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A free-standing fume hood A fume hood is typically a large piece of equipment enclosing five sides of a work area, the bottom of which is most commonly located at a standing work height. Two main types exist, and recirculating (ductless).
The principle is the same for both types: air is drawn in from the front (open) side of the cabinet, and either expelled outside the building or made safe through and fed back into the room. This is used to:. protect the user from inhaling toxic gases (fume hoods, biosafety cabinets, glove boxes). protect the product or experiment (biosafety cabinets, glove boxes).
protect the environment (recirculating fume hoods, certain biosafety cabinets, and any other type when fitted with appropriate filters in the exhaust airstream) Secondary functions of these devices may include, and other functions necessary to the work being done within the device. Fume hoods are generally set back against the walls and are often fitted with infills above, to cover up the exhaust ductwork. Because of their recessed shape they are generally poorly illuminated by general room lighting, so many have internal lights with vapor-proof covers. The front is a, usually in glass, able to move up and down on a mechanism. On educational versions, the sides and sometimes the back of the unit are also glass, so that several pupils can look into a fume hood at once. Low air flow are common, see below.
Fume hoods are generally available in 5 different widths; 1000 mm, 1200 mm, 1500 mm, 1800 mm and 2000 mm. The depth varies between 700 mm and 900 mm, and the height between 1900 mm and 2700 mm. These designs can accommodate from one to three operators. For exceptionally, an enclosed may be used, which completely isolates the operator from all direct physical contact with the work material and tools.
The enclosure may also be maintained at negative air pressure to ensure that nothing can escape via minute air leaks. Liner materials. (for general applications). (FRP). Square-corner (for durability and heat resistance).
stainless steel (easier to, for and applications). (for rough usage) Control panels Most fume hoods are fitted with a -powered control panel. Typically, they perform one or more of the following functions:. Warn of low air flow.
Warn of too large an opening at the front of the unit (a 'high sash' alarm is caused by the sliding glass at the front of the unit being raised higher than is considered safe, due to the resulting air velocity drop). Allow switching the exhaust fan on or off.
Allow turning an internal light on or off Specific extra functions can be added, for example, a switch to turn a waterwash system on or off. Ducted fume hoods. A common ducted fume hood Most fume hoods for industrial purposes are ducted. A large variety of ducted fume hoods exist. In most designs, conditioned (i.e.
Heated or cooled) air is drawn from the lab space into the fume hood and then dispersed via ducts into the outside atmosphere. The fume hood is only one part of the lab ventilation system. Because recirculation of lab air to the rest of the facility is not permitted, air handling units serving the non-laboratory areas are kept segregated from the laboratory units. To improve indoor air quality, some laboratories also utilize single-pass air handling systems, wherein air that is heated or cooled is used only once prior to discharge. Many laboratories continue to use return air systems to the laboratory areas to minimize energy and running costs, while still providing adequate ventilation rates for acceptable working conditions. The fume hoods serve to evacuate hazardous levels of contaminant. To reduce lab ventilation energy costs, variable air volume (VAV) systems are employed, which reduce the volume of the air exhausted as the fume hood sash is closed.
This product is often enhanced by an automatic sash closing device, which will close the fume hood sash when the user leaves the fume hood face. The result is that the hoods are operating at the minimum exhaust volume whenever no one is actually working in front of them. Since the typical fume hood in US climates uses 3.5 times as much energy as a home, the reduction or minimization of exhaust volume is strategic in reducing facility energy costs as well as minimizing the impact on the facility infrastructure and the environment. Particular attention must be paid to the exhaust discharge location, to reduce risks to public safety, and to avoid drawing exhaust air back into the building air supply system. Auxiliary air This method is outdated technology.
The premise was to bring non-conditioned outside air directly in front of the hood so that this was the air exhausted to the outside. This method does not work well when the climate changes as it pours frigid or hot and humid air over the user making it very uncomfortable to work or affecting the procedure inside the hood. This system also uses additional ductwork which can be costly. Constant air volume (CAV) In a survey of 247 lab professionals conducted in 2010, Lab Manager Magazine found that approximately 43% of fume hoods are conventional CAV fume hoods. Non-bypass CAV. A conventional (non-bypass) constant-air-volume fume hood Closing the sash on a non-bybass CAV hood will increase (“pull'), which is a function of the total volume divided by the area of the sash opening. Thus, a conventional hood’s performance (from a safety perspective) depends primarily on sash position, with safety increasing as the hood is drawn closed.
