On a p-V diagram, lines of constant temperature curve from the upper left to the lower right. A process performed at constant temperature is called an isothermal process. During an adiabatic process no heat is transferred to the gas, but the temperature, pressure, and volume of the gas. When we plot temperature versus the entropy of the gas the plot is called a T-s diagram. Lines of constant pressure curve from the lower left to upper right on a T-s diagram. A constant pressure process is called an isobaric process and this type of process occurs in the combustor of a gas turbine engine. During an isentropic process there is no change in the entropy of the system and the process is reversible. An isentropic process appears as a vertical line on a T-s diagram. The area under a process curve on a T-s diagram is related to the amount of heat transferred to the gas.