Waste heat recovery of organic Rankine cycle using dry fluids

06 Electrical power supply and utilization (scientific, technical) At the present status of electric vehicle (EV) technologies, none of the available energy sources can solely fulfill all the demands of EVs to enable them to compete with gasoline powered vehicles. In this paper, an energy management system, adopting the so-called hybridization of energy sources, is proposed to coordinate multiple energy sources for EVs. Hence, the unique advantages of various EV energy sources can be fully utilized, leading to optimized fuel economy while fulfilling the expected driving range and maintaining other EV performances. The proposed optimization is performed by tuning two ratios, namely the mass ratio and the hybridization ratio. 02/00947 Life-cycle emission of oxidic gases from powergeneration systems Nomura, N. er cl. Applied Energy, 2001, 68, (2), 215-227. Life-cycle emissions of nitric oxide and sulphurous oxides from various types of electric-power generation systems have been estimated. Emissions from the process of building energy systems, as well as from the mining and transportation of the fuel were accounted for as well as the emissions from power situations. Two types of thermoelectric systems, namely a LNG-fuelled gas-turbine combined cycle and an integrated coal-gasification combined cycle, and four types of renewable energy systems - photovoltaic, hydropower, wind power and ocean thermal energv conversion -were evaluated. The estimated amounts of nitric oxide emitted per generated unit of electricity range from 0.06 to 0.3 g/kWh, while the amounts of sulphur oxides range from 0.3 to 0.53 g/kWh. There is a tendency for renewable-energy systems to emit lower amounts of nitric oxide. 02/00948 Nanostructured materials for energy storage Nazar, L.F. et crl. Inrernuriond Journul of Inorpnic Moterids, 2001, 3, 191-200. Traditional electrode materials for lithium-ion storage cells are based on materials which have both mixed electron and ion transport (for Li+). They are typically crytalline layered structures such as metal oxides that have high redox potentials, and act as positive electrodes; and graphitic carbons capable of reversible uptake of Li at low potentials which act as negative electrodes, Recently, however, nanostructured solid state materials, which are comprised of two or more compositional or structural phases, have been considered. This new area has been particularly exploited in the area of negative electrode design, where the intimate mix of components at the nanoscale permits and enhances Li reversibility. It also include cathode materials where materials that function on the basis of intergrowth structures (internal composites) have been found to be beneficial; and insulating materials where the limitations to electron transport must be overcome by judicious design of nanostructured composites. The research trends and future prospects are discussed. 02/00949 Optimal design of small A7 thermoelectric generation systems Stevens, J.W. Energ~v Conversion und Monagemmr, 2001, 42, (6) 709720. Thermoelectric generation systems for utilizing waste heat and ambient temperature swings have been proposed that would involve temperature differences on the order of l-10 K. The inherently low thermodynamic efficiency of such systems requires that a relatively large amount of heat pass through the system for a given rate of electricity production. The coupled design of the thermoelectric module and the hot side and cold side heat exchangers is fundamental to the creation of a useful device. An approximate optimal design is derived that is applicable to systems with a small temperature difference between the reservoirs, For a fixed thermal resistance in the heat exchangers, the optimal configuration splits the total temperature drop evenly between the thermoelectric module and the heat exchangers. For heat exchanger thermal resistances that vary with time, optimal configuration are derived for linear, sawtooth function and sinusoidal variations. The application of these equations to a typical system design is described. 02/00950 Performance analyses of an Nb-lZr/C-103 vapor anode multi-tube alkali-metal thermal-to-electric conversion cell El-Genk, M.S. and King, J.C. Energy Conversion cmd Mrmugm~enr, 2001, 42, (6), 721-739. The results of performance analyses of a refractory Nb-lZr/C-103 vapour anode multi-tube alkali-metal thermal-to-electric conversion (AMTEC) cell are presented and discussed. This cell could be used with a radioisotope heater unit to provide electric power from tens to a few hundreds of watts, In the tens of kilowatts electric range, the AMTEC cells could be used with a parabolic solar concentrator or a nuclear reactor heat source. The present cell measures 41.27 mm in diameter and is 125.3 mm high and has eight sodium &alumina solid electrolyte (BASE) tubes, which are connected electrically in series to provide a load voltage in excess of 3 V. The hot structure of the cell, including the hot plate, the BASE tube support plate, the hot plenum 116

