1. What is Q-value in Distillation?

Definition: The Q-value in mass transfer represents the moles of liquid flow in the stripping section that results from the introduction of each mole of feed.

Purpose: It helps chemical engineers determine the thermal condition of the feed entering a distillation column.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( q \) — Q-value (dimensionless)
• \( H_v - f \) — Heat required to convert feed to saturated vapor (J/mol)
• \( \lambda \) — Molal latent heat of vaporization (J/mol)

Explanation: The heat required to vaporize the feed is divided by the latent heat of vaporization to determine the Q-value.

3. Importance of Q-value Calculation

Details: The Q-value determines whether the feed is:

• Subcooled liquid (q > 1)
• Saturated liquid (q = 1)
• Partially vaporized (0 < q < 1)
• Saturated vapor (q = 0)
• Superheated vapor (q < 0)

4. Using the Calculator

Tips: Enter the heat required to convert feed to saturated vapor and the molal latent heat of vaporization. Both values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What does the Q-value indicate?
A: It indicates the thermal condition of the feed entering the distillation column.

Q2: How do I determine H_v-f?
A: It's the difference between the saturated vapor enthalpy of the feed and the feed enthalpy at inlet conditions.

Q3: Where can I find λ values?
A: Latent heat values are typically available in chemical engineering handbooks or thermodynamic tables.

Q4: What's a typical range for q?
A: Most industrial distillation columns operate with q-values between 0 (saturated vapor) and 1 (saturated liquid).

Q5: How does q affect column operation?
A: The q-value affects the slopes of the operating lines and thus the number of theoretical stages required.