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Energy, Environment, and Industrial Development. Michael B. McElroy Lecture 11 March 13, 2006. What was the maximum possible efficiency of the Newcomen engine (or more properly that of the Watt modification)?. Consider a cylinder of length L, cross-section S

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energy environment and industrial development

Energy, Environment, and Industrial Development

Michael B. McElroy

Lecture 11

March 13, 2006

slide2
What was the maximum possible efficiency of the Newcomen engine (or more properly that of the Watt modification)?
  • Consider a cylinder of length L, cross-section S
  • Suppose that the cylinder must be filled with steam to a pressure of 1 atm
  • First calculate the mass of H2O corresponding to this steam

The Perfect Gas Law: P = NRT

 N = P/RT = 1atm / (8.31 J mol-1K-1 * 373K)

= 1.013x105 Pa / (8.31 J mol-1K-1 * 373K)

= 32.68 mol/m3

Mass of H2O = N * L* S * 18g/mol = 588.23LS (gram)

slide3
What was the maximum possible efficiency of the Newcomen engine (or more properly that of the Watt modification)?
  • Then calculate heat required to produce this steam

Heat required = heat to raise water from 293K to 373K + latent heat of evaporation

Q = (558.23LS)g * 4.8 J K-1g-1 * (373-293)K + (588.23LS)g * 2500J/g

= 1.56x106 LS (Joule)

  • Work done in one stroke of engine

W = 1atm * S * L = 1.013x105 LS (Joule)

  • Efficiency = 1.013x105 LS / (1.56x106 LS) = 6.5%
slide4
Calculate the energy required to raise 100 gallons of water by 100 ft.

E = mgh

m = density * volume

= 1 g/cm3 * 100 gallons * 3785 cm3/gallon

= 3.785x105 gram = 3.785x102 kg

h = 100 ft = 100 ft * 0.305m/ft = 30.5 m

E = 3.785x102 kg * 9.8 m/s2 * 30.5m

= 1.13x105 J

slide5
Calculate the power required to raise 100 gallons of water by 100 ft per minute

E = mgh = 1.13x105 J

power = 1.13x105 J / min

= 1.13x105 J / 60 sec

= 1.89 x 103 W

= 2.53 horse power

(1 hp = 746 Watts)

james watt highlights of a remarkable life
James Watt: Highlights of a Remarkable Life
  • Born 19 January 1736, Greenock, Scotland, 25 miles from Glasgow.
  • Grandfather, Thomas Watt (1642-1734): “ professor of mathematicks”. Taught navigation and surveying.
  • Father, James Watt (1698-1782), merchant, supplied nautical goods and mathematical instruments.
  • Watt studied Mathematics (Euclid), Latin and Greek at Elementary and Secondary (Grammar) School. Worked in father’s workshop.
  • Father ran into financial difficulties 1753-1754. Watt moved to Glasgow to take up apprenticeship as instrument maker June 1774 (age 18).
james watt highlights of a remarkable life1
James Watt: Highlights of a Remarkable Life
  • Worked with John Morgan, “philosophical instrument maker”, expert on brass, in London.
  • June 1756, struck out on his own.
  • Robert Dick, professor of natural philosophy arranged his first job, fixing a collection of astronomical instruments bequeathed to Glasgow College, October, 1755 (age 19). Room to work in the College.
  • Mathematical instrument maker to the University.
  • Moved his tools to University July 1757 (age 21).
  • Met John Robison (1739 – 1805) then an undergraduate who graduated in 1759, who later became professor of natural philosophy in 1774 in Edinburgh
james watt highlights of a remarkable life2
James Watt: Highlights of a Remarkable Life
  • Met Joseph Black, professor of anatomy and botany, later professor of medicine. Long term associate.
  • Partnership with merchant John Craig, October, 1759.
  • By 1764, Watt had 16 employees (age 28). Bankrolled by Craig.
  • Married his cousin, Margaret Miller, 1764.
  • James Watt Jr. born (1769 – 1848).
  • Robison first planted idea of a steam carriage, 1759.
  • Robison passed on books on steam from university library.
  • Watt measured relation between steam pressure and temperature
james watt highlights of a remarkable life3
James Watt: Highlights of a Remarkable Life
  • Began to work with model Newcomen engine 1764 (age 28).
  • Measured heat capacities of wood, iron and copper. Measured latent heat. Black’s influence.
  • April 1765, thought up idea of separate condenser (age 29).
  • Watt admitted steam above piston. Valve connected above and below piston at bottom of stroke.
  • Beginning of partnership with John Roebuck (1718 – 1794), former pupil of Black, successful industrialist. Use of Roebuck’s Carron foundry and workshop at Kinneil House.
  • Worked on canals beginning 1767
james watt highlights of a remarkable life4
James Watt: Highlights of a Remarkable Life
  • Returned to work on engine 1768 completing a model 6 months later. Roebuck agrees to pay for patent in return for “two thirds of the property of the inventions”.
  • Met Dr. William Small, friend of Roebuck, first in Birmingham in 1767. Franklin had introduced Small to Matthew Boulton (1728 – 1809).
  • Soho Works.
  • Patent awarded 5 January 1769.
  • Correspondence between Small and Watt. Watt sought to draw Boulton into the Watt-Roebuck partnership.
  • Roebuck in financial trouble. Bankrupt. Transfer of interest in patent to Boulton May 1773 (Watt age 37)
james watt highlights of a remarkable life5
James Watt: Highlights of a Remarkable Life
  • Wife dies 1773.
  • Watt, with James Hutton (1726 – 1779), moves to Birmingham, May 1774.
  • Bill extending patent introduced in Parliament, February, 1775. In May, 1775, patent extended to 1800.
  • John Wilkinson 91728 – 1808), iron master, casts 18 inch diameter cylinder, investing accurate boring machine. Wilkinson orders first engine.
  • Watt remarries July 1776 (age 40).
  • William Murdock (1754 – 1819) joins firm 1777. Becomes important on-site manager
  • Difficulties in constructing engines. Difficulty in extracting payments. Financial stress
james watt highlights of a remarkable life6
James Watt: Highlights of a Remarkable Life
  • Boulton suggests developing rotary motion, 1781. Neglects to take out patent. Patent taken out by John Steed working for James Pickard Assertion that idea was stolen by Cartwright (later hanged!) .
  • Watt patents five new methods of rotative motion including sun-planet arrangement, 1781 (age 45).
  • Double action engine patented 1782.
  • Patented technique for using expansive action in 1782. Had begun to work on this idea as early as 1769.
  • Many other inventions on the side: a copying machine; drying machine for cloth; instrument for measuring specific gravity of liquids.
  • 1782 patent also envisaged coupled engines
work done as piston expands through a distance d
Work done as piston expands through a distance d

