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IN THIS ISSUE

### Guest Editorial

J. Energy Resour. Technol. 2010;132(2):020301-020301-2. doi:10.1115/1.4001684.
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Population and societal growth coupled with technological progress, have all lead to a rapid increase in energy usage and consequent depletion of fossil fuel reserves. Although one could question the credibility of these estimations as supported by the recent revision in the case of natural gas reserves, the fact that the worldwide demand will keep on growing unabated leaves no doubt that the solution is not to procrastinate but to look for alternative sources of energy. At the same time, there is a growing belief that the use of fossil fuel and the consequent release of greenhouse gases are mainly responsible for the observed global warming trend. Hence there is a big push for developing new sources of clean, alternative energy for replacing the fossil fuels. In addition, if the source is renewable, that will further help provide a long term solution. However, one should note that the Sun is the main source of energy; the energy received from the Sun is transformed into various sources like solar, wind, ocean, geothermal, nuclear, biomass, fossil fuel, etc., over widely differing space and time scales by mainly ecological and artificial processes. The term renewable has a spatial and temporal connotation. Hence what is “renewable” for one nation or part of the world may not be renewable and in fact even be available for another part of the world. Thus energy source has become an important commodity for survival and progress and has to be evaluated on thermoeconomic and socioeconomic bases. It requires 21st century cutting edge science, technology and systems for harvesting energy from the available sources and transforming it efficiently and economically into electricity, heat or power required for human consumption with minimal perturbation to the ecology. It is also important to note that the present energy crisis has occurred mainly because of dependence on only a few sources. Hence this needs to be addressed not only by exploring and evaluating all possible sources but also by developing systems for efficient transformation, storage and distribution of energy. All this involves development of technology in all areas and their cross transplantation for reaching the goal and sustaining the progress.

Commentary by Dr. Valentin Fuster

### Research Papers

J. Energy Resour. Technol. 2010;132(2):021001-021001-9. doi:10.1115/1.4001568.

The compression process necessary for the liquefaction of natural gas on offshore platforms generates large amounts of heat, usually dissipated via sea water cooled plate heat exchangers. To date, the corrosive nature of sea water has mandated the use of metals, such as titanium, as heat exchanger materials, which are costly in terms of life cycle energy expenditure. This study investigates the potential of a commercially available, thermally conductive polymer material, filled with carbon fibers to enhance thermal conductivity by an order of magnitude or more. The thermofluid characteristics of a prototype polymer seawater-methane heat exchanger that could be used in the liquefaction of natural gas on offshore platforms are evaluated based on the total coefficient of performance $(COPT)$, which incorporates the energy required to manufacture a heat exchanger along with the pumping power expended over the lifetime of the heat exchanger, and compared with those of conventional heat exchangers made of metallic materials. The heat exchanger fabricated from a low energy, low thermal conductivity polymer is found to perform as well as, or better than, exchangers fabricated from conventional materials, over its full lifecycle. The analysis suggests that a $COPT$ nearly double that of aluminum, and more than ten times that of titanium, could be achieved. Of the total lifetime energy use, 70% occurs in manufacturing for a thermally enhanced polymer heat exchanger compared with 97% and 85% for titanium and aluminum heat exchangers, respectively. The study demonstrates the potential of thermally enhanced polymer heat exchangers over conventional ones in terms of thermal performance and life cycle energy expenditure.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2010;132(2):021002-021002-6. doi:10.1115/1.4001569.

The design of cooling solutions is an important consideration for the efficient management of different types of energy technologies. In the present work, we adapt the method of thermo-volumes—which has been used for nearly a decade in the design of electronic cooling solutions—for purposes of expeditiously understanding the thermal resistance of a given solution (in terms of cooling performance) along with its flow resistance (an indicator of the pumping power or energy consumption, which will be required by the thermal solution). Furthermore, we expand on thermo-volumes by including the lifetime exergy cost as a means to enable the consideration of resource consumption (and thus the environmental sustainability) of the cooling solution. We apply this framework for evaluation of thermal management solutions in terms of the heat removal capacity per unit lifetime exergy consumption. This paper concludes by illustrating applicability of the method to the design of a fuel cell thermal management solution.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2010;132(2):021003-021003-8. doi:10.1115/1.4001573.

