Trystan Casey
Electrical mobility is the ability of charged particles, such as electrons or protons, to move through a medium in response to an electric field. The electrical mobility diameter, dme, is the diameter of a sphere carrying the same electric charge and with the same electrical mobility as the particle under consideration. In other words, the electrical mobility of a particle is defined as the ratio of the drift velocity to the magnitude of the electric field. This is also known as the Einstein-Smoluchowski relation, which connects the diffusion constant with electrical mobility.
| Characteristics | Values |
|---|---|
| Definition | Electrical mobility is the ability of charged particles (such as electrons or protons) to move through a medium in response to an electric field that is pulling them. |
| Formula | The electrical mobility of a particle is defined as the ratio of the drift velocity to the magnitude of the electric field. |
| Example | The mobility of the sodium ion (Na+) in water at 25 °C is 5.19×10−8 m2/(V·s). This means that a sodium ion in an electric field of 1 V/m would have an average drift velocity of 5.19×10−8 m/s. |
| Relation to Other Concepts | Electrical mobility is proportional to the net charge of the particle. It is also inversely proportional to the Stokes radius of the ion, which is the effective radius of the moving ion, including any molecules of water or other solvents that move with it. Electrical mobility is related to the Einstein-Smoluchowski relation (also known as the Einstein relation), which connects the random motion of electrons in a wire (without a voltage difference applied) to a current flow through a wire (when a voltage difference is applied). |
| Applications | Electrical mobility analyzers are used as particle-size classifiers for condensation particle counters or electrical aerosol detectors. They can be used to study the effects of electric wind on size distribution measurements. Electrical mobility is also the basis for electrostatic precipitation, which is used to remove particles from exhaust gases on an industrial scale. |
| Related Terms | Electric vehicle, e-mobility, electro mobility, electrical car, electrical vehicle. |
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What You'll Learn
- Electric wind distorts size distribution measurements using Differential Mobility Analyzers (DMAs)
- The electrical mobility diameter is the diameter of a sphere carrying the same charge and mobility as the particle under consideration
- Electrical mobility is the ability of charged particles to move through a medium in response to an electric field
- Electrical mobility is proportional to the net charge of the particle
- The electrical mobility analyzer is a particle-size classifier for a condensation particle counter or an electrical aerosol detector
Electric wind distorts size distribution measurements using Differential Mobility Analyzers (DMAs)
Electric wind is the movement of gas induced by ions moving in an electric field. It can be a distorting factor in size distribution measurements using Differential Mobility Analyzers (DMAs). DMAs are narrow-band linear ion mobility filters that operate at atmospheric pressure. They are used for size classification of nanometer-sized aerosol particles.
The performance of DMAs can be affected by electric wind, which is influenced by factors such as electric field strength, aerosol layer thickness, particle number concentration, and particle size. This can result in three types of distortion in the measured size spectra: a widening of the size distribution, a shift of the mode of the distribution to smaller diameters, and a smoothing out of the peaks of the multiply charged particles.
To mitigate the impact of electric wind on DMA measurements, various vapor-removal schemes can be employed to increase the noise-suppression capacity of the DMA. This helps to reduce the attachment of impurity vapors to the reagent ion or the analyte of interest, improving the accuracy of size distribution measurements.
Additionally, the sizing accuracy and resolution of DMAs can be probed and optimized through techniques such as voltage stepping mode, which allows for the retrieval of size distribution data. By comparing measurements from different commercial mobility spectrometers, scientists can also ensure the reliability and accuracy of DMA measurements.
Overall, while electric wind can distort size distribution measurements using DMAs, a combination of experimental techniques and data analysis methods can help minimize its impact and provide more accurate results.
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The electrical mobility diameter is the diameter of a sphere carrying the same charge and mobility as the particle under consideration
Electrical mobility is the ability of charged particles, such as electrons or protons, to move through a medium in response to an electric field. The electrical mobility of a particle is defined as the ratio of the drift velocity to the magnitude of the electric field. For example, the mobility of the sodium ion (Na+) in water at 25 °C is 5.19 x 10^-8 m^2/(V·s). This indicates that a sodium ion in an electric field of 1 V/m would have an average drift velocity of 5.19 x 10^-8 m/s.
The electrical mobility diameter, or 'dme', is the diameter of a sphere carrying the same charge and mobility as the particle under consideration. In other words, it is the diameter of a sphere with the same electric charge and electrical mobility as the particle being studied. This diameter is used to measure the size distribution of submicron particles. The most common instrument used for this purpose is the SMPS (Scanning Mobility Particle Sizer), which consists of an impactor to remove large particles, a neutralizer to charge the particles to a predictable charge distribution, a DMA (Differential Mobility Analyzer) to classify the particles, and a CPC.
The DMA is a crucial component in determining the electrical mobility diameter. It consists of a pair of concentric metal cylinders. Filtered air is introduced at the top and exits at the bottom, with the flow regulated to create a laminar flow. Particles from a charge neutralizer enter the classifier as an annular sheath in the outer cylinder. By applying an attractive voltage on the collector rod, the trajectory of the particle stream can be varied, allowing particles of a specific mobility range to be collected by the annular inlet in the center cylinder.
