Effects of Air Flow and Heating on Temperature: Experiment

OBJECTIVE:

1. To study the Air Flow effect on Temperature changes.
2. To study the Heating Effect on Temperature changes.
3. To study the Effect of Air Flow and Heating on Temperature changes.

INTRODUCTION:

The purpose of this experiment is to investigate the effects of air flow or heating on temperature. An enclosed duct (Model LS17024) is used as assistance to complete our task. The reason of setting the entire component in enclosures is to prevent unnecessary problems during control design, air flow and effect of heating process. The enclosed duct is made up by several components which include fan, control panel, cooler section, observation door, condensing unit, and dry bulb thermocouple. Fan functions to provide air flow rate and there will be a controller installed on it in order to adjusting the spinning speed. Control panel was connected to that controller on fan as well as heater to control both variables – air flow rate and the heating rate.

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Next, temperature is defining as one of the most important parameter because it represents the motion of particles. The air molecules gain more energy on average (move faster and bounce around more energetically) when the temperature increases as the result of high heating rate. In this experiment, the air flow and heating rate alter the temperature changes.

Furthermore, heat transfer in three main ways: through radiation, conduction, and natural or forced convention. Heat transfer via radiation occurs through electromagnetic waves, an example being the sun’s energy reaching the earth with including emissivity and energy absorption. Besides that, heat can also be transferred through conduction between the inner surface and outer surface of an object. As long as it is conducted by heat energy, the heat will flow from hotter region to lower region. For example, there is only one end of iron rod being heated by candle, and sooner or later the other end of the rod will become warmer. This phenomenon is a common heat conduction example which explained the heat energy can transfer through particles in one object. Doesn’t like heat conduction, heat convection happened between particles in fluid and non-fluid. Just like we can feel the heat of the hot iron plate once we get near to it even no contact at all. It is because the particles in iron plate pass the heat energy to air molecules in surrounding and the air molecules carry out heat convection again from air molecules onto our sensor cells on our body.

MATERIAL/APPARATUS:

1. An enclosed duct (Model LS17024) 2. Fan 3. Control panel 4. Cooler section 5. Observation door 6. Condensing unit 7. Dry bulb thermocouple

EXPERIMENTAL PROCEDURE:

Control State of the Duct

1. The apparatus main power supply was switched on.
2. The system was allowed to reach steady state whereby all readings on the instrument panel show no more changes.
3. All the readings displayed on the digital meters were recorded in Table 1.

Part A: Air Flow Effect on Temperature

1. The axial fan was switched on. The frequency was set to 5.0Hz by adjusting the frequency inverter.
2. The system was allowed to reach steady state whereby there were no more changes in duct temperature.
3. All the readings displayed on the digital meters were recorded in Table 1.
4. All the above steps were repeated with frequency of 30.0Hz.
5. The readings were recorded down in the Table 1 for different air flow rates 5.0Hz and 30.0Hz by adjusting fan frequency.

Part B: Heating Effect on Temperature

1. The heater was switched on and the heating rate was set to 40.0°C.
2. The system was allowed to reach steady state whereby no observable changes in heater and duct temperature.
3. All the readings displayed on the digital meters were recorded in Table 1.
4. All the above steps were repeated with heating rate of 60.0°C.
5. The readings were recorded down in the Table 1 for different rates 40.0°C and 60.0°C.

Part C: Effect of Air Flow and Heating on Temperature

1. Heating rate of 31.0°C and a fan rate of 5.0Hz, and another set with heating rate of 31.0°C and fan rate of 30.0Hz were selected to study their combined effect.
2. The system was allowed to reach steady state whereby no observable changes in the duct temperature.
3. All the readings displayed on the digital meters were recorded in Table 1.

RESULTS:

DISCUSSION:

The purpose of this experiment is to study the effects of heating and air flow on temperature. The more kinetic energy inside an object particles cause vigorous collision which indicates that more heat been transferred from it. For sure it gives rise in temperature. Temperature is a parameter to measure the amount of thermal energy in one object based on the kinetic action between the particles. Air is made up of molecules that are constantly in motion. Once air is being warmed up, the molecules will gain energy to increase its mobility. The molecules will then collide to each other to cause effective collision. A higher temperature indicates more thermal motion between particles. So as return, a decrease in temperature will slow the movement of particles down. Fan frequency and heating rate are two factors that will alter the temperature changes. The faster the air flow rate, the more readily the surface cools as air forming a boundary layer is replaced and the temperature measured in the area is maintained low.

