Silica Gel Water Research Articles

Interfacial Structure and Evolution of the Water–Silica Gel System by Reactive Force-Field-Based Molecular Dynamics Simulations

Nanoporous silica gel structures and associated interfaces formed on the surface of silicate and borosilicate glasses play an important role in understanding the dissolution mechanisms of these glasses. Interfacial models that consist of bulk silica, nanoporous hydrated silica gel, and bulk water were constructed and their evolution was studied to understand the water–glass reaction fronts using the Reactive Force Field (ReaxFF)-based molecular dynamics simulations. The short- and medium-range structures of the gel and the interfaces as well as water diffusion and silica dissolution behaviors were studied in detail. It was found that the gel region exhibited an increase in Si–O network connectivity with time, consistent with recent NMR results, due to cross-linking of siloxane bonds in the gel and the dissolution of less connected [SiO4] groups into the water region. Higher network connectivity of the silica gel can regulate transport of ions and plays the role of passivation. Dissolved silica clusters in...

Enhancement efficiency of organic Rankine cycle by using sorption system

This paper focuses a method to enhance an organic Rankine cycle (ORC) efficiency by using the sorption systems (absorption and adsorption) for reducing the ORC condenser temperature. Energy efficiency, exergy efficiency and levelized electricity cost (LEC) are used to evaluate the optimal combined unit. Testing data from a 25kWe R-245fa ORC prototype, a 1 TR water-LiBr absorption chiller and a 1 TR water-silica gel adsorption refrigeration are tested and analyzed performance curve of each technology to predict thermal performance of the ORC-sorption units at various operating conditions. Projection of the integrating unit of the ORC and sorption systems represent the better energy and exergy efficiencies, when the ORC condenser temperature is decreased. The ORC-absorption efficiencies in terms of energy and exergy increase 7.22%, while the ORC-adsorption system improve 12.46% compared with the normal ORC efficiencies. In economic impact, the LEC of the normal ORC unit is 0.1145USD/kWh, which is higher than the ORC-absorption unit and the ORC-adsorption unit of 0.1088USD/kWh and 0.1043USD/kWh, respectively, at chilled water temperature output the absorption system at 7°C. Thus, it could be concluded that the ORC-adsorption system is the optimal technique to enhance the ORC electricity generation process in terms of energy efficiency, exergy efficiency and electricity cost.

Preparation of biodiesel by three step method followed purification by various silica sources

The preparation of biodiesel by three step transesterification three-step method consists of Saponification followed by acidification to produce KOME (Karanja Oil Methyl Ester)and finally esterification of KOME to produce biodiesel.The objective of this research is the comparison among different adsorbents such as Ludox (Colloidal Silicate) and Fumed silica which were used for the purification of biodiesel. Used adsorbents werereused again as adsorbents for the removal of glycerin from biodiesel and evaluate the effectiveness of biodiesel purity. Furthermore, this study compared the results of distilled water washing also. It was observed that Ludox, fumed silica gel and distilled water produced yield about 93%, 91% and 83% respectively. Highest yield was obtained with Ludox at 100°C temperature with H3PO4 as acid catalyst and NaOH as base catalyst with methanol, (3:1) alcohol to oil molar ratio in 90 min.

Performance comparison of a silica gel-water and activated carbon-methanol two beds adsorption chillers

The aim of the study is to compare the efficiency of adsorption refrigerating equipment working with different working pairs. Adsorption cooling devices can operate with a relatively low temperature of heat sources while consuming only a small amount of electricity for the operation of auxiliary equipment. Refrigerants used in adsorption devices are substances that do not have a negative impact on the environment. All that makes that adsorption refrigeration seems to be a good solution for utilizing renewable and waste heat sources for cold production. To carry out the experiment the adsorption cooling device has been developed and researched in Institute of Heat Engineering at Warsaw University of Technology. The test bench consisted of two cylindrical adsorbers, condenser, evaporator, oil heater and two oil coolers. In order to perform the correct action it has been developed and implemented special control algorithm device, allowed to keep the temperature in the evaporator at a preset level. The unit tested for two sorption pairs: activated carbon – methanol, and silica gel – water. For activated carbon - methanol working pair it was obtained energy efficiency rating (EER) equals to 0.14 and specific cooling power (SPC) of 16 W/kg. For silica gel - water EER of refrigeration unit was 0.25 and SPC was equal to 208 W/kg.

