Thermodynamic Systems MCQ Quiz in தமிழ் - Objective Question with Answer for Thermodynamic Systems - இலவச PDF ஐப் பதிவிறக்கவும்

Concept:

The quantity of heat water contains is = ṁ × c_pw × T

If two streams are mixed together then the resulting stream will contain the summation of heat quantity of individual streams.

ṁc × Cpw × Tc + ṁh × Cpw × Th = (ṁh + ṁc) × Cpw × Texit

Where ṁ is the mass flow rate, C is the specific heat, and T is the temperature. 

Calculation:

Given for cold water, 

ṁ_c = 5 kg/min, T_c = 27°C = 300 K,

For hot water,

ṁ_h = 15 kg/min, T_h= 77°C = 350 K

Here both the fluids are water so the specific heat terms are removed from both sides of the equation, now the equation becomes

5 × 300 + 15 × 350 = 20 × T_exit

T_exit = 337.5 K = 64.5°C

Key Points:

Explanation:

A control volume is a fixed, identifiable region in space through which fluid flows. The boundary of the control volume is called a control surface.

• It is a system of fixed volume
• This type of system is usually referred to as an "open system” or a "control volume"
• Mass transfer can take place across a control volume
• Energy transfer may also occur into or out of the system
• A control volume can be seen as a fixed region across which mass and energy transfers are studied

But, there can be cases when you will need to have a moving control volume. 

• For example, if you wanted to analyze a jet engine or a rocket, you will need to use a moving control volume. 
• In certain cases, the control volume itself may even deform. Such as if you were analyzing a deflating balloon
  that was moving around a room after you let go of it. 
• Depending on what you are looking at, moving control volumes can become complex

System and Control Volume:

• In order to analyse the Engine, the control volume will have to move with the engine at the same velocity.
• When you are solving this type of problem you will need to realize that there is a relative velocity as well as an absolute velocity. 
• As with a stationary control volume, there is a fluid that is moving through the control volume. However, in this case, the control volume is moving. 
  Hence, the relative velocity of the fluid is the fluid moving through the control volume. 

So, Option (3) is the correct answer.

Concept:

For the isentropic process the relation is,

PV^γ  = Constant

Calculation:

Given:

Pressure increased = 0.5%, So P₂ = 1.005 P₁

For monoatomic γ  = 1.667

P₁V₁^1.667 = P₂V₂^1.667

P₁V₁^1.667 = 1.005 P₁ V₂^1.667

^{\(\frac{{{P_1}}}{{1.005{P_1}}} = {\left( {\frac{{{V_2}}}{{{V_1}}}} \right)^{1.667}}\)}

\({\left( {\frac{1}{{1.005}}} \right)^{\frac{1}{{1.667}}}} = \left( {\frac{{{V_2}}}{{{V_1}}}} \right)\)

(0.995)^0.6 × V₁ = V₂

0.997 V₁ = V₂

V₂ = 99.7 % of V₁

The volume will decrease 0.3%.

Concept:

Intensive Property: These are the properties of system which are independent of mass under consideration. For e.g. Pressure, Temperature, Density

Extensive Properties: The properties which depend on the mass of system under consideration.

For e.g Internal Energy, Enthalpy, Volume, Entropy

Note: All specific properties are intensive properties. For e.g. specific volume, specific entropy etc.

Explanation:

Thermodynamic system:

• A thermodynamic system is a region of space containing a quantity of matter that is distinct from its surroundings and can be the subject of thermodynamic study.
• The study of thermodynamic systems is a fundamental part of thermodynamics, which is a branch of physics that deals with the relationships and transformations of energy within a system.

Thermodynamic systems are classified into different types:

Open System:

• In this type of system, both mass and energy, transfer takes place across the boundary of the system.
• Examples include pumps, compressors, reactors, distillation columns, heat exchangers, car radiators, etc.

Closed System:

• There is no mass transfer across the system boundary, but energy transfer takes place in or out of the system.
• Examples: A gas confined within a piston-cylinder arrangement, A hot water tank in a residential heating system, The combustion process that occurs within a car engine, A sealed container filled with a gas, The refrigeration cycle in a household refrigerator or air conditioner, etc.
• The contents of a pressure cooker on a stove with its lid tightly closed and the whistle in position is a closed system as no mass can enter or leave the pressure cooker, but heat can be transferred to it. 
• A bomb calorimeter only allows heat to be exchanged. Such a system is called closed.

Isolated system:

•  In an Isolated system, there is no mass and energy interaction across the system boundary i.e. Interaction between the system and the surroundings is absent.
• Therefore, mass and the energy of the isolated system are fixed e.g. Universe, A well-insulated thermos flask, Liquid nitrogen stored in a sealed and insulated container, etc.
• When a body of material starts from a non-equilibrium state of inhomogeneity or chemical non-equilibrium and is then isolated, it spontaneously evolves towards its own internal state of thermodynamic equilibrium.
•  It is not necessary that all aspects of internal thermodynamic equilibrium be reached simultaneously; some can be established before others. For example, in many cases of such evolution, internal mechanical equilibrium is established much more rapidly than the other aspects of the eventual thermodynamic equilibrium.

Explanation:

Intensive Property: These are the properties of the system which are independent of mass under consideration.

e.g. Pressure, Temperature, density, Specific enthalpy, Specific Volume, etc.

Extensive Properties: The properties which depend on the mass of the system under consideration.

e.g Mass, Internal Energy, Enthalpy, Volume, Entropy etc.

Note: All specific properties are intensive properties. For e.g. specific volume, specific entropy etc.

Explanation:

A thermodynamic system is defined as a quantity of matter or a region in a space upon which attention is concentrated in the analysis of a problem.

There are three classes of systems:

1. Closed system
2. Open system
3. Isolated system

Closed system: The system of fixed mass is called the closed system. There is no mass transfer across the system boundary. The energy transfer into or out of the system may happen. 

It is also called the Control Mass system.

The arrangement of piston-cylinder with a certain quantity of fluid is an example of a closed system.

Open system: The open system is one in which matter crosses the boundary of the system. The energy transfer into or out of the system may happen.

It is also called a Control Volume system.

Most of the engineering devices are open systems, Air compressors, turbines, pumps, etc. are examples of open systems.

Isolated system: The isolated system is one in which there is no interaction between the system and surroundings. It is of fixed mass and energy, and there is no mass or energy transfer across the system boundary.

A Thermo flask and Universe is an example of an isolated system.

Concept:

Open system: Both mass and energy interaction between the system and the surroundings

Ex: Boiler, Turbine, Condenser, Evaporator, Pump, Compressor, nozzle, diffuser

Closed system: Only Energy interaction between the system and the surroundings

Ex: Piston cylinder arrangement without valves

Isolated system: No mass and energy interaction:

Ex: Universe, Thermoflask

Explanation:

Closed System: There is no mass transfer across the system boundary but energy transfer takes place into or out of the system.

Open System: In this type of system both mass and energy transfer takes place across the boundary of the system.

Closed System: There is no mass transfer across the system boundary but energy transfer takes place into or out of the system.

Open System: In this type of system both mass and energy transfer takes place across the boundary of the system.