Dwane Paulsen’s Blog

Many aerosol particle sensing instruments benefit from concentrating the incoming particle stream. Aerosol particles can be concentrated using a technique known as virtual impaction. I am currently working an original design. I don’t have a laboratory available so I will first try to build a concentrator similar to versions published in peer-reviewed journals. I will make sure I can reproduce the flow analysis described in these designs before running an analysis of my own design.

My version of the Circumferential-slot Virtual Impactor (CSVI) based on McFarland and coworkers

Just a coffee cup. I used the decal function to put one of my favorite photos on the face.

Coffee cup designed and rendered in Solidworks

A few years ago I wrote a paper describing a system to measure the volatility of nano-sized aerosol particles (nanoparticles). The particles were exposed to elevated temperatures from approximately 100 to 200°C in a coiled-tube heater. The design was simply a a coil of stainless steel tubing housed in an aluminum cylinder. In the wall of the cylinder were four (4) cartridge heaters. A schematic of the heater is shown in Figure 1.

Figure 1: Volatility-TDMA coiled-tube heater

An interesting property of coiled-tube flow is the enhancement of the heat and mass transfer by a secondary flow formation. This property has been thoroughly explored and heat transfer correlations for coiled-tube flow are available to assist in system design [Futagami and Aoyama, 1988; Mori and Nakayama, 1965; 1967; Patankar et al., 1974]. Figure 2 shows the secondary flow pattern which occurs in the cross-sectional plane normal to the main flow. Compared to straight-tube flow, coiled tubes yield higher heat transfer coefficients and induce radial mixing. For instance, conclusions from numerical and experimental results show that the thermal entrance lengths in coiled tubes are expected to be 20–50% smaller than those of straight tubes [Kakaç, 1987].

Figure 2: Secondary flow pattern common of coiled-tube flow

I performed thermal finite element analysis (FEA) and computational fluid dynamics (CFD) of the heater and coiled tube.  The steady-state FEA model of the heater shows the temperature distribution for a design setpoint of 100°C. The air flow rate through the coiled tube is 1 l/min.

Futagami, K. and Y. Aoyama (1988). Laminar heat-transfer in a helically coiled tube. International Journal of Heat and Mass Transfer, 31(2):387–396. 

Kakaç, S. (1987). Handbook of single-phase convective heat transfer. Wiley, New York. 

Mori, Y. and W. Nakayama (1965). Study on forced convective heat transfer in curvedpipes (1st report, laminar region). International Journal of Heat and Mass Transfer, 8:67–82. 

Mori, Y. and W. Nakayama (1967). Study on forced convective heat transfer in curved pipes (3rd report, Theoretical analysis under condition of uniform wall temperature and practical formulae). International Journal of Heat and Mass Transfer, 10(5):681–695. 

Patankar, S. V., V. S. Pratap, and D. B. Spalding (1974). Prediction of laminar-flow and heat-transfer in helically coiled pipes. Journal of Fluid Mechanics, 62:539–551.

Paulsen, D., E. Weingartner, M. R. Alfarra, U. Baltensperger (2006). Volatility measurements of photochemically and nebulizer-generated organic aerosol particles. Journal of Aerosol Science, 37:1025-1051.

Illustration of the atmospheric aerosol surface area-weighted size distribution which arises from different mechanisms of aerosol generation.

I’ve spent more than a third of my life studying particles, specifically, aerosol particles. Much of my experience has been with particles much smaller than the naked eye can see. Particles are so ubiquitous in our atmosphere that they are often overlooked.

With respect to the atmosphere, aerosol particles affect the earth’s climate in two ways. First, aerosol particles absorb and scatter the incoming solar radiation, thus providing a “direct” positive (warming) or negative (cooling) radiative forcing of the climate. Second, aerosol particles increase the number density of Cloud Condensation Nuclei (CCN), thereby enhancing the cloud albedo (optical properties) (1, 2). These changes in cloud albedo are termed an “indirect” effect, resulting in negative radiative forcing of the climate.