The SMPS and DMA work together to provide valuable insights into the size distribution of particles based on their electrical mobility. By ramping up the voltage to the DMA, typically from 0 V to 10,000 V, the full range of electrical mobility corresponding to different particle sizes can be covered. This helps in classifying and analyzing particles with precision, making it a valuable tool in fields such as chemical engineering and aerosol science.
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Electrical mobility is the ability of charged particles to move through a medium in response to an electric field
Electrical mobility is a fundamental concept in physics and chemistry, describing the ability of charged particles, such as electrons and protons, to move through a medium in response to an electric field. This phenomenon is crucial in various scientific and technological applications, from electrochemistry to the development of batteries.
When a charged particle is subjected to a uniform electric field, it accelerates until it attains a constant drift velocity. This velocity is influenced by the strength of the electric field and the characteristics of the particle itself. Electrical mobility is defined as the ratio of the drift velocity to the magnitude of the electric field. For example, the mobility of a sodium ion (Na+) in water at 25°C is 5.19×10−8 m2/(V·s). This indicates that in an electric field of 1 V/m, the sodium ion would have an average drift velocity of 5.19×10−8 m/s.
The electrical mobility of a particle is influenced by several factors. Firstly, it is directly proportional to the net charge of the particle. This relationship was demonstrated by Robert Millikan, who showed that electrical charges exist in discrete units, with the magnitude of the electron's charge as the fundamental unit. Secondly, electrical mobility is inversely proportional to the Stokes radius of the ion. The Stokes radius refers to the effective radius of the moving ion, including any solvent molecules that accompany its motion. Therefore, ions with smaller radii tend to have higher mobilities.
The concept of electrical mobility is utilised in various instruments and techniques. One example is the electrical mobility analyzer, which acts as a particle-size classifier. This instrument consists of a pair of concentric metal cylinders through which filtered air flows. By applying a voltage to the collector rod, particles with different mobilities can be collected and counted, allowing for the determination of particle size. Another technique that relies on electrical mobility is electrostatic precipitation, used to remove particles from exhaust gases on an industrial scale. By imparting an electrical charge to the particles and applying a strong electric field, they can be directed to a collecting electrode, facilitating their removal from the gas stream.
In summary, electrical mobility represents the ability of charged particles to traverse a medium under the influence of an electric field. This concept is essential in understanding and manipulating the behaviour of charged particles, with applications in various scientific and industrial contexts.
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Electrical mobility is proportional to the net charge of the particle
Electrical mobility is the ability of charged particles (such as electrons or protons) to move through a medium in response to an electric field. It is defined as the ratio of the drift velocity to the magnitude of the electric field. For example, the mobility of the sodium ion (Na+) in water at 25 °C is 5.19×10−8 m2/(V·s). This means that a sodium ion in an electric field of 1 V/m would have an average drift velocity of 5.19×10−8 m/s.
The electrical mobility diameter is the diameter of a sphere carrying the same electric charge and with the same electrical mobility as the particle under consideration. Differential mobility analyzers (DMAs) are used to measure particle mobility sizes and act as an electric filter, allowing only particles with certain electrical mobilities to pass through.
The relationship between electrical mobility and net charge can be further understood through the concept of conductivity. Conductivity is proportional to the product of mobility and carrier concentration. This means that the same conductivity can result from a small number of electrons with high mobility or a large number of electrons with low mobility.
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The electrical mobility analyzer is a particle-size classifier for a condensation particle counter or an electrical aerosol detector
The electrical mobility analyzer is an instrument used as a particle-size classifier for a condensation particle counter or an electrical aerosol detector. It consists of a pair of concentric metal cylinders. The process begins by introducing filtered air at the top, which exits at the bottom. The flow is regulated to create a laminar flow. Particles from a charge neutralizer are given a charge of known polarity and magnitude as a Boltzmann equilibrium charge distribution. They then enter the classifier as an annular sheath in the outer cylinder. The trajectory of the particle stream is altered by applying a voltage to the collector rod.
Particles with a finite mobility range are collected by the annular inlet in the center cylinder and are counted using a CNC. By adjusting the voltage on the collector, particles of different sizes are collected. This process allows for the classification of particles according to their electrical mobility. The size of the particles is then reported.
Electrical mobility analyzers are used in conjunction with condensation particle counters (CPCs), which are the most widely used UFP detection instruments. CPCs grow ultrafine particles (UFPs) into micro-sized droplets through condensation and count them using optical methods. By using a differential mobility analyzer (DMA) as a particle size selector, CPCs can achieve higher particle size resolution than other particle sizing instruments.
Additionally, electrical mobility analyzers can be used with electrical aerosol detectors, which are conductive filters that trap particles of any type sampled. The charge on the particles is drained to the ground through an electrometer, a sensitive current-measuring device. This method allows for the detection of a significant fraction of sampled particles.
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