Title of Invention

A PORTABLE HUMIDITY GENERATOR

Abstract

A portable humidity generator which comprises: an isothermal container (1) so as to withstanding pressures of the order of 15 bar, characterised in that the said container having adjacent top open saturator chamber (3) and top open test chamber (4), the said top open saturation chamber(3) and top open test chamber (4) being provided with openably fixed metal cover plates (5), the said cover plates (5) being provided with openings for temperature sensors (7), pressure sensors (8) and fluid inlet (9) , the said cover plates (5) of each of the chambers (3,4) being also provided on the inside with tubular coils (14) having inlets (13), the said inlet (13) of the tubular coil (14) inside saturation chamber (3) being connected through a valve (19) to an external gas inlet (18), nozzle outlet (16) of the said tubular coil (14) inside saturator chamber (3) opening into the said saturator chamber (3), the cover plate (5) of the said saturator chamber (3) being interconnected to the cover plate (5) of test chamber (4) through interconnect pipe (10,11,12) having an expansion valve (17), the said interconnect pipe (10,11,12) being connected to the inlet (13) of another tubular coil (14) placed inside the test chamber (4), the nozzle outlet (16) of the said tubular coil (14) inside the test chamber (4) opening into the said test chamber (4) , the said test chamber (4) being provided with a gas outlet (20).

