Turndown Ratio Research Articles

Advanced Hydrogen Crossover Characterization: Closing the Mole Balance through Coupled Anode and Cathode Exhaust Analysis

Hydrogen crossover in proton exchange membrane water electrolysis (PEMWE) is an unwanted phenomenon that leads to both efficiency losses and safety hazards. This issue is expected to worsen as PEMWE systems move towards thinner membranes and high-pressure operation (two straightforward avenues to reduce operating expenses), as well as high turn-down ratios [1]. To address the safety aspect, next-generation PEM architectures are being developed that include a recombination catalyst (e.g., Pt) to consume the H2, i.e. H2 + O2 → H2O, before it makes its way to the anode exhaust. An accurate method for assessing this recombination rate is necessary to evaluate the performance and optimize the recombination catalyst.In a previous work, we and others demonstrated that the H2 crossover flux can be calculated by analyzing the H2:O2 ratio of the anode exhaust [2 – 4]. However, some assumptions involved in this analysis are not valid in systems with significant H2 + O2 recombination. To get a full picture of the reactions that take place in such systems, it is necessary to analyze the cathode exhaust. By measuring the rates of hydrogen leaving both anode and cathode and comparing them to Faraday’s law, the amount of H2 being consumed in various recombination reactions inside the cell can be quantified.Figure 1 shows a schematic of the additions required to our previously reported H2 crossover quantification technique. The top exhaust path (grayed out) shows our earlier method for analyzing the anode exhaust. The bottom exhaust path shows the added method that enables analyzing the cathode exhaust. Both techniques use a GC to analyze and quantify the gas composition. In this presentation we will discuss results that verify the technique using H2NEW’s reference FuGeMEA system. We will further demonstrate how the technique can be applied to membranes with recombination catalysts to assess their crossover mitigation capabilities.

A “Ship-in-a-Bottle” Method for Hydrogen Crossover Mitigation in PEM Water Electrolyzers

This work presents a new approach to address hydrogen crossover in proton exchange membrane water electrolyzers (PEMWEs), a pivotal challenge that not only compromises safety but also affects the system’s compatibility, especially when integrated with fluctuating renewable energy sources like wind turbines and solar panels. Platinum (Pt), a critical component for recombination reaction in PEMWEs, is traditionally integrated into ionomers through mechanical processing methods such as ball milling, sonication, or inline milling. These processes disperse Pt particles directly within ionomer dispersions1, but they have limitations in terms of efficiency and cost. Our "ship-in-a-bottle" method involves introducing Pt ions into the ionomer substrate, which are subsequently chemically reduced to form Pt nanocrystals within the polymer matrix. It offers numerous benefits over traditional routes, including a more uniform distribution of Pt nanocrystals within the hydrogen channels of the polymer network. This leads to significantly enhanced recombination efficiency and allows for the use of thinner membranes, production of high-pressure H2, reducing the quantity of platinum required, and consequently lowering the cost of the PEMWE technology.Moreover, our research delves into the creation of a unique recombination layer within membrane electrode assemblies (MEAs), significantly curtailing hydrogen crossover, especially at low turn-down ratio—a persistent issue in PEMWE industry. Utilizing the non-conductive PTFE backbone of PFSA ionomers to isolate well dispersed Pt nanocrystals from areas of high voltage, our approach markedly increases efficiency of hydrogen crossover mitigation. The result not only improves the safety and operational flexibility of PEMWEs but also underscores a shift towards a more economical, safe, and adaptable hydrogen production methodology. By addressing key challenges associated with hydrogen crossover, this study lays the groundwork for transformative changes in the green hydrogen sector, emphasizing a sustainable future powered by renewable energy sources. Klose et al 2018 J. Electrochem. Soc. 165 F1271

Experimental study of twin-fluid flow differences and Sauter mean diameter prediction according to Y-jet nozzle mixing-tube design

