Experiment 1 Utube Collector PDF

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STUDENT PLAGIARISM DISCLAIMER FORM

PLAGIARISM DISCLAIMER

STUDENT NAME:

Daniel Burke

STUDENT NUMBER:

A00223508

PROGRAMME:

Mechanical and Renewable energy

YEAR:

3rd

MODULE:

Solar Energy

LECTURER:

Niall Burke

ASSIGNMENT TITLE:

Experiment 1: U-tube collector

DUE DATE:

25/11/2018

DATE SUBMITTED: ADDITIONAL INFORMATION:

I understand that plagiarism is a serious academic offence, and that AIT deals with it according to the AIT Policy on Plagiarism. I have read and understand the AIT Policy on Plagiarism and I agree to the requirements set out therein in relation to plagiarism and referencing. I confirm that I have referenced and acknowledged properly all sources used in preparation of this assignment. I understand that if I plagiarise, or if I assist others in doing so, that I will be subject to investigation as outlined in the AIT Policy on Plagiarism. I understand and agree that plagiarism detection software may be used on my assignment. I declare that, except where appropriately referenced, this assignment is entirely my own work based on my personal study/or research.

Contents Title:

2

Aim

2

Introduction

3

Thermocouple’s

3

Solarimeter 4 Collector efficiency Results

5

Apparatus

6

Procedure

8

Conclusion

8

Appendix

9

Formulae used Bibliography

11

4

9

Title: Solar thermal laboratory experiment

Aim The aim is to conduct an experiment on a direct flow u-tube collector while varying the solar flux density, record the results and analyse them.       

Setup the system Set the bleed flow rate Wait for system to reach steady state Vary solar flux density Show the result’s mathematically and graphically Comment on the accuracy of the instruments used in the experiment Suggested improvements

Introduction

Figure 1: U-Tube Collector[ CITATION Alt18 \l 2057 ]

Direct flow evacuated u-tube collectors consist of a u shape pipe inside an evacuated cylinder. The vacuum helps to reduce convection and conduction losses. The only mode that heat can transfer through a vacuum is by radiation[ CITATION Pau18 \l 2057 ]. One side of the u shape pipe is the inlet (cold water in) and the opposite side is the outlet (hot water out), within the cylinder there is an absorber plate/fin. The fin is coated in a selective coating to attract all the visible light spectrum. This fin absorbs the solar radiation energy from the sun and then it is transferred from the fin to the fluid flowing within the u tube via conduction. As this system is a direct flow system, water is flowing within the pipes. The water then exits the u-tube pipe and flows to a storage tank.

Thermocouple’s When conducting this experiment there are sensors that data will be recorded from. It is important to note the accuracy of these sensors to show potentially how inaccurate or accurate the results obtained are. A thermocouple is a sensor for measuring temperature. They are one of the most common ways used in industry to measure temperature[CITATION How15 \l 2057 ]. They consist of at least two wires made from different metals, joined together at one side to form a junction. The junction is placed on the surface or object of which the temperature is to be determined. As a change in temperature occurs the metals start to deform causing a change in resistance, a thermocouple outputs a voltage signal, the change in voltage can be measured. This change in voltage is linearly proportional to the change in temperature, therefore the temperature change can be calculated[ CITATION Har13 \l 2057 ]. Thermocouples can have different tolerance’s depending upon the accuracy required and temperature range. A letter is assigned to a thermocouple to tell you what tolerance it has and its operational temperate range. The thermocouple used in this experiment was a type K. It’s made from nickel chromium and nickel aluminium, has a tolerance of ± 1.5°C at a temperature range of -40°C to -375°C. These values where obtained from Figure 4.

Solarimeter A Solarimeter is a pyranometer[ CITATION Nat15 \l 2057 ], which is an instrument used to measure the flow of direct or diffused solar radiation on a surface. A pyranometer operates by the thermoelectric detection principle, which is when a horizontal blackened surface fully absorbs the incoming energy over a wide range of wavelengths. The temperature of the surface then increases. This temperature increase is measured using thermocouples in series or parallel to form a thermopile. The thermocouples produce a voltage, which is linearly proportional to the solar flux density; from this, the solar flux density can be obtained[ CITATION Kip15 \l 2057 ]. Figure 2 is an example of a solarimeter. Figure 2: Solarimeter[ CITATION Hos18 \l 2057 ]

Collector efficiency A solar thermal system can never be 100% efficient because there will always be optical losses and possibly thermal losses unless ideal conditions exist, see Figure 3 for a generic example of optical losses. Optical loses are caused by the light reflecting off the transparent cover of the collector and the absorption rate of the absorber. Thermal losses are caused by the three modes of heat transfer: conduction, convection and radiation.

