Question for GATE Past Year Questions: Free & Forced Convection
Try yourself:Match List-I with List-ll and select the correct answer using the code given below the lists:
List-I
A. Grashof number
B. Schmidt number
C. Weber number
D. Fourier number List-II
1. Mass diffusion
2. Transient heat conduction
3. Free convection
4. Forced convection
5. Surface tension
6. Radiation

[1996]
Question for GATE Past Year Questions: Free & Forced Convection
Try yourself:The ratio of momentum diffusivity (v) to thermal diffusivity (α), is called [2015]
Question for GATE Past Year Questions: Free & Forced Convection
Try yourself:Grashof number signifies the ratio of [2016]
Explanation
Grash of number = inertia force x 
Question for GATE Past Year Questions: Free & Forced Convection
Try yourself:In pool boiling the highest HTC occurs in [1990]
Question for GATE Past Year Questions: Free & Forced Convection
Try yourself: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]
Question for GATE Past Year Questions: Free & Forced Convection
Try yourself:For the three-dimensional 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/m2K. 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]
Question for GATE Past Year Questions: Free & Forced Convection
Try yourself: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/m2. 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]
Question for GATE Past Year Questions: Free & Forced Convection
Try yourself: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/m2. If q"w = 5000 and the convection heat transfer coefficient at the pipe outlet is 1000 W/m2K, the temperature in °C at the inner surface of the pipe at the outlet is
[2013]
Question for GATE Past Year Questions: Free & Forced Convection
Try yourself: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]
Explanation
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.
Question for GATE Past Year Questions: Free & Forced Convection
Try yourself:The properties of mercury at 300 K are: Density = 13529 kg/m3, cp = 0.1393 kJ/kgK, dynamic viscosity = 0.1523 × 10–2 Ns/m2 and thermal conductivity = 8.540 W/mK. The Prandtl number of the mercury at 300 K is [2002]
Explanation
Prandtl number = 

Question for GATE Past Year Questions: Free & Forced Convection
Try yourself: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]
Explanation
When

Question for GATE Past Year Questions: Free & Forced Convection
Try yourself:For a hydrodynamically and thermally fully developed laminar flow through a circular pipe of constant cross-section. The Nusselt number at constant wall heat flux (Nuq) and that at constant wall temperature (NuT) are related as [2019]
Explanation
(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 cross-section is 4.36 and 3.66 respectively.
Question for GATE Past Year Questions: Free & Forced Convection
Try yourself: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]
Explanation
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.