Why Does a Hot Day Feel Hot?

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Did you know that it's not just high temperatures that makes us feel hot on sunny days in the summer? 

Normal skin temperature for an adult ranges between 33 °C and 37 °C. Our bodies are cooled naturally by perspiration that's released from pores in the skin. When sweat evaporates, it carries away heat from the body, reducing skin temperature. Capillaries in the surface layers of the skin also help with cooling by circulating blood, which also loses heat to the ambient air. Anything that interferes with this process changes the perception of how hot or cold it is at any one time. So higher humidity reduces the rate at which perspiration evaporates, making it feel clammy and warmer. A less humid day doesn't feel as warm, even though the temperature may be the same. Air movement also increases the rate of heat loss from the skin. So a windy day feels colder than a day when the air is still. The air blown out of a room fan feels cold. Fans don't actively cool air (air conditioners do) The air they circulate is at the same temperature as the air in the rest of a room. They simply remove air that has been in contact with skin and has absorbed heat from it. They do this continuously so new air is always moved into contact with the skin. Since this "new" air is at room temperature and not warmed, heat flows at a faster rate from skin. The reason for the greater rate of heat transfer is because heat flows from a region of hot temperature to one at a lower temperature. The greater the difference in temperature, the higher the rate of heat flux. And so this cools our bodies faster than natural cooling. Blowing on hot soup in a spoon does the same thing.

"Take Your Coat Off"

Attic cold tank. © Eugene Brennan

The insulation on the cold water tank in my attic is an ad hoc setup from 20 years ago or more. I just used leftover fibreglass insulation from doing the floor and shrink-wrapped it around the tank. I'm thinking of replacing it with a removable jacket that I can take off in the summer so the water insides absorbs ambient heat. Might lower the cost for heating water somewhat. At this time of the year, water from the mains is colder than the air temperature. However a heat exchanger would improve things. That would take heat from the attic and put it into the water. A heat exchanger uses fins for increasing surface area to maximise the rate of heat transfer. That's why radiators in vehicles and in your home are finned or have accordion-like metal corrugations. Similarly for the heatsinks on some electronic components such as power transistors and microprocessors. The ambient temperature in an attic that doesn't have the slope of the roof insulated can reach the mid-thirties on a sunny day in the summer. Unfortunately water, compared to other a liquids has a huge specific heat capacity. That means it takes a lot of heat to raise the temperature of a kilo of water by 1 deg Celsius. (4200 J⋅kg−1⋅K−1, expressed as "joules per kilogram per Kelvin. The joule is the SI unit of energy).

I remember in the 70s, water was always warm when it came out of the cold tap. I guess that was before the cavernous reservoir (which lorries were able to drive around in, I'm told) was constructed in the hill at Old Kilcullen. Before that, I think our water came from a reservoir on the elevated ground behind Dunlea's garage. The likely smaller volume of water in the tank and lower population in the town resulting in less water flowing from the tank probably gave it time to warm up.

Sewerage Network in the Town Centre

Image courtesy RPSGroup.

From the Draft Kilcullen Settlement Plan. The first number on pipes I think is diameter in mm, and the code that follows is the material: uPVC is unplasticised Polyvinyl Chloride, VC is vitreous clay, CO is concrete and CL is cast iron. Sewage flows through the sewerage network to the pumping station at the back of the Kilcullen Farm & Nature Trail. From there it's pumped to the Osberstown Sewage Treatment Plant.
A clay pipe seems to be visible in the bed of the river, south of the bridge. This is probably the original sewer from the southern part of the town to the old treatment plant in the woods across the river from the farm trail. (Maybe somebody more knowledgeable could confirm this?). Or possibly it's one of the overflows shown on the map? I'm not aware of any obvious outflow pipes above the waterline.

Re-Use Your Waste Oil

Waste oil. © Eugene Brennan

Did you know WD-40 isn't specifically a lubricant? Its primary function is as a penetrating oil, for freeing stuck bolts and similar. Waste engine oil is perfectly suitable for hedge cutter blades and garden shears., although probably not good for the environment. It's thicker than light machine oil and so stays longer in contact with metal surfaces, without being squeezed out. Lubrication is a Goldilocks process. The lubricating layer shouldn't be too thin, or surfaces will still rub together, increasing friction. If the layer is too thick, it results in viscous friction, which can cause energy loss and drag on fast moving parts in contact.

