Heat Engine and Heat Pumps
One of the most important things we can do with heat is to use it to do work. Do you know how a heat engine or a pump works? Well, let us see how heat engines and heat pumps operate in terms of thermodynamics.
A heat engine involves a thermodynamic process that converts the heat supply in it into mechanical work. Let’s look at the types of heat engines.
· Internal combustion engine
· Gas turbine
There are three main parts in an engine. A hot body called source, a working substance, and a body called sink.
Source : There must be the source of heat of infinite thermal capacity, and that should be at a constant high temperature so that if any amount of heat is withdrawn from it or given to it, that does not affect its temperature.
Working Substance : It must be some substance through which the heat is absorbed or rejected into the sink. This is the working substance.
Sink : There must be a sink of finite thermal capacity, and that should be at a constant high temperature so that if any amount of heat is withdrawn from it or given to it, that does not affect its temperature.
The efficiency ‘η’ of the heat engine is the ratio between its output of work to the heat supply of the heat engine. Let us derive an expression for the efficiency of a heat engine.
η =W/Q1
where, W is the work done by the engine and Q1 is the heat absorbed from the source. After each cycle, the engine returns to its original state so that it does not affect its internal energy.
ΔU = 0
W = Q1−Q2
Hence the engine efficiency is:
η =(Q1−Q2)/Q1
η = 1−Q2/Q1
so here efficiency will be 100% but in actual, this is not possible because there will be some loss of energy in the system. Hence for every engine, there is a limit for its efficiency. Gasoline and diesel engines, jet engines, and steam turbines that generate electricity are all examples of heat engines.
The heat pump is a device used to pump heat into the system.
The purpose of a heat pump is to transfer energy to a warm environment, such as interiors of a house in the winters. The great advantage of using a heat pump to keep your house warm rather than just burning fuel in a fireplace or furnace is that a heat pump supplies. It runs on electricity, so you can save substantially on the fuel consumption.
Heat pump warms air from one place to another, to where it is needed depending on the season. Even in the air that seems too cold, heat energy is present. When it’s cold outside, a heat pump extracts this outside heat and transfers it inside. When it’s warm outside, it reverses directions and acts like an air conditioner, removing heat from your home.
The disadvantage of a heat pump is that the work input is sometimes more expensive than simply burning fuel, especially if the work is provided by electrical energy.