Use Of Porous Media Research Articles

Investigation of the lattice Boltzmann method to resolve combined radiation-conduction heat transfer in participating media with curved boundaries

PurposePresent study aims to extend the lattice Boltzmann method (LBM) to simulate radiation in geometries with curved boundaries, as the first step to simulate radiation in complex porous media. In recent years, researchers have increasingly explored the use of porous media to improve the heat transfer processes. The lattice Boltzmann method (LBM) is one of the most effective techniques for simulating heat transfer in such media. However, the application of the LBM to study radiation in complex geometries that contain curved boundaries, as found in many porous media, has been limited.Design/methodology/approachThe numerical evaluation of the effect of the radiation-conduction parameter and extinction coefficient on temperature and incident radiation distributions demonstrates that the proposed LBM algorithm provides highly accurate results across all cases, compared to those found in the literature or those obtained using the finite volume method (FVM) with the discrete ordinates method (DOM) for radiative information.FindingsFor the case with a conduction-radiation parameter equal to 0.01, the maximum relative error is 1.9% in predicting temperature along vertical central line. The accuracy improves with an increase in the conduction-radiation parameter. Furthermore, the comparison between computational performances of two approaches reveals that the LBM-LBM approach performs significantly faster than the FVM-DOM solver.Originality/valueThe difficulty of radiative modeling in combined problems involving irregular boundaries has led to alternative approaches that generally increase the computational expense to obtain necessary radiative details. To address the limitations of existing methods, this study presents a new approach involving a coupled lattice Boltzmann and first-order blocked-off technique to efficiently model conductive-radiative heat transfer in complex geometries with participating media. This algorithm has been developed using the parallel lattice Boltzmann solver.

Thermal performance of microchannel heat sink integrated with porous medium, slip coefficient and phase change material and machine learning approach

In this study, the thermal performance (TP) of the microchannel heat sink (MCHS) under the influence of the slip coefficient on the microchannel wall, the use of porous medium (PM) and phase change material (PCM), and the changes in the geometrical parameters and the shape of the microchannel have been discussed. The flow and energy equations were solved using the finite volume method. The validation of the melting process, slip coefficient, and porous medium with the previous literature demonstrate the high accuracy of the numerical solution, with the difference between the results being <8 %. The results indicate that using a wavy microchannel can improve TP by approximately10.6 % and 5 % compared to smooth and converging microchannels. Additionally, using non-Newtonian fluids with a power characteristic of 0.53 leads to improved TP about 2.8 % by reducing shear stress compared to Newtonian fluids. Furthermore, the presence of slip on the microchannel wall influences the flow pattern, resulting in reduced convection resistance and improved TP about 3.2–3.8 %. The highest TP was observed at a slip coefficient of 0.00001. Incorporating PM in the microchannel (either in the center or around it) can enhance TP by approximately 8–15 % compared to the base state, with greater improvements observed when PM is placed around the microchannel. The type of PM material and the porosity coefficient significantly impact TP. Varying the cross-sectional shape of the microchannel (square, rhombus, and triangle) has a substantial effect on improving TP compared to a circular cross-section, with the highest TP (with a 71 % increase) observed in microchannels with a square cross-section. Lastly, the use of PCM and PM on the active surface leads to a significant TP improvement of over 80 % compared to the base state. Using the Group Method of Data Handling algorithm, thermal resistance was estimated with an R-square value of 0.94 to validate the available data.

