1 2011
Systems & Biomedical Engineering Department Faculty of Engineering, Cairo
University
Prof. Bassel Tawfik
Biomedical Measurements
1/1/2011

2
Lecture 4: Flow & Velocity Measurements (2)
1.
Other methods of flow measurement
2.
Biomedical Applications
3.
Topic of the Day: Biomimetic Sensors
1.1 Differential Pressure (The Pneumotachometer)
In a differential pressure transducer device, flow is calculated by measuring the pressure drop across an obstruction inserted in the flow. The differential pressure flow meter is based on the
Bernoulli Equation, where the pressure drop and the further measured signal is a function of the square flow speed (see figure next page and Bernoulli equation in Appendix B).
Adjacent figure is from the website of
OMEGA corp. It shows the basic concept of using differential pressure to measure flow rate.
The calculation of fluid flow rate by reading the pressure loss across a pipe restriction is perhaps the most commonly used flow measurement technique in industrial applications (Figure 2-1). The pressure drops generated by a wide variety of geometrical restrictions have been well characterized over the years.
In medical applications, flow (denoted in the figures below as V') is derived from the pressure difference across a small fixed resistance . This resistance is offered by either a fine metal mesh ( Lilly type – Figure 3) or arrays of capillaries arranged in parallel ( Fleisch type – Figure 4).
Figure 3: Physical appearance of differential pressure transducers.
The pressure drop across the resistance is linearly proportional to flow
at relatively low flows, when the flow pattern is laminar. Turbulence makes the relationship nonlinear. The tapered conic shape of the pneumotachometer’s ends helps achieve laminar flow over a wide range of flows.
Biomedical Measurements | Bassel Tawfik

3
Lecture 4: Flow & Velocity Measurements (2)
Figure 3: Fleisch type pneumotachometer Figure 4: Lilly-type pneumotachometer
Figure 5: Pressure-Flow relationship of the differential pressure type flow meter
Biomedical Measurements | Bassel Tawfik

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Lecture 4: Flow & Velocity Measurements (2)
1.2 Variable Area Flow meters (Rotameters)
The rotameter is the most widely used variable area flow meter because of its low cost, simplicity, low pressure drop, relatively wide range, and linear output. It is constructed of a calibrated (transparent) tube with a trapped bob (float) that moves freely inside the tube. The tube is mounted vertically where the upper end is slightly wider than the lower one
(tapered). This increasing area requires a larger amount of fluid to force the float higher.
Rotameters can be used to manually set flow rates by adjusting the valve opening while observing the scale to establish the required process flow rate. The Figure 6: A primitive (portable) fluid to be measured enters at the bottom of the anesthesia machine with 2 rotameters, one for O2 and the other for N2O. tube, passes upward around the float, and exits the top. When no flow exists, the float rests at the bottom. When fluid enters, the metering float begins to rise. In liquids, the float rises due to a combination of the buoyancy of the liquid and the velocity head of the fluid. With gases, buoyancy is negligible, and the float responds mostly to the velocity head.
Float
The float moves up and down in proportion to the fluid flow rate and the annular area between the float and the tube wall.
As the float rises, the size of the annular opening increases. As this area increases, the differential pressure across the float decreases. The float reaches a stable position when the upward force exerted by the flowing fluid equals the weight of the float.
In an early design, the rotameter had slots which caused the float to spin for stabilizing and centering purposes. Because this float rotated, the term rotameter was coined.
Every float position corresponds to a particular flow rate for a particular fluid's density and
viscosity. Hence, the flow rate can be determined by matching the float position to a calibrated scale on the outside of the rotameter. Many rotameters come with a built-in valve for adjusting flow manually.
Several shapes and materials of float are available depending on the application under consideration. Floats typically are machined from glass, plastic, metal, or stainless steel for corrosion resistance. They should have a sharp edge at the
Figure 7: Cross section of a rotameter.
Biomedical Measurements | Bassel Tawfik

