Desalination has been increasingly adopted over the last decades as an option, and sometimes as a necessity to overcome water shortages in many areas around the world. Today, several thermal and physical separation technologies are well established in large scale production for domestic and industrial purposes.  Membrane distillation is a novel thermally-driven process that can be adapted effectively for water desalination or water treatment in industrial applications, due to its potential lower energy consumption and simplicity. The general objective of this thesis is to contribute to the technical understanding of membrane distillation as a new technology in water treatment for both industrial and drinking water purposes, as a starting point for further improvement. The thesis includes experimental and numerical investigations that highlight some aspects of the technology application and fundamental aspects. In the field of industrial application, an experimental and numerical assessment has been carried out on an Air Gap Membrane Distillation (AGMD) prototype to assess the utilization of the technology in thermal cogeneration plants; in particular, demineralization of water boiler feed water and treating flue gas condensate. The main assessment parameters were water quality and energy consumption. The results from full-scale simulations of a system of 10 m3/hr production capacity,  connected to the district heating network were as follows: 5 to 12 kWh/m3 specific thermal energy consumption, and  0,6 to 1,5 kWh/m3 specific electricity consumption, depending upon the heat source (district heat supply line or low-grade steam). For desalination applications, experimental and simulation work was conducted on an AGMD semi-commercial system as part of the EU MEDESOL project. The aim was to evaluate AGMD performance with saline water of 35 g/l NaCl in order to establish an operation data base for simulation of a three-stage AGMD desalination system. Specific thermal energy consumption was calculated as 950 kWht/m3 for a layout without heat recovery, and 850 kWht/m3 for a layout with one stage heat recovery.  The lack of internal heat recovery in the current MD module means that most of the heat supplied to MD system was not utilized efficiently, so the thermal energy consumption is high. This would mean that a large solar field is needed. In order to analyze the flow conditions in feed flow and cooling channels, CFD was used as tool to analyze a spacer-obstructed flow channel for different types of spacer geometrical characteristics: flow of attack angle, spacer to channel thickness ratio, and void ratio. Velocity profiles, shear stress, and pressure drop were the main assessment criteria. Results show the flow of attack angle has a very minimum effect on the performance of spacers. The effect of spacer to channel thickness ratio was significant in all assessment parameters. Higher void ratios were found advantageous in promoting flow mixing, but resulted in lower sheer stress and hence reduced heat transfer. Physical modifications were implemented on a semi-commercial AGMD prototype to assess experimentally any improvement in its performance. These modifications were mainly focused on reducing the conductive heat transfer losses by modifying the physical support in the air gap that separates the membrane from the condensation surface. In addition, several feed channel spacers were tested and assessed based on their effect in increasing the mass transfer while maintaining or reducing pressure drop. The modifications yielded a two-fold augmentation: slight increase in the distillate mass flow rate (9-11%), and increased thermal efficiency (6%). The pressure drop in the module was reduced by 50% through selecting the appropriate spacer that would achieve the above mass flow rate increase. / QC 20111021

Water stress is an ongoing problem in many places in the world, while the demand for clean and safe freshwater is growing due to the increasing population. In many developing countries, water supplies often are contaminated with arsenic, fluoride, etc. Therefore, it is important to realize that water scarcity and contamination issues concern only one sector but many. HVR Water Purification AB is developing a water purification prototype – ELIXIR 500 - using the air gap membrane technology and is implemented in Odisha, India, aiming to supply with 200 litre water daily. This thesis aims to estimate future energy sources to supply this prototype and explore the possibilities of using only renewable energy resources from technical, economic, and environmental perspectives. These are achieved by firstly identifying the energy possibilities in Odisha, India, and then calculating the feasibility of each solution chosen and finally analyzing the results. Among the energy sources, which are power grid, wind and