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University of Mumbai 2009-2nd Sem M.E Thermal Engineering Design of Heat Exchangers -e - Question Paper

Tuesday, 16 July 2013 03:10Web

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(4 Hours) (Total Marks : 100

N.B. (1) Question No. 1 is compulsory. Attempt any three from remaining five questions. (2) Use of standard data book and graphs is permitted.

. (3) Assmc suitable data i/neccssary wilh justification.

	appropriate reasons) that may be 10
(wit!

the specific heat exchanger construction used in each of the following applications

\m)

Power condenser Milk pasteurizing Automobile radiators Air preheater in power plant Marine oil coolers.

Discuss a general design methodology of heat exchanger with a flow chart representing the sequence of various design activities.

For a two fluid counter flow arrangement, show a general variation of temperature along the length of heat exchanger (through sketches) for the following cases.

(i) both fluid undergoing temperature change,

(ii) hot fluid is cooled from superheated to sub-cooled state,

(iii) cold fluid is heated from saturated to superheated state

(iv) both fluid undergoing phase change (Clearly state if any assumption is made)

What does the effectiveness of a heat exchanger represents? On what factors do it depends ? Can it be greater than one? Under what conditions is the effectivcness-NTU method definitively preferred over the LMTD method in heat exchanger analysis?

Derive efFectiveness-NTU relation fora parallel flow heat exchanger.

Explain the methodology of heat exchanger design in brief

A shell and tube heat exchanger is designed to heat water from 40C to 60C with a mass flow rate of20,000 kg/h. Water at 180C flows through the tubes with a mass flow rate of 10,000 kg/h. The tube have a inner diameter of 20 mm, the Reynolds number 10000. U = 450 W/m².FC Calculate the heat transfer rate of the heat exchanger and the exit temperature of the fluid. If the HX is the counter flow with one tube and one shell pass, determine the following using e: -NTU method:

(I) The outer heat transfer area,

The velocity of fluid through the tubes The cross-sectional area of the tube The number of tubes and the length of the heat exchanger.

(>i)

(iii)

(iv)

(v)

(b)

(c)

10

2. (a)

10

<b)

(a)

<b)

15

10

15

3.

(ii)

(iii)

(iv)

1/2

1+C*-(1 + C*²)

2-e

Where, NTU =

In

(l + C'^z)

1/2

1 + C* + (1 + c*²)

2-8

Discuss (with a sketch) the constructional features of a shell and tube heat exchanger with a focus on the following.

4. (a)

10

(i) shell, (ii) tube and tube bundles, (iii) lube passes, (iv) lube layout and (iv) baffles.

A shell and tube heat exchanger is selected for a particular application with following parameters: Shell side fluid: Hot water, Inlet and outlet temp: 67C and 53C,

(b)

15

Tube side fluid: Water at average temperature of 28.5C.

Shell internal diameter: Number of tubes:

0.39 m 124

od : 19mm, id: 16mm k=60 W/m²K 0.25 25%

Square 0.024 m

Tube diameter:

Tube material:

Baffle spacing;

Baffle cut:

Tube layout:

Pitch size:

Number of tube passes

2

Estimate shell side and tube side heat transfer coefficient and pressure drop. Following correlation can be used for shell side :

fTTTOM f\\rr?n

5763-Uy.

'~7hJLAAKJ*J[

5. (a)

_ iscuss the advantages and limitations of compact heat exchangers.

Air enters the core of a finned lube heat exchanger of the type shown in fig.l at 12 atm and 150C. The air mass flow rate is 10 kg/s and flow perpendicular to the tubes. The core is 0-5 m long with a 0.30 m² frontal area. The height of the core is 0*5 m. Water at 15?C. and at a flpw rate of 50 kg/s flows inside the tubes. Air side data is given in fig. I. For water side data, assume a = 0.129, b_h= 0.373 cm, and water side heat transfer area/ total volume = 138 m²/m³ Calculate :

(i) The air side and water side heat transfer coefficient,

(ii) Total heat transfer,

(iii) Outlet temperature of air and water.