Patent Grant
7815718
The invention relates to a method of and apparatus for collecting particulates. More particularly, the invention relates to collecting air particles into a liquid buffer.
Bio-threat detectors are used to monitor the ambient air to detect the presence of potentially harmful pathogens. In general, air is drawn into a detection apparatus, or trigger, where the particulates in the air are evaluated. Airflow into the detection apparatus is typically generated by a fan within the apparatus. The trigger continuously monitors the air and the individual molecules within a given airflow. Some triggers use lasers to scan the air path to interrogate the particles passing through. A harmless particle, such as a dust particle, can be discriminated from a harmful particle, for example an anthrax spore, because each different type of particle reflects a different wavelength of light. The laser light reflected of the passing particles is matched to database of known harmful wavelengths. When a harmful wavelength is detected, the trigger signals that a potential pathogen is present. However, the specific type of particle is not identified by the trigger.
A confirmation module takes over once the trigger signals the presence of a possible pathogen. The trigger signal initiates the confirmation module into action. The confirmation module identifies the particles detected by the trigger. Conventionally, when the trigger goes off, the potential pathogen is collected and taken to a lab where the confirmation module performs the analysis. Some detection apparatuses are configured with a secondary fan assembly, such as a muffin fan, such that the potential pathogens collect on the fan blades of the secondary fan assembly as the air flows through the detection apparatus. In such configurations, the secondary fan assembly is activated via the trigger signal. The fan blades or the fan assembly is removed from the detection apparatus and taken to a laboratory for analysis. At the lab, a swab is used to wipe the particles from the fan blade surface, or a solution is manually applied to the fan blades to elute the particles off the fan blade surface. This is a time-consuming process that is impractical for real-time threat assessment.
A particle collection apparatus is configured to collect airborne particles into a liquid solution. In some embodiments, the particles are collected from an airflow provided by an air collector and/or a particle detection apparatus. The particle collection apparatus includes a fan assembly, for example a muffin fan, and in some embodiments a fluid collector apparatus. The fluid collector apparatus is coupled to a collection vessel via one or more drain lines.
Fan blades within the fan assembly are rotated in a first rotational direction, thereby generating airflow from above the fan blades downward past the fan blades. The airborne particles adhere to the surface of the fan blades, hub, and fan housing as the air flows past. In this manner, particles are collected on the surfaces of the fan for a predetermined period of time. When the particle collection is completed, the fan direction is reversed to a second rotational direction and maintained at a relatively low rotational rate.
A fluid, such as a rinse buffer, is slowly dispensed onto the hub of the fan blades. Due to the centripetal force of the spinning fan blades, the fluid is spread thin across the top surface of the fan blades and the liquid film washes the blade of the fan, removing particulates from the fan blade. The solution is pushed outward against the inner wall of the fan housing forming a fluid meniscus.
The fluid meniscus is contained between the spinning fan blades and the inner wall of the fan housing. The fluid surface tension and the upward airflow caused by the fan blades rotating in the second rotational direction prevents the fluid meniscus from dripping downward.
Once the fluid is forced against the inner wall of the fan housing to form the fluid meniscus, the fan speed is increased in the second rotational direction. The centripetal force from the fan blades pushes the fluid contained in the fluid meniscus over the fan housing wall and into an annular reservoir of the fluid collector apparatus. The collected fluid is then vacuumed and consolidated into the collection vessel, where it can be subsequently analyzed.
In some embodiments, the fluid collector apparatus is eliminated and drain holes are drilled directly into the wall of the fan housing. The drains holes are positioned proximate to the outer edges of the fan blades. Drain lines are connected to the drain holes. The fluid, or fluid meniscus if one is formed, drains through the drain holes into the drain lines, and is consolidated in the collection vessel.
Embodiments of the particle collection apparatus are described relative to the several views of the drawings. Where appropriate and only where identical elements are disclosed and shown in more than one drawing, the same reference numeral will be used to represent such identical elements.
The particle collection apparatus 10 is shown in
The fan blades 24 are configured such that when rotated in the first rotational direction, airflow is generated in a direction from the air collector and particle detection module 4 towards the top surface of the fan blades 24. In relation to
Under control of the processing module 6, the fan motor 26 rotates in the first rotational direction for an amount of time and a rotational speed sufficient for a detectable amount of particles 60 to collect on the fan blades 24. This amount of time and rotational speed is predetermined. After the predetermined amount of time, a second phase of operation is performed in which the rotational direction of the fan motor 26 is reversed to a second rotational direction at a rotational speed reduced relative to the rotational speed in the first direction.
