FIELD OF INVENTION:
The present invention in particular relates to a method of controlling a device
having a(/array of) shape memory alloy element(/s) and more specifically, the
invention relates to methods, for using Shape Memory Alloy (SMA) Wire as
Sensor for Flow Regime detection in particular, flow characterization of Taylor
Bubble Flow Regime of Two- Phase Flows, under internal flow conditions.
DESCRIPTION OF THE RELATED ART:
Shape Memory Alloy (SMA) is referred as a group of alloys generally consisting
of Cu-Al-Ni, Ni-Ti, Fe-Mn-Si and Cu-Zn-AI. These alloys can return to their predeformed
shape upon heating to higher temperature. Because of this capability of
memorizing its original shape, they are known as Shape Memory Alloys. The
reason behind Shape Memory effect is attributed to the phase transformation from
martensite (low temperature) to austenite (high temperature) phase, which also
leads to a considerable difference in the electrical resistance of the SMA. If
properly tuned, this resistance change can capture the change of flow
characteristics which further can be used to determine several two-phase flow
parameters.
US20120065744 relates to a method of modeling Shape Memory Alloy (SMA)
element to predict the response of the SMA element. This includes obtaining the
resistivity of the SMA element over a range of a physical property of the SMA
element; correlating variations in the obtained resistivity with respect to the
physical property of the SMA element, identifying behavioral differences in the
resistivity for the different phases of the SMA element; calculating a rate of
change of the resistivity of the SMA element over a period of time; calculating the
derivative of the rate of change in the resistivity of the SMA element over the
period of time; and comparing real time data of the physical property to the
derivative of the rate of change to predict the response of the shape memory alloy
element. This invention relates to modeling SMA properties in contrast to use of
SMA as a sensor.
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US Publication No. 20120109573 relates to a method of sensing an ambient heat
transfer condition surrounding a shape memory alloy element which includes
heating of the shape memory alloy element, sensing the resistance of the shape
memory alloy element, and measuring the period of time taken to heat the shape
memory alloy element to a pre-determined level of resistance characteristics. The
ambient heat.transfer condition surrounding the shape memory alloy element is
calculated by referencing a relationship between the period of time taken to heat
the shape memory alloy to the pre-determined level of the resistance
characteristics and .the ambient heat transfer condition.
US Publication "No. 20120046791 relates to a method of improving the speed and
consistency of response of a shape memory alloy actuator under varying ambient
and operating conditions. The method includes probing the shape memory alloy
by periodically determining an electric signal strength at which it will undergo
forward or reverse phase transformation, while avoiding actual phase
transformation; priming the shape memory alloy by bringing it close to phase
transformation; initiating phase transformation; and maintaining the shape
memory alloy in the phase transformed state. The electric signal strength at which
the shape memory alloy will undergo phase transformation is determined by
identifying a cusp feature in the electric resistance of the shape memory alloy
which closely precedes phase transformation.
US Patent No. 6,546,806 provides a multi-range force sensor comprising a load
cell made of a shape memory alloy, a strain sensing system, a temperature
modulating system, and a temperature monitoring system. The ability of the force
sensor to measure contact forces in multiple ranges is affected by the change in
temperature of the shape memory alloy. The heating and cooling system functions
to place the shape memory alloy of the load cell in either a low temperature, low
strength phase for measuring small contact forces, or a high temperature, high
strength phase for measuring large contact forces. Once the load cell is in the
desired phase, the strain sensing system is utilized to obtain the applied contact
force. The temperature monitoring system is utilized to ensure that the shape
memory alloy is in the desired phase. This invention is different from the
proposed invention as the proposal measures two-phase flow characteristics.
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US Patent No. 5735607 relates to. a temperature sensor that permanently indicates
that it has been exposed to temperatures exceeding a critical temperature for a predetermined
time period. An element of the sensor made from shape memory alloy
changes shape when exposed, even temporarily, to temperatures above the .
austenitic temperature of the SMA. The shape change of the SMA element causes
the sensor to change between two readily distinguishable states.
The article entitled "Exploitation of shape memory alloy actuator using resistance
feedback control and its development" talks about the exploitation of shape
memory alloy actuator using resistance feedback control and its development The
resistivity of SMAs can be determined from the volume fractions or the
martensitic and austenitic phases.. This characteristics leads to the application
where the resistance of the SMAs is used as a parameter of strain of SMAs
[Hiroki Cho, Takaei Yamamoto, Yuji Takeda, Akihiko Suzuki, Toshio Sakuma;
Progress in Natural Science: Materials International, Volume 20, Pages 97-103;
13 March 2012]. The present invention does not measure strain but the change in
resistance due to change in.the thermal boundary condition manifested by the
flowing phases, i.e. liquid and gas, over the SMA wire.
