Category: Non-disposable

Posts that may have some sort of permanent value, or that I consider to be the best of what I have posted here.

Post #1997: Fixing a resin-cased watch with a broken lug

 

If you are reading this, you probably have a resin(plastic)-cased wristwatch with a broken lug.  The lug being the place where the watch band attaches to the watch case.

The question you need to ask yourself is, how much effort do you want to go to, to fix a cheap resin-case watch?

In my case, I was so irked by the thought of tossing a functioning wristwatch into the trash that I started small and just kept ramping it up until I finally got a repair that stuck.

What finally worked, for me was to glue the steel watch band to the steel case back, using a thin patch of baking soda and superglue that spanned the watch back and the first links of the metal watch band.  In effect, I bypassed the resin case and broken lug entirely.

Edit 9/1/2024:  This repair failed about a month later, following three sweat-drenched hours of helping a friend move furniture.  The patch came away cleanly from the stainless steel.  I’m guessing that prolonged moisture exposure was the issue.  (Superglue is not waterproof.)  But, two different dishwasher-safe super glues failed to work for this repair because they would not soak into the baking soda.

The upshot that I fixed it one last time, using regular liquid (not gel) super glue, as shown below.  My final take on this baking-soda-and-superglue repair is that this repair is strong enough, but not sufficiently water-resistant.  And water-resistant (dishwasher-safe) superglue won’t work, because (for whatever reason) it’s not sufficiently runny (and so beads up on, rather than thoroughly wets, the thin baking-powder patch.)

So, now I know not to wear the repaired watch in a wet situation.  It’s once again my daily-wear watch.  If it breaks again, I’m tossing it, and if that happens, I’ll try to remember to come back here and record the time to final failure. 

For now, the re-repair is solid.

Edit 10/24/2024:  The re-repair remains solid, and I continue to wear the watch daily.

The original post continues below. 

Ultimately, I chose this method because superglue has a reputation for adhering well to stainless steel.  I’m not sure how well it would adhere to a plastic (resin) strap.  But I wouldn’t rule it out.  If nothing else, the mix’s adhesion to stainless was way above my expectations.I’d be willing to try the same repair with a resin strap.  Certainly if the alternative is to throw the watch away.

You can’t see the repair when wearing the watch (a Casio A158WA).

And you don’t want to see it, when you take the watch off.

Despite the looks, the watch is still comfortably wearable, and the repair seems to be holding up well.

But the reality is that nothing else even came close to working.

Plus, it’s cheap and easy.  My only cash expense was for a new battery, because it seemed prudent to change my watch battery before doing this.  Once I figured out what to do, the repair itself took just a few minutes.

If that’s success, what were the failures?

Source:  WalMart. 

The best way to understand why I ended up with this expedient repair is to see what didn’t work.  In particular, these four approaches failed:

A drop of superglue on the lug takes essentially zero effort, but was a total fail.  Couldn’t even get the watch back onto my wrist before that gave way.

A drop of two-part liquid epoxy on the lug, ditto.  The act of buckling the clasp broke that free.

A small amount of JB Quik (two-part epoxy paste), applied between watch body and watch band, failed after a few hours.  It didn’t stick well to either the plastic case or the stainless watch band.

A larger amount of of two-part epoxy paste (JB Weld’s Quik Weld), applied as a patch across the stainless watch back and stainless watchband, held for almost a day.  But the JB Weld adhered poorly to the stainless steel, e.g., it was easily removed with a knife.

Why did this repair work?

To summarize the failures:

  • Glues don’t stick well to plastics, no matter what anybody tells you.
  • If you try to fix the lug itself, the surface area you’re working with is tiny, so there’s little area for the glue to adhere to anyway.
  • The resulting piece of hardened glue/epoxy is so tiny that it has little physical strength.

All of which told me that I needed to:

  • Glue to some surface where I could get some adhesion.
  • Glue to a much larger surface.
  • Use a much larger patch, so that it has some physical strength.

The breakthrough was in realizing that a) this was a $20 watch, b) the battery lasts seven to ten years, and so c) there was really nothing to stop me from literally gluing the watch band to the watch back.  Basically, just take the plastic case and plastic lug out of the equation entirely.

I chose superglue because it has a good reputation for sticking to stainless steel.

But I also needed a physically strong patch, because it needs to keep the watch band rigidly attached to the watch.  That way, the broken lug simply doesn’t matter.   All the force between watch and watch band is transmitted through the glue patch.

That suggested trying the baking soda and superglue hack.  I had always thought that was just internet-based nonsense, but in fact, there’s some good chemistry behind it (reference).  Assuming that reference is correct, the baking soda isn’t merely a filler, it actually cures the superglue in a completely different fashion from what would normally happen.  The result is stronger than superglue alone, and has better adherence to whatever you’re trying to glue to.

Instructions, such as they are.

In any case, the repair was simple.  In concept.  The tricky step is wetting the powder with the glue, which turns out to be a timed test, as the superglue sets rapidly under these conditions.  If you try this, and read nothing else, read the paragraph below on wetting your baking soda with superglue.

