Factors Influencing Energy Transfer Efficiency

Instructor: Matthew Bergstresser
Energy is constantly be transferred from one form to another. In this lesson, we will discuss the factors that influence energy transfer efficiency. We will also cover the types of heat generated from energy transfer.

Energy Transfer

Imagine that you have to do three different activities in a short amount of time. The activities are:

  1. going for a swim
  2. painting your room
  3. going to a formal event

Transferring from one event to another takes time, but having to change attire takes more time. Think of the time taken to change attire as ''time lost'' during the transfer from one activity to another. This is an analogy for energy transfer and energy lost during the transfer. Whenever energy is transformed from one form to another, there is always a lost of energy, which reduces the efficiency of the energy transfer. Efficiency can be calculated by dividing energy output by energy input and multiplying that quotient by 100. Let's go through some examples of energy loss.

Electrical Energy Transfer

It is quite amazing that when we flip a light switch in our residence or at work a light comes on. The journey this electrical energy took is quite impressive. Let's look at where it started and trace it to our light bulb noting the energy loss along the way. Let's use a nuclear reactor as the starting point for the electrical energy.

Nuclear Power Plant

Radioactive uranium-235 is used in a nuclear power plant to generate high energy steam. This means the energy starts as nuclear energy, or the energy stored in the nucleus of the atom. When the atom splits, heat energy is released and is used to heat water that moves through a series of pipes and eventually turns into steam. The hot water loses heat to the pipes themselves, which is the transfer of heat through conduction. Conduction is the transfer of heat through physical contact.

The steam turns a turbine, which generates kinetic energy. Kinetic energy is the energy of moving objects. When the turbine turns, it generates more thermal energy through friction. Any energy that is not used to turn the turbine is considered lost, which lowers the efficiency of the transfer. The rotating turbine makes wire bundles rotate in a magnetic field generating electrical energy. The energy efficiency of a nuclear power plant is just over 40% efficient. The next step in the energy transfer is moving electrical current through the electrical power lines.

Turbine from a nuclear power plant
turbine

Power Lines

When current moves through power lines, friction is generated by the moving electrons. Friction always generates heat and this heat is lost to the air surrounding the power lines. The transfer of heat through a fluid such as air (in this case), is called convection. Let's fast forward to the lit light bulb that was turned on when we flipped the light switch.

Heat energy is lost from from the power lines through convection
power_lines

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