In this study, we experimentally investigate the effect of internal flow variation on the design characteristics of a Y-jet twin-fluid nozzle and its utilization for spray droplet size prediction. For this study, a laboratory-scale twin-fluid nozzle spray test system was constructed. Sauter mean diameter (SMD) measurements were made by a droplet measurement system using the laser diffraction principle, and spray images were obtained using a high-speed camera. The mass flow rate of the twin fluids under different spray conditions was expressed in terms of the gas-to-liquid mass flow rate ratio (GLR) and turn-down ratio. The GLR tended to decrease when the nozzle orifice diameter increased because the pressure of the supplied twin-fluid was the same. By contrast, increasing the nozzle mixing-tube length resulted in a negligible increase in GLR. This is because the nozzle design characteristics affect the internal pressure of the nozzle, which changes its spray characteristics. In general, the spray characteristics of Y-jet nozzles are most affected by GLR. However, in this study, a generalised GLR was devised to consider not only GLR but also the difference in the flow rate of the twin-fluid due to nozzle design factors. The generalised GLR has the advantage that it is constant under changes in twin-fluid pressure, unlike the GLR expressed by considering only the mass flow rate of the twin-fluid. Therefore, to estimate the SMD more accurately under different spray pressures for a constant GLR, we investigated the SMD estimation using the internal pressure ratio and generalised GLR.

Characterization of a highly integrated, natural convection-driven, condensing methanol reactor

A highly integrated, natural convection-driven, condensing methanol reactor with the catalyst bed, heat integration section and liquid product separation in a single pressure vessel without moving parts is successfully tested. Space-time yields of up to 600kgMeOHmcat.−3h−1 are demonstrated, comparable to other CO2-to-methanol processes. The internal recycle by natural convection is successfully achieved as well as significant heat integration. A further reduction of heat losses to the environment is needed for autothermal operation. The dynamic characteristics of the process, with fast start-up times, a high turn-down ratio add to the potential to deal with intermittent feed supply. Overall the LOGIC 2.0 reactor concept is a promising process configuration for green methanol production.

On Leakage Flows In A Liquid Hydrogen Multi-Stage Pump for Aircraft Engine Applications

Abstract A comprehensive operational characterisation of a representative, Liquid Hydrogen (LH2) aircraft engine pump is presented in this work. The implications of leakage flows are investigated in a 2-stage, high-pressure pump for a wide range of flow rates and rotational speeds, through 3D (U)RANS simulations. Two configurations are compared: a baseline model comprising the primary flow path components - inducers, impellers and volutes and a realisable pump hardware that includes hub, shroud and power unit cavities. Performance metrics, including head changes and efficiencies, are extracted both at a component and system level. Leakage flow rates of 27.6% and up to 92.9% of the overall pump flow rate are recorded at design and lowest flow points respectively. The head loss in the mid to low flow rates does not exceed 4.5%, but the efficiency diminishes by up to 13.5% at off-design operation. The component analysis indicates significant penalties in impeller efficiency. At high flow rates, the presence of leakage flows improves the overall pump performance by 43% and 27% in head rise and efficiency, due to reduced losses in volutes and connecting ducts. The characterisation of pump behaviour described in this work is crucial for developing and designing safe and predictable LH2 aircraft pumps. Contrary to LH2 pumps utilized in rocketry and for cooling in nuclear industry, aircraft pumps are required to operate with wider turn-down ratios and often at low specific speeds. Therefore, this study addresses design considerations for this enabling technology.

Analysis of in-bin low-temperature and high-temperature grain drying in Alberta: Specific energy, carbon costs and policy implications

