0

IN THIS ISSUE

### RESEARCH PAPERS

J. Energy Resour. Technol. 2005;127(4):265-271. doi:10.1115/1.1926310.

Performance analysis and cost estimation are carried out for a cogeneration system consisting of a solid high-polymer-film-type fuel cell with a methanol reformer applied to individual houses. For the operation of the fuel cell under a partial load, a unique point of this system is the shifting of the driving point by the electric heater. Considering the annual energy cost for an average house in Sapporo, Japan, the energy cost of this system is shown to be 1.42 times that of conventional systems in which a cogeneration system is not installed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2005;127(4):272-279. doi:10.1115/1.1944008.

A tangential flow prototype turbine with a rotating channel containing five optimized deflectors is presented. This atypical turbine configuration may be useful for application in the low $ns$ high $ds$ region of the Balje chart, where conventional turbines offer very poor performances. A $70kW$ maximum brake power, pressured-air test rig has been used for the analysis of operating characteristics, such as pressure, temperature, flow rate, and brake power. An electronic data acquisition system for automated measurement management was employed. An experimental campaign was carried out to identify the distribution of the pressure in the rotary ducts of the turbine. The results indicate the presence of a pressure gradient in the immediate vicinity of the inlet jet that is strongly attenuated when the ducts are not directly in contact with the jet.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2005;127(4):280-284. doi:10.1115/1.1926311.

The objective of this paper is to analyze the uncertainty associated with pump efficiency measurements and to determine reasonable confidence intervals for these data. In the past, many industrial sales and some pieces of academic research have been based upon the experimental data of pump efficiencies; yet few have questioned the accuracy of the experimental data and no one has provided a confidence interval which reflects the range of uncertainty in the measurement. In this paper, a method for calculating this confidence interval is presented and it is shown that substantially large confidence intervals exist within the testing results of a pump. Furthermore, it is recommended that these confidence intervals be included with the efficiency data whenever it is reported.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2005;127(4):285-292. doi:10.1115/1.2000274.

Experimental and theoretical investigation of a recently patented down-hole direct-acting reciprocating pump system is presented. The technology, (US Patent No. 5,860,795) consists of operating a gas well with gas and liquid phases being produced separately by using the gas phase to power a pump to bring the liquid phase to the surface. This would increase the duration of profitability of many gas wells in North America. Experiments and modeling were used to determine optimum design parameters to maintain flow at a minimum reservoir pressure; an optimum area ratio for the gas/liquid pistons is approximately 40. The effect of friction in the pumping system was predicted to have a small effect on this optimum design. The results of this investigation will now be used to design and construct a prototype for field testing.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2005;127(4):293-301. doi:10.1115/1.1924467.

First oil production from a deep-water oil field is to be achieved by the installation of an initial development system (IDS). Well testing is required for field development and reservoir management. The well testing system requires high-accuracy oil and water rates to provide the data needed for decision analysis in ongoing drilling programs. The well testing system must also be integrated with other platform operations, such as well cleanup after drilling. We introduce here, the concept of a multiphase meter in series with conventional separation technology for improved process control. This feedback control loop configuration is simulated in MATLAB and shown to extend the capabilities of both technologies. The principle of gas volume fraction control in two-phase separator liquid lines is shown to be supplementary to conventional level control systems for performance enhancement of oil field well testing. Concepts demonstrated here can also be easily applied as retrofits to existing separation facilities, which show accuracy or upset problems.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2005;127(4):302-309. doi:10.1115/1.2047591.

Pigging has been recognized as the most cost-effective method for preventing flow restriction by wax deposits in subsea flowlines. However, the pigging mechanics for wax removal in pipelines is still very poorly understood. A unique test facility was designed and constructed for experimental studies on the mechanics of wax removal in pipelines. The test facility consisted of a test section, a support structure, an apparatus to pull the pig through the test pipe, and a computer-based data acquisition system. The test section was $6.4m(21ft)$ long and was made from $0.0762m(3in.)$ inner diameter schedule-40 steel pipe. The mixture of commercial wax and mineral oil was cast inside the test section at different wax thickness and oil contents. A series of experiments was performed to investigate the wax removal mechanics with three different types of conventional pigs, i.e., cup, disc, and foam pigs. The experiments showed that a typical wax removal process using a pig followed four distinct phases, namely, wax breaking, plug formation, accumulation, and production phases. Wax accumulation can be very significant and is expected to be the dominating factor for the force required for moving a pig in long pipelines. As wax thickness and hardness increases, the required force to move the pig increases. The shape and material of the pig have a profound effect on the wax removal performance. While the disc pig provides the most efficient wax removal, the force requirement is excessive, especially for thicker and harder wax deposits. The wax removal performance of a cup pig is very similar to that of a disc pig. However, the cup pig can withstand higher load without mechanical damages than the disc pig. The foam pig offers the poorest wax removal performance.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2005;127(4):310-317. doi:10.1115/1.1924465.

Asphaltene precipitation and deposition during primary oil recovery and resulting reservoir formation damage are described by a phenomenological mathematical model. This model is applied using experimental data from laboratory core flow tests. The effect of asphaltene deposition on porosity, permeability, and the productivity of vertical wells in asphaltenic-oil reservoirs are investigated by simulation.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2005;127(4):318-322. doi:10.1115/1.1924466.

A model for analysis and interpretation of the simultaneous deposition of paraffin and asphaltene in laboratory core tests is presented. This model incorporates the mass balance equations for the oil, gas, paraffin, and asphaltene pseudocomponents; the paraffin and asphaltene solubility and deposition models; the energy and momentum balance equations; and the porosity and permeability reduction models. This model is numerically solved and validated with two sets of laboratory experimental data. It is demonstrated that the present model satisfactorily represents the simultaneous deposition of paraffin and asphaltene and the resultant damage caused on the porosity and permeability of porous media. The model is used for determination of the various process parameters with the help of the experimental data obtained by laboratory core tests.

Commentary by Dr. Valentin Fuster

### TECHNICAL BRIEFS

J. Energy Resour. Technol. 2005;127(4):323-327. doi:10.1115/1.1926309.

The theory of metal forming has been used to study the mechanical response of a solid tubular under radial plastic expansion. A mathematical model of an expanded thin walled tube under compression has been developed in this paper. The study showed that as the friction coefficient and mandrel angle increase the drawing force and induced stresses increase. However, the final tube thickness and length were found to decrease with an increase in both parameters.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2005;127(4):328-333. doi:10.1115/1.1949624.

Worldwide power resources that could be extracted from the steady-state operation of ocean thermal energy conversion (OTEC) plants are estimated using a simple model. This order-of-magnitude analysis indicates that about $3×109kW$ (3 TW) may be available, at most. This value is much smaller than estimates currently suggested in the technical literature. It reflects the scale of the perturbation caused by massive OTEC seawater flow rates on the thermal structure of the ocean. Not surprisingly, maximum OTEC power nearly corresponds to deep cold seawater flow rates of the order of the average abyssal upwelling representative of the global thermohaline circulation.

Commentary by Dr. Valentin Fuster