Instytut Fizyki Doświadczalnej Wydział Matematyki, Fizyki i Informatyki

UNIWERSYTET GDAŃSKI

Instytut Fizyki Doświadczalnej 1.

Experiment 6 : Determination of the efficiency factor of solar collector in various operating conditions

I. Background theory.

1. Heat transfer processes:

a) heat conduction:

energy flux,

energy flux density,

coefficient of thermal conductivity;

b) thermal radiation:

Kirchhoff’s law,

Stefan–Boltzmann law,

Wien's displacement law,

Rayleigh–Jeans law,

Planck’s quantum theory;

c) diffusion:

convection,

Fick’s law.

2. Electromagnetic radiation of the Sun.

3. The greenhouse effect.

4. Solar Collectors:

a) types of collectors;

b) construction and operation of solar collectors;

c) collector efficiency.

5. Construction of a measuring station and overview of the experiment.

Instytut Fizyki Doświadczalnej 2.

Experiment 6 : Determination of the efficiency factor of solar collector in various operating conditions

II. Experimental tasks.

1. Refer to the measurement system shown in Picture 1, and the description of the measurement procedures given in the Appendix.

2. Set the collector perpendicular to the lamp’s light beam (an angle of 00 on the collector’s mount scale).

3. Take a reading of the ambient room temperature TEN. 4. Determine the efficiency of the collector operating under different conditions, simulating

natural environmental phenomena including the effect of the reservoir water temperature, the outer casing of the collector, lighting, and wind (cold air). Take a series of temperature measurements TIN and TOUT of the inlet and outlet of the collector respectively, and the temperature TR of the reservoir for the conditions given in Table 1 and for two different water flow rates m following the detailed measurement instructions given in the Appendix.

Table 1. Simulated environmental conditions for measurements.

Nr insulation glass wind lighting TIN [0C] m [cm3/min]

1. + + ― ― ≈10 100 2. ― ― ― ― ≈10 100 3. + + ― + ≈20 100 4. ― ― ― + ≈20 100 5. + + ― + ≈40 200 6. + + + + ≈40 200 7. + ― ― + ≈40 200 8. + ― + + ≈40 200

Picture 1. Measuring system for investigating the properties of a solar collector: 1 - halogen lamp with a power of 1 kW; 2 - hairdryer; 3 - solar collector; 4 - thermocouple probe; 5 - water pump with flow

meter; 6 - water pump power supply; 7 - digital temperature gauge; 8 - reservoir with heat exchanger.

Instytut Fizyki Doświadczalnej 3.

Experiment 6 : Determination of the efficiency factor of solar collector in various operating conditions

5. Based on the obtained results, plot graphs of temperature dependence TIN, TOUT and TR as a function of time on the same set of axes.

6. Calculate the differences in temperature at the collector’s inlet and outlet. 7. Deduce the efficiency of the collector from the measurements without illumination using the

formula:

η = TEN−TRTEN

(1)

where: TEN – ambient temperature,

TR – the water temperature in the reservoir.

8. Deduce the efficiency of the collector from the measurements with lighting using the formula:

η = cwm(TOUT−TIN)qA

(2)

where: TOUT – water temperature at the outlet of the collector,

TIN – water temperature at the inlet of the collector,

cw – specific heat of water, cw = 4186 J/kg·K,

m– water flow rate, mR1 = 100 cm3/min, mR2 = 200 cm3/min,

A – active surface of the collector, A = 0,12 m2,

q – intensity of incident light at a distance of 70 cm from the collector, q = 1 kW/m2.

9. Calculate the uncertainties in the calculated collector efficiency equations (1) and (2). 10. Tabulate the obtained collector efficiencies.

Analyse the results, specifying all factors that may affect the efficiency of the device.

III. Apparatus.

1. Solar collector. 2. Halogen lamp with power of 1 kW. 3. Heat exchanger. 4. Heat exchanger reservoir. 5. Digital temperature gauge. 6. Three thermocouple probes. 7. Water pump with power supply. 8. Hair dryer. 9. Heater. 10. Tape measure. 11. Stopwatch.

Instytut Fizyki Doświadczalnej 4.

Experiment 6 : Determination of the efficiency factor of solar collector in various operating conditions

IV. Literature.

1. PHYWE Systeme GmbH & Co.KG – “Solar Ray Collector”, Laboratory Experiments, Physics 3.6.01- 00, 2008.

2. L. Andrèn – “Solar Installations. Practical Applications for the Built Environment”, James & James Science Publishers, London 2003.

