Page 3 - Papers, Reports and Publications

Microelectronic Sensor for the Measurement of Shear Stress within a Domestic Washing Machine Drum

                            Paper presented at IMAPS’99.
                            Annual Italian conference for Microelectronics Applications.
                            July 1999, University of Milan, Italy.
 

Abstract
A wireless monitoring system is proposed that allows remote dynamic pressure sensing and data acquisition for the first time inside a domestic washing machine.          The scope of the system is to measure the dynamic pressure inside the wash load so as to relate it to the average flow velocity. The system is based on matching, single channel, 433Mhz transmitter and receiver units that transmit and receive pressure data supplied by a piezo-resistive pressure transducer connected to special small block probes developed by the authors.The system is suitable for other single channel monitoring applications including temperature, humidity, conductivity etc.

 
Numerical Simulation of a Rectangular-section Water Duct equipped with Small Block Shear Stress Probes

Paper presented at CAPI’99.
Annual Italian conference for Advanced Numerical Simulation.
Nov. 1999, University of Milan, Italy.

Abstract
This paper presents the findings of a series of numerical simulations of a rectangular-section water duct that has been purpose-built to investigate the effects of hydrodynamic shear stress on the removal of soil from textile surfaces.
The scope of the simulation was to predict the hydrodynamic behaviour of the duct in terms of wall shear stress, velocity contours, pressure drop etc. in the test section of the duct.
The simulation and investigation included the development of miniature shear stress probes in the form of small triangular and square shaped thin (7-9x0.35mm) blocks attached to the inner face of the upper wall of the duct. These probes were used to measure local duct wall shear stress both in magnitude and direction. The measurement is based on the “law of the wall” and is compared with Preston tube measurements.
The simulation has been carried out using version 5 of FLUENT/UNS and a total of four runs were made. Each run was based on FLUENTs standard K-Epsilon model and usage of the standard wall functions. The simulation essentially focussed on the central part or test section of the duct, which measures 3.5m in length (of a total length of 11.05m), where the experimentation and simulation was affected. The meshing of the test section was done with GAMBIT, FLUENTs latest meshing tool, and divided in two domains. The first domain had a rough mesh of approx. 23000 cells situated before and after the measurement zone while the second domain, where the probes were mounted and tested, had approx. 204000 cells.
The main outcome of the simulation was two fold:
a.) The confirmation of the shear stress magnitude measured during experimentation with the Preston tube and shear stress probe, with a discrepancy of less than 10% between simulated and experimental measurements.
b.) Reliable prediction of shear stress probe and tunnel behaviour.
The paper also includes a brief discussion on indirect shear stress measurement techniques with particular focus on pressure measurement, the Preston tube and small block probes.

Modelling of a Horizontal-Axis Domestic Washing Machine

David Ward
Journal of the Textile Institute
Vol. 91, Part 1, No. 2, 2000

Abstract
This paper examines the design of the horizontal axis washing machine by means of parametric modelling and the description of clothes motion during the washing process.
A series of dimensionless factors have been determined that characterise the horizontal-axis washing machine. These parameters can be linked and correlated to machine performance, including soil removal efficiency and effectiveness. In this way it is possible to optimise machine parameters such as drum diameter, angular speed, depth etc.
The motion of the wash load has also been modelled by means of an imaginary fabric plug and by dividing the rotation of the wash load into 3 distinct steps. The resulting cycle has provided a means of calculating the theoretical fabric plug pressure drop, which is known to drive local hydrodynamic conditions including fluid flow.
Two methods of determining fabric plug impact velocity are also proposed including one based on the “added” mass concept.
The question of machine comparison and scalability is also tackled by means of geometric, dynamic and kinematic similarity.

La Misura dell’Attrito di Parete tramite Sonde di Pressione
(una Rassegna ed una Proposta)
“Measuring Skin Friction with Pressure Probes
(An Overview and Proposal)”

ACQUA – Italian Journal of Hydraulics, June 2000

Daniele Bocchiola, Giovanni Menduni, Marco Viterbo, David Ward

Abstract
The paper first provides a brief classification of the methods available for the measurement of wall shear stress. The authors then focus on methods, namely block probes that are based on the measurement of differential pressure readings. The theoretical background to these methods is then explained and the most favoured versions reported further. The paper is concluded with the description and discussion of an experiment in which block probes, appropriately developed by the authors, were tested to measure both shear stress magnitude and direction in water flows.

