Explanation:

When a thermocouple is mounted flush in an insulated flat surface in a supersonic laminar flow of air, it measures the temperature of the surface. However, due to the supersonic flow, the temperature measured by the thermocouple is not the same as the static temperature of the flow. The correct answer is option 'B', i.e., the temperature measured by the thermocouple is greater than the static temperature but less than the total temperature of the flow.

Static Temperature:

The static temperature of a fluid is the temperature measured when the fluid is brought to rest. In a supersonic flow, the fluid is moving at a high velocity, and therefore, the static temperature cannot be measured directly.

Total Temperature:

The total temperature of a fluid is the temperature that would be measured if the fluid is brought to rest adiabatically (without any heat transfer) by slowing it down to subsonic speeds. The total temperature is higher than the static temperature due to the conversion of kinetic energy into thermal energy.

Temperature Measurement by Thermocouple:

A thermocouple is a temperature sensor that measures the temperature difference between two junctions. In this case, the thermocouple is mounted flush in an insulated flat surface, and one of the junctions is in contact with the surface. The temperature measured by the thermocouple is the temperature of the surface.

In a supersonic flow, the temperature measured by the thermocouple is not the same as the static temperature of the flow. This is because the high-speed flow generates frictional heating, which increases the temperature of the surface. However, the temperature measured by the thermocouple is less than the total temperature of the flow because the thermocouple is not able to measure the temperature rise due to the conversion of kinetic energy into thermal energy.

Conclusion:

The correct answer is option 'B', i.e., the temperature measured by the thermocouple is greater than the static temperature but less than the total temperature of the flow.