Showing papers on "Pressure drop published in 2008"

Capture of CO2 from flue gas streams with zeolite 13X by vacuum-pressure swing adsorption

Abstract: Vacuum swing adsorption (VSA) capture of CO2 from flue gas streams is a promising technology for greenhouse gas mitigation. In this study we use a detailed, validated numerical model of the CO2VSA process to study the effect of a range of operating and design parameters on the system performance. The adsorbent used is 13X and a feed stream of 12% CO2 and dry air is used to mimic flue gas. Feed pressures of 1.2 bar are used to minimize flue gas compression. A 9-step cycle with two equalisations and a 12-step cycle including product purge were both used to understand the impact of several cycle changes on performance. The ultimate vacuum level used is one of the most important parameters in dictating CO2 purity, recovery and power consumption. For vacuum levels of 4 kPa and lower, CO2 purities of >90% are achievable with a recovery of greater than 70%. Both purity and recovery drop quickly as the vacuum level is raised to 10 kPa. Total power consumption decreases as the vacuum pressure is raised, as expected, but the recovery decreases even quicker leading to a net increase in the specific power. The specific power appears to minimize at a vacuum pressure of approximately 4 kPa for the operating conditions used in our study. In addition to the ultimate vacuum level, vacuum time and feed time are found to impact the results for differing reasons. Longer evacuation times (to the same pressure level) imply lower flow rates and less pressure drop providing improved performance. Longer feed times led to partial breakthrough of the CO2 front and reduced recovery but improved purity. The starting pressure of evacuation (which is not necessarily equal to the feed pressure) was also found to be important since the gas phase was enriched in CO2 prior to removal by vacuum leading to improved CO2 purity. A 12-step cycle including product purge was able to produce high purity CO2 (>95%) with minimal impact on recovery. Finally, it was found that for 13X, the optimal feed temperature was around 67°C to maximize system purity. This is a consequence of the temperature dependence of the working selectivity and working capacity of 13X. In summary, our numerical model indicates that there is considerable scope for improvement and use of the VSA process for CO2 capture from flue gas streams.

Heat transfer enhancement by winglet-type vortex generator arrays in compact plain-fin-and-tube heat exchangers

Abstract: The potential of winglet type vortex generator (VG) arrays for air-side heat transfer enhancement is experimentally evaluated by full-scale wind-tunnel testing of a compact plain-fin-and-tube heat exchanger. The effectiveness of a 3VG alternate-tube inline array of vortex generators is compared to a single-row vortex generator design and the baseline configuration. The winglets are placed in a common-flow-up orientation for improved tube wake management. The overall heat transfer and pressure drop performance are assessed under dry-surface conditions over a Reynolds number range based on hydraulic diameter of 220 ≤ Re ≤ 960. It is found that the air-side heat transfer coefficient increases from 16.5% to 44% for the single-row winglet arrangement with an increase in pressure drop of less than 12%. For the three-row vortex generator array, the enhancement in heat transfer coefficient increases with Reynolds number from 29.9% to 68.8% with a pressure drop penalty from 26% at Re = 960 to 87.5% at Re = 220. The results indicate that vortex generator arrays can significantly enhance the performance of fin-tube heat exchangers with flow depths and fin densities typical to those used in air-cooling and refrigeration applications.

Apparatus for adjustably controlling the inflow of production fluids from a subterranean well

Abstract: A flow control apparatus (800) includes a tubular member (818) having a plurality of openings (820, 822, 824, 826) that allow fluid flow between an exterior and an interior flow path (828) of the tubular member (818) and a multi-stage flow restricting section (804) operably positioned in a fluid flow path between a fluid source disposed exteriorly of the tubular member (818) and the interior flow path (828). The flow restricting section (804) including a plurality of flow restricting devices (838, 844, 850) each operable to create a pressure drop. Actuatable devices (830, 832, 834, 836) operably associated with the openings (820, 822, 824, 826) are sequentially actuatable to allow fluid flow through the associated openings (820, 822, 824, 826), thereby sequentially reducing the pressure drop experienced by fluids flowing from the fluid source to the interior flow path (828).

Hydrodynamics of Taylor flow in small channels: A Review

Abstract: The improved mass transfer characteristics of Taylor flow, make it an attractive flow pattern for carrying out gas-liquid operations in microchannels. Mass transfer characteristics are affected by the hydrodynamic properties of the flow such as thickness of the liquid film that surrounds the bubbles, bubble velocity, bubble and slug lengths, mixing, and flow circulation in the liquid slugs, and pressure drop. Experimental, theoretical, and modelling attempts to predict these properties are reviewed and relevant correlations are given. Most of these refer to capillaries but there are number of studies on square channels. In general, flow properties are well understood and predicted for fully formed Taylor bubbles in a developed flow and in clean systems, particularly in circular channels. However, the presence of impurities and their effect on interfacial tension cannot be fully accounted for. In addition, there is still uncertainty on the size of bubbles and slugs that form under certain operating and inlet conditions, while there is little information for channels with non-circular cross-sections.

Convective Heat Transfer and Fluid Dynamic Characteristics of SiO2-Ethylene Glycol/Water Nanofluid

Abstract: Nanofluids comprised of silicon dioxide (SiO2) nanoparticles suspended in a 60:40 (% by weight) ethylene glycol and water (EG/water) mixture were investigated for their heat transfer and fluid dynamic performance. First, the rheological properties of different volume percents of SiO2 nanofluids were investigated at varying temperatures. The effect of particle diameter (20 nm, 50 nm, 100 nm) on the viscosity of the fluid was investigated. Subsequent experiments were performed to investigate the convective heat transfer enhancement of nanofluids in the turbulent regime by using the viscosity values measured. The experimental system was first tested with EG/water mixture to establish agreement with the Dittus-Boelter equation for Nusselt number and with Blasius equation for friction factor. The increase in heat transfer coefficient due to nanofluids for various volume concentrations has been presented. Pressure loss was observed to increase with nanoparticle volume concentration. It was observed that an incr...