To address this issue, many conventional CAV hoods specify a maximum height that the fume hood can be open in order to maintain safe airflow levels. A major drawback of conventional CAV hoods is that when the sash is closed, velocities can increase to the point where they disturb instrumentation and delicate apparatuses, cool hot plates, slow reactions, and/or create turbulence that can force contaminants into the room. Bypass CAV. A bypass fume hood. The grille for the bypass chamber is visible at the top. Bypass CAV hoods (which are sometimes also referred to as conventional hoods) were developed to overcome the high velocity issues that affect conventional fume hoods.
These hood allows air to be pulled through a 'bypass' opening from above as the sash closes. The bypass is located so that as the user closes the sash, the bypass opening gets larger. The air going through the hood maintains a constant volume no matter where the sash is positioned and without changing fan speeds. As a result, the energy consumed by CAV fume hoods (or rather, the energy consumed by the building HVAC system and the energy consumed by the hood's exhaust fan) remains constant, or near constant, regardless of sash position. Low flow/high performance bypass CAV 'High-performance' or 'low-flow' bypass CAV hoods are the newest type of bypass CAV hoods and typically display improved containment, safety, and energy conservation features.
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Low-flow/high performance CAV hoods generally have one or more of the following features: sash stops or horizontal-sliding sashes to limit the openings; sash position and airflow sensors that can control mechanical baffles; small fans to create an air-curtain barrier in the operator’s breathing zone; refined aerodynamic designs and variable dual-baffle systems to maintain laminar (undisturbed, nonturbulent) flow through the hood. Although the initial cost of a high-performance hood is typically more than that of a conventional bypass hood, the improved containment and flow characteristics allow these hoods to operate at a face velocity as low as 60 fpm, which can translate into $2,000 per year or more in energy savings, depending on hood size and sash settings. Reduced air volume (RAV) Reduced air volume hoods (a variation of low-flow/high performance hoods) incorporate a bypass block to partially close off the bypass, reducing the air volume and thus conserving energy. Usually, the block is combined with a sash stop to limit the height of the sash opening, ensuring a safe face velocity during normal operation while lowering the hood’s air volume.
By reducing the air volume, the RAV hood can operate with a smaller blower, which is another cost-saving advantage. Since RAV hoods have restricted sash movement and reduced air volume, these hoods are less flexible in what they can be used for and can only be used for certain tasks. Another drawback to RAV hoods is that users can in theory override or disengage the sash stop. If this occurs, the face velocity could drop to an unsafe level. To counter this condition, operators must be trained never to override the sash stop while in use, and only to do so when loading or cleaning the hood.
Variable air volume (VAV). A variable airflow (constant-velocity) fume hood, with a visible flow sensor VAV hoods, the newest generations of laboratory fume hoods, vary the volume of room air exhausted while maintaining the face velocity at a set level. Different VAV hoods change the exhaust volume using different methods, such as a damper or valve in the exhaust duct that opens and closes based on sash position, or a blower that changes speed to meet air-volume demands.
Most VAV hoods integrate a modified bypass-block system that ensures adequate airflow at all sash positions. VAV hoods are connected electronically to the laboratory building’s HVAC, so hood exhaust and room supply are balanced. In addition, VAV hoods feature monitors and/or alarms that warn the operator of unsafe hood-airflow conditions.
Although VAV hoods are much more complex than traditional constant-volume hoods, and correspondingly have higher initial costs, they can provide considerable energy savings by reducing the total volume of conditioned air exhausted from the laboratory. Since most hoods are operated the entire time a laboratory is open, this can quickly add up to significant cost savings. These savings are, however, completely contingent on user behavior: the less the hoods are open (both in terms of height and in terms of time), the greater the energy savings. For example, if the laboratory's ventilation system uses 100% once-through outside air and the value of conditioned air is assumed to be $7 per CFM per year (this value would increase with very hot, cold or humid climates), a 6-foot VAV fume hood at full open for experiment set up 10% of the time (2.4 hours per day), at 18 inch working opening 25% of the time (6 hours per day), and completely closed 65% of the time (15.6 hours per day) would save approximately $6,000 every year compared to a hood that is fully open 100% of the time. Potential behavioral savings from VAV fume hoods are highest when fume hood density (number of fume hoods per square foot of lab space) is high.
This is because fume hoods contribute to the achievement of lab spaces' required air exchange rates. Put another way, savings from closing fume hoods can only be achieved when fume hood exhaust rates are greater than the air exchange rate needed to achieve the required ventilation rate in the lab room. For example, in a lab room with a required air exchange rate of 2000 cubic feet per minute (CFM), if that room has just one fume hood which vents air at a rate of 1000 square feet per minute, then closing the sash on the fume hood will simply cause the lab room's air handler to increase from 1000 CFM to 2000 CFM, thus resulting in no net reduction in air exhaust rates, and thus no net reduction in energy consumption. In a survey of 247 lab professionals conducted in 2010, Lab Manager Magazine found that approximately 12% of fume hoods are VAV fume hoods. Canopy fume hoods Canopy fume hoods, also called exhaust canopies, are similar to the range hoods found over stoves in commercial and some residential kitchens.
