INTRODUCTION
Energy consumption is an index of prosperity in a country.
Due to technological and industrial development, the demand of energy is rapidly increasing. Pakistan will be facing the serious challenge of energy shortfall in the near future and even today the primary energy supplies are not sufficient to encounter the present demand. This is forcingus to give serious thoughts to the development of alternative and renewable energy resources. In addition, environmentally friendly renewable energy sources need to be developed and endorsed to attain the goal of ecological development. Other reasons for preferment of such energy technologies, particularly in the developing countries like Pakistan, are clean environment, energy independence, new employment opportunities and improvement of living conditions in rural areas resulting in reduction of mass movement to urban areas.
The life cannot survive on earth without solar energy. The environment friendly ecology can be produce by effective use of solar energy. From last few decades, after the awareness of the environmental effect and the high increase in the price of
the fossil fuels, the researchers have diverted towards alternative energy resources (Jayakumar, 2009). For several decades man has been depending upon coal, oil and gas, but these resources are going to be worn-out in a coming few years and their prices are increasing rapidly. Now a day, emphasize upon alternative source of energy is profitable such as nuclear, solar, bio mass, hydro power and wind energy, etc. Nuclear power is on the top of the list but it is difficult to develop due to lack of technology and expert staff to deal with it especially in developing countries.
Resources of fossil fuels (non-renewable resources) are being depleted day by day and they take millions of years to form.
Environmental concerns are also increased by the use of fossil fuels. Therefore, a global movement toward the generation of renewable energy is under way to help meet increased energy needs. Recent reports oncurrent status of the reserves of fossil fuels point to the need to switch to alternative energies such as Solar Power. With the passage of time we will not able to face rapidly increasing energy demand because the fossil fuels resources are limited.
ISSN (Online): 2311-3839; ISSN (Print): 2312-5225 http://www.jgiass.com
MODIFICATION AND OPTIMIZATION OF SOLAR PARABOLIC TROUGH USING COPPER TUBE FOR STEAM GENERATION
Rizwan Ali
1,*, Muhammad Waqar Akram
1,2, Muhammad Aleem
3and Muhammad Waqas Sarwar
41 Department of Farm Machinery and Power, University of Agriculture Faisalabad, 38000, Pakistan;
2 Department of Precision Machinery and Instrumentation, University of Science and Technology China, Hefei, 230026, Anhui, P.R.China; 3 College of Environment, Hohai University, Nanjing, 210098, Jiangsu P.R. China;
4Department of Structures and Environmental Engineering, University of Agriculture Faisalabad, 38000, Pakistan.
*Corresponding author’s e-mail: [email protected]
Pakistan is an energy deficient country, where a large fraction of the population still does not have easy access to modern day energy facilities such as electricity. This is due to limited fossil fuel resources and poor economy, which restrains the import of fossil fuels on a large scale. To overcome energy crises, Pakistan needs to utilize its renewable energy resources like solar, wind and hydropower. Pakistan is located within solar-drenched belt and lucky to have long sunshine hours and excessive radiation. This huge potential can be used to produce electricity, which could be provided to off-grid communities in the northern hilly areas and the southern and western deserts. Utilization of solar energy in areas other than electricity generation such as solar parabolic trough for steam generation and solar cookers also have vast applications. All this can help in both reducing the import of fossil fuels and reliance of people on wood fuel, which in turn will provide some relief for the dwindling forest assets of Pakistan. Solar parabolic trough is one which can prove beneficial in utilization of solar potential. Parabolic trough technology uses parabolic reflectors to concentrate the sun rays into a receiver pipe along the reflector’s focal line.
Parabolic trough is modified by using copper tube as an absorber of sun rays reflected from glass mirrors. The trough is made of glass mirrors. These mirrors are pasted on riveted GI sheet. The trough is placed in both North-South and East-West direction. The modified parabolic through is evaluated in Farm Machinery Workshop, University of Agriculture Faisalabad.
Keywords: Modification, trough, fossil fuel, renewable, solar, parabolic, southern.
Renewable energy resources are environmental friendly and far more abundant than fossil resources, but they tend to be dispersed and more expensive to collect. Many of them, such as solar energy and wind, are irregular in nature. Also, the direct cost of fossil fuel is usually less than the direct cost of renewable energy. But problem is that, fossil fuels have also indirect or external costs, such as acid rain, global warming and pollution. There are three common types of solar energy.
The passive solar energy, which wisely uses stuffs like insulation, window settlement, thermal mass and architecture to minimize the cost of heating, cooling and lighting of the structures. The active solar energy, collects the heat emitted from the sun, transported and stored into beneficial places such as swimming pools, solar geysers, room heaters and heat for industrial processes. The photovoltaic (PV), (photo-light, voltaic- electric) solar energy, which converts sun light directly into direct current (DC). This DC can be stored into batteries for further use or by inverting DC into alternating current (AC) for different appliances.
