STUDY4MECHANICAL for Mechanical Engineers

What is isentropic process? In thermodynamic process, an isentropic process is an idealized process that is both adiabatic and reversible. Isentropic is the process in which the entropy is constant so it is also called constant entropy process. Thus, ∆S = 0 .  Example of the isentropic process: Pump, Gas compressor, Turbine, Nozzles, Diffusers are some example and follows the isentropic process of thermodynamics.  Theoretical explanation: According to first law of thermodynamics,  H = U + P V d H = d Q + V d P   OR   d H = T d S + V d P In this equation, V d P is a flow process work. Where d P is a change in pressure.  Now, at constant entropy, the enthalpy change equals to the isentropic process.  Thus, d Q = 0.    So, d H = V d P  Therefore, W = H2 - H1 = Cp ( T2 - T1) 

In the subject thermodynamics, there are two often discussed concepts that are mostly used in many industrial practical applications. These concepts are the adiabatic and isothermal processes. Both of these processes are opposite sides of the coin. Before we start our discussion on the difference between them. First of all, we must know what is the adiabatic process? and what is the isothermal process? What is the adiabatic process? A process without transfer of heat or mass between a thermodynamic system and surroundings.  An adiabatic process, in which the working substance neither receives nor given out heat or mass to the surroundings, during the expansion or compression is called an adiabatic process. What is the isothermal process? The process in which the temperature of the working substance remains constant during its expansion or compression is called isothermal or constant-temperature process. Difference between adiabatic and isothermal process:  Work

A process without transfer of heat or mass between a thermodynamic system and surroundings. Thus, Q = 0 is called the adiabatic process and such a system is said to be an adiabatically isolated system. Unlike an isothermal process, an adiabatic process transfer energy to the surrounding called work done.  What is the adiabatic process? An adiabatic process, in which the working substance neither receives nor given out heat or mass to the surroundings, during the expansion or compression is called an adiabatic process. In the adiabatic process following point is important.  No heat leaves or enters the gas The internal energy of the gas changes is equal to the work done. The temperature of the gas changes equal to the work done.  Now, let us check what is an adiabatic expansion and adiabatic compression process? What is adiabatic expansion? The process when an ideal behaviour for a closed system, in which the pressure remains constant and temperature decreasing

A constant temperature process is also called isothermal process is one type of thermodynamic process during the temperature is constant. The term isothermal is derived from the Greek word 'ISO' means constant or equal and "THERM' means temperature.  What is the constant temperature isothermal process? The process in which the temperature of the working substance remains constant during its expansion or compression is called isothermal or constant-temperature process. This will happens under isothermal conditions such as melting or evaporation these two are phase changes isothermal processes. The working substance remains in perfect thermal contact with the surroundings so that the heat sucked in or squeezed out is compensated exactly for the mechanical work done by or on the gas respectively. So, it is obvious that in an isothermal process two things happen which are noted below.  There is no change in temperature There is no change in internal ene

A constant pressure process is also called the isobaric process is one type of  thermodynamic process  during the pressure stays constant. The term isochoric is derived from the Greek word 'ISO' means constant or equal and 'BAR' means pressure.  What is the constant pressure isobaric process? When the gas is heated at constant pressure, it raises its temperature and volume. Since there is a change in its volume the heat supplied is utilized in increasing the internal energy and also doing some external work. This process is governed by Charle's Law.  Thus, Isochoric process is one in which  ∆P =  0  Example of Isobaric process:  The heating of water in an open vessel and the expansion of a gas in a cylinder with a freely moving piston is an example of this process.   Theoretical explanation: PV diagram for an Isobaric process Now, from the above figure m kg of gas is heated at constant pressure fro

A constant volume process is also called the isochoric process, an isovolumetric process is one type of thermodynamic process during the volume of a closed system is constant. The term isochoric is derived from the Greek word 'ISO' means constant or equal and 'CHORIC' means space or volume.  What is the constant volume isochoric process? When the gas is heated at constant volume, its pressure and temperature will increase. Since we take volume constant no change in volume, thus no external work is done by the gas. All the heat supplied is stored in the body of gas in the form of internal energy. This process is governed by Gay-Lussac Law.  Thus, Isochoric process is one in which  V f = V i (  ∆V =  0 dv = 0) Example of Isochoric process:  The gas is heated in a closed cylinder is an example of the isochoric process.  Theoretical explanation: PV diagram for an isochoric process Now, from the above figure m

