Sensors & Transducers · Sensors & Transducers Volume 132, Issue 9, ... Pullini, Daniele, Centro Ricerche FIAT, Italy Pumera, Martin, National Institute for Materials Science, Japan

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Volume 132, Issue 9, September 2011

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Editors-in-Chief: professor Sergey Y. Yurish, tel.: +34 696067716, e-mail: [email protected]

Editors for Western Europe Meijer, Gerard C.M., Delft University of Technology, The Netherlands Ferrari, Vittorio, Universitá di Brescia, Italy

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Thailand Sun, Chengliang, Polytechnic University, Hong-Kong Sun, Dongming, Jilin University, China Sun, Junhua, Beijing University of Aeronautics and Astronautics, China Sun, Zhiqiang, Central South University, China Suri, C. Raman, Institute of Microbial Technology, India Sysoev, Victor, Saratov State Technical University, Russia Szewczyk, Roman, Industrial Research Inst. for Automation and Measurement,

Poland Tan, Ooi Kiang, Nanyang Technological University, Singapore, Tang, Dianping, Southwest University, China Tang, Jaw-Luen, National Chung Cheng University, Taiwan Teker, Kasif, Frostburg State University, USA Thirunavukkarasu, I., Manipal University Karnataka, India Thumbavanam Pad, Kartik, Carnegie Mellon University, USA Tian, Gui Yun, University of Newcastle, UK Tsiantos, Vassilios, Technological Educational Institute of Kaval, Greece Tsigara, Anna, National Hellenic Research Foundation, Greece Twomey, Karen, University College Cork, Ireland Valente, Antonio, University, Vila Real, - U.T.A.D., Portugal Vanga, Raghav Rao, Summit Technology Services, Inc., USA Vaseashta, Ashok, Marshall University, USA Vazquez, Carmen, Carlos III University in Madrid, Spain Vieira, Manuela, Instituto Superior de Engenharia de Lisboa, Portugal Vigna, Benedetto, STMicroelectronics, Italy Vrba, Radimir, Brno University of Technology, Czech Republic Wandelt, Barbara, Technical University of Lodz, Poland Wang, Jiangping, Xi'an Shiyou University, China Wang, Kedong, Beihang University, China Wang, Liang, Pacific Northwest National Laboratory, USA Wang, Mi, University of Leeds, UK Wang, Shinn-Fwu, Ching Yun University, Taiwan Wang, Wei-Chih, University of Washington, USA Wang, Wensheng, University of Pennsylvania, USA Watson, Steven, Center for NanoSpace Technologies Inc., USA Weiping, Yan, Dalian University of Technology, China Wells, Stephen, Southern Company Services, USA Wolkenberg, Andrzej, Institute of Electron Technology, Poland Woods, R. Clive, Louisiana State University, USA Wu, DerHo, National Pingtung Univ. of Science and Technology, Taiwan Wu, Zhaoyang, Hunan University, China Xiu Tao, Ge, Chuzhou University, China Xu, Lisheng, The Chinese University of Hong Kong, Hong Kong Xu, Sen, Drexel University, USA Xu, Tao, University of California, Irvine, USA Yang, Dongfang, National Research Council, Canada Yang, Shuang-Hua, Loughborough University, UK Yang, Wuqiang, The University of Manchester, UK Yang, Xiaoling, University of Georgia, Athens, GA, USA Yaping Dan, Harvard University, USA Ymeti, Aurel, University of Twente, Netherland Yong Zhao, Northeastern University, China Yu, Haihu, Wuhan University of Technology, China Yuan, Yong, Massey University, New Zealand Yufera Garcia, Alberto, Seville University, Spain Zakaria, Zulkarnay, University Malaysia Perlis, Malaysia Zagnoni, Michele, University of Southampton, UK Zamani, Cyrus, Universitat de Barcelona, Spain Zeni, Luigi, Second University of Naples, Italy Zhang, Minglong, Shanghai University, China Zhang, Qintao, University of California at Berkeley, USA Zhang, Weiping, Shanghai Jiao Tong University, China Zhang, Wenming, Shanghai Jiao Tong University, China Zhang, Xueji, World Precision Instruments, Inc., USA Zhong, Haoxiang, Henan Normal University, China Zhu, Qing, Fujifilm Dimatix, Inc., USA Zorzano, Luis, Universidad de La Rioja, Spain Zourob, Mohammed, University of Cambridge, UK

Sensors & Transducers Journal (ISSN 1726-5479) is a peer review international journal published monthly online by International Frequency Sensor Association (IFSA). Available in electronic and on CD. Copyright © 2011 by International Frequency Sensor Association. All rights reserved.