A huge amount of solar energy is available all over the earth sphere during the year. The incident solar energy assessed on the earth surface is about 1.5×1018 kWh per year, which is about 10,000 times greater than current annual power utilization of whole world. The available energy at the outside of the earth’s atmosphere (extraterrestrial), which is about 1367 Wm-2 and known as solar constant (Duffie and Beckman, 2006). The earth receives solar energy in the form of electromagnetic radiation in a huge quantity. It has been studied that more than 50% of the incident radiation is reflected back into the atmosphere by ozone and clouds, about 10% is reflected, absorbed and diffused by the dust in the atmosphere and about 5% absorbed by the bare soil. About 35% of the total radiation energy coming from the sun is useful for energy production especially in sunny areas (Duffie and Beckman, 1974).
Pakistan lies between latitude 24 and 37 degrees north and longitude 62 and 75 degrees east. Pakistan is receiving on an average 5.3 kWh m-2 per day.The mean global irradiation falling on horizontal surface in Pakistan is about 200–250 watt per m2 in a day with about 1500–3000 sunshine hours in a year. (Mirza et al., 2003). Pakistan is located ideally to get maximum available solar radiation and possess ample capacity to overcome its energy crises. The growing industrial sector is the main cause of increasing the use of hot water. Hot water is used in tanneries, pharmaceutical industries, manufacturing of ceramics, glass, and like other productions in industries. To fulfill the requirements of hot water, industrialists uses electricity and gas for the production of hot water. The alternative source of energy “The Sun” for water heating system is the best solution (Rahman, 2010).A cost effective solar renewable energy program like solar water heaters with minimum danger and high returns is the necessity for residing (Guiney et al., 2006). With a view to attain wider market saturation, it is important to beat monetary
restrictions. To encourage the solar water heaters in domestic areas can be instrumented to lower start-up expenditure and thus greater urge for high market saturation (Kalogirou, 2004).
MATERIALS AND METHODS
The current chapter has been focused on the materials that were used in the evaluation process of solar parabolic trough and the methodology that was adopted to continue the research.
Study Area: The research has been conducted in the Workshop of Department of Farm Machinery and Power, Faculty of Agricultural Engineering and Technology, University of Agriculture Faisalabad. The latitude and longitude of the experimental area was 31.4377ºN and 73.07ºE and at the elevation of 190.76 m from sea level. It is 34797 km away from the equator. The university is located at the middle of the Faisalabad city. The city proper covers an area of approximately 1,230 km2 while the district covers more than 16,000 km2. There are no natural boundaries between Faisalabad and adjoining districts. The Chenab River flows about 30 km to the north-west while the River Ravi meanders about 40 km south-east of the city. The lower Chenab canal is the main source of irrigation water, which meets the requirements of 80% of cultivated land. The soil of Faisalabad comprises alluvial deposits mixed with loess having calcareous characteristics, making it very fertile.
Climatic Conditions: Faisalabad features a hot desert climate.
The extreme climate of the district can be observed in a summer maximum temperature 50 °C (122 °F) and winter minimum temperature of 2 °C (28 °F). The mean maximum and minimum temperature in summer are 39 °C (102 °F) and 27 °C (81 °F) respectively. In winter its peaks are around 17
°C (63 °F) and 6 °C (43 °F) respectively.
Table 1. Climatic Condition of Faisalabad.
Month Average high Temp.
(ºC)
Mean daily Temp.
(ºC)
Average low Temp.
(ºC)
Precipitati on (mm)
January 19.9 11.9 4.4 14
February 22.4 14.9 7.4 15
March 27.3 19.9 12.6 21
April 33.8 25.9 18.1 14
May 38.9 31.1 23.3 13
June 40.7 34.0 27.4 26
July 37.3 32.3 27.4 26
August 36.3 31.6 26.9 91
September 36.0 30.1 24.2 33
October 33.6 25.6 17.6 6
November 27.5 18.9 10.4 3
December 21.8 13.7 5.7 8
Year 31.25 24.16 17.12 346
Source: Climate-Data.org (2010)
The summer season starts from April and continues till October. May, June and July are the hottest months. The winter season starts from November and continues till March.
December, January and February are the coldest months. The average yearly rainfall lies only at about 300 mm (12 in) and is highly seasonal with approximately half of the yearly rainfall in the two months July and August in the moon soon season which starts from 15 July. The average winds in the Faisalabad region is about 3m/sec and the wind direction in most of the year is North-West and South-East directions, wind also moves other than these directions like West, South- West, East and South directions throughout the year. The average data of temperature and precipitation of Faisalabad is shown in Table 1, while the wind direction and speed is shown in Table 3.
Tools and Machinery used
Table 4. List of tools and machinery used.
Sr.N0. Tool Name
1 Pipe Wrench
2 Cutter
3 Measuring Tape
4 Hammer
5 Drill Machine
6 Grinding Machine or Grinder
7 Screws
8 Riveting Gun
9 Rolla Machine or roller
10 Saw
11 Sprayer
12 Silicon Gun
13 Glass Cutter 14 Sheet Cutter
15 L-key set
Data Acquisition: Following instruments were used to acquire the required data
Thermocouples: K-Type thermocouples usually work in most applications as they are nickel based and exhibit good corrosion resistance. It is the most common sensor calibration type providing the widest operating temperature range. Due to its reliability and accuracy the K-Type thermocouple is used extensively at temperatures up to 2300°F (1260°C). This type of thermocouple should be protected with a suitable metal or ceramic protection tube, especially in reducing atmospheres. In oxidizing atmospheres, such as electric furnaces, tube protection is not always necessary when other conditions are suitable; however, it is recommended for cleanliness and general mechanical protection. K-Type generally outlast than J-Type because the JP wire rapidly oxidizes, especially at higher temperatures. Two K-Type thermocouples with calibrated temperature meter were used
in the development, to read the upper and lower side temperature of absorber sheet.
Temperature Gauges/Thermometer: Bimetal thermometer was used for measuring temperature of liquid/fluid. This is suitable for measurement, regulation and direct monitoring of the fluid and meets the most stringent criteria on resistance to corrosive atmosphere and exceptional climatic circumstance.
Pyranometer:Pyranometer is the device used to measure the solar radiations. In this pyranometer the black portion was held towards south and the directed towards the sun. The reading was shown on theLCD of the pyranometer. Only readings of beam radiations were taken. These readings were then multiplied by 86.5 to gain the solar radiations in W/m2. Fabrication of Absorber Tube: There are number of materials available for the receiver. Tube material selection was on the basis of thermal conductivity and cost. Copper is an excellent electrical conductor. Most of its uses are based on this property or the fact that it is also a good thermal conductor (k=398 kWm-1 K-1, where k represents thermal conductivity). However, many of its applications also rely on one or more of its other properties. For example, it wouldn't make very good water and gas pipes if it were highly reactive.
The sun radiates at an average of two calories of heat per sq.
cm. per minute. This is also calledsolar constant. This is the total heat available for utilization. The main problem in the design of solar appliances is to absorb or focus the maximum percentage of solar radiation and its use in such a way that the calories obtained is sufficient to do the work required i.e. to boil water, oil, to cook foods, to distill water, to dry fruits and to produce electricity from steam.
In all types of solar parabolic trough, the principle is either to concentrate parallel sun rays to a focus point or absorbs solar energy radiant on the surface of the earth in a parabolic concentrator and transfer it to some heat exchange like fluid or utilize it directly. The solar radiations parallel to the axis of concentrator are focused at a point after reflection. Therefore, heat is generated at that point. This heat can be used for boiling water and cooking. The performance of the proposed solar parabolic trough was checked during the dates of 21-05- 2015 to 08-06-2015. The parabolic trough was consists of a steel sheet of 20 gauge thickness, 80 strips of glass mirrors with 25mm width, 737.5mm and 1.6mm thickness stick with silicone gel. The solar parabolic trough is a one dimensional parabola that focuses the solar energy on to a focal line. This focal line was a copper tube in which water was moving.
Transparent glass tube can also be used to cover copper tube in order to increase the temperature of flowing fluid. The copper tube was placed on the focal line to get the maximum radiations falling onto it. When the evaluation of solar parabolic trough was in progress, the control lever was adjusted after every fifteen minutes. So that the maximum solar radiations should be concentrated at the focal line of the solar concentrator. When the temperature of the copper tube reached at maximum then this temperature is feasible for
heating water, boiling, cooking, roasting, sterilizing clinical instruments and many other domestic applications. The solar parabolic trough system was placed in sunshine from 10:00 AM to 03:00 PM. The daily working period was five hours.
The overall assembly of solar parabolic trough was placed in two directions.Firstlywhole assembly was placed and checked. Secondly it was checked in North-South direction and the efficiency was checked. Finally their efficiencies were compared and analyzed which results in conclusion that efficiency is higher in East-West direction due to shadow losses. The assembly placement in East-West and North- South directions is shown in figure 3.7 and 3.8 respectively.
