This invention relates generally to methods and apparatus for the rapid drying of materials. More specifically, it is for the rapid drying of porous materials which must be dried for a determination of dry weight or mass. Dry weight is an important parameter in many industries, including the construction industry, where a specified dry weight maybe a requirement for evaluation of material quality.
The dry weight of the material may be important in determining the density and moisture content of the material. There are many industries where the density and moisture content of material is an important value. In the asphalt industry, samples of asphalt are cut from a newly paved roadway or area where asphalt has been applied. To obtain the density of these materials, a dry weight must be determined. However, water is often introduced into the asphalt sample during the paving process itself. Also, to cut a sample from an asphalt pavement or for preparing samples of a certain size or shape, wet saws or augers are sometimes used. These introduce extra water into the sample, saturating the sample. Because of the natural water that may be present in the sample and because of water that may be introduced in the sample during the paving process or during the cutting process, it is necessary to dry samples to determine a dry weight, hence to calculate accurate density. Under the current practice, samples are placed in an oven heated to a temperature of 105° to 115° centigrade for a predetermined period of time, usually 16 to 24 hours. The water contained within the sample will be evaporated from the sample by the elevated temperature during this period of time. This will give a dried sample which then may be weighed to determine the dry weight. However, in some applications, the drying time required for this method is a drawback. It does not give an opportunity to take quick corrective action during a construction project, should it be determined that the density of the sample is outside of the parameters assigned the project and sample may be damaged by heat applied during drying period.
In the construction industry, compacted asphalt samples are tested using the ASTM Test D2726, the ASTM Test D6752, and the AASHTO Test T166. These tests require the determination of the density of the materials. This requires that the dry mass of a sample along with a sample volume be determined in order to calculate the density, which is the ratio of the mass to the volume. Moisture may be introduced into the sample by the cutting process or may be naturally present in the sample. Consequently, moisture is eliminated from the sample using the oven method described above or by placing the samples in front of a fan. Both methods require a period of time amounting to hours or, in the fan method, days for completely drying samples. Oven drying at higher temperatures could provide a quicker evaporation of the water from the sample, but ordinarily is not recommended. High temperatures can potentially change the characteristics of the sample and damage the sample for other tests that may be required.
In loose asphalt mixtures, it is important to determine the amount of moisture in the mixture. Excessive water can result in stripping of the asphalt binder film from the aggregate. Stripping can cause premature failure and pot hole creation in asphalt pavements. Currently, samples are taken at a site, placed in a sealed jar or container, weighed before drying, an oven-drying method is used to dry the sample, and then a second weight is taken. This will determine the amount of moisture in the sample. This method is not very practical and could be inaccurate because the sample can gain moisture from the atmosphere during the processing of the sample and during weighing of the sample.
Drying is also important in a variety of other industrial contexts. The moisture content of aggregates themselves oftentimes is measured as part of evaluation. The moisture content in raw material used in paper making process, including wood chips, pulp, and finished paper can be important during the manufacturing process. In the chemical industry, various powders and gels are dried during research and production testing. However, powders and gels cannot be exposed to high temperatures without a risk that the chemical composition of the powder or gel would be altered by the higher temperatures. Consequently, vacuum ovens are frequently used to dry gels or powders, but the drying process is a slow one and can take a long time.
Electronic components used in the electronic industry, including the computer industry, must be dried after washing with a solvent. Mae et al., U.S. Pat. No. 5,755,039 proposes a component dryer. A sealed chamber is used where components that are wet with solvent are placed in a vat with a bottom surface permeable to the solvent. Heated air is drawn into the chamber through an air inlet. A fan or other means is placed at the bottom of the chamber to pull air through an air outlet. The heated air is brought into the chamber by the draw created by the fan, passes through the components, and is pulled into the air outlet for exhaust from the chamber by the fan. The air allowed into the chamber is less than the volume of air removed from the chamber by the fan, hence a negative pressure is created in the chamber below the vat containing the components.
Ito et al., U.S. Pat. No. 4,686,852 discloses a mechanical method for preparing mortar or concrete. Here, a fine aggregate is placed in an enclosed container, a centrifugal force is applied to the container of a predetermined period, the centrifugal force removes a portion of the water deposited on the fine aggregate, which allows appropriate determinations to be made. Kuboyama, U.S. Pat. No. 4,319,408 discloses a general drying apparatus. A partially sealed chamber is evacuated forcibly by a rotary means installed in the chamber. The air pressure within the chamber is reduced. A certain amount of air is allowed to be introduced into the chamber while maintaining a balanced pressure within the chamber. Air friction heat is generated by continuous rotation of the rotary air evacuator causing an increased air temperature within the chamber.
