Massachusetts 3rd Class Engineer Practice Exam

In a Curtis stage of a steam turbine, pressure drop occurs primarily due to the configuration of the steam passages. In a turbine, steam enters and moves through the blades, converting thermal energy into mechanical work. As steam exits the turbine stage, the design typically involves a reduction in the cross-sectional area of the steam passages compared to the inlet.

When the steam passes into a smaller outlet area, it accelerates, which leads to a reduction in pressure. This phenomenon is a result of the principles of fluid dynamics, specifically Bernoulli's principle, which states that an increase in the fluid's speed occurs simultaneously with a decrease in pressure. Therefore, in the Curtis stage, the expansion of steam through narrower passages is a key factor in the pressure drop.

The other options do not adequately describe the mechanism behind the pressure drop in this context. For instance, cooling of the steam upon exit would not solely define the pressure dynamics; the main aspect here is related to the change in cross-sectional area. Increasing the heat content of the steam would lead to increased pressure and energy. Lastly, adjusting the angle of the blades may affect efficiency and velocity but does not directly cause the pressure drop in this specific scenario.