They have only a canopy (and no enclosure and no sash) and are designed for venting non-toxic materials such as non-toxic smoke, steam, heat, and odors. In a survey of 247 lab professionals conducted in 2010, Lab Manager Magazine found that approximately 13% of fume hoods are ducted canopy fume hoods. Pros Cons Fumes are completely removed from the workplace. Additional ductwork.
Low maintenance. Temperature controlled air is removed from the workplace. Quiet operation, due to the extract fan being some distance from the operator. Fumes are dispersed into the atmosphere, rather than being treated. Ductless (recirculating) fume hoods Mainly for educational or testing use, these units generally have a fan mounted on the top (soffit) of the hood, or beneath the worktop. Air is sucked through the front opening of the hood and through a filter, before passing through the fan and being fed back into the workplace.
With a ductless fume hood it is essential that the filter medium be able to remove the particular hazardous or noxious material being used. As different filters are required for different materials, recirculating fume hoods should only be used when the hazard is well known and does not change.
Air filtration of ductless fume hoods is typically broken into two segments:. Pre-filtration: This is the first stage of filtration, and consists of a physical barrier, typically open cell foam, which prevents large particles from passing through. Filters of this type are generally inexpensive, and last for approximately six months depending on usage. Main filtration: After pre-filtration, the fumes are sucked through a layer of which absorbs the majority of chemicals that pass through it. And will, however, pass through most carbon filters. Additional specific filtration techniques can be added to combat chemicals that would otherwise be pumped back into the room. A main filter will generally last for approximately two years, dependent on usage.
Ductless fume hoods are often not appropriate for research applications where the activity, and the materials used or generated, may change or be unknown. As a result of this and other drawbacks, some research organizations, including the University of Wisconsin, Milwaukee, Columbia University, Princeton University, the University of New Hampshire, and the University of Colorado, Boulder either discourage or prohibit the use of ductless fume hoods. A benefit of ductless fume hoods is that they are mobile, easy to install since they require no ductwork, and can be plugged into a 110 volt or 220 volt outlet. In a survey of 247 lab professionals conducted in 2010, Lab Manager Magazine found that approximately 22% of fume hoods are ductless fume hoods. Pros Cons Ductwork not required.
Filters must be regularly maintained and replaced. Temperature controlled air is not removed from the workplace. Greater risk of chemical exposure than with ducted equivalents. Contaminated air is not pumped into the atmosphere.
The extract fan is near the operator, so noise may be an issue. Specialty designs Acid digestion These units are typically constructed of to resist the corrosive effects of acids at high concentrations. If is being used in the hood, the hood's transparent sash should be constructed of which resists etching better than glass.
Hood ductwork should be lined with polypropylene or coated with PTFE. Downflow Downflow fume hoods, also called downflow work stations, are typically ductless fume hoods designed to protect the user and the environment from hazardous vapors generated on the work surface.
A downward air flow is generated and hazardous vapors are collected through slits in the work surface. Perchloric acid These units feature a waterwash system in the. Because dense fumes settle and form explosive crystals, it is vital that the ductwork be cleaned internally with a series of sprays. Radioisotope This fume hood is made with a coved stainless steel liner and coved integral stainless steel countertop that is reinforced to handle the weight of lead bricks or blocks. Scrubber This type of fume hood the fumes through a chamber filled with plastic shapes, which are doused with water. The chemicals are washed into a sump, which is often filled with a neutralizing liquid.
The fumes are then dispersed, or disposed of, in the conventional manner. Waterwash These fume hoods have an internal wash system that cleans the interior of the unit, to prevent a build-up of dangerous chemicals. Energy consumption Because fume hoods constantly remove very large volumes of conditioned (heated or cooled) air from lab spaces, they are responsible for the consumption of large amounts of energy. Key statistics laid out in a 2006 article by Evan Mills et al.:. For standard two-meter (six-foot) hoods, per-hood energy costs range from $4,600/year for moderate climates such as, to $9,300/year for extreme cooling climates such as. With an estimated 750,000 hoods in use in the US, the aggregate energy use and savings potential is significant.
Estimate the annual operating cost of US fume hoods at approximately $4.2 billion, with a corresponding peak electrical demand of 5,100 megawatts. As a result, fume hoods are a major factor in making typical laboratories four to five times more energy intensive than typical commercial buildings. With emerging technologies, per-hood savings of 50% to 75% can be safely and cost-effectively achieved while addressing the limitations of existing strategies.