Pore-scale analysis of two-phase nanofluid flow and heat transfer in open-cell metal foams considering Brownian motion

Simultaneous use of porous media and nanofluids will increase the convective heat transfer multiple times compared to non-porous and pure fluid conditions. Heat transfer and flow transport of nanofluids inside porous media are usually simulated in large-scale with average properties, which are typically highly uncertain. Pore-scale simulation as an alternative approach can capture the characteristics of flow and heat transfer more accurately. Only few studies have been conducted to study nanofluid flow through porous media in pore-scale, and most of them employed single-phase approach without focus on different affective forces. This paper uses a pore-scale approach to investigate the flow characteristics and convective heat transfer of two-phase nanofluid flow in open-cell metal foams (OCMFs). Simulation of fluid flow and heat transfer is achieved by Buongiorno’s model. Therefore, a computational code through the OpenFOAM library that operates by a direct numerical simulation (DNS) approach and the finite volume method (FVM) is used. The momentum, energy, continuity, and nanoparticle distribution equations are discretized, and the SIMPLE algorithm is utilized for pressure and velocity coupling. In the present study, three OCMFs with a constant porosity (0.86) and various pore densities are investigated. Also, variations of pressure gradient, Nusselt number, and Darcy velocity are investigated as a function of pore density (as a geometric parameter), nanoparticle diameter, concentration, and Brownian motion force. The results indicate that the Brownian force enhances the heat transfer in OCMFs from 2% by up to 14% for the nanofluid flowing with 3% nanoparticle concentration. Also, increasing the diameter of nanoparticles reduces the Darcy velocity and heat transfer by up to 4%. On the other hand, increasing particle concentration from 3% to 5%, increases heat transfer by up to 10% and reduces the Darcy velocity by up to 9%. Finally, doubling the pore density demonstrates the complex behavior of the flow patterns, in which the heat transfer increases by up to 30% and permeability and velocity are reduced by up to 70%.

Numerical investigation on forced convection enhancement within an oil cooler through the simultaneous use of porous media and nanofluid

Traditional strategies for improving heat transmission in industrial systems include nanofluids and porous inserts. In these kinds of systems, increasing the rate of thermal transmission can also be accomplished by utilizing porous materials that have a higher thermal conductance. Al2O3, CuO, and ZnO in engine oil (20w50) nanofluid are studied numerically in three dimensions to see how they affect forced convection in a porous media oil cooler. Within the oil cooler, the porous medium was placed. A two-phase mixture model was used in conjunction with the Darcy–Brinkman–Forchheimer equation indicating the drag forces to simulate nanofluid flow in porous media. In addition, utilizing temperature laboratory data, a more specific thermophysical feature of the fluid was identified and characterized. ANSYS-FLUENT, a commercial computational fluid dynamics (CFD) software, is used to partition the governing equations using the finite volume method. In addition, the thermal boundary parameters of the oil cooler walls were made to be temporally constant and spatially uniform. The effects of varying volume fractions (ranging from 0% to 5%), Darcy number (ranging from 10−2 to 102), overall Nusselt number, pressure reduction, and the performance evaluation criteria (PEC) were analyzed and compared for a variety of distinct nanoparticles. The increased Darcy number (10−2 to 102) had a significant effect on the enhanced heat transfer coefficient, according to the data. In light of the findings, it can be deduced that the high-volume percentage of the nanoparticles will improve thermal transmission and, more significantly, the PEC factor. Furthermore, the given variables were compared, leading to the creation of diagrams for different variables.

Experimental analysis to improve charge/discharge of thermal energy storage in phase change materials using helical coil and porous metal foam

The use of phase change materials (PCM) for latent heat thermal energy storage (LHTES) is a common method of storing thermal energy in buildings. Because the thermal conductivity of the PCMs is low, so the rate of their energy charge/discharge would be confined. To overcome this issue, a new design is proposed using helical coil to maximize the contact surface between the heat transfer fluid (HTF) and the PCM. Both sides of the helical coil are filled with PCM, while in the inner region, copper metal foams (porosity of 0.9 and density of 12 PPI) are utilized for heat transfer rate enhancement. Effects of various parameters, including the inlet HTF flow rate, its temperature, and use of porous media on thermal energy storage performance in charge and discharge processes are analyzed experimentally. Six thermocouples are placed inside the PCM in different regions and melting and solidification processes are recorded using a thermal imaging camera. Results are presented in terms of temperature variation in different regions, temperature contours, mean temperature response, Stefan number, the charge/discharge time, and the extracted power of discharge. The results reveal that using porous media can remarkably reduce the charge/discharge time up to 57 %, which is depended on the inlet working fluid temperature. The charging time reduction is higher when the inlet HTF temperature increases. When the flow rate of HTF is increased, the charging time can be slightly shortened, while this effect becomes dominant when using porous media. Use of porous media could also accelerate the discharge time, while a faster discharge rate was observed for lower HTF flow rates during discharging the stored energy. Also, a lower initial temperature of the inlet HTF provides faster depletion rate.