Remote Measurement and Monitoring of Critical Washing Process Data directly inside the Washing machine drum

IEEE Instrumentation and Measurement Technology Conference
Baltimore Hilton and Towers, Baltimore, Maryland, USA May 1-4, 1999
M. Lazzaroni, D. Ward, E. Pezzotta, G. Menduni, D. Bocchiola

Abstract
The system proposed allows the remote sensing of pressure inside the wash load of a domestic washing machine via a wireless data acquisition system.
The system is based on a piezoresistive pressure transducer and a matched pair of battery operated hybrid transmitters and receivers with a working frequency of 433MHz. The transducer and transmitter are housed within a small plastic sphere designed to follow the wash load during its movement in the washing machine drum. A small block probe is fitted to the surface of the sphere to pick up the surface dynamic pressure of the sphere and relate this to the local surface velocity. The receiver is mounted on the outside of the washing machine where it picks up the modulated signal from the transmitter and stores it through a dedicated data acquisition system.
The system has been designed to offer the maximum flexibility and is therefore applicable to many other remote sensing circumstances including those outside domestic appliances.
The system is capable of measuring pressure within the washing machine and providing an estimation of the flow conditions within the drum during the rotation of the wash load. Perhaps the most appealing part of this work is that the system certainly lends it self to a whole series of transducer and monitoring applications within the washing machine e.g. temperature, humidity etc.
Also the cost of the whole system is not prohibitive since it is based on off-the-shelf industrial solutions thus providing both reliability and cost effectiveness.
Clearly the advent of smaller transducers and hybrid wireless monitoring systems will push this type of solution even further, even to the stage where the garments themselves will have not only identification but also monitoring features.

Literature Review - Textiles

D. Ward, Whirlpool Internal Report, Nov. 1997

Scope and Executive Summary
The scope of the literature review was to acquire a basic understanding of textiles and relative fabrication so as to relate this knowledge to the fluid dynamics inside the washing machine.
Ample documentation was found concerning textiles ranging from weaving to dyeing however very little was found concerning fluid mechanics. What was found involved mainly the filtration and separation industries where textiles are used as the porous media.
Henceforth the major outcome of the literature review is that the most urgent goal is to acquire accurate information of the local fluid flow velocity and domain in general. For the time being we may state that past research has identified typical flow velocities below 1ms-1 and Reynolds numbers below 1000. However, much higher magnitudes may be useful to verify the adhesion study or, for example, to create flow conditions to demonstrate the influence of vorticity in soil removal. In fact perhaps the measurement of flow characteristics within the weave is the most demanding task at this stage of the project, especially if one considers that to do this will require the development of purpose-built tools, including micro-sensors.

Literature Review – Shear Stress Measurement

D. Ward, Whirlpool Internal Report, Nov. 1997

Abstract
This literature review, which is also found in chapter 4 or issues 1 and 2, of the Boundary Layer report, concerns the measurement of hydrodynamic shear stress.
As discussed in the previous chapters a fluid flowing past a wall exerts both a normal and tangential stress on it. The measurement of normal stress is relatively straight forward and generally requires only a simple tap in the wall to which a pressure gauge e.g. a manometer or pressure transducer is connected. Difficulties in this instance may arise due to damping of the piping, sensor pressure range, sensor frequency response etc. However, the major drawback with normal stress measurement is that it generally provides limited information about the fluid flow.
On the other hand the measurement of tangential or shear stress is considerably more complex but potentially yields considerably more information about the fluid flow and is therefore more rewarding than normal stress measurements.
The measurement of wall shear stress is generally divided into two macro categories i.e. Direct and Indirect, the latter category providing the majority of methods and devices.
Perhaps the biggest drawback with indirect methods is that they all require some form of calibration. Ideally, this should be done with a direct measurement technique, which may not be feasible or rational. Henceforth an indirect method is often compared with another indirect method e.g. small block probes versus a Preston tube and theoretical value of shear stress.
Direct methods are also not without shortcomings, since they need adequate installation, calibration, compensation and a certain degree of freedom in order for the sensor to accurately detect the shear force.
Ideally, the measurement of shear stress should be supported by the visualisation of the flow and possibly CFD simulation using programs such as FLUENT, ANSYS etc. In this way it is possible to observe and/or predict turbulence, secondary flows, pressure gradients and other flow phenomena.
Thus, this chapter addresses both shear stress measurement and flow visualisation concurrently. CFD simulation is briefly discussed in chapter 5 (see thesis).

