# Papers

B.E. (Mechanical)

INDUSTRIAL HEAT TRANSFER EQUIPMENTS (2008 Pattern) (Elective – IV) (Sem. – II)

Time :3 Hours]                                                                                              [Max. Marks :100

Instructions to the candidates:-

1)           Answers to the two sections should be written in separate books.

2)           Neat diagrams must be drawn wherever necessary.

3)           Use of logarithmic tables, slide rule, Mollier charts, electronic pocket calculator and steam tables is allowed.

4)           Assume suitable data, if necessary.

SECTION – I

Q1) a) Classify heat exchangers according to construction.                      [5]

b)        Explain construction and working of hairpin heat exchanger.           [5]

c)         State general assumptions for thermal design of heat exchanger.      [6]

OR

Q2) a) Explain series arrangement of hairpin heat exchangers with figure and state advantages of arrangement.                                                                                     [5]

b)         State uses of pipe in pipe heat exchangers.                                            [5]

c)        What will be the hydraulic diameter of an annulus with longitudinal finned tube with following specifications?                                                                                 [6] Inner diameter of shell 0.0525 m

Outer diameter of tube 0.0266m Number of tubes 1 Thickness of fin 0.9 mm

Axial height of fin from outer periphery of tube is 0.0127m Number of fins per tube 30

Q3) a) Oil with a flow rate of 50 kg/s enters a baffled shell and tube heat exchanger at 32°C and leaves at 25° C. Heat will be transferred to 150 kg/s of water (through tube) coming from a supply at 20°C. A single tube pass and single shell pass is used. The tube diameter is 19 mm OD and 16 mm ID and tubes are laid out on a 25mm square pitch. The max length of exchanger is of 8m. The maximum flow velocity through tube is to be 2m/s . Perform tube side analysis of heat exchanger with following steps.                                 [8]

i)              Calculate Reynolds number at tube side (considering properties of water at 20°C)

ii)           Calculate h. – Inside heat transfer coefficient, assuming f = 0.0058 (Data / charts attached can be used)

b)        Explain tube layout pattern with figure.

c)

 [4] [4]

What is impingement baffle? State its use.

OR

Q4) a) Draw block diagram and temperature profile for ‘G’ Shell 1-2 heat exchanger : Nozzles are at center, split flow, longitudinal baffles, Hot fluid enters from shell whereas cold fluid passes from tube.                                                                                                [5]

b)        Explain : Segmental baffles have a tendency to poor flow distribution if spacing of baffle is not properly selected.                                                                                     [5]

c)        Explain stepwise process of heat exchanger analysis by Kern’s method. [6]

Q5) a) State salient features of Plate fin heat exchanger.                                               [5]

b)        Compare ‘shall and tube Heat Exchanger’ and ‘compact heat exchanger’.[5]

c)        An automotive radiator has 40 tubes of inner diameter of 0.5 cm and 60 cm long in a closely spaced plate finned matrix, so that both fluids unmixed. Hot water enters the tube at 90°C at a rate of 0.6 kg/s and leaves at 65°C . Air cross flows the radiator through the inner fin spaces and is heated from 20°C to 40°C. Calculate overall heat transfer coefficient using LMTD method, based on inner surface of this radiator. (Data/ charts attached can be used)                                                                                         [8]

OR

Q6) a) Draw sketch showing plate fin heat exchanger (PFHE) flow arrangement : (a) crossflow; (b) counter flow; and (c) cross – counter flow.                                                    [5]

b)        What are Tube – Fin Heat Exchangers? Describe with fiutre.                    [5]

c)        A shell – and – tube heat exchanger with 2 – shell passes and 8 – tube passes is used to heat ethyl alcohol (Cp = 2670 J/kg. °C) in the tubes from 25°C to 70°C at a rate of 2.1 kg/s. The heating is to be done by water (Cp = 4190 J/kg. °C) that enters the shell at 95°C and leaves at 60°C. If the overall heat transfer coefficient is 800 W/m2. °C, determine the heat transfer surface area of the heat exchanger using Effectiveness –

NTU method.(Data / charts attached can be used)                                        [8]

SECTION – II

Q7) a) Explain vertical condenser with figure.                                                                 [5]

b)        Which parameters are to be specially considered for design of condensers/ evaporators compared to design of heat exchangers?                                               [5]

c)        Draw sketch and explain in brief spiral condenser.                               [6]

OR

Q8) a) Explain any one air cooled condenser with its disadvantages.                          [5]

b)        Why condenser operations fail? State any five reasons.                     [5]

c)        Describe direct expansion evaporator with sketch.                               [6]

Q9) a) Explain Direct – Contact or Open Evaporative Cooling Tower in brief. [5]

b)        How cooling tower is to be maintained in good working condition? [5]

c)        The cooling used in a power plant consists of 10 big fans. The quantity of cooling water circulated through the tower is 1000kg per minute and it is cooled from 35°C to 30°C. The atmospheric conditions are 35°C DBT and 25°C WBT. The air leaves tower at 30°C and 90% RH. Find capacity of each fan in cubic meter per minute. (Data/charts attached can be used).                                                                                                               [6]

OR

Q10) a) What is Fogging (Cooling Tower Plume)? How it can be estimated? [5]

b)        Explain Horizontal Spray cooling tower with figure.                          [5]

c)        Enlist factors to be considered during selection of pump for cooling tower.     [6]

Q11) a) Explain any three types of wicks used in heat pipes?                                       [6]

b)        Enlist prime requirements of working fluid used in heat pipes. [6]

c)        Describe heat pipe start up process.                                                         [6]

OR

Q12) a) What is the need of cooling of electronic components?                                   [6]

c)        What are effective lengths of pipes? How it is important in liquid cooling of electronics system?                                                                                                          [6]

♦              ♦♦♦

Co – relations for fully developed Turbulent forced convection through acirculate duct with cost properties.

 N4 Relation Conditon N4 = 0.022Re08 Pr03 Pr (0.5 – 1) Re (5000 and above) N (f / 2)(Re – 1000)Pr 4 1 +12.7( f /2)X[PrK -1] Re(2300 – 104) Pr (0.5 – 2000) N (f/2)Re.Pr 4 1.07 +12.7( f /2)X[PrK -1] Pr (0.5 – 2000) Re (104 – 5 x 106)

 Temp. Density T P *F •c kg/m1 32 0 1.293 41 5 1.269 50 10 1.242 59 15 1.222 68 20 1.202 77 25 1.183 86 30 1.164 95 35 1.147 104 40 1.129 113 45 1.111 122 50 1,093 131 55 1.079 140 60 1.061 149 65 1.047 158 70 1.030 167 75 1.013 176 80 , 1.001 185 85 0.986 194 90 0.972 203 95 0.959 212 100 0.947

Pune University Industrial Heat Transfer Equipments Question Papers