Inlet Ambient Temperature Research Articles

Impact of Preheating on Flame Stabilization and NOx Emissions From a Dual Swirl Hydrogen Injector

Abstract Flame stabilization, flame structure, and pollutant emissions are investigated experimentally on a swirled injection system operating with globally lean air/hydrogen mixtures at atmospheric conditions and moderate Reynolds numbers. This injector consists of two coaxial ducts with separate injection of hydrogen into a central channel and of air into an annular channel. Both streams are swirled. The resulting flames exhibit two stabilization modes. In one case, the flame takes an M-shape and is anchored to the hydrogen injector lips. In the second case, the flame is aerodynamically stabilized above the injector and takes a V-shape. Regions of existence of each stabilization mode are determined according to the operating conditions. For low air flow rates, the flame can be either anchored or lifted above the hydrogen injector lips depending on the path followed to reach the operating condition. At high air flow rates, the flame is always lifted regardless of the trajectory followed. The impact of air inlet temperature on these stabilization regimes is then evaluated from T= 300 K up to 770 K. Flame re-attachment is shown to be controlled by edge flame propagation and the impact of preheating is well reproduced by the model. Unburnt hydrogen and NOx emissions are finally evaluated. Unburnt hydrogen is only observed for global equivalence ratios below 0.4 and at ambient inlet temperature. NOx emissions decrease when the global equivalence ratio is reduced. Furthermore, at fixed global equivalence ratio, NOx emissions decrease as the thermal power increases, regardless of air preheating and the flame stabilization regime. At high power, NOx emissions reach an asymptotic value that is independent of the thermal power. The impact of flame shape, air preheating, and combustion chamber wall heat losses on NOx production is also evaluated. NOx emissions are shown to scale with the adiabatic flame temperature Tad at the global equivalence ratio and the residence time inside the combustor.

Modeling Improved Li-Ion Cell Capacity through Suppression of Temperature with Internal Electrolyte Flow

Lithium-ion cells are ubiquitous in portable electronic applications and are growing in popularity for electric vehicles including passenger cars. Yet, a dramatic reduction in global emissions to combat climate change calls for significantly broader adoption of carbon neutral technologies in electric vehicles and in stationary energy storage to complement variable renewable sources and growing electricity demand.1 For lithium-ion batteries, a critical barrier to such broader adoption is the inability to sustain high rate while also accessing the full capacity of cells. In addition to mass transport effects, overheating commonly limits the duration of high-rate discharge or charge due to excessive heat generation and inadequate heat removal.Here, we provide a brief illustrative tutorial of these coupled effects in a pseudo two-dimensional electrochemical model and build on our previous modeling and dimensional analyses2-4 of how internal electrolyte flow across Li-ion cells reduces both mass and thermal transport limitations.First, we describe the intentional and sudden onset of internal electrolyte convection to curb or to avert further temperature rise in a Li-ion cell during high-rate discharge. We examine two modes for introducing electrolyte flow: temperature-triggered (“reactive”) and discharge-rate triggered (“proactive”) modes. In the reactive case, flow is introduced in the simulation when a cell under high-rate discharge reaches a high safety cutoff temperature. In the proactive case, flow begins as the discharge rate is step changed from midrate to high rate. A practical application of proactive mode is that a battery thermal management system could be programmed to initiate electrolyte flow in anticipation of greater heat generation at a higher rate.Next, using the aforementioned continuum modeling with circulation through an external tank, we compare and contrast Li-ion cell thermal responses to the onset of flow in reactive mode versus in proactive mode. In both cases, the threshold flow rate (~μm/s) to suppress temperature rise agrees in order of magnitude with dimensionless group estimates reported in our previous work.4 Namely, temperature rise is suppressed when the heat generation rate becomes lower than the heat removal rate. At the highest electrolyte flow rates simulated (>>μm /s), the heat removal by internal electrolyte flow dominates, and the cell achieves nearly full discharge capacity without prematurely crossing temperature or voltage cutoffs. For low flow rates (<μm /s), the proactive and reactive cases show quantitatively different transient temperature trajectories due to the temperature dependences of heat generation and removal. Heat generation rate decreases with elevated cell temperature due to facile mass transfer and resultant concentration uniformity, optimal electrolyte conductivity, and ease of charge transfer kinetics. Also, heat removal using internal electrolyte flow becomes more effective with high cell temperature relative to ambient inlet temperature. Hence, the flow rate needed to cool a cell that has reached a high safety cutoff temperature (in reactive mode) is lower than the flow rate required to curb temperature rise in a cell just above ambient temperature (in proactive mode) as high-rate discharge starts.

