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Mohammed Zaid Shaikh – H00114083Mohammed Zaid Shaikh – H00114083This document contains a report on forced convection around a cylindrical copper rod of diameter 0.0125 m This document contains a report on forced convection around a cylindrical copper rod of diameter 0.0125 m Forced CovectionThermo lab ReportForced CovectionThermo lab Report
Mohammed Zaid Shaikh – H00114083
Mohammed Zaid Shaikh – H00114083
This document contains a report on forced convection around a cylindrical copper rod of diameter 0.0125 m
This document contains a report on forced convection around a cylindrical copper rod of diameter 0.0125 m
Forced Covection
Thermo lab Report
Forced Covection
Thermo lab Report
FORCED CONVECTION – THERMO LAB REPORT
INTRODUCTION
This report covers the heat transfer rate from a cylindrical copper rod to the surrounding air moving at a certain fixed velocity in an isolated system. Besides showing how the heat transfer rate is affected by varying the velocity of air in the isolated system this experimental lab report also shows the calculations for Reynolds number, Nusselt number, as well as the film heat transfer coefficient. Moreover, it covers brief discussion on the comparison of the experimental values of 'K' and 'n' from the below equation with that of their literature values.
Nu=KRen
In this experiment the heat transfer rate associated with the cross flow of air across a cylindrical copper rod at various velocities has been investigated. The aim of the experiment is to determine the heat transfer characteristics of a cylinder under cross flow forced convection conditions when the cylinder is isolated. The following equation is used to plot the graph and hence the slope of the graph was used to calculate the estimated heat transfer coefficient α.
This experiment also helps in understanding the complexities in heat transferring during the cross flow across a cylindrical copper rod. On changing the velocity of the wind, the Reynolds number of the flow changes which then affects the heat transfer. (Fig. a) below shows a graphical representation on how increasing the Reynolds number changes the nature of the flow.
Practical and Real Life Applications:
Some of the practical applications of forced convention are:
Car radiator,
Cooling towers,
Air cooled heat exchangers etc.
For example in car radiators the cooling fan used to cool down the heated radiator is an application of heat transfer due to forced convection. Also when the car is in motion the fast air moving through the radiator cooling it down is also an example of forced convection in the car radiators. The data from this report can hence be used as reference when designing a car radiator with copper metal for ambient temperature of 23°C.
Fig. a
PROCEDURE AND APPARATUS
The following procedures were undertaken for this experiment:
The apparatus was checked by the lab supervisor
The air duct was switched on
The air speed was set to 3 m/s using the knob
The copper cylindrical rod was heated up to 97°C in an electric heated
The copper rod was then placed inside the air duct through one of the hole
The temperature drop was noted after every 5 seconds using a thermometer and stopwatch
Steps 3-6 were repeated to take readings at different wind speed
The following apparatus were used for the experiment
Cross flow heat exchanger (Fig. B)
Electric heater
Copper cylindrical rod
Stop watch
RESULTS
Given Data:
Ambient Temperature Ta=23°C
Surface area of copper cylinder A = 0.00404 m2
Mass of copper cylinder m = 0.21 kg
Specific heat of copper Cp= 0.38 kJ/kg.K
Width of working section b = 12.5 cm
Height of working section h= 12.5 cm
Diameter of rod d= 1.25 cm
Recorded Data:
Time(s)
Temp @ v=3m/s(°C)
Temp @ v=5m/s(°C)
Temp @ v=7m/s(°C)
Temp @ v=9m/s(°C)
Temp @ v=11m/s(°C)
0
97.0
97.0
97.0
97.0
97.0
5
97.0
97.0
97.0
96.1
97.0
10
92.7
91.9
95.9
90.9
91.6
15
92.7
88.2
89.1
90.9
91.6
20
88.6
86.8
89.1
83.9
83.5
25
88.6
81.1
81.4
83.9
83.5
30
87.1
81.1
81.4
78.0
78.0
35
87.1
77.3
76.0
78.0
76.9
40
82.0
76.5
76.0
72.9
71.4
45
82.0
73.2
71.5
72.9
71.4
50
79.1
72.3
71.5
68.8
66.8
55
79.1
69.3
67.6
68.8
66.8
60
77.1
68.7
67.6
65.0
62.9
65
77.1
66.0
64.1
65.0
62.9
70
74.2
66.0
64.1
61.6
60.2
75
74.2
63.0
61.1
61.6
60.2
80
72.4
62.5
61.1
58.4
56.7
85
72.4
60.3
58.1
58.4
56.7
90
70.4
60.3
58.1
