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Technology SolutionsEnvironmental Measurement Laboratory

THE IMPORTANCE OF ANEMOMETER

CALIBRATION


The Importance of Anemometer Calibration

WHAT IS AN ANEMOMETER?

An anemometer is a device that is used for measuring wind speed.

The term is derived from the Greek word anemos, meaning wind. The first known description of an anemometer was given by Leon Battista Alberti in around 1450.




Anemometers can be divided into two classes: those that measure the wind's velocity, and those that measure the wind's pressure

but as there is a close connection between the pressure and the velocity, an anemometer designed for one will give information about both.




There are 3 types of measuring equipment :

Hotwire Anemometer

Pitot Tube

Vane Anemometer



HOTWIRE ANEMOMETER



HOTWIRE ANEMOMETERHot wire anemometers use a very fine wire (on the order of several micrometers) heated up to some temperature above the ambient. Air flowing past the wire has a cooling effect on the wire.



HOTWIRE ANEMOMETERAs the electrical resistance of most metals is dependent upon the temperature of the metal (tungsten is a popular choice for hot-wires), a relationship can be obtained between the resistance of the wire and the flow velocity.



HOTWIRE ANEMOMETERHot-wire anemometers, while extremely delicate, have extremely high frequency-response and fine spatial resolution compared to other measurement methods, and as such are almost universally employed for the detailed study of turbulent flows, or any flow in which rapid velocity fluctuations are of interest.



PITOT TUBEA pitot (pronounced /pi-to-/) tube is a pressure measurement instrument used to measure fluid flow velocity.



PITOT TUBEThe pitot tube was invented by the French engineer Henri Pitot in the early 1700s [and was modified to its modern form in the mid 1800s by French scientist Henry Darcy]. It is widely used to determine the airspeed of an aircraft and to measure air and gas velocities in industrial applications.



PITOT TUBEThe basic pitot tube consists of a tube pointing directly into the fluid flow. As this tube contains fluid, a pressure can be measured; the moving fluid is brought to rest (stagnates) as there is no outlet to allow flow to continue.



PITOT TUBE

This pressure is the stagnation pressure of the fluid, also known as the total pressure or (particularly in aviation) the pitot pressure.



PITOT TUBE

The measured stagnation pressure cannot of itself be used to determine the fluid velocity (airspeed in aviation). However, Bernoulli's equation states:



PITOT TUBE

Stagnation Pressure = Static Pressure + Dynamic Pressure



VANE ANEMOMETER



VANE ANEMOMETER

A vane anemometer is a portable instrument used to measure low wind speeds and airspeeds in large ducts; consists of a number of vanes radiating from a common shaft and set to rotate when facing the wind.



VANE ANEMOMETER

A small fan is turned by air flowing over the vanes. The speed of the fan is measured by a rev counter and converted to a wind speed by an electronic chip.



WHAT IS VELOCITY?In physics, velocity is the rate of change of displacement (position). It is a vector physical quantity; both magnitude and direction are required to define it. The scalar absolute value (magnitude) of velocity is speed, a quantity that is measured in meters per second (m/s or ms−1) when using the SI (metric) system.


http://en.wikipedia.org/wiki/International_System_of_Units


WHAT IS VELOCITY?



WHAT IS VELOCITY?An airflow that enters a channel undergoes quite a change on its way downstream. It is evident that the only exact way to characterise such a flow is as velocity field. That type of specification is of course complex but computers can easily manage this problem.



AIR VELOCITY MEASUREMENTS Aircrafts Mines Fume cabinets Cranes



AircraftsPitot tubes on aircraft commonly have heating elements called pitot heat to prevent the tube from becoming clogged with ice. The failure of these systems can have catastrophic consequences, as in the case of Austral Líneas Aéreas Flight 2553, Northwest Orient Airlines Flight 6231, AeroPeru Flight 603 (blocked static port), and of one X-31.



MinesChile’s Mine, San José, disaster! On 5 August 2010, 33 people were trapped underground, because the roof of the copper mine collapsed. These men are trapped 700 meter underground, and 5 kilometres from the mine entrance.



San JosèMine in Chille



Mines in Cille



Mines Temperature Humidity Fresh Air



The basic requirement for the mine ventilation system is to provide air for people to breath and in a state that will not cause any immediate or future ill effects.



The ventilation system must therefore be sufficient to deal with the contaminants released during mining. If they are not adequately dealt with, as they are identified, they may become at best a discomfort to mine workers, and at worst cause serious or even fatal illness.



The prime contaminants produced during mining are

dustheatgases (including water vapour i.e.

Humidity)



and the prime method for dealing with these is an effective ventilation system that

supplies oxygen and coolsdilutes dust and gases andremoves the contaminants from the

workplace.Technology SolutionsEnvironmental Measurement Laboratory


It is possible that any known substance will be identified, in either the air we breathe or the food we eat. Although the human body is equipped to reject or absorb these substances this can only be done providing the quantities involved are not excessive.



“Heavy or strenuous work increases lung ventilation, thereby increasing the uptake of airborne contaminants. Similarly, heavy physical work under adverse climatic conditions, such as excessive humidity or heat, or work at high altitudes, may lead to an increased uptake of contaminants.



It is therefore of particular importance that any evaluation of the working environment considers the lung ventilation rate where there is a significant airborne concentration of contaminant.”



