US2733594A - dew-point detecting device - Google Patents

Description

Feb. 7, 1956 l. slLvL-:RMAN

DEW-POINT DETECTING DEVICE Filed D66. 16, 1953 REFRWERATOR DEW-POINT DETEC'IING DEVCE VThis invention relates generally to dew-point detecting devices and more particularly it is concerned ywith apparatus for visually detectingv the dew-point in a manner which will render the said apparatus accurate and reliable.

The invention comprises a variation of the invention described and claimed in a co-pending application entitled Dew-Point Measuring Device and Method, Serial No. 251,2137led October 13, 1951, by Edwin W. Donath and assigned to the same assigner as the application herein.

ln the said co-pending application, the dew-point was determined by producing a contrasting appearance between wetted and unwetted surfaces of a moisture collector, the collector being roughened so as to provide interstices and pits into which the moisture collected to provide a variation in the appearance ofthe surface in reflective light.

At the dew-point, the localized portion of the surface would become wetted and retiect light instead ofscattering the same so that the spot become darker in appearance.

In order to achieve the required contrast, the said c ollector comprised some member of glass or the like having a roughened top surface and having a localized cooling member engaged against its lower surface to concentrate the cooling.

This invention differs from that of the said co-pending application principally in that the cooling of the collector need not be localized in order to achieve the contrast and hence any refrigeration means could be used to be applied to the entire bottom surface of the collector if desiredbut the results achieved are substantially of the sameor a similar degree of accuracy.

4It is the general object of the invention to achieve the many advantages as set forth in the prior application, but only generally and in emphasis of the objects of the said invention. It is the primary object, with reference only to this invention ,to provide a dew-pointdetermining device ,in which no localizedcooling ofthe collector is required in order to achieve accurate and reliable results through the use of simple and economical means easily operable by persons of ordinary skill.

Still a further object of the inventionis to provide a n dew-point detecting device in which there is a moisture collector, the bottom of which is subject torcooling over a relatively large area, but the surface of which is roughened only in a predetermined smaller area so that when the dew-point occurs the contrast between the roughened and unroughened area will be heightened, by the roughened area becoming wet and light reflective in' character.

Still a further object of the invention is to provide dewl point determining apparatus of the character described in which the surface ofthe colletoror the back thereof is treatedto produce contrasting areas which exist as such when dry, but which lose their contrasting appearance when one of the said areas becomes wet at the dew-point.

Still a further object of the invention is to provide a dew-point detecting apparatus of the character described in which contrast or lack of contrast between the two areas described in the immediately above referred to object is achieved by means of pigment.

nited States Patent YO "ice Still a further object of the invention is to provide a dew-point detecting apparatus in which the contrast or lack of contrast referred to is achieved by means of light.

Many other objects will appear and advantages become apparent as the description of the invention proceeds in connection with which description there has been set forth in considerable detail the construction and operation of preferred embodiments of the invention. The same are likewise fully illustrated in the attached drawings as required by the patent laws.

In the drawings:

Fig. l is a sectional view through an apparatus constructed in accordance with the invention, the same being shown more or less diagrammatically utilizing representations for structure which are well-known to those skilled in the art.

Figs. 2, 3 and 4 are respectively diagrammatic Views of different forms of the collector member of the invention, the iirst two being perspective views and the last being a sectional view. All of the views .are exaggerated as to dimensions in order to illustrate various features of construction and arrangement.

in Fig. l there is illustrated apparatus in diagrammatic form as stated, the same consisting of a dew-point measuring device 10 including a housing 11 of insulating material mounted adjacent or immediately upon a refrigerator 12 of any suitable construction. It will be recalled in the co-pending application above referred to that the refrigerating means required a localized cooling of the collector. This is not always practical, either economically or structurally, especially where some cooling means is available remote from the apparatus. There is illustrated a cooling chamber 14 formed by a metal diffusing cylinder 15 whose cap end 16 engages against the bottom` of the collector member-1S. Any refrigerating means which will provide a cooling effect upon a relatively large area of the collector 13 is considered within the scope of the invention, and hence it is pointed out that the refrigerator 1.2 with its coolant carrying coils 20 inside the cylinder 15 are illustrated merely by way of example.

The housing 11 has a cavity 22 formed in the top thereof and within this cavity there is inserted the collector 1S, which of course must be of the same shape and size as the cross section of the cavity. Obviously for those collectors illustrated in Figs. 2 and 3 the cavity would have to be cylindrical. The collector 18 is at the bottom of the cavity 22 and va retaining barrel 24 of insulating material preferably is engaged upon the collector 18 to hold the same in position. Inlet and outlet ports 26 and 27 of the barrel24 are readily aligned withu the inlet and outlet gas;

or vapor conduits 28 and 29 which pass through the side walls of the housing 11. The valves Sil and 31 may be provided in the conduits to render the gas admitted to the chamber 32 quiescent if desired. Such Vvalvesmay be omitted and the barrel rendered revolt/ able in which case. a rotation of the same bridging the ports 26 and 27 out of alignment with theconduit ends will entrap a sample' of gas. t

The upper end of the barrel is closed oif by a suitable sight glass 34 which in turn may be covered by alight" lter 35 as will be described hereinafter. A thermocouple 36 having leads38connecting same to atemp'era'tureindieating potentiometer or galvanometer dtlcompletes ftheV apparatus, except for the specic description of the collector 1S which is the heart of thedevice. i

It will be noted that there is a localized roughened" note a great and marked increase in contrast at the dewpoint. He notes the temperature indicated by the instrument 40 at that instant and has an accurate indication of the true dew-point.