Similarity and General Considerations for the Weave Model

D. Ward and M. Viterbo, Whirlpool Internal Report, Issue 1, June 1998

Scope and Executive Summary
The scope of this report was to address the issues involving the design of the similarity model necessary for the understanding of fluid flow within the textile or fabric. The similarity issue concerns the problem of scaling the weave and relative fluid flow and, more specifically, tackling the geometric, dynamic and kinematic similarities.
This document is therefore focused on addressing how the microscopic level hydrodynamic flow conditions can be scaled to a more convenient macroscopic level, such as that found in the water tunnel. The need for scaling up the weave and flow is to simplify the analysis of the boundary layer and thus provide an acceptable answer to fundamental questions such as: what is hydrodynamic shear force near the fabric, weave, thread or fibre surfaces, what is the pressure drop that drives the velocity field through a weave. The objective was to design and build a scaled model of the fabric which can be tested in a tailor made water tunnel.
To achieve perfect similarity it is necessary to include geometric (size), dynamic (force) and kinematic (motion) similarity in the dimensioning of the model. This is true whether the model is scaled-up or scaled-down.
There is ample evidence of achieving geometric similarity, and to a lesser extent dynamic similarity, while kinematic similarity is particularly difficult. This is especially true if one intends modelling motion such as machine and fabric motion.
To this end the authors suggest that a compromise be accepted and the model be based on geometric and dynamic similarities with the inclusion of simplifying assumptions to accommodate kinematic effects.
The most significant assumption is to consider the fabric as a porous media, hence we consider relative motion only i.e. whether the fabric or fluid moves is deemed irrelevant. To implement this approach suitable model adjustments are made by exploiting the work of past researchers in the fields of filtration and textile development.
Next to the similarity issue is the question of shear force measurement. The primary aim of this work is to establish the shear force via the measurement of dynamic and static pressures within the similarity model’s boundary layer. With this data in hand a comparison will be made with the findings of the adhesion studies at Purdue University.

Boundary Layer Theory, Shear Stress Measurement and the Washing machine-Tunnel Investigation
D. Ward, Whirlpool Internal Report, issue 2, Dec. 1999
(formerly the Boundary Layer report, issue 1 Dec. 1998)

