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DISCUSSION

J. Energy Resour. Technol. 2004;126(4):249-257. doi:10.1115/1.1834851.
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This article presents a critical analysis of all the major pathways to produce hydrogen and to utilize it as an energy carrier to generate heat or electricity. The approach taken is to make a cradle to grave analysis including the production of hydrogen, the conversion of hydrogen to heat or electricity, and finally the utilization of that heat or electricity for a useful purpose. This methodology shows that no currently available hydrogen pathway, irrespective of whether it uses fossil fuels, nuclear fuels, or renewable technology as the primary energy source to generate electricity or heat is as efficient as using the electric power or heat from any of these sources directly. Furthermore, electric vehicles using batteries to store electricity are shown to be more efficient and less polluting than fuel cell powered vehicles using energy stored in hydrogen.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS

J. Energy Resour. Technol. 2004;126(4):258-261. doi:10.1115/1.1811119.

Membrane temperature field of a polymer electrolyte fuel cell (PEFC) has been visualized experimentally. PEFCs need further breakthrough for deployment in the market. One of the major issues is the temperature management of the polymer membrane and the whole cell that strongly govern system performance through electrochemical reactions, ion transport, water management, and gas supply. The temperature field of the membrane, however, had not been visualized due to the cell configuration. In our experiment, the thermography technique is applied to visualize an operating test cell. Despite the unique configuration, measured i-V characteristics guarantee the cell performance. The visualization results revealed several important characteristics that help us understanding the physics and suggest design knowledge. One major result is the existence of so called a hot spot. The membrane does have a temperature distribution, and a local temperature maximum may exceed the membrane design limitation. This trend, of course, is not favorable for design purposes. Also, the impact of the major operation parameters, such as current density, humidification, and gas flow configuration, have been clearly exhibited. The experimental results are examined by using the results of our previously developed numerical code. The code includes the conjugate nature of the electrochemical reaction and the heat and mass transport processes. By comparing the experiment and the calculation, the mechanisms of the hot-spot generation and the parameter dependence have been explained. The results revealed the physics and suggested essential design criteria.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2004;126(4):262-270. doi:10.1115/1.1789519.

The flow of fuel and oxidant through a PEMFC is analyzed for prediction of maldistribution. Flow distribution of both fuel and oxidant from the port to the individual cells critically control the performance of a PEMFC stack in combination. The distribution of fluids was simulated by analytical approach utilizing flow channeling model of a manifold. A detailed numerical modeling is also carried out considering flow in each cell between the electrodes as flow through an equivalent porous medium offering identical resistance. The results show a close match between the analytical and numerical results. The parametric study reveals that flow rate and port size plays major role determining maldistribution of the fluids, which can be considerably skewed when large numbers of cells are stacked for larger power output.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2004;126(4):271-278. doi:10.1115/1.1786928.

Transport of solid-liquid slurries in pipeline transport over short and medium distances is very important in many industries, including mining related processes. The particle image velocimetry technique was successfully utilized to investigate the velocities and kinetic energy fluctuations of slurry particles at the tongue region of an optically-clear centrifugal pump. The experiments were conducted using 500 micron glass beads at volumetric concentrations of 2.5% and 5% and at pump speeds of 725 rpm and 1000 rpm. The fluctuation kinetic energy increased approximately 200% to 500% as the pump speed was increased from 725 rpm to 1000 rpm. The directional impingement mechanism is more significant at the pressure side of the blade, tongue and the casing. This mechanism becomes more important as the speed increases. This suggests that the impeller, tongue and the casing of the slurry pump can wear out quickly, especially with an increase in speed. In this paper the emphasis is on the tongue region. The random impingement mechanism caused by the fluctuation kinetic energy of the solids can play an important role on the erosion of the tongue area.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2004;126(4):279-284. doi:10.1115/1.1789518.