The figure above depicts the atmospheric aerosol particle surface area-weighted size distribution which arises from different mechanisms of aerosol generation. I adapted the figure from (3). Aerosol dynamics limit the fine particles from growing to diameters greater than approximately 1–2 μm. The fine and coarse particle regions have distinctly separate origins, transformations, removal mechanisms, and chemical compositions (4). The nuclei range is composed of both primary combustion particles and newly formed Secondary Organic Aerosol (SOA) in the 0.001 to 0.08 μm range, but physical mechanisms such as condensation and coagulation quickly transfer the particle mass from the nuclei mode to the accumulation mode. Mechanically generated aerosol particles, on the other hand, typically contain particles greater than 1 μm in diameter, with only a small portion of the mass smaller than 1 μm.

1.    R. J. Charlson, J. E. Lovelock, M. O. Andreae, S. G. Warren. Oceanic Phytoplankton, Atmospheric Sulfur, Cloud Albedo and Climate. Nature 326, 655 (1987).
2.    S. A. Twomey. Pollution and Cloud Albedo. Transactions-American Geophysical Union 58, 797 (1977).
3.    K. T. Whitby, B. C. Cantrell, paper presented at the ICESA  Conference Proceedings, (1975).
4.    K. T. Whitby. Physical Characteristics of Sulfur Aerosols. Atmospheric Environment 12, 135 (1978).

Every year my family would go to the Sycamore Pumpkin Festival. My parents still go to see the Lions’ Pumpkin Display on the courthouse lawn. My mom sent me one of her favorites of 2008.

The Incredible Pumpkin

I had many different jobs while growing up in Northern Illinois.  My buddies would joke about how many W-2 forms I would have to collect every year for taxes.  One of the jobs was building Gazebos at Leisure Woods. I know they print it on the front of their brochure, but it really is true, these are the finest gazebos made. I was told that, years back, Mohammad Ali purchased one. In addition, one of their largest gazebos was shipped down to Disney World in Florida for some extravaganza.

Leisure Woods Gazebos - Truly the Finest Gazebos Made!

The owners, Chuck and Cheryl, started the company in their garage. When I worked for them, Leisure Woods also built custom decks, which were also the best around. Chuck could build anything. He made a high quality product for his customers and I still look at decks and gazebos to see how well they measure up to what he produced.

I started out delivering and installing the gazebos in the Summer of 1993. I worked with a really funny guy, Brian. He was from my brother’s high school class, ‘88 so I already knew him a little. Brian and I would use the two-man, gas-powered post-hole digger to make the holes for the footings. Brian made me laugh so hard I can remember my side hurting a couple of times. We carried a lot of concrete that summer.

One time, actually many times, but this particular time, we hit a rock in the ground which stopped the digger cold. When I got up from the ground, I knew the Briggs & Stratton had finally done me in.  Still in pain and in need of some serious chiropracti, for some reason, we continued to drill the holes. I just sat on the ground holding on to the handles with my arms raised above my head, praying we didn’t hit another rock.

Since the gazebo business is seasonal, orders tapered off come Fall and most of the staff were laid-off. Brian found a factory job and Chuck let me stay to work part-time while I was going to college.

That Fall and Winter, I worked in the shop most of the time with the foreman, Randy. This guy was one-of-a-kind. He started out building custom staircases and was a seasoned craftsman. I learned as much as I could about woodworking in the six months I worked with him. Randy had a great approach to teaching in the shop. He always expressed the importance of foresight.

Although Randy was always looking out for my safety, he had at least one finger lopped off from a chop saw in his “learning years”. He rarely brought a lunch in, so I sometimes packed enough for two.

I remember how much Chuck liked to listen to Rush Limbaugh in the shop. The radio would blare with the apparent political rights and wrongs of the day. I had to listen to it, and I consider it a good experience. You have to hear both sides to know what you are up against and where you sit on the political roadmap anyway.