Figure 3: Collector Efficiency[ CITATION Dav18 \l 2057 ]

As seen in figure 3, as the difference in temperature between the collector and ambient air increases, the thermal losses increase. This thermal loss in turn reduces the overall efficiency. As the solar flux density increases, the collector efficiency also increases [ CITATION Dav18 \l 2057 ]

0045 Results Table: 1 Test 1 Results

Specific heat capacity of water

4186.00 [ J/kg.K ]

Area of panel

0.98 [ m² ]

Density of water

997.00 [ kg/m³ ]

sample no.

1

QS solar

2

740.00 [ W/m² ]

540.00 [ W/m² ]

3

4

140.00 340.00 [ W/m² ] [ W/m² ]

T1 water in

14.80 [ °C ]

15.90 [ °C ]

T2 Water to the panel

24.00 [ °C ]

21.20 [ °C ]

21.10 [ °C ]

20.20 [ °C ]

T3 water to drain

29.70 [ °C ]

24.10 [ °C ]

22.80 [ °C ]

21.00 [ °C ]

T4 ambient air

19.40 [ °C ]

18.40 [ °C ]

19.80 [ °C ]

20.40 [ °C ]

Bleed volume

0.0003 [ m³ ]

0.0003 [ m³ ]

0.0003 [ m³ ]

0.0003 [ m³ ]

Time for volume

30.00 [ s ]

30.00 [ s ]

30.00 [ s ]

30.00 [ s ]

mṁ panel flow rate

20.00 [ g/s ]

20.00 [ g/s ]

20.00 [ g/s ]

20.00 [ g/s ]

Bleed mass

0.30 [ kg ]

0.30 [ kg ]

0.30 [ kg ]

0.30 [ kg ]

mṁ bleed

0.01 [ kg/s ]

0.01 [ kg/s ]

0.01 [ kg/s ]

0.01 [ kg/s ]

QS solar

725.20 [ W ]

T mean

529.20 [ W ]

26.85 [ °C ]

QS water (useful energy) Solar panel efficiency [η]

22.65 [ °C ]

621.84 [ W ]

342.22 [ W ]

85.75 [ % ]

63.37 [ % ]

16.30 [ °C ]

333.20 [ W ] 21.95 [ °C ] 271.27 [ W ] 81.41 [ % ]

Table:2 Test 2 Results

Density of water

997 [ kg/m³ ]

Area of panel

0.98 [ m² ]

specific heat capacity of water

4186.00 [ J/kg.K ]

sample no.

1

QS solar T1 water in

310 [ W/m² ] 12.2 [ °C ]

2 670 [ W/m² ] 12.2 [ °C ]

16.80 [ °C ]

137.20 [ W ] 20.60 [ °C ] 175.28 [ W ] 127.76 [ % ]

T2 Water to the panel

14.1 [ °C ]

15.8 [ °C ]

T3 water to drain

16.4 [ °C ]

22.5 [ °C ]

T4 ambient air

17.4 [ °C ]

18.5 [ °C ]

Bleed volume

0.0004 [ m³ ]

0.0004 [ m³ ]

Time for volume

45 [ s ]

45 [ s ]

mṁ panel flow rate

20 [ g/s ]

20 [ g/s ]

Bleed mass

0.4 [ kg ]

0.4 [ kg ]

mṁ bleed

0.009 [ kg/s ]

0.009 [ kg/s ]

QS solar T mean QS water (useful energy) Solar panel efficency [η]

304 [ W ]

657 [ W ]

15.3 [ °C ]

19.2 [ °C ]

156 [ W ]

375 [ W ]

51 [ % ]

56 [ % ]

140 120

Efficency [ % ]

100 80 2nd attempt 1st attempt

60 40 20 0 100

200

300

400

500

QS solar [W/m² ]

Qsolar vs Efficiency

600

700

800

Apparatus Apparatus diagram key can be seen in the appendix on Table: 3

2

1

4

Figure 4 Head Unit

Figure 5 Circulating Pump & Control Vales

5

6

7

15

16

Figure 6 Solar panel system

Procedure The system is to be turned on and the control unit is checked to ensure all sensors are plugged in correctly. Once the system has power and is ready to initialize the experiment the first task is to set the bleed control valve. To do this a beaker and a timer is used. The times taken was divided by the quantity of water in the beaker to give a bleed mass flow rate. The flow control is then to be set at 20g/s.    

