Phosphate Rocks Chapter 17: Thermodynamics

When the sun shone on the ammonia storage spheres, the contents began to warm, despite a thick layer of insulation. The energy from the sun caused the cold liquid to evaporate and the temperature and pressure in the spheres began to rise. The pressure could be lowered by sucking away the ammonia gas to feed production. 

If you remove the gas above a liquid, some liquid evaporates, vaporising or ‘flashing off’ to replace the lost gas, and this causes cooling, just like when you sweat. So sending the ammonia as flash gas to the production plants reduced both the pressure and temperature in the storage spheres. 

It had other benefits as well, although these weren’t fully appreciated until later. 

But if the Granny or Nitram plants weren’t running, the pressure in the ammonia spheres had to be lowered in another way. 

Using the Joule-Thomson effect³⁴. 

James Prescott Joule^(xv) was born in 1818. Fascinated by electricity as a child, he experimented by giving shocks to family members and servants. To keep him out of trouble, he was given the family brewery to run.  

Good call. The practical and economic challenges proved inspirational to the amateur scientist. He was the first to experimentally prove a connection between heat and work. 

So dedicated was Joule to his science, he invited a friend along on his honeymoon to measure the temperature differences between the top and bottom of waterfalls in Chamonix. His waterfall honeymoon friend was William Thomson^(xvi) who later became the famous Lord Kelvin. In 1852 the two men showed how gases and liquids drop in temperature as they expand. 

How did his new wife, Amelia Joule, née Grimes^(xiv), feel about thermodynamics on her honeymoon? Did her feelings toward her husband cool? Was she tempted to throttle him? Cooling with throttling is called the Joule-Thomson effect.