High Feed Flow Rate Research Articles

Thin hybrid capillary two-phase cooling system

A novel hybrid two-phase cooling system was developed that integrated a mechanically pumped two-phase loop with a capillary-driven two-phase cooling device. The latter cooling mechanism was based on evaporation/boiling from wick structures made by sintering copper particles on the interior surfaces of a copper cold plate. The cold plate provided cooling to two surfaces and each of them included four heaters in series. The novelty of the developed technology was preventing flooding of the evaporator wicks by isolating the evaporation surface from the pumped liquid flow that fed them. This arrangement allowed for a high liquid feed flow rate much greater than would be allowed by a capillary pumped system while maintaining a low thermal resistance at the evaporation surface. Using this approach, the cooling system removed over 850 W with a low pumping power below 1.0 W while using R245fa as the working fluid. The equivalent heat fluxes exceeded 970 W/cm2 over areas less than 0.12 cm2. The measured thermal resistance was as low as 0.09 K-cm2/W. The presented thermal management solution enables an increase in the power of high heat flux electronic devices beyond the state-of-the-art.

Numerical study of desalination by vacuum membrane distillation – Transient three-dimensional analysis

The performance of vacuum membrane distillation (VMD) modules can be optimized through careful selection of design parameters. The present study examines how the addition of cylindrical filaments in the feed channel increases momentum mixing and the overall performance of VMD modules under different operating inlet conditions. Three-dimensional transient Computational Fluid Dynamics (CFD) simulations are conducted using Wall-Adapting Local Eddy-Viscosity (WALE) subgrid-scale Large Eddy Simulation (LES) turbulence model. Local concentration, temperature, and flux are coupled at the membrane surface to predict the rate of water vapor diffused through the membrane by Knudsen and viscous diffusion mechanisms. The predicted and measured vapor flux agrees reasonably well; validating the employed model. The small-scale eddies induced by the presence of spacer filaments promote mixing in the module, thus the temperature and concentration polarization is alleviated and the water vapor flux is immensely improved. The insertions of filaments in the feed channel increase the water permeate rate by more than 50% at higher feed flow rates and inlet temperatures. The pressure drop by the spacer reduces the allowable module length by one order of magnitude, but the module length increases two folds at feed temperature 80°C. Even though the power consumption of the module containing the filaments is increased, the addition of filaments is strongly recommended since the required power for the process could be supplied from readily available low-grade heat source.

Tubular membrane used in continuous and semi-continuous diffusion dialysis

Tubular membrane is firstly developed from the polyvinyl alcohol based casting solution. The membrane is compact with the diameter of 1.27–1.72 cm and the length of 30–60 cm, which is like a piece of “sieve tube” or “blood vessel” from bionic aspect. The membrane can be used in the static and continuous diffusion dialysis (DD) processes to separate an acidic liquor containing HCl and glyphosate (Gly). The acidic liquor is filled or pumped into the tubular membrane, while the membrane is immersed in the matrix solution of water. The matrix solution can also be static while the acidic liquor is continuous to form a semi-continuous process.Static DD process shows that the recovery ratio (RH) can reach up to 70.2% with the Gly rejection of 95.3% after 1 h. Continuous process shows that the water osmosis coefficient (UH2O) is in the range of 1.54–3.09 × 10−4 m h−1. The RH increases from 64% to 74% as the water flow rate increases. The Gly productivity is 43–72% after precipitation from the residual liquor. Finally, semi-continuous process shows high feed flow rate of 1.86 L m−2 h−1, stable RH values of 71.1–75.5%, and high Gly productivity of 65.1–87.9%.

