Heat and Mass Transfer Concepts
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Questions and Answers

What is the primary mechanism of heat transfer through direct contact without mixing?

  • Conduction (correct)
  • Radiation
  • Convection
  • Evaporation

Which law describes the relationship between heat flow rate, area, temperature drop, and length of path in conduction?

  • Newton's Law of Cooling
  • Fourier’s Law (correct)
  • Stefan-Boltzmann Law
  • Ohm’s Law

What characterizes forced convection in fluid heat transfer?

  • Heat exchange in still air
  • Natural density changes in fluid
  • Use of an agitator or pump (correct)
  • No external influence on fluid movement

Which statement is true about natural convection?

<p>It creates currents due to density changes in the fluid. (A)</p> Signup and view all the answers

Which of the following is the method by which heat can be transferred through electromagnetic waves?

<p>Radiation (C)</p> Signup and view all the answers

What is a 'black body' in the context of thermal radiation?

<p>An object that absorbs all radiation without reflection (B)</p> Signup and view all the answers

Which law gives the total amount of radiation emitted by a black body?

<p>Stefan-Boltzmann Law (A)</p> Signup and view all the answers

What determines the film coefficient in forced convection heat transfer?

<p>The size and shape of the heating surface (A)</p> Signup and view all the answers

What characteristic defines a gray body in physics?

<p>It absorbs a certain fraction of incident electromagnetic radiation. (D)</p> Signup and view all the answers

What describes a conveyor belt system?

<p>A system consisting of two or more pulleys with a continuous loop of carrying medium. (B)</p> Signup and view all the answers

Which type of conveyor uses a rotating helical screw blade?

<p>Screw conveyor (B)</p> Signup and view all the answers

What is a primary use for chain conveyors?

<p>Conveying heavy unit loads like pallets (D)</p> Signup and view all the answers

What is the main characteristic of pneumatic conveyors?

<p>They convey materials using compressed air in enclosed tubes. (A)</p> Signup and view all the answers

The emissivity and absorptivity of a substance being equal indicates what type of body?

<p>Black body (C)</p> Signup and view all the answers

What function does a bucket conveyor primarily serve?

<p>Transporting bulk material in various positional paths. (D)</p> Signup and view all the answers

How does the rest of the conveyor systems differ from a screw conveyor?

<p>They utilize various methods (like belts or chains) for transport. (B)</p> Signup and view all the answers

Flashcards

Heat Conduction

Heat transfer through a material without mixing, based on Fourier's law.

Fourier's Law

The rate of heat flow is proportional to the area and temperature difference, and inversely proportional to the length.

Forced Convection

Heat transfer with fluid mixing due to external forces (e.g., pumps, stirrers).

Natural Convection

Heat transfer caused by density differences in fluids due to temperature variations.

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Film Coefficient

Heat flow per unit area per unit temperature difference in a film.

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Thermal Radiation

Heat transfer by electromagnetic waves.

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Black Body

An ideal emitter that radiates the maximum possible energy at a given temperature.

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Grey Body

A body that radiates less than a black body.

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Emissivity

The ratio of energy radiated by a body at a given temperature to the energy radiated by a black body at the same temperature.

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Absorptivity

The ratio of energy absorbed by a body to the energy incident on it.

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Belt Conveyor

A system that moves material using an endless loop of carrying medium (belt) rotating around pulleys.

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Screw Conveyor

A mechanism that uses a rotating helical screw blade (flighting) to transport material within a tube.

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Pneumatic Conveyor

A system for transporting bulk material through an enclosed tube using compressed air.

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Chain Conveyor

A system for moving materials through production lines using chains with attached components to carry heavy loads.

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Study Notes

Heat and Mass Transfer

  • Heat flows from high temperature regions to low temperature regions
  • Heat flow is governed by thermodynamic principles
  • Heat flows into or leaves a system during any physical or chemical transformation

Conduction

  • Heat transfer within a body by momentum transfer of atoms/molecules without mixing
  • Based on Fourier's law

Fourier's Law

  • Heat flow rate through a uniform material is proportional to area and temperature difference
  • Heat flow rate is inversely proportional to the length of the path

Convection

  • Forced Convection

    • Fluid mixing is achieved by agitators, stirrers, or pumping for recirculation
    • Heat transfer process is called forced convection
    • Stagnant film coefficients are crucial for determining heat transfer rate
    • Film coefficient quantifies heat flow through unit area for unit temperature drop

  • Natural Convection

    • Fluid mixing due to density changes caused by temperature differences
    • Depend on:
      • System geometry (size, shape, heating surface arrangement)
      • Shape of the vessel containing the fluid
    • Observed when extracts are evaporated in open pans

Radiation

  • Heat transfer through electromagnetic waves
  • Thermal radiation is the heat transfer by radiation
  • Various emitters are used to supply heat
  • Examples of radiation sources, wavelengths, and applications are presented in a table format

Black Body

  • Radiates maximum possible energy at a given temperature
  • Hot bodies emit radiation (Stephen-Boltzmann Law)
  • Total radiation amount is defined by black body

Grey Body

  • Absorbs a certain fraction of any incident electromagnetic radiation
  • The same fraction applies for all wavelengths

Conveyors

  • Belt Conveyors
    • System of pulleys/drums with an endless belt
  • Screw Conveyors
    • Mechanism with a helical screw blade (flighting) within a tube lifting material
  • Pneumatic Conveyors
    • Bulk material transport in an enclosed tube by compressed air or another medium
  • Chain Conveyors
    • Used to transport heavy loads like pallets, containers, grid boxes for material flow
  • Bucket Conveyors
    • Consists of endless chains or belts with attached buckets for bulk material transport in horizontal, vertical, and inclined paths; buckets remain in carrying position until tipped to discharge

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Heat Flow Unit Operations PDF

Description

This quiz covers essential concepts in heat and mass transfer, including conduction, convection, and Fourier's Law. Learn how heat flows within systems and the principles governing these processes. Test your understanding of how temperature differences influence heat transfer rates.

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