experint laminar

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CUKUROVA UNIVERSITY

Faculty of Engineering & Architecture Department of Mechanical Engineering

THE EXPERIMENT OF LAMINAR VISCOUS FLOW HEAT TRANSFER UNIT

Name : Erhan Ekici

Number : 2010257017

Group No : 3

Due Date : 11/12/2014

Instructor : RESEARCHER GOKHAN TUCCAR

LAMINAR VISCOUS FLOW HEAT TRANSFER UNIT

Results and calculations

Determination of mass flow rate of oil:


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Core tube Outer tube

Material copper Copper

Outer diameter (domm) 12,7 15,9

Inner diameter (dimm) 11,3 14,4

Effective length (L mm) 910 910

Dimensions of tubes

oiloil

oil

t

Vm .

= skg/03805,085,07,6

3,0 where

Voil: volume of oil collected in the glass measuring tank.

t: time to collect oil in glass measuring tank.

oil: density of oil at mean temperature (T1+T2)/2 from graphic of properties of shell thermia oil B.

oil=0.85 kg/l w=0.996 kg/l

Simple energy account for a heat exchanger:

)( 21

..

TTcmQ poiloiloil = 03805,0 *1,92*2.3=0,168kj/s

)( 56

..

TTcmQ pwww = 1*0,132*1=0,132 kj/s where

oilQ.

: rate of heat transferred from oil.

wQ. : rate of heat transferred to cold water.

cpoil: specific heat of oil at mean temperature (T1+T2)/2 .

cpw: specific heat of water at mean temperature (T5+T6)/2.


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Determination of surface heat transfer coefficients on both the oil and water sides and of the

overall heat transfer coefficient:

toi

oilot

TA

Qh

ln

.

= 148

09,35*0323,0

/168,0

skj (W/m2C0)

wt

oil

twTA

Qh

ln0

.

= 47298,0*0363,0

/168,0

skj (W/m2C0)

wm

oil

TA

Qu

0ln

.

= 1352,36*0343,0

168,0 (W/m2C0) where

hot: Surface heat transfer coefficient between oil and tube.

htw: Surface heat transfer coefficient between tube and water.

u: Overall heat transfer coefficient.

Ai: Internal heat transfer surface area of the inner tube. Ai= 0.0323 m2

Ao: outer heat transfer surface area of the inner tube. Ao= 0.0363 m2

Am: Logarithmic heat transfer surface area of the inner tube.

)(i

o

iom

A

A

Ln

AAA

toT ln : Logarithmic mean temperature difference between oil and tube.

42

31

4231

ln

TT

TTLn

TTTTto =

C

Ln

009,35

1,1752

193,54

1,1752193,54

wtT ln : Logarithmic mean temperature difference between tube and water.


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64

53

6453ln

TT

TTLn

TTTTwt

=

C

Ln

098,0

5.161,17

5,1719

5,161,175,1719

woT ln : Logarithmic overall mean temperature difference between oil andwater.

)(

)(

62

51

6251ln

TT

TTLn

TTTTT wo

=

C

Ln

02,36

5.1652

5,173,54

5.16525,173,54

Mean velocity of Oil (Uoil) and Water (Uw):

ioil

oiloil

A

mU

*

.

= 4476,0

0001,0*85,0*1000

03805,0 (m/s)

506,100002,0*996,0*1000

03,0

*

.

ww

w

wA

mU

(m/s) where;

Ai: Flow cross-sectional area of the oil passed in the inner tube.

Aw: flow cross-sectional area of the water passed between inner and outer tubes.

Ai= 0.0001 m2 Aw=0.00002 m

2

Calculation of nusselt numbers and z*

What does nusselt number represents ?: For forced convection of a single-phase fluid with

moderatetemperature differences, the heat flux is nearly proportional to the temperature difference T=Tw

Tf(Tw: temperature of the wall, T f: temperature of the fluid).This was discovered by Newton who then

inferred that q T. Thus arrive at Newtonslaw of cooling.

q = h ( TwTf) where h is the heat transfer coefficient with units of W / m20C


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But h is dimensional and thus its value depends on the unit used. The traditional dimensionless

form of h is theNusselt Number.Nu, which may be defined as the ratio of convection heat transfer to fluid

conduction heat transfer under the same conditions. Lets consider a fluid of width L and temperaturedifference ( TwTf). Assuming that the layer is moving so that the convection occurs, the heat flux would

be,

q = h (TwTf)

If on the other hand, the layer were stagnant, the heat flux would be entirely due to the fluid

conduction through the layer.

q = k (TwTf) / L

We define the nusselt numberas the ratio of these two

k

Lh

q

qN

conduction

convectionu

*

A nusselt number of order unity would indicate a sluggish motion little more effective than pure

fluid conduction; for example, laminar flow in a long pipe. A large nusselt number means very efficient

convection; for example, turbulent pipe flow yield Nuof order 100 to 1000.