Full Text

The present invention relates to a portable humidity generator. More particularly the present invention provides a process to generate humidity in a chamber. Generation of controlled environment is a very important industrial aspect be it for conducting quality assurance checks or preservation of goods and articles. Among the various parameters of temperature, humidity , pressure, cleanliness of air etc in the regime of environment control, humidity has a special place. Uncontrolled humidity has a very deleterious effect in such industries like micro electronics, food preservation, floriculture etc. therefore it is of paramount interest to industries to monitor the relative humidity levels by means of humidity measurements and adoption of corrective measures by generating the desired levels of humidity. The humidity measuring devices also need a careful standardization which essentially needs a controlled generation of humidity with as much accuracy as possible. Reference may be made to US Patent No. 5,056,547 of 1991 which describes a humidity generating method and apparatus based on two (mixed or divided) flow technique. It utilizes air as the carrier gas and desired relative humidity is obtained by controlling cyclical supplying of alternating timed quantities of wet and dry air streams. This invention is capable of being fabricated as a portable humidity generator using a time domain control technique. A humidity generator, based on a conventional mixed/divided/two flow method, uses two flowmeters, in which a flow of dry nitrogen/air is divided into two, each flow is measured and controlled, and one of the gas flows in saturator with water vapour in a saturator. The saturated air and the dry air are then mixed together and the mixture is fed into a test chamber to thereby generate nitrogen/air of the desired humidity in the test chamber. The relative humidity in the test chamber is strongly dependent upon the flow precision of each flow path, thus, an accurate flow ratio is required to ensure the reliability of the humidity generated. With respect to the flow meters, periodic calibration is essential but calibration after a flow meter has been incorporated in a humidity generator is a difficult job. The flow meters undergo change with a passage of time that is difficult to detect, and the apparatus may give incorrect readings until the next calibration. It is therefore, possible that flow measurements may not be very reliable and the humidity generator as disclosed thus can not be used as a reference humidity standard. The other disadvantage is that the generated RH is to be measured either by a dew point meter or a RH meter that adds to the cost of the invention. Another US Patent No. 5,648,605 of 1997 describes the flow meter calibration method and apparatus for measuring a prescribed amount of a divided-flow or mixed fluid such as when a gas or fluid supplied from one flow'path is made to flow along a plurality of divided flow paths, or a gas or fluid supplied from a plurality of divided flow paths is mixed in a mixing flow path. This invention particularly relates to a method of controlling a flow meter incorporated in a humidity generator or standard gas divider. The main disadvantages in this invention is that it is not portable and thus can not be used as traveling reference humidity standard. It is also very expensive as it uses mass flowmeter, mass flow meter controller and a computer for calculating instrumental error. Another US Patent No. 5,988,003 of 1999 describes a method and apparatus for controlling the level of relative humidity within a corrosion test chamber. In this invention, a method of regulating relative humidity within a corrosion testing apparatus is disclosed. The corrosion test apparatus includes a testing chamber, an atomizer which fogs the testing chamber with an operating fluid, a sensor which senses a relative humidity level within the testing chamber, a humidifying valve coupled to the atomizer which regulates a supply of an operating medium to the atomizer, and a controller coupled to the sensor and to the humidifying valve. The controller includes a heating control process loop which generates an output signal proportional to a differential between a relative humidity set point and the relative humidity level. The humidifying valve regulates the supply of operating medium to the atomizer based on the output signal. The atomizer regulates the amount of operating liquid fogged into the test chamber based on the supply of operating medium received from the humidifying valve. The main disadvantages in the present invention is that, it is not portable, it cannot be used as a humidity standard as it uses several solenoid valves that may not give precise results of the generating relative humidity. Another Patent No. JP 11218510 of 1999 describes an assembly structure of constant humidity generator utilized for calibrating humidity sensors - comprises constant humidity generating element mounted on mesh structure supported by detachable frames and fan installed below mesh structure, entire arrangement held in airtight container. In this invention the structure includes a constant humidity generating element