Practicum Report - KR 01.pdf
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PRACTICUM REPORT Heat Dissipation of Hotwire Name/Student Number
: Indira Zahra Zafira/1406545390
Faculty/Major
: Engineering/Chemical Engineering
Group
:7
Number and Name of Experiment
: KR 01 – Heat Dissipation of Hotwire
Week of Experiment
: Week 2
Date of Experiment
: October 3rd 2014
Basic Physics Laboratory Unit Pelaksana Pendidikan Ilmu Pengetahuan Dasar (UPP-IPD) Universitas Indonesia Depok
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KR 01 – Heat Dissipation of Hot wire I.
Experiment Objective
Using hotwire as a sensor to measure airflow velocity. II.
Equipment
1. Hotwire 2. Fan 3. Voltmeter and Ampere-meter 4. Adjustable Power Supply 5. Camcorder 6. Unit PC, DAQ, and Automatic Control Device
Picture 1. Heat Dissipation of Hotwire
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III.
Basic Theory
Single normal probe is a type of hotwire that is most widely used as a sensor to give information speed flow in the direction of the axial course. Probe as it consists of a metallic wire that is short and smooth are lumped together on two steel wires. Each of the probe’s edge are connected to a source of tension. Electrical energy that flows into the probe is to be dissipated by wire and become heat energy. The amount of electrical energy, which is dissipated is proportional to voltage, electric current that flows into the probe and length of time the electric current flows.
P= v I Δt
...(1)
If the probe is exhaled air, it would change the value of resistance wire, thus change the amount of an electric current that flows. The sooner the air that flows and change in value of resistance, the bigger the electric current flow change as well. The sum of the displacements of heat received probe are expressed by overheat ratio that is formulated as:
Overheat Ratio:
!" !"
Rw = The resistance of wires in the operation of temperature (exhaled air) Ra = The resistance of wires in temperature ambient (in room)
A hot wire probe is to be calibrated to determine an equation that expresses the relation between the tension wires (wire voltage, E) with the speed reference (reference velocity. U).
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After an equation obtained, then information speed in any of the experiment can be evaluated by the use of equation. An equation obtained shaped of linear equations or polynomial equations. In the experiment, we will measure the tension wire at ambient temperature and measure the tension wire if passed by a current of air with the speed with which produce by fan. The speed of the flow of air by fan are varied through power given to fan, which are 70, 110, 150 and 190 from maximum power of 230 m/s. In practical applications, hot-wire sensor probes consists of material suitable for making a sensor, it should have some properties of a high value of the temperature coefficient of resistance, to increase its sensitivity to velocity variations, an electrical resistance such that it can be easily heated with an electrical current at practical voltage and current levels, possibility of being available as wire of very small diameters, a high enough strength to withstand the aerodynamic stresses at high flow velocities. Materials which are commonly used for hot-wire are tungsten, platinum and platinum-iridium alloys. Tungsten wires are mechanically strong and have a high temperature of coefficient of resistance (0.004/°C). Platinum has good oxidation resistance, has a good temperature coefficient of resistance (0.003/°C), but is mechanically weak, particularly at high temperatures. The pl ti a num-i idi r um ally is a compromise between tungsten and platinum with good oxidation resistance, and higher tensile strength than platinum, but it has a low temperature coefficient of resistance (0.00085/°C). Heat dissipation is energy in transit due to temperature difference . Whenever there exists a temperature difference in a medium or between media, heat transfer must occur. The basic requirement for heat transfer is the presence of temperature difference. There can be no net heat transfer between two mediums that are at the same temperature. The temperature difference is the driving force for heat transfer, just as the voltage difference is the driving force for electric current flow and pressure difference is the driving force for fluid flow. The rate of heat transfer in a certain direction depends on the magnitude of the temperature gradient (the temperature difference per unit length or the rate of change of temperature) in that direction. The larger the temperature gradient, the higher the rates of heat transfer.
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IV.
