This document is a summary of thermodynamics concepts prepared by Abu Umeer Chaman lal and submitted to Zulfiqar Solangi. It discusses the conservation of mass and energy principles for control volumes, and covers steady state and transient forms of the mass and energy rate balances. Specific topics covered include the one-dimensional flow form of the mass rate balance, the integral form, and the steady state form. Equations for the steady state mass and energy rate balances are presented.

1. Prepared by: Abu Umeer
Chaman lal
Submitted to: Zulfiqar Solangi
Subject: thermodynamics
Roll no:
14ch 42
14ch 39
Mehran
university
Faculty of
science
Chemical
department
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2. 1. Conservation of mass and
energy principles in control
volume.
2.. Steady state and transient
form of mass and energy rate
balances.
contents
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10. Forms of the mass and energy rate balance
The mass rate balance is a form that is
important for control volume analysis,
In many cases however, it is convenient to
apply the mass balance in forms suited to
particular objectives.
Some alternative form are as under,
1. One-dimensional flow form of the mass rate
balance .
2.Integral form of the mass rate balance
3.Stady state form of the mass rate balance
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11. STEADY STATE FORMS OF THE MASS
AND ENERGY RATE BALANCES
For a control volume at steady state, the
conditions of the mass within the control
volume and at the boundary do not vary
with time. The mass flow rates and the rates
of energy transfer by Heat and work are
also constant with time, there can be no
accumulation of mass within the
Control volume so,
dm/dt=o and the mass rate balance eq:
takes the form:
……… eq: 14/20/2015 11

12. Further more, at steady state de/dt=0 , so eq can be written as
… eq: 2
Alternatively,
………… eq: 3
Equation 1 asserts that at steady state the total rate at which
mass enters the control volume Equals the total rate at which
mass exits. Similarly, eq 3 asserts that the total rate at which
Energy is transferred into the control volume equals the total
rate at which energy is transferred out.
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13. many important application involve one-inlet,
one exit control volumes at steady State, it is
instructive to apply the mass and energy rate
balances to this special case.
The mass rate balance reduces simply to m1=m2
that is the mass flow rate must be the same At the
exit as it is at the inlet . The common mass flow
rate is designed simply by m . Next applying
The energy rate balance and factoring the mass flow
rate gives…
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14. or dividing by the mass flow rate.
…eq
5
The enthalpy, kinetic energy and
potential energy terms all appear in eq
5 as differences between their values
at the inlet and exit, this illustrates that
the datum used to assign values to
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15. In eq: 5, the ratio q/m and wln are rates of
energy transfer per unit mass flowing
through
The control volume.
the foregoing steady-state forms of
the energy rate balance relate only energy
Transfer quantities evaluated at the
boundary of the control volume. no details
concerning
Properties within the control volume are
required by, or can be determined with,
these
Equation when applying the energy rate
balance in any of its forms, it is necessary to4/20/2015 15