Tag Archives: heat transfer

Popping balloons

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Balloons ready for popping

Balloons ripe for popping!

Each year in my thermodynamics class I have some fun popping balloons and talking about irreversibilities that occur in order to satisfy the second law of thermodynamics.  The popping balloon represents the unconstrained expansion of a gas and is one form of irreversibility.  Other irreversibilities, including friction and heat transfer, are discussed in the video clip on Entropy in our MOOC on Energy: Thermodynamics in Everyday Life which will rerun from October 3rd, 2016.

Last week I was in Florida at the Annual Conference of the Society for Experimental Mechanics (SEM) and Clive Siviour, in his JSA Young Investigator Lecture, used balloon popping to illustrate something completely different.  He was talking about the way high-speed photography allows us to see events that are invisible to the naked eye.  This is similar to the way a microscope reveals the form and structure of objects that are also invisible to the naked eye.  In other words, a high-speed camera allows us to observe events in the temporal domain and a microscope enables us to observe structure in the spatial domain.  Of course you can combine the two technologies together to observe the very small moving very fast, for instance blood flow in capillaries.

Clive’s lecture was on ‘Techniques for High Rate Properties of Polymers’ and of course balloons are polymers and experience high rates of deformation when popped.  He went on to talk about measuring properties of polymers and their application in objects as diverse as cycle helmets and mobile phones.

And then we discovered thermodynamics

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sunEnergy, matter, space and time came into existence in the Big Bang 13.5 billion years ago. 10 billion years later biological organisms started to appear. 70,000 years ago one of those organisms, man started to organise in structures, called cultures and history began. For most of history if you wanted something moved then you had to do it yourself or persuade someone else to do it. The agricultural revolution began 12,000 years ago and shortly afterwards we realised that if you fed fuel to an animal then it would ‘burn’ it and do work for you. And that’s how it remained for thousands of years – we didn’t know how to convert heat into work or work into heat. The average energy consumption per capita was about 20GJ per year. Then, 200 years ago we discovered how to imitate nature by burning fuel and producing power in the steam engine. We had discovered thermodynamics and our average energy consumption started rising towards 80GJ per year today.

As a consequence, ‘we have now all but destroyed this once salubrious planet as a life-support system in fewer than two hundred years, mainly by making thermodynamic whoopee with fossil fuels’ as Kurt Vonnegut wrote. And that’s because nature starts from solar energy and recycles everything and we haven’t learnt how to do either very effectively. But energy or power engineering has been around for less than a blink of eye relatively speaking and we are just learning how to perform a trick nature has been using for billions of years: convert solar radiation into other energy forms. The sun delivers about 340 Watts per square metre to the Earth so we have plenty energy available.

If you would like to know more about energy engineering or thermodynamics and its potential then join the 5000 people who have signed up for the MOOC that I am teaching for five weeks from next Monday.  Listen to me interview Ken Durose, Director of the Stephenson Institute for Renewable Energy on the prospects for renewable energy.

Sources:

http://ourfiniteworld.com/2012/03/12/world-energy-consumption-since-1820-in-charts/

Yuval Noah Harari, Sapiens: A brief history of mankind. London: Vintage (Penguin, Random House), 2014.

Kurt Vonnegut, A Man without a Country, New York: Seven Stories Press, 2005.

Counting photons to measure stress

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TSA pattern around a crack propagating from the left with its tip in the centre.

TSA pattern around a crack propagating from the left with its tip in the centre.

Some might find it strange that I am teaching thermodynamics when my research expertise is in structural materials and mechanics. However, the behaviour of structures is largely controlled by energy and how they absorb, store and release it; while thermodynamics is the study of energy flows and transformations, so there is a connection. In my research group, we exploit this connection in a technique for measuring stress fields in components by monitoring the temperature changes that occur when a component is loaded. In Thermoelastic Stress Analysis (TSA) as it is known, we use very sensitive infrared cameras to monitor the cyclic variations of temperature that occur when cyclic load is applied to a material. The temperature changes are of the order of milli-Kelvin, that’s thousandths of a degree, and are positive with negative, or compressive stress and negative with tensile stress. What we are actually measuring is the rate of change in the release of photons by atoms as they are pushed closer together in compression or pulled further apart in tension; but that’s another story and takes us into physics.