formed by sealing a high water-absorbent fiber sheet In a water- proof bag. The high water-absorbent fiber sheet is impregnated with saturated aqueous solution of salt chosen from some chloride, bromide, nitrate, sulphate, carbonate salts. The water-proof bag has air, moisture permeability characteristic. The main disadvantages of this invention is ; humidity is generated using salt solutions which is not a continuous method of humidity generation; one has to use different salt solution to achieve different humidity , it is not a true portable device which can be used as a traveling reference humidity standard and the humidity generation using salt solutions is messy and not preferred over other methods. The main object of the present invention is to provide a portable humidity generator. Another object of the present invention is to provide a portable humidity generator for humidity generation in a wide range of 5-95%. Yet another object of the invention is to provide a portable humidity generator for humidity generation accurate to within + 1%. The present invention provides a portable humidity generator which utilizes a source of nitrogen or air. It is based on the two-pressure technique. The carrier gas stream at an elevated pressure is supplied to a saturator which is expanded to a lower pressure into a test chamber. The ratio of the two absolute pressures provides the desired relative humidity. The invention is described with the help of the accompanying drawings. In FIG 1 is shown a sectional view of the humidity generator of the present invention, wherein (1) is an isothermal container capable of withstanding pressure of the order of 15 bar having adjacent top openable chambers (3,4) called the saturator (3) and test chamber (4) respectively. (2) are a set of handles. (5) are metal cover plates for covering top of saturator (3) and test chamber (4). (6) are nuts for tightening the metal cover plates (5) onto top of container (1). (7) are temperature sensors passing through the cover plate (5) into saturator (3) and test chamber (4). (8) are pressure measuring sensors for measurement of pressures in saturator (3) and test chamber (4). (9) is an inlet on the cover (5) of chamber (3) ;.-? ; for pouring water into the said saturator chamber (3). In FIG 2 is shown the plan view of the present invention, wherein (1) is the isothermal container. (3) is the saturation chamber. (4) is the test chamber. (5) are the top metal cover plates on top of saturation (3) and test chamber (4). (12) is an interconnect pipe having an expansion valve (17). The interconnect pipe (12) is connected through hollow nuts (11) and pipes (10) to the respective cover plates (5)of saturator (3) and test chamber (4). In Fig 3 is shown the tubular coil arrangement of the present invention, wherein (13) is an inlet for gas to tubular coil (14) for providing large gas path length. (15) is a plate connected at the bottom of the tubular coil (14). (16) is a nozzle outlet opening at the bottom of the tubular coil (14). Fig 4 shows a schematic assembly of the present invention, wherein (1) lis the isothermal container. (2) are the pair of handles. (5) are the openably fixed metal co^er plates having means for fixing the temperature sensors (7) and pressure sensors (8). (9) is! inlet in the cover plate (5) for pouring liquid in saturation chamber (3) (not shown). (6) are nut$ for fixing the top covers (5) on saturator chamber (3) and test chamber (4). The saturator chaimber (3) and test chamber (4) having separate tubular coils (14) placed inside the test chamber (4) and saturator chamber (3). The tubular coil inside saturator (3) and test chamber (4) are fixed onto the inside of top cover (5). (18) is a gas inlet having a valve (19) capable of feeding gas through the inlet (13) of the tubular coil (14). (10,11,12) is the interconnect pipe arrangement connected to each of the two cover plates (5) on top of the saturator (3) and test chamber (4). (17) is a nozzle valve fixed in the central portion of connecting, pipe (12). (20) is a gas outlet from test chamber (4). Accordingly the present invention provides a portable humidity generator which comprises: an isothermal container (1) so as to withstanding pressures of the order of 15 bar, characterised in that the said container having adjacent top open saturator chamber (3) and top open test chamber (4), the said top open saturation chamber(3) and top open test chamber (4) being provided with openably fixed metal cover plates (5), the said cover plates (5) being provided with openings for temperature sensors (7), pressure sensors (8) and fluid inlet (9) , the said cover plates (5) of each of the chambers (3,4) being also provided on the inside with tubular coils (14) having inlets (13), the said inlet (13) of the tubular coil (14) inside saturation chamber (3) being connected through a valve (19) to an external gas inlet (18), nozzle outlet (16) of the said tubular coil (14) inside saturator chamber (3) opening into the said saturator chamber (3), the cover plate (5) of the said saturator chamber (3) being interconnected to the cover plate (5) of test chamber (4) through interconnect pipe (10,11,12) having an expansion valve (17), the said