Design, fabrication and analysis of helical coil receiver with varying pitch for solar parabolic dish concentrator 1 Manav Sharma, 2 Jaykumar Vaghani, 3 Nitesh Bihani, 4 Niranjan Shinde, 5 Vijay.C. Gunge 1,2,3,4 BE, Department of Mechanical Engineering, Sinhgad College of Engineering, Pune-41 5 Asst. Prof., Department of Mechanical Engineering, Sinhgad College of Engineering, Pune-41 Email: 1 manash92@yahoo.co.in, 2 jay.happypalace@gmail.com, 3 niteshbihani26@gmail.com, 4 niranjanshinde1@gmail.com, 5 vijaygunge15@gmail.com Abstract The discrete small scale solar powered systems generally low cost are used for medium temperature applications including laundry, boiler feed water, dish washer and for water heating purpose in steam generation applications. The solar parabolic dish concentrator has a fixed focus with concentration ratios in the range of 20-200 which is the best among all the solar s. In present study, the parabolic dish of opening diameter 1.4 m was fabricated using galvanized steel and its interior surface covered with reflective surface of ionized aluminum with a reflectivity of 92.5%. The system is equipped with a receiver fabricated using copper metal positioned at the focal point. The working fluid is water. The research focuses on the temperature variations achieved from changes in the geometry of the helical receiver. This paper reveals the temperature variations achieved with a bare tube helical receiver with zero pitch and with black coated helical receiver with non-zero pitch and capped. The maximum attainable temperature with non-zero pitch helical receiver coated with black paint and capped was approximately 43% higher than that of bare tube helical receiver with zero pitch. Index Terms Solar parabolic dish, concentration ratio, helical coil receiver, Pitch variation. I. INTRODUCTION 2. Diffused radiation (I d ) is that solar radiation which is received directly from sun after its direction has been changed by reflection. 3. Global radiation (I g ) is the sum of beam and diffused radiations. The solar energy can be converted into thermal energy either by flat plate or a concentrator. Different types of concentrators include parabolic trough, parabolic dish and linear Fresnel reflector. Parabolic Dish Concentrator (PDCs) has the maximum concentration ratio (CR) among all the solar concentrators. [5] II. THEORETICAL BACKGROUNDS Several parameters are used to describe solar concentrating s. Some of the important parameters are given below: Collector area: It is the area of the that intercepts the solar radiations coming from the sun. [10] Receiver area: It is the total area of the receiver that absorbs solar radiation reflected from the. [10]. Concentration Ratio: It is defined as the amount of light energy concentration achieved by a given. [12] The sun is the only star of our solar system located at its center. The sun is a sphere of intensely hot gaseous matter with a diameter of 1.39x10 9 m and is about 1.5x10 11 m away from the earth, the sun rotates on its axis once about every four weeks. The intensity of solar radiation per unit time on a unit surface outside the earth s atmosphere is known as solar constant. Its value is 1353 W/m 2. The solar radiation as received on the earth s surface is composed of the following: 1. Beam radiation (I b ) is that solar radiation which is Rim Angle (Φ): It is defined as the angle between the axis and the reflected beam from the edge of the parabola. The rim angle measures extend of truncation of the general parabola. [8] Intercept factor (γ): It is the ratio of energy intercepted by receiver to energy intercepted by the parabola. Figure 1.1 shows segments of a parabola having a common focus F and constant aperture W. The effect of rim angle on the height of the parabola and curved surface received directly from sun without change of direction. is evident from the Figure 1.1. 49
From the above equation the rim angle is found to be 100.34. The total surface area for the parabolic dish is given by: [9] The total area is found to be 2.002 m 2. But due to manufacturing constraints a small circular part of the dish is removed from the bottom, Hence the effective surface area (Ac) is 1.986 m 2. Fig.1.1 Segment of a parabola having a common focus F and the same aperture. [12] Table І Solar Energy Collectors Sr. No. 1 2 3 Collector type Flat Evacuated plate tube Parabolic trough Concentrat ion ratio (CR) Temperature range 1 303.15-353.15 1 323.15-473.15 10-85 333.15-573.15 The total available heat from the sun for the tested solar parabolic dish is Q total = total intercepted heat from the system + losses due to convection where the total heat intercepted by the system is given as: where I B = beam radiation, A r = area of the, ρ = reflectivity, α = absorptivity, τ = transmissivity, I f = intercept factor. Initially for calculations the C.R is assumed to be 40. 