  • Scrub the watch back and the watch band to remove dirt and oils.  Dry them.
  • Gently re-attach the watch band to the watch, using the broken lug.  This doesn’t have to be physically strong, it just has to look OK.  The repair itself is concealed on the back of the watch.
  • Set that face-down in a position that approximates the curve of the wrist.  (Because one or two links of the watch band will end up rigidly attached to the watch case, if this repair holds.)
  • Lay and sculpt your baking soda.  Spoon on and smooth out a bit of baking soda, being sure to cover a large area of both the watch back and the watch band, and making it thick enough that it will have some physical strength.  And yet, not too thick, or it’ll be uncomfortable to wear.  I was shooting for something about as thick as the pad portion of a band-aid.
  • Wet your baking soda with superglue.   Slowly drip on liquid (not gel) superglue until the baking soda is saturated.  I used most of a one-gram tube of Ace Hardware Future Glue liquid super glue.  See below for greater detail.
  • Dust a little more baking soda on, to cure any liquid glue remaining on the surface.
  • Let it sit for five minutes or so.
  • Clean up any excess glue using a sharp knife.
  • Use a bit of sandpaper to smooth out the surface that will touch the wrist.

In hindsight, cleanup would have been a lot easier if I’d taped over the parts where I didn’t want glue to stick.  But it wasn’t hard to remove the excess glue with a knife.

I don’t know if this baking-soda-and-superglue patch will stick to a resin band.  But it should be easy enough to try it and find out.

Wet your baking soda with superglue, some details. 

The tricky step in this repair turned out to be wetting the baking soda.  It’s a timed test, because the baking soda/super glue mix sets up fast.  And it’s critical to wet the baking soda patch thoroughly with superglue, because where you don’t, it won’t stick.  For sure, you need to get the full depth of the patch wet with superglue, all the way down to the substrate (e.g., stainless steel, in this case).

On the plus side, you’ll be done with it before you know it.  Because it behooves you to move fast.   Once I figured that out, I essentially paved the top of the baking-soda patch with closely-spaced drops of superglue.

I can tell you from experience that you pretty much can’t go back and fix any mistakes.  So if you (e.g.) get too little glue on a spot, by the time you go back to re-wet it, the top will already have skimmed over with hardened superglue, and you’re out of luck.  For a couple of “dry pockets”, I ended up using the tip of a knife to pierce the thinnest part of the dried layer of the superglue, then added fresh superglue.

Separately, in the end, I wish I’d done more (or, really, anything) to prevent adhesion of excess glue and excess glue/baking soda mix.  I wish I had used some tape, or light oil, or similar.  As it was, I ended up using the tip of a sharp pocket knife to scrape off excess glue and glue/soda mix.  FWIW, that’s a task that you should do as soon as feasible, e.g., before the mixture has had hours to cure.

An irrational repair?

To be clear, this is a cheap watch.  I could replace this watch — literally a more-recently manufactured clone of the unchanged model — for about $20.

But I like this watch.  It’s lightweight.  The only material that touches skin is stainless steel.  The quartz works are guaranteed accurate to within 30 seconds a month (or about twice as accurate as the best mechanical watches.)  This particular watch only gains seven seconds a month.  This makes the watch low maintenance, in that it stays within a minute of true time as long as I set it twice a year for the change in daylight savings time.  It’s waterproof enough that I can scrub the schmutz off of it.

And it’s simple.  Unlike any other digital watch I have owned, I can use all of its functions without reading the manual.

It has some faults.  The LED back-light is comically dreadful.  And the clasp is insecure in several ways.  And, as I now know, the plastic case is a potential failure point.  But Casio does not put this works into a metal case.

Anyway, I already own it.  And I hate tossing stuff that’s still (mostly) working.

Once I made my mind up to try to fix it, I was just too stubborn to give up.

Boiled down

How much effort are you willing to go through, in order to keep wearing a cheap plastic-bodied watch with a broken lug?

If you already own baking soda and liquid (not gel) superglue, it will take you just a few minutes to try this repair.

The big surprise was how strong and adhesive the super-glue-and-baking-soda patch is.  Before this, I had assumed that was all internet hype.  But, in fact, there’s good science behind it. And in this instance, it worked better than JB Weld epoxy, which is high praise indeed.

And when you get right down to it, what have you got to lose?  If it doesn’t work, then you are left with a broken wristwatch.  Which is what you already have.

 

Post #1903: Hallelujah! Return to normalcy.

 

Background

Two nights ago my wife and I attended the 52nd annual Messiah sing-along at Clarendon United Methodist Church.  Because we do this every year, and I write it up, I can directly compare last year’s sing-along to this year’s.

For those of you unfamiliar with this tradition, Messiah is a baroque oratorio about the birth and death of Christ.  The words are straight out of the King James Bible (ca. 1611).  The music is straight out of the early 18th century (ca. 1741).  Despite these handicaps, the Christmas portion of it is still widely performed at this time of year (ca. 2023).  To reach for the LCD here, it’s where the Hallelujah Chorus comes from.

This is now one of my acid tests of how well we, as a society, have gotten past COVID.  That’s because a) sing-alongs are an extremely high-risk event for spread of airborne disease, and b) the typical in-person participant for this event, in the past, tended to be elderly. Continue reading Post #1903: Hallelujah! Return to normalcy.

