Critical Flow Orifices Research Articles

Experimental investigation of B20 combustion and emissions under various intake conditions for low-temperature combustion

Recently, biodiesel has emerged as an alternative fuel for achieving low-temperature combustion (LTC). Several articles in the literature have showed that oxygenated biofuels, including biodiesel, can improve combustion stability under high exhaust gas recirculation (EGR) operation, which is considered to be necessary for the removal of nitric oxides (NOx). The objective of this study was to investigate the performance and emissions of 20% biodiesel blended diesel fuel (B20) at various intake pressures and oxygen concentration levels to characterize the fuel for LTC application. The experimental investigation of B20 was carried out using a single-cylinder engine (SCE) at 1400 rpm and 50% load condition. A set of critical flow orifices with synthetic EGR was employed to simulate various intake pressures and EGR levels. The behavior of the B20 was first characterized under various intake conditions. The results showed that with high oxygen intake, B20 exhibited combustion and emission levels that were very similar to conventional diesel. However, B20 reduced combustion deterioration while exhibiting lower carbon monoxide (CO) and hydrocarbon (HC) emissions than diesel under low oxygen intake conditions.

A dynamic gravimetric standard for trace water

A system for generating traceable reference standards of water vapor at trace levels between 5 and 2000 nmol/mol has been developed. It can provide different amount fractions of trace water vapor by using continuous accurate measurements of mass loss from a permeation device coupled with a dilution system based on an array of critical flow orifices. An estimated relative expanded uncertainty of ±2% has been achieved for most amount fractions generated. The system has been used in an international comparison and demonstrates excellent comparability with National Metrology Institutes maintaining standards of water vapor in this range using other methods.

Effects of Geometry on Aerodynamics of CFO

CFO(Critical Flow Orifice), micro sonic nozzle, is a device in tobacco industry to give a standard gas flow rate. Adopting the blocking effect of the convergent nozzles for compressible fluid, CFO can produce an accurate flow rate in pipe line. CFO can be used in micro flow calibration such as in the measurement of the pressure drop of filter rod or draw resistance of cigarette. To study the effect of convergent shapes on the aerodynamic characteristics of CFO, the 3D numerical simulations are carried out on two kinds of CFO structure shapes with finite volume method, based on the equations of compressible gas. The adopted turbulence model is the realizable k-ε model. According to the results of simulation, using Vyshinsky curve as the convergent curve is better than to apply the cone-shaped curve with the same exit diameter of nozzle. This is difficult to be observed in the experiments. The influence of convergent shapes can provide a basis for optimization design of CFO.

High-accuracy stable gas flow dilution using an internally calibrated network of critical flow orifices

A network of critical flow orifices has been developed to form a gas flow dilutor capable of stable and repeatable operation, which is not influenced by environmental conditions. When used with a novel self-calibration method it achieves dilutions of up to 31:1 with a relative standard uncertainty of ±0.1%. This new approach avoids the uncertainty generated by setting and controlling the flow which is present in devices based on variable flow elements.

Accurate, Adjustable Calibration Source for Measurements of Trace Water Vapour

A number of manufacturing processes are adversely affected by the presence of trace amounts of water vapour in purge and process gases. It is important for the operators of such processes to monitor the levels of water vapour in these gases continuously. There are many analytical methods for determination of trace water vapour which all require regular, traceable calibration. In this paper, a new standard facility for generating an adjustable level of trace water vapour is described. It uses continuous accurate measurements of the mass loss from a permeation device coupled with a dilution system based on an array of critical flow orifices. Details of the verification of the facility are presented along with results of comparisons with the National Physical Laboratory thermally-based dew/frost point humidity standards facility.

Accurate measurements of airway mucosal blood flow, a new biomarker of asthma: Comparison of two soluble gases

Rationale Airway mucosal vasculature participates in absorption of inhaled drugs and inflammatory processes. We tested two soluble gases, HFA 134a and acetylene to determine non-invasively airway mucosal vascularity as a marker of airway inflammation. Methods Six steroid naive asthmatics and six healthy subjects were tested. Deadspace volume was assessed using Fowler's method. Subjects inhaled to TLC one soluble gas mixture containing 0.3% acetylene and another containing HFA 134a which were exhaled into a spirometer through a critical flow orifice to standardize flow. Instantaneous concentrations of these gases in the anatomical dead-space fraction were measured at the airway opening using a mass spectrometer. Time dependent uptake was assessed by increasing breathold times between 2.5 and 20 secs. Results Mean percentage uptake of acetylene and HFA 134a was for asthmatic subjects, median 25.1% (15.76%-31.79%) and 3.87% (2.0%7.48%) compared to normal subjects, median 14.4% (6.10%-20.83%) ( p<0.05) and 2.25% (0.9% - 5.37%) ( p<0.05) respectively. Mean time dependent percentage uptake of acetylene with three randomly performed breatholds at 2.5, 5 and 10 seconds breatholds was for asthmatic subjects 32.12%, 35.7% and 39.22% respectively and for healthy subjects 26.0%, 27.71% and 36.12% respectively. Time dependent uptake was not seen with HFA 134a. Conclusions Lack of time dependent uptake of HFA 134a renders it unsuitable to determine airway mucosal blood flow (AMBF). Our results demonstrated acetylene is the better gas to determine AMBF as a marker of airway inflammation. It has the potential to evaluate new and existing treatments with utility across the range of asthma severity and other inflammatory airway diseases.

