Archive for December, 2012

Harppy Crhistmas

December 20, 2012
Harppy Crhistmas 2012

Harppy Crhistmas 2012

I am a bit behind with Christmas cards this year. I have printed the first few – but in case you haven’t recieved yours yet, please enjoy the design above.

I would improve it now. At the time I couldn’t think how to get the ‘d‘ in ‘wonderful’ and used Dy, Dysprosium, but now I realise I could have used Nd, Neodymium followed by Er, Erbium (Picture at the end). But I haven’t found a better way to do the e in ‘Year’ other than using an electron 😦

In case you feel like spelling out the the names of things with elemental symbols, I present an alphabetical list of elemental symbols which include a particular letter as either the first or second letter.

H Ar P P Y  C Rh I S Tm As

 

Ac Ag Am Ar At Au Ba Ca Ga La Na Pa Ra Ta

B Ba Be Bi Bk Br Nb Pb Rb Sb Tb Yb

C Ca Cd Ce Cf Cm Co Cr Cs Cu Ac Sc Tc

Dy Cd Gd Md Nd Pd

Er Es Eu Be Ce Fe Ge He Ne Re Se Te Xe

F Fe Fm Fr Cf Hf

Ga Gd Ge Ag Hg Mg

H He Hf Hg Ho Rh Th

I In Ir Bi Li Ni Ti

K Kr Bk

La Li Lr Lu Tl

Md Mg Mn Mo Am Cm Fm Pm Sm Tm

N Na Nb Nd Ne Ni No Np In Mn Rn Sn Zn

O Os Co Ho Mo No Po

P Pa Pb Pd Pm Po Pr Pt Pu Np

Ra Rb Re Rh Rn Ru Ar Br Cr Er Fr Ir Kr Lr Pr Zr

S Sb Sc Se Sm Sn Cs Es Os

Ta Tb Tc Te Th Ti Tl Tm At Pt

U Au Cu Eu Lu Pu Ru

V

Xe

Y Yb Dy

Zn Zr

Harppy Crhistmas 2012

Harppy Christmas 2012

Watching pots boil

December 16, 2012

My previous article about kettles left me wondering: Can gas hobs really waste more than half of the calorific energy in the gas? I decided to try a few more experiments and finally I think I have an answer: ‘Yes’. Gas hobs really do fail to transfer a great deal of the calorific energy in the gas to the pan or kettle they are heating.

Experiment#1: Heating different amounts of water in the same pan

Experiment#1: Heating different amounts of water in the same pan

Experiment#1 Rather than measuring the total time to reach 100 °C, I measured the rate of temperature rise. Because the heat capacity of water is well known, this allowed me to estimate how much thermal power was entering the water. So I spent a happy hour or so heating up various amounts of water: first 200g, then 400 g, 600g and finally 800g and I measured the temperature every 20 seconds.

The temperature rise versus time of four different amounts of water on a 1.75 kW burner

The temperature rise versus time of four different amounts of water on a 1.75 kW burner.

I knew the burner power was 1.75 kW, and after a little jiggery pokery with a spreadsheet I estimated the power entering the water as a function of temperature rise.

The temperature rise versus time of four different amounts of water on a 1.75 kW burner

The estimated amount of thermal power entering the water for water on a 1.75 kW burner.

The data is a little noisy but it shows that initially only about 850 W of the burner power reaches the water. Since this is 1750 W (nominal) burner, this raises the question of where the remaining 900 W of power is going! It is also interesting that rate of heat input to the water decreases with temperature rise such that the rate of heat input at the boiling temperature (roughly 80 °C temperature rise) is barely more than half the initial rate of heat input. I have calculated the radiated heat from the upper surfaces of the kettle and it cannot account for this.

Experiment#2: Heating the same amount of water in the four different size pans

Experiment#2: Heating the same amount of water in the four different size pans.

Experiment #2 Now I fixed the amount of water (0.5 kg) but I used four different pans: a baby pan (0.487 kg: diameter 15 cm); a mother pan (0.601 kg: diameter 17 cm); a daddy pan (0.834 kg: diameter 19 cm) and a big daddy pan (1.8 kg: diameter 24.5 cm). I measured the water temperature at the start, heated for 60 seconds and measured the temperature again, and then heated for another 60 seconds. The results are shown in the chart below.