Heat transfer in three main ways: through radiation, conduction, and natural or forced convention. Heat transfer via radiation occurs through electromagnetic waves, an example being the sun’s energy reaching the earth with including emissivity and energy absorption. Besides that, heat can also be transferred through conduction between the inner surface and outer surface of an object. As long as it is conducted by heat energy, the heat will flow from hotter region to lower region. For example, there is only one end of iron rod being heated by candle, and sooner or later the other end of the rod will become warmer. This phenomenon is a common heat conduction example which explained the heat energy can transfer through particles in one object. Doesn’t like heat conduction, heat convection happened between particles in fluid and non-fluid. Just like we can feel the heat of the hot iron plate once we get near to it even no contact at all. It is because the particles in iron plate pass the heat energy to air molecules in surrounding and the air molecules carry out heat convection again from air molecules onto our sensor cells on our body.

One of the criteria for heat transfer to occur is temperature difference. As we all know, the heat will only transfer from hotter region to cooler region. According to First Law of Thermodynamic, the heat energy transferred from cooler place to hotter place is impossible. For convection, the rate of heat loss depends on the speed of ambient air flow above the surface. There will be an insulating boundary layer of warm air forming against the surface as the object surface heats the air around it. Moving air will destroy the boundary layer, letting the new cold air in and replace the original hot air. That is why the duct temperature is getting lower as the fan frequency goes higher. There are two types of convective heat transfer which are forced convection and natural convection. Forced convection was happened when there is external force existed for example Fan is considered as external force since it provides air flow. Forced convection can transfer faster heat rate compared to natural convection due to the stronger air flow rate which speed up the moving air that carries the heat energy. Furthermore, the temperature increases slowly for natural convection because heat energy is transferred in natural condition.

At the early state of experiment, heater and fan were switched off so that we can observe the initial reading of all temperature gauges. The duct, heater and surrounding / ambient temperature were noted as 30.0 ËšC, 30.0 ËšC and 30.0ËšC respectively. This set of data is the controlled set in this experiment. In part B experiment, the fan frequency was initially set to 5Hz. The results came out for duct, ambient and heater temperature were 29.9 ËšC, 29.9ËšC, 30.0 ËšC respectively. After this, we need to wait for the whole component to stabilize (cool down) before carry out next set of part A experiment. Next, the fan frequency was reset to 30Hz. The duct, ambient and heater temperature were recorded 29.8 ËšC, 29.9 ËšC and 30.0 ËšC respectively. From the result, we can conclude that the duct temperature is getting low as we increase the fan frequency. This is fan has create a force convection with disrupt all the insulating boundary layer and allow the new and cooler air to come into enclosing duct. For part B experiment, the heating rate was initially set to 40 ËšC. The duct and ambient temperature came out as 31.1 ËšC and 30.1 ËšC. After that we repeat the cooling down process as what we did in part B experiment for system stabilization, the heating rate was then reset to 60 ËšC. The duct and ambient temperature were recorded as 35.5 ËšC and 30.9 ËšC .The readings prove that the duct temperature had rose compared to last set experiment. This is because the particles in air gained greater kinetic energy and collides with each other faster, causing an increase in temperature. In part C experiment, both fan and heater were involved. In first trial (first condition), we had the combination of 5Hz fan frequency and 31.0 ËšC of heater temperature. The duct and ambient temperature came out as 31.0 ËšC and 30.6 ËšC. Again the system needed to be stabilized in order to get more accurate reading for next part. For second trial (second condition) we made the condition as 30Hz fan frequency and 31.0 ËšC of heater temperature together. The duct and ambient temperature were recorded as 30.9 ËšC and 30.6 ËšC. The data proves that the duct temperature in second trial is higher than that in first trial. This is because the air flow has again destroyed the insulating boundary layer and the heating rate can’t counter with intruding of new cold air.

In conclusion, there is few precaution steps need to be taken throughout the whole experiment. Firstly, the temperature should be adjusted from low temperature reading to high temperature reading so that the remained heat won’t affect the next coming set. Next, this experiment should be conducted in a closed room and located far away from heating or cooling system so that the temperature won’t be easily affected.

CONCLUSION:

The objective of the experiment which is to study the effects of heating and air flow on temperature was successfully determined. Air flow rate and heating rate are the main factors that affect the temperature. In this experiment, heat transferred by using convection. Fan was acting as forced convection which alters the velocity of moving air to disrupt the insulating boundary layer to allow the cool air to replace the original warm air. When heater was switched on, air is heated and expands. The molecules in warm gained greater kinetic energy and collide with each other faster, causing an increase in temperature.

REFERENCES:

1. Convection. (n.d). Retrieved March 20, 2014 from

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatra.html

2. Effects of Heat and Airflow inside an Enclosure. (n.d). Retrieved March 20, 2014 from http://www2.emersonprocess.com/siteadmincenter/PM%20DeltaV%20Documents/Whitepapers/WP_Heat_Airflow_Encl.pdf
3. Jain,R. (n.d). Heat Transfer. Retrieved March 20, 2014 from http://www.budind.com/pdf/BasicsofEnclosureCoolingWhitePaper2.pdf