US3651686A

US3651686A - Programable readout for delta t bar spectrometer

Info

Publication number: US3651686A
Application number: US23277A
Authority: US
Inventors: Steven F Dizio
Original assignee: Aero Vac Corp
Current assignee: Aero Vac Corp; Sanwa Business Credit Corp
Priority date: 1970-03-27
Filing date: 1970-03-27
Publication date: 1972-03-28
Anticipated expiration: 1989-03-28

Abstract

A delta T bar spectrometer, for concentration of trace quantities of a gas in a mixture as the mixture is transported along a thermal gradient tube from a warm end to a cold end, produces an enrichment sufficient for measurement by separately depositing condensed gas portions according to temperatures along the delta T bar. Removal of the concentrated gas portions according to temperature involves selectively warming portions of the delta T bar in succession beginning at the low temperature end. Zones of deposition are made sharp at the temperature at which the particular constituent first condenses, to thereby separate constituents from each other along the length of the bar. Evaporation of the condensates in succession occurs as the successive portions are warmed in an arrangement in which the delta T bar is not warmed but only segmented portions of the surface on which the condensate lies are warmed incrementally, in partial isolation from the temperature of the bar itself by the use of insulating material separating the bar from thermally conducting strips exposed to the gas mixture. A partially insulated ring so formed remains in conformity with the temperature of the bar itself during deposition. In the evaporation stage each segment or ring element is warmed through a range of only a few degrees. The quantity of heat required for this purpose is made very small. A very rapid readout of the quantities of gas constituents is achieved by sending an incremental temperature rise wave along the tube from the cold end to the hot end, without materially disturbing the overall temperature of the delta T bar and the elements return to their respective temperatures so that deposition is resumed after a brief evolution period for one or all of the deposited constituents.

Description

1ite States Patent Dizio [54] PROGRAMABLE READOUT FOR DELTA T BAR SPECTROMETER [57] ABSTRACT A delta T bar spectrometer, for concentration of trace quantities of a gas in a mixture as the mixture is transported along a [72] Inventor: Steven Dino Troy thermal gradient tube from a warm end to a cold end, 3 Assignee; v produces an enrichment sufficient for measurement by separately depositing condensed gas portions according to Filed! 27, 1970 temperatures along the delta T bar. Removal of the concentrated gas portions according to temperature involves selec- [211 23277 tively warming portions of the delta T bar in succession beginning at the low temperature end. Zones of deposition are [52] U.S. Cl ..73/25,23/294, 55/82, made sharp at the mp r at which the particular 73 17 73/23 stituent first condenses, to thereby separate constituents from 51 1111. C1. ..G0ln 25/14 oooh other along the length of. tho Evaporation of tho [58] Field of Search 73/17723 25 26,4215422 GC, densates in succession occurs as the successive portions are 73/231 23/264 273 F 294- 55/20 32 67 269 warmed in an arrangement in which the delta T bar is not warmed but only segmented portions of the surface on which 56] References Cited the condensate lies are warmed incrementally, in partial isolation from the temperature of the bar itself by the use of insu- UNITED STATES PATENTS lating material separating the bar from thermally conducting strips exposed to the gas mixture. A partially insulated ring so 3,589,169 6/1971 Lafitte et al. ..73/23 formed remains in conformity with the temperature of the bar 2,944,878 7/1960 Jacque et al. .....23/294 itself during deposition. In the evaporation stage each segment 3,043,128 7/1962 Ayers ....73/23.l or ring element is warmed through a range of only a few 3,168,823 2/1965 Reinecke etal. ....73/23.1 g The q y of hoot required for this Purpose is 3,429,904 2/1969 Eisentraut et al... .....23/294 made y small- A y rapid readout of the quantities of gas constituents is achieved by sending an incremental tempera- Primary Examiner-Richard C. Queisser ture rise wave along the tube from the cold end to the hot end, Assistant Examiner Ems Koch without materially disturbing the overall temperature of the Attorney Beveridge and De Grandi delta T bar and the elements return to their respective temperatures so that deposition is resumed after a brief evolution period for one or all of the deposited constituents.

