You need to prepare to perform a First Law analysis on a device. The device contains 2 inlets and one outlet. The device is very large, with the two inlets located ~30 m above the outlet. There is a mechanical shaft entering the system, which the operator informs you is to aid in the mixing of the two fluids. The operators informs you that the flow rates used in this system are low, despite the large size of the system. The operator informs you that the device operates in a steady manner. Beginning with the general equation for the First Law of Thermodynamics, develop a simplified expression that should be suitable for use with this device.
What will be an ideal response?
From the information given and observations, one should assume
(1) The device has multiple inlets and one outlet – open system
(2) Potential energy may be significant
(3) Work is present
(4) The system can be interpreted as steady-state, steady-flow
(5) The low flow rates suggest kinetic energy is not significant
Therefore, starting with the general first law on a rate basis:
dE/dt = 0
All V = 0
Consider the two inlets to be states 1 and 2, and the outlet to be state 3:
Q??W?= m? 3(h3 + gz3) ? {m? 1(h1 + gz1) + m? 2(h2 + gz2)}
with m? 3 = m? 1 + m? 2
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