Optical Analyzer with Dehumidifier

[0001] The present invention relates to an optical analyzer with a dehumidifier.

[0002] In the present context, an optical analyzer is an instrument adapted to measure discrete wavelength (or frequency) dependent intensity values of optical radiation over a specific portion of the electromagnetic spectrum after its interaction with a sample. Characteristics of that sample may then be determined in a data processor from these measured values.

[0003] Generally, the known optical analyzer comprises an enclosure formed with walls to define an internal space and a spectrometer housed within the internal space. The spectrometer unit is in optical communication with a light source and corresponding detector; none, one or both of which may also be accommodated within or in gaseous communication with the internal space of the enclosure.

[0004] The presence of water vapour in the light path of an optical analyzer, from source to detector and along which light path the spectrometer is located, often has a detrimental effect on the performance of the analyzer. This is particularly true for an optical analyzer operating in the infrared, particularly the mid-infrared, region of the electromagnetic spectrum as water presents a broad absorption of energy within this region. Variations in the amounts of water vapour will therefore cause variations in the intensity of the radiation traversing the light path of the optical analyzer, which variations are independent of any sample.

[0005] In order to mitigate the effect of the water vapour in the air the known

optical analyzer also has a dehumidifier included. The dehumidifier comprises a body filled with desiccant, such as silica granules, and is removably locatable in the enclosure to provide contact between water vapour inside the enclosure and the desiccant. However, there is a disadvantage that water vapour cannot be removed from the air when the desiccant is saturated. Indeed the performance of the dehumidifier is significantly deteriorated well before the desiccant is fully saturated. This necessitates the regular exchange of the desiccant, which results in shorter maintenance intervals, particularly in geographic locations with high or strongly fluctuating atmospheric humidity. The corresponding optical analyzer is not available to perform analysis during maintenance and this 'down-time' will increase the cost of ownership. Moreover, the external regeneration of the desiccant or use of new desiccant will further increase the cost of ownership.

[0006] According to the present invention there is provided an optical analyzer comprising an enclosure formed with peripheral walls to delimit an internal space; a spectrometer located in the internal space; and a dehumidifier; wherein the dehumidifier comprises a Peltier effect device having a cooling surface and a warming surface, the Peltier effect device being mounted with the cooling surface located in thermal communication with a gas, typically air, in the internal space; the dehumidifier further comprising a wicking element extending between internal and external of the internal space and having a first portion in contact with the cooling surface.

[0007] In this manner water vapour in the air internal of the enclosure can

preferentially condense at the cooling surface of the Peltier effect device to be transported to the first portion through the capillary action of the wicking element.

[0008] In some embodiments the wicking element has a second portion mounted on the warming surface external of the internal space. Warming of the second portion of the wicking by the warming surface of the Peltier effect device facilitates the removal of the condensed water from the wicking element and helps make the dehumidifier self-regenerating.

[0009] Usefully, the first portion of the wicking element is mounted only about a periphery of the cooling surface. This leaves a section, preferably a substantial portion, of the cooling surface exposed except about its periphery to thereby improve the thermal communication between the cooling surface and the internal space and hence improve condensation of water vapour from air within that internal space.

[0010] In an embodiment the Peltier effect device also comprises a heat sink in thermal contact with the warming surface, usefully forming the warming surface, and in some embodiments exposed to external of the enclosure. [001 1] Usefully, the cooling surface and warming surface are opposite one another on opposite sides of a wall section of the enclosure. The water which is condensed, typically as droplets, at the cooling surface portion may then be conveniently transported from the internal space of the enclosure by the wicking element towards the warming surface, whereat the heat may cause the so transported water to vaporize.

[0012] The invention will now be described in greater detail with reference to the drawings of the figures of an exemplary embodiment of which:

Fig. 1 is a sectional view of an exemplary embodiment of an optical analyzer according to the present invention; and Fig. 2 is a sectional view of an exemplary embodiment of

dehumidifier useable in the analyzer of Fig. 1.

[0013] An exemplary embodiment of an optical analyzer 2 is illustrated in Fig. 1.

The analyzer 2 comprises an enclosure 4 which has four side-walls 4a,b,c,d, a base 4e and a top (not shown) which together delimit an internal space 6. The enclosure 4 may be formed from a thermally conductive material such as aluminium. A spectrometer 8 as well as, in the present embodiment, a motor drive 10 and circuit board 12 are located within the internal space 6. The spectrometer 8 is illustrated as being a conventional Fourier transform spectrometer and, as shown, has a fixed mirror 8a and a moveable mirror 8b orthogonal to the fixed mirror 8a and operably connected to motor drive 10 for reciprocating movement. It will be appreciated that other optical spectrometers, such as a conventional monochromator with a fixed or a moveable optical dispersion element, may be located in the internal space 6 in place of the Fourier transform spectrometer 8 without departing from the invention as claimed.

[0014] A light unit 14 is attached to a side-wall, here side-wall 4c, and in the

present embodiment comprises a light source 14a and reflector 14b arranged to reflect optical radiation emitted by the light source 14a, preferably as a collimated beam, towards an inlet (not shown) of the spectrometer 8. Suitably the light source 14a emits optical radiation from the infrared, particularly mid-infrared, radiation region of the electromagnetic spectrum. In this embodiment a through hole 16 is provided in the side-wall 14c in order to permit optical radiation to pass from the light source 14a to the spectrometer 8. Whilst in some

embodiments a window may be provided to seal the through hole 16 and provide gaseous isolation between the internal space 6 of the enclosure 4 and internal of the light unit it is, as will be described below, advantageous to leave the through hole 16 unsealed and thereby provide for gaseous communication between the internal space 6 and internal of the light unit.

