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Experimental study on the effect of bio-functionalized graphene nanoplatelets on the thermal performance of liquid flat plate solar collector

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Abstract

Synthesis of carbon-based working fluid involves toxic acids that are hazardous to the human and surrounding environment. In the current experimental investigation, thermal analysis of liquid flat plate solar collector was carried out using distilled water and environmentally friendly, covalent functionalized graphene nanoplatelets. Gallic acid was grafted on GNPs using the green free radical technique. Chemical characterization was analyzed using EDX and FESEM. Colloidal stability of GGNP nanofluids was found to be stable for more than 60 days. GGNPs were dispersed in distilled water with varying mass concentrations from 0.025 to 0.1%, and analysis was carried out for flow rate ranging from 0.5 to 1.5 L min−1 for different heat flux intensities and inlet temperature. The thermal performance of LFP solar collector augments with the surge in GGNP concentration, flow rate and heat flux intensities, whereas declines with the increase in reduced temperature parameter. Maximum thermal efficiency enhancement of 21.48%, 16.06% and 12.36% is achieved using 0.1%, 0.05% and 0.025% GGNP nanofluid than distilled water. A penalty in the form of a slight surge in pressure drop and pumping power was observed with a subsequent increase in GGNP concentration. The maximum increase in pressure drop and pumping power was about 0.85% and 0.567% for 0.1% concentration and mass flow rate 1.5 L min−1. A maximum reduction of about 25% in the size of the LFP solar collector area is attained using 0.1% GGNPs than base fluid.

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Abbreviations

\(A_{{\text{c}}}\) :

Aperture area of the solar collector (m2)

AR :

Inner area of the riser tubes (m2)

\(A_{{{\text{RC}}}}\) :

Reduction of size of solar collector (m2)

ASHRAE:

American Society of Heating, Refrigeration, and Air-Conditioning Engineers

ASME :

American Society of Mechanical Engineers

CTAB:

Cetyltrimethylammonium bromide

\(C_{{\text{p}}}\) :

Specific heat (J kg−1 K−1)

Di:

Inner diameter (mm)

EDX:

Energy-dispersive X-ray spectroscopy

FESEM:

Field emission scanning electron microscope

\(F_{{\text{R}}}\) :

Heat removal factor

\(F_{{\text{R}}} \left( {\tau \alpha } \right)\) :

Absorbed energy parameter

\(F_{{\text{R}}} U_{{\text{L}}}\) :

Energy loss parameter

GA:

Gum Arabic

GNP:

Graphene nanoplatelets

GGNP:

Gallic acid graphene nanoplatelets

h:

Heat transfer coefficient (W m−2 K−1)

\(I_{{\text{T}}}\) :

Heat flux intensity (W m−2)

k :

Thermal conductivity (W m−1 K−1)

L :

Length of the tube (m)

LFP:

Liquid flat plate

\(\dot{m}\) :

Fluid flow rate (kg s−1 or L min−1)

PEG-400:

Polyethylene glycol—400

\(Q_{{\text{u}}}\) :

Useful heat gain from the solar collector (W)

\(Q_{{{\text{conv}}}}\) :

Power input (W)

SDBS:

Sodium dodecyl benzene sulfonate

SLS:

Sodium lauryl sulfate

Tw-80:

Tween-80

\(T_{{{\text{out}}}}\) :

Outlet temperature of working fluid (K)

\(T_{{{\text{in}}}}\) :

Inlet temperature of working fluid (K)

\(T_{{\text{p}}}\) :

Absorber plate temperature (K)

\(T_{{\text{b}}}\) :

Bulk temperature (K)

\(U_{{\text{L}}}\) :

Overall loss coefficient (W m−2 K−1

ρ :

Density (kg m−3)

µ :

Dynamic viscosity (m Pa. s)

∆P :

Pressure drop (N/m2)

\(\eta_{{\text{T}}}\) :

Thermal efficiency of LFP solar collector (%)

\(\tau \alpha\) :