Optimizing grain drying process is pivotal for both economic viability and environmental sustainability. In cold countries, supplemental heating is paramount but instigates the issue of carbon release at the same time. To curve the emission, a carbon levy has been imposed that varies with fuel types. However, there is limited knowledge of the impact of field-adaptable technologies utilizing commercialized fuels on the optimal execution of grain drying. To explore this, a comprehensive three-year on-farm grain drying study was conducted in the province of Alberta, Canada. This comparative analysis centered on three critical aspects, i.e., specific energy consumption, greenhouse gas emissions (GHGs), and operating costs. Furthermore, the research extended its projections into the year 2030, accounting for the impact of gradual carbon levies on natural gas, propane, and diesel fuel systems. Resultsshowed that indirect heaters in in-bin systems were 38 % more energy-efficient than direct heaters due to better airflow and higher initial grain temperatures, while indirect heaters with diesel burners exhibited 27.8 % lower burner turndown ratios and 35.4 % higher energy consumption than natural gas counterparts. In high-temperature drying, natural gas consumption decreased as supply air temperatures rose, with double-flow dryer showing the lowest energy consumption (6.3±1.9 GJ/t) in comparison to mixed-flow and cross-flow dryer due to waste heat recovery. Heaters and Dryers operated at varying load capacities, indicated 126–135 % increase in natural gas cost with carbon levy by 2030. Achieving lower specific energy consumption in grain drying requires precise burner and process control, along with maintenance, offering valuable guidance for producers.

Liquid-fueled high-performance burner utilizing a coarse porous matrix

In this study, a kerosene-fueled premixed burner system with a thick and large pore-sized (“coarse”) porous matrix was developed to achieve less-soot stable premixed combustion with variable combustion loads, i.e., turn-down ratio, TDR, defined as the ratio between the maximum and minimum loads. The present burner system mainly consists of the thick and coarse porous matrix made by packed ceramic balls of 8 mm-diameter, which acts as a vaporizer, mixer, and flame holder. The liquid fuel is fed into the porous matrix along with air. As the air and vaporized fuel are supplied toward the top-end (surface) of the porous matrix, a premixed flame is formed at this surface. Benefits of the adopted porous matrix include reduced wettability of the liquid fuel to pores of the porous matrix, which prevents its direct supply to the flame, promotes vaporization and mixing, and functions as a flame holder, allowing the flame to be sustained within the porous matrix. Combustion experiments were then carried out under various equivalence ratios (φ) between 0.47 and 1.34, and temperature measurement was conducted to evaluate the vaporization capability within the porous matrix. The experimental results confirmed that the quasi-steady and stable premixed combustion across the entire surface of the porous matrix throughout the burning event was successfully achieved under all φ values considered in this study. A simplified (one-dimensional) analytical model was developed to examine achievable range of TDR. It was found that the expected achievable TDR was higher than the value for the conventional spray combustion technology (∼ 6). Thus, the present burner system with a thick and coarse porous matrix was effective for attaining stable premixed combustion and a high TDR.

Experimental and numerical study on flow/flame interactions and pollutant emissions of premixed methane-air flames with enhanced lean blowout hydrogen injection

This study investigates experimentally and numerically the stability, combustion, and emissions characteristics of premixed swirl-stabilized methane/air flames with enhanced lean blowout (ELBO) injection of hydrogen in the non-premixed mode for higher turndown ratio gas turbines. The study analyzed the effects of hydrogen fraction (HF: volumetric percentage of H2 in the total fuel) ranging from 0 to 25% and equivalence ratio (φ) ranging from 0.5 to 0.893 on flow/flame interactions and flame stability, structure, and emissions. The introduction of non-premixed H2 yields two conflicting outcomes, with enhancements in reaction kinetics and flame speed yet counteracted by increased hydrogen jet momentum dispersing the flame. The combustor lean blowout (LBO) limit remains relatively unaffected (φoverall≈ 0.5) by H2 injection. Flame temperature is primarily influenced by φ and minorly by HF. Increasing HF resulted in localized temperature rises around H2 jets without an overall increase in flame temperature, offering a promising strategy for reduction of NOx emissions. Nevertheless, using H2 as a pilot fuel leads to an increase in intermediate species like OH, H, and O, contributing to flame stabilization. However, this practice also results in higher CO and unburned hydrocarbons emissions due to the inherent characteristics and heightened reactivity of H2.