Scope and Executive Summary
The Mass Transfer project extends from understanding the adhesive forces at a nano-microscopic scale level to the macroscopic scale level of the boundary layer of the fluid flow at the weave-thread surfaces and possibly further.
This report tackles this latter aspect and focuses on shear stress theory and measurement in turbulent flow, with particular reference made to the water tunnel or duct tests.
This focus is by far from casual since shear, in general, is considered a fundamental indicator of soil removal by hydrodynamic forces and turbulent flow is known to provide the highest surface shear stresses.
Thus, it is hoped that by determining the turbulent shear stress near the surface of soil or weave it is possible to evaluate its importance in terms of washing performance. This report is also a broad-based report covering many practical aspects of boundary layer theory, and explaining how tunnel and washing machine conditions are correlated. Moreover, because of the broad background of potential readers the report is aimed at providing a detailed overview without going into unnecessary depths, for example the Navier-Stokes equations are only briefly introduced.
Summarising, the scope of this document is to provide an overall background to boundary layer theory with particular emphasis on hydrodynamic shear stress, shear stress measurement methodologies and generally discuss the washing machine-tunnel investigation carried out so far. The intent is therefore to explain the characteristics of the boundary layer, how they are measured and/or calculated and how they relate to soil removal from textile surfaces.
High Speed Filming of the Wash load in a Horizontal-axis Washing m/c
D. Ward, Whirlpool internal report, Issue 1, Dec. 1999
Scope and Executive Summary
The scope of this report was to verify the theoretical model described in the paper titled “Modelling of a Horizontal axis Washing Machine” and determine a fist approximation of the impact velocity of the wash load and wash water velocity near the door.
The investigation has demonstrated the validity of mathematical model although more from a qualitative than a quantitative perspective. The parabolic shape of the free fall has been confirmed and the critical (release) angle found to be 45° (against 40° predicted by the model). The impact velocity shows the largest difference between model (4-4.5ms-1) and experimental measurements (1.6ms-1). However, the high speed filming has shown why this discrepancy exists, in particular the sphere is subject to resistance caused by the air and rolling effects caused by the adjacent fabric. Other differences were found in the total distance travelled in the x and y directions, in both cases reductions of 20 to 60% were found with respect to the model predictions. However, when the real conditions are put in the model the impact velocity discrepancy is reduced to just 0.1-0.2ms-1, a more than acceptable result.
Clearly to upgrade the model implies investigating more load conditions and acquiring more high speed imaging data.
Analysing bubble movement demonstrated that the flow velocity on the outside of the wash load is indeed considerably higher than inside it. This demonstrates that there are at least two flow domains (1.Inside 2. Outside) and the ratio between the two is at least 100. Outside velocity is far from insignificant with an average velocity of approx. 2.2ms-1, although this value will decrease as wash load increases. My personal prediction is that the velocity will drop to 1ms-1 when the machine is fully loaded (5kg) since the wash load tends to dampen movement because of compactness and rolling effects.
Finally the water line motion was also analysed. The most significant outcome was that the pressure head rate (variation of pressure per second) was remarkably high being typically 1000Pas-1. This change in pressure provides an insight into just how the water may be “pumped” through the wash load hence the diffusion through the wash load is characterised by a pumping effect and not a constant pressure head.

Roughness and Waviness measurements of EMPA soiled samples
D. Ward, Whirlpool internal report, Issue 1, Dec. 1999

Scope and Executive Summary
The scope of this research activity was to determine the surface profile characteristics of EMPA samples used in the water tunnel investigation and establish the impact this may have on the removal of soil in the water tunnel investigation.
The investigation has demonstrated the validity of a non-contact surface roughness measurement method using the Conoscan 2000 surface profiler and relative Viewer SW. Hence we now have a reliable method for determining the roughness of flexible surfaces including those of the EMPA samples used in washing machine performance tests and the water tunnel experimentation.
The overall outcome of the investigation is that the typical roughness of the EMPA samples is lower than 1mm and therefore the boundary layer (in both the washing machine and water tunnel) on the EMPA sample surface amply contains both soil and weave profile.
The water tunnel experimentation therefore remains valid and the measurements reported here confirm that surface roughness and profile do change when the weave is wet. No further work is foreseen for the measurement of weave roughness.

Una Metodologia per la Misura Puntuale dell'Attritto di Parete in Correnti Cilindriche

(A Method for Measuring Local Skin Friction in Cylindrical flows)
Politecnico di Milano, 1998

Author               : Daniel Bocchiola
Supervisor         : Prof. Giovanni MENDUNI
Co-supervisor   : Ing. David WARD

Abstract
In this thesis an indirect method of measuring localised skin friction in closed channel water flows is discussed. The method is based on two types of small block probes in the form of a thin square and triangular shaped obstacles, equipped with static and dynamic pressure tappings. Both probes exploit the ‘law of the wall’ and local pressure recordings to provide the magnitude of local wall shear stress.
The thesis discusses an experiment carried out in a tailor-made water tunnel, which shows how the probes can be calibrated to reveal wall shear stress magnitude within 40k<Re<160k.
The calibration technique used is the Preston tube, a development of the Stanton tube, which has been used to characterise also the shear stress contours of the upper tunnel wall. These contours were found to be in accordance with work carried out by Knight and Rhodes.
The major outcome of the research was that the small block probes can be used to measure wall shear stress up to 8Pa in closed channel water flows.

