For gas absorption, how is the height of a transfer unit based on the gas phase expressed, where G is superficial molar gas velocity, L is superficial molar liquid velocity, FG is mass transfer coefficient in moles/m2, and a is interfacial area per unit volume ?
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Answer: A. G/(FG . a)
Explanation
Height of a transfer unit is defined by the superficial gas velocity divided by volumetric mass transfer. The gas-phase mass transfer coefficient multiplied by interfacial area gives volumetric mass transfer capability. Dividing superficial gas velocity by volumetric transfer coefficient yields the correct dimension of length. Transfer units measure the difficulty of a separation task in continuous contact mass transfer towers. Superficial molar gas velocity represents the molar flow rate divided by total cross-sectional tower area. Interfacial area per unit volume depends on the specific packing type and hydrodynamic loading.
Packed column designers use height of transfer units to calculate total required tower packing height. Gas absorption and stripping calculations rely on accurate transfer unit height estimations. Understanding HTU expressions allows engineers to scale up laboratory columns to industrial sizes. Option B inverts the numerator and denominator resulting in incorrect dimensional units of inverse length. Option C multiplies velocity by area incorrectly which does not yield a length dimension for height. Option D introduces liquid velocity incorrectly into a gas-phase transfer unit height definition.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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