UNDER THE GUIDENCE OFProf. BASAVARAJ H TALIKOTI

Mechanical dept.SPCE Bengaluru

SHRI PILLAPPA COLLEGE OF ENGINEERING

OVERVIEWOVERVIEW Abstract Introduction Literature Survey Layout of experimental set up Specifications Experimental Work Methodology Operating procedure Sample Reading Results And Discussion Graphs Conclusions Scope for future Work References

ABSTRACTABSTRACT

In the present work the experimental setup for convective heat transfer coefficient of air flowing through a copper tube of circular cross section is fabricated. This setup can be used to find out heat transfer coefficient at different operating conditions.

Using the experimental setup, convective heat transfer coefficient of air passing through circular duct was determined under the following conditions.o By varying heat input.o By varying blower valve position.o By varying inclination of circular duct.

INTRODUCTIONINTRODUCTIONHeat transfer is defined as “transmission of energy from one region to another as a result of temperature gradient”.

LITERATURE SURVEYLITERATURE SURVEY Hilpert was one of the earliest researchers in the area of forced convection from heated pipe surfaces. He developed the correlation

Nu= ﴾hd/K) =C Rem Pr0.333.

Fand and Keswani reviewed the work of Hilpert and recalculated the values of the constants C and m in the above equation using more accurate values for the thermo physical properties of air.

Zukaukasz Another correlation proposed by Zukaukas for convective heat transfer over a heated pipe is given by

Nuf = c Ref Prf0.3 7( Prf/ Prw)0.25

Churchill and Bernstein Churchill and Bernstein proposed a single comprehensive equation[5] that covered the entire range of ReD for which data was available, as well as a wide range of Pr. The equation was recommended for all ReD.Pr > 0.2 and has the form

NuD= 0.3+ *[1+(ReD/282,000)5/8]4/5

This correlation was based on semi-empirical work and all properties were evaluated at the film temperature.

Contd…..Contd…..

Dittus Boelter relation The conventional expression for calculating the heat transfer

coefficient in fully developed turbulent flow in smooth pipes is the Dittus Boelter equation

Nu = C Rem Prn

where C, m and n are constant determined experimentally. these values - C=0.023, m=0.8 and

n = 0.4 for heating of the fluid n = 0.3 for cooling of the fluid Properties of this relation have been calculated at the average fluid

bulk temperatures. Equation is valid for single phase heat transfer in fully developed turbulent flows in smooth pipes for fluids with Prandtl number ranging from 0.6 to 100 at low heat fluxes. At high fluxes the fluid properties changes resulting in higher errors.

LAYOUT OF EXPERIMENTAL LAYOUT OF EXPERIMENTAL SET UPSET UP

Where T1= inlet temperature of air T6= outlet temperature of air T2,T3,T4,T5= Specimen surface temperature

SPECIFICATIONSSPECIFICATIONS Specimen : Copper circular Tube. Size of the Specimen : 33 mm x 33 mm x 500 mm

long. Heater : Externally heated, Nichrome wire

Band Heater 500W. Ammeter : Digital type,0-20amps, AC. Voltmeter : Digital type, 0-300volts, AC. Dimmer stat for heating Coil : 0-230v, 2amps. Thermocouple Used : 6 no. k-type, range: 0 to 4000c. Centrifugal Blower : Single Phase 230v, 50 Hz,

13000rpm. G. I pipe diameter : 33 mm. Outer duct : Aluminum

EXPERIMENTAL WORKEXPERIMENTAL WORK

Fig. 1Test section copper circular duct with insulation and heater at 0º.º.

.

Fig 2: Experimental Setup of circular duct with Insulation and Heater at 30º.

Fig 3: Experimental Set up of circular duct with Insulation and Heater at 60º.

Fig 4: Experimental Setup of circular duct with Insulation and Heater at 90º.

Contd….Contd….

Fig 5:Experimental Setup of Circular Cross Section Duct at 1200

Fig 6:Experimental Setup of Circular Cross Section Duct at 1500

The above figure shows an experimental setup which comprises of test specimen made up of copper having circular cross section having dimensions 33x33x500mm, which is connected to a blower through a GI pipe and bellows.

