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Joshua P Schimel - One of the best experts on this subject based on the ideXlab platform.
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rainfall intensification increases the contribution of Rewetting pulses to soil respiration
Biogeosciences Discussions, 2020Co-Authors: Stefano Manzoni, Joshua P Schimel, Arjun Chakrawal, Thomas Fischer, Amilcare Porporato, Giulia VicoAbstract:Abstract. Soil drying and wetting cycles promote carbon (C) release through large heterotrophic respiration pulses at Rewetting, known as Birch effect. Empirical evidence shows that drier conditions before Rewetting and larger changes in soil moisture at Rewetting cause larger respiration pulses. Because soil moisture varies in response to rainfall, also these respiration pulses depend on the random timing and intensity of precipitation. In addition to Rewetting pulses, heterotrophic respiration continues during soil drying, eventually ceasing when soils are too dry to sustain microbial activity. The importance of respiration pulses in contributing to the overall soil respiration flux has been demonstrated empirically, but no theoretical investigation has so far evaluated how the relative contribution of these pulses may change along climatic gradients or as precipitation regimes shift in a given location. To fill this gap, we start by assuming that Rewetting pulses and respiration rates during soil drying can be treated as random variables dependent on soil moisture fluctuations, and develop a stochastic model for soil heterotrophic respiration rates that analytically links the statistical properties of respiration to those of precipitation. Model results show that both the mean Rewetting pulse respiration and the mean respiration during drying increase with increasing mean precipitation. However, the contribution of respiration pulses to the total heterotrophic respiration increases with decreasing precipitation frequency and to a lesser degree with decreasing precipitation depth, leading to an overall higher contribution of respiration pulses under future more intermittent and intense precipitation. Moreover, the variability of both components of soil respiration is also predicted to increase under these conditions. Therefore, our results suggest that with future more intermittent precipitation, respiration pulses and the associated nutrient release will intensify and become more variable, contributing more to soil biogeochemical cycling.
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linking no and n2o emission pulses with the mobilization of mineral and organic n upon Rewetting dry soils
Soil Biology & Biochemistry, 2017Co-Authors: Sonja Leitner, Peter M Homyak, Joseph C Blankinship, Jennifer Eberwein, Darrel G Jenerette, Sophie Zechmeisterboltenstern, Joshua P SchimelAbstract:Abstract Drying and Rewetting of soils triggers a cascade of physical, chemical, and biological processes; understanding these responses to varying moisture levels becomes increasingly important in the context of changing precipitation patterns. When soils dry and water content decreases, diffusion is limited and substrates can accumulate. Upon Rewetting, these substrates are mobilized and can energize hot moments of intense biogeochemical cycling, leading to pulses of trace gas emissions. Until recently, it was difficult to follow the Rewetting dynamics of nutrient cycling in the field without physically disturbing the soil. Here we present a study that combines real-time trace gas measurements with high-resolution measurements of diffusive nutrient fluxes in intact soils. Our goal was to distinguish the contribution of different inorganic and organic nitrogen (N) forms to the Rewetting substrate flush and the production of nitric oxide (NO) and nitrous oxide (N 2 O). Diffusive flux of N-bearing substrates (NO 2 − , NO 3 − , NH 4 + and amino acids) was determined in situ in hourly resolution using a microdialysis approach. We conducted an irrigation experiment in a semi-arid California grassland at the end of the dry season, and followed soil N flux and N trace gas emissions over the course of 30 h post-wetting. Upon Rewetting, both inorganic and organic N diffused through the soil, with inorganic N contributing most to the Rewetting N flush. Emissions of NO and N 2 O rapidly increased and remained elevated for the duration of our measurements, whereas diffusive soil N flux was characterized by large temporal variation. Immediately after Rewetting, NO 3 − contributed 80% to the total diffusive N flux but was consumed rapidly, possibly due to fast microbial uptake or denitrification. Ammonium flux contributed only ∼10% to the initial diffusive N flux, but it dominated total N diffusion 27 h post-wetting, coinciding with peak N-gas emissions. This suggests nitrification may control most of the N trace gases produced during the late stages of a Rewetting pulse. Nitrite contributed only 1% to total N diffusion and did not show a clear temporal pattern. Amino acids contributed roughly as much as NH 4 + to the initial diffusive N flux, but the organic N pulse was short-lived, indicating that organic N did not contribute substantially to N-gas formation shortly after Rewetting at our study site. Our results support the hypothesis that in semi-arid environments N-bearing substrates concentrate during dry periods and, upon Rewetting, can lead to pulses of NO and N 2 O when they react chemically or are transformed by microorganisms.
