LAB C aakash chauhan
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Applied Science (SCIE8020)
Submitted by:
Aakash Rajeshkumar Chauhan
8913874
Submission Date:20-10-23
Lab C
“Heat Transfer Methods”
Prof. Ijaz Rauf
Objective:
Observe and understand the methods of heat transfer.
Introduction – Heat Transfer Methods
The objective of this lab is to explore the various mechanisms of heat transfer outlined below:---
Conduction
: This refers to the transfer of heat that occurs when two materials or objects make direct contact. It involves the movement of heat energy within a solid
substance or between two solids in contact with one another, flowing from an area
of higher temperature to an area of lower temperature. The transmission of heat is
facilitated by the vibrations and collisions of atoms or molecules within the material. When objects in contact have different temperatures, heat is transferred from the hotter object to the cooler one. This is achieved as the particles in the hotter object, owing to their higher kinetic energy, collide with particles and thus transfer energy. This process continues until both objects reach thermal equilibrium, meaning they are at the same temperature. Materials with mobile electrons, such as metals, are effective conductors of heat.
Convection
: Convection is a heat transfer method that relies on the movement of fluids. Heat energy is transferred through the collective motion of particles in the fluid. There are two forms of convection: natural and forced. Natural convection pertains to the heat transfer resulting from density changes within a fluid triggered
by temperature variations. Cooler fluid, being denser, descends while warmer fluid expands, becoming less dense and rising. This creates a recurring flow known as a convection current. In contrast, forced convection involves the flow of fluid driven by an external force or mechanical means to facilitate heat transfer. Examples of equipment that achieve this include fans, pumps, and air conditioning systems. Enhancing contact between the fluid and heated or cooled surfaces is the key to improving heat transfer through forced fluid movement.
Radiation
: Radiation is a method of heat transfer that doesn't rely on a medium or direct physical contact between objects. It involves the transfer of thermal energy via infrared electromagnetic waves. Unlike conduction and convection, radiation doesn't require physical contact or a material medium. Radiation is the process by which heat is emitted from a hotter object in the form of electromagnetic waves. These waves, carrying energy, can traverse an empty vacuum as well as transparent
substances like glass or air. When they encounter a cooler object, they may be transferred, reflected, or absorbed as they transmit.
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Performed task during the experiment.
I performed the part two of the convection experiment.
we assembled two constant-temperature hot plates and one regular hot plate for the experiment.
We prepared four beakers, each filled with 100ml of liquid (about 75% full). We placed one beaker on the lab bench. In the second beaker, we added a magnetic mixer bar but didn't apply any heat. We set the magnetic mixer to half speed. The third beaker went on a constant-temperature hot plate set to 60°C, and the fourth beaker on the regular hot plate at its maximum settings.
Then, we took the temperature of the beaker on the lab bench. Then, we carefully squeezed three drops of food coloring onto the water's surface from a short distance.
We observed how fast the food coloring dispersed in the water due to natural convection currents at that temperature.
After that, we noted the temperature of the beaker on the constant-temperature hot plate with the mixer running. We squeezed three drops of food coloring gently onto the water's surface.
We watched to see how quickly the food coloring spread through the water due to the forced convection currents at that temperature.
Once the beaker on the 60°C constant-temperature hot plate reached the right temperature, we squeezed three drops of food coloring onto the water's surface from a short distance.
We carefully observed the speed at which the food coloring dispersed in the water due
to natural convection currents at 60°C
When the beaker on the regular hot plate reached a boil, we took its temperature. Wearing heat-proof gloves, we gently added three drops of food coloring from a close distance.
And then we monitored how fast the food coloring spread through the water due to natural convection currents at 100°C.
Procedure
Procedure Part 1 – Radiation Heating and Cooling 1.
Measure the length and width of the space heater’s emitting surface and calculate its area: L = ..0.09
.....
m; W = ..0.095
.....
m; A = …0.0085…. m
2
2.
Measure the mass of the aluminum strips: m
metallic
= 10g; m
red
= 10g; m
blue
=8g 3.
