Le Vu Anh Phuong (U1320848B)

SCHOOL OF CHEMICAL AND BIOMEDICAL

ENGINEERING (Division of Chemical & Biomolecular Engineering)

Nanyang Technological

University

Yr 2 / SEMESTER 2

N1.2-B4-16

CH2702

Experiment C4

Heat Exchanger

Name: Le Vu Anh Phuong Student ID: U1320848B Group: 14 Date: 10/2/15

Le Vu Anh Phuong (U1320848B)

I. Log sheet and sample calculations

Sample calculation

Parallel flow

𝑚ℎ̇ =(𝑉 + 𝑡6 × 0.0041 − 0.0796)𝜌

60=

(3.00 + 61.5 × 0.0041 − 0.0796) × 977

60 × 1000= 0.0517 𝑘𝑔/𝑠

𝑄ℎ = 𝑚ℎ̇ 𝐶𝑝(𝑡3 − 𝑡6) = 0.0517 × 4180 × (70.4 − 61.5) = 1921.84 𝑊

𝑄𝑐 = 𝑚𝑐̇ 𝐶𝑝(𝑡7 − 𝑡10) = 0.015 × 4180 × (29.9 − 54.3) = −1529.88 𝑊

𝜃𝑖𝑛 =(𝑡3 − 𝑡7) − (𝑡6 − 𝑡10)

ln 𝑡3 − 𝑡7𝑡6 − 𝑡10

=(70.4 − 29.9) − (61.5 − 54.3)

ln70.4 − 29.961.5 − 54.3

= 19.28𝑜𝐶

𝑈 =𝑄ℎ̇

𝐴𝑚𝜃𝑖𝑛=

1921.84

0.0288 × 19.283461.22 𝑊/𝑚2𝐾

Test Parallel Flow Counter Flow

Metal wall at inlet, t1 (oC) 59.5 67.8

Metal wall at exit, t2 (oC) 58.2 47.8

Hot stream at inlet t3 (oC) 70.4 70.7

Hot stream 1st intermediate, t4 (oC) 66.3 68.3

Hot stream 2nd intermediate, t5 (oC) 63.5 65.2

Hot stream at exit, t6 (oC) 61.5 60.2

Cold stream entry (parallel)/exit (counter), t7 (oC) 29.9 56.5

Cold stream intermediate, t8 (oC) 42.6 49.5

Cold stram intermediate, t9 (oC) 50.0 40.9

Cold stream entry (counter)/exit (parallel), t10 (oC) 54.3 30.3

Hot water indicated flow V, L/min 3.00 3.00

Water density at hot water inlet, ρ, kgm-3 977 977

Hot water actual flow rate, mh (kg/s) 0.0517 0.0516

Mean hot water temperature (t3+t6)/2 65.95 65.45

Cooling water flow rate, mc (kg/s) 0.015 0.015

Heat transfer from hot water, Qh (W) 1921.84 2263.53

Heat transfer from cold water, Qc (W) 1529.88 1642.74

Log mean temperature difference (θin) 19.28 15.35

Overall heat transfer coefficient, U (W/m2K) 3461.22 5119.37

Le Vu Anh Phuong (U1320848B)

Test 1 (100%)

2 (80%)

3 (60%)

4 (40%)

5 (20%)

Metal wall at inlet, t1 (oC) 67.0 67.0 67.5 67.6 67.5

Metal wall at exit, t2 (oC) 53.9 52.2 50.5 47.1 40.1

Hot stream at inlet t3 (oC) 68.4 68.6 69.9 70.8 75.4

Hot stream 1st intermediate, t4 (oC) 67.4 67.5 68.2 68 68.8

Hot stream 2nd intermediate, t5 (oC) 66.2 65.7 66 64.9 62.2

Hot stream at exit, t6 (oC) 63.7 62.6 62.1 60 54

Cold stream entry/exit, t7 (oC) 58.8 58 57.3 55.5 50

Cold stream intermediate, t8 (oC) 52.7 51.5 50.6 48 42.5

Cold stram intermediate, t9 (oC) 43.7 42.7 41.8 40.1 36.1

Cold stream entry/exit, t10 (oC) 30.3 30.3 30.4 30.2 29.7

Hot water indicated flow V, L/min 8.5 6.8 5.1 3.4 1.7

Hot water actual flow rate, mh (kg/s) 0.142 0.114 0.086 0.058 0.030

Cooling water flow rate, mc (kg/s) 0.02 0.02 0.02 0.02 0.02

Water density at hot water inlet, ρ, kg/m3

978.5 978.0 977.5 977.0 973.0

Mean hot water temperature (t3+t6)/2 66.05 65.6 66 65.4 64.7

Linear velocity at inner tube v (m/s) 2.953 2.373 1.794 1.213 0.626

Reynolds No. at mean hot water temperature, Re

54349 42641 32989 21774 11465

Surface heat transfer Coeff. at inner tube, hh, (W/m2K), iii

24688 23245 18385 14436 9640

Surface heat transfer Coeff. at outer tube, hc, (W/m2K), iv

5276 5149 4971 4749 4013

Overall heat transfer coefficient, U (W/m2K), v

5059 5085 4700 4185 3734

water viscosity at mean hot water temperature µ (x10-6 Nsm-1)

420 430 420 430 420

θinh 4.32 4.70 5.84 6.96 10.62

θinc 14.57 14.51 14.59 14.37 13.64

Qh 2781.52 2852.25 2801.95 2621.64 2671.74

Qc 2382.60 2315.72 2248.84 2115.08 1697.08

θln(overall) 19.09 19.48 20.70 21.75 24.85

Sample calculation

100%

Re:

Linear velocity at inner tube

𝑣 =𝑚ℎ̇

𝐴𝜌=

0.142

49 × 10−6 × 978.5= 2.95 𝑚/𝑠

𝑅𝑒 =𝑣𝐷𝜌

𝜇=

2.95 × 7.9 ÷ 1000

420 × 10−6= 54349

𝑄ℎ = 𝑚ℎ̇ 𝐶𝑝(𝑡3 − 𝑡6) = 0.142 × 4180 × (68.4 − 63.7) = 2781.52 𝑊

𝑄𝑐 = 𝑚𝑐̇ 𝐶𝑝(𝑡7 − 𝑡10) = 0.02 × 4180 × (58.8 − 30.3) = 2382.6 𝑊

Le Vu Anh Phuong (U1320848B)

ℎℎ =𝑄ℎ

𝐴ℎ(𝑡3 − 𝑡1) − (𝑡6 − 𝑡2)

ln 𝑡3 − 𝑡1𝑡6 − 𝑡2

=2781.52

0.0261 ×(68.4 − 67.0) − (63.7 − 53.9)

ln68.7 − 67.063.7 − 53.9

= 24688 W/m2K

ℎ𝑐 =𝑄𝑐

𝐴𝑐(𝑡1 − 𝑡7) − (𝑡2 − 𝑡10)

ln 𝑡1 − 𝑡7𝑡2 − 𝑡10

=2382.6

0.031 ×(67.0 − 58.8) − (53.9 − 30.3)

ln67.0 − 58.853.9 − 30.3

= 5276 W/m2K

𝑈 =𝑄ℎ̇

𝐴𝑚(𝑡3 − 𝑡7) − (𝑡6 − 𝑡10)

ln 𝑡3 − 𝑡7𝑡6 − 𝑡10

=2781.52

0.0288 ×(68.4 − 58.8) − (63.7 − 30.3)

ln68.4 − 58.863.7 − 30.3

= 5059 W/m2K

II. Results and discussion

1. Parallel and counter flow

0

10

20

30

40

50

60

70

80

1 2

Tem

per

atu

re (

oC

)

position t

Temperature distribution of the metal wall

Parallel Flow Counter Flow

0

10

20

30

40

50

60

7 8 9 10

Tem

per

atu

re (

oC

)

Position t

Temperature distribution of the cold stream

Parallel Flow Counter Flow

Le Vu Anh Phuong (U1320848B)

From the data collected, in both parallel and counter flows, the exit temperature of the hot

stream (t6) is always higher than the exit temperature of the cold stream (t10 in parallel and t7 in

counter flow). Additionally the metal wall temperatures are always in between the

temperatures of the cold and hot streams across it. This shows the thermodynamic law that heat

spontaneous flows from a hot body to a colder body. In theory, the amount of heat loss by the

hot stream is fully received by the cold stream. However this cannot be achieve in practice due to heat loss, and the data demonstrate this loss. Heat loss in the parallel flow is about 20% of the

total heat transferred from the hot stream, while that loss in the counter flow is slightly higher,

at about 27%. From the calculation, the log mean temperature difference of the parallel flow

(19.28oC) is higher than that of the counter flow (15.35oC). However the overall heat transfer

coefficient U (W/m2K) of the counter flow (5119.37) is higher than that of the parallel flow

(3461.22). This shows that the counter flow is more effective for heat transfer. Hence in

conclusion, the counter flow heat exchanger is more preferable in practice.

2. Effect of fluid velocity on the surface heat transfer coefficients

From the data collected, it can be seen that an increase in fluid flow rate, corresponding to a

higher velocity, leads to an increase in rate of heat transfer, shown by the higher heat transfer

coefficients for both the convective heat transfer (h1 and h2) and the overall heat transfer

coefficient (U). This is in good agreement with the theory as higher velocity leads to higher

Reynolds number and more turbulent flow, resulting in higher heat transfer. The overall heat

transfer coefficient U is also close to the theoretical values obtained from 𝑈 = 1/(1

ℎℎ+

1

ℎ𝑐),

neglecting the thermal resistance of the metal wall. It is noteworthy that the overall U is closed

to hh because Qh is used to calculate U to minimise the effect of heat losses, which are relatively

significant as shown in part 1.

58

60

62

64

66

68

70

72

3 4 5 6

Tem

per

atu

re (

oC

)

Position t

Temperature distribution of the hot stream

Parallel Flow Counter Flow

Le Vu Anh Phuong (U1320848B)

.

0

5000

10000

15000

20000

25000

30000

0.000 0.500 1.000 1.500 2.000 2.500 3.000 3.500

Hea

t Tr

ansf

er C

oef

f. (

W/m

2 K)

Linear velocity at inner tube (m/s)

Inner Tube hc

0

1000

2000

3000

4000

5000

6000

0.000 0.500 1.000 1.500 2.000 2.500 3.000 3.500

Hea

t Tr

ansf

er C

oef

f. (

W/m

2 K)

Linear velocity at inner tube (m/s)

Outer Tube hh

0

1000

2000

3000

4000

5000

6000

0.000 0.500 1.000 1.500 2.000 2.500 3.000 3.500

Hea

t Tr

ansf

er C

oef

f. (

W/m

2 K)

Linear velocity at inner tube (m/s)

Overall U