5
Lecture 4: Flow & Velocity Measurements (2) point where the reading is observed on the tube-mounted scale. For improved reading accuracy, a glass-tube rotameter should be installed at eye level.
Different Gases
A correlation rotameter has a scale from which a reading is taken. This reading is then compared to a correlation table for a given gas or liquid to get the actual flow in engineering units. Correlation charts are readily available for nitrogen, oxygen, hydrogen, helium, argon, and carbon
Where q is the volumetric flow rate, U max maximum velocity of fluid, D diameter, and D f t
is the float diameter.
is the
is the tube dioxide. While not nearly as convenient as a direct reading device, a correlation meter is more accurate. This is because a direct-reading device is accurate for only one specific gas or liquid at a particular temperature and pressure. A correlation flow meter can be used with a wide variety of fluids and gases under various conditions. In the same tube, different flow rates can be handled by using different floats.
Glass-tube rotameters are often used in applications where several streams of gases or liquids are being metered at the same time or mixed in a manifold, or where a single fluid is being exhausted through several channels.
It also is possible to operate a rotameter under vacuum. For applications requiring a wide measurement range, a dual-ball rotameter can be used. This instrument has two ball floats: a light ball (typically black) for indicating low flows and a heavy ball (usually white) for indicating high flows. The black ball is read until it goes off scale, and then the white ball is read. One such instrument has a black measuring range from 235-2,350 ml/min and a white to 5,000 ml/min.
Performance
Rotameters can be calibrated to an accuracy of 0.50 % AR over a 4:1 range, while the inaccuracy of industrial rotameters is typically 1-2 % FS over a 10:1 range. Purge and bypass rotameter errors are in the 5% range. If operating conditions remain unaltered, rotameters can be repeatable to within 0.25 % of the actual flow rate.
Because the float is sensitive to changes in fluid density, a rotameter can be furnished with two floats (one sensitive to density, the other to velocity) and used to approximate the mass flow rate. The more closely the float density matches the fluid density, the greater the effect of a fluid density change will be on the float position. Mass-flow rotameters work best with low viscosity fluids such as raw sugar juice, gasoline, jet fuel, and light hydrocarbons.
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Lecture 4: Flow & Velocity Measurements (2)
Rotameter accuracy is not affected by the upstream piping configuration. The meter also can be installed directly after a pipe elbow without adverse effect on metering accuracy. Rotameters are inherently self cleaning because, as the fluid flows between the tube wall and the float, it produces a scouring action that tends to prevent the buildup of foreign matter. Nevertheless, rotameters should be used only on clean fluids which do not coat the float or the tube. Liquids with fibrous materials, abrasives, and large particles should also be avoided.
1.3 (Axial) Turbine Flow meters 1
A turbine flow meter is a volumetric flow metering device. It is a transducer which senses the momentum of the flowing stream. It consists of a rotor and bearing assembly suspended on a shaft, which is mounted to a support device. This assembly is mounted inside a housing with a known internal diameter (Figure 1). As fluid passes through the flow meter housing, the rotor will spin at a rate proportional to
Figure 8: Details of a turbine flow meter. the volume of liquid passing through the housing.
The blades, which are usually flat but may be slightly twisted, are inclined at
Example an angle to the incident flow velocity and hence experience a torque that drives the rotor. The rate of rotation, which can be up to several tens of thousands of rpm for smaller meters, is detected by a pickup, usually a magnetic type, and registration of each rotor blade passing implies the passage of a fixed volume of fluid. A modulated carrier pick-off sensor may also be used to detect the turn (passing) of each rotor blade and generates a
The XYZ Turbine System is a precision volumetric instrument designed specifically for respirometry volume-flow measurements. The Turbine System consists of 3 modules: Electronic Module, Flow
Transducer body with cable and connector, and the removable Turbine Cartridge. The Transducer body comprises infrared optoelectronics and cable with connector. It is not immersible. The operation of the transducer is strictly digital. It transmits electrical pulses and the pulses are counted as volume increments or calculated as flow velocity. This is the principle for the drift-free operation, long-term stability and consistent accuracy. frequency output. The frequency output can be read directly via an electronic circuit.
1 Mostly used in aerospace, petroleum and water municipality industry.
Biomedical Measurements | Bassel Tawfik

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Lecture 4: Flow & Velocity Measurements (2)
Characteristics:

The flow sensing element is relatively compact and light weight

Works with both liquid and gas

Can be used bidirectionally

Response time: is on the order of 5 ms (Depends on size and mass of the rotor and the fluid being measured)

Repeatability: up to ± 0.05% (Typically 0.1%)

Overall accuracy: up to ± 0.25% of reading over a wide turndown

Ruggedness of the design: Turbines are unaffected by vibration

Mostly invasive except when flow is measured at an end point (respired gas at mouth)

Wide operating temperature ranges: –270°C to 650°C (–450°F to 1200°F)
SPECIFICATIONS (Simplified Version)
ELECTRONIC VOLUMETRIC MODULE
FLOW RANGE:
VOLUME RANGE:
RESPIRATION RATE:
ACCURACY:
STABILITY:
WARM-UP TIME:
0.05 - 16.50 L/sec (3.0 - 1000 L/min),
Unlimited.
0 - 150 Breaths/minute.
3% (Typically 1%).
Short and long term, 100%.
None.
BTPS* COMPENSATION: Compensates from 19 to 39 C in 2 C steps
DIGITAL OUTPUT: 1: 100 pulses/liter nominal (100 us); BTPS*
POWER REQUIREIMENT: +5 V, 5%, 120 mA with the Flow Transducer plugged in
DIMENSIONS: 85 mm wide, 45 mm high, 135 mm deep;
WEIGHT: 170 gram (6.0 oz)
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Lecture 4: Flow & Velocity Measurements (2)
1.4 Hot Wire Anemometry 2
A thermal (hot wire) anemometer uses a heated probe element that is inserted into an airstream. As air velocity increases, the temperature of the heated wire decreases. Air speed (velocity) can then be inferred either from the heating power necessary to maintain the probe at a constant temperature (constant temperature type) or the change in wire temperature (constant current type). A simplified sketch of the sensor is shown in figure 9.
A hot wire type sensor must have two characteristics to make it a useful device:
(1) A high temperature coefficient of resistance
(2) An electrical resistance such that it can be easily heated with
Figure 9 an electrical current
Tungsten, platinum and a platinum-iridium alloys are commonly used materials with Tungsten having the highest temperature coefficient of resistance, (0.004/

