Patent Grant
11549750
This disclosure is directed towards a microwave and vacuum drying device, system, and related methods.
Asphalt cores are removed from a road surface for subsequent testing in order to determine the structural characteristics of the road surface. One such characteristic is the density of the road surface. This is particularly important because of the granular and aggregate makeup of paving materials, which can have voids and other gaps that impact the structural integrity of the road surface.
Due to the interconnected voids and gaps found in an asphalt core, and the moisture content trapped within the voids due to the environment or core extraction process, it is important to remove the moisture from the asphalt core in order to determine a dry density or other mechanistic or volumetric parameter thereof. Removing the moisture content can be time consuming. One could air dry the core, but doing so would take an unacceptably long time. One could apply heat to the core, but doing so could cause unintended consequences to the core integrity. Previous attempts to dry cores involved lowering the pressure surrounding the core. This results in rapidly lowering the sample temperature through an evaporation process. Relying exclusively on heat conduction from a support or plate, or typical convection methods is not a reasonable solution; as with a vacuum process, convection does not exist. Infrared Radiation heats only the surface of the sample or core, thus further relying on the conduction of heat energy from the surface to gradually heat the center or volume of the sample. By incorporating RF, RF induction, or microwave sources, a substantial volume of the core or pavement material is instantly filled with energy, thermally inducing evaporation and drastically reducing time to remove the moisture.
A need therefore exists for a method or solution that addresses these disadvantages.
This Summary is provided to introduce a selection of concepts in simplified forms that are further described below in the Detailed Description of Illustrative Embodiments. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
Disclosed herein are one or more microwave and vacuum drying systems, devices, and methods for drying asphalt samples, cores, aggregates, soils and pavement materials. Obtaining the moisture content of a soil quickly in the field or laboratory is also desired.
The foregoing summary, as well as the following detailed description of preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purposes of illustration, there is shown in the drawings exemplary embodiments; however, the presently disclosed invention is not limited to the specific methods and instrumentalities disclosed. In the drawings:
The presently disclosed invention is described with specificity to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventors have contemplated that the claimed invention might also be embodied in other ways, to include different steps or elements similar to the ones described in this document, in conjunction with other present or future technologies.
One or more systems 10 are generally designated throughout the drawings, and with particular reference to
The enclosure 14 may define an outlet 20 that is configured for communicating to a pump 22 as will be further described herein. The enclosure 14 may additionally define an aperture 24 and an opening 25 that are configured for communicating with one or more microwave sources 26.
The pump 22 may be provided for applying vacuuming forces to the interior of chamber 12 in order to reduce the pressure therein to aid in removal of moisture within the sample of material as will be further described herein. The microwave source 26 is provided for applying heating to the samples interior of chamber 12 in order to aid in removal of moisture within the sample of material as will be further described herein.
A wave guide 50 as is further described herein may be in communication with openings 25 and 26 in order to direct microwaves into the chamber 12. The waveguide 50 is illustrated in
The sample may be an asphalt core 1, as illustrated in
This is vacuum chamber inside microwave cavity. One or more alternate configurations of a system are illustrated in
One or more alternate configurations of a system are illustrated in
One or more alternate configurations of a system are illustrated in
The microwave containment system can be the same as the vacuum cavity, or the vacuum cavity and microwave cavity can be separate. In one case, the vacuum cavity can be interior to the microwave cavity, on the other hand the microwave cavity can be interior to the vacuum cavity, or one in the same. Multiple vacuum enclosures can be included such as when each sample has its own microwave transparent vacuum canister. A single large vacuum chamber can contain multiple samples.
