Search

Purpose: This paper aims to model solar unit equipped with mirrors with numerical simulation. To augment the efficiency of system, absorber pipe was equipped with fins and nanomaterial was used as carrier fluid. Existence of secondary reflector results in better optical efficiency. Design/methodology/approach: Finite volume approach is used for modeling which is done in two steps. The first one is done to achieve the heat flux distribution and second step to model turbulent flow inside the pipe. Verification has been presented for calculation of important functions (f and Nu). Outputs reveal the impacts of fin height (HF), number of fin (NF), inlet temperature (Tin) and velocity on irreversibility, thermal treatment. Findings: Surface temperature decreases by 0.498, 0.07 and 0.017% with intensify of Re, HF and NF, respectively, when other factors were minimum. With augment of Tin, wall temperature increases about 9.87%. Given NF = 8, HF = 3 mmm, growth of Re makes Darcy factor to decrease about 28.28%, but it augments the Nu by 2.63%. Nu augments with rise of NF and HF about 2.63 and 7.66%. Irreversibility reduces about 29.5 and 11.65% with augment of NF and HF, respectively. Originality/value: Numerical simulations for solar unit equipped with mirrors were reported in this modeling. To augment the efficiency of system, absorber pipe was equipped with fins and nanomaterial was used as carrier fluid. Existence of secondary reflector results in better optical efficiency. Finite volume approach is used for modeling which is done in two steps. The first one is done to achieve the heat flux distribution and second step to model turbulent flow inside the pipe. Verification has been presented for calculation of important functions (f and Nu). Outputs reveal the impacts of fin height (HF), number of fin (NF), inlet temperature (Tin) and velocity on irreversibility, thermal treatment. [ABSTRACT FROM AUTHOR]

This technical note addresses robust stability of uncertain systems with rational dependence on unknown time-varying parameters constrained in a polytope. First, the technical note proves that a sufficient linear matrix inequality (LMI) condition that we previously proposed, based on homogeneous polynomial Lyapunov functions (HPLFs) and on the introduction of an extended version of Polya's theorem, is also necessary. Second, the technical note proposes a new sufficient and necessary LMI condition by exploiting properties of the simplex and sum-of-squares (SOS) parameter-dependent polynomials. Lastly, the technical note investigates relationships among these conditions and conditions based on the linear fractional representation (LFR). It is worth remarking that sufficient and necessary LMI conditions for this problem have not been proposed yet in the literature. [ABSTRACT FROM AUTHOR]