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Volume 132 Issue 9 September 2011

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Research Articles

Gas Sensors Based on Inorganic Materials: An Overview K. R. Nemade ..................................................................................................................................... 1 Control Valve Stiction Identification, Modelling, Quantification and Control - A Review Srinivasan Arumugam and Rames C. Panda..................................................................................... 14 Numerical Prediction of a Bi-Directional Micro Thermal Flow Sensors M. Al-Amayrah, A. Al-Salaymeh, M. Kilani, A. Delgado ..................................................................... 25 The Linearity of Optical Tomography: Sensor Model and Experimental Verification Siti Zarina Mohd. Muji, Ruzairi Abdul Rahim, Mohd Hafiz Fazalul Rahiman, Zulkarnay Zakaria, Elmy Johana Mohamad, Mohd Safirin Karis ...................................................................................... 40 Structure Improvement and Simulation Research of a Three-dimensional Force Flexible Tactile Sensor Based on Conductive Rubber Shanhong Li, Xuekun Zhuang, Fei Xu, Junxiang Ding, Feng Shuang, Yunjian Ge...................................................... 47 Modeling and Simulation of Wet Gas Flow in Venturi Flow Meter Hossein Seraj, Mohd Fuaad Rahmat, Marzuki Khaled, Rubiyah Yusof and Iliya Tizhe Thuku ......... 57 Improvement Study of Wet Nitrocellulose Membranes Using Optical Reflectometry Hariyadi Soetedjo ............................................................................................................................... 69 Use of Balance Calibration Certificate to Calculate the Errors of Indication and Measurement Uncertainty in Mass Determinations Performed in Medical Laboratories Adriana Vâlcu ..................................................................................................................................... 76 Improved Web-based Power Quality Monitoring Instrument I. Adam, A. Mohamed and H. Sanusi ................................................................................................. 89 Design and Fabrication of a Soil Moisture Meter Using Thermal Conductivity Properties of Soil Subir Das, Biplab Bag, T. S. Sarkar, Nisher Ahmed, B. Chakrabrty .................................................. 100 Numerical Study of Mechanical Stirring in Case of Yield Stress Fluid with Circular Anchor Impeller Brahim Mebarki, Belkacem Draoui, Lakhdar Rahmani, Mohamed Bouanini, Mebrouk Rebhi, El hadj Benachour .............................................................................................................................. 108 Computer Vision Based Smart Lane Departure warning System for Vehicle Dynamics Control Ambarish G. Mohapatra ..................................................................................................................... 122

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Simple Implementation of an Electronic Tongue for Taste Assessments of Food and Beverage Products Abdul Hallis Abdul Aziz, Ali Yeon Md. Shakaff, Rohani Farook, Abdul Hamid Adom, Mohd Noor Ahmad and Nor Idayu Mahat........................................................................................... 136 Aluminum-Selective Electrode Based on (1E,2E)-N1,N2- dihydroxy )-N1,N2- bis (4-hydroxy phenyl) Oxalimidamide as a Neutral Carrier Aghaie M., Esfandyar Baghdar, Fekri Lari F., Ali Kakanejadifard, Aghaie H. .................................... 151

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Sensors & Transducers Journal, Vol. 132, Issue 9, September 2011, pp. 25-39

25

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Numerical Prediction of a Bi-Directional Micro Thermal Flow Sensors

a M. Al-Amayrah, a, b A. Al-Salaymeh, b M. Kilani, a A. Delgado

a Lehrstuhl für Strömungsmechanik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Cauerstr. 4, 91058 Erlangen, Germany

Fax: +49-9131-8529503 b Mechanical Engineering Department, The University of Jordan, Amman 11942, Jordan

E-mail: [email protected], [email protected], [email protected], [email protected], [email protected]

Received: 26 July 2011 /Accepted: 19 September 2011 /Published: 27 September 2011 Abstract: Thermal flow sensors such as hot-wire anemometer (HWA) can be used to measure the flow velocity with certain accuracy. However, HWA can measure the flow velocity without determining the flow direction. Pulsed-Wire Anemometer (PWA) with 3 wires can be used to measure flow velocity and flow directions. The present study aims to develop a numerical analysis of unsteady flow around a pulsed hot-wire anemometer using three parallel wires. The pulsed wire which is called the heated wire is located in the middle and the two sensor wires are installed upstream and downstream of the pulsed wire. 2-D numerical models were built and simulated using different wires arrangements. The ratio of the separation distance between the heated wire and sensor wire (x) to the diameter of the heated wire (D) ratios (x/D) was varied between 3.33 and 183.33. The output results are plotted as a function of Peclet number (convection time / diffusion time). It was found that as the ratio of x/D increases, the sensitivity of PWA device to the time of flight decreases. But at the same the reading of the time of flight becomes more accurate, because the effects of the diffusion and wake after the heated wire decrease. Also, a very good agreement has been obtained between the present numerical simulation and the previous experimental data. Copyright © 2011 IFSA. Keywords: Pulsed wire anemometer (PWA), Hot-wire Anemometer (HWA), Bi-Directional sensor, three parallel wires, Numerical prediction.