4 Parabolic dish 20-200 (Practically) 373.15-673.15 The volume of the receiver is given by: [10] III. MATHEMATICAL MODELLING The focal distance for a parabolic dish concentrator is given by the following expression: [9] Where h is the depth of the dish and d is the diameter of the opening parabolic surface. The focal length for the dish is found to be 290.2 mm. It is almost equivalent to the focal length provided by the manufacturer i.e. 292 mm. The focal length f can also be obtained from (Stine and Harrigan, 1985): For small scale application the total volume of the receiver is approximated to be 5 l m 3. The diameter obtained for the helical coil is 18.533 cm. The receiver is assumed to be a cylinder of equal diameter and length. Considering that the concentrated radiation fall on the bottom half of the helical coil hence the formula for receiver area is: The receiver area is found to be 0.0539 m 2. The Concentration ratio is given by: [8] Where is the rim angle. From the calculations it is found to be 37. 50
IV. DESIGNING AND MANUFACTURING A. Design of solar dish The dish was manufactured under the guidance of Solar Akson Pvt. Ltd. The frame of the dish was made from galvanized steel and consisted of simple links welded together. The links were of hollow cross-section to reduce the overall weight of the frame. [6] At the same time gas welding was preferred for strong linkage connection to hold the dish and sustain the wind flow. The internal surface was covered with ionized aluminum of reflectivity of 92.5%. The aluminum sheet was cut into several pieces with decreasing area of equal size. The parabola shape was formed by inter connecting the aluminum sheet with thin metal wires as shown in fig 1.2. The second helical coil was manufactured for a non-zero pitch of 5 mm and its surface was powder coated with black color. A cap was manufactured for the same using a thin metal sheet covered with ionized aluminum foil. The cap dimensions were kept in accordance with the helical coil. The cap was fitted with simple hook arrangement as shown in fig 1.3. Fig. 1.4Coated helical coil receiver with non -zero pitch and capped V. EXPERIMENTAL SETUP The schematic sketch of the setup is shown below. Fig.1.2 Parabolic dish concentrator B. Design of helical coil receiver Copper metal was selected for receiver designing due to its high thermal conductivity (k=401w/mk). A copper tube was procured from the market of O.D 10mm and thickness 1mm for testing purpose. The helical coil was manufactured using bending process in which sand is inserted in the tube and the tube is enclosed on both sides by a cork. In this study we have used two helical coils as receivers, the first one was manufactured with zero pitch and its surface was kept bare as shown in fig. 1.3. Fig.1.5 The schematic sketch of the system Fig.1.3 Bare helical coil receiver with zero pitch The figure shows the complete assembly of the system. The input is taken from the reservoir with the help of a submersible pump. The water from the reservoir goes to the input side of the helical coil through the flexible pipe via rotameter. A flow control valve is also attached for flow rate controlling. The water absorbs the heat while flowing through the receiver coil and is collected in the collection tank at the outlet. Temperature sensors (K-type thermocouple) are provided at the inlet and outlet of the helical coil for temperature measurement. 51
VI. RESULTS AND DISCUSSIONS The readings for bare helical coil and the one with black coating and capped is shown below. The testing was done in cold conditions which are considered hostile for such systems which are solely dependent on solar direct radiations. Table II Readings from 15 Dec, 2014 to 15 Jan, 2015 Time Temp. of bare (sec.) coil with zero pitch 11.00 318.15 335.17 11.30 322.68 342.59 12.00 325.86 348.37 12.30 329.75 354.75 13.00 333.05 364.19 13.30 336.18 369.73 14.00 338.38 375.19 14.30 334.54 373.64 15.00 329.87 368.19 Temp. of non zero pitch, coated and capped coil Table III Readings for 16 Jan, 2015 with constant flow rate = 0.00223 10-3 m 3 /s Temp. with Temp. of non Mass flow rate, ( 10-3) (m3/sec) zero pitch of bare coil zero coated capped coil 0.00667 318.15 335.23 0.00611 321.35 339.51 0.00556 323.67 344.63 0.00416 325.98 350.75 0.00333 326.00 357.15 0.00278 329.46 361.33 0.00223 330.38 365.10 pitch, and From Table II, the output temperature with change in mass flow rate is shown and points to the fact that with increase in mass flow rate, the output temperature from the coil goes on reducing for both types of geometries. The temperatures obtained for non-zero pitch coil (coated and capped) is higher than that compared to zero pitch coil. The same can be shown in the graph plotted below. Fig.1.5 Graph for mass flow rate vs. temperature From Table III, the output temperature with change in time on a certain bright sunny day increases from morning till afternoon and is found to be maximum at 14:00 which