Blog Purpose

The CTG Technical Blog is intended as a source of information on subjects related to industrial and precision cleaning technology. The writer of the blog, John Fuchs, has 40+ years of experience covering the entire gamut of cleaning. Mr. Fuchs has extensive knowledge of ultrasonic cleaning technology having been employed by Blackstone-Ney ultrasonics and its predecessors since 1968. The blog is also intended to serve as a forum for discussion of subjects related to cleaning technology. Questions directed to the blog will be responded to either in the blog (if the topic has general interest) or directly by email. Emails with questions about the current blog should be entered in the comments section below. Off-topic questions related to cleaning may be sent to

Questioning Particle Generation Due to Cavitation Erosion as a Source of Contamination

June 1st, 2016

Ultrasonic cleaning is widely used for removing particles from surfaces.  It is generally agreed that the high energy of implosions of cavitation bubbles break the bonds holding particles to the surface being cleaned and that liquid motion (streaming) carries the particles away once they have been dislodged.  However, it is also well known that ultrasonic cavitation and implosion will generate particles as material is eroded from surfaces as cavitation bubbles implode in proximity to them by a process of ultrasonic erosion similar to that seen on a ship’s propeller.  A glass beaker, aluminum foil or a lead coupon subjected to long term exposure to ultrasonic cavitation in liquid provides adequate evidence that ultrasonic erosion is real.

A lead coupon shows evidence of cavitation erosion after several hours exposure to ultrasonic energy in water.

A lead coupon shows evidence of cavitation erosion after several hours exposure to ultrasonic energy in water.

This leads to an interesting question – – How do you achieve a balance between the removal of foreign particles and the generation of particles from the substrate to give a completely particle free surface?  Or, asked in another way, when does cleaning stop and the replenishment of particles due to surface erosion begin.

Published articles widely support the notion that virtually all substrates generate particles due to ultrasonic erosion and that although the rate of particle generation may diminish or “level off” over extended exposure times there is no termination point.  Surfaces continue to shed particles indefinitely.  This leads to the question of how is it possible, then, to provide a surface with absolutely NO particles.  The simple answer, it would seem, is that it is not.  But let’s consider what means might be used to leave the smallest number of free particles.

One way might be to reduce ultrasonic intensity as cleaning progresses.  Again, published articles support the notion that the rate of particle generation is directly related to ultrasonic intensity.  Logic would say that particles eroded from a surface might be displaced from the surface by slightly less ultrasonic energy that was required to produce them in the first place.  In the end, when the ultrasonic intensity reached zero, the minimum number of particles released by erosion would be left behind.

However, published articles also verify that rate of surface erosion is reduced and that the size of particles liberated by cavitation erosion becomes smaller at higher ultrasonic frequencies.

Combining the ultrasonic intensity effect and the frequency effect would suggest that the most effective way to produce a surface free of both foreign and particles eroded from the surface would be to cycle through a series of ultrasonic bursts with increasing frequency a number of times with reduced power at each iteration thereby successively removing smaller and smaller particles while producing fewer and fewer particles as a result of cavitation erosion.

Although ultrasonic hardware is readily available that has the ability to vary both frequency and power, it seems that most researchers have investigated only the effect of frequency on the ability to remove particles and produce a surface free of particles.  This approach, of course, does not take into account the generation of particles from the surface as mentioned above.  It also excludes the effect of successive use of multiple frequencies as I discussed in an earlier blog which may provide a significant benefit.

–  FJF  –

Conductivity Calculations

May 25th, 2016

Previous blogs have talked about heat conductivity in very general terms to produce a foundation for this somewhat more technical view for those of you who like formulas and numbers.

