FR2745383A1 - Psychrometry device for measuring humidity of gas, such as air for wood drying - Google Patents

Abstract

The device uses a dry temperature sensor(11) and a humidity temperature sensor(12). It has a moisture collection casing in the form of a glove finger(30) covering the humidity sensor(12). A pipe evacuates the collected water and returns it back to the collection casing. The humidity sensor(12) as well as the end part(31) of the pipe are mounted on a common support(28). The dry sensor(11) as well as the tube(32) containing the two sensors(11,12) are also mounted on the common support(28). One end of the tube(32) is mounted on lateral output(40) of the common support(28), this support(28) has a protecting cylindrical part(34), in which is fixed the probes(11,12) and the end part(31), all of which are fitted into the tube(32). The other end of the tube(32) is connected to an annular breather(41), so as to form a seal over a hole(42) through which the gas whose humidity is to be measured arrives. A diaphragm(43) with a calibrated orifice(9) is fitted into the tube(32) at the end adjacent to the breather(41).

Description

 The invention relates to psychrometric devices for measuring the humidity of a gas, especially air.

 We know that these devices include two temperature probes, respectively a so-called dry temperature probe, directly immersed in the gas, and a so-called wet temperature probe, which is placed in the gas while being coated with a coating, soaked in water, having the shape of a thermowell, the humidity of the gas being deduced from the respective temperatures given by the two probes.

 The invention aims to improve the precision of these devices, and also to allow their manufacture and maintenance in a way that is simpler, more convenient and more economical.

 To this end, it proposes a psychrometric device for measuring the humidity of a gas, comprising, for wetting the covering having the shape of a thermowell with which the wet temperature probe is coated, a pipe which has an orifice for outlet by which the wetting water which it has led to this orifice leaves it to rejoin said covering, characterized in that the wet temperature probe as well as an end section of said piping in which said said is formed outlet, are mounted on a common support.

 The relative positioning of, or even, the outlet orifice (s) vis-à-vis the wet temperature probe (and therefore vis-à-vis the covering thereof) can therefore be much more precise than in prior psychrometric devices , where the end section of the piping is fixed to the wall of a conduit where the gas whose humidity is to be measured circulates, so that it is difficult and delicate to correctly position its (single) outlet orifice vis-à-vis the dressing, while a good positioning is essential to have a correct and regular imbibition of the dressing to obtain measurements with good accuracy, and this is all the more true as the temperature of the gas is high.

 In addition, mounting on a common support prevents after a maintenance operation, in particular to change the dressing of the wet temperature sensor, there is a relative positioning which is no longer the same, as is likely to occur in the aforementioned prior device, where the reproducibility of the measurements may no longer be ensured after a maintenance operation.

 According to preferred characteristics of the device according to the invention, the dry temperature probe as well as a tube where the respective dry temperature and wet temperature probes are arranged, are also mounted on said common support.

 The positioning of the probes with respect to the measurement tube or conduit is thus also made more precise and reproducible during successive dismantling.

Preferably, for reasons of simplicity, convenience and economy of implementation of the characteristics which have just been exposed:
said tube is mounted by fitting one of its ends onto said common support, and has at least one lateral outlet orifice for said gas,
said common support comprises a projecting cylindrical part in which said probes and said end section are fitted, and which is itself fitted into said tube,
- An annular bellows is disposed on the end of said tube which is opposite to said common support, to form a sealed connection with the periphery of an inlet hole of said gas whose humidity is to be measured, and / or
- A diaphragm with calibrated orifice is placed in said tube at its end which is opposite to said common support.

 According to other preferred characteristics of the device according to the invention, it comprises means for mounting said common support which make it possible to position the latter selectively with respect to fastening elements of said device, in one of several positions from one to the next, which it swivels 90 ".

 The fastening elements can thus be mounted both on a horizontal and vertical load-bearing wall, the support being placed in the correct position so that the end section of the piping is above the covering of the wet temperature sensor. .

 According to other preferred characteristics of the device according to the invention, said common support is mounted in a measurement chamber in which a wall has a pipe connection connected to a source of fountain water, said common support carrying a pipe connection which is connected to said end section, a section of piping being engaged at one end on the connection of the common support and at the other end on the connection of said wall.

