Answer:
Free convection:
When heat transfer occurs due to density difference between fluid then this type of heat transfer is know as free convection.The velocity of fluid is zero or we can say that fluid is not moving.
Force convection:
When heat transfer occurs due to some external force then this type of heat transfer is know as force convection.The velocity of fluid is not zero or we can say that fluid is moving in force convection.
Heat transfer coefficient of force convection is high as compare to the natural convection.That is why heat force convection reach a steady-state faster than an object subjected to free-convection.
We know that convective heat transfer given as
q = h A ΔT
h=Heat transfer coefficient
A= Surface area
ΔT = Temperature difference
Answer:
No
Explanation:
Heat engines are used for converting the heat into mechanical energy which is used for doing mechanical work.
The efficiency of heat engine is the fraction of mechanical energy to the thermal energy. The efficiency can not be 100% as some of the energy always loss due to friction and motion of the body parts of the heat engine.
Answer:
The theoretical density for Niobium is 
.
Explanation:
Formula used :
where,
= density of the unit cell
Z = number of atom in unit cell
M = atomic mass
= Avogadro's number
a = edge length of unit cell
We have :
Z = 2 (BCC)
M = 92.91 g/mol ( Niobium)
Atomic radius for niobium = r = 0.143 nm
Edge length of the unit cell = a
r = 0.866 a (BCC unit cell)
On substituting all the given values , we will get the value of 'a'.
The theoretical density for Niobium is .