Coal consumption accounted for 36% of America’s $CO2$ emissions in 2005, yet because coal is a relatively inexpensive, widely available, and politically secure fuel, its use is projected to grow in the coming decades (USEIA, 2007, “World Carbon Dioxide Emissions From the Use of Fossil Fuels,” International Energy Annual 2005, http://www.eia.doe.gov/emeu/iea/carbon.html). In order for coal to contribute to the U.S. energy mix without detriment to an environmentally acceptable future, implementation of carbon capture and sequestration (CCS) technology is critical. Techno-economic studies establish the large expense of CCS due to substantial energy requirements and capital costs. However, such analyses typically ignore operating dynamics in response to diurnal and seasonal variations in electricity demand and pricing, and they assume that $CO2$ capture systems operate continuously at high $CO2$ removal and permanently consume a large portion of gross plant generation capacity. In contrast, this study uses an electric grid-level dynamic framework to consider the possibility of turning $CO2$ capture systems off during peak electricity demands to regain generation capacity lost to $CO2$ capture energy requirements. This practice eliminates the need to build additional generation capacity to make up for $CO2$ capture energy requirements, and it might allow plant operators to benefit from selling more electricity during high price time periods. Post-combustion $CO2$ absorption and stripping is a leading capture technology that, unlike many other capture methods, is particularly suited for flexible or on/off operation. This study presents a case study on the Electric Reliability Council of Texas (ERCOT) electric grid that estimates $CO2$ capture utilization, system-level costs, and $CO2$ emissions associated with different strategies of using on/off $CO2$ capture on all coal-fired plants in the ERCOT grid in order to satisfy peak electricity demand. It compares base cases of no $CO2$ capture and “always on” capture with scenarios where capture is turned off during: (1) peak demand hours every day of the year, (2) the entire season of peak system demand, and (3) system peak demand hours only on seasonal peak demand days. By eliminating the need for new capacity to replace output lost to $CO2$ capture energy requirements, flexible $CO2$ capture could save billions of dollars in capital costs. Since capture systems remain on for most of the year, flexible capture still achieves substantial $CO2$ emissions reductions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2010;132(2):021004-021004-6. doi:10.1115/1.4001603.

A life cycle assessment of nuclear-based hydrogen production using thermochemical water splitting is conducted. The copper-chlorine thermochemical cycle is considered, and the environmental impacts of the nuclear and thermochemical plants are assessed. Environmental impacts are investigated using CML-2001 impact categories. The nuclear plant and the construction of the hydrogen plant contribute significantly to the total environmental impacts. The environmental impacts of operating the hydrogen production plant contribute much less. Changes in the inventory of materials or chemicals needed in the thermochemical plant do not affect significantly the total impacts. Improvement analysis suggests the development of more sustainable processes, particularly in the nuclear plant and construction of the hydrogen production plant.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2010;132(2):021005-021005-9. doi:10.1115/1.4001566.

A reference design for a commercial-scale high-temperature electrolysis (HTE) plant for hydrogen production was developed to provide a basis for comparing the HTE concept with other hydrogen-production concepts. The reference plant design is driven by a high-temperature helium-cooled nuclear reactor coupled to a direct Brayton power cycle. The reference design reactor power is $600 MWt$, with a primary system pressure of 7.0 MPa, and reactor inlet and outlet fluid temperatures of $540°C$ and $900°C$, respectively. The electrolysis unit used to produce hydrogen includes 4,009,177 cells with a per-cell active area of $225 cm2$. The optimized design for the reference hydrogen-production plant operates at a system pressure of 5.0 MPa, and utilizes an air-sweep system to remove the excess oxygen that has evolved on the anode (oxygen) side of the electrolyzer. The inlet air for the air-sweep system is compressed to the system operating pressure of 5.0 MPa in a four-stage compressor with intercooling. The alternating current to direct current conversion efficiency is 96%. The overall system thermal-to-hydrogen-production efficiency (based on the lower heating value of the produced hydrogen) is 47.1% at a hydrogen-production rate of 2.356 kg/s. This hydrogen-production efficiency is considerably higher than can be achieved using current low-temperature electrolysis techniques. An economic analysis of this plant was performed using the standardized hydrogen analysis methodology developed by the Department of Energy Hydrogen Program, and using realistic financial and cost estimating assumptions. The results of the economic analysis demonstrated that the HTE hydrogen-production plant driven by a high-temperature helium-cooled nuclear power plant can deliver hydrogen at a competitive cost. A cost of \$3.23/kg of hydrogen was calculated assuming an internal rate of return of 10%.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2010;132(2):021006-021006-9. doi:10.1115/1.4001567.

