DR. T. THIMMAIAH INSTITUTE OF
TECHNOLOGY
Oorgaum, Kolar Gold Fields, Karnataka - 563120
(Affiliated to VTU, Belgaum, Approved by AICTE - New Delhi)
Estd. 1986

Heat flow takes place when there is a temperature gradient in a system.
Hence it becomes necessary to study heat transfer as well as temperature
distribution in various systems. Analysis of heat transfer for example is the first
step in the design of heat exchangers, boilers, heaters, refrigerators and radiators.
Further modern electric and electronic equipment require efficient dissipation of
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Thermal diffusivity is the measure of the ratio of heat conducted to the heat
stored and consequently can be used qualitatively to predict how fast the
temperature of the body changes. A material having a lower value of will show a
lower rate of temperature change than that with a higher value of .

In chapter 2 while deriving the equation, the thermal conductivity k, was
assumed as constant. This assumption is justified for materials involving only
small temperature differences across them. However, it is seen that in practice,
the thermal conductivity of most materials depends on temperature.

The addition of insulation on plane wall surface will not affect the surface
area of heat transfer, but for pipes and spherical surfaces, the addition of
insulation thickness increases the outside surface of heat transfer. Due to this
increase in surface area, heat transfer rate increases. The increase in heat transfer
rate depends on outside radius of insulation, i.e., heat transfer rate incr
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The heat transfer from a heated surface to the ambient is given by the
relation q = hA (T). In this relation “h” is heat transfer coefficient. T is the
temperature difference, A is surface area of heat transfer. To increase the value of
q, h may be increased or surface area may be increased. In some place it is not
possible to increase the value of heat transfer coefficient and
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The lumped parameter analysis presumes that a solid possesses infinitely
large thermal conductivity. Internal conduction resistance is then so small
that heat flow to and from the solid is controlled primarily by the convective
resistance. Temperature gradients are negligible within the sold. Consequently the
solid is spacewise isothermal i.e., T = f(t) only. Typical examples of the type flow
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Numerical heat transfer is the procedures to solve for the solution, on a
computer. A set of algebraic equations that approximate the differential and
integral equations describing conduction, convection and / or radiation heat
transfer can be solved.
The objective of any heat transfer calculation is the determination of the rate
of heat transfer to or from some surface or object. In conducti
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Thermal radiation is the energy emitted by matter that is at finite
temperature. The emission may occur not only from solid surfaces, but also from
liquids and gases. The emission may be attributed to changes in electron
configurations of the constituent atoms or molecules. The radiation energy is
transported by electromagnetic waves or alternately photons. The energy transfer
by conduction o
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The rate of heat transfer in convection is given by q = hA T, where h is the
convective heat transfer coefficient or film coefficient of heat transfer, “h” depends
upon the fluid properties, type of flow and geometry of the surface.
Convection heat transfer occurs by the movement of fluid particles. If the
motion of fluid particles occurs by the variation of density of fluid due to
te
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In the previous chapter, the fundamentals of convection was discussed. In
this chapter, the method of computing heat transfer rates in forced convection
problems related to both external and internal flows will be discussed.
First force convection concerning flow over external surfaces such as
flat plate, cylinders, spheres and flow across tube banks will be considered.
Further problems conce
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The mechanism of heat transfer in natural convection involves the motion of
fluid particles past a solid boundary which is a result of the density differences
resulting from the energy exchange. As a result the heat transfer coefficients will
vary with geometry of a system.

The heat transfer processes discussed in the earlier chapters were restricted
to homogeneous single phase systems. However in engineering practice, the
processes involving a phase change, like boiling and condensation are also
important. Boilers and condensers are essential components of modern thermal
power plants and so are the evaporators and condensers in a vapour compression
refrigeratio
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Heat exchanger is a device or equipment used to transfer heat from one fluid
to another which are at different temperatures. Heat exchangers are widely used
in many industrial applications where heat has to be transferred from one flowing
fluid to another through a solid barrier separating them. The specific applications
of heat exchangers may be found in space heating and air conditioning, po
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