J. Energy Resour. Technol. 2000;122(4):169-176. doi:10.1115/1.1318204.

Full-scale experiments were conducted in order to investigate flow pattern transitions in horizontal pipelines carrying oil-water mixtures. In the experiments, a 16-in. pipeline conveying light crude oil was used. The line was connected to a freshwater network to control the input water volume fraction. A gate valve installed at the pipeline inlet controlled the oil flow rate. The transition from stratified flow to dispersed flow was determined by measuring the transversal water fraction profile. For this purpose, a special device, the multi-point sampling probe, was designed and installed into the pipeline. The probe has movable sampling tubes that allow taking samples simultaneously at six points along the diameter of the pipe. The rate of withdrawal of each sample was adjusted by a needle valve according to the mixture velocity in order to minimize the effect of the probe on the measured water fraction profile. The samples were analyzed for water content in a laboratory using a standard method for determining the water fraction in crude oils. Based on the data obtained, a flow pattern map was constructed. The experimental stratified/nonstratified transition boundary was compared with two theoretical criteria obtained in the linear stability analysis of stratified two-phase liquid-liquid flow. The results of this study can be useful for the design and operation of pipelines transporting crude oil, as well as for the validation of multifield multidimensional models of two-phase flow. [S0195-0738(00)00404-0]

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;122(4):177-184. doi:10.1115/1.1318203.

The control system performance of gas liquid cylindrical cyclone (GLCC© ) separators can be considerably improved by adopting suitable control strategy and optimizing the design of the controller PID settings. Dynamic simulators have been developed in this study, based on Matlab/Simulink® software for evaluation of several different GLCC control philosophies for two-phase flow metering loop and bulk separation applications. Detailed analysis of the GLCC control system simulators indicates that for integrated liquid level and pressure control strategy, the level control loop compliments the operation of the pressure control loop, and vice versa. This strategy is ideal for reducing the pressure fluctuations in the GLCC. At severe slugging conditions, the integrated liquid level control is more desirable because of its faster response. However, there is no control of the GLCC pressure fluctuations. The results also show that the simulators are capable of representing the dynamic behavior of real physical systems. [S0195-0738(00)00504-5]

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;122(4):185-192. doi:10.1115/1.1319496.

The performance of gas-liquid cylindrical cyclone (GLCC©) separators for two-phase flow metering loop can be improved by eliminating liquid overflow into the gas leg or gas blow-out through the liquid leg, utilizing suitable integrated control systems. In this study, a new integrated control system has been developed for the GLCC, in which the control is achieved by a liquid control valve in the liquid discharge line and a gas control valve in the gas discharge line. Simulation studies demonstrate that the integrated level and pressure control system is highly desirable for slugging conditions. This strategy will enable the GLCC to operate at constant pressure so as not to restrict well flow and simultaneously prevent liquid carry-over and gas carry-under. Detailed experimental studies have been conducted to evaluate the improvement in the GLCC operational envelope for liquid carry-over with the integrated level and pressure control system. The results demonstrate that the GLCC equipped with integrated control system is capable of controlling the liquid level and GLCC pressure for a wide range of flow conditions. The experimental results also show that the operational envelope for liquid carry-over is improved twofold at higher liquid flow rate region and higher gas flow rate region. GLCC performance is also evaluated by measuring the operational envelope for onset of gas carry-under. [S0195-0738(00)00804-9]

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;122(4):193-197. doi:10.1115/1.1318202.

When a slug is formed a mixing vortex is created which contains pulses of bubbles which are shot toward the bottom of the pipe where they may impact and collapse. Bubble collapse creates high localized pressure, temperature, and wall shear stress, which cause a reduction in corrosion inhibitor efficiency. The average wall shear stress can be calculated using a conventional equation. However, using a conventional equation will not give the fluctuations in wall shear stress, which can be significant for slug flow conditions. Wall shear stress instruments are generally not accurate for fluids other than water, therefore, it would be beneficial to develop a relationship between the fluctuations in wall shear stress and the fluctuations in differential pressure. A differential pressure transducer, which can be used with any fluid, can be used to measure the fluctuations in differential pressure and then translate those values to fluctuations in wall shear stress. This study shows that wall shear stress fluctuations are related to differential pressure fluctuations to the 1.16 power. [S0195-0738(00)00604-X]

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;122(4):198-204. doi:10.1115/1.1325407.

Erosion is a complex phenomenon that depends on many factors such as fluid properties, solid particle properties, flow stream velocity, flow geometry, and type of metal. Flow modeling and particle tracking are important tools for predicting erosion. In erosion modeling, it is important to account not only for the factors that influence erosion, but also for changes in some of these factors that occur as the erosion process continues. For example, the change in the geometry resulting can have a significant impact on the erosion results. Geometry changes result when corners, found in couplings and chokes, are eroded with time. This change in geometry due to erosion can drastically change the flow field, especially the turbulent kinetic energy and dissipation rate. Recognizing this change is imperative, since the prediction of particle behavior is heavily dependent on the turbulent kinetic energy. Furthermore, more particle impingements occur in regions with higher turbulent kinetic energy. This paper shows that neglecting the change in the flow field solution resulting from the change in geometry can cause erroneous erosion predictions. A computational study was performed on a choke geometry to demonstrate the importance of incorporating the change in geometry resulting from erosion. Predicted turbulent kinetic energy contours are presented as a function of the changing choke geometry. The predicted erosion rates along the choke are also examined for the various scenarios, and these results are compared to experimental results. Additionally, experimental results obtained from laser doppler velocimeter (LDV) measurements also demonstrate the change in fluctuating velocity (turbulent kinetic energy) as a result of rounding of the entrance of the choke. Results from this study show that it is necessary to update the flow geometry and flow model based on the changing geometry due to erosion. [S0195-0738(00)01004-9]

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;122(4):205-211. doi:10.1115/1.1325406.