Post #1803: Why are fine particulates (PM 2.5) so variable? It’s over my head.

 

One thing I’ve noticed about the AQI for particulates is how variable it is.  On any given day, my local hourly estimate from Accuweather will differ significantly from the EPA’s Airnow map.  Which, in turn, differs from readings just a few miles away.  For example, above, my AQI for particulates (as of 1 PM 7/6/2023 is either 63 (Airnow) or 33 (Accuweather).  Or somewhere between.

And readings within a few miles go as low as 13.  At the same time, the seemingly accurate meter I just bought shows “9”, sitting on my back screen porch.

At first, I chalked that up to instrumentation.  Maybe particulates are hard to measure, and what I’m looking at is more-or-less instrumentation error.

Because, serious, how could the air be so different, just a few miles away?  If I were to take some other measure of the atmosphere — temperature, humidity, pressure — it would vary smoothly over vast areas.   E.g., if it’s 90 degrees here in Vienna, VA, there isn’t going to be a pocket of 45 degree air five miles away in the City of Fairfax.  Yet you see that sort of apparent PM 2.5 disparity all the time.

So I thought, it must be poor instrumentation.  Then I bought a cheap air quality meter, noted above.  Not only are the readings stable from hour to hour, they are frequently in good agreement with the Accuweather numbers.  They clearly respond to ambient conditions in a hurry.  (The 4th of July fireworks briefly sent the meter into the “purple” AQI range, consistent with predictions from the Airnow map.)  The stated accuracy of the PM 2.5 measurement is +/- 10%.  All that, from a device that measures all five of the key air pollutants and costs under $75.

So, this isn’t due to instrumentation error.  Or shouldn’t be.  You can get reasonably reliable PM 2.5 measurements with a cheap off-the-shelf device.

Maybe my local variation is due to the presence of large local point-sources of PM 2.5.  But, to a large degree, we have no large point sources of particulate emissions in this area.  Largely because we are almost devoid of industry, in the DC area, and our power plants are (mostly) located outside of the metro area.

Which also matches my observation, because it’s not as if one area is consistently dirty.  It’s that the readings consistently vary a lot from place-to-place in this region.

So why do the PM2.5 readings in my area appear to be so highly localized?  Is there really that little mixing of the air between PM2.5 emitters, and local air?

Trying to understand how air mixes — a fool’s errand.

After about an hour of looking, I’m going to say that short of getting a graduate degree in atmospheric science, this ain’t gonna happen. 

It’s surprisingly complicated, but the joker in the deck is “turbulent mixing”?  Once I found out about that, I realized it was time to call it quits on trying to understand this.

First, physicists distinguish “bulk flow” (e.g., a breeze) from “diffusion processes” (molecules or particles moving through still air).  In this case, the latter would be the movement of water molecules or fine particulates through still air.

So, smoke spreads out because it 1) blows smoothly downwind, and because 2) the particles diffuse outward into surrounding clean air.

That said, it also spreads due to 3) turbulent mixing.  Any time the flow of air is not smooth (laminar, or layered), turbulent mixing is said to occur.  This sort of mixing can apparently distribute that smoke fully and more-or-less uniformly in the adjacent clean air.

Turbulent mixing occurs a lot in the atmosphere.  I’m pretty sure that it occurs at the level at which clouds form above the ground.  It occurs within clouds.  I occurs if sufficiently strong wind sweeps past fixed objects, e.g., tree branches.  And so on.  Anything sufficient energetic will kick the flow of the atmosphere from laminar flow to turbulent flow and turbulent mixing.

The bottom line is that there is no back-of-the-envelope way to determine how well PM 2.5 (including smoke) typically mixes into the surrounding atmosphere.  In the end, it’s all empirical, and depends on how hard the wind is blowing horizontally, how turbulent the atmosphere is in vertical profile, and so on.

Presumably, both water vapor and PM 2.5 move at the same speed, and mix at the same rate, when it comes to bulk transport and to turbulent mixing.  In both those cases, they are merely being carried along by the surrounding air.

But PM 2.5 diffuses a lot less rapidly than (say) water vapor.  A theoretical rule (via Einstein and Stokes) is that rate of diffusion is inversely proportional to the radius of the particle trying to diffuse.  Getting hold of some data (but not showing the calculation), that suggest that PM 2.5 diffuses about a thousand times more slowly than water vapor.

Diameter of a water molecule seems to be given as 2.75 Angstrom, where an Angstrom is 1/(10^10) meters.  Ah, round down to 2.5.  But PM 2.5 is in microns, or 1/(10^6) meters.  This means PM2.5 particle is about 10^4 = 1000 times larger than a water molecule.  Thus under this  simple theory, water (humidity) diffuses through still air roughly a thousand times faster than a PM 2.5 particle would.

At the end of the day, I have no clue whether that matters or not, with regard to widely varying PM 2.5 readings across my area. 

All I know is that even without big local point-sources of PM 2.5, it’s common to see big difference in (what appears to be) actual PM 2.5, across different locations in my area.  Whereas for other parameters of the atmosphere — temperature, pressure, humidity — true local variation in those quantities is tiny.

