UNITI GAS POWER CYCLES
I.C engine?
° C respectively. The pressure at the beginning of compression is 1 bar. Calculate (I) The pressure and temperature at’ key points of the cycle. (ii) The heat supplied at constant volume, (iii) the heat supplied at constant pressure. (Iv) The heat rejected. (v) The work output. (vi) The efficiency and (vii) mep.
= 200 KJ/Kg minimum temperature in the cycle = 25°C Suction pressure = 1 bar Calculate
1.5. If the power required by the compressor is 20 kW, determine the size of the cylinder.
compressor runs at 250 rpm .If clearance volume of the cylinder is 5% of stroke volume and the mechanical
efficiency of the compressor is 85%, determine volumetric efficiency, power, and mass of air delivered per minute.
(ii) An electrical wire of 10 m length and 1 mm diameter dissipates 200 W in air at 25°C.
The convection heat transfer coefficient between the wire surface and air is 15 W/m2K. Calculate the critical radius of insulation and also determine the temperature of the wire if it is insulated to the critical thickness of insulation.

of 10 cm from the wall. 

(ii) A large iron plate of 10 cm thickness and originally at 800°C is suddenly exposed to an 

environment at O°C where the convection coefficient is 50 W/m2K. Calculate the 

temperature at a depth of 4 em from one of the faces 100 seconds after the plate is exposed 

to the environment. How much energy has been lost per unit area of the plate during this 

time? 
5. (i) ) Explain the different modes of heat transfer with appropriate expressions. 


(ii) A composite wall consists. of 10 cm thick layer of building brick, K = 0.7 W/mK and 

3 cm thick plaster, k = 0.5 W/mK. An insulating material of K = 0.08 W/mK is to be 

added to reduce the heat transfer through the wall by 40%. Find its thickness. 
6. 
Circumferential aluminium fins of rectangular profile (1.5cmwide and 1mm thick) 

are fitted on to a 90 mm engine cylinder with a pitch of 10 mm. The height of the 

cylinder is 120 mm. The cylinder base temperature before and after fitting the fins are 

200°C and 150°C respectively. Take ambient at 30°C and h(average) =100 W/m2K. 

Estimate the heat dissipated from the finned and the unfinned surface areas of cylinder 

body. 
7. (i) Derive the heat conduction equation in cylindrical coordinates using an elemental 


volume for a stationary isotropic solid. 

(ii) A 3 cm OD steam pipe is to be covered with two layers of insulation each having a 

thickness of 2.5 cm. The average thermal conductivity of one insulation is 5 times that of 

the other. Determine the percentage decrease in heat transfer if better insulating material is 

next to pipe than it is the outer layer. Assume that the outside and inside temperatures of 

composite insulation are fixed. 
8. (i) Explain briefly the concept of critical thickness of insulation and state any two 


applications of the same. 
(ii) A 6 em long copper rod (k = 300 W/mK) 6mm in diameter is exposed to an 


environment at 20°C. The base temperature of the rod is maintained at 160°C. The heat 

transfer coefficient is 20 W/m2K. Calculate the heat given by the rod and efficiency and 

effectiveness of the rod. 
(ii) What is meant lumped capacity? What are the physical assumptions necessary for a lumped capacity unsteady state analysis to apply? (4) (iii)A slab of Aluminum 5 cm thick initially at 200°C is suddenly immersed in a liquid at 70°C for which the convection heat transfer coefficient is 525 W/m2K. Determine the
temperature at a depth of 12.5 mm from one of the faces 1 minute after the immersion. Also calculate the energy removed per unit area from the plate during 1 minute of immersion. Take P = 2700 bar, Cp
= 0.9 kJlkg. OK, k=215W/mK, ά = 8.4X 105 m2/s.(8)
temperature between asbestos and fiber plate. (16)
each layer. 
(16) 
01. Air at 200 kPa and 200°C is heated as it flows through a tube with a diameter of 25 mm at a velocity of 10 m./sec. The wall temperature is maintained constant and is 20°C above the
air temperature all along the length of tube. Calculate: 

(i) The rate of heat transfer per unit length of the tube. 