interconnect pipe (10,11,12) being connected to the inlet (13) of another tubular coil (14) placed inside the test chamber (4), the nozzle outlet (16) of the said tubular coil (14) inside the test chamber (4) opening into the said test chamber (4) , the said test chamber (4) being provided with a gas outlet (20). In an embodiment of the present invention the isothermal container may be of a material such as aluminum, brass, copper. In another embodiment of the invention the saturator may have a volume in the range of 300-500 ml. In yet another embodiment the test chamber may have a volume in the range of 300-500 ml. In still another embodiment of the invention the temperature sensor may be a conventional standard platinum resistance thermometer. In yet further embodiment of the invention the fluid medium used in the saturator chamber may be such as distilled water, deionised water. In an embodiment of the present invention the nozzle outlet (16) in the tubular coil may be an orifice of diameter in a range of 1-2 mm. In a further embodiment of present invention the expansion valve (17) may have an orifice of a diameter in a range of 0.1 -0.5 mm. In yet another embodiment of the present invention the accuracy of humidity generated may be of the order of ±1 %. In a further embodiment of the invention the response time of generation of humidity may be less than 1 min. In still further embodiment of the present invention the humidity generated may be in a range of 5-95%. In the drawing accompanying the specification Figures: 1-4 represent an embodiment of the portable relative humidity generator of the present invention. The front view of the RH generator of the present invention shows the isothermal container made out of preferably aluminum block (1) though one can use brass, copper, also. Aluminum has been preferred due to its good thermal conductivity and light weight characteristics.. A pair of aluminum handles (2) are provided for lifting/shifting the generator. Two nicely polished eccentric holes (3) and (4) are made inside the Al block (1). These two eccentric holes are called saturator (3) and test chamber (4). These chambers contain specially designed tubular coils (14) as shown in Fig 3 made from copper tube. Typically, the specifications of tubular coils are : 12 number of turns out of a total length of about 4 meters of straight copper tube. This large number of turns is chosen to give a large path length for the gas in the saturator so that the gas attains a uniform temperature of the liquid medium in the saturator (3). The copper tube coil (14) has near its bottom free end a plate (15) of diameter just sufficiently smaller than the diameter of the saturator/test chamber and a small orifice at the free end below the plate. The saturator contains distilled water, preferably. These chambers are sealed through neoprene gasket and cover plates (5) preferably of brass, by tightening with brass screws (6). The covers (5) hold the tubular coils by inlets (13) as shown in Fig 3. The covers (5) are also good polished in order to achieve high pressure sealing. The covers (5) have the provision of inserting the temperature measuring sensors (7), the absolute pressure measuring sensors (8) and the blank holes (9) covered with brass nuts , one of these blank hole is used to put distilled water inside the saturator (3). Figure 2 shows the top view of the generator. The saturator and test chamber are interconnected through brass pipes (10), hollow brass nuts (11) and copper interconnecting pipe (12). The interconnecting pipe (12) contains an expansion valve (17). The interconnect pipe is connected to covers (5) on saturator (3) and test chamber (4). The expansion valve has a small orifice facing the test chamber side. The purpose of this expansion valve is to expand the carrier gas from the saturator (elevated pressure) to the desired pressure in the test chamber. The interconnecting tube rests on an aluminum clamp as shown in Figure 4. In actual operation, a carrier gas, preferably dry nitrogen from a pressurized cylinder or air from the compressor is fed into the saturator through the gas inlet (18) via a valve (19). The carrier gas on passing through the coil (14) attains the temperature of the fluid medium, water in this case. The carrier gas then comes out as a vapour stream out of the nozzle outlet (16) of the tubular coil (14) in saturator chamber (3), saturated with water, rising through the side space between the plate and the saturator chamber wall and finally enters the interconnecting pipe (12).This water vapour saturated stream of gas then gets to encounter the expansion valve (17) and finally enters the test chamber and flows through the coil (14) and comes out of the nozzle outlet (16) at the end of the coil at a pressure lower than the pressure before the expansion valve (17) and finally comes out from the gas outlet tube (20). The RH generator was used to generate humidity in the range of 5 % to 95 % RH. Suitable amount of triple distilled water was poured through (9) into the saturator. All the brass screws were tightened and checked so that there is no leakage. The nitrogen gas from the cylinder has been used as the carrier gas, though one