The Grashoff number (gβ(Ts-T∞)ρ2L3/μ2) scales as the ratio of buoyancy forces to ____________ forces?
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Answer: A. Viscous
Explanation
The Grashoff number represents the exact mathematical ratio of buoyancy forces to viscous forces in natural convection. Buoyancy forces drive natural convection flow, while viscous forces act to resist fluid motion near solid surfaces. This dimensionless ratio determines the transition from laminar to turbulent natural convection boundary layer flows. Natural convection currents arise from fluid density variations caused by temperature gradients near heated surfaces. Viscous shear stresses within the fluid boundary layer oppose the upward buoyant rise of warm fluid elements. Dimensionless scaling parameters allow engineers to correlate heat transfer data across diverse fluids and geometries.
Natural convection heat transfer calculations are critical for designing passive nuclear reactor cooling systems. Understanding buoyancy and viscous force balances helps engineers prevent overheating in electrical transformer enclosures. Grashoff and Prandtl numbers combine to form the Rayleigh number used in natural convection Nusselt correlations. Option B elastic forces characterize compressible wave propagation rather than standard incompressible fluid convection. Option C inertial forces are paired with viscous forces in the Reynolds number for forced convection flows. Option D is incorrect because option A correctly identifies viscous forces as the denominator.
- Subject
- Engineering
- Category
- Chemical Engineering
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- —
- Difficulty
- medium
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