The bulk of the energy that fume hoods are responsible for is the energy needed to heat and/or cool air delivered to the lab space. Depending on the type of (heating, ventilation, and air conditioning) system installed, this energy can be electricity, natural gas, heating oil, coal, or other energy types. Additional electricity is consumed by fans in the HVAC system and fans in the fume hood exhaust system. Calculating energy consumption has developed a that estimates annual fume hood energy use and costs for user-specified climates and assumptions about operation and equipment efficiencies. Behavioral programs to reduce energy use A number of colleges, universities, and other research institutions run or have run programs to encourage lab users to reduce fume hood energy consumption by keeping VAV sashes closed as much as possible. These programs typically use tactics such as placing stickers or magnets on VAV fume hoods to prompt users to keep them closed, providing feedback to lab users on the amount of energy consumed by fume hoods, and running competitions in which labs compete to see which building or lab can achieve the largest percentage reduction in fume hood height or energy consumption.
Organizations that have run behavior programs to reduce fume hood energy use include. Harvard University: A 'Shut the sash' campaign in the Chemistry & Chemical Biology (CCB) Department resulted in a sustained 30% reduction in fume hood exhaust rates as a result of increased attentiveness to fume hood sash height. The total pre-campaign exhaust from the 150 VAV fume hoods monitored was 85,000 cubic feet/minute (CFM), and the post-campaign average 59,000 CFM.
This translated into cost savings of approximately $180,000 per year, and a greenhouse gas emission reduction of 300 MTCDE (metric tons carbon dioxide equivalent). The campaign included a number of components:. Competition: A competition in which labs competed against each other to reduce their fume hood energy use the most.
Prompts: Placement of “Shut the Sash” magnets on each fume hood as a prompt/reminder. Communication: General outreach through posters, flyers, and emails.
Goal Setting: Monthly goals were set for each lab. These goals were re-evaluated as research groups’ size changes and as their work changes to more or less hood-intensive research. Incentives: Labs that achieved their monthly goal were entered into a monthly raffle in which they could win movie passes or a beer & pizza party. Labs that met their monthly goal at least 4 of the most recent 6 months were invited to highly popular bi-annual wine & cheese parties. Feedback: Real time meters at the exit to most labs allow users to quickly check whether all the hoods are closed each evening if they are the last one to leave the lab. Feedback on performance is distributed twice a month – once to let lab users know if they are on track for their goal, and the other time to let them know who won the raffle that month.
Massachusetts Institute of Technology:. Air volume through all VAV hoods in the department is modulated by a Venturi-type air valve by Phoenix Controls. A nominal face velocity of 100 ft/min is maintained. Data from sash position sensors on each fume hood are sent to a central processor that controls laboratory-scale and building-level exhaust. Software automatically collects and redistributes the 15 minutes average sash position by laboratory from this central database. The first fume hood behavior intervention in the MIT Chemistry Department occurred mid-November 2006, when the Chemistry Department’s EHS Coordinator reinforced the importance of closing fume hood sashes at the regularly scheduled EHS laboratory representative meeting.
The presentation covered the reasons for shutting the sash (cost savings, benefit to the environment, personal safety), a description of how fume hoods work and how energy is consumed, the dangers of improper fume hood use, and the magnitude of the potential energy savings (up to $400/inch of hood opening per year in the widest hoods in the Chemistry Department (and $80/in/year for the hoods in Building 18). Representatives were encouraged to respond after the presentation and after discussion with their labs. This message was reinforced by an e-mail from the department head to the faculty with the goal of ensuring the entire department was familiar with the program. The “shut-the-sash” message was subsequently integrated into the Chemistry Department’s EHS training sessions that are required for all new graduate students. The second intervention was the release of fume hood use data to the faculty principal investigator in charge of each lab. The first datasets were distributed by the department EHS coordinator to the Chemistry faculty in early August 2007.
These data were then distributed to other members of the lab at the faculty PI’s discretion. Findings: Average sash height was lowered by 26% (from 16.3 +- 0.85% open to 12.1 +- 0.39% open) throughout the department, saving an estimated $41,000/year. Sash position during inactive periods was lowered from 9% to 6% open. Half of all department savings occurred in four (of 25) labs. Energy savings are substantially less than original expectations because most installed fume hoods use combination sashes. Labs with vertical sashes use the most energy, and see the most savings from the intervention. North Carolina State University - During sash closing campaigns conducted at the beginning of each semester, Energy Management and Environmental Health and Safety conduct campus presentations highlighting the University’s responsibility to conserve energy and provide safe working conditions with the goal of educating scientists and research assistants on proper lab protocol and ways to reduce their carbon footprints.