The temperature rise after 60 seconds and 120 seconds of 500 g water heated in four different size pans.

The temperature rise after 60 seconds and 120 seconds of 500 g water heated in four different size pans.

The main observation is that the water heats significantly faster in the largest pan. After 60 seconds the temperature of the water in the small pan had risen 20 °C whereas the water in the largest pan was 5 °C hotter – despite the extra 0.347 kg of steel that needed heating. This is consistent with the idea that a great deal of the heat energy is lost because the hot gas from the combustion does not remain in contact with the base long enough to transfer its heat. On small pans, hot gases escape around the edge of the pan.

Estimated efficiency of heat transfer to a pan versus the area of the base of the pan.

Estimated efficiency of heat transfer to a pan versus the area of the base of the pan.

I estimated the heat capacity of the pans and then calculated the fraction of the energy of the gas that the [pan + water] combination had captured. The data show a linear dependence on area with the largest pan capturing a plausible 83% of the calorific energy of the fuel.

Two images of a kettle on a hob taken using infra red light. The image on the left shows the general situation of the kettle - notice the hot handle! The thermograph on the left shows details of the base with an estimated temperature of approximately 224 C

Two images of a kettle on a hob taken using infra red light. The image on the left shows the general situation of the kettle – notice the hot handle! The thermograph on the right shows details of the base with an estimated temperature of approximately 224 C.

Experiment #3 It occurred to me that the underside of the kettle (or pans) might become extremely hot and radiate a significant amount of energy. However borrowing a thermal camera from work, the hottest features I could see were only just over 200 °C. Even accounting for the considerable uncertainties in this estimate, the radiated energy from the base of the kettle is only a few tens of watts at most, and can’t account for the energy losses of hundreds of watts that I have observed. A picture of the kettle on the hob shows the strong heating of the base of the cooker and the handle – which was indeed too hot to hold.

Summary

So now a general picture emerges: although cooking with gas uses a primary fuel, typically half of that energy is lost on the hob. Using a large pan on a small flame, I managed to capture as much as 83% of the primary energy, but for a kettle, 50% is probably more typical. Using a large flame on a small kettle will easily waste more than 50% of the energy.

And I can now answer my initial question: Should I use an electric kettle (in which 60% of the primary energy is discarded at the power station, but which is essentially 100% efficient in my kitchen) or a gas kettle (in which nearly all the energy of the primary fuel is delivered but which is only rough 50% efficient in my kitchen)? My answer is that it makes very little difference. It is best to use whichever device allows you to easily boil the correct amount of water – and not to boil water which is then unused.

Which kettle to choose: Gas or Electric?

December 16, 2012
Which kettle is more energy efficient?

Which kettle is more energy efficient?

Boiling water is an essential pre-requisite for the preparation of tea – and as such it is an activity central to the cultural life in England. For example, six cups of tea were drunk while preparing this article. Boiling water is also an energy intensive activity and so for all the usual reasons, it’s a good idea to boil water in an efficient manner. But should one use an electric kettle or a gas kettle? This was the subject of my first ever blog posting back on 1st January 2008 – and because that blog is no longer available, I thought it worthwhile to re-post and re-visit the problem now.

Initially, I was confident that using a gas kettle would save energy compared with an electric kettle. This is because electricity is generated at power stations which have an overall efficiency which is often less than 40%. That’s a guideline figure for any thermally-generated electricity (coal, gas or nuclear). It means that roughly 60% of the energy content of the fuel is lost before the electricity leaves the power station. Some gas generation using CCGT technology is more efficient: up to 60% in the best cases but relatively little electricity is generated this way. Additionally, typically 10% of the energy which leaves the power station is lost in transmission to my home. So only perhaps 36% of the original energy content of the fuel is fed into my kettle element.

Since raw methane is distributed directly to my kitchen, all a gas kettle has to do is capture a bit more than one third of the chemical energy and I would be better off than using electricity. So I was confident that by using a gas kettle I would be making an environmentally friendly decision.

Was I right? I compared the time boil 1 litre of water with the time expected if the device used the energy supplied to it in the kitchen with 100% efficiency. I then applied a ‘Network Efficiency’ factor.