The fluid dispensing tube 40 dispenses fluid from the fluid dispensing module 42 onto the fan blades 24. In some embodiments, the fluid is water or water-based. Alternatively, the fluid is any fluid that does not damage the particles 60. The fluid dispensing module 42 regulates the amount of fluid that is dispensed by the fluid dispensing tube 40. The fluid is dispensed onto the center, or hub, of the fan blades 24. Due to the centripetal force of the rotating fan blades 24, the fluid spreads from the center of the fan blades 24 toward the out edge of the fan blades 24, thereby providing a liquid film over the top surface of the fan blades 24. During this step, the second rotational direction is maintained at a first speed. The first speed is low enough that the fluid maintains contact with the fan blades, but high enough that the fluid does not fly off the fan blades.
The speed in the second rotational direction is then increased to a second speed. The increased speed results in increased centripetal force applied to the fluid on the fan blades 24. This increased centripetal force forces the fluid to move to the outer edge of the fan blades 24, in the process removing collected particulates from the surface of the fan blades 24. In this manner, a wiping action is performed, whereby the particles accumulated on the surface of the fan blades are wiped off by centripetal force applied to the fluid.
The fluid is pushed outward against an inner wall of the fan housing 22, thereby forming a fluid meniscus 70. The fluid meniscus 70 is contained between the outer edges of the spinning fan blades 24 and the inner wall of the fan housing 22. By rotating the fan blades at the proper second speed, the upward airflow caused by the fan blades rotating in the second rotational direction along with the fluid surface tension substantially prevents the fluid meniscus 70 from dripping downward. As such, the second speed is low enough that the fluid does not fly off the fan blades 24, but the second speed is high enough to force the fluid to the inner wall of the fan housing 22 and high enough to generate sufficient upward airflow to form the fluid meniscus 70 and prevent the fluid from dripping downward off the fan blades 24.
In some embodiments, the second phase of operation is performed using a single speed, instead of the first speed and the second speed as described above. The single speed is low enough to prevent fluid from flying off the fan blades 24, but high enough to force the fluid to the inner wall of the fan housing 22 and to form the fluid meniscus 70.
Vacuum is applied to the drain tubes 50 by the vacuum 62 so that the fluid collected in the reservoir 32 is drawn through the holes 34, into the drain tubes 50, and into the collection vessel 60. In one embodiment, vacuum is applied to the drain tubes 50 when the fan motor 26 is increased to the third speed at the onset of the third phase. Alternatively, vacuum is applied to the drain tubes 50 during the second phase and the third phase of operation. Still alternatively, vacuum is applied to the drain tubes 50 any time the fan motor 26 rotates in the second rotational direction.
A single pass is referred to as performing the first phase, the second phase, and the third phase of operation. One or more passes can be performed to collect a larger percentage of the particles from the fan blades 24 and/or to increase the fluid sample size collected in the collection vessel 60. A maximum amount of fluid that can be dispensed onto the fan blades 24 during each pass is determined by the dimensions of the fan blade assembly 20, the material of the fan blades 24 and the fan housing 22, the viscosity and surface tension of the fluid, and the speeds necessary to perform the second operation and the third operation. If the amount of fluid dispensed onto the fan blades 24 exceeds the maximum amount, then the fluid meniscus 70 does not properly form and a significant portion of the fluid flows off the fan blades 24 and into the fan housing 22. This fluid, and the particles contained therein, are lost and unable to be collected in the fluid collector 30.
In an alternative embodiment, the step 120 and the step 140 are combined into a single step such that when the spin direction of the fan blades 24 is reversed to rotate in the second rotational direction, the rotational spin rate of the fan blades 24 in the second rotational direction is set to the second speed. In this alternative embodiment, the fluid is dispensed onto the fan blades 24 while the fan blades 24 are rotating at the second speed in the second rotational direction, and the fluid is forced to the edge of the fan blades 24 to form the fluid meniscus.
At the step 150, the rotational spin rate of the fan blades 24 in the second rotational direction is increased to a third speed. The additional centripetal force generated while rotating at the third speed forces the fluid meniscus over the upper rim 28 and into the fluid collector 30. At the step 160, a vacuum is applied to the drain tubes 50 that are coupled to the fluid collector 30. The vacuum draws the fluid collected in the fluid collector 30 through the drain tubes 50 and into the collection vessel 60. At the step 170, the step 130 through 160 are repeated as many times as deemed necessary to sufficiently elute the particles 60 from the surface of the fan blades 24.
The fan blades 24 are composed of any material to which one or more types of particles to be collected will adhere. In some embodiments, the fan blades are composed of plastic. Alternatively, the fan blades 24 are coated with any material to which one or more types of particles to be collected will adhere.