Design optimization of a residential scale solar driven adsorption cooling system in upper Egypt based

This study provides a decision support approach for selecting the best size of the main components of a small scale solar assisted, silica gel-water, adsorption cooling system in arid areas located in Assiut, Egypt. To achieve the objective of this work, an optimization based on a computer simulation has been performed on the design variables, which are: solar collector area, the volume of the hot storage tank, the volume of the cold storage tank, and thermostat set point of the auxiliary heating element. Economic and environmental evaluations of the proposed systems have been performed as well. A validation of the model results is performed with the experimental results of solar driven silica gel-water adsorption cooling system at Assiut University Campus which has worked since 2012. The results show that the tilt angle of 5° for the surface of the solar collectors achieved the best absorbed solar radiation by the collector filed. For all proposed systems, the solar fraction did not affect the volume of the cold water storage tank while it has a significant effect on the area of the solar collector field and as well as the volume of the hot water storage tank. The initial cost of the proposed systems ranges from 2897€/kWc to 4808€/kWc and this can be considered as a hindrance to spreading at the commercial level. Meanwhile, the running cost over a year achieves low values, and it ranges from 13.9€/kWc to 99.11€/kWc.The proposed systems of lower solar fraction give lower carbon dioxide emissions. The carbon dioxide emissions range from193kg of CO2eq./kWc per year for the fully solar driven cooling system to 1062kg of CO2eq./kWc per year for the cooling system fully driven by natural gas. Based on the solar saving approach the proposed system of 24m2 solar collector area, 0.6m3 hot storage tank, and 1m3 cold storage tank with 94°C auxiliary heater set-point temperature can be considered as the most economically feasible solution.

The effect of fin design parameters on the heat transfer enhancement in the adsorbent bed of a thermal wave cycle

A 2D coupled heat and mass transfer model is used to analyze both finless and finned tube-type adsorbent bed for a thermal wave adsorption cooling cycle. A comparison between the finless and finned tube adsorbent beds is made in terms of heat transfer inside the bed. A significant enhancement in the heat transfer is obtained using a finned tube such that the temperature of the adsorbent in the finned tube adsorbent bed is at most 47.8K higher than that in the unfinned tube adsorbent bed. The effect of fin design parameters on the heat transfer inside the bed is also investigated using four different fin configurations. Defining a base-case for the fin geometry, fin thickness, fin radius and number of fins are increased. Increasing the fin thickness double increases temperatures only by 2–3K and has not a significant effect on the heat transfer. Increasing the fin radius decreases temperatures by 10–17K while increasing the number of fins enhances the heat transfer significantly. Results are presented in multicoloured plots in 2D domains. The working pair used in the simulations is white silica gel–water.

Study of a two-bed silica gel–water adsorption chiller: performance analysis

ABSTRACTIn this study, a lumped parameter simulation model has been developed for analysis of the thermal performance of a single-stage two-bed adsorption chiller. Since silica gel has low regeneration temperature and water has high latent heat of vaporisation, silica gel–water pair has been chosen as the working pair of the adsorption chiller. Low-grade waste heat or solar heat at around 70–80°C can be used to run this adsorption chiller. In this model, the effects of operating parameters on the performance of the chiller have been studied. The simulated results show that the cooling capacity of the chiller has an optimum value of 5.95 kW for a cycle time of 1600 s with the hot, cooling, and chilled water inlet temperatures at 85°C, 25°C, and 14°C, respectively. The present model can be utilised to investigate and optimise adsorption chillers.

Experimental investigation of a solar adsorption refrigeration system working with silicagel/water pair: A case study for Bou-Ismail solar data

The objective of the present work is to build and test a solar adsorption refrigeration device with an adsorbent–adsorbate silicagel–water pair in the weather conditions of Bou-Ismail, Algeria. The refrigeration system proposed in this study consists of three major components: a solar collector (tubular adsorbent bed, reflecting surface, single glazed cover, and 4.5kg of silicagel material), an air-cooled condenser, an evaporator and supplementary system components. The working operation parameters of the cooling adsorption system were tested successfully. Experimental results indicated that the maximum temperature generated varied from 95°C to 117°C, 33°C of average ambient temperature, the condensing temperature varied from 45°C to 53°C, +5°C of minimum evaporator temperature, and the pressure values recorded in the adsorbent bed during the heating desorption period varied from 80 to 100mbar. With a total energy received of around 19MJ/m2, this solar adsorption refrigeration device can provide a solar COP ranging from 0.083 to 0.09. Such results show the practicability of our solar adsorption refrigeration module and that it has a favorable design for use in medical storage in areas without an electrical network (e.g. the Algeria Sahara region).

