﻿HEAT 
  IN 
  EXPANSIVE 
  MACHINES. 
  

  

  209 
  

  

  from 
  those 
  formulae, 
  that 
  the 
  proportion 
  of 
  the 
  total 
  heat 
  converted 
  into 
  power 
  in 
  

   any 
  possible 
  steam-engine 
  is 
  less 
  than 
  that 
  indicated 
  by 
  Equation 
  {66.) 
  

   The 
  annexed 
  Table 
  illustrates 
  this 
  : 
  — 
  

  

  CASE. 
  

  

  Absolute 
  temperature 
  in 
  the 
  

   boiler 
  =«"] 
  centigrade. 
  

  

  Absolute 
  temperature 
  in 
  the 
  

   condenser 
  = 
  Tp 
  centigrade. 
  

  

  Total 
  heat 
  

   expended 
  in 
  

  

  centigrade 
  

   degrees 
  ap- 
  

   plied 
  to 
  

   liquid 
  water. 
  

  

  Heat 
  trans- 
  

   formed 
  into 
  

   expansive 
  

   power, 
  in 
  

   centigrade 
  

   degrees 
  ap- 
  

   plied 
  to 
  

   liquid 
  water. 
  

  

  Proportion 
  

   of 
  heat 
  ren- 
  

   dered 
  effec- 
  

   tive. 
  

  

  Maximum 
  

  

  proportion 
  

  

  according 
  to 
  

  

  Carnot's 
  

  

  Law. 
  

  

  First 
  Ideal 
  Example 
  in 
  1 
  

   Section 
  4, 
  Art. 
  32, 
  J 
  

  

  144°-l+274°-6 
  = 
  418°-7 
  

  

  81°-7+274°-6 
  = 
  356°-3 
  

  

  568°-7 
  

  

  83°-2 
  

  

  01463 
  

  

  0-1490 
  

  

  Second 
  Ideal 
  Example, 
  

  

  l70 
  o> 
  9 
  + 
  274°-6 
  = 
  445°-5 
  

  

  100° 
  + 
  274°-6 
  = 
  374°-6 
  

  

  558°-6 
  

  

  86°- 
  3 
  

  

  0-1545 
  

  

  0-1592 
  

  

  Mr 
  Wicksteed's 
  En- 
  "j 
  

  

  

  

  

  

  

  

  gine, 
  Experiment 
  F, 
  J» 
  

  

  135°-2 
  + 
  274°-6 
  = 
  409°-8 
  

  

  30° 
  + 
  274°-6 
  = 
  304°-6 
  

  

  6l7°-7 
  

  

  7l°-2 
  

  

  0-1153 
  

  

  0-2567 
  

  

  by 
  calculation, 
  . 
  . 
  J 
  

  

  

  

  

  

  

  

  Do., 
  by 
  observation, 
  . 
  . 
  

  

  Ditto. 
  

  

  Ditto. 
  

  

  Ditto. 
  

  

  73°'23 
  

  

  0-1185 
  

  

  Ditto. 
  

  

  (1) 
  

  

  (2) 
  

  

  (3) 
  

  

  (4) 
  

  

  (5) 
  

  

  (6) 
  

  

  (7) 
  

  

  The 
  heat 
  transformed 
  into 
  power, 
  as 
  given 
  in 
  the 
  fifth 
  column, 
  has 
  been 
  reduced 
  

   to 
  centigrade 
  degrees 
  in 
  liquid 
  water, 
  by 
  dividing 
  the 
  duty 
  of 
  a 
  pound 
  of 
  steam 
  by 
  

   Mr 
  Joule's 
  equivalent, 
  138.9*6 
  feet 
  per 
  centigrade 
  degree. 
  Hence 
  the 
  first 
  two 
  

   numbers 
  in 
  that 
  column 
  are 
  less 
  than 
  those 
  given 
  in 
  Art. 
  32, 
  which 
  were 
  com- 
  

   puted 
  from 
  too 
  small 
  an 
  equivalent. 
  

  

  The 
  first 
  two 
  cases 
  fulfil 
  the 
  conditions 
  required 
  by 
  Carnot's 
  law 
  in 
  every 
  respect 
  

   except 
  one, 
  viz. 
  : 
  — 
  that 
  the 
  steam 
  remaining 
  at 
  the 
  end 
  of 
  the 
  stroke, 
  instead 
  of 
  

   being" 
  partially 
  liquefied 
  by 
  refrigeration, 
  and 
  then 
  reduced 
  to 
  water 
  at 
  the 
  tem- 
  

   perature 
  of 
  the 
  boiler 
  by 
  compression, 
  is 
  supposed 
  to 
  be 
  entirely 
  liquefied 
  by 
  

   refrigeration. 
  This 
  occasions 
  the 
  loss 
  of 
  the 
  heat 
  necessary 
  to 
  raise 
  the 
  water 
  

   from 
  the 
  temperature 
  of 
  the 
  condenser 
  to 
  that 
  of 
  the 
  boiler 
  ; 
  but 
  at 
  the 
  same 
  time, 
  

   there 
  is 
  a 
  gain 
  of 
  the 
  power 
  which 
  would 
  be 
  required 
  to 
  liquefy 
  part 
  of 
  the 
  steam 
  

   by 
  compression, 
  and 
  those 
  two 
  quantities 
  partially 
  compensate 
  for 
  each 
  other's 
  

   effects 
  on 
  the 
  ratio 
  of 
  the 
  power 
  to 
  the 
  heat 
  expended, 
  so 
  that 
  although 
  it 
  is 
  below 
  

   the 
  maximum, 
  the 
  difference 
  is 
  small. 
  

  

  In 
  the 
  third 
  and 
  fourth 
  examples, 
  founded 
  on 
  the 
  calculated 
  and 
  observed 
  

   duty 
  of 
  Mr 
  Wicksteed's 
  engine 
  during 
  experiment 
  F, 
  the 
  actual 
  ratio 
  is 
  less 
  than 
  

   half 
  the 
  maximum. 
  This 
  waste 
  of 
  heat 
  is 
  to 
  be 
  ascribed 
  to 
  the 
  following 
  causes. 
  

  

  First, 
  The 
  mode 
  of 
  liquefaction, 
  which 
  has 
  already 
  been 
  referred 
  to. 
  

  

  Secondly, 
  The 
  initial 
  pressure 
  in 
  the 
  cylinder 
  is 
  but 
  18*93 
  lb. 
  on 
  the 
  square 
  inch, 
  

   while 
  that 
  in 
  the 
  boiler 
  is 
  45*7 
  ; 
  so 
  that 
  although 
  the 
  steam 
  is 
  produced 
  at 
  135 
  0, 
  2 
  

   centigrade, 
  it 
  only 
  begins 
  to 
  work 
  at 
  107° 
  '26. 
  This 
  great 
  fall 
  of 
  pressure 
  is 
  

  

  VOL. 
  XX. 
  PART 
  II. 
  3 
  K 
  

  

  