Sash opening labels have been placed on all fume hoods on campus to serve as constant reminders for all lab users. In addition to these campaigns, periodic surveys are conducted to inventory which labs are practicing correct lab safety procedures. These surveys also highlight buildings with high energy consumption where further monitoring or outreach is needed. University of British Columbia UBC held their first fume hood competition in 2012. Over the course of the six weeks competition, an 85 per cent reduction in fume hood energy consumption was achieved. Six labs were recognized for exemplary fume hood practices at a wrap-up event attended by 130 researchers, with first place groups receiving $500 and second place groups receiving $250. All winning groups also received a commemorative sash (pun intended).
University of California, Berkeley UC Berkeley's “Shut the Sash” Fume Hood Campaign educates lab researchers to close the sashes on fume hoods when they are not in use to reduce energy consumption and improve air quality. As of May 2011, the program targets Tan Hall and uses stickers, flyers, and emails to disseminate information.
It also involves a competition to see which lab can “Shut the Sash” most consistently. University of California, Davis: In summer 2009, about 600 vinyl stickers were installed on the exterior sidewall of fume hoods in ten buildings at UC Davis. The sticker uses a traffic light color scheme, with a red zone above 18 inches, and a large arrow pointing down with the words, “More Safe, Less Energy” changing from yellow at the midpoint to green at the bottom when the sash is closed completely. Visual surveys of sash-position status were conducted before sticker deployment, about 2 months after sticker installations, and again in spring, 2011, to assess persistence. The survey method estimated sash status by benchmarks in approximate quartiles to streamline the survey effort.
This also helped capture information on VAV-system response. These benchmarks were incorporated into energy savings calculations. Sash positions were averaged by floors at each sample time. Survey results showed 90-100% compliance 22 months after installation with no additional reinforcement of closure.
Given a per hood sticker installation cost of $5 and a conditioned air cost of $7/CFM/year, the simple payback of the project was estimated to be 15 hours, and the return on investment (ROI) was estimated to be 599%. University of California, Irvine: In order to get the fume hoods sashes closed, UC Irvine's PowerSave Campus Program uses a three-pronged approach. The first method is direct education, in which teaching assistants (TAs) are asked to encourage their students to close the hoods before leaving the labs. The second approach is placing “point-of-decision” reminder stickers on the hoods themselves, explaining that a closed fume hood saves up to 50,000 lbs of CO2 a year. The third method is an incentive-based competition among three buildings that contain fume hoods. During the three-week competition, volunteers periodically audit the buildings’ fume hoods, noting the total number of inches each fume hood has been left open.
The building with the fewest total number of inches at the end of the competition wins a catered luncheon for its professors and lab users, and an energy-efficiency certificate provided by the Green Campus Program. In 2007, the Fume Hood Use campaign won an award for “Best Practices in Student Energy Efficiency,” at the sixth annual Sustainability Conference at UC-Santa Barbara, beating all other PowerSave Campus Programs in the UC system. The PowerSave Campus team estimates that the Fume Hood Use campaign saves over 80,000 lbs of CO2 and $13,000 every quarter. University of California, Los Angeles: As its first initiative, UCLA EH&S's Laboratory Energy Efficiency Program (LEEP) jointly sponsored a competition with the Alliance to Save Energy's PowerSave Campus Program to encourage reduced fume hood sash heights in research laboratories. The first fume hood competition took place in the Molecular Sciences Building (MSB) during Fall 2008 and included about 230 fume hoods.
Overall, the competition saw a 40% sash height decrease from 13.4” to 8” (as shown by competition behavior and the long-term followup). In order to identify the lasting, long-term behavior change, LEEP and UCLA PowerSave Campus conducted follow-up audits each month after the competition. Sash heights were measured throughout one week, using the same method for recording baseline measurements. The follow-up data showed that MSB’s new average sash height was 7.8”—a 5.6” decrease from baseline measurements.
Ultimately, this 40% reduction translates into an annual estimated savings of 1,415,278 lbs of CO2 emissions and $149,730. Several additional competitions have been held following the success of this original one. University of California, Riverside: Make posters & stickers available for download on their website.
University of California, San Diego: The UC San Diego Annual Shut the Sash Competition is a 5-week campaign sponsored by the PowerSave Campus Program, Facilities Management, Environmental Health & Safety, and the Biology Department. The first competition began in January 2009 and, as of October 2012, has happened every year since. The campaign involves 11 labs in a challenge to reduce their energy consumption and improve air quality by closing the sashes on fume hoods when not in use. The “Shut the Sash” competition helps promote energy savings by challenging laboratories to save more energy than other laboratories from a set baseline. The Shut the Sash Competition educated researchers, raised awareness of lab energy efficiency and showed real savings in energy use and cost.