 These characteristics offer good convenience in manufacturing and mounting, and also give the possibility, in the case where the pipe section, which is in the measurement chamber, is quite long and made of thermally conductive material, to heat up. if necessary, the wetting water to bring it to the temperature of the measurement chamber in order to avoid an intake or a departure of calories at the level of the wet temperature probe, which would disturb the measurement.

According to other preferred characteristics of the device according to the invention
- Said end section of said piping is formed by a hollow rod arranged parallel to said wet temperature probe, and one end of which is engaged in said support, which has an internal conduit for supplying it with wetting water, andlou
- The device comprises a mixer for diluting hot air with fresh air in order to obtain a mixed air which constitutes said gas whose humidity it measures.

The description of the invention will now be continued with the description of exemplary embodiments, given below by way of illustration and not limitation, with reference to the appended drawings, in which
- Figure 1 is a schematic view showing a mixer which is part of a hot air drying installation, where it is used to measure the humidity of the drying air, the invention being implemented in this mixer;
- Figure 2 is a sectional view taken in this mixer along its horizontal plane of symmetry;
- Figure 3 is the sectional view along the plane indicated in 111-111 in Figure 2, that is to say along the vertical plane of symmetry of the mixer;
- Figure 4 is a broken sectional view showing certain elements of a fountain water supply pipe which is provided in the mixer; and
- Figures 5 and 6 are schematic sectional views each showing a variant of the filter provided at the inlet of the filtration assembly with which the illustrated mixer is equipped.

 This is part of a hot air drying installation as described in French patent application 93.06113 belonging to the applicant, to which we can refer if we want more details on this installation than those given here. below.

In the oven (not shown) that this installation contains,
The hot air is circulated to dry a charge, for example wood, placed in the oven, where an air intake is provided which is placed in communication with the mixer 1, thanks to the pipe 2.

 The mixer 1 is designed to dilute, under known conditions, the hot drying air which comes from the oven, with fresh air, in this case outside air, the humidity of which is known, in order to obtain a mixed air whose temperature is sufficiently low (for example of the order of 80 "C) so that its humidity can be measured by a psychrometric device (which can only be used below the boiling temperature of l water, i.e. 100 "C), the humidity of the hot drying air being deduced from the measurement given by the psychrometric device, from the known dilution conditions, and from the known humidity of the fresh air, as explained in the aforementioned French patent application 93.06113.

 The enclosure 3 which the mixer comprises, which communicates as has just been said by line 2 with the source of hot air constituted by the oven, furthermore communicates exclusively with the source of fresh air formed by the air outside, and with a suction source 4. This enclosure is divided into a mixing chamber 5 and a measuring chamber 6, the chamber 5 communicating only with the source of hot air, the source of fresh air and the measurement chamber 6, while the latter communicates only with the mixing chamber 5 and the suction source 4.

 This extracts air from chamber 6, which in turn sucks air into the mixing chamber 5 which itself sucks air from the oven and outside. There is thus carried out in chamber 5 a continuous mixing between the air of the drying oven and the outside air, and chamber 6 is crossed by a regular flow of mixed air which comes from chamber 5 and is sucked in by the suction source 4.

 The three orifices 7, 8 and 9 of the chamber 5, through which the latter communicates respectively with the source of hot air (the drying oven), the source of fresh air (the exterior) and the measure 6 are all at predetermined calibration; and in the chamber 6 there is provided a measuring conduit 10 of predetermined section which communicates with the mixing chamber 5 through the orifice 9.

 The calibration of the orifices 7 and 8 makes it possible to fix the conditions of dilution of the hot air by the fresh air while the calibration of the orifice 9 and the section of the duct 10 makes it possible to fix the speed of the mixed air in this conduit.

 In the latter, are arranged the temperature probes of the psychrometric device for measuring the humidity of the mixed air, respectively the dry temperature probe 11 and the wet temperature probe 12 coated with its covering in the shape of a finger. of glove soaked in dampening water, the psychrometric device comprising a computer (not shown) to which the probes 11 and 12 are connected by the respective electrical lines 13 and 14.