Conductive heat transfer can be expressed with “Fourier’s Law

  • q = k A dT / s
  • where
  • q = heat transfer (W, J/s, Btu/hr)
  • A = heat transfer area (m2, ft2)
  • k = thermal conductivity of material (W/m K or W/m oC, Btu/(hr oF ft2/ft))
  • dT = temperature gradient – difference – in the material (K or oC, oF)
  • s = material thickness (m, ft)

Using this equation, one can easily calculate the amount of heat that will be conducted through a given material in a given period of time knowing its thermal conductivity, its cross section, length of the conductive path (thickness in the case of something more flat) and temperature differential between the heat source and the heat sink.  Let’s look at each in a little more detail – –

First, you need to make sure that the (k) you are using is in the proper units, English or metric.  The heat transfer area (A) is the cross section of the conductive path in either square meters or square feet (inches).  This could be the cross section of a conductive bar or the surface area of an electric heater, for example. The temperature gradient (dT) is the difference in degrees centigrade (or degrees kelvin) or degrees Fahrenheit between the temperature of the heat source and the temperature of the heat destination.  This equation works in the case that the heat source and the heat sink are able to maintain their temperatures despite the removal and addition of heat as heat is conducted from one to the other.

Note – Calculating what will happen if the temperature of the source is lowered by the removal of heat and the temperature of the destination is increased by the addition of conducted heat is a little more complex requiring calculus (which I do as infrequently as possible).

The material thickness (s) is the length of the conductive path in meters or feet between the heat source and the heat destination.

Although this equation can give specific numbers, it can also be useful in getting an intuitive feel for the effect that can be expected when various parameters are changed.  For example, the greater the area of the conductive path, the greater the heat transfer.  Doubling the contact area of a heater will double the ability for it to conduct heat to the heated surface.  In another example, reducing the thickness of a metal by 1/2 will double the amount of heat that can be conducted through it.

The equation also tells us that if you need to increase the temperature differential between the source of heat and the heat sink as in the case of an insulator, you need to either reduce the conductivity of the material between them, increase the length of the conductive path or decrease the cross section of the conductive path.  To decrease the temperature differential as in the case of transferring heat to a heating bath, reverse procedures will produce the desired effect.

It is convenient that everything changes in direct proportion as there are no squared factors.  Doubling or halving any given parameter will either double or halve the result.

 –  FJF  –

Heat Conductivity and Convection

May 23rd, 2016

Heat conductivity is a measure of the ability of a material to transfer heat within itself.  For example, if you heat one end of a short piece of copper wire, the heat is quickly distributed throughout the wire by conduction.  This can be easily demonstrated using a short piece (1 to 2 inches) of heavy gage copper wire and a small torch or gas lighter.  Hold the wire at one end and apply the torch to the other.  It won’t take long before the copper becomes too hot to hold.

Heat moves by conduction through different materials at different rates depending on their structure.  If one were to substitute a glass rod for the copper wire in the above example, it would take a considerable time for sufficient heat to be conducted through the glass rod to make it uncomfortable to hold.  Copper is a better heat conductor than glass.

In general, we think of metals as good conductors. In fact, metals vary widely in their conductivity but, overall, they are better conductors of heat than most liquids and gasses. Other solids also vary in their capability to conduct heat.  Wood is an example of a solid that is a poor heat conductor.  A poor conductor is called an insulator. The following chart shows the conductivity of several common materials.  A higher number indicates better conductivity.

Thermal Conductivity TableThe amount of heat that can be conducted also depends on an object’s cross section, the distance of heat travel (thickness of the material) and the temperature differential between the heat source and destination.  A thin copper wire will conduct less heat from one end to the other than a thicker wire of the same length in a given period of time.  A longer wire will conduct less heat from one end to the other.  Increasing the temperature of the heat source will result in more heat conduction provided that other conditions remain the same.

With relevance to industrial cleaning, heat conductivity is a major consideration on many fronts. For example, the efficient conduction of heat from heaters into a cleaning bath will have a major impact on the ability of the heaters to achieve and maintain the necessary process temperature.  Heat sinks (devices to collect and dissipate heat from electronic components) are found in controls and ultrasonic generators.

Interestingly, as you will see above, water is a notably poor conductor of heat even compared to many other liquids despite its extremely high heat capacity.  It is for this reason, that we can not rely on conduction alone as a means of distributing heat within a cleaning tank. Some sort of mechanical movement is needed to distribute heat.  In some cases this motion is supplied by simple convection.  Convection is a movement within a fluid or gas caused by the temperature differential within the liquid.  Warmer material is lighter in weight and therefore rises displacing cooler material which moves toward the bottom.  Convection is not dependent solely on the conductivity of the liquid although it does play a minor role in distributing heat on a small scale as the hotter and cooler material mix.

