Michel Daguenet

Performance of a new solid adsorption ice maker with solar energy regeneration

A predictive model for an adsorption solar cooling system using the activated carbon–methanol pair and its numerical simulation are presented. This model accounts for instantaneous heat and mass transfers in each one of the machine components along a characteristic average day for each month. The solar powered ice maker consists of the following basic components: a reactor containing an adsorptive bed coupled to a static solar collector covered by Transparent Insulation Material (TIM), a condenser and an evaporator. A uniform pressure model for the reactor is considered. The bed’s radial temperature distribution is determined by means of a one-dimensional numerical method based on a finite difference technique. The machine’s performance is evaluated according to meteorological data valid for the hottest six months in Joao Pessoa (7°8′S, 34°50′WG), whose climate is typically hot and humid. The results are compared with those obtained from an identical system with a single cover solar collector. These last data are then compared to the results obtained in a particular month from the experimental study of a prototype with equivalent components, tested in Tunisia. The TIM cover’s system proved to be about 40% more efficient than the single cover solar system. The average net solar COP was 0.13 for the TIM cover system during the six month considered period. This corresponds to 7–10 kg/day of ice production per square meter of solar collection surface, respectively, for March and December, with solar irradiations ranging from 20 to 23 MJ/m2, during the October–March period.

Experimental determination of the sorption isotherms of mint (Mentha viridis), sage (Salvia officinalis) and verbena (Lippia citriodora)

Abstract Mint (Mentha viridis), verbena (Lippia citriodora) and sage (Salvia officinalis) are the most produced and consumed aromatic herbs in Morocco. The sorption isotherms of the three plants were determined within the range of 10–90% relative air humidity at three different temperatures (25°C, 40°C and 50°C), using saturated salt solutions method. Hendersons equation was fitted to the experimental data and the agreement between experimental and calculated values was satisfactory. The comparison between the sorption isotherms of mint, verbena and sage is studied.

Thermosolutal natural convection in a vertically layered fluid-porous medium heated from the side

The authors formulate the natural thermosolutal convection in an elongated enclosure of horizontal axis, partitioned by a vertical porous layer. They use the Boussinesq approximation, the stream function, the vorticity and the extended Darcy–Brinkman formulation to describe the transfer occurring in the porous layer. The chosen dimensionless parameters allow obtaining a single set of conservation equations, valid both in the two fluid compartments and in the porous layer. They solve numerically the set of coupling equations using the volume control approach. After recovering some literature results, they study, in an enclosure of square section which is partitioned by a porous layer into two equal fluid compartments, the influences of the main parameters on the Nusselt and Sherwood numbers for the Rayleigh number varying from 104 to 107, the Darcy number from 10−5 to 10−3, the thermal conductivity ratio from 1 to 100, the solutal diffusivity ratio from 0.01 to 1, the Lewis number from 0.1 to 5 and the buoyancy ratio from −5 to 5. For Ra≥104, a multicellular convective fluid flow can appear when −3≤N≤−0.5 and if, at least, Le, Rk or Rd is different from unity.

Design and analysis of solar thermoelectric power generation system

This article reports on the design and performance analysis of a solar thermoelectric power generation plant (STEPG). The system considers both truncated compound parabolic collectors (CPCs) with a flat receiver and conventional flat-plate collectors, thermoelectric (TE) cooling and power generator modules and appropriate connecting pipes and control devices. The design tool uses TRNSYS IIsibat-15 program with a new component we developed for the TE modules. The main input data of the system are the specifications of TE module, the maximum hot side temperature of TE modules, and the desired power output. Examples of the design using truncated CPC and flat-plate collectors are reported and discussed for various slope angle and half-acceptance angle of CPC. To minimize system cost, seasonal adjustment of the slope angle between 0° and 30° was considered, which could give relatively high power output under Bangkok ambient condition. Two small-scale STEPGs were built. One of them uses electrical heater, whereas the other used a CPC with locally made aluminum foil reflector. Measured data showed reasonable agreement with the model outputs. TE cooling modules were found to be more appropriate. Therefore, the TRNSYS software and the developed TE component offer an extremely powerful tool for the design and performance analysis of STEPG plant.

Numerical Study of the Transition Toward Chaos of Two-Dimensional Natural Convection within a Square Cavity

ABSTRACT The authors present the results of a numerical study involving unsteady natural convection inside an air-filled square cavity, heated from two opposite sides and cooled from the other two sides. The behavior of the system with increasing Rayleigh number is analyzed. Results obtained using centered finite differences (CFD), Patankar, and QUICK methods are compared. The last method has been found to yield results similar to the other two but with much less computational effort. This article confirms and expands our previously published study, in which the CFD method was used. Using the QUICK method, the authors show that the system transits from a fixed point toward chaos via a limit cycle, a period-doubling cascade, periodic windows, and tangential bifurcations.

Étude numérique de l'évaporation dans un courant d'air humide laminaire d'un film d'eau ruisselant sur une plaque inclinée

Abstract Numerical study of the evaporation in laminar humid air flow of a liquid film flowing over an inclined plate. By using an implicit centered finite differences method with a non-uniform grid, the authors study numerically the evaporation of a thin liquid film flowing over an inclined plate in a forced humid-air flow. They consider the existence of two-dimensional laminar boundary-layers with variable physical properties and show that the term of enthalpy diffusion is always negligible, whether the plate is adiabatic, isothermal or heated by a constant heat flux density. By using in the liquid film transfer equations which are one-dimensional, partially two-dimensional and two-dimensional, the authors additionally show the following features. If the plate is adiabatic, the liquid mass flow rate is without influence on the transfers and the gas–liquid interface behaves like an isotherm surface at rest. In this case, one may use a one-dimensional model in the film whatever liquid mass flow rate is. If the wall is isotherm or heated by a constant heat flux and when the liquid mass flow rate is less than 10−3 kg·m−1·s−1, the one-dimensional model is sufficient; if it is included in the interval [10−3 kg·m−1·s−1, 10−2 kg·m−1·s−1[, the partially two-dimensional model is useful; if it is superior to 10−2 kg·m−1·s−1, it is necessary to use the two-dimensional model. Generally, whatever the thermal conditions on the plate are, heat transfer is dominated by the liquid-vapor transition.

Numerical study of the Boussinesq model of natural convection in an annular space: having a horizontal axis bounded by circular and elliptical isothermal cylinders

The authors present a new calculation code using a two-dimensional finite element method valid in a steady and laminar flow. If the enclosure impedes the movement of the fluid, it becomes possible to observe multicellular flows even if the Rayleigh number is small. In this case, the increase of this number induces a fusion of the cells. If the Rayleigh number is large enough, there exists an interval of values of Rayleigh number for which the relaxation coefficients do not only influence the speed of calculation convergence but also the solution of transfer equation. Beyond this interval, the relaxation coefficients no longer influence this solution. At large values of Rayleigh number just before the divergence of the calculations, the stream function takes two values according to the value of relaxation coefficients, in case that the iterations number increases; this phenomenon is most manifest when the boundary conditions contain elements of symmetry in consideration of the vertical direction.

Numerical analysis of the effect of radiation on laminar steady natural convection in a two-dimensional participating medium between two horizontal confocal elliptical cylinders

Combined radiation and natural convection in a participating medium between two horizontal confocal elliptical cylinders is investigated numerically. The equations of steady, laminar two-dimensional natural convection are written by using an elliptic-cylinder coordinates system, the stream function, and the vorticity. The finite volume radiation solution method and the control volume technique are used to discretize the coupled equations of momentum, energy, and radiative transfer. Numerical solutions are obtained for Rayleigh numbers in the range 104 to 2x105 and the radiation-conduction parameter ranging from 0 to infinity. The special case corresponding to the convective flow within the annulus formed by an elliptical cylinder surrounding a flat plate is also considered.

Sizing solar-assisted natural rubber dryers

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.

Heat and mass transfer in a high temperature packed moving bed subject to an external radiative source

A numerical model of a moving chemical bed reactor for gasifying coal using concentrated solar radiation is proposed. It permits the determination of the temperature profiles for both the gas and the solid phases, the velocity and the pressure drop profiles as a function of control parameters such as incident radiative flux, gas flow rate and particle size. The results of this model are in a satisfactory agreement with the experiment ones.