Adiabatic Processes

ADIABATIC PROCESSES (from Greek a - negative particle, and diabasis - transition), processes in which a physical body cannot receive heat from outside nor release it outward. A. p. include, for example, the compression or expansion of a gas contained in a vessel with walls that absolutely do not conduct heat. If the gas is compressed under such conditions, its temperature will rise. Conversely, during expansion the temperature will fall. In this case, the pressure of the gas will be related to its volume by a ratio known as Poisson's law: p.V^γ = Const. Here p is pressure, V is volume; Const denotes some constant value; γ = cₚ/cᵥ is the ratio of the heat capacities of the gas: cₚ - when it is heated at constant pressure, cᵥ - at constant volume. The change in temperature during A. p. can be calculated by the formula: T₁/T₂ = (V₂/V₁)^(γ-1). Here the subscripts (1) and (2) refer to the volume and temperature at the beginning and end of the adiabatic processes. Adiabatic expansion of gases is used for their rapid cooling (for example, in the production of liquid air, liquid carbon dioxide, etc.).