• Energy Research

Abstract This paper focuses on theoretical and experimental analysis used to establish the limiting heat flux for passively cooled thermoelectric generators (TEG). 2 commercially available TEG’s further referred as type A and type B with different allowable hot side temperatures (150 °C and 250 °C respectively) were investigated in this research. The thermal resistance of TEG was experimentally verified against the manufacturer’s specifications and used for theoretical analysis in this paper. A theoretical model is presented to determine the maximum theoretical heat flux capacity of both the TEG’s. The conventional methods are used for cooling of TEG’s and actual limiting heat flux is experimentally established for various cold end cooling configurations namely bare plate, finned block and heat pipe with finned condenser. Experiments were performed on an indoor setup and outdoor setup to validate the results from the theoretical model. The outdoor test setup consist of a fresnel lens solar concentrator with manual two axis solar tracking system for varying the heat flux, whereas the indoor setup uses electric heating elements to vary the heat flux and a low speed wind tunnel blows the ambient air past the device to simulate the outdoor breezes. It was observed that bare plate cooling can achieve a maximum heat flux of 18,125 W/m2 for type A and 31,195 W/m2 for type B at ambient wind speed of 5 m/s while maintaining respective allowable temperature over the hot side of TEG’s. Fin geometry was optimised for the finned block cooling by using the fin length and fin gap optimisation model presented in this paper. It was observed that an optimum finned block cooling arrangement can reach a maximum heat flux of 26,067 W/m2 for type A and 52,251 W/m2 for type B TEG at ambient wind speed of 5 m/s of ambient wind speed. The heat pipe with finned condenser used for cooling can reach 40,375 W/m2 for type A TEG and 76,781 W/m2 for type B TEG.

A sustainable circular economy involves designing and promoting products with the least environmental impact. This research presents an experimental performance investigation of direct contact membrane distillation with feed approaching supersaturation salinity, which can be useful for the sustainable management of reverse osmosis reject water. Traditionally, reject water from the reverse osmosis systems is discharged in the sea or in the source water body. The reinjection of high salinity reject water into the sea has the potential to put the local sea environment at risk. This paper presents a design of a solar membrane distillation system that can achieve close to zero liquid discharge. The theoretical and experimental analysis on the performance of the lab scale close to zero liquid discharge system that produces supersaturated brine is studied. The lab-based experiments were conducted at boundary conditions, which were close to the real-world conditions where feed water temperatures ranged between 40 °C and 85 °C and the permeate water temperatures ranged between 5 °C and 20 °C. The feed water was supplied at salinity between 70,000 ppm to 110,000 ppm, similar to reject from reverse osmosis. The experimental results show that the maximum flux of 17.03 kg/m2·h was achieved at a feed temperature of 80 °C, a feed salinity of 10,000 ppm, a permeate temperature of 5 °C and at constant feed and a permeate flow rate of 4 L/min. Whereas for the same conditions, the theoretical mass flux was 18.23 kg/m2·h. Crystal formation was observed in the feed tank as the feed water volume reduced and the salinity increased, reaching close to 308,000 ppm TDS. At this condition, the mass flux approached close to zero due to crystallisation on the membrane surface. This study provides advice on the practical limitations for the use of membrane distillation to achieve close to zero liquid discharge.

Abstract Potential energy from fluid flow of small rivers or irrigations could be extracted become electricity by using screw turbine. This turbine is promising because the advantages of ultra-low head and fish friendly.Experimental performance of screw turbine for ultra-low head hydro resource is presented in this paper. The screw turbine with anoutside diameter of 142 mm and the water flowrate of 1.2 l/s with the head of 0.25 m, can produce maximum power 1.4 W with 49% efficiency at 22 o angle of inclination. This turbine has one blade screw and screw turbine experiment apparatus is made by using locally available materials. The screw turbine has shown good potential to be used for low head micro hydro-electric installations. This paper reports on a performance analysis based on the experimental data collected from different performance tests carried out on some inclination angle position of screw turbine prototype.

Abstract This paper presents the experimental performance of a curved nozzle two-phase reaction turbine design for trilateral flash cycle heat engine. Results from two tests have been presented, for first test the average feed water temperature was maintained around 97 °C under local atmospheric pressure, while for the second test the average feed water temperature was maintained around 115 °C under 200 kPa absolute pressure. For both the tests the initial condenser pressure was maintained around 6 kPa absolute. The maximum power output of the turbine is estimated to be around 1330 W with an isentropic efficiency of around 25%.

The interest of using solar powered membrane distillation systems for desalination is growing worldwide due to the membrane distillation (MD) attractive features. This study experimentally investigates the utilization of direct contact membrane distillation (DCMD) coupled to a salinity-gradient solar pond (SGSP) for sustainable freshwater production and reduction of brine footprint on the environment. A mathematical model for heat and mass flux in the DCMD module and thermal model for SGSP are developed and coupled to evaluate the feasibility of freshwater production. The experiment results on RMIT University SGSP coupled with DCMD are presented. The feed stream of 1.3% salinity is heated up by the SGSP and circulated through DCMD module then injected to an evaporation pond. Also, a thermal energy system is used to recover heat from the outlet brine stream of DCMD and use it as preheating for inlet feed water stream. Results are compared and showed that if the flow is laminar, the connecting DCMD module to the SGSP could induce a marked concentration and temperature polarisation phenomenon that reduces fluxes. Therefor turbulence has to be created in the feed stream to reduce polarisation. Also, to reduce the environmental footprint, the brine is recirculated after passing through the heat exchanger.

The Design Optimisation of small energy Microgrids involves establishing the equipment configuration (size and capacity of components) and the operational rules for ongoing in service use. Existing techniques support the analysis of individual days of incident solar energy. In this paper a technique that uses Stochastic programming is proposed. The new technique allows the probability of occurrence of a particular day of incident solar energy, and the probability occurrence of particular consecutive days of incident solar energy to be considered by the optimisation process. The technique outlined supports the pre processing of incident solar energy and system loads as discrete probability functions which subsequently allows simple linear programming techniques to be utilised. This results in the ability to create easy to modify and easily scalable design tools.

This work reviews the current operational condition and activities on design modification for different applications of ejectors. Ejectors being a simple mechanical system capable of performing multiple fluid related functions (vacuum generation, pumping, mixing, condensing and heat exchanging), have been an essential part of several industrial processes. Two areas have been emphasized; internal flow and application-based modifications in components of ejectors. The geometry and inlet flow conditions were found to be the prime influencing factor of its performance. The objective and application-based modifications were performed on the primary nozzle, secondary nozzle, mixing chamber, throat and diffuser. The resultant performance was found to be dependent on operational condition and fluid type. This emphasizes the requirement of application-based design selection of the technology. In addition, the flow dynamics of condensing, non-condensing, particle and slurry flow has been studied based on available literatures. The one-point final objective is to identify the usability of primary water jet ejectors for active vapor transport and condensation, to replace vacuum pump and condenser in compact domestic water desalination system.