solar power, diesel generator and solar-diesel hybrid system. It is found that the energy source to the prototype supplied by the power grid is 0.057 USD per litre water, which is the cheapest option. However, it is not feasible due to the lack of electrification from the local network. Meanwhile, the solar-diesel hybridized energy system is the most economical option if renewable energy sources are integrated with 0.11 USD per litre water. / Vattenstress ett pågående problem på många ställen i världen medan efterfrågan på rent och säkert dricksvatten växer på grund av den ökande befolkningen. I många utvecklingsländer är vattenförsörjningen ofta förorenade med arsenik, fluor osv. Det är därför viktigt att inse att vattenbrist och föroreningar inte bara rör en sektor utan många. HVR Water Purification AB utvecklade en prototyp för vattenrening - ELIXIR 500 - med hjälp av luftspaltmembrantekniken (eng: air gap membrane distillation och implementeras redan i Odisha, Indien, med målet att förse 200 liter rent vatten dagligt. Denna avhandling syftar till att uppskatta de framtida energikällorna för att tillhandahålla denna prototyp och utforska möjligheterna att endast använda förnybara energikällor ur tekniska, ekonomiska och miljömässiga perspektiv. Dessa uppnås genom att först identifiera de olika energimöjligheter i Odisha, Indien, följt av beräkningar om utförbarhet för varje vald lösning och slutligen en analys av resultaten. Bland energikällorna elnät, vind, sol, diesel generator och sol-diesel hybrid system har visat sig att energikällan till prototypen som levereras av elnätet som kostar 0.057 USD per liter vatten som det billigaste alternativet, men det är inte möjligt på grund av bristen på elektrifiering från det lokala elnätet. Å andra sidan är det hybridiserade energiskombinationen med solkrafts och diesel det billigaste alternativet om förnybara energikällor ska integreras, resultatet visade att vara 0.11 USD per liter vatten.

Une thermofrigopompe (TFP) est une machine frigorifique qui produit du froid et de la chaleur utiles. L’objectif de ces travaux est de développer le concept de thermofrigopompe pour la production de froid et le dessalement. Le dessalement est réalisé en utilisant la chaleur rejetée au condenseur de la TFP. La technique de dessalement retenue après étude bibliographique est l’AGMD (air gap membrane distillation) pour ses températures de fonctionnement compatibles avec la température de condensation des machines frigorifiques classiques. Ce procédé de distillation a été caractérisé grâce à une installation pilote pour diverses conditions de températures, de débits, d’épaisseurs d’air gap et de compositions de solutions. Une étude de longue durée associée à une observation au MEB a permis évaluer le niveau colmatage des membranes. Un modèle numérique a ensuite été développé à partir des premiers résultats expérimentaux. Des simulations ont permis de dégager des tendances de comportement d’une machine couplée TFPMD. Enfin, un prototype a été construit à partir d’un petit réfrigérateur et d’une cellule d’AGMD fabriquée par impression 3D. Les mesures expérimentales ont permis de valider le concept de TFPMD et d’obtenir de premiers résultats de performance prometteurs. La valorisation de l’énergie thermique perdue par les équipements frigorifiques pour effectuer du dessalement semble donc une solution intéressante au manque d'eau douce qui peut survenir dans de nombreuses régions de la planète. / A heat pump or a refrigerating device produces simultaneously cooling and heating energies. The objective of this research is to develop the concept of heat pump for simultaneous cooling and desalination. Desalination is carried out by recovering the heat rejected by the condenser of the machine. The desalination technique, chosen thanks to the literature review, is AGMD (air gap membrane distillation) because of the compatibility of operating temperatures with the condensing temperature of standard heat pumps. AGMD was characterized using a pilot for different conditions of temperature, flow rate, air gap thickness and solution compositions. A long term study associated to scanning electron microscope images enabled to evaluate the fouling level of the membrane. A numerical model was then developed using the first experimental results. Simulations have revealed patterns of behaviour for a coupled heat pump and AGMD machine. Finally, a prototype was built with a small refrigerator and an AGMD cell manufactured by 3D printing. Experimental measurements were used to validate the concept of heat pump for simultaneous cooling and desalination and to obtain promising performance results. The valorization of the heat lost by refrigeration equipment for desalination seems therefore an interesting solution to overcome the lack of fresh water that can occur in many regions of the planet.

