The energy losses in pneumatic conveying are supplied by the change of the total internal energy of the conveying gas.
The total energy of the conveying gas is given by the enthalpy.
Enthalpy (H) = the total energy of the gas.
Enthalpy of a gas is the sum of internal energy (U) and the energy to create the system.
d(H)=dQ+Vdp
This formula expresses that:
- d(H is the change in internal energy (enthalpy) of the gas
- In case of dQ=0 (no heat exchange with the surroundings) the work done by the conveying system the equation Vdp is represented by the change in total energy of the conveying gas.
Using this formula, equalizing the change in enthalpy of the gas to the involved energies of the pneumatic conveying process (acceleration (kinetic), elevating, , suspension and material resistance, gas resistance + additional losses)) and correcting for the actual heat exchange with between the gas and the conveyed product, the surroundings and the actual work done by the gas (expansion) in time increments d(time), the pneumatic conveying calculation is executed.
The heat balance between the conveying gas and the material and the surroundings are to be accounted for, whereby some of the conveying energy losses are directly converted into heat.
If that heat exchange did not exist, the expansion of air from 2 barg at 50 degrC (3 bara) to atmospheric (1 bara) would result in a temperature of -37 degrC.
In reality, this is not happening, because the conveyed particles, the surroundings and the friction heat up the gas to approx. the particle temperature, resulting in a mixture conveying temperature close to isothermal in most cases, but not always.
The conveying energy of a pneumatic conveying system is for a considerable part delivered by the conveyed material itself, due to the higher heat content of the material, compared to the conveying gas.
When calculating a pneumatic conveying system, the temperature along the pipeline normally decreases (influenced by the ambient temperature and the degree of insulation of the pipeline), influencing the gas pressure along the pipeline and thereby the gas velocity and the material velocity and the pressure drops.
Temperature and heat exchange can not be ignored in a pneumatic conveying calculation algorithm. ■
Energy theorem pneumatic conveying calculations.
The energy losses in pneumatic conveying are supplied by the change of the total internal energy of the conveying gas.
The total energy of the conveying gas is given by the enthalpy.
Enthalpy (H) = the total energy of the gas.
Enthalpy of a gas is the sum of internal energy (U) and the energy to create the system.
d(H)=dQ+Vdp
This formula expresses that:
- d(H is the change in internal energy (enthalpy) of the gas
- In case of dQ=0 (no heat exchange with the surroundings) the work done by the conveying system the equation Vdp is represented by the change in total energy of the conveying gas.
Using this formula, equalizing the change in enthalpy of the gas to the involved energies of the pneumatic conveying process (acceleration (kinetic), elevating, , suspension and material resistance, gas resistance + additional losses)) and correcting for the actual heat exchange with between the gas and the conveyed product, the surroundings and the actual work done by the gas (expansion) in time increments d(time), the pneumatic conveying calculation is executed.
The heat balance between the conveying gas and the material and the surroundings are to be accounted for, whereby some of the conveying energy losses are directly converted into heat.
If that heat exchange did not exist, the expansion of air from 2 barg at 50 degrC (3 bara) to atmospheric (1 bara) would result in a temperature of -37 degrC.
In reality, this is not happening, because the conveyed particles, the surroundings and the friction heat up the gas to approx. the particle temperature, resulting in a mixture conveying temperature close to isothermal in most cases, but not always.
The conveying energy of a pneumatic conveying system is for a considerable part delivered by the conveyed material itself, due to the higher heat content of the material, compared to the conveying gas.
When calculating a pneumatic conveying system, the temperature along the pipeline normally decreases (influenced by the ambient temperature and the degree of insulation of the pipeline), influencing the gas pressure along the pipeline and thereby the gas velocity and the material velocity and the pressure drops.
Temperature and heat exchange can not be ignored in a pneumatic conveying calculation algorithm. ■
Teus