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adding an empirical factor to better represent the Rewetting pulse mechanism in a soil biogeochemical model
Geoderma, 2010Co-Authors: Xuyong Li, Joshua P Schimel, Amy E Miller, Thomas Meixner, John M Melack, James O SickmanAbstract:The Rewetting of a dry soil causes a pulse in decomposition of soil organic matter (SOM). This mechanism may dominate carbon (C) and nitrogen (N) cycles in arid, semi-arid and Mediterranean ecosystems. Existing biogeochemical models perform poorly for systems characterized by pulsed events. In this study, we added a Rewetting factor into the DAYCENT soil biogeochemical model to better represent the drying-Rewetting pulses. Based on a 4-month laboratory incubation from a parallel study, we developed a simple Rewetting factor for representing the enhanced mineralization pulse by Rewetting stimulation. The Rewetting factor was then incorporated into DAYCENT by modifying the soil moisture factor. The DAYCENT modification significantly improved model performance in predicting soil C respiration rates in drying-Rewetting treatments through the capture of Rewetting pulses. The modification also improved prediction performance for net N mineralization in treatments with shorter Rewetting intervals, but did not improve predictions in treatments with longer Rewetting intervals. The model modifications were validated by using a laboratory incubation data set from a different field site. The modified DAYCENT predictions showed that active and slow SOM pools were major contributors to mineralization pulses while the contribution from the passive pool was minimal. The modifications we made improved model performance and should be considered in future field representations of biogeochemical processes. (C) 2010 Elsevier B.V. All rights reserved.
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episodic Rewetting enhances carbon and nitrogen release from chaparral soils
Soil Biology & Biochemistry, 2005Co-Authors: Amy E Miller, Joshua P Schimel, Thomas Meixner, James O Sickman, John M MelackAbstract:The short-term pulse of carbon (C) and nitrogen (N) mineralization that accompanies the wetting of dry soils may dominate annual C and N production in many arid and semi-arid environments characterized by seasonal transitions. We used a laboratory incubation to evaluate the impact of short-term fluctuations in soil moisture on long-term carbon and nitrogen dynamics, and the degree to which Rewetting enhances C and N release. Following repeated drying and Rewetting of chaparral soils, cumulative CO2 release in rewet soils was 2.2–3.7 times greater than from soils maintained at equivalent mean soil moisture and represented 12–18% of the total soil C pool. Rewetting frequency did not affect cumulative CO2 release but did enhance N turnover, and net N mineralization and nitrification increased with Rewetting in spite of significant reductions in nitrification potential. Litter addition decreased inorganic N release but enhanced dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) from dry soils, indicating the potential importance of a litter-derived pulse to short-term nutrient dynamics.
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a proposed mechanism for the pulse in carbon dioxide production commonly observed following the rapid Rewetting of a dry soil
Soil Science Society of America Journal, 2003Co-Authors: Noah Fierer, Joshua P SchimelAbstract:The rapid Rewetting of a dry soil often yields a pulse in soil CO 2 production that persists for 2 to 6 d. This phenomenon is a common occurrence in surface soils, yet the mechanism responsible for producing the CO 2 pulse has not been positively identified, We studied the effects of a single drying and Rewetting event on soil C pools, to identify which specific C substrates are mineralized to produce the observed pulse in respiration rates. We labeled two soils with C-glucose and measured the enrichment and pool sizes of the released CO 2 , extractable biomass C, and extractable soil organic matter (SOM-C) throughout a drying and Rewetting cycle. After Rewetting, respiration rates were 475 to 370% higher than the rates measured before the dry down. The enrichment of the released CO 2 was 1 to 2 times higher than the enrichment of the extractable biomass C pools and 10 to 20 times higher than the enrichment of the extractable organic C, suggesting that the CO 2 pulse was generated entirely from the mineralization of microbial biomass C. However, there was no evidence of substantial microbial cell lysis on Rewetting. We hypothesize that the pulse of CO 2 is generated by the rapid mineralization of highly enriched intracellular compounds as a response by the microbial biomass to the rapid increase in soil water potentials. The drying and Rewetting process also releases physically protected SOM, increasing the amount of extractable SOM-C by up to 200%. The additional SOM-C rendered soluble by the Rewetting event did not contribute substantially to the Rewetting CO 2 pulse. Overall, the rapid Rewetting of a dry soil can influence soil C cycling in the short-term, by increasing the microbial mineralization of cytoplasmic solutes, and in the longer-term, by decreasing the total amount of SOM physically protected within microaggregates.