(ii) Increase in the bulk temperature of air over a 3 m length of the tube. 
(16) 
02. 
(i) Write down the momentum equation for a steady, two dimensional flow of an 


incompressible, constant property newtonian fluid in the rectangular coordinate system and 


mention the physical significance of each term. 
(6) 

(ii) A large vertical plate 5 m high is maintained at 100°C and exposed to air at 30°C 


Calculate the convection heat transfer coefficient. 
(10) 
03. 
Sketch the boundary layer development of a flow over a flat plate and explain the 


significance of the boundary layer. 
(6) 
(ii) Atmospheric air at 275 K and a free stream velocity of 20 m/s flows over a flat plate
1.5 m long that is maintained at a uniform temperature of 325 K. Calculate the average heat transfer coefficient over the region where the boundary layer is laminar, the average heat transfer coefficient over the entire length of the plate and the total heat transfer rate from the plate to the air over the length 1.5 m and width 1 m. Assume transition occurs at Ree = 2xl05

(10) 
04. (i) What is Reynold's analogy? Describe the relation between fluid friction and heat 

transfer? 
(4) 
(ii) Air at 25°C flows over 1 m x 3 m (3 m long) horizontal plate maintained at 200°C at 10 mls.
Calculate the average heat transfer coefficients for both laminar and turbulent
regions. Take Re (critical) = 3.5 x 105 
(12) 
05. (i) Define Reynold’s, Nusselt and Prandtl numbers. 
(6) 
(ii) A steam pipe 10 cm outside diameter runs horizontally in a room at 23°C. Take the outside surface temperature of pipe as 165°C. Determine the heat loss per unit length of the pipe. (10)
(ii) The water is heated in a tank by dipping a plate of 20 cm X 40 cm in size. The
temperature of the plate surface is maintained at 100°C. Assuming the temperature 

of the surrounding water is at 30° C, Find the heat loss from the plate 20 cm side is 

in vertical plane. 
(8) 
07. Air at 400 K and 1 atm pressure flows at a speed of 1.5 m/s over a flat plate of 2 m long.
The plate is maintained at a uniform temperature of 300 K. If the plate has a width of 0.5 m, 

estimate the heat transfer coefficient and the rate of heat transfer from the air stream to the 


plate. Also estimate the drag force acting on the plate. 
(16) 
08. 
Cylindrical cans of 150 mm length and 65 mm diameter are to be cooled from an initial 


temperature of 20°C by placing them in a cooler containing air at a temperature of 1°C and 


a pressure of 1 bar. Determine the cooling rates when the cans are kept in horizontal and 


vertical positions. 
(16) 
09. A circular disc heater 0.2m in diameter is exposed to ambient air at 25°C. One surface of the disc is insulated at 130°C. Calculate the amount of heat transferred from the disc when it is.
(i) Horizontal with hot surface facing up 
(5) 
(ii) Horizontal with hot surface facing down 
(5) 
(iii) Vertical 
(6) 
10. (i) Distinguish between free and forced convection giving examples. (4)
= 0.2 and £"2 = 0.7 respectively. Determine the net rate of radiation heat transfer between the two plates per unit surface area of the plates and
compare the result to that without shield. 
(16) 
03.(i) Discuss how the radiation from gases differ from that of solids. 
(6) 
(ii) Two very large parallel plates with emissivities 0.5 exchange heat. 

Determine the percentage reduction in the heat transfer rate if a polished aluminium radiation
shield of c = 0.04 is placed in between the plates. 
(10) 
04. (i) Define emissivity, absorptivity and reflectivity 
(06) 
(ii) Describe the phenomenon of radiation from real surfaces. 
(10) 
05. (i) What are the radiation view factors and why they are used? 
(04) 
(ii) determine the view factor (F14) for the figure shown below. 
(12) 
06. (i) State and prove the following laws:
(ii} Showfrom energybalance consideration that the radiation heat transfer from a plane composite surface area A4 and made up of plane surface areas A2 and A3 to a plane surface area Al is given by: A4F41=A3F31+A2F21 & F14=F12+F13 (8)
7. 
Explain briefly the following: (i) Specular and diffuse reflection 
(5) 

(ii) reflectivity and transmissivity 
(5) 

(iii) reciprocity rule and summation rule 
(6) 
(8) 
(ii) Two equal and parallel discs of diameter 25 cm are separated by a distance of 50 cm. If the 
discs are maintained at 600°C and 250°C. Calculate the radiation heat exchange between 
them. (8)
9 . Two large parallel planes with emissivities 0.35 and 0.85 exchange heat by radiation. The planes are respectively 1073K and 773K . A radiation shield having the emissivity of 0.04 is placed between them. Find the percentage reduction in radiation heat exchange and temperature
of the shield. 
(16) 
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