Category Archives: energy science

Sounds of the city

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cornerRegular readers of this blog will know that I spent a relaxing day painting railings a few weeks ago [see post entitled ‘Engineering archaeology‘ on July 23rd, 2014].  A day or so later, I went out with my pail of whitewash to paint the walls of the light-well that the railings protect.  ‘The summer world was bright and fresh, and brimming with life’ but unlike Tom Sawyer I was not looking for Jim to do my white-washing for me.  I was looking forward to another therapeutic session painting the walls at the front of our house.  It was an interesting standing in the light-well facing the wall, un-noticed by most passers-by.  We live on a city street close to tourist attractions and there is a constant stream of coaches and taxis stopping to drop-off and pick-up tourists. I have written about the noise insulation in our house before [see Noise Transfer on April 13th, 2013] which means that we don’t notice the constant growl of diesel engines outside but I did while I was painting.  However, there were other sounds in the city.  The voices of pedestrians  deep in conversation as they passed by on the pavement just above my head.  I recognised Chinese, French, Italian and English but there were many different languages that I didn’t recognise.  There were young children asking parents questions as they walked down the street.  For a while I could hear cathedral bells.  When there was a pause in the traffic then it was possible to hear the cooing of pigeons, a neighbour’s radio or television and an ever-present idling diesel engine which I discovered was an ice-cream van dispensing a constant trickle of black soot and an occasional ice-cream.  It is curious that as a society we tolerant high levels of noise pollution at tourist attractions, especially ones that are meant to be places of calm and contemplation. Most tourists are, almost by definition, on holiday seeking relaxation and a lowering of stress levels – how much more pleasant would it be to glide to your destination in a silent electric coach or taxi?

We have the technology to provide such a service [see Are electric cars back? on May 28th, 2014]. Yes, it requires some investment by tour operators and taxi firms in hybrid or electric vehicles and by the city council in re-charging facilities. Induction charging stations at tourist attractions would allow vehicles to recharge while dropping off and picking up passengers. The technology is available and has been used by buses in Genoa and Turin for more than a decade.  So a little bit a regulatory pressure and investment from city councils acting together could create a calmer, quieter and cleaner environment for everyone.

Can we look forward to solar-powered ice-cream vans?

Sources: Thank you to Richard for reminding me about Tom Sawyer.

Thunderous applause

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2d543f31-6f09-43ba-875c-c2d5d3bd0cebI have had cause to applause enthusiastically on two recent occasions. We went to see ‘Dead Dog in a Suitcase’ at the Everyman Theatre in Liverpool. It was fantastic and we joined in a standing ovation at the end. It’s a beggar’s opera that throughly deserved the rave reviews that it has received. It is full of energy, music, wit and spectacular performances.

The second occasion was my son’s graduation in Durham Cathedral. The programme asked us not to applaud as each graduand’s name was read out and they walked onto to the podium to shake the hand of the Chancellor, Sir Thomas Allen, but to hold our applause until the end. So, the last graduand walked off the podium to thunderous applause. Sir Thomas is an opera singer with a sonorous speaking voice and he gave a theatrical entertaining speech that we applauded enthusiastically and appreciatively. It is the tradition at Durham to applaud the new graduates as they walk down the aisle to leave the Cathedral. It’s a long aisle, there were a lot of graduates and we clapped energetically so that by the time the end of the line reached the door our hands were smarting.

You are right. There has been no mention of engineering, yet. However, here it comes. The heat and stinging sensation in the palms of my hands as the last graduate left the cathedral reminded me briefly of an example from my first year thermodynamics lectures in which I estimated the temperature rise in the skin of the hand from vigorous clapping ten times. This was more an exercise in estimating and problem definition than thermodynamics as you will see from the attached worksheet (clapping_example.pdf), but those skills are as important to an engineer as a knowledge of the laws of thermodynamics. Its also another Everyday Example and the experimental part can be performed at home.

Energy efficiency

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We were sent a summary of our annual gas and electricity consumption recently by our local utility company. The utility quantified our consumption of both gas and electricity in units of kilowatt-hours (kWh). It is usual to be sold electricity in kilowatt-hours but most people are confused by this unit. Perhaps because they learnt at school that the units of energy are Joules in the SI system and the power rating of appliances is usually given in Watts. They might know that a Watt is a Joule of energy per second, so what is a kilowatt-hour? Well it is about 3.6 x 106 Joules or 3.6 MJ, because it is 1000 Joules per second (= Watt) for one hour. So, I think the utility company should be telling me how many MegaJoules (MJ) we have consumed. After all we are used to seeing the energy content of our food quoted in kiloJoules (kJ), as well as calories.