 For the proper functioning of the psychrometric device, the calibration of the orifice 9 and the section of the duct 10 are such that the air mixed at a speed of the order of 2 m / s at the level of the probes 11 and 12 with a flow in established regime.

 To know the conditions of dilution of the hot air by the fresh air, it is necessary to know not only the calibration of the openings 7 and 8, but also data of temperature and pressure, which are provided with regard to the air hot by a temperature sensor 15 and by a pressure sensor 16 provided just upstream of the orifice 7, and connected by respective electrical lines 17 and 18 to the same computer as the probes 11 and 12, the temperature and the pressure of the outside air, and moreover its humidity, being known by means not shown.

 We will now describe in more detail the mixer 1, with the support of FIGS. 2 to 4.

 The enclosure 3 has a generally cylindrical shape whose side wall 19 is common to the chambers 5 and 6, these being separated by a transverse annular wall 20, each of the chambers 5 and 6 being closed opposite the wall 20 by a transverse wall 21 or 22, respectively.

 Electric heating collars 23 are provided on the external side of the wall 19, and as the latter and the walls 21 and 22 are metallic, the heat communicated by the collars 23 is transmitted in all these walls. To avoid heat loss, the mixer 14 has a layer 24 of thermal insulation around the wall 19, under an external protective wall 25.

 Thanks to the collars 23, the walls of the chambers 5 and 6 are heated in contact with the outside, to a higher temperature than that of the air contained in these chambers, in order to avoid condensation phenomena both on their walls and '' inside these chambers, the heat supplied allowing the air therein to take a temperature such that all the vapor it contains remains in the vapor phase (temperature such that the saturated vapor pressure is greater than that of the dew point). Provision has been made to distribute several heating collars 23 along the wall 19, so that the temperature is as uniform as possible in the enclosure 3 in order to avoid condensation due to changes in air temperature.

 The suction source 4 is obtained by an ejector device 26 supplied with compressed air by means not shown so that air is sucked through the tube 27 (Figure 3) of the device 26 which opens at the lowest part of the chamber 6, the device 26 being fixed to the outside of the mixer 1 by screwing the tube 27, which is threaded, in a tapped hole in the wall 22.

 A block 28 in Teflon is attached to the internal face of the wall 22, coaxial to the latter, by means of three screws 29. This block forms a common support for the dry temperature probe 11, for the coated wet temperature probe 12 of its covering 30 (shown only in FIG. 3, in a very schematic manner), for an end section 31 of a pipe for supplying wetting water to the covering 30, and for a tube 32 which is part of the measurement line 10.

The block 28 comprises two coaxial cylindrical parts, respectively a large diameter part 33, the transverse face of which
We see on the right in the drawings, door against the internal face of the wall 22, and the other end face of which serves as support for the head of the screws 29; and a cylindrical part 34 of small diameter projecting from this latter transverse face of the part 33.

 As can be seen more particularly in FIG. 2, the probes 11 and 12 are fitted into the block 28 by the transverse end face of the part 34, to a depth less than that of the block, the rear of the probes 11 and 12 opening into a tube 35 which passes through the wall 22 and opens to the outside, this tube allowing the outlet of the electrical conduits 13 and 14 (not shown in FIGS. 2 and 3) which connect the probes 1 1 and 12 to the computer of the psychrometric device.

 The end section 31 of the fountain water supply pipe, is also fitted into the block 28 by the transverse end face of the part 34, and is connected internally to the block 28, by an elbow conduit 36 drilled in it (Figure 4), to a pipe fitting 37 carried by the block 28, a section of pipe 38 (not shown in Figure 3) disposed in the chamber 6, being engaged at one end on the fitting 37, and at the other end on a connector 39 carried by the wall 22, the connector 39 being connected on the outside to a source of dampening water not shown.

 In the example shown in FIG. 4, which is a broken section the lower half of which is taken along the same plane as FIG. 3 while the upper half is taken along an inclined plane containing the longitudinal axis of symmetry of the mixer and that of the fitting 37, the pipe section 38 is a simple piece of flexible plastic pipe, the source of wetting water being at about the same temperature as that of the mixed air, the humidity of which is measured with the psychrometric device.