C). The anemometer is capable of reading instantaneous values of velocity up to very high frequencies. Therefore it responds to and is capable of measuring the turbulent fluctuations in the flow field. (Most velocity measuring instruments, such as the pitot tube, respond very slowly effectively giving an average velocity over some longer time.)
A. Constant Temperature Anemometer (CTA)
Here, the current through the wire is adjusted to maintain a constant film temperature. It works based on the fact that the probe’s resistance will be proportional to the temperature of the hot wire. The bridge circuit shown in Figure 10 below is set up by setting the adjustable resistor to the resistance you wish the probe and its leads to have during operation. (The other two legs of the bridge have identical resistance.)
The servo (feedback) amplifier tries to keep the error voltage zero (meaning the resistances of the two lower legs of the bridge are equal). It will adjust the bridge voltage such that the current through the probe heats it to the temperature, which gives the selected resistance. When we put the probe in a flow, the air (or water) flowing over it will try to cool it. In order to maintain the temperature (resistance) constant, the bridge voltage will have to be increased. Thus, the faster the flow, the
Figure 10
2 An anemometer was first perceived as a device for measuring wind speed. The term is derived from the
Greek word, anemos, meaning wind.
Biomedical Measurements | Bassel Tawfik

9
Lecture 4: Flow & Velocity Measurements (2) higher the voltage.
A very simplified version of the relationship between the output voltage (shown in figure 10 as a dial symbol) and fluid velocity (for more accurate analysis, see Appendix C):
E o
2 = A +B v n (6)
Where E o
is the voltage across the wire, v is the velocity of the flow normal to the wire and A, B, and n are constants. We may assume n = 0.45 (or for classroom purposes, just a square root) this is common for hot-wire probes. “A” can be found by measuring the voltage on the hot wire with no flow, i.e. for v = 0, A = E o
2 .
Hot-wire anemometry can be used to measure and test respiratory
(pulmonary) function similar to turbine flow meters. The hot wires may be installed within the same tapered tube as shown in figure 11. In other industrial applications and in calibration devices, the flow meter may look like that of figure 12.
Notice that temperature probes also look like hot wire anemometer probes, so do not judge the function of a device just by its appearance!
Figure 11 Figure 12
B. Constant Current Anemometer (CCA)
In the constant current mode, nearly fixed electric current flows through the wire which is exposed to the flow velocity. The wire attains an equilibrium temperature resulting from the balance between internal heat generation due to electrical resistance (Joule heating) and the convective heat loss from the wire to the moving fluid. The wire temperature must adjust itself to changes in the convective losses until a new equilibrium temperature is obtained. Since the convection coefficient is a function of the flow velocity, the equilibrium wire temperature is a measure of the velocity. The wire temperature can be measured in terms of its electrical resistance where the relationship between the resistance and temperature is known a priori.
Biomedical Measurements | Bassel Tawfik

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Lecture 4: Flow & Velocity Measurements (2)
Typical Specifications
Specifications Airflow series -
Hot Wire Anemometer
TAVM410
Metric Imperial
Velocity
Velocity range
Volume
Accuracy of velocity reading
- greater of :
Resolution
Temperature
0- 20.00 m/s none
±5% of reading or ±0.025m/s
±0.01 m/s
Range
Temperature Accuracy
Temperature Resolution
Probe
-10C° to +60°C
±0.3°C
0.1°C
Probe dimensions extended
Diameter at tip 7mm
Diameter of telescope at base 13 mm
Cable length
Data Logging
1016 mm
1 m none
Logging Interval
Battery
Battery life
Weight
4 x AA
270 g
~ 15 hours with alkaline cells
0.0 to 4000 fpm none
±5'/min
1 ft/min
32 °F to +176°F
±1°F ±1 digit
0.1°F
40.00"
0.28"
0.51 "
39.5"
9.6 oz
TAVM430
Metric Imperial
0-30 m m/s 0.0 to 6000 fpm
0 - 2700 m3/sec 0 - 999,999 cfm
±3% of reading or
±0.015m/s
1 ft/min
±3'/min
±0.01 m/s
-18C° to +93°C 0°F to +200°F
±0.3°C ±0.5°F
0.1°C 0.1°F
1016 mm
7mm
13 mm
1 m
40.00"
0.28"
0.51 "
39.5"
12700 readings +100 IDs
1 second to 1 hour
270 g 9.6 oz

11
Lecture 4: Flow & Velocity Measurements (2)
Spirometry is the measurement of volume and flow rate of gas breathed in and/or out of the lungs under maximal effort. Spirometers may be handheld or PC-based. They are mostly based on flow rate measurements (figure 1) but sometimes measure volumes directly
(figure 2).
Spirometry relies on the cooperation of the subject, and hence is not suitable for babies, subjects under anesthesia or bed-ridden patients.
Figure 1: Desktop spirometer. Notice some of the specs of the system such as the LCD display screen, printout, keypad to enter data, and type of data displayed
(figure 3). Notice also the noseclip.
Figure 3: Typical maximum flow-volume curve (loop).
Figure 2: Direct volume measuring spirometer.