26

Nomenclature

Pc Specific heat at constant pressure, J ( k g C )

D Heated wire diameter, m sD Sensor wire diameter, m

f Frequency, Hz g Gravitational acceleration, m2/s

k Thermal conductivity, W (m C) p Pressure, Pa T Temperature, K

staT The sending temperature average, K

max,rT

The maximum value of the received temperature, K

min,rT The minimum value of the received temperature, K

t Time, s U Free stream velocity, m/s

iu

Cartesian velocity components where u1 = u and u2 = v

ix Cartesian coordinates (x, y)

X Distance between the heated wire and the sensor wire, mm Greek Symbols ø Time of flight, s

ρ Fluid density, kg/m3 1 ( )T T

α Thermal diffusivity of the fluid, m2/s μ Dynamic viscosity, N.s/m2

ψ The angle between the direction normal to the plane of the probe and the instantaneous velocity vector

The viscous dissipation function given by j

,j i i

i j

u u u

x x x

Non-dimensional Numbers Pe Peclet number, Pe Re Pr U X

Pr Prandtl number, Disspation heat

PrConduction heat

,

p

f

c

k

Re Reynolds number, Inertia forces

ReViscous forces

w

f

U d

DGr Grashof number, 3

2

( )Buoyancy forces

Viscous forcesw

D

g D T TGr

Ec Eckert number 2Kinatic energy

Ec= ;Enthalpy ( )p w

U

c T T


27

1. Introduction It is often desirable in flow studies and survey work to be able to measure the velocity of gases at points within the flow pattern inside both pipes and open channels to determine either mean velocity or flow profile. The most common techniques used in such measurements are the Laser-Doppler Anemometer (LDA), Hot-Wire Anemometer (HWA) and Pitot tube, e.g. Walt [1]. The pitot tube is suitable for high velocity measurements but becomes inaccurate for low velocity fields. In addition, it is used in one directional flow. The LDA uses the Doppler shift of light scattered by moving particles in the flow stream to determine particles velocity and hence fluid flow velocity. It is difficult to measure the flow velocity in regions near walls by using LDA because of the beam reflections. LDA needs high cost for production and is particularly suited to velocity studies in systems that would not allow the installation of a more conventional system, for example, around propellers and in turbines, e.g. Al-Salaymeh [2]. The hot-wire/film anemometer (HWA) method is widely used for flow studies in gases flows. It requires calibration and it can be produced at a low cost for Industrial applications. It has a fast response, small sizes and low noise, e.g. Chen [3]. Conventional HWA is assembled by mounting a thin wire, made of platinum or tungsten, on support prongs. The HWA even the ideal one is subjected to serious errors; this is due not only to the nonlinear response of this instrument to fluctuations in the magnitude of the velocity vector, but also to its ambiguous response to variations in the flow direction, e.g. Bradbury and Castro [4] and Castro [5]. The idea of Bi-directional hot wire anemometer came from PWA that usually consists of three wires; the middle wire is the heated wire which is located at right angles to the sensor wires to produce an instrument with a wide yaw response, e.g. Durst et al. [6]. This device measures the time shift between the sending and receiving temperature signals, and this time is called the Time-of-Flight (TOF), e.g. Durst et al. [7]. Al-Salaymeh et al. [8] described a pulsed hot wire anemometer that consists of three parallel hot wires; the heated wire in the middle and the two sensor wires on each side. The range of the measured velocity was varied between 0.05 < U< 25 m/s. In addition, the distance between the heated wire and the received wire was selected to be1.25 mm. They used sinusoidal signals for heating the pulsed wire. Bauer [9] used a PWA with square sending signal and the distance between the wires was selected to be 2.0 mm. Experimental investigations of the TOF of a tracer of heated air from an electrically pulsed wire to one of two sensor wires at right angles to the pulsed wire placed on either side of a pulsed wire was described Elliott et al. [10]. Kielbasa et al. [11] pointed out that the TOF depends not only on the flow velocity and the distance between the two wires, but also on some other parameters such as the wire time constants and the dynamic properties of the amplifier. TOF for slowly changing flows can be increased by using wires with large thermal inertia (time constant) and heating the sending wire with continuous sinusoidal current, instead of square-wave pulses, e.g. Al-Salaymeh [2]. At higher velocities, the TOF eventually becomes comparable to the decay time of the picked up signal, and the signal from the heat pulse merges into the decaying “tail” of the interference signal, e.g. Bradbury and Castro [4]. However, in the recent few years, the new micromachining process which was developed in the last decades encouraged the use of small physical size of the HWA for better performance, e.g. Breuer et al. [12]. Many experiments of the micro machined hot wire anemometers with the steady state characteristics, frequency response and directional dependence were reported, Jiang et al. [13]. Experimental studies of Jiang et al. [13] resulted a micro hot-wire model with 10 μm long, 1 μm wide and 0.5 μm thick where polysilicon was used as hot wire material. They developed trapezoidal cross section defined by cross section of the micro hot-wire instead of circular section. Al-Salaymeh and


