Hydraulic radius for heat transfer through the annulus of a concentric double-pipe heat exchanger is_________________?
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Answer: C. More than that for fluid flow
Explanation
Hydraulic radius for heat transfer accounts for heated perimeters rather than wetted frictional perimeters alone. Concentric annular geometries have distinct effective flow areas for thermal energy transfer versus fluid friction. Mathematical definitions show that the thermal hydraulic radius yields higher numerical values than the fluid flow equivalent. Hydraulic radius is defined as the flow cross-sectional area divided by the wetted perimeter of the conduit. Double-pipe heat exchangers transfer heat across annular spaces formed by inner and outer cylindrical tubes. Thermal calculations must distinguish between inner and outer boundary heat transfer surfaces in annular spaces.
Heat exchanger design for double-pipe units requires accurate convective coefficient estimations in annular spaces. Failing to use the correct thermal hydraulic radius leads to errors in predicted heat transfer performance. Chemical engineers evaluate annular heat exchangers carefully when handling high-temperature or corrosive fluids. Stating they are equal ignores the fundamental difference between fluid momentum friction and thermal conduction perimeters. Claiming the thermal radius is less contradicts the geometric derivation of annular heat transfer areas. Listing inner and outer diameter differences represents raw gap dimensions rather than a true hydraulic radius.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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