The University of Waikato - Te Whare Wānanga o Waikato
Faculty of Science and Engineering - Te Mātauranga Pūtaiao me te Pūkaha
Waikato Home Waikato Home > Science & Engineering > Physics Stop
Staff + Student Login

February 2014 Archives

I've just been shifting around various bits of equipment and computers in our 2nd and 3rd year physics lab, to make way for an item that's shifting in there from a nearby lab. It's gone something like this...(rising in semitones, with apologies to the original performers) 

Da power socket is connected to da extension cord;

Da extension cord is connected to da monitor;

Da monitor is connected to da computer;

da computer is connected to da control box;

da control box is connected to da MRI machine;

da MRI machine is connected to da MRI-machine stand;  

da MRI-stand is connected to da floor*;  

Now why are there so many cables?

Dem cables, dem cables, dem power cables;

dem cables, dem cables, dem ethernet cables;

dem cables, dem cables, dem USB cables;

What a mess of knitting!  [Roll on wireless power transmission!]

 

*The MRI-stand is connected to the floor because we don't want the thing to move. The unit is calibrated for the position it's currently in; I'm not inclinded to move it in a hurry. The other things, however, might be more sensibly located. 

| | Comments (0)

I've been reading through a student's report of his summer work placement. He  had a project on improving the performance of a heat exchanger used for getting rid of heat from a cryogenic cooler. The basic concept is that materials are being cooled to about 40 kelvin (that's 40 degrees above absolute zero, minus 233 degrees celsius, by removing heat from them. That heat needs to go somewhere, and the job of the heat exchanger is to dump it.

I was struck by the similarities of the problem of 'dumping waste heat' with that of 'dumping rubbish'.  What do we do with household rubbish - stuff we don't want that is generated by our day-to-day activities. Well, various things happen to it. 1. Some of it gets put in the pretty blue (in Waipa) recyling box and gets put out on a Thursday morning.  2. Some of it gets put into the equally pretty yellow pre-paid rubbish sacks and also goes out on a Thursday morning, and ends up in landfill :-( 3. Some of it accumulates in the garage, until such time that 1. or 2. applies (or it gets taken to the recycling centre / tip, which is the same as 1. or 2.) 

We do the same with waste heat. It is generated by just about everything that we do. Car engines generate waste heat, car brakes generate heat through friction, electrical appliances generate it, running up and down stairs creates it - basically it's an inescapable consequence of the second law of thermodynamics. Heat gets made, and usually we want to get rid of it. So, what do we do with it?

1. We can, if we're clever, recycle it. A sensibly-designed industrial plant will tap into the waste heat it makes to do useful things. Smart tumble dryers will use the waste heat in their exhaust to pre-heat the dry air being sucked into the machine, saving electricity. Heat engines can be put into effect where there is a consistent difference in temperature between two objects. 

2. We can dump it. That's what happens to most of it. We let it end up in cooling water, or the atmosphere, where we conveniently forget about it. However, unlike landfill, it's not usually a problem in itself (warm rivers near power stations might be, however). The amount we generate over the earth is pretty tiny compared to the amount that the sun gives us. The real issue is the amount of carbon dioxide and other greenhouse gases that have been generated in the process (plus, economically, the generation cost of the energy that is being wasted). 

3. We can store it and do something with it later. This isn't so easy, but can be done. We can exploit gels that have high latent heats, meaning that as they undergo a phase change they take in heat, and then as they undergo the reverse change they will give it out again. We can heat up objects with high heat capacity, keep them well insulated, and then release the heat later (e.g. night storage heaters). 

So does 'dumping' heat mean that we're treating energy in a similar manner to rubbish? Chuck it away and pretend it's not an issue. With the landfill problem, the first thing to address is not recyling, but simply not to consume so much stuff in the first place. If we did the same with heat, we'd have lower energy bills and lower greenhouse gas emissions. The two, and their problems, are perhaps not so wildly different. 

Here's a final thought then. My work emails (if I don't delete them) get stored somewhere in the world on a server belonging to a well-known and rather enormous company. How much power does it take to keep one of my emails on file? I don't know the answer to that one. If everyone in the world deleted their email and the data they really didn't need anymore, what difference does it make to the world's energy consumption? Anyone know?