12
Lecture 4: Flow & Velocity Measurements (2)
Spirometry can only obtain information about spontaneous breathing (volume, flow, and pressure at mouth during rest, exercise, and maximal efforts). This is due to the fact that spirometry measures volume deviations from a baseline (FRC = Lung volume at rest).
Consequently, spirometry cannot obtain information about absolute lung volume, namely, FRC
(Functional Residual Capacity) and RV (Residual Volume).
Measurement of absolute lung volume can be obtained by three techniques known as Nitrogen washout, Helium dilution, and Body plethysmography. We shall describe these methods in brief.
B.1 Nitrogen Washout
Nitrogen represents approximately 80% of the air in the lungs at any point of time 3 . Measuring
Nitrogen is useful in many medical, industrial and environmental applications such as monitoring environmental regulatory compliance. Nitrogen is measured using gas analyzers and the resulting values are displayed in particles per million (ppm). Other important gas analyzers in the medical field are Oxygen and Carbon dioxide analyzers.
The method is based on the premise that if we can extract all the nitrogen in the lungs (from which the word “washout” came) and calculate its volume, then this volume would be equal to
0.8 FRC. How would we collect all the N2 in the lungs? The answer is by continually inspiring air that has no N2, or simply pure O2, while directing expired gas to a collection chamber. Nitrogen concentration in the expired gas would then be measured until it displays no change in concentration. This indicates that the lungs are completely depleted of N2. Finally,
FRC = [1/0.8] [concentration of N2 in chamber] x [Total volume of gas expired]
There are several sources of error in this measurement, namely:
(1) Gas trapped in dead space of instrument
(2) Gas trapped in alveoli due to emphysema and other pulmonary diseases, i.e. poorly
ventilated or non-ventilated areas will not be included as part of FRC
(3) Existence of gas in chamber prior to beginning of experiment
(4) Need for adjustment to BTPS (Body Temperature & Saturated Pressure)
3 Assuming very little or no trapped air in alveoli which would contain more CO2 and hence less N2.
Biomedical Measurements | Bassel Tawfik

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Lecture 4: Flow & Velocity Measurements (2)
B.2 Helium Dilution (Closed Circuit)
Poorly ventilated or non-ventilated areas will not be included as part of FRC when measured with this technique.
B.3 Body Plethysmography
Assuming that the change in volume (

V) = 71 ml, and that the change in lung gas pressure (

P) =
20 mmHg, and that Ps = 760 mmHg, the calculation proceeds as follows:
PV

( P
 
)(
 
V )
Multiplying out
PV

PV
      
Adding out PV’s, rearranging, and factoring
V


(
 
P )

P
Since

P is quite small relative to P (20 mmHg versus 713 mmHg), then
V


V

P
P
V

71 ml (713 mmHg)

20 mmHg
, ml = Volume at FRC
Biomedical Measurements | Bassel Tawfik

14
Lecture 4: Flow & Velocity Measurements (2)
F i i g u r e e 4 T h e e “ M e a a d t y p e
” ” b o d y p l e e t t h y s m o g r a p h .
.
T h e s u b j j e c c t t b r r e e a t t h e e s n o r r m a a l l l y w h i i l e e t h e e s s t t o p c o c k i s s c c o n n e c c t t e d t o t h e e e e n v i i r o n m e e n t t .
T h e e n t h e e s s t t o p c c o c k i i s t t u r n e d t t o o c c c l l u d e t h e e a i r r w a y w h i l l e t t h e s u b j e e c c t m a a k e s s i n s s p i r r a a t t o r y a n d e e x p i r r a a t t o r y e f f o r t s s , h i i s s a a l l v e o l l a a r r p r r e s s s u r r e b e e i i n g r r e e c c o r r d e d u s i i n g a a p r r e s s u r r e e g a u g e e c o n n e e c t t e e d t t o t t h e a a i i r r w a y p r r o x i i m a l l t t o t t h e e s t t o p c o c c k .
.
T h e e K r r o g h s p i i r r o m e e t t e e r r m e e a s s u r r e s s

V , , a n d t t h u s o n e e d e t t e e r r m i i n e e s s

V / /

P , , a a n d c a a n c c a l l c c u l l a a t t e T G V .
.
Biomedical Measurements | Bassel Tawfik

15
Lecture 4: Flow & Velocity Measurements (2)
Laboratory fume hoods are designed to protect laboratory personnel by preventing contaminants such as chemical vapors, dusts, mists and fumes from escaping into the laboratory environment. Fume hoods also provide lab personnel with a physical barrier to chemicals and their reactions.
Fume hoods are evaluated each year to verify their proper operation. Where possible, face velocity will be set at 100 feet per minute (fpm) with sash at 18". The method most commonly used to verify this velocity is anemometry.
Sketch showing one type of fume hoods
Urodynamic investigations are the only way to evaluate bladder and urethral functions. Urodynamic investigations allow characterization of the pathophysiological aspects of the different symptoms, give some elements to determine accurately the prognosis and help for the choice of the therapeutic strategy.
Measurement of the urinary flow rate confirms the presence of a bladder outlet obstruction. Urine flow rate is measured with a flow-meter that measures a quantity of fluid passed per unit time, expressed in milliliters per second.
Figure 1: A photo of a urodynamic system showing the control/display module and the catheter.
Uroflow depends on detrusor contractility and urethra-sphincter resistance. The voided volume should be more than 150ml. Patients are instructed to void normally, as in usual conditions, with a comfortably full bladder. Measurement of residual urine volume (by means of ultrasound or catheterization) is necessary to interpret the uroflowmetry results. The precise shape of the flow curve is decided by detrusor contractility, the presence of any abdominal straining and by the bladder outlet.
Biomedical Measurements | Bassel Tawfik