The dew-point as referred to herein signifies the actual physical point without regard to methodv of determination at which the vapor or gas first changes state so that the first molecules of liquid vapor are produced. This may be slightly before the actual instant of detection by the apparatus, but it is believed that through the use of the invention determinations are obtained which are more accurate than those possible through the use of known apparatus requiring the visual powers of an observer.

They reason for the increase in contrast is that the light which heretofore was scattered by the roughened spot is now reflected in a diierent manner through the water filling in the interstices, pits and valleys of the roughened spot. This is the first moisture condensed upon the carrier, since the peaks of the roughened spot tend to seed the vapor while the smoother portions 4l) tend to cause the vapor occurring over such smooth areas to retain a super-saturated condition until long after the dew-point is reached. If the lowering of the temperature is continued obviously dew or fog will eventually appear upon the smooth surfaces as Well.

The lack of contrast between the roughened and smooth areas 39 and 46 may be heightened through the use of light of various colors. VThe iilter is shown to provide such color eiects. projected colors may accomplish the same purpose.

A modified form of the invention is shown in Fig. 3. Here instead of decreasing the contrast when the collector 18'is dry it is increased through the use of die or pigment on the surface as indicated atl 42. The spot 43 is not so treated. Thus, for example, suppose the apparent color of the spot 43 when wet is a certain shade of grey or blue, depending upon the material from which the collector is made. The collector surface is painted or dyed that precise color in annular formation about the spot 43 so that the observer when looking through the sight glass 32 will see a great contrast. He can obviously note the uncolored spot in the center. Then as the temperature is reduced, at a given point the spot 43 will suddenly darken like its surrounding annulus 42 and blend thereinto. This marks the dew-point, since the moisture caught by the roughened surface will darken that surface to the color of the remainder of the collector. In this case it is preferred that the spot 43 be rough and the other portion 42 smooth but this is not essential.

In Fig. 4 there is illustrated a collector 18 which is translucent so that the pigment or dye 44 can be applied in an annulus to the bottom surface leaving the center spot 45 on the top surface untreated.

Light can also be used in connection With the modications of Figs. 3 and 4 to heighten or lessen the contrast as desired.

It is pointed out also that the collector itself may be formed of some colored material which will either enhance or reduce the contrast for the purposes described. Likewise, the light can come either from the top, side or bottom depending upon the construction and materials used.

Variegated colors or aligned It is believed that the invention has been fully explained such as to enable those skilled in the art to which the same appertains to construct the apparatus and use the same, and it is desired to be limited as to variations and changes only insofar as thescopeof the invention is limited by the claims appended hereto.

What is claimed is:

l. A dew-point ,detecting device which operates by providing an optical change in a surface area, which comprises a housing having a chamber therein, means for leadinga gas sample into said chamber, a moisture collector in said chamber having a surface exposed to said gas sample in the chamber, means cooling substantially all of said surface whereby to lower the temperature of the gas at the said surface, means for measuring the temperature of the deposited condensate when the dew point of the gas is reached, said surface having two portions of predetermined optical contrast relationship when both portions are dry, .but producing a visible change in said optical contrast relationship when one of said portions is wetted at the dew-point, said one portion having means rendering the same light-scattering in character Y when dryk and non-light-scattering in character when wet,

the second portion being non-light-scattering in character whendry, said one portion of said surface having a rough texture provided with interstices and peaks whereby to provide an encouragement of moisture deposition on said one portion, and said second portion is of texture substantially smoother than that of said one portion and inhibiting the deposition of moisture thereon.

2. A dew-point measuring device which comprises a housing having a chamber therein and means for leading a gas sample into the chamber, a planar moisture collector closing oif a side of the chamber and presenting a face to the chamber, refrigeration means on the opposite face of said collector cooling the collector and lowering the temperature of the gas impinging against the face presented to the chamber, the exposed face being pigmented except for a local part, said part having a roughened surface to enable the seeding and capturing of moisture condensed out of said gas, the color of the pigmented portion being substantially the same as that of the roughened part but only when said roughened part is wetted, and being of contrasting color relative thereto when dry, whereby when the dew-point is reached and moisture deposited upon the roughened part, the entire exposed face will assume a substantially homogeneous hue. v

3. A dew-point meter as described in claim l in which said moisture collectorV has pigment applied thereto of a character substantially to decrease the color contrast between the roughened portion when Wet and the smooth portion when dry such that upon deposition of moisture uponrthe roughened portion the same will substantially blend with the smooth portion and appear to disappear to an observer.

4. A dew-point meter as described in claim 1 in Which the moisture collector is illuminated as to the smooth portion by means of colored light of substantially the same color of the roughened portion when wet, whereby to cause apparent substantial blending of the roughened portion when wet.

1,883,116 Tomlinson Oct. 18, 1932 2,593,313 Kamm et a1 Apr. 15, 1952 2,697,933V Donath Dec. 28, 1954

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