Category Archives: Learning & Teaching

Georgian interior design and efficient radiators

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My lecture last week, to first year students studying thermodynamics, was about energy flows and, in particular, heat transfer.  I mentioned that, despite being called radiators, radiation from a typical central heating radiator represents less than a quarter of its heat output with rest arising from convection [see post entitled ‘On the beach‘ on July 24th, 2013 for an explanation of types of heat transfer].  This led one student to ask whether black radiators, with an emissivity of close to one, would be more efficient.  The question arises because the rate of radiative heat transfer is proportionate to the difference in the fourth power of the temperature of the radiator and its surroundings, and to the surface emissivity of the surface of the radiator.  This implies that heat will transfer more quickly from a hot radiator but also more slowly from a white radiator that has an emissivity of 0.05 compared to 1 for black surface.

Thus, a black radiator will radiator heat more quickly than a white one; but does that mean it’s more efficient?  The first law of thermodynamics demands that the nett energy input to a radiator is the same as the energy input required to raise the temperature of the space in which it is located.  Hence, the usual thermodynamic definition of efficiency, i.e. what we want divided by what we must supply, does not apply.  Instead, we usually mean the rate at which a radiator warms up a room or the size of the radiator required to heat the room.  In other words, a radiator that warms a room quickly is considered more efficient and a small radiator that achieves the same as large one is also considered efficient.  So, on this basis a black radiator will be more efficient.

Recent research by a team, at my alma mater, has shown that a rough black wall behind the radiator also increases its efficiency, especially when the radiator is located slightly away from the wall.  Perhaps, it is time for interior designers to develop a retro-Georgian look with dark walls, perhaps with sand mixed into the paint to increase surface roughness.

Sources:

Beck SMB, Grinsted SC, Blakey SG & Worden K, A novel design for panel radiators, Applied Thermal Engineering, 24:1291-1300, 2004.

Shati AKA, Blakey SG & Beck SBM, The effect of surface roughness and emissivity on radiator output, Energy and Buildings, 43:400-406, 2011.

Image details:

Verplank 2 002<br />
Working Title/Artist: Woodwork of a Room from the Colden HouseDepartment: Am. Decorative ArtsCulture/Period/Location: HB/TOA Date Code: Working Date: 1767<br />
Digital Photo File Name: DP210660.tif<br />
Online Publications Edited By Steven Paneccasio for TOAH 1/3/14

https://www.metmuseum.org/toah/works-of-art/40.127/

Re-engineering engineering

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More than a decade ago, when I was a Department Head for Mechanical Engineering, people used to ask me ‘What is Mechanical Engineering?’.  My answer was that mechanical engineering is about utilising the material and energy resources available in nature to deliver goods and services demanded by society – that’s a broad definition.  And, mechanical engineering is perhaps the broadest engineering discipline, which has enable mechanical engineers to find employment in a wide spectrum areas from aerospace, through agricultural, automotive and biomedical to nuclear and solar energy engineering.  Many of these areas of engineering have become very specialised with their proponents believing that they have a unique set of constraints which demand the development of special techniques and accompanying language or terminology.  In some ways, these specialisms are like the historic guilds in Europe that jealously guarded their knowledge and skills; indeed there are more than 30 licensed engineering institutions in the UK.

In an age where information is readily available [see my post entitled ‘Wanted: user experience designers‘ on July 5th, 2017], the role of engineers is changing and they ‘are integrators who pull ideas together from multiple streams of knowledge’ [to quote Jim Plummer, former Dean of Engineering at Stanford University in ‘Think like an engineer‘ by Guru Madhaven].  This implies that engineers need to be able work with a wide spectrum of knowledge rather than being embedded in a single specialism; and, since many of the challenges facing our global society involve complex systems combining engineering, environmental and societal components, engineering education needs to include gaining an understanding of ecosystems and the subtleties of human behaviour as well as the fundamentals of engineering.  If we can shift our engineering degrees away from specialisms towards this type of systems thinking then engineering is likely to enormously boost its contribution to our society and at the same time the increased relevance of the degree programmes might attract a more diverse student population which will promote a better fit of engineering solutions to the needs of our whole of global society [see also ‘Where science meets society‘ on September 2nd 2015).

For information on the licensed engineering institutions in the UK see: https://www.engc.org.uk/about-us/our-partners/professional-engineering-institutions/

Steamy show

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The Australian Academy of Technology and Engineering published a report sometime ago called ‘Technology is really a way of thinking‘.  They were right.  Once you become an engineer, then you can’t help looking at everything through the same ‘technology’ lens.  Let me give you an example.

A couple of weekends ago we went to see  ‘Anthony and Cleopatra‘ performed by the Royal Shakespeare Company in Stratford-upon-Avon.  It was a magnificient spectacle and a captivating performance, especially by Josette Simon as Cleopatra.  Before the performance started, we couldn’t help noticing the columns of steam forming in the auditorium from the ceiling downwards.  Initially, we thought that they were a stage effect creating an atmosphere in the theatre; but then I realised, it was ‘steam’ forming as the air-conditioning pushed cold air into the auditorium.  It’s the same effect that sometimes causes alarm on an aircraft, when it appears that smoke is billowing into the cabin prior to take-off.

The air in the theatre was a mixture of air and water vapour that was warm enough that the water was completely gaseous, and hence, invisible.  However, when the air-conditioning pumped cold air into the theatre, then the mixture of air and water was cooled to below the dew point of the water vapour causing it to condense into small droplets that were visible in the auditorium’s downlighters, forming the columns of ‘steam’.  Of course, the large mass of warm air in the auditorium quickly reheated the cold air, causing the droplets to evaporate and the columns of steam to disintegrate.  Most people just enjoyed the play; it’s just the technologists that were preoccupied with what caused the phenomenon!

If you want a more technical explanation, in terms of partial pressures and psychrometry, then there is an Everyday Engineering Example lesson plan available : 5E lesson plan T10 – psychrometric applications.

Picture: https://www.rsc.org.uk/shop/item/30200-anthony-and-cleopatra-poster-2017/

Wanted: user experience designers

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A few weeks ago, I listened to a brilliant talk by Professor Rick Miller, President of Olin College.  He was talking at a conference on ‘New Approaches to Higher Education’.  He tolds us that the most common job description for recent Olin graduates was ‘user experience designer’ rather than a particular branch of engineering.  Aren’t all engineers, user experience designers?  We design, manufacture and maintain structures, machines, goods and services for society.  Whatever an engineer’s role in supplying society with the engineered environment around us, the ultimate deliverable is a user experience in the modern vernacular.

Rick Miller’s point was that society is changing faster than our education system.  He highlighted that the relevance of the knowledge economy had been destroyed by internet search engines.  There is no longer much advantage to be gained by having an enormous store of knowledge in your head, because much more is available on-demand via search engines, whose recall is faster than mine.  What matters is not what you know but what you can do with the knowledge.  And in the future, it will be all about what you can conceive or create with knowledge.  So, knowledge-intensive education should become a thing of the past and instead we need to focus on creative thinking and produce problem-solvers capable of dealing with complexity and uncertainty.