It was amazing how much work we would still try to do outside in the dead of winter. We would go out to build decks in near-blizzard conditions. Even the Skil saw wouldn’t want to turn in the cold weather. You could hear the motor slowly start to turn and eventually warm up as you squeezed the trigger.

The Leisure Woods Gazebo has a trademark copper-top and ball. I always look for it when I see a gazebo.

Thanks, Chuck and Cheryl, for a wonderful opportunity.

Professor David Y.H. Pui (University of Minnesota) et al. recently published a journal article entitled, “Recirculating Air Filtration Significantly Reduces Exposure to Airborne Nanoparticles.” The article characterizes the reduction of nanoparticle number concentrations when using the recirculation mode of the ventilation system in a Saab 93 (2003 model) and a Toyota Camry (2007 model). In simulated heavy-traffic situations, where particle number concentrations can be greater than 50,000 particles/cubic centimeter (cc) for particle diameters less than 50 nanometers (nm), the authors determined that setting the cars’ air ventilation systems in recirculation mode can decrease the number concentrations to background levels of less than 4000 particles/cc in approximately 3 minutes (1, 2).

Nanoparticle and Ultrafine Particle Jargon

By definition, ‘nano’ is one-billionth of a meter. A strand of human hair, for example, is approximately 70,000 nm (70 microns) and a water molecule is about one-third of a nanometer (0.3 nm).

Companies are constantly finding new ways to incorporate nanomaterials in products to improve design and cost effectiveness. New methods for manufacturing and handling nanomaterials are constantly being discovered. In addition, exciting applications are being developed such as tumor detection and targeted nanoparticle delivery for cancer treatment along with nanoparticle-based pollution control and remediation (3, 4).

The definitions of nanoparticles (NPs) and ultrafine particles (UFPs) are closely related. Particles can be referred to as a NPs if one of their dimensions is less than 100 nm, while UFPs are defined as particles which are less than 100 nm (0.1 microns) in all dimensions (4, 5).

UFPs are considered to be generated unintentionally and are not engineered to any great extent. On the other hand, NPs are the engineered building blocks of nanomaterials such as carbon nano-tubes (CNTs) (5, 6).

Health Effects

There are ongoing discussions in medical, public health, and scientific fields concerning the human health effects of inhaled nanomaterials. The short- and long-term toxic effects of human exposure to inhaled nanoparticles are unknown (6, 7).

The pulmonary toxicity of UFPs has been demonstrated in controlled laboratory experiments (8-10). In addition, studies continue to link environmental exposure to fine particles less than 2.5 μm in size to adverse health effects, such as respiratory irritation, reduced lung function, and associated cardiopulmonary impairment (11-13).

UFPs are widespread in the urban atmosphere because they are predominantly produced from the combustion of fossil fuels. If you are in the vicinity of  an automobile, commercial truck, power plant, or oil-burning furnace, you are likely exposed to nanoparticles in varying concentrations. In general, the reported health effects from fine particulate matter air pollution are dependent upon the exposure concentration and the length of exposure (13).

Recirculation Mode ON? Check.

When I drive in the city I often use the air recirculation option of my car’s ventilation system. This means that, neglecting outside air infiltration, no outside, unfiltered air is entering the cabin and the cabin air is being recirculated through the ventilation system. In newer cars, the air may pass through the cabin air filter repeatedly in this recirculation mode.

One-hundred percent of new cars in Europe and Japan and more than 60% of new American cars have cabin air filters. Pui et al. mentions that there has been no systematic study showing the filtration efficiency of automobile cabin air filters for particles less than 300 nm. The study demonstrated that the cabin air filters were relatively inefficient when compared to the high efficiency particulate air (HEPA) filters. However, tests conducted with and without the cabin air filter in the recirculation loop of the Toyota Camry (2007 model) showed significant reductions in UFP number concentrations for the filtered case. Therefore, even with a relatively inefficient cabin air filter, the recirculation mode can significantly reduce exposure to UFPs.