Johannes Rousk - One of the best experts on this subject based on the ideXlab platform.
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partial drying accelerates bacterial growth recovery to Rewetting
Soil Biology & Biochemistry, 2017Co-Authors: Annelein Meisner, Ainara Leizeaga, Johannes Rousk, Erland BaathAbstract:Fluctuations in soil moisture create drying-Rewetting events affecting the activity of microorganisms. Microbial responses to drying-Rewetting are mostly studied in soils that are air-dried before Rewetting. Upon Rewetting, two patterns of bacterial growth have been observed. In the Type 1 pattern, bacterial growth rates increase immediately in a linear fashion. In the Type 2 pattern, bacterial growth rates increase exponentially after a lag period. However, soils are often only partially dried. Partial drying (higher remaining moisture content before Rewetting) may be considered a less harsh treatment compared with air-drying. We hypothesized that a soil with a Type 2 response upon Rewetting air-dried soil would transform into a Type 1 response if dried partially before Rewetting. Two soils were dried to a gradient of different moisture content. Respiration and bacterial growth rates were then measured before and during 48 h after Rewetting to 50% of water holding capacity (WHC). Initial moisture content determined growth and respiration in a sigmoidal fashion, with lowest activity in air-dried soil and maximum above ca. 30% WHC. Partial drying resulted in shorter lag periods, shorter recovery times and lower maximum bacterial growth rates after Rewetting. The respiration after Rewetting was lower when soil was partially dried and higher when soils were air-dried. The threshold moisture content where transition from a Type 2 to a Type 1 response occurred was about 14% WHC, while >30% WHC resulted in no Rewetting effect. We combine our result with other recent reports to propose a framework of response patterns after drying-Rewetting, where the harshness of drying determines the response pattern of bacteria upon Rewetting dried soils.
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the impact of salinity on the microbial response to drying and Rewetting in soil
Soil Biology & Biochemistry, 2017Co-Authors: Kristin M Rath, Arpita Maheshwari, Johannes RouskAbstract:In saline soils, the severity of drought for the soil microbial community is exacerbated by accumulating concentrations of salts during drying. In this study we investigated how bacterial growth and respiration responses to drying-Rewetting were affected by salinity. To do this, we adjusted a non-saline soil to four different salinities (0, 2, 7 and 22 mg NaCl g−1), followed by addition of plant material and a one-month incubation. Following the incubation period, we assessed the moisture dependence of respiration and growth, as well as the responses of bacterial growth and respiration to a cycle of air-drying followed by Rewetting to optimal moisture. The inhibition of bacterial growth and respiration by reducing moisture increased with higher salt concentrations. As such, salinity was shown to increase the negative impact of drying on bacterial growth and alter the bacterial growth and respiration dynamics after Rewetting. Drying-Rewetting of soils with low salinity resulted in an immediate onset and gradual resuscitation of bacterial growth to levels similar to before drying. In contrast, in soils with higher salinity growth increased exponentially after a lag period of several hours. The duration of the lag period induced by salinity increased with the amount of salt added. The observed lag period matched previously reported results observed in response to more severe drying by e.g. longer duration of drought and drought combined with starvation. In treatments with a salt concentration ≤7 mg NaCl g−1 a high respiration pulse occurred immediately after Rewetting and subsequently respiration declined. In the most saline treatment the initial respiration was reduced below the level of continuously moist soil to later increase exponentially in parallel with the increase in bacterial growth. We conclude that soil salinity increases the inhibition of microbial activity by low moisture, that fundamentally different responses to drying-Rewetting cycles can be induced, and that high salt concentrations can substantially delay the pulse of respiration induced by Rewetting dry soil. (Less)
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The impact of salinity on the microbial response to drying and Rewetting in soil