can use air from a compressor. Nitrogen gas from a cylinder at different pressures in a range of 1-15 bar, was passed through the copper tubing into the saturator. The nitrogen gas in the saturator became saturated with water vapour and passed into the test chamber through an expansion valve. The absolute pressure of the gas inside the saturator and test chamber were measured using conventional pressure sensors. The temperature of the gas in both the chambers was also recorded, in order to see the deviation from the isothermal expansion of the gas from the saturator to the test chamber. The relative humidity is then calculated by the expression RH= (Py/Ps )x100 % The novelty of the present invention lies in the ability to provide humidity generation over a wide range of 5-95 % with a stability of ± 1% in a short response time of less than a minute. The novelty is realized by the inventive step of using an expansion valve between the saturator and test chamber and also due to the use of a coiled tubular coil having a nozzle outlet which allows carrier gas resulting in sudden expansion of vapour stream. The following examples are given by way of illustration only and should not be construed to limit the scope of the present invention. Example-1 200 ml of triple distilled water was poured into the saturator of the portable humidity generator through the blind hole and sealed. Pure nitrogen gas at a pressure of 1.5 bar was bled into the saturator. The gas is allowed to pass through the expansion nozzle into the test chamber. The recorded stabilized pressure measurements were PS = 1.22 bar, PT = 1.02 bar giving the Relative Humidity= 83.60 % . The stability of the generated RH at an ambient temperature of 24 °C was checked over a period of 30 minutes and is found to be stable within ±1%RH. Example-2 200 ml of triple distilled water was poured into the saturator of the portable humidity generator through the blind hole and sealed. Pure nitrogen gas at a pressure of 2.0 bar was bled into the saturator. The gas is allowed to pass through the expansion nozzle into the test chamber. The recorded measurements were PS = 1.47 bar, PT = 1.01 bar and RH = 68.70 % . The stability of the generated RH at an ambient temperature of 24 °C was checked over a period of 20 minutes and is found to be stable within ± 1% RH. Example-3 250 ml of triple distilled water was poured into the saturator of the portable humidity generator through the blind hole and sealed. Pure nitrogen gas at a pressure of 2.0 bar was bled into the saturator. The gas is allowed to pass through the expansion nozzle into the test chamber. The recorded measurements were Ps = 1.51 bar, PT = 1.0.1 bar and RH = 66.88 % . The stability of the generated RH at an ambient temperature of 24.1 °C was checked over a period of 20 minutes and is found to be stable within ± 1% RH. Example-4 250 ml of triple distilled water was poured into the saturator of the portable humidity generator through the blind hole and sealed. Pure nitrogen gas at a pressure of 2.5 bar was bled into the saturator. The gas is allowed to pass through the expansion nozzle into the test chamber. The recorded measurements were Ps = 1.87 bar, PT = 1.02 bar and RH = 54.54 % . The stability of the generated RH at an ambient temperature of 24.2 °C was checked over a period of 30 minutes and is found to be stable within ± 1% RH. Example-5 250 ml of triple distilled water was poured into the saturator of the portable humidity generator through the blind hole and sealed. Pure nitrogen gas at a pressure of 3.0 bar was bled into the saturator. The gas is allowed to pass through the expansion nozzle into the test chamber. The recorded measurements were PS = 2.10 bar, PT = 1.02 bar and RH = 48.57 % . The stability of the generated RH at an ambient temperature of 24.3 °C was checked over a period of 25 minutes and is found to be stable within ± 1% RH. Example-6 250 ml of triple distilled water was poured into the saturator of the portable humidity generator through the blind hole and sealed. Pure nitrogen gas at a pressure of 3.5 bar was bled into the saturator. The gas is allowed to pass through the expansion nozzle into the test chamber. The recorded measurements were PS = 2.70 bar, PT = 1.03 bar and RH = 38.14 % . The stability of the generated RH at an ambient temperature of 24.5 °C was checked over a period of 20 minutes and is found to be stable within ±1% RH. Example-7 250 ml of triple distilled water was poured into the saturator of the portable humidity generator through the blind hole and sealed. Pure nitrogen gas at a pressure of 4.0 bar was bled into the saturator. The gas is allowed to pass through the expansion nozzle into the test chamber. The recorded measurements were Ps = 3.89 bar, PT = 1.07 bar and RH = 27.50 % . The stability of the generated RH at an ambient temperature of 24.4 °C was checked over a period of 20 minutes and is found to be stable within ± 1% RH. Example-8 250 ml of triple distilled water was poured into the saturator of the portable humidity generator through the blind hole and sealed. Pure nitrogen gas at a pressure of 7 bar was bled into the saturator. The gas is allowed to pass through the expansion nozzle into the test