Engineering Thermodynamics Part 1Published on 24/2/2012 & updated on Thursday 10th of May 2018 at 07:12:31 PM
Science of thermodynamics exists since 19th century and from that time scientists and engineers are making constant and continuous effort of making it as user-friendly as possible. The objective of this section is to throw some light on the art of changing energy available from the sources of fuel like fossil fuel and nuclear fuel in to more usable forms like electrical energy and heat ventilation and air conditioning through the understanding of important concepts of thermodynamics.
Fundamentals of ThermodynamicsThe word thermodynamics is derived from the Greek word theme (means heat) and dynamics (means force). Engineering professionals are interested in studying systems and their interaction with the surroundings. Concepts/Definitions used in this section are helpful for readers in understanding the concept of engineering thermodynamics which is also called Heat-Power Engineering.
System, Surrounding and UniverseSystem is something which we want to study and interested in, thus the first step is to fix precisely the objective of system study. The objective system study can be improving the efficiency of the system or to reduce the losses etc. Example of System can be to analyse the refrigeration cycle in cold storage plant or to analyse the Rankine cycle in power plant. System is defined as a definite mass of pure substance bounded by a closed or flexible surface; similarly the composition of matter inside the system can be fixed or variable depending upon the cycle.
System dimensions need not to be necessarily constant (like air in a compressor is compressed by a piston) it can be variable (like inflated balloon). Matter which interacts with the system externally is called Surrounding and Universe is the outcome of system and surrounding. The element which separates the system from its surrounding is called boundary. Boundary of the system can be fixed or in motion. The interaction between the system and the surrounding takes place by crossing the boundary and thus plays a very important role in thermodynamics (heat and power engineering).
Type of SystemsThere are basic two types of system:
- Closed System or Control Mass: is associated with the definite quantity of matter. Unlike open system in closed system there is no mass flow of matter occurs across the boundary of the system. There is also a special type of closed system which does not interact and isolated itself from the surrounding is called an isolated system.
- Control Volume (Open System): Control volume is limited to a region of space through which mass and energy can flow and cross the boundary of the system. The boundary of a open system is called a controlled surface; this controlled surface can be actual or unreal. Examples of control volume are the equipments that involve flow of mass to cross the boundary of the system like flow of water through pumps, steam flow in turbines and air flow through air compressors.
Microscopic ThermodynamicsMicroscopic approach in thermodynamics is also called statistical thermodynamics and is associated with the structure of matter and the objective of the statistical thermodynamics is to characterize the average behaviour of the particle making up the system of interest and in turn used this information to observe the macroscopic behaviour of the system.
Property, State and Process
PropertyA Property is macroscopic characteristic of a system. Value of property can be assigned at any given time without the knowledge of previous value and its behaviour.
Extensive PropertyProperties that are dependent on mass are called extensive properties and its value for the overall system is the summation of its values for the parts into which the system is divided. Examples of extensive property are Volume, Energy and mass. Extensive property depends upon the size of a system and it can change with time.
Intensive PropertyIn contrast to the Extensive property, intensive property is not mass dependent and non additive in nature and does not depend upon on the total size of the system. It can vary at different places within the system at any moment. Examples of intensive property are pressure and temperature.
StateA state is defined as the condition of a system which is best described by its properties. The mass enclosed in system can be found in a variety of the unique conditions, called state. There are relations among the properties of a system but the state can be specified by providing value of a subset of the properties.
ProcessProcesses are the conversion of one state to another state. If the value of the macroscopic property of the in a system at two different time are identical then the system is said to be in a same state at that time. Steady state condition of the system is achieved if none of its properties changes with respect to time.
System Equilibrium CycleA thermodynamic system equilibrium cycle is a sequential process that starts and terminates with the condition of same state. When the cycle completes then it’s all properties are having the same value what they were at the beginning. All cycles that repeats regularly plays vital role in many areas of application, like circulation of condensate in a thermal power generating station executes a cycle.
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