# Thermodynamics Interview Questions

Here are the top 50 commonly asked questions in Thermodynamics interviews. Whether you’re just starting your preparation or need a quick refresher, these questions and answers will help you tackle your interview with confidence.

## Basic Thermodynamics Interview Questions with Answers

### 1. What is a thermodynamic boundary?

A boundary that separates the system from the surrounding is called as thermodynamic boundary. It can be fixed or moveable.

### 2. What is work in thermodynamics?

Work is said to be done by the system if the sole effect on the things external to the system can be reduced to lifting of weight.

### 3. What is a heat engine in thermodynamics?

Heat engine is a cyclically operating thermodynamic device that converts the supplied heat energy into useful work.

### 4. What is isochoric process in thermodynamics?

The process in which volume of the system remains constant is called as isochoric process.

### 5. What is isobaric process in thermodynamics?

The process in which pressure of the system remains constant is called as isochoric process.

### 6. What is adiabatic process in thermodynamics?

The reversible process in which there is no energy transfer across the boundary of the system is called as adiabatic process.

### 7. What is a thermodynamic cycle?

A process or combination of processes undergone by a system, as a result of which the system is restored to its initial state is called a cycle.

### 8. What is an ideal gas in thermodynamics?

A gas that obeys the ideal gas equation at all pressure, temperature and volume is called as ideal gas.

### 9. What is a refrigerator in thermodynamics?

A refrigerator is a cyclically operating device which absorbs energy as heat from a low temperature body and rejects energy to high temperature body when work is performed on the device.

### 10. What is temperature in thermodynamics?

Temperature is defined as the property by virtue of the difference of that property heat flows. Temperature is also defined as the average kinetic energy of molecules.

### 11. What is specific heat?

The specific heat is defined as the amount of heat required to increase the temperature of 1kg of substance through 1oC.

### 12. What is free expansion in thermodynamics?

Expansion against the evacuated chamber is known as free expansion. In free expansion the work done is zero, because there is no resistance offered from the surrounding.

### 13. What is steady flow in thermodynamics?

A flow is said to be steady flow if the properties does not change with respect to time at a given location.

### 14. What is uniform flow in thermodynamics?

A flow is said to be uniform flow if the properties do not change with respect to location at a given time.

### 15. What is entropy change for a system when heat is added to the system?

When heat is added to the system the entropy of the system always increases.

### 16. What is third law of thermodynamics?

The entropy of perfect crystal of any pure substance approaches zero, as the temperature approaches to absolute zero.

### 17. What is sensible heat in thermodynamics?

The heat which we can sense, it is the energy used to change the temperature of the body.

### 18. What is latent heat in thermodynamics?

Latent heat is the heat that is involved in the phase transformation of a substance.

### 19. What is primary refrigerant in thermodynamics?

Primary refrigerant are those refrigerants that absorbs heat directly from the storage space by undergoing a cycle. It absorbs the latent heat.

### 20. What is a secondary refrigerant?

The refrigerant is first cooled by primary refrigerant and then used for cooling at the required place is called secondary refrigerant. Secondary refrigerant absorbs sensible heat.

## Intermediate Thermodynamics Interview Questions with Answers

### 21. What is a heat source in thermodynamics?

A heat source is a type of thermodynamic reservoir which can supply any amount of heat, without undergoing any temperature change.

### 22. What is a heat sink in thermodynamics?

A heat sink is a type of thermodynamic reservoir which can absorb any amount of heat, without undergoing any temperature change.

### 23. What is thermal efficiency of vapour power cycle?

The thermal efficiency of the vapour power cycle is the ratio of net work done by the cycle upon heat supplied to the cycle. It is denoted by ηth.

### 24. What is the work ratio in vapour power cycle?

The ratio of net-work output of the cycle to the work developed by the turbine is called back work ratio.

### 25. What is the back work ratio in vapour power cycle?

The back work ratio is defined as the ratio of pump work input to the work developed by the turbine.

### 26. What is steam rate in vapour power cycle?

It is also called as specific steam consumption. It relates the power output to amount of steam necessary to produce it. It is the amount of steam required to produce 1kWh of power.