Demonstration of dual-thrust capability in hybrid rockets using multi-layered tubular fuel grains

This study demonstrates the thrust modulation capabilities of a hybrid rocket motor employing a Multi-Layered Tubular (MLT) fuel grain. The MLT configuration involves arranging the fuel grains with distinct regression rates as layers. As combustion progresses, the regression rate changes based on the burning of each fuel layer, leading to variable thrust while maintaining a constant oxidizer flow rate. Variable-thrust fuel grains are suitable for diverse mission types, including employment in sounding rockets and cruise missiles, particularly those designed for anti-ship operations and missions wherein a boost-sustain thrust profile is required. The MLT fuel grains were designed for a boost-sustain phase thrust profile generally observed in missiles. Wax was used as a booster fuel, and wax with 20%EVA was used as a sustainer fuel. Two MLT configurations with different durations for the boost phase were demonstrated. During the tests, the boost-sustain phase was achieved successfully. However, a transition phase was observed while shifting from the boost to the sustain phase. The delay of the transition phase was observed to increase when the duration of the boost phase increased. The combined effect of axial variation of fuel regression rate and local mass flux is the reason for the transition phase. The Thrust Turn-Down Ratio (TDR) for Multi-Layered Tubular (MLT) fuel grains was calculated. At a web thickness (for booster fuel) of 4 mm, the TDR was approximately 1.23:1, and at a 5.5 mm web thickness, it was 1.28:1. Further, 20%Mg was added to the wax to increase the regression rate of booster fuel. The Wax/20%Mg fuel showed 41% and 14% improvement in regression rate and thrust, respectively. The TDR was improved marginally compared to pure wax-based MLT grain.

Ultrathin Microporous Transport Layers: Implications for Low Catalyst Loadings, Thin Membranes, and High Current Density Operation for Proton Exchange Membrane Electrolysis

AbstractPorous transport layers (PTL) and their surface properties have the potential to improve the performance of proton exchange membrane water electrolyzers (PEMWE), which is imperative to reduce feedstock costs and lead to their widespread implementation. This work introduces a novel generation of titanium microporous layers (MPLs) with ultra‐low thicknesses of ≈20 µm which reduces raw material costs. They also feature advanced interfacial properties tailored to maximize catalyst utilization at low Ir‐loadings. The bulk morphology and surface properties of the hierarchically structured PTLs are assessed by X‐ray tomographic microscopy. The low surface roughness of the MPL allows the use of thinner membranes since it minimizes possible deformations in the membrane. Cells containing the MPLs outperformed those containing state‐of‐the‐art commercially available PTL materials by up to 100 mV at 7 A cm−2 in combination with low‐loaded catalyst‐coated membranes of 0.4 mgIr cm−2. Hydrogen crossover is also reduced, especially at low current densities, leading to a larger turndown ratio which can enable more cost‐effective operating strategies. Finally, these rationally designed MPLs also lead to high catalyst utilization by overcoming the naturally occurring high in‐plane resistance of low‐loaded catalyst layers.

Triangular fin array passively actuated by bimetallic coils for CubeSat thermal control

CubeSat thermal control can be especially demanding due to volume and size constraints, high power dissipation per unit surface area, and highly variable internal and external heat loads. As such, CubeSat developers must rely on thermal control systems that meet the specific requirements of their mission and environmental conditions. Deployable radiators enable satellites to increase their radiative surface area and to reveal highly emissive surfaces during times when increased heat rejection is desired. In colder conditions, when decreased heat loss is preferable, the radiators can be stowed. Passive thermal control systems are unpowered and can increase system reliability by not relying on control electronics while offering decreased weight and power requirements. In this work, we propose a deployable array of triangular radiator panels that are independently and passively actuated by bimetallic coils in response to changes in temperature. This system demonstrates the use of bimetallic coils to passively deploy and stow the radiator fins as well as the use of multiple CubeSat radiator fins with independent actuators to provide increased redundancy. An experimental prototype of the system design was subjected to vacuum chamber testing with panels held in a fixed, deployed position to obtain temperature data used to tune a thermal simulation model. The prototype was then placed in a cryogenically cooled vacuum chamber environment with the panels free to actuate passively in response to varied heating conditions. Both steady state and transient testing were performed. Through this testing and the use of the tuned thermal simulation, the experimental prototype is determined to have a turndown ratio (largest cooling power / smallest cooling power) of 5.4. Deployment of the radiator panels serves to reduce CubeSat body temperatures by 45 °C. Results show the efficacy of the bimetallic coil actuators and radiator fin array in providing passive, dynamic thermal control to small satellites. Recommendations are made to further enhance the performance of the system. Of these recommendations, the most critical is to improve the thermal conductive path from the CubeSat body to the bimetallic coils and to the triangular radiator panels across the deployable radiator hinge. Such changes provide the possibility of increasing the maximum heat rejection, responsiveness of the thermal control system, and turndown ratio to 9 or greater.

