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Refrigeration

Pumping heat out of a box

Date
1834
Era
Industrial age
Rebuild stage
IV Science & industry
Difficulty

Plate

Legend
  1. 1Jacketed pan with the water to be frozen
  2. 2Box packed with charcoal
  3. 3Pump
  4. 4Flywheel and handle
  5. 5Worm in its cooling-water tub
  6. 6Weighted valve box

Anatomy

Ether: liquid in solid colour, vapour as dots of equal massHigh-pressure side, warm: delivery pipe and wormLow-pressure side, cold: from the valve through the jacket to the pumpCut along the pipes; shafts, rods and pins drawn wholeThe ice machine John Hague built to Jacob Perkins's patent of 1834, cut in half along its pipes. The flywheel works a pump 2.5 in across with a 5 in stroke (400 cm³). Each up stroke draws ether vapour out of the jacket round the copper pan, so the ether there keeps boiling below 0 °C and takes heat from the water in the pan. Each down stroke squeezes the vapour and drives it into the worm. A valve loaded to 15 lb/in² keeps the worm 1.03 bar above the jacket, so the vapour condenses at about 40 °C and hands its heat to the water running through the tub; the liquid then passes the valve, where about 12 % of it boils off as it cools to the jacket's temperature, and runs back into the jacket. The readout uses ether's measured vapour pressure (it boils at 34.5 °C in open air). Turning faster lowers the jacket's pressure: the ether boils at -1.6 °C at 10 turns a minute and -8.4 °C at 60, making 0.1 to 0.5 kg of ice an hour. No record gives the pump's size or how fast heat crosses the pan, so both are assumed, the second at 6 W per kelvin. Each dot stands for the same mass of vapour: they are spread out in the vapour pipe and packed close in the delivery pipe. At 30 turns a minute the vapour moves at about 0.3 m/s in the vapour pipe and the liquid at 1.1 mm/s; the drawing runs 2 times slower than the machine. The readout ends with the heat taken from the pan and the heat given to the tub. The parts keep their sizes but stand closer together than on the 5 ft machine, the tub and the box are drawn tight round what they hold, and the flywheel and its frame are left out.

Refrigeration keeps a space colder than its surroundings by making a liquid boil inside it, so that it soaks up heat, then carrying the vapour outside, compressing it and turning it back into liquid. Jacob Perkins patented the first closed vapour-compression machine in London in 1834; ammonia machines ran breweries and ships by the 1870s, and electric home refrigerators spread from the late 1920s.

What it is

A refrigerator moves heat out of a closed space and dumps it outside, from cold to warm, the opposite of the way heat flows on its own. Food keeps longer because the bacteria and moulds that spoil it grow slowly in the cold. The same machines make ice, cool beer during brewing, carry frozen meat across oceans and air-condition buildings.

Nearly all of them work on the vapour-compression cycle. The plate shows its first working form: an ether machine that the engineer John Hague built in London to Jacob Perkins’s patent of 1834. The pump was worked by hand.

How it works

A pot-in-pot cooler: a small unglazed clay pot inside a larger one, the gap filled with damp sand and covered with a wet cloth A clay pot-in-pot cooler uses the same effect: water evaporating from the damp sand draws heat from the inner pot.

A liquid that evaporates takes heat from whatever it touches. Sweat cools skin in the same way. The lower the pressure, the lower the temperature at which a liquid boils: ether boils at about 35 °C in open air, but in a vessel where a pump keeps the pressure low it boils well below the freezing point of water.

On Hague’s machine the jacketed copper pan holds the water to be frozen in its inner bowl, and ether fills the space between its two walls. The pump draws ether vapour from the top of the jacket, so the liquid ether keeps boiling and pulls heat out of the water until it freezes. Powdered charcoal packed around the pan slows the heat coming in from the room.

The same pump then pushes the vapour into a copper coil, the worm, standing in a tub of running water. A valve loaded to about 15 pounds per square inch, a little over one bar, holds the vapour in the worm under pressure. Compressed and cooled by the water, the vapour turns back into liquid and gives up the heat it took from the pan, together with the work put in at the pump. The liquid passes the valve, its pressure falls, and it runs back into the jacket to boil again. The same charge of ether goes round and round without being used up.

