An evaluation method for small-scale conduction cooled SMES cryogenic cooling system based on thermal analysis

The current flowing through a SMES is subjected to variations at a rate ranging from 0.1 A/s to 300 A/s under the influence of the power grid. The duration of power exchange varies from milliseconds to minutes, even to hours. When operating, the impact of AC losses in HTS tapes on the cryogenic cooling system should be considered. If the cryogenic cooling system fails to take away the generated heat effectively, this may lead to the temperature rise of the magnet and its possible damage. Therefore, it is essential to evaluate the technical and economical characteristic of cryogenic cooling system. Thus, a 5 MJ SMES model is built to calculate the temperature characteristic. A new factor δ is defined to assess the technological and economical validity of the chosen cryogenic scheme. The suitable capacity of the cryogenic cooling system is evaluated for different applications. The effect of the operating temperature on the technical and economical factor is also discussed.     

Effects of metal mass on the performance of adsorption heat pumps utilizing zeolite 4A coatings synthesized on heat exchanger tubesEffets de la masse métallique sur la performance des pompes à chaleur à adsorption utilisant des revêtements en zéolite 4A synthétisé sur les tubes de l'échangeur de chaleur

The effects of the wall thickness of stainless steel heat exchanger tubes on the performance of adsorption machines, employing zeolite 4A coatings synthesized on metal heat exchanger tubes, are investigated. A recently developed mathematical model is used to determine the cycle durations when various wall thicknesses of the heat exchanger tubes as well as different zeolite layer thicknesses are utilized. For each case, the power and the COP_cycle values of the system are estimated. In general, very high power and quite low COP_cycle values are obtained when the proposed arrangement is utilized in the adsorption heat pumps. The zeolite layer thicknesses that may result in obtaining high COP_cycle values are generally much higher than the optimum layer thickness value that maximizes the power and the utilization of layers thicker than the optimum value may lead to significant extensions in the cycle durations and hence to a decrease in the power obtained from the system. Decreasing the wall thickness of the heat exchanger tubes increases both the power and the COP_cycle values when the optimum zeolite layer thickness for each wall thickness is taken into account. The possibility of such an enhancement will most probably be limited by the minimum wall thickness value that can actually be obtained by the available technology. The COP values of adsorption heat pumps may also be increased by using regenerative processes. Due to the generally low COP values obtained, the proposed arrangement seems especially suitable to be employed in adsorption machines utilizing energy sources of low economical value, such as waste heat. An optimum compromise between the COP value, which is closely related to the operating costs, and the power of the system should be provided, in case more valuable energy sources are utilized.     

Power factor definition in single phase system with arbitrary waveform according to similarity

Abstract

A new definition of power factor, which is suitable for an arbitrary waveform of voltage and current in a single‐phase system, is presented according to similarity between voltage and current waveforms. The similarity is described in infinite dimensions real vector space, and the power factor is defined as the multiplication of rootmean‐ square (RMS) value factor λ _RMS and phase factor λ_?. The new definition is compatible with IEEE Trial‐Use Standard 1459–2000, and can be a useful reference for power factor measurement, power factor correction and power compensation.     

An approach to machining process optimization

Optimization is rightly claimed to be the most significant factor distinguishing the modern approach to machining processes from the orthodox one. Practical results can be obtained from the application of mathematical modelling and optimization techniques.

The paper presents a procedure for solution of machining process optimization problems, with the use of theory of graphs and Bellman's optimum principle.

The finite graph G=(N, A) (where -N denoted a set of nodes and A the set of arcs) here presents the set of feasible solutions. Each are represents a corresponding machining operation and each path the feasible machining process.

A number can be associated with each are : the increment of criterion for optimality. Using the optimum principle we can find the shortest possible path in the graph, thus solving given problems of choice for the optimal machining process.

There is a variety of ways in which the performance criterion can be formulated. In this paper only those performance measures having sufficient economical justification are considered. We may minimize the costs of machining processes, or optimize economical effectiveness of capital engaged.

The method presented can be applied with every additive criterion, as well as with some non-additive ones. A practical example illustrates the field of possible application of this method.     