Experimental and kinetic analyses on the flame dynamics and stabilization of ammonia/hydrogen-air mixtures in a micro-planar combustor

With the combination of experimental and numerical techniques, flame dynamics and stability of ammonia/hydrogen co-firing combustion are unraveled. Five types of fundamental micro-flame structures are, for the first time, experimentally confirmed with varying blending ratios (ε) and equivalence ratios (ϕ), along with a flame stability diagram delineated. It is shown that elevating ε from 30% to 50% extends the blowoff limit by a factor of 2.77 by suppressing or delaying the occurrence of certain flames. This thus leads to a turndown ratio of 15 in ammonia/hydrogen mixtures comparable to those of hydrocarbon fuel-based industrial combustors. To gain insights into the flame stabilization enhancement, further kinetics analyses are conducted with the validated reaction mechanism. The laminar burning velocity of the binary mixture is found to be increased remarkably with increasing ε, which facilitates flame propagation. Kinetics analyses reveal that varying hydrogen content not only enables the production/destruction pathways of major steps to be changed but also leads to the different sensitivity responses of the laminar burning velocity to reaction steps. This is also accompanied by the increase in the reaction rate of the major chain-branching step, thus signifying the importance of the chemical effect for enhanced flame stability. This work sheds light on the fundamental flame dynamic and enhancement mechanisms of ammonia/hydrogen co-firing combustion from macro and molecular perspectives.

A novel mechanism for low- and high pressure measurement with variable-thickness diaphragm

ABSTRACT In pressure sensors, pressure measurement is based on the movements of the elastic elements under different pressures. Since there is no elastic element able to move under low and high pressures, there is a serious limitation to measuring low and high pressures concurrently. This paper proposes an innovative mechanism for measuring high and low pressures concurrently. In the proposed mechanism, a variable-thickness diaphragm and a protective part were used to measure a broad range of pressures. The proposed mechanism was manufactured and the accurate pressure source was used to test the behavior of the mechanism under different pressures. Using this configuration raised the sensitivity and accuracy of high-range pressure sensors, and increased the turndown ratio to 1500 by employing a new elastic element. Employing this mechanism in pressure sensors leads to use one pressure sensor for measuring a broad range of pressure instead of using several distinct sensors.

Decarbonization of the Electric Power Sector and Implications for Low‐Cost Hydrogen Production from Water Electrolysis

AbstractIncreasing development of wind and solar generation in the power sector can create economic opportunities for the deployment of water electrolyzers that produce hydrogen. Temporal variation in the marginal cost of energy in future decarbonized grids can make it favorable for electrolyzers to dispatchably ramp hydrogen production up and down in response to low‐ and high‐cost times. Using this strategy, low‐cost hydrogen production is enabled by electrolyzers that are low‐capital cost and tolerant to frequent on/off cycling. Ramping down hydrogen production to a designated turndown ratio can avoid performance degradation caused by on/off cycling by not shutting the electrolyzer completely off. This comes with a slight cost penalty which can be minimized if the turndown ratio is low (i.e., the system ramps down hydrogen production to close to zero). These results suggest that electrolyzers integrated into future power systems are likely to benefit from the ability to ramp operation up and down quickly and operate in a standby mode. This analysis forms a basis for comparative tradeoffs between electrolyzer capital cost, operating strategy, and system durability and demonstrates the importance of considering all three factors in technoeconomic analysis.

