﻿106 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  the 
  sun 
  shines 
  and 
  to 
  be 
  completely 
  cut 
  off 
  when 
  the 
  sun 
  is 
  obscured. 
  

   This 
  requires 
  a 
  pump 
  able 
  to 
  force 
  water 
  in 
  against 
  full 
  steam 
  pres- 
  

   sure, 
  and 
  so 
  regulated 
  by 
  the 
  temperature 
  of 
  the 
  boiler 
  that 
  the 
  water 
  

   flow 
  ceases 
  when 
  the 
  boiler 
  cools, 
  and 
  reaches 
  a 
  maximum 
  when 
  the 
  

   boiler 
  temperature 
  reaches 
  the 
  point 
  for 
  the 
  desired 
  pressure 
  of 
  

   steam. 
  

  

  I 
  accomplish 
  these 
  objects 
  by 
  employing 
  a 
  diaphragm 
  pump, 
  whose 
  

   stroke 
  is 
  governed 
  from 
  zero 
  to 
  maximum 
  displacement 
  by 
  a 
  rotating 
  

   cam 
  of 
  regularly 
  increasing 
  throw, 
  operating 
  through 
  a 
  pitman 
  upon 
  

   the 
  pump. 
  The 
  cam 
  is 
  driven 
  from 
  the 
  60-cycle 
  motor, 
  above-men- 
  

   tioned, 
  and 
  is 
  mounted 
  on 
  a 
  longitudinally 
  displaceable 
  carriage. 
  The 
  

   position 
  of 
  the 
  carriage, 
  and 
  hence 
  the 
  throw 
  of 
  the 
  cam, 
  is 
  governed 
  

   by 
  the 
  differential 
  heat 
  expansion 
  between 
  the 
  boiler 
  tube 
  and 
  a 
  tape 
  

   of 
  the 
  nonexpansible 
  alloy, 
  invar, 
  attached 
  thereto. 
  

  

  The 
  water 
  is 
  forced 
  through 
  a 
  small 
  tube 
  centrally 
  to 
  the 
  lower 
  

   end 
  of 
  the 
  boiler 
  tube, 
  where 
  it 
  is 
  guided 
  by 
  a 
  spreader 
  tube 
  into 
  a 
  

   thin 
  sheet 
  bathing 
  the 
  inner 
  wall 
  of 
  the 
  boiler 
  tube. 
  The 
  water 
  bursts 
  

   immediately 
  into 
  steam, 
  which 
  flows 
  out 
  to 
  the 
  engine 
  through 
  con- 
  

   nections 
  from 
  the 
  upper 
  end 
  of 
  the 
  boiler 
  tube. 
  A 
  maze 
  of 
  heat-con- 
  

   ducting 
  copper 
  vanes 
  extends 
  throughout 
  the 
  upper 
  part 
  of 
  the 
  boiler 
  

   tube, 
  so 
  that 
  only 
  dry 
  steam 
  can 
  escape 
  therefrom. 
  In 
  large 
  solar- 
  

   power 
  installations, 
  no 
  doubt 
  it 
  would 
  be 
  desirable 
  to 
  use 
  auxiliary 
  

   superheaters. 
  

  

  The 
  efficiency 
  of 
  such 
  a 
  device 
  is 
  a 
  matter 
  of 
  critical 
  interest 
  for 
  

   the 
  future 
  of 
  solar 
  power. 
  It 
  may 
  be 
  estimated 
  as 
  follows 
  : 
  

  

  Percent 
  

  

  Mirror 
  reflection 
  82 
  

  

  Sheath 
  transmission 
  85 
  

  

  Boiler 
  absorption 
  95 
  

  

  Heat 
  not 
  wasted 
  90 
  

  

  Boiler 
  efficiency 
  0.82X0.85X0.95X0.90= 
  60 
  

  

  Thermodynamic 
  factor 
  (as 
  above) 
  36 
  

  

  Assumed 
  mechanical 
  efficiency 
  of 
  engine 
  75 
  

  

  Over-all 
  efficiency 
  of 
  conversion 
  : 
  0.60X0.36X0.75= 
  16. 
  2 
  

  

  Recalling, 
  as 
  stated 
  above, 
  that 
  the 
  average 
  receipt 
  of 
  solar 
  energy 
  

   throughout 
  cloudless 
  days 
  in 
  a 
  favorable 
  region 
  corresponds 
  to 
  1.15 
  

   horsepower 
  per 
  square 
  yard 
  of 
  surface 
  normal 
  to 
  the 
  beam, 
  we 
  con- 
  

   clude 
  that 
  it 
  will 
  require 
  a 
  mirror 
  of 
  not 
  less 
  than 
  5.4 
  square 
  yards, 
  or 
  

   48.6 
  square 
  feet, 
  surface 
  per 
  horsepower 
  under 
  the 
  most 
  favorable 
  of 
  

   circumstances. 
  Such 
  a 
  mirror 
  might 
  well 
  be 
  10 
  by 
  5 
  feet 
  in 
  projection. 
  

   When 
  we 
  consider 
  wind 
  resistance 
  and 
  other 
  limitations, 
  including 
  

   especially 
  the 
  glass 
  tubing 
  of 
  the 
  evacuated 
  sheath, 
  it 
  seems 
  difficult 
  

  

  