Chapman et al., U.S. Pat. No. 5,732,478 supplies heated fresh air to a chamber then evacuating the chamber to remove residual moisture. The flow of air is interrupted to the chamber during evacuation. Air knives are used to introduce the warm dry air into the chamber, which also insures entrained ambient air and a turbulent flow around the devices within the chamber which are to be dried. The Chapman device recognizes that interrupting the flow of heated air during evacuation of the chamber vaporizes moisture but cools the device, resulting in a risk of freezing.
Despite this earlier work there is still need for an improved rapid drying method and apparatus for use in industrial applications. It is an object of the invention to reduce the drying time required for samples. It is an object of the invention to do so in a controlled vacuum. It is an object of the invention to do so at a controlled temperature. It is an object of this invention to do so by controlling the time for vacuum and time for temperature applications. This maintains the material integrity of the samples while, at the same time, expediting the drying process. It is an object of the invention to provide a trap for liquids removed from the sample during the drying process.
The current invention consists of multiple components. First, is a sealable chamber that is vacuum tight. It may have at least one air inlet and at least one air outlet. Appropriate valves to open and close are attached to the air inlet and to the air outlet. Second, there is a heater, which can be controlled to heat air entering the chamber or to heat the interior of the chamber to a preset temperature. A heat pad may be placed on the bottom of the sample chamber to help in eliminating water particles that could fall on the bottom surface of the chamber during the drying process of the sample or to heat the chamber. This heat pad operates at a controlled temperature and may stay on at all times during the operation of the unit. On the air outlet line, there is a cold trap, which is designed to trap liquid or vapor exiting the chamber on the outlet air line. Ordinarily, this liquid would be water. Next there is a vacuum pump connected to the outlet line, which will pull air from the chamber. Air may be pulled directly through the vacuum pump or through the cold trap before being pulled through the vacuum pump. Finally, there are associated controls, usually electronic, to monitor and control the pump, the valves, any heaters, and function of the invention and to provide an interface with a user to allow a user to monitor and control operation of the invention. A sample is ordinarily placed inside the chamber. The inlet valve is closed. The outlet valve is opened. The vacuum pump is turned on, withdrawing air from the chamber and creating a vacuum within the chamber. The air that is withdrawn from the chamber is passed through the cold trap before being drawn through the vacuum pump. The cold trap effectively removes moisture or vapor from the air that is being withdrawn from the chamber. This prevents moisture or vapor from entering the vacuum pump, which can damage the pump and hurt pump performance. The cold trap uses a thermoelectric cooler to chill a metal container. Air flow is directed through the cold trap in a way to obtain maximum contact of air with cold surfaces. Vapor in the air removed from the sample chamber condenses on the cold surfaces and collects at the bottom of the chilled container cold trap. The cold trap also helps in reducing the pressure in the sample chamber by providing a natural air flow path from the chamber because of condensation of vapor in the cold trap reducing pressure in the cold trap. The air from the chamber will naturally flow to cold trap container causing a drop in pressure inside the sample chamber. The vacuum pump is operated for a predetermined amount of time reducing the pressure inside the chamber and causing evaporation of water from the sample and from the chamber. The vacuum pump can reduce the pressure inside the chamber to a particular and controllable vacuum setting. Due to the evaporation and low pressure, the temperature inside the sample chamber would be reduced significantly if not heated in some way. In one embodiment, the air may be heated to a preset temperature and allowed to enter the sealed sample chamber or, in another embodiment, the sample and the inside of the chamber may be heated directly. The vacuum pump continues to operate, which pulls the heated air from the chamber. However, if air entering the chamber is heated, then this heated air may be directed around the cold trap, so as not to affect the temperature within the cold trap. If so, this heated air bypasses the cold trap to go directly to the vacuum pump. The valve controlling the entry of heated air into chamber and the vacuum pump operation can be coordinated in a way that the vacuum level inside the sample chamber is at a controlled predetermined value. This means the vacuum within the chamber stays at a desirable level, which allows the moisture to continue to evaporate even during the heating cycle, thus further expediting the drying process. Without the introduction of heat, evacuation of air from the chamber, with the resulting vaporization of moisture on the sample, will lower the temperature of the sample, which slows the drying process. The heated air continues to pass through the sample chamber for a predetermined time keeping the sample at a predetermined desirable temperature and continuing the drying process. The heated air also passes through the vacuum pump and can dry any residual moisture that many have collected on the vacuum pump or its components. The chamber may be designed in such a way as to maximize the flow of heated air through the chamber so as to evenly distribute heated air around the sample within the chamber before the heated air is drawn through the air outlet by the operating vacuum pump. Keeping the temperature within the chamber at a predetermined desirable level avoids the slower drying caused by evaporation reducing the temperature in the sample, creating lower vapor pressure. Thus, the introduced heat shortens the drying time.