Seems kind of crazy to worry about it, but there has to be some good reason why this aspect of the atmosphere is so qualitatively different from others.

Maybe Hawaii wasn’t just a nice place to hang out.

Maybe my only clue comes from the Keeling curve (above) and how that is measured.  When Keeling started measuring atmospheric C02 in the late 1950s, he established his laboratory on the windward side of Mauna Loa.

And found average atmospheric C02 around 315 PPM.  Currently, it’s around 422 PPM.

But the point is why he chose that locale.  His goal was to get “well mixed” atmospheric gasses, and, apparently, having circa 6000 (?) miles of open ocean to windward was just the ticket for getting that.

By contrast, you can frequently find city air with C02 levels in the 1000-PPM range, near congested roads (reference).  That air hadn’t had a chance to get mixed with the rest of the atmosphere.

So, maybe Keeling located there for some reason other than it’s being a nice place.  Maybe you really need that much distance to ensure uniform mixing.  And maybe the mere 500 miles or so between me and the nearest Canadian mega-fire isn’t enough to ensure uniform mixing of the air.

So I’m guessing that the atmosphere doesn’t mix all that uniformly.  For whatever reason.  And that the small-area variation in PM 2.5 is true.  And that I should not expect it to get any smaller as the summer progresses.

G23-026 Winnowing, or, Rube Goldberg does agriculture.

 

On the plus side, I bet you didn’t expect a blog post about winnowing.

On the down side, this entire blog post is about winnowing.

Image above: Winnowing Grain, Eastman Johnson, 1879, via https://www.wikiart.org/

Continue reading G23-026 Winnowing, or, Rube Goldberg does agriculture.

Post #1794: Why filtering forest fire soot is not the same as filtering aerosol droplets.

 

I learned a lot about air filtration during the recent pandemic.  At some point, I wrote down and compared all the different standards used for air filtration.  For example, what does HEPA actually mean, and how does it compare to the various members of the MERV clan?  And how do all of those relate to N95? (Post 593, April 1, 2020).

The problem-du-jour isn’t about filtering tiny little viruses out of the air.  Instead, it’s about filtering tiny little soot particles out of the air.  In the U.S. Northeast, we’re now in an era of Canadian wildfires and the resulting air pollution alerts.

Nicely enough, I get to re-use what I think I already know about air filtration.  The knowledge that applied to filtering aerosol droplets (droplets less than 5 microns in size) applies equally to filtering fine particulates such as the soot from wildfires.  This soot typically falls into the PM 2.5 air pollution category, that is, any particulate matter in the air less than 2.5 microns in size.  (For comparison, a human hair is typically around 70 microns thick.)

Except that there is one key difference between filtering the air for pandemic purposes, and filtering the air for forest fire purposes:  Outdoor air is no longer our friend.  In fact, outdoor air is now the enemy.

When filtering viruses, outdoor air could be assumed to be clean.  The likely concentration of virus droplets in outdoor air was typically negligible.  Disease transmission in outdoor settings was virtually unheard-of.  You only had to worry about the “pollution” that you generated inside the indoor space.

But for forest fires, the entire problem IS the outdoor air.  In some sense, the entire battle to keep indoor air breathable is about dealing with the dirty air outside.

To crystalize this, recall that one standard suggestion for improving the COVID safety of (e.g.) schools and other spaces was to open the windows.  Perfectly rational if you’re dodging COVID.  Not so smart if you’re trying to avoid forest fire smoke.  So, from the get-go, you now see that dealing with forest fire smoke is a completely different engineering challenge from minimizing aerosolized COVID. 

Why does this matter?  Outside air is always leaking into indoor spaces.  For the virus filtering, that was a good thing.  Now it’s not, and you need to strategize your air filtration accordingly.  Why?  Because outdoor air doesn’t just leak into indoor spaces, it typically pours in.  The minimum standard for houses, from a health standpoint, is that outdoor air should replace indoor air at least once every three hours (reference).  But a typical well-constructed older home, in good shape (storm windows, caulked) would exchange all the indoor air with outdoor air once per hour (random reference).  Leakier construction (no storm windows, caulk missing) would experience air exchanges more rapid than that.

Whatever air filtration setup you use, you now need to account for that.

My particular problem.

My daughter lives in New York City.  Shown above, New York just had a bout of extremely bad air quality, due to Canadian forest fires.  At the peak, PM 2.5 (particular matter 2.5 microns or smaller) reached 460 micrograms per cubic meter.  This is way beyond what the EPA considers hazardous, and is maybe 10 to 20 times the typical value for that area.

Given that those fires continue to burn, I’m guessing this isn’t a one-and-done.

So I wanted to get her an effective air purifier for her apartment.  (And even if forest fire soot does not return, a New York City apartment would probably benefit from having an air purifier).

My options were to go with a redneck air purifier (20″ box fan, and a high-quality electrostatic air filter), or to buy a purpose-made room-sized HEPA air purifier.   The redneck air purifier is a variation on the “Corsi box”, a D-I-Y air purifier that was promoted as an easy fix for indoor air filtration during the pandemic.

