Hebra The Physics of Metrology

All about Instruments: From Trundle Wheels to Atomic Clocks
2010
ISBN: 978-3-211-78381-8
Verlag: Springer Wien
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, 383 Seiten, eBook

Conceived as a reference manual for practicing engineers, instrument designers, service technicians and engineering students. The related fields of physics, mechanics and mathematics are frequently incorporated to enhance the understanding of the subject matter. Historical anecdotes as far back as Hellenistic times to modern scientists help illustrate in an entertaining manner ideas ranging from impractical inventions in history to those that have changed our lives.

Zielgruppe

Research

Autoren/Hrsg.

Hebra, Alex

Inhaltsverzeichnis

The measurement of length.- Angles and arcs.- Clocks and the measurement of time.- Velocity and acceleration.- Force, mass, weight, and torque.- Vibrations.- Thermodynamics.- Pressure.- Density of solids, liquids, and gases.- Light and radiation.- Acoustics.- Electrical and electronic instruments.- Automation — Instruments that think.

Leseproben

"12 Electrical and electronic instruments (S. 301-302)

In the late 1990s, General Motors ventured into a trial run of 1100 electric cars in compliance with California’s legislation, which demanded dominance of electric vehicles by the year 2000. Dubbed EV1, 800 such cars were initially leased for 3 years to third parties, but as soon as the lease expired, got heartlessly crushed along with all the rest of zero-emission cars. Why did this foray into the kingdom of unpolluted air, intact ozone layer, and freedom from the global warming threat, end in such an undigni?ed demise?

Should GM have followed Alva Edison’s market strategy of selling the ?rst twoyears production of lightbulbs at a loss in order to generate a market for his invention wile fending off potential competitors? After all, why should consumers have coughed up some USD 30,000.00 for an electric car while gasoline cars were available at 1=3 of that price? Let alone the costs for replacement batteries within the ?rst 3 years of use. But even that could hardly have been the reason for the regulators to let go of such a popular law so willingly. So, what happened?

By comparison, the familiar gasoline-guzzling car with an average of, say, 20 miles to the gallon of gas, uses up 5 gallons per 100 miles driven. With 0.68 for the density of commercial gasoline, and 3.785 liter to the gallon, those 5 gallons convert into 5 x 3:785 x 0:68 ¼ 12:87 kg of gasoline. From the heat of combustion of gasoline, 11700 Cal=kg, and the conversion factor of 860 Cal ¼ 1 kilowatt x hour ðkWhÞ, the electric equivalent of the 5 gallons (12.87 kg) of gas per 100 miles becomes 12:87 x 11700=860 ¼ 75 kWh per 100 miles: However, the output of the internal combustion engine in our cars is limited to the Carnot process value, namely, some 34% of the energy input, while 3% of the remainder get lost in the gearbox and power train; that leaves us with about 32% of 175 kWh “energy on the wheels”, namely, 0:32 x 175 ¼ 56 kWh.

To compare this performance ?gure with that of an electrically powered car, we ?gure backwards from those 56 kWh to ?nd out how much energy must be generated to supply them. Utilities generate electricity at a somewhat better rate than the engines in our cars, namely, at about 40% and up, but some 7.2% of their power output is lost in transmission through power lines and substations. On the other hand, electric cars consume extra energy in a number of ways: First of all, present days batteries deliver in the average only 0.80 kWh for every 1 kWh they get charged with, and the car’s electric motors can be expected to run at about 90% ef?ciency.

Here again, another 3% go into frictional losses in the cars’ transmission train. Summing it all up, we get 20 þ 7:2 þ 10 þ 3 ¼ 40:2% of losses, which brings the demand of an electric car to 56=ð1 x 0:402Þ ¼ 93:65 kWh per 100 miles. Generated at 40% ef?ciency, this becomes 93:65=0:40 x 234 kWh utilities have to come up with. Compared with the 175 kWh per 100 miles of the standard car, this is 234=175 ¼ 1:34 times higher. Rather than providing clean air, the use of electric cars in the cities would boost CO2 pollution by a whopping 34%; however, electricity for charging up those cars would be produced far from the cities where they strive. Call it the counties’ contribution to better city air, but it still wouldn’t help cleaning the atmosphere or mobilizing voters in the project’s support."