Introduction to Food Engineering

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Energy Balance

Learning Outcomes

At the end of this module, you will be able to:

  1. conduct an energy balance using first law of thermodynamics
  2. consider various forms of work interactions in an energy balance
  3. differentiate between sensible and latent heat
  4. conduct energy balance of an open system involing mass flow

In this module, we will use the first law of thermodynamics to obtain an expression for the change in energy for a closed system involving both heat and work. A mathematical development for this purpose will provide us with an expression for the change in enthalpy of a system, a term used widely in process calculations. In the next video, you will learn the steps in the mathematical derivation to get a fundamental understanding of the energy balance of a system.

There are various forms of work in closed systems such as work due to a moving boundary, gravitational forces, change in velocity, shaft rotation, and frictional forces. In the next video, you will learn about work interactions for each of these situations.

Now that you have learned the various energry terms in a clsoed system, we will write an energy balance.

In the next video, you will learn about sensible heating. This expression involves a thermal property of the system, namely specific heat capacity. You will also learn the difference between sensible heat and latent heat involved in phase change.

The previous videos were about closed systems. In the next video, we will learn how to conduct an energy balance for an open system. As we saw in the last module, in cases when mass flows across a system boundary, then the energy associated with the flow is flow work. These concepts will be later used in another module when we design a pumping system to cause the flow of liquids from one location to another.


In this module, you learned how to use the first law of thermodynamics to obtain the energy balance of a closed system. You derived an expression for enthalpy of a system, including sensible and latent heat. For an open system, you leaned about flow work associated with energy involved with the flow of mass.