Abstract: A solar collector is a device which helps to harnesses solar radiation into useful form of energy. Among various solar collectors, the parabolic trough collector (PTC) is considered to be the best option for medium temperature (150–400 °C) heat requirements. The popularity of solar parabolic trough technology has generated interest in higher efficiency energy recovery potential. The absorber tube, also called the receiver tube or heat collection element, is one of the main functional units of a solar PTC in addition to other elements like parabolic mirrors, metal support structure and tracking unit assembly. Parabolic mirrors reflect to a focal point and concentrate falling sun rays onto an absorber tube, which is made up of a long metallic structure covered by an evacuated glass envelope to reduce convective heat transfer losses. Many techniques were attempted to enhance the heat transfer potential in the receiver tube portion of a solar PTC which includes techniques such as half insulation receiver, cavity receivers, vacuum outer shell, inclusion of inserts, baffles, artificially roughened sinks, selective coatings etc. In some of the research works, nanoparticles were also used to enhance heat transfer properties of the heat transfer fluid. In this paper, detailed review of the experimental and numerical works carried out on heat transfer enhancement techniques which focus on minimization of heat loss, use of turbulators, addition of nanofluid and selective coatings in the receiver tube of a solar PTC are presented. Further the major reasons for heat loss in the receiver tube and comparative study of various heat transfer enhancement techniques are summarised.

Abstract: In chemical engineering, numerous processes require the suspension of particles in a laminar or transitional regime. For such operations, predicting the fraction of suspended particles as well as their distribution and homogeneity is a major concern. In this work, the unresolved CFD-DEM model introduced by our group for solid–liquid mixing is used to investigate the mixing dynamics of viscous suspensions. The techniques chosen to characterize the degree of suspension, the homogeneity and the distribution of the particles are presented. They are used to assess the efficiency of a pitched blade turbine with a clearance of C = T/4. The impact of solid properties on mixing dynamics is investigated by varying the Young's modulus, the coefficient of restitution and the sliding friction coefficient in the DEM model. Lastly, five alternative configurations of the mixing rig are investigated by varying the clearance of the impeller and introducing baffles.

Abstract: Convective heat transfer and entropy generation in a 3D closed cavity, equipped with adiabatic-driven baffle and filled with CNT (carbon nanotube)-water nanofluid, are numerically investigated for a range of Rayleigh numbers from 103 to 105. This research is conducted for three configurations; fixed baffle (V = 0), rotating baffle clockwise (V+) and rotating baffle counterclockwise (V−) and a range of CNT concentrations from 0 to 15%. Governing equations are formulated using potential vector vorticity formulation in its three-dimensional form, then solved by the finite volume method. The effects of motion direction of the inserted driven baffle and CNT concentration on heat transfer and entropy generation are studied. It was observed that for low Rayleigh numbers, the motion of the driven baffle enhances heat transfer regardless of its direction and the CNT concentration effect is negligible. However, with an increasing Rayleigh number, adding driven baffle increases the heat transfer only when it moves in the direction of the decreasing temperature gradient; elsewhere, convective heat transfer cannot be enhanced due to flow blockage at the corners of the baffle.