Experimental and computational characterization of mass transfer in high turndown bioreactors.

Single-use bioreactors (SUBs, or disposable bioreactors) are extensively used for the clinical and commercial production of biologics. Despite widespread application, minimal results have been reported utilizing the turndown ratio; an operation mode where the working range of the bioreactor can be expanded to include low fluid volumes. In this work, a systematic investigation into free surface mass transfer and cell growth in high turndown single-use bioreactors is presented. This approach, which combines experimental mass transfer measurements with numerical simulation, deconvolutes the combined effects of headspace mixing and the free surface convective mass transfer on cell growth. Under optimized conditions, mass transfer across the interface alone may be sufficient to satisfy oxygen demands of the cell culture. Within the context of high turndown bioreactors, this finding provides a counterpoint to traditional sparge-based bioreactor operational philosophy. Multiple monoclonal antibody-producing cell lines grown using this high turndown approach showed similar viable cell densities to those cells expanded using a traditional cell bag rocker. Furthermore, cells taken directly from the turndown expansion and placed into production showed identical growth characteristics to traditionally expanded cultures. Taken together, these results suggest that the Xcellerex SUB can be run at a 5:1 working volume as a seed to itself, with no need for system modifications, potentially simplifying preculture operations.

Experimental and numerical investigation of flame stabilization and pollutant formation in matrix stabilized ammonia-hydrogen combustion

Ammonia (NH3) is a carbon-free fuel that offers an attractive alternative for reducing greenhouse gas emissions. However, the slow flame speed, low heating value, and emissions of nitrogen-containing pollutants present significant issues for practical combustion applications. To address these issues, we investigate the use of matrix stabilized combustion. In this type of burner, combustion is performed within an inert porous ceramic foam, heat is recirculated by solid conduction and radiation, which enhances flame speed and combustion stabilization, thereby permitting combustion over a wide range of equivalence ratio conditions. We present a new porous media burner (PMB) capable of stabilizing NH3/air flames at ambient conditions. An extensive experimental characterization of the stability of this burner is conducted with up to 30% by volume of hydrogen (H2) in the fuel stream. A 15:1 turndown ratio is demonstrated, with a high thermal power density of 62MWm−3. Concentrations of NO, unburnt NH3, and H2 in the exhaust stream are measured. Two regimes are identified for low NO operation: rich and very lean. For rich conditions, NO emissions decrease with increasing equivalence ratio and decreasing H2 blending. Unburnt NH3 emissions follow opposite trends. These measurements are complemented by simulations in which the burner is represented by a coupled solid-gas reactor network. This model captures the burner’s pollutant emissions to good accuracy and is used to analyze the mechanisms of pollutant formation.

Ultra‐High Transmission Broadband Tunable VO2 Optical Limiter

AbstractAn optical limiter (OL) is a nonlinear device that protects sensitive photodetectors or human eyes from high‐intensity illumination. However, current OLs have low open‐state transmittance and a limited turndown ratio in some cases. In this study, first it is demonstrated that combining the insulator‐to‐metal transition (IMT) of vanadium dioxide (VO2) with anti‐reflection layers can enable both high and broadband open‐state transmittance (>−0.9 dB at the peak wavelength) while preserving a large turndown ratio (>21.8 dB). Furthermore, optothermal simulation is conducted to analyze the performance of the VO2 OL under ultrafast laser irradiation. The result reveals that IMT of the VO2 OL occurs at 0.23 µs when the incident laser intensity is 90 kW cm−2. These benefits offer a promising alternative to OLs in technologies ranging from sensor protection to human eye defense.