The one or more systems disclosed herein combine a pressure vacuum and an electromagnetic source in order to dry one or more samples. The electromagnetic source may be a microwave. Microwaves are electromagnetic waves having wavelength (peak to peak distance) varying from 1 millimeter to 1 meter (frequency of these microwaves lies between 0.3 GHz and 30 GHz) and have greater frequency than lower frequency radio waves so they can be more tightly concentrated. For lower frequencies, coupling of electromagnetic energy into the cavity may not be possible, and large areas of the cavity may have dead spots or no RF energy at all. If the frequency is too low, the cavity would behave as a capacitive load with no power delivered. Microwaves bounded by the inside of the conducting enclosure produce volumetrically high and low energy locations. This is caused by wavelength of the microwaves being on the order of ½ the size of the cavity or less, or on the order of ½ to 10 times smaller than the dimensions of the cavity offering many electromagnetic modes. Hence, constructive and destructive electromagnetic field configurations form and allow for uniform volumetric heating of a sample. Even better uniformity of the microwave energy is accomplished using mode stirring, such as by rotating samples. This dynamically causes the field configurations interior to the cavity to dynamically change. Typical mode stirring can be accomplished using a mechanical stirrer. Typical structures look like a fan with conducting blades that force different coupling modes into the chamber. Optical sources such as infrared irradiative sources, do not have these properties as the cavity is millions of times larger than the wavelength. The principles guiding the physics on these large scales are entirely different. Infrared energy does not penetrate the surface more than a few microns, and the sample surfaces are heated by heat conduction flow resulting from the temperature differential between the surface and center of the sample. The microwaves, which inherently and instantly penetrate to interior of the sample, result in the water absorbing the microwave energy and becoming heated within the core of the sample. The temperature of the water is increase, allowing fast transfer of moisture out of the sample. Hence, microwave drying is rapid, more uniform and energy efficient compared to conventional hot air drying. The problems in microwave drying, however, include product damage caused by excessive heating due to poorly controlled heat and mass transfer. In this manner, the combination of a vacuum force and a microwave source are used to counter balance each other. Here, on one hand, the vacuum reduces the pressure thus further evaporating the water in the sample. This reduces sample temperature as water is evaporated and removed. On the other hand, the microwave source is directed at the sample, whereby the microwave energy is absorbed increasing the thermal energy of the water molecules; thus counteracting the cooling process from the forced evaporation. Hence the samples can remain at relatively constant temperatures throughout a drying process.
One or more methods are disclosed herein. Since the Microwaves will tend to heat and the Vacuum cool the pucks, the one or more methods herein may attempt to maintain the sample material at a constant temperature of 20 degrees C. during the entire drying cycle. Conversely, the object is to not exceed a predetermined sample temperature such as 50 degrees C. The power or duty cycle of the microwave controller is adjusted in concert with the pressure to regulate the temperature and pressure and maximize mass transfer with the vacuum pump.
One or more sensors are in communication with the one or more systems disclosed herein to monitor one or more characteristics of the method and process. The one or more sensors may include a temperature sensor that measures the temperature inside of the containers described herein. The one or more sensors may be a thermocouple, a thermistors (PTC: Positive Temperature Coefficient/NTC: Negative), and an RTD Resistance Temperature Detector (USA)/PT100 (Europe). Alternatively, an infrared based measurement device, including an IR thermocouple. An infrared thermometer measures temperature by detecting the infrared energy emitted by all materials which are at temperatures above absolute zero, (0° Kelvin). The IR part of the spectrum spans wavelengths from 0.7 micrometers to 1000 micrometers (microns). Within this wave band, only frequencies of 0.7 microns to 20 microns are used for practice, because the IR detectors currently available to industry are not sensitive enough to detect the very small amounts of energy available at wavelengths beyond 20 microns. Infrared Thermocouples (IRt/c's) have an infrared detection system which receives the heat energy radiated from objects the sensor is aimed at, and converts the heat passively to an electrical potential. A millivolt signal is produced, which is scaled to the desired thermocouple characteristics. Since some IRt/c's are self-powered devices, and rely only on the incoming infrared radiation to produce the signal through thermoelectric effects, the signal will follow the rules of radiative thermal physics, and be subject to the non-linearities inherent in the process. However, over a range of temperatures, the IRt/c output is sufficiently linear to produce a signal which can be interchanged directly for a conventional t/c signal. For example, specifying a 2% match to t/c linearity results in a temperature range in which the IRt/c will produce a signal within 2% of the conventional t/c operating over that range. Specifying 5% will produce a somewhat wider range, etc. The IRt/c is rated at 1% (of reading) repeatability and to have no measurable long term calibration change, which makes it well suited for reliable temperature control.
The one or more methods disclosed herein are illustrated well in the flowcharts of
The method 1010 may further include applying pressure through a vacuum force until a desired pressure is reached 1016. This may be monitored by one or more pressure gauges disclosed herein. The method 1010 may further include powering on the microwave source 1018. Microwave source may be provided by the one or more microwave sources disclosed herein.