Diagram showing convection distribution of heat

Heated liquid or gas rises to produce convection currents which distribute heat.

In other cases, it is necessary to employ some other means of mechanical mixing to get the job done.  A simple propeller-type mixer or a pumping loop are common ways of doing this.

 –  FJF  –

Heat – Definitions and Concepts

May 18th, 2016

Temperature has been identified as one of the important variables in cleaning – arguably the most important.  So I thought it might be worth some time to develop a little understanding of heat – – especially how it is generated and transmitted.

Heat is a form of energy.  The amount of heat contained in an object determines its temperature.  The more heat an object contains, the higher its temperature will be.   The amount of heat in an object can be increased by adding heat via conduction or radiation from another object at a higher temperature.  In the case of conduction, the two objects must be physically in contact with one another while in the case or radiation, heat is radiated as electromagnetic waves from the hotter object and is absorbed by the cooler object.  Heat moving from one object to another results in a change of temperature of those objects as heat moves from one to another.

The heat in an object may also be increased by adding work in the form of vibration, bending, etc.  In this case, heat is generated by internal friction due to motion.

Note – Heat also moves by convection but that is another process.  Convection is the physical mixing of liquids or gasses to achieve a uniform overall temperature.

Heat conduction between two masses at different temperatures will result in their temperatures being equal. A - Two masses at different temperatures. B - Heat transfer. C - Equal temperatures

Heat conduction between two masses at different temperatures will result in their temperatures being equal.  “A” – Two masses at different temperatures.  “B” – Heat transfer.  “C” – Equal temperatures

Heat transfer stops when the two objects reach the same temperature.  Heat transferred by conduction and/or radiation always moves from the object with the higher temperature to the object with the lower temperature.  The speed at which heat moves from one object to another depends on the temperature difference between the two.  A greater temperature difference results in a higher rate of heat transfer.


Heat is measured in British Thermal Units (BTU’s).  The addition of one BTU of heat energy will increase the temperature of one pound of water by one degree Fahrenheit.  There are corresponding metric units that apply with calories being the unit of measure for heat and joules being the measure of work.

Specific Heat –

The specific heat of a material is a measure of how much temperature change will be produced by the introduction of a specific amount of heat to a given mass of matter.  The specific heat of water is one (one BTU of heat will increase the temperature of a pound of water by one degree Fahrenheit).  A lower specific heat indicates that less heat will be required to produce an equivalent temperature change to the same mass while a higher specific heat indicates that more heat will be required.

Heat Capacity –

Different materials are able to absorb different amounts of heat per unit of volume to produce the same temperature change.  Specific Heat and Heat Capacity are ratios which are often used interchangeably and are often confused.

Thermal Conductivity –

Thermal conductivity is a measure of the rate of heat transfer across a given thermal gradient over a specific dimension within a material.  Higher thermal conductivity indicates faster heat transfer.  Thermal conductivity will be discussed in more detail in the next blog.

–  FJF  –

Exhausting Gasses Produced by the Cleaning Process

December 10th, 2015

In many industrial cleaning processes it is necessary to exhaust emissions that unavoidably result from the cleaning process.  The reasons for exhaust can take on a large range –

  • Remove heat that would otherwise raise the temperature in the cleaning area
  • Remove humidity that would otherwise raise the humidity in the cleaning area
  • Remove toxic fumes that might otherwise be dangerous to workers
  • Remove mists of oil and other contaminants
  • Remove dust and other particles to prevent air contamination

The process of exhausting usually starts with an exhaust fan with appropriate inlets or vents designed to capture the contaminants to be exhausted.  Capturing the offending contaminants, however, is only a part of the story.  Once captured, they must be collected or neutralized and disposed of appropriately.