[0015] A detector 18 is here located outside of the enclosure 4 to receive optical radiation emitted by the light source 14a after it having traversed an optical path from the light source 14a, through the spectrometer 8 and a sample 20 in a sample holder 22, and to the detector 18. It will be appreciated that the invention according to the present invention is not delimited by the relative spatial configuration of the components of the optical analyzer 2 and that other known configurations may be made without departing from the invention as defined by the claims. For example, in an alternative embodiment of the optical analyzer 2 the sample 20 and sample holder 22 may be located in the light path between the light source 14a and the spectrometer 8. In a still further embodiment the detector 18 may be disposed relative to the sample holder 22 in order to detect optical radiation reflected from the sample 20.

[0016] It may be useful to be able to maintain the analyzer at a temperature at or below ambient and therefore in some embodiments the analyzer 2 may be provided with a temperature regulator 24 in thermal contact with the thermally conductive material of the enclosure 4, here a side-wall 4c. A suitable temperature regulator may comprise a Peltier element arranged with its cold face in thermal contact with the internal space 6 of the enclosure 4 and its opposing warm face in thermal contact with a heat sink 26 which is thermally isolated from the enclosure 4. In order to help maintain temperature regulation a thermally insulating material 28 may be placed in thermal contact with some or all of the outer surface of the enclosure 4. [0017] Essentially, the analyzer 2 further comprises a dehumidifier 30 which is adapted to remove water vapour from the internal space 6 at least along a portion, preferably the majority, of the light path of the optical radiation through the enclosure 4. Usefully, the through hole 16 remains unsealed to allow removal of water vapour from air within the light unit 14 by the dehumidifier 30.

[0018] According to the present invention and with reference to Fig. 2, the

dehumidifier 30 comprises a Peltier effect device having one or more (here one) Peltier elements 32, arranged to provide a cold side 34 and a warm side 36, and a heat sink 38 thermally coupled to the warm side 36 of the Peltier element 32 to provide a warming surface 40 at an end of the heat sink 38. The dehumidifier 30 also comprises a wicking element 42, such as may be provided in the form of a fibrous cloth, porous plastic or glass fibre material. The wicking element 42 extends from the cold side 34 of the Peltier element 32 to external of the internal space 6, in this embodiment to the warming surface 40 of the heat sink 38. The wicking element 42 is provided with a first portion 42a around and in contact with only the periphery of an upper surface 44 of the cold side 34 of the Peltier element 32, which upper surface 44 acts as a cooling surface of the Peltier device and with a second portion 42b in thermal contact with the warming surface 40 which is located outside of the internal space 6. In the present embodiment a fastener, such as a screw 46 is employed to secure the second portion 42b of the wicking element 42 in thermal contact with the warming surface 40.

[0019] A housing 48 may usefully be provided as an element of the dehumidifier 30 to house the Peltier device and wicking element 42. In the present embodiment the housing 48 comprises a body section 50 and detachable cap section 52. The Peltier element 32 is housed within the cap section 52 with the cold side 42 facing a through hole 54 in an upper surface 56 of the cap 52. The through hole 54 overlies, at least a part of, the exposed portion of the cooling surface 44 not covered by the first portion 42a of the wicking element 42. Thermal isolation 58 may advantageously also be provided within the cap 52 and arranged to leave the cooling surface 44 exposed to the through hole 54. The heat sink 38 extends into the body portion 50 so that the warming surface 40 terminates within or outside of the body portion 50, which may, as illustrated in Fig. 2 terminate in an open end 60. Also as illustrated in the embodiment depicted in Fig. 2, the housing 48 may have an external surface, here threaded region 62 of the body 50, that is adapted to cooperate with a corresponding portion of the enclosure 4 to facilitate the desired collocation of the dehumidifier 30 and the enclosure 4 so as to locate the cooling surface 44 on one side of the wall portion (here 4d) and within the internal space 6 and the warming surface 40 on the opposite side of the wall portion (here 4d) outside of the internal space 6.

As illustrated in Fig. 1 , the dehumidifier 30 is collocated with the enclosure 4 to ensure that the cooling surface 44 is placed in thermal communication with the internal space 6 of the enclosure 4, by ensuring that the cap 52 passes through a side-wall 4d. In use, when electric current is applied to the Peltier element 32, the cold side 34 will begin to cool. When the temperature at the cooling surface 44 falls below the dew point water vapour in the air from within the internal space 6 that enters the through hole 54 will condense as droplets on the portion of the cooling surface 44 of the Peltier device which is not covered by the wicking element 42. The condensed water droplets will move under gravity to the first portion 42a of the wicking element 42 that overlays the periphery of the cooling surface 44. Water entering the first portion 42a of the wicking element 42 will move successively through the wicking element 42 towards the second portion 42b of the wicking element 42 which is preferably in thermal contact with the warming surface 40 of the heat sink 38 that is thermally coupled to the warm side 36 of the Peltier element 32. The water moving through the wicking element 42 that reaches the second portion 42b is evaporated successively by the heat provided by the warming surface 40. In this manner water vapour is removed from the internal space 6.