The power, water extraction, and refrigeration (PoWER) engine has been investigated for several years as a distributed energy (DE) system among other applications for civilian or military use. Previous literature describing its modeling and experimental demonstration have indicated several benefits, especially when the underlying semiclosed cycle gas turbine is combined with a vapor absorption refrigeration system, the PoWER system described herein. The benefits include increased efficiency, high part-power efficiency, small lapse rate, compactness, low emissions, lower air and exhaust flows (which decrease filtration and duct size), and condensation of fresh water. The present paper describes the preliminary design and its modeling of a modified version of this system as applied to DE, especially useful in regions, which are prone to major grid interruptions due to hurricanes, undercapacity, or terrorism. In such cases, the DE system should support most or all services within an isolated service island, including ice production, so that the influence of the power outage is contained in magnitude and scope. The paper describes the rather straightforward system modifications necessary for ice production. However, the primary focus of the paper is on dynamic modeling of the ice making capacity to achieve significant load-leveling via thermal energy storage during the summer utility peak, hence reducing the electrical capacity requirements for the grid.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2010;132(2):021007-021007-10. doi:10.1115/1.4001571.

Increasing the coefficient of performance of a vapor compression refrigeration system may be realized by utilizing work recovering expansion devices that additionally lower the enthalpy of the refrigerant at the inlet of the evaporator. Depending on the operational and geometrical parameters of the expander, laminar and viscous two-phase leakage flows within the expander may be present. Single-phase leakage models available in the literature must then be modified or rederived accordingly. A dynamic frictional model for the expander must also be developed for ideal operation (i.e., no internal leakage) and modified to account for internal leakage accordingly. This paper presents a comprehensive component-level model of inherent friction and internal leakage losses in a two-phase circular rotary-vane expander used in a vapor compression refrigeration system. The model establishes the performance of the expander as a function of geometric and fluid parameters. Accurate modeling and prediction of frictional and internal leakage losses is vital to being able to accurately estimate the efficiency, rotational speed, and the torque and power produced by the expander. Directions for future work are also discussed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2010;132(2):021008-021008-8. doi:10.1115/1.4001572.

National energy security concerns related to liquid transportation fuels have revived interests in alternative liquid fuel sources. Coal-to-fuel technologies feature high efficiency energy conversion and environmental advantages. While a number of factors are driving coal-to-fuel projects forward, there are several barriers to wide commercialization of these technologies such as financial, construction, operation, and technical risks. The purpose of this study is to investigate the performance features of coal-to-fuel systems based on different gasification technologies. The target products are the Fischer–Tropsch synthetic crude and synthetic natural gas. Two types of entrained-flow gasifier-based coal-to-fuel systems are simulated and their performance features are discussed. One is a single-stage water quench cooling entrained-flow gasifier, and another one is a two-stage syngas cooling entrained-flow gasifier. The conservation of energy (first law of thermodynamics) and the quality of energy (second law of thermodynamics) for the systems are both investigated. The results of exergy analysis provide insights about the potential targets for technology improvement. The features of different gasifier-based coal-to-fuel systems are discussed. The results provide information about the research and development priorities in future.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2010;132(2):021009-021009-7. doi:10.1115/1.4001574.

The world’s energy supplies will continue to be pressured as the population grows and the standard of living rises in the developing world. A move by the rest of the world toward energy consumption rates on par with the United States is most probably unsustainable. An examination of population trends, current energy utilization rates, and estimated reserves shows that a major worldwide transition to renewable resources is necessary in the next 100 years. This paper examines one possible scenario of how energy usage and renewable power generation must evolve during this time period. As the global standard of living increases, energy consumption in developing nations will begin to approach that of the developed world. A combination of energy conservation and efficiency improvements in developed nations will be needed to push the worldwide energy consumption to approximately 200 million Btu per person per year. Fossil fuel resources will be exhausted or become prohibitively expensive, necessitating the development of renewable energy resources. At this projected steady state population and energy consumption, the required contribution of each type of renewable resource can be calculated. Comparing these numbers to the current renewable capacities illustrates the enormous effort that must be made in the next century.

Commentary by Dr. Valentin Fuster