Next the lights are to be turned on. After 25 minutes has elapsed the values should be recorded It should be noted that it may take longer than 25 minutes for the system to reach stable conditions. The lights should then be moved to change the solar flux density and again wait for the system to reach stable conditions and record the results

Conclusion The results obtained in the first test where deemed to be highly inaccurate. They were deemed to be inaccurate because as the solar flux density was decreasing the efficiency of the system was increasing. This is the inverse of what should be happening[ CITATION EBE11 \l 2057 ]. The inaccuracies may have been caused by multiple factors. It can be seen in the results from test 1 that T1 water in increased from 14.8°C to 16.8°C, that gives us a change in temperature of 2°C. This change in temperature of the mains water supply is highly unlikely and therefore this error was deemed to be caused by the inaccuracy of the thermocouples which have a tolerance of ± 1.5°C. If the experiment was required to be conducted with high accuracy, it would be advised to change the thermocouples to type T thermocouples (see figure2) which have a tolerance of ± 0.5°C. It would also be advised to reduce the mass flow rate as this in turn would increase the change in temperature range. It is also possible that these inaccuracies may have been caused by a change in pressure of the mains water supply in loop 1, As the college has its own water storage tank the water pressure is inversely to the demand profile. It would be advised that in order to have a constant water supply pressure that a flow regulator should also be incorporated into loop 1, when conducting the experiment, the bleed mass flow rate was checked every 10 minutes and an average was taken to improve accuracy when test 2 was being conducted. Although only 2 efficiencies where calculated for test two it was deemed that the test results are a fair result. It can be seen on Q solar vs efficiency that as the solar flux density increases so does the overall efficiency of the system. The inlet temperature on Table:2 can also be seen to remain at a constant value of 12.2°C

Appendix Ap Cp mṁBleed mṁPanel Q Water Q solar T η t q QS T1 T2 T3 T4 Tmean

Effective Panel Area Specific Heat Capacity at constant pressure Bleed Mass flow rate Panel Mass flow rate Useful energy Solar flux Elapsed time Efficiency Elapsed time Heat flux Heat input Inlet Temperature of water Temperature of water to the panel Temperature of water at the drain Ambient Air Temperature Temperature average

Table 3 Units & Symbols

Formulae used Qwater ´ bleed ×c p ×( T 3−T 1 ) ´ =m

Q }} rsub {solar} × {A} rsub {panel ´¿ ´Q solar=¿

T mean=

T 2 +T 3 2

m ´ bleed= η=

´ Q water ´ Q solar

Bleed volume g Time s

m2 J/kg.K kg/s g/s W W s % s W/m2 W °C °C °C °C °C

Table 4:Apparatus Diagram Key

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Apparatus Diagram Key Solarimeter digital display Digital Temperature display Main on/off switch T1 Thermocouple socket T2 Thermocouple socket T3 Thermocouple socket T4 Thermocouple socket Pump speed control Pressure relief valve and gauge Bleed flow control valve Panel flow control valve Adjustable pressure regulator Water inlet Water outlet Solar panel Solarimeter sensor

Appeddix C

Figure 7[ CITATION Pro14 \l 2057 ]

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How

do thermcouples work. [Online] https://www.azosensors.com/article.aspx?ArticleID=376

David Darling, Available at: [Accessed 14 11 2018].

n.d. solar collector. [Online] http://www.daviddarling.info/encyclopedia/S/AE_solar_collector.html

Ettah, E. B., 2011. THE RELATIONSHIP BETWEEN SOLAR RADIATION AND THE EFFICIENCY OF SOLAR, Nigeria: International Journal of Applied Science and Technology. Hoskin Scientific , n.d. [Online] Available at: https://www.google.ie/search? q=solarimeter&rlz=1C1CHBF_enIE817IE817&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiuntbFtHeAhUIVsAKHX-oBzgQ_AUIDigB&biw=1680&bih=939#imgrc=uAWs0GDDs0jGXM: [Accessed 13 11 2018]. Khemani, H., 2013. What is a Thermocouple & How Does it Work?. [Online] Available at: https://www.brighthubengineering.com/manufacturing-technology/53682-what-is-athermocouple-how-thermocouple-works/ [Accessed 14 11 2018]. Kipp & Zonen, 2015. Thermopile Pyranometers – How Do They Work?. [Online] Available at: https://www.azosensors.com/article.aspx?ArticleID=616 [Accessed 13 11 2018]. National Oceanic & Available [Accessed 13 11 2018].

Atmospheric at:

Administration, 2015. Solarimeter. [Online] https://wikivisually.com/wiki/Solarimeter

Process parameters, 2014. [Online] Available at: https://i0.wp.com/43kgbm1hv08oqvpcm46yzuu3-wpengine.netdna-ssl.com/wpcontent/uploads/2014/06/Thermocouple-Tolerance-Chart-jpg.jpg?ssl=1 [Accessed 13 11 2018]. Walorski, P., n.d. Is the most heat lost by the means of conduction, convection or radiation?. [Online] Available at: http://www.physlink.com/education/AskExperts/ae601.cfm [Accessed 14 11 2018]....