report thermodynamics and heat transferlab me2014 determining the state of moist air and calculating the heat balance of air duct
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VIET NAM NATIONAL UNIVERSITY HO CHI MINH CITY
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY
<b>THERMODYNAMICS AND HEAT TRANSFER(LAB)-ME2014</b>
<b>Class: CC02Semester:HK222</b>
<b>Lecturer: Mr.Nguyen Van HapGroup:2</b>
</div><span class="text_page_counter">Trang 2</span><div class="page_container" data-page="2"><b>MEMBER</b>
</div><span class="text_page_counter">Trang 3</span><div class="page_container" data-page="3"><b>“THERMODYNAMICS & HEAT TRANSFER”</b>
<b>EXPERIMENT No.1: DETERMINING THE STATE OF MOIST AIRAND CALCULATING THE HEAT BALANCE OF AIR DUCT1.1 EXPERIMETNAL OBJECTIVES AND REQUIREMENTS</b>
<b>1.1.1 Experimental objectives</b>
- Knowing how to measure the temperatures (dry and wet bulb temperature), air flow, pressure and volume;
- Understanding the cooling and dehumidifying process of humid air;
- Understanding the working principle and main components of a basic refrigeration cycle;- Calculating the heat balance in air duct;
<b>1.1.2 Requirements</b>
Students carefully read the following sections in theory before doing the experiment:- Pure substance;
- Moist air;- Refrigeration cycle;
<b>1.2 EXPERIMENTAL DESCRIPTION1.2.1 Equipment and supplies</b>
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</div><span class="text_page_counter">Trang 4</span><div class="page_container" data-page="4">At the outlet of air duct, an anemometer is used to measure the speed and temperature of moist air.
Refrigerant in refrigeration system is R22.
Figure 1: Experimental model of an air duct
thermometer <b><sup>7: Pressure gauge </sup><sup>11: Condenser fan</sup></b>
<b>4: </b>Evaporator coil <b>8: </b>Compound gauge <b>12: </b>Condenser coil
- Using dry and wet bulb thermometers to determine the state of moist air at the inlet (it is also the surrounding temperature) and outlet of the cooling coil.
- Using anemometer to measure the velocity and temperature at outlet of air duct in order to estimate airflow.
- Determining the evaporating and condensing temperature of refrigeration system.- From above data, student determines:
Demonstrating the processes of humid air on the t-d diagram (or I-d)The heat released when humid air passes through the cooling coil
Moisture is removed at cooling coil according to theoretical calculations and experiments.
</div><span class="text_page_counter">Trang 5</span><div class="page_container" data-page="5">Demonstrating the states of refrigerant on the T-s diagram (corresponding withn theoretical refrigeration cycle, neglecting the superheat and sub-cooling processes)
</div><span class="text_page_counter">Trang 6</span><div class="page_container" data-page="6">Velocity at outlet of air duct
(m/s) <sup>Temperature at outlet of air </sup>duct (℃) <sup>Water condensed (ml)</sup>
(m/s) <sup>Temperature at outlet of air </sup>duct (℃) <sup>Water condensed (ml)</sup>
</div><span class="text_page_counter">Trang 7</span><div class="page_container" data-page="7">pressure (Gauge) temperature
(℃) <sup>pressure (Gauge) temperature</sup>(℃)
pressure (Gauge)
Evaporating temperature(℃)
Condensing pressure (Gauge)
Condensing temperature(℃)
</div><span class="text_page_counter">Trang 8</span><div class="page_container" data-page="8">EXPERIMENT 1:We have:
Amount of water condensed:
Amount of water condensed after 10 minutes:Error (%):
The heat released when humid air passes through the cooling coil:
EXPERIMENT 2:We have:
Amount of water condensed:
Amount of water condensed after 10 minutes:Error (%):
The heat released when humid air passes through the cooling coil:Demonstrating the processes of humid air on I-d diagram:Experiment 1:
At the inlet of air conduct
</div><span class="text_page_counter">Trang 9</span><div class="page_container" data-page="9">At the outlet of air conduct:
</div><span class="text_page_counter">Trang 10</span><div class="page_container" data-page="10">Experiment 2:At the inlet of air conduct
</div><span class="text_page_counter">Trang 11</span><div class="page_container" data-page="11">At the outlet of air conduct:
States of refrigerant on the T-s diagram Experiment 1:
</div><span class="text_page_counter">Trang 12</span><div class="page_container" data-page="12">Experiment 2:
</div><span class="text_page_counter">Trang 38</span><div class="page_container" data-page="38">Calculating the overall efficiency:
</div><span class="text_page_counter">Trang 39</span><div class="page_container" data-page="39">Firstly, we have to calculate :
</div><span class="text_page_counter">Trang 40</span><div class="page_container" data-page="40">Then we can calculate k:
<b>c. Determining the Reynolds number:</b>
Cross-section area of steel coil: We need to calculate first:
</div><span class="text_page_counter">Trang 41</span><div class="page_container" data-page="41">Reynolds number calculating:
</div><span class="text_page_counter">Trang 42</span><div class="page_container" data-page="42"><b>a. Calculating the heat transfer and overall efficiency at several flow rate:</b>
Where and c are taken at the average temperature of inlet and outlet water.<small>p</small>We calculate the heat transfer for each test:
</div><span class="text_page_counter">Trang 43</span><div class="page_container" data-page="43">Similar with cold water:
</div><span class="text_page_counter">Trang 44</span><div class="page_container" data-page="44">Calculating the overall efficiency:
</div><span class="text_page_counter">Trang 45</span><div class="page_container" data-page="45">Firstly, we have to calculate :
Then we can calculate k:
</div><span class="text_page_counter">Trang 46</span><div class="page_container" data-page="46">Cross-section area of steel coil: We need to calculate first:
</div><span class="text_page_counter">Trang 47</span><div class="page_container" data-page="47">Reynolds number calculating:
</div><span class="text_page_counter">Trang 48</span><div class="page_container" data-page="48">Comment on overall heat transfer coefficient in two cases and between experiment E1 and E2:
- In both cases, it seems that the heat transfer coefficient tends to increase when the amount of hot water is set and the amount of water is changed. Increasing the amount of hot water also increases the heat transfer coefficient.
- Both parallel and counter-flow heat transfer coefficients are almost the same. However, parallel flow seems to be more effective than counter-flow.
- The heat transfer coefficients of coil heat exchanger systems typically do not differ significantly between tests.
- The heat transfer coefficient is higher in counterflow than in parallel flow in shell and tube heat exchanger systems, but vice versa in coiled tube systems.
- The heat transfer coefficient of the spiral coil method is lower than that of the shell and tube method.
The heat exchange capacity of the shell and tube system is superior to that of the spiral tube system.
Comment on Reynolds number in two cases and between experiment E1 and E2:
- In both cases of E2, the heat transfer coefficient seems to have an downward trend. Ifwe decrease the amount of hot water, the heat transfer coefficient will decrease. Thecounter flow seems to be more effective than parallel flow.
- We can see that Re > 10 in both counter and parallel so these flows are turbulent flow.<small>4</small>- The Reynolds number of experiment E1 is smaller than the Reynolds number of experiment E2.
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