Water distiller/condenser by radiative cooling of ambient air

A water distiller/condenser system by radiative cooling of ambient air is designed. A mathematical model is proposed to describe the thermal performance of the radiative distiller. The results of the mathematical model predicts condensation rates within the range 3–7 litre/m² night. Also, the effects of different design parameters on the distiller performance are investigated.     

Numerical simulation of three-dimensional double diffusive free convection flow and irreversibility studies in a solar distiller

Numerical results of double-diffusive natural convection are presented in a three-dimensional solar distiller. The flow is considered laminar and caused by the interaction of the thermal energy and the chemical species diffusions. Equations of concentration, energy and momentum are formulated using vector potential-vorticity formulations in its three-dimensional form, then solved by the finite volume method. The Rayleigh number is fixed at Ra = 10⁵ and the effects of the buoyancy ratio are studied for opposed temperature and concentration gradients, with a particular interest to the three-dimensional aspects and entropy generation.     

Theoretical study and practical application of the capillary film solar distiller

In the south of Algeria, to supply sufficient fresh water for the population, desalination is necessary because water resources (underground and geothermal) are brackish.This paper presents the theoretical study and the results of experiments carried out with a capillary film multi-effect distiller installed in the south of Algeria (in a village near Touggourt, where the temperature of the groundwater is about 65°C at the source). The name of this device is DIFICAP (stiller with a lm in illary motion).The aim of our study is to improve the efficiency of this distiller. The research and development of this desalination process is carried out under the following aspects: modelisation of heat and mass transfer, experimentation under direct solar radiation in South Algeria and technical development to aim to optimize the efficiency of this distiller.The theoretical and experimental results show that the efficiency of this distiller increases when the temperature of the brackish water, the intensity of the solar radiation and the number of stages increase.     

Optical design of a high radiative flux solar furnace for Mexico

In the present work, the optical design of a new high radiative flux solar furnace is described. Several optical configurations for the concentrator of the system have been considered. Ray tracing simulations were carried out in order to determine the concentrated radiative flux distributions in the focal zone of the system, for comparing the different proposals. The best configuration was chosen in terms of maximum peak concentration, but also in terms of economical and other practical considerations. It consists of an arrangement of 409 first surface spherical facets with hexagonal shape, mounted on a spherical frame. The individual orientation of the facets is corrected in order to compensate for aberrations. The design considers an intercepted power of 30 kW and a target peak concentration above 10,000 suns. The effect of optical errors was also considered in the simulations.     

Experimental validation of a thermal model of an evaporative cooling system

A periodic thermal model for an evaporative cooling system over the roof has been presented. Open roof pond, water film and flowing water layer are the the special cases of the analysis. The time dependency of solar radiation, ambient air, sol-air and room air temperatures has explicitly been taken into account by expressing as a Fourier series of time for a 24 h cycle. Experimentally observed air temperature of rooms, treated with and without evaporative cooling over the roof, has been found in good agreement with theoretical results.     

Transient performance of closed loop solar water heating system with heat exchanger

The present paper deals with an analysis of a forced circulation closed loop solar water heating system; withdrawal of hot water of constant flow rate from a storage tank through a heat exchanger is considered. The effect of flow rate and heat exchanger length on the performance has also been discussed for a typical set of parameters and for a typical cold day in Delhi (26 January 1980).     

Semi-empirical characterization of a greenhouse-effect cascades solar distiller

The analysis in steady state of the different modelizations made on solar flat-plate functioning in low and average temperatures (especially the bridges of surface water) has allowed us to develop a simple linear model. By a swift experimental way, this model is able to approximate the thermal and optical performances of a greenhouse-effect solar distiller. This model has equally served for the verification of the time constant of the system in the same functioning and environment conditions.     

Transient analysis of solar still

This paper presents an analysis of the transient performance of a basin type mounted still; explicit expressions for hourly variation of temperature of glass cover and water in the basin and distillate output have been obtained. The results of the analysis are in good agreement with experiments.     

Transient analysis of a solar air heater of the second kind

This paper presents a theoretical analysis along with the experimental validation study of a solar air heater of the second kind. The heater consists of a flat passage between two metallic plates through which the heat transfer fluid air is made to pass by some auxiliary means. Study of the periodic response of different parameters of this solar air heater is attempted. The heat balance equations governing the behaviour of the system are solved explicitly. The results obtained from the analytical expressions for the transient variation of outlet air temperature compare well with experimental data. Predictions are also made regarding effects of different performance parameters of the air heater with variations of air mass flow rate and plate emissivity with the hope of optimizing the collector configuration.     

Measuring and evaluating solar radiative properties of plastic shading nets

Plastic shading nets are being used extensively in hot and sunny regions to protect plants from intense solar radiation. Different varieties of these nets are commercially available. However, the choice of net to fulfill specific shading requirements often depends on empirical or economic criteria and not on scientific considerations because essential information used to characterize the different types of nets is not available.In order to replace expensive measuring facilities that use artificial lighting to investigate the radiative properties of plastic shading nets, a simple method was presented to investigate these properties under global, diffuse and direct beam solar radiation conditions. Measurements were performed on clear sunny days, (December 28, 2008-February 10, 2009). Nets with colors and shading factors that are most commonly used in hot regions were selected for the study. The results showed that the behaviors of the plastic nets under solar radiation conditions were similar to those of translucent materials. Accordingly, it is possible to (i) treat plastic nets as translucent materials and (ii) investigate the equivalent optical constants (i.e., refractive indexes and extinction coefficients) for plastic nets as functions of the net solidity, texture type and color. Solidity and color of the net had significant effects on the radiative properties and the effect of color was much more than the effect of solidity. The shading factor of a plastic net, is a function of the daytime, depends on several design and meteorological parameters, so it cannot be used to describe a net. However, the net solidity together with color, and the daily integrals of the shading factor and of the radiative properties are appropriate parameters for describing a net.     

Performance investigation of a solar water distiller integrated with a parabolic collector using fuzzy technique

A recent study of the design of solar distillation with solar radiation concentration was carried out by an independent device. Transformer oil was used as a fluid to transfer heat to the distilled basin. The design and operational variables are essential, such as distiller dimensions, concentration ratio, pressure, and temperature. A mathematical model was proposed to simulate the system for 2 July 2018 from 10 am to 4 pm  in the climatic conditions of the city of Kirkuk, Iraq. Fuzzy logic (FL) was used to select the affected parameters: water temperature (T_w), water pressure (P_w), glass temperature (T_g), and vapor pressure (P_g) which have a separated membership function that control the linguistic variables. The results showed that the best performance of the distiller is at T_w = 100°C, P_g = 10 000 Pa, T_g = 20°C, and P_w = 20 000 Pa, and concentration ratio of 30. This study used FL to analyze solar distiller performance and identify optimum temperature, pressure, and concentration ratio on the productivity of solar distiller.     

Parameterization of aerosols from burning biomass in the Brazil-SR radiative transfer model

A new aerosol parameterization was developed and implemented for operational use with the BRASIL-SR model. The goal is to improve the assessment of solar energy resources in Brazil. Optical properties of the aerosols from burning biomass were obtained using software package OPAC and are in good agreement with previous field measurements made in Brazil. Three different mixture ratios of black carbon were used to cover the full range of typical measured values. The atmospheric transport model SMOKE provided the aerosol profile. An evaluating period of 11 days in August/1995 and ground measurements from six sites situated in Amazon region was used to validate the results. The global solar irradiation estimates obtained with new aerosol parameterization, presented smaller mean bias error in all ground sites. The correlation among estimates and measured values for surface global solar irradiation improved about 2.5 times by adopting an aerosol composition with 5% of black carbon.     

Transient analysis of a cylindrical solar water heater

An unsteady analysis of a cylindrical solar water heater has been performed. The physical parameters which govern the physical system are identified. The governing equations have been solved using the fourth order Runge-Kutta method for different values of the parameters. A good agreement between the numerical and experimental results has been obtained.     

Transient thermal behavior of porous media under oscillating flow condition

An analytical characterization of the heat transfer in an oscillating flow through a porous medium is presented in this work. Based on a two-equation model, two important dimensionless parameters are identified as the ratio of the thermal capacities between the solid and fluid phases and the ratio of the interstitial heat conductance between the phases to the fluid thermal capacity. The analytic solutions are obtained for both the fluid and solid temperature variations, and the heat transfer characteristics between the phases are classified into four regimes. In addition, a criterion for the validity of the local thermal equilibrium is suggested in a simple form as the ratio of the two time scales intrinsically involved in any transient heat transfer in porous media, namely the time scale relevant to the thermal inertia of porous media and the time scale pertinent to the transient variation of the boundary condition.     

