Dates: |
|
||||
Institution: | University of Warwick | ||||
Theses Department: | Warwick Manufacturing Group | ||||
Thesis Type: | EngD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | McNally, Tony | ||||
Sponsors: | Warwick Manufacturing Group ; Honeywell Inc. ; Engineering and Physical Sciences Research Council | ||||
Format of File: | |||||
Extent: | ii, vi, 223, IV leaves : illustrations, charts | ||||
Language: | eng |
Request changes or add full text files to a record
Repository staff actions (login required)
View Item |