http://orcid.org/0000-0003-1174-098X
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ABSTRACT
The objective of this paper is to study and analyse heat losses from the absorber tube of a parabolic trough solar collector (PTSC) system and development of heat loss correlation. Computational fluid dynamics has been employed to obtain the convective and radiative heat losses. Heat loss model is simulated by employing the discrete ordinate (DO) radiation model to account for the radiation exchange in an enclosure between steel tube and glass cover, which is maintained as vacuum. Heat losses from the glass cover due to forced convection and radiation have been modelled and simulated. The effect of different emissivity on the absorber tube, different diameter ratio between absorber tube and glass cover, different heat transfer coefficients due to wind effects are studied in the considered PTSC system. Results are mentioned in dimensionless numbers for wider applicability. The result indicates that by varying the emissivity of the tube wall from 0.2 to 0.8, Nusselt number increases from 5.66 to 18.6. Similarly, when the heat transfer coefficient is changed from 6.89 to 19.49 W/m2K, Nusselt number increased from 5.66 to 5.81. Effect of vacuum has been studied as well. Finally, the correlation between Nusselt number and its influencing parameters has been obtained for the PTSC.
Nomenclature
| Cp | = | specific heat capacity (J/kg-K) |
| ds | = | diameter of steel tube(m) |
| dg | = | outer diameter of glass envelope (m) |
| d1 | = | inner diameter of steel(m) |
| d2 | = | outer diameter of steel(m) |
| d3 | = | inner diameter of vacuum(m) |
| d4 | = | outer diameter of vacuum(m) |
| d5 | = | inner diameter of glass(m) |
| d6 | = | outer diameter of glass(m) |
| h | = | convection heat transfer coefficient of air (W/m2-K) |
| k | = | thermal conductivity (W/m-K) |
| Nu | = | Nusselt number |
| Nuext | = | external Nusselt number |
| Tg | = | glass envelope outer surface temperature (K) |
| Ts | = | steel envelope outer surface temperature (K) |
| Tatm | = | atmospheric temperature (K) |
| Q | = | heat loss (W/m) |
| Qc | = | heat loss by convection per unit length (W/m) |
| Qr | = | heat loss by radiation per unit length (W/m) |
| U | = | overall heat transfer coefficient (W/m2K) |
| u | = | velocity in x direction (m/s) |
| Vatm | = | wind velocity (m/s) |
| υ | = | velocity in y direction (m/s) |
| aλ | = | spectral absorption coefficient |
| Ibλ | = | black body intensity given by the Planck function |
Greek symbols
| ρ | = | density (kg/m3) |
| σ | = | Stephan–Boltzmann constant (5.67 × 10−8 W/m2-K4) |
| ɛg | = | glass envelope emissivity |
| ɛs | = | steel absorber emissivity |
Subscripts
| atm | = | atmospheric |
| c | = | convection |
| ext | = | external |
| g | = | glass cover |
| int | = | internal |
| r | = | radiation |
| s | = | steel cover |
| total | = | total |
| λ | = | wavelength |
| 1 | = | inner of steel |
| 2 | = | outer of steel |
| 3 | = | inner of vacuum |
| 4 | = | outer of vacuum |
Additional information
Notes on contributors
Upasana Bhuyan
Upasana Bhuyan received her B.Tech in Mechanical Engineering from CUTM Paralakhemundi, M.Tech in Thermal Engineering Specialisation from CET Bhubaneswar. She is working as an Assistant Professor in Mechanical Engineering Department of GIET Gunupur, India. Her research interests include solar thermal and computational fluid dynamics.
Sudhansu S. Sahoo
Sudhansu S. Sahoo received his B.E. in Mechanical Engineering from UCE Burla, M.Tech in Thermal Engineering from IIT Delhi and Ph.D from IIT Bombay in the Renewable Energy Specialisation. He is working as an Assistant Professor in Mechanical Engineering Department of CET Bhubaneswar, India. He authored many national and international journal papers and published a book and book chapters as well. His research interests include solar thermal, computational fluid dynamics, multiphase flow and turbomachines.
Prasanta K. Satapathy
Prasanta K Satapathy received his B.E. in Mechanical Engineering from Sambalpur University, M.Tech and Ph.D in Thermal Engineering of IIT Kharagpur. He is working as an Associate Professor in Mechanical Engineering Department of CET Bhubaneswar, India. He authored many national and international journal papers and published a book and book chapters as well. His research interests include HVAC, Energy systems.
Pramod K. Parida
Pramod K Parida received his B.Tech in Mechanical Engineering from CET Bhubaneswar, M.Tech and Ph.D from Jadavpur University and NIT Rourkela respectively. He is working as an Assistant Professor in Mechanical Engineering Department of CET Bhubaneswar, India. He authored many national and international journal papers and published a book and book chapters as well. His research interests include Robotics. Manufacturing processes and modelling & simulations.