Transient analysis of double basin solar still

The effect of water flowing over the upper glass cover of a double basin solar still on its transient performance has been presented. A comparative study of the daily distillate production of a double basin solar still with and without water flowing over the upper glass cover has been made, and some interesting conclusions have been drawn. Numerical calculations have been made for a typical hot day (viz 2 May 1980) in Delhi.     

Using the condenser effluent from a nuclear power plant for Ocean Thermal Energy Conversion (OTEC)

There has been increasing interest in clean energy over past few years. Ocean Thermal Energy Conversion (OTEC) power plants have been examined as a viable option for supplying clean energy. This paper evaluated the thermodynamic performance of the OTEC power system. Computer simulation programs were developed under the same conditions but with various working fluids for a closed system, a regeneration system, an open system, a Kalina system, and a hybrid system. The results showed that the regeneration system using R125 showed a 0.17 to 1.56% increase in system efficiency. Moreover, the system can generate electricity when the difference in temperature between the warm and cold seawater inlet temperatures is greater than 15 °C. In addition, the system efficiency of OTEC power plants using the condenser effluent from a nuclear power plant instead of surface water was increased by approximately 2%.     

Local entropy generation and exergy analysis of the condenser in a direct methanol fuel cell system

This paper aims to identify the irreversibilities in the condenser of a direct methanol fuel cell (DMFC) system and present possible enhancements in its design through local entropy generation analysis (L-EGA). For this purpose, the local entropy generation terms originating from heat and mass calculated from results of a pseudo two-phase computational fluid dynamic (CFD) model of the condenser. Through this analysis, the total irreversibilities due to heat and mass transfer are calculated locally (e.g., film boundary layer, vapour-gas boundary layer) under the variable operating conditions of a DMFC (undersaturated, saturated, and supersaturated conditions of the cathode exhaust gas). Moreover, the exergy destruction ratio of condenser is found to estimate the exergy performance of the condenser. The results show that in the case of supersaturated cathode exhaust gas (CEG) flow, the entropy generation rate due to mass transfer in the film region is found as 0.032 W/(m·K) which is 18 times higher than that for the undersaturated CEG flow. However, entropy generation rate due to mass transfer decreases significantly when the hot flow is just over the film region. In the film region, the entropy generation rates originating from heat transfer are found as 0.0055 W/(m·K) (for the undersaturated case), 0.0032 W/(m·K) (for the saturated case), and 0.0015 W/(m·K) (for the supersaturated case). Moreover, the maximum exergy destruction ratio is found as 0.72 when the CEG is undersaturated and the CEG velocity is 0.18 m/s, while the lowest exergy destruction ratio is calculated as 0.28 when the CEG is saturated.     

Monte Carlo radiative transfer simulation of a cavity solar reactor for the reduction of cerium oxide

Radiative heat transfer in a solar thermochemical reactor for the thermal reduction of cerium oxide is simulated with the Monte Carlo method. The directional characteristics and the power distribution of the concentrated solar radiation that enters the cavity is obtained by carrying out a Monte Carlo ray tracing of a paraboloidal concentrator. It is considered that the reactor contains a gas/particle suspension directly exposed to concentrated solar radiation. The suspension is treated as a non-isothermal, non-gray, absorbing, emitting, and anisotropically scattering medium. The transport coefficients of the particles are obtained from Mie-scattering theory by using the optical properties of cerium oxide. From the simulations, the aperture radius and the particle concentration were optimized to match the characteristics of the considered concentrator.     

Transient electrolyser response in a renewable-regenerative energy system

In a renewable-regenerative electrolyser/fuel-cell system, the electrolyser performs the critical function of converting excess renewable input energy into hydrogen. Electrolyser operation on time scales and duty cycles that are relevant to common renewable resources (e.g., wind and solar) were probed using an experimental residential-scale system. Experimental results indicate that the electrolyser's transient characteristics have a significant impact on the efficiency of the conversion process. Two key findings are presented. First, a reduction in electrolyser hydrogen production, relative to steady-state levels, is observed due to the thermal transient and time-dependent decay in current draw. These time-dependent aspects are typically not addressed in the theoretical models proposed to date for electrolyser operation. Second, it was found that maintaining a minimum electrolyser current is critical to avoid performance decline induced by dynamic operation. The requirement for a minimum operating current (and therefore minimum power input) places constraints on the common operating methodology for renewable-regenerative systems.