You might normally say that HEPA must be better, because it’s a higher filtration standard.  In theory, HEPA filters must remove 99.97% of fine particulates in a single pass (based on the Wikipedia entry for HEPA).  In practice, I think 99.5% is more typically advertised.  Whereas a high-end air filter (in this case, Filtrete 1900) only removes about 65% of fine particulates in a single pass.  Seems like the case for HEPA is a no-brainer.

And if I were trying to filter the air in a hermetically-sealed box, HEPA probably is the better choice.  The only drawback to HEPA is the back-pressure of doing that high level of filtration limits air flow, for a given power input.  HEPA units advertised as “room-sized” air cleaners typically filter just a few hundred cubic feet of air per minute.  By contrast, the entire selling point of the 3M Filtrete electrostatic filters is that they achieve a reasonable degree of fine-particle filtering with minimal back pressure.  With a box fan on low, I can push 1000 cubic feet of air per minute, through a Filtrete filter.

My gut tells me that, for older construction, with a lot of air infiltration, the cheap setup (box fan and filter) is better than the equivalent purpose-built HEPA air filtration unit. A typical room-sized HEPA unit isn’t going to be able to “keep up with” the inflow of dirty outside air.  Or, at least, not as well as the high-air-flow fan-and-filter setup.  If a lot of air is flowing into the room, my gut tells me that that HEPA (high-filtration/low-volume) actually does a worse job than box-fan-and-filter (low-filtration/high-volume).

Many mathematical paths to the sea.

At some level, I realize that I’m trying to solve a classic calculus problem.  Typically, it’s a water tank with inputs and outputs.  Here, it’s a room with leaks and a filter.  There must be a classic closed-form solution that would tell me the final concentration of particulates in the air. Just plug in the parameters, and view the output.

Somewhere along the line, I have lost the ability to cast a problem such as this into that classic format.  No problem.   Much of what used to require actual intelligence and insight can now be done with brute-force computing power.

In this case, all I need to do is the simple numerical simulation, in a spreadsheet.  Start with a room full of dirty air, with a known rate of infiltration of outside air.  Turn on an air cleaner with known properties.  And just do the accounting, minute-by-minute.  Air in, air cleaned, air out.  And track the resulting concentration of pollutants in the air.

Does anybody ever care about the details of methodology?

Answer:  Only if they disagree with the results.  By contrast, if I end up saying something you agree with, you won’t care how I arrived at that.  That’s just human nature.  People just want to say Amen and move on.

My redneck air purifier consists of a box fan pushing 1000 CFM (on low), through a 3M Filtrete (r) filter.  The Filtrete is a 3M “1900”, rated at MERV 13.  It grabs 65% of the PM 2.5-sized particles with each pass, and about 95% of PM 10-sized particles.  For this simulation, I’m only tracking PM 2.5.

B

The only practical detail you should care about is that if you do this — a single filter stuck on the back of a fan — you must use a low-back-pressure electrostatic filter.  Otherwise, if you want to use el-cheapo MERV 13 filters, you need to go to the trouble of actually constructing a literal Corsi box, using four filters taped together.  That’s because with cheap filters, you need all that surface area to avoid the high back pressure that would starve the fan of air.  See this reference for Corsi box.  Even with that, my take on it is that it provides slower air movement than using a single Filtrete 1900 placed on the back of a fan.

Below is a literal Corsi box, via Wikipedia.  If you use cheap filters, go that route.

By contrast,  my theoretical HEPA filter pushes 100 CFM through a filter that grabs (say) 99.5% of PM 2.5 particles.  (Separately, I’ll show the results for a filter pushing higher rates of air flow).

The room is 20′ x 20′, with an 8′ ceiling, and has one full air exchange per hour, typical for sound older construction.  That is, enough outside air enter the room through various leaks and cracks that it would be enough to replace the air in the room once per hour.

The outside air is at 450 micrograms per cubic meter of PM 2.5, the peak of the air pollution in the New York City area.

Based on this, I’ve written the spreadsheet that does the accounting.  Air in, air purified, air out.

Results.

The results of my Excel-based numerical simulation validate what my gut was telling me.  Due to the high rate of air infiltration typical in older construction, filtering the air rapidly is far more important that filtering the air extremely well.

On the left, you see the results for my redneck, box-fan-plus-Filtrete air filtration unit.  It passes 1000 cubic feet per minute, but only filters out 65% of the finest (PM 2.5) particles.  On the right, you see the results for a slower HEPA unit.  It passes one-tenth of the air per minute, but it filters it more than 10x better.

The equilibrium level of particulates in the room is vastly lower with the high-volume, lower-efficiency filter (left graph above).  Why?  Because the slow pace of the HEPA filter (right graph) can’t keep up with the level of outside-air infiltration that is typical in older construction.

To get the HEPA filter to work almost as well as the simple Filtrete (r) 1900 plus box fan, in this typical leaky room, you’d have to crank it up to a much higher air-volume throughput.

A HEPA filter is a beautiful device.  It would work wonderfully in a hermetically-sealed room.  But in an actual room, with high-volume exchange of air between inside and exterior, it just can’t keep up.  You’re better off using a cheap box fan on low (1000  CFM) and a low-back-pressure air electostatic air filter, such as a 3M Filtrete (r) filter.

