Important Questions with Answers

ANNA UNIVERSITY PART – A '2' Marks Q & A

 

1. Define heat conduction.

Conduction is the process of transmission of heat from one point to another through substance (or some medium) without the actual motion of the particles (atoms/ molecules) of the substance.

 

2. Define coefficient of thermal  conductivity and mention its unit.

 It is defined as the quantity of heat conducted per second normally across unit area of cross-section per unit temperature difference per unit length of the material.

Its unit is Wm^-1 K^-1

 

3. Derive the unit in which thermal conductivity is measured.

Thermal conductivity of material

 

4. How are heat conduction and electrical conduction analogous to each other?

Heat conduction

1. Heat is conducted from a point of higher temperature to a point of  ower temperature.

2. In metals, heat conduction is mainly due to free electrons.

3. The ability to conduct heat is measured by thermal conductivity.

Electrical conduction

1. Electricity is conducted from a point at higher potential to a point at   lower potential.

2. In metals, electrical conduction is due to free  electrons.

3. The ability to conduct electricity is measured by electrical conductivity.

 

5. What are the characteristics of good and bad conductors?

Good conductors

 1. They have high electrical & thermal conductivity

2. They can be easily heated or cooled

3. Examples: Metals like iron, copper

Bad conductors

They have very low electrical and thermal conductivity

They cannot be easily heated cooled

Examples: Non metals like glass, wood

 

6. What is thermal resistance?

The thermal resistance of a body is a measure of its opposition to the flow of heat through it.

 

7. Write down an expression for the amount of heat conducted through a compound media of two layers.

Amount of heat conducted through a compound media of two layer is

A - Area of the cross section

θ₁- temperature at outer face of the material at hot end

θ₂ - temperature at the outer face of the material at cold end

x₁ - thickness of the material at hot end

x_{2 -} thickness of the material at cold end

K₁ - thermal conductivity of the material at hot end

K₂- thermal conductivity of the material at cold end

 

8. Mention the methods to determine thermal conductivity of good and bad conductors.

 

• Searle's method - for good conductors like metallic rod

• Forbe's method - for determining the absolute conductivity of metals

• Lee's disc method - for poor conductors

• Radial flow method - for bad conductors

 

9. What are three modes of transferring heat?

• Conduction

• Convection

• Radiation

 

10. Define convection.

It is the process in which heat is transmitted from one place to another by the actual motion of the heated particles.

 

11. Define radiation.

It is the process in which heat is transmitted from one place to the other directly, without the agency of any material medium.

 

12. Define fenestration.

It is defined as any opening or arrangement of openings in a building (normally filled with glazing).

 

13. What are the various fenestration systems?

There are various fenestration systems like glazing, windows, curtain walls, sloped glazing and exterior doors.

 

14. What are the three main components of fenestration?

1. Glazing

2. Framing

3. Shading devices and/or screens

 

15. What is the total heat transfer through fenestration?

The heat gain through fenestration consists of two main components:

• Q _thermal = heat transfer between indoor and outdoor air. This is positive or negative depending on temperature.

• Q s_olar =   heat transfer from solar radiation.

This is always a positive number.

The total heat transfer through fenestration

Q_total = Qt_hermal + Q_solar

 

16. What is thermal insulation?

• Thermal insulation is to resist the he flow to I of heat to and ene mofrom a body. It is a material that reduces the rate of  heat flow.

• It is the reduction of heat transfer (i.e the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence.

 

17. Mention a few methods of thermal insulation.

• Use of materials with low conductivity

• Thickness of walls and roofs

• Provision of spaces

• Heat insulation by orientation

• Thermal insulation by shading

• Providing sufficient height of ceiling

• Using thermal insulating materials

 

18. What are the benefits of thermal insulation?

Due to thermal insulation, the room remains cooler in summer and warmer in winter than outside. Hence a room provided with thermal insulation gives comfort both in summer and winter. etsed

Energy Saving: Due to thermal insulation transfer of heat between inside and outside of the room is restricted. This results in less quantity of energy required for maintaining the desired temperature in the room.

 

19. What is thermal performance of buildings?

It refers to the process of modeling the energy transfer between building and its surroundings.

 

20. What is thermal comfort?

It is the condition of mind that expresses satisfaction with the thermal environment and it is assessed by subjective evaluation. It is the occupants satisfaction with the surrounding thermal conditions.

 

21. What is the need for shading devices?

Well-designed sun control and shading devices dramatically reduce building peak heat gain and cooling requirements. These devices also improve the natural lighting quality of building interiors.

 

22. How are shading devices classified?

Shading devices are classified into two types they are

 (i) internal shading devices and

(ii) external shading devices. gaiblind meinem

 

23. What is central heating?

A central heating system provides warmth to the whole interior of a building or portion of a building from one point  to multiple rooms.

 

24. What are the components of central heating system?

• A gas supply lines, oil tanks and supply lines or distinct heating supply lines.

• A boiler (or a heat exchanger for district heating) whi heats water in the system.

• Pump to circulate the water in the closed system.

• Radiators which are wall-mounted panels through which the heated water passes in order to release heat into rooms.

Anna University Part B '16' Marks Questions

1. Derive an expression for the quantity of heat flow through a metal slab whose faces are kept at two different temperatures.

2. Describe with relevant theory the method of determining the coefficient of thermal conductivity of a rubber tube.

3. Describe method to determine thermal conductivity of powder material.

4. Discuss heat transfer through fenestration.

5. Describe methods of thermal insulation.

6. Explain heat gain and loss estimation in the components of buildings.

7. Discuss the factors affecting thermal performance of buildings.

8. Describe thermal measurements in buildings.

9. Explain thermal comfort and indices of thermal comfort.

10. Describe climate and design of solar radiation.

11. Discuss the different types of shading devices. lqislum

12. Explain central heating system.