Product of transmissivity and absorptivity

References

  1. Masson-Delmotte V, Zhai P, Pörtner H-O, Roberts D, Skea, Shukla PR, Pirani A, Moufouma-Okia W, Péan C, Pidcock R, Connors S, Matthews JBR, Chen Y, Zhou X, Gomis MI, Lonnoy E, Maycock T, Tignor M, Waterfield T (eds.) Summary for policymakers—global warming of 1.5 °C. World Meteorol Organ [Internet]. 2018;32. Available from: https://www.ipcc.ch/sr15/chapter/spm/

  2. IEA. The impacts of the Covid-19 crisis on global energy demand and CO2 emissions [Internet]. Global Energy Review 2020. 2020. Available from: https://www.iea.org/reports/global-energy-review-2020

  3. Holeczek H. Renewables: Global status report 2014. vol. 105, Galvanotechnik. 2014. p. 2016–2021.

  4. IEA, International Renewable Energy Agency, United Nations Statistics Division, The World Bank, World Health Organization. The Energy Progress Report. IEA, IRENA, UNSD, WB, WHO (2019), Track SDG 7 Energy Prog Rep 2019, Washingt DC [Internet]. 2019;176. Available from: https://trackingsdg7.esmap.org/

  5. Rasih RA, Sidik NAC, Samion S. Recent progress on concentrating direct absorption solar collector using nanofluids: a review. J Therm Anal Calorim. 2019;137(3):903–22.

    CAS  Google Scholar 

  6. Sudhakar P, Cheralathan M. Thermal performance enhancement of solar air collector using a novel V-groove absorber plate with pin-fins for drying agricultural products: an experimental study. J Therm Anal Calorim. 2020;140(5):2397–408. https://doi.org/10.1007/s10973-019-08952-9.

    Article  CAS  Google Scholar 

  7. Akhter J, Gilani SI, Al-kayiem HH, Ali M, Masood F. Characterization and stability analysis of oil-based copper oxide nanofluids for medium temperature solar collectors. Materwiss Werksttech. 2019;50(3):311–9.

    CAS  Google Scholar 

  8. Chen M, He Y, Ye Q, Zhang Z, Hu Y. Solar thermal conversion and thermal energy storage of CuO/Paraffin phase change composites. Int J Heat Mass Transf. 2019;130:1133–40.

    CAS  Google Scholar 

  9. Sukhatme SPP, Nayak JK, Naik JK. Solar energy principles of thermal collection and storage. 4th ed. New Delhi: Tata McGraw-Hill Education; 2014. p. 1–431.

    Google Scholar 

  10. Karami M, Bozorgi M, Delfani S. Effect of design and operating parameters on thermal performance of low-temperature direct absorption solar collectors: a review. J Therm Anal Calorim. 2020. https://doi.org/10.1007/s10973-020-10043-z.

    Article  Google Scholar 

  11. Dehaj MS, Mohiabadi MZ. Experimental investigation of heat pipe solar collector using MgO nanofluids. Sol Energy Mater Sol Cells. 2019;191:91–9.

    CAS  Google Scholar 

  12. Iranmanesh S, Ong HC, Ang BC, Sadeghinezhad E, Esmaeilzadeh A, Mehrali M. Thermal performance enhancement of an evacuated tube solar collector using graphene nanoplatelets nanofluid. J Clean Prod. 2017;162:121–9.

    CAS  Google Scholar 

  13. Rashidi S, Mahian O, Languri EM. Applications of nanofluids in condensing and evaporating systems: a review. J Therm Anal Calorim. 2018;131(3):2027–39.

    CAS  Google Scholar 

  14. James A, Mohanraj M, Srinivas M, Jayaraj S. Thermal analysis of heat pump systems using photovoltaic-thermal collectors: a review. J Therm Anal Calorim. 2020. https://doi.org/10.1007/s10973-020-09431-2.

    Article  Google Scholar 

  15. Gupta HK, Agrawal GD, Mathur J. An experimental investigation of a low temperature Al2O3-H2O nanofluid based direct absorption solar collector. Sol Energy. 2015;118:390–6.

