Thermodynamics concepts like heat transfer, phase changes, and water activity help explain important food processing techniques. The three laws of thermodynamics state that (1) energy is conserved, (2) entropy increases over time, and (3) no process is 100% efficient. Refrigeration uses phase changes - compressing and expanding gases to lower temperatures for cooling. Water activity measures the chemical potential of water in solutions and gases in contact, helping understand phenomena like dissolving, boiling, and humidity. Thermodynamics provides insights into limits and equilibrium states in many food processing applications.