US2660882A - Apparatus for determination of the temperature of deposition of electrically nonconducting solids from gases - Google Patents

Description

Dec. 1. 1953 T. J. WEBSTER 2,660,882

APPARATUS FOR DETERMINATION OF THE TEMPERATURE OF DEPOSITION 0F ELECTRICAL-LY NONCONDUCTING SOLIDS FROM GASES Filed April 2, 1952 2 Sheets-Sheet 1.

I/VI E/VTOP THOM'A5 3 WEBSTER.

G (AM ATTORNEY 'r. J. WEBSTER 2,660,882 ETERMINATION OF THE TEMPERATURE F DEPOSITION OF ELECTRICALLY NONCONDUCTING Dec. 1, I953 AIBPARATUS FOR D A SOLIDS FROM GASES Filed April 2, 1952 2 Sheets-Sheet 2 ,8 QEEOQ H -HH I 88: U mwm I! I/VI ENTOR J-WEBSTER THOMAS Patented Dec. 1, 1953 APPARATUS FOR TEMPERATURE DETERMINATION OF THE OF DEPOSITION F ELEC- TRICALLY NONCONDUCTING SOLIDS FROM GASES Thomas John Webster,

signer to The British ited, London, England Application April 2, 1952, Serial N 0. 280,116

Claims priority, application Great Britain April 9, 1951 3 Claims. (01. 73-17) This invention relates to a method and apparatus for the determination of the temperature of deposition of an electrically non-conducting solid from a gas, such as, for example, the determination of the so-called ice point of a gas, that is the temperature at which ice is deposited from a gas containing Water vapour at so low a concentration that the gas becomes saturated with water vapour at a temperature below 0 C. so that the water vapour is deposited in the form of ice when the temperature of the gas falls below its saturation point. A knowledge of the ice point allows the humidity of the gas readily to be calculated. For the sake of clarity, the invention will throughout be described with reference to the determination of the temperature of deposition of ice from a gas, but it will be appreciated that it may similarly be employed for the determination of the temperature of deposition of any other electrically non-conducting solid from a gas.

Hitherto, the determination of the ice point of a gas has depended upon visual or photoelectric observation of the formation of an ice film on a suitable surface which is progressively cooled in contact with the gas. Such visual observation cannot be made with a gas at high pressure, owin to difiiculties in construction imposed by the necessity for using transparent materials, and in such cases it is accordingly necessary to expand the gas to a relatively low pressure before making the determination, thereby decreasing the sensitivity of the method.

A further source of error in the determination lies in the fact that certain gases, for example, air, tend to become supersaturated with water on being cooled below the condensation point, so that the observed ice-formation takes place at a temperature below the true ice point.

It is an object of the present invention to provide an apparatus for the determination of the temperature of deposition of ice or other electrically non-conductin solid from a gas which can be used directly for gases either at high or low pressure and which for a considerable range of temperatures of deposition are not subject to errors caused by supersaturation of the gas at the condensation temperature.

It is a further object of the invention to provide an apparatus which can be made fully automatic in itsoperation and can be adapted to operate continuously.

According to a further feature of the invention, apparatus for the determination of the temperature of deposition of ice or other electrically London, England, as- Oxygen Company Limnon-conducting solid from a gas comprises an electrical conductor arranged to form part of an electrical circuit, means formaking and breaking the circuit at frequent intervals at the surface of the conductor, means for passing a stream of gas over the said surface, means for progressively reducing the temperature of the said conductor and means for recording the temperature of the surface of the conductor exposed to the gas stream at which completion of the electrical circuit ceased to take place owing to the formation of a deposit of the electrically nonconducting solid on the surface.

The electrical conductor is preferably of metal adapted to be cooled at a controlled rate and is made to form part of an electric circuit which is closed at frequent intervals by causing the free end of an electrically conducting feeler, for example a metal wire, also included in the circuit to touch the surface of the conductor exposed to the gas stream. This surface ispreferably polished or plated to ensure good electrical contact. The motion of the feeler towards or away from the surface may be effected by hand or preferably mechanically, for example by a motor-driven cam mechanism.

