Freshwater Yield Research Articles

A visualization study of vacuum enhancement on vapor flow and yield in tubular solar still

Operating solar still under vacuum is known to significantly boost the freshwater yield, and the bonus yield could be mainly attributed to the enhanced vapor flow. Smoke visualization technique can characterize the vapor flow field within a distillation chamber, and help to reveal structural/operational shortcomings and achieve an optimal design. To quantitatively explain the mechanism of vacuum enhancement on vapor flow within a tubular solar still (TSS), a visualization experiment using laser sheet and smoke tracer was conducted to capture the flow pattern and diffusion process of vapor. The accelerations of the vapor flow with decreasing pop and elevating Tw were captured. At Tw = 60 °C, average velocity of vapor flow (vavg) under 40 kPa was 66.6 mm/s, increased by 153% compared with that under 95 kPa. An empirical correlation was then presented with an accuracy of −12% ∼ 22%. Based on the correlation, a novel model for predicting the yield of solar still was proposed, and validated through independent data, showing an average deviation of 5.11%. Furthermore, three flow regimes (laminar, transition, turbulent) were classified with different Grashof number, where laminar flow was observed at Gr < 3.0 × 104 and turbulence was occurred when Gr exceeded 5.6 × 104. This work visualized the acceleration of vapor transportation under vacuum, and supplied guidance for further optimal design in solar stills.

Performance, energy and economic investigation of airgap membrane distillation system: An experimental and numerical investigation

Airgap membrane distillation (AGMD) is an efficient configuration employed widely for the solar membrane distillation desalination process. In the present work, 1-D Knudsen and molecular transport (KMT) model has been developed to investigate the performance of the flat sheet PVDF membrane. A new solution algorithm for the co-current and counter-current flow regime has been designed to solve the heat and mass transfer equations iteratively for a single-stage AGMD module. The feed temperature, feed flow rate, airgap size, salinity, membrane porosity and module length were varied and compared with experimental results. The increase in feed temperature from 40 °C to 80 °C resulted in 10.38 times increase in flux for co-current flow and 11.05 times for counter-current flow. The maximum permeate flux at 80 °C was 8.668 kg/m2h and 8.871 kg/m2h for the co-current and counter-current processes, respectively. Optimizing the feed temperature, flow rate, and membrane length using RSM suggests 80 °C, 1.528 LPM and 10 m as the optimum operating condition. An AGMD module of size 0.8 m width and 10 m length under the optimum operating condition exhibited a freshwater yield of 8.73 kg/h by consuming 24.98 kWh/m3 of specific energy, and the water production cost would be around $2.25/m3.

An active solar desalination system integrated with collective condenser heat pipe solar evacuated tube collector: a thermoeconomic analysis.

An experimental investigation was executed on the solar evacuated tube collector containing a collective condenser unit of heat pipe arrangement attached to a single slope solar desalination system. The brackish water preheating was done by the unique solar collector before entering the still. Performance analysis of the system was carried out with 0.001, 0.002 and 0.003kg/s brackish water flow rate in the collector and 0.01, 0.02 and 0.03m of brine water depth in a single-slope solar desalination system. The feasibility of the proposed system was evaluated by thermodynamic analysis, embodied energy, CO2 mitigation and economic analysis. Active desalination system with collective condenser heat pipe evacuated tube collector at 0.001kg/s brackish water flow rate and 0.01m water depth produced maximum freshwater yield, average daily thermal and exergy efficiency of 3.085l/m2day, 30.25% and 3.17% respectively. An increase of maximum freshwater yield of 37.11% and average daily thermal efficiency of 43.5% respectively were achieved at a brackish water flow rate of 0.001kg/s and 0.01m of basin water depth in comparison with a traditional single slope solar desalination system. The embodied energy of the system was estimated as 630.77 kWh, and 0.001kg/s and 0.01m of water depth resulted in the highest earned carbon credit of 16,954.48 INR. The minimum payback period of 2.19years was achieved at the lower brackish water flow rate and basin water depth of 0.001kg/s and 0.01m respectively.