A study of a wind catcher assisted adsorption cooling channel for natural cooling of a 2-storey building

This study proposes a new system composing of a wind catcher and a solar driven two-bed silica gel–water adsorption chiller in order to provide natural cooling of a two-story building. The wind catcher provides the required ventilation, and the air flowing though the wind catcher is cooled by the cooling plates fed by the adsorption chiller. The performance of the system is studied theoretically under different ambient conditions such as wind velocity, solar radiation, air temperature and relative humidity. In addition, the influence of geometric parameters such as size of the apertures, wind catcher's height and dimensions of the cooling plates and the number of them are studied. Furthermore, the system's capability to provide thermal comfort in the living space is investigated. It is found that at lower ACH (air change per hour) values, inlet air's temperature and absolute humidity reduce more. In addition, with the rise of the cooling plates' length, the cooling effect increases. The results indicated that with the increase of ACH values, thermal comfort condition is achieved for larger cooling demands. Furthermore, the system was found to be able to cool the air between 10 and 20 °C under different ambient conditions.

Solar driven air conditioning and refrigeration systems corresponding to various heating source temperatures

Solar driven air conditioning systems can cope with solar collectors working in a wide range of temperatures. Sorption systems, including absorption and adsorption refrigeration systems, are among the best choices for solar cooling. Five systems including modular silica gel–water adsorption chiller, single/double effect LiBr–water absorption chiller, 1.n effect LiBr–water absorption chiller, CaCl2/AC (activated carbon)–ammonia adsorption refrigerator, and the water–ammonia absorption ice maker with better internal heat recovery were presented. The above five sorption chillers/refrigerators work under various driven temperatures and fulfill different refrigeration demands. The thermodynamic design and system development of the systems were shown. All these systems have improvements in comparison with existing systems and may offer good options for high efficient solar cooling in the near future.

表面修飾シリカゲルにおける重金属イオンの分配・放出過程の解析

Distribution and release processes of heavy-metal ions between spherical surface-modified silica gel microparticles and water were analyzed by microcapillary manipulation and absorption microspectroscopy. Silica gel modified with triamine (QuadraSil-TA, Q-TA) or thiol groups (QuadraSil-MP, Q-MP) was used as a surface-modified silica gel. A single microparticle was injected into an aqueous HAuCl4 or CuSO4 solution containing 0.01 M KCl (pH = 6), and the distribution rate of the metal ion from water into the microparticle was measured. The rate of release of Au(III) or Cu(II) from Q-TA into water (pH = 6) was much smaller than that of the distribution of the metal. The microparticle radius dependence of the absorbance of the metal in the microparticle and distribution of the metal by cross-sectional SEM-EDS analysis at the distribution equilibrium indicate that Au(III) and Cu(II) distribute into the microparticle interior for Q-TA, while Au(III) distributes at the outer layer in the spherical microparticle for Q-MP. The distribution processes were analyzed as the intraparticle diffusion, and the diffusion coefficient (Dp) observed in the present systems was compared with that calculated from the theoretical pore and surface diffusion model. We consider that the rate-determining step of the distribution of Au(III) in the Q-TA (pore diameter = 5.9 nm) system is the intraparticle diffusion of AuCl4−. On the other hand, the distribution of Cu(II) into Q-TA was much slower than the intraparticle diffusion.

Cycle Optimization on Reheat Adsorption Cycle Applying Fixed Chilled Water Outlet Temperature

This study investigated the cycle optimization of four-bed, silica gel–water adsorption with reheat cycle, where the desorber (upper bed) and adsorber (lower bed) always interact with the condenser and evaporator, to exploit a low heat-source temperature. In a previous study, the performance of a reheat cycle with chilled water outlet temperature fixed at 9°C was observed without considering the cycle optimization. Maintaining a constant chilled water outlet temperature is also of equal importance to improve the conversion efficiency so that maximum cooling capacity can be derived. In this paper, a simulation model of reheat adsorption cycles is developed to analyze the optimization of the cycle time, including adsorption/desorption time, mass recovery time, and preheating/precooling time, with chilled water outlet temperature fixed. The reheat working principle is also introduced. The proposed cycle is compared with the four-bed versison without reheat cycle in terms of coefficient of performance (COP) and cooling capacity. The result shows that the performance of a reheat cycle is superior to that of four-bed version without reheat, especially for low heat-source temperature. For low heat-source temperature (55–65°C) both COP and cooling capacity of the reheat cycle with optimization were raised significantly compared to the high heat-source temperature (70–80°C).

Fundamental and application aspects of adsorption cooling and desalination

Adsorption (AD) cycle is recently pioneered for cooling and desalination applications. For water treatment, the cycle can be used to treat highly concentrated feed water, ranging from seawater to ground water and to chemically-laden waste water. This paper presents a review of the recent development of AD cycle and its hybridization with known conventional cycles such as the MED and MSF. We begin by looking at the basic sorption theory for different adsorbent–adsorbate pairs, namely (i) silica gel-water, (ii) the zeolite–water, (iii) parent Maxsorb III/ethanol, (iv) KOH-H2 surface treated Maxsorb III/ethanol, and (v) a metal organic framework (MOF) material namely, MIL-101Cr/ethanol.We also present the basic AD cycle for seawater desalination as well as its hybridization with known conventional thermally-driven cycles for efficiency improvement. We demonstrate the water production improvement by 2–3 folds by hybridization in a pilot comprising a 3-stage MED and AD plant and the top-brine temperature 50 °C.

In situ Raman and 13C NMR spectroscopic analysis of gas hydrates formed in confined water: application to natural gas capture

This study investigates the formation characteristics of gas hydrate from bulk water as well as dispersed water in silica gel and dry water particles when they are exposed to natural gas. The inclusion process of methane, ethane, and propane molecules in hydrate cages were observed with in situ Raman spectroscopy, and the resulting cage occupancies were estimated from 13C NMR spectra. A high-pressure autoclave was used to monitor the formation process to determine hydrate onset time, initial growth rate, and conversion ratio. The obtained data from Raman spectra and gas consumption profiles suggested that hydrate formed within less than 20 min when the temperature is sufficiently lower than the hydrate equilibrium condition at a given pressure. Methane molecules started to occupy the small cages of structure II, but about 6 min later ethane and propane were also included in hydrate cages. 13C NMR spectroscopy confirms that only 23% of large cages of structure II are occupied by methane molecules when hydrate formed from dispersed water in silica gel, which was much less than 68% from dry water. These results suggest that the dispersion of water in silica gel and dry water would enhance the formation process by increasing gas-to-water ratio, although the composition of hydrate phase may vary depending on the formation condition. However the formation of hydrate in silica gel and dry water still provide an effective option to capture the natural gas without using complex rotating machineries.

Study of Solar Driven Silica gel-Water based Adsorption Chiller

In this study, a dynamic behaviour of a solar powered single stage four bed adsorption chiller has been analysed designed for Malaysian climate. Silica gel and water have been used as adsorbent-refrigerant pair. A simulation program has been developed for modeling and performance evaluation of the chiller using the meteorological data of Kuala Lumpur. The optimum cooling capacity and coefficient of performance (COP) are calculated in terms of adsorption/desorption cycle time and regeneration temperature. Results indicate that the chiller is feasible even when low temperature heat source is available. Results also show that the adsorption cycle can achieve a cooling capacity of 14 kW when the heat source temperature is about 85°C.

Continuous vapour adsorption cooling system with three adsorber beds

In this paper, the design of a new solar operated adsorption cooling system with two identical small and one large adsorber beds, which is capable of producing cold continuously, has been proposed. In this system, cold energy is stored in the form of refrigerant in a separate refrigerant storage tank at ambient temperature. Silica gel–water is used as a working pair and system is driven by solar energy. The operating principle is described in details and its thermodynamic transient analysis is presented. Effect of COP and SCE for different adsorbent mass and adsorption/desorption time of smaller beds are discussed. Recommended mass and number of cycles of operation for smaller beds to attain continuous cooling with average COP and SCE of 0.63 and 337.5 kJ/kg, respectively are also discussed, at a generation, condenser and evaporator temperatures of 368 K, 303 K and 283 K, respectively.

Transient behavior of a cylindrical adsorbent bed during the adsorption process

A transient two dimensional local thermal non-equilibrium model is developed to investigate the influences of heat transfer and operating parameters on the dynamic behavior of a cylindrical adsorbent bed during the adsorption process. Local volume averaging method is used to drive the macro scale governing conservation equations from the micro scale ones. In the model, linear driving force model and Darcy’s equation are considered to account for the resistances to internal and external mass transfer, respectively. Silica gel–water pair widely used in the adsorption cooling systems is chosen to be an adsorbent–adsorbate working pair. The parameters of interest are convective heat transfer coefficient, solid phase thermal conductivity, bed thickness, evaporator pressure, condenser pressure, driving heat source temperature and cooling source temperature. It is found that amount of refrigerant circulated through the system increases with increasing evaporator pressure-driving heat source temperature and decreasing condenser pressure-cooling source temperature. The duration of adsorption process is more sensitive to heat transfer resistances than to mass transfer resistances. The conductive and convective resistances need to be reduced to reach the equilibrium conditions in a short period of time and hence to have a better specific cooling power.

Performance Analysis of Four Types of Adsorbent Beds in a Double-Adsorber Adsorption Refrigerator

Four advanced types of adsorbent beds were designed, investigated and compared to each other in a double-adsorber adsorption refrigerator. The four types of adsorbent beds were assembled by several vehicle radiators with two different sizes. A prototype of the adsorption refrigerator built up in our laboratory was used to test the performances of the adsorbent beds. Silica gel-water was used as the working pair. The length, width and thickness of the radiators were measured. The amount of adsorbent filled into these four types of adsorbent beds was recorded. The dead area volume was estimated. The coefficient of performance (COP) and specific cooling power (SCP) of the system were tested after utilizing the four types of adsorbent beds. The COP and SCP of the four types of adsorbent beds were estimated under the standard operating condition and optimized operating condition. A SCP and a COP of the small-radiator adsorbent beds with 198.4W/kg and 0.30 were achieved under the optimized operating condition with 480 s adsorption/desorption time, 90 s heat and mass recovery time, 9 L/min hot water and cooling water flow rate, 2 L/min chilled water flow rate, 16°C chilled water inlet temperature, 90°C hot water and 25°C cooling water. Under the standard operating condition, the result showed that smaller dead volume leads to a slightly higher SCP. The adsorbent bed with smaller size radiator had a better heat and mass transfer ability and a higher SCP and COP could be achieved.

Оценка влагоемкости силикагеля для обеспечения безопасной эксплуатации пневматических систем

An analysis of main methods for silica gel water capacity determining has been presented. A new method of silica gel water
 capacity’s experimental evaluation in pneumatic systems’ operating conditions has been developed. Bases of fundamental
 method for constant humidity assurance of compressed air used for silica gel water capacity evaluations have been
 revealed. A description of a test bench for this fundamental method practical realization has been presented. A technique
 for experimentation with proposed method’s different modifications has been described. Measurement error estimation
 has been performed. Experimental results of finely porous silica gel water capacity evaluation in static conditions and in
 absorption process’s different parameters while using this method have been presented. These results’ correlation between
 similar data obtained by other methods has been carried out. Analyses results’ statistical processing has been carried out
 and it has been shown that a packed density of finely porous silica gel can be considered only as the indirect and qualitative
 characteristic of its water capacity which isn´t allowing to provide the necessary accuracy of quantitative estimates for
 pneumatic systems’ operation safety assurance.

Experimental performance investigation of small solar air-conditioning systems with different kinds of collectors and chillers

Different types of solar collectors should be integrated with different sorption chillers. Traditional evacuated tube U pipe solar collector, high efficient CPC (Compound Parabolic Concentrating) solar collector and PTC (Parabolic Trough Collector) solar collector can provide 60–85°C, 85–125°C and 125–150°C of hot water. So, they can drive silica gel–water adsorption chillers, single-effect LiBr absorption chillers and double-effect LiBr absorption chillers, respectively. This paper will present the experimental performance investigation and economic analysis of three small solar cooling systems with these different kinds of collectors and chillers. The test results show that the solar COP (Coefficient of Performance) of the solar cooling system with adsorption chiller and U pipe solar collectors is about 0.15 and the silica gel–water adsorption chiller can be driven by 55°C of hot water. The solar COP of the system with CPC solar collector and single effect absorption chiller can reach 0.24 in the sunny weather condition. The solar COP of the solar cooling system with PTC solar collectors is about 0.5 and the double-effect LiBr absorption chiller is more attractive because of its higher solar COP (Coefficient of Performance) and better economy.