28

Ashhab [14] utilized the neural nets to model hot-wire thermal flow sensor under different operating conditions. Amayrah et al. [15] investigated numerically the micro HWA using three parallel wires. He calculated the TOF for a certain wires arrangements. The TOF depends on many physical parameters such as the properties of the fluid, the heated wire material, the separation distance between the heated and sensor wires, the diameters of each wire and the kind of boundary conditions (shear wall, the velocity, pressure and temperature at inlet and outlet). This study discusses the influence of separation distance ratio (X/D) and the free stream velocity on the sensitivity of the bi-directional thermal flow sensor. 2. Model Description The probe configuration for the micro thermal flow sensor which has been investigated in the present work is shown in Fig. 1a. It consists of three parallel wires and the length of each wire is several hundred times the diameter of the pulsed wire. The central wire is the heated wire and the other two wires are the sensor wires. The use of two sensor wires on either side of the heated wire would ensure that the direction of the flow at that instant could be unambiguously determined. If the heated wire connected with an AC current the temperature appears as a sinusoidal thermal signal. If the flow basses from left to right, the left sensor will record a constant temperature and the right sensor will

shows a thermal sinusoidal signal with a delay as appears in Fig.1b. The time of delay between the pulsed signal and the received signal consists of the time delay in the heated wire and the sensor wire due to the thermal inertia of the wires in addition to the time of flight.

(a) 3D Schematic of bi-directional micro hot-wire anemometer using three parallel wires.

(b) Explain of the pulsed hot wire anemometer work, main

parameters, coordinate and boundary conditions.

Fig. 1. Description of the model.

3. Mathematical Formulation 3.1. Thermal Inertia of the Heated and Sensor Wires The heat balance in the heated wire can be shown in Fig. 2. The heat generated inside the hot wire is balanced by radioactive heat to surrounding, convective heat to the fluid, accumulated heat inside the wire and conductive heat to the prongs of the finite wire, e.g. Bruun [16].

,U T T

left sensor wire Right sensor wire

T ( ) sin(2 )w t A B ft T ( , , ) sin(2 ( ))w t x y F D f t

The thermal wake

wT =T

0iu

0iu

0iu

Heated wire

Wall

0PP

Wall

Heated Wire Right Sensor Wire Tungsten

Left Sensor Wire Tungsten

L

Ds

Ds D


29

2 24 4

2

stored

ww ww w w w w w w w w

wConvection HeatheatElectricalHeate conduction radiation

heat heat

IT Tc A d h T T k A d T T

t A z

(1)

where 42ww dA is the cross section area of the wire and the heat conduction to the support needles

is negligible. The length to the diameter ratio is large in our case 400/ dL . The heat radiation term is negligible less than 0.1% of the heat convection loss, e.g. Al-Salaymeh [17].

2

.( ) ( )

w ww a

w w w w w w w

T IDh T T

t c A A c A

(2)

A sinusoidal signal has been used to define the current. The electrical current has the form as: sin(2 )I A B ft (3) The heat transfer coefficient h can be calculated from the correlation equation of Nusselt number that described by Collis and Williams [18]. f

w

kh Nu

d

(4)

0.17

0.45Nu= 0.24 0.56Re fT

T

(5)

This equation can be used for Reynolds numbers up to about 45. The film temperature defined as:

2f wT T T .

Fig. 2. Heat balance of the heated wire.

