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In the direct contact membrane distillation (DCMD) system, the temperature polarization due to boundary layer formation limits the system performance. This study presents the experimental results and heat transfer analysis of a DCMD module coupled with a salinity gradient solar pond (SGSP) under three different flow channel configurations. In the first case, the feed and permeate channels were both empty, while in the next two cases, the feed and permeate channels were filled with a porous spacer material. Two different spacer geometries are examined: 1.5 mm thick with a filament angle of 65°, and 2 mm thick with a filament angle of 90°. The study considers only the heat transfer due to conduction by replacing the hydrophobic membrane normally used in a DCMD module with a thin polypropylene sheet so that no mass transfer can occur between the feed and permeate channels. The Reynolds number for all three configurations was found to be between 1000 and 2000, indicating the flow regime was laminar. The flow rate through both the feed and permeate sides was the same, and experiments were conducted for flow rates of 5 L/min and 3 L/min. It has been found that the highest overall heat transfer coefficient was obtained with the spacer of 2 mm thickness and filament angle of 90°. [ABSTRACT FROM AUTHOR]

This research aimed to examine the effect of the thermal conductivity model of hydrophobic membranes on performance modelling of direct contact membrane distillation systems. The parallel, series, and two types of Maxwell models were studied. Simultaneously, an iterative numerical model was developed to choose the most appropriate model by analysing the mass flux (Jw) and the heat transfer rate (Q-P). Comparison with the experimental results, showing that Maxwell Type II was the most appropriate for modelling the thermal conductivity of the membrane. Also, based on the chosen model of membrane thermal conductivity, the direct contact membrane distillation performance (the global heat transfer coefficient, temperature polarization coefficient, energy efficiency, and gain output ratio) was studied. It was found that the membrane thermal conductivity model with a higher value of membrane thermal conductivity (km) resulted in an underestimation of the predicted mass flux, temperature polarization coefficient, and energy efficiency. In contrast, the total heat transfer coefficient and predicted heat rate were overestimated. The gain output ratio values seemed not to be affected by this choice with only 8% deviation among the four models. [ABSTRACT FROM AUTHOR]

Abstract This paper describes the experimental method to establish a salinity gradient in a MgCl 2 solar pond (SGSP) at Bundoora East campus of Royal Melbourne Information of Technology (RMIT) University, Melbourne, Australia. The pond was instructed in 2001, with a 15 m 2 surface area. This experiment involves using saturated brine to establish the lower thermal storage (or convective) zone (LCZ) as well as the middle insulating layer in which the salinity decreases with height. This non-convective zone (NCZ) is proctored from mixings caused by the wind and the destabilizing effects of diurnal variation of the ambient temperature by an upper convicting layer (UCZ). In this top layer (UCZ) both the temperature and salinity are uniform. These properties increase with depth in the (NCZ). Density and temperature usually assume their maximum values at the interface between the NCZ and the lower convective zone (LCZ). Both these properties y are usually constant in the (LCZ).In order to set up the salinity gradient using an injection filling technic introduced by Zangrando technique (1980). In this method, the pond is first filled to half the depth of the planned gradient zone with highly concentrated salt water. Next, fresh water, or salt water of a low concentration, is injected horizontally into the brine through a diffuser. The novelty for this paper is investigation redistribution method experimentally using simple technic to find the required volume of injected fresh water. [ABSTRACT FROM AUTHOR]

Abstract This research is investigating the possibility of using heat stored in solar ponds for salt drying. At present, Pyramid Salts, a salt producing company located in the north of Victoria, Australia, use electric heaters to heat ambient air from around 20 °C to around 70 °C in their salt crystallizers for salt drying. This research paper aims to develop a solar PV driven heat pump coupled with a solar pond to supply necessary hot air. According to the collected data solar pond performance in Pyramid Hill indicates that heat will be available at the bottom of the pond between 35 °C to 50 °C (winter to summer). Coupling the salinity gradient solar pond with the heat pump is the novelty of this research paper. The heat pump's evaporation boosts from ambient temperature to available solar pond heat (40 °C) and above 24/7 all year around. As a result, the amount of electrical energy saving in this project has been estimated to be about 1 GWh per year. In this work, the preliminary data on the developments of salinity, temperature, and turbidity profiles will be considered and discussed. [ABSTRACT FROM AUTHOR]

Abstract Membrane distillation (MD) is a thermally-driven separation technology that can produce highly pure water. Direct contact membrane distillation (DCMD), where both hot and cold solution is directly in contact with the hydrophobic membrane is the most studied system due to its condensation method without an external condenser as well as its overall structural simplicity. In this paper, heat transfer analysis was carried out in DCMD experimentally to investigate how the presence of a spacer can effect on heat transfer coefficient. Results revealed that the heat transfer coefficient for spacer-filled channels (plastic and metallic material) is approximately from 3 to 3.5 times higher than that for empty channels. Additionally, from specific pumping power (SPP) for 1 cubic meter of freshwater production, it is predicted that DCMD with spacer-filled channels can consume far less electrical or mechanical energy than that with empty channels. [ABSTRACT FROM AUTHOR]

Abstract This paper describes the practical experience gained from setting up salinity gradient in a MgCl solar pond at Bundoora East campus of Royal Melbourne Institute of Technology (RMIT) University, Melbourne, Australia. This involves using saturated brine to establish the lower thermal storage (or convective) zone (LCZ) as well as the middle insulating layer in which the salinity decreases with height. This non-convective zone (NCZ) is protected from mixings caused by the wind and the destabilising effects of diurnal variation of the ambient temperature by an upper convicting layer (UCZ). In this top layer (UCZ) both the temperature and salinity are uniform. These properties increase with depth in the (NCZ). Density and temperature usually assume their maximum values at the interface between the NCZ and the lower convective zone (LCZ). Both these properties are usually constant in the (LCZ). [ABSTRACT FROM AUTHOR]

This study examines the effect of spacers and operating conditions (feed inlet temperature, velocity, and feed concentration) on mass transfer characteristics in direct contact membrane distillation (DCMD) systems. The experimental results showed that velocity of the feed and permeate influenced the mass transfer properties more significantly than the temperature and concentration factors. Among the five investigated spacers, the plastic spacer (PL4) had the most influence on mass transfer characteristics, which was proven through analysing the mass transfer coefficient (k s), boundary layer thickness (δ), shear stress (τ) as well as flow property in DCMD spacer-filled channels. Moreover, the mass transfer correlation for each spacer and a general mass transfer correlation for all spacers were determined. Through comparisons between theoretical and experimental Sherwood numbers, the mass transfer correlation developed by Grober for empty channels could be used to describe the mass transfer characteristic in spacer-filled channels in this study. • Propose a new methodology to describe adequately mass transfer properties in spacer-filled DCMD channels. • Identify the mass transfer correlation for all investigated spacers in direct contact membrane distillation module. • Determine the most appropriate spacer for the best improvement in mass transfer property and permeate flux. [ABSTRACT FROM AUTHOR]