The method 1010 may further include determining if the temperature measured is greater than 50 degrees C. 1022. If the measured temperature is above 50 degrees C., meaning the temperature is approaching not being relatively constant throughout the drying cycle, then the microwave source is stopped 1026. If the measured temperature remains below 50 degrees C., then additional microwave energy may be applied or, alternatively, the microwave energy may be ceased and pressure held. The method 1010 may further include determining if the microwave cycle has finished 1024. This may be accomplished with reference to a predetermined microwaving period of time. If it is determined that the microwave period of time is over, then the microwave is stopped 1026. If it is determined that that microwave period of time is not over, then additional microwave source is provided. Once the microwave is stopped in either of 1026 or 1020, the mass constant is measured 1028 of the sample material. If it is determined that the sample is dry, then the system is stopped 1030. Dryness can be measured by weighing, humidity instrumentation, or ultimate pressure. As long as water is evaporating, it is “out-gassing” and the ultimate pressure is not achieved. To calibrate, the ultimate pressure is measured without a sample, and is the lowest pressure attainable after all water is pumped off the chamber walls. Water is bound to the walls even in an empty chamber. In other words, the one or more methods include pumping (vacuum) an empty chamber, recording the minimum or best vacuum pressure obtained, which in one or more experiments, may be about 2 or 3 Torr, placing the sample in the chamber and the method includes further pumping (vacuum) of the chamber containing the sample. The pressure will remain higher than the ultimate pressure until all the water is evaporated. For this example, when the sample chamber reaches 2 or 3 Torr, it is dry.
One or more additional methods are illustrated in
One can tell when a sample is dry because the sample stops losing weight, or humidity sensor indicator, temperature stabilizes at zero microwave power, as microwaves counter balance the thermodynamic cooling of the sample, or ultimate pressure is obtained. The temperature of the samples is monitored via IR thermocouple and a feed back and control system keeps the microwave energy from heating the cores above a certain value, for example, 40 C, 50 C or 60 C.
Alternatively, a regular microwave oven could be used without the expense of making it vacuum worthy. Then each porous sample that was to be dried could be inserted into its own personal small vacuum chamber and placed into the microwave oven. Inside would be quick release vacuum hookups to reduce pressure for each individual sample. The microwave disclosed methods and instrumentation would be then used to monitor each sample separately, with feedback to a programmable computer to monitor and control microwave power directed to each sample. Alternatively, an economical microwave oven could be modified to accept a single vacuum cavity where one or more samples can reside for drying and monitoring.
Shrink Wrapping Cores and Aggregates Duel Use
Asphalt samples, cores, and aggregates may have a shrink wrap applied thereon for sealing off the core from water intrusion during a volume determination method that uses water. For example, in one or more embodiments, the volume of a core may be determined by submerging the core in a water bath, and measuring the volume increase of the water bath/core combination. Or the weight of the dry sample in air compared to the weight submerged in a fluid or powder allows for the buoyancy effects to calculate volume provided that the specific gravity of the fluid is known. However, for porous materials, water can infiltrate into voids in the core and then the water is difficult to remove. Furthermore and more importantly, water seepage to the interior of the core gives a false mass reading in the water, thus resulting in an underestimate of the actual volume of the sample. In other words, if the core needs to be subsequently weighed in order to, for example, determine density of the core, the infiltrated water impacts the accuracy of the weight measurement and the volume calculation.
A shrink wrap envelope may be applied to the core or pavement sample in order to seal off the core interior while conforming to the complex shape of the surface features before the core is submerged in water. The shrink wrap may be heated with microwave heating, infrared heating, or any other suitable heat source. A vacuum may also be applied. A slight or greater increase in pressure may also be used to make the shrink wrap material flow into the pits and surface of the asphalt core and/or aggregates. For example, one or more shrink wrapping techniques may be employed that are described in U.S. Pat. Nos. 6,615,643 and 6,615,643, the entire contents of which are hereby incorporated by reference. Shrink wrap material may be of a conformal shape to the sample such as in a cylindrical conforming shape, or it may be rectangular in shape and conform to the sample leaving excess material of negligible volume in the finished sealing product.
The shrink wrap can be coated with a microwave lossy material such as carbon or conductor or a semiconductor to increase the energy absorption to the bag and more quickly shrink the plastic. Conversely, if the envelope material is not a shrinkable polymer, forming the polymer to the surface imperfections can be accomplished by heating the material while applying vacuum or pressure cycles. The polymer or bag can be wrapped around the core and inserted into the vacuum chamber. The procedure may be to decrease pressure so that the bag adheres to the surface, while applying energy to mold and shrink the bag.