Development of hybrid ROCOF and RPV method for anti-islanding protection

ABSTRACT

Distributed generation (DG) must have the capability to quickly and accurately detect islanding operations under various operating conditions. An ideal islanding detection method should be without a non-detection zone (NDZ) and exempt from deteriorating power quality. A novel Anti-islanding protection technology that is a hybrid of rate of change of frequency (ROCOF) and reactive power variation (RPV) is proposed in this paper. The method can differentiate between a DG that falls into the NDZ for ROCOF and one that does not, and the RPV method will be initiated when the DG is within the NDZ. The amplitude of the reactive power variable can be accurately calculated using the proposed method. Thus, the degree of deterioration of power quality and power consumption can be effectively limited. The method has been implemented on a 3 kW DG to prove its feasibility. The experimental results demonstrated that in the proposed method, the DG was able to use the minimal amplitude of RPV to detect islanding in the NDZ. The breaker tripping time under various operating conditions conformed to the criteria specified in IEEE Std. 1547.     

The magneplane system

The results of the magneplane project carried out by a joint MIT-Raytheon-United Engineers team are summarized. These include preliminary design of a full-scale system with analysis of guideway and power distribution costs, vehicle requirements, and vehicle dynamics. The theoritical results were tested practically by building a fully operational $\text{1}\text{25}$ scale model system using both samarium-cobalt and superconducting magnet vehicles with on-board control telemetering systems, operating on a 116 m long actively synchronized guideway. The construction and testing of this scale model is also described.     

Hyperboloid mass spectrometer with a truncated trap

A hyperboloid mass spectrometer is proposed in which the analyzer is a three-dimensional ion trap truncated by the plane z=0. The mass peaks for different operating regimes of the mass analyzer are constructed from the results of a numerical modeling of the electric field and a simulation of the process of sorting the charged particles. The results serve as a basis for the construction of a hyperboloid mass spectrometer with a simple electrode system and a high resolving power. Pis’ma Zh. Tekh. Fiz. 25, 51–56 (May 26, 1999)     

Degradation of heat exchanger materials under biomass co-firing conditions

Abstract

Co-firing biomass in conventional pulverised coal fired power stations offers a means to rapidly introduce renewable and CO₂ neutral biomass fuels into the power generation market. Existing coalfired power stations are both much larger and more efficient than current designs of new biomass combustion systems, so feeding a few percent of biomass feed into an existing large coal fired station will give more biomass derived power than a new dedicated biomass station. Co-firing levels started at ～2% biomass, but this has increased to ～5–10% biomass, with higher levels of biomass co-firing being investigated, although supply of biomass becomes an issue with increasing co-firing levels. The lower levels of biomass co-firing (up to ～5%) can be achieved with relatively minor modifications to existing plants, so avoiding the large capital costs and risks of building new biomass-only fired power systems. However higher levels of co-firing are more difficult to achieve, requiring dedicated biomass supply systems and burners. For existing coal-fired power stations, the co-firing of biomass causes some practical problems, e.g.: the control of co-firing two fuels; changes to bottom/fly ash chemistry; changes to deposition (fouling and slagging) within the boiler; reduced reliability of key high temperature components (e.g. heat exchangers) due to increased corrosion problems relative to those experienced with coal alone.

This paper reports the results of assessments carried out to evaluate the potential operating conditions of heat exchangers in combustion systems with biomass (wood or straw) and coal cofiring, as well as laboratory corrosion tests that have been carried out to give an initial assessment of potential effects of biomass-co-firing.

The corrosion tests have been carried out using the deposit recoat method in controlled atmosphere furnaces. A series of 1000 hour tests have been carried out at typical superheater and evaporator metal temperatures using simulated deposit compositions and gaseous environments (selected on the basis of plant experience and potential fuel compositions). Five materials were exposed in these tests: 1Cr steel, T22 steel, X20CrMoV121, TP347HFG and alloy 625. In order to produce statistically valid data on the actual metal loss from the materials, the performance of the materials in these tests was determined from dimensional metrology before and after exposure. For each material, these data have been used to determine the sensitivity of the corrosion damage to changes in the exposure conditions (e.g. deposit composition, gas composition) thereby producing initial models of the corrosion performance of the materials. The corrosion data and model outputs have been compared with data available from power plants operating on coal, straw or wood fuels.     

A study of uv preionization pulsed tea CO2 laser

Abstract

A uniform volumetric discharge was obtained by means of an auxiliary UV preionization in a home‐made TEA CO₂ laser. The maximum output pulse energy of this laser system was about 12J per pulse with a pulse duration of 80 ns. The ratio of electric field to neutral particle density (E/N) in this laser was 7.6×10^‐16 V cm². The peak power and pulse shape of the laser were studied. The time delay between the predischarge and the maindischarge during the stable operation of this laser system has also been studied. It was observed that the laser was operating with uniform glow discharges when the time delayed between the predischarge and the maindischarge was in the range of 1.0 μs to 6.0 μs. The spark array used as a preionizer for producing the UV radiation in this system is new, simple, durable, and can be easily fabricated.     

Parametric study of economical energy usage in freezing tunnels

Large amounts of electricity are consumed in food freezing tunnels. An actual freezing tunnel at a citrus processing plant was studied experimentally to determine its operating characteristics. A computer model was also developed, and predicted temperature profiles were compared to experimental data. A parametric study was performed to determine the effect of the bed velocity, ambient temperature, internal fan loads, and can spacing on the tunnel bed. Methods for improving the effectiveness of the freezing tunnels are discussed. It is concluded that a factor, K, the ratio of fan work divided by the useful refrigeration effect, was the best indicator of economical energy usage in the freezing tunnel.     

Lasing characteristics of lasers with a vertical cavity based on In0.2Ga0.8As quantum wells

Semiconductor lasers with a vertical cavity with a high external quantum efficiency and high radiation power have been developed and constructed. Powers up to 10 W at T=300 K and 20 W at T=250 K have been obtained for 500 μm aperture lasers operating in the pulsed regime. Pis’ma Zh. Tekh. Fiz. 25, 40–44 (October 12, 1999)     

A strategy for the optimization and economic evaluation of an ORC system for energy recovery

Abstract

A strategy for the performance prediction and economic evaluation of an ORC (organic Rankine cycle) system for power conversion is studied. Different assumptions and system boundaries are used to understand the constraints of the boundaries as well as their effects on the evaluation results. A series of methods, including cost estimation, operation’ research, sensitivity analysis and optimal design of heat exchangers, is employed in evaluating this thermal to power conversion system. It is found that the resultant variations in the economic evaluation, no matter what economic index is used, are mostly depending on the input parameters and the unpredictable variables at the preliminary design stage. The analysis strategy, the detailed procedures as well as the computer programs, is presented with a 400°F, 2.5 ×10⁷ Btu/hr flue gas recovery case as an illustration. This study shows a large variation of payback period ranging from 5 to 15 years, depending on different assumptions, operating conditions, and system boundaries. This analysis recommends a more conservative approach to evaluate an energy recovery project to avoid an inappropriate judgement of an engineering design project.     

Optical tweezers with increased axial trapping efficiency

Abstract

We demonstrate that the axial trapping efficiency in optical tweezers is improved by using a Laguerre-Gaussian laser mode as the trapping beam. For a wide range of particle sizes and sample cell depths, the laser power required with an l = 3 Laguerre-Gaussian mode is reduced by a factor of two compared with that of the fundamental mode. This is important for biological applications where a reduction in the laser power lessens the risk of damage to living samples.     

Robust controllers design and efficiency analysis for a brushless servo system

Abstract

This paper investigates the design of robust controllers for a class of ac servo drives, the brushless servo motor drive, and presents the efficiency and power factor analysis of the drive system. Robust PI, H ², and H ⁸ control techniques are applied to the design of servo controllers. A fully digital control system is constructed to experimentally verify the controller performance. The steady‐state characteristics of the servo drive are derived and are measured on‐line by a microcomputer‐based efficiency measurement system. The theoretical development is validated by the experimental work.     

A joint replenishment policy with individual control and constant size orders

We consider inventory systems with multiple items under stochastic demand and jointly incurred order setup costs. The problem is to determine the replenishment policy that minimises the total expected ordering, inventory holding, and backordering costs–the so-called stochastic joint replenishment problem. In particular, we study the settings in which order setup costs reflect the transportation costs and have a step-wise cost structure, each step corresponding to an additional transportation vehicle. For this setting, we propose a new policy that we call the (s, 𝒬) policy, under which a replenishment order of constant size 𝒬 is triggered whenever the inventory position of one of the items drops to its reorder point s. The replenishment order is allocated to multiple items so that the inventory positions are equalised as much as possible. The policy is designed for settings in which backorder and setup costs are high, as it allows the items to independently trigger replenishment orders and fully exploits the economies of scale by consistently ordering the same quantity. A numerical study is conducted to show that the proposed (s, 𝒬) policy outperforms the well-known (𝒬, S) policy when backorder costs are high and lead times are small.     

Analysis of Modulational Instability in Monomode Optical Fibres with High-order Nonlinearity

Abstract

The modulational instability (MI) in monomode optical fibres with fifth-order nonlinearity, fibre loss, higher-order dispersion, and the temporal variation of third-order nonlinearity is studied theoretically. The conditions for the existence of the MI and the maximal modulational growth are given and discussed in detail. The results obtained show that the key factor dominating the producing condition of the MI is the power P of the continuous wave initially launched into the optical fibres. If P falls into 3/10<P/P ₀ <1/2 where P ₀ is defined as characteristic power, the MI can be produced in the range of not only anomalous group velocity dispersion but also the normal in which the final evolution state of the modulated wave is dark soliton.     

Solid-state AC breaker with parallel switched capacitor circuits for microgrid system

ABSTRACT

In this paper, a novel solid-state AC breaker, based on double-paralleled switched capacitors controlled with complementary pulse width modulation technique, is proposed for transition of microgrid due to its advantages of low di/dt stress to power devices and controllable resistance features. The circuit topology of the breaker is based on parallel switched capacitors, its operating and control theory are analyzed in detail to show its advantage in theory. The equivalent impedance of proposed parallel switched capacitor circuits is up to the switching frequencies, and the proposed switch is suitable for seamless transition between the island mode and grid-connected mode to reduce the current shock by changing the switching frequencies. Simulation and experimental results verify the effectiveness and feasibility of the new AC breaker.     

Scheme for implementing 1 → M symmetric economical phase-covariant telecloning based on quantum logic network

The quantum logic network to implement 1?→?M symmetric economical phase-covariant telecloning is presented. The scheme includes two parts: the first part is used to create the telecloning channel and the second part to teleport the input state. The telecloning channel which works without ancilla is constructed by two kinds of elementary unitary transformations, single-qubit rotation and multiple-qubit controlled operation. The probability of success is 50%, which is the same with the scheme in [Meng, F.Y.; Zhu, A.D. J. Mod. Opt. 2009, 56, 1255–1259].     

A Rosen-type piezoelectric transformer employing lead-free K0.5Na0.5NbO3 ceramics

Lead-free K_0.5Na_0.5NbO₃–K_5.4Cu_1.3Ta₁₀O₂₉–MnO₂ (KNN–KCT–Mn) ceramics have been prepared by a conventional ceramic sintering technique. The ceramics show excellent piezoelectric properties for application in power devices, and the optimum properties measured are as follows: piezoelectric constant d ₃₃ = 90 pC/N, planar electromechanical coupling factor k _p = 0.40, mechanical quality factor Q _m = 1900, remanent polarization P _r = 11.8 μC/cm², coercive field E _c = 0.85 kV/mm. A Rosen-type piezoelectric transformer with a dimension of 21 mm × 6 mm × 1.2 mm was fabricated using the KNN–KCT–Mn ceramics. Properties of the piezoelectric transformer operating in the first and second modes have been characterized. For the first mode, the transformer has a maximum output power of 0.7 W with a temperature rise of 14 °C. For the second mode, the maximum output power of the transformer is 1.8 W with a temperature rise of 33 °C. KNN–KCT–Mn ceramics have shown to be a potential lead-free candidate to be used in high-voltage–low-current devices.     

Potential for cost effective magnetocaloric air conditioning systems

Magnetic refrigeration is an emerging technology that exploits the magnetocaloric effect found in solid-state refrigerants. The combination of solid-state refrigerants, water-based heat transfer fluids, and high efficiency will lead to environmentally desirable products with minimal contributions to global warming. Among the numerous applications of refrigeration technology, air conditioning applications provide the largest aggregate cooling power and use the greatest quantity of electric energy. The primacy of the air conditioning application makes the establishment of cost targets for this application an essential feature of the R&D plan for magnetic refrigeration technology. A preliminary assessment of the permanent magnet costs and magnetocaloric material costs indicates that, for suitably chosen materials and operating conditions, these costs lay well below the total manufactured costs for vapor compression based air conditioners.