Aerosol Dilution Control for Pressure-Independent Measurements
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Solution Overview
Problem
Aerosol measurement systems face challenges in maintaining a constant dilution factor despite varying inlet pressures, leading to potential particle loss and condensation issues during aerosol sampling, particularly in applications like engine emissions measurement.
Innovation Solution
An aerosol diluting apparatus comprising a first diluting unit that combines an aerosol sample flow with a diluting gas flow, an ejector unit for mixing a second dilution gas, and a control system to adjust flow rates based on pressure signals, ensuring a choked flow condition and maintaining a constant dilution factor by forming a protective annular layer around the aerosol sample flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous diluting tunnel is used to dilute aerosol sample, then particle loss and condensation are reduced, but the dilution factor varies with inlet pressure
Solution Approach 1:
The patent implements dynamic control of dilution gas flow rates based on real-time inlet pressure measurements. The control unit continuously adjusts the flow rates of first and second dilution gases according to the measured inlet pressure, ensuring the dilution factor remains constant despite pressure variations. This dynamic adaptation resolves the contradiction by making the system responsive to changing conditions while maintaining measurement reliability.
Solution Approach 2:
The patent employs a feedback control mechanism where a pressure sensor measures the inlet pressure of the aerosol sample, and this measurement is fed back to the control unit. The control unit processes this feedback signal and adjusts the dilution gas flow rates accordingly through control valves. This closed-loop feedback system ensures the dilution factor remains stable under varying inlet pressure conditions, resolving the technical contradiction between reliability and adaptability.
2Reliability
If dilution gas flow rate is increased to maintain constant dilution factor, then pressure control is improved, but energy consumption increases
Solution Approach 1:
The system dynamically adjusts dilution gas flow rates based on actual inlet pressure conditions rather than operating at fixed high flow rates. When inlet pressure is stable, lower dilution gas flows suffice. When inlet pressure varies, the system increases flow rates only to the extent necessary to maintain constant dilution factor. This dynamic approach reduces overall energy consumption while maintaining reliability.
Solution Approach 2:
The patent changes the operational parameters of the dilution gas flow rates in response to inlet pressure variations. By adjusting flow rates as a variable parameter rather than maintaining a constant high value, the system optimizes the balance between maintaining constant dilution factor and minimizing energy consumption. The control unit modulates flow rates within a range, using higher flows only when necessary.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution ensures a constant dilution factor independent of inlet pressure variations, reduces particle loss, and prevents condensation, enabling accurate aerosol measurements across varying pressure conditions.
Implementation Method 1
an ejector unit to draw the first modified sample flow from the first diluting unit to the ejector unit and to provide a second modified sample flow by mixing a second dilution gas flow with the first modified sample flow
Implementation Method 2
mixing a second dilution gas flow with the first modified sample flow
Implementation Method 3
the first diluting unit comprises a gas permeable tunnel element or a nozzle to form a protective annular layer from the first diluting gas flow such that the protective annular layer surrounds a central portion of the first modified sample flow
Implementation Method 4
maintain the flow rate of the second dilution gas flow higher than a predetermined value such that the minimum pressure in the ejector unit during operation is lower than or equal to 500 mbar, so as to ensure a choked flow condition for the first modified aerosol sample flow in the ejector unit
Data Source
AI summary
The aerosol diluting apparatus includesa first diluting unit to provide a first modified sample flow by combining an aerosol sample flow with a first diluting gas flow,an ejector unit to draw the first modified sample flow from the first diluting unit to the ejector unit and to provide a second modified sample flow by mixing a second dilution gas flow with the first modified sample flow,a control unit, anda control valve,wherein the control unit and the control valve are arranged to adjust flow rate of the second dilution gas flow according to an inlet pressure of the aerosol sample flow, so as to keep the dilution factor of the diluting apparatus substantially independent of the inlet pressure.