 Sonde  di Strato Limite per la Misura dello Sforzo di Attritto: Studio Sperimentale ed Analisi Teorica

(Boundary Layer probes used for the measurement of wall shear stress and skin friction – An Experimental investigation and Theoretical analysis)
Politecnico di Milano, 1999

Author              : Marco VITERBO
Supervisor        : Prof. Giovanni MENDUNI
Co-supervisors : Ing. David WARD and Ing. Daniele BOCCHIOLA

Abstract
In this thesis an indirect method, known as ‘small block probes’, for the measurement of shear stress conditions in closed channel water flows is discussed. These probes, in the form of a thin triangular shaped obstacles, are equipped with static and dynamic pressure tappings. The exploitation of the differential pressure recordings and the ‘law of the wall’ provide a direct indication of wall shear stress.
The thesis discusses an experiment carried out in a tailor-made water tunnel, which shows how the probes can be calibrated to simultaneously reveal both wall shear stress magnitude and direction.
One of the major difficulties in the indirect measurement of wall shear stress magnitude and direction is the calibration and comparison with a more reliable, and preferably direct, method. However, reliable direct methods are hard to come by and hence the approach preferred by many researchers is another indirect method known as the ‘Preston tube’, a development of the Stanton tube.
The research therefore discusses the findings of both the Preston tube and small block probes experimentation and links them to the theory behind the ‘law of the wall’.
The major outcome of the research was that the small block probes can be used to measure wall shear stress up to 8Pa in closed channel water flows as well as predict the direction of the shear simply measuring differential pressures (static and dynamic) across the probes.

Virtual Reality Presentation

Whirlpool 1999-2000, IMAPS'99 and CAPI'99

Presenter and Author : David Ward
Co-author                  : Marco Viterbo
Support                      : TTM group (Virtual Lab.)

Scope and Executive Summary
Project communication was one of the toughest challenges in the Mass Transfer research project because of its globalness.
It was therefore decided to use virtual reality to convey the project approach and illustrate some of the results using advanced audio-visual technology.  This was the first time VR was used in R & D. A total of three presentations were prepared with each one being an upgrade of the previous one both in terms of quality and quantity of information.
Presentations were given not only during project meeting updates but also at IMAPS’99 and CAPI’99 using virtual reality presentations by the TTM (Time-to-Market) group.
The VR presentations were basically a series of animated or real video scenes that demonstrated one or more of the 5 project steps. The VR presentations were aimed at a general audience with a technical background and stored on CD-ROM so that they could be projected using standard information technology.
All presentations were in colour with a maximum duration of no longer than 5minutes.

Weave Model Construction using Stereolitography
....an example of Rapid-Prototyping and the advance use of Pro-E and Fluent

Whirlpool Internal Seminar held by David Ward and Marco Maritan
March 1998

Scope and Executive Summary
Stereolithography is an example of rapid prototyping which allows the design engineer to first design solid models with advanced CAD systems like Pro-E and then build the models using a special machine based on stereolithography technology.
The machine works by solidifying photosensitive wax-like resin using a UV or LASER light source exactly where the model needs to be solid. In practice the machine can be visualised as a 3D printer, which creates layers of solidified special resin according to the 3D model downloaded into the machine.
The model therefore consists of a series of layers, one on top of each other, with each layer having an area of solidified resin and an area of semi-solid resin-like wax. At the end of the process all this resin-like wax is simply washed away leaving the solid model behind.
The stereolithography technology was presented within the R & D group of Whirlpool in March 1998, since then this technology has become a standard tool for prototype building.
The scope of the presentation was not only to illustrate applications of stereolithography but also to the development of the weave threads and weave model. This included showing how the threads and model were developed with Pro-E SW and the use of the same solid model transferred to FLUENT where a CFD simulation was successfully carried out.
The model was subsequently used to in conjunction with small, triangular shaped, block stress to measure flow conditions on the models surface. These blocks were connected externally via pipe tubing routed and integrated in the model itself so that pressure measurements could be recorded.