All-day working photovoltaic cooling system for simultaneous generation of water and electricity by latent heat recycling

The photovoltaic (PV) cooling system based on solar-driven interfacial water evaporation (SIWE) system can effectively reduce the temperature of PV panels and obtain fresh water, but it cannot work at night during which there is no heat source input. In this work, we proposed a novel SIWE-based PV cooling systems with optimized performance that can achieve all-day working. In this hybrid system, the heat generated by the PV panel is extracted as the form of vaporization latent heat through membrane distillation (MD). Then it transferred along with the condensation of water vapor and stored in Phase Change Material (PCM), which is used to achieve electric power generation by thermoelectric effect at night. The hybrid system can achieve an 19.5 % improvement of output power compared with that without cooling method. Additionally, a 1.55 kg m-2 h−1 fresh water output with a salt rejection rate more than 99.9 % are realized under 3-sun irradiation. At the same time, it can also achieve a peak power output of 6 W m−2 at night by the release of latent heat stored in PCM. This hybrid system may provide a new idea to broaden application scenarios of traditional SIWE-based PV cooling systems.

Energy, exergy, economic, environmental analysis for solar still using partially coated condensing cover with thermoelectric cover cooling

The declining freshwater resources can be overcome using thermal desalination methods such as solar still. However, the productivity of a solar still is highly dependent on the environment and design. In this study, an improvement of the passive solar still with a partially coated condensation cover and a thermoelectric cooling system was made. The effect of varying thermoelectric cooling power (12 W and 36 W) was investigated and compared with a reference solar still under the tropical weather conditions of Malaysia. The performance of the solar still was analysed in detail based on freshwater yield, energy, exergy, environmental and economic aspects. The results showed that freshwater production could be increased by up to 126% with a 36 W thermoelectric cooling capacity. The energy efficiency improved by 44%, but the exergy efficiency decreased by 25% compared to the reference solar still. The results of the energy matrices show that the minimum energy payback time and maximum energy production factor for the coated glass solar still are 6.55 years and 0.15, respectively. The amount of carbon dioxide mitigated by the modified solar still was 2.97 tonnes of CO2 in a lifetime. The lowest cost per litre was found to be $0.036 with a thermoelectric cooling power of 36 W. The highest exergo-economic and enviro-economic values analysed for the coated glass solar still with thermoelectric cooling were 4.64 kWh/$ and $83.21, respectively.

IMPACT OF TREATED WASTEWATER AND FRESH WATER ON GROWTH AND YIELD OF TOMATO (LYCOPERSICON ESCULENTUM) AT DISTRICT-JALGAON, MAHARASTRA

A study was carried out in Maharashtra’s Jalgaon District to investigate the effects of two water sources on the growth and yield of tomatoes (Lycopersicon esculentum). The irrigation water came from two sources: treated wastewater and freshwater. For three months, the quality of these sources was monitored (2018). Samples from both sources were collected and sent to the laboratory for analysis. For three months, each water source was used to irrigate tomatoes planted in the field using a Split Plot Design (SPD) as the experimental design. The treatments consisted of three replications of treated wastewater and freshwater. Plant height, number of branches, number of leaves, number of flowers, and number of fruits were all measured during this time period. The results show that treated wastewater was also used for irrigation and yielded 01-05% less than freshwater yield. As a result, wastewater containing appropriate plant protection measures was found to be suitable for the irrigation of tomato crops.

Performance enhancement of water output via latent heat storage system with single slope solar stills

The purpose of this study was to design, build, and assess the performance of a latent heat storage system in tandem with a single slope solar still. Using a solar accumulator to transfer hot water to a shell and a spiral finned tube filled with 30 kg of paraffin wax ? 1.2 wt.% of Al2O3 nanocomposites, latent heat was stored. To test the effect of the storage system?s performance, two trials were conducted, with and without storage, under as similar of conditions as could be arranged. The proposed storage system design eliminates any potential issues with usage of paraffin wax as the storage system in conjunction with the solar still. An outcome indicated that daily fresh water output was enhanced by 4.63% when the solar still was used in conjunction with the storage system.