Is this a fair comparison?  Judging from what I see on Amazon, I’d say so.  When they even bother to show the approximate air flow rate, HEPA units offered as whole-room units typically run at:

Whereas the box-fan-and-filter turns over the air in my example room about 20 times per hour, at roughly 1000 cubic feet per minute.

Further, it makes almost no difference whether I use 99.5% efficiency or 99.9% efficiency for the HEPA unit.  At slow rates of air turnover, the HEPA filter gets overwhelmed by the infiltration of outside air.

Conclusion

I just sent my daughter two Filtrete 1900 filters.  Plus, oxymoronically, a stylish 20″ box fan.  Hoping that on low, the fan will be quiet enough not to be bothersome.

My final finding is that the folks who run Amazon don’t miss a trick.  If you search for a stylish box fan, Amazon suggests a few packs of MERV-13 filters, as an add-on purchase.

My conclusion from the above is that, between viruses and soot, a whole lot of people have figured out that the best and cheapest way to filter indoor air is with some form of “Corsi box”.  So these days, as soon as you pick your fan, Amazon is right there, suggesting the add-ons you need to do that.

G23-021: Dance of the mustard flowers.

 

Recall that I swore my mustard plants were moving.

Heliotropic?  That is, moving to face the flowers into the sun?

Maybe.

So I did a little time-lapse video.  This is one day of the mustard bed in my garden.  Roughly 8 AM to 8 PM, with a brief interruption in the middle to add a tin-foil shield.  All condensed into about 30 seconds via YouTube.

The dance of the mustard flowers appears far more complex than simple heliotropism.  And far weirder.

Enjoy.

 

Post #1790: Surface energy, or one of the many reasons why stone countertops are inferior.

 

The featured image above is from Formica.com

I dislike many aspects of the kitchen in my house.  The previous owners took a well-designed and well-built 1959 house, and basically screwed it up by, among other things, putting in a trendy “designer” kitchen.  Amongst the hate-able aspects of that kitchen are the obligatory granite countertops.

Today, as I was housecleaning, scraping little bits of crap off those perpetually-grungy kitchen countertops, I had a flash of insight.

Seems like stuff sticks to these granite countertops to an extent that never happened with our old Formica (r) countertops.  It’s almost as if granite countertops are mostly for show, and are a really poor choice if you are actually going to use your kitchen intensively.  Heck, I keep a plastic paint scraper at the sink, just for scraping up the most-stuck-on stuff from those countertops.  I’m pretty sure I never needed that with Formica (r).

Gunk just seems to glue itself to those granite countertops.

That’s when the light bulb lit.  It really isn’t my imagination that granite is tougher to keep clean than Formica (r).  My perpetually grungy granite is the flip side of the difficulty of gluing certain types of plastic.  If Teflon is at one end of the spectrum, then polished granite is somewhere near the other end.

It’s all about surface energy.

Continue reading Post #1790: Surface energy, or one of the many reasons why stone countertops are inferior.

Post #1789: The deadweight loss of credit card rewards

 

There are good reasons that economics is called “the dismal science.”

“The Deadweight Loss of Christmas” (Google reference for .pdf) is surely a case in point.  In that scholarly analysis, a Yale economics professor takes the time and effort to quantify the economic inefficiency of Christmas gift-giving.

The idea is simple.  If you buy something for yourself, you know exactly what you want.  By contrast, if somebody buys you a gift, they have to guess what you’d like.  And to the extent that they guess wrong — by a little or a lot —  the value of the gift, to you, may be well be below the purchase price.  And that gap between what the gift-giver paid, and what the gift-recipient would have been willing to pay — that’s the deadweight loss of Christmas.

Economists have a simple (if entirely soulless) solution:  just give money.  The gift recipient can then buy themselves exactly what they want, and the total satisfaction or “utility” of the transaction is maximized.   A gift of money eliminates the deadweight loss involved in trying to guess somebody else’s preferences.

A different deadweight loss

Which brings me to my newly-acquired, soon-to-be-cancelled Best Buy credit card.

I made a major electronics purchase a few weeks back.  The sales clerk at Best Buy talked me into getting a Best Buy credit card.  Normally, I say no to all such offers.  But the deal was that this would give me an instant 10% off the not-inconsiderable sales price.

Cash back, right?  Who would turn that down.

Only, this credit card doesn’t work like that.  What I actually got was, in effect, store credit.  I got “rewards” equal to 10% of the value of the purchase.  Rewards that could only be redeemed in Best Buy merchandise.  Worse, that’s how the card works for all purchases made on it.  There is no “cash back” feature.  All rebates are in the form of additional “rewards” that can be cashed in for Best Buy merchandise.

I guess this is a fairly good deal, if you have an ongoing need for the stuff Best Buy sells.  But I don’t.  Worse, I’m on a tear to get rid of stuff, the process of Döstädning, or Swedish death cleaning (Post #1667).  The last thing I need is yet another electronic doo-dad or small appliance.

And so, what ensued was not unlike the deadweight loss of Christmas.  I wasn’t given specific gifts, for sure.  But in order to get my money’s worth, in effect, I had to choose my gifts out of a catalog of stuff that I didn’t really need or want.

For something that was free*, it was a surprisingly grueling process.

