Search

Water gap membrane distillation is an effective configuration to improve the productivity of the membrane distillation process. This study provides a comprehensive theoretical analysis of a novel water gap membrane distillation (WGMD) design where the gap water is circulated. Circulating the gap water improves the output flux due to the forced convection characteristics inside the water gap and hence improves mass and heat transfer coefficients. The model outcomes are compared with the experimental findings for validation, and it shows a very good agreement with a maximum deviation of less than 10%. The influences of operational variables on the energy efficiency, output flux, and freshwater cost are presented and compared to the standard WGMD process, without circulated gap, under the same operation conditions. Results reveal that the circulated water gap enhances the output flux by a maximum of 350% and reduces the production cost by a maximum of 32%. Regarding energy efficiency, a slight improvement is obtained when the gap water is circulated at a rate of up to 4 L/min; however, using a higher circulation rate reduces the energy efficiency. Using a multistage system to increase productivity can minimize production costs by roughly 82%. [ABSTRACT FROM AUTHOR]

This study presents a theoretical model based on integrated heat and mass transfer in a vacuum membrane distillation module. The vacuum membrane distillation is being investigated using a parametric analysis with the objective of investigating the influence of operating parameters on process performance. The study considers various factors associated with VMD operation, such as feed inlet temperature, feed inlet flowrate, and vacuum pressure. Two key performance metrics, namely permeate flux and gained output ratio (GOR), are employed to evaluate the system's performance. The results reveal that raising the feed temperature and flowrate results in improved output flux and GOR. Nevertheless, the impact of changing the feed temperature on performance enhancement surpasses that of adjusting the feed flowrate. Furthermore, decreasing the pressure in the permeate channel, thereby achieving higher vacuum levels, significantly improves the permeate flux, particularly at lower feed temperatures. However, this productivity increase comes at the expense of increased heat loss and reduced GOR. Additionally, all the parameters investigated demonstrate substantial effects on the permeate flux, while their influences on the GOR are negligible. [ABSTRACT FROM AUTHOR]

The performance of a multistage direct contact membrane distillation system (MS-DCMD) is experimentally investigated using a laboratory-scale three stages system. The effects of operating conditions on the system performance are studied for parallel, series, and mixed flow stages connections for the feed and coolant streams. Results showed that the productivity of the parallel flow arrangement is well-higher than the series and mixed flow arrangements due to fewer temperature changes from stage to another. The experimental investigation showed that maintaining the feed and permeate temperatures at the required values required high energy consumption for heater and chiller circulation baths due to the high conduction heat transfer between feed and permeate sides across the membrane of the DCMD stages. Energy analysis showed lower specific energy consumption and higher gain output ratio for the parallel flow arrangement of the MS-DCMD system operating at feed temperature around 60°C. Salt rejection factor of 99.7% had been achieved for feed salts concentration of 35 g/L. [ABSTRACT FROM AUTHOR]

Bubble column humidification and dehumidification (HDH) system is considered one of the promising and new techniques for enhancing the performance of the HDH desalination systems. In this paper, we experimentally examine the performance of a bubble column water and air heated HDH systems. The effect of water column height in the humidifier, water temperature, and air temperature and flow rate on gain output ratio (GOR), production and effectiveness are investigated and discussed. Results show that the system can produce 0.6 L/h freshwater and GOR can reach 0.95. At low temperatures, increasing airflow rate leads to an increase in the production at a high rate than the rate of increase in heat input. Therefore, GOR slightly increases at a higher airflow rate. Furthermore, GOR increases with increasing water temperature in the dehumidifier because the decrease in input energy needed to cool water in the dehumidifier has more impact than the decrease in the production. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is a promising thermally driven membrane separation technique. In MD, water vapor is being separated from the hot feed water solution using a microporous hydrophobic membrane, due to the difference in temperature, and hence vapor pressure, across the membrane. Air gap membrane distillation (AGMD) process is one of the common configurations of applying the MD process for water desalination and other applications. In AGMD, a stagnant air gap is introduced between the membrane and a condensation surface within the membrane module to reduce the conduction heat loss through the membrane. In this review article, design characteristics and operating conditions of AGMD and its modified designs to enhance the productivity and reduce the energy consumption are surveyed and discussed. Previous work on pilot AGMD systems and multi-stage or multi-effect systems with energy saving modules is highlighted. Membrane materials and developments used with the AGMD modules are presented with discussion of membrane fouling and scaling problems. In addition, modeling techniques based on the heat and mass transfer equations and simulation approaches of the AGMD process are presented. The merits of operating the AGMD systems with solar and other renewable energies are discussed along with the economic aspects. The future research directions of AGMD are highlighted in this review. This will help researchers to direct their research without repetition of previous known studies. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is a non-isothermal membrane separation process capable of operating at low temperature and low transmembrane hydrostatic pressure. Air gap membrane distillation (AGMD) is one of the MD configurations. In this study, the performance of double-stage AGMD unit at different AGMD-operating parameters such as feed temperature, feed flow rate, coolant temperature, coolant flow rate and air gap width is presented. Experimental results revealed that the built double-stage AGMD unit is capable of achieving a maximum cumulative distillate production of 128.46 kg/m2h, a total (average) flux of 64.23 kg/m2h and a single-stage flux of 65.81 kg/m2h. One key feature of the proposed design is the ability of the unit to use a common cooling chamber to provide the necessary cooling required by the two feed chambers. This reduces the total capital, maintenance and total energy consumption costs. Other benefits include simple module design, easy modules installation and improved system productivity. Furthermore, the system can be operated either as a single-stage or double-stage unit. A simple theoretical model for predicting flux in single-stage AGMD unit was equally presented. The model predicted fluxes with less than 13% discrepancy. [ABSTRACT FROM PUBLISHER]

Premixed oxy-propane flames are investigated numerically in a multihole model gas turbine combustor at various inlet mixture compositions over a range of equivalence ratios (Ø: 0.241-0.500), oxygen fractions (OF: 32.4-60.0%), and adiabatic flame temperatures ( T ad : 1600-1900 K) at a constant bulk throat velocity of 5.2 m/s. The flames in multihole combustors are highly influenced by their corresponding adiabatic flame temperatures. Similar flame shapes are observed at constant T ad , where cases with (Ø = 0.241, OF = 60%) and (Ø = 0.50, OF = 32.4%) both represent lifted flames at T ad = 1600 K, anchored flames in (Ø = 0.276, OF = 60%) and (Ø = 0.50, OF = 36.6%) at T ad = 1750 K, and anchored stronger flames in cases (Ø = 0.313, OF = 60%), (Ø = 0.392, OF = 50%), and (Ø = 0.50, OF = 40.8%) at T ad = 1900 K. Flames in a multihole combustor are characterized by the presence of an outer recirculation zone (ORZ) only. In comparison with a swirl-stabilized combustor in identical inlet conditions, flames in a multihole combustor demonstrate a lower Damköhler number ( Da ), higher flame thickness, elevated pattern factor, and increased CO emission. Due to the reduced vorticity level because of the absence of swirl motion, the multihole flames have higher axial temperature than the swirl-stabilized ones., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)