Thermal measuring and testing – Heat flux measurement
Reexamination Certificate
1999-08-23
2001-12-04
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Heat flux measurement
C374S141000, C374S179000, C122S504200
Reexamination Certificate
active
06325535
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to devices for determining radiant heat flux.
2. Description of the Related Art
When a mass is placed in an enclosure whose walls are at a temperature above that of the mass, the temperature of the mass will increase even if the enclosure is evacuated. The process by which heat is transferred from the enclosure to the mass by virtue of the temperature difference between the enclosure and the mass, without the aid of any intervening medium, is called thermal radiation. The emission of thermal radiation is governed by the temperature of the enclosure.
Direct-fired heaters are commonly used in many applications. Direct-fired heaters have an interior combustion chamber in which an ignition source, fuel and oxygen react to form a flame. The flame is commonly formed near the bottom of the heater and the combustion products exit the top of the heater through a flue. Fluid tubes are positioned along walls of the heater. The difference between density of the hot gases inside the heater and the density of cooler ambient air creates a vacuum pressure inside the heater. A vacuum pressure is a pressure below the ambient atmospheric pressure.
Radiant heat flux is the radiant heat transfer per unit area across a control surface. In direct-fired heaters, it is desirable to measure the radiant heat flux rate because locally high flux rates may shorten equipment life and increase the need for frequent cleaning of the equipment. High flux rates also cause carbon deposits to form in a fluid film at the inside wall of fluid tubes positioned inside the heater.
In order to determine the heat flux, a cooling mechanism is needed to maintain a probe tip cooler than a static equilibrium temperature inside the heater, so that a net heat transfer will occur through the tip. In the past, in-situ heat flux probes have been cooled by pumping or compressing a fluid (gas or liquid) through the probe. These devices, however, have several disadvantages. One disadvantage is these devices require moving parts such as pumps, metering devices and valves. Another disadvantage is these devices require an external supply to power the pump or compressor that transports the cooling fluid.
SUMMARY OF THE INVENTION
The present invention is for a radiant heat flux probe which may be cooled by the induction of cool air outside the heater. The probe is also capable of receiving air compressed by an external source if the gas pressure in the heater at the probe is above the outside air pressure. The heat flux probe is cooled by providing an air passage from ambient outside air to a portion of the heater having a pressure below the outside atmospheric pressure, thus causing ambient air to be induced through the heat flux probe into the heater.
A heat absorber is attached to a first end of a hollow ceramic insulating tube. A drum of the heat absorber fits through an opening in the first end of the ceramic tube and into a bore of a receptacle located inside the ceramic tube. A head of the heat absorber protrudes from the first end of the ceramic tube. The ceramic tube is a conduit to provide pressure communication between the inside of the heater and the ambient atmosphere. The ceramic material of the tube is an insulator and prevents ambient air induced through the tube from becoming too hot before it reaches the heat absorber and receptacle.
The modes of heat transfer within, from, and to the probe are different for different parts of the probe. The outside surface of the absorber head, which is exposed to the flame and hot combustion products inside the heater, is called a target. A portion of the receptacle and the heat absorber (when connected together) which has a surface exposed to the induced cooling air is referred to as a base. The portions of the heat absorber head and receptacle (when connected together) located between the base and the target is referred to as a body. At the target, there are two primary heat transfer modes. Heat is transferred to the target by thermal radiation and transferred away from the target by conduction. Within the body, heat is transferred to, through, and from the body by heat conduction. Heat is transferred to the base by conduction and is removed at the surface of the base by convection.
A thermocouple is positioned in a cylindrical slot at the second end of the receptacle. A compression nut holds the thermocouple in place in the cylindrical slot. Thermocouple wires extend from the thermocouple, through the ceramic tube, and to a temperature indicating device, such as a solid-state digital meter, located outside the heater. The ceramic tube butt fits into a first end of a pipe adapter. A second end of the pipe adapter fits into a first end of a pipe reducer. The pipe reducer is threadably connected to a plate which is rigidly attached to a wall of the heater, with the first end of the reducer inside the heater and a second end of the reducer positioned outside the heater.
A first end of a first pipe nipple fits into the second end of the pipe reducer. A second end of the first pipe nipple fits into a first port of a pipe tee. The pipe tee has a first port, a second port, and a third port. The third port of the pipe tee is open to ambient air. A first end of second pipe nipple fits into the second port of the pipe tee. A second end of the second pipe nipple fits into a first opening of a weatherhead. The weatherhead also has a second opening which is open to ambient air. The weatherhead has electrical contacts which connect to ends of the thermocouple wiring and to wire leads for instrumentation, such as a digital meter.
To determine the heat flux through a heat absorber head outer surface, a thermocouple is used to determine the temperature at a point inside the receptacle attached to the heat absorber. Using an experimental correlation, one can then determine the heat flux passing through the target.
It is, therefore, a principal object of the present invention to provide a radiant heat flux probe which is capable of being cooled without the use of an independent power supply to compress gas or pump fluid.
It is another object of the present invention to provide a radiant heat flux probe which is capable of being cooled without any moving parts.
Other objects and further scope of the applicability of the present invention will become apparent from the detailed description to follow taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 1478821 (1923-12-01), Foster
patent: 3774297 (1973-11-01), Wagner
patent: 3935032 (1976-01-01), Brandeberry et al.
patent: 4514096 (1985-04-01), Wynnyckyj et al.
patent: 4519830 (1985-05-01), Wolak
patent: 4722610 (1988-02-01), Levert et al.
patent: 4854729 (1989-08-01), Lovato
patent: 4889483 (1989-12-01), Gentry
patent: 5152608 (1992-10-01), Dutcher et al.
patent: 5718512 (1998-02-01), Ngo-Beelmann
S. B. H. C. Neal et al, “Measurement of Radiant Heat Flux in Large Boiler Furnaces-II Devel. of Flux Measuring Inst.”, Int'l J. Heat and Mass Transfer, vol. 23, pp. 1023-1031, Great Britain, 1980.*
M.C. Ziemke, Heat Flux Transducers, Instruments and Control Systems, vol. 40, pp. 85-88, (5 pages) Dec. 1967.*
TSI Technical Bulletin No. C26 “Heat Flux System”, Thermo-Systems Inc., Minneapolis, Minn., (4 pages) Dec. 1963.*
TSI Technical Bulletin No. 263 “Heat Flux System”, Thermo-Systems Inc., Minneapolis, Minn., Jul. 1963.*
NASA SP-5050, “NASA Contributions to Development of Special-Purpose Thermocouples”, pp. 55-66 1968.
Duffield Mike
Eischen James T.
Gibson Robert L.
Gibson William C.
Gutierrez Diego
Head Johnson and Kachigian
Petro-Chem Development Co. Inc.
Pruchnic Jr. Stanley J.
LandOfFree
In-situ radiant heat flux probe cooled by suction of ambient... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with In-situ radiant heat flux probe cooled by suction of ambient..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and In-situ radiant heat flux probe cooled by suction of ambient... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2573819