16
Lecture 4: Flow & Velocity Measurements (2)
Different parameters are studied. Flow rate (ml/s) is defined as the volume of fluid expelled via the urethra per unit time. Voided volume is the total volume expelled via the urethra. Maximum flow rate is the maximum measured value of the flow rate after correction for artifacts; it must be greater than 15ml/s. Voiding time is total duration of micturition and includes interruptions.
Flow time is the time over which a measurable flow actually occurs. Average flow rate is voided volume divided by flow time. A normal flow curve is a smooth curve without any rapid changes in amplitude. A decreased detrusor power and/or a constant increased urethral pressure determine a lower flow rate and a smooth, flat flow curve. A constrictive obstruction (urethral stricture) results in a plateau-like flow curve. A compressive obstruction (cystocele) shows a flattened asymmetric flow curve. Rapid changes in flow rate may have several causes: sphincter/pelvic floor contraction or relaxation (detrusor sphincter dyssynergia), voluntary flow interruption, abdominal straining and artifacts (movement of the stream in the collecting device, patient movements).
Cystometry is the method used to measure the pressure-volume relationships of the bladder.
Classically, the intravesical (total bladder) pressure is measured while the bladder is filled, but this simple technique is not accurate because intravesical pressure is not representative in all the cases of true detrusor pressure.
Reference: Elemental Healthcare (UK)
Biomedical Measurements | Bassel Tawfik

17
Lecture 4: Flow & Velocity Measurements (2)
4
CUSA® consists of a hollow titanium tip that vibrates along its longitudinal axis at 23 kHz.
When the tip of the instrument is brought in contact with tissue, mechanical energy is transferred, creating high- and low-pressure areas. When the pressure is below the vapor pressure of tissue fluid, vaporfilled vacuoles form within the cells. These vacuoles expand and collapse as pressure rises and falls with each cycle, generating forces that fragment
Figure D-1: Principle of an Acoustic Vibrator. The vibrating titanium tip of the distal end of the handpiece provides fluid pressure waves the cells.
Tissue damage is confined to an forcing existing intra- and extra-cellular cavities to grow and collapse. This sudden collapse at supersonic speeds leads to tissue cavitation. Vibration is initiated by a transducer that contracts and area of about 25 to 50µm next to the tip, with minimal thermal expands. On top of the transducer a titanium tip is mounted that is designed specially to function as an amplifier for the amplitude of the transducer. Magnifications up to ten times the amplitude are injury and protein denaturation.
A greater amount of tissue possible. The largest possible amplitude is preferred. A large amplitude can be achieved more easily by lower frequencies. damage results from the use of Twenty-three kHz is more or less the lower limit to ensure that we a scalpel or laser. With are well above the audible frequency. Frequencies are typically 19 electrosurgical manipulation, to 40 kHz, with maximum amplitudes 180 to 350 kHz.
the extent of tissue damage exceeds 1,000 to 4,000 mm.
Another potential advantage of the CUSA® system is the selectivity of its dissection, a consequence of the fact that the rate of cavitational activity is proportionate to the water content of the cells, i.e., soft, fleshy tissues with high-water content are fragmented readily.
Therefore, different tissues fragment at different rates leading to the possibility of dissection without affecting blood vessels. Because of these advantages, the CUSA® has been utilized for dissection of water-dense collagen and elastin-rich structures, including ureters and nerves.
4 Surgical Technology International: Website at: www.ump.com/articles/cusa/CUSA.htm
Biomedical Measurements | Bassel Tawfik