 

| | Comments (1)

Wow! That was a real nailbiting finish to the first test. Well done to the New Zealand bowlers to hold their nerve as India's batsmen got close. There was some great bowling, and also some great batting at times. Maybe the difference between the teams was that New Zealand in that final innings made fewer tactical blunders. 

I'm sure every armchair pundit has their own opinion of where the match was won and lost, but one that stands out for me is Virat Kohli's lapse of concentration against Neil Wagner. Aggressive batting is great to watch, but it has to give way to common sense if you want to stay at the crease. Trying a pull shot at a ball that isn't terribly high and  w-i-d-e outside off stump would be a suspect choice of shot even in a Twenty20 game, bad in any Test match, and downright appaling in a test that was as closely balanced as this one. What did he expect to happen? 

Anyone who has ever faced fast bowling will know that there are some basic laws of physics going on. What's of great importance in determining where the ball will end up after hitting your bat is the relative motion of the ball with respect to the bat, and the angle of incidence of the ball on the bat. The ball doesn't go in the direction that you hit it. Since it's carrying momentum (and a fair bit of it), what you do when you apply a force with the bat is that you change the ball's momentum. It's the change in momentum, not the final momentum itself, that's equal to the impulse (force times time) that you give to the ball. These things are vector quantities, that is, they have directions.  If you don't hit the ball in the exact opposite direction to where it is coming from, the final momentum of the ball won't be in the direction in which you hit it (apply a force on it). 

To pull a cricket ball through midwicket means that your bat's got to be pointing somewhere towards mid-on when you make contact with it. Try doing that when you're stretching out for a ball that's w-i-d-e outside off stump and you'll get the idea of why this shot was never going to work. Guiding it to the point boundary would have been a whole lot safer and effective, but then I'm sure Mr Kohli is well aware of that now. 

 

 

 

| | Comments (0)

Last week I had a very interesting and useful visit to the Measurement Standards Laboratory in Lower Hutt. I went along with my summer scholarship student to discuss the measurement of electrical properties of biological tissue. While the procedure for measuring the conductivity of a piece of solid is pretty-well established, biological tissue is soft, squishy, easily damaged, reacts chemically with what you try to measure it with,  and changes its properties considerably between 'alive' and 'dead' states. There's no clear-cut method here.  

We were also shown around some of the labs. What I found particularly interesting is the progress towards ditching the kilogram. By that I don't mean getting rid of the unit and using pounds and ounces, I mean doing away with the need to have a single, standard kilogram locked away in Paris. One can get away with this problematic beast through using a Watt Balance machine and defining Planck's constant. More on that later, I think.

But today's blog entry is about a discussion I had one evening in a cafe in Wellington train station, with a friend of mine who works for what is now known as Worksafe. As their name suggests, their purpose is to ensure  workplaces are healthy and safe (Not that this replaces the obligation on everyone to ensure a safe work environment, I should add.)  My friend has been having some discussion around the health issues associated with nanotechnology. Engineering tiny things has opened a huge range of possibilities - intensely strong fibres, minature motors, molecular-sized electronics - it's all possible, and it's going to get more common place. But have the risks of such technology been thought about? More specifically, are the monitoring processes keeping track with the development of the technology. My friend refers to nanotechnology as 'The asbestosis of the future'. That might prove to be unfounded, but the point is we simply don't know. Asbestos was a wonder-material that has been used intensively in the 20th century and a huge number of buildings (including the one I'm sitting in as I write this) is loaded with the stuff. It makes a great fire retardant and insulator, with the teeny-weeny drawback that inhaling asbestos dust can kill you. It is a massive headache for Worksafe as the whole country is full of the stuff - cue the story about the arguments between EQC, insurance companies and ACC regarding what to do with the great many earthquake damaged houses found to contain (now exposed) asbestos.

And nanotechnology could follow. By definition, it consists of tiny, tiny particles. What will they do in someone's lungs for twenty years? Who knows? How does one monitor the exposure to nanotechnology? That's maybe a more useful question to ask, and one to pursue properly. We have measures of exposure to radiation, for example, that we can apply to those who work with it, so what about a practical measure of nanotechnology exposure, that can be implemented in a workplace? An open question. 

 

 

 

| | Comments (0)