Particle diffusion is the main mechanism of removal for particles in the size range of 10-100 nm. This means that UFPs are removed in the recirculation mode by filtration and deposition on the ventilation system walls and fan. Generally, if particles in 10-100 nanometer size range are given enough time to diffuse to available surfaces, a decrease in number concentrations will be observed.

After seeing the effect of the recirculation mode quantified, you can bet that I will keep the recirculation option on during high-, slow-, stalled-traffic occurrences. Finally, although there currently isn’t a standard to determine nanoparticle filtration efficiency of automobile cabin air filters, they are still likely to reduce nanoparticle number concentrations and exposure.

1.    D. Y. H. Pui, C. Qi, N. Stanley, G. Oberdörster, A. Maynard. Recirculating Air Filtration Significantly Reduces Exposure to Airborne Nanoparticles. Environmental Health Perspectives 116, 863 (2008).
2.    D. B. Kittelson, W. F. Watts, J. P. Johnson. Nanoparticle emissions on Minnesota highways. Atmospheric Environment 38, 9 (2004).
3.    S. Azarmi, W. H. Roa, R. Löbenberg. Targeted delivery of nanoparticles for the treatment of lung diseases. Advanced Drug Delivery Reviews (2008).
4.    P. Biswas, C. Y. Wu. Nanoparticles and the environment. Journal of the Air & Waste Management Association 55, 708 (2005).
5.    K. Donaldson et al. Combustion-derived nanoparticles: a review of their toxicology following inhalation exposure. Particle and Fibre Toxicology 2, 10 (2005).
6.    M. R. Gwinn, V. Vallyathan. Nanoparticles: Health Effects—Pros and Cons. Environmental Health Perspectives 114, 1818 (2006).
7.    W. Yang, J. I. Peters, R. O. Williams. Inhaled nanoparticles—A current review. International Journal of Pharmaceutics 356, 239 (2008).
8.    A. Nemmar et al. Passage of intratracheally instilled ultrafine particles from the lung into the systemic circulation in hamster. American Journal of Respiratory and Critical Care Medicine 164, 1665 (2001).
9.    A. Nemmar et al. Passage of inhaled particles into the blood circulation in humans. Circulation 105, 411 (2002).
10.    G. Oberdorster et al. Extrapulmonary translocation of ultrafine carbon particles following whole-body inhalation exposure of rats. Journal of Toxicology and Environmental Health-Part A 65, 1531 (2002).
11.    M. Brauer et al. Air pollution and retained particles in the lung. Environmental Health Perspectives 109, 1039 (2001).
12.    R. D. Brook et al. Air pollution and cardiovascular disease – A statement for healthcare professionals from the expert panel on population and prevention science of the American Heart Association. Circulation 109, 2655 (2004).
13.    C. A. Pope III, D. W. Dockery. Health Effects of Fine Particulate Air Pollution: Lines that Connect. Journal of the Air & Waste Management Association 56, 709 (2006).

Since my wife and I moved out to Portland, OR in July, I’ve been looking for a challenging engineering position. One of the job-finding resources I came across a few weeks ago was this award-winning website developed by the Oregon Employment Department, called iMatchSkills.

Sarcasm aside, I enjoyed going through a VERY thorough set of questions and checking the boxes according to my experience and skill set. Today I checked the site to see if there were any new matches. After clicking the ‘Run Match’ button I was matched up with two job postings. The first was for a position with Daimler Trucks North America. Wow. That’s cool. The second position was a ‘Food Demonstrator’.

Don’t get me wrong, a position as a ‘Food Demonstrator’ is probably a rewarding and fun job, but it is a little divergent with respect to my current career path as a mechanical engineer. I wondered, is this what today’s economy is going to lead me towards? This, on a day that the DOW drops below 9000.