Performance Evaluation of Solar Parabolic Trough: The overall efficiency of the system is defined as the ratio of energy output of the solar parabolic trough to the total energy input. Thus, overall efficiency of the system is given below (Schirmeret al., 1996)
Ƞ = Qd/Qs
Qs = Ac. It/1000 Where,
Qs = Available energy in J/sec Ac = Collector area in m2
It = Total solar radiations in W/m2
Collector efficiency is defined as the ratio of energy output of the collector to energy input to the collector. Solar energy input on the collector is computed as given in
Qd = m.Cp.ΔT (Khurmi& Gupta, 2005) Where,
m = Liter/sec x Density of water (1litre = .001m3) Density of water = 1000kg/m
Qd = Energy obtained in J/sec m = Mass flow rate in kg/sec
Cp = Specific weight of water i.e. 4178 kJ/kg.k ΔT = Temperature difference in K
RESULTS AND DISCUSSIONS
The solar parabolic trough is modified by using copper tube and evaluated in Workshop of Agricultural Engineering, Department of Farm Machinery and Power, University of Agriculture, Faisalabad. Many experiments were conducted to evaluate the performance of solar parabolic trough by placing both in East-West and North-South direction. The different parameters which were under consideration during experiments are given below with detail and the results of different experiments are shown in graphical form with detail.
Results in East-West Direction: The solar parabolic trough was firstly evaluated by placing it in East-West direction, the inlet temperature T1 and outlet temperature T2 was observed by Bimetal Thermometer and K type Thermocouple respectively,their difference was taken as ΔT, the air temperature was calculated by thermometer, and the solar radiations were measured by pryanometer. Then measured the efficiency of the system after achieved all these parameters.
All these parameters were calculated each after half an hour from 10:00AM to 3:00PM. The height of the inlet from the ground 725mm and height of the outlet from the ground 875mm and the angle between outlet and ground surface 57˚.
The trough was adjusted in East-West direction by tightening the nuts and the collector surface of the trough to the sun to attained maximum solar radiations. The earth makes one complete revolution of 360° in 24 hours, so in one hour, it moves 360°/24= 15°. To keep the reflector in line with the sun, it must be rotated 15° per hour. The angle at which the sun’s rays strike the earth varies by geographical location and time ofyear. Rotated the whole assembly manually by 5˚ after every 20 minutes to attain the maximum solar radiations and thus, reduced time to heat up the water. The overall assembly placed in East-West direction is in fig. 3. All figure and tanel set in numerical
Inlet and outlet temperature variation with time: Inlet temperature, the temperature of the water inside tank was measured with Bimetal thermometer. It was increased with time and was maximum at 3PM. Outlet temperature was increased first with and maximum at 12:30PM then gradually decreased with time. Outlet temperature is the temperature at outlet tap of the tank from where hot water entered into the tank and was measured with K-type thermocouple.
Figure 1. Inlet temperature variation with time in E-W direction
Figure 2. Outlet temperature variation with time in E-W direction
Variation of Temperature Difference and Ambient Temperature with time
Temperature difference and ambient temperature both increased with at start and maximum at 12:30 PM and then both decreased with time. Ambient temperature was measured with thermometer. Variations of both temperatures are shown below in graphs.
Figure 3. Temperature difference variation with time in E-W direction
Figure 4. Ambient temperature variation with time in E- W direction
Variation of solar radiation and mass flow rate with time Solar radiations and mass flow rate both increased with time at start and maximum at 12:30 PM. Solar radiations measured with pryanometer. Mass flow rate measured in kg/sec. The variation of solar radiations and mass flow rate with time both shown below in graphs.
Figure 5. Solar radiations variation with time in E-W direction
Figure 6. Mass flow rate variation with time in E-W direction
Variation of efficiency with time: Efficiency is the ratio of output to the input. Output was the energy gained from the solar parabolic trough and input was the available energy obtained from the sun. Efficiency increased with time initially and maximum at 12:30PM and gradually decreased with time.
Efficiency was more in East-West direction due to large temperature difference and high solar radiations. The variation of efficiency is shown below in figure. Here the values on x-axis are the time from 10:00AM to 3:00PM shows that 1 equal to half an hour. All the readings were taken after half an hour.
Figure 7. Efficiency variation with time in E-W direction
Conclusions: Following conclusions were drawn during the research. This parabolic trough is simple in construction and can easily be constructed using locally available materials. It was concluded that the efficiency was more when overall assembly was placed in East-West direction as compared to North-South direction. It was concluded that use of copper tube as an absorbing material is better option instead of silver.
It was concluded that this type of solar parabolic trough system is best suited for the regions having more beam radiations.
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