The thermodynamic performance of an encapsulated ice thermal energy storage (ITES) system for cooling capacity is assessed using exergy and energy analyses. A full cycle, with charging, storing, and discharging stages, is considered. The results demonstrate how exergy analysis provides a more realistic and meaningful assessment than the more conventional energy analysis of the efficiency and performance of an ITES system. The overall energy and exergy efficiencies are 99.5 and 50.9 percent, respectively. The average exergy efficiencies for the charging, discharging, and storing periods are 86, 60, and over 99 percent, respectively, while the average energy efficiency for each of these periods exceeds 99 percent. These results indicate that energy analysis leads to misleadingly optimistic statements of ITES efficiency. The results should prove useful to engineers and designers seeking to improve and optimize ITES systems. [S0195-0738(00)00904-3]

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;122(4):212-216. doi:10.1115/1.1326914.

A cycle model of a multi-stage combined heat pump system, which includes the irreversibility of finite rate heat transfer across finite temperature differences and the irreversibilities inside the working fluid, is established and used to investigate the influence of these irreversibilities on the performance of the system. The profit of operating the heat pump system is taken as an objective function for optimization. The maximum profit is calculated for a given total heat transfer area or total thermal conductance of heat exchangers. The coefficient of performance, heating load, and power input at the maximum profit are determined. The distribution of the heat transfer areas or the thermal conductances of heat exchangers and the temperature ratios of the working fluids of two adjacent cycles in heat exchange processes are optimized. The results obtained here are generally significant. They are suitable for an arbitrary-stage irreversible and endo- reversible combined heat pump system. [S0195-0738(00)01104-3]

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;122(4):217-223. doi:10.1115/1.1318201.

This paper presents a design procedure for a dual solar/gas-fired generator of an absorption chiller. The solar energy is the primary driving source for the generator, while the natural gas serves as the backup heat when the solar energy is unavailable or insufficient. Saturated forced convective boiling for binary mixtures has been considered to account for the reduction in the heat transfer coefficient observed for most mixtures. The simultaneous solar and gas-fired desorption process was investigated. The generator constructed based on modeling results yielded good performance in the experiment. [S0195-0738(00)00704-4]

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;122(4):224-228. doi:10.1115/1.1318205.

A study of the effects of nitric oxide (NO) models on the prediction of NO formation in a gas-fired regenerative furnace with highly preheated air was undertaken. Three chemical kinetic processes for NO formation/depletion, i.e., thermal NO, prompt NO, and NO reburning, are included. In the thermal NO model, the sensitivity encountered when using two different approaches, namely the equilibrium approach and the partial equilibrium approach, for determining the O radical concentration was studied. The effects of the third reaction in the thermal NO mechanism, NO reduction (reburning) mechanism, and different types of probability density functions (PDFs) on the NO predictions have also been tested. The sensitivity of the excess air ratio on the NO generation rate in the furnace has been investigated. Finally, the impact of the temperature on the NO formation rate in the regenerative furnace was discussed. [S0195-0738(00)00304-6]

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;122(4):229-238. doi:10.1115/1.1326915.

Flowing aviation fuel is used as a coolant in military aircraft. Dissolved O2 reacts with the heated fuel to form undesirable surface deposits which disrupt the normal flow. For purposes of aircraft design, it is important to understand and predict jet fuel oxidation and the resulting surface deposition. Detailed multi-dimensional numerical simulations are useful in understanding interactions between the fluid dynamics and fuel chemistry. Unfortunately, the detailed simulation of an entire fuel system is impractical. One-dimensional and lumped parameter models of fluid dynamics and chemistry can provide the simultaneous simulation of all components which comprise a complex fuel system. In this work, a simplified one-dimensional model of jet fuel oxidation and surface deposition within cylindrical passages is developed. Both global and pseudo-detailed chemical kinetic mechanisms are used to model fuel oxidation, while a global chemistry model alone is used to model surface deposition. Dissolved O2 concentration profiles and surface deposition rates are calculated for nearly isothermal and nonisothermal flow conditions. Flowing experiments are performed using straight-run jet fuels, and the predicted dissolved O2 concentrations and surface deposition rates agree reasonably well with measurements over a wide range of temperature and flow conditions. The new model is computationally inexpensive and represents a practical alternative to detailed multi-dimensional calculations of the flow in cylindrical passages. [S0195-0738(00)01204-8]

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;122(4):239-247. doi:10.1115/1.1288206.

The current paper examines the effects of using MTBE as a replacement of lead additives in gasoline on exhaust emissions of a typical SI engine. The MTBE was blended with a base unleaded fuel in three ratios (10, 15, and 20 vol. percent). The emissions of CO, HC, and NOx were measured at a variety of engine operating conditions using an engine dynamometer setup. The results of the MTBE blends were compared to those of the base fuel and of a leaded fuel prepared by adding TEL to the base. With respect to the base fuel, the addition of MTBE decreased the CO emissions, decreased the HC emissions at most operating conditions, but generally increased the NOx emissions. The emissions results for the leaded fuel were comparable to those of the base fuel. [S0195-0738(00)00103-5]

Commentary by Dr. Valentin Fuster

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