An exciting feature of this technique is that as a crack evolves new surfaces are formed which releases energy as heat. We can detect not only the stress field around the crack but also the heat released during the formation of the crack prior it being visible and its subsequent growth.

Sources:

Greene, R.J., Patterson, E.A., Rowlands, R.E., 2008, ‘Thermoelastic stress analysis’, in Handbook of Experimental Mechanics edited by W.N. Sharpe Jr., Springer, New York.

Yang, Y., Crimp, M., Tomlinson, R.A., Patterson, E.A., 2012, Quantitative measurement of plastic strain field at a fatigue crack tip, Proc. R. Soc. A., 468(2144):2399-2415.

Patki, A.S., Patterson, E.A., 2010, ‘Thermoelastic stress analysis of fatigue cracks subject to overloads’, Fatigue and Fracture of Engineering Materials and Structures, 33(12):809-821.

 

Free: Energy! Thermodynamics in Everyday Life

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sunTalking to camera is difficult…

For the last few weeks I have been spending a considerable proportion of my working hours in front of a camera shooting video clips for a MOOC, a Massive Online Open Course. The first results of this effort and those of my colleagues Matt O’Rourke and Rob Lindsay in the University’s Centre for Lifelong Learning are now available as a trailer. The initial reviews were ‘cool’ and ‘awesome’, so go ahead and watch it!

Innovation to support learning

Some people have commented on the lack of pedagogical foundation in many MOOCs. However, I think we are being quite innovative in the following ways:

  • we are using an established pedagogy, 5Es (see the next paragraph for more explanation),
  • we have designed three do-it-at-home laboratory exercises,
  • the five-week MOOC will run in parallel with the delivery of the traditional course to first year undergraduates in Liverpool and,
  • the traditional lectures will be repeated at the university’s campus in London two evenings each week.

The lectures in London will allow students living around London to meet each other and me, as well as, of course, experience the energy of the live delivery of the course.

For students worldwide (and in London)

If you are a student who has or is struggling with elementary Thermodynamics then register for the free MOOC which will start in February 2016. I will cover the curriculum content of most ‘A’ level modules and introductory undergraduate courses in Thermodynamics. If you are in London and would like to attend the lectures then contact me and I will send you more details.

For teachers/instructors anywhere

If you are a teacher, tutor or lecturer then consider bringing it to the attention of your students. I will be taking a different approach to the traditional way of teaching classical thermodynamics based on my experience teaching at the University of Liverpool using the Everyday Engineering examples featured on this blog together with the 5Es approach to lecture or lesson plans. If you would like to use it in parallel with your own lectures then get in touch with me so that we can talk about synchronization.

5Es

The 5Es are Engage (the students), Explore (the topic), Explain (the principles underpinning the topic), Elaborate (using the principles to analyse the topic) and Evaluate (ask the students to evaluate their learning by performing some analysis). The course has been well-received by students and nearly a thousand have taken it over last four years. This year we are making into a five-week MOOC so that thousands more can learn using it.

Sources:

Real life thermodynamics

Bybee RW, Taylor JA, Gardner A, van Scotter P, Powell JC, Westbrook A & Landes N, The BSCS 5E Instructional model: origins, effectiveness and applications, BSCS Colorado Srings, 2006.

Sian Bayne & Jen Ross, The pedagogy of the MOOC: the UK view,  Higher Education Academy, 2014

Paul Stacy, The pedagogy of MOOCs, http://edtechfrontier.com/2013/05/11/the-pedagogy-of-moocs/