Heat Exchangers-Introduction
Transcript of Heat Exchangers-Introduction
Heat Exchangers-Introduction
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Heat Exchangers-Introduction
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Heat Exchangers-Introduction
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Heat Exchangers-Types
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Heat Exchangers-Types
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Heat Exchangers--Types
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Heat Exchangers-Types
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Heat Exchangers
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Heat Exchangers-Overall Heat Transfer Coefficient (U)
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Heat Exchangers-Overall Heat Transfer Coefficient (U)
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Heat Exchangers-Overall Heat Transfer Coefficient (U)
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Heat Exchangers-Overall Heat Transfer Coefficient (U)
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Heat Exchangers-Fouling Factor (Rf)
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Heat Exchangers-Fouling Factor (Rf)
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Heat Exchangers-Overall Heat Transfer Coefficient (U)
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Fouling factors must be obtained experimentally by determining the values of U for
both clean and dirty conditions in the heat exchanger. The fouling factor is thus
defined as
Heat Exchangers-Fouling Factor (Rf)
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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The above derivation for LMTD involves two important assumptions:
(1) the fluid specific heats do not vary with temperature, and (2) the
convection heat-transfer coefficients are constant throughout the heat
exchanger. The second assumption is usually the more
serious one because of entrance effects, fluid viscosity, and thermal-
conductivity changes, etc. Numerical methods must normally be
employed to correct for these effects. If a heat exchanger other than the
double-pipe type is used, the heat transfer is calculated by using a
correction factor applied to the LMTD for a counter flow double-pipe
arrangement with the same hot and cold fluid temperatures.
Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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Heat Exchangers-LMTD
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The LMTD approach to heat-exchanger analysis is useful when the inlet and
outlet temperatures are known or are easily determined. The LMTD is then easily
calculated, and the heat flow, surface area, or overall heat-transfer coefficient may
be determined. When the inlet or exit temperatures are to be evaluated for a given
heat exchanger, the analysis frequently involves an iterative procedure because of
the logarithmic function in the LMTD. In these cases the analysis is performed
more easily by utilizing a method based on the effectiveness of the heat
exchanger in transferring a given amount of heat. The effectiveness method also
offers many advantages for analysis of problems in which a comparison between
various types of heat exchangers must be made for purposes of selecting the type
best suited to accomplish a particular heat-transfer objective.
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