13 Claims, 3 Drawing Figures 12 13" 13' 13 11 L l 1 f IPIROGIRAMAIBLIE READOUT FOR DELTA T BAR SPECTROMETER GENERAL DESCRIPTION Copending US. Pat. application Ser. No. 12,602, filed Feb. 19, 1970, by Donald J. Santeler for Delta T Bar Spectrometer discloses a number of forms of a delta T spectrometer for use in concentrating minute quantities of gas in a mixture, whether in a vacuum or in a passage through which gas is flowing, and outlines various means for reading out the quantities of the different gas constituents present in the mixture, beginning at the low temperature end, generally by warming the body of the delta T bar from the low temperature end toward the warm end. A different form of readout device for a delta T spectrometer is disclosed in the copending US. Pat. application Ser. No. 12,990, filed Feb. 20, 1970, by Frank Pagano for Delta T Bar Spectrometer Readout Device, which permits determination of the relative quantities of gas constituents already deposited by optical means without warming the bar during the time of the readout.

Experience shows a need for a readout of a faster kind in which the gases are stripped one at a time from the bar while maintaining the equipment in readiness for further collection and detection of gas constituents. An effective delta T bar, whether in the form of a solid bar or tubular structure, has a considerable thermal capacity and conductivity in order to establish and maintain a fixed temperature gradient between two fixed temperature points with sufficient control of the uniformity of gradient so that condensing gases contained in widely different relative amounts will be condensed out with little change in the resulting temperature at the points of deposition as heat is absorbed from the bar, corresponding to the heat of vaporization of the particular gas constituent being deposited. If the entire bar is warmed beginning at the low temperature end a considerable time is required to return the bar precisely to the initial thermal gradient condition needed for reliable deposition for the gases, particularly those present in minute quantity or those having closely similar condensation temperatures.

A principal object of the invention is to provide a selective readout for a delta T bar spectrometer.

This invention constitutes an improvement in readout by successive evaporation of the constituents condensed along the interior of a tubular delta T bar wherein the delta T bar temperature itself is not much changed during the stripping of the gas constituents therefrom. A hollow delta T bar adapted to receive a mixture therethrough from a warm toward a cold end is provided with relatively massive wall materials for maintaining the temperature gradient once it has been established between two fixed temperature points. A coating of thermally insulating material on the delta T bar is provided in a thickness, varied according to conductivity but sufficient to permit the heat of vaporization to be carried away without much change of temperature while permitting variation of the temperature of individual segments upon the addition of thermal energy. For this purpose strips of thin metallic film, wires or bars are disposed on the inner surface of the insulating coating in contact with gas flowing therethrough, and these individual segments are momentarily heated by an electric current individually, or by radiant energy in succession, to an extent of a few degrees and heating thereupon discontinued. This results in the return of each segment to its initial temperature so that the desorption phase is accomplished by moving a rising temperature wave up along the bar from the low end to the upper end without a substantial change in the temperature of the bar itself. Other objects will become more apparent as the description proceeds in connection with the drawings, in which:

FIG. 1 is a schematic diagram of an apparatus employing a delta T bar according to this invention;

FIG. 2 is a longitudinal section of a tubular delta T bar for use in the apparatus of FIG. 1;

FIG. 3 is a cross-sectional drawing somewhat enlarged of a delta T bar according to FIG. 2 showing means for heating sections of the bar in succession and at particular gated times.

A delta T bar as disclosed in the above referenced patent applications may be in the form of a thermally conducting tube having two fixed reference temperatures one usually corresponding to atmospheric temperature or higher and a second at a much lowered temperature, such as liquid nitrogen temperature when only gases of higher boiling point than nitrogen are to be investigated. The delta T bar may itself be a tube or solid copper or aluminum rod disposed within a region surrounded by the gases under test being enclosed axially in a tube which conveys the gases from the hot end to the cold end of the delta T bar.