18
Lecture 4: Flow & Velocity Measurements (2)
5
Specifications 730944 730945 730946
Connection Diameter
Metric
Dead Space Volume
7 mm
0.1 ml
Differential Pressure
(mmH2O)
6.25 mmH2O
Inner Diameter Metric 1.35 mm
75 mm Length Metric
Maximum Flow Rate
(ml/sec)
Nominal Flow Rate
(ml/sec)
Nominal Sensitivity
(ml/sec/mmH2O)
0.8 ml
6.25 mmH2O
6 mm
75 mm
0.9 ml
6.25 mmH2O
6 mm
75 mm
12 ml/sec 20 ml/sec 60 ml/sec
9 ml/sec 15 ml/sec 40 ml/sec
1.4
7 mm
2.08
7 mm
6.4
Simple Calirations
(pressure = flow)
Species
Weight Metric
6 mmH2O
= 6 ml/sec,
10 mmH2O
= 10 ml/sec
Mouse
(50 gr)
140 g
1 mmH2O
= 2 ml/sec, 5 mmH2O
= 10 ml/sec,
10 mmH2O
= 20 ml/sec
Small
Guinea
Pig or rat
(170 gr)
140 g
1 mmH2O
= 6.4 ml/sec, 5 mmH2O
= 32 ml/sec,
10 mmH2O
= 64 ml/sec
Guinea
Pig or Rat
(350 gr)
140 g
730947
10 mm
2 ml
6.25 mmH2O
9 mm
75 mm
150 ml/sec
100 ml/sec
10.56
1 mmH2O
= 1.12 ml/sec, 5 mmH2O
= 5.61 ml/sec,
10 mmH2O
= 7.9 ml/sec
Small animal,
Cat (750 gr)
140 g
730948
1 mmH2O
= 52.8 ml/sec, 5 mmH2O
= 264 ml/sec,
10 mmH2O
= 528 ml/sec
Cat or
Dog (5.5 kg)
140 g
11 mm
4 ml
6.25 mmH2O
10 mm
60 mm
350 ml/sec
250 ml/sec
52.8
730949 730950
19 mm 30 mm
14 ml
6.25 mmH2O
18 mm
60 mm
35 ml
6.25 mmH2O
28 mm
60 mm
1200 ml/sec 3000 ml/sec
1000 ml/sec 2500 ml/sec
160
1 mmH2O =
140 ml/sec,
5 mmH2O =
700 ml/sec,
10 mmH2O
= 1327 ml/sec
320
1 mmH2O =
321 ml/sec,
5 mmH2O =
605 ml/sec,
10 mmH2O
= 3076 ml/sec
730951
45 mm
80 ml
6.25 mmH2O
43 mm
60 mm
8000 ml/sec
6500 ml/sec
800
1 mmH2O
= 800 ml/sec, 5 mmH2O
= 4000 ml/sec,
10 mmH2O
= 8000 ml/sec
Dog or Pig
(27 kg)
140 g
Large
Animal
150 g
Large
Animal
250 g
730952
60 mm
172 ml
6.25 mmH2O
58 mm
70 mm
14000 ml/sec
11000 ml/sec
1600
1 mmH2O
= 1400 ml/sec, 5 mmH2O
= 7000 ml/sec,
10 mmH2O
= 14000 ml/sec
Large
Animal
400 g
730963
NA
460 ml
6.25 mmH2O
78 mm
100 mm
25000 ml/sec
21000 ml/sec
3200
NA
Large
Animal
650 g
5 From the datasheet of Harvard Apparatus: http://www.harvardapparatus.com/webapp/wcs/stores/servlet/product_11051_10001_41166_-
1_HAI_ProductDetail_37841__N

19
Lecture 4: Flow & Velocity Measurements (2)
6
A special form of the Euler’s equation derived along a fluid flow streamline is often called the
Bernoulli Equation
6 Source: www.engineeringtoolbox.com