The heating and cooling process of a gas is defined as a thermodynamic process of a perfect gas. During the thermodynamic process, change takes place in different properties of the gas such as pressure, temperature, volume, specific enthalpy, specific energy etc. Now let us discuss the types of thermodynamic process of perfect gases in this article.  List of thermodynamic process:  Constant volume process OR Isochoric process Constant pressure process OR Isobaric process Constant temperature process OR Isothermal process Adiabatic process    Constant entropy process OR Isentropic process Polytropic process Hyperbolic process Free expansion process Throttling process

In this article, you will learn the relations between two specific heats Cp and Cv.  Relations between specific heats:  The difference between two specific heats is equal to a gas constant.  Cp - Cv = R  The ratio of two specific heats is known as an adiabatic index and it denoted as ϒ. We know above equation, Cp - Cv = R  Cp / Cv = 1 + R / Cv  Now we take Cp / Cv =  ϒ ϒ = 1 + R / Cv As we have seen in the article  Why is the specific heat at constant pressure greater than specific heat at constant volume? We all know that Cp is always greater than Cv therefore the value of  ϒ is always greater than unity.  The value of  ϒ for air is 1.4. 

Basic Explanation:  When a gas is heated at constant pressure, the heat supplied to the gas is utilized in the following ways.  To raise the temperature of the gas. The heat remains within the body and represents the increase in internal energy. dU = m Cv (T2-T1)  To do some external work during expansion. W = p (V2-V1) = m R (T2-T1) Thus, specific heat at constant pressure is greater the specific heat at constant volume. Mathematical Explanation:  According to the first law of thermodynamics   Q = ΔU + W Where, (W= P ΔV ) Internal energy measures the temperature of the body.  At constant volume as there is no work done on the gas so  ΔV = 0. All the heat supplied utilize an increase in internal energy. Hence, the temperature of the body increases with less supply of heat. Whereas, at constant pressure, the supply of heat accounts for both internal energy and gas work. Thus, more heat is required to increase the temperature.  Thus, Cp >

Definition of specific heat: The amount of heat per unit mass required to raise the temperature by one degree Celcius is called specific heat. It is denoted as c. All the solids and liquids have only one specific heat and gas can have any number of specific heat depending upon conditions, under which it is heated.  Types of specific heat: Specific heat at constant volume  Specific heat at constant pressure Specific heat at constant volume: The amount of heat required to raise the temperature of a unit mass of gas by one degree Celcius is called specific heat at constant volume. It is denoted by Cv.  Formula: The total heat supplied to the gas at constant volume is given below.  Q = Mass × Rise in temperature × Specific heat at constant volume Q = m ×(T2 - T1) × Cv  Where m = mass of the gas T1 = Initial temperature of the gas T2 = Final temperature of the gas When specific heat at constant volume Cv is multiplied by the molecular

The universal gas constant is also called molar constant. It is generally denoted as Ru. It is the product of a gas constant and the molecular mass of the gas.  Ru = R M  Where R = Gas constant M = Molecular mass of gas expressed in kg mol In general, we take the different molecular mass of the different gas such as M1, M2, M3 and R1, R2, R3 are their gas constant respectively. So, we conclude that  M1 R1 = M2 R2 = M3 R3 Important Notes:  The value of Ru is same for all the gas.  SI Unit of Ru is 8314 J / kg mol K or 8.314 kJ / kg mol K 

The principle of Joule's law is that at a constant temperature the internal energy of an ideal gas is independent of volume.  Statement of Joule's Law: The change of internal energy of a perfect gas is directly proportional to the change of temperature.  Let we see above statement in mathematical form. Formula: dE ∞ dT or dE = m c dT Where m = mass of the gas c = Constant of proportionality, also known as specific heat Notes: We see that its internal energy, as well as temperature, does not change as the gas expands, without doing any external work and without taking in or giving our heat.