Experiment 2 Tubular Heat Exchanger

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Experiments in Chemical Engineering,2nd

ed Performance of a Tubular Condenserby Servillano S.B. Olao, Jr.

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EXPERIMENT B2

PERFORMANCE OF A TUBULAR CONDENSER

INTRODUCTION

In a modern industrial plant, many heating processes require steam. Key ingredients are

heated to a desirable temperature required for efficient processing. Reactions usually require

a definite operating temperature and more importantly, final products must be set toconditions that are most convenient for handling and selling. More often that not, heat

exchange among various plant process streams transpire in heat exchanger equipment such

as a tubular condensers. It is therefore essential that future plant engineers be exposed to thiskey industrial equipment, be learned of the concepts and theories of condensation and most

importantly be trained with the operation of this type of heat transfer equipment.

OBJECTIVES

1. To determine the capacity of the tubular condenser as a function of the flow rate of thecooling water used.

2. To determine the experimental overall heat transfer coefficient for a vertical tubular

condenser.

3. To calculate theoretical surface coefficients of steam condensing inside the tubes and ofthe cooling water flowing upwards the shell side of the condenser.

4. To compare experimental and theoretical values of the overall heat transfer coefficients

as obtained in (2) and (3).

5. To determine the heat lost to the surroundings.

THEORY

The capacity of the tubular heat exchanger may be expressed in terms of the amountof steam condensed per unit time which is dependent upon the conditions of the cooling

water supplied. The maximum capacity, however, can be considered as the amount of steam

condensed when an infinite flow rate of cooling water is supplied. This also means that thereis practically no heat transfer resistance in the cooling water side such that its temperature

throughout the operation remains constant.


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To determine the experimental heat transfer coefficient, one measures first the

amount of steam condensed per unit time, ( )measuredh

m . In order to account for the losses in

the amount of steam condensed due to the flashing of steam when the condensate leaves the

steam trap due to sudden reduction in pressure, a correction known as the flashing

effect, ( )correctionh

m correction is added.

The total amount of steam is therefore

mh= ( ) ( )correctionhmeasuredh mm + .

By applying heat balance, the total heat given off by the steam is

( )chpshs TTcmq += (1)

where qs = Total amount of heat transferred by steam, Btu/hr

s = Latent heat of vaporization, Btu/lbm

mh = Total amount of steam used, lbm

cp = Specific heat, Btu/lbm-F

Th = Condensing temperature of steam,F

Tc = Temperature of condensate,F

The amount of heat absorbed by the water is given by

( )2w1wpww TTcmq = (2)

where qw = Amount of heat gained by the water, Btu/lb

mw = Mass flow rate of cooling water, lbm/hr

Tw1 = Outlet temperature of cooling water,F

Tw2 = Inlet temperature of cooling water,F

cp = Specific heat, Btu/lbm-F

The heat lost to the surroundings, qL, is the difference between the two which is expected

to be small since the cooling water is flowing through the shell side. Hence,

wsL qqq = (3)


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Based on the heat transferred by the steam, the experimentalUois calculated by

( )oo

h

erimentalexpoTA

mU

= (4)

where Ao = Total heat transfer area of the tubes

N = Number of tubes

The determination of the surface coefficients of steam condensing inside the tubes isdone by assuming that film type condensation occurs. This is most likely since the

condenser is old and the tubes are positioned vertically. The heat transfer coefficien t hifor

the tube side fluid is estimated by

25.0

f

c

2

f

3

f

iLT

gk

943.0hO

=

(6)

The subscriptfrefers to the average film temperature evaluated by (MS 13-11)

( ) ( )whhohf TT4

3TT

4

3TT == (7)

where Tf = Film temperature of condensate, F

Th = Temperature of condensing vapor, F

Tw = Assumed temperature of the tube wall, F

However, Equation (5) is derived on the assumption that the condensate flow is laminar.

This limits its use to cases where 4 is less than 2100. For long tubes, the condensate film

becomes sufficiently thick and its velocity sufficiently large to cause turbulence. Even whenthe flow becomes laminar, coefficients calculated are increased by 20%. This is due to the

effect of the ripples on the surface of the falling film. For turbulent flow, the coefficient h

increases with an increase in the Reynolds number. Refer to Figure 13-2 (MS) in case such acondition is encountered.

