PPT: Convection | Heat Transfer - Mechanical Engineering PDF Download

 Page 1


CONTENT:
•
Basic Definitions
•
Natural And Force Convection 
•
Factor Affecting convective Heat Transfer Coefficient
•
Nusselt Number And Prandlt Number
•
Dimensional  Relationship of Natural Convection With Gr and Pr
Page 2


CONTENT:
•
Basic Definitions
•
Natural And Force Convection 
•
Factor Affecting convective Heat Transfer Coefficient
•
Nusselt Number And Prandlt Number
•
Dimensional  Relationship of Natural Convection With Gr and Pr
BASICS DEFINIONS 
1. Heat Transfer:
                 Heat Transfer Define As The Transmission of Energy From One Region to another Region 
as a result of Temperature Gradient.
•
Conduction:
    Conduction Transfer Heat via Direct Molecular Collision. Area of Greater kinetic energy will 
Transfer Thermal energy to an area with lower kinetic energy.
•
 Convection: 
      When a Fluid, such as air or Liquid, is  heated and then travels away 
from the source,  it carries the thermal energy along. This type of Heat 
Transfer is called  convection. 
•
 Radiation: 
     Thermal Radiation Generates from the emission of electromagnetic 
waves. These waves carry the energy away from the emitting object.
                                                        
                                                        
                                             
                                                       
Page 3


CONTENT:
•
Basic Definitions
•
Natural And Force Convection 
•
Factor Affecting convective Heat Transfer Coefficient
•
Nusselt Number And Prandlt Number
•
Dimensional  Relationship of Natural Convection With Gr and Pr
BASICS DEFINIONS 
1. Heat Transfer:
                 Heat Transfer Define As The Transmission of Energy From One Region to another Region 
as a result of Temperature Gradient.
•
Conduction:
    Conduction Transfer Heat via Direct Molecular Collision. Area of Greater kinetic energy will 
Transfer Thermal energy to an area with lower kinetic energy.
•
 Convection: 
      When a Fluid, such as air or Liquid, is  heated and then travels away 
from the source,  it carries the thermal energy along. This type of Heat 
Transfer is called  convection. 
•
 Radiation: 
     Thermal Radiation Generates from the emission of electromagnetic 
waves. These waves carry the energy away from the emitting object.
                                                        
                                                        
                                             
                                                       
Natural And Force Convection
 
•
Natural Convection is a type of heat transfer, in which the fluid motion is not generated by 
any external source (like a pump, fan, suction pump etc.) but only by density differences in the 
fluid occurring due to temperature gradients.
•
The Example of free convection is a heated plate when kept in an atmosphere, it gets cooled by air. 
Here the circulation of air take place due to density difference, which is caused by temperature 
difference between solid plate and air.
•
Natural convection is the process of heat transfer which occurs due to movement of the fluid 
particles by density change associated with temperature differential in a fluid.
•
Some Example are given below:
1. The cooling of electrical transformers and 
      rectifiers.
2.   The heat transfer from hot pipes by cooled air .
Page 4


CONTENT:
•
Basic Definitions
•
Natural And Force Convection 
•
Factor Affecting convective Heat Transfer Coefficient
•
Nusselt Number And Prandlt Number
•
Dimensional  Relationship of Natural Convection With Gr and Pr
BASICS DEFINIONS 
1. Heat Transfer:
                 Heat Transfer Define As The Transmission of Energy From One Region to another Region 
as a result of Temperature Gradient.
•
Conduction:
    Conduction Transfer Heat via Direct Molecular Collision. Area of Greater kinetic energy will 
Transfer Thermal energy to an area with lower kinetic energy.
•
 Convection: 
      When a Fluid, such as air or Liquid, is  heated and then travels away 
from the source,  it carries the thermal energy along. This type of Heat 
Transfer is called  convection. 
•
 Radiation: 
     Thermal Radiation Generates from the emission of electromagnetic 
waves. These waves carry the energy away from the emitting object.
                                                        
                                                        
                                             
                                                       
Natural And Force Convection
 
•
Natural Convection is a type of heat transfer, in which the fluid motion is not generated by 
any external source (like a pump, fan, suction pump etc.) but only by density differences in the 
fluid occurring due to temperature gradients.
•
The Example of free convection is a heated plate when kept in an atmosphere, it gets cooled by air. 
Here the circulation of air take place due to density difference, which is caused by temperature 
difference between solid plate and air.
•
Natural convection is the process of heat transfer which occurs due to movement of the fluid 
particles by density change associated with temperature differential in a fluid.
•
Some Example are given below:
1. The cooling of electrical transformers and 
      rectifiers.
2.   The heat transfer from hot pipes by cooled air .
• Forced convection is a type of transfer in which fluid motion is generated by an external 
source (like a pump, fan, suction device, etc.)
• It is mostly used in all heat transfer application because the convection due to it, will be much higher 
as compared to free convection. 
• If a heated plate is kept under a fan for cooling, it is called as forced convection. 
Page 5


CONTENT:
•
Basic Definitions
•
Natural And Force Convection 
•
Factor Affecting convective Heat Transfer Coefficient
•
Nusselt Number And Prandlt Number
•
Dimensional  Relationship of Natural Convection With Gr and Pr
BASICS DEFINIONS 
1. Heat Transfer:
                 Heat Transfer Define As The Transmission of Energy From One Region to another Region 
as a result of Temperature Gradient.
•
Conduction:
    Conduction Transfer Heat via Direct Molecular Collision. Area of Greater kinetic energy will 
Transfer Thermal energy to an area with lower kinetic energy.
•
 Convection: 
      When a Fluid, such as air or Liquid, is  heated and then travels away 
from the source,  it carries the thermal energy along. This type of Heat 
Transfer is called  convection. 
•
 Radiation: 
     Thermal Radiation Generates from the emission of electromagnetic 
waves. These waves carry the energy away from the emitting object.
                                                        
                                                        
                                             
                                                       
Natural And Force Convection
 
•
Natural Convection is a type of heat transfer, in which the fluid motion is not generated by 
any external source (like a pump, fan, suction pump etc.) but only by density differences in the 
fluid occurring due to temperature gradients.
•
The Example of free convection is a heated plate when kept in an atmosphere, it gets cooled by air. 
Here the circulation of air take place due to density difference, which is caused by temperature 
difference between solid plate and air.
•
Natural convection is the process of heat transfer which occurs due to movement of the fluid 
particles by density change associated with temperature differential in a fluid.
•
Some Example are given below:
1. The cooling of electrical transformers and 
      rectifiers.
2.   The heat transfer from hot pipes by cooled air .
• Forced convection is a type of transfer in which fluid motion is generated by an external 
source (like a pump, fan, suction device, etc.)
• It is mostly used in all heat transfer application because the convection due to it, will be much higher 
as compared to free convection. 
• If a heated plate is kept under a fan for cooling, it is called as forced convection. 
Factor Affecting convective Heat Transfer Coefficient
1.  Temperature Difference (T) 
                                   T the greater the heat transfer rate.
2.  Fluid flow rate 
                                     Increasing flow rate increasing heat transfer rate.
3.  Surface area 
                                     the larger the surface area of conducting interfaces, the greater the heat    
       transfer rate.