The equipment is mounted on a 2ftX3ft rectangular table which is made up of mild steel sheets and plane woods.

Contd….Contd….

Angle of inclination can be varied in terms of 300, 600 , 90°,120° and 150° with the help of lever and nut-bolt arrangement.

Here five thermocouples of k-type, two for inlet and outlet i.e. T4 and T5, rest of the three (i.e. T1,T2 andT3) thermocouples are placed at equal distance on the surface of test specimen.

With the help of blower regulator, velocity of air can be set. Heat input can be set with the help of variac provided on

control panel and same can be read out digitally with the help of voltmeter and ammeter.

Manometer is provided on the board to indicate the level and

hence velocity for different valve opening can be calculated.

METHODOLOGYMETHODOLOGY

The apparatus consists of a blower for forced circulation. The air from the blower passes through a flow passage at

different valve positions, heater and then to the test section. A heater placed around the tube heats the air, heat input is

controlled by a dimmer stat. Heat input is measured with the help of voltmeter and ammeter.

Temperature of the air at inlet and at outlet are measured using thermocouples. The surface temperature of the tube is measured at different sections using thermocouples embedded on the circular duct.

Test section is enclosed with wool and rope, where the circulation of rope avoids the heat loss to outside.

The entire test rig is mounted on a table as shown earlier.

OPERATING PROCEDUREOPERATING PROCEDURE

Plug the 230 Volts AC mains to the main supply line and switch ON mains.

Put on the heater and adjust the voltage to a desired value by using electronic voltage regulator and maintain it as constant

Switch ON the Blower and regulate the flow for desired value by using electronic regulator (First press the switch on the blower and then control through the electronic regulator)

Allow the system to stabilize (reach steady state).This may take about 10-15 minutes.

Note down all the temperatures T1 to T5, voltmeter, ammeter readings and manometer readings.

Repeat the experiment for different heat input and air flow rates.

SAMPLE READINGSSAMPLE READINGS

Readings for the velocity of 11.097 m/s and 40v heat input at 00

Procedure for calculation

Sl No.

Manometer reading in cm

V volts

I amps

T1 0c T2 0c T3 0c T4 0c T5 0c

h1 h2 hw

01 0.7

0 0.7

40 0.61 40.6 42.7 40.3 40.6 40

Contd….

Note down all the parameters which are displayed on control panel,which includes voltage, current & all temperatures.

Calculate the surface temperature and ambient temperatures by using the following formulae :surface temp = (T1+T2+T3)/3

Ta= (T6+T5)/2Tfilm =( Ts+Ta)/2

Find the properties of air at film temperature like kinematic viscosity (ν), prandtl number (Pr), thermal conductivity (K) from heat transfer data hand book.

Calculate the Reynolds number (Re), with the formula Re = ρvD/μ Based on the Reynolds number, select the Hilpert’s constants like C

and m. Calculate Nusselt number using parameters Pr,C,m,ReD and the

formula is Nu = C Remx pr0.333.

Calculate the convective heat transfer coefficient by using the formula. h=( KxNu)/ D

Contd….

Repeat the calculation part for following different situations.

By keeping the valve openening and varying the heat input in terms of 40,60,80,100,120 and 140 m/sec ,for various angle of inclinations like 00,300,600,900,120° and 150°.

And also varying the blower valve positions by 1/4th,1/2,3/4th and full open, for various angle of inclinations like 00,300,600,900,120° and 150°.

Tabulate all the calculations for separate angle of inclinations.

RESULTS AND DISCUSSIONRESULTS AND DISCUSSION

SL NO.