Analysis of water gap membrane distillation process for water desalination

A detailed theoretical model of water gap membrane distillation process is presented for water desalination. The model predicts the permeate flux through the analysis of the coupled heat and mass transfer and steady-state energy balance through membrane and module layers. Natural convection inside the water gap is studied. Effects of membrane support plate and its geometry are included to account for different areas of heat and mass transfers. Model validation shows that considering the natural convection in the water gap is critical, except for gap widths less than 1 mm, where pure conduction prevails inside the gap. A modified correlation of the gap Nusselt number is adopted and validated. The new correlation provides very good match to experimental results for the water gap module under study. System performance indicators like evaporative efficiency, polarization coefficients, and gain output ratio (GOR) are studied. The efficiency reached a maximum of 93% at high feed temperature of 90 °C and high feed flow rate of 6 L/min. GOR reached a maximum value of about 1.3 at 90 °C and low feed rate of 1.5 L/min. The width of water gap has marginal effects on EE and GOR.

Innovative swirling flow-type microbubble generator for multi-stage DCMD desalination system: Focus on the two-phase flow pattern, bubble size distribution, and its effect on MD performance

In this study, we proposed a novel air-assisted swirling flow-type microbubble generator (MBG) to improve the downstream transmembrane flux of a multistage direct contact membrane distillation (MDCMD) based seawater desalination system, and experimentally demonstrated its performance under various operating conditions. To simulate the downstream operating conditions of the MDCMD system, low temperature and high concentration conditions were implemented on the feed side in the experiments. It was observed that the formation of a gas–liquid two-phase flow in the feed stream demonstrated a positive influence on the performance of the direct contact membrane distillation (DCMD) process; particularly, microbubbles less than 100 μm performed an important role in improving the heat and mass transfer. The DCMD performance using MBG was demonstrated to be more pronounced at lower feed temperatures and higher feed flow rates, where the enhancement in permeation flux was as high as 37%. The optimal air flow rate to achieve maximum DCMD performance was determined to be 50 cc/min at a given feed flow rate, while a further increase in air flow rate incurred a slug flow in the feed channel, which resulted in a decrease in the number of microbubbles and hence a decrease in the DCMD performance. In addition, the process performance was evaluated using highly concentrated brine as the feed solution, and the results demonstrated the feasibility of applying MBG to practical desalination processes.

Removal of Dyes from Wastewater by Ceramic Membrane

The current study aimed to investigate the elimination of dyes from sewerage, using microfiltration membrane mechanism. Three dyes were applied, acid yellow-23, disperse blue -79 and acid orange -7. Experiments were performed with feed concentration (40 -120) ppm, feed flow rate (25 -65) l/h and time (0.25 -1.5) h. The membrane used ceramic membrane, constructed as a candle. It was discovered that water flow diminishes with an elevation in running time, feeding oil concentration and enhancing with elevation in the feed flow rate. In addition, it was determined that the elimination (rejection) rate of dyes enhances with elevation in the flow rate, and the elimination (rejection) rate diminishes as time passes. In cross flow microfiltration, the rejection concentration (concentrate) goes up as time passes, with high feed concentration and flow rate. It was also discovered that the modal infusion concentration declines with high feed concentration and working time. In addition, it was found that product rate goes down as time passes and with high feed concentration. Increasing feed concentration of dyes was associated with an increase in the concentration of rejecting solution. The highest elimination of disperse blue -79, Acid Yellow- 23 and acid orange -7, are 97%, 96.4% and 95.8%, respectively. The maximum recovery percentage of disperse blue - 79, acid yellow- 23 and acid orange -7are 57.7%, 58.5% and 59% respectively.