This thesis presents investigations on air-cooled air gap membrane distillation for desalination and the application of radial waveguides based on total internal reflection for solar thermal desalination. Using an air-cooled design for an air gap membrane distillation (AGMD) process may result in significantly lower energy requirements for desalination. Experiments were conducted on AGMD module to study the effect of air gap, support mesh conductivity and hydrophobicity, condensing surface hydrophobicity. A novel modular design was used in which modules could be used in a series configuration to increase the flux value for the distillate. The output from the series configuration was found to have about three times the production from a single pass water-cooled system with the same temperature difference between the saline and clear water streams. The results also indicated that the mesh conductivity had a favorable effect on the flux value whereas the hydrophobicity of the mesh had no significant effect. The hydrophobicity of the condensing surface was favorable on two accounts: first, it led to an increase in the flux of the distillate at temperatures below 60 °C and second, the temperature difference of the saline feed when it enters and leaves the module is lower which can lead to energy savings and higher yields when used in a series configuration. The second part of the thesis considers use of low-cost radial waveguides to collect and concentrate solar energy for use in thermal desalination processes. The optical-waveguide-based solar energy concentrators are based on total internal reflection and minimize/eliminate moving parts, tracking structures and cost. The use of optical waveguides for thermal desalination is explored using an analytical closed-form solution for the coupled optical and thermal transport of solar irradiation through a radial planar waveguide concentrator integrated with a central receiver. The analytical model is verified against and supported by computational optical ray tracing simulations. The effects of various design and operating parameters are systematically investigated on the system performance, which is quantified in terms of net thermal power delivered, aperture area required and collection efficiency. Design constraints like thermal stress, maximum continuous operation temperature and structural constraints have been considered to identify realistic waveguide configurations which are suitable for real world applications. The study provides realistic estimates for the performance achievable with radial planar waveguide concentrator-receiver configuration. In addition to this, a cost analysis has been conducted to determine the preferred design configurations that minimize the cost per unit area of the planar waveguide concentrator coupled to the receiver. Considering applications to thermal desalination which is a low temperature application, optimal design configuration of waveguide concentrator-receiver system is identified that result in the minimum levelized cost of power (LCOP). / Master of Science

Water purification systems have made access to drinking water easier by treating water sources which previously could not be used for drinking. Such systems however require energy and materials to build and operate which means they have environmental impacts. This thesis performs a cradle to grave life cycle assessment of a solar driven HVR water purification system used to treat contaminated groundwater in Odisha, India. The system has three subsystems each with different components – a water purification subsystem that uses an air gap membrane distillation (AGMD) process to purify ground water to produce drinking water, a solar photovoltaic subsystem to provide electricity and a solar thermal subsystem with evacuated tube collectors to provide hot water. The timeframe of the study is 15 years and the chosen functional unit is 590 m3 of drinking water produced over 15 years. The environmental impacts of the system are evaluated using the ReCiPe Midpoint (H) impact assessment method and the life cycle is modelled in the software SimaPro using the Ecoinvent database for inventory data. A comparison is then made between the lifecycle impact of a solar driven HVR water purification system and a grid driven HVR system as well as a water purification system with conventional end of life treatment and a system with state of the art end of life treatment. Along with the lifecycle impact, the levelized cost of water of the water purification system has also been calculated. The results show that within the entire system the solar PV subsystem has the highest impact due to the high electricity consumption during silicon purification for manufacturing the solar panels. The solar thermal subsystem has the next highest impact with the biggest contributor being the manufacturing of glass tubes for the solar collectors. The water purification subsystem has the least impact with the highest share due to use of acetic acid during its use phase for maintenance. The modelling results focus on four impact categories and show the following life cycle impacts - global warming potential : 27 180 kg CO2eq, human carcinogenic toxicity : 2 412 kg 1.4-DCB eq, marine ecotoxicity : 2 662 kg 1.4-DCB eq, freshwater ecotoxicity : 1 967 kg 1.4-DCB eq. The grid operated system shows a lifecycle impact 70 to 170 times higher across these four impact categories compared to the solar driven system. This is due to the high share of fossil fuels in the Indian electricity grid. The state-of-the-art end of life treatment shows a 17% and 22% reduction in freshwater as well as marine ecotoxicity impacts of the system compared to conventional end of life treatment with negligible impacts on global warming and human carcinogenic toxicity. The levelized cost of water calculations show that the system with its current runtime of 6 hours when run using solar energy or the grid is not economically competitive compared to bottled water in India. A sensitivity analysis is then performed to evaluate the sensitivity of lifecycle impact to maintenance frequency and the lifetime of components and the sensitivity of the levelized cost of water to discount rate and the production cost of AGMD modules. The analysis shows that only the lifetime of components has a significant influence on the life cycle impactof the system, the maintenance frequency has a significant impact on freshwater and marine ecotoxicitywhile the discount rate and production cost of AGDM modules has no impact on the levelized cost of water. In conclusion the findings of this thesis agree with the major findings of previous studies done on the topic and adds to the limited knowledge in the literature on the life cycle impact of solar powered AGMD systems. / Vattenreningssystem har gjort förenklat tillgången till dricksvatten genom att behandla vattenkällor som tidigare inte gick att komma åt för att dricka. Sådana system kräver dock energi och material för att bygga och fungera, vilket innebär att de kommer med en miljöbelastning. Detta examensarbete utför en livscykelanalys från vagga till grav av ett vattenreningssystem som används för att behandla förorenat grundvatten i Odisha, Indien. Systemet renar grundvatten genom en destillationsprocess för luftgapmembran och möter sitt elbehov med hjälp av ett solcells-PV-delsystem och varmvattenbehov genom ett solvärmedelsystem med evakuerade rörkollektorer. Den valda funktionsenheten är 590 m3 dricksvatten producerat över 15 år. Systemets miljöpåverkan utvärderas med hjälp av konsekvensbedömningsmetoden ReCiPe Midpoint (H) och livscykeln modelleras i programvaran SimaPro med hjälp av Ecoinvents databas. En jämförelse görs sedan mellan miljöpåverkan från ett solcellsdrivet och ett elnätsdrivet vattenreningssystem och en mellan ett vattenreningssystem med konventionell samttoppmodern avfallshantering. Tillsammans med miljöpåverkan har även den utjämnade kostnaden (LCOW) för vatten i vattenreningssystemet beräknats. Resultaten visar att solcellsdelsystemet har störst miljöpåverkan på grund av den höga elförbrukningen under kiselrening för tillverkning av solpanelerna. Solvärmedelsystemet har den näst högsta påverkan med näst högsta andelen på grund av tillverkningen av glasrör för solfångarna. Delsystemet för vattenrening har minst påverkan varav den högsta andelen kommer från användningen för underhåll av systemet under operationella fas. Modelleringsresultaten fokuserar på fyra påverkanskategorier och visar följande potentiell miljöpåverkan - global uppvärmningspotential: 27 180 kg CO2ekv, mänsklig cancerogen toxicitet: 2 412 kg 1,4-DCB ekv, marin ekotoxicitet: 2 662 kg 1,4-DCB ekv, sötvattensekotoxicitet: 1 967 kg 1,4-DCB ekv. Det nätdrivna systemet visar 70 till 170 g[nger högre stor miljöpåverkan jämfört med det solcellsdrivna systemet i de fyra påverkanskategorierna på grund av den höga andelen fossila bränslen i det indiska elnätet. Medtoppmodern avfallshantering minskat systemets akvatiska och marina ekotoxicitetseffekter med en 10 % jämfört med konventionell avfallshantering och med försumbar påverkan på global uppvärmning och mänsklig cancerogen toxicitet. Den utjämnade kostnaden för vatten visar att när systemet med sin nuvarande drifttid på 6 timmar per dag varken kopplad till solenergi eller elnätet är ekonomiskt konkurrenskraftigt jämfört med vatten på flaska i Indien. En känslighetsanalys utförs sedan på fyra parametrar - underhållsfrekvens, komponenters livslängd, diskonteringsränta och kostnaden för destillationsmodulerna för luftgapmembran för att se deras inverkan på systemets miljöpåverkan och utjämnade vattenkostnader. Analysen visar att endast komponenternas livslängd har en betydande inverkan på systemets livscykelpåverkan, underhållsfrekvensen har en betydande inverkan på sötvatten och marin ekotoxicitet medan diskonteringsräntan och produktionskostnaden för AGDM-moduler inte har någon inverkan på den utjämnade kostnaden för vatten. Sammanfattningsvis kommer resultaten av denna studie att lägga till den begränsade kunskapen i litteraturen om livscykelpåverkan av soldrivna luftgapmembrandestillationssystem.

In this thesis, the potential to purify water utilizing waste heat from a unit which stores thermal energy and converts it to electricity is studied. The unit, called TES.POD, is developed by Azelio AB and is in this thesis used as a heat source to drive an air gap membrane distillation (AGMD) unit developed by Scarab Development AB. Heat from the TES.POD and ambient air temperature constitutes a temperature difference over a membrane used as a driving force to vaporize a part of the water that transfer through the membrane, and later condensates as clean distilled water as the contaminations stays in the hot stream of feed water. An analysis has been conducted to determine quasi-steady performance of the combined system for estimating the amount of purified water that can be supplied when the TES.POD unit is in peak electricity discharge mode. The 26 kW of waste heat accessible from the TES.POD is shown to enable two AGMD-modules producing purified water at a production of 7, 1l/h per unit having the feed water at 50°C and cooling water at 25°C. A correlation between the amount of waste heat and distilled water production is determined, as the TES.POD could be configured to produce less electricity and more waste heat at a higher temperature. The correlation showed that an 9% increase in cooling temperature, lead to an 30% increase in pure water output and a 33% decrease in electricity output. The results show that when implementing the two companies’ units together, a system that both provides electricity and distilled water is obtained. This is a system with a high demand, especially in off-grid areas with lack of both resources but with accessible renewable energy sources. Moreover, by using waste heat to purify water, it can also reduce the production cost compared to cases where conventional energy sources are used. The potential revenue of the production was estimated to 673 790 SEK/year with an implementation cost of 93 861 SEK with yearly operational expenses estimated to 14 080 SEK/year. / I detta arbete undersöks möjligheten att rena vatten med spillvärme från ett system vilket lagrar termisk energi och av den producerar elektricitet, när det behövs. Systemet är utvecklat av Azelio AB och har produktnamnet TES.POD. Vattendestillationen utförs med en så kallad air gap membrane distillation (AGMD) modul, utvecklad av Scarab Development AB. Värmen från TES.POD och omgivningstemperaturen utgör, i AGMD-modulen, en temperaturdifferens vilken i sin tur skapar en partielltryckskillnad över membranet. Denna partielltryckskillnad låter en del av det förorenade vattnet som flödar i AGMD-modulen att förångas och passera genom membranet. Föroreningarna stannar kvar i det strömmande vattnet och ångan kondenserar som renat vatten.  Arbetet visar att de 26kW som finns att tillgå i form av spillvärme är tillräckligt för att driva två AGMD-moduler att producera 7,1 l/h destillerat vatten per modul. Detta är under förutsättningar att det förorenade vattnet är 50°C och kylvattnet är 25°C. I rapporten återfinns också ett samband mellan mängden spillvärme och produktionen av destillerat vatten, eftersom TES.POD kan konfigureras till att producera spillvärme vid en högre temperatur. Sambandet visade på att 9% ökning av spillvärmens temperatur motsvarar 30% ökning i produktionen av destillerat vatten och en minskad elektricitetsproduktion på 33%.  Resultatet visar på att integrationen av dessa två produkter bildar ett system som både producerar rent vatten och elektricitet när så önskas. Detta system har till synes en stor efterfrågan, speciellt i områden utanför fast el- och vattennätverk men med goda förnyelsebara energikällor. Dessutom, eftersom vattendestillationen sker med spillvärme, kan produktionskostnaderna vara lägre än då konventionella energikällor används. Den potentiella inkomsten från produktionen estimeras till 673 790 SEK/year med en inköpskostnad om 93 861 SEK samt årliga omkostnader om 14 080 SEK/year.

See file / Se bif. fil

<div>Thermal desalination of high salinity water resources is crucial for increasing freshwater supply, but efficiency enhancements are badly needed. Nanomaterial enhancements and novel condensation regimes offer enormous potential for improving promising technologies like membrane distillation (MD). In this work, we first examined nanofluids for MD, including the role of nanoscale physics, and model system-level energy efficiency enhancements. Our model included the dominant micro-mixing from Brownian motion in fine particle nanofluids (copper oxide) and the unusually high axial conduction from phonon resonance through Van der Waals interaction in carbon nanotube nanofluids. Carbon nanotubes resulted in a consistent, wide range of improvements; while copper oxide particles showcased diminishing returns after a concentration of 0.7%, where Brownian motion effects reduced. However, the enhancements at higher concentrations from liquid layering around nanoparticles were impractical in MD, since the related high surfactant levels compromised the membrane hydrophobicity and promoted fouling. Dilute solutions of metallic nanofluids can be actively integrated to enhance the performance of MD, whereas stronger nanofluid solutions should be limited to heat exchangers that supply thermal energy to MD systems. We then investigated slippery liquid infused porous surfaces (SLIPS) for enhanced condensation rates in MD. Dropwise condensation heat transfer was modelled considering the effects of the departing, minimum droplet radii and the interfacial thermal resistances. Effective droplet shedding from these surfaces led to an experimental thermal efficiency of 95%. Alternatively, porous condensers with superior wicking properties and conductive heat transfer offered a robust solution to high salinity desalination. We modelled the onset of flooding in porous condensers using Darcy’s law for porous media, including the effects of the condenser permeability and determined the optimal condenser thickness at varying system length scales. The increased active area of condensation resulted in a significant enhancement (96.5%) in permeate production and 31.7% improvement in experimental thermal efficiency. However, porous condensers were only compatible with flat plate module designs limiting their practicality.</div>

<p>The water crisis is increasing with every passing day due to climate change and increase in demand. Different desalination methods have been developed over the years to overcome this shortage of water. Reverse Osmosis is the most widely used desalination technology, but cannot treat many fouling-prone and high salinity water sources. A new desalination technology, Membrane distillation (MD), has the potential to purify wastewater as well as highly saline water up to a very high purity. It is a thermal energy-driven desalination method, which can operate on low temperature waste heat sources from industries, powerplants and renewable sources like solar power. Among the different configurations of MD, Air Gap Membrane Distillation (AGMD) is the most versatile and flexible. However, the issue that all MD technology, including AGMD face, is the low energy efficiency. Different sections of AGMD system have been modified and improved over the years through consistent research to improve its energy efficiency, but one section that is still new and unexplored, and has a very high potential to improve the energy efficiency of AGMD, is the ‘air gap’.</p><p> </p><p> </p><p>The aim of this research is to tap into the potential of the air gap and increase the energy efficiency of the AGMD system. It is known that decreasing the air gap thickness improves the energy efficiency parameter called Gained output ratio (GOR) to a great extent, especially at very small air gap thickness. The minimum gap thickness that maximizes the performance is smaller than the current gap thicknesses used. But it is difficult to attain such smaller air gap thickness (< 2mm) without the constant risk of flooding. Flooding can be prevented, and smaller air gap thickness can be achieved if instead of film wise condensation on the condensing surface, a different condensation flow regime is formed. This study tests different novel condensing surfaces like Slippery liquid infused porous surfaces (SLIPS) and Superhydrophobic surfaces (fabricated with different methods) inside the AGMD system with a goal of attaining smaller air gap thickness and improve the performance of AGMD system for the first time. The performance of these surfaces is compared with plain copper surface as well as with each other. Finally, numerical models are developed using the experimental data for these surfaces.</p><div><div><div> </div> </div> </div>