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Showing posts with label Quiz. Show all posts
Showing posts with label Quiz. Show all posts

What would happen if compressor is removed from the refrigerator?

Simply, refrigerator would STOP! but why? 

To answer this question, one need to know the Second law of thermodynamics (Clausius Statement) which states "It is impossible to construct a heat pump which continuously takes away the heat from low temperature region to high temperature region without taking any external work". 

Here, heat pump is our refrigerator which keep on throwing heat from low temperature environment to room temperature. As per the above statement, external work is must to run the refrigerator. That external work is represented by "Compressor".

Second thing, to have heat transfer from evaporator to condenser, you need to  change the phase of the substance. The change of phase absorb or liberate the heat depending on the phase change. Thus, heat of food can be transferred to condenser by changing the liquid phase refrigerant to vapor phase in evaporator and this heat is rejected at condenser at room temperature. This task is performed by compressor by changing the pressure of the refrigerant.


Why overall efficiency of thermal power plant is very low?

Are you wondering why overall efficiency of thermal power plant is very low? Reason?

The major part of the electricity that world is producing nowadays comes from Thermal Power Plant (which works on Rankine Cycle or Modified Rankine Cycle).

The principal parts of the Thermal Power Plants are

  • Boiler (to generate steam from water)
  • Turbine (where the steam expands and produces the work in form of rotation of shaft which in turn rotate the generator)
  • Condenser (where major part of heat is rejected to convert steam into water for reuse)
  • Feed Pump (to pump back the feed water to boiler for steam conversion) 
All parts except the condenser have 80 % to 90 % efficiency. The only condenser has 50% efficiency. 

Overall Efficiency: Multiplication of all efficiency of plant's principal parts
Thus overall efficiency comes down to 30 % - 40 %

Online Mechanical Quiz-GPSC Assistant Professor 2015-16

This online quiz consists of some selected multiple choice questions from GPSC Entrance exam for Assistant professor Mechanical Engineering (Year 2015-16).

Appear for the quiz and get your score instantly.


Best books on Objective Questions in Mechanical Engineering

In today's competitive world, one has to come out of crowd and has to prove by SCORE in various competitive exams like State Public Service Commission (Like GPSC - Gujarat Public Service Commission in Gujarat), Graduate Aptitude Test in Engineering (GATE), Indian Engineering Services (IES) or any State, Centre level exams.

Difference between 'Thermodynamics' and 'Heat Transfer'

Thermodynamics and Heat Transfer both are part of thermal engineering and each has its own meaning and importance. Both deals with heat and energy then, one might ask, what is the real difference between the two subjects ? i.e. Thermodynamics and Heat Transfer

"Thermodynamics" deals with the amount of energy in form of heat or work during a process and only considers the end states in equilibrium. It will not give information about how long it will take to reach to the final state in equilibrium. While,




"Heat Transfer" deals with the rate of energy transfer thus, it gives idea of how long a heat transfer will occur? Heat transfer deals with time and non equilibrium phenomena. Heat can only transfer when there is a temperature gradient exists in a body and which is indication of non equilibrium phenomena.


In short, Thermodynamics gives "Why"  a process will occur and Heat Transfer will tell, "How" a process will occur when there is a concern about transfer of heat.

To support all these arguments, Thermodynamics uses following laws,

  • Zeroth Law of Thermodynamics
  • First law of Thermodynamics
  • Second Law of Thermodynamics
  • Third Law of Thermodynamics

While, Heat Transfer uses,

  • Fourier's Law (Heat conduction)
  • Newtons Law of Cooling (Heat convection)
  • Planck's Law (Thermal Radiation)
  • Stephan Boltzman's Law (Thermal Radiation)
  • Wein's Law (Thermal Radiation)
  • Kirchoff's Law (Thermal Radiation)
  • Lambart's Law (Thermal Radiation)
Learn more about such important questions to be asked in Mechanical Engineering Interview


Why compression ratio of petrol engine is kept low compared to diesel engine?

What is the need of high compression ratio? 

Today every machine is expected to give higher efficiency. When we talk about petrol engine and diesel engine whose thermal efficiency is directly related to 'compression ratio'. That means if we want to achieve higher thermal performance in terms of efficiency, we should provide high compression ratio for both the engine.

Quiz-2 Objective questions in mechanical engineering: Heat transfer

Get ready for the quiz on 'Heat Transfer' subject and check your knowledge by appearing for the test given below. By the end of the quiz, you will get your score out of 10 as well as answer keys. So, get ready to check your knowledge in basics of thermodynamics.

You need to enter Your Name & Passcode which is mechanicalduniya to enter into the quiz interface.

The quiz is based on following topics of Heat transfer

Quiz-1 Objective questions in mechanical engineering: Basic of thermodynamics-1

This is a multiple choice question quiz. To appear for the test, you need to enter following details at the quiz interface. 1. Your name and passcode i.e. thermotest

By the end of quiz, you will get your score out of 10 as well as answer keys. So, get ready to check your knowledge in basics of thermodynamics.