The Graetz number is mathematically defined as__________________?
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Answer: A. mCp/kL
Explanation
The Graetz number is mathematically defined as mass flow rate multiplied by heat capacity divided by thermal conductivity and length. This specific dimensionless group characterizes internal laminar forced convection heat transfer within circular conduits. Alternative formulations exist in literature, but the standard engineering definition matches the mass flow and thermal property ratio. Dimensionless groups allow engineers to scale heat transfer performance across different fluid systems and geometries. The Graetz number incorporates flow rate, heat capacity, thermal conductivity, and channel length parameters. Laminar flow regimes feature parabolic velocity profiles where molecular transport mechanisms dominate radial energy transfer.
Graetz numbers are essential when designing equipment with long entrance regions or highly viscous laminar fluid flows. Food processing and polymer manufacturing often involve laminar flow conditions requiring specialized dimensionless correlations. Understanding Graetz parameters helps predict thermal entry lengths and Nusselt number variations along pipe walls. Option B inverts the thermal conductivity and length terms, creating an incorrect dimensional grouping. Option C replaces length with dynamic viscosity, which changes the dimensionless nature of the parameter. Option D combines viscosity and thermal conductivity incorrectly, failing to represent thermal capacity properly.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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