Question 2.2: Danger of Cavitation in a Propeller The analysis of a propel...
Danger of Cavitation in a Propeller
The analysis of a propeller that operates in water at 20°C shows that the pressure at the tips of the propeller drops to 2 kPa at high speeds. Determine if there is a danger of cavitation for this propeller.
The minimum pressure in a propeller is given. It is to be determined if there is a danger of cavitation.
Properties The vapor pressure of water at 20°C is 2.34 kPa (Table 2–2).
Analysis To avoid cavitation, the pressure everywhere in the flow should remain above the vapor (or saturation) pressure at the given temperature, which is
The pressure at the tip of the propeller is 2 kPa, which is less than the vapor pressure. Therefore, there is a danger of cavitation for this propeller.
Discussion Note that the vapor pressure increases with increasing temperature, and thus there is a greater danger of cavitation at higher fluid temperatures.
TABLE 2–2
Saturation (or vapor) pressure of water at various temperatures
| Temperature T, °C | Saturation Pressure , kPa |
| -10 | 0.26 |
| -5 | 0.403 |
| 0 | 0.611 |
| 5 | 0.872 |
| 10 | 1.23 |
| 15 | 1.71 |
| 20 | 2.34 |
| 25 | 3.17 |
| 30 | 4.25 |
| 40 | 7.38 |
| 50 | 12.35 |
| 100 | 101.3 (1 atm) |
| 150 | 475.8 |
| 200 | 1554 |
| 250 | 3973 |
| 300 | 8581 |