Etiket Arşivleri: Energy Balance
Mass and Energy Balances
In this chapter we will apply the conservation of mass and conservation of energy laws to open systems or control volumes of interest. The balances will be applied to steady and unsteady system such as tanks, turbines, pumps, and compressors.
4.1 Conservation of Mass
The general balance equation can be written as
Accumulation = Input + Generation – Output – Consumption
The terms (Generation – Consumption) are usually combined to call Generation with positive value for net generation and negative value for net consumption.
Material quantities, as they pass through processing operations, can be described by material balances. Such balances are statements on the conservation of mass. Similarly, energy quantities can be described by energy balances, which are statements on the conservation of energy. If there is no accumulation, what goes into a process must come out. This is true for batch operation. It is equally true for continuous operation over any chosen time interval.
Material and energy balances are very important in an industry. Material balances are fundamental to the control of processing, particularly in the control of yields of the products. The first material balances are determined in the exploratory stages of a new process, improved during pilot plant experiments when the process is being planned and tested, checked out when the plant is commissioned and then refined and maintained as a control instrument as production continues. When any changes occur in the process, the material balances need to be determined again. The increasing cost of energy has caused the industries to examine means of reducing energy consumption in processing. Energy balances are used in the examination of the various stages of a process, over the whole process and even extending over the total production system from the raw material to the finished product.