Soil Biology & Biochemistry, 2017Co-Authors: Kristin M Rath, Arpita Maheshwari, Johannes RouskAbstract:Abstract In saline soils, the severity of drought for the soil microbial community is exacerbated by accumulating concentrations of salts during drying. In this study we investigated how bacterial growth and respiration responses to drying-Rewetting were affected by salinity. To do this, we adjusted a non-saline soil to four different salinities (0, 2, 7 and 22 mg NaCl g−1), followed by addition of plant material and a one-month incubation. Following the incubation period, we assessed the moisture dependence of respiration and growth, as well as the responses of bacterial growth and respiration to a cycle of air-drying followed by Rewetting to optimal moisture. The inhibition of bacterial growth and respiration by reducing moisture increased with higher salt concentrations. As such, salinity was shown to increase the negative impact of drying on bacterial growth and alter the bacterial growth and respiration dynamics after Rewetting. Drying-Rewetting of soils with low salinity resulted in an immediate onset and gradual resuscitation of bacterial growth to levels similar to before drying. In contrast, in soils with higher salinity growth increased exponentially after a lag period of several hours. The duration of the lag period induced by salinity increased with the amount of salt added. The observed lag period matched previously reported results observed in response to more severe drying by e.g. longer duration of drought and drought combined with starvation. In treatments with a salt concentration ≤7 mg NaCl g−1 a high respiration pulse occurred immediately after Rewetting and subsequently respiration declined. In the most saline treatment the initial respiration was reduced below the level of continuously moist soil to later increase exponentially in parallel with the increase in bacterial growth. We conclude that soil salinity increases the inhibition of microbial activity by low moisture, that fundamentally different responses to drying-Rewetting cycles can be induced, and that high salt concentrations can substantially delay the pulse of respiration induced by Rewetting dry soil.
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prolonged drought changes the bacterial growth response to Rewetting
Soil Biology & Biochemistry, 2015Co-Authors: Annelein Meisner, Johannes Rousk, Erland BaathAbstract:Rewetting a dry soil can result in two response patterns of bacterial growth and respiration. In type 1, bacterial growth starts to increase linearly immediately upon Rewetting and respiration rates are highest immediately upon Rewetting. In type 2, bacterial growth starts to increase exponentially after a lag period with a secondary increase in respiration occurring at the start of the exponential increase in growth. We previously observed that the type 1 response occurred after Rewetting 4-day dried soil and type 2 for 1-year dried soil. Here we studied in detail how the duration of drought related to the two types of responses of bacterial growth and respiration to Rewetting. Soil was air dried for different time periods from 4 days up to 48 weeks. Upon Rewetting, bacterial growth and respiration was measured repeatedly at 17 °C during one week. Drought periods of ≤2 weeks resulted in a type 1 response whereas drought periods of ≥4 weeks resulted in a type 2 response. The lag period increased with drought duration and reached a maximum of ca. 18 h. The bacterial growth response was also affected by incubation of moist soil before drying–Rewetting. The lag period increased with duration of moist soil incubation before the 4-day drying–Rewetting event and reached also a maximum of ca. 18 h. The exponential growth increase in the type 2 response coincided with a secondary increase in respiration, which increased in magnitude with increasing drought duration. Cumulative respiration increased with drought duration and was ca. 4 times higher after 48 weeks of drought compared to 4 days. Thus, prolonged drought affected the response type of bacterial growth and respiration to Rewetting, and also increased lag period, the magnitude of the secondary increase in respiration and total C release. The effect of drought was, however, modified by the lenght of the incubation period of moist soil before drought, suggesting that soil conditions before a drying–Rewetting event need consideration when evaluating microbial responses.
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microbial growth responses upon Rewetting soil dried for four days or one year
Soil Biology & Biochemistry, 2013Co-Authors: Annelein Meisner, Erland Baath, Johannes RouskAbstract:A pulse of respiration is induced by Rewetting dry soil. Here we study the microbial responses underlying this pulse of respiration when Rewetting soil dried for 4-days or 1-year. In the 4-days dried soil, respiration increased to a maximum rate immediately upon Rewetting after which it decreased exponentially. In the 1-year dried soil, respiration also increased immediately, but then remained high for 16 h, after which it increased further, exponentially, with a peak rate after 20 h. The level of bacterial growth was initially lower in rewetted than in constantly moist soil, but started to increase linearly immediately upon Rewetting 4-days dried soil. In 1-year dried soil, bacterial growth started only after a 16 h lag period of zero growth, and then increased exponentially to a peak after 30 h, at rates superseding those in continually moist soil. Fungal growth started to increase immediately upon Rewetting, and reached the rate of the control soil after 2 days for the 4-days dried soil, and after a week for the 1-year dried soil. Thus, prolonged drying altered the pattern of bacterial and fungal growth after Rewetting. Our results suggest that both fungal and bacterial growth are uncoupled from the initial respiration pulse and that growth responses and microbial C-use efficiency can be affected by prolonged drying. (C) 2013 Elsevier Ltd. All rights reserved. (Less)