The present invention contemplates a collecting arrangement in which the mixture is passed along the delta T bar at a rate to provide thermal equilibrium between bar and gas temperature for successively depositing condensates between a first fixed temperature point and a second fixed temperature point which arrangement is not a part of this invention. Desorption of the condensed gases is usually either into a vacuum chamber as the deposits are evaporated in sequence beginning at the low temperature end, or by pumping out through the high temperature end to a detection area, for detection of the gases as they are desorbed by any well known technique of detecting the presence of an evolved gas in a carrier gas. As in the above referenced applications the carrier gas may be a gas such as helium maintained in continuous flow while the desorbed gases are evaporated thereinto, generally passing from the cold end toward the warm end, at which point a detector responsive to changes in the conductivity or mass constants of the gas is employed for determining which gas is present and the quantity evolved. In delta T bar desorption a precise knowledge of the temperature of desorption is made available so that detection of the quantity of gas in each instance is sufficient for identification when correlated with the temperature obtaining at the point of desorption. Apparatus according to FIG. 1 has been described, along with other variations of such apparatus, in the above-mentioned copending patent applications.

This invention relates to an improved method of effecting readout and to method and apparatus for depositing constituents of a gaseous mixture in a manner so that they can be read out in a programmed order. FIG. 2 illustrates a form of delta T bar which is particularly adapted to accomplish the objective of the present invention. There is shown generally at 10 a delta T bar in the form of a hollow tube having relatively massive walls 11 of copper, aluminum, etc. along which a temperature gradient is maintained by means not herein shown. In order that the readout may be programmable an insulating barrier is applied along the wall 11 on the side which receives the gas mixture flowing therealong. This is illustrated as a thin coating 12, which might be a painted coating of the order of one mil thickness when materials such as epoxy are used as the insulating material. Secured to the wall 11 in close thermal contact therewith are bands 13 comprising heat conductive elements such as of copper, silver, or aluminum, having good thermal conductivity. A coating of insulating material 12 is selected for thermal conductivity which is very low with respect to the conductivity in walls 11 and bands 13 but is made thin enough so that each of the bands 13 tends to assume the same temperature as the wall 11 on which the gradient is maintained at each position therealong during the deposition phase. While epoxy is one of the suitable substances many other materials may of course be employed, being selected for thickness and thermal conductivity so that each of bands 13 may be momentarily heated without greatly changing the temperature of wall 11 adjacent thereto when a large influx of heat is produced within a particular band 13. At the same time, material 12 is made thin enough or of sufficient thermal conductivity so that bands 13 return to approximately the temperature of the adjacent portion of wall 11 when the desorption heat flow to the particular band is terminated.

Coating 12 also has suitable electrical insulating properties to permit electrically energizing successive bands 13 without leakage ofcurrent to adjacent bands or to wall 11.

Bands 13, as illustrated in FIG. 2, may be cemented in place before the coating 12 hardens being preferably painted on and partially hardened before bands 13 are applied thereto. One form of bands 13 is metal foil cut into strips cemented to wall 1 and separated a small distance from each other coating 12 arranged to have end terminals brought out along the length of tube for successively switching a source of electrical energy to heat the bands. Another form of bands suitable for the purpose is flattened round wire laid in close juxtaposition along the length of the tube, either as discrete circumferential bands or as a helix with separate zoned energizing connections to the energy source. For example, a small diameter wire may be flattened to width dimensions such as 0.005 or 0.020 inch and separated from each other by 0.001 or 0.002 inch when the thickness of the coating is approximately 0.001 inch.

In FIG. 3 there is shown a cross-section of a tube such as that illustrated in FIG. 2, being a section taken along lines 2 2 of FIG. 3 so as to show terminations for the ends of bands 13 on the outside of walls 11. A longitudinal slot may be cut throughout the length of the tube 10 so that bands 13 are brought out apertures 14 while being separated from walls 11 by insulating material 12, the gas passage 15 being kept fluidtight as by an insulating plugging member 16. Apertures 14 maybe individual to the bands or may be continuous such that terminations 17 lie along one side ofthe aperture and terminations 18 lie along the opposite side thereof, preferably against the insulated tube wall 11 as a backing element. In order to secure electrical connection to each of the bands in succession. :1 common lead 19 is provided for connection to each of terminations 17 along the length of the tube. Contact with the opposite end of the band is made at terminations 18 by a convenient movable contact. Rail 21 carrying a sliding collar 22 which in turn carries a brush 23 in contact with terminations 18 as collar 22 is moved along the length of the tube is a suitable contacting arrangement.