Investigation of osmosonication pretreated chili (Capsicum frutescensL.) drying in solar‐assisted fluidized bed dryer utilizing dehumidified air

AbstractThe heat and moisture sensitivity of spices and a consistent supply of electrical energy is the challenging factors in developing a relevant drying system for rural applications. A novel solar‐assisted fluidized bed dryer was developed for drying locally harvested unique spices like bird's eye chili (Capsicum frutescens L.). The chili was pretreated by the osmosonication method prior to drying to expedite the elimination of intercellular and intracellular moisture. In order to make the dryer more reliable, the recirculation strategy and dehumidified air supplied by liquid desiccant were acclimatized to constrict the heat loss through outflowing moist drying air. The experiments were conducted up to the permissible water activity (0.4–0.6) under variable drying conditions (50–70°C). By raising the ambient inlet temperature (maximum 25.9°C), the developed solar FBD was able to supply the drying air up to 50°C (in continuous mode) and a maximum of up to 65°C without aiding any heat energy sources except solar. It was found that osmosonication opened up the possibility of reducing the required drying temperature (↓10°C) and energy consumption (up to ↓31.7%). The dried red chili was fortified by pretreatment, as it could retain more capsaicin (&gt;6%) and reddishness (&gt;5%) compared to untreated samples. The Fourier transform infrared (FTIR) analysis showed the structural integrity of pretreated samples. The relative humidity of the drying air could be reduced by as much as 5% using the composite lithium chloride and calcium chloride (35% + 5%) desiccant dehumidifier. Dehumidification of air was found advantageous, with an inclination to shorten the drying duration (about ↓0.5 h) and energy (↓12.43%).Practical ApplicationsThere are various commercially valuable unique agro‐products that are exclusively being produced in rural areas. The inaccessibility of relevant drying technology and inconsistency of grid electricity are the main constraints in the value addition of those products. Open sun drying is most popular in rural areas; however, it is not reliable, and the product quality can't maintain. The developed solar‐assisted fluidized bed dryer utilizing dehumidifying air and integrated with osmosonication pretreatment could be a relevant technology for drying heat and moisture‐sensitive products like spices. Cost‐effective drying using locally accessible solar energy compared to open sun drying and superior dried product quality can be achieved by using the current drying system.

A comparative study on 3E (energy, exergy and economic) analysis of solar PV operated dome-shaped solar stills

The present investigation centers on the empirical examination of a solar photo-voltaic system that is integrated with a dome-shaped solar still in order to facili-tate the process of desalination. The objective is to increase the production of freshwater through the utilization of saline water at elevated temperatures. The assessment of the dome-shaped solar still system's efficacy is conducted through the examination of various parameters, including water yield, energy, exergy, concentrator performance, and economic feasibility. The study's results demon-strate that the dome-shaped solar still system's water yield, energy, and exergy were evaluated under varying inlet temperatures and mass flow rates. The study recorded the water yield, energy, and exergy at 4.73, 4.27, and 4.91 L per m?, re-spectively, with respect to the ambient inlet temperature. The water yield was ob-served to range from 6.9-7.7 L per m2 under different input temperatures and air mass-flow rates. The dome-shaped solar still system's energy and exergy efficien-cy were evaluated, indicating encouraging results for various inlet air tempera-tures. Furthermore, the economic evaluation revealed that the rate of freshwater production was cost-effective in comparison to conventional solar stills. In sum-mary, this research offers empirical proof of the efficacy of a solar photovoltaic -powered dome-shaped solar still for the purpose of desalination. It emphasizes enhancements in the output of fresh water, energy and exergy efficiency, and the economic viability of this technology.

The performance of a Horizontal Ground Heat Exchanger (HGHE) under the seasonal ground energy storage behaviour

A well-known backfill soil was considered to be used as the backfill substitutive material. The hydrothermal properties of the backfill material were estimated in laboratory and then injected in a numerical framework considering the atmosphere-soil-HGHE interaction. Numerical simulations were performed for a HGHE installed in the compacted backfill soil and the local materials. Two heat storage scenarios at three different installation depths were also investigated. The results show that an inlet fluid temperature of 50°C in summer increases highly the system performance (13.7% to 41.4%) while the improvement is less significant (0% to 4.8%) for the ambient inlet temperature scenario. A deeper installation depth increases also the system performance.

Energy and exergy analyses of a helicoidal water to air geothermal heat exchanger for arid regions

ABSTRACT Helicoidal water-air geothermal heat exchanger (HWAGHE) uses the water well as a heat source/sink for air refreshing purposes in space. It has been exploited as a passive technique to minimize the energy uses in buildings. This work goals to estimate the energy and exergy characteristics of HWAGHE for arid zone weather condition of Algeria. The helicoidally geometry enhancing the heat exchange with the soil is chosen to decrease the operating cost and the needed area. The studied HWAGHE was constructed from a flexible PVC pipe with 30 m length and 0.6 m diameter. It was immersed into a drilled borehole with 1 m diameter and 5 m depth. The heat exchange rate with the ground and exergy and energy efficiencies of HWAGHE is evaluated. Experimental findings revealed that the inlet ambient temperature has a considerable impact on the HWAGHE performances mainly when the change in temperature between the ambient and the water well increments. Maximal exergy and energetic efficiencies of the HWAGHE, reaching 89% and 92%, respectively, are obtained at 0.035 kg s−1 mass flow rate.

A numerical study into effects of soil compaction and heat storage on thermal performance of a Horizontal Ground Heat Exchanger

The good capacity of the numerical simulations makes possible to bring some further responses on the backfill soil selection and its installation depth in the Horizontal Ground Heat Exchanger (HGHE). Therefore, a well-known backfill soil was considered to be used as substitutive material. The hydrothermal properties of the backfill material were estimated in laboratory and then injected in a numerical framework considering the atmosphere-soil-HGHE interaction. Numerical simulations were performed for a HGHE installed in the compacted backfill soil and the local natural soil. The simulation results showed that the compacted backfill soil improves by 8.5% the HGHE performance compared to local uncompacted soil. Two heat storage scenarios at three different installation depths were also investigated. The results showed that an inlet fluid temperature of 50 °C in summer increased highly the system performance by 13.7%–41.4%, while the improvement was less significant (0%–4.8%) for the ambient inlet temperature scenario. A deeper installation depth of HGHE increased also the system performance, the more energy could be stored and extracted.

Catalyst ignition and extinction: A microkinetics-based bifurcation study of adiabatic reactors for oxidative coupling of methane

Understanding ignition and extinction behavior is of crucial importance for oxidative coupling of methane (OCM). Therefore, for the first time the bifurcation behavior of OCM has been investigated while considering both homogeneous gas phase reactions and heterogeneous reactions using a detailed microkinetic model. Three different adiabatic reactor models are considered: a plug flow reactor (PFR), a continuously stirred tank reactor (CSTR) and a lumped thermal reactor (LTR) model. The latter represents the limiting case with zero backmixing (cf. PFR behavior) for species and perfect thermal backmixing (cf. CSTR behavior). For homogeneous processes this reactor type could for example be realized by adding a high thermal conductivity inert to the reactor tubes, for catalytic processes a high thermal conductivity catalyst could be used.The bifurcation behavior in these reactor types is compared with a focus on methane conversion, C2 yields and their dependence on operating conditions such as inlet composition, inlet temperature and space time. Steady state multiplicity is observed for adiabatic CSTR and LTR models. This multiplicity of steady states is not observed for isothermal reactor models, indicating that it is caused solely by thermal backmixing and is not related to chemical feedback features such as autocatalysis. The start-up procedures or initial conditions determine the actual steady state that is obtained. Among the three investigated reactor types, a LTR shows the highest product yields and the lowest extinction temperatures, which allows autothermal operation at a much lower inlet temperature compared to a PFR and CSTR. For OCM without catalyst, autothermal operation on the ignited branch at ambient inlet temperatures and reasonable space times is only possible by using methane-to-oxygen ratios below 3 leading to low selectivities. For catalytic OCM compared to OCM without catalyst, the range for autothermal operation is much broader and it is much easier to find feasible operating conditions allowing autothermal operation at ambient inlet temperatures.By operating a LTR on the ignited branch at ambient inlet temperature of 300 K, methane-to-oxygen ratio CH4:O2 = 6, space time V/FCH4,0 = 0.02 s, bulk density of Sn-Li/MgO = 1000 kgcat/m3 and pressure P = 1 bar, overall C2 selectivities (i.e. sum of ethane, ethylene and acetylene selectivity) of 80% can be obtained at methane conversions as high as 30%.

Design and experimental characterization of a membrane-based absorption heat pump

A membrane absorption heat pump uses absorbent and refrigerant (solvent) flows separated by a membrane to create temperature gradients (aka temperature lifts) used for heating or cooling. Compared to vacuum absorption heat pumps, an atmospheric-pressure membrane heat pump provides more compact designs, potentially enabling applications such as energy-efficient cooling for electronics. In addition, storing concentrated absorbent offers unique options for energy storage for solar heating and cooling of buildings. A new membrane heat pump module was built using two sets of rows of hollow fibers with stagnant air between the fibers to reduce conductive heat transfer. Transport coefficients for the complex air-gap geometry were estimated with a three-dimensional finite-volume heat transfer analysis of the air gap region with results fitted to a modified conduction shape factor. A two-dimensional finite-difference model of the entire process shows good agreement with experiments performed over different air-gap widths, flow rates, inlet temperatures, and absorbent concentrations. Temperature lifts up to 9 °C were achieved with 39% (mass) LiCl (aq) feed solution and 35 °C inlet temperatures. Extensions of the modeling to higher-porosity, larger-pore-size membranes suggest that temperature lifts of 14 °C at ambient inlet temperatures are achievable in our module geometry.