Let area of the piston be given by A.

Assume pressure p acting from left; vacuum to the right

Work done = (Force) (Distance)

= (pA) d = pAd = pΔV

where ΔV = volume of expansion

thermodynamics
Thermodynamics

ΔQ = ΔE + p ΔV

Heat added increase in internal energy work done

ΔE = N CvΔT

Number of moles specific heat per mole

ΔQ = N CvΔT + p ΔV

Suppose expansion takes place without addition of heat  process is adiabatic

 N CvΔT + p ΔV = 0

thermodynamics1
Thermodynamics

But pV = NRT

james watt highlights of a remarkable life7
James Watt: Highlights of a Remarkable Life
  • 1783 Watt delivers a 700 lb. stamp hammer to Wilkinson. Works a hammer raised 2 ft making up to 300 blows per minute.
  • 1784 parallel motion patent – “one of the most ingenious simple pieces of mechanism I have contrived”.
  • 1785 – Watt’s last patent. For improved methods of constructing furnaces and fireplaces (age 49).
  • The centrifugal governor was not invented by Watt but was critical in ability to maintain a uniform speed
james watt highlights of a remarkable life8
James Watt: Highlights of a Remarkable Life
  • 1784 Watt and Boulton elected Fellows of the Royal Society of Edinburgh
  • 1785 Watt and Boulton both elected as Fellows of the Royal Society of London (age 50)
  • Watt credited with developing the unit “horse power”. Savery believed that to have 1 horse work all the time, you needed 3 horses. Watt claimed “average horse” could work several hours raising 22,000 pounds one foot in one minute. Defined 1 horse power as 33,000 ft. pounds per minute
  • Original patent expires 1800. Transferred shares to sons, James Watt Jr., Matthew Robinson Boulton and Gregory Watt. Gregory dies 1804. Firm continues successfully for 40 years until sons retired.
james watt highlights of a remarkable life9
James Watt: Highlights of a Remarkable Life
  • Soho works, up to 1824, completed 1164 steam engines, nominal horsepower 25,945
  • Watt died August 19, 1819, age 83. Buried in the local parish churchyard alongside Boulton. Joined later by Murdoch.
  • Monument to Watt in Westminster Abbey. Statue by Chantrey, inscription by Lord Brougham.
watt as scientist
Watt as Scientist
  • Was Watt first to identify the composition of water? Priestley proved that the weight of water deposited on sides of a vessel following reaction of oxygen and hydrogen is the same as the weight of the two gases. (Priestley is credited with the discovery of oxygen)

Watt’s Letter to Priestley, April 26, 1783

“ What are the products of your experiment? They are water, light and heat. Are we not, thence, authorized to conclude that water is a compound of the two gases, oxygen and hydrogen, deprived of a portion of their latent or elementary heat; that oxygen is water deprived of its hydrogen but still united to its latent heat and light? If light be only a modification of heat, or a simple circumstance of its manifestation, or a component part of hydrogen, oxygen gas will be water deprived of its hydrogen, but combined with latent heat.”

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