Monthly Archives: December 2014

New Year Resolution

I started 2014 with a post on January 1st about the ‘Knowledge Economy‘ in which I extolled the virtues of knowledge-based rather than energy-based agriculture and engineering.  At the end of the year, oil prices have dropped from $110 to about  $60 per barrel, making it likely that in most countries the energy-based economy will continue to dominate.  In the USA, sales are rising of huge gas-guzzling cars, such as the Escalade, which is 5.15m (17ft) long, weighs 2.59 tonnes and only manages an average of 17 miles per gallon!  Fossil fuels account for approximately 80% of world energy consumption and are responsible for most greenhouse gas production.  During 2014 it was reported that greenhouse gases were rising at the fastest rate for 30 years but still the countries of the UN meeting in Lima before Christmas only agreed that those countries who were ‘ready to do so’ should submit national pledges on cutting emissions in the first of quarter of 2015.

The global average temperature is within one degree of the maximum temperature in the last million years, and a 2 degree rise would be equal to the temperature three million years ago when the sea level was 15 to 23m (80 to 130 feet) higher.  A 1 metre rise in sea level would displace 145 million people, and there is evidence that it has been  rising at 3.5mm per year during the last 20 years which is twice as fast as during the previous 80 years.

How bad does the condition of the planet need to get before effective action is taken?  How many more islands, like the Carteret Islands, will have to disappear?  How many more people than the 7 million in 2012 will have to die prematurely as a consequence of air pollution? Cities such as Beijing are beginning to be described as ‘almost uninhabitable’Kofi Annan has suggested that grass roots action is needed because our leaders will not take action in time. So tonight make it your New Year Resolution to reduce your carbon footprint in 2015 by 15%.

Estimate your current carbon footprint using an on-line calculator and starting working out how to reduce it.  If you want to find out the carbon footprint of your organization then the Carbon Trust has useful information and services.


Inside Beijing’s airpocalypse – a city made “almost uninhabitable” by pollution‘ by Oliver Wainwright in The Guardian on Tuesday 16th December, 2014.

Blockstein DE, Wiegman L, The Climate Solutions Consensus. Island Press, Washington, 2010.

Links to previous posts:

Year of Air:2013‘ on November 20th, 2013 or ‘Mass-produced nuclear power plants?‘ on November 12th, 2014.

Stimulating students with caffeine

milk in coffeeFood and drink seems to have been a recurring theme in my undergraduate lectures recently which as we are approaching a festive season is perhaps not inappropriate. At the moment, I am teaching thermodynamics to three hundred first year undergraduate students.  Zeroth and first laws of thermodynamics before the Christmas break and then the second and third laws in the New Year. Toast, pizza, barbecued steaks, hot coffee, bottled water, and cold milk shakes have all featured as Everyday Engineering Examples of thermodynamic systems in recent lectures. We can define a thermodynamic system as a quantity of matter capable of exchanging energy with its environment. And, most food preparation processes involve heating, chilling and, or doing work on the food by stirring, beating etc. which are all forms of energy exchange, so the opportunities for Everyday Engineering Examples are many and varied.

In one recent lecture, I asked the class to consider the quickest way to cool your coffee with milk. It was a multiple choice question to which students could respond in real-time using their phones and a website called There was more than one correct answer depending on the assumptions you made about the quantity and temperature of the milk as well as the temperature of the coffee and environment. The core issue is that the rate of cooling is proportional to the temperature difference. While discussing the possible answers, I made a throw-away remark about stirring the coffee involving doing work on the coffee and thus increasing its internal energy and temperature, which would be a step in the wrong direction. I was delighted when one of my students picked me up on this and sent me this link about stirring tea.

It is great to know that at least one student is listening and sufficiently engaged to do a little research. Only 299 left to inspire!