chamber. The recorded measurements were Ps = 5.95 bar, PT = 1.14 bar and RH = 19.15 % . The stability of the generated RH at an ambient temperature of 24.2 °C was checked over a period of 15 minutes and is found to be stable within ± 1% RH. Example-9 250 ml of triple distilled water was poured into the saturator of the portable humidity generator through the blind hole and sealed. Pure nitrogen gas at a pressure of 8 bar was bled into the saturator. The gas is allowed to pass i through the expansion nozzle into the test chamber. The recorded measurements were PS = 7.64 bar, PT = 1.23 bar and RH = 16.09 % . The stability of the generated RH at an ambient temperature of 24 °C was checked over a period of 20 minutes and is found to be stable within ± 1% RH. Example-10 250 ml of triple distilled water was poured into the saturator of the portable humidity generator through the blind hole and sealed. Pure nitrogen gas at a pressure of 12 bar was bled into the saturator. The gas is allowed to pass through the expansion nozzle into the test chamber. The recorded measurements were Ps = 10.65 bar, PT = 1.42 bar and RH = 13.33 % . The stability of the generated RH at an ambient temperature of 24 °C was checked over a period of 15 minutes and is found to be stable within ± 1% RH. The advantages of the invention are following: 1. The device is portable so as to be readily carried by a user from one location to another. 2. It can be used as a traveling RH standard. 3. It is comparatively very easy to fabricate and operate. 4. It has an excellent stability of the order of ± 1 % . 5. It is a low cost device and takes up significantly less space. 6. It finds immense use for calibrating industrial hygrometers. 7. The portable humidity generator can give humidity in a range of 5-95%. We claim: 1. A portable humidity generator which comprises: an isothermal container (1) so as to withstanding pressures of the order of 15 bar, characterised in that the said container having adjacent top open saturator chamber (3) and top open test chamber (4), the said top open saturation chamber(3) and top open test chamber (4) being provided with openably fixed metal cover plates (5), the said cover plates (5) being provided with openings for temperature sensors (7), pressure sensors (8) and fluid inlet (9) , the said cover plates (5) of each of the chambers (3,4) being also provided on the inside with tubular coils (14) having inlets (13), the said inlet (13) of the tubular coil (14) inside saturation chamber (3) being connected through a valve (19) to an external gas inlet (18), nozzle outlet (16) of the said tubular coil (14) inside saturator chamber (3) opening into the said saturator chamber (3), the cover plate (5) of the said saturator chamber (3) being interconnected to the cover plate (5) of test chamber (4) through interconnect pipe (10,11,12) having an expansion valve (17), the said interconnect pipe (10,11,12) being connected to the inlet (13) of another tubular coil (14) placed inside the test chamber (4), the nozzle outlet (16) of the said tubular coil (14) inside the test chamber (4) opening into the said test chamber (4) , the said test chamber (4) being provided with a gas outlet (20). 2. A portable humidity generator as claimed in claim 1 , wherein the isothermal container is of a material such as aluminum , brass, copper. 3. A portable humidity generator as claimed in claim 1 wherein the saturator has a volume in the range of 300-500 ml. 4. A portable humidity generator as claimed in claim 1 wherein the test chamber has a volume in the range of 300-500 ml. 5. A portable humidity generator as claimed in claim 1, wherein the temperature sensor is a conventional standard platinum resistance thermometer. 6. A portable humidity generator as claimed in claim 1. wherein the fluid medium used in the saturator chamber is such as distilled water, deionised water 7. A portable humidity generator as claimed in claim 1 wherein the nozzle outlet (16) in the tubular coil is an orifice of diameter in a range of 1-2 mm. 8. A portable humidity generator as claimed in claim 1 wherein the expansion valve (17) has an orifice of diameter in a range of 0.1 -0.5 mm. 9. A portable humidity generator as claimed in claim 1, wherein the accuracy of humidity generated is of the order of ± 1 %.. 10. A portable humidity generator as claimed in claim 1 , wherein the response time of generation of humidity is less than 1 min. 11. A portable humidity generator as claimed in claim 1, wherein, the humidity generated is in a range of 5-95%. 12. A portable humidity generator substantially as herein described with reference to the examples and drawings accompanying this specification.

Documents:

393-DEL-2002-Abstract-(05-12-2008).pdf

393-del-2002-abstract.pdf

393-DEL-2002-Claims-(05-12-2008).pdf

393-del-2002-claims.pdf

393-DEL-2002-Correspondence-Others-(05-12-2008).pdf

393-del-2002-correspondence-others.pdf

393-del-2002-correspondence-po.pdf

393-DEL-2002-Description (Complete)-(05-12-2008).pdf

393-del-2002-description (complete).pdf

393-del-2002-drawings.pdf

393-del-2002-form-1.pdf

393-del-2002-form-18.pdf

393-del-2002-form-2.pdf

393-DEL-2002-Form-3-(05-12-2008).pdf

393-del-2002-form-3.pdf