In a calandria-type evaporator, the tube height (tube length within the calandria) is normally less than how many metres?

Introduction / Context:
Calandria-type evaporators employ a short vertical tube bundle housed in a steam chest (the calandria). The geometry promotes vigorous boiling and circulation while limiting pressure drop and mechanical height.

Given Data / Assumptions:

• Typical single-effect calandria design for aqueous solutions.
• Conventional industrial practice for tube length.
• Focus is on normal (not extreme) design ranges.

Concept / Approach:
Calandria units generally use relatively short tubes to maintain good circulation and to contain the steam chest height. Values under 2 metres are commonly cited for standard designs, which differentiates them from long-tube vertical evaporators.

Step-by-Step Solution:
Identify the characteristic tube height range for calandria units.Standard references place tube height under approximately 2 m.Select the nearest limit in the options: 2 metres.

Verification / Alternative check:
Comparative designs (e.g., long-tube vertical) use much longer tubes; calandria types are recognized for short tube bundles.

Why Other Options Are Wrong:

• 1 and 0.75: Possible in small units but too restrictive as a general “normal” upper bound.
• 3.5 and 5.5: Too high for typical calandria practice; more in line with other evaporator styles.

Common Pitfalls:
Confusing calandria-type with long-tube vertical evaporators; generalizing specialized designs as “normal.”

Final Answer:
2