The second embodiment of the particle collection apparatus operates in two phases. The first phase is identical to the first phase of the first embodiment in which the fan motor 26 and the fan blades 24 rotate in the first rotational direction to collect particles on the fan blades 24.
The fluid dispensing tube 40 dispenses fluid from the fluid dispensing module 42 onto the fan blades 24. The fluid is dispensed onto the center, or hub, of the fan blades 24. Due to the centripetal force of the rotating fan blades 24, the fluid is forced from the center of the fan blades 24 toward the inner wall of the fan housing 22, in the process removing collected particulates from the surface of the fan blades 24. The rotational speed during this second phase is low enough to prevent fluid from flying off the fan blades 24, but high enough to force the fluid to the inner wall of the fan housing 22.
Vacuum is applied to the drain tubes 50 by the vacuum 62 so that the fluid forced toward the inner wall of the fan housing 22 is drawn through the drain holes 80, into the drain tubes 50, and into the collection vessel 60. Vacuum is applied to the drain tubes 50 during the second phase of operation. One or more passes can be performed to collect a larger percentage of the particles from the fan blades 24 and/or to increase the fluid sample size collected in the collection vessel 60.
In some embodiments, the second phase is performed using two separate steps. During the first step, the fluid is dispensed onto the fan blades 24 and spreads from the center of the fan blades toward the outer edge of the fan blades, thereby providing a liquid film over the top surface of the fan blades 24. During this step, the second rotational direction is maintained at a first speed. The first speed is low enough that the fluid maintains contact with the fan blades, but high enough that the fluid does not fly off the fan blades. The speed in the second rotational direction is then increased to a second speed. The increased speed results in increased centripetal force applied to the fluid on the fan blades 24. This increased centripetal force forces the fluid to move to the outer edge of the fan blades 24.
In some embodiments, vacuum is not applied to the drain lines 50 during this second phase. Instead, the fluid is pushed outward against the inner wall of the fan housing 22, thereby forming the fluid meniscus 70, as in the first embodiment. The fluid meniscus 70 is contained between the outer edges of the spinning fan blades 24 and the inner wall of the fan housing 22. By rotating the fan blades at the proper speed, the upward airflow caused by the fan blades rotating in the second rotational direction along with the fluid surface tension substantially prevents the fluid meniscus 70 from dripping downward. As such, the rotational speed is low enough that the fluid does not fly off the fan blades 24, but the second speed is high enough to force the fluid to the inner wall of the fan housing 22 and high enough to generate sufficient upward airflow to form the fluid meniscus 70 and prevent the fluid from dripping downward of the fan blades 24. Subsequent to forming the fluid meniscus 70, and while maintaining rotation of the fan blades 24 in the second rotational direction, vacuum is applied to the drain lines 50 and the fluid meniscus 70 drains through the drain holes 80. It is understood that a portion of the fluid meniscus 70 may drain through the drain holes 80 prior to application of the vacuum.
In an alternative embodiment, the step 230 is performed after the step 240. In this manner, vacuum is not applied to the drain tubes 50 until after a fluid meniscus is formed between the edge of the fan bladed 24 and the inner wall of the fan housing 22.
The particle collection apparatus 10 is automated to collect a fluid sample that includes the particles eluted from the surface of the fan blades. The processing module 6 controls the automated functions associated with performing the first phase, the second phase, and the third phase described above. In this manner, airborne particles can be automatically collected into a liquid solution. In alternative embodiments, operation of the particle collection apparatus can be manually performed, either in part or in full.
As described herein, the term “speed” is a relative term. The third speed is faster than the second speed, and the second speed is faster than the first speed. Each of the actual speeds is dependent on many factors, including but not limited to, the size of the fan blades, the amount of fluid dispensed onto the fan blades, the distance between the outer perimeter of the fan blades and the inner wall of the fan housing, the height of the fan housing rim relative to the fan blades, and the type of fluid used. For a specific fan assembly and fluid, the actual first speed, second speed, and third speed are experimentally determined.
The particle collection apparatus is described above in relation to a bio-threat application. It is understood that the particle collection apparatus can also be used to collect non-harmful air particles and in general the particle collection apparatus can be used to collect any particles that collect on the surface of a fan blade. It is also understood that the particle collection apparatus can be used within a system, such as the bo-threat detection system described above, or the particle collection apparatus can be used as a stand alone device.
The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of the principles of construction and operation of the invention. Such reference herein to specific embodiments and details thereof is not intended to limit the scope of the claims appended hereto. It will be apparent to those skilled in the art that modifications may be made in the embodiment chosen for illustration without departing from the spirit and scope of the invention.
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