A Comparison of some Atmospheric Exposure Standards Adjusted for Shift Duration


CONTAMINANT 8-hour TWA10-hour

12-hour STELAny

* Carbon Monoxide (CO) 30 21 15 400* Carbon Dioxide (CO2) 5,000 3500 2,500 35,000* Nitrogen Dioxide (NO2) 3 2 1.5 5* Nitrous Oxide (NO) 25 18 12* Sulphur Dioxide (SO2) 2 1 1 5* Hydrogen Sulphide (H2S) 10 7 5 15


A Comparison of some Atmospheric Exposure Standards Adjusted for Shift Duration

NOTES: * = ppm # = mg/m3 UR = Under ReviewNA = Not ApplicableTWA = Time Weighted AverageSTEL = Short Term Exposure Limit


CONTAMINANT 8-hour TWA10-hour

12-hour STELAny

# Respirable Dust 5.00 3.50 2.50 NA

# Quartz Bearing Dust 0.20 0.14 0.10 NA

# Respirable Combustible Dusts 2.00 1.40 1.00 NA


Short-term exposure limits (STELs) provide guidelines for the control of short-term exposure.

These are important supplements to the eight-hour TWA exposure standards that are more concerned with the total intake over long periods of time. Generally, STELs are established to minimise the risk of the occurrence in nearly all workers of: intolerable irritation chronic or irreversible tissue change, and narcosis to an extent that could precipitate industrial

accidents.Technology SolutionsEnvironmental Measurement Laboratory


A significant number of these hazards can result in serious health problems, ranging from long-term physical impairment (e.g. lung disease) to immediate death (e.g. carbon monoxide poisoning, or heat stroke). It is the role of a mine’s ventilation systems to control these hazards, but before any ventilation engineering design work is carried out, it is vital that the hazards are well understood.



It should be noted that the human body is very resilient and well equipped to deal with nature’s climatic and atmospheric extremes. However, some processes involved in activities such as mining produce contaminant levels and environmental conditions which are beyond those with which the body’s natural defence systems can cope.



The human capacity to function at the maximum potential will reduce rapidly in atmospheres contaminated with dust, gases, heat and humidity and the long term effects of exposure to contaminants may have serious impact on general medical health.



Respitory System



Gases, vapours and dusts may enter the human body in three ways

Inhaled into the respiratory systemIngested with food and saliva into the

digestive systemAbsorbed through the skin



The danger posed by fire is another aspect of large-scale mechanization in mining operations. Fire is a constant hazard wherever large sources of energy are stored and used, as is the case in mining machinery. The outbreak of a sudden, highly intense fire underground has the potential for catastrophic outcomes and must be avoided at all costs.



The combination of combustible materials such as hydraulic oils and rubber tyres in the vicinity of hot surfaces has to be managed continuously and safely wherever vehicles operate. The fire risk posed by diesel powered machinery is further intensified by the presence of diesel fuel, which may participate in the combustion process and increase the intensity of the heat, smoke and gas emissions in the event of a fire.



A further dimension to the risk in terms of using diesel power underground is found in the large-scale transport and distribution of the fuel as part of routine operations. The storage of fuel underground requires awareness in terms of a thorough risk assessment and the adoption of protective and preventative measures to limit the fire risk.



The large-scale use of conveyor belts also presents a significant risk for the rapid development of underground fires. The flow of fresh air over conveyor belts provides a continuous source of oxygen that may cause the fire to become self-sustaining under certain circumstances. In addition, the location of conveyor belts in intake airways provides the potential for large-scale contamination of the mine’s atmosphere.



These hazards are managed effectively by the analysis of various risk scenarios and the implementation of protective and preventative measures devised in accordance with such analyses:



Routing of fresh air away from high risk areas (conveyor belts, underground rubber tyre, fuel and oil storage areas, etc.) will limit air contamination during a fire.



The provision of early detection systems, action protocols and fire fighting procedures is essential in limiting the spread of a fire. This includes the remote monitoring of the air flowing through high risk areas, the provision of adequate and back-up communication systems and protocols, the provision of effective fire fighting equipment



The timely provision of protective measures and the training of workers in the use of protective equipment is the last component of the strategy. Of particular importance are systems designed to provide respirable atmosphere to workers who are affected by the smoke and gases emanating from the fire and who may not be able to reach a point in fresh air.



Fume cabinets



The primary function of a fume cupboard system is to contain and convey potentially dangerous or obnoxious fumes from the fume cupboard enclosure to an outside discharge point where it can be safely dispersed at low concentration. The operational system performance will be demonstrated in terms of a containment test and face velocity measurements.



In the past, fume cupboard performance has been monitored by measuring the rate at which air is drawn across the open aperture, this being known as face velocity, and a nominal range of acceptable values have been suggested by various sources usually between 0.5 - 1meter per second.



Research has shown that the mechanisms by which contaminants migrate across the aperture boundary are a function of complex aerodynamic conditions, and are not necessarily related to face velocity, making its measurements an unreliable indicator of performance.



It is now generally accepted that a better indicator is the ability to arrest and retain a gaseous challenge released within the enclosure, the leakage being quantified by means of externally positioned detection devices, and referred to as containment testing.



In addition to the above measurements it is necessary to monitor the performance of the prime movers and other engineering components within the system, including the measurement of air velocity and pressure in ducting, and the speed and direction of fan impellers.



In addition to the above measurements it is necessary to monitor the performance of the prime movers and other engineering components within the system, including the measurement of air velocity and pressure in ducting, and the speed and direction of fan impellers.



AIR VELOCITY MEASUREMENTS CranesImagine working on a crane high up in the air.Strong wind blowing.Are you safe?What about monitoring wind speed?



ConclusionIs the equipment use for measuring air

velocity accurate? Is the equipment calibrated?



ConclusionIs it the correct instrument for the correct

application?How serious is health and safety to you? What are you going to do about it?



QUESTIONS?


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Technology Solutions Environmental Measurement Laboratory