## THERMAL SCIENCE

International Scientific Journal

### Thermal Science - Online First

online first only
### Entropy generation analysis for forced convection boiling in absorber tubes of linear fresnel reflector solar thermal system

**ABSTRACT**

A methodology has been presented related to entropy generation due to forced convection boiling in long absorber tubes used in linear Fresnel reflector (LFR) solar thermal system. Variable heat flux has been applied on the tube which replicates the scenario for above-mentioned tubes and local entropy generation has been obtained for various parameters. Mathematical modeling has been made separately for single phase and two phase regions in flow boiling conditions encountered in LFR tubes. Entropy generation in two phase region has been formulated using Homogeneous Equilibrium Model (HEM). The entropy generation at varying mass flux and heat flux cases are calculated. The entropy generation due to heat transfer is found to be more than that of pressure drop. Still, entropy generation due to pressure drop in two phase region plays a major role of increasing nature of it. Present approach will help researchers and industry to optimize the solar thermal systems where flow related phase change occurs and measures can be taken accordingly to increase energy efficiency of those systems.

**KEYWORDS**

PAPER SUBMITTED: 2018-03-31

PAPER REVISED: 2018-06-30

PAPER ACCEPTED: 2018-08-01

PUBLISHED ONLINE: 2018-09-30

- Kalogirou, S.A., Karellas, S., Badescu, V. and Braimakis,K., Exergy analysis on solar thermal systems: A better understanding of their sustainability, Renewable Energy, 85 (2016), pp. 1328-1333.
- Jafarkazemi, F. and Ahmadifard, E., Energetic and exergetic evaluation of flat plate solar collectors, Renewable Energy, 56 (2013), pp. 55-63.
- Ge, Z., Wang, H., Wang, H., Zhang, S. and Guan, X., Exergy analysis of flat plate solar collectors, Entropy, 16 (2014), pp. 2549-2567.
- Fudholi, A., Sopian, K., Othman, M. Y., Ruslan, M.H. and Bakhtyar, B., Energy analysis and improvement potential of finned double tube-pass collector, Energy Conversion and Management, 75 (2013), pp. 234-240.
- Al-Sulaiman, F.A., Exergy analysis of parabolic trough solar collectors integrated with combined steam and organic Rankine cycles, Energy Conversion and Management, 77 (2014), pp. 441-449.
- Hou, H., Yu, Z., Yang, Y., Zhou, C. and Song, J., Exergy analysis of parabolic trough solar collector', Taiyangneng Xuebao/Acta Energiae Solaris Sin, 35 (2014), pp.1022-1028.
- Padilla, R.V., Fontalvo, A., Demirkaya, G., Martinez, A. and Quiroga, A.G., Exergy analysis of parabolic trough solar receiver, Applied Thermal Engineering, 67(2014), pp. 579-586.
- Nixon, J.D., Dey, P.K. and Davies, P.A., Design of a novel solar thermal collector using a multi-criteria decision-making methodology, Journal of Cleaner Production, 59 (2013), pp.150-159.
- Madadi, V., Tavakoli, T. and Rahimi, A., First and second thermodynamic law analyses applied to a solar dish collector', Journal of Non-Equilibrium Thermodynamics, 39 (2014), pp. 183-197.
- Nishi, Y. and Qi, X., Exergy analysis on solar heat collection of three-dimensional compound parabolic concentrator, International Journal of Exergy,13 (2013), pp. 260-280.
- Ghachem, K., Maatki, C., Kolsi, L., Alshammari, N., Oztop, H.F., Borjini, M.N., Aissia, H.B. and Al-Salem, K, Numerical study of heat and mass transfer optimization in a 3-D inclined solar distiller, Thermal Science, 21 (2017), pp. 2469-2480.
- Alper Ozalp, A., Entropy analysis of laminar-forced convection in a pipe with wall roughness, International Journal of Exergy, 6 (2009), pp. 249-275.
- Revellin, R. and Bonjour, J., Entropy generation during flow boiling of pure refrigerant and refrigeration oil mixture, International Journal of Refrigeration, 34 (2011), pp. 1040-1047.
- Sahoo, S. S., Singh, S. and Banerjee, R., Steady sate hydrothermal analysis of absorber tubes used in Linear Fresnel Reflector solar thermal system', Solar Energy, 87 (2013), pp. 84-95.
- Sahoo, S. S., Singh, S. and Banerjee, R., Thermal Hydraulic simulation of absorber tubes in linear Fresnel reflector solar thermal system using RELAP, Renewable Energy, 86 (2016), pp. 507-516.
- Bejan, A., Convective heat transfer, Second Ed. John Wiley & Sons, New York, USA,1999.
- Bejan, A., Fundamentals of exergy analysis, entropy generation minimization, and the generation of flow architecture', International Journal of Energy Research, 2002, Special Issue, pp. 545-565.
- Friedel, L. Improved friction drop correlations for horizontal and vertical two-phase pipe flow. European Two-phase Flow Group Meeting, 1979, paper E2, Ispra, Italy.