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Jose Angel S.
Dr.-Ing, MSc, Chemical Engineering Engineering Tutoring for understanding & success
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Physics (Heat Transfer)
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Question:

When is the overall heat transfer coefficient (U) in a shell and tube heat exchanger almost equal than the heat transfer convection coefficient of the shell side, hshell?

Jose Angel S.

If the heat transfer coefficient for the tube side, htube, is very large comparing to the heat transfer coefficient of the shell side, hshell, it is said that the shell resistance to heat transfer controls the energy transport, therefore the overall heat transfer coefficient (U) is almost identical for practical purposes to the heat transfer convection coefficient of the shell side,

Physics (Fluid Mechanics)
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Question:

What does the Linear Momentum Conservation Principle say for the case of an arbitraty pipe (one entry-one exit) expressed in terms of the measured pressure drop?

Jose Angel S.

This principle states that the pressure drop existing between two points in a arbitrary pipe has three components: - the pressure change due to change in elevation - the pressure change due to acceleration (velocity changes) - the pressure change due to friction effects

Chemical Engineering
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Question:

Is it correct to say that a process stream entering an equipment, for example a reactor or a distillation tower, has an absolute enthalpy value?

Jose Angel S.

Yes and not!!!! Enthalpy absolute values actually does not exists, but...... in many actual applications, in particular in process simulation software it is usual and usefull to give an "absolute" enthalpy value to each stream, i.e. the stream entering the equipment has a given composition, a pressure and a temperature, therefore all its properties are given and for having an "absolute" value for enthalpy, a reference is chosen for all components..... It is particularly useful to establish the elements at 25 C and 1 atm as reference; doing so, the entalpy at refernece is set to zero at any enthalpy difference between reference and actual thermodynamic state is computed as the involved enthalpy to go from reference state (ho= 0) to actual state (h = h) is delta h (delta h = h - ho = h - 0 = h).... in this form the apparent "absolute" enthalpy appears and spreadsheet calculations are straightforward

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