Thermal energy balance for the receiving wire is that the stored energy in the sensor equals to the heating convection, i.e.:


30

w

w w w f a w

dTc A Nu k T T

d t

(6)

Equation (6) could be written as:

( )ww a

dTM T T t

d t

, (7)

where M is the wire time constant and it can be written as: w w w

f

c AM

Nu k

(8)

Since the thermal conductivity and the kinematics viscosity are very sensitive to the temperature, the simulation in the present work considered the correlation equations of the Kannuluik et al. [19]: 2 2( ) 2.41 10 (1 0.00317 0.000002 )fk T T T (9.a) )000008.0009414.03349.1(10)( 25 TTTf

(9.b)

3.2. The Time of Flight In order to find the time of flight between the heated and sensor wires, the governing equations of the fluid flow and heat transfer around the heated wire and sensor wires should be solved. A two dimensional model has been solved with configuration shown in Fig. 1 (b). The distance between the heated wire and each of the sensor wire in both sides is equal. The flow enters from the left with a given flow velocity U, the upper wall is assumed to be far away from the heated wire. At outlet the gage pressure is assumed to be zero, i.e. similar to the atmospheric pressure. To solve the 2-D governing equations, the following dimensionless parameters have been used: * * *

1,2* *1,2 2

* * * *

,

( ); ;

( )

; ;

; ; ; ;pff p

f p

T Tx yx y T

D D Tw T

u Pu p

U U

ckk c

k c

(10)

The unsteady governing equations (continuity, momentum and energy equations) can be written in a dimensionless form after inserting the parameters shown in Eq. 10 to be as the following: Continuity equation:

0)(1

*

**

*

*

x

u

Stt

i

(11)

*2

P pP

U

t

t *

*


31

Momentum equation

*2*

*

*

**

**

*

*

**

*

**

Re)(

Re

1T

Gr

x

u

x

u

xx

P

x

uu

t

uSt

D

D

j

i

i

j

iDji

ji

j

. (12)

Energy equation

**

**

**

***

*

***

ReRePr

1)(

D

c

iiDi

ip

E

x

Tk

xx

uT

t

TStc

, (13)

where i, j = 1, 2 for 2-D and * is the normalized viscous dissipation function which can be given by

* * *

** * *

* j i i

i j j

u u u

x x x

(14)

and

,P TT

or can be written in the form: 1 ( )T T

, (15)

where denotes the coefficient of thermal expansion at temperature T . The value of coefficient of thermal expansion explained in Schlichting [20] is given as: (1 / )1 1

PT T T T T

(16)

4. Problem Solution The governing equations for the flow around the heated and sensor wires which are consisting of the partial differential equations (9)–(14) have been solved with finite volume method (FVM). This method (FVM) transforms the partial differential equations into linear continuous equations and therefore enables us to solve complex geometries. The geometry discretization of the 2-D of the computation domain was generated in the programme Gambit. The computation domain is shown in Fig. 3. The structure of the grid layers around the three wires has constructed with a growth factor of 1.1 and a triangular grid was selected to connect between the grid layers. The number of the computed control volumes is 18,000. The diameter ratio between the heated wire and the sensor wire has been chosen to be 3. For boundary conditions; the inlet was defined with a certain value of the flow velocity and the outlet was defined with zero gauge pressure. The upper and lower boundaries are walls with no slip conditions. Also, the walls of the wires are defined as walls with no slip conditions.


32

The computational fluid dynamics program Fluent 12.1 was used to solve the system of partial differential equations of the governing equations. This program uses control-volume-based technique to convert the governing equations to algebraic equations. The equations of the mathematical model are applied to each control volume, or cell, in the computational domain. The solution of the continuity, momentum, and energy could be separated from each other by using segregated solver with an upwind differencing scheme such as second-order upwind that is used to find the face values. A 2 CPUs has been used to conduct the numerical computation. Firstly, the problem was solved for a steady state conditions. Also, a user defined function (UDF) code which was written in C language has been added to the fluent program to define the temperature of the heated wire as a function of time. The received signal in the sensor wire is defined as the average values of the temperature nodes at the wall of the sensor wire. The ordinary differential equations, Eq. 6, are solved in the function MATLAB ODE45 code considering that the heat conduction and the specific heat are functions of temperature.

Fig. 3. Sample of generated grid.

5. Results and Discussions The time shift between the current, the sending temperature signal and the received temperature signal is shown in Fig. 4 for free stream velocity of 0.1 m/s and the separation distance between pulsed wire and received wire X = 1 mm. The delay time in the heated wire (time constant) is smaller than the delay time in the fluid (time of flight). The three time components of the time lag between the sending and received wires (time inertia of the sending and receiving wires in addition to the time of flight) as a function of the flow velocity can be shown in Fig. 5a. Also, the summation of the three time components as a function of the flow velocity is shown in Fig. 5a. A comparison between the output result of the current simulation work and the experimental data of Al-Salaymeh et al. [8] appears has been carried out as shown in Fig. 5b. The distance between the heated wire and the sensor wire is 1.0 mm and the diameter of the wires is 12.5 m . Fig. 5b illustrates also the three time components which are the time constant for the pulsed and received wires in addition to the time of flight. The effect of the free stream velocity on the time constant of the wires and the time of flight is illustrated in Fig. 5b.


