ICARE 2010


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The International Conference on Advances in Renewable Energy (ICARE) was held at National Institute of Technology (NIT), Bhopal in June 2010.

The topic of my presentation was: A simple procedure for estimating heat capacity and optical efficiency of solar box type cooker

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ICARE 2010

  1. 1. A SIMPLE PROCEDURE FOR ESTIMATING HEAT CAPACITY AND OPTICAL EFFICIENCY OF SOLAR BOX TYPE COOKER Naveen Kumar, G.Vishwanath Indian Institute of Information Technology Design and Manufacturing (IIITD&M) , Kancheepuram IIT Madras CampusICARE 2010 June 24, 2010
  2. 2. Outline • Solar Box Type Cooker (SBC) • Figures of Merit • Optical Efficiency of a SBC • Heat Capacity of a SBC • Existing Methodology • Proposed Methodology • Experimental Data Analysis • Result & ConclusionICARE 2010 June 24, 2010
  3. 3. Solar Box Type Cooker (SBC) A solar thermal device, which is used at domestic level mainly for boiling type of cooking. The optical efficiency and heat capacity of the SBC are the two key parameters, which determines effectiveness of SBC. In order to evaluate the performance of the solar cooker for cooking, two figures of merit (FOM) viz. F1 and F2, are generally calculated. [BIS Test Standards]ICARE 2010 June 24, 2010
  4. 4. Figures of Merit (FOM) F1 first FOM F oe Tpz Taz F1 F U LS Gs F : Heat exchange efficiency factor F : Optical efficiency oeIt is a measure of the differentialtemperature gained by the absorbing F U LS : Heat loss factor at stagnationplate at a particular level of solarinsolation during no-load test. T pz : Plate temperature at stagnationThe value of F1 should be ≥ 0.11 ( as Taz : Ambient Temperature at stagnationper BIS standards). Gs : Solar Insolation at stagnationICARE 2010 June 24, 2010
  5. 5. Figures of Merit (FOM) F2 second FOM The second FOM,F2 is independent of climatic conditions and gives an indication of heat transfer from absorbing plate to the water in the containers kept on the plate. The value of F2 is generally determined using the equation: ( MC) w F1 ( MC) w 1 (Tw1 Tad ) / F1Gav F2 F noe ln ( MC) ( MC) w A(t w2 t w1 ) 1 (Tw2 Tad ) / F1Gav( MC ) w: Heat Capacity of water(MC) : Heat Capacity of Interior Materials A : Area of the plate Tw1 : Temperature of water at time t w1 The value of F2 should be ≥ 0.4 (as per : Temperature of water at time t w 2 Tw 2 BIS standards). Tad : Ambient temperature Gav : Average Solar InsolationICARE 2010 June 24, 2010
  6. 6. Optical Efficiency of SBC Optical efficiency (F’noe) is the product of the transmittance of the glazing of the SBC and the heat absorption coefficient of the bottom plate. A high optical efficiency is always desirable as it is corresponds to high value of F1 i.e the first figure of merit. Using the equation of first figure of merit, we can express optical efficiency as: Tpz Taz F oe F U LS F1 F U LS GsICARE 2010 June 24, 2010
  7. 7. Heat Capactity of SBC ( MC ) w ( MC ) ( MC ) w Where (MC)’w is the heat capacity of the cooker and is equal to the sum of the heat capacity of the cooker interior materials (MC)’ (to be found) and the heat capacity of water (MC)w For the given value of optical efficiency we can find heat capacity using equation: 1 (MC) 1 F2 F oe (MC) w F oeICARE 2010 June 24, 2010
  8. 8. Existing Methodology Full load tests were conducted for different loads of water and the value of F2 was experimentally determined. Heat capacity and optical efficiency were considered constant because the duration of the experiment is apprx. 1.5 hour and temperature limits were fixed. The experimentally determined values of 1/F2 are then linearly plotted with respect to heat capacity of the water of different loads filled in the vessel 1 (MC) 1 F2 F oe (MC) w F oe The optical efficiency and heat capacity of cooker materials are obtained from the intercept and slope of the linear regression line achieved from the plot [1]. 1. Subodh Kumars, Estimation of design parameters for thermal performance evaluationICARE 2010 of box-type solar cooker, Renewable Energy. 30(2005)1117-1126 June 24, 2010
  9. 9. , Proposed Methodology The rate of useful heat energy gained by water for an infinitesimal time dt during full load testing of SBC is given by: dTw dTw ( MC ) w AF oe GT U L (Tw Ta ) ( MC ) dt dt Since the value of (MC)’ is un-known and will vary depending on the material used in SBC, we are approximating this term by writing it in the form of unknown heat loss coefficient (Us) and area (As). dTw (MC) AsU s(Tw Ta ) dtThus the final equation is: dTw (MC) w AF [ oeG T U L (Tw Ta )] A s U s (Tw Ta ) dtICARE 2010 June 24, 2010
  10. 10. Proposed MethodologyRearranging the final equation, we get: dTw ( MC ) w AF U L AsU s (Tw Ta ) AF oe GT dtComparing the above equation with Y= mX + C ; which is a straight line, we get dTw Y ( MC) w dt C AF oe GT X (Tw Ta ) m AF U L AsU sThus from the experimental data taken during full load test, we plot the cookingpower (Y) v/s temperature difference (X) and from the intercept and slope wedetermine the value of optical efficiency and heat capacity respectively. Optical Efficiency: F oe C /(AGT ) Heat Capacity: (MC) m C /(F1G T ) (Tw Ta )dt / dTwICARE 2010 June 24, 2010
  11. 11. Experimental Data Analysis Variations in the cooking power Variations in the cooking power with the temperature difference with the temperature difference of of a SBC; Load = 2.5 Kg [1] a SBC; Load = 1.5 Kg [1]. Variations in the cooking power with the temperature difference of a SBC; Load = 2Kg [1].ICARE 2010 June 24, 2010
  12. 12. Results CALCULATION TABLE: Mass of water in kg Initial Temperature in °C Final Temperature in °C A sU s (M) (Twi) (Twf) (W/K) 1.5 60.6 96.9 0.244 2 58.2 96.4 0.269833 2.5 62 95.4 0.184498Comparison between calculated and expected values of the parameters: Parameters Average Value Expected Value [1] (Calculated) Heat capacity of the solar 2257.1533 2252.86 cooker (MC) (J/°C) Optical Efficiency (F’noe) 0.60847 0.6216 1. Subodh Kumars, Estimation of design parameters for thermal performance evaluationICARE 2010 of box-type solar cooker, Renewable Energy. 30(2005)1117-1126 June 24, 2010
  13. 13. Results F2 PARAMETERS: Mass of water F2cal F2exp | F2cal- F2exp| % difference M (kg) 1.5 0.4205 0.3743 0.0462 10.9869 2 0.4816 0.4931 0.0115 2.38787 2.5 0.5267 0.51239 0.01431 2.71691ICARE 2010 June 24, 2010
  15. 15. If you have any queries then please send us a mail at vatsnaveen@yahoo.co.in (Naveen Kumar) vish777.2006@gmail.com (G.Vishwanath)