The heat transfer coefficient of water flowing in the shell side may be estimated usingEquation 15-4 (MS).14.0

w

33.066.0

oooo

k

CpGD20.0

k

Dh

=

(8)

wheremin

w

OS

mG = (9)


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( )otismin NDD4

S =

(10)

N = Number of tubes

Dis = Inside diameter of the shell

Dot = Outside diameter of the tube

The theoretical Uois calculated using

ii

o

L

o

oo Dh

D

kD

D

h

1

U

1++= (11)

Check for the assumed Twusing resistance form of heat transfer,

oo

wh

oo

ch

Ah

1

TT

AU

1

TT =

(12)

Compare the theoretical Uowith the experimental Uo.


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EQUIPMENT

A. Schematic Diagram of the Equipment

Figure 2: Tubular Heat Exchanger


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Figure 3 Cross-Sectional View of a Tubular Heat Exchanger


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B. Description of the Equipment

The equipment used for this experiment is a vertical tube condenser. The tubular

condenser has 38 tubes within the shell. These tubes are 85 inches long and made of

steel. Consequently, the tubes have outside diameters of 18 mm or 0.7086 inch. The

inside diameter of these tubes are 0.4375 inch each.

The shell is also made of steel with the outside diameter measuring 8.52 inches.

Moreover, the shell's thickness is 0.332 inch with the computed inside diametermeasuring 7.856 inches.

The steam enters the bottom of the condenser through the header then rises insidethe tubes where the steam condenses on the inside surface of the tubes. The condensate

flows downwards as thin film and collects at the bottom where it is discharged through

the steam trap then to the condensate collection tank.

The cooling water is introduced at the bottom of the shell and rises outside thebundle of tubes and exits on top, flows through the double pipe heat exchanger and is

discharged to the hot water collection tank. This tank gives a direct reading in pounds ofwater.

PROCEDURE

Note: This experiment should be performed in close coordination with Experiment B1.

1. Drain the residual steam condensate by opening the drain valve.

2. Allow cooling water to flow through the condenser by opening fully the water supplyvalves.

3. Stabilize the equipment by allowing small amount of steam inside to escape (this willalso remove residual condensate). Close the drain valve and make sure that the

condensate line with the steam trap is fully open. Then increase pressure to the desired

level (say 30 psig). Allow equipment to heat to a stable temperature. Read temperature

occasionally until the system has reached an almost steady state condition. Thecondensate collected must already be clean.

4. Operate the system for about 10 to 15 minutes at constant steam pressure. Within thisinterval determine temperature and pressure readings, flow rates of condensate and

cooling water used. Note that the condensate collection tank has a gauge for direct

reading of mass collected. Since the amount of condensate is usually small, it issuggested that one measures the total condensate collected within the time interval of the

run. For the cooling water, (used as the hot fluid in the experiment involving double pipe

heat exchanger), the flow rate is measured in the collection tank of Experiment No. 1.


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5. Repeat the procedure making use of various water flow rates and various steam

pressures. The water pressure gauge may be used as a guide in varying the water flowrate. It is suggested that three different steam pressures (say 30, 40, & 50 psig) and three

water flow rates for a total of nine runs be conducted to complete the experiment.

DATA SHEET

A. Shell and Tube Specifications

Shell Outside Diameter __________ Tube Sheet Outside Diameter __________

Shell Inside Diameter __________ Tube Length __________

Shell Thickness __________ Test Pressure __________

Shell Length __________ Number of Tubes __________

Tube Outside Diameter __________ Number of Baffles __________

Tube Inside Diameter __________

Tube Thickness __________

B. First Run

Steam Pressure __________

Water Pressure __________

Temperature (C) Flow Rate (kg/s)Time

(min) Steam Hot Water Condensate Cold Water CondensateCooling

Water

0

3

6

9

12

15


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C. Second Run





Water

0

3

6

9

12

15

D. Third Run





Water

03

6

9

12

15

ANALYSES AND CALCULATIONS

1. For each run, calculate the heat supplied by the steam, the heat absorbed by the coolingwater and the difference. This difference should indicate the heat lost to thesurroundings. Present results as Table 1.

2. For each run, calculate the heat transfer coefficient of steam condensing inside the tubes,

hi; the coefficient of water outside the tubes, ho; and the theoretical Uo. Compare theexperimental Uoand determine the percentage deviation. Present as Table 2.


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3. For the six runs, plot the value of ( ) 31

2

fff gkh versus fRe 4N = for the

condensing steam and compare this with Fig. 13-2 (MS).

4. For the six runs, plot the mass of steam condensed versus the mass flow rate of water

used. Is there any correlation obtained?

GUIDE QUESTIONS

1. With the aid of a diagram, describe the operating principles of at least four types of

steam traps.

2. Using data gathered, determine theoretically the maximum capacity of the condenser.Compare this with the capacity obtained using the maximum flow rate of cooling water.

Experiment 2 Tubular Heat Exchanger

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