Fuel and Energy Abstracts

March 2002

wall and conduction stud, the evaporator standoff and porous wick and the side wall facing the BASE tubes, is made of Nb-1Zr. The cell’s colder structure, which, includes the condenser structure, the interior thermal radiation shield, the casing and wick of the liquid sodium return artery and the side wall above the BASE tubes, is made of C103. This niobium alloy is stronger and has a lower thermal conductivity than Nb-lZr, reducing the parasitic heat conduction losses in the cell wall, hence enhancing the cell’s performance. The base cell weighs 163.4 g and delivers 7 W, at 17% conversion efficiency and load voltage of 3.3 V (cell specific mass of 23.4 p/W,). These performance parameters were for TIN BASE electrodes characterized by B = 75 AK”‘/m Pa and G = 50, assuming a BASE/electrode contact resistance of 0.06 w cm2 and a BASE braze structure leakage resistance of 3 w. Also, the inner surfaces of the thermal radiation shield and the cell wall above the BASE tubes were covered with low emissivity rhodium. The temperatures of the BASE brazes and the evaporator were below the recommended design limits (1123 and 1023 K, respectively), and the temperature margin was 2 + 20 K to avoid sodium condensation inside the BASE tube, shorting the cell. When high performance electrodes, characterized by B = 120 AK’ ‘/m’ Pa and G = IO, were used, the cell’s electric power increased to 8.38 W, at 3.5 V, and the efficiency increased to 18.8%, decreasing the specific mass of the cell to 19.7 g/W, without exceeding any of the design temperature limits.

02/00951 TCSC control based on passivity for power system damping enhancement Ramirez-Arredondo, J.M. and Davalos-Marin, R. Elecrricul Power rmd Energy S~s/m~s, 2001, 23, (2). 81-90. A passivity-based controller is designed for the thyristor controlled series capacitor (TCSC) aimed at enhancing power system stability. This controller rest on a Hamiltonian formulation of the power system, employed due to its structural properties. A study of two major models of the TCSC is presented pointing out relevant modelling details. Digital simulations show the performance of the proposed controller when the power system is subject to major disturbances.

02/00952 Unbalanced transient-based finite-element modeling of large generators Wamkeue, R. et crl. Elcciric POUT Systems Reseurch, 2000, 56, (3), 205-2 IO. Finite-element modelling is used to study the steady-state and transient performance of a large synchronous machine. In the present paper, we carry out a two-dimensional, non-linear, time-stepped finite-element simulation of a line-to-line short circuit on a large salient-pole synchronous generator with multiple rotor circuits under no-load conditions. The work is validated for performance prediction using a Hydro-Quebec network generator.

02lOO953 UPFC damping control strategy based on transient energy function Lo, K.L. and Ma, T.T. Ekcrric Power SL.S/~IS Resecrrclr,2000, 56, (3), 195-203. In this paper an innovative UPFC damping control strategy based on time-domain analysis of the system transient energy function (TEF) is proposed to damp low frequency electromechanical power oscillations. Comprehensive computer simulations are carried out to verify the proposed control scheme. The control effectiveness of using a combination of different control modes in the UPFC system with respect to different input signals to improve the transient performance of power systems is investigated and discussed. Simulation results show that the proposed damping control strategy is extremely effective and the UPFC is able to provide flexible control functions required for the real-time power flow regulation and fast transient control of power systems.

02/00954 Waste heat recovery of organic Rankine cycle using dry fluids Hung, T-C. Energy Conversion mdMunugement, 2001,42, (5), 539-553. A Rankine cycle using organic fluids as working fluids, called organic Rankine cycle (ORC), is potentially feasible in recovering low enthalpy containing heat sources. Efficient operation of the ORC depends heavily on two factors: working conditions of the cycle and the thermodynamic properties of the working fluids. The working fluids under investigation are Benzene (ChH6), Toluene (C,Hs), p-Xylene (CHHIo), RI13 and R123. Among the working fluids under investigation, p-Xylene shows the highest efficiency while Benzene shows the lowest. The study also shows that the irreversibility depends on the type of heat source. Generally speaking. p-Xylene has the lowest irreversrbility in recovering a high temperature waste heat, while RI13 and RI23 have a better performance in recovering a low temperature waste heat.