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The evaporation of falling water liquid film in air flow is used in different solar energy applications as drying, distillation and desalination, and desiccant systems. The good understanding of the hydrodynamics and heat exchange in falling liquid film and gas flow, with interracial heat and mass transfer, can be applied in improving solar systems performance. The solar system performance is dependent on the operating conditions, system conception and related to several physical parameters, where the effects of some of these parameters are not completely clarified. In the present numerical study, we examine the effects of inlet conditions on the evaporation processes along the gas-liquid interface. The liquid film streams over an inclined plate subjected to different thermal conditions. Liquid and gas flows are approached by two coupled laminar boundary-layers. The numerical solution is obtained by utilizing an implicit finite-difference box method. In this analysis an air-water system is considered and the coupled effects of inclination, inlet liquid mass flow rate and gas velocity are examined. The results show that, for imposed heat flux or uniform wall temperature, the effect of inclination is highly dependent on the liquid mass flow rate and gas velocity. An increase in the liquid mass flow rate causes an enhancement of the effect of inclination on the heat and mass transfer. The inclination affects the heat and mass transfer, especially at lower gas velocities. In the range of inclination angles of 0-10[degrees], an increase in the inclination improves the evaporation by increasing the vapor mass flow rate. The maximum effect of inclination is nearly achieved at an inclination angle of 10[degrees]. Keywords: Liquid film; Gas-liquid interface; External flow; Boundary-layer; Heat and mass transfer; Inclined plate; Evaporation

We study three different configurations of solar supplemented systems for simultaneous production of hot air and hot water needed during the processing of vanilla. Correlations for the monthly solar fraction versus two dimensionless factors defined in terms of physical characteristics of the system have been developed. Not only have the various solar systems been evaluated against each other from a techno-economic point of view, but we have also proposed correlations for the optimal system which directly relate the mass of the product to be dried with the area of the solar collector.

Due to the lack of firewood, the use of solar energy in drying of natural rubber has been envisaged and it has been the subject of several works. The present work is concerned with the design of solar-assisted natural rubber dryers. The system performance is estimated using the average day method. The possibility of heat dumping and the configuration of the collector array are taken into account. To facilitate the user in making a rapid estimation on the collector area required, a simplified sizing method is developed. To this end, an empirical relation is performed by correlating the results of short-cut simulation to design parameters which are easily determined.

Numerical study of the 2-D heat transfer stimulated by free laminar convection in an enclosure reveals that the stream function of heat flow consists of a two-cellular flow pattern. The pattern is symmetric to the vertical axis which has a positive counterclockwise and negative clockwise eddy. A four-cellular flow is observed when the heat flux is applied to inner cylinder at very high magnitudes.

Thermal natural convection of air (Pr = 0,71) in a two dimensional square cavity with two vertical walls nonuniformly heated and the two others held adiabatic, is studied numerically. With increasing Rayleigh number (considered here as a control parameter), the system transits to oscillatory regime via a super critical Hopf bifurcation followed by an under critical Hopf bifurcation at critical Rayleigh number of 4,26 × 106. As Rayleigh number increases further a quasi-periodic regime with two frequencies settles. While continuing to increase Rayleigh number, the ratio between the two fundamental frequencies becomes rational. In this case, phase-locking motion is the main regime before chaos. Chaotic state is observed for Rayleigh number greater than 1,4 × 107. The system is sensitive to initial conditions. All numerical results have been characterized by looking to the Poincaré sections and phase portraits. For the chaotic state, the largest Lyapunov exponent is positive and the attractor dimension is fractional. [ABSTRACT FROM AUTHOR]