Present invention provides a Shape Memory Alloy (SMA) based sensor for the
determination of important two-phase flow characteristics namely average and
instantaneous phase velocities, length of the liquid and gas phases and frequency
of bubbles, etc., during Taylor Bubble flows or intermittent flows. It is a very
novel application of SMA wires in characterizing two-phase flow parameters. The
sensor is compact, high fidelity response, can be integrated in pipes and ducts,
requires minimum peripheral support devices, provides repeatable and reliable
data, which can be quickly post-processed to provide the required information of
interest. A single measured quantity, i.e., resistance of the wire is sufficient to
generate all the quantities of interest.
OBJECTS OF THE INVENTION:
The principal objective of the present invention is to provide a Shape Memory
Alloy (SMA) based sensor for the determination of certain two-phase flow
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characteristics namely velocity and length of the liquid and gas phase during
Taylor Bubble flows.
Another objective of the present invention is to capture the changing heat transfer
characteristics in a Taylor bubble type two-phase flow using the resistance
feedback of a SMA wire that leads to the determination of two-phase flow
parameters such as velocity and length of the gas phase.
Another objective of the present invention is to use the physical characteristics of
the SMA wire for the purpose of detecting two-phase flows parameters, i.e.,
considerable change in resistance of SMA wire because of the phase
transformation happening in it in- between the transition temperature range. This
drastic change in resistance is brought about by flowing two-phases; i.e. when
liquid plug flows over the SMA wire, which is subjected to a constant voltage, it
offers a different heat transfer characteristics as compared to when a gas bubble is
flowing over it. Thus, the changing boundary conditions in terms of the flowing
liquid, changes the operating temperature of the SMA, which triggers a phasetransition,
eventually leading to a change in resistance of the SMA wire,, which
can be detected via measurement of th voltage and current flowing across the
wire.
SUMMARY OF THE INVENTION:
The present invention provides a Shape Memory Alloy (SMA) based sensor for
. the determination of certain important two-phase flow characteristics namely
average and instantaneous phase velocity and length of the liquid and gas phases,
respectively, during two-phase • flows, especially Taylor Bubble flows and
intermittent flows. The invention also provides a method to capture the changing
heat transfer characteristics of such flows. The resistance feedback offered by the
SMA can lead to determination of two-phase flow parameters such as velocky and
length/phase-distribution of the liquid and/or gas phases. Taylor flow regime is
one category in the ambit of two-phase flows and it is a type of flow pattern
wherein elongated gas bubbles separated by liquid slugs flow in a thermal system.
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It is a subset of intermittent flows which are commonly encountered in Two-ohase
flows, especially in mini-micro flow channels.
The invention also provides a method to capture the changing heat transfer
characteristics in a Taylor bubble type two-phase flow or intermittent flows using
a SMA wire comprising the following steps:
a) Characterization of the change in the electrical resistance of SMA wire on
increasing its temperature owing to the phase transformation happening
from martensite to austenite;
b) Measurement of Phase transformation time scale; and
c) Determination of design parameters required for the detection of twophase
flow upon getting the resistance-temperature characteristics and
phase transformation time scale of the SMA wire.
In the present invention, a SMA wire with an input DC voltage source is
surrounded by silicone oil. Total energy given to the SMA is the DC voltage
across it times the current flowing through it. A part of this energy is dissipated in
the medium via the forced heat convection by the fluid flowing across it and the
remaining part is expected to raise the temperature of the SMA wire.
As soon as the phase changes in a two-phase flow, thermal diffusivity changes
and the IMusselt Number also changes because of a change in the Prandtl number
of the new convective fluid medium (either gas phase or the liquid phase, as the
case may be). Variation in these two parameters changes the heat transfer
coefficient which results in changing heat dissipation from the SMA wire, this
finally resulting to a change in its temperature which is captured by its change in
the effective electrical resistance of the SMA.
BRIEF DESCRIPTION OF THE DRAWINGS:
Further objectives and advantages of this invention will be more apparent from
the ensuing description when read in conjunction with the accompanying
drawings and wherein:
Figure 1 shows flow chart of the operating principle of SMA based sensor for
two-phase flow detection (h is the heat transfer, coefficient in the medium);
Figure 2 shows schematic view of experimental setup used to demonstrate the
applicability of Shape Memory Alloy (SMA) based sensor in two-phase flow (in
this case, Oil-Air);
Figure 3 shows the pictorial view of two SMA wires in a T-junction glass tube;
Figure 4 presents schematic of a Taylor bubble flow pattern; and
Figure 5 presents schematic of flow around SMA wire (v: velocity of flow, d:
diameter of SMA wire).