On average, there was a 27% reduction in sash heights over a five-week period in 2009. The Shut the Sash competition and awareness campaign also saves 21,734 kWh/year or $1695.25 annually, assuming sash heights stay at a similar level. University of California, Santa Barbara: In summer 2009, about 200 vinyl were installed on the exterior sidewall of fume hoods in seven buildings at UC Santa Barbara. The sticker uses a traffic light color scheme, with a red zone above 18 inches, and a large arrow pointing down with the words, “More Safe, Less Energy” changing from yellow at the midpoint to green at the bottom when the sash is closed completely. Surveys were conducted by collecting real-time sash position data provided by the campus’ building monitoring system (BMS). Data were collected for 10-day periods prior to sticker installation for select fume hoods, and one, two, and three months following sticker installation.
The average sash height for each hood was calculated for each 10-day period. In the Engineering Science Building, average sash opening was 15 inches prior to sticker installation, 6.5 inches 3 months after sticker installation, and 9.5 inches 23 months after sticker installation. In the California NansoSystems Institute building, average sash opening was 7.5 inches prior to sticker installation, 6 inches 3 months after sticker installation, and 5 inches 23 months after sticker installation. University of Central Florida: Have placed reminder stickers on fume hoods. University of Colorado, Boulder: Using stickers and educational posters to reminder users of VAV fume hoods to keep them closed. University of Toronto The University of Toronto ran their first fume hood sash closing campaign from October 2008 until March 2009.
The campaign included workshops, posters, a website, and individual and group competitions. Before the campaign, sashes were regularly left in the same position whether the hoods were in use or not (around 11 inches). During the campaign, sash heights of unused hoods dropped to just under 4 inches on average, resulting in estimated annual savings of at least 49,000 kWh of electricity, 770 mmBTU of heating energy and 51 tonnes of greenhouse gases and as much as 240,000 kWh, 3800 mmBTU of heating energy and 260 tonnes of greenhouse gases. The changes also resulted in between $20,000 and $100,000 in energy cost savings annually. When the campaign organizers inspected sash heights 7 months after the conclusion of the campaign, they found that users had largely reverted to pre-campaign habits.
Maintenance. Improper monitoring of fume hood velocity may create a that can expose workers to hazardous materials from inside the fume hood.
Fume hood maintenance can involve daily, periodic, and annual inspections:. Daily fume hood inspection. The fume hood area is visually inspected for storage of material and other visible blockages. Periodic fume hood function inspection.
Capture or is typically measured with a velometer. Hoods for most common chemicals have a minimum average face velocity of 100 feet (30 m) per minute at sash opening of 18 inches (460 mm). Face velocity readings should not vary by more than 20%. A minimum of six readings may be used determine average face velocity. Other local exhaust devices are to determine if the contaminants they are designed to remove are being adequately captured by the hood. Annual maintenance.
Exhaust fan maintenance, (i.e. Lubrication, belt tension, fan blade deterioration and rpm), is performed in accordance with the manufacturer’s recommendation, or as adjusted for appropriate hood function. Wooden fume hood at Gdansk University of Technology (2016 photo of 1904 installation still in use) The need for ventilation has been apparent from early days of chemical research and education. Some early approaches to the problem were adaptations of the conventional. A hearth constructed by in 1822-1826 at the was equipped with a and special flues to vent toxic gases. In 1904 the at the was equipped with wooden fume hoods. Harmful and corrosive gaseous byproducts of reactions were actively removed using the natural draft of a fireplace chimney.
This early design is still functioning after over 100 years. The draft of a chimney was also used by as what has been called the 'first fume hood'. The first known modern 'fume cupboard' design with rising sashes was introduced at the in 1923.
Modern fume hoods are distinguished by methods of regulating air flow independently of combustion, improving efficiency and potentially removing volatile chemicals from exposure to flame. Fume hoods were originally manufactured from wood, but during the 1970s and 1980s epoxy became the norm.
During the 1990s, derivatives treated with (plastic laminates and solid grade laminates) for chemical resistance and flame spread retardance started to become widely accepted. See also. References. Pickard, Quentin (2002).
The Architects' Handbook. Oxford, England: Wiley-Blackwell.
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Sublimate of Corosive Arsnick: Let all your Operations be perform'd in a Chimney, that the Pernicious Fumes may be freely ascend without Prejudice to the Operator; and when you grind the Arsnick, Muffle your Mouth and Nostrils. Gillian Mohney (2015-10-18). Marzena Klimowicz-Sikorska (2010-09-30). John Buie (2011-12-09).