    CAS  Google Scholar 

  16. Gupta HK. Investigations of nanofluid based direct absorption type flat plate solar collector. Jaipur, India: Malaviya National Institute of Technology; 2015.

  17. He Q, Yan G, Wang S. Experimental investigation on solar thermal properties of magnetic nanofluids for direct absorption solar collector. ASME 5th Int Conf Micro Nanoscale Heat Mass Transf MNHMT 2016. 2016;1:150–7.

    Google Scholar 

  18. Raj P, Subudhi S. A review of studies using nanofluids in flat-plate and direct absorption solar collectors. Renew Sustain Energy Rev. 2018;84:54–74.

    CAS  Google Scholar 

  19. Milanese M, De Risi A, Colangelo G. Energy simulation of a nanofluid solar cooling system in Italy. Proc Inst Civ Eng Eng Sustain. 2018;172(1):32–9.

    Google Scholar 

  20. Verma SK, Tiwari AK, Chauhan DS. Experimental evaluation of flat plate solar collector using nanofluids. Energy Convers Manag. 2017;134:103–15.

    CAS  Google Scholar 

  21. Verma SK, Sharma K, Gupta NK, Soni P, Upadhyay N. Performance comparison of innovative spiral shaped solar collector design with conventional flat plate solar collector. Energy. 2020;194:116853.

    Google Scholar 

  22. Pang W, Cui Y, Zhang Q, Wilson GJ, Yan H. A comparative analysis on performances of flat plate photovoltaic/thermal collectors in view of operating media, structural designs, and climate conditions. Renew Sustain Energy Rev. 2020;119:109599.

    Google Scholar 

  23. Sakhaei SA, Valipour MS. Investigation on the effect of different coated absorber plates on the thermal efficiency of the flat-plate solar collector. J Therm Anal Calorim. 2020;140(3):1597–610.

    CAS  Google Scholar 

  24. Aghili Yegane SP, Kasaeian A. Thermal performance assessment of a flat-plate solar collector considering porous media, hybrid nanofluid and magnetic field effects. J Therm Anal Calorim. 2020;141(5):1969–80.

    CAS  Google Scholar 

  25. Saffarian MR, Moravej M, Doranehgard MH. Heat transfer enhancement in a flat plate solar collector with different flow path shapes using nanofluid. Renew Energy. 2020;146:2316–2329. https://doi.org/10.1016/j.renene.2019.08.081.

    Article  CAS  Google Scholar 

  26. Bioucas FEB, Vieira SIC, Lourenço MJV, Santos FJV, Nieto de Castro CA. Performance of heat transfer fluids with nanographene in a pilot solar collector. Sol Energy. 2018;172:171–6.

    CAS  Google Scholar 

  27. MichaelJosephStalin P, Arjunan TV, Matheswaran MM, Dolli H, Sadanandam N. Energy, economic and environmental investigation of a flat plate solar collector with CeO2/water nanofluid. J Therm Anal Calorim. 2020;139(5):3219–33.

    CAS  Google Scholar 

  28. Sarsam WS, Kazi SN, Badarudin A. Thermal performance of a flat-plate solar collector using aqueous colloidal dispersions of graphene nanoplatelets with different specific surface areas. Appl Therm Eng. 2020;172:115142.

    CAS  Google Scholar 

  29. Shafiey Dehaj M, Zamani Mohiabadi M. Experimental study of water-based CuO nanofluid flow in heat pipe solar collector. J Therm Anal Calorim. 2019;137(6):2061–2072. https://doi.org/10.1007/s10973-019-08046-6.

    Article  CAS  Google Scholar 

  30. Verma SK, Tiwari AK, Chauhan DS. Performance augmentation in flat plate solar collector using MgO/water nanofluid. Energy Convers Manag. 2016;124:607–17.

    CAS  Google Scholar 

  31. Shafieian A, Khiadani M, Nosrati A. Strategies to improve the thermal performance of heat pipe solar collectors in solar systems: a review. Energy Convers Manag. 2019;183:307–31.

    Google Scholar 

  32. Bashirnezhad K, Rashidi MM, Yang Z, Bazri S, Yan WM. A comprehensive review of last experimental studies on thermal conductivity of nanofluids. J Therm Anal Calorim. 2015;122(2):863–84.

    CAS  Google Scholar 

  33. Zayed ME, Zhao J, Du Y, Kabeel AE, Shalaby SM. Factors affecting the thermal performance of the flat plate solar collector using nanofluids: a review. Sol Energy. 2019;182:382–96.

    CAS  Google Scholar 

  34. Choudhary S, Sachdeva A, Kumar P. Investigation of the stability of MgO nanofluid and its effect on the thermal performance of flat plate solar collector. Renew Energy. 2020;147:1801–14.

    CAS  Google Scholar 

  35. Alawi OA, Mohamed Kamar H, Mallah AR, Kazi SN, Sidik NAC. Thermal efficiency of a flat-plate solar collector filled with pentaethylene glycol-treated graphene nanoplatelets: an experimental analysis. Sol Energy. 2019;191:360–70.

    CAS  Google Scholar 

  36. Wlazlak A, Zajaczkowski B, Woluntarski M, Buschmann MH. Influence of graphene oxide nanofluids and surfactant on thermal behaviour of the thermosyphon. J Therm Anal Calorim. 2019;136(2):843–55.

    CAS  Google Scholar 

  37. Anin Vincely D, Natarajan E. Experimental investigation of the solar FPC performance using graphene oxide nanofluid under forced circulation. Energy Convers Manag. 2016;117:1–11.

    CAS  Google Scholar 

  38. Akram N, Sadri R, Kazi SN, Ahmed SM, Zubir MNM, Ridha M, et al. An experimental investigation on the performance of a flat-plate solar collector using eco-friendly treated graphene nanoplatelets–water nanofluids. J Therm Anal Calorim. 2019;138(1):609–21.

    CAS  Google Scholar 

  39. Tong Y, Chi X, Kang W, Cho H. Comparative investigation of efficiency sensitivity in a flat plate solar collector according to nanofluids. Appl Therm Eng. 2020;174:115346.

    CAS  Google Scholar 

  40. Choudhary S, Sachdeva A, Kumar P. Time-based assessment of thermal performance of flat plate solar collector using magnesium oxide nanofluid. Int J Sustain Energy. 2020;115931. Available from: https://linkinghub.elsevier.com/retrieve/pii/S135943112033413X

  41. Moravej M, Bozorg MV, Guan Y, Li LKB, Doranehgard MH, Hong K, et al. Enhancing the efficiency of a symmetric flat-plate solar collector via the use of rutile TiO2-water nanofluids. Sustain Energy Technol Assess. 2020;40:100783.

    Google Scholar 

  42. Hussein OA, Habib K, Muhsan AS, Saidur R, Alawi OA, Ibrahim TK. Thermal performance enhancement of a flat plate solar collector using hybrid nanofluid. Sol Energy. 2020;204:208–22.

    CAS  Google Scholar 

  43. Sundar LS, Misganaw AH, Singh MK, Pereira AMB, Sousa ACM. Efficiency, energy and economic analysis of twisted tape inserts in a thermosyphon solar flat plate collector with Cu nanofluids. Renew Energy Focus. 2020;35:10–31.

    Google Scholar 

  44. Choudhary S, Sachdeva A, Kumar P. Influence of stable zinc oxide nanofluid on thermal characteristics of flat plate solar collector. Renew Energy. 2020;152:1160–70.

    CAS  Google Scholar 

  45. Okonkwo EC, Wole-Osho I, Kavaz D, Abid M, Al-Ansari T. Thermodynamic evaluation and optimization of a flat plate collector operating with alumina and iron mono and hybrid nanofluids. Sustain Energy Technol Assess. 2020;37:100636.

    Google Scholar 

  46. Eltaweel M, Abdel-Rehim AA. Energy and exergy analysis of a thermosiphon and forced-circulation flat-plate solar collector using MWCNT/Water nanofluid. Case Stud Therm Eng. 2019;14:100416.

    Google Scholar 

  47. Mirzaei M, Hosseini SMS, Moradi Kashkooli AM. Assessment of Al2O3 nanoparticles for the optimal operation of the flat plate solar collector. Appl Therm Eng. 2018;134:68–77.

    CAS  Google Scholar 

  48. Farajzadeh E, Movahed S, Hosseini R. Experimental and numerical investigations on the effect of Al2O3/TiO2[sbnd]H2O nanofluids on thermal efficiency of the flat plate solar collector. Renew Energy. 2018;118:122–30.

    CAS  Google Scholar 

  49. Sharafeldin MA, Gróf G. Experimental investigation of flat plate solar collector using CeO2-water nanofluid. Energy Convers Manag. 2018;155:32–41.

    CAS  Google Scholar 

  50. Sadri R, Hosseini M, Kazi SN, Bagheri S, Ahmed SM, Ahmadi G, et al. Study of environmentally friendly and facile functionalization of graphene nanoplatelet and its application in convective heat transfer. Energy Convers Manag. 2017;150:26–36.

    CAS  Google Scholar 

  51. Yarmand H, Gharehkhani S, Shirazi SFS, Goodarzi M, Amiri A, Sarsam WS, et al. Study of synthesis, stability and thermo-physical properties of graphene nanoplatelet/platinum hybrid nanofluid. Int Commun Heat Mass Transf. 2016;77:15–21.

    CAS  Google Scholar 

  52. Sarsam WS, Amiri A, Kazi SN, Badarudin A. Stability and thermophysical properties of non-covalently functionalized graphene nanoplatelets nanofluids. Energy Convers Manag. 2016;116:101–11.

    CAS  Google Scholar 

  53. Arshad A, Jabbal M, Yan Y, Reay D. A review on graphene based nanofluids: preparation, characterization and applications. J Mol Liq. 2019;279:444–84.

    CAS  Google Scholar 

  54. Montazer E, Salami E, Yarmand H, Chowdhury ZZ, Dahari M, Kazi SN, et al. Development of a new density correlation for carbon-based nanofluids using response surface methodology. J Therm Anal Calorim. 2018;132(2):1399–407.

    CAS  Google Scholar 

  55. Kobyliukh A, Olszowska K, Szeluga U, Pusz S. Iron oxides/graphene hybrid structures—preparation, modification, and application as fillers of polymer composites. Adv Colloid Interface Sci. 2020;285:102285. https://doi.org/10.1016/j.cis.2020.102285.

    Article  CAS  PubMed  Google Scholar 

  56. Sadri R, Zangeneh Kamali K, Hosseini M, Zubir N, Kazi SN, Ahmadi G, et al. Experimental study on thermo-physical and rheological properties of stable and green reduced graphene oxide nanofluids: hydrothermal assisted technique. J Dispers Sci Technol. 2017;38(9):1302–10.

    CAS  Google Scholar 

  57. Bindhu MR, Umadevi M. Synthesis of monodispersed silver nanoparticles using Hibiscus cannabinus leaf extract and its antimicrobial activity. Spectrochim Acta Part A Mol Biomol Spectrosc. 2013;101:184–90.

    CAS  Google Scholar 

  58. Feng L, Gao G, Huang P, Wang X, Zhang C, Zhang J, et al. Preparation of pt Ag alloy nanoisland/graphene hybrid composites and its high stability and catalytic activity in methanol electro-oxidation. Nanoscale Res Lett. 2011;6:1–10.

    Google Scholar 

  59. Bindhu MR, Umadevi M. Antibacterial and catalytic activities of green synthesized silver nanoparticles. Spectrochim Acta Part A Mol Biomol Spectrosc. 2015;135:373–8.

    CAS  Google Scholar 

  60. Anon. Methods of testing to determine the thermal performance of solar collectors. ANSI Stand B198. 1. Atlanta: ASHRAE; 1977.

  61. Faizal M, Saidur R, Mekhilef S, Alim MA. Energy, economic and environmental analysis of metal oxides nanofluid for flat-plate solar collector. Energy Convers Manag. 2013;76:162–8.

    CAS  Google Scholar 

  62. Anto Joseph Deeyoko L, Balaji K, Iniyan S, Sharmeela C. Exergy, economics and pumping power analyses of flat plate solar water heater using thermal performance enhancer in absorber tube. Appl Therm Eng. 2019;154:726–37.

    Google Scholar 

  63. Abernethy RB, Benedict RP, Dowdell RB. Asme measurement uncertainty. Am Soc Mech Eng. 1983;107(2):161–4.

    Google Scholar 

  64. Moffat RJ. Describing the uncertainties in experimental results. Exp Therm Fluid Sci. 1988;1(1):3–17.

    Google Scholar 

  65. Alawi OA, Sidik NAC, Kazi SN, Najafi G. Graphene nanoplatelets and few-layer graphene studies in thermo-physical properties and particle characterization. J Therm Anal Calorim. 2019;135(2):1081–93.

    CAS  Google Scholar 

  66. Sadri R, Hosseini M, Kazi SN, Bagheri S, Abdelrazek AH, Ahmadi G, et al. A facile, bio-based, novel approach for synthesis of covalently functionalized graphene nanoplatelet nano-coolants toward improved thermo-physical and heat transfer properties. J Colloid Interface Sci. 2018;509:140–52.

    CAS  PubMed  Google Scholar 

  67. Sadri R, Hosseini M, Kazi SN, Bagheri S, Zubir N, Ahmadi G, et al. A novel, eco-friendly technique for covalent functionalization of graphene nanoplatelets and the potential of their nanofluids for heat transfer applications. Chem Phys Lett. 2017;675:92–7.

    CAS  Google Scholar 

  68. Corumlu V, Ozsoy A, Ozturk M. Evaluation of heat transfer mechanisms in heat pipe charged with nanofluid. Arab J Sci Eng. 2019 [cited 2020 May 13]; 44(6):5195–213. Available from: http://link.springer.com/https://doi.org/10.1007/s13369-019-03742-9

  69. Vakili M, Hosseinalipour SM, Delfani S, Khosrojerdi S, Karami M. Experimental investigation of graphene nanoplatelets nanofluid-based volumetric solar collector for domestic hot water systems. Sol Energy. 2016;131:119–30.

    CAS  Google Scholar 

  70. Karami M, Akhavan-Bahabadi MA, Delfani S, Raisee M. Experimental investigation of CuO nanofluid-based direct absorption solar collector for residential applications. Renew Sustain Energy Rev. 2015;52:793–801. Available from: http://www.sciencedirect.com/science/article/pii/S1364032115007789

  71. Garg HP, Agarwal RK. Some aspects of a Pv/T collector forced circulation flat-plate solar water-heater with solar-cells. Energy Convers Manag. 1995;36(2):87–99.

    Google Scholar 

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Acknowledgements

The authors gratefully acknowledge the FRGS Grant FP143-2019A and research Grant GPF019A-2019, IIRG006B-19IISS, University of Malaya, Kuala Lumpur, Malaysia, for the support to conduct this research work.

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Authors and Affiliations

  1. Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia

    L. Harish Kumar, S. N. Kazi, H. H. Masjuki, M. N. M. Zubir & Oon Cheen Sean

  2. Department of Mechanical Engineering, Faculty of Engineering, International Islamic University Malaysia, Kuala Lumpur, Malaysia

    H. H. Masjuki

  3. NANOCAT, University of Malaya, Kuala Lumpur, Malaysia

    Afrin Jahan

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  1. L. Harish Kumar
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Kumar, L.H., Kazi, S.N., Masjuki, H.H. et al. Experimental study on the effect of bio-functionalized graphene nanoplatelets on the thermal performance of liquid flat plate solar collector. J Therm Anal Calorim 147, 1657–1674 (2022). https://doi.org/10.1007/s10973-020-10527-y

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