Variation of thermal stratification, first and second law efficiency due to the use of porous media in hot water tank

ABSTRACT Thermal energy storage tanks are one of the widely used energy storage systems. In these systems, thermal stratification and energy storage capacity are the most important parameters affecting system performance. In this study, a porous medium was placed in the upper part of the tank, where the water in the tank is the hottest, in order to increase the system performance for standby mode. Thus, convection-induced movement of the water in the upper part of the tank was tried to be minimized and it was aimed to reduce the temperature drop. The results were determined experimentally in terms of first law and second law efficiency, maximum temperature difference, and overall heat transfer coefficient over a 48 hours cooling period. The porous media thickness was used as a parameter and its values were chosen as 10, 12, 14, and 16 cm. The best results were obtained for the porous media thickness of 16 cm, at which thermal stratification, first law, and second law efficiency increased by an average of 1.8 times, 1.6%, and 2.3%, respectively.

Phase-change materials for thermal management of electronic devices

The increase in power density of electronic devices, driven by the higher performance and miniaturization demands, has led researchers seek new and alternative thermal management techniques. Since most of the electronic devices often experience high frequency power cycles, cooling systems must also be capable of managing transient thermal profiles to delay the temperature response and reduce the temperature gradients within the device, which can cause thermal stresses and, in the long run, the failure of the electronic device. The integration of Phase-Change Materials (PCM) into heat sinks for electronic devices represents an interesting technique to increase the thermal inertia of the cooling system, while also ensuring more stable operating temperatures within the electronic components. However, several technical challenges still limit their commercial viability in electronic applications. The present paper critically discusses the latest research trends in this field, with a special focus on electric batteries, power electronic and portable device applications. Methods to enhance PCM-based heat sinks for electronic devices are also discussed. Generally, integrating PCMs into the thermal management system of electronic devices is an effective technique to reduce hot spots (between 6%–10%) and have a more uniform temperature distribution inside the component. However, more experimental research is needed to test their suitability over extended usage period and to establish practical design procedures. • Integration of PCMs in electronic devices can reduce temperature hot spots by 6%–10%. • PCMs are effective for the thermal management of EV batteries. • Microencapsulated PCM thin-film layers can be integrated in portable devices. • The use of porous media and metal foams can enhance the performance. • More experiments are needed to fully characterize PCMs in electronic applications.

Simultaneous use of porous medium and phase change material as coolant of photovoltaic modules; thermodynamic analysis

Conversion of light into electricity is possible by means of photovoltaic (PV) technology. The negative impact of increasing the temperature of PV cells on their output power is one of the most important weaknesses of this technology. In this experimental study, a porous medium integrated with phase change material (PCM) as two passive cooling methods of PV modules are employed and their effects on cooling the PV panel are investigated, either separately or simultaneously. Two thickness values of the aluminum porous medium were mounted at the back side of PV module. The results show that a 2 cm thick porous medium reduces the module temperature by 14.5 °C, while when PCM is added, the temperature drop reaches 21.5 °C compared to a conventional PV module. Moreover, adding PCM, downgrades the rate of temperature rise. Increasing the output power due to the use of PCM and porous media, causes 18.6 % less PV modules to run a 10-kW photovoltaic power plant. The entropy generation of the system was also calculated and 4 % difference between the mentioned cases was calculated. An important concern about the thermal exergy assessment is discussed in details.