In a variant not shown, where the source of wetting water is at room temperature, the section 38 is replaced by a section of tubing made of copper or another thermally conductive material, much longer thanks to a winding in a helix, so that
The wetting water remains in the measurement chamber 6 long enough for it to be warmed up to the desired temperature.

 The end section 31 of the piping for supplying the wetting water to the covering 30, is formed by a hollow rod arranged parallel and overhanging the wet temperature probe 12 (see FIG. 3), rod which is closed at its free end and which is provided in its side wall, facing the probe 12, with a number of elongated openings distributed along its length which serve as outlet orifices through which the wetting water conducts up to these orifices leaves the hollow rod 31 to join the covering 30, each outlet orifice being contiguous to this covering, that is to say sufficiently close to it so that there can be no drop dampening water which is detached from the orifice when it is not yet in contact with the covering.

 This is favorable to the regularity of the water soaking of the covering 30, as explained in a parallel patent application filed at the same time as the present application.

 In the example illustrated, the covering 30 exclusively covers the probe 12, the hollow rod 31 being external to this covering and directly immersed in the mixed air which circulates in the tube 32.

 In variants not shown, the covering 30 is replaced by a wider covering, inside which the rod 31 is arranged, or else by a covering on which is attached an attached pocket in which the rod 31 is engaged, preferably with a bulge provided at the end of the covering of the probe 12 so that the free end of the covering is located beyond the free end of the probe, for the reasons explained in French patent application 94.09102 belonging to the plaintiff.

 In other variants not illustrated, the hollow rod 31 is replaced by a rod without openings in its side wall, but with its free end which is open and which forms the outlet port of the wetting water, this free end being located approximately mid-length of the covering 30.

 The mounting of the tube 32 on the block 28 is done by fitting part 34 into one of the ends of this tube, which is thus blocked, the outlet of the mixed air which circulates inside the tube 32, being made by openings 40 arranged just upstream of the part 34, the openings 40 here being two in number, formed respectively in the upper part and in the lower part of the tube 32, with a rectangular shape.

 On the end of the tube 32 which is opposite the support 28, an annular bellows 41 is disposed, the free end of which comes to bear against the wall 20 to form a tight connection around the hole 42 formed in this wall, the tight connection thus formed requiring all the mixed air arriving in the measurement chamber 6, to pass through the measurement conduit 10 in which the probes 11 and 12 are arranged.

 To form the calibrated orifice 9 which is used in particular to fix the speed of flow of the air mixed inside the duct 32, a diaphragm 43 is placed in the end of this duct which is opposite to the support block 28.

 The tube 32 is normally at the same temperature as the air contained in the enclosure 3 since it is entirely immersed in this air. The tube 32 can thus serve to protect the probes 11 and 12 from the radiation emitted by the wall 19, which is warmer. In the event that this radiation causes a rise in temperature of the tube 22, an anti-radiation screen can be provided inside of it comprising a reflective surface facing the internal wall of the tube 32. The block 28, which is thermally insulating, for its part protects the probes 11 and 12 from the radiation emitted by the wall 22.

 It will be observed that the assembly formed by the wall 22, by the ejector 26, and by the block 28 and the various elements carried by it (temperature probes 11 and 12, end section of piping 31, and tube 32 provided with the bellows 41 and the diaphragm 43) reaches its illustrated mounting position by moving with respect to the rest of the mixer 1 in a direction going from the right to the left of the drawings, the bellows 41, which has been stretched beforehand, coming to meet the wall 20 before the wall 22 is completely in place, the contraction of the bellows occurring at the end of the fixing of the wall 22 allowing the bellows to be properly pressed against the wall 20.

 The use of the bellows 41 has the advantage of allowing misalignments between the hole 42 and the tube 32 without this resulting in sealing defects with the wall 20 or mechanical stresses in the tube 32 which would be unfavorable to the accuracy of the measurements and to the reproducibility thereof after the assembly and disassembly operations necessary for the maintenance operations, and in particular for changing the covering 30.

 The fact that the diaphragm 43 is directly installed in the tube 32, makes it possible to center the orifice 9 very precisely relative to the tube 32, and therefore to have therein an air flow which is well centered on the axis of this tube, and which is perfectly reproducible.

