The basic concepts of thermodynamics in real-time applications

How to do thermodynamic analysis?

Introduction

The concepts of thermodynamic analysis are applied in many real time applications. One should have understood certain basic concepts so as to do thermodynamic analysis . Energy plays a vital role in many engineering and real time applications. There are so many forms of energy such as light energy, thermal energy, potential energy, kinetic energy, sound energy, magnetic energy, electrical energy, nuclear energy, chemical energy, flow energy or pressure energy. Energy can be transformed from one form to another without increase or decrease in total energy by the law of conservation of energy. This universal law is applied in thermodynamic analysis provided that the system obeys the concept of continuum. During this transformation of energy, the properties of the system change accordingly. For understanding the change of properties due to energy interaction, one must understand the concepts behind these.  This article helps to achieve it. This article exemplifies the terminology, classification of thermodynamic system. It focuses on the real time applications and energy transfer involved in it.

Terminology

2.1 System

A system is anything on which our study, thermodynamic analysis and attention is focused.  It may be a device, a component, an equipment, a machine or combination of these. A system can be combination of small sub-systems.

2.2 Surroundings

Anything external to the system which is influenced by the changes in properties of the system is termed ‘surroundings’ or ‘environment’. Surrounding can be another system or combination of systems.

2.3 Boundary

A layer which distinguishes the system from its surroundings is ‘boundary’. A working fluid exchanges energy from system or surroundings through the boundary, or vice-versa. The characteristics of boundary are listed below.

1. It can be fixed or movable or combination of both
2. It can be diabetic or adiabatic
3. It can be real or imaginary or combination of both
4. Its size, shape and volume can be varied.

2.4 Phase

If the working fluid has uniform chemical composition and physical structure throughout the system, it is said to exist in a single phase. There are three phases of matter, namely solid, liquid and gaseous phase.

2.5 Ways of changing the equilibrium condition

There are two ways to alter the equilibrium condition of a system viz., energy transfer and mass transfer.

1. Mass transfer: The flow of working substance(s) to the system/from the system or both occurs through the boundary of a system is called ‘mass transfer’. Total energy content of any system is increased or decreased either by adding or removing a certain mass of a substance into it or from it.
2. Energy transfer: Energy can also be transferred without transfer of mass. Energy can be transferred in two modes. Increase or decrease in energy may be of due to heat transfer or work transfer or both.

• Heat transfer: This occurs by virtue of temperature difference of the system and its surroundings and the rate of heat transfer is directly proportional to the magnitude of temperature difference. Heat transfer stops when there is no temperature difference i.e., both the system and its surroundings attain an equilibrium condition with each other.
• Work transfer: All modes of energy transfer that happens without the driving force of temperature difference is work transfer.

3. Classification

When a concept is classified, a better understanding of it is arrived at.

3.1 Based on the energy transfer involved

Thermodynamic system can be classified into three types.

1. Open system – Both mass and energy transfer cross the boundary. It is a fixed volume system. Control volume approach is used for thermodynamic analysis. Mass transfers into and out of the system.

Real-time applications	Considerations	Energy transfer involved
	System              – Gases in an incandescent lamp. Working fluid – Inert gases in it Boundary       – Body and the lid of the lamp	Work transfer and heat transfer
	System             – Blades with motor Working fluid – Air Boundary       – Cover of the fan	Work transfer
	System              – Pump with motor Working fluid  – Water Boundary         – Pump shell	Work transfer
	System              – Pump Working fluid – Water Boundary        – Enclosure of pump i.e outer body	Work transfer

2. Closed system – Only energy transfers through the boundary. It is a fixed mass system. Volume can change with a movable boundary.

Examples:

1. Incandescent bulb
2. Fluorescent lamp
3. Hurricane lamp
4. Petromax lamp
5. Automotive battery
6. Food items in a pressure cooker
7. Soap bubble
8. Electric iron
9. Hot boiled egg/Baked potato
10. Gas(es) trapped in a piston cylinder device
11. Induction stove
12. Bicycle dynamo lamp

The above real time applications are considered into thermodynamic analysis and the concepts involved in it are tabulated below.

Real-time application		Considerations	Energy transfer(s) involved
		System            – Gases in a Tube light or an incandescent lamp Working fluid – Inert gases Boundary        – the body and the terminals of the lamp	Work transfer and heat transfer
		System             – Air trapped inside a soap bubble or Gas entrapped in an insulated piston cylinder device Working fluid – Air or gas Boundary        – Soap film or Piston head and cylinder walls	Work transfer
		System             – Vapors of Kerosene in a Petromax lamp or Hurricane lamp Working fluid – Kerosene Boundary        – Enclosure	Heat transfer
		System            – Boiled egg or Potato Working fluid – Nutrients Boundary         – Egg shell or Peel of the Potato	Heat transfer
		System           – Food items entrapped in a pressure cooker or fixed quantity of milk in tea pan. Working fluid – Water and food items or milk Boundary         – Lid and walls of Pressure cooker or Tea pan	Heat transfer and work transfer
		System           – Automotive batteries or Old Bicycle dynamo lights Working fluid – Gases in the light or Battery electrolyte Boundary           – Enclosure	Heat transfer and work transfer

3. Isolated system- This system involves neither mass transfer nor energy transfer. It is isolated from its surrounding. It does not interact with the environment at all.

This is a special kind of closed system where energy transfer is also absent.

Example: Thermos flask, Ice box

      3.2 Based on the phase of the working fluid

1. Single Phase system – If the working fluid is in a single phase i.e either of three phases, then it is ‘Single Phase system’ or ‘Homogeneous system’.
2. Two phase system – If the working fluid is in two phase i.e either of three combinations (Solid-liquid, Solid-gas, Liquid-gas) then it is ‘Two Phase system’ or ‘Heterogeneous system’.
3. Three phase system – It is possible to have all the three phases co-exist in equilibrium condition at a particular state and such a system is three phase system.  In a freezer of a domestic refrigerator, solid ice, liquid water with its traces of vapour co-exists.

    3.3 Based on the heat transfer

1. Diabetic system – Heat transfer is allowed to and or from the system
2. Adiabatic system – Heat transfer is not allowed to and or from the system.

4.Conclusion

The concepts of energy transfer, system and its applications have been discussed with examples. First of all, it is to be clear how a system should be selected for thermodynamic analysis. The assumptions are usually made to simplify the analysis. It is significant to understand the type of system before applying thermodynamic laws and relations. Then, the kind of energy transfer involved in the change of state of system must be identified. After that, the laws and relations which are more relevant to the real-time applications can be applied and the required properties can be found out.