Experiment Procedure
1. Turn on web cam by clicking the icon video on web page R-lab. 2. Insert air flow with velocity of 0 m/s by clicking “click” on the option and drop down on icon “Atur kecepatan aliran” 3. Turn on the motor generating fan by clicking the radio button icon “menghidupkan power supply kipas” 4. Measure the tension and electrical current in the hotwire by clicking icon “ukur” 5. Repeat the second step four times and take measure of each velocity that are 70, 110, 150, 190, and 230 m/s. V.
Tasks and Evaluation
1. Based on the data available, make a graph depicting relations with voltage hotwire and time of every airflow speed. 2. Based on data and graph above, make a graph depicting the relation of average voltage of hotwire with speed of the flow of wind. 3. Make an equation of wind speed as a function of voltage hotwire. 4. Based on experiment and the data available, can we use hotwire wires to measure wind speed? 5. Give analysis of the experiment results.
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VI.
Answers to Tasks and Evaluation Problems
1. Graph between voltage of hot-wire against time During airflow velocity of 0 m/s:
Time 1 2 3 4 5 6 7 8 9 10
V-‐HW 2.112 2.112 2.112 2.112 2.112 2.112 2.112 2.112 2.112 2.112
Air.low Velocity 0 m/s 2.5
Voltage (V)
2
1.5 V-‐HW 1
0.5
0 1
2
3
4
5
6
7
8
9
10
Time (s)
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During airflow velocity of 70 m/s:
Time 1 2 3 4 5 6 7 8 9 10
V-‐HW 2.069 2.069 2.069 2.068 2.068 2.07 2.069 2.071 2.07 2.069
Air.low Velocity 70 m/s 2.0715 2.071 2.0705
Voltage (V)
2.07 2.0695 2.069
V-‐HW
2.0685 2.068 2.0675 2.067 2.0665 1
2
3
4
5
6
7
8
9
10
Time (s)
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During airflow velocity of 110 m/s:
Time 1 2 3 4 5 6 7 8 9 10
V-‐HW 2.051 2.05 2.052 2.051 2.051 2.052 2.051 2.051 2.051 2.05
Air.low 110 m/s 2.0525 2.052
Voltage (V)
2.0515 2.051 V-‐HW
2.0505 2.05 2.0495 2.049 1
2
3
4
5
6
7
8
9
10
Time (s)
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During airflow velocity of 150 m/s:
Time 1 2 3 4 5 6 7 8 9 10
V-‐HW 2.044 2.042 2.043 2.043 2.043 2.043 2.043 2.043 2.043 2.043
Air.low Velocity 150 m/s 2.0445 2.044
Voltage (V)
2.0435 2.043 V-‐HW
2.0425 2.042 2.0415 2.041 1
2
3
4
5
6
7
8
9
10
Time (s)
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During airflow velocity of 190 m/s:
Time 1 2 3 4 5 6 7 8 9 10
V-‐HW 2.039 2.039 2.039 2.039 2.038 2.039 2.039 2.039 2.039 2.038
Air.low Velocity 190 m/s 2.0392 2.039
Velocity (V)
2.0388 2.0386 2.0384 V-‐HW
2.0382 2.038 2.0378 2.0376 2.0374 1
2
3
4
5
6
7
8
9
10
Time (s)
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During airflow velocity of 230 m/s:
Time 1 2 3 4 5 6 7 8 9 10
V-‐HW 2.036 2.036 2.036 2.036 2.036 2.036 2.036 2.036 2.035 2.035
Air.low Velocity 230 m/s 2.0362 2.036 2.0358
Voltage (V)
2.0356 2.0354 V-‐HW
2.0352 2.035 2.0348 2.0346 2.0344 1
2
3
4
5
6
7
8
9
10
Time (s)
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Combined graphs of the graphs above:
Graph depicting Voltage and Time 2.12 2.1
Voltage (V)
2.08
Series1 Series2
2.06
Series3 2.04
Series4 Series5
2.02
Series6
2 1.98 1
2
3
4
5
6
7
8
9
10
Time (s)
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2. Graph depicting the relation between average voltage and airflow velocity:
Airflow Velocity (m/s) 0 70 110 150 190 230
Voltage Average (V) 2.112 2.0692 2.051 2.043 2.0388 2.0358
Corellation between air.low velocity and voltage average 2.12
Voltage (V)
2.1 2.08 2.06 Voltage average
2.04 2.02 2 1.98 1
2
3
4
5
6
Time (s)
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3. Equation of airflow velocity as a function of hotwire voltage: The equation of airflow velocity as the function of hotwire voltage using the smallest square power, whereas y = a + bx Y = Voltage X = Airflow Velocity
From above, we can find the equation between airflow as a function from hot-wire voltage is: Y = a + bx Y = 2,1 – 0,00032x
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4. Based on experiment and the data available, can we use hotwire wires to measure wind speed/airflow velocity? With regard to the experiment and the results of the data, it can be taken to a conclusion that the hot-wire wire can be used for measuring velocity of the wind, but not the exact value of the pace. This is proven by the graph between velocity of the wind and voltage of hotwire. Furthermore, if the wind velocity increases, the voltage in hot-wire will be reduced. The cause is a wind that blows through the hotwire and changes the resistance of the hotwire resulting the current in the hotwire to change. The higher velocity of wind speed, the higher resistance of the wire, thus this influences the electric currents. So in the end, we can conclude that the wire of hot-wire can be used to measure the velocity of the wind.