Experimental study of the effects of apex section internals and conical section length on the performance of solid–liquid hydrocyclone

Several new type hydrocyclones were designed for fine particles removal from the liquid by adding internals to the underflow section of the typical solid–liquid hydrocyclone. Both separation efficiency and energy consumption of these hydrocyclones were verified experimentally, aiming to determine whether adding internals could make the hydrocyclone more compact and energy-saving. The results indicated that adding an inner cylinder to the underflow pipe can reduce the Euler number remarkably and has little influence on the separation efficiency. The fixing method of the inner cylinder on the underflow pipe could influence the performance of hydrocyclones in some specific feed flow rates, and it is better to fix the inner cylinder using two crossed thin rods. When the conical section length was reduced by about 1/3, the separation efficiency of the hydrocyclone with an inner cylinder decreased only 1.1%–2.0% and was similar to the traditional one under high feed flow rates. Under low feed flow rates, the separation efficiency of this shortened hydrocyclone decreased as high as 5.8%. Meanwhile, both the overflow and underflow Euler number decreased significantly when the conical section length was shortened. In addition, it is shown that the separation efficiency under low feed flow rates can be enhanced by adding a short inner cone at the bottom of the hydrocyclone’s conical section. New conceptions proposed in this work can be used to design compact industrial hydrocyclones for fine particles separation under low inlet pressure.

Fatty acids characterization and oxidative stability of spray dried designer egg powder

BackgroundDesigner eggs (DEs) have gained positive importance in maintaining cholesterol level, triglyceride profile and protection towards cardiovascular diseases due to the presence of essential fatty acids (EFAs) such as omega-3 (or) n-3 fatty acids. However, extreme heat conditions effect the quality as well as quantity of EFAs during the production of designer egg dried powder (DEDP). Therefore, the main mandate of research was the development of DEDP and determination of spray drying conditions impact on fatty acids composition of DEDP samples.MethodsThe DEs were produced, collected, de-shelled, homogenized and diluted before spray drying to get fine powder. The spray drying of DEs was carried out using a laboratory spray drier. An experimental design was used for the drying parameters, where the inlet air temperature was varied (160, 180 and 200 °C), feed flow rate (200, 300 and 400 mL/hr), atomization speed (16,000, 20,000 and 24,000 rpm) and outlet air temperature (60, 70 and 80 °C) at different levels. For convenience of experimental design coding was used. The DEDP was collected in a single cyclone separator and was stored after packaging for consecutive 2 months at 25 °C and 4 °C, respectively. The powder yield was calculated from the collected dry mass in the collecting vessel divided by the processed whole egg diluted matter. The total lipids of DEDP samples were determined gravimetrically. The esters of fatty acids in each sample were prepared and analyzed through Gas Chromatograph apparatus. The oxidative stability of DEDP samples was estimated by following standard procedure of peroxide value.ResultsThe powder yield of DEDP as a result of different operating conditions was found in the range of 30.06 ± 0.22 g/500 mL to 62.10 ± 0.46 g/500 mL DEs sample. The decreasing trend in moisture content (4.4 ± 0.16% towards 4.0 ± 0.09%) and total fat content (45 ± 0.65 g/100 g towards 41 ± 0.35 g/100 g) in DEDP samples was observed with increased inlet and outlet temperature while fat content increased at high feed flow rate and atomization speed. In this study, loss of PUFAs in DEDP samples was followed due to their active role regarding to human health. For alpha-linolenic (ALA) fatty acids, maximum value at 4 °C observed was 127.32 ± 0.27 mg/50 g egg and 124.43 ± 0.32 mg/50 g egg while the minimum value observed for ALA was 100.15 ± 0.09 mg/50 g egg and 97.15 ± 0.06 mg/50 g egg after 30 and 60 days storage, respectively. The significant decrease trend for eicosapentaenoic (EPA) fatty acids values from 11.78 ± 0.31 mg/50 g egg to 2.18 ± 0.14 mg/50 g egg at 25 °C under spray dried conditions of inlet air temperature (180 °C), feed flow rate (300 mL/hr), atomization speed (24,000 rpm) and outlet air temperature (80 °C) after 60 days storage period was noted. The docosahexaenoic (DHA) fatty acids value in DEDP was decreased from 15.49 ± 0.79 mg/50 g egg (0 day) to 10.10 ± 0.64 mg/50 g egg at 60 days (4 °C) and same decreasing trend was observed at 25 °C. The decreasing order for total omega-3 fatty acids retention in DEDP during storage intervals was found as 162.33 ± 1.64 mg/50 g egg > 158.61 ± 1.53 mg/50 g egg > 148.03 ± 1.57 mg/50 g egg (0, 30 and 60 days stored at 4 °C) and 162.33 ± 1.64 mg/50 g egg > 151.56 ± 1.54 mg/50 g egg > 135.89 ± 1.62 mg/50 g egg (0, 30 and 60 days stored at 25 °C). The peroxide value (PV) levels obtained in DEDP samples after 60 days were higher (0.78 ± 0.06, 0.81 ± 0.02 meq/kg O2) when compared to initial readings at 0 day (0.65 ± 0.04 meq/kg O2). The PV of DEDP samples reached their maximum peaks after 60 days at 25 °C. The increasing order showed that lipid oxidation increased with storage. However, the overall PV never exceeded the limit of 10 (meq/kg) considered as a threshold limit.ConclusionsExtreme hot conditions (> 180 °C) of spray dryer reduce the quality of designer egg dry powder. Extreme conditions assist PUFAs loss and decrease in storage stability due to high lipid oxidation.

Characterization and Testing of Copper-Containing Catalysts for Dehydrogenation of Cyclohexanol to Cyclohexanone

Main characteristics of currently used industrial catalysts and an innovative catalyst MAK-K for dehydrogenation of cyclohexanol were compared. Main attention was paid to comparison of the activity and selectivity of MAK-K and the best catalyst H3-11 (BASF) at 220–270 °C and feed flow rate of 0.6–1.3 h–1. Similar behaviors were characteristic of both catalysts, the use of MAK-K being preferable at lower temperatures and higher feed flow rates. The MAK-K catalyst manufactured by LLC «NIAP-KATALIZATOR» was tested. The catalyst (1.4 m3) was loaded to a reactor for dehydrogenation of cyclohexanol at Shchekinoazot Co. and employed for more than 2000 h to demonstrate its high activity and selectivity. The catalyst was competitive against all the samples under study.

Effects of spray drying process conditions on the quality properties of microencapsulated cream powder

Effects of spray drying conditions including inlet drying temperature (150, 170 or 190 °C), feed flow rate (9.0, 19.5 or 30 mL min−1), and aspiration rate (50, 75 or 100%) on the composition, water activity, reconstitution, density, colour, morphology, surface fat and free fatty acid content of microencapsulated cream powder were evaluated. The variation in the wettability, bulk and tapped densities, surface fat and volatile fatty acid contents of the powders showed similar tendencies with the spray drying parameters. In contrast, moisture content, fat content, water activity, solubility, and colour properties were not influenced by the processing conditions. High inlet drying temperature, low or high aspiration rates, and high feed flow rate caused undesirable powder properties. According to the results, processing conditions that cause high drying rates should not be applied for production of a high-quality microencapsulated cream powder.

Ultrafiltration behavior of partially retained proteins and completely retained proteins using equally-staged single pass tangential flow filtration membranes.

This work examines the ultrafiltration behavior of partially retained proteins like lysozyme and completely retained proteins like monoclonal antibodies using single pass tangential flow filtration (SPTFF) modules with different screen channels and molecular weight cut-offs. When the staging of the SPTFF used the same membrane area in each stage, there was no impact of the module screened channel or the buffer matrix on the final concentration achieved for completely retained monoclonal antibodies. A hybrid configuration containing 30 kDa membranes and 50 kDa membranes increased the maximum achievable concentration for both the monoclonal antibodies used in this work, at the same time, allowing a two-fold to four-fold increase in normalized feed flow-rate through the system compared to only the 30 kDa or only the 50 kDa membranes. The sieving coefficient of lysozyme measured and calculated using SPTFF was lower than those measured during conventional recirculation TFF indicating a more complicated concentration polarization effect than conventional recirculation TFF. Moreover, the sieving coefficients of lysozyme were the same for the 10 kDa regenerated cellulose and 50 kDa PES membranes while it was higher for the 30 kDa regenerated cellulose membrane. The difference in TFF and SPTFF behavior is important when the product of interest is desired to be permeated. This work presents the first body of data for partially and completely retained solutes together in the SPTFF mode and provides a strategy to increase protein concentration at higher feed flow rates. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 2018 © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1137-1148, 2018.

Application of asymmetric Si3N4 hollow fiber membrane for cross-flow microfiltration of oily waste water

The asymmetric morphology of silicon nitride (Si3N4) ceramic hollow fiber membrane with a selective spongiform outer layer was optimized by the air gap distance and the internal rate of coagulate for oil/water emulsion microfiltration. The effect of trans-membrane pressure (TMP), feed flow rate (FFR), and pH of the feeding emulsion on the separation performance were determined experimentally. Membrane fouling has increased by dissociation of oil droplets during filtration at high TMP and FFR values. Fouling phenomena were studied based on standard pore blocking model. The pH by affecting the surface charge of the Si3N4 hollow fibers and zeta potential of the feed emulsion has also been introduced as a prominent influential factor on separation efficiency. The highest values of permeate flux (390 Lm−2h-1) and oil rejection (95%) were recorded in alkaline pH. The fabricated Si3N4 ceramic membranes were completely recovered (≤99%) by simple thermal treatment at 400 °C.

Development of a powerful CO2 methanation process using a structured Ni/CeO2 catalyst

The purpose of this study is to develop a powerful CO2 methanation process using a variety of structured Ni/CeO2 catalysts. Various configurations of metallic honeycomb-type catalysts, which are plain, stacked, segment, and multi-stacked were constructed and tested under various reaction conditions; i.e. inlet temperature, feed flow rate and CO2 partial pressure. Effects of the developed configurations including stack and gap distance were examined. The random-flow channels of stacked type and the gap distance of segment type could improve the catalytic activity, resulting in high CO2 conversion. Under industrial-like high feed rate condition and pure feed gas component, a moderate hot spot over the multi-stacked catalyst was observed and reported for the first time. The moderate hot spot reboosted the conversion to a high level even at high feed flow rate condition of 3000 mL/min (contact time of 235 ms). As a result, high CO2 conversion > 90%, high CH4 selectivity > 99.5%, and high stability with dropped conversion < 0.6%, could be maintained over 76 h test at setting temperature of 300 °C, flow rate of 3000 mL/min and feed ratio of pCO2/pH2=0.12/0.88. The stability of the Ni/CeO2 catalyst under the moderate hot spot condition was revealed by BET, SEM and XRD analyses.

Atomistic and continuum scale modeling of functionalized graphyne membranes for water desalination.

Recent theoretical and experimental studies reported ultra-high water permeability and salt rejection in nanoporous single-layer graphene. However, creating and controlling the size and distribution of nanometer-scale pores pose significant challenges to application of these membranes for water desalination. Graphyne and hydrogenated graphyne have tremendous potential as ultra-permeable membranes for desalination and wastewater reclamation due to their uniform pore-distribution, atomic thickness and mechano-chemical stability. Using molecular dynamics (MD) simulations and upscale continuum analysis, the desalination performance of bare and hydrogenated α-graphyne and γ-{2,3,4}-graphyne membranes is evaluated as a function of pore size, pore geometry, chemical functionalization and applied pressure. MD simulations show that pores ranging from 20 to 50 Å2 reject in excess of 90% of the ions for pressures up to 1 GPa. Water permeability is found to range up to 85 L cm-2 day-1 MPa-1, which is up to three orders of magnitude larger than commercial seawater reverse osmosis (RO) membranes and up to ten times that of nanoporous graphene. Pore chemistry, functionalization and geometry are shown to play a critical role in modulating the water flux, and these observations are explained by water velocity, density, and energy barriers in the pores. The atomistic scale investigations are complemented by upscale continuum analysis to examine the performance of these membranes in application to cross-flow RO systems. This upscale analysis, however, shows that the significant increase in permeability, observed from MD simulations, does not fully translate to current RO systems due to transport limitations. Nevertheless, upscale calculations predict that the higher permeability of graphyne membranes would allow up to six times higher permeate recovery or up to 6% less energy consumption as compared to thin-film composite membranes at currently accessible operating conditions. Significantly higher energy savings and permeate recovery can be achieved if higher feed-flow rates can be realized.

Physical properties, morphology and saltiness of salt particles as affected by spray drying conditions and potassium chloride substitution

Since excessive intake of sodium increases the risk of an array of diseases, much effort has been made to reduce sodium in food. Here, combined use of spray drying and KCl substitution to modify the physical properties and morphology of KCl/NaCl salt particles was attempted. The effects of inlet air temperature, feed flow rate and KCl substitution level on the moisture content, particle size, surface area, bulk density, hygroscopicity, crystallinity, morphology, N2-sorption characteristics, crystallinity and saltiness of the salt particles were determined. Combined use of KCl and NaCl created surface irregularities and pore interiors of the salt particles. Although higher feed flow rate and KCl substitution level resulted in significantly larger particle size, salt particles with the highest KCl substitution level (30%) exhibited highest hygroscopicity and saltiness because of their lower bulk density and existence of agglomeration, surface roughness and macro pores. All spray-dried salt particles were noted to be crystal-like.

Enabling Process Intensification by 3 D Printing of Catalytic Structures

AbstractSmall‐scale, intensified chemical reactors (i.e., process intensification) mediated by structured catalysts substantially diminishes the advantages of large‐scale gas‐to‐liquid (transport fuels) process plants and can be realized at low capital costs, minimum energy consumption, and zero/small CO2 footprints. Current structured‐catalysts approaches are complex and expensive; therefore, simple methods are crucial that are capable of depositing a desired geometry of catalysts into engineered channels. Herein, we developed printable composition by incorporating nickel and molybdenum ions into water‐soluble PVA and starch; the subsequent pyrolysis of organic compounds resulted into three‐dimensional carbon scaffold with micro/macro interconnected pores (dpore, 6.5 Å; dpore, 100 μm) containing up to 25 wt % catalyst loading. 2 D (TEM, SEM) and 3D (X‐ray computed tomography) microstructural analyses and catalytic tests (conversion of syngas to alcohols) were performed for 3 D printed catalysts and compared with conventional pelleted catalysts. At a high feed flow rate (6000 h−1), CO conversion is rapidly reduced to 16 mol % for pelleted catalysts, whereas 3 D printed catalysts converted 35 mol % of CO, with the same catalyst loading.

Analysis of key factors influencing the evaporation performances of an oriented linear cutting copper fiber sintered felt

Porous structure can effectively enhance the heat transfer efficiency. A kind of micro vaporizer using the oriented linear cutting copper fiber sintered felt is proposed in this work. Multiple long cutting copper fibers are firstly fabricated with a multi-tooth tool and then sintered together in parallel to form uniform thickness metal fiber sintered felts that provided a characteristic of oriented microchannels. The temperature rise response and thermal conversion efficiency are experimentally investigated to evaluate the influences of porosity, surface structure, feed flow rate and input power on the evaporation characteristics. It is indicated that the temperature rise response of water is mainly affected by input power and feed flow rate. High input power and low feed flow rate present better temperature rise response of water. Porosity rather than surface structure plays an important role in the temperature rise response of water at a relatively high input power. The thermal conversion efficiency is dominated by the input power and surface structure. The oriented linear cutting copper fiber sintered felts for three kinds of porosities show better thermal conversion efficiency than that of the oriented linear copper wire sintered felt when the input power is less than 115 W. All the sintered felts have almost the same performance of thermal conversion at a high input power.

Comparison of conventional and spherical reactor for the industrial auto-thermal reforming of methane to maximize synthesis gas and minimize CO2

Auto-thermal reforming (ATR), a combination of exothermic partial oxidation and endothermic steam reforming of methane, is an important process to produce syngas for petrochemical industries. In a commercial ATR unit, tubular fixed bed reactors are typically used. Pressure drop across the tube, high manufacturing costs, and low production capacity are some disadvantages of these reactors. The main propose of this study is to offer an optimized radial flow, spherical packed bed reactor as a promising alternative for overcoming the drawbacks of conventional tubular reactors. In the current research, a one dimensional pseudo-homogeneous model based on mass, energy, and momentum balances is applied to simulate the performance of packed-bed reactors for the production of syngas in both tubular and spherical reactors. In the optimization section, the proposed work explores optimal values of various decision variables that simultaneously maximize outlet molar flow rate of H2, CO and minimize molar flow rate of CO2 from novel spherical reactor. The multi-objective model is transformed to a single objective optimization problem by weighted sum method and the single optimum point is found by using genetic algorithm. The optimization results show that the pressure drop in the spherical reactor is negligible in comparison to that of the conventional tubular reactor. Therefore, it is inferred that the spherical reactor can operate with much higher feed flow rate, more catalyst loading, and smaller catalyst particles.

Energy consumption and exergy analyses of a supercritical water oxidation system with a transpiring wall reactor

A supercritical water oxidation system with a transpiring wall reactor was simulated by Aspen Plus, and simulation model was validated by comparisons with experimental reactor outlet temperatures and product properties (total organic carbon and CO). Energy and exergy analyses were conducted to reduce energy consumption and exergy loss of the system. It is indicated that the system’s energy efficiency and exergy efficiency are 97.73% and 13.28% at typical operating conditions, respectively. The exergy loss of electric heater, heat exchanger and reactor account for 39.89%, 26.64%, and 17.23% of the system’s total exergy loss, respectively. The process optimization is conducted by preheating the middle branch of transpiring water with the heat of the reaction products to reduce energy consumption, and the net electric cost is reduced from 7.43 ¥/h to 5.96 ¥/h. It can be observed that when the split coefficient for split 2 equals to 0.6, the minimum electricity input is required for the system. When the feed concentration is increased from 2wt.% to 10wt.%, net electric cost per COD significantly decreases from 14.05 ¥/kg to 1.31 ¥/kg, which indicates that higher feed concentrations are beneficial for reducing the cost of energy consumption. What is more, when feed flow rate increases from 6kg/h to 16kg/h, net electric cost per COD increases from 3.21 ¥/kg to 4.61¥/kg, which shows that higher energy consumption costs will be required at higher feed flow rates.

Occurrence of salt breakthrough and air-vapor pocket in a direct-contact membrane distillation

A polyvinylidene fluoride (PVDF) hollow fiber module with a low packing density and the permeate orifices on one side was used in a direct-contact membrane distillation process (DCMD). Comparative tests were also performed using a highly hydrophobic polytetrafluoroethylene (PTFE) membrane and a low hydrophobic PVDF membrane with different packing densities. Under varying operating conditions such as the feed and permeate flow rates as well as temperature, the performances of the DCMD were comprehensively investigated. It was rarely found that salt breakthrough in an idle mode and air-vapor pocket in an operative mode could occur. Partial wetting was for the first time found tending to happen in the PVDF membrane in idle mode, which led to salt breakthrough. High feed temperature and flow rate accelerated partial wetting. On the contrary, the PTFE membrane prevented partial wetting and blocked salt permeation. The air-vapor pocket formation at the shell side was attributed to a high vapor flux and incomplete condensation. An increase in packing density and the inversion of permeate orifices could help the mixture of hot vapor and cold permeate eliminate the air-vapor pocket, which was for the first time observed and illustrated.