 The fact that the tube 32 is mounted on the same support as the probes 11 and 12, also allows a positioning of the probes very symmetrically on either side of the axis of the tube 32, which allows each of the probes to see the air flows around it in a similar way, in a way that is reproducible.

 Finally, the fact that the end section of the pipe 31 is mounted on the same support (the block 28) as the wet temperature probe 12, makes it possible to position them relative to each other without difficulty and so reproducible.

 In FIGS. 2 and 3, the mixer 1 is shown in the position it assumes when it is fixed to a floor, on which the free wing of each of the two fixing lugs 44 which it comprises, wing which is drilled to allow the passage of a screw which is caught on this floor.

 Because the wall 22 is fixed to the rest of the mixer 1 by the screws 45, which are four in number and which are regularly distributed on the angular plane, the fixing of the wall 22, and therefore of all the elements which it door, is possible in four different positions from one to the next of which the wall 22 passes by pivoting 90 "around the common axis of symmetry of this assembly.

 It is thus possible to have the wall 22 and all of the elements which are fixed thereto which retain the illustrated position with respect to the vertical, where the ejector 26 is in the lowest position of the chamber 6 and the pipe end section 31 above the probe 12, in the three other positions that the rest of the mixer 1 can take, respectively when the lugs 44 are fixed to a vertical wall on one side of the mixer 1, on the other, and on a ceiling.

 The transverse wall 21 is mounted in a similar manner to the wall 22, by means of four screws 46. It has two horizontally aligned holes in which are respectively mounted a support 47 for a diaphragm (not shown) in which the orifice is formed calibrated 8, and a support 48 for a diaphragm (not shown) in which the orifice 7 is formed, as well as for the temperature probe 15 and the pressure probe 16, which are screwed respectively in the tapped holes 49 and 50 provided in the side wall of the support 48, the thread 51 provided at the free end of the support 48 used for fixing the rest of the pipe 2 which goes to the air intake which is provided in the drying oven.

 Each of the diaphragms, not shown, intended to be mounted respectively on the support 47 or on the support 48, is in the form of an annular washer, which is held on the internal side of the support, by means of a pierced plug, respectively 52 or 53 , which is caught on the thread through which the support is maintained in the threaded hole provided for this purpose in the wall 22, in order to take the diaphragm sandwich between the support and itself.

 A filtration assembly 54 is provided between the chambers 5 and 6, and more precisely in the chamber 5 upstream from the orifice 42.

 This assembly comprises a filtration conduit formed by a tube 55 welded coaxially on the wall 20 and by a pierced plug 56 screwed on the free end of the tube 55, which is threaded, the inlet orifice of this conduit being formed by the piercing of the plug 56, and its outlet orifice through the hole 42 of the wall 20, the mixed air circulating in this filtration duct first passing through the filter 57 then the filter 58 where it gets rid of its dust before to pass through the measurement conduit 10, which is useful in particular to prevent this dust from being deposited on the covering 30, which would then extremely quickly lose the porosity which is necessary for the proper functioning of the psychrometric device.

 The filter 57 has a cross section which corresponds to that of the fixing duct, and is arranged with its periphery which is fixed on the periphery of the inlet orifice. More precisely, it comprises a pad of fiber material, here made of mineral fibers (rock wool), and a relatively rigid wire mesh cage which surrounds the pad, and which has a peripheral annular flange 59 which at one of its ends, the flange 59 being sandwiched between the internal periphery of the hole in the plug 56 and an elastic ring 60.

 The filter 58, which is made of porous material, here sintered bronze, has a generally tubular shape, and more precisely frustoconical, with its large base which is open and its small base which is closed, it is narrower than the tube 55 and is arranged there coaxially with its open end which has its periphery fixed on the periphery of the hole 42 while its closed end looks at the filter 57, so that there exists between the filter 57 and the filter 58, an intermediate chamber 61 by which passes the mixed air between its exit from the filter 57 and its penetration into the filter 58.

 This configuration of the intermediate chamber 61 makes it possible to prevent the mixed air from retaining the form given to it by the filter 57 before entering the filter 58, even in the event of partial obstruction of the filter 57.