Can't Make Decent Tea Anymore

My grandmother's teapot. © Eugene Brennan

Once upon a time, it was possible to get nearly two cups of tea from a Barry's tea bag. Now it takes nearly two bags per cup. I remember learning in Inter Cert science that one of the attributes of hard water is that it's difficult to make tea with it. So that's the consequences of getting our water from the Barrow instead of from the Liffey, which has its source in the granite of the Wicklow Mountains. I don't think BRITA water filters or their clones remove lime from water. The lime also clouds shower doors and takes forever to clean with vinegar, the coating returning within a week. So I just gave up regular cleaning and only do it when the stalactites are ready to snap off.

TV Signal Problems

Sarah777 at English Wikipedia, Public domain, via Wikimedia Commons

If you get your Saorview signal from Kippure and are experiencing reduced signal strength and picture breakup, this may have been the reason: essential maintenance.
FM was mentioned, but TV programmes were also affected for a short period this evening.
The flashing beacons on the Kippure transmitter mast can be seen from several vantage points in the town at night: on New Abbey road and at the Riverside development. The mast itself can be made out on a clear day from the crossroads at the top of McGarry's Lane.

2rn is the trading name of the RTÉ Transmission Network, named after Ireland's first radio station 2RN, which started broadcasting in 1926.

Saorview and radio signals can be received in Kilcullen from Mount Leinster in Carlow, as an alternative to Kippure.

 

Edit, UHF digital TV transmissions are of course FM

More Boiler Woes

Cleaning the filter on the oil tank. © Eugene Brennan

I let the oil run out a couple of weeks ago while waiting for price to drop. Got a fill of oil and thought I'd just have to bleed the boiler, but no air and oil escaped from the bleed vent when unscrewed. Checked the filter at the tank and it's not blocked. So fine sludge has probably got through the screen mesh of the filter and perhaps blocked the pre-filter in the boiler. So hopefully the oil line won't have to be dug up, because it's under concrete, and the boiler service people can just clear the line with compressed air or flush it. Anyway it's more expense. Moral of the story, check your oil regularly. I always do, but just let it down a bit far while waiting for price to drop.

Bleeding air on the boiler. © Eugene Brennan

A Vintage Flyback Transformer

Teravolt at English Wikipedia, CC BY 3.0  via Wikimedia Commons.

These were used in TVs until cathode ray tubes (CRTs) were replaced by plasma and then LED displays. CRTs use an electron beam that traces out an image line by line on a glass screen, starting at the top left of the screen and working downwards. The path followed by the beam is just like how we read text on a page. A flyback transformer is used to produce a high voltage, in the order of tens of kilovolts, to accelerate the beam and make it strike a phosphor coating, the latter emitting light on impact. Only one point on the screen is illuminated at any one time, hence the bright spot at the centre of the screen when old TVs were powered down and the scanning coils were turned off. Persistence of vision and the 25 Hz scanning rate (50 Hz in total because of interlacing) give the impression that a complete image is displayed all at once.

Digby Bridge and OPW Work

Digby Bridge on the Grand Canal, north of Naas in Co. Kildare. © Eugene Brennan

My cycle today was along the canal from Naas to Digby Bridge between Sallins and Prosperous. Good to see that the OPW (or Waterways Ireland?) took on my suggestion to remove a dangerous board from the cover on the feed/overflow channel from the canal at the bridge. It was rotten at the ends and only supported by two steel joists and none in the middle, liable to collapse if anyone jumped on it. They used a steel plate and galvanised steel grating as a replacement. The wider boards seem to have been trimmed, although I didn't think this was necessary and an adjacent board to the one that was rotted could have been removed also, but I guess they knew what they were doing. I think this might be a temporary measure, maybe until all the timbers are replaced. The first few photos were from last September.

Rotting timber on edges of boards. © Eugene Brennan 

Rotting timber on edges of boards. © Eugene Brennan

Rotting timber on edges of boards. © Eugene Brennan

After remedial work, with grid and steel plate in place. 

© Eugene Brennan

© Eugene Brennan

© Eugene Brennan

 

The Science of Length Measurement

Lidl Parkside brand measuring tape. © Eugene Brennan

An excuse to add a post about one of my favourite things, the centre isle of Lidl. I saw these 50 m tapes yesterday. I already have two, bought in other places and had to resist the urge to triple up. These things are useful for measurements in the garden or laying out foundations for sheds. When I was building the garden shed, I used two of these to square the foundations and concrete base (made the timber formwork for the base, placed it into position and then adjusted it by trial and error until the diagonals were the same length). Four pieces of rebar hammered into the ground then marked the four corners and I tied the 4 x 2 formwork to these.

Stud wall frame for my garden shed. © Eugene Brennan

Formwork for the concrete base was adjusted so the diagonals were of equal length. © Eugene Brennan

I built the shed on a concrete slab. © Eugene Brennan

 

A 19th Century Light Bulb

Oliver F. Brastow, Public domain, via Wikimedia Commons. Image pixel size doubled.