*  As a responsible parent, and an economist, whenever my children used the f-word (free) around me, I would immediately snap “pre-paid”.  So I use the term loosely here.   The plain fact is that the cost of all such givebacks has to be worked into the original purchase prices, so that Best Buy can remain in business.  So these “rewards” aren’t free, they are merely pre-paid.

At my wife’s suggestion, I went for batteries, because those are consumables, and we’ll eventually use them up.  Once I got past about $50 worth of alkaline batteries, I was stumped.  But, gosh darn it, I was not going to leave money on the table.  So I spent hours swapping stuff into and out of my on-line shopping cart, in an attempt to get things I might use, whose prices summed to just over the total “rewards” I had been granted.

I recall buying a flashlight.  And a pocket knife (a.k.a, future contribution to the TSA).  Because you can always use another one of those.  The rest of it is a blur.

I hope I’ll be pleasantly surprised when the packages show up.  Or at least recall that I ordered it.

In any case, once I’d finally made my purchases, and burned up those rewards, I had the funny feeling that I had come across this process before.  But it took me another day to realize that what I was experiencing was the deadweight loss of Christmas.

In effect, I gave myself some gifts that I didn’t much want.

For sure, if there had been a straight-up cash-back option, I’d have taken it.  In fact, in hindsight, if they’d offered me half that dollar amount, as cash back, I’d have taken it.

Thus validating the fundamental insight of The Deadweight Loss of Christmas.

Post #1788: Recycling plastics, Part 2: My Town tells me to do the wrong thing. Does yours?

 

I am in the middle of looking at plastics recycling in my area.

Any internet search in this area feeds you a lot of pessimism about the entire concept of plastics recycling.  People say that it’s not worth doing, that it’s greenwashing, that it’s a scam, that it all ends up in the landfill, and so on.

But is that true?  It all seems to start from a figure that just 5 to  8 percent of U.S. waste plastic is recycled.

Less than an hour of internet search, and I now know that figure is totally irrelevant to the situation I’m investigating.  The often-cited 5% is for every conceivable form of plastic waste — stuff that was tossed in the trash, stuff that was tossed on the ground, plastic resins that are not recyclable, plastic items that are not inherently recyclable, plastic integrated into multi-material items, and so on.

That’s a problem, for sure.  But right now, I just want to know what happens if I properly handle a recyclable plastic object, where I live.  I want to know two simple things:

  • What plastic should go in the recycling bin, here in Vienna, VA, and
  • What fraction of (say) a clean #1 (PETE) bottle actually gets recycled?

Continue reading Post #1788: Recycling plastics, Part 2: My Town tells me to do the wrong thing. Does yours?

Post G23-013: Bee hotel success, Part 1

Edit 5/19/2024:  This year, I made my own bee hotels, and those worked out a lot better than the off-the-shelf bee hotel that I discuss in this post.  See Post G24-014 for this year’s bee hotel results, and Post G24-008 for construction details, such as they are.

Original post follows:

I try to maintain a reasonably bee-friendly property, out here in the wilds of Northern Virginia.

It’s not just that I need them to pollinate my vegetable garden. Or that bumblebees do, in fact, sleep in squash blossoms (aw!).  Or that the hum of bees at work in my garden marked the never-to-be-repeated peak of mid-pandemic suburban quiet (Post #G11).

It’s more bee-as-coal-mine-canary. If I’m doing something in the yard or garden that’s likely to be killing off my bees, odds are I shouldn’t be doing that.  It’s a quick way to rule out some environmentally stupid behavior.

In any case, I’ve had a couple of bee hotels (native bee nesting boxes) kicking around my yard for a few years now.  Shown above.  But those were never very successful.  It took years to get the first bees to use them.  And I might get a one or two tubes filled, per year.  There are clear exit holes on some tubes, so some new bees were produced.

But not a big hit, over all.

This year, on a whim, I bought a different model of bee hotel, at my local Home Depot.  The Home Depot mason bee box is already working vastly better than the previous model.  It’s been up a few days and I already have more tubes filled than I got in the first few years of the other model.  In short, my bees love this new bee hotel.

Now that I’m finally doing something right, I’d like to keep that going.  In a radical and very un-guy-like step, I actually read the directions.    And — surprise — I’ve been clueless as to how these things actually work. 

But now that I know, I realize this new bee motel is a fundamentally terrible design.  Not for what you can see — that part’s OK.  And, as noted, it’s definitely attracting bees.  The problem is that those bamboo tubes are permanently attached.  As discussed below, that’s a no-no.  You want nice clean new nesting tubes each year.  And that means that, unless I tear it apart next year, this lovely little bee hotel is a single-use disposable item.

So this post is going to summarize everything I think I learned about mason bee nest boxes (“bee hotels”).  And about the difficulty of making smooth-ended splinter-free replacement tubes for this, from bamboo I have on hand.

Three-minute tutorial:  Bee hotel or roach motel?

Key point: For best results, you need two bee hotels (or equivalent) for every site at which you wish to maintain a bee hotel.

