Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
2000-01-19
2004-01-27
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
C073S204270, C073S204150
Reexamination Certificate
active
06681625
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to integrated flow and temperature sensors for fluids, and more particularly to bidirectional flow sensors in which a heater is maintained at a constant temperature differential above the temperature of the flowing fluid.
BACKGROUND OF THE INVENTION
Modern ships employ crew members whose function is to monitor various parts of the vessel, and to operate equipment such as hoists, radar, bridge equipment, and to monitor and control valves located throughout the ship. The costs associated with maintaining a large crew are disadvantageous, and such costs include the costs associated with paying wages, maintaining the crew member in terms of food and life support (bathrooms, hot water, and the like), and also includes the costs of training the crew member for the particular job. To the extent that a ship's functions can be automated, the necessary crew can be reduced.
The problem is particularly acute in war vessels, as a relatively large crew must be maintained in order to have the resources to perform battle damage repair and recovery.
If reliable and inexpensive integrated flow sensors were available, such sensors could be located in various pipes within a ship or a factory, and their readings could be compared to determine if there were a break or leak (break) in the intervening pipe or flow path. Once identified, the damaged flow paths could be disabled by remotely-controllable valves. These flow sensors could also advantageously be used with integrated pressure sensors for determination of the state of the fluid system. Such inexpensive sensors could also be used to improve process controls in chemical and other processes.
Present-day flow sensors include rotating-propeller or linear types, differential-pressure aperture, ball-in-tapered-tube, vane or deflection type, ultrasonic, and hot-wire anemometer. The rotating-propeller is very accurate, but may degrade over time as a function of corrosion and deposits, and may fail catastrophically in the presence of large debris. The differential-pressure type of flow sensor requires an obstructing aperture or change of geometry of the flow path, which is very undesirable, and when the application requires many such sensors to be cascaded, may substantially impede the flow. Also, the small pressure changes attributable to relatively large apertures may undesirably introduce noise into the measurement. The ball-in-tube type requires a vertical orientation, and the tube must be transparent in order to optically detect the location of the ball. Additionally, in a vehicle which has vertical motion, the vertical acceleration tends to add to the gravitational force acting on the ball, and will tend to affect the reading, and therefore the accuracy. The vane deflection type of flow sensor obstructs the flow with the vane, and is not known for its accuracy. The ultrasonic type of flow sensor does not necessarily impede the flow, but is expensive, and may not be suitable for use in a noisy environment, or in an environment in which many such sensors are in use, so that the ultrasonic signals of one affect the others in the same flow path. The hot-wire anemometer is not known for use in fluids other than air, would not work in a conductive fluid, and the thin wire would be subject to breakage by circulating debris in some applications.
FIG. 1
a
is an illustration of a flow sensor as described in copending patent application Ser. No. 09/349,576, filed Jul. 8, 1999 in the name of the inventors herein. In
FIG. 1
a
, a sensor
10
includes a fluid path
12
in the form of a round pipe
14
through which fluid flows in a direction designated by an arrow
16
. Sensor
10
supports an annular peripheral electrical heating element or heater
18
. A flow of electrical energy or power is applied to heater
18
from a controller
20
by way of a set
22
of wires. A temperature sensor
24
is coupled to heating element
18
, for producing a signal representing the temperature of the heating element. The temperature-representative signal is applied to controller
20
by way of a set of wires
24
w
. Controller
20
includes a memory (Mem) designated
21
. A further temperature sensor
26
is mounted to pipe
14
at a location upstream from heating element
18
, for sensing the temperature of the fluid flowing in pipe
14
, and for generating a signal representing the temperature of the fluid. The signal representing the temperature of the fluid is applied over a set of wires
26
w
to controller
20
.
FIG. 1
b
is a representation of a cross-section of the structure of
FIG. 1
a
. In
FIG. 1
b
, the wall of pipe
14
is made from conventional materials, designated as
33
. The conventional materials may, depending-upon the temperature and pressure of the fluid flowing in path
12
, be materials such as brass, galvanized steel, stainless steel, or composite materials. In the sensing region
36
, the pipe wall can be made of the same material as pipe
14
, or can be made from a high-strength material
34
, as for example titanium, which can be substantially thinner in cross-section than the conventional materials
33
. This thinner cross-section, in turn, generally translates into better thermal transfer properties between the heater
18
, the sensors
24
and
26
, and the fluid within the sensing region
36
. The sensing region
36
is connected to pipe
14
using standard connecting techniques.
In operation of the sensor
10
of
FIG. 1
a
, the velocity of the flow of fluid is determined by sensing the upstream fluid temperature with sensor
26
, and applying electrical energy from the controller
20
to the heating element
18
at a rate sufficient to raise the temperature of the heating element, as measured by sensor
24
, to a second temperature, greater than the upstream-fluid temperature, by a fixed temperature difference. The measurement of power or the time rate of energy required to maintain the fixed temperature difference is an indication of the velocity of fluid flow in the fluid path.
In an alternative arrangement that provides a lower-cost, but lower-accuracy solution, upstream fluid temperature is estimated, rather than directly sensed, based on details of the system into which the sensor is installed. For example, if the upstream fluid is water which comes from the bottom of a lake in which the water temperature always remains at about 55° F., the upstream temperature measurement is not needed, and the upstream temperature may be assumed. This estimation obviates the need for upstream temperature sensor
26
. All calculations are then based on the assumed upstream temperature.
In yet another alternative arrangement, the heater
18
of
FIG. 1
a
is turned off periodically and allowed to attain the temperature of the fluid to provide the ambient, or upstream value. This heater-ON to heater-OFF duty cycle or period depends upon the thermal characteristics of the fluid, the sensor wall
14
(or
34
) of
FIG. 1
b
, and the expected temperature range of the fluid.
Once the fluid flow rate is known, the volume flow rate (gallons per minute, for example) is easily determined to be the product of the effective cross-section of the fluid path (the diameter of the pipe, taking into account boundary effects) multiplied by the fluid flow velocity. Given the density of the fluid, the mass flow rate (kilograms per second, for example) is easily determined as the product of the volume flow rate multiplied by the density of the fluid. Controller
20
produces a signal representing one (or all) of fluid velocity, volume flow rate, and mass flow rate, and applies it over a signal path
20
w
to a remote indicator (not illustrated).
FIG. 2
a
is a simplified schematic diagram of an analog embodiment of a temperature controller
220
which may be used in controller
20
of
FIG. 1
a
to maintain the heater temperature at a fixed value above the temperature of the upstream fluid. In FIG.
2
a
, heater
18
is illustrated as a resistor having a resistance designated as R
heater
. One end of resistor
18
is
Berkcan Ertugrul
Hoyle Scott Baxter
Duane Morris LLP
Lockheed Martin Corporation
Patel Harshad
LandOfFree
Constant-temperature-difference bidirectional flow sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Constant-temperature-difference bidirectional flow sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Constant-temperature-difference bidirectional flow sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3240282