# Fluid Mechanics and Thermal Sciences (Test 5)

## Gate Exam : Me Mechanical Engineering

| Home | | Gate Exam | | Me Mechanical Engineering | | Fluid Mechanics and Thermal Sciences | Fluid Mechanics and Thermal Sciences
| Fluid Mechanics and Thermal Sciences |
Q.1
The values of enthalpy of steam at the inlet and outlet of a steam turbine in a Rankine cycle are 2800kJ/kg and 1800kJ/kg respectively. Neglecting pump work, the specific steam consumption in kg/kW-hour is
A. 3.60
B. 0.36
C. 0.06
D. 0.01
Explaination / Solution:

Work done by the turbine
W = 2800 – 1800 = 1000 kJ/kg = 1000 kW-s/kg
Specific fuel consumption = (1/1000)×3600 = 3.6 kg / kw-hr

Workspace
Report
Q.2
In an experimental set-up, air flows between two stations P and Q adiabatically. The direction of flow depends on the pressure and temperature conditions maintained at P and Q. The conditions at station P are 150kPa and 350K. The temperature at station Q is 300K.
The following are the properties and relations pertaining to air:
Specific heat at constant pressure, Cp = 1.005kJ / kgK;
Specific heat at constant volume, Cv = 0.718kJ / kgK;
Characteristic gas constant, R = 0.287kJ / kgK
Enthalpy, h = CpT
Internal energy, u = CvT
If the air has to flow from station P to station Q, the maximum possible value of pressure in kPa at station Q is close to
A. 50
B. 87
C. 128
D. 150
Explaination / Solution:

To cause the flow from P to Q, change in entropy (SP - SQ) should be greater than zero ∴ The maximum value of pressure at Q = 87 kPa

Workspace
Report
Q.3
The emissive power of a blackbody is P. If its absolute temperature is doubled, the emissive power becomes.
A. 2P
B. 4P
C. 8P
D. 16P
Explaination / Solution:
No Explaination.

Workspace
Report
Q.4
The velocity profile of a fully developed laminar flow in a straight circular pipe, as shown in the figure, is given by the expression u (r) = where dp/dx is a constant. The average velocity of fluid in the pipe is A. -R2/8μ (dp/dx)
B. -R2/4μ (dp/dx)
C. -R2/2μ (dp/dx)
D. -R2/μ (dp/dx)
Explaination / Solution:
No Explaination.

Workspace
Report
Q.5
Radiative heat transfer is intended between the inner surfaces of two very large isothermal parallel metal plates. While the upper plate (designated as plate 1) is a black surface and the warmer one being maintained at 727oC, the lower plate ( plate 2) is a diffuse and gray surface with an emissivity of 0.7 and is kept at 227oC. Assume that the surfaces are sufficiently large to form a two-surface enclosure and steady state conditions to exist. Stefan Boltzmann constant is given as 5.67 × 10-8 W/m2K4
If plate 1 is also a diffuse and gray surface with an emissivity value of 0.8, the net radiation heat exchange (in kW/m2) between plate 1 and plate 2 is
A. 17.0
B. 19.5
C. 23.0
D. 31.7
Explaination / Solution:
No Explaination.

Workspace
Report
Q.6
The figure below represents a triangle PQR with initial coordinates of the vertices as P(1,3),Q(4,5) and R(5,3.5). The triangle is rotated in the X-Y plane about the vertex P by angle θ in clockwise direction. If sinθ= 0.6 and cosθ= 0.8, the new coordinates of the vertex 𝑄 are A. (4.6, 2.8)
B. (3.2, 4.6)
C. (7.9, 5.5)
D. (5.5, 7.9)
Explaination / Solution: Since the triangle is rotated in CW direction, hence, for the new point Q’ (x,y),
x > 4 and y < 5 __________(1)
and PQ = PQ’ or QR = Q’R’ Now we can get the answer easily by checking the option

Workspace
Report
Q.7
In a steam power plant operating on the Rankine cycle, steam enters the turbine at 4MPa, 350ºC and exits at a pressure of 15kPa. Then it enters the condenser and exits as saturated water. Next, a pump feeds back the water to the boiler. The adiabatic efficiency of the turbine is 90%. The thermodynamic states of water and steam are given in the table. h is specific enthalpy, s is specific entropy and v the specific volume; subscripts f and g denote saturated liquid state and saturated vapour state.
The net work output (kJ kg-1) of the cycle is
A. 498
B. 775
C. 860
D. 957
Explaination / Solution:
No Explaination.

Workspace
Report
Q.8
Consider an incompressible laminar boundary layer flow over a flat plate of length L, aligned with the direction of an incoming uniform free stream. If F is the ratio of the drag force on the front half of the plate to the drag force on the rear half, then
A. F < 1/2
B. F = 1/2
C. F = 1
D. F > 1
Explaination / Solution:
No Explaination.

Workspace
Report
Q.9
In a counter flow heat exchanger, hot fluid enters at 60oC and cold fluid leaves at 30oC. Mass flow rate of the fluid is 1 kg/s and that of the cold fluid is 2 kg/s. Specific heat of the hot fluid is 10 kJ/kgK and that of the cold fluid is 5 kJ/kgK. The Log Mean Temperature Difference (LMTD) for the heat exchanger in oC is
A. 15
B. 30
C. 35
D. 45
Explaination / Solution:
No Explaination.

Workspace
Report
Q.10
Match List-I with List-II and select the correct answer using the codes given below the lists : Codes:
A. 2 3 4 1
B. 2 3 1 4
C. 3 4 1 2
D. 1 2 3 4