B. Chatterjee - One of the best experts on this subject based on the ideXlab platform.
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Rewetting of Vertical Hot Surface during Round Water Jet Impingement Cooling
Heat Transfer Engineering, 2016Co-Authors: Chitranjan Agrawal, Ravi Kumar, Akhilesh Gupta, B. ChatterjeeAbstract:ABSTRACTA stainless steel vertical surface of 0.25 mm thickness at 800 ± 10° C initial temperature was quenched by jet impingement technique. The Rewetting phenomenon of the surface was investigated for the jet of 2.5 – 4.8 mm diameter and jet Reynolds number of 5000–24000. The observations are made from the stagnation point to the 24 mm downstream spatial locations, for both upside and downside directions. The quenching performance of the test surface was evaluated on the basis of different Rewetting parameters i.e. Rewetting temperature, wetting delay, and Rewetting velocity. It has been observed that with the rise in jet Reynolds number and jet diameter, the surface Rewetting performance increases. A correlation has also been proposed to determine the dimensionless Rewetting velocity that predicts the experimental data within an error band of ±20 percent.
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Rewetting of hot vertical rod during jet impingement surface cooling
Heat and Mass Transfer, 2015Co-Authors: Chitranjan Agrawal, Ravi Kumar, Akhilesh Gupta, B. ChatterjeeAbstract:A stainless steel (SS-316) vertical rod of 12 mm diameter at 800 ± 10 °C initial temperature was cooled by normal impinging round water jet. The surface Rewetting phenomenon was investigated for a range of jet diameter 2.5–4.8 mm and jet Reynolds number 5000–24,000 using a straight tube type nozzle. The investigation were made from the stagnation point to maximum 40 mm downstream locations, simultaneously for both upside and downside directions. The cooling performance of the vertical rod was evaluated on the basis of Rewetting parameters i.e. Rewetting temperature, wetting delay, Rewetting velocity and the maximum surface heat flux. Two separate Correlations have been proposed for the dimensionless Rewetting velocity in terms of Rewetting number and the maximum surface heat flux that predicts the experimental data within an error band of ±20 and ±15 % respectively.
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determination of Rewetting on hot horizontal surface with water jet impingement through a sharp edge nozzle
International Journal of Thermal Sciences, 2013Co-Authors: Chitranjan Agrawal, Ravi Kumar, Akhilesh Gupta, B. ChatterjeeAbstract:Abstract The Rewetting phenomenon was experimentally investigated for the hot horizontal stainless steel surface of 0.25 mm thickness and 800 ± 10 °C initial surface temperature. The round water jet of 2.5 mm diameter at 22 ± 1 °C temperature was injected through a sharp edge nozzle. The investigation was done for the stagnation point to 12 mm (≈5d) radial distance and jet Reynolds number varied in the range of 5000–24,000. The Rewetting phenomena during the transient cooling was accessed on the basis of Rewetting temperature, wetting delay, wetting speed and maximum surface heat flux. It has been observed that with rise in jet Reynolds number, the Rewetting performance increased for the entire measured spatial locations. However, for downstream region the surface Rewetting has been delayed and occurred at the reduced surface temperature as compared to the stagnation region. The maximum surface heat flux is the highest at the stagnation point and in a range of 2.1–2.45 MW/m2. The correlation developed for the wetting front speed predicts 85 percent of experimental data within an error band of ±20 percent and the correlation for maximum surface heat flux predicts 90 percent of experimental data within an error band of ±10 percent.
