Summary Innovative hybrid solar panels combining photovoltaic cells along with an efficient heat exchanger with attached fins to the parallel plates and water‐Al2O3 nanofluid as a working fluid is presented in this work. Twenty‐seven fins at the upper wall and 27 fins at the lower wall in labyrinth arrangement are used in simulations with fin lengths of 0, ¼, ½, and ¾ of the flow path height. Moreover, nanosolid particles dispersed in the base fluid range as 0 ≤ ϕ ≤ 0.2. In addition, Reynolds number Re at the inlet was varied such that 10 < Re < 80. Numerical finite element analysis using COMSOL software is utilized to investigate flow and thermal characteristics as well the overall efficiency of the hybrid system. Results show that as the Reynolds number, the length of the fin, and the volume fraction of the nanosolid particles increase, the overall efficiency increases. Moreover, increasing nanoparticle volume fraction and the fin length was found to increase the friction coefficient.

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Computational Fluid Dynamics (CFD) is utilized to study entropy generation for the rarefied steady state laminar 2-D flow of air-Al2O3 nanofluid in a square cavity equipped with two solid fins at the hot wall. Such flows are of great importance in industrial applications, such as the cooling of electronic equipment and nuclear reactors. In this current study, effects of the Knudsen number (Kn), Rayleigh number (Ra) and the nano solid particle’s volume fraction (ϕ) on entropy generation were investigated. The values of the parameters considered in this work were as follows: 0≤ Kn ≤0.1, 103 ≤Ra≤ 106, 0≤ ϕ ≤ 0.2. The length of the fins (LF) was considered to be fixed and equal to 0.5 m, whereas the location of the fins with respect to the lower wall (HF) was set to 0.25 and 0.75 m. Simulations demonstrated that there was an inverse direct effect of Kn on the entropy generation. Moreover, it was found that when Ra was less than 104, the entropy generation, due to the flow, increased as ϕ increases. In addition, the entropy generation due to the flow will decrease at Ra greater than 104 as ϕ increases. Moreover, the entropy generation due to heat will increase as both the ϕ and Ra increase. In addition, a correlation model of the total entropy generation as a function of all of the investigated parameters in this study was proposed. Finally, an optimization technique was adapted to find out the conditions at which the total entropy generation was minimized.

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The paper presents a finite‐difference scheme to solve the transient conjugated heat transfer problem in a concentric annulus with simultaneously developing hydrodynamic and thermal boundary layers. The annular forced flow is laminar with constant physical properties. Thermal transient is initiated by a step change in the prescribed isothermal temperature of the inner surface of the inside tube wall while the outer surface of the external tube is kept adiabatic. The effects of solid‐fluid conductivity ratio and diffusivity ratio on the thermal behaviour of the flow have been investigated. Numerical results are presented for a fluid of Pr = 0.7 flowing in an annulus of radius ratio 0.5 with various values of inner and outer solid wall thicknesses.

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