is expected. The temperatures obtained for non-zero pitch coil (coated and capped) is higher as compared to zero pitch coil. The same can be seen in the graph plotted below. Fig.1.6 Graph for time vs. temperature As the study indicates that the helical coil receiver with non zero pitch (coated and capped) provides better results hence the temperature obtained from the same is validated with theoretical calculations which is given below in the table. Table IV Comparison between practical and theoretical temperatures outputs obtained Date Flux (W/m 2 ) T practical T theoretical 15-12-2014 690 332.1 365.36 21-12-2014 706 334.84 365.28 26-12-2014 722 337.21 367.94 29-12-2014 734 340.15 368.17 31-12-2014 741 342.15 369.13 03-01-2015 757 344.65 372.98 05-01-2015 766 347.08 374.43 09-01-2015 793 351.82 377.96 12-01-2015 811 354.48 379.29 16-01-2015 825 357.59 380.46 The temperature and flux values in table IV indicate the average temperatures and fluxes obtained on the mentioned dates. The percentage variation between the practical and theoretical temperatures is within ±10% and hence acceptable. The variations are plotted in the graph below: 52
VII. CONCLUSION The variation of output temperature with respect to change in helical coil geometry has been studied. It is concluded that the output temperature of the system is increased for the non-zero pitch coil as compared to zero pitch coil. The increase in temperature for non-zero pitch coil is approximately 43% more than that of zero pitch coil. Hence the system is more efficient for helical coil with non-zero pitch which is black coated and capped. Fig. 1.7 Graph for date vs. Temperature The variations are obtained for the output temperatures for time lapses within a particular day as shown in the table below. Table V Comparison for practical and theoretical temperature outputs obtained Time T practical T theoretical 11.00 335.20 365.68 11.30 342.59 366.57 12.00 348.37 368.58 12.30 354.75 369.94 13.00 364.19 386.04 13.30 369.73 397.70 14.00 375.19 401.00 14.30 337.64 403.05 15.00 368.19 382.91 The variations are plotted in the graph below: REFERENCES [1] Eric W. Brown: An introduction to solar energy ; 1988 [2] Tarujyoti Buragohain: Impact of solar energy in rural development in India ; International Journal of Environmental Science and Development, Vol. 3 No.4, 2012 [3] Geoffrey Jones, Loubna Bouamane: Power from sunshine: A business history of solar energy ; Harvard Business School Paper 2012 [4] Yinghoa Chu, Peter Meisen: Review and comparison of different solar energy technologies ; Global Network Energy Institute, 2011 [5] F. Mohammed Sukki, R. Ramirez Iniguez, Scott G McMeekin, Brian G Stewart, Barry Clive : Solar concentrators ; International Journal Of Applied Sciences (IJAS), Vol. 1 Issue1, 2012 [6] Carl W. Richter, Arthur G. Birchenough, Gerald A. Marquis, Thaddeus S. Mroz : Design and fabrication of a low specific weight parabolic dish concentrator ; NASA Technical Paper 1152, 1978 [7] Lloyd C. Ngo: Exegetic analysis and optimization of a parabolic dish for low power application ; Centre for Renewable and Sustainable Energy Studies, University of Pretoria Fig. 1.8 Graph for time vs. Temperature The variations in the practical and theoretical values are due to the following reasons: 1. The convective losses due to wind flow. 2. Defects in manufacturing of dish and coil 3. Human errors due to manual tracking. [8] Ibrahim Ladan Mohammed: Design and development of a parabolic dish thermal cooker ; International Journal Of Engineering Research And Applications (IJERA), Vol. 3, Issue 4, pp. 1179-1186, 2013 [9] A.R. El Ouederni, A.W. Dahmani, F. Askri, M. Ben Salah, S. Ben Nasrallah : Experimental study of a parabolic dish concentrator ; Reveu Des Energies Renouvables, Vol 12, No.3, pp. 395-404, 2009 53
[10] Ibrahim Ladan Mohammed : Design and development of a parabolic dish for solar water heater ; International Journal Of Engineering Research And Applications (IJERA), Vol. 3, Issue 4, pp. 822-830, 2012 [11] Kailash Karunakaran, Hyacinth J. Kennedy : Thermal analysis of parabolic dish snow melting device ; International Journal for Research in Technological Studies, Vol. 1, Issue 3, 2014 [13] N.D. Kaushika, K.S. Reddy: Performance of a low cost solar paraboloidal dish steam generating system ; Centre for Energy Studies, Indian Institute of Technology, Delhi, 1999 [14] Atul Sagade, Nilkanth Shinde : Performance evaluation of parabolic dish type solar for Industrial Heating Application ; International Journal Energy Technology and Policy, Vol. 8, No.1, 2012 [12] Fareed M. Mohammed, Auatf S. Jassim, Yaseen H. Mahmood, Mohamad A.K.Ahmed : Design and study of portable solar dish concentrator ; International Journal of Recent Research and Review, Vol III, 2012 [15] Meenakshisundaram Arulkumaran and William Christraj: Experimental analysis of Non Tracking solar parabolic dish concentrating system for steam generation 54