Gas and liquid contact apparatus – With external supply or removal of heat – Temperature or humidity sensor
Reexamination Certificate
1998-09-10
2001-02-06
Smith, Duane (Department: 1724)
Gas and liquid contact apparatus
With external supply or removal of heat
Temperature or humidity sensor
C261S043000, C261S064300, C261S107000
Reexamination Certificate
active
06182951
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and apparatus for introducing a precise amount of a first fluid into a second flowing fluid. This invention particularly relates to a new and improved method and apparatus for providing a precise amount of gas having a precisely controlled humidity.
Many applications in science and industry require an apparatus that creates a controlled amount of a first fluid to be introduced into a second fluid, such as a gas having a precise flow rate and a precisely controlled humidity. For instance, some material corrosion testing applications require such an apparatus to determine the reaction of a material over time upon exposure to a controlled liquid-gas mixture. Tests are typically performed using a higher liquid concentration of the liquid-gas mixture, in an effort to decrease the duration of the test. Data is then extrapolated to model the material's reaction over time. However, because the results are extrapolated, any error caused by an imprecisely controlled liquid-gas mixture will be magnified. Thus, the need for an apparatus that creates a controlled testing environment with a gas having a precise flow rate and a precisely controlled humidity is critical to ensure the accuracy of these types of tests.
A wide variety of conventional devices and methods used to produce a precise gas flow having a precisely controlled humidity are known in the art. Various systems introduce a liquid, such as water, into a gas stream using a calibrated leak. Generally, water is stored in a small vial having a very small orifice through which water vapor is metered. The humidity of the gas stream is modified by either adjusting the gas flow over the device or by adjusting the temperature of the vial. The accuracy of this apparatus is limited because changes in the gas stream flow rate or the temperature of the vial of water result in substantial changes in the humidity of the gas. Furthermore, this known apparatus requires controllers for varying gas flow and vial temperature.
Flow regulators and pressure regulators are distinct devices having different functions and characteristics. A pressure regulator differs from a flow regulator in that pressure regulators are actuated into opening or closing by sensing pressure of a fluid at its outlet, which regulation can be independent of the fluid flow. A flow regulator is actuated into opening or closing by sensing the flow rate of a fluid, which regulation can be independent of pressure.
Another conventional apparatus, known as a permeation cell, employs a permeable vial containing the liquid to be introduced into the gas stream. The liquid permeates through the vial and into the gas stream to produce the desired humidity. However, the aforementioned problems also affect this apparatus. In particular, vial temperature changes result in significant gas stream humidity changes. This apparatus also requires additional components for controlling gas flow.
Successive dilution is another known method for producing a precise gas flow with a precise humidity. With this method, dry gas is split into minor and major gas streams. After both gas streams are passed through separate flow controllers, the minor gas stream is passed through a liquid bubbler and reintroduced into the major gas stream. The reintroduction of the minor gas stream into the major gas stream produces the desired humidity. However, this method also has a number of inherent problems. First, the system requires that the major gas stream have a very large volumetric flow rate—on the order of liters per minute—to blend the gas streams to the required humidity. As a result, production of a product gas stream having a low flow rate cannot be practically accomplished. Also, costly detection equipment is required for measuring moisture vapor content. Further limitations of this method include the need for flow control valves in each gas stream, for controlling the process based on detection equipment data, and a proportional integral derivative controller for continuous adjustment of the flow control valves in order to maintain the desired humidity in the product gas stream.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a fluid transfer system for introducing a first fluid into a second fluid flowing through a fluid carrier, wherein the system is designed for precisely controlling both the mixture rate of the fluids and the flow rate of the second fluid through the fluid carrier.
It is another object of this invention to provide a fluid transfer system capable of maintaining production of a precisely controlled fluid mixture under changing external conditions, such as fluctuations in ambient temperature and pressure.
It is another object of this invention to provide an instrument for independently verifying the calibration of dew point measurement devices.
It is another object of this invention to provide a fluid transfer apparatus that does not require costly components such as flow control valves, proportional integral derivative controllers, and humidity detection equipment.
In accordance with the present invention, these and other objects are accomplished by a fluid transfer system comprising a first fluid, a second fluid, a fluid carrier length having an inlet and an outlet, a constant temperature source for maintaining the first fluid at a constant temperature, and a constant pressure source connected to the fluid carrier inlet for introducing the second fluid into the fluid carrier at a constant pressure. The first fluid surrounds and permeates at least a portion of the fluid carrier length. A mixture of the first and second fluids is exhausted through the fluid carrier outlet.
In the preferred embodiment, a tubular fluid carrier is provided for directing the second fluid through the fluid carrier system. In this embodiment, the first fluid constant temperature source comprises a liquid bath, and the second fluid constant pressure source comprises a pressure regulator connected to the fluid carrier inlet.
A fluid transfer system in accordance with an alternate embodiment of the invention further comprises an inlet manifold, an outlet manifold, and at least one additional permeable fluid carrier length. In this embodiment, the constant pressure source is connected to the inlet manifold for regulating pressure which, in turn, regulates the flow of the second fluid into the inlet manifold. The first fluid surrounds and permeates at least a portion of each of the fluid carrier lengths, and a controlled mixture of the first and second fluids exits the fluid carrier lengths through the outlet manifold.
In yet a further embodiment of the invention, a fluid transfer system comprises a permeable fluid carrier tube having inlet and outlet ends, a water bath having a constant water temperature, and a gas source connected to the inlet end of the permeable fluid carrier tube via a pressure regulator. The gas source communicates a gas, through the pressure regulator, to the tube inlet. The pressure regulator fixes the pressure of the gas. The constant temperature bath surrounds and permeates at least a portion of the fluid carrier tube, allowing the water to mix with the flowing gas. A controlled mixture of dry gas and water vapor is expelled through the outlet end of the carrier tube. The flow rate of the gases through the tube is controlled, at least in part, by controlling the ratio of carrier tube inner diameter to carrier tube length.
A method of producing a mixture of a first and second fluids includes providing a first fluid at a constant temperature, communicating a second fluid at a constant pressure into an inlet end of a fluid carrier, submersing a length of the fluid carrier within the first fluid such that the first fluid permeates the fluid carrier to mix with the second fluid, and flowing the mixture toward an outlet end of the fluid carrier.
REFERENCES:
patent: 4036915 (1977-07-01), Lucero et al.
patent: 4474051 (1984-10-01), Fukuda et al.
patent: 5996976 (1999-12-01), Murphy et al.
Kin-Tek, “Certified C
Hallman, Jr. Russell L.
Truett James C.
Ackerman Senterfitt & Eidson, P.A.
Hopkins Robert A.
Lockheed Martin Energy Systems, Inc.
Smith Duane
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