33

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.100.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11 current

curr

ent [

A]

time [s]

0

50

100

150

200

250

300

sen

din

g te

mpe

ratu

re [C

]

heated wire

14.6

14.8

15.0

15.2

15.4

rece

ivin

g te

mpe

ratu

re [C

]

receiving temperature from the sensor

Fig. 4. The current signal in the heated wire, the sending temperature signal and the received temperature signal. The effect of the ratio of the separation distance between the pulsed wire and the sensor wire to the pulsed wire diameter, X/D, on the sensitivity and the uncertainty of results of the thermal flow sensor has been investigated. About 19 numerical models were built with different values of X/D ratio within the range 3 < X/D < 183 and for different free stream velocities starting from 0.1 m/s till 10 m/s, i.e. 0.1 m/s < U < 10 m/s. The diameter of the heated wire is selected to be 3 times the diameter of the sensor wire (D/Ds=3) in order to have a good temperature signal to reach the sensor wire. If the diameter of the heated wire is chosen to be small, then the temperature signal vanishes before it reaches to the sensor wires. The numerical simulation has been conducted for unsteady flow and therefore the time step for the computation was selected to be 0.01 ms. Fig. 6 shows the time shift as a function of free stream velocity for different values of the separation distance ratio X/D.

0 5 10 15 20 25

0.1

1

10

time

[s]

velocity [m/s]

total time lag [experimental] total time lag [numerical] time of flighttime lag in sending wiretime lag in reciving wire

Fig. 5a. The three time components of the time lag between the sending and received wires (time inertia of the sending and receiving wires in addition to the time of flight) as a function of the flow velocity.


34

0 5 10 15 20 25

5

10

15

20

25

30

Tim

e [s

]

Velocity [m/s]

Total time lag (experimental) Total time lag ( Numerical )

Fig. 5b. A comparison between the present numerical results and the experimental data of the total time lag at X = 1.2 mm and U=.01 m/s.

0,010

0,100

1,000

10,000

100,000

0,01 0,10 1,00 10,00

U (m/s)

Tim

e (m

s)

X/D=3.33

X/D=6.67

X/D=8.33

X/D=12.5

X/D=16.67

X/D=41.67

X/D=66.67

X/D=75

X/D=83.33

X/D=91.67

X/D=100

X/D=108.33

X/D=116.67

X/D=125

X/D=141.67

X/D=150

X/D=158.33

X/D=166.67

X/D=183.33

Fig. 6. The time lag between the heated and sensor wires as a function of free stream velocity for different ratios of separation distance X/D.

Figs. 7 (a-f) show the heated and received temperature signals at different values of the separation distance X and at a certain value of the flow velocity. It is clear from Figs. 7 (a-f) that as the flow velocity increases, the time shift between the sending and received temperature signal decreases, which makes it difficult to determine the time shift at high flow velocities. In addition, the amplitude of the temperature signal at the sensor wire decreases as the separation distance increase until it almost vanishes in case of X/D > 183.33. The influence of the wires separation distance on the strength of the received temperature signal can be shown in Fig. 8. The strength of the received temperature signal can be defined as:


35

ratio max, min, sta T = /r rT T T, (17)

where max,rT and min,rT values are taken from Figs. 7 (a-f). Bradbury and Castro [4] explained that the

time of flight consist of two components; the diffusive time and the convection time which depends mainly on the velocity of the free-stream velocity and the separation distance ratio X/D, in other wards,

/c X U . At low flow velocity the diffusion method dominates the heat transfer and the value of

diffusion time is 2 /d X . The Peclet number (Pe) is used usually to show the influence of the

diffusion time on the convection time. The Peclet number could be defined as:

2

/ Time of convection ( ) Re.Pr

/ Time of diffusion

X UPeclet number Pe

X

(18)

From this equation, when 0Pe this means that there is no convection and there is pure diffusion. In contrast, as Pe , the convection time is dominant and the convection governs the fluid and heat with no diffusion.

450 455 460 465 470 475 480 485 490 495 500 505300

350

400

450

500

550

Time (ms)

Tem

pera

ture

(K

)

Sending temperatureX/D=3.33X/D=6.67X/D=8.33X/D=12.5X/D=16.67X/D=41.67X/D=66.67X/D=75X/D=83.33X/D=91.67X/D=100X/D=108.33X/D=116.67X/D=125X/D=141.67X/D=150X/D=158.33X/D=166.67

Fig. 7a. The sending and the received temperature signal at different values of X and U=0.01 m/s.