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Lecture 4: Flow & Velocity Measurements (2)
For steady state incompressible flow the Euler equation becomes (1). If we integrate (1) along the streamline it becomes (2). (2) can further be modified to (3) by dividing by gravity.
Head of Flow
Equation (3) is often referred to the head because all elements has the unit of length.
Dynamic Pressure
(2) and (3) are two forms of the Bernoulli Equation for steady state incompressible flow. If we assume that the gravitational body force is negligible, (3) can be written as (4). Both elements in the equation have the unit of pressure and it's common to refer the flow velocity component as the dynamic pressure of the fluid flow (5).
Since energy is conserved along the streamline, (4) can be expressed as (6). Using the equation we see that increasing the velocity of the flow will reduce the pressure, decreasing the velocity will increase the pressure.
This phenomena can be observed in a venturi meter where the pressure is reduced in the constriction area and regained after. It can also be observed in a pitot tube where the
stagnation pressure is measured. The stagnation pressure is where the velocity component is zero.
Example - Bernoulli Equation and Flow from a Tank through a small Orifice
Liquid flows from a tank through a orifice close to the bottom. The Bernoulli equation can be adapted to a streamline from the surface (1) to the orifice (2) as (e1):
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Lecture 4: Flow & Velocity Measurements (2)
Since (1) and (2)'s heights from a common reference is related as (e2), and the equation of continuity can be expressed as (e3), it's possible to transform (e1) to (e4).
A special case of interest for equation (e4) is when the orifice area is much lesser than the surface area and when the pressure inside and outside the tank is the same - when the tank has an open surface or "vented" to the atmosphere. At this situation the (e4) can be transformed to
(e5).
"The velocity out from the tank is equal to speed of a freely body falling the distance h." - also known as Torricelli's Theorem.
Example - outlet velocity from a vented tank
The outlet velocity on a tank were
h = 10 m can be calculated as
V
2
= [2 x 9.81 x 10] 1/2 = 14 m/s
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Lecture 4: Flow & Velocity Measurements (2)
If the tanks is pressurized so that product of gravity and height (g h) is much lesser than the pressure difference divided by the density, (e4) can be transformed to (e6).
The velocity out from the tank depends mostly on the pressure difference.
Example - outlet velocity from a pressurized tank
The outlet velocity of a pressurized tank where p
1
= 0.2 MN/m 2 , p
2
= 0.1 MN/m 2 A
2
/A
1
= 0.01, h = 10 m can be calculated as
V
2
= [(2/(1-(0.01) 2 ) ( (0.2 - 0.1)x10 6 /1x10 3 + 9.81 x 10)] 1/2 = 19.9 m/s
Coefficient of Discharge - Friction Coefficient
Due to friction the real velocity will be somewhat lower than this theoretic examples. If we introduce a friction coefficient c (coefficient of discharge), (e5) can be expressed as (e5b).
The coefficient of discharge can be determined experimentally. For a sharp edged opening it may be as low as 0.6. For smooth orifices it may bee between 0.95 and 1.
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Lecture 4: Flow & Velocity Measurements (2)
Consider a wire that's immersed in a fluid flow. Assume that the wire, heated by an electrical current input, is in thermal equilibrium with its environment. The electrical power input is equal to the power lost to convective heat transfer,
Where I is the input current, R w
is the resistance of the wire, T w
and T f
are the temperatures of the wire and fluid respectively, A w
is the projected wire surface area, and h is the heat transfer coefficient of the wire. The wire resistance R w
is also a function of temperature according to,
Where a is the thermal coefficient of resistance and R
Ref
is the resistance at the reference temperature T
Ref
. The heat transfer coefficient h is a function of fluid velocity v f
according to
King's law,
Where a, b, and c are coefficients obtained from calibration (c ~ 0.5). Combining the above three equations allows us to eliminate the heat transfer coefficient h,
Continuing, we can solve for the fluid velocity,
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Lecture 4: Flow & Velocity Measurements (2)
Two types of thermal (hot-wire) anemometers are commonly used: constant- temperature and constant-current.
The constant-temperature anemometers are more widely used than constant-current anemometers due to their reduced sensitivity to flow variations. Noting that the wire must be heated up high enough (above the fluid temperature) to be effective, if the flow were to suddenly slow down, the wire might burn out in a constant-current anemometer. Conversely, if the flow were to suddenly speed up, the wire may be cooled completely resulting in a constantcurrent unit being unable to register quality data.
For a hot-wire anemometer powered by an adjustable current to maintain a constant temperature, T w
and R w
are constants. The fluid velocity is a function of input current and flow temperature,
Furthermore, the temperature of the flow T f
can be measured. The fluid velocity is then reduced to a function of input current only.
For a hot-wire anemometer powered by a constant current I, the velocity of flow is a function of the temperatures of the wire and the fluid,
If the flow temperature is measured independently, the fluid velocity can be reduced to a function of wire temperature T w
alone. In turn, the wire temperature is related to the measured wire resistance R w
. Therefore, the fluid velocity can be related to the wire resistance.
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Lecture 4: Flow & Velocity Measurements (2)
The volume of a number (n) of gas molecules depends on the thermodynamic temperature (T) and the ambient pressure (P). The following relationship holds for dry gas:
V = n·R·T/P
Where R = gas constant, and T is expressed in Kelvin (K = 273.2 + ºC). Air and expired gas are made up of gas molecules and water vapor. In a gas mixture saturated with water vapor and in contact with water (such as occurs in the lung) the number of water molecules in the gas phase varies with temperature and pressure. As the number of molecules is not constant, the above gas law should be applied to dry gas. This also holds outside the lung when gas saturated with water vapor is compressed or cools down.
As gas volumes vary with temperature and pressure, the conditions during which they are measured must be recorded. To that end volume displacement spirometers need to be equipped with a thermometer; if meters employ other measuring principles the manufacturer should state clearly how corrections need be performed as the composition of the gas and gas viscosity may then come into play.
BTPS In respiratory physiology lung volumes and flows are standardized to barometric pressure at sea level, body temperature, saturated with water vapor: body temperature and pressure, saturated.
ATPS Measured at ambient temperature, pressure, saturated with water vapor (e.g. expired gas, which has cooled down): ambient temperature and pressure, saturated.
ATP Like ATPS, but not saturated with water vapor (e.g. room air).
STPD Oxygen consumption and carbon dioxide delivery are standardized to standard temperature (0 ºC), barometric pressure at sea level (101.3 kPa) and dry gas: standard temperature and pressure, dry.
Temp.
ºC
16
17
18
19
20
Corr. factor
1.123
1.118
1.113
1.107
1.102
Conversion from ATPS to BTPS conditions
Temp.
ºC
Corr. factor
Temp.
ºC
Corr. factor
21
22
23
24
25
1.097
1.091
1.086
1.080
1.074
26
27
28
29
30
1.069
1.063
1.057
1.051
1.045
Temp.
ºC
31
32
33
34
35
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Corr. factor
1.039
1.033
1.026
1.020
1.013