A modern refrigerator does the same with an electric compressor, a grid of tubes at the back that warms the kitchen, a narrow tube or valve where the pressure drops, and an evaporator inside the cabinet. Absorption refrigerators replace the pump with a liquid that soaks up the refrigerant vapour and a burner or heater that drives it out again.

How to build it

A real refrigerating circuit holds a volatile fluid under pressure. Ether is highly flammable and its vapour can explode; ammonia is toxic; modern refrigerants are stored as liquids under several bars and some are flammable. Machines are built and charged in factories; leave any opening, filling or emptying of a circuit to qualified refrigeration technicians, following local rules. Do not make a compressor or a pressure vessel, and never cut or drill the pipes of an old refrigerator.

The effect behind it can be shown safely with a pot-in-pot evaporative cooler.

Choose the pots. Take two new, clean unglazed terracotta pots, one about 5 cm wider than the other all round; the inner one, which touches the food, should be sold for food use, never an old garden pot. Plug the drainage holes with clay or a cork.

Fill the gap. Put a layer of sand in the bottom of the large pot, stand the small pot on it, and fill the gap between them with sand up to the rim.

Wet it. Pour clean water into the sand until it is soaked but not flooded. Cover the inner pot with a damp cotton cloth.

Place it. Stand the cooler in shade where dry air can move around it. Water seeping through the outer wall evaporates and draws heat from the sand and the inner pot. In hot, dry air the inside can stay several degrees cooler than the surroundings; in humid air the effect is small. Add water once or twice a day.

Safety. An evaporative cooler only slows spoilage: it does not reach the 5 °C or below needed for meat, fish or dairy, so keep it for whole, uncut vegetables and fruit that keep at room temperature, never for cut fruit, salads or cooked food, and check its temperature with a thermometer. Keep the sand and cloth clean and dry the pots out regularly to stop mould. Never open, puncture or heat the circuit of a refrigerator or air conditioner.

History and evolution

A late nineteenth-century wooden icebox with its upper door open on a block of ice in a zinc-lined compartment Before machines reached the kitchen, a zinc-lined icebox was cooled by a block of ice.

People stored winter ice in pits and ice houses, and cooled water in porous jars, long before any machine. In Scotland, William Cullen showed that a liquid evaporating quickly under reduced pressure, ether in his best-known demonstration, can cool the water around it until it freezes; accounts date the work between 1748 and 1756. It remained a laboratory demonstration. In 1805 Oliver Evans described a closed vapour-compression cycle in the United States but never built it.

Jacob Perkins, an American inventor living in London, patented a closed machine on 14 August 1834. Hague built it, and it made a small amount of ice, but it found no buyers. The idea became a business in the 1850s, when James Harrison in Australia and Alexander Twining in the United States built the first ice machines sold commercially. In 1859 Ferdinand Carré in France patented an absorption machine that used ammonia dissolved in water. In the 1870s Carl von Linde in Munich designed ammonia compression machines; one of the first, sold in 1876, went to a brewery in Trieste. The same year the French ship Frigorifique, fitted out by Charles Tellier, carried the first cargo of refrigerated meat by sea between Rouen and Buenos Aires.

A white enamelled refrigerator on four short curved legs, with a single door and a cylindrical drum on top ringed by a copper coil The Monitor Top of 1927: the compressor sits in the drum, and the copper coil around it gives off the heat taken from the cabinet.

Small electric motors made home refrigerators possible. General Electric’s Monitor Top of 1927, with its compressor in a drum on the cabinet, cost about 525 dollars at launch and fell to about 200 within a few years. Chlorofluorocarbons such as Freon, developed in 1928 and made commercially from the early 1930s, then replaced the toxic or flammable refrigerants used in early household machines, such as sulphur dioxide, methyl chloride and ammonia. They were later found to destroy the ozone layer, and the Montreal Protocol of 1987 phased them out; in 2016 the Kigali amendment added their replacements, the HFCs, which are strong greenhouse gases. In 2024 the International Institute of Refrigeration estimated that refrigeration and air conditioning use about a fifth of the world’s electricity.

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