A good vacuum at most can apply about 14 psi to the surface area of the shrinkable material. However adding positive pressure allows for much higher surface forces to be applied to the shrinkable bag. For example, 14, 28, 42 or up to 100 psi can be applied easily. One possible method for sealing may include inserting a sample, pulling a good vacuum, heating the bag and sealing the bag, then bringing the system back to atmospheric pressure, and then adding air pressure to further set the shrinkable bag, while still adding microwave energy. IR energy could also be used to shrink the bag.
Once the vacuum has set the bag, a gas such as ambient air, or dry air or nitrogen could be added to the chamber to increase pressure. Positive pressures could be formed further pushing the polymer or bag into the surface imperfections. Typical shrink bags tend to not form precisely into the imperfections, making the material sample look like it has a larger volume when the Archimedes principle or rather water bath is used to determine volume or density. Adding positive pressure reduces this non conformal effect.
In another approach, convection principles only could be used whereby the vacuum is made, then positive pressure is applied with respect to atmospheric pressure. This will help set the bag.
In general the samples in any case could rotate and spin in the microwave vacuum oven. Turnstile tables are controlled inside the microwave or vacuum chamber to the proper speed and position. These could be rotated through hermitically sealed shafts, or through a wind up mechanism. Several axes of rotation can be used. The turntables are microwave invisible and could be of a plastic, ceramic, or Pyrex® glass.
Experimental Results
The following experiments have been made using a microwave source in which a plastic vacuum chamber (pycnometer) has been placed interior to the microwave oven. A hole is drilled on top of the microwave so that a hose connects the Vacuum chamber, the pumping installation and the pressure gage. This is illustrated schematically in
In early experiments, the pumping installation included a no water trap where the water evaporated directly in the vacuum pump, whereas later tests included a desiccant 450 illustrated in
In the one or more experiments, the vacillation of the Microwave and the Vacuum, for example, a cycle during which the Microwave oven heats the sample only when the vacuum pressure is raised to a certain level, is advantageous, namely, by letting “dry” air in the vacuum chamber. Here dry is in comparison to the chamber interior, mainly constituted of water vapor, The proportion of water vapor is decreased and therefore the relative humidity becomes lower. As a result, the condensation of water vapor on the surfaces of the vacuum chamber, which increase the efficiency of the drying, is limited. When the vacuum is low enough, below about 10 T, the microwave electric fields strip electrons off the air and water molecules. At this low pressure, the mean free path of the gas molecules is long enough that the electrons can accelerate via the E fields and ionize another particle. Thus avalanche plasma was formed. This plasma aids in mode stirring and uniform heating as it becomes randomly in the chamber. To control the plasma, either the electric field is reduced, or the pressure is raised above the mean free path of the molecules. As the water vapor decreases and the samples become dry, exciting the plasma becomes less probable, and finally ceases to exist below the pressure threshold of about 10 to 15 Torr.
Experimental Results I
In each of the following experiments, the system 110 disclosed in
As illustrated in
Other uses include a portable field device for quick and accurate soil moisture measurements.
Certain samples tested and experimental results of those tests are detailed in TABLE I.
Certain samples tested and experimental results of those tests are detailed in TABLE II.
Certain samples tested and experimental results of those tests are detailed in TABLE III.
The one or more experiments conducted herein were measured with respect to a vacuum only cycle and a vacuum with microwave cycle. The experimental results of those tests are detailed in TABLE IV.
The one or more experiments conducted herein were measured with respect to a vacuum only cycle and a vacuum with microwave cycle. The experimental results of those tests are detailed in TABLE V.
The one or more experiments conducted herein were measured with respect to a vacuum only cycle and a vacuum with microwave cycle. The experimental results of those tests are detailed in TABLE VI.
The combined cycles are more than twice as efficient for small pucks (which can be dried quickly).
For bigger pucks (for which the drying last longer), the gain is not as high but still significant: 10% to 50%.
In these one or more experiments, where substandard results were determined, it was determined that this was mostly likely the cause of an inability to hold vacuum or attain a quality vacuum due to vacuum leaks.
Experimental Results II
In this sets of experimental tests, the system 110 of
In addition the operator performs the MW/Vacuum cycles. That is to say that the operator runs the pump, waits for 1 minute, turns the microwave on while raising the pressure (manually through a button on top of the cold trap 150), and then turns the microwave off and lets the pressure down in a cycle that may be later repeated. While in this experiment, the operator records the vacuum pressure read by the pressure gage 130.