The Electric Kettle (2 kW) took 210 seconds to boil 1 litre compared with an expected time of 188 seconds, so the ‘in-kitchen’ efficiency was 90%.

The Gas kettle had three burners:

  • The 1 kW Burner took 680 seconds to boil 1 litre compared with an expected time of 380 seconds, so the ‘in-kitchen’ efficiency was 56%.
  • The 1.75 kW Burner took 450 seconds to boil 1 litre compared with an expected time of 210 seconds, so the ‘in-kitchen’ efficiency was 48%.
  • The 3 kW Burner took 380 seconds to boil 1 litre compared with an expected time of 127 seconds, so the ‘in-kitchen’ efficiency was 33%.

The Microwave Oven (800 W) took 720 seconds to boil 1 litre compared with an expected time of 300 seconds, so the ‘in-kitchen’ efficiency was 66%.

And the results? 

Result #1 Heating water using a gas kettle is a more efficient use of fuel, but only at low gas settings. And even at low settings, a gas kettle wastes 50% of the energy supplied to it. Using higher gas settings wastes an even larger fraction, up to 67%!

Result #2 Heating water using an electric kettle is the fastest way to heat water, being roughly twice as fast as the high-power gas burner – and with very similar efficiency.

Result #3 Using a microwave to heat water was definitely the least efficient of any of the methods – but this result may change when heating small quantities of water.

Overall the data indicate that gas kettles are amazingly wasteful. In subsequent articles I will be looking to see if they really are as bad as they seem.

The efficiency of different ways of heating water. The blue dots show the efficiency with which fuel supplied to the kitchen is converted to heat energy in the water. The red dots show the efficiency when taking account of the conversion of chemical energy from the primary fuels. Teh shocking news is that even when boiling water slowly with gas, around half of teh energy is wasted! If one is boiling the water quickly then there is no difference in overall efficiency. The efficiency of different ways of heating water. The blue dots show the efficiency with which fuel supplied to the kitchen is converted to heat energy in the water. The red dots show the efficiency when taking account of the conversion of chemical energy from the primary fuels. Teh shocking news is that even when boiling water slowly with gas, around half of teh energy is wasted! If one is boiling the water quickly then there is no difference in overall efficiency. The efficiency of different ways of heating water. The blue dots show the efficiency with which fuel supplied to the kitchen is converted to heat energy in the water. The red dots show the efficiency when taking account of the conversion of chemical energy from the primary fuels. Teh shocking news is that even when boiling water slowly with gas, around half of teh energy is wasted! If one is boiling the water quickly then there is no difference in overall efficiency.

The efficiency of different ways of heating water. The blue dots show the efficiency with which fuel supplied to the kitchen is converted to heat energy in the water. The red dots show the efficiency when taking account of the conversion of chemical energy from the primary fuels. The shocking news is that even when boiling water slowly with gas, around half of the energy is wasted! If one is boiling the water quickly then there is no difference in overall efficiency between using gas or electricity – they both waste two thirds of the energy!

Experimental Details

  • I began by measuring the initial temperature of water from the tap which turned out to be close to 10 Celsius.
  • I then weighed the vessel (electric kettle, gas kettle or glass jug ) before and after filling with water.
  • I estimated the energy required to raise water from 10 °C to 100 °C using the measured water mass and the heat capacity of water (roughly 4200 J per °C per kg and rather constant in this temperature range).
  • For the electric kettle I used its power rating of 2000 W (which I had previously measured and found to be a good estimate.)
  • For the gas I used data for the gas burners which indicated they had a rated power of 1 kW, 1.75 kW and 3 kW.
  • For the microwave (rated power 800 W) I used a power meter to record the actual consumed power (1240 W)
  • I then recorded the time taken for the water to reach 100 °C and compared with the expected time if the device were 100% efficient.

I then factored in the efficiency of the network, assuming that

  • For electrical heating: 36% or the original calorific energy of the fuel was delivered to the house.
  • For gas: 90% of the original calorific energy of the fuel was delivered to the house, with the remainder being used to power the pumps on the gas pipeline.

Finally on rewriting this in December 2012 I decided to re-check my numbers. I boiled the same kettle on the 1.75 kW burner and got an ‘in-kitchen’ efficiency of 41% compared with 43% that I estimated previously. So I estimate that these numbers have an uncertainty of around 1% or so.