Currently, there exist large heavy-oil reserves in countries like Venezuela and Canada. In Venezuela, heavy oil represents 69% of the reserves, and its exploitation is not always feasible using traditional pumping technologies. In particular, this is the case of some in-lake oil wells in Venezuela, which are impossible to exploit by means of any known efficient way of oil lifting. An alternative is the gas-chamber pumping (GCP), an intermittent artificial lift method used in diverse areas of USA, in shallow wells with heavy oil and in areas where a source of high-pressure gas exists. Few works are reported on the modeling of the phenomena associated to GCP, the most rigorous being the one published by PDVSA-Intevep in the year 2000. This model, however, omits some key aspects related with gas injection, which affects its precision to simulate or design GCP systems. The present work develops a model to rigorously simulate the stage of gas injection into the chamber, incorporating aspects like the flow of gas from the supply manifold up to the wellhead, the gas expansion within the injection valve, the descending flow along a coiled tubing, and the heat transfer associated. The pressurization process and chamber venting are also modeled. The model predictions are in excellent agreement with experimental data [1].

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2004;126(4):285-292. doi:10.1115/1.1803849.

A great number of variables significantly influence the energetic, environmental and economic results of CHP (Combined Heating and Power) and CHCP (Combined Heating Cooling and Power) plants operation, and as a consequence their project activity is rather complex. In order to select the best layout and properly size the machines, detailed data on hourly electric, thermal, and cooling demand are necessary, so that a series of plant life cycle simulations may have to be carried out. Unfortunately, such detailed data are rarely available, because energy consumptions data for existing buildings are usually derived from aggregated monthly or bimonthly gas and electricity bills. Even more difficulties are encountered for new types of buildings, for which no consumptions data are available. In such cases, the most common procedure consists in performing, using case-oriented criteria, an estimate of the thermal and cooling consumption levels, and to refine it during construction, if necessary. This is the case of an existing medium size CHCP pilot plant for office buildings that covers the electrical, thermal, and cooling loads of two office buildings situated in a Mediterranean area (Palermo, Sicily, Italy). Estimated demand profiles were used; the effect on thermal demand of the conversion of the cooling load into thermal one through an absorption chiller was assessed. This is a very significant aspect in all warm climates zones. Cumulative curves were obtained for the aggregate thermal demand, by summing the heat direct applications and the heat consumptions for feeding the absorption chiller. In this paper the existing plant was compared with other plant configurations, varying both for machine sizes and management criterion, in order to affirm whether or not the plant selected by the designer in a simplified manner was or not an appropriate solution. The comparison was performed from an energetic and economic viewpoint.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2004;126(4):293-301. doi:10.1115/1.1805540.

This paper deals with a thermo-mechanical exergy analysis of Balcova Geothermal District Heating System (BGDHS) in Izmir, Turkey using actual system data and an assessment of the district heating system performance, energy and exergy efficiencies, and exergy destructions. The exergy destructions in the overall BGDHS are quantified and illustrated using an exergy flow diagram. Also, both energy and exergy flow diagrams are compared. The exergy destructions in the system particularly occurs in terms of the exergy of the fluid lost in the pumps, the heat exchanger losses, the exergy of the thermal water (geothermal fluid) reinjected and the natural direct discharge of the system, accounting for 3.06%, 7.24%, 22.66% and 24.1%, respectively of the total exergy input to the BGDHS. Both energy and exergy efficiencies of the overall BGDHS are investigated for system performance analysis and improvement and are determined to be 37.60% and 42.94%, respectively.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2004;126(4):302-310. doi:10.1115/1.1794696.

The authors have previously developed and proposed methods to estimate the in situ rock strength and tooth wear while drilling with roller-cone bits [Karasawa et al., 2002, ASME J. Energy Resour. Technol. 124, pp. 125–132 (Pt. 1) 133–140 (Pt. 2)]. The purpose of this paper is to provide a follow-up to these two reports and to propose, for both previous methods, alternate techniques that can be more readily implemented in the field than those originally presented. The data presented in Part 1 of the previously mentioned work [1] were reanalyzed in order to find a new and simple parameter that can be used to estimate rock strength. This parameter uses only one set of data that consists of bit weight, torque, penetration rate, rotary speed, and bit diameter. It was also demonstrated that the effect of tooth wear on this new parameter is small. In addition, more practical methods, which employ two parameters, are derived and proposed to evaluate the tooth wear of roller-cone bits.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2004;126(4):311-319. doi:10.1115/1.1790537.