In the case of heat and humidity, disposal is usually accomplished by venting the exhaust directly to the outside atmosphere.  Many municipalities have requirements for stack height and emission limits to prevent exhaust gasses from encroaching on other nearby properties.   Although in some cases, simple dilution of contaminants by the atmosphere is adequate, others require additional measures to assure capture and removal.  When it comes to oil, particles and toxins the disposal issue becomes much more complex usually requiring a device called a “scrubber.”

Scrubbers come in variety of forms.  For removal of oil mist, the scrubber may simply be a pipe with a number of baffles inside.  The baffles are positioned in such a way that the air flowing through the scrubber reverses direction several times.  As the air containing mist impinges on the baffles, the particles of oil collide with the baffles stick on them until the buildup is sufficient for the collected oil to drain by gravity to a collection point.  This process may also be enhanced by the use of electrostatic devices and other more advanced technologies.

There are also wet scrubbers and dry scrubbers.  In a wet scrubber, a spray head produces a mist of liquid (water or a chemical solution) through which the contaminated air stream must pass.  In the process, contaminants either adhere to the liquid spray or combine with it and are neutralized.  This results in a secondary contaminated liquid stream which must be disposed of, possibly after secondary treatment.

In a dry scrubber, a powder is levitated by air pressure or mechanical means.  In some cases, the contaminated stream itself levitates the powder as it bubbles up through it in much the same way as a fluidized bed operates.  As the contaminated air stream passes through the levitated powder, contaminants either adhere to the powder or, especially in the case of liquids, may be neutralized by it.  Again, the result is usually a secondary contaminant stream although in some cases, the reaction may be of a catalyst type which is self-sustaining.

These are just a few words about how contaminants may be dealt with in industrial cleaning processes.  A complete discussion of this topic (if there is such a thing as the technology is so broad) is beyond the scope of this blog.  The “take away” here is that responsible handling of effluents from the cleaning process does not necessarily end with an exhaust blower and a stack.

–  FJF  –

How do you measure surface tension?

December 3rd, 2015

In the world of industrial cleaning technology we talk about surface tension a lot! So much so, in fact, that it is hard to enter into any discussion of cleaning without having the subject of surface tension arise.  In cleaning chemistry, for example, we are always looking for lower surface tension to promote penetration of small surface features and blind holes.  Surface tension has a major effect on ultrasonic cavitation and implosion.  A less well-known fact is that surface tension has a significant effect on the droplet size and pattern produced by spray nozzles.  So, if this thing called surface tension is as important as it appears, we should be able to put numbers on it and measure it, right?  Absolutely!  But there are also some difficulties.

In preparing to write this blog, I decided (as always) to do a little research.  My thought was that this must be a simple thing with a simple answer – – well, not so much!  There are several general methods of measuring surface tension with several different implementations of each.  The most common method appears to be lowering a thin plate, rod, wire shape or tube into the liquid to wet it and then, using a balance or other weighing device, lifting the immersed item while measuring the weight exerted on it by the surface tension of the liquid.  The maximum force corrected for the weight of the item, buoyancy and other factors including the adhesion of the liquid being measured to the item immersed can be used to measure surface tension.

Basic method for measuring surface tension.

Basic method for measuring surface tension.

But what if the liquid does not wet the surface?  The technique then becomes one of measuring the force that must be exerted downward to break the surface tension which is a completely different problem.

Another method uses the droplet size that can be generated at the end of a hypodermic needle with one of several end configurations as an indicator of surface tension.  Higher surface tension liquids, of course, produce larger droplets.  This method is complicated by the extension of the droplet as it breaks free, the density of the liquid and several other factors.

Finally, there are methods that use the size bubble produced as a gas is introduced into a liquid through a small tube to determine surface tension.  Smaller bubbles indicate lower surface tension.

What I expected to be a simple challenge turned out to be majorly complex involving a number of different techniques and a LOT of math – – much more than I can cover in this blog.  What I did get out of all of this was that there seems to be no single way of measuring surface tension that is applicable in all situations.  The other thing is that it is very easy to confuse surface tension and wettability.  Using mercury as an example, mercury has a very high surface tension but will not wet glass yet it easily wets copper despite its high surface tension.

