Degrees of freedom, steady and unsteady balances, recycle and purge, reactive systems, humidity and combustion.
44 cards · basic cards · AI-written, checked twice. Edit anything.
- What is degrees of freedom in process calculations?
Show answer
The number of independent variables that must be specified to completely define the state of a system.- Write the degrees of freedom equation.
Show answer
DOF = N - E, where N is the number of variables and E is the number of independent equations.- What does DOF = 0 mean for a process?
Show answer
The system is completely specified and can be solved with the available information.- What does DOF > 0 indicate?
Show answer
The system is under-specified; additional information or constraints are needed.- List typical types of equations counted in DOF analysis.
Show answer
Material balances, energy balances, equilibrium relations, physical property relations, and stoichiometric equations.- In steady-state operation, which term in the general balance equation equals zero?
Show answer
The accumulation term (dM/dt or dE/dt) equals zero because system properties do not change with time.- Write the steady-state material balance equation for a flow process.
Show answer
Input mass rate = Output mass rate, or sum of mass in = sum of mass out.- Write the steady-state energy balance equation for a flow process.
Show answer
Energy in + work in = Energy out + work out, or in rate form: rate in + rate of work in = rate out + rate of work out.- When can steady-state assumptions be applied?
Show answer
When operating conditions do not change with time and the system has reached equilibrium after startup.- What is unsteady-state operation?
Show answer
Operation where system properties or conditions change with time, so the accumulation term in the balance is not zero.- Give three examples of unsteady-state processes.
Show answer
Filling or draining a tank, batch reactions, and system startup or shutdown.- In unsteady-state balances, what term represents accumulation?
Show answer
The accumulation term dM/dt or dE/dt, representing the rate of change of mass or energy in the system with respect to time.- What initial condition is required to solve unsteady-state balance differential equations?
Show answer
The initial amount, concentration, or temperature of the material or energy in the system at time t = 0.- What is a recycle stream in a process?
Show answer
A portion of the outlet stream that is returned to the inlet and mixed with fresh feed.- Name three reasons to use recycle in a process.
Show answer
To improve conversion of reactants, recover valuable unreacted material, or increase selectivity to desired products.
FlashKeepers