Performance analyses on a novel evacuated U-tube solar collector powered direct contact membrane distillation hybrid system for seawater desalination

Short lifespan and low thermal efficiency are two key hindering factors for the development of solar desalination system. Herein, a novel hybrid system model of a direct contact membrane distillation (DCMD) desalination system powered by a durable and efficient evacuated U-tube solar collector (EUSC) is proposed. The models of both EUSC and DCMD are mathematically formulated and validated. The permeate flux, energy efficiency and exergy efficiency of the proposed system are deduced as performance indicators. The performance of the proposed system is predicted under the weather conditions of Ningbo city, China. Under the typical weather condition, the maximum permeate flux, energy efficiency and exergy efficiency of the proposed system are 4.45kgm- 2h- 1, 25.47 % and 4.73 %, respectively. The freshwater yields of August and total year of 2021 in Ningbo city, China are presented. Additionally, the long-term performance with past 41 years is also studied. The effects of solar irradiance, environment temperature, feed flow velocity, feed water Reynold number, permeate liquid temperature, permeate flow velocity, porosity and average pore radius of DCMD membrane are investigated via parametric studies. The proposed EUSC/DCMD coupling system may provide a promising alternative to stand-alone, small-scale desalination systems for freshwater generation.

A portable solar still's productivity boost combining a magnetic stirrer and thermoelectric

Salt water desalination using solar still is a successful technique to supply clean water in distant locations using low-cost settlements. In this research, the fabrication and experimental performance of a new portable multi-slope solar still is outlined. Considering the low efficiency of solar stills, different modifications were used to intensify productivity. The modified solar still was investigated in passive and active operational modes in which the passive mode only relies on solar radiation, while the active mode uses different modifications to improve productiveness. In the active mode, the impact of using a magnetic stirrer and thermoelectric cover cooling is investigated in different case studies. All experiments were done at the University of Kurdistan, Sanandaj, Iran, in October 2021 in daylight time. The maximum fresh water yield from the modified solar still was 1550 ml/m2·d, which was 143.14 % more than the conventional still at the same meteorological condition. Furthermore, the energy and exergy efficiency of the solar still was calculated to be the highest at 28 % and 1.67 %, and the cost per liter was 0.081 $/l/m2. Therefore, the efficacy of the recommended design and modifications was proven to be a sustainable and low-cost method for clean water demand in rural regions.

Numerical and experimental study of a single-slope double-effect solar still integrated with paraffin wax

• The condensation theory takes into cognizance the heat and mass transfers in the humid air medium in estimating the freshwater yield. • The productivity of a solar distillation system can be improved by increasing the number of condensing surfaces. • The double-effect unit performed better than the single-effect unit by 48.7%. • The upper and lower chambers had different phases of production due to the effect of the ambient environment and the heat retention capability of the lower condensing cover. • The lower chamber of the double-effect unit had a maximum yield rate of 0.28kg/m 2 /h while the system had a maximum cumulative yield of 4.06kg/m 2 /day. The demand for freshwater has continued to soar amidst an increasing population, industrialization, and environmental pollution. The continuous shrinkage of this important resource has necessitated the need for a concerted effort on seawater desalination. Solar-powered desalination occupies a strategic position in the water-energy nexus and offers an alternative to taking off pressure from the already stressed freshwater sources. A numerical study with experimental validation of a single-slope double-effect solar still integrated with paraffin wax is thus presented. A transient mathematical model considering the humid air media in the upper and lower chambers was developed. Previous works in this area ignored the thermal analysis of the humid air medium, and as such, adopted the evaporation theory in the estimation of the freshwater yield. However, this study considers the thermal resistance offered by the humid air in the computation of the yield using the condensation theory. The energy-balance equations were discretized using the finite element method and solved with the aid of version 7.12 of the FlexPDE numerical solver. The model was validated with data from the experimental study. The correlation coefficients between the predicted and experimental data showed good agreement with values in the range of 0.97 ≤ r ≤ 0.99 , and values of root mean square percent deviation of 3.2 % ≤ e ≤ 16.8 % . The system achieved its best performance in November with a daily yield of 4.06 kg/m 2 and a mean efficiency of 33.7%. The upper basin contributed an average of 52% of the total yield with a greater percentage of its yield occurring during the nocturnal phase. The effects of the upper basin and the PCM on the diurnal performance of the system were evaluated.