–  FJF  –

Surface Tension and/or Wettability

November 17th, 2015

A few days ago, I sat down to write what I thought would be a simple explanation of surface tension and how it is measured in the laboratory (a blog which will be published shortly if I can figure all of this out).  In doing the normal background research, however, I started to see contradictions that did not align with what I thought I knew about surface tension.  The culprit was wettability.  Soon I was in a circular argument with myself regarding the two and how to differentiate them.  Contact angle, for example, is a measure of wettability but we also use it (in an inverse way) to measure surface tension.  In fact, the concepts of surface tension and wettability are so intertwined that it is difficult, for me at least, to view them independently.

In an effort to get a grip on this, let’s start by looking at the definitions of the terms wettability and surface tension.

Wettability – Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting (wettability) is determined by a force balance between adhesive and cohesive forces. (Wikipedia)

The classical model is a drop of liquid on a smooth solid surface.  The contact angle is established by the balance of the adhesive force (the liquid wanting to maintain contact with the solid) and the cohesive force within the liquid (both the internal cohesive force and the force of surface tension).  An increase in adhesive force between the liquid and the solid or a decrease in the cohesive force (surface tension) within the liquid will result in greater wettability and a smaller contact angle.  It is important to note that a change in the adhesive force can be the result of a change in either the solid or the liquid while a change in the cohesive force can only be the result of a change in the cohesive force or surface tension of the liquid.

Surface TensionSurface Tension is the attractive force exerted upon the surface molecules of a liquid by the molecules beneath that tends to draw the surface molecules into the bulk of the liquid and makes the liquid assume the shape having the least surface area. (Mirriam-Webster)

It works to think of surface tension like the rubber of a balloon attempting to form the contents into the most compact shape (although not exactly since in the case of the balloon, the initial shape of the balloon may have an influence on the final shape).  It is surface tension that is the “cohesive force” described above.  Without gravity and the influence of a solid in contact with the liquid, a water droplet will assume a perfectly spherical shape (as I’m sure we’ve all seen in those science broadcasts from space).  Things change as soon as the droplet comes into contact with something.

The above mentioned quandary may be fueled by the fact that it is common for one to say that they have, for example, reduced the surface tension of water by adding a surfactant.  In fact, most surfactants change the surface properties of the liquid and may not affect the chemical nature of the liquid at all.  There is, however, a change in the apparent surface tension.

To Be Continued

–  FJF  –





Reliability of Plumbing Fittings – Threaded vs. Compression

October 28th, 2015

Wherever there are liquids there are leaks – it’s inevitable.  Leaks, of course cost money in downtime and repair of industrial cleaning systems.  So, you ask, what is the best defense against leaks.

Most leaks occur where one piece of plumbing connects with another.  A pipe to a valve, unions, connections to pumps and filters and connections to tank fittings.  Other than connections that are metallurgically or adhesively bonded by techniques such as welding or brazing in the case of metals or adhesives in the case of polymer materials, liquids are contained simply by two surfaces wedged against each other.  Let’s use threaded fittings as a starting example.

Threaded Fittings

Threaded fittings serve well on materials that are somewhat malleable like iron, copper, aluminum, brass and polymers.  As the fittings are tightened, the metal or polymer deforms to fill in all crevices to effect a leak-tight joint.  A threaded fitting on harder materials like stainless steel, however, is very difficult to make leak free.  The problem is that because the material does not deform readily, there is nearly always a small opening around the root of the thread.  In many cases, trying to stop a leak by further tightening the mating pieces may make result in a larger leak as the roots of the thread separate further as the metal is deformed along its length.  Teflon tape and pipe “dopes” are helpful but seldom provide a reliable and permanent solution.  These materials may also be a source of contamination.

Alternatives to threaded fittings include a variety of compression fittings including those with a collar that is compressed around the circumference of the male pipe as it is seated into the mating female part.

In a typical compression fitting, a ferrule (often made of a softer material) is squeezed to make a tight seal between the tube and the ID of the fitting.