56.0
54.5
95
70.4
57.4
55.4
56.0
54.5
100
68.3
57.4
55.4
53.0
51.4
105
68.3
55.5
53.6
53.0
51.4
110
66.4
55.5
53.6
51.2
49.7
115
66.4
53.3
51.2
51.2
49.7
120
64.6
53.3
51.2
49.1
47.6
Calculated Data @ u= 3 m/s
Time(s)
Temp T @ v=3m/s(°C)
Ambient Temp Ta (°C)
T-Ta (°C)
Ln(T-Ta)
0
97.0
23
74
4.304065
5
97.0
23
74
4.304065
10
92.7
23
69.7
4.2442
15
92.7
23
69.7
4.2442
20
88.6
23
65.6
4.183576
25
88.6
23
65.6
4.183576
30
87.1
23
64.1
4.160444
35
87.1
23
62.1
4.128746
40
82.0
23
59.0
4.077537
45
82.0
23
59.0
4.077537
50
79.1
23
56.1
4.027136
55
79.1
23
56.1
4.027136
60
77.1
23
54.1
3.990834
65
77.1
23
54.1
3.990834
70
74.2
23
51.2
3.93574
75
74.2
23
51.2
3.93574
80
72.4
23
49.4
3.89995
85
72.4
23
49.4
3.89995
90
70.4
23
47.4
3.858622
95
70.4
23
47.4
3.858622
100
68.3
23
45.3
3.813307
105
68.3
23
45.3
3.813307
110
66.4
23
43.4
3.770459
115
66.4
23
43.4
3.770459
120
64.6
23
41.6
3.7281
Calculations:
@ u = 3 m/s
u= 3 m/s
v=u0.9=30.9=3.33
µ=18.3808 Pa.s
ρa=1.17656 kg/m3
d=0.0125 m
b=0.125 m
h=0.125 m
k =0.0259 W/(m.K)
Heat transfer coefficient, α=-Slope of graph 1×m×CpA
α3= - -0.0048 ×0.21×3800.00404
α3=94.8 W/(m2.K)
Similarly, @ u = 5, 7, 9, and 11 heat transfer coefficient is calculated
α5=150.12 W/(m2.K)
α7=167.9 W/(m2.K)
α9=169.87 W/(m2.K)
α11=185.67 W/(m2.K)
Nusselt number, Nu= α dk
Nu3= 94.8×0.01250.0259=46
Similarly, @ u = 5, 7, 9, and 11 Nusselt number is calculated
Nu5=73
Nu7=82
Nu9=83
Nu11=90
Re =ρa v dµ
Re 3= 1.17656 ×3.333 ×0.012518.3808=2667
Similarly, @ u = 5, 7, 9, and 11 Reynolds number is calculated
Re5=4445
Re7=6315
Re9=8119
Re 11=9924
Prandlt Number, Pr =Cp × μk
Pr = 0.27
Graphical Calculations:
GRAPH #1
GRAPH #2
GRAPH #3
Values from Graphical Equations:
From Graph #1: Slope = - 0.0048
From Graph #3: Nu = KRen
Where,
K = 1.5066, n =0.4462
DISCUSSION
The Correlation literature value for 'k' and 'n' for the equation Nu = KRen were found as follows:
K= 1.15
n= 0.5
Error Analysis for K and n values:
Error % = Experimental value-Literature valueLiterature value×100
Error % for K = 1.5066-1.151.15 ×100=31%
Error % for n =0.4462-0.50.5 ×100= -10.7%
Using above values of K and n, we find Nu theoretical
Velocity u (m/s)
Reynolds Number (Re)
Nusselt Number (Nu)
3
2667
59
5
4445
77
7
6315
91
9
8119
103
11
9924
114
Plotting the graph for literature value of Nu vs. Re we get,
GRAPH #4
Comparing the graph #3 and graph #4:
According to the graphical power equations the experimental values of 'K' and 'n' are fairly comparable to the literature values. The slight difference may have occurred due to some errors during the experiment. Some of these errors are discussed below. The graph below shows the comparison of experimental values against the literature value. The experimental graph line is slight deviated below the literature value line which shows that the Nusselt number is lower of the experimental value as compared to that of the literature vales. This deviation is mainly due to the errors occurred while performing the experiment. But taking into consideration the error % values the graph shows fairly little deviation.
GRAPH #5
Possible errors during the experiment:
Varying ambient temperature
Slow digital thermocouple
Timing calculation while using the stopwatch
Varying wind speed from the air duct
CONCLUSION
The experimental results were almost as expected. Error % for the calculations was less. This experiment shows how the heat transfer rate changes under the circumstances of forced convection. In conclusion to the experimental result the following points can be noted:
On increasing the wind speed the copper rod cools faster
The thermal coefficient increases with the increase in Reynolds number
Copper is a good conductor of heat
Convection is an important part of real life applications and can cause serious engineering problems if not dealt with properly.
REFERENCE
Lienhard, J.H, IV & Lienhard, J.H. V, A Heat Transfer Textbook, 4th Ed, Cambridge, MA, Phlogiston Press, 2011. (A Free Electronic Textbook)
Berndt Wischnewski. (2011). Air Calculator. Available: http://www.peacesoftware.de/einigewerte/calc_luft.php5. Last accessed 20th oct 2013.
http://www.egr.msu.edu/~somerton/Nusselt/i/i_a/i_a_3_(ii)/i_a_3_(ii).html
(T-Ta) vs t
Time
T-Ta
Nu vs Re
Reynolds number
Nusselt number
Nu vs Re
Reynold number
Nusselt number
Reynolds number
Nusselt number
Ln (T-Ta) vs t
Time
ln ()T-Ta