Individual heating of bands 13 can be accomplished in any ordered succession over a limited length of tube such as 13 A 13", which may encompass the region of condensation for a particular constituent desired to be investigated separately. Otherwise a longer length oftube may be warmed in a succession of zones beginning, for example, at 13 and extending to 13". In other applications it may be desired to strip the entire tube of its condensed gases after a sample has been completely adsorbed In this case warming from the cold end continues throughout the length of the tube, each individual band 13 being warmed in succession through a small increment of temperature above that temperature existing by virtue of the temperature gradient along wall 11. Any suitable means may be employed for imparting the desired degree of heat energy to the bands in succession. Whenever the quantity of condensed gas to be evaporated is relatively small the thermal energy supplied to the successive bands may be made approximately equal such as might be provided by discharging capacitors or energization for a period ofone second at a heat rate such as 1 watt to 100 watts, according to electrical conductivity. size and capacity ofbands 13.

One means of providing this fixed increment of heating at each position along the bar is illustrated in FIG. 3 wherein a variable series resistor 24 connects a power supply to collar 22 and thence to termination 18. Power is supplied through resistor 24 by way of a gating switch 25, of any conventional design, preferably controlled by a timer 26 which causes a pulse of energy to pass for a limited time through a band 13 when brush 23 is in contact therewith, the connection being completed from a power line 28 through a switch 27 and common lead 19. During the readout mode where the temperature gradient region is to be scanned in a programmed order, switch 27 will be closed to connect line 28 to terminal 19 and the gating switch is thereupon controlled by timing either in respect to the duration of the power pulse or in respect to the commencement ofthe power pulse, or both.

Alternatively power may be supplied between terminal 19 and brush 23, for whichever terminal 18 is immediately contacted, by the use of a stored energy device which has a particular form of gating switch 25. For example a series of capacitors may be connected for discharging through the respective bands in which each individual capacitor has energy sufficient to heat a particular band 13. Gating switch 25 thus connects an appropriate one of the capacitors to a particular band termination 18 contacted by brush 23. Timer 26 then serves to discharge individual capacitors through individual bands 13 in any programmed order of heating which may be desired. Generally the ordered program will progress from a low temperature point on the bar 10 to an upper limit of movement for collar 22 along rail 21 according to the range of temperatures at which the desired constituents are to be removed during a particular aspect ofa gas mixture analysis.

In addition to providing a programmed readout of gases condensed along the interior of tube 10, apparatus of FIGS. 2 and 3 may be supplied with a temperature monitoring device such as a lead from switch 27, which may be normally closed, shown at 29 and a corresponding lead 29 to collar 22, leads 29, 29 extending to a resistance thermometer of conventional design shown at 30. Any well known type of resistance thermometer arrangement may be employed for this purpose so as to provide a continuous reading of temperatures at whatever position is contacted by brush 23. Switch 27 can of course be tiedin with timer 26 or otherwise operated successively to its two positions so that a temperature reading is obtained before or after each pulsing to evaporate the condensate on the particular band 13 connected in circuit.

The invention has been described in connection with particular apparatus found to be effective for programmed readout of gas or vapor condensate on the interior of a delta T bar tube. It is to be understood that other forms of apparatus are mechanically equivalent to that herein shown and described as means for effecting incremental heating of portions of the tube interior according to a timed or otherwise programmed sequence of warming from the temperature gradient temperature at each position to a temperature suffcient to boil off any condensed constituent thereon.

Iclaim:

1. In an apparatus for condensing constituents of a gas mixture during flow along a thermally conducting bar held to a temperature gradient between upper and lower temperature limits thereon the improvement comprising a thermal insulation coating substantially covering the surface of said bar exposed to the passage ofsaid mixture,

a series of thermally conductive rings disposed in mutually separated positions along the surface of said insulating material in contact with a gas mixture flowing there along, and

means energizing said rings of thermally conductive material to raise the temperature thereof above the distillation point for a gas deposited thereon, said rings being heated in a programmed succession.

