Journal of Energy Engineering

A miniature wind turbine (MWT) has received great attention recently for powering low-power devices. In this paper, a physics-based comprehensive model for predicting the performance of a miniature horizontal axis wind turbine (MHAWT) was established. The turbine rotor performance was investigated and an approximation of the power coefficient of the turbine rotor was made. Incorporation of the approximation with the equivalent circuit model, which was proposed in accordance with the principles of the MHAWT, in addition to its overall system performance versus the resistive load and ambient wind speed, was predicted. To demonstrate predictive modeling capability, the MHAWT system comprised of commercially available off-the-shelf components was designed and its performance was experimentally tested. The results matched well with those by prediction modeling, which implies that the proposed model holds promise in estimating and optimizing the performance of the MWT.

Given the important role of hydropower in peak electricity management, Middle Eastern countries are actively pursuing development of more hydropower resources by construction of large dams. Nonetheless, climate change is expected to affect the future productivity of hydropower by influencing the hydrologic cycle and different climate variables in the region. Although reactive plans to minimize climate change impacts on hydropower production have been implemented in the developed world, the developing world can still benefit from proactive actions. Studies of climate change impacts before and during implementation of hydropower projects can result in timely responses and adaptation to climate change with a potential of considerable cost savings. This study investigates the potential impacts of climate change on the hydropower systems in the Karkheh River Basin—the third largest river basin in Iran—in terms of potential for hydroelectricity generation. A simulation model is developed to examine how hydropower generation levels vary for different future climate change scenarios in this representative Middle Eastern basin. The obtained results suggest that the existing operation rules and design specifications, developed based on the historical climatic conditions, can lead to inefficient operations of the hydropower in the basin. Because of insignificant streamflow reductions in the short term, hydropower production may not change considerably in the near future. However, a serious hydropower generation deficit is expected in the midterm and long-term horizons in the Karkheh River Basin. Therefore, adaptation to the future climate change conditions and revision of the operation rule curves and design specifications are essential to optimal hydropower operations in this basin.

In this paper, a new practical robust water level control system for the U-tube steam generator (UTSG) using the quantitative feedback theory (QFT) is proposed. The steam generator is a nonlinear uncertain plant. However, the steam generator behaves as a linear uncertain and nonminimum phase plant at its different operating points, which makes its control a challenging problem. The control problem is to design controllers such that the closed-loop plant satisfies the robust stability, disturbance rejection, and robust tracking specifications that are derived from a desired steam generator performance. In the QFT design methodology, these specifications are satisfied by generating the plant templates, the composite bounds, and a nominal plant loop shaping procedure to satisfy these bounds. Simulation results reveal that the designed QFT water level controllers will ensure all the designers’ closed-loop specifications. Also, comparison results are provided that show the effectiveness of the robust QFT controllers with respect to the previously employed internal model-based controller.

In this study, a feasibility-analysis-based inexact fuzzy multistage model (FA-IFMSM) was developed for supporting the planning of energy and environmental systems under multiform uncertainties. In FA-IFMSM, methods of feasibility-analysis-based fuzzy linear programming (FA-FLP) and inexact multistage stochastic programming (IMSP) with recourse were integrated into a general mixed-integer linear programming framework, such that the developed model could tackle uncertainties described in terms of probability distributions, interval values, fuzzy sets, and their hybrid and mixture. Moreover, it could reflect dynamic features of facility-capacity expansions and energy supplies over a multistage context. It could also quantify constraint violation degrees through the adoption of various acceptable degree levels. Then the proposed model was applied to a regional energy and environmental system to illustrate its applicability, where conventional and renewable energy resources and their economic and environmental implications were considered. The results indicated that reasonable solutions were generated. They were helpful for supporting (1) adjustment or justification of allocation patterns of regional energy resources and services; (2) formulation of local policies regarding energy consumption, economic development, and environmental protection; and (3) in-depth analysis of trade-offs among system cost and satisfaction degree, and environmental requirements under multiple uncertainties.

The present paper conducts the experimental evaluation of the performance of a regenerative organic Rankine cycle (ORC) system working with refrigerant R123 and generating 10-kW-level power. The ORC system consists of an axial-flow single-stage turbine, a regenerator, an evaporator, a condenser, and a pump. The regenerative ORC and the basic ORC system efficiency are evaluated under the same conditions. The degree of superheat of the turbine inlet vapor is controlled by the evaporating temperature. The cooling water flow rate is controlled by adjusting the opening of the valve. The experiment results show that the thermal efficiency of the regenerative ORC is higher than that of the basic ORC by about 25%. The thermal efficiency of basic ORC with saturated vapor at turbine inlet is higher than that with superheated vapor by 3.2%, and the thermal efficiency of the regenerative ORC with saturated vapor at turbine inlet is higher than that with superheated vapor by 4.36%. The enthalpy drop across the turbine and the thermal efficiency of regenerative ORC both increase with increasing cooling water flow rate. The superheating at turbine inlet should be avoided, while a large cooling water flow rate should be considered to obtain higher system efficiency.

A thermoeconomic model for a double-stage coupled heat pump (DSCHP) with finite-rate heat transfer, heat leakage, and internal irreversibility has been developed. The heating load per unit total cost has been taken as the objective function. The optimal performance characteristics of the DSCHP have been discussed in detail and the optimum design parameters have been deduced analytically. The theoretical model has been exemplified in a particular case study. The investigation results demonstrate that the model is accurate to within 15% of the experimental data. The DCSHP design, with thermoeconomic optimization, leads to a significant increase of the specific heating load and a clear improvement of the economic performance with a small decrease of the coefficient of performance. When the values of ambient temperature, irreversibility of cycle I, irreversibility of cycle II, and investment cost per unit power have the same variation (5%), the objective function changes about 5, 5, 4.4, and 4.5%, respectively. The present paper provides a theoretical basis for design, thermoeconomic performance evaluation, and improvements of the DSCHP system.

A second-law thermodynamic analysis is carried out for a solar-driven power plant subjected to radiation and convection heat transfer. The collective role of radiation and convection modes of heat transfer is investigated. Heat transfer from a hot reservoir is assumed to be radiation dominated, whereas convection heat transfer is assumed to be the primary mode of heat transfer to a low temperature reservoir. The irreversibilities resulting from these finite rates of heat transfer are considered in determining the limits of efficiency and power generation that are discussed through varying process parameters. The upper limit is found to be a function of both the functional temperature dependence and of heat transfer and relevant system parameters.

As a result of China’s rapid economic growth, energy demand has increased significantly in recent years. Consequently, energy pricing has become increasingly prominent. This paper defines reasonable energy price ratios and establishes models to analyze them from the aspects of input/output standards, economic standards, and international standards according to the structure of the energy prices. Furthermore, based on the socioeconomic conditions in China, prices of coal, natural gas, and electric power are selected as examples for analyzing the price ratios of regulated and nonregulated energy prices under three evaluation criteria. Finally, reasonable energy price ratios in China are determined through a comprehensive analysis. The paper concludes that these ratios are significant for developing countries undergoing energy market oriented reforms such as China.

A small wind turbine generator system applied in coastal areas and islands must have good structures and protective actions to ensure reliable operation. In this paper, a small wind turbine prototype with high reliability is designed and examined in the real island conditions. With respect to lightning resistance, the whole structure has good lightning discharge channels, especially for the protection of the blades. Extensive use of nonmetallic materials on the critical components dramatically improves the turbine’s corrosion resistance and ensures the mechanical strength of the structures. For overspeed protection and power regulation, a furling device based on electric-driven control technology is designed and applied. After operation of the prototype for a year and a half, the results indicate that the performance of the turbine is very stable, and the electric-driven method of furling is very effective for protecting the turbine in strong winds. These measures are effective for improving the turbines’ reliability and are helpful for the application of small wind turbines in the marine environments.

Permeable pavements offer a solution for rainwater runoff treatment in urban areas, combining water management with water reuse purposes when the sealed subbase become rainwater reservoirs. Furthermore, the thermal behavior investigations of these systems have proved their contribution to palliate the urban heat island effect in the hottest season and to delay freezing during the coldest season. Increasing knowledge of heat-transfer mechanisms into the permeable pavements and their subbase has enabled the use of these structures combined with ground source heat pumps (GSHP) in addition to the other well-known applications. The aim of the present study is to investigate the thermal response observations of permeable pavements under specific weather conditions while paying attention to the temperature distribution in the subbase, where rainfall water is stored for others uses, to evaluate the possibility of introducing GSHP technology. The bedding layer and subbase temperature of reinforced grass permeable pavements was monitored during three months in summer 2008, and the preliminary results obtained show the subbase temperature different from the air temperature during the period of the study and demonstrate that the subbase is less affected by the air temperature than the bedding layer because of the insulating capacity of permeable pavements, explained through the heat-transfer processes that take place into the pavements.