Enhancing the energy and exergy performance of a photovoltaic thermal system with [formula omitted]-shape collector using porous metal foam

The use of porous media in heat transfer systems leads to a rise in the heat transfer surface area and pressure loss of the working fluid, the first of which is desirable and the second is undesirable. The effect of porous metal foam positioning on the energy and exergy performances of an air-based photovoltaic thermal system with ∇-shape collector is investigated in this research. For this purpose, porous foam is placed once in the channel between the photovoltaic panel and the collector (system II), again in the channel between the collector and the back insulation wall (system III), and finally in both channels (system IV). The results are compared with each other and with those of the system without porous metal foam (system I). The energy balance equation is written for each part of the system, and the resulting system of equations is solved with a code written in MATLAB. The mathematical modeling was performed for several values of air mass flow rate. The results showed that the maximum overall energy efficiency (61.53–111.49%) and overall exergy efficiency (14.18–17.46%) belong to systems II and IV.

NUMERICAL STUDY ON THE THERMAL BEHAVIOR OF POROUS MEDIA AND NANOFLUID AS VOLUMETRIC ABSORBERS IN A PARABOLIC TROUGH SOLAR COLLECTOR

In this paper, a combination of Monte Carlo ray tracing (MCRT) and finite volume method (FVM) was utilized to numerically investigate the application of CuO/water nanofluid and porous media (as volumetric absorber agents) in a direct absorption parabolic trough solar collector (DAPTC). The main purpose of this study is the numerical evaluation of the effect of the nanofluid and porous media (separately and simultaneously) to compare their influences on the efficiency of DAPTCs using Ansys Fluent software. The effects of volume fraction, porosity, pore diameter, input temperature, and flow rate on the collector thermal performance are also examined. The results indicated 40.5% and 49.9% improvement in the thermal efficiency of the collector due to the use of nanofluid and porous media, respectively. Thermal efficiency showed a reduction with increasing the inlet temperature as well as decreasing the flow rate. Applying the porous media can reduce the temperature concentration near the absorber tube wall, which will decrement the heat loss. However, using full porous media as a volumetric absorber leads to a great pressure drop. Results showed that the use of porous media enhanced the friction factor of pure water without metal foam 1500-1750 times. Therefore, nanofluids and partially filled porous media can be simultaneously used for their synergistic benefits. The combination of direct absorbers can increment the thermal efficiency up to 69.5%. The numerical simulation is validated with available experimental data.

PERTURBATION SOLUTION OF COUETTE FLOW OF CASSON NANOFLUID WITH COMPOSITE POROUS MEDIUM INSIDE A VERTICAL CHANNEL

Background Various investigations revealed that the addition of nanoparticles in base fluid enhanced the thermal transfer properties of the fluid. The accumulation of nanoparticles, having ranges (〖10〗^(-7) to 〖10〗^(-9)), in the base fluid, is termed as nanofluid. Nanoparticles have several applications in industry as nanofluid coolant, which is used to decrease the heat produced as a result of air resistance on roads. Another important procedure that is applicable to enhance the thermal performance of different instruments on an industrial scale is the use of porous media. A porous medium is any surface having pores or voids filled with some fluid. Porous media has widespread applications in productions especially for filtration processes, catalytic reactions, and distillation towers, etc. Method Couette flow of Casson nanofluid with variable viscosity and porous medium inside a vertical channel is examined in this work. We have assumed three different regions in which regions I and III are clear viscous regions while region II is the porous medium saturated region. The Tiwari and Das model is used to obtain governing equations of the existing problem and Darcy’s law is considered for porous medium. The energy equation also included viscous and Darcy dissipation terms. By using the regular perturbation technique, the results of developed dimensionless governing equations are calculated. Results On the flow characterization of the Casson nanofluid, the inspections are executed with the help of graphs for altering values of the porous parameter, Grashof number, Brinkman number, and solid volume fraction. It is examined that the Brinkman number and Grasho

The Thermohydraulic Characteristics and Optimization Study of Radial Porous Heat Sinks Using Multi-Objective Computational Method