In a typical compression fitting, a ferrule (often made of a softer material) is squeezed to make a tight seal between the OD of the tube and the ID of the fitting.

Although there are threads involved, their only purpose is to provide the force required to compress the ferrule.  The actual seal is separate from the threads.

compression fitting schematic

Seating of the ferrule on the tube is a non-reversible process although the connection can be disassembled and reassembled repeatedly if desired.  In many cases, leaks can be repaired by simply tightening the nut more firmly.  Compression fittings can be used in high pressure applications and may even become more reliable as pressure is increased as the pressure tends to expand the tube against the ferrule.

Although compression fittings are generally considered more reliable than threaded fittings, there are some potential problems.  In general, compression fittings are not as resistant to vibration as soldered or welded fittings.  Repeated bending may cause the ferrule to lose its grip on the tube.  Also, for a reliable seal, the surface of the tube being joined must be reasonably round and free of longitudinal scratches.

Compression fittings can be applied to materials ranging from plastic and rubber to the hardest metals.  It is important to choose the appropriate fitting for the application.  In the case of softer materials, the fitting may include an insert to support the inside diameter of the tube thereby assuring a good seal to its outside diameter.  Other special adaptations are common to accommodate the wide variety of applications for compression fittings.

–  FJF  –

Ultrasonic Drying – Not Yet but Possible???

September 23rd, 2015

There has been a lot of buzz lately on the internet regarding work at the Oak Ridge National Laboratory to develop a dryer that uses ultrasonics instead of heat to dry things.  The major thrust seems to be to replace the conventional domestic clothes dryer (which uses heat to evaporate water) with one that uses ultrasonics to atomize instead of vaporize water to dry clothes.  Claims include drastically reduced energy consumption and shorter drying times.  As a result, there has also been some buzz about using the same idea (ultrasonics) to dry parts after ultrasonic cleaning.  The logic being that the ultrasonic transducers are already there, why not put them to double use? But, whoa, wait a minute, let’s not get carried away.

What Oak Ridge has been doing is drying tiny pieces of fabric less than 1″ square by actually contacting them with ultrasonic transducers.  In the videos I’ve been able to find on line, a small piece of wet, saturated fabric (cut round to fit perfectly into an indentation in the transducer) is placed directly in contact with the output face of a high intensity ultrasonic transducer.  When the ultrasonic energy is activated an impressive cloud of water vapor is generated as the liquid is atomized by the ultrasonic vibrations.  The same thing, of course, would happen if there was just water and not fabric in contact with the ultrasonic transducer (just like an ultrasonic vaporizer).  After about 15 seconds, production of the atomized water vapor cloud stops and the fabric is declared dry.  Maybe, but maybe not.  Atomization of water will only continue as long as there is a liquid conductive path between the transducer and the wet fabric.  Although there is a possibility that airborne ultrasonic energy in such close proximity might be sufficient to continue to atomize liquid until the fabric is totally dry, I believe the odds are against it.  In the videos, no measure of the actual dryness was offered.  I would, at least, like to see the fabric pressed against a blotter.

Can this technology be scaled to practicality for drying a typical load of laundry in a domestic setting?  In my opinion it is highly doubtful.  The claimed energy savings is due to the fact that the liquid is only being broken into small droplets and does not actually undergo the energy-hungry phase change required for evaporation.  But you still have to prevent the atomized liquid from re-depositing onto the fabric.  How do they propose doing this?