Newer incandescent lighting uses filaments typically made from less fragile tungsten. Materials such as copper or steel aren't practical because the metal has to have sufficient resistance in a short length to dissipate power in the form of light (although incandescent lighting is woefully inefficient: 95% of the power dissipated is heat and only 5% light). Copper or steel could be used, but power dissipated in a resistor is I²R where I is the current and R is the resistance. Since copper and steel have low resistivity, a filament made from these materials would have low resistance and so a much larger current (or longer section of filament) would be needed to create the same amount of power (meaning that supply cables would also have to have to be beefed up).

I just checked a table and actually the resistivity of iron doesn't differ hugely from that of tungsten. It's only around half the value. This would mean that a filament of the same length made from iron rather than tungsten would have half the resistance. For the same voltage applied to the filament, current would be double and the power equation would give a value for power consumption of twice that produced for a tungsten filament. Tungsten however has a higher meting point and can become white hot in a lamp, without melting or losing its integrity on supporting wires.

The Great Irish Fossil Hunt and Church of the Sacred Heart and St. Brigid, Kilcullen

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At least one of the marble columns in the parish church in Kilcullen has a series of somewhat regularly-spaced white patches. I've often wondered whether they were the vertebrae of the back bone of some prehistoric marine animal. Marble is a metamorphic rock, formed when limestone is "cooked" and melted by heat from magma within the Earth. Limestone itself is a sedimentary rock, formed when marine organisms die and their skeletons or shells settle to the bottom of the ocean. Over tens or hundreds of millions of years of geological time, the deposits build and the layers are compressed into rock by the immense pressures.

The most interesting fossil I've found was from about 6 feet deep when I was helping to dig a hole near Kilmeague. The lump of red rock was embedded with cockle shells, presumably dating back hundreds of millions of years to an era when Ireland, or rather the land fragments that would become the island, were located south of the equator.

University College Cork are running a project at the moment called the Great Irish Fossil Hunt, lasting from the 2nd April to 31st August. They're asking the public to be on the lookout for what might be fossils, some of them even hidden in the fabric of buildings. Photos can then be sent to the UCC team. More info here.

Electric Motors Drive Wheels on Diesel Trains

O71 Class locomotive in Enterprise livery at Belfast Grand Central Station. No author provided, CC BY-SA 4.0 , via Wikimedia Commons.

The locomotives that pull carriages, known as diesel-electric have engines that run on diesel. However the engines don't drive the wheels directly. Instead, they power a generator and the wheels are driven by electric motors. This makes it easier to control speed using electronics/electrics, rather than controlling injectors on a diesel engine to vary power. Also electric motors have full torque at zero RPM, unlike an engine which has to spin up to suck in fuel to produce power, and has zero torque at zero RPM. (Interestingly, steam engines also have full torque at zero RPM). Both the 071 and 201 class locomotives, used for intercity passenger and freight transport use this system. The DART is of course electric and is supplied with power from overhead lines that operate at 1500 V DC. Electricity is "collected" using pantographs attached to the roofs of carriages. Suburban commuter service trains are diesel multiple units (DMUs). They don't have a locomotive, apart from a driving cab, each carriage being individually powered by a diesel engine. While DMUs can be diesel-mechanical (i.e. direct-drive), diesel-electric or diesel-hydraulic, the 2200 class units, widely used by Iarnród Éireann for suburban use are diesel-hydraulic, hydraulic motors being used to drive the wheels (like the tracks on a digger).
The new DART+Fleet will use battery-electric carriages in advance of an extension of the electrification of lines beyond the Greater Dublin area. 155 of the 185 carriages on order are battery electric and a five-carriage train will have a range of up to 80 km, with an onboard 840 kWh battery. These batteries are charged by regenerative braking and also "replenished via fast charging stations at chosen terminus locations". According to Iarnród Éireann, charging infrastructure is currently under construction.
More info on the DART+ Programme here.

Google Maps Errors

Image courtesy Google Maps/

The map is full of errors: incorrect names on places, missing rivers and canals or they're following the wrong route, businesses in the wrong place etc. Here's the latest one I've spotted, fixed and submitted. The entire Naas Dual Carriageway from The Ball to the Red Cow Roundabout is the "Naas Byp", presumably meaning "Naas Bypass"". Maybe the whole dual carriageway has been designated as the Naas Bypass? Some of this may be due to vandalism, or people put things in the wrong place or don't zoom in sufficiently when they're adding their businesses. Routes of waterways may be created automatically from satellite images, or traced manually, but the routes are frequently wrong. Several miles of the Herbertstown branch of the Grand Canal as far as Corbally Harbour were missing up until I reported it last year.