AbstractThe use of porous media (PM) to improve conductive heat transfer has been at the focus of interest in recent years. Limited studies, however, have focused on heat transfer in radial heat sinks (RHSs) fully and partially saturated porous media with a different arrangement. As a development of the above-mentioned investigations, this research, therefore, addresses the ability of radial porous heat sink solutions to improve the thermohydraulic characteristics and reduce the effect of the second thermodynamics law. The response surface methodology (RSM) technique with ansysfluent-cfd is utilized to optimize the thermohydraulic features and the total entropy generation by the multi-objective optimum design for different design parameters such as porosity (Ø), inlet temperature (Tin), and applied heat flux (Q) simultaneously after achieving the optimum porous media arrangement related to the flow direction. The results show that, in terms of the flow direction, the optimum radial porous heat sink of the 100%PM model is recognized as providing the best results and the best option (fully saturated porous media). Moreover, a significant agreement between the predicted and numerical simulation data for the optimum values is also seen. The optimum and undesirable designs of the thermohydraulic features, the total entropy generation, and the optimum thermal management are detected in this investigation.

Review: Technological Development of Heat Transfer Enhancement in Two Phase Flow by using Passive Method

The Heating, Ventilation, Air conditioning & Refrigeration application always shows an opportunity to enhance the heat transfer rate. With these motives, researchers explored the use of passive methods in single phase flow which exhibits promising results of heat transfer enhancement. On the other hand, researchers investigated the effect of the passive method in Two phase flow, which also shows promising results in heat transfer enhancement. Two phase flow includes Boiling, Evaporation & condensation phenomenon. This paper focused on the review of the experimental studies conducted on the use of heat transfer enhancement in the condensation process mostly. Out of this passive method, Micro fin tube shows better heat transfer enhancement and less pressure drop compared to other methods. It has been observed that the use of porous media also showing promising effects in heat transfer enhancement and it’s fetching the attention of researchers. Therefore, this review work also reviewed the numerical studies on the use of porous media in two phase flow. It is needed to explore the different structure and optimum design of porous media, which have high heat transfer enhancement with low pressure drop penalty. Also, the use of low Global Warming Potential refrigerant effects needs to be explored, which could be a better alternative for existing refrigerants.

Parameter analysis and fast prediction of the optimum eccentricity for a latent heat thermal energy storage unit with phase change material enhanced by porous medium

The melting performance of porous-medium-enhanced phase change material (PCM) in a horizontal shell-and-tube latent-heat thermal energy storage unit (LHTESU) with eccentric structure is studied through a fixed-grid numerical method. The effects of ratio of outer and inner diameter, thermal conductivity of porous medium, porosity and heating temperature on the recommended eccentricity of LHTESU are discussed. Correlations for fast prediction of the optimum eccentricity are built. Results show that the mixed use of porous medium and eccentric structure can save as much as 43.1% of the total melting time compared with the pure use of porous medium. There exists an optimum eccentricity to get the shortest total melting time. The optimum eccentricity increases with the increase of ratio of outer and inner diameter, porosity and heating temperature, and decreases with the increase of thermal conductivity. For fast prediction of the optimum eccentricity and saved melting time, a modified Rayleigh number is proposed to reflect the effect of porous medium on natural convection, especially the flow resistance caused by porous medium. The effects of the four parameters on the optimum eccentricity can be integrated by the relationship between the optimum eccentricity and the modified Rayleigh number. Correlations of The optimum eccentricity and saved melting time are obtained respectively for convenient calculation and evaluation of the feasibility of eccentricity.

A Novel Modeling Approach to Stochastically Evaluate the Impact of Pore Network Geometry, Chemistry and Topology on Fluid Transport

Fine-grained sandstones, siltstones, and shales have become increasingly important to satisfy the ever-growing global energy demands. Of particular current interest are shale rocks, which are mudstones made up of organic and inorganic constituents of varying pore sizes. These materials exhibit high heterogeneity, low porosity, varying chemical composition and low pore connectivity. Due to the complexity and the importance of such materials, many experimental, theoretical and computational efforts have attempted to quantify the impact of rock features on fluids diffusivity and ultimately on permeability. In this study, we introduce a stochastic kinetic Monte Carlo approach developed to simulate fluid transport. The features of this approach allow us to discuss the applicability of 2D vs 3D models for the calculation of transport properties. It is found that a successful model should consider realistic 3D pore networks consisting of pore bodies that communicate via pore throats, which however requires a prohibitive amount of computational resources. To overcome current limitations, we present a rigorous protocol to stochastically generate synthetic 3D pore networks in which pore features can be isolated and varied systematically and individually. These synthetic networks do not correspond to real sample scenarios but are crucial to achieve a systematic evaluation of the pore features on the transport properties. Using this protocol, we quantify the contribution of the pore network’s connectivity, porosity, mineralogy, and pore throat width distribution on the diffusivity of supercritical methane. A sensitivity analysis is conducted to rank the significance of the various network features on methane diffusivity. Connectivity is found to be the most important descriptor, followed by pore throat width distribution and porosity. Based on such insights, recommendations are provided on possible technological approaches to enhance fluid transport through shale rocks and equally complex pore networks. The purpose of this work is to identify the significance of various pore network characteristics using a stochastic KMC algorithm to simulate the transport of fluids. Our findings could be relevant for applications that make use of porous media, ranging from catalysis to radioactive waste management, and from environmental remediation to shale gas production.

Flow control and heat transfer enhancement inside a two-dimensional channel using porous blocks and applying bleeding condition between them

There are different methods to enhance forced convective heat transfer. In the current study, porous blocks are used on the hot wall of a two-dimensional channel. Use of porous media can enhance the heat transfer by improving the flow mixing with subsequent increment in the effective thermal conductivity of the domain at the position of the used permeable media. However, a cavity-like flow appears between the blocks, which deteriorates heat transfer there. In this study, a bleeding condition by suction is applied to improve heat transfer there. Effects of some important parameters including porous media permeability, porous blocks relative height, flow Reynolds number, and the bleeding coefficient on the thermal performance and pressure loss are investigated. The outcomes reveal that the bleeding condition effect on heat transfer mainly depends on the bleeding coefficient. For example, the effect of bleeding condition on the total average Nusselt number is negligible for the bleeding coefficient (σ) less than 0.01, while it could improve the average Nusselt number by 36% at σ = 0.05. Furthermore, increasing the permeability of porous blocks, the effect of the bleeding condition becomes more highlighted from the performance number point of view.

Numerical Assessment of Heat Transfer and Entropy Generation of a Porous Metal Heat Sink for Electronic Cooling Applications

In the present study, the thermal performance of an electronic equipment cooling system is investigated. The heat sink used in the current cooling system consists of a porous channel with a rectangular cross-section that is assumed to be connected directly to the hot surface of an electronic device. In this modeling, a fully developed flow assumption is used. The Darcy–Brinkman model was used to determine the fluid flow field. Since using the local thermal equilibrium (LTE) model may provide results affected by the error in metal foams, in the present research, an attempt has first been made to examine the validity range of this model. The local thermal non-equilibrium (LTNE) model taking into account the viscous dissipation effect was then used to determine the temperature field. To validate the numerical solution, the computed results were compared with other studies, and an acceptable agreement was observed. Analysis of the temperature field shows that if the fluid–solid-phase thermal conductivity ratio is 1 or the Biot number has a large value, the difference between the temperature of the solid phase and the fluid phase decreases. Moreover, the effect of important hydrodynamic parameters and the porous medium characteristics on the field of hydrodynamic, heat, and entropy generation was studied. Velocity field analysis shows that increasing the pore density and reducing the porosity cause an increase in the shear stress on the walls. By analyzing the entropy generation, it can be found that the irreversibility of heat transfer has a significant contribution to the total irreversibility, leading to a Bejan number close to 1. As a guideline for the design of a porous metal heat sink for electronic equipment, the use of porous media with low porosity reduces the total thermal resistance and improves heat transfer, reducing the total irreversibility and the Bejan number. Moreover, the increasing of pore density increases the specific porous surface; consequently, it reduces the total irreversibility and Bejan number and improves the heat transfer.

Mixed thermomagnetic convection of ferrofluid in a porous cavity equipped with rotating cylinders: LTE and LTNE models

In the present study, the impressions of the MHD and porous medium on mixed convection of Fe3O4-water nanofluid in a cavity with rotating cylinders in three different temperature cases with local thermal equilibrium and local thermal non-equilibrium approaches were studied. The effect of the presence of cylinders in three different temperature cases to improve the heat transfer rate was investigated. A finite volume method was used to solve equations. The Richardson, Hartmann, and Darcy numbers ranges are 1 ≤ Ri ≤ 100, 0 ≤ Ha ≤ 30, 0.001 ≤ Da ≤ 0.1, respectively. The volume fraction of nanoparticles varies in the range of 0–3%. The results show that the use of porous media has a beneficial effect on increasing the heat transfer rate, but the combination of the porous medium and the magnetic field can increase or decrease the heat transfer. Also, the most effective and highest heat transfer rate was occurred at Da = 0.01 and Da = 0.1, respectively. In addition, when the cylinders are cold or hot, the highest and lowest heat transfer rates occur, respectively. Finally, it was concluded that the magnetic field could control the fluid flow inside the cavity.

Variable air gap membrane distillation for hybrid solar desalination

While a low temperature solar still for water production is simple in design, the accompanying productivity is quite low. This factor has necessitated development of enhancement techniques for water production. Alternatives suggested are the use of porous media in a solar still such as sponge, blackened jute cloth, pebble pieces, and floating carbonaceous material for absorbing solar energy. The use of a hydrophobic porous membrane in a solar still has not been investigated systematically thus far. The formation of a convex liquid meniscus alters vapor pressure across the pores of the membrane and is the origin of increased evaporation rates. The goal of the present study is to examine the performance of a solar still configuration towards water production in the presence of a surface-mounted hydrophobic membrane. Vertical arrangement is possible in a prototype but is inconvenient to setup in a laboratory-scale experiment. Hence, the device is compared with another without a membrane in a horizontal solar still configuration. Variable air gap is necessary to drain the condensed drop from an inclined condensing surface. The air gap membrane distillation system (AGMD) thus configured is selected for investigation and further comparison with a mathematical model. Experiments carried out in the present work show that a 40–70% increase in water production is obtained with the use of a membrane. The increase in evaporation rate is visible in the dropwise condensation patterns over the condensing surface. The present study thus confirms the utility of using a hydrophobic membrane in increasing water productivity of a solar still apparatus. Exergy analysis of the solar still when a chiller is used for the condensing surface is also presented.

Temperature Distribution and Evaporation Rate in Porous Media

Various studies have been done to improve solar still performance, especially in water streams. Various methods create thin water flow on the absorbent plate, including using porous media. The research aims to identify temperature distribution and evaporation rate in porous media. The use of porous media as an absorber plate material in solar still applications is investigated in this study. Five types of porous media have been researched, such as concrete consisting of river sand and iron with a particle size of 0.125 and 0.250 mm, and natural stone. A comparison of 5 specimen types is held by conducting evaporation tests. The pore media specimen 5x1x10 cm is heated by an electric heater with a power of 36, 4 W. The bottom side of the specimen is exposed to a constant high salt water reservoir. Data is collected periodically for 2 hours. Research produces specimens at smaller particle sizes with thermal conductivity and greater heat transfer rates. Iron sand concrete as aggregate has better temperature distribution than the specimen of river sand. The largest high-dampened front reduction is obtained on specimen C with a value of 0.051 m. The largest evaporation rate is owned by specimen C with the amount of 2.38 ml in 7200 s. Concrete with an aggregate of iron sand (0.125 mm particle size) is recommended as a solar still absorbent plate material; however, natural stone materials also have a high potential to be used as a solar still absorbent plate material.