INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) COMPARATIVE STUDY OF PARABOLIC TROUGH CONCENTRATORS

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1 INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN (Print) ISSN (Online) Volume 5, Issue 7, July (2014), pp IAEME: Journal Impact Factor (2014): (Calculated by GISI) IJMET I A E M E COMPARATIVE STUDY OF PARABOLIC TROUGH CONCENTRATORS Santosh Chandra Anand, Dr. Ajeet Kumar Rai, Vivek Sachan MED, SSET, Sam Higginbottom Institute of Agriculture Technology and Sciences, Allahabad (U.P.), India ABSTRACT In the present work two parabolic trough concentrator system of different rim angle and different reflector aperture area is designed, fabricated, and evaluated, and operated for generate hot water.there one system is 45 rim angle and next is of 90 rim angles, here reflector aperture area of 45 rim angle has operatically 20% more than 90 rim angle system, but remaining all other features are same for both the 90 and 45 system. On operation of the system we gets nearly same efficiency for both the system thus we observe that for all same equal features except of reflector aperture area, the efficiency got 20+% more for 90 rim angle compare to 45 rim angle. The Supporting stand of concentrator is made of mild steel & reflector is made of acrylic sheet with a rim angle of 45 and 90 degree and aperture area of 2.20 m square and 1.84 m square with a concentration ratio of and Both the receiver tube has made of aluminum metal material. The thermal performance of the PTC was determined based on ASHRAE (RA 91).The maximum instantaneous thermal efficiency separately both system is obtained closely to 58.32% % range. The total cost for each separate system is calculated Rs 4500 Indian. Keywords: Reflector Aperture Area, Rim Angle, Concentration Ratio. INTRODUCTION The Improper use of fossil fuels has led to negative imbalance in the natural environment so need of using both non-renewable and renewable energy resources were taken to be the main aim and the utilization objective outlined the need to use energy efficiently. Power plants and domestically uses parabolic trough collectors to concentrate the direct solar radiation onto a tubular receiver to generate hot water and water steam for Boiler and turbines for Industrial and domestic and Buildings uses also. Parabolic trough power plants are participates in the biggest part of the total installed concentrating solar power technology. Hence other technologies systems like Fresnel power 65

2 plants, solar tower power plants and dish/ Sterling systems are also using but parabolic trough power plants provide over 90% of the capacity of concentrating solar power plant technology that is in operation or under construction up to September In the projected additional capacity more than 70% are constituted by parabolic trough power plants. PTC mainly consists of a cylindrical parabolic reflector and a metal tube receiver at its focal plane. The receiver is black coated for heat loss resistant and much absorb heat radiation purpose black paint coated at the outside surface covered by concentrator and rotated about one axis to track the sun`s directional motion. The sun tracking system has two types, one is single tracking and another is double tracking system. In PTC concentrated heat is transferred through the absorber tube to working fluid for required purpose. The aperture diameter, rim angle, reflector property and absorber size and shape is defines the PTC. The absorber tube is made of aluminum for quick heat, low cost; reduce weight and protection from salt decomposition and corrosion on outer surface of tube. Hence it is difficult to curve a very large, mirror strips so used in the shape of parabolic cylinder. Reflectors are made of anodized, aluminum Mylar or curved silvered glass. The concentration ratio for a cylindrical. Absorber tube varies from 5 to 30+. The Concentration ratios for composite system can be theoretically very high with the imaging concentrators of precise optical elements and continuous automatic tracking system is in the range of 10 to The reflector and absorber with collector are fixed on the frame structure. The major energy losses from a concentrator-receiver assembly for normal incidence rays deflected away from concentrating plane, losses during reflection from reflecting surface and convection loss from the receiver to surrounding. PTC can be oriented in these three directions, East-west, north-south or polar directions. The East-west, north-south is simple to assemble and have higher incidence angle cosine losses. The polar configuration intercepts more solar radiation per unit area as compared to other modes. DESIGN CONSIDERATIONS In the present PTC has following innovative characteristics; easy constructible, strong and stable in structure, light in weight and low in cost. There we have used for reflecting mirror two Acrylic Mirror Sheets of the size 0.92 meter wide, 1.22 meter long and 4 mm thick has placed longitudinally in each system. The parabolic profile is determined by the shape of the ribs and the width of the sheets. The weight of sheets is rest on said ribs. The total aperture area is for 45 is 2.208m² and for 90 included collectors shadow is m², but the reflector s total area is equal for both the systems. PTC DESIGN PARAMETERS The PTC dimensions and designing parameters has determined by these considerations. For these two separate systems of 90 and 45 rim angle of parabola these two considerations has determined. The first is aperture of the parabola of 1.22m wide acrylic sheet is determined by Wa and second is focal length of parabola. And D₀ is the outer diameter of the receiver tube. Aperture of parabola Wa Wa 66