Mouse Surgery

Circuit board from a computer mouse. © Eugene Brennan.

I've been struggling with the left button on my cordless optical mouse for the last six weeks or so. The momentary microswitch for the left button has worn out (they're good for something like 100,000 operations) and a single click is frequently doing a double click, which is really frustrating (known as "switch bounce"). I replaced the switch today with one harvested from a mouse I bought from Dealextreme and which only lasted a week before breaking down. I have a pack of five microswitches on order from AliExpress, but the double-click symptoms were getting worse and I couldn't wait any longer to fix the problem. 

 

Eugene Brennan

To get an idea of the size of the switches, they're 6 mm square as shown in the photo below.

 

© Eugene Brennan

This is the second time I've replaced the switch on this particular mouse due to it wearing out from use. It's a Microsoft Wireless Notebook Optical Mouse 4000 that's very ergonomic and a "Goldilocks" product: not too big or small, comfortable in the palm and the scroll wheel has a really smooth movement. The product is no longer manufactured and the replacement Microsoft mouse hasn't had good reviews. Also computer mice can't normally be "test driven" in stores because they're usually blister-packed, hence my decision to keep fixing this one.

 

Related reading: My guide to cleaning the scroll wheel on a mouse.

Wave Analysis Research

Public domain image by Geralt via Pixabay.

Wave Analysis Tools is published in the journal Nature and can be used by anyone as a guide for analysing waves. Waves occur throughout nature and are typically propagated through a medium such as air, water or through the ground. Examples include sound waves, seismic waves from earthquakes, marine waves, oscillations in the components of musical instruments (e.g. stringed and wind instruments) and vibrations in structures such as bridges. It was thought in the 19th century that electromagnetic waves such as infrared, visible light, ultra violet and radio waves needed a medium for propagation. A fictitious medium called ether was invented and experiments were devised to detect it. However those experiments were in vain and we now know that EM waves can propagate through space without an intervening medium. This is how we receive heat and light from the Sun, through the vacuum of space.

This report from RTÉ has more details on pioneering wave research. 

The First White LED

Public domain image courtesy sinisamaric on Pixabay.

I heard this on the BBC World Service Witness History programme in the early hours of this morning. Red LEDs date back to the 60s, but became more common in the 70s in consumer products such as calculators, watches, instrument displays and indicators (replacing midget incandescent bulbs). The green LED was invented in 1971 followed by a yellow version in 1972. It would be two decades before suitable semiconductor materials were developed to create blue LEDs in the early 90s. White LEDs can in theory be made by using red, green and blue semiconductor chips in an LED encapsulation and mixing the emitted light in equal proportions. However this gives poor colour rendering and inferior "quality" white light. The breakthrough came by combining blue LED technology with an integrated phosphor to convert the blue light into white light. This is similar to the way a fluorescent tube has an internal phosphor coating on the glass that converts UV to visible light. Up until the end of the 20th century, LEDS had a quite low luminous output and were primarily used for displays and as indicators. However improvements in technology have increased output dramatically, meaning they can now replace incandescent and discharge lighting in many applications. They're also typically five times more efficient than traditional incandescent lamps in converting electrical energy into light and have over twenty times the lifespan (a 100 W incandescent light bulb turns 95 W into heat and 5 W into light).

Battery Storage for the Grid

Battery storage facility for grid. Made with Bing Image Creator.

We could do with more though to act as buffers or reservoirs of energy when the sun doesn't shine or wind doesn't blow. (Think of them as the electrical analog of the flywheel on your lawn mower engine that stores energy between the power strokes). Traditional thermal or hydro power station generation is predictable and the output can be switched into the grid as necessary. Renewable generation because of its unpredictability needs the backup of battery storage to take up the slack. More info in this ESB YouTube video.

Big Picture Science Podcast — Vroom!

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In this episode, astronomer Seth Shostak and co-host of BPS, Molly Bentley take a ride in a Waymo self-driving car. Seth also talks with Witold Rybczynski, professor emeritus of architecture and design at the University of Pennsylvania and author of the book, The Driving Machine: A Design History of the Car.

Local History Diversion

Headstone in Tournant graveyard, Dunlavin, Co. Wicklow © Eugene Brennan

Off topic again. I ended up in Tournant Graveyard in Dunlavin yesterday on one of my bicycle ramblings, to take shelter from the heavy showers under some yew trees. I hadn't been there since the 90s, so the other reason I visited was to wander around the graveyard and read the inscriptions. This Doyle headstone has lots of detail about the family's history. Tournant Graveyard is the location where those who were executed in 1798 on the village green in Dunlavin were buried in a mass grave, now marked with a memorial headstone listing all the names.