3. R. Eisberg, R. Resnick – “Quantum Physics of Atom, Molecules, Solids, Nuclei and Particles”, John Wiley & Sons Ltd, New York 1985.

4. D. Halliday, R. Resnick, J. Walker – “Fundamentals of Physics”, John Wiley & Sons Ltd, New York 2001.

5. M. Fox –“Optical Properties of Solid”, Oxford University Press, Oxford 2001.

Instytut Fizyki Doświadczalnej 5.

Experiment 6 : Determination of the efficiency factor of solar collector in various operating conditions

Appendix Temperature measurements TIN, TOUT and TR of the solar collector under different operating

conditions

I. Taking measurements with the water temperature at the collector inlet TIN ≈ 10 0C and in the absence of lighting.

1. Reduce and stabilise the water temperature at the collector inlet to TIN ≈ 100 C. To achieve this, fill the reservoir with an integrated heat exchanger (8 in Picture 1) with ice cubes and chilled water. Stir thoroughly.

2. Turn on the water pump power (5 in Picture 1), and set the voltage knob to 4 V and the current limiter control knob to 1 A.

3. Open the circulation pump valve to maximum (Picture 2).

4. Using the water pump valve, set the flow rate to 100 cm3/min. When making measurements, continuously monitor the rate of water flow circulating through the collector.

The contents of the reservoir should be stirred, throughout the course of the measurements, approximately every 2 minutes. Maintain a constant temperature of the reservoir by adding ice cubes as necessary.

Picture 2. Circulation pump: 1 - flow rate control valve; 2 - flow rate indicator.

Instytut Fizyki Doświadczalnej 6.

Experiment 6 : Determination of the efficiency factor of solar collector in various operating conditions

5. Use a digital temperature meter (Picture 3) to note the temperatures at the inflow TIN and outflow TOUT of the collector and in the heat exchanger reservoir TR every minute for 30 minutes. After completing each measurement, stir the water with ice cubes in the reservoir.

6. Repeat measurements in points I. - 5. in the Appendix for the collector without windows and rear panels.

II. Taking temperature measurements with the water temperature of the collector inlet TIN ≈ 20 0C and with lighting.

1. Place the heater in the heat exchanger reservoir (8 in Picture 1).

While stirring, heat the water to a temperature of about 20 0C, then turn off the heater power.

During subsequent stages of the experiment, one should regularly stir the water in the reservoir to maintain a constant water temperature at the collector inlet.

Picture 3. Digital thermometer: 1 - displays indicating the temperature of the selected input channel; 2 - input channels, red light – measured temperature is displayed on

the upper display, green light - on the lower display; 3 - channel control buttons, from the left: change the channel input, change the temperature scale, change mode, zero

reset; 4 – shows selected temperature scale.

Instytut Fizyki Doświadczalnej 7.

Experiment 6 : Determination of the efficiency factor of solar collector in various operating conditions

2. Set the halogen lamp at a distance of 70 cm from the collector, and set the collector perpendicular to the direction of the incident light. Turn on the lamp.

3. Take measurements as in 4. - 6. of part I of the Appendix and perform calculations as in 4. – 9. of Experimental Tasks.

4. Repeat step II.3. of the Appendix for the collector without glass and rear panels.

III. Taking temperature measurements with the water temperature of the collector inlet TIN ≈ 40 0C and with lighting.

1. Turn on the lamp. 2. Increase the rate of water flow to 200 cm3/min. 3. Place the heater in the heat exchanger reservoir and heat the water to about 400C. Monitor the

water temperature carefully during the experiment. Take a series of measurements – as in point 3. Of part II in the Appendix.

4. Repeat the steps from 3. in part II of the Appendix for the collector without glass. 5. Set the hairdryer at a distance of 30 cm from the glass of the collector. Set it to blow cold air.

Carry out the steps in point 3. in part II of the Appendix.

6. Turn off the lamp and hairdryer. 7. Turn the power supply voltage knob to the minimum and then turn off the water pump. 8. Drain the water tank with the drain tap.

The lamp housing can become extremely hot! It is forbidden to touch it as well as the ventilation grills. The lamp should be turned off immediately after completing the measurements.