The completion of the circuit may if desired be indicated each time the feeler touches the surface by a micro-ammeter or other sensitive electrical device incorporated in the circuit, the temperature of the surface being continuously measured by means of a thermocouple or other temperature measuring device in intimate contact therewith. In operation, a slow stream of gas whose ice pointis to be determined is passed over the surface of the conductor and the temperature of the latter progressively reduced. As soon as the ice point of the gas is reached, ice begins to condense on the cooled metal surface and formed thereon an insulating layer which interferes with the circuit when the feeler is subsequently brought into contact with the surface. The failure of the wire to complete the circuit as indicated by the lack of reaction by the micro-ammeter indicates that the ice point has been reached and the temperature of the surface at the instant when this failure first occurs is recorded as the ice point temperature.

Alternatively, the system can readily be made fully automatic in operation; for example, the failure of the feeler to complete the circuit may be made to operate an automatic temperaturerecording device by a suitable system of relays. Further, after recording the temperature, the

completion of the electricalrelay system may be made to operate a heating device to raise the temperature of the surface sufliciently to remove the ice deposited thereon, and thereafter to restore the system to its original condition. By this means, the apparatus can be adapted automatically to provide a continuous series of readings of the ice point of the gas stream.

A convenient method of cooling the metal surface at a controlled rate is to form the surface at one end of a tube or rod of copper or other metal of high heat conductivity and to immerse the other end of the rod or tube in a bath of refrigerant, such as, for example, liquid oxygen or liquid nitrogen. The rate of cooling may be controlled by adjusting the depth of immersion of the rod or tube in the refrigerant bath, or by heating an intermediate portion of the rod or tube in a controlled manner. Alternatively, the tube or rod may consist of two sections of copper joined by a section, for example of brass, acting as: a therma'l'resistanee, in which case the rate of cooling will be independent of the depth of immersion of the rod or tube in the refrigerant, so long as only the lower section of copper is so immersed.

In using the apparatus of the present invention todetermine the ice point of a gas, it has been found that when the ice point is, below about -20- C. the ice film is not deposited uniformly over the whole of the surface of the conductor exposed to the gas stream but forms preferentially at the point of contact between the surface and the contacting feeler. This efiectincreases considerably the sensitivity of the method since it localises the formation of the effective ice film within a very small area. Moreover, the moving. contact tends to seed the formation of ice crystals from the gas which prevents the gas from becoming supersaturated with water vapour as it is cooled below the condensation point.

Since the present method does not depend upon visual or photoelectric observation for detection of the ice film, when the ice point of a gas at high pressure is to be determined, the detecting device may be totally enclosed within an opaque vessel constructed of material capable of withstanding the pressure of the gas. It is therefore unnecessary to expand the gas to a low pressure before the determination and the sensitivity of the method is thereby maintained.

At atmospheric pressure it has been found that the ice point of air saturated at a temperature as low as -l C. can be determined by the method of the present invention within an accuracy of one or two degrees centigrade.

The invention will now be more particularly described with reference to the accompanying drawings which illustrate one form of apparatus according to the invention adapted automatically to provide a continuous series of determinations of the ice point of a gas at atmospheric pressure.

In the drawings Figure 1 shows in diagrammatic side elevation the apparatus proper; and

Figure 2 shows diagrammatically the relay system associated therewith.

Referring to Figure l, a feeler I consisting of a short length of fine platinum wire, is attached to one end ofa thin strip 2 of spring material, the other end of which is adjustably fixed to one end of a cam-follower 3, the relative positions ofstrip 2 and cam-follower 3 being adjustable as. hereinafter described.

