Real Lime Application of Heat & Mass Transfer

P M V Subbarao

Associate Professor

Mechanical Engineering Department

IIT Delhi

Understand Philosophy Through Experience……

The Bare Pentium 4 Processor

Heat Sinks for Pentium 4

Pentium 4 While Performing

                                                           

                                         

Heat Transfer :: An Engineering Science

• The first law of thermodynamics establishes a relationship between heat and work (Energy Interactions).

• The second law of thermodynamics states that the spontaneous energy interactions are unidirectional.

• Thermodynamics is totally silent on the question the rate at which heat travels.

• How to control the rate of heat transfer?

• Heat Transfer is an Engineering science to design thermal infrastructure.

• It evolved over 200 years.

Applications of Mass Transfer

Mass Transfer

• Mass transfer: The transfer of mass into or out of a substance

• The transfer of a chemical compound from one phase to another

• Examples:

• Evaporation: liquid gas

• Diffusion: high concentration low concentration

Evaporation:DryingConcentrationBakingFryingBoiling

Various Mass Transfer Phenomenon

Diffusion:Salt through cheese curdSmoke through meatMarinade or curing solution through meatLye in tomato peeling

Not mass transfer:Moving a fluid from one place to another

Osmosis

• Osmosis is the net movement of water across a partially permeable membrane from a region of high solvent potential to an area of low solvent potential, up a solute concentration gradient.

• Osmosis is responsible for the ability of plant roots to suck up water from the soil.

• Since there are many fine roots, they have a large surface area, water enters the roots by osmosis, and generates the pressure required for the water to travel up the plant.

• Osmosis can also be seen very effectively when potato slices are added to a high concentration of salt solution.

• The water from inside the potato moves to the salt solution, causing the potato to shrink and to lose its 'turgor pressure'.

• The more concentrated the salt solution, the bigger the difference in size and weight of the potato slice.

• For example, freshwater and saltwater aquarium fish placed in water of a different salinity than that they are adapted to will die quickly, and in the case of saltwater fish, rather dramatically.

DIFFUSION OF 02 AND C02 ACROSS THE ALVEOLAR-CAPILLARY MEMBRANE

• All gas movement in the lung occurs as a result of passive diffusion, i.e., gas moves from one region to another only when the partial pressure of gas is greater in one region than another.

• The transfer of gas from the alveolus to the blood occurs by simple diffusion.

• The rate of transfer depends on what?

Desert Cooler

Evaporative Cooling

• Cooling through the evaporation of water is an ancient and effective method of lowering temperature.  

• Both plants and animals use this method to lower their temperatures.  

• Trees, through the process of evapotranspiration, for example, remain cooler than their environment. 

• People accomplish the same thing when they perspire. 

• For both trees and people the underlying scientific principle is the same: when water evaporates, that is, changesfrom a liquid to a gas, it takes heat energy from the surrounding environment, thus leaving its environment cooler.

Primitive Products

• Finally, some of us may have discovered that water kept in a canvas bag, porous clay container, or in a canteen with a water-soaked cloth cover, is much cooler, especially on a hot day, than water kept in plain metal or plastic containers.  

• As the water evaporates from the surfaces of these containers it draws heat away from the containers and the water they hold, as well as fromthe air around them, thus leaving the water cooler.

Syllabus• Introduction :3 Lecture• Introduction to Heat Transfer; Relationship to

thermodynamics; Heat Transfer as an engineering science; Practical relevance; Mechanisms of Heat transfer: conduction, convection and radiation; related parameters.

• Conduction Heat Transfer : 8 Lectures• Heat Conduction equation and its approximations:

steady and unsteady, single and multidimensional, constant and variable properties, with and without heat generation. Steady state conduction; thermal resistance networks in planar, cylindrical and spherical systems; critical radius of insulation; extended surface heat transfer; fin effectiveness and efficiency; thermal insulation. Transient conduction in semi-infinite and finite media; lumped capacitance method. Introduction to numerical solution of heat conduction equations.

• Diffusion Mass Transfer :3 Lectures• Constitutive equations and definitions for

composition of binary mixtures; Fick's law of diffusion and binary diffusion coefficient; conservation equation for species; steady and transient diffusion; analogy to conduction heat transfer.

• Convection Heat Transfer :11 Lectures• Mechanism of convection; analogy of heat,

momentum and mass transport in moving fluids; th concept of transport in a boundary layer; similarity, scaling laws and analogy between momentum, heat and mass transfer; turbulence.

• External flows: flat plate in parallel flow; cylinder in cross flow; applications. Internal flows: concepts of mean velocity and mixing cup temperature; hydrodynamically and thermally fully developed and developing flows; energy balance; circular tubes -- laminar and

• turbulent flows. Free convection: governing parameters; external and internal flows; mixed convection.

• Boiling and Condensation :3 Lectures• Basic phenomena: boiling modes and boiling

curve; regimes in pool boiling; forced convection boiling; regimes of flow for forced convection boiling in a tube; condensation: film and drop-wise condensation: applications.

• Heat Exchangers ;4 Lectures• Heat exchanger types; definition of overall

heat transfer coefficient; heat exchanger analysis: rating and sizing of heat exchangers; Log mean temperature difference method; Number of Transfer Units – effectiveness method; compact heat exchangers.

• Radiation Heat Transfer :10 Lectures• Basic concepts and definitions: Intensity, emissive power, irradiationand radiosity; black body radiation and spectral dependence of emissive power; emissivity absorptivity and reflectivity; Kirchhoff's law; gray and diffuse surfaces; Radiative Exchange: view factor; black body radiation exchange; exchange between gray, diffuse surfaces; gas radiation; radiation combined with conduction and convection.

BOOKS

• Fundamentals of Heat and Mass Transfer (Fifth edition): Incropera F.P. and De Witt, D.P.

• Heat Transfer -- a practical approach Cengel Y.

• Heat Transfer (Ninth edition): Holman J.P.

• Fundamentals of Heat & Mass Transfer: M. Thirumaleshwar.

• Heat Transfer: Kreith F. and Bohn

What is Heat Transfer?

• Thermal energy is related to the temperature of matter. • For a given material and mass, the higher the temperature, the

greater its thermal energy. • Heat transfer is a study of the exchange of thermal energy

through a body or between bodies which occurs when there is a temperature difference.

• When two bodies are at different temperatures, thermal energy transfers from the one with higher temperature to the one with lower temperature.

• Heat always transfers from hot to cold. • Heat is typically given the symbol Q, and is expressed in joules

(J) in SI units. • The rate of heat transfer is measured in watts (W), equal to joules

per second, and is denoted by q. • The heat flux, or the rate of heat transfer per unit area, is

measured in watts per area (W/m2), and uses q" for the symbol.