The proportion of kinematic viscosity relative to thermal diffusivity is known as the _______________ number?
Show answer Hide answer
Answer: B. Prandtl
Explanation
The Prandtl number is formally defined as the ratio of momentum diffusivity to thermal diffusivity. Momentum diffusivity is represented by kinematic viscosity, while thermal diffusivity reflects heat conduction. This dimensionless number characterizes the relative thicknesses of hydrodynamic and thermal boundary layers. Dimensionless numbers simplify convective heat transfer and fluid flow analysis in engineering problems. Kinematic viscosity has SI units of square meters per second. Thermal diffusivity combines thermal conductivity, density, and specific heat capacity into one parameter.
Fluid properties like the Prandtl number determine heat transfer behavior in internal pipe flows. Liquid metals have very low Prandtl numbers, whereas heavy oils exhibit exceptionally high values. Engineers use Prandtl numbers in correlations to calculate convective heat transfer coefficients accurately. Peclet number represents the ratio of advective to diffusive transport rates of a fluid property. Stanton number measures the ratio of heat transferred to thermal capacity of fluid flowing. Nusselt number expresses the ratio of convective to conductive heat transfer across boundaries.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
Related questions
Q1. Natural convection heat transfer from a vertical plate depends on the wall-to-bulk temperature difference (ΔT) according to a proportionality expressed as______________?
Show answer Hide answer
Answer: D. (ΔT)3/4
For laminar natural convection on a vertical plate, the heat transfer coefficient is proportional to (ΔT)^0.25, while for turbulent natural convection it is proportional to (ΔT)^0.33.
Q2. The primary objective of adding fins to a heat transfer surface is to enhance the_________________?
Show answer Hide answer
Answer: C. Heat transfer area
Fins physically extend the outer surface area available for convective heat transfer with surroundings. Increasing the available surface area compensates for low convective heat transfer coefficients on gases. More surfa...
Q3. The rate at which a body emits radiation is independent of the__________________?
Show answer Hide answer
Answer: D. Shape and porosity of the body
Emissive power depends strictly on surface temperature, wavelength, and material emissivity characteristics. Macro-scale shape and porosity do not alter the fundamental atomic radiation emission rate of a surface. Radiat...
Q4. The function of incorporating bleed points within the evaporator is to__________________?
Show answer Hide answer
Answer: C. Facilitate removal of non-condensable gases
Non-condensable gases accumulate inside evaporators and blanket heat transfer surfaces, reducing efficiency. Bleed points or vent lines allow operators to purge these unwanted gases continuously. Removing non-condensable...
Q5. Evaporators rely on a/an _____________ to separate liquid droplets entrained in the vapor?
Show answer Hide answer
Answer: B. Entrainment separator
Entrainment separators are specifically designed devices used to catch liquid droplets in vapor streams. High vapor velocities inside evaporators often tear tiny droplets away from the boiling surface. Passing vapor thro...
Q6. What is the ratio of velocity head to tube side return loss in a multipass shell and tube heat exchanger ________________?
Show answer Hide answer
Answer: D. 1/4
Multipass shell and tube exchangers force tube-side fluid to reverse direction at channel heads. Fluid momentum losses occur during these U-turns between successive tube passes in the channel. Hydraulic design standards...