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Match ListI with Listll and select the correct answer using the code given below the lists:
ListI
A. Grashof number
B. Schmidt number
C. Weber number
D. Fourier number
ListII
1. Mass diffusion
2. Transient heat conduction
3. Free convection
4. Forced convection
5. Surface tension
6. Radiation
[1996]
The ratio of momentum diffusivity (v) to thermal diffusivity (α), is called
[2015]
Grashof number signifies the ratio of
[2016]
Grash of number = inertia force x
In pool boiling the highest HTC occurs in
[1990]
Heat transfer coefficients for free convection in gases, forced convection in gases and vapours, and for boiling water lie, respectively, in the range of
[1998]
For the threedimensional object shown in the figure below, five faces are insulated. The sixth face (PQRS), which is not insulated, interacts thermally with the ambient, with a convective heat transfer coefficient of 10W/m^{2}K. The ambient temperature is 30°C. Heat is uniformly generated inside the object at the rate of 100 W/m3. Assuming the face PQRS to be at uniform temperature, its steady state temperature is
[2000]
Given data;
Volume,
V = 2×1×2=4 m^{3}
Heat generated,
Q = q_{G} × V = 100 × 4 = 400 W
Convection heat transfer from face PQRS,
Water (specifie heat, c = 4.18 kJ/kgK) enters a pipe at a rate 0.01 kg/s and a temperature of 20°C. The pipe, of diameter 50 mm and length 3 m, is subjected to a wall heat flux q"w in W/m^{2}.
If q"w = 2500x, where x is in m and in the direction of flow (x = 0 at the inlet), the bulk means temperature of the water leaving the pipe in °C is
[2013]
At the inlet of pipe
x = O
q "_{wi} = 2500 x 0 = 0
At the exit of pipe,
x = 1
Average heat transfer,
Net heat transfer
By solving above equation, we get
T_{o} = 62° C
Water (specifie heat, c = 4.18 kJ/kgK) enters a pipe at a rate 0.01 kg/s and a temperature of 20°C. The pipe, of diameter 50 mm and length 3 m, is subjected to a wall heat flux q"w in W/m^{2}.
If q"_{w} = 5000 and the convection heat transfer coefficient at the pipe outlet is 1000 W/m^{2}K, the temperature in °C at the inner surface of the pipe at the outlet is
[2013]
Heat transfer through pipe wall,
Q = mC_{P}(T_{0}–T_{i}), amount of heat gained by the water
2355 = 0.01 × 4180 (T_{0} – 20)
T_{0} = 76.33°C
5000 = 1000 (Tso – 76.33)
Tso = 81°C
For laminar forced convection over a flat plate, if the free stream velocity increases by a factor of 2, the average heat transfer coefficient
[2014]
Forlaminar flow, Nu = 0.664 (Re)^{0.5} (Pr)^{0.33}
So when free stream velocity increases by a factor of 2, then the average heat transfer coefficient rises by a factor of √2.
The properties of mercury at 300 K are: Density = 13529 kg/m^{3}, c_{p} = 0.1393 kJ/kgK, dynamic viscosity = 0.1523 × 10^{–2} Ns/m^{2} and thermal conductivity = 8.540 W/mK. The Prandtl number of the mercury at 300 K is
[2002]
Prandtl number =
In the laminar flow of air (Pr = 0.7) over a heated plate, if δ and δT denote, respectively, the hydrodynamic and thermal boundary layer thicknesses, then
[2015]
When
For a hydrodynamically and thermally fully developed laminar flow through a circular pipe of constant crosssection. The Nusselt number at constant wall heat flux (Nu_{q}) and that at constant wall temperature (Nu_{T}) are related as
[2019]
(Nu)_{q} for constant wall heat flux and (Nu)_{T} at constant wall temperature for a hydrodynamically and thermally fully developed laminar flow through a circular pipe of constant crosssection is 4.36 and 3.66 respectively.
The wall of a constant diameter pipe of length 1 m is heated uniformly with flux q” by wrapping a heater coil around it. The flow at the inlet to the pipe is hydrodynamically fully developed. The fluid is incompressible and the flow is assumed to be laminar and steady all through the pipe.
The bulk temperature of the fluid is equal to 0°C at the in let and 50°C at the exit. The wal l temperatures are measured at three locations, P, Q an d R as shown in the figure. The flow thermally develops after some distance from the inlet. The following measurements are made :
Among the locations P, Q and R, the flow is thermally at :
[2019]
In case of uniform heat flux, bulk mean temperature varies linearly. The difference between bulk mean temperature and wall temperature is constant in thermally developed region so bulk tempeature,
Here,
So, Q and R in thermally developed region.
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