The hot coffee will transfer heat to its cooler surroundings by natural convection and radiation at its free surface and by conduction through the ‘walls’ of the cup. Similarly, the cup will transfer heat to its surroundings by natural convection and radiation from its outer surfaces. This process will establish a temperature gradient in the coffee that will induce a very slow convection flow that would be accelerated by stirring, i.e. introducing forced convection. This is likely to increase heat transfer slightly by carrying hotter coffee to the surfaces. The additional heat transfer (loss) might be more or less than the work done to stir the coffee. Who would have thought something as simply as stirring coffee or tea could be so complicated!

Previous posts on Zeroth Law:  ‘All Things Being Equal ‘ on December 4th, 2014, ‘Arbitrary Zero‘ on February 13th, 2013 and ‘Lincoln on Equality‘ on February 6th, 2013.

Previous posts on First Law:Thunderous Applause‘ on July 16th, 2014,  ‘Sizzling Sausages‘ on July 3rd, 2013, ‘Closed system on BBQ‘ on June 19th, 2013 and ‘Renewable energy‘ on January 7th, 2013


The Thermodynamics of Pizza‘ by Harold J. Morowitz, Rutger University Press, 1992.

Is Earth a closed system? Does it matter?

 Earth's annual global mean energy budget,  from Kiehl and Trenberth 1997

Earth’s annual global mean energy budget, from Kiehl and Trenberth 1997

The dictionary definition of a system is ‘a set of things working together as parts of a mechanism or an interconnecting network; a complex whole’. So it is easy to see why ‘systems engineering’ has become ubiquitous: because it is difficult to design anything in engineering that is not some kind of system.  Perhaps the earliest concept of a system in post-industrial revolution engineering is the thermodynamic system, which is a well-defined quantity of matter that can exchange energy with its environment.

Engineers define thermodynamic systems by drawing arbitrary boundaries around ‘quantities of matter’ that are of interest, for instance the contents of a refrigerator or the inside of the cylinder of a diesel engine [see my post entitled ‘Drawing Boundaries‘ on December 19th, 2012].  These boundaries can be permeable to matter in which case the system is described as an ‘open system’, as in the case of an diesel engine cylinder into which fuel is injected and exhaust gases ejected. Conversely, the boundary of a ‘closed system’ is impermeable to matter, i.e. the refrigerator with the door closed.  The analysis of a closed system is usually much simpler than for an open one.  In his Gaia theory, James Lovelock proposed that the Earth was a self-regulated complex system.  Is it also a closed thermodynamic system?  It is clear that energy exchange occurs between the Earth and its surroundings as a consequence of solar radiation incident on the Earth (about 342 Watts/square meter) and radiation from the Earth as a consequence of reflection of solar radiation (about 107 Watts/square meter) and its temperature (235 Watts/square meter).  This implies that we can consider the Earth as a thermodynamic system.  The Earth’s gravitation field ensures that nothing much leaves; at the same time the vast of emptiness of space means that collisions with matter happen only very occasionally, so the inward flow of matter to Earth is negligible.  So, perhaps we could approximate Earth as a closed thermodynamic system.

Does it matter?  Yes, I believe so, because it influences how we think about our complex life support system, or spaceship Earth that sustains and protects us, as Max Tegmark describes it in his book ‘Our Mathematical Universe’.  In a closed system there is finite amount of matter that cannot be replenished, which implies that the Earth’s resources are finite.  However, our current western lifestyle is focused on consumption which is incompatible with a sustainable society in a closed system.  Even the Earth’s energy balance appears to be in equilibrium based on the data in the figure and so we should be careful about massive schemes for renewable energy that might disturb the Gaia.


Kiehl, J.T., and Trenberth, K.E., 1997, Earth’s annual global mean energy budget, Bulletin – American Meteorological Society, 78(2):197-208.

Thess, A., The Entropy Principle – Thermodynamics for the Unsatisfied, Springer-Verlag, Berlin, 2011.

Tegmark, M., Our Mathematical Universe, Penguin Books Ltd, 2014.