Effects of baffle inclination angle on flow and heat transfer of a heat exchanger with helical baffles

Abstract: Numerical simulations were carried out to study the impacts of various baffle inclination angles on fluid flow and heat transfer of heat exchangers with helical baffles. The simulations were conducted for one period of seven baffle inclination angles by using periodic boundaries. Predicted flow patterns from simulation results indicate that continual helical baffles can reduce or even eliminate dead regions in the shell side of shell-and-tube heat exchangers. The average Nusselt number increases with the increase of the baffle inclination angle α when α α > 30°. The pressure drop varies drastically with baffle inclination angle and shell-side Reynolds number. The variation of the pressure drop is relatively large for small inclination angle. However, for α > 40°, the effect of α on pressure drop is very small. Compared to the segmental heat exchangers, the heat exchangers with continual helical baffles have higher heat transfer coefficients to the same pressure drop. Within the Reynolds number studied for the shell side, the optimal baffle inclination angle is about 45°, with which the integrated heat transfer and pressure drop performance is the best. The detailed knowledge on the heat transfer and flow distribution in this investigation provides the basis for further optimization of shell-and-tube heat exchangers.

Oil–water two‐phase flow in microchannels: Flow patterns and pressure drop measurements

Abstract: This paper investigates oil–water two-phase flows in microchannels of 793 and 667 µm hydraulic diameters made of quartz and glass, respectively. By injecting one fluid at a constant flow rate and the second at variable flow rate, different flow patterns were identified and mapped and the corresponding two-phase pressure drops were measured. Measurements of the pressure drops were interpreted using the homogeneous and Lockhart–Martinelli models developed for two-phase flows in pipes. The results show similarity to both liquid–liquid flow in pipes and to gas–liquid flow in microchannels. We find a strong dependence of pressure drop on flow rates, microchannel material, and the first fluid injected into the microchannel.

Analysis of supercritical CO2 cooling in macro- and micro-channels

Abstract: A comprehensive analysis of heat transfer and pressure drop experimental data and correlations for supercritical CO2 cooling in macro- and micro-channels is presented in this article. First, the physical and transport properties of CO2 at supercritical conditions are discussed and then their influence on heat transfer and pressure drops. Next, a review of experimental studies on heat transfer and pressure drops of supercritical CO2 cooling is provided and detailed comparisons and analysis relative to the available heat transfer and pressure drop correlations for supercritical CO2 cooling were done where possible. Furthermore, noting the lack of all pertinent experimental details required to use the data published in many of these studies, comments are given on how to reduce and present supercritical CO2 experimental data properly in the future. In addition, the effect of oil on heat transfer and pressure drops for supercritical CO2 is shown to significantly decrease the former and to increase the latter. Comparison of experimental data to a selection of heat transfer correlations shows that the Fang et al. [2001b. Modeling and analysis of gas coolers. ASHRAE Trans. 107 (1), 4–13] correlation gives the closest values to the experimental data but is still not satisfactory. According to the comparison and analysis, it is recommended that further efforts be made to develop good heat transfer methods for supercritical CO2 cooling based on accurate database in the future. To achieve this, more careful experiments should be done over a wide range of test parameters to meet the requirement in practical applications. In addition, four experimental studies show that the Blasius equation works well for CO2 cooling in the near supercritical region. More careful experimental data are still needed to further validate this conclusion because some experimental data are much different from others.

Control of Three-Dimensional Separations in Axial Compressors by Tailored Boundary Layer Suction

Abstract: One of the important ways of improving turbomachinery compressor performance is to control three-dimensional (3D) separations, which form over the suction surface and end wall corner of the blade passage. Based on the insights gained into the formation of these separations, this paper illustrates how an appropriately applied boundary layer suction of up to 0.7% of inlet mass flow can control and eliminate typical compressor stator hub corner 3D separation over a range of operating incidence. The paper describes, using computational fluid dynamics, the application of suction on the blade suction surface and end wall boundary layers and exemplifies the influence of end wall dividing streamline in initiating 3D separation in the blade passage. The removal of the separated region from the blade suction surface is confirmed by an experimental investigation in a compressor cascade involving surface flow visualization, surface static pressure, and exit loss measurements. The ensuing passage flow field is characterized by increased blade loading (static pressure difference between pressure and suction surface), enhanced average static pressure rise, significant loss removal, and a uniform exit flow. This result also enables the contribution of the 3D separation to the overall loss and passage blockage to be assessed.

Optimal design of magnetorheological valves via a finite element method considering control energy and a time constant

Abstract: This study presents an optimal design for magnetorheological (MR) valves for minimizing the control energy to be applied to coils to control the pressure drop of the valves The optimization problem identifies parameters such as applied current, coil wire size and geometric dimensions of the valves which satisfy the specified pressure drop and inductive time constant requirements After describing the configuration of MR valves, their pressure drops are obtained on the basis of the Bingham model of MR fluid Then, the control energy which is an objective function and the inductive time constant are derived Subsequently, an optimization procedure using a golden-section algorithm and a local quadratic fitting technique is constructed via a commercial finite element method parametric design language Using the optimization tool developed in this study, optimal MR valve configurations are identified, which are constrained to a specific cylindrical volume defined by its radius and height In addition, optimization results for MR valves with different required pressure drops and different constrained volumes are obtained and presented