ENG1010 â Process Systems Analysis Summary Notes
ENG1010 – Process Systems Analysis Summary Notes Contents Introduction to Proc. Sys. Anal.......................................................................................... 2 The Balance Equation ............................................................................................................ 2 Mass Balance ......................................................................................................................... 2 Reactions and Reactors.......................................................................................................... 2 CSTR ....................................................................................................................................... 4 Energy Balance ................................................................................................................. 4 Calculating ∆H .................................................................................................................. 6 Heating ................................................................................................................................... 6 Phase Change ......................................................................................................................... 6 Chemical Reaction.................................................................................................................. 7 Cycles ..................................................................................................................................... 7 Mechanical Energy Balance ................................................................................................... 8 Heat Transfer ................................................................................................................... 9 Mechanics of Heat Transfer ................................................................................................... 9 Energy Balance for Heat Transfer .......................................................................................... 9 Heat Transfer by Conduction ................................................................................................. 9 Heat Transfer by Convection ............................................................................................... 10 Combined Conduction and Convection ............................................................................... 11 Heat Exchangers................................................................................................................... 12 Prediction of Film Transfer Coefficients .............................................................................. 13 Heat Transfer in CSTR .......................................................................................................... 13
Finn Andersen, 2011
1
Introduction to Proc. Sys. Anal The Balance Equation For either amount over time interval or as rate per time, for an open or flow system: Accumulated in system
Into system from outside
Leaving system
Generated within system
Inputs and outputs can cross system boundary via two mechanisms: • •
Disappearance within system
Flow (convection) – NO flow in a closed system Diffusion (transfer)
In and Out terms in balance equation can be split into these two components. NO inputs or outputs for an isolated system.
Generation and disappearance can be due to: • •
Chemical reactions Conversion of energy (potential kinetic)
However there is NO generation or disappearance for conserved quantities e.g. total mass, total energy, linear momentum.
For systems in steady state (usually): 0 Mass Balance Matter cannot be transferred across system boundary and mass is a conserved quantity, so: , since dealing with steady state, simply: , effectively mass entering = mass leaving Reactions and Reactors There is disappearance/generation , so (quantities in kmole or kmole/hr etc):
Mass balances, moles not necessarily
Finn Andersen, 2011
2
Mechanical Energy Balance In steady flow systems with negligible heat flow and negligible internal energy changes due to chemical reaction or phase change:
Friction loss – fluid friction transforms useful energy into internal energy.
Specific work transferred from system to surroundings (work per kg)
Above equation can be divided through by g to express in terms of ‘head’. •
This changes dimension of equation to length and units to metres.
A simplified version called Bernouilli equation applies when: • • •
Friction loss is negligible No shaft work Fluid is incompressible (constant density)
When friction losses are involved: = 0 if no pumping/external work supplied & 2 ! " #$ % 2 KL value for different fittings given in table. Finn Andersen, 2011
' (
For laminar flow (Re < 2100),
16 &
For turbulent flow (Re > 2100) 0.079 & ./. 0 8
Finn Andersen, 2011
1
Introduction to Proc. Sys. Anal The Balance Equation For either amount over time interval or as rate per time, for an open or flow system: Accumulated in system
Into system from outside
Leaving system
Generated within system
Inputs and outputs can cross system boundary via two mechanisms: • •
Disappearance within system
Flow (convection) – NO flow in a closed system Diffusion (transfer)
In and Out terms in balance equation can be split into these two components. NO inputs or outputs for an isolated system.
Generation and disappearance can be due to: • •
Chemical reactions Conversion of energy (potential kinetic)
However there is NO generation or disappearance for conserved quantities e.g. total mass, total energy, linear momentum.
For systems in steady state (usually): 0 Mass Balance Matter cannot be transferred across system boundary and mass is a conserved quantity, so: , since dealing with steady state, simply: , effectively mass entering = mass leaving Reactions and Reactors There is disappearance/generation , so (quantities in kmole or kmole/hr etc):
Mass balances, moles not necessarily
Finn Andersen, 2011
2
Mechanical Energy Balance In steady flow systems with negligible heat flow and negligible internal energy changes due to chemical reaction or phase change:
Friction loss – fluid friction transforms useful energy into internal energy.
Specific work transferred from system to surroundings (work per kg)
Above equation can be divided through by g to express in terms of ‘head’. •
This changes dimension of equation to length and units to metres.
A simplified version called Bernouilli equation applies when: • • •
Friction loss is negligible No shaft work Fluid is incompressible (constant density)
When friction losses are involved: = 0 if no pumping/external work supplied & 2 ! " #$ % 2 KL value for different fittings given in table. Finn Andersen, 2011
' (
For laminar flow (Re < 2100),
16 &
For turbulent flow (Re > 2100) 0.079 & ./. 0 8
