Wood engraving illustration of the Ancient Mariner by Gustave Dore
Water, water, every where,
And all the boards did shrink;
Water, water, every where,
Nor any drop to drink.
These lines are from the Rime of the Ancient Mariner by Samuel Taylor Coleridge published in 1798. They were brought to my mind when I was looking at the data in the GIO report on ‘Water’ that I mentioned in my post entitled ‘Closed system: water’ [17th July, 2013].
The quantity of water used to produce some everyday familiar items is staggering, for instance 140 liters to make one cup of coffee [growing the beans, harvesting, transporting and processing them], or 1,300 litres for a kilogram of wheat resulting in 40 litres per slice of bread but that is tiny compared to 1800 litres for a 4oz beef burger. You might be reading this in a part of the world that is constantly, or at least frequently, deluged with rain and so be thinking that none of this matters, except that much of what you consumes probably comes from a part of the world where water is less readily available and massive civil engineering projects are required to ensure an adequate supply, which have enormous ecological consequences.
And that pair of jeans you are probably wearing, well, they required 10,855 litres of water!
Maybe you are lying on the beach reading this, or if not dreaming about lying on the beach. We enjoy lying on the beach, or next to a swimming pool, in part because it involves doing nothing and in part because of the heat transfer. Heat transfer is transfer of energy from a high to a lower temperature zone. It can occur in four ways: conduction, free convection, forced convection and radiation; and all of them occur on the beach on a hot day.
Conduction occurs as a flow of kinetic energy from one molecule to the next by direct contact. When you are lying on the beach it occurs between you and the surface that you are lying on. When you first lie down on hot sand, then the energy flows from the hot sand to your cooler body by conduction.
Free or natural convection is heat transfer carried by a rising current of fluid due to buoyancy effects created by the hotter fluid being less dense. This tends to happen above your warm body after you have been lying in the sun for a while. It also happens above the hot sand and you can sometimes see a heat haze caused by the rising hot air that has a lower density and thus different refractive index compared to the surrounding air.
Forced convection also involves heat transfer by a moving current of fluid but in this case the flow is caused by an external source. So if there is breeze across the beach then you will be cooled by forced convection as you lie on the beach.
Radiation consists of electromagnetic waves in the infrared spectrum travelling away from a source in all directions. This is the heat from the sun that makes it so pleasant to lie on the beach on a sunny day.
Ok, shut your eyes and go back to sleep. The heat transfer lesson is over – though some of you might want to think about whether that breeze is really forced convection since it is probably caused by natural convection on a climatic scale.
Sometime ago I wrote about the need to consider the planet as a closed system, i.e. a system to which no new mass is being added, other than the occasional meteor from space [see my posts ‘Closed systems in nature?’ and ‘Open-world mind-set’ on December 21st, 2012 and January 4th, 2013, respectively]. This closed system approach applies to water. The total amount of water on the planet does not change and it has been moving around the hydrologic cycle for thousands of years. Mankind interacts with this cycle changing the chemistry, usefulness and availability of water. All of us contribute to these changes in a small way but 6.5 billion of us make a big impact.
Most of us are aware of pollution to rivers and groundwater caused by use of fertilizers and pesticides. We are perhaps less aware that removing groundwater for irrigation, industrial processes and domestic consumption can reduce water pressure underground in coastal regions causing saltwater to percolate and mix with freshwater reserves. Or that discharges from desalination plants increases the local salinity of seawater while carbon emissions in the atmosphere is sequestered by the oceans raising water acidity levels. All of these effects can damage ecosystems.
80% of available freshwater resources in the world are used to grow food. Yet, we also need it in huge quantities for industrial processes, for instance it requires 10 litres of water to make a sheet of paper and 200 litres to make one kilogram of plastic. Just as in energy consumption, there are huge global variations in daily domestic consumption per capita from 778 litres in Canada, 139 litres in the UK and India to 95 litres in China.
So, in addition to thinking about energy consumption when designing products and services, engineers need to think about water requirements since although there is a renewable supply it is not infinite or even constant.
The data above was taken from ‘Water: A Global Innovation Outlook Report’ available at http://www.ibm.com/ibm/gio/media/pdf/ibm_gio_water_report.pdf
‘Engineering is the most important profession: the future of our planet, and the quality of human life upon it, depends on engineering more than it does on any discipline.’
This bold statement was made as an opening gambit by one of my colleagues, Matt during a University Open Day for potential undergraduate students. These events are particularly important for engineering because students usually don’t study engineering at school and so have little idea about what it involves. Matt continued to say that ‘a decision to study engineering provides you with an opportunity to make a real and lasting impact on the world’.
Medical doctors and nurses have a considerable impact on our individual health and welfare, lawyers help us to resolve disputes and administer justice, philosophers advise us on how we should think while journalists and bloggers attempt to tell us what we should think but engineers manage the conception, design, development, manufacture or construction, maintenance, recycling or disposal of everything in our man-made world, i.e. products, processes & systems. As Theodore von Karman, the great aeronautical engineer said ‘scientists discover the world that exists; engineers create the world that never was’. Engineers tend to supply what society wants and so have to share with society responsibility for the massive consumption of the world’s resources but engineers are also working to create solutions. We need a massive level of innovation to create sustainable technologies that will allow everyone to enjoy the lifestyle of the average American or European.
‘If you really want to change the world then choose a career in engineering, and I mean real engineering, not financial engineering’ Lord Mandelson, March 2009
In my post on 19th June 2013 [Closed system on the BBQ], I discussed the thermodynamics of sausages cooking on a barbeque in the context of the first law of thermodynamics. This is an everyday example of engineering principles [see my post entitled ‘Bridging cultures’ on June 12th, 2013]. I mentioned that the energy gained by a sausage causes it to be cooked and for the water-content to boil as the temperature is raised. The rise in temperature causes the pressure inside the sausage to increase, which is Gay-Lussac’s law in action. When the water-content of the sausage starts to boil, the steam produced raises the pressure even further providing the sausage skin remains impervious to the transfer of matter, i.e. the steam. The sausage as a closed system that becomes a miniature pressure vessel.
Pressure vessels fail as a result of the stresses in their wall. In engineering, stress is defined as force divided by the area of material carrying the force. My sausages always fail longitudinally, i.e. they burst open with splits running along their length. This is because the stress across the split, known as the circumferential or hoop stress, is the largest stress in the skin.
It is relatively simple to use Newton’s Third Law, about there being an equal and opposite reaction for every action force, to show that the circumferential stress is larger than the longitudinal stress; but it is a level of detail beyond what I feel is appropriate here. Bursting sausages are a good illustration of Everyday Examples of Engineering, which became the ‘poster-child’ of the NSF-funded project that developed them in the USA . The pedagogy underpinning the use of Everyday Examples is explained in detail in a paper in the European Journal of Engineering Education (vol 36, pages 211-224, 2011) and a 5Es lesson plan is available here [for more on 5Es lesson plans see my post entitled ‘Disease of the modern age’ on June 26th, 2013].
You can see a video of me talking about these sausages at http://www.youtube.com/watch?v=nsSxKuRo4H0
EJEE paper: http://www.tandfonline.com/doi/abs/10.1080/03043797.2011.575218#.UbG9TZyPMx4