In heat exchangers, degree of approach is defined as the difference between temperatures of
Cold water inlet and outlet
Hot medium inlet and outlet
Hot medium outlet and cold water inlet
Hot medium outlet and cold water outlet
Correct Answer :
D. Hot medium outlet and cold water outlet
Related Questions
The critical thickness of insulation for a sphere is
k/h₀
2k/h₀
h₀/k
h₀/2k
The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as
Wien's law
Stefan's law
Kirchhoff's law
Planck's law
Reynolds number is the ratio of
Energy transferred by convection to that by conduction
Kinematic viscosity to thermal diffusivity
Inertia force to viscous force
None of the above
The use of heat exchangers is made in
Radiators in automobile
Condensers and boilers in steam plants
Condensers and evaporators in refrigeration and air conditioning units
All of the above
Thermal conductivity of non-metallic amorphous solids with decrease in temperature
Increases
Decreases
Remain constant
May increase or decrease depending on temperature
Film coefficient is defined as the ratio of
Thermal conductivity to the equivalent thickness of the film of fluid
Temperature drop through the films of fluids to the thickness of film of fluids
Thickness of film of fluid to the thermal conductivity
Thickness of film of fluid to the temperature drop through the films of fluids
The automobile radiator is a heat exchanger of
Parallel flow type
Counter flow type
Cross flow type
Regenerator type
Thermal diffusivity of a substance is
Directly proportional to the thermal conductivity
Inversely proportional to density of substance
Inversely proportional to specific heat
All of the above
The unit of overall coefficient of heat transfer is
kcal/m²
kcal/hr °C
kcal/m² hr °C
kcal/m hr °C
In heat transfer, conductance equals conductivity (kcal/hr/sq.m/ °C/cm) divided by
Hr (time)
Sq. m (area)
°C (temperature)
K.cal (heat)
The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number) n, where n is equal to
-1/3
-2/3
1
-1
According to Newton's law of cooling, the heat transfer from a hot body to a cold body is
Directly proportional to the surface area
Directly proportional to the difference of temperatures between the two bodies
Either (A) or (B)
Both (A) and (B)
Heat is closely related with
Liquids
Energy
Temperature
Entropy
The rate of energy transferred by convection to that by conduction is called
Stanton number
Nusselt number
Biot number
Peclet number
The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to
Stanton number
Biot number
Peclet number
Grashoff number
Sensible heat is the heat required to
Change vapour into liquid
Change liquid into vapour
Increase the temperature of a liquid of vapour
Convert water into steam and superheat it
Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be
One
Two
Three
Four
Film coefficient is defined as Inside diameter of tube
Equivalent thickness of film
Thermal conductivity Equivalent thickness of film Specific heat × Viscosity
Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity
Film coefficient × Inside diameter Thermal conductivity
Unit of thermal conductivity in M.K.S. units is
K cal/kg m² °C
K cal m/hr m² °C
K cal/hr m² °C
K calm/hr °C
The radiation emitted by a black body is known as
Black radiation
Full radiation
Total radiation
All of these
The heat transfer by conduction through a thick cylinder (Q) is given by (where T₁ = Higher temperature, T₂ = Lower temperature, r₁ = Inside radius, r₂ = Outside radius, l = Length of cylinder, and k = Thermal conductivity)
Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁)
Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)]
Q = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁)
Q = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁)
A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,
The better insulation must be put inside
The better insulation must be put outside
One could place either insulation on either side
One should take into account the steam temperature before deciding as to which insulation is put where
Metals are good conductors of heat because
Their atoms collide frequently
Their atoms are relatively far apart
They contain free electrons
They have high density
The unit of overall coefficient of heat transfer is
W/m²K
W/m²
W/mK
W/m
Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity)
h = k/ ρS
h = ρS/k
h = S/ρk
h = kρ/S
The most commonly used method for the design of duct size is the
Velocity reduction method
Equal friction method
Static regains method
Dual or double method
Thermal conductivity of wood depends on
Moisture
Density
Temperature
All of the above
Thermal diffusivity is a
Function of temperature
Physical property of a substance
Dimensionless parameter
All of these
The expression Q = ρ AT4 is called
Fourier equation
Stefan-Boltzmann equation
Newton Reichmann equation
Joseph-Stefan equation
A composite slab has two layers of different materials with thermal conductivities k₁ and k₂. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be
k₁ k₂
(k₁ + k₂)
(k₁ + k₂)/ k₁ k₂
2 k₁ k₂/ (k₁ + k₂)