After a predetermined period of time, the warm air flow through the chamber is turned off. The inlet valve is closed. The air outlet line is again directed to pass through the cold trap, and the vacuum pump operates again pulling air from the now sealed chamber with air passing through the cold trap before passing through the vacuum pump. These processes will continue until there is a determination made that there has been a complete loss of moisture in the sample. This can be measured in a variety of ways, including the degree of vacuum obtained within the sample chamber or a change of weight in the sample itself. For example, if the pressure inside the chamber drops below approximately 10 TORR (10 mm HgA), which is known to be the pressure when the chamber is completely dry, then there is no moisture in the system. Alternatively, in another embodiment the sample can be sequentially or continuously weighed and as long as the process is causing a loss of weight within the sample, then it can be assumed that the moisture is being evacuated from the sample. However, if over a period of time, the sample weight remains constant (i.e., three consecutive weights within +or −0.05 grams) then it may be determined that all moisture has been effectively evacuated from the sample. In another embodiment, a transparent window may be provided to allow an infrared heating lamp to be installed and to continuously, in a controlled way, directly heat the sample eliminating the need for an air inlet and only having an outlet to the vacuum pump and cold trap. With the pump running continuously, this allows the pressure inside the chamber to remain very low and keep the sample temperature to a desirable level significantly speeding the drying process. The use of an infrared heat allows for more precise control of the heat inside the chamber. In this fashion, the chamber may be kept at a desirable temperature, like room temperature, without the concern that heat will build up in the chamber and degrade the sample. A potential drawback to heating air that is allowed to enter the chamber is that the amount of heat applied to the air can be difficult to control depending on the flow of the air through the heater into the chamber. Without careful control, there is a risk that the air temperature could rise too high affecting the sample or perhaps damaging components used in the drying process.
In one mode of operation of the rapid drying invention (10), the valve (50) may be opened on the inlet line (110) to allow a controlled amount of air heated by the heater (310) to enter the sample chamber (100) and then to exit the sample chamber (100) through the outlet (120). In this mode, the valve (54) will be closed and the valve (55) will be opened, which means the heated air in the sample chamber (100) will be pulled to the vacuum pump (200) through the bypass line (125), bypassing the cold trap (300). In this embodiment, the vacuum pump (200) will be operated at a sufficient level to pull more air from the sample chamber (100) than is entering the sample chamber (100), at least until a vacuum at a desirable level is achieved in the sample chamber (100). Ordinarily, the vacuum achieved when air is entering the sample chamber (100) through the inlet line (110) through a partially opened valve (50) will be lower (hence, the pressure inside the chamber is higher) than would be the case when the sample chamber (100) is completely sealed and air is being drawn through the cold trap (300). Heated air drawn into the vacuum pump (200) will help dry the vacuum pump (200) and its components and increase the efficiency of the vacuum pump (200) and reduce the possibility of damage from moisture. The cold trap (300) as mentioned above removes moisture from air exiting the sample chamber (100), but also increases the efficiency of the vacuum pump (200) by creating a natural pressure gradient as water vapor condenses in the cold trap (300), thus reducing the air pressure in the cold trap (300).
This is a continuation application of U.S. patent application Ser. No. 14/472,919, filed Aug. 29, 2014, which is a continuation application of U.S. patent application Ser. No. 13/533,153, filed Jun. 26, 2012, now U.S. Pat. No. 8,826,564, which is a divisional application of U.S. patent application Ser. No. 12/822,638, filed Jun. 24, 2010, now U.S. Pat. No. 8,225,526, which is a continuation application of U.S. patent application Ser. No. 10/714,471, filed Nov. 15, 2003, the disclosures of which are incorporated herein in their entireties.
Number | Date | Country | |
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Parent | 12822638 | Jun 2010 | US |
Child | 13533153 | US |
Number | Date | Country | |
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Parent | 14472919 | Aug 2014 | US |
Child | 15626927 | US | |
Parent | 13533153 | Jun 2012 | US |
Child | 14472919 | US | |
Parent | 10714471 | Nov 2003 | US |
Child | 12822638 | US |