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There is no easy way to get it accurately. You need to define: static thrust or at what speed do you want the thrust. The inlet lip radius has a huge static thrust effect; does the duct converge,diverge or is it straight?
Those also have an effect. Martin Hollman's book on ducted fans gets into this. 98 - Thrust in lbs= 9.35 x ( hp x D)2/3 power hp = horsepower D= rotor diameter, ft inside the partrentheses is raised to the 2/3 power Optimum blade number, chord, angle of attack of the blades, and the tolerance between the blade tip and the shroud all have major effects.
The there's compressibility effects as the tips get over 0.80 Mach. It's a bitch to design one of these suckers. Chasbo RE: Ducted Fan (Industrial) 5 Sep 03 04:53.
RobWard, I will attempt a (partial) answer your question. A fan usually has a higher pressure ratio across its face than a propeller, and a fan often has more blades.
A fan and shroud unit will have a smaller overall diameter than an ordinary airplane propeller for a given horsepower, mostly because the shrouded fan blades have a higher and more uniform loading along their span. A ducted fan will be quieter for a given power level; because sideline noise, which is the worst part of a fan's or propeller's noise signature, is largely captured by the shroud. A ducted fan usually runs at higher rpm than a bare propeller, which helps to make the ducted fan a good match for a high speed engine. Static and low speed thrust for a ducted fan are typically higher than for a bare propeller at a given power level, because pressures induced on the shroud by the fan flowfield add to the thrust. However, the static and low speed thrust advantage of the ducted fan is lost if its diameter is too small. The thrust of an ordinary propeller at low speeds (under 50 knots)is generally poor.
Ultralights could gain both thrust and noise benefits from a well designed ducted fan, if the weight can be kept low - a major challenge. At higher speeds (above 100 knots, depending on the details of the overall fan & duct design, the duct drag exceeds the duct thrust gain. Duct weight is considerable, because the low internal and leading edge pressures can result in very high loads. The weight and high speed drag penalties are the main reasons you don't often see ducted fans, except on jets.
Jet engines with bypass fans always use ducts, despite the weight and drag penalties. Ducted fans are not essential for fanjets, however. Douglas Aircraft did tests on a DC-9 with 'unducted fan' engines. Their fan blades were fewer in number and larger in diameter than the fan blades on an equivalent ducted fanjet engine. The unducted fan engine was a somewhat more efficient propulsion system; but it had noise issues. (On a typical fanjet engine, the duct helps contain the fan noise, plus the fan duct exhaust is mixed with the core jet exhaust to reduce jet noise as well. The unducted fan can do neither of these.) There may also have been certification issues due to extreme unbalanced forces resulting from loss of a large fan blade.
RE: Ducted Fan (Industrial) 8 Sep 03 07:21. I am hoping DORD2002 sees this post.
I am in need of a copy of R. Hovey's book, 'Ducted Fans for Light Aircraft' or at least copies of critical pages on how to calculate static thrust from a ducted fan.
If you could scan and e-mail to me the critical calculation pages, I'd be most appreciative. I also desire the title page with ISBN. I have done searches at amazon.com and bibliofind with no luck. There must not have been many copies published.
Any help from anyone regarding this matter is appreciated! Phil RE: Ducted Fan (Aeronautics) 23 Oct 03 18:40. A further very usefull reference fot those interested in designing ducted fans or shrouded propulsors is 'Aerodynamics of VSTOL flight', MxCormick,B.W. Academick press.
Library of congress no 66-30093 chapter 9 A low pressure ducted fan, usually called a shrouded propulsor, can be designed in the same way as a free propellor with the adition of the flow from a series of ring vortices to simulate the duct as well as the flow field from a fuselage or nacelle. I designed one for a twin engined amphibian and compared it with a free propellor. Both using the same high rpm engine (suzuki 993 cc). The smaller diameter fan had benefits in lower off set thrust line and higher low speed thrust at take off float hump speeds.
The weight of the ducts was more than compensated by the shorter propulsor supports and by the lack of need for a reduction drive for the shrouded propulsor. May i thank miper for his very succinct reply happy new year to everyone motorglider RE: Ducted Fan (Mechanical) 2 Oct 04 20:39. I've been reading this thread with interest and I would like to know what the ideal duct shape would be, tapered or straight in front and behind the fan? Will a small (5%)reduction in cross section behind the fan increase thrust as I seem to recall an idea that it would? Can anyone help with the calculation for the ideal bellmouth radius and shape? I'm looking at an 1100mm fan (number of blades to be tried between 2 and 12)with a maximum tip speed of 165 m/s using 50HP - 80Hp.