Progetto e Realizzazione di un Sistema di Misure delle Condizioni Fluidodinamiche in una Lavatrice Domestica

("The Design and Development of a Measurement System for the Monitoring of Hydrodynamic Conditions in a Domestic Washing Machine")
Politecnico di Milano, 2000

Author   : Elio Pezzotta
Supervisor  : Ing. Massimo Lazzaroni
Dipartimento di Elettrotecnica, Politecnico di Milano.
Co-supervisors : Ing. David Ward

Abstract
In this thesis the design, development and testing of a remote data acquisition system is discussed. The system, based on the sphere concept and used in step 5 discussed previously, uses a matched pair of hybrid radio transmitter and receivers. The scope of the system was to establish the flow velocity within the wash load during the initial washing phase of the fabric care process. The system used a small, triangular shaped, block probe connected to a miniature pressure transducer to detect the dynamic pressure, which was then converted into an average flow velocity.
The research activity also involved the development of a purpose-built LABVIEW program.

 REMOTE MEASUREMENT AND MONITORING OF CRITICAL WASHING PARAMETERS INSIDE A DOMESTIC WASHING MACHINE

D. Ward, E. Pezzotta, M. Lazzaroni, M. Viterbo, G. Menduni

Paper presented at NIDays2000.
National Instruments, Annual Italian conference.
28th Nov. 2000, Milan, Italy.

Abstract
This concise paper discusses the measurement system based on National Instruments SW (LABVIEW) and HW (SC2040 and DAQCard). The scope was to describe the measurement system from a SW and HW point of view. The paper therefore emphasises the systems side of the washing machine measurements and briefly discusses the integration of HW and SW.
The paper was presented at the NiDays2000 conference organised by National Instruments Italy.

Wash load Motion......A Theoretical Approach and Experimental Analysis

D. Ward and D. Conrad

Accepted for the 52nd International Appliance Technical Conference
Ohio State University, Ohio USA, March, 2001.

Abstract
This paper is essentially an extended version of the Journal of the Textile Institute paper regarding the modelling of the wash load motion. The paper includes the experimental part of the fabric plug model and hence provides a description of the high speed filming technique used for this purpose.

EUROPEAN PATENT APPLICATION
Title: System for the remote measurement and monitoring of critical washing parameters inside a domestic washing machine
Inventors: David Ward and Ivano Frattini, CTED, Whirlpool Europe
No. MI2000A002122
Deposited: 2nd Oct. 2000

Reports - not available outside of Project Team
@ Boundary Layer Theory, Shear Stress Measurement and the Washing Machine-Tunnel Investigation - 333pages
@ Literature review of Textile Fluid Mechanics - 31 pages
@ High-speed Filming of the Wash load in a Horizontal-axis Washing Machine - 15 pages
@ Introductory Evaluation of Soil Removal Conditions - 57 pages
@ Non-contact Roughness measurements of EMPA samples - 10 pages
@ Similarity and General Considerations for the Weave Model - 140 pages
@ Boundary Layer report - 150pages

Co-author of the following undergraduate Dissertations (as desribed above):

D. Bocchiola, Una Metodlogia per la Misura Puntuale dell'Attritto di Parete in Correnti Cilindriche ("A Method for Measuring Local Skinb Friction in Cylindrical Flows"), Tesi di Laurea, Mat. 611090, Politecnicio di Milano, Italy, 1998.

M. Viterbo, Sonde di Strato Limite per la Misura dello Sforzo d'attritto - Studio Sperimentale ed Analisi Teoricaa ("Boundary Layer probes used for the Measurment of Wall Shear Stress and Skin Friction - An Experimental Investigation and Theoretical Study"), Tesi di Laurea, Mat. 599289, Politecnicio di Milano, Italy, 1999.

E. Pezzotta, Progetto e Realizzazione di un Sistema di Misure delle Condizioni Fluidodinamiche in una Lavatrice Domestica ("The Design and Development of Measurement System for the Monitoring of Hydrodynamic Conditions ina Domestic Washing Machine"), Tesi di Laurea, Mat. 855766, Politecnicio di Milano, Italy, 2000.

Papers- Texts  in the Pipeline
Abstract Titles:
# Wash Load Motion Analysis Part 2 - Model Validation and Experimental Results - Journal of the Textile Institute, 2001.

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