Annual thermal performance analysis and economic assessment of an evacuated tube coupled solar still for Indian climatic conditions.

In this experimental study, the annual performance and economic analysis of an evacuated tube augmented solar still is presented from June 2020 to May 2021. The experiments are also performed simultaneously on a conventional still as well. The experiments are performed throughout the year at 6cm water depth for both solar stills in the climate of Kurukshetra City, India. The main output parameters, namely, maximum daily water output, maximum hourly water output, thermal efficiency, and maximum basin water temperature have been taken into account and represented in this study. In addition, thermal analysis for both solar stills is performed in this study. The results from experimentation showed 149% improvement in the daily freshwater output from the modified still in comparison to the conventional still. Also, an increase of 1.7% in overall thermal efficiency is achieved for the modified still in comparison to the conventional still. The maximum still performance is achieved in the month of June 2020. In the economic analysis, the cost of water obtained per litre after distillation is $0.0098 for a conventional still and $0.022 in the case of a modified still.

Performance of multi-stage tubular solar still operating under vacuum

Multi-stage solar desalination running under vacuum is a low-cost, effective and sustainable way to mitigate fresh water shortage. However, questions remain on the operation pressure (Pop) and stage number of the multi-stage solar still. To address these questions, a predictive model was developed for the yield of multi-stage tubular solar still under vacuum (MSSV) and validated against field experiments. A 3-stage tubular still under typical weather (i.e. 19.75 MJ/m2 cumulative solar radiation) produced maximum water yield (7.15 kg/m2) with optimal Pop (48 kPa), much higher than under normal (5.81 kg/m2) and lower pressure (1.58 kg/m2 with Pop=20kPa). At optimal Pop, a delicate balance exists between the energy adsorbed and dissipated. Stronger solar intensity leads to more water yield and higher optimal Pop, while increasing the stage number improved the fresh water yield with diminishing marginal effect and slightly shifted the optimal Pop to a lower value. Using water immersion cooling other than air cooling significantly increased the water yield from 7.15 kg/m2 to 10.51 kg/m2. The MSSV model enriched the fundamental understanding of energy utilization for solar desalination and could serve as a design tool to maximize the performance of multi-stage solar still by optimizing still parameters and geometry.

Environmental and embodied analysis of partial shading pyramid solar still.

The novelty of this research is shading position in the transparent cover of partially shaded pyramid solar still. The square pyramid transparent cover is used as top cover of partially shaded pyramid solar still. The square pyramid has four sides and each side named as per the direction. Each one of the sides is shaded in the square pyramid transparent cover. The single side or direction shaded is known as 25% of shading in the transparent cover. Similarly, two sides are 50%, and three sides are 75%. Totally, fourteen configurations of experiments are conducted in the partially shaded pyramid solar still for improving the freshwater yield. Fifty per cent of shading in the transparent cover produced higher freshwater yield compared to 25 and 75%. The partial shading increased productivity of freshwater yield by reducing 4°C of transparent cover temperature compared to conventional pyramid solar still. The north and south direction shaded (50% of shading) produced 4% higher freshwater yield compared to conventional pyramid solar still. The embodied analysis is studied for partially shaded pyramid solar still. The lifecycle conversation efficiency is around 38%, and CO2 mitigation is 34.1 for 50% shading of partially shaded pyramid solar still.

Concentrator-assisted solar still for improving freshwater yield: an experimental approach.