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5. Practicum Analysis A. Experiment Analysis On experiment using rlab this time.Rlab with the manual that is, the difference if lab work with rlab praktikan not directly connected with tools lab work.When lab work rlab must also that the internet should function properly and smoothly.The aim of this is to know hotwire lab work can be used for measuring the velocity of the wind.There is weakness and profits if lab work using rlab.Unprofitableness is praktikan not capable of being imagined the state of being behold of tools lab work and things happen in lab work.The advantage is ease offered to praktikan, so praktikan can take some data whenever and wherever.In this experiment hot wire there are some variable that is the velocity of wind ( 0 m / s, 70 m / s, 110 m / s, 150 m / s, 190 m / s, 230 m / ' s ).After login and ignite webcam, we will immediately change the speed according to the necessary data and turning on a button power, then can the data needed, and charts hypocrisy.
B. Result Analysis This time, in the experiment of comparative data obtained from 6 variable wind speed and voltage is produced.Furthermore, in variable speed 1 m / s, e.g. 0 viewed a change of stresses within a time lapse 10 seconds noted per second.Than 10 value voltage is obtained in the 10 seconds so that got taken value at the average value voltage the average for each velocity of the wind.This is to see how the influence of time against the tension on hotwire on the velocity of wind particular and how the influence of time against voltage on average.Then voltage electric in hotwire produce electric energy to be dissipated to heat energy.Of energy heat this is what will be used for preserves temperature of censorship so that constant to calculate the speed of the wind. The velocity of wind that is worn is 0 m / s, 70 m / s, 110 m / s, 150 m / s, 190 m / s, 230 m / s. if the data obtained observed, some of the data voltage undergo a change even though change shown very small.In general if we take voltage average, for every velocity of the wind then we will get a decrease in voltage average as shown by a graph follows.
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Corellation between air.low velocity and voltage average 2.12
Voltage (V)
2.1 2.08 2.06 Voltage average
2.04 2.02 2 1.98 1
2
3
4
5
6
Time (s)
Then can be made equation to determine wind speed ( x ) against voltage hotwire ( y ) as follows: Y = 2,1 – 0,0003x
C. Graph Analysis From graphs of the relation of wind speed up the stairs, with an average of voltage we can take the conclusion that the higher the velocity of the wind and the smaller also voltage is obtained.It is because at high wind velocity will increase the resistance of hotwire and a voltage indicated getting smaller.
D. Conclusion Based on lab work dissipation of heat engine hotwire this, can be known wind speed through an equation are made via the results of observations.But, the error relatively great cause of these tools can ' t measuring wind speed properly.A tool can only be used to estimate big or small the velocity of the wind with see change of voltage and current on the hotwire.Finally, the velocity of wind inversely proportional to voltage and is directly proportional to the current.
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VII.
Reference
1. Giancoli, D.C.; Physics for Scientists & Engeeners, Third Edition, Prentice Hall, NJ, 2000. 2. Halliday, Resnick, Walker; Fundamentals of Physics, 7th Edition, Extended Edition, John Wiley & Sons, Inc., NJ, 2005.
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