Cultural Vertigo

December 15, 2012
London at night from the air

London at night from the air. The roads look like the veins and arteries of a living being.

ver·ti·go (Noun): A sensation of whirling and loss of balance, associated particularly with looking down from a great height, or caused by disease…

I have known for some time that I suffer from two forms of vertigo. The first is the normal form, induced by looking down over the edges of cliffs or tall buildings: I have to believe that this perfectly normal.

The second is age vertigo which involves similar dizziness, nausea and panic, but is induced by meeting adults who are much younger than me. My head spins as I focus on the vastness of the gap separating me from them – a gap across which we can converse, but not traverse. I cannot travel back to meet them, and by the time they reach my place on the cliff-face of life, I will have moved on. Or fallen off.  To the best of my knowledge I am the originator of this description of this sensation which must be surely be commonplace amongst those who are 52-ish.

Last night, as I flew back from a work visit to the European Space Agency in the Netherlands, I was visited by a third incarnation of vertigo – cultural vertigo.

The night was clear and I could see lights in towns from Holland to Belgium. On arriving above London the plane circled over the eastern edge of the M25. The view was astonishing: the roads resembled the arteries and veins of a living being – a being of unimaginable size and with an unimaginable appetite.

My sense of dizziness at the grandness and precariousness of our city was added to by the fact that I was observing this from a plane – and there was a queue of half a dozen similar observatories visible in the air behind us.

In addition to my flight, almost everything I could see below me involved burning carbon: for heating on this chilly night: for electricity to keep the lights on: and for fuel for the cars and lorries. The vastness of the city and the intensity and voracity of its need to burn carbon induced dizziness and panic. Will we ever give up our dependence on carbon? I realised I needed to add ‘despair’ to the list of characteristic symptoms of cultural vertigo.

My only relief came from remembering that we had just flown over the London Array – an offshore wind farm – visible as a regular array of red lights against the blackness of the North Sea. Surely if our culture could create and sustain this vast city – and yet realise it needed to change and create offshore wind farms – then surely we can change our ways.

In the same way that nobody envisaged London growing as large and as energy intensive as it has grown – surely we could imagine a world in which our renewable energy infrastructure grew until it met our needs. Surely we could imagine that?

Carbon Emissions: Stating the obvious

December 3, 2012
Since the dawn of time we have emitted approximately 1271 billions tonnes of carbon dioxide and we show no signs of slowing down. In 2008 we emitted approximately 32 billion tonnes of carbon dioxide. The BBC figure for 2012 is 35.6 billion tonnes.

Since the dawn of time we have emitted approximately 1271 billions tonnes of carbon dioxide and we show no signs of slowing down. In 2008 we emitted approximately 32 billion tonnes of carbon dioxide. The BBC figure for 2012 is 35.6 billion tonnes.

Friends – I am barely keeping my head above water – work has never been busier – and there never seems to be a moment to reflect on things. But it is quarter-to-midnight on Sunday, and even though I have just spent several hours answering the Protons for Breakfast feedback, I feel like have a few more minutes of attention in me.

This week Protons for Breakfast was about Global Warming, and as I was answering the feedback I looked up the latest data on carbon dioxide emissions. By chance the BBC covered the same story with more recent data and the gloriously obvious headline

Carbon emissions are ‘too high’ to curb climate change

The numbers are astounding. Each year we collectively emit more than 1% of the total amount of carbon dioxide in the atmosphere. And an annual figure of 35 billion tonnes is an almost inconceivably large amount of ‘stuff’. If we wanted to do this for some other reason – then the task would seem overwhelming!

I got the impression that people at Protons for Breakfast really wanted to do something about this phenomenon – but they wanted guidance as to what would make a difference!. At it is at times like this that it is worthwhile to remember the words of Mahatma Ghandi who said:

“You may never know what results come of your actions, but if you do nothing, there will be no results.”

I wish I could find something more inspiring to say. I do feel that people’s consciousness is changing, and it does seem inevitable that we will – eventually – begin to face up to this problem. At some point in time, the graph at the top of the page will peak – and we will begin move beyond the carbon age. Let’s hope it is sooner rather than later.


%d bloggers like this: