• Energy Research

Abstract This paper is an introductory prospect and experiment of generated force measuring of applying two-phase nozzle and an impulse turbine design for trilateral flash cycle heat engine. In this concept of trilateral flash cycle (TFC), pressurized working fluid (Isopentane) being heated by low temperature hot water and pumped through a two-phase nozzle to impact the impulse turbine blade. Then the generated force, measured by a load cell behind the turbine blade and isentropic efficiency of nozzle is discussed. Based on the investigations carried out so far, there is a high potential of power generation from low temperature heat recourses. Further the basic working principles of power generation system are presented followed by of the governing equations and the thermodynamics. The theory of this paper calculates isentropic efficiency of the nozzle based exit speed of the working fluid out of the nozzle and experimentally measured generated force from lab scale test rig. The initial results from experimental test shows, promising isentropic efficiency for the novel system is around 45%. Also it was observed that the trust generated force increased from 2.5N to 5N by increasing the working fluid temperature from 30°C to 70°C respectively.

Abstract In this paper, a trilateral flash cycle (TFC) based system has been developed and studied to find out its prospect for utilizing more energy and enhancing the power generation capacity. To hold simplicity and minimize the cost of system construction, an impulse turbine and a converging-diverging (CD) stationary nozzle setup have been used as the expander. The experimental study introduced impulse turbine incorporates with a stationary CD nozzle and organic working fluid, which showed a promising power generation capability from a heat source below 80 °C in spite of the increasing size of the heat exchanger, condenser, and pump. In addition to the use of proper impulse turbines, however, the power generation capacity of such type of system is basically a function of the nozzle isentropic efficiency, which lies on the nozzle geometry and the alignment with respect to the turbine. A case study on the application of the TFC system for commercial power generation in associate with economic analysis has also been included in this study which shows a payback time less than 10 years with typical operational life of 20 years, considering only 40% nozzle isentropic efficiency and by using more efficient nozzle, the capital cost per unit power generation could be minimized.

Thermoelectric generators (TEGs) convert heat energy into electricity. Currently, these devices are attached to heat exchangers by means of mechanical devices such as clamps or fixtures with nuts and bolts. These mechanical devices are not suitable for use in harsh environments due to problems with rusting and maintenance. To eliminate the need for such mechanical devices, various kinds of adhesives used to attach thermoelectric generators to heat exchangers are investigated experimentally in this work. These adhesives have been selected based on their thermal properties and also their stability to work in harsh environments to avoid damage to the integrity of the attachment over long periods of time. Stainless-steel plates were attached to a thermoelectric generator using the adhesives. The introduction of the adhesive as a means of attachment for thermoelectric generators contributes to increase the thermal resistance to heat transfer across the TEG. The adhesive layers increased the thermal resistance of the thermoelectric generator by 16% to 109%. This work examines the effect of the adhesives on the thermal performance and power output of a single thermoelectric generator for various heat inputs.

A three-dimensional (3D) coupled thermo-hydrogeological numerical model for a confined aquifer thermal energy storage (ATES) system underlain and overlain by rock media has been presented in this paper. The ATES system operates in cyclic mode. The model takes into account heat transport processes of advection, conduction and heat loss to confining rock media. The model also includes regional groundwater flow in the aquifer in the longitudinal and lateral directions, geothermal gradient and anisotropy in the aquifer. Results show that thermal injection into the aquifer results in the generation of a thermal-front which grows in size with time. The thermal interference caused by the premature thermal-breakthrough when the thermal-front reaches the production well results in the fall of system performance and hence should be avoided. This study models the transient temperature distribution in the aquifer for different flow and geological conditions which may be effectively used in designing an efficient ATES project by ensuring safety from thermal-breakthrough while catering to the energy demand. Parameter studies are also performed which reveals that permeability of the confining rocks; well spacing and injection temperature are important parameters which influence transient heat transport in the subsurface porous media. Based on the simulations here a safe well spacing is proposed. The thermal energy produced by the system in two seasons is estimated for four different cases and strategy to avoid the premature thermal-breakthrough in critical cases is also discussed. The present numerical model results are validated using an analytical model and also compared with results from an experimental field study performed at an ATES test site at Auburn University. The present model results agree with the analytical model very well and have been found to approximate the field results quite well.

Many regions around the world have limited access to clean water and power. Low-grade thermal energy in the form of industrial waste heat or non-concentrating solar thermal energy is an underutilized resource and can be used for water desalination and power generation. This paper experimentally and theoretically examines a thermoelectric-based simultaneous power generation and desalination system that can utilize low-grade thermal energy. The paper presents concept design and the theoretical analysis of the proposed system followed by experimental analysis and comparison with the theoretical estimations. Experiments were carried out at three heat loads 50, 100 and 150 W to achieve varying temperature gradients across thermoelectric generators. During the experiments, thermoelectric generators were maintained at a hot to cold side temperature difference between 20 to 60 °C. The experiments showed that the power generation flux and freshwater mass flux increased with the increase in the thermal energy source temperature. The power flux varied between 12 to 117 W/m2 of thermoelectric generator area, while freshwater mass flux varied between 4.8 to 23.7 kg/m2⋅h. The specific thermal energy consumption varied between 3.6 to 5.7 MJ/kg of freshwater; this is comparable to the single-stage conventional distillation system.

AbstractThe energy consumption in residential house sectors contributes enormously to the greenhouse gas emission and soaring energy bills. Energy efficient residential house envelopes can reduce our dependency on fossil fuel and environmental pollution. It is difficult to achieve high energy savings for ongoing heating and cooling with currently used mainstream residential house envelopes. A new energy smart house wall system is required to achieve energy conservation. Therefore the main objective of this study is to investigate the thermal performance of a new house wall envelope and compare its performance with a conventional house envelope. The study was undertaken for several climate zones encompassing all major cities in Australia. The findings indicate that a considerable energy saving can be achieved using the new house wall system.

Abstract Humidification–dehumidification (HDH) desalination with direct contact dehumidifier system is designed and fabricated. Experimental tests are performed under various operating conditions in order to explore the influence of temperatures and mass flow rates of seawater and freshwater on system performance by utilizing non-dimensional parameters. It is shown that, for any case, there is an optimum flow rate ratio of water to air, which results in a maximum water production rate. A mathematical model is utilized to evaluate the system performance and compare the outcomes with the experimental results. In addition, the effect of feed water salinity from 0–30% on the water production rate is experimentally investigated. The results showed that the maximum achieved recovery ratio of the proposed HDH system is 5% under the working condition of seawater temperature at 73 °C with 3% salinity and cold freshwater at 28 °C. Furthermore, the system was able to produce water at nearly saturated seawater feed.

Abstract In this analysis the simple reaction water turbine known as Barker’s Mill is revisited. The major geometrical and operational parameters have been identified and, using principles of conservation of mass, momentum and energy, the governing equations have been developed for the ideal case of there being no frictional losses. The solutions of the resulting equations are offered in a non-dimensional form. It is shown that the maximum torque produced by the machine is developed when the turbine is stationary. At this point the net output power is zero. As the load torque is decreased the turbine rotates and power is produced. Furthermore, because of a centrifugal pumping effect, the mass flow rate of water through the turbine increases during acceleration. Further decrease in the load torque is accompanied by increases of speed, output power, water mass flow rate and efficiency. It is shown that when the load torque is reduced towards half the value of the torque at the stationary condition, water mass flow rate, rotational speed and output power tend towards infinity. Under this condition the efficiency of the machine approaches unity. The non-dimensional characteristics of the idealized turbine are used to investigate the general characteristics of the machine and to explore its application for production of power from water reservoirs with low heads. Theoretical analysis of a simple reaction turbine is presented including consideration of the fluid frictional losses for a practical situation. A practical turbine will never run away towards infinite speed and the maximum power and efficiency of such a turbine will depend on the fluid frictional losses. Here a new factor is defined, representing the overall fluid frictional losses within the turbine. Finally this paper presents briefly the experimental performance results for two simple reaction water turbine prototypes. The two turbine prototypes under investigation have rotor diameters O0.24 m and O0.12 m respectively. The two turbine models were tested under supply heads ranging from 1 m to 4 m. The simple reaction water turbine can operate under very low hydro-static head with high energy conversion efficiency. This type of turbine exhibits prominent self-pumping ability at high rotational speeds. Under low head to achieve high rotational speeds the turbine diameter should be very small and this limits the volumetric capacity and hence the power generation capacity of such a turbine. Consequently the practical applications of this turbine would be limited to micro-hydro power generation. The split pipe design of the reaction turbine tested is easy to manufacture and it has been shown to have overall energy conversion efficiency of approximately 50% even under low heads.

This paper presents a study, numerically and experimentally, on a new thermal enhancement method for improving the heat transfer performance of latent heat energy storage (LHTES) using miniature heat pipes (MHPs). As commonly known, heat pipes are passive heat transfer devices which are capable in transferring large amount of heat with a small temperature drop. The heat pipe used in this study is copper-water charged MHP and has physical dimensions of 2 mm diameter and 100 mm long. The phase change material (PCM) used in the LHTES is paraffin wax (RT60) which is an organic based PCM and has a melting point of 60 °C. The attractive thermal features of using PCM as thermal mass are high heat capacity, exhibit constant temperature during phase change and poor thermal response. However, the poor thermal conductivity (∼0.2 W/m·K) of the PCM has greatly limited its potential to be used as high heat storing materials for future thermal storage developments. One of the potential developments is the concentrated solar power (CSP) plant, where LHTES can play an important role for improving the power generating efficiency. Providing simple and yet effective thermal enhancement method is favourable for LHTES to be widely applicable. In this study, MHPs are randomly mixed in the PCM to provide better heat spreading and improve the effective thermal conductivity of the LHTES. The numerical method adopted is three-dimensional heat conduction and the numerical results are validated against experimental data. The results have shown that the effective thermal conductivity of MHP-PCM composition has improved exponentially with the increasing number of MHPs used.