There is a lot to think about here. So, let’s quickly look at what would be required to make ultrasonic drying applicable to drying parts cleaned in an industrial parts cleaner.  There are two possibilities that I can think of.  The first would be to provide a sufficiently powerful ultrasonic sound field in the air surrounding the part to actually atomize the liquid on the part surface.  The only means of delivering this energy would be through air and air, for all practical purposes, does not conduct ultrasonic energy.  The amount of power required to deliver substantial enough power would be huge! Maybe it would work on a small scale where the power requirement would be minimal, but certainly not anything larger than a few millimeters in size.  The other possibility would be to vibrate the part ultrasonically (much like a dog shaking off water after a swim).  This, of course would require contacting the part with an ultrasonic transducer and establishing a good enough conductive path to vibrate the part at the ultrasonic frequency.  Although this is not quite what Oak Ridge is doing, it is similar in that they are contacting and vibrating the liquid directly instead of the fabric.  Again, it may be possible to work this out on a small scale or under specialized conditions but I don’t see drying a 50 pound basket of steel parts using this concept. For the time being, I think the manufacturers of industrial parts cleaning equipment would do well to concentrate on other methods of improving drying technology.  I have offered several seeds for thought in the blog and invite you to look them over again if you haven’t already.  Meanwhile, I don’t think ultrasonic parts drying is in our future – at least the immediate future.

–  FJF  –


September 16th, 2015

The environment in the area of an industrial cleaning system is often not a “healthy” one for personnel or equipment.  Caustic and acidic cleaning chemistries rise as mist above cleaning processes along with humidity and heat.  Although our first thought is to protect personnel from these hazards, the equipment can also suffer serious consequences as a result of long term exposure to the unfriendly and corrosive environment.  Although the problem is relatively easy to grasp, solutions are a bit more difficult and often prove to be more challenging than one might expect.

Everything would be rather simple if we could just build a box around the cleaning system to contain harmful effluents.  There are machines which accomplish this with mechanized material handling behind enclosures.  This, however, is not a universal solution as it is frequently necessary to have access to the machine as well.  The difficulty is to provide the necessary access to the process while sufficiently isolating it from the surrounding environment.  The answer is to provide a means of venting that will capture and direct the harmful fumes away while still providing access to the process.  This is accomplished in different ways depending on the nature of the process and the design of the equipment.  Vents along the back or side(s) of the cleaning tank are probably the most simple and common form of venting.

In the case of smaller tanks, lip vents may be an effective solution to providing the required venting.

Powered vents along the sides of a process tank can be an effective means of venting smaller tanks.  As the tank width increases, the effectiveness of side vents diminishes rapidly allowing vapors from the center of the tank to escape.

Powered vents along the sides of a process tank can be an effective means of venting smaller tanks. As the tank width increases, the effectiveness of side vents diminishes rapidly allowing vapors from the center of the tank to escape.

Larger tanks require a different approach to venting.  The most common type of vent consists of a tower placed behind the tank as shown below.  A simple vent tower, however, may not be effective in totally capturing all vapors.

An exhaust platen along the back of a cleaning system is one of the most common forms of venting. The collection platen is equipped with adjustable louvers to help regulate flow. The platen may be connected to an open exhaust to atmosphere or to an exhaust powered by a fan.

An exhaust tower along the back of a cleaning system is one of the most common forms of venting. The tower is equipped with adjustable louvers to help regulate airflow. The tower may be connected to an open exhaust to atmosphere (provided there is no negative pressure in the building) or to an exhaust powered by a fan.

Although used in many cases, the simple vent tower has some problems.  In order to be effective it is almost imperative that the exhaust be powered.  As the front to back dimension of the process tank increases, the amount of exhaust required for effective venting rises exponentially.  Of course, as the amount of air vented is increased, the amount of makeup air required increases as well.  Makeup air, especially if it needs to be heated or cooled, can be more costly than using a more efficient venting option.

The efficiency of the venting system described above an be greatly increased by adding a blower to direct fumes to the vent as shown below.

Adding a blower to direct exhaust to the collection tower can improve collection efficiency while reducing the need for makeup air.

Adding a blower to direct exhaust to the collection tower can improve collection efficiency while reducing the need for makeup air.

Obtaining optimum results with a blower system requires careful adjustment to assure that the collection tower can accept the flow produced by the blower.  Too much blower air can result in reduced effectiveness as shown below.

A balance between blower air and the tower exhaust is required to prevent turbulence that disburses exhaust rather than collecting it.

A balance between blower air and the tower exhaust is required to prevent turbulence that disburses exhaust rather than collecting it.

There are, of course, other venting options in addition to the above but these are the most commonly used.  An upcoming blog will address the issues of handling exhaust.

–  FJF  –