You ideally want the female bees to use clean, new nesting materials each year.  The use of new (or carefully sanitized) nesting tubes each year minimizes the presence of diseases and parasites in the nest.  If you don’t keep the premises clean, your bee hotel can end up as the bee equivalent of a roach motel.  With poor enough conditions, the bees check in, but they never check out.  Your bee hotel becomes a catch-and-kill trap. 

The problem is that each spring, some bees are ready to check into your bee hotel before your existing guests have checked out.  Some are ready to lay their eggs before others have emerged from their cocoons.  The reason for this chaos is that these bees are quite short-lived.  The emerge, mate, forage for food, lay their eggs, and die, all in the course of a few weeks in the spring.

The solution is to put last year’s bee hotel (or, at least, the nesting tubes) aside in an “emergence box”, to give the bees time to emerge from their cocoons.  At the same time, you need fresh, new nesting tubes nearby, for the emerging bees to lay the next generation of eggs.  An emergence box is just an opaque weather-protected box with a small opening.  This allows the newly-emerged bees to exit, but prevents bees outside the box from seeing (and therefore attempting to re-use) the old nesting tubes.

No matter how you cut it, you would ideally have two sets of nesting tubes in rotation at each bee hotel site.  One set of clean, new tubes, for this year’s eggs.  And last year’s tubes, from which bees continue to emerge.  You want to keep the emergence box with last year’s nesting tubes near your new bee hotel, because, as noted above, the bees get right down to business as soon as they emerge.

Here are my five Ws for bee hotels.

Who?  These bee hotels provide nesting places for some species of solitary bees, that is, bees that don’t form big communal hives.  Mainly, that means these are NOT for honeybees.  The bees that use these devices are typically referred to as “native bees”, but that’s imprecise.  For one thing, bumblebees are typically native bees, but those are ground-nesting bees, and won’t use these tube-type bee hotels.  Your primary target bee is a “mason bee”, so called exactly because they build those little mud walls at the end of the nesting tube where they’ve laid their eggs.

What?   A bee hotel provides tubular structures into which a mason (or similar) bee lays eggs.  The bee lays a series of eggs in the tube, providing each with food, separating them with mud walls, and capping off the tube with more mud.  Over the course of a year (in some cases, two years), each egg hatches into a larvum (worm), eats the food that its mother left for it, pupates (cocoons itself), and eventually emerges from that cocoon, the subsequent year, as a bee.

When?  The eggs are laid in spring.  The eggs hatch/larvae emerge in summer.  They cocoon in the fall.  And they re-emerge as bees the next spring/summer.  (In some areas, there are species that spend two years in the cocoon, but I’m not sure how relevant that is to most places.)

Place your bee hotel outside in the spring.  It appears to be fairly important not to disturb this during summer, as the larvae are delicate.  That means you attach it to something solid in the spring, so it doesn’t shake around, and you leave it alone.  The larvae pupate in fall.  At that point — late fall, early winter — they are tough enough to be moved.  Place the bee hotel in a sheltered, unheated location (such as an unheated shed).  Then, next spring, place the bee hotel (or the tubes from it) in an “emergence box”, move them back outside, and let the bees emerge as the weather warms. Google “emergence box”, but it’s basically a sheltered box with a hole in it, to let the hatched bees escape.

Some experts “harvest” the cocoons as an extra sanitation measure.  They break open the nesting tubes, remove and possibly clean the cocoons exteriors, and place the cocoons in fresh material for eventual hatch-out in the spring.   The claimed advantage of this is that it separates the bees from various parasites that may linger in the nesting tubes and this allows them to emerge from overwintering parasite-free.  If you are going to do that, you need to use relatively fragile nesting tubes (paper liners, reeds) that allow the cocoons to be removed undamaged, and not sturdy ones such as bamboo tubes shown above.

As of this writing, it’s not clear to me how much of an advantage you gain by harvesting cocoons, or what evidence basis there is for it.  The only obvious advantage is that if certain fungal diseases are present in the nest, you’ll see them if you harvest the cocoon.  As I plan to use all-new materials each year, I’m not sure that’s much of a concern to me.

Where?  These bee nests ought to be protected from rain, protected from getting cooked in the afternoon sun, and so on.  he most common advice is to locate them to catch morning (but not afternoon) sunlight.  They need to be firmly attached to something substantial because the larvae are delicate and don’t want to be tossed about.  In plain sight, so the bees can find it.  And near a ready source of mud.  Because bees need mud to cap off their egg cells.

Upshot:  Facing east-ish, under eaves if possible, firmly attached to something, near water or mud, maybe 5′ off the ground, and plainly visible.

Why and how? Different bee species want different sized tubes.  So from the get-go, a rack of identical tubes limits the species that can use that particular hotel.   The tubes need to be closed off at the back, in some fashion.  The tubes need to be sturdy enough to keep out various bee predators.  Paper straws alone, for example, appear to be frowned upon, thought to be too fragile to keep out certain types of bee predators.  In rare cases, you need to put hardware cloth across the front to keep birds from pecking out the larvae.  That’s only necessary if you wake up one morning and all the previously-filled tubes appear empty.

The simple upshot of all this is:

  • Each Spring, put last year’s nest out in an emergence box.
  • Nearby, place a clean, new nest out to attract bees.
  • Each Fall, refurbish last year’s nest, to be placed out the next spring.