The situation with our gas consumption is rather different because the utility does not supply energy but gas. The amount of energy that I get from it depends on what I do with it. If I burn it under conditions of constant volume, e.g. in a closed rigid container with exactly the correct concentration of oxygen then it will generate more energy in terms of heat than when it is burnt in constant pressure conditions, such as at atmospheric pressure in air. This is because in constant pressure conditions some of the energy released by combustion is used to expand the exhaust gases against the constant pressure, i.e. to do work, and only what is left is released as heat. So the utility should sell the gas by weight. If they sold it by volume then I would be paying more for the same amount of gas (i.e. number of hydrocarbon molecules) when the supply pressure was reduced.

Oil companies don’t sell gasoline or diesel in Joules for the same reason but they can sell by volume because it is always supplied to our cars at atmospheric pressure and the volume of a liquid is essentially constant.

We like to compare the efficiency of cars in terms of miles per gallon, or kilometres per litres. Efficiency can be loosely defined as what you want divided what you have to put in [See my post entitled ‘National Efficiency‘ on May 29th, 2013]. So for a car, what you want is kilometres travelled and what you put in is litres of fuel. However, when we are all driving plug-in electric cars then we will probably talk about how many kilometres per megajoule our car achieves [see my post entitled ‘Are electric car back?‘ on May 28th, 2014] . Unfortunately, while we are in transition with plug-in hybrids, car manufacturers like to quote very attractive kilometres per litre and ignore the electricity supplied via the plug – as if it were free!

Image courtesy KKN Liebstadt NPP from http://www.nucleartourist.com/systems/ct.htm

Are electric cars back?

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roadchaosDid you know that before Henry Ford developed the Model T Ford motorcar, the nearly 40% of automobiles on US roads were electric vehicles? I think we will be heading back in this direction if we are to have any hope of achieving reductions in carbon dioxide emissions. The implications for the national electricity grid of a major shift to plug-in cars would be very serious and has been the subject of several recent studies including a third year undergraduate dissertation that I have been supervising and from which came the opening factoid.

It is relatively easy, through not without obstacles, to envision a shift to all-electric cars; after all there are several models on the market now. However, an all-electric aircraft seems further in the future, if only because of the weight of the batteries required. Engineers would talk about the energy density, i.e. the amount of energy that can be extracted from a kilogram of kerosene compared to a kilogram battery. However, perhaps the future is not far away because the New Scientist reported earlier in the month [3rd May, 2014] that Airbus had completed the test flight of an electric plane, the E-fan. It is a two-seater plane with a pair of 65 kilogram lithium battery packs driving a pair of 30 kilowatt motors attached to the fans. The E-fan will cruise at 185 kilometres per hour and flies for an hour. Relative to a modern computer jet, this performance is similar to the early plug-in cars relative to their internal-combustion-engined rivals. But, it is an indication of bigger things to come. In the meantime, if you want an E-fan then a new division of Airbus called Voltair will be producing them by 2017.

I mentioned undergraduate dissertations because they have filled a sizeable chunk of my waking hours for a few weeks. This is an annual ritual in the UK during May when final-year undergraduate students are busy submitting and defending their dissertations. I had a pile of twelve dissertations to read and assess. Eight of them belonged to students that I have supervising in weekly one-to-one meetings since last October and the remainder were dissertations for which I was the assessor. All of the students that I supervised were studying either Mechanical or Aerospace Engineering and so the topics of their projects were associated mainly with energy and, or transportation. Some of these projects are provided by engineering companies (those with an asterisk in the list below), which guarantees their topicality and relevance, while others spin-out from my interests and research activities. So many of the topics in the list below will come as no surprise to regular readers of this blog.

Dissertation projects supervised during 2013-14:

Investigation into a redesign of graphite re-entrant seals for a nuclear power station*

Conceptual design for a carbon sequestration system for automobiles

Recommendations for achieving a low carbon airline industry

Strain-based defect analysis of industrial pipe-work*

Investigation of random frequency excitation of an aerospace body panel

Assessment of preload control of threaded fasteners in motorcycle production*

Recommendations for technology-based approaches to reduced ecological footprints

Investigation of low carbon power for plug-in electric vehicles