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effect of jet diameter on the Rewetting of hot horizontal surfaces during quenching
Experimental Thermal and Fluid Science, 2012Co-Authors: Chitranjan Agrawal, Ravi Kumar, Akhilesh Gupta, B. ChatterjeeAbstract:Abstract A horizontal stainless steel surface of 0.25 mm thickness and at 800 ± 10 °C initial temperature was cooled by a round water jet. The water jet at 22 ± 1 °C temperature impinged onto the hot surface through tube type nozzles of 250 mm length. The experiments were performed for the jet diameters in the range of 2.5–4.8 mm and the jet Reynolds number remained within 5000–24,000. The transient cooling performance of the test surface was determined on the basis of Rewetting temperature, wetting delay and the Rewetting velocity. A rise in the Rewetting temperature and the Rewetting velocity has been observed with the increase in jet diameter and jet Reynolds number, leading to decline in the wetting delay. The results of the steady state cooling are in agreement with the findings of other investigators. The correlations have also been developed to evaluate the stagnation and the local Nusselt number for the steady state cooling condition. These correlations predict 80% experimental data within an error band of ±10%.
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Rewetting and maximum surface heat flux during quenching of hot surface by round water jet impingement
International Journal of Heat and Mass Transfer, 2012Co-Authors: Chitranjan Agrawal, Ravi Kumar, Akhilesh Gupta, B. ChatterjeeAbstract:Abstract The transient cooling of hot stainless steel surface of 0.25 mm thickness is done with round water jet impingement. Initially, the surface was heated up to the temperature of 800 °C before the water was injected through straight tube type nozzle of 2.5 mm diameter and 250 mm length. During impingement cooling, the surface temperature was measured up to 12 mm radial distance away from the stagnation point. The jet exit to surface spacing, z/d, and jet Reynolds number, Re, varied in the range of 4–16 and 5000–24,000 respectively. The surface Rewetting and transient heat flux of the test-surface was studied for these operating parameters. During impingement cooling process the initial Rewetting occurred at stagnation region with the lowest wetting delay period. In fact, the Rewetting temperature, Rewetting velocity and the maximum heat flux reduced for extreme spatial location. However, the wetting delay increased significantly for the locations away from the stagnation point. The surface Rewetting and transient heat flux were increased with the rise in jet Reynolds number, resulting in the enhancement in Rewetting temperature, Rewetting velocity and reduced wetting delay. The maximum heat flux was obtained for 4–6 mm radial location. The effect of jet exit to surface spacing on the Rewetting parameters is found to be marginal. A correlation has been developed which predicted the maximum heat flux within an error band of ±10%.
Chitranjan Agrawal - One of the best experts on this subject based on the ideXlab platform.
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Rewetting of Vertical Hot Surface during Round Water Jet Impingement Cooling
Heat Transfer Engineering, 2016Co-Authors: Chitranjan Agrawal, Ravi Kumar, Akhilesh Gupta, B. ChatterjeeAbstract:ABSTRACTA stainless steel vertical surface of 0.25 mm thickness at 800 ± 10° C initial temperature was quenched by jet impingement technique. The Rewetting phenomenon of the surface was investigated for the jet of 2.5 – 4.8 mm diameter and jet Reynolds number of 5000–24000. The observations are made from the stagnation point to the 24 mm downstream spatial locations, for both upside and downside directions. The quenching performance of the test surface was evaluated on the basis of different Rewetting parameters i.e. Rewetting temperature, wetting delay, and Rewetting velocity. It has been observed that with the rise in jet Reynolds number and jet diameter, the surface Rewetting performance increases. A correlation has also been proposed to determine the dimensionless Rewetting velocity that predicts the experimental data within an error band of ±20 percent.
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Rewetting of hot vertical rod during jet impingement surface cooling
Heat and Mass Transfer, 2015Co-Authors: Chitranjan Agrawal, Ravi Kumar, Akhilesh Gupta, B. ChatterjeeAbstract:A stainless steel (SS-316) vertical rod of 12 mm diameter at 800 ± 10 °C initial temperature was cooled by normal impinging round water jet. The surface Rewetting phenomenon was investigated for a range of jet diameter 2.5–4.8 mm and jet Reynolds number 5000–24,000 using a straight tube type nozzle. The investigation were made from the stagnation point to maximum 40 mm downstream locations, simultaneously for both upside and downside directions. The cooling performance of the vertical rod was evaluated on the basis of Rewetting parameters i.e. Rewetting temperature, wetting delay, Rewetting velocity and the maximum surface heat flux. Two separate Correlations have been proposed for the dimensionless Rewetting velocity in terms of Rewetting number and the maximum surface heat flux that predicts the experimental data within an error band of ±20 and ±15 % respectively.
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determination of Rewetting on hot horizontal surface with water jet impingement through a sharp edge nozzle
International Journal of Thermal Sciences, 2013Co-Authors: Chitranjan Agrawal, