Explanation:

The Mach number is a dimensionless parameter that represents the flow velocity of a fluid relative to the speed of sound in that fluid. It is commonly used to analyze and characterize the compressibility effects in high-speed flows, such as those found in gas turbines.

In this given scenario, the Mach number at the inlet of the gas turbine diffuser is 0.3. Based on this information, we can determine the shape of the diffuser.

Determining the Shape of the Diffuser:

The shape of the diffuser can be determined by considering the Mach number at the inlet. The Mach number provides valuable information about the flow conditions and the behavior of the fluid.

Converging Diffuser:
- A converging diffuser is used when the Mach number at the inlet is greater than 1 (M > 1).
- In this case, the flow is supersonic, and the converging shape helps to decelerate the flow and increase the static pressure.

Diverging Diffuser:
- A diverging diffuser is used when the Mach number at the inlet is less than 1 (M < />
- In this case, the flow is subsonic, and the diverging shape helps to accelerate the flow and decrease the static pressure.

Stagnation Enthalpy and Stagnation Pressure:
- Stagnation enthalpy and stagnation pressure are thermodynamic properties that describe the flow conditions at a specific point.
- They are not directly related to the shape of the diffuser but can be used to analyze the performance and efficiency of the gas turbine.

Conclusion:
Based on the given information that the Mach number at the inlet of the gas turbine diffuser is 0.3, we can conclude that the shape of the diffuser would be diverging. This is because the Mach number is less than 1, indicating a subsonic flow, and a diverging shape is utilized to accelerate the flow and decrease the static pressure.