3 Focal length of parabola Geometrical concentration ratio C for tubular receive We have taken D₀= 0.03 m The three parameters rim angle, aperture width and focal length are determine the crosssection of PTC. ψ is expressed as a function of the ratio of the aperture width to the focal length. tan ψ= / The function of the rim angle is expressed as the ratio of the aperture width to the focal length that is = a/f Here is the focal length, i.e. the distance between the vertex of the parabola and the focal point. Equation of parabola on x axis: Table 1: Specifications of PTC 1 Rim angle( φ r ) Focal length ( ) 0.51m 0.25m 3 Aperture width ( Wa) 1.20m 1.04m 4 Diameter of receiver tube (D₀) m m 5 Length of Parabola (L) 1.84m 1.84m 6 Effective Aperture Area (A a ) 1.56m 1.30m 7 Concentration Ratio (C) Reflectivity of collector (ρ) Absorptivity of receiver tube (α) Transitivity of receiver tube (τ) Intercept Factor (γ) FABRICATION OF PTC The PTC parts has constructed according to given below process and descriptions. 1-Frame structure for PTC system holding and support For holding and support the receiver and reflector a frame structure of made by mild steel Iron has assembled with use of arc welding, drilling and nut-bolt joint. The reflector support frame portion was adjustable to horizontal axis for automatic or manual sun tracking. The single Sun tracking and double Sun tracking structure is designs according structure frame manner. 67

2- Parabolic Trough or Receiver-Absorber assembly Commonly parabolic trough has four parameters are used to determine, in this system, trough length (1.

4 2- Parabolic Trough or Receiver-Absorber assembly Commonly parabolic trough has four parameters are used to determine, in this system, trough length (1.84m), focal length (25cm, 51cm), aperture width (104cm, 120cm) and rim angle ψ (90, 45 ). Rim angle is angle between optical axis and line between focal point and rim angle. Focal length is distance between focal point and vertex. Aperture width is distance between one rim to other rim in one parabola. Rim angle has an effect on the concentration ratio and on the total irradiance per meter absorber tube in W/m. If the rim angle is very big then the way of reflected radiation from outer part of mirror is very long and the beam spread is very big, reducing, hence, the concentration ratio. Hence a mirror with a smaller rim angle and the same aperture width would permit a higher concentration ratio. At 45 rim angle the highest concentration ratio is reaches and on increasing rim angle the Sun image is widening and then concentration ratio is decreasing capture to 45 rim angle, and when below the 45 rim angle now Sun image is more widening compare to first condition and then C.R. is much more decreases. In higher rim angle the absorber tube is nearer allocated the mirror then radiation beam is spread and reduces C.R. The shadow of tubular also reduces mirror receiver area, aperture and C.R. also. The absorber distance is larger in very large rim angle as well as very small rim angle. The more weight carries the radiation aberration due to mirror slope error. Mirror is determined as at a Sun position it captures the radiation beams. EXPERIMENTAL SETUP In this experimental setup of parabolic trough concentrator we have used a 30 liter storage source tank for supply the working fluid to receiver tube. The storage source tank level is 0.25m higher than the receiver tube s maximum height and the connecting tube is flexible and 0.75m long to rotate the receiver movement and direction for Sun tracking. Our system was oriented in northsouth to capture maximum isolation. The system was able for manual tracking. Figure 1: Experimental Setup In the system collector performance over the day is quit uneven and is reduces in the hours after sunrise and before sunset. So to reduce this problem we have enlarged 0.50m length of receiver tube at inlet and outlet side in the focal plane. 68

5 We have applied adjustable flow control valve arrangement at collector end to variance the different, constant mass-flow rate with drop-wise flow. Our flow rate was 2 liter/3 liter/4 liter per hour droplet-wise constant mass-flow rate condition 8 hours day observations. We have fitted the thermocouple sensors to observe the temperature at point of receiver s in/mid/out points, source storage tank, collector storage, reflector sheet s front/back sides and ambient temperature pick out. We have used solarimeter to measure the solar radiation intensity on mirror sheet and receiver tube. For measuring wind velocity we used anemometer. PERFORMANCE OF PARABOLIC TROUGH COLLECTOR In this system estimated performance are the solar field efficiency and useful heat output from solar effected area under different operating conditions for characterizing the performance. Thermal Efficiency In thermal efficiency, it is affected by thermal losses. Thermal losses depend on the temperature difference between the heat transfer medium and the surrounding air. Heat loss from a warmer surface to ambient air is because of convection and thermal radiations. Q conv = h.a. T Q rad = Ԑ.ρ.A.(T 4 amb-t 4 abs) Q cond = ( /b).a. T Here b is insulation thickness. Collector overall efficiency c is defined as the ratio between the useful output Q u by collector to global irradiance I on A a c= *Ib For collector useful output Q u Q u =mcp(t 0 -T c )=A a I b ₀-A abs *U l (T abs -T a ) Optical efficiency Optical efficiency ₀ is defined as total amount of radiation absorbed on absorber tube outer surface to the amount of direct normal radiation incident on aperture area. If incident radiation is normal to the aperture is ( =0 ) then the optical efficiency ₀=ρ.(τ.α).γ RESULT AND DISCUSSION Number of observations has taken on both the system in the month of May 2014, in solar lab ground of SHIATS Allahabad, Uttar Pradesh, India. The observation data of both 90 rim angle and 45 rim angle PTC has taken and calculated the thermal efficiency at separately particular day. The maximum thermal efficiency has got 58% for 45 rim angle and 59% for 90 rim angle systems. 69

