Question

The steam pressure required to maintain the drum dryer surface temperature of 150°C is in the range

• A. 1.5 - 2.0 bar
• B. 4.5 -5.0 bar
• C. 8.0 - 10.0 bar
• D. 11.0 - 14.0 bar

Hint:

Steam Table Values: Saturated Steam Pressure at $150^\circ\text{C}$ = $\mathbf{4.76\text{ bar}}$ (Range: 4.5 to 5.0 bar). At $100^\circ\text{C} = 1.013\text{ bar}$.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Saturated steam thermodynamic property tables: the saturation pressure ($P_{ ext{sat}}$) corresponding to saturated steam temperature of $150^\circ ext{C}$ is exactly 4.76 bar (475.8 kPa 4.76 atm), falling directly in the range of 4.5 to 5.0 bar.
Key Formula or Approach:
\[ \text{Saturated Steam Tables: } T_{\text{sat}} = 150^\circ\text{C} \quad \implies \quad \mathbf{P_{\text{sat}} = 4.76 \text{ bar} \approx 4.5 - 5.0 \text{ bar}} \]

Step 2: Detailed Explanation:
In steam engineering and roller drum drying of milk (Roller Dried Milk Powder):
- In atmospheric drum dryers (roller dryers), saturated steam is fed inside rotating hollow cast iron/steel cylinders to heat the outer surface:
1. Saturated steam condenses on the inner cylinder wall at constant saturation temperature ($T_{\text{sat}}$), transferring its latent heat of vaporization through the drum shell.
2. According to standard Thermodynamic Saturated Steam Tables:
- At $T = 120^\circ ext{C} \implies P = 1.98\text{ bar}$.
- At $T = 140^\circ ext{C} \implies P = 3.61\text{ bar}$.
- At $T = 150^\circ ext{C \implies P = 4.76 ext{ bar}$ (0.476 MPa)}.
- At $T = 160^\circ ext{C} \implies P = 6.18\text{ bar}$.
3. Therefore, the required steam pressure to maintain a drum surface temperature of $150^\circ ext{C}$ is 4.5 to 5.0 bar (4.5 - 5.0 bar) (B).

Step 3: Final Answer:
Therefore, steam pressure required is in the range 4.5 -5.0 bar, corresponding to option (B).