2. In apparatus according to claim 1, said insulation coating comprising a cement for holding said rings to said bar having thermal and electrical insulation sufficient to permit momentary electrical heating of said rings without substantial change of temperature of the adjacent bar portions.

3. In apparatus according to claim 1, said means energizing said rings in programmed succession comprising an electrical power source, contact means for engaging said rings according to a program and gated timing means in control ofthe time of energization of the rings according to the programmed succession.

4. In a delta T bar spectrometer including a thermally conductive walled tube subjected to a thermal gradient between fixed temperature points of heat supply and heat withdrawal wherein a gas sample is traversed along the gradient,

circularly disposed electrically and thermally conductive members distributed along the tube adjacent the path ofa traversing sample,

5. In a spectrometer according to claim 4, said members being metallic strips secured to the wall of said tube by a cement.

6. In the spectrometer of claim 5, said cement being substantially uniform in thickness between the walls of the tube and the adjacent conductive members and being thicker between said members to provide insulation between members.

7. In a spectrometer according to claim 4, said members having exposed terminations along one side ofsaid tube.

8. In the spectrometer of claim 7, one termination of each member being connected in common, and means electrically engaging other members in succession for application of thermal energy.

9. In a spectrometer according to claim 4, said members being connected for pulsing in an ordered sequence and means applying thermal pulses to said members in successive order according to a timed gating control.

10. In a spectrometer according to claim 4, said members having respective electrical terminations, and temperature measuring means for connection in succession to said terminations for determining their respective temperatures.

1 l. The method of recovering minor constituents of a vapor mixture which comprises condensing said constituents in successive order along a segmented thermally conductive surface subjected to a temperature gradient comprehending temperatures of condensation thereof,

individually heating selected segments in successive rising temperature order above the temperature corresponding to said gradient sufficiently to evaporate condensate thereon, and

substantially terminating the heating of each segment prior to heating other segments at positions corresponding to higher temperatures in said gradient.

12. The method of claim 11, said condensing being accomplished by flowing said mixture through a thermal gradient tube and said heating of segments comprising electrically pulsing each segment in succession with energy pulses proportioned to somewhat exceed the heat of vaporization for the quantities of condensate to be deposited on the segments corresponding to the constituents condensed.

13. The method of claim 11, said heating of segments comprising the passing of a heating current through a resistance band extending transversely across the gradient and there along a distance to comprehend the position of condensate for a constituent to be recovered.

Claims

1. In an apparatus for condensing constituents of a gas mixture during flow along a thermally conducting bar held to a temperature gradient between upper and lower temperature limits thereon the improvement comprising a thermal insulation coating substantially covering the surface of said bar exposed to the passage of said mixture, a series of thermally conductive rings disposed in mutually separated positions along the surface of said insulating material in contact with a gas mixture flowing there along, and means energizing said rings of thermally conductive material to raise the temperature thereof above the distillation point for a gas deposited thereon, said rings being heated in a programmed succession.

3. In apparatus according to claim 1, said means energizing said rings in programmed succession comprising an electrical power source, contact means for engaging said rings according to a program and gated timing means in control of the time of energization of the rings according to the programmed succession.

4. In a delta T bar spectrometer including a thermally conductive walled tube subjected to a thermal gradient between fixed temperature points of heat supply and heat withdrawal wherein a gas sample is traversed along the gradient, circularly disposed electrically and thermally conductive members distributed along the tube adjacent the path of a traversing sample, means for substantially thermally isolating said members from each other and from walls of the tube in respect to pulses of thermal energy while substantially conducting heat steadily applied so as to hold said members generally at the gradient in the tube portions adjacent thereto respectively, and means for pulsing selected members each with a quantity of heat sufficient to elevate the member above its respective place in the temperature gradient.

7. In a spectrometer according to claim 4, said members having exposed terminations along one side of said tube.

11. The method of recovering minor constituents of a vapor mixture which comprises condensing said constituents in successive order along a segmented thermally conductive surface subjected to a temperature gradient comprehending temperatures of condensation thereof, individually heating selected segments in successive rising temperature order above the temperature corresponding to said gradient sufficiently to evaporate condensate thereon, and substantially terminating the heating of each segment prior to heating other segments at positions corresponding to higher temperatures in said gradient.