Category Archives: everyday engineering examples

From nozzles and diffusers to stars and stripes

Schematic diagram of explanation in textAt the end of a lecture on energy flows in my first year undergraduate course on thermodynamics, I talk about nozzles and diffusers as examples of practical applications of the rest of the material in the lecture.  It is hazardous to sit in the front row of the lecture theatre because I take in a water bottle with a trigger spray to demonstrate how the nozzle increases the velocity of the fluid at the expense of pressure while gently sprinkling water on the front row.  I am always intrigued by the symmetry of nozzles and diffusers.  Diffusers increase pressure of a fluid at the expense of its velocity, i.e., a mirror image of the action of a nozzle.  The cross-sections are also mirror images because a nozzle has a cross-section that decreases in the flow direction while a diffuser has a cross-section that increases in the flow direction.  At least for sub-sonic flows, because the shapes are reversed for super-sonic flow; so a sub-sonic nozzle looks like a super-sonic diffuser and a sub-sonic diffuser looks like a super-sonic nozzle.  If that all sounds like fluid mechanics then the thermodynamic message is that, in nozzles and diffusers, the rates of heat and work transfer are approximately zero while the change in the kinetic energy of the fluid is very large.  I finish the lecture with a video clip of a school quartet of trombones playing ‘Stars and Stripes Forever’ which wakes up the students who have slept through the lecture and allows me to point out the diffusers (bell of the trombone) transmitting acoustic pressure.

You can watch the video clip on YouTube at https://www.youtube.com/watch?v=mHw8P8NnUvI

Letting the grass grow while learning some engineering

Photograph of ATCO 17-inch petrol lawnmower in a gardenLast month was #NoMowMay during which we were encouraged to let the grass grow and allow bees, butterflies and other wildlife to thrive unmolested by your lawnmower.  Our townhouse in the centre of Liverpool does not have enough space for a lawn so I have not mown a lawn since we moved here from the USA nearly a decade ago.  In the USA we followed the convention and maintained our front lawn as manicured green carpet by watering daily, mowing weekly and feeding it monthly during the summer.  An automatic sprinkler system looked after the watering and a lawn service provided monthly doses of chemicals; however, we walked up and down behind the lawnmower each week.  Much to my disappointment, our garden was not really large enough to justify a garden tractor or sit-on mower which has been a dream since I learnt my first self-taught engineering by ‘repairing’ my father’s green ATCO lawnmower when I was about 10 or 12.  I was not allowed lift the bonnet or hood of the family car; and so as the only other piece of mechanical engineering in the garage that has an engine, the lawnmower became the focus of my attention.  I suspect that old lawnmower did not run any better as a result of my ministrations but I certainly understood how an internal combustion engine worked by the time I went to university.  I am an enthusiastic supporter of letting the grass grow, perhaps with a mown pathway so that the lawnmower has to be re-assembled periodically by whichever budding engineer has dismantled your lawnmower.

Source: Joy Lo Dico, How the lawn became a no-mow area, FT Weekend, 29/30 May 2021.

Image: An ATCO 17-inch petrol lawnmower similar to the one mentioned above, from http://www.lawnmowersshop.co.uk/atco-17-inch-self-propelled-petrol-lawnmower-b17.htm

Democratizing education

One motivation for developing Massive Open Online Courses (MOOC) has been to democratize education by giving everyone access to knowledge often presented by leading professors.  It was certainly one reason why I developed and delivered two MOOCs on ‘Energy: Thermodynamics in Everyday Life‘ in 2015/16 and ‘Understanding Super Structures’ in 2017.  The workload involved in supporting thousands of learners around the global is not insignificant and was unsustainable for me so I gave up after running them for a couple of years despite the intangible rewards [see ‘Knowledge spheres‘ on March 9th, 2016 and ‘A liberal engineering education‘ on March 2nd, 2016] . However, I incorporated the MOOC on energy into my undergraduate module on thermodynamics to create a blended approach to learning [see ‘Blended learning environments‘ on November 14th, 2018].  This paid dividends for me when the pandemic forced our campus into lock-down in the middle of semester last March and I already had a large number of bite-sized activities available online for our students.  Most universities have had to move their teaching online due to the pandemic; but not all students are able to access the online materials as easily others.  The Booker shortlisted novelist, Tsitsi Dangarembga has reported how one of her neighbours has struggled to access resources recommended to him by lecturers at his college in Bulawayo due to the cost and unreliability of Wi-Fi in Zimbabwe.  She tried to help him by registering him for her hotspot package but, in common with many students, he studies mainly at night when hotspot venues are closed.  The maps shows the global distribution of learners in one of the Energy MOOCs that I delivered and you can see the holes in Africa and South America which, at the time, we thought might be due to a lack of computer and internet access and Dangarembga’s account seems to support this hypothesis.  So, we designed our second MOOC on Structures to be accessible via a mobile phone by using fewer videos and more audio clips that could be quickly downloaded and listened to offline.  Unfortunately, we ran out of resources to complete the research on whether it was accessed more successfully in those grey areas on the map; however, the audio recordings were unpopular with the more traditional audience in the USA and UK who gave us immediate and vocal feedback!

Source:

Tsitsi Dangarembga, Protest and prizes, FT Weekend, 26/27 September 2020.

Patterson EA, Using everyday engineering examples to engage learners on a massive open online courseInternational Journal of Mechanical Engineering Education, p.0306419018818551

 

Homework practical exercises in structural mechanics

Last week I wrote about the practical exercises that I have been setting as homework in my first year undergraduate course on thermodynamics.  The instruction sheets that I published had been used by thousands of learners on my MOOC, Energy! The Thermodynamics of Everyday Life; and slightly modified versions had been used by more than a thousand students at the University of Liverpool.  A few years ago, I produced another MOOC called ‘Understanding Superstructures’ which also contained three practical exercises for online learners to perform in their kitchens.  I have not used them as part of a blended undergraduate course but nevertheless they have been completed by hundreds of participants in the MOOC.  I have decided to share them for colleagues to use in support of first year courses on the Mechanics of Solids or the Mechanics of Structures.  There is strong food flavour and no additional equipment is needed. Please feel free to use them to support your teaching.

Instruction sheets for thermodynamics practical exercises as homework:

Structural collapse | Crushing and toppling of towers

Stress concentrations | Newspaper tension tests

Residual stresses | Bending carrots