umerical simulation of atmospheric boundary layer and wakes of horizontal-axis wind turbines

Simulations of wind turbine wakes are presented in this paper using the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations employing the k-e turbulence model appropriately modified for the atmospheric flows. The actuator disk approach is used to model the action of the turbine rotor. Modified formulations of the inlet conditions and the wall functions are used to allow consistency between the fully developed atmospheric boundary layer (ABL) inlet profiles and the wall function formulation. Results are presented and compared with three wind turbines running under neutral atmospheric conditions. The results demonstrate that the accurate simulation of the atmospheric boundary layer applying enhanced inlet conditions and wall function formulation consistent with the k-e model can give very useful information about the wakes, directly contributing to the accurate estimation of the power of the downstream turbines

A COMPARATIVE STUDY ON ENVIRONMENTAL EMISSIONS AND PERFORMANCE OF A STATIONARY TYPE DIESEL ENGINE FUELLED WITH BIODIESELS DERIVED FROM TWO DIFFERENT FEEDSTOCKS

The objective of the present study was to experimentally investigate environmental emissions and performance of a stationary type diesel engine fuelled with biodiesels derived from two different feedstocks; one is more unsaturated (rice bran biodiesel) and the other one is more saturated in nature (palm biodiesel) and compare with petrodiesel. Tests were conducted in a single cylinder, air cooled, direct injection diesel engine. From the experimental results, it was found that the nitrogen oxides emissions were higher with biodiesel fuels. The hydrocarbon and carbon monoxide emissions of palm biodiesel were lower than the other test fuels. The smoke emission of rice bran biodiesel was the lowest compared to the rest of the fuels. A considerable reduction in thermal efficiency was found with both the biodiesels when compared to diesel. From the present study, it is concluded that the biodiesels derived from palm and rice bran oils with their different fatty acid composition, show lower exhaust emissions and closer performance characteristics to diesel

Fabrication and investigation of superhydrophobic surface by dip coating

The present research work is focused on to fabricate and examine the characteristics of a superhydrophobic surface on copper (Cu) substrates by dip coating method. Three different samples of ‘Cu’ are set with chemical etching, mechanical rubbing and the combination of above two methods. The variations in the exteriorsurface morphologies have been examined by profilometer, scanning electron microscope and energy-dispersive X-ray spectroscopy. The adapted samples are immersed in a solution of silver nitrate follow by immersing in a combination of ethanol and perflurodecyltriethoxysilane for 10 min. The presence of leaf and dendrites assemblies have been observed on the surface, which are useful to trap the air between them and the entrapment allows water to roll off from the surface. The outcomes reveal that the modified substrates have a water contact angle (WCA) of 159° in the case of ‘Cu’ using combination of chemical etching and mechanical rubbing followed by immersion coating. The proposed methodology has the advantage of size compatibility and easy scale up for the development of superhydrophobic surface on copper in a cost and time effective manner

Productivity enhancements of compound parabolic concentrator tubular solar stills

The performance of compound parabolic concentrator assisted tubular solar still (CPC-TSS) and compound parabolic concentrator-concentric tubular solar still (CPC-CTSS) (to allow cooling water) with different augmentation systems were studied. A rectangular saline water trough of dimension 2 m × 0.03 m × 0.025 m was designed and fabricated. The effective collector area of the still is 2 m × 1 m with five sets of tubular still – CPC collectors placed horizontally with north-south orientation. Hot water taken from the CPC-CTSS was integrated to a pyramid type and single slope solar still. Diurnal variations of water temperature, air temperature, cover temperature and distillate yield were recorded. The results showed that, the productivity of the un-augmented CPC-TSS and CPC-CTSS were 3710 ml/day and 4960 ml/day, respectively. With the heat extraction technique, the productivity of CPC-CTSS with a single slope solar still and CPC-CTSS with a pyramid solar still were found as 6460 ml/day and 7770 ml/day, respectively. The process integration with different systems cost was found slightly higher but the overall efficiency and the produced distilled water yield was found augmented

Experimental investigation and CFD analysis of a air cooled condenser heat pipe

In the present work a heat pipe of one meter length and 0.031m outer diameter was constructed and the experiments are conducted to determine the surface and vapour temperature at steady and transient conditions for two different input power in the evaporator section and cooling the condenser section by air. A CFD analysis was also carried and the results under steady state conditions are compared with the results obtained from the experiments and reported in this paper.</jats:p