Maximum operating speed would be aroung 100km/h so I'm mainly interested in static/low speed thrust for acceleration. Keeping it as quiet as possible would be nice. Motorglider, have you any further info on the twin engined amphibian as this sounds close to what I need? I also intend to use a Suzuki motor albeit 658cc and with a reduction drive. RE: Ducted Fan (Aeronautics) 2 Oct 04 21:11. I am looking for similar help.
We are building a remote control car w/ a ducted fan in the middle for the possibility of going up walls. The fan will suck air in at a high velocity from the undercarriage and spit it out the top creating a suction effect. I need a ducted fan that is approimately 5' in diameter.
If anyone has any advice(on a type of ducted fan, or if we should use a reducing duct to increase the air velocity) I would greatly appreciate it. RE: Ducted Fan (Aeronautics) 23 Oct 04 17:10. Hi Jon8088, I have seen the drawings for the Jetpack, it is quite alarming and a very amature design, tho I am sure someone will try to kill themselves with one probably quite successfully. The fans are chain driven from a single engine, failure of one chain would spin the occupant into the ground before he realised there was a problem. If the engine fails this machine cannot autorotate like a helicopter, it will simply fall to the ground.
If anyone does intend to fly one of these machines I would recommend an explosively deployed parachute. Even with a parachute an engine failure between 20ft and 300ft altitude would almost certainly be fatal. Having seen footage of the test flights for the origional jetpack, I would imagine serious injury or death would result long before anyone managed to master the control of this thing. Karl RE: Ducted Fan (Automotive) 12 Oct 05 02:15. 2 feet is a bit exaggerated, when you see him standing in profile he leans a bit forward, I 'd say a few inches. Seems to me that, or the thing is actively stabilized, or you 'll need weeks of practice to learn how to fly it because it can not be naturally stable.
Also a landing with more than 125 lb on your shoulders seems to me almost impossible to achieve. A chair or some other stand might have helped to take the weight of the pilot's shoulders. Nevertheless, I think it looks nice and it would be fun to fly it although I would never do it. Checking if it has enough power to lift 330 lb: From the Rankine-Froude Momentum Theory of Propulsion: 1. Power = (Thrust).
(Air Speed of the accelerated air mass): P = T. (V + v) 2. Thrust = Flow of accelerated air Mass. (Final Air Velocity Increase of this mass flow): T = ?. A. (V + v).
(2. v) Note: a.
The air mass being accelerated by the fan disk will increase speed before passing the fan disk, when it reaches the disk the speed increase is v, then it continues to increase behind the disk until it reaches a total increase of = 2.v. In hovering conditions V = 0. When we consider hovering conditions, the Thrust (T) equals the aircraft Weight (W), and using this in the 2 above equations by eliminating v you get: For T = W, P = SQrt((W^3)/(2.?.A)) In reality P will be higher (for a ducted fan, probably about 10%) because in the above equations there are no losses considered like for example the energy lost in rotational momentum. Doing the calculation P necessary for hovering at sea level is about 51 HP.
With all losses included let's say about 20% more is about 61 HP. In other words, he can not even lift 330 lbs. Maybe it is a bit insane, but I like it anyway, and it could undoubtedly find useful utilities, maybe in the army or so. RE: Ducted Fan (Aerospace) 24 Jan 06 02:33. GregLocock, where could I find information on fan efficiencies? Specifically speaking fan blades/impellers. I’ve purchased the book mentioned in this thread (Marc de Piolenc) and gives great information, but I would like to see graphs.
I have lots of info on DF’s since my master’s thesis was related to them. But in it I’ve always treated impellers as another component that only reduced efficiency and never looked at it. I was evaluating the losses due to obstructions inside high speed air ducts. It would be nice to see a graph with ‘x’ number of blades, ‘y’ fan swept area and ‘z’ fluid speed (air). Maybe throw in ID and OD, RPM and or blade angle also. Any combination would be interesting to see. RE: Ducted Fan (Automotive) 23 Feb 06 18:07.
While I'm not as lofty as aero eng I do mech stuff. Here is the end of the line in small ducted fans for model airplanes. A few years ago they were the ultimate rage. Some got over 200 mph!! They are vastly complex models. However thay have been of late surpassed by the turbine engine.
These are very fast. Easly 200 mph straight and level. Honest ingen. You get a pretty nice car for the cost of these. And yes they do crash. Some even leave a smoking hole.literaly. Check this site for ducted fans RE: Ducted Fan (Aeronautics) 29 Mar 06 13:33.