.. the feeler I is touching by means of a screw 4. The cam-follower 3 is formed with a right-angled bend and is mounted to pivot at the bend on a. fixed horizontal pivot 5. The feeler I: is caused to perform, a. vertical reciprocating motion by a cam 6 rotating about a. spindle I driven by a synchronous motor (not shown) at a suitable speed, against the surface of which cam a projection 8 from the end of the; cam-follower 3 to which the feeler I is attached bears.

At the bottom of its stroke the feeler I makes contact with the end 9 of a copper rod II], this contact being made at su'table intervals and maintained for about 0.5 second. Both the feeler I. and. the rod II) are included in an electrical circuit. forming part of the relay system The force between the feeler I and the end 9 of the rod I0 may be adjusted" by means of a screw II which acts as a stop for the end of the cam-follower 3 remote from the feeler I and thus controls the position of thelower end of the stroke. The time for which: contact is made may be adjusted by means of the screw 4 controlling the position of the feeler I- relative'tothe cam-follower 3. r

A second cam-follower 12', also pivoted at a right angled bend on. the. horizontal pivot 5, is provided at the end adjacent. to the. cam B with a threaded extension I3 on which works on a nut It which bears against the surface of the cam. The other end of. the cam-follower l2 carries an electrical contact I5 which is caused by themovement of the. ca -fol1ower I2 to touch momentarily a screw l6, during the period when the. surface 9 of the rod Is; that is it makes contact after the feeler I touches the surface 9 and breaks contact before the feeler leaves the surface. The time of operation of this contact relative to that of the feeler i may be varied by altering the position of the nut It on the threaded extension l3. Both the contact 15 and the. screw I6 are included an electrical circuit forming, part. of the relay system as hereinafter described. The cam-fol- 1owers'3, I2 are constrained to follow the cam surface by springs t1. I8 attached to their respective lower ends. I The surface 9 of the copper rod i is plated with rhodium. or other electrically conducting protective material to prevent corrosion and to give a good electrical contact, and acts as the cool surface on which depositionof iceoccurs. Athermocouple l 9 passes axially up the rod it? its operating junction being located close behind the surface 9. The thermocouple I9 is connected to a dottin recorder of conventional pattern (not shown) which records the temperature of the surface 9 on a continuous motor-driven chart by means of a chopper bar mechanism actuated by the relay system as hereinafter described. A heater 2G is wound round the rod IE near the top thereof for removal of frost.

The lower end of the rod. I8 has screwed toit a brass rod 2| to which is in turn screwed a further length of copper rod 22 which is immersed.

in a liquid oxygen bath (not shown) The brass rod 2i acts as a thermal resistance so that the rate of cooling of the surface 9 is independent of the level of liquidoxygen so long as the lower section 22 of copper and this alone is immersed.

The surface 9 of therod It is enclosedin a housing 23 of a transparent material which is provided with a gas entry port 26 and a gas exit 25, the latter in this example also serving as an entry for the feeler I. The housing 23 has the double function of directing the stream of gas to be tested against the surface 9 and of excluding atmospheric air.

In operation, a stream of the gas to be tested is passed through the housing 23 and the surface 9 is progressively cooled while the feeler I continues to contact the surface 9 at regular intervals, thus making and breaking regularly the electric circuit. As soon as frost appears on the surface 9 when the ice point is reached, the feeler can no longer complete the circuit and a relay system is operated as hereinafter described to effect the sequence of operations involving (1) recording the temperature, (2) thawing oif the frost and (3) re-cooling the rod I0.