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Lecture 4: Flow & Velocity Measurements (2)
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Lecture 4: Flow & Velocity Measurements (2)
Biomimicry (from bios , meaning life, and mimesis , meaning to imitate) is a relatively new science that studies nature, its models, systems, processes and elements and then imitates or takes creative inspiration from them to solve human problems sustainably. (Wikipedia)
In general, sensors provide us with a quantified and objective scale to evaluate things. This helps us determine their properties (e.g. temperature, force, weight, etc.).
Some of the human sensors (senses) have been supplemented or enhanced by external manmade sensors. These are the senses of sight, hearing, and touch. For instance, sight can be enhanced (make minute things appear larger, far objects closer), extended (unseen objects seen as in IR sensing), or replaced (still in its primitive form where the optic nerve is directly fed with signals from imaging devices). Sound can also be amplified and processed to improve hearing.
But smell and taste have always been challenging to replicate or enhance. There is no need to stress the importance of these two senses to human life.
Today industries such as: aircraft, automobile, sensor, chemical and pharmaceutical makers are investigating biomimetic processes for several reasons such as: superior performance, low cost raw materials, recyclability and mass production compatibility.
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Lecture 4: Flow & Velocity Measurements (2)
1.1 Flying Robotic Insects
DARPA’s latest call for proposals merited an interesting article in the Toronto Star. The advanced projects agency has requested labs to submit research plans that will lead to:
“.. the controlled arrival of an insect within five meters of a specified target located 100 meters away. It must then remain stationary indefinitely, unless otherwise instructed … to transmit data to sensors providing information about the local environment.”
The preferred methodology is to implant computational units in the larvae and allow them to integrate with the nervous system through pupation; a high goal indeed and one that is so far from any proven science that it certainly qualifies as ‘blue sky’ research. Last year DARPA gave out 3.1 billion for equally outside the box, high concept research.
1.2 Sharks on demand ( http://technology.newscientist.com/article/mg18925416.300.html
)
The Defense Advanced Research Projects Agency (DARPA) has been funding several labs interested in basic sensory biology. Their goal is to define a system that will allow remote control of a free swimming shark. The project has been under way for two years now with the major focus on the olfactory and the electrosensory systems. A recent meeting of the research group held in Hawaii has been reported in the New Scientist. Jelle Atema, better known for working on lobsters, has successfully implanted an electrode in each olfactory tract that causes a shark to veer one way or another. Tim Tricas is attempting similar things with the electrosensory system but is not yet able to build the interface with the shark. There are apparently trials scheduled for the Atema system to be held in open ocean off Florida.
(2) NSF (National Science Foundation – USA)
The National Science Foundation has a CAREER award that rewards particularly promising young scientists with a 5 year (rather than the standard three year) research grant. The University of
Delaware’s Xinyan Deng has won one to study robotic flies.
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Lecture 4: Flow & Velocity Measurements (2)
“…one of the goals of the research is to study the flight attributes observed in insects and to investigate the underlying principles that result in flight stability and also lead to differences in performance in order to develop a methodology and guidelines for designing flapping-wing microaerial vehicles.”
Beside mathematical modeling and theoretical studies, Deng hopes to design and fabricate workable flapping-wing microaerial vehicles, or miniature flying robots, that are capable of stable and maneuverable flight with biomimetic sensors.
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Lecture 4: Flow & Velocity Measurements (2)
Jacquie van Santen Wednesday, 22 February 2006
ABC Science Online
Some Australian frogs create their own insect repellent, some resembling rotten meat and others roasted cashew nuts or thyme leaves, researchers find.
The research team, which includes Associate Professor Mike
Tyler of the University of Adelaide and entomologist Dr Craig
Williams from James Cook University , publishes its findings online in the journal Biology Letters .
Frogs produce a number of chemicals in their skin, including hallucinogens, glues and antimicrobials, to ward off infection and stop other animals from trying to eat them.
"We wanted to test Professor Tyler's [belief] that they should also produce an insect repellent," says Williams.
The research team studied five species of Australian frogs, including the Australian green tree frog.
Using massage and acupuncture techniques, they stimulated the muscles beneath the frogs' skins to produce secretions.
Frogs produce a range of chemicals in their skins, including ones that smell like cashew nuts.
Now scientists say some of these
"What we found was that frogs produce a variety of chemicals in their skin and these ooze out of the pores of their skin when they are stressed," says Williams. chemicals repel insects (Image:
Michael Tyler)
The secretions, some of which repel mosquitos, have different smells depending on a number of factors such as what the frog eats.
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Lecture 4: Flow & Velocity Measurements (2)
"The frogs produce hundreds of chemicals and one frog's smell might be made up of six or seven different chemicals, so they all smell quite different," Williams says.
"The chemicals evaporate very quickly from the skin and it's the volatile smell that repels [the mosquitos]."
A new mosquito repellent?
The team found that skin secretions from an Australian green tree frog, for example, protected a mouse from mosquitos when the secretion was applied.
The researchers say this is the first time a vertebrate has been found to have its own in-built mosquito repellent.
But the frog secretion was not as repellent as DEET, diethyl-m-toluamide, the ingredient in most commercial mosquito sprays.
Williams doesn't believe that a new brand of natural insect repellent will result from the research.
"The smell is just not very good ... some smell of rotting flesh, some of nuts, some of thyme leaves."
Last year the frog-sniffing research team won an Ig Nobel prize for its work on skin secretions.
The prizes honour "achievements that first make people laugh, and then make them think".
At the time, the researchers talked about frog smells that reminded them of Bombay curry and cut grass.
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