could cave man make a fridge?
yes..
using bamboo..
and a wind vortex cooler
vortex tube or Ranque-Hilsch vortex tube
instead of using air.. water is used to power it.. this will solve the pressure need as rivers are abundant.. and water has a better heat capacity and thermal conductivity.. even so it will only drop temps of the water by about 25°C wich is better then an optimal 15c for wind.. combine this with evaporative cooling .. a deep pit with a clay pot that evaporates water to wind currents and you can get your food to almost frozen overnight
tally...
clay pot
bamboo
river
master crafting in wood working
master crafting in clay pot making
estimated cooling -20-30C
the water wicks up the pot so the inner water level is low.. a glazed in ash inner pot can keep food dry
if you use a fire to draw air past the evaporator cooler you could maybe get near freezing