Design, experimental demonstration, and validation of a composite morphing space radiator

Future manned space missions will require thermal control systems that can adapt to larger fluctuations in temperature and heat flux exceeding the capabilities of current state-of-the-art technologies. Specifically, these missions will demand novel space radiators that can vary the system heat rejection rate to maintain the crew cabin at habitable temperatures throughout the entire mission. While current systems can provide a turndown ratio (defined as the ratio of maximum to minimum heat rejection rates) of 3:1 under adverse conditions, future missions are projected to demand thermal control systems that can provide a turndown ratio of more than 6:1. A novel morphing radiator concept autonomously varies the system heat rejection rate by altering the shape of the panel exposed to space, where composite materials can provide an ideal compromise between thermal conductivity, restorative stiffness and deformation capability. Shape change is accomplished through the use of shape memory alloys, a class of active materials that exhibit thermomechanically driven phase transformations and can be used as simultaneous sensors and actuators in thermal control applications. This work details progress towards testing and modeling a spaceflight-quality, high turndown ratio morphing radiator prototype in a relevant thermal environment. A prototype composite morphing radiator with shape memory alloy strip actuators and high performance thermal coatings achieved a turndown ratio of 7.2:1, while an associated multi-physical model thereof has been shown to capture all major effects and will enable future design improvements.

Experimental Investigation into Liquid and Solid Separation by an Industrial Mesh-Vane-Type Separator on Natural Gas at 4–5 MPa, Different Liquid Loadings and Gas Flows

AbstractInline vertical separators are commonly employed in natural gas transmission facilities (e.g., receipt stations) to filter liquid contaminants such as compressor oil, glycol, and free water from the gas stream. Manufacturers of these separators have claimed liquid removal efficiencies of 98–99% for droplet sizes ≥ 8 μm. However, these contaminants have been found invariably in piping systems downstream of these separators, suggesting inadequate separator performance. Currently, there is a lack of ability to verify manufacturer claims due to difficulties in quantifying liquid contaminants and droplet characteristics. The potential consequences of having such contaminants include lower gas quality, impaired gas metering accuracy, corrosion and damage to equipment/instrumentation, and adverse impacts on industrial and residential end users. This paper presents performance testing of a mesh-vane-type vertical separator conducted on high pressure, pipeline quality, natural gas in the range of 4–5 MPa and flow velocity in the range of 1.3–13 m/s in the DN150 separator inlet (hence turndown ratio of 10:1). Four different spray nozzles were used to inject and atomize industrial compressor oil with a liquid-to-gas mass loading ratio of 0.06–1.8%. Test results revealed that the average bulk efficiency separation performance for this separator is approximately 90.34%. This was found to be independent of the liquid-to-gas mass loading ratio. The effective Souders–Brown K-factor was found to be 0.15 m/s. This is below literature published data in the range of 0.27–0.3 m/s for horizontal flow, vane-pack-type separators. Liquid separation tests were also conducted following the injection of solid glass beads. Liquid separation efficiency decreased by approximately 9%, following the injection of 7 kg of industrial glass beads over a period of approximately 4 h. This was attributed to accumulation of solids in the vane pack.

Investigation of different cooling tower fan control strategies using COP of actual chillers and calibrated models of actual cooling towers and fans

Open-loop fan speed control and closed-loop approach temperature control of cooling towers were recommended by different researchers. With the further consideration of the coefficient of performance (COP) change of chillers over 30 years and the potential turndown operation of cooling towers, the paper is to reinvestigate different cooling tower fan control strategies. First a total power model of condensing water systems is developed to calculate the total system power and obtain the optimal fan speed, leaving water temperature and approach temperature of cooling towers. Then a studied condensing water system with the cooling tower turndown ratio of 50 % is selected and calibrated. Finally, the developed model is applied on the studied system to evaluate different optimal and conventional controls and give the recommendations. The evaluation reveals that the optimal fan speed is significantly impacted by the chiller load and the total system power is less sensitive to the fan speed near the optimal speed. Thus, the simplified optimal speed control by resetting the setpoint with the chiller load is recommended. When physical models are not available, the conventional fixed fan speed control with the setpoint equal to the cooling tower turndown ratio is recommended with the energy penalty of 1.1 %.