Using the metal stand, place the three aluminum strips with different finishes standing in parallel about 1cm apart from one another
. Ensure that they have parallel surfaces. Take the temperature of the surrounding air in the room. Convert to Kelvin. T
surroundings
= …21.2….. o
C = ……294.35……. K Table 1. Data collection for Part 1 – Radiation Heating
Time (sec) Temperature
of Metallic
Strip (
o
C) Temperature of
Red Strip (
o
C) Temperature of Blue Strip (
o
C) Temperature of
Heater (
o
C) 0 37.6
43
42
94
30 38.2
51.1
60.9
116
60 40
54.1
61.7
120.9
90 37.6
63.9
58.5
98.4
120 35.3
54.3
59.6
128.2
150 40.1
51.8
53.4
125.8
180 35.3
53.1
49.7
122.0
210 40.2
49.2
41.1
117
240 35.5
49.6
50.3
117.6
270 35.7
56.1
51.2
121
300 34.1
46.5
50.5
119.6
330 34.5
48.2
46.8
117.8
360 33.1
50.6
46.8
126
390 32.6
49.1
46.1
124.3
420 31.6
52.6
46
119
450 33.1
53.2
45.9
113.7
480 33.2
49.9
48.1
117.7
510 38.2
50.9
46.7
116.1
540 37
48.1
45.7
111.3
570 37.6
47.1
54.2
123.6
600 30.9
49.6
51.2
119.2
Table 2. Conversion of all temperatures in Part 1 to Kelvin
Time (min) Temperature of
Metallic Strip (K) Temperature of
Red Strip (K) Temperature of Blue Strip (K) Temperature of
Heater (K) 0 310.75
316.15
315.15
385
30 301.35
324.25
334.05
389.15
60 313.15
327.25
334.85
394.05
90 310.75
337.05
331.65
371.55
120 308.45
327.45
332.75
401.35
150 313.25
324.95
326.55
398.95
180 308.45
326.25
322.85
395.15
210 313.35
322.35
314.25
390.15
240 308.65
322.75
323.45
390.75
270 308.85
329.25
324.35
394.15
300 302.95
319.65
323.65
392.75
330 307.65
321.35
319.95
390.95
360 302.55
323.75
319.95
399.15
390 305.75
322.25
319.25
397.45
420 304.75
325.75
319.15
392.15
450 306.25
326.35
319.05
386.85
480 306.35
323.05
321.25
390.85
510 311.35
324.05
319.85
389.25
540 310.15
321.25
318.85
384.45
570 310.75
320.25
327.35
396.75
600 304.05
322.75
324.35
392.35
Table 3. Log-Mean Temperatures from Part 1 Temperature
of
Metallic Strip (K) Temperature of
White Strip (K) Temperature of Black Strip (K) Temperature of
Heater (K) Log-Mean
307.77
326.34
324.29
393.04
Table 4. Radiative Cooling – Temperatures of Aluminum Strips Every 30 Seconds
Time (min) Temperature of
Metallic Strip (
o
C) Temperature of
Red Strip (
o
C) Temperature of Blue Strip (
o
C) 0 38.7
44.3
46.9
30 25.9
35.6
36.9
60 25.9
33.1
29.2
90 22.3
27.4
27.3
120 22.3
25.9
25.5
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150 22.7
23.3
24.7
180 22
23
24.3
210 21.4
22.6
23.6
240 21.2
22.3
23.1
270 20.4
23.2
22.8
300 20.3
22.5
22.3
330 20.7
21.3
22.1
360 21
21.5
22.2
390 20.2
21.5
22.3
420 22.2
21.3
22
450 20
22.3
21.5
480 20.1
23.2
22
510 20.1
21.2
23.1
540 20
22.5
22.1
570 20.3
21.6
21.7
600 19.9
22.1
21.9 Procedure Part 2 – Convection Experiment 1 Lower Plate Temperature in Celsius
Side Plate Temperature in Celsius
Upper Plate Temperature in Celsius
1
191.2 129.7
50.7
2
200.1
139.6
52.6
3
212
147.4
55.4
4
196.2
214.3
57.7
5
189.5
123.7
60
6
181.5
129.5
61.1
7
193
121.5
71.1
Part 2 – Convection Experiment 2 Object
Time
1
Constant Temperature Hot Plate Magnetic Mixer
2.1 sec
2
On Bench 40 sec
3
Regular Hot Plate
4 sec
4
60 degree C Constant Temperature Hot plate
45 sec
Questions:
1.