370 380 390 400 410 420 430

350

400

450

500

550

Time (ms)

Tem

pera

ture

(K

)

Sending TemperatureX/D=3.33X/D=6.67X/D=8.33X/D=12.5X/D=16.67X/D=41.67X/D=66.67X/D=75X/D=83.33X/D=91.67X/D=100X/D=108.33X/D=116.67X/D=125X/D=141.67X/D=150X/D=158.33X/D=166.67X/D=183.33

Fig. 7b. The sending and the received temperature signal at different values of X and U=0.1 m/s.


36

330 340 350 360 370 380300

350

400

450

500

Time (ms)

Tem

pera

ture

(K

)

Sending temperatureX/D=3.33X/D=6.67X/D=8.33X/D=12.5X/D=16.67X/D=41.67X/D=66.67X/D=75X/D=83.33X/D=91.67X/D=100X/D=108.33X/D=116.67X/D=125X/D=141.67X/D=150X/D=158.33X/D=166.67X/D=183.33

Fig. 7c. The sending and the received temperature signal at different values of X and U=1 m/s.

230 240 250 260 270 280 290 300300

350

400

450

500

Time (ms)

Tem

pera

ture

(K

)


Fig. 7d. The sending and the received temperature signal at different values of X and U=3 m/s.

245 250 255 260 265 270 275 280

300

350

400

450

500

Time (ms)

Tem

pera

ture

(K

)


Fig. 7e. The sending and the received temperature signal at different values of X and U=5 m/s.


37

340 345 350 355 360 365 370 375300

350

400

450

500

Time (ms)

Tem

pera

ture

(K

)


Fig. 7f. The sending and the received temperature signal at different values of X and U= 10 m/s.

0

0,1

0,2

0,3

0,4

0,5

0 50 100 150 200X/D

(Tm

ax-T

min

)/T

sta

U=0.1 m/sU= 1 m/sU= 3 m/sU=5 m/sU=10 m/s

Fig. 8. The received temperature ratio as a function of the separation distance ratio X/D for different values of the free-stream velocity.

The uncertainty of the results and the sensitivity of HWA could be discussed in Fig. 9 which shows the position intercept /U X at different values of X/D ratio. The true value of the result should be at the position of intercept / 1.0U X .The uncertainty could be define as the deviation from this value. The sensitivity of the time-of-flight sensor at a certain Peclet number could be defined as the slope of the curve. For the ratio of X/D < 66.67, the reading of the phase shift (time shift) has a big uncertainty because the diffusion governs more than convection. However, the sensitivity is high in this region. When the ratio of X/D > 66.67, the results show a big uncertainty at low Peclet numbers and therefore the uncertainty becomes low at higher values of Peclet number. Any how, the sensitivity of HWA becomes very low at a high separation distance between the heated and received wires. 6. Conclusion This work has presented a numerical investigation for the behavior of bi-directional micro thermal flow sensors which utilizes three parallel wires. The goal of this study is to determine the effects of the sensor parameters such as the flow velocity U and aspect ratio X/D on the time shift between the heated and the sensor wire.


38

0,000

0,500

1,000

1,500

2,000

2,500

3,000

0,01 0,10 1,00 10,00 100,00 1000,00

Peclet number

(U

)/X

X/D=3.333X/D=6.667X/D=8.333X/D=16.667X/D=66.667X/D=75X/D=83.333X/D=91.667X/D=100X/D=108.33X/D=116.667X/D=125X/D=141.667X/D=150X/D=158.33X/D=166.667X/D=183.33

Fig. 9. The position of intercept /U X as a function of the Peclet numbers for different values of X/D ratio and a certain value of diameter ratio D/Ds=3.

The effect of the aspect ratio X/D on the time of flight was investigated. Many numerical models were built using the ratio of the heated wire diameter to the sensor diameter / 3D Ds for the range of aspect ratios of 3.33 / 183.33X D . The frequency of the current in the heated wire was selected to be 30 Hz to prevent interface between the temperature signals of the heated and received wires within the desired velocity range and to keep the temperature amplitude of the received signal. It has been found that the influence of diffusion heat transfer on the time of flight can be occurred at low values of the Peclet number, i.e. / 66.67 X D . The Peclect number which is the ratio between the convection time and the diffusion time determines the relative contribution of the convective and diffusive heat transfer modes between the heated and received wires. The sensitivity and the uncertainty of the present micro thermal flow sensors increase when the separation distance X decreases due to the influence of diffusion on the time of flight. Acknowledgments The authors greatly appreciate the support received from the Lehrstuhl für Strömungsmechanik (LSTM), Friedrich-Alexander-Universität, Erlangen-Nürnberg. The financial support of the first author, Mr. M. Al-Amayreh, from Alexander Mayer-Stiftung is highly appreciated. Prof. A. Al-Salaymeh was financially supported by DFG (Deutsche Forschungsgemeinschaft) when carrying out this research. References [1]. B. Walt, Instrumentation Reference Book, 3rd edition, Butterworth-Heinemann, U. S., 2003. [2]. A. Al-Salaymeh, Flow velocity and volume flow rate sensors with a wide band width, Ph. D. Dissertation,