Calibration and demonstration of a condensation nuclei counting system for airborne measurements of aircraft exhausted particles

A system of multiple continuous-flow condensation nuclei counters (CNC) was assembled, calibrated, and demonstrated on a NASA T-39 Sabreliner jet aircraft. The mission was to penetrate the exhaust plumes and/or contrails of other subsonic jet aircraft and determine the concentrations of submicrometer diameter aerosol particles. Mission criteria required rapid response measurements ( ∼ 1 s) at aircraft cruise altitudes (9–12 km). The CNC sampling system was optimized to operate at 160 Torr. Aerosol samples were acquired through an externally mounted probe. Installed downstream of the probe was a critical flow orifice that provided sample to the CNC system. The orifice not only controlled volumetric flow rate, but also dampened probe pressure/flow oscillations encountered in the turbulent aircraft-wake vortex environment. Laboratory calibrations with NaCl particles under representative conditions are reported that indicate small amounts of particle loss and a maximum measurement efficiency of ∼ 75% for particles with diameters ranging from ⩾ 0.01− ⩽ 0.18 μm Data from exhaust/contrail samplings of a NASA B757 and DC-8 at cruise altitude are discussed. Data include exhaust/contrail measurements made during periods in which the B757 port jet engine burned low-sulfur fuel while the starboard engine simultaneously burned specially prepared high-sulfur fuel. The data discussed highlight the CNC systems performance, and introduce new observations pertinent to the behavior of sulfur in aircraft exhaust aerosol chemistry.

Note On The Use of Watch Jewels as Critical Flow Orifices

Note On The Use of Watch Jewels as Critical Flow Orifices

An Infrared Method for the Determination of Carbon Monoxide and Carbon Dioxide Levels in Cigarette Smoke

AbstractA method for the simultaneous determination of the CO and CO2 concentrations in each puff of a cigarette was developed. Puff characteristics of single and multiport smoking machines were controlled by selection of critical flow orifices. The CO and CO2 were rapidly measured by nondispersive infra-red analysers, which required no wave length scanning and were free from interference by other smoke components. Precision was increased by a six-port head compared to a single port but was not improved by a 12-port head. The procedure has been applied in studies of various commercial and experimental cigarettes

Description of a Controllable Sonic Flow Orifice

By varying the length of a constant area passage in which the mass flow is limited by frictional effects a controllable valve results with characteristics close to those of the critical flow orifice. This design principle leads to a simple valve geometry which is easier to manufacture and is generally sturdier than a comparable needle valve. For a prototype and a bank of 10 similar valves designed to furnish 0.025 kg/sec from a 10 MN/m2 source of air, the results confirm fine control of the mass flow rate by a factor of 2 or more and a mass flow rate dependent on the square root of upstream stagnation pressure.

The Efficiency of Various Liquid Impinger Samplers in Bacterial Aerosols

The liquid impinger was first described by Greenburg and Smith (1922) as a dust cloud sampler. More recently the device has come into wide use for bacterial aerosol sampling, as it is often very con venient for this purpose both in laboratory apparatus and in the field. Rosebury (1947) and Henderson (1952) describe the use of the Port?n develop ment of the original device. For estimating the number of viable organisms trapped in the impinger fluid they use the technique of Miles and Misra (1938) in which serial dilutions of the fluid are plated out for subsequent incubation and colony counting. Valuable features of the impinger when sampling airborne organisms are: (1) It is compact and inex pensive. (2) The sample fluid can be plated out simultaneously on differing media thus ensuring optimum growth conditions for organisms of interest. (3) An extreme range of airborne concentra tion can be accommodated by the serial dilution technique. (4) Virus aerosols can be estimated effectively, provided that they do not contain a high proportion of very small, single virus particles which are difficult to impinge. (5) The particle retention efficiency is very high, effectively all particles down to about 0-5/x being trapped in the impinger fluid. (6) It gives a measure of the number of individual viable organisms in an aerosol, not the number of infective particles or clusters of organisms. (7) It acts as its own constant-flow metering device. (8) It is unaffected by repeated autoclaving. Impingers similar to that shown in Fig. 1 were originally developed by Prof. J. H. Gaddum and have been in use in this establishment for many years. Fig. 1 shows the modern all-glass Port?n type. Suction is applied to the small side arm and draws air in through the curving intake tube and down through the impinging jet. The jet is a short length of capillary tubing and acts as a critical flow orifice, i.e., when the suction reaches about half an atmosphere the flow in the jet attains sonic velocity (Druett, 1955) and any subsequent increase in suction cannot increase the jet velocity further. Provided therefore that there is at least half an atmosphere of suction the impinger operates at constant flow and, once calibrated, does not require a flowmeter. The sonic velocity air jet strikes the flat base of the flask, throwing out its burden of particles which become suspended in the violently agitated circulating liquid. The apparatus shown in Fig. 1 has a jet diameter of 11 mm. giving a flow rate of 11 litres/min. and it holds 10 ml. of liquid in the flask, which has an internal diameter of li inches. The flask is made long in proportion to its width so that splashes of liquid cannot be entrained out of the suction tube (Rosebury used a conical flask which splashes less owing to the broader base, and which stands safely on the bench). The dis tance between the jet and flask base is 4 mm. It will readily be seen that the im pingement process is of great violence, for in a distance of about 1 cm. particles are accelerated up to sonic speed (about 760 m.p.h.) and are thrown against the hard glass base of the flask at approxi -All-glass Port?n impinger. 287

The Measurement of Chemical Equilibria by Means of the Critical Flow Orifice

First Page