This process is described in detail in the flowchart of
In these one or more experiments, the test compared a conventional asphalt drying unit with the one or more systems disclosed herein. In order to do so, the test compared the time necessary to dry the sample as well as the quantity of water removed.
In order to quantify theses differences, an improvement factor (6%) was defined:
As far as performance of the large puck made of coarse graduates, an improvement was observed by the one or more systems disclosed herein over the ADU because, while removing similar amounts of water, the one or more systems disclosed herein accomplished doing so in about 25% less time than the ADU.
As far as performance of the small puck made of coarse aggregates, within the same drying period, the one or more systems disclosed herein removed about 20% more water.
As far as performance of the small puck made of small aggregates, the one or more systems disclosed herein did not perform as well as the ADU, which had twice the drying time, but also removed twice as much water.
As far as performance for rocks, the drying time with the one or more systems disclosed herein was 75% less than the drying time for the ADU, however, the amount of water removed from the rocks was half of that removed from the ADU.
As far as performance for sands, the one or more systems disclosed herein were more efficient than the ADU.
As far as performance of water, the one or more systems disclosed herein remove 99% of water, whereas the ADU removed less.
In the tables that follow, various experiments were conducted. In the section of each respective table labeled “Equipment use,” the equipment used and subject matter being tested is listed. Any relevant conditions of experiment are listed in the “Conditions of experiment” section.
Protocol of Experimentation:
In the one or more experiments that follow, testing for a puck was performed. In the experiment, air (ambient) was vacuumed out of the chamber of
While the embodiments have been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function without deviating therefrom. Therefore, the disclosed embodiments should not be limited to any single embodiment, but rather should be construed in breadth and scope in accordance with the appended claims.
This application is a continuation of U.S. patent application Ser. No. 16/400,397, filed on May 1, 2019, which is a continuation of U.S. patent application Ser. No. 16/154,968, filed on Oct. 9, 2018, which claims priority to U.S. patent application Ser. No. 14/214,630 filed on Mar. 14, 2014, which claims priority to U.S. Provisional Patent Application No. 61/785,524, filed on Mar. 14, 2013, the entire contents of which are incorporated by reference herein.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3839616 | Risman | Oct 1974 | A |
| 4250628 | Smith | Feb 1981 | A |
| 4257173 | Smith | Mar 1981 | A |
| 4348817 | Bradshaw | Sep 1982 | A |
| 4615125 | Wyborn | Oct 1986 | A |
| 5671546 | Haala | Sep 1997 | A |
| 5675909 | Pare | Oct 1997 | A |
| 5680712 | Kiyokawa et al. | Oct 1997 | A |
| 5732476 | Pare | Mar 1998 | A |
| 5884417 | Pare | Mar 1999 | A |
| 6865821 | Merschat | Mar 2005 | B2 |
| 7194821 | Edamura et al. | Mar 2007 | B2 |
| 7334346 | Nomine | Feb 2008 | B2 |
| 7367139 | Ando et al. | May 2008 | B2 |
| 7383643 | Blankenship et al. | Jun 2008 | B2 |
| 7665226 | Tsuruta et al. | Feb 2010 | B2 |
| 8196312 | Taguchi | Jun 2012 | B2 |
| 8205353 | Ramhold et al. | Jun 2012 | B2 |
| 8756825 | Priebe | Jun 2014 | B2 |
| 9587938 | Troxler | Mar 2017 | B2 |
| 10309722 | Troxler | Jun 2019 | B1 |
| 11035612 | Troxler | Jun 2021 | B1 |
| 20100282272 | Godot et al. | Nov 2010 | A1 |
| 20120171462 | Tsai | Jul 2012 | A1 |
| 20140283408 | Chun et al. | Sep 2014 | A1 |
| 20200158430 | Guan | May 2020 | A1 |
| Number | Date | Country |
|---|---|---|
| 3839616 | Jun 2021 | EP |
| WO-2005097486 | Oct 2005 | WO |
| WO-2014153263 | Sep 2014 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 61785524 | Mar 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16400397 | May 2019 | US |
| Child | 17347092 | US | |
| Parent | 16154968 | Oct 2018 | US |
| Child | 16400397 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14214630 | Mar 2014 | US |
| Child | 16154968 | US |