Technischen Fakultat der Universitat Erlangen –Nurnberg, 2001. [3]. J. Chen, Development and Characterization of Surface Micromachined, Out-of-Plane Hot-Wire

Anemometer, Journal of Microelectromechanical System, Vol. 12, Issue 6, 2003, pp. 7-18. [4]. L. J. Bradbury, I. P. Castro, A Pulsed-Wire Technique for Measurements in Highly Turbulent Flows,

J. Fluid Mech., Vol. 49, 1971, pp. 657-691.

High sensitivity High uncertainty


39

[5]. I. P. Castro, Pulsed Wire Anemometry, Experimental Thermal and Fluid Science, Elsevier Science Publishing Co., 1992.

[6]. F. Durst, A. Al-Salaymeh, J. Jovanovic, Theoretical and Experimental Investigations of a Wide Range Thermal Velocity Sensor, Meas. Sci. Technol., Vol. 12, 2001, pp. 223-237.

[7]. F. Durst, A. Al-Salaymeh, P. Bradshaw, J. Jovanovic, The Development of a Pulsed-Wire Probe for Measuring Flow Velocity with a Wide Bandwidth, Int. J. of Heat and Fluid Flow, Vol. 24, 2003, pp. 1-13.

[8]. A. Al-Salaymeh, J. Jovanovic, F. Durst, Bi-Directional Flow Sensor with a Wide Bandwidth for Medical Applications, Int. J. Medical Engineering and Physics, Vol. 26, 2004, pp. 623-637.

[9]. A. B. Bauer, Direct measurement of velocity by hot-wires anemometry, AIAA J., Vol. 3, 1965, pp. 1189-1191.

[10]. J. M. Elliott, J. P Davis, D. L. Beduhn, Thermal Time of flight Signal Guard, U. S. Patent 5 698 795, 1997. [11]. J. Kielbasa, J. Rysz, A. Z. Smolarski, B. Stasicki, The Oscillatory Anemometer, Fluid Dynamic

Measurements (D. J. Cockrell, Ed. ), Leicester University Press, Leicester, 1972, pp. 65-67. [12]. K. Breuer, MEMS Sensors for Aerodynamic Applications - the Good, the Bad (and the Ugly), AIAA,

Vol. 251, 2000, pp. 1-10. [13]. F. Jiang, Y. Tai, R. Karen, M. Gaustenauer, C. Ho, Theoretical and Experimental Studies of

Micromachined Hot-Wire Anemometers, International Electron Devices Meeting (IEDM), San Francisco, 1994, pp. 139-142.

[14]. A. Al-Salaymeh, and M. Ashhab, Modelling of A Novel Hot-Wire Thermal Flow Sensor with Neural Nets under Different Operating Conditions, Sensors and Actuators, Vol. 126, Issue 1, 2006, pp. 7-14.

[15]. M. I. Amayrah, A. Al-Salaymeh, M. Kilani, A. T. Al-Halhouli, Numerical Prediction of a Bi-Directional Micro Hot Wire Anemometer Using Three Parallel Wires, in Proceedings of the 3rd International Conference on Thermal Engineering: Theory and Applications, Amman, Jordan, May 21-23, 2007.

[16]. H. H. Bruun, Hot-Wire Anemometry, Principles and Signal Analysis, Oxford University Press, Oxford, 1995.

[17]. A. Al-Salaymeh, On the Convective Heat Transfer from Circular Cylinders with Applications to Hot-Wire Anemometry, Int. Journal of Heat and Technology, Vol. 23, Issue 2, 2005, pp. 109-114.

[18]. D. C. Collis, M. J. Williams, Two-dimensional convection from heated wires at low Reynolds numbers, J. Fluid Mech., Vol. 6, 1959, pp. 357-384.

[19]. W. G Kannuluik, E. A Carman, The Thermal Conductivity of Rare Gases, Proc. Phys. Soc., B 65 1952, pp. 701-709.

[20]. H. Schlichting, K. Gersten, K. Gersten, Boundary-Layer Theory, 8th Edition, Springer Press, Germany, 2000.

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