6 Fig 2: Variation of solar intensity with respect to time of a day on a particular day in the month of may (23/05/2014) Figure 3: Variation of wind velocity with respect to time of a day in the month of May at a particular day (23/05/2014) Figure 4: Variation of temperature with respect to time of a day of receiver tube at in/mid/end point at a particular day (23/05/2014) 70

7 Figure 5: Variation of temperature rise (inlet-outlet) difference with respect to time of a day of on a particular day 23/05/2014 Figure 6: Variation of thermal efficiency with respect to time of a day, at mass flow rate of 2 liter/hour on a particular day in the month of May (21/05/2014) Figure 7: Variation of thermal efficiency with respect to time of a day, at mass flow rate of 3 liter/hour on a particular day in the month of May (22/05/2014) 71

8 Figure 8: Variation of thermal efficiency with respect to time of a day, at mass flow rate of 4 liter/hour on a particular day in the month of May (23/05/2014) The result shows that the thermal efficiency of both PTC at different mass flow rate of drop wise constant continue flow of working fluid (Water). The result has shows that for same size mirror sheet at rim angle 45 and 90, the thermal efficiency has closely equals. Hence in 90 rim angle PTC has active Sun radiation receiving active aperture area of reflector sheet receiver is 20% less due to aperture width and absorber tube is closely to reflector sheet appears the shadow on mirror sheet. Thus 90 rim angle PTC system is 20% more efficient than 45 rim angle PTC system for same equal area of receiver mirror sheet and absorber tube system. CONCLUSION From the observations, calculated data and calculations in relation with analysis and discussion, this research investigation can be calculated that fabricated PTC has maximum thermal efficiency has got 58% for 45 rim angle system and 59% for 90 rim angle system. The result concludes that 90 rim angle PTC has 20% more efficient compare to 45 rim angle PTC system. And 90 degree rim angle system is permits easy protection with flat glass mirror reflector sheet. REFERENCES 1. Bernhard Scheffler (2012) Solar junction does it again set new cpv efficiency record. 2. Matthias Gunther, Michel Joemann, Simen Csambor (2011) Advanced csp teaching materials Chapter 5, pp Arasu, A. Valan & Sornakumar, T. (2007) Design, manufacture and testing of fiberglass reinforced parabola trough for parabolic trough solar collectors, Solar Energy, Vol. 81, pp Hachicha, A. A., Rodríguez, I., Capdevila, R. & Oliva, A. (2013) Heat transfer analysis and numerical simulation of a parabolic trough solar collector, Applied Energy, Vol. 111, pp Jaramillo, O. A., Venegas-Reyes, E., Aguilar, J. O., Castrejon-Garcia, R. & Sosa- Montemayor, F. (2013) Parabolic trough concentrators for low enthalpy processes, Renewable Energy, Vol. 60, pp Kalogirou, Soteris (1998) Use of parabolic trough solar energy collectors for sea-water desalination, Applied Energy, Vol. 60, pp

9 7. Kalogirou, Soteris A. (2004) Solar Thermal Collectors, Progress in Energy and Combustion Science, Vol. 30, pp Ajeet Kumar Rai, Shahbaz Ahmad and Sarfaraj Ahamad Idrisi (2013), Design, Fabrication and Heat Transfer Study of Green House Dryer, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 4, pp. 1-7, ISSN Print: , ISSN Online: Hasan Falih M., Dr. Ajeet Kumar Rai, Vivek Sachan and Omar Mohammed I. (2014), Experimental Study of Double Slope Solar Still with Energy Storage Medium, International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 5, Issue 3, pp , ISSN Print: , ISSN Online: Omar Mohammed Ismael, Dr. Ajeet Kumar Rai, Hasanfalah Mahdi and Vivek Sachan (2014), An Experimental Study of Heat Transfer in a Plate Heat Exchanger, International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 5, Issue 4, pp , ISSN Print: , ISSN Online: Ajeet Kumar Rai, Pratap Singh, Vivek Sachan and Nripendra Bhaskar (2013), Design, Fabrication and Testing of a Modified Single Slope Solar Still, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 4, pp. 8-14, ISSN Print: , ISSN Online: G.N.Tiwari, Solar energy volume, pp , pp

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