Solar Ray Collector

OBJECTIVE: – To determine the efficiency of the solar ray collector under various experimental conditions. 1. Illumination with halogen lamp. Water temperature ? e? 20 °C. a) Complete collector b) Collector without glass plate 2. Illumination with halogen lamp. Water temperature ? e ? 60 °C. c) Complete collector d) Complete collector, cold jet of air impinges e) Collector without glass plate f) Collector without glass plate, cold jet of air impinges INTRODUCTION: Solar ray collectors  transform solar radiation into heat and transfer that heat to water. Then solar heat can be used for heating water, to back up heating systems.The heart of a solar collector is the absorber, which is usually composed of several narrow metal strips. The carrier fluid for heat transfer flows through a heat-carrying pipe, which is connected to the absorber strip. In plate-type absorbers, two sheets are sandwiched together allowing the medium to flow between the two sheets. Absorbers are typic ally made of copper or aluminum. CALCULATION: Important formula for calculating the useful power, PN and efficiency, ? : 1. Useful power, PN = c  · m  · (? o – ? i) where, m = 100 g/min = 1. 667 x 10-3 kg/s c = specific thermal capacity of water = 4. 182 kJ/kg  · K o = average absorber outlet temperature ?i = average absorber inlet temperature 2. Efficiency, ? = PN / (qi x A) where, qi = 1 kW/m2 A = 0. 12 m2 Sample calculation: PART A I. Complete collector ( t=15 min ) – useful power, PN = c  · m  · (? o – ? i) = (4. 182 kJ/kg  · K)  · (1. 667 x 10-3 kg/s)  · (32. 5 – 28. 5) K = 0. 0279 kW – efficiency, ? = PN / (qi x A) = 0. 0279kW / (1 kW/m2 x 0. 12 m2) = 0. 232 II. Complete without glass plate ( t=15min ) – useful power, PN = c  · m  · (? o – ? i) = (4. 182 kJ/kg  · K)  · (1. 667 x 10-3 kg/s)  · (35. 0 – 30. 0) K = 0. 0348 kW – efficiency, ? = PN / (qi x A) = 0. 0279kW / (1 kW/m2 x 0. 2 m2) = 0. 29 PART B I. Complete collector ( t=15 min ) – useful power, PN = c  · m  · (? o – ? i) = (4. 182 kJ/kg  · K)  · (1. 667 x 10-3 kg/s)  · (50. 0 -50. 5) K = 3. 49 W – efficiency, ? = PN / (qi x A) = 3. 49W / (1 kW/m2 x 0. 12 m2) = 0. 029 II. Collector without glass plate ( t=10min ) – useful power, PN = c  · m  · (? o – ? i) = (4. 182 kJ/kg  · K)  · (1. 667 x 10-3 kg/s)  · (52. 0 -52. 0) K = 0. 0 W – efficiency, ? = PN / (qi x A) = 0. 0 W / (1 kW/m2 x 0. 12 m2) = 0. 0 III. Complete collector, cold jet of air impinges ( t=15 min ) – useful power, PN = c  · m  · (? o – ? i) = (4. 182 kJ/kg  · K)  · (1. 67 x 10-3 kg/s)  · (51. 5-51. 5) K = 0. 0 W – efficiency, ? = PN / (qi x A) = 0 W / (1 kW/m2 x 0. 12 m2) = 0. 0 IV. Collector without glass plate , cold jet of air impinges ( t=15min ) – useful power, PN = c  · m  · (? o – ? i) = (4. 182 kJ/kg  · K)  · (1. 667 x 10-3 kg/ s)  · (43. 0 – 49. 0) K = 0. 0418 kW – efficiency, ? = PN / (qi x A) = 0. 0418 kW / (1 kW/m2 x 0. 12 m2) = 0. 349 DISCUSSION: In this laboratory session, we have conducted an experiment regarding Solar Ray Collector. The main idea of this experiment is to determine the efficiency of the solar ray collector under various experimental conditions.Theoretically, solar collectors transform solar radiation into heat and transfer that heat to a medium (water, solar fluid, or air). Then solar heat can be used for heating water, to back up heating systems. The efficiency of a solar collector is defined as the quotient of usable thermal energy versus received solar energy. Absorbers are usually black, as dark surfaces demonstrate a particularly high degree of light absorption. The level of absorption indicates the amount of solar radiation being absorbed that means not being reflected.As the absorber warms up to a temperature higher than the ambient temperature, it gives off a great part of the accumulated solar energy in form of heat rays. From the Part A of the experiment we can observed that the temperature increases for collector with glass is lesser than collector without a glass. This is because for the condition without glass plate, the light emitted from the halogen lamp not being reflected. Thus the light is emitted directed to the solar ray collector and gives their full efficiency without any disturbance or obstacles.In other scenario, collector with the glass plate, the light that emitted from the halogen lamp is being reflected by the glass plate and also reduced the heat that cross from the glass to the solar collector and hence reduced their efficiency. When the glass is placed, the maximum efficiency recorded was 0. 23 and when the glass is not used the maximum efficiency reached 0. 29. Efficiency indicates how well an energy conversion or transfer process is accomplished. In Part B , we can said that when we use heated water around 60? C , we can see that PN and ? ecome constant zero at the end of the time for natural air with glass. This is because the inlet and outlet temperature have become the same. So we can say that there is no useful power in the system. For the experiment that using the blower, the useful power and efficiency of the absorber for the blower without glass plate is higher than blower with glass plate. This is because the air from the blower relieves the heat from the surface of the absorber thus directly reducing the effectiveness of the absorber significantly. There are several error that occurred while we doing the experiment.First is as parallax errors, for instance the reading of the thermometer not taken precisely. Thus it might be give a slightly error in the data . If the parallax errors occurred, it might influence the results and calculation that we got. Secondly is to get temperature of water at 60 Celsius °C and sometime the temperature drop and affected the heat exchanger. Besides , we are having difficulty in order to maintain the flow rate of 100 cm3/min, because it sometimes goes down and up. Thus we have to check it frequently and its quite disturbing because we also need to take measurement for every minutes for 15 minutes.Moreover the thermometer is not precise because it scale is only 0. 5. Thus it is very difficult to get a correct measurement CONCLUSION: In conclusion, we can say that this experiment has achieve its objectives since we can determine the efficiency of the solar ray collector under various experimental conditions. In this experiment we can said that, the greater heat losses of the absorber the higher its temperature. Although there a lack of technique in handling the apparatus, we managed to complete the experiment with the guide of instructor.