The present experimental study aims to make advancements in the daily production of freshwater by a single solar still, with the ultimate goal of increasing its efficiency. The experiment was carried out in the solar still with and without integration at four different water masses within the basin, and metrics such as water, glass, basin temperature, and drinkable water generated were measured. The results showed that the daily distillate collected from the integrated system using 2.5kg/h of mass flow in the parabolic concentrator produced 2.99kg at the minimum water mass of 20kg placed in the basin. When the flow velocity of water in the parabolic concentrator is raised from 2.5 to 5kg/h, the amount of freshwater generated decreases from 2.99 to 2.66kg. Compared to traditional single slope solar still, the potable water generated increases by roughly 18.24, 18.29, and 18.33% for water mass of 30, 40, and 50kg, respectively, with the mass flow rate of water in the serpentine tubes as 2.5kg/h. The results also reveals that, in addition to the PTC collector, the mass flowrate of fluid in the serpentine tube arrangement submerged in the basin affects daily solar efficiency. There is a significant reduction of about 1-2.3% in the daily efficiency of the system with increased mass flow rate of fluid in the serpentine tube arrangement. Similarly, the daily efficiency in all the cases reduces with increased water depth.

Effect of energy storage material on a triangular pyramid solar still operating with constant water depth

In the current study, the impact of energy storage material on triangular pyramid solar still operating under constant water depth is investigated in an experimental setting. Experiments were carried out in a pyramidal solar still with various types of energy storage materials to determine their effectiveness. To increase the amount of freshwater that can be obtained from the solar still, materials such as quartz rock, mild steel, and sieved red bricks were utilized as a part of the construction of the basin material. The conventional correlation method was used to calculate the evaporative and convective heat transfer coefficients based on experimental data. It is dependent on the kind of material utilized within the basin for efficient energy storage as well as the depth of water maintained whether or not the output of fresh water improves. As a result of using 1 1/4” red bricks within the basin rather than a typical solar still, the results indicate that the utilization of thermal energy storage inside the basin increased the output of fresh water by 30 %. Additionally, the yield of fresh water obtained was found to be 3.5, 4, 4.3, and 4.2 for 14-inch quartz rock, 3/4-inch quartz rock, 1-1/4-inch red bricks, and mild steel scraps, while the yield of fresh water obtained was found to be 3.5, 4, 4.3, and 4.2 Litres/day.

Investigation on an underwater solar concentrating photovoltaic-membrane distillation (CPV-MD) integrated system

This paper presents an underwater solar concentrating photovoltaic-membrane distillation (CPV-MD) integrated system for regions of coastal cities and islands where land resources are insufficient and suffer from critical shortages in electricity and freshwater. A deformable solar concentrator that works underwater is innovatively designed and matched with the photovoltaic-membrane distillation module. Given its application scenario, the integrated system is designed without metallic components to prevent seawater corrosion. The concentrator's optical characteristics are revealed via optical simulations. The results illustrate that the concentrator bears optimal optical performance when its elastic membrane's deformation ratio α is 0.25 and height ratio γ is 0.35. An experimental setup with a solar cell radius of 50 mm is developed and tested in actual weather to reveal its electricity and freshwater yield performance. It is found that the integrated system exhibits similar performance under the light incident angle of 0°and 10°. Additionally, for the experiment with average solar radiation of 514 W/m2, the integrated system's output power varies between 1.53 W and 1.0 W, with an average electrical efficiency of 3.16 %. The accumulated freshwater yield is 67.8 g, with an average water yield efficiency of 28.5 %. This work may provide a new perspective on underwater solar energy utilization.

Performance analysis of tubular solar still with different water depths on corrugated and flat absorbers

Abstract One of the biggest impediments in solar distillation is the lower fresh water yield. In the present study, the effect of water depth on the thermal performance of tubular solar still (TSS) with v-corrugated and flat absorbers has been analyzed experimentally and optimized using the response surface methodology (RSM) technique. Experimental results showed that the water temperature of TSS using a v-corrugated absorber is improved by increasing the surface area of water. The peak temperature of water from the TSS using corrugated fins is improved by about 7.54, 7.12, and 3.77% than the TSS with a flat absorber for water depths of 5, 10, and 15 mm, respectively. The average temperature difference between water and cover is improved by about 53.19, 64.28, and 112.90% for water depths of 5, 10, and 15 mm using the TSS with a corrugated absorber rather than a flat absorber. The influence of water depth on cumulative yield using 5, 10, and 15 mm in the v-corrugated absorber is recorded as 4.35, 3.86, and 3.83 kg, and it is higher by about 108.13, 128.40, and 216.52% compared to the cumulative yield of TSS with a flat absorber, respectively.

Solar energy desalination distillate yield and cost evolution, and statistical relationship between meteorological variables and distillate yield

In this paper, a hybrid solar desalination system was fabricated and incorporated with a water heater powered by a photovoltaic (PV) system. It was experimentally evaluated at Universiti Teknologi Petronas, Malaysia. Daytime operating conditions without the use of a PV system were considered for the conventional operation, while the use of PV alone or combined with direct solar radiation was considered as the modified system. This study was carried out to determine the freshwater yield, weather variabilities impact on yield, economic analysis, and system efficiency of hybrid solar desalination systems. An encyclopaedic review of five years of different researchers from different countries was critically analysed and compared with this study to see their trends and relationship. Within the study period, solar still distillate cost ranges from 0.0051 to 0.8857$/L, and 0.006 to 0.789$/L for the modified and conventional systems respectively. Similarly, the distillate cost for this study is 0.0374$/L and 0.0892$/L for the conventional and modified systems respectively. Also, the distillate yield ranges from 0.93 to 24.3 L/m2.day with an average of 12.1 L/m2.day, for the modified system, and 0.55 to 6.63 L/m2.day with an average of 3.35 L/m2.day for the conventional systems. The hourly system efficiency is 30.07 %, and 8.29 % for the modified and conventional systems respectively. Solar still is economically reasonable with good efficiency as obtained from the result. The findings also suggested that researchers should target a distillate yield of at least 6 L/m2.day and a distillate cost of 0.2$/L or lower for innovation, for a good and economical system.

The Effect of Geometry on the Yield of Fresh Water from Single Slope Solar Stills

When examining the research literature relating to single slope solar stills it is apparent that much of the work has been conducted in an ad-hoc manner. This has led to several recommendations relating to the geometry of stills having developed that do not appear to have a sufficient evidentiary basis. To address this issue, this study used computational fluid dynamics simulations to examine the natural convection in single slope solar stills with cover angles between 0° and 60° and aspect ratios ranging from 1 to 8, with the results validated experimentally. Treating cover angle and aspect ratio as independent design variables showed that there are some features of the natural convection flow that account for the variation in yields reported in the literature (transitions between uni- and multi-cellular flow). More specifically, it was shown that the geometric effects could be correlated in the form of a generalized relationship and that this was able to predict the yield from several independent solar stills reported in the literature. As such, the use of the relationship will allow single slope solar stills designers to predict their yield far more accurately than is currently possible.

Experimental research on the operation characteristics of solar chimney power plant combined with distillation (SCPPCD)

In this paper, a comprehensive test platform for solar chimney power plant combined with distillation (SCPPCD) that can realize water-electricity cogeneration was designed and built. Experimental research on SCPPCD was carried out under actual meteorological conditions to explore the system operation performance and the laws of freshwater production and power generation. The interaction mechanism between parameters such as seawater temperature, airflow temperature, temperature difference between seawater and solar still cover, freshwater yield and generated power was revealed. The results show that the daily water yield of solar stills decreases from the heat collector inlet to the chimney. Solar stills are recommended to be arranged in the area from collector inlet to the one-third radius of the collector. The high-water yield period occurs between sunset and 1–3 a.m., and it contributes most of the freshwater produced. Temperature difference is the main factor affecting water production during the rising period of freshwater production, and seawater temperature is the main factor affecting freshwater production during the decline period. The maximum temperature rise of airflow in the chimney is 17 ℃, and the temperature rise is maintained above 5 ℃ at night. The variation of generator power is similar to that of airflow temperature rise, and the maximum power reaches 0.71 mW. This study provides detailed experimental data and theoretical reference for future mathematical simulation research and commercial application of SCPPCD.