In natural convection heat transfer, the Nusselt number depends on the Prandtl number and the ______________ number of the fluid?
Show answer Hide answer
Answer: A. Grashoff
Explanation
In natural convection heat transfer, the Nusselt number depends on both the Prandtl number and the Grashoff number. Buoyancy forces represented by the Grashoff number drive fluid motion in natural convection environments. Fluid property characteristics defined by the Prandtl number combine with Grashoff to determine convective heat transfer. Natural convection correlations express dimensionless heat transfer coefficients as power law combinations of Grashoff and Prandtl. The Grashoff number quantifies the ratio of buoyancy forces to viscous forces within the boundary layer. Prandtl number represents the ratio of momentum diffusivity to thermal diffusivity for the specific fluid medium.
Cooling electrical transformers and natural draft heat exchangers relies entirely on these dimensionless correlations. Engineering calculations for natural convection on vertical plates utilize established Grashoff-Prandtl relationships. Predicting heat loss from uninsulated industrial equipment requires accurate natural convection Nusselt number estimations. Biot number compares internal conductive resistance of a solid body to external convective resistance. Stanton number measures the ratio of heat transferred to thermal capacity of fluid flowing through conduits. Reynolds number characterizes forced flow inertia, making it irrelevant for purely buoyancy-driven natural convection.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
Related questions
Q1. Natural convection processes are marked by__________________?
Show answer Hide answer
Answer: A. Grashoff number
Natural convection heat transfer is fundamentally characterized and correlated using the dimensionless Grashoff number. The Grashoff number represents the ratio of buoyancy forces to viscous forces acting within the flui...
Q2. Open-pan evaporators are selected when the solution being concentrated is_________________?
Show answer Hide answer
Answer: B. Highly viscous
Open-pan evaporators are typically selected when the liquid solution being concentrated exhibits very high viscosity. High viscosity solutions create severe circulation difficulties and fouling problems inside closed tub...
Q3. The Nusselt number represents the ratio of the wall temperature gradient to_________________?
Show answer Hide answer
Answer: C. That across the entire pipe
The Nusselt number is defined as dimensionless temperature gradient at the fluid-solid boundary. Comparing wall temperature gradients to a reference gradient across the entire pipe defines Nusselt behavior. Dimensionless...
Q4. Forced convection Nusselt numbers are a function of the _____________ number?
Show answer Hide answer
Answer: B. Reynolds
Forced convection Nusselt numbers are primarily dependent on the Reynolds number and the Prandtl number. Fluid velocity and turbulence represented by the Reynolds number dictate forced convection heat transfer rates. Flu...
Q5. Total thermal resistance for conductive heat transfer through a series of flat layers equals the____________________?
Show answer Hide answer
Answer: B. Sum of all resistances
For heat conduction through flat layers in series, total thermal resistance equals the sum of individual resistances. Resistances in series add together linearly in exact analogy to electrical resistance circuits in phys...
Q6. With 100 kcal/s of incident radiant energy on a thermally transparent body, 300 kcal/s is reflected (wait, phrasing preserved). If transmissivity is 0.25, the surface emissivity is_________________?
Show answer Hide answer
Answer: B. 0.45
Energy balances on a transparent body equate incident radiant energy to the sum of reflected, absorbed, and transmitted fractions. Subtracting known reflection and transmission coefficients from unity yields the surface...