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
In the present invention, a SMA wire with an input DC voltage source is
surrounded by silicone oil. Total energy given to the SMA is the DC voltage
across it times the current flowing through it. A part of this energy is dissipated in
the medium via the forced heat convection by the fluid flowing across it and the
remaining part would raise the temperature of the SMA wire. Mathematically, the
energy conservation equation for SMA wire can be stated by equation (1.1)-
mCp¥- = VI-hA{T-TJMd)
dt (1.1)
where
V: voltage (V), I: current (A)
h: heat transfer coefficient (W/m2K), A: surface area of the wire (m2)
T: temperature of the wire (°C), Tnuid: temperature of the surrounding fluid (°C)
m: mass of wire (kg), Cp: Specific heat capacity of the wire (J/KgK)
Heat transfer coefficient for a single phase flow is determined as following:
Nuxk
«=—
* ' (1-2)
where
Nu: Nusselt Number
k: Thermal conductivity of the convective flow medium
d: Diameter of SMA wire (Characteristic length)
- i _ I 3 1 - 0 - 3 - 2 0 1 S. 17 : 2 5
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As soon as the phase flowing over the SMA wire changes in a two-phase flow,
thermal diffusivity and the 'Nusselt Number also changes because of a change in
the Prandtl number of the new convective fluid medium. Variation in these two
parameters changes the resulting heat transfer coefficient which results in
changing heat dissipation rate from the SMA wire, this finally resulting in a
change in its own temperature, which is captured by its altering effective electrical
resistance.
Referring to Figure 2, which shows flow chart of the operating principle of SMA
based sensor for two-phase flow detection (h is the heat transfer coefficient in the
medium). A SMA wire with an input voltage source is kept across a cross section
in a two-phase flow. Its heat dissipation in each phase will change because of
different heat transfer coefficient of gas and liquid medium which then would
result in temperature variation of SMA wire, further leading to a change in its
electrical resistance. Detection of the start and finish of gas and liquid phase leads
to determination of two-phase flow parameters.
Depending on the requirement of determining two-phase flow characteristics,
different configurations (single wire, wire mesh, parallel wires etc.) of SMA wire
could be used across the cross section of tube. In the present invention,
determination of velocity of gas phase is focused upon and accordingly a single
wire across a cross section is used. Shape Memory Alloy (SMA) wires are readily
available, NiTi being most common for its stability and availability.
The method to capture the changing heat transfer characteristics in a Taylor
bubble type two-phase flow using a SMA wire comprises the following steps:
Characterisation of SMA Wire: The idea behind this invention' is the drastic
change in the electrical resistance of SMA on increasing its temperature owing to
the phase transformation happening from martensite to austenite. Therefore,
firstly it is important to. determine how electrical resistance changes with
temperature and stress (in any). '
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Measurement of Phase transformation time scale: Phase transformation time scale
is the time taken by SMA to complete the phase transformation either from
austenite to martensite or for the reverse phase transformation from martensite to
.austenite. It is to be noted that the two time scales could be different depending on
the type of SMA wire employed. These time scales impose a lower limit on the
length of each phase and an upper limit on the frequency of phase change in a
two-phase flow which can be handled effectively by the SMA, making it
imperative top design the SMA according to the required specific practical
applications.
Upon getting the resistance-temperature characteristics and phase
transformation time scale of the SMA, design parameters required for the
detection of two-phase flow are determined.
Input Voltage to SMA wire is ascertained by Austenite Start (As) transition
temperature. It should be adjusted such that the resistance of SMA wire in the
liquid phase corresponds to its resistance of the SMA wire at As. This is done to
ensure that the sensor has maximum sensitivity and as it starts heating on the
onset of air bubble, there is a considerable change in the resistance value to be
detected easily.
Frequency of phase change for the two-phase flow is decided by the sum of phase
transformation time .scale of the SMA wire from martensite to austenite and from
austenite to martensite. Again this is to secure that SMA wire gets enough time to
reach its steady state during heating as well as codling.
— r +r +f
(1.3)
where
theating: Time taken for phase transformation from martensite to austenite
tcooiing: Time taken for phase transformation from austenite to martensite
tbutrei-: Buffer time allowed for SMA to reach its steady state
BE LH I 3 1 - 0 3 - 2 0 1 5 - 17 : 2 5-
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Zero stress or loosely held wire condition is maintained to safeguard the SMA
wire from stress, as stress and strain-affects the resistance-temperature behavior of
the SMA wire. SMA wire may contract upon heating i.e. on its phase
transformation from martensite phase to austenite phase; hence sufficient length
of SMA wire should be used in a loosely held condition for consistent results.
