Estimated Heat Distribution by Convection in Water Essay

Published: 2019-12-18 09:52:10
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Category: Water

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Introduction

This report assesses the distribution of heat by convection in water to estimate the heat conductivity of water. The transfer of heat from a heating coil to a fluid is conduction but the heat transfer within the fluid is convection. This is basically fluid flow of particles arising from nature, heat, chemical or kinetics. The distribution of heat is assessed with various factors introduced. In this case a magnetic stirrer and a motor. This report presents an estimate of the effect of free and forced convention on the distribution of heat in water.

Experimental method

The apparatus were arranged as shown in fig. 1. A beaker of five litre capacity was places on a motor, four litres (4L) of cold water was put in a beaker. A heating coil and three thermometers were placed at various depths in the beaker of water and their various distances from the base of the beaker were recorded. Power was supplied to the motor and heating coil and at intervals of four minutes each; the temperatures on all three thermometers were read simultaneously. After four successful readings, the electricity supply was disconnected and the ambient temperature was recorded. This same procedure was repeated twice, the first with a magnetic stirrer and the next time without the magnetic stirrer but the motor operating.

Distance from base (m)

Temperature (C)

Heating Coil

0.08



T1

0.02

24

T 2

0.09

24

T 3

0.12

24

Table 1. Distances of apparatus and initial temperature readings of the water.

Table 1 shows the ambient temperature readings collected before the experiment was carried out. It also shows the positions of the heating coil and thermometers from the base of the of the beaker.

Results

The time was kept in minutes to measure the intervals at which readings were taken. The temperature of the water was measured with thermometers in degreed Celsius and recalculated in degrees Kelvin and the positions of the heating coil and thermometers were also measured in meters.

Time (minutes)

T1 (0.02m)

T2 (0.09m)

T3 (0.12m)

0

24

24

24

4

24

28

32

8

24

39

42

12

24

46

49

16

24

54

56

Table 2: Free convection

Time (minutes)

T1 (0.02m)

T2 (0.09m)

T3 (0.12m)

0

20

20

20

4

26

26

26

8

32

32

32

12

37

37

37

16

42

42

42

Table 3: Forced convection (stirrer and motor)

Time (minutes)

T1 (0.02m)

T2 (0.09m)

T3 (0.12m)

0

20

20

20

4

20

29

32

8

21

36

38

12

21

44

46

16

22

51

54

Table 4: Forced convection (motor only)

Fig 2: Free convection

Fig 3: Forced convection (stirrer and motor)

Fig 4: Forced convection (motor only)

The readings and results derived from the experiment are being used to calculate an estimate amount of energy input and compare it with the theoretical value.

Q represents energy input

represents the power input

t represents the duration for which the water was heated

at 220v = 300w, but since 240v was used corrected value of = 300 240220 = 358 w

= 16 minutes60 = 960s

= 327.3960 = 314208J = 314.2 KJ

Experiment 1. Free convection

Assuming density of water to be 1000kg/m3

Cp = 4.18KJ/kgK

= 24 24 = 0

= 54 24 = 30

= 56 24 = 32

= 4/34.18(0 +30 +32)

= 345.55KJ

Experiment 2. Forced convection (stirrer and motor)

= 42 20 =22

= 42 20 =22

= 42 20 =22

= 4/34.18(22 +22 +22)

= 367.84KJ

Experiment 3. Forced convection (motor only)

= 22 20 = 2

= 51 20 = 31

= 54 20 = 34

= 4/34.18(2 +31 +34)

= 373.41KJ

Estimates of errors involved in this experiment are a follows:-

Time = 1 second in 60 seconds

Length = 0.01 meters of 0.1 meters

Temperature = 1 C

Discussion

In the experiment that involved forced convection from both the motor and stirrer the heat distribution was better and more accurate. This can be confirmed by the comparison of the energy input calculated based on experimental values with the energy input calculated based on the theoretical values. Readings to support this is shown in Table 3 and fig 3. A poor distribution of heat occurred in the first experiment where the water was heated freely. This is represented in Table 2 and figure 2 and by comparison of the experimental and theoretical values of the energy inputs. In experiment 3 where only the motor was used the graph 3 and figure 4 shows a better distribution of heat compared to experiment 1.

Conclusion

In a freely heated body of water, higher temperatures are taken from closer to the surface and lower temperatures towards the bottom. With introduction of kinetic energy from the stirrer and motor, the velocity of fluid flow increased thereby increasing the rate of heat transfer and the even distribution of heat through the water. This shows that water is a poor conductor of heat energy if heated with free convection.

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