﻿JOURNAL 
  

  

  OF 
  THE 
  

  

  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  

  

  Vol. 
  12 
  November 
  4, 
  1922 
  No. 
  18 
  

  

  PHYSICS. 
  — 
  Temperature 
  changes 
  accompanying 
  isentropic, 
  isen- 
  

   ergic, 
  and 
  isenkaumic 
  expansion.'^ 
  Leason 
  H. 
  Adams, 
  Geo- 
  

   physical 
  Laboratory, 
  Carnegie 
  Institution 
  of 
  Washington. 
  

  

  The 
  pressure 
  on 
  a 
  fluid 
  may 
  be 
  changed 
  from 
  its 
  initial 
  value 
  to 
  

   some 
  final 
  value 
  in 
  several 
  well-recognized 
  ways. 
  The 
  temperature 
  

   changes 
  accompanying 
  the 
  release 
  of 
  pressure 
  depend 
  on 
  the 
  method 
  

   by 
  which 
  the 
  pressure 
  is 
  released, 
  and 
  may 
  be 
  calculated 
  from 
  the 
  

   conventional 
  equations 
  of 
  thermodynamics. 
  It 
  is 
  the 
  object 
  of 
  this 
  

   communication 
  to 
  note, 
  largely 
  because 
  of 
  the 
  connection 
  with 
  geo- 
  

   physical 
  problems, 
  the 
  changes 
  in 
  temperature 
  of 
  typical 
  fluids 
  when 
  

   pressure 
  is 
  released 
  according 
  to 
  three 
  principal 
  methods. 
  

  

  These 
  methods 
  are 
  as 
  follows 
  : 
  

  

  (A) 
  Reversible 
  release 
  of 
  pressure. 
  Isentropic 
  expansion. 
  — 
  This, 
  

   the 
  most 
  familiar 
  of 
  the 
  three 
  kinds 
  of 
  expansion, 
  takes 
  place 
  when 
  

   a 
  fluid 
  {i.e., 
  a 
  gas 
  or 
  a 
  liquid) 
  is 
  expanded, 
  for 
  example 
  in 
  a 
  cylinder 
  

   with 
  movable 
  piston, 
  without 
  exchange 
  of 
  heat 
  with 
  the 
  surroundings 
  

   under 
  such 
  conditions 
  that 
  frictional 
  effects 
  are 
  (sensibly) 
  absent 
  

   and 
  slowly 
  enough 
  so 
  that 
  equilibrium 
  is 
  maintained, 
  i. 
  e., 
  that 
  the 
  

   external 
  force 
  acting 
  on 
  the 
  piston 
  is 
  (sensibly) 
  equal 
  to 
  the 
  opposing 
  

   force 
  exerted 
  by 
  the 
  fluid. 
  

  

  Under 
  such 
  conditions 
  the 
  entropy 
  (5) 
  of 
  the 
  fluid 
  remains 
  constant, 
  

   the 
  process 
  is 
  called 
  isentropic, 
  and 
  the 
  relation 
  between 
  temperature 
  

   and 
  pressure 
  is 
  given 
  by 
  the 
  equatoin 
  : 
  

  

  -(f)r-f 
  

  

  in 
  which 
  T 
  is 
  the 
  absolute 
  thermodynamic 
  temperature, 
  Cp 
  is 
  the 
  

   specific 
  heat 
  at 
  constant 
  pressure, 
  a 
  is 
  the 
  coefficient 
  of 
  expansion 
  

  

  — 
  j 
  , 
  V 
  being 
  the 
  volume 
  of 
  unit 
  mass. 
  The 
  first 
  member 
  of 
  

  

  1 
  Received 
  October 
  13, 
  1922. 
  

  

  407 
  

  

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