CONVECTION AND CONDUCTION Flashcards
There is no actual movement of molecules in receiving from surface of heat, molecules vibrates and pass on energy to adjacent molecule
Conduction
It is a physical process involving the transfer of heat from hot area to cold area
Heat Transfer
3 basic mechanisms of Heat Transfer
Conductio, Convection, Radiation
Difference of temperature between two end
Driving force
There is a actual physical movement of molecules
Convection
Volume of K mainly depends upon:
Temperature, Nature of Material
It is the quantity of heat that flows across a unit surface area in unit time, when the temperature drop is unity
Thermal Conductivity
Two types of resistance
Resistance in series
Resistance in Parallel
Thermal Conductivities of liquid
0.62
Thermal Conductivity of Copper
379
Thermal conductivity of gases
0.03
What are the methods need to take average area
Arithmitic Mean
Log Mean Value
If the tempearture is not constant, what are the 2 methods need to be use
Aritmitic Temperature
LMTD
It takes place in solid and fluids whose movement is restricted
Conduction
Longer distance
Radiation
There is no actual contact in source of the heat
Convection
The motion of the fluid results from the density changes in heat transfer
free or natural convection
the fluid is forced to flow by pressure differences
forced convection
what flow when the reynolds number is above 6000
Turbulent Flow
Nre below 2100
Laminar flow
What type of resistance when the total amount of heat transfer is equal to the sum of heat transfer by all the individual resistance in the same time of period
Parallel
individual fluid has a great effect on the heat-transfer coefficient h, often called
film coefficient
the motion of the fluid results from the density changes in heat transfer
Free or Natural Convection
NRe between 2100 and 6000
Transitional region
Formula of rate?
rate= driving force/resistance
The most important convective heat-transfer process industrially is
cooling or heating a fluid flowing inside a closed circular conduit or pipe
it takes place in solid and fluids whose movement is restricted
Conduction
bodies that reject heat trasnfer
refracted
it is the most important of all heat transfer
radiation
heat can floe only when there is a temperature difference
conduction - fourier’s law
