ISOTHERMAL CAES

Isothermal gas compression and expansion cycles, such as those employed by SustainX can achieve very high thermal efficiencies. Isothermal gas compression and expansion occurs when the rate of volume change is slow relative to the rate of heat transfer to or from the system, allowing for significant heat transfer to occur.

As gas is compressed, it tends to increase in temperature. During a sufficiently slow (i.e., isothermal) compression, this increase in temperature is countered by heat flow from the gas to the surroundings, allowing the gas to remain at roughly constant temperature. Similarly, as gas expands, it tends to cool down. During a sufficiently slow expansion, this decrease in temperature is countered by heat flow from the surroundings back into the gas, again allowing the gas to remain at roughly constant temperature. If the gas remains at the same temperature during both compression and expansion, then the heat recovered from the surroundings during expansion is equal to the heat originally emitted to the surroundings during compression.