A new pumping concept has been developed and patented by the Alberta Research Council to address the problem of liquid loading in natural gas wells at low, depleted pressures. This concept consists of a pump installed at the bottom of the wellbore that is driven by the reservoir gas pressure to bring the produced liquids to the surface as they accumulate thereby improving gas production from shallow gas wells. The above pump concept has been investigated in two stages of research. In the first stage, a mathematical model was developed to estimate the minimum reservoir pressure required to prevent liquid build up in a gas well with either: 1) the reservoir pressure (and flow) itself carrying the produced liquids to the surface in a two-phase flow or 2) the reservoir gas pressure powering a pumping system to carry the produced liquids to the surface in the most efficient manner possible. The objective of the second stage of this investigation was to look at the feasibility of using a reciprocating pump powered by gas pressure. In particular, the effect of the pump Area Ratio (ratio of the area being pushed by the gas to the area pushing the liquid) on the use of reservoir gas pressure was investigated. There are approximately 75,000 flowing gas wells in western Canada and these gas wells were categorized by depth and production rate. From this list of gas wells, a typical well was chosen and its production data and well characteristics were incorporated into the mathematical model. The model was tested in both the above-mentioned investigations and the results show that there is a significant increase in the operating range when the reservoir pressure is used more efficiently to produce gas from the well. It was determined that higher pump-area ratios lead to a more efficient use of reservoir pressure and for the gas well investigated in this study, an optimum area ratio of 40 was identified as the best design. The concept of multistage pumping was also investigated. The results presented are the basis for experiments presently being designed that will validate the current model of the system and allow for possible improvements.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2004;126(4):320-325. doi:10.1115/1.1789524.

Based on a conventional walking-beam pumping unit, a dual-beam pumping unit for increasing stroke and reducing force is presented, and an approach involving computer kinematic and dynamic simulation of this pumping unit is introduced in this paper. First, all three-dimensional parts are constituted and assembled to create a three-dimensional virtual mechanism of the dual-beam pumping unit for increasing stroke and reducing force. Second, all necessary joints are constituted, and all prescribed loads and input rotation are exerted onto the relative joints of the virtual mechanism. Finally, some simulation curves of the displacement, velocity, acceleration of the sucker rod, the working force exerted onto some key joints, and the driving torque of the crank from the three-dimensional virtual mechanism are obtained. The simulation results prove that the stroke of the sucker rod is 4.5-fold compared to a conventional walking-beam pumping unit, while the driving torque of the crank and all working forces exerted onto the key joints are notably reduced.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2004;126(4):326-333. doi:10.1115/1.1805539.

Local measurements and 3D CFD simulations in gas-liquid cylindrical cyclone separators are scarce. The main objective of this study is to conduct local measurements and 3D CFD simulations to understand the swirling flow behavior in a cylindrical cyclone with one inclined tangential inlet. Axial and tangential velocities and turbulent kinetic energy across the cylinder diameter (ID=0.089 m) were measured at 24 different axial locations (0.32–0.90 m below the inlet) by using a laser Doppler velocimeter (LDV). The liquid flow rate was 16.4 m3/h, which corresponds to an average axial velocity of 0.732 m/s and Reynolds number of 66,900. Measurements are used to create color contour plots of axial and tangential velocity and turbulent kinetic energy. Color contour maps revealed details of the flow behavior. Additionally, 3D CFD simulations with different turbulence models are conducted. Simulations results are compared to LDV measurements.

Commentary by Dr. Valentin Fuster

TECHNOLOGY REVIEW

J. Energy Resour. Technol. 2004;126(4):334-341. doi:10.1115/1.1831282.

Water inflow to petroleum wells hampers production of oil or gas leading to early shut downs of the wells without sufficient recovery of hydrocarbons in place. Downhole water sink (DWS) is a completion/production technique for producing water-free hydrocarbons with minimum amount of water from reservoirs with bottom water drive and strong tendency to water coning. DWS eliminates water invasion to hydrocarbon production by employing hydrodynamic mechanism of coning control in situ at the oil-water or gas-water contact. The mechanism is based upon a localized water drainage generated by another well completion (downhole water sink) installed in the aquifer beneath the oil/water or gas/water contact. The paper summarizes the development and state-of-the-art of DWS technology. Presented are results from theoretical studies, physical and numerical experiments, and field projects to date. It is demonstrated that DWS could increase recovery and control water production in vertical and horizontal oil wells—with natural flow, downhole pumps or gas lift, and in the gas wells producing from low-pressure tight gas reservoirs. To date, DWS has been used in reservoirs with bottom water. Moreover, in principle, the technology might also be used in the dipping reservoir structures with encroaching side-water.

Commentary by Dr. Valentin Fuster

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