This sequence is performed automatically and repeatedly by means of the circuit shown in Fig ure 2. The relays are shown therein in the position corresponding to that part of the sequence during which the rod It is being cooled and before frost has been produced. Relay R3 is the operating relay of a conventional post oiiice rotary selector having six rotating contacts CI-CS, shown in the figure as each having four positions. These contacts are connected as follows:

Cl at the fourth position closes a circuit including the relay R3 and a switch S3 normally closed;

C2 at the second position closes a circuit including the chopper bar motor of the temperature recording device connected directly to a main source of alternating current at 230 v.;

03 at the second position closes a circuit including the relay R3 and a switch S actuated by the chopper bar of the instrument recording the temperature of rod ID as hereinafter described;

C4 at the third position closes a circuit including the relay R3 an also including switch S5 through a conventional amplifier indicated at A within the panel enclosed by the broken line, the switch S6 being operated by the pointer of the instrument recording the temperature of rod If! as hereinafter described;

C5 at the first position closes a circuit including switch S4, relay I2 and the contacts l5 and I6; and

G6 at the second and third positions closes a circuit including the heater 2i! and a warning lamp L in parallel therewith.

Each of these circuits includes the requisite source of alternating or direct current at the appropriate voltage, such current being obtained from the main voltage source through the necessary transformers and rectifiers.

In operation, when the rod I9 is being cooled, the contacts CI-CES will be in the position shown in the diagram. When the feeler 4 makes contact with the surface 9 of the rod I3, it completes a circuit including the moving-coil relay MMCR which opens switch S4 in series with the contact I5, so that when contacts I5 and I 6 touch during the period when the feeler I and surface 9 are in contact as hereinbefore described, no current flows through the circuit including contact C5. When frost first appears on the surface 9, however, the feeler I does not make electrical contact with the surface 9 so that switch S4 remains closed; hence when the contact I5 touches the screw I6 the circuit including contact C5 is completed energising relay R2.

Relay R2 closes switch 82 thus in turn energising relay R3 which moves the contacts C1-C6 to the second position, and at the same time opens switch S3 which de-energises relay R3. Contacts C6 and C2 switch on the heater 20 and the chopper bar motor respectively. When one dot recording the temperature of the surface 9 has been recorded, the movement of the chopper bar closes the switch S5 which is coupled thereto and completes the circuit through contact C3 again energising relay R3 and moving the contacts Cl-C6 into the third position.

During this period the heater remains on until the temperature of the rod II! has been raised to a predetermined value at which all the frost has been evaporated from surface 9, when the switch S6 attached to the pointer of the temperature recording instrument closes and operates the relay R3 through the amplifier A. The contacts CI-Cfi are moved to the fourth position when contact CI completes a circuit again energising relay R3 and thus restoring the contacts Cl-CB to the first position and the system to its initial condition.

By the use of this instrument a series of readings Of the ice point of the gas stream can be taken automatically over as long a period as may be desired.

I claim:

1. Apparatus for the determination of the temperature of deposition of an electrically nonconducting solid from a gas which comprises an electrical conductor arranged to form part of an electric circuit, an electrically conducting feeler also included in said electric circuit, means for making and breaking contact between the surface of said conductor and an end of said feeler at frequent intervals thereby making and breaking the circuit at frequent intervals at the surface of the conductor, means for passing a stream of the gas over the said surface, means for progressively reducing the temperature of said sursaid surface, temperature recording means, and relay means operable automatically on the failure perature at which such failure 3. Apparatus occurs. for the determination of the deposition of an electrically non conducting solid from a gas which comprises an electrical conductor arranged to form part of ice pregressivelyreducin th -tempe atu e 0f the said-surface, t mp ratur r c rding mea heating means jor raising the temperature of said conductor, and relay means operable automatically on the failure of the circuit to be completed Owing to the formation of a deposit of the electrically non-conducting solid on said surface first to actuate said temperature recording means to record the temperature at which such failure occurs and thereafter to actuate said 10 heating means until the temperature of said suriaee has been raised to a predetermined value sufiiciently high to ensure that all the electrically non-conducting solid deposited on said surrace-has been evaporated therefmmand thereafter to .de-activate said heating means.

THOMAS JOHN WEBSTER.

References Cited in the file of this patent Number Number UNITED STATES PATENTS Great Britain Aug. 12, 1929

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