 The entire surface of the filter 58 is thus used, which is favorable to its lifespan, and therefore makes it possible to limit the frequency of maintenance operations or changes of this filter.

In addition, the passage of air through the intermediate chamber 61 makes it possible to perfect the mixture between the hot air and the fresh air by providing a certain homogenization of the mixed air, homogenization which continues, before the orifice. calibrated 9, in the chamber formed by the interior of the filter 58,
The orifice 42, and the interior of the bellows 41.

 The filter 57 'shown in FIG. 5 is similar to the filter 57, but the peripheral flange which it comprises for its fixing is situated in an intermediate position, instead of being at one of its ends; and in the 57 "variant shown in FIG. 6, there is no peripheral mounting flange: the diameter of the pad and of the cage being larger, it is directly the periphery of the cage and of the pad which is sandwiched between the cap 56 and the ring 60.

 In a variant not shown of the mixer 1, a filtration assembly similar to the assembly 54 is also provided upstream of the fresh air inlet, in order to rid the latter of its impurities before it enters the mixing chamber 5.

 It will be observed that the filtration assembly 54 can be used in many other devices than the mixer 1, in particular at the level of the air inlet of a heat engine or of an air conditioning installation.

 It will also be observed that the psychrometric device described can be used in another device than the mixer 1, and in particular in a similar device, but without mixing chamber, with or without filtration assembly at the inlet of the psychrometric device, in the case where the gas whose humidity is to be measured is at a temperature directly compatible with the conditions of use of the psychrometric device.

 More generally, many variants are possible depending on the circumstances, and it is recalled in this regard that the invention is not limited to the examples described and shown.

Claims (10)

 1. Psychrometric device for measuring the humidity of a gas, comprising for wetting the covering having the shape of a thermowell with which the wet temperature probe is coated, a pipe which has an outlet orifice through which the wetting water which it has led to this orifice leaves it to rejoin said dressing; characterized in that the wet temperature probe (12) and an end section (31) of said piping in which said outlet orifice is formed, are mounted on a common support (28).  2. Device according to claim 1, characterized in that the dry temperature probe (11) and a tube (32) where the respective dry temperature and wet temperature probes (11, 12) are arranged, are also mounted. on said common support (28).  3. Device according to claim 2, characterized in that said tube (32) is mounted by interlocking one of its ends on said common support (28), and has at least one orifice (40) lateral outlet for said gas .  4. Device according to any one of claims 2 or 3, characterized in that said common support (28) comprises a projecting cylindrical part (34), in which are fitted said probes (11, 12) and said section of end (31), and which is itself fitted into said tube (32).  5. Device according to any one of claims 2 to 4, characterized in that it comprises an annular bellows (41) disposed on the end of said tube (32) which is opposite to said common support (28), to form a connector watertight with the periphery of an inlet hole (42) of said gas, the humidity of which is to be measured.  6. Device according to any one of claims 2 to 5, characterized in that it comprises a diaphragm (43) with calibrated orifice (9) disposed in said tube (32) at its end which is opposite to said common support (28).  7. Device according to any one of claims 1 to 6, characterized in that it comprises means (22, 45) for mounting said common support (28) which make it possible to position the latter selectively with respect to elements of fixing (44) of said device, in one of several positions from one to the next of which it passes by pivoting 90 ".  8. Device according to any one of claims 1 to 7, characterized in that said common support (28) is mounted in a measurement chamber (6) in which a wall (22) has a pipe connection (39) connected to a source of fountain water, said common support (28) carrying a pipe fitting (37) which is connected to said end section (31), a pipe section (38) being engaged at one end on the fitting (37) of the common support (28) and at the other end on the fitting (39) of said wall (22).  9. Device according to any one of claims 1 to 8, characterized in that said end section of said piping is formed by a hollow rod (31), arranged parallel to said wet temperature probe (12), and of which one end is engaged in said support (28), which has an internal conduit (36) for supplying it with wetting water.  10. Device according to any one of claims 1 to 9, characterized in that it comprises a mixer (1) for diluting hot air with fresh air in order to obtain a mixed air which constitutes said gas whose humidity it measures.