 

Inclination Valve position

Velocity (m/s)

Heat input (W)

Re Nu

H

(kW/m2 0k)

01 00

1/4th 11.097 140.3 21369 81.02 64.98

1/2 12.578 140.3 25132.5 89.6 70.911

3/4th 12.58 140.3 24736.01 88.768 70.038

Full 11.094 140.3 22266.085 83.1905 65.237

02 300

1/4th 8.386 140.3 16052.12 68.052 54.533

1/2 12.58 140.3 24729.285 88.73 70.243

3/4th 12.58 140.3 24926.84 89.183 70.397

Full 11.86 140.3 23680.18 86.397 67.967

03 600

1/4th 9.375 140.3 17835.88 72.45 58.314

1/2 16.245 140.3 31869.22 103.637 81.99

3/4th 16.245 140.3 32268.645 104.615 82.49

Full 16.245 140.3 32191.638 104.498 82.45

SL NO. Inclination Valve position

Velocity (m/s)

Heat input (W)

Re Nu

h(kW/m2 0k)

04 900

1/4th 9.375 140.3 18026.91 72.92 120.86

1/2 20.54 140.3 40866.74 120.86 95.382

3/4th 22.966 140.3 46128.92 130.99 102.74

Full 23.72 140.3 47907.577 135.04 105.64

05 1200

1/4th 13.26 140.3 25766.61 90.988 72.51

1/2 21.787 140.3 43276.04 124.92 98.48

3/4th 23.345 140.3 46297.83 131.1 103.56

Full 23.34 140.3 46990.67 132.915 104.26

06 1500

1/4th 12.57 140.3 21042.95 81.36 70.12

1/2 19.66 140.3 39401.96 117.44 92.255

3/4th 24.08 140.3 48753.44 136.91 108.44

Full 23.34 140.3 46549.82 130.92 103.88

Variation of heat transfer coefficient with Variation of heat transfer coefficient with inclination for different velocities inclination for different velocities

As it seen from the above graph velocity of air flow influences the heat transfer coefficient at a greater extent than the inclination.

GRAPHS

Variation of Reynolds number and Variation of Reynolds number and Nusselts number at all inclinations Nusselts number at all inclinations

From the above graph it is clear that, irrespective of angle of inclination of duct, there is a direct proportionality between the Reynolds number (Re) and Nusselts (Nu) number. i.e., by increasing the velocity of air there must be an increase in the Reynolds number and Nusselts number, thus increasing the heat transfer coefficient.

CONCLUSIONSCONCLUSIONS

During the test it was found that convective heat transfer coefficient increases in air stream velocity at constant heat input and inclination.

From the result it is evident that heat transfer coefficient is maximum for a constant heat input of undergoes and 9.375 m/sec velocity when the when the duct was inclined at 900 inclination.

The minimum heat transfer coefficient was observed for heat input of 292.6watts and air stream velocity of 8.386 m/sec with 300 inclinations.

The decrease in heat transfer coefficient may be due to restriction in the flow of air when the duct is above 900.

SCOPE FOR FUTURE WORKSCOPE FOR FUTURE WORK The experimentation can be carried out for different fluids. The determination of variation of heat transfer coefficient for

varying cross section of the copper duct. The test rig can be computerized to obtain more accurate results. Fins can be attached on the specimen and the effect of fins on heat

transfer coefficient can be studied.

ReferencesReferences Krishpersad Manohar, Kimberly Ramroop. “A Comparison of

Correlations for Heat Transfer from Inclined Pipes” Volume 4, Issue 4, October 2010.

2. Hilpert, R. “Heat Transfer from Cylinders,” Forsch. Geb. Ingenieurwes, 4:215, 1933.

3. Fand, R. M. and K. K. Keswani. “A Continuous Correlation Equation for Heat Transfer from

Cylinders to Air in Crossflow for Reynold’s Numbers from 10-2 to 2(10)5,” International Journal of Heat and Mass Transfer, 15:559-562, 1972.

4.Zukauskas, A. “Heat Transfer From Tubes in Crossflow,” Advances in Heat Transfer, 8:87-159, 1987.

5. Churchill, S. W. and M. Bernstein. “A correlating Equation for Forced Convection from Gases and Liquids to a Circular Cylinder in Crossflow,” J. Heat Transfer, 99:300-306, 1977.

Sunil S and Basavaraj H Talikoti, “Fabrication Of Experimental Setup To Evaluate The Convective Heat Transfer Coefficient Of Air Flowing Through An Inclined Circular Cross Section Duct”. ISSN: 2278-0181 www.ijert.org IJERTV4IS020027 Vol. 4 Issue 02, February-2015.

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