Another number that is called Prandtl number used in our calculations to determine z * and

theoritical Nusselt number. The Prandtl number is another dimensionless number representing the ratio of

momentum transport in a flow. Reynolds number is another one giving the characteritics of flow. f it is

greater than 2300 the flow is called as turbulant. Numbers less than this indicates a laminar flow.

Experimental Nusselt number can be calculated using equation below;

oil

ito

uek

dhN

* = 84,121302,0

0113,0*148

oil

ioil

v

du *Re =

6^10*14

0113,0*4476,0

= 27.361

oilidLz

PrRe**

* = 001486.0

150*27.361*0113,0910,0


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The theoritical Nusselt number can be calculated using equation below:

11,03

1

*

8

1

*4

3*

PrPr*0861,0

*5,341*

0704,01657,32

w

utz

zz

N

= 27,3800

150*

001486.0

0861,0

)3*5,341(*5,1

0704,01657,3

11,031

81

where

Nue: Experimental Nusselt number.

Nut: TheoriticalNusselt number.

koil: Thermal conductivity of oil at arithmetic mean temperature (T1+T2)/2, from table 5 koil = 0,1302

W/m0C.

oil: Kinematics viscosity of oil at arithmetic mean temperature (T1+T2)/2, from table 2 oil=14*10-6m2/s.

Proil: Prandtl number of oil at (T1+T2)/2, from table 1 Proil= 150

Prw: Prandtl number at wall temperature (T3+T4)/2, from table 1 Prw= 800.

All values calculated from above equations and recorded values are given below in the tables.

For Water Flow Rate is Constant

con-current flowExperiments T1 T2 T3 T4 T5 T6 Voil t mwater

1 54,5 52,1 19,9 19,3 16,1 18,7 0,2 4,89 18

For Water & Oil Flow Rate is Constant

counter-current

flow

1 54,3 52 19 17,1 17,5 16,5 0,3 6,7 30

2 55,5 52,1 18,6 17 17,3 16,5 0,3 11,5 30


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3 56,6 52,3 18,4 16,9 17,2 16,5 0,3 16,6 30

4 57,7 54,1 22,6 17,7 19,6 16,5 0,3 11,4 10

5 58,2 54,5 19,8 17,1 17,9 16,4 0,3 11,4 20

6 58,7 54,9 17,9 16,7 16,8 16,4 0,3 11,4 45

Table 1: Values recorded during experiment

m oil Q oil h o-t u oil Re z Nu e Nu t Exp. No:

0,03805 168 148 0,4476 361,27 1,486/

10-3

12,84 3,271

DISCUSSION

a)

Experimental value of Nusselt Number is greater than the theoretical value. It can caused

experiment conditions. For example; relative errors, precision of measurement, calibration of

instrument

b) Con-current flow: The hot and cold fluid enter at the same end of the heat exchanger flow

through in the same direction and leave together at the other end.

Counter-current flow: The hot and cold fluids enter in the opposite ends of the heat exchanger flow

through in the opposite direction and leave together at the other end

c) These differences are depend on the water and oil mass flow rate, specific heats of oil and water,

entering and leaving temperatures of oil and water. Because of these, we can say that the volumes

of oil and water collected in the glass measuring tank, time to collect oil in the glass measuring

tank and density of the oil at mean temperature from graphic are important for changing the rate of

heat transfer.

d)Shell and tube, plate, plate and shell, platefin, pillow plate.


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e)Shell and tube, plate, plate and shell, platefin, pillow plate, adiabatic, fluid heat exchanger regenerative

heat exchanger , dynamic scraped surface , phases change .

f)Regenerative heat exchanger is a type of heat exchanger where heat from the hot fluid is

intermittently stored in a thermal storage medium before it is transferred to the cold fluid.

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