### 27. What is heat rate in vapour power cycle?

The heat rate of the vapour power cycle is defined as the amount of heat required by a power plant to produce 1kWh of power.

### 28. What is Carnot vapour power cycle?

It is a cycle which has maximum efficiency, operating between given temperature limits and its efficiency is independent of property of working fluid. The Carnot cycle is an ideal vapour power cycle.

### 29. What is the use of boiler in vapour power cycle?

A boiler is one of the basic components of vapour power cycle, the boiler is used to supply the heat to the working fluid.

### 30. What is the use of turbine in vapour power cycle?

A boiler is one of the basic components of vapour power cycle, the turbine is used to expand the high pressure and high temperature steam coming from the boiler. The output from the power cycle is obtained at the shaft of the turbine.

### 31. What is the use of condenser in vapour power cycle?

A condenser is one of the basic components of vapour power cycle, the condenser is attached at the exit of the turbine. The vapour coming from the turbine is wet vapour and is completely condensed into the condenser.

### 32. What is the use of a pump in vapour power cycle?

A pump is one of the basic components of vapour power cycle, the liquid condensate from the condenser is pumped to the operating pressure of the boiler with the help of pump. The pump operation is considered isentropic.

### 33. What are the two methods for improving the efficiency of vapour power cycle?

The two methods used for improving the efficiency of vapour power cycle are reheating and regeneration.

### 34. What is a binary vapour power cycle?

The binary vapour power cycle is the combination of two cycles. One cycle operates in the high temperature region and the other operates in the low temperature region.

### 35. What is the thermal efficiency of boiler in vapour power cycle?

The thermal efficiency of boiler is expressed in terms of ratio of the heat energy utilized to generate steam to the heat energy supplied to the boiler by burning of fuel.

### 36. What are boiler mountings used in the vapour power cycle?

The item which is used for safety of the boiler is called as boiler mounting. The items such as stop valve, safety valve, fusible plug, pressure gauges are some examples of boiler mounting.

### 37. What are boiler accessories used in vapour power cycle?

The item which is used to increase the efficiency of boiler is called boiler accessories. The items such as super-heaters, economizers are some examples of boiler accessories.

### 38. What are fire tube boilers used in vapour power plant?

The fire tube boilers are boilers in which, the hot gases are inside the tubes and the water is surrounding the tubes. Examples of fire tube boilers are: Cochran and Lancashire boilers.

### 39. What are water tube boilers used in vapour power plant?

The water tube boilers are boilers in which, the water is inside the tubes and the hot gases surrounds them. Examples of water tube boilers are: Babcock and Wilcox, Stirling boiler and Yarrow boiler.

### 40. What is super critical boiler used in vapour power plant?

The boiler whose operating parameters are above critical point which is pressure= 221.2 bar and temperature 373 oK is called as super critical boiler.

### 41. What is natural circulation boiler used in vapour power plant?

The boiler in which the circulation of water takes place due to the natural convection current is called as natural convection boiler.

### 42. What is forced circulation boiler used in vapour power plant?

The boiler in which the circulation of water is done with the help of a pump is called as forced circulation boiler.

### 43. What is the mean effective pressure used in power calculation of internal combustion engine?

The pressure inside the cylinder is continuously varying during the cycle, the mean effective pressure is defined as the hypothetical pressure which is thought to be action on piston throughout the cycle.

### 44. What is exergy in thermodynamics?

The portion of energy supplied as heat which can be converted into work by a reversible engine is called as exergy.

### 45. What is the equation of Gibbs phase rule?

The equation of Gibbs phase rule is written as F+P = C+2 where, F is degrees of freedom of system, P is the number of phases and C is the number of components.

### 46. What are azeotropes in refrigeration?

An azeotrope is a mixture of two refrigerants which cannot be separated into its constituents with the change in temperature or pressure or both.

### 47. What is an antifreeze solution in refrigeration?

Antifreeze compounds are those which when added to water decrease its freezing point. The most commonly used antifreeze compounds are glycols and glycerine.

### 48. What is a quasi-static process?

When a system changes its state very slowly under the influence of infinitesimal driving forces such a process is called as quasi-static process.

### 49. What is the main difference between work and heat?

The main difference between work and heat is that work can be converted 100% into heat but heat cannot be converted 100% into work.

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