Calculate the heat absorbed by each aluminium strip between its minimum and maximum temperature state using equation 1. c
aluminum
= 0.89 J/(g*K). 2.
Which aluminium strip heated up the fastest? Why? Blue Strip Heated up the fastest because dark colour absorbs broad spectrum of light which convert it into heat more effectively. Among those three strips blue is the darkest coloured strip, and it will heat up faster. Red will also heat faster than metallic as it is darker in shade.
3.
The space heater on maximum setting has a power output of 1500W. Using equation 4, calculate the emissivity of the space heater.
4.
Using equation 5 and the log-mean temperatures of the space heater and each aluminium strip, calculate the average rates of radiation heat transfer from the space heater to the aluminium strips.
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5.
Multiply the average rate of radiation heat transfer from question 3 by the time in seconds of the experiment before the aluminium strip reached its maximum temperature to estimate the total heat transferred to each aluminium strip. Do these values agree with your answer from question 1? Why? 6.
Which aluminium strip cooled the fastest? Why?
Metallic Strip is expected to cool down more rapidly. This is because lighter and metallic surfaces are best at emitting heat more efficiently when compared to darker shades such as blue or red. Lighter and metallic surfaces have the capacity to reflect a greater amount of heat and exhibit a higher emissivity, allowing them to release heat energy more smoothly. Therefore, under similar conditions, a metallic aluminum strip is likely to shed heat more swiftly and cool down faster than aluminum strips with blue or red coloring. 7.
In addition to radiative cooling, what other kinds(s) of cooling are a significant factor? Is the rate of non-
radiative cooling equal or different for each of the strips? In addition to radiative cooling, convection and evaporative cooling play significant roles. Convection cooling occurs when heat is transferred from a surface to the surrounding liquid, resulting in the immediate warming of the adjacent fluid, causing it to ascend and be replaced by cooler fluid. Evaporative cooling is fixed in the process of liquid evaporation, where a substance absorbs heat from its surroundings, subsequently lowering its temperature and generating a cooling effect as the liquid evaporates, effectively removing heat energy.The surface characteristics and finishes of different aluminum strips impact the rate of non-radiative cooling, influencing the aluminum's ability to dissipate heat through non-radiative mechanisms such as conduction and convection. In comparison to a red or blue metallic strip, a smoother metallic strip may establish better contact with the environment. A smooth surface can facilitate
improved airflow compared to a colored surface, and this, in turn, can affect the flow dynamics and the fluid's capacity to extract heat from the material.
8.
How long does it take the rotor to spin? Did you have to overcome friction to get it going? It took around 16 minutes for the rotor to spin. Yes, we did have to give a push to overcome friction and get the
roter in motion.
9.
Once the rotor starts spinning, does it speed up or slow down or does it keep a constant rate of spinning? The speed of the rotor was almost constant as we observed.
of 10.
In the second convection experiment, which temperature beaker distributed the food colouring the fastest with natural convection? Why? The food colour was dispersed fastest in convection experiment. Because the magnetic mixer stir bar's forced mixing.
11.
How does forced convection affect the rate of distribution of the food colouring compared to the natural convection of the beaker at the same temperature? The rate at which food colouring disperses in a beaker at the same temperature depends upon whether convection is natural or forced.
In natural convection, the movement of fluids occurs due to differences in density resulting from temperature variations. As the fluid closer to the heat source warms up, it expands and becomes less dense,
causing it to arise. This gradual upward movement generates convection currents that gradually disperse the
food colouring. Whereas, forced convection involves the use of external mechanisms, such as magnetic stir bars, to induce fluid motion. Consequently, fluid motion and mixing in the beaker occur more rapidly and efficiently. Therefore, forced convection accelerates the rate at which food colouring is distributed.
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