Sampling frequency of the Data Acquisition System should be such that the time
interval between continuous readings is much smaller than the phase
transformation time scale of SMA wire so that the start and finish of the bubble
can be easily identified.
Figure 2 shows schematic view of experimental setup used to demonstrate the
applicability of Shape Memory Alloy (SMA) based sensor in two-phase flow (in
this case, Oil-Air). Two-phase flow of oil and air in a T-junction glass tube is
generated by using thermal bath, control valve, air cylinder and rotameter. Source
of oil is thermal bath and air cylinder for air, both of which are passed
continuously to create a bubble train in the glass tube. Control Valve and
rotameter controls the length, speed of air bubble and oil flow, while the electrical
circuit records the resistance of SMA wire with respect to time.
Figure 3 shows the pictorial view of two SMA wires in a T-junction glass tube.
One SMA wire is sufficient for the detection of two-phase flow; however two
SMA wires fixed at a known distance can determine certain two phase flow
characteristics like velocity and length of air bubble. Time lag in the resistance
drop for two SMA wires would lead to the velocity of air bubble which if used
with time taken by SMA wire to reach its initial state would lead to air bubble
length. Two SMA wires separated by 20 cm are inserted 40 cm downstream of the
T-junction. An electrical circuit consisting of NI Chassis cDAQ-9172, NI 9025,
voltage source, two standard \Cl resistors is utilized to record the resistance-time
data of both SMA wires with a sampling frequency of 1000 Hz.
Figure 4 presents schematic of a Taylor bubble flow pattern. Taylor flow regime
is one category in the ambit of two-phase flows and it is a type of flow pattern
wherein elongated gas bubbles separated by liquid slugs are flowing.
I P Q DE L.HI . 3 1 - 8 3 - .2 G1 5- 1 7 : 2 5,
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Figure 5 presents schematic of flow around SMA wire where v represents velocity
of flow and d represents diameter of SMA wire.
Numerous modifications and adaptations of the system of the present
invention will be apparent to those skilled in the art, and thus it is intended
by the appended claims to cover all such modifications and adaptations
which fall within the true spirit and scope of this invention.

WE CLAIM:
1. A Shape Memory Alloy (SMA) based sensor for the determination of two-phase flow characteristics of the liquid and gas phase during Taylor Bubble flows and a method to capture the changing heat transfer characteristics in a Taylor bubble type two-phase flow using a SMA wire.
2. The Shape Memory Alloy (SMA) based sensor and method wherein twophase
flow characteristics are velocity and length of the liquid and gas
phase during Taylor Bubble flows.
3. The Shape Memory Alloy (SMA) based sensor and method as claimed in
claim 1 wherein the method to capture the changing heat transfer
characteristics in a Taylor bubble type two-phase flow by using a SMA
wire with which its resistance feedback can lead to determination of twophase
flow parameters namely velocity and length of gas phase.
4. The Shape Memory Alloy (SMA) based sensor and method as claimed in
claim 1 wherein the method to capture the changing heat transfer
characteristics in a Taylor bubble type two-phase flow using a SMA wire
comprises the following steps:
a. Characterization of the change in the electrical resistance of SMA
wire on increasing its temperature owing to the phase
transformation happening from martensite to austenite;
b. Measurement of Phase transformation time scale; and
c. Determination of design parameters required for the detection of
two-phase flow upon getting the resistance-temperature
characteristics and phase transformation time scale of the SMA
wire.
5. The Shape Memory Alloy (SMA) based sensor and method as claimed in
claim 1 wherein a SMA wire with an input DC voltage source is
surrounded by silicone oil.
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6. The Shape Memory Alloy (SMA) based sensor and method as claimed in
claim 1 wherein total energy given to the SMA is the DC voltage across it
times the current flowing through it. A part of this energy is dissipated in
the medium via the forced heat convection by the fluid flowing across it
and the remaining part would raise the temperature of the SMA wire.
7. The Shape Memory Alloy (SMA) based sensor and method as claimed in
claim 1 wherein as soon as the phase changes in a two-phase flow, thermal
conductivity changes and the Nusselt Number also changes because of a
change in the Prandtl number of the new convective fluid medium.
8. The Shape Memory Alloy (SMA) based sensor and method as claimed in
claim 1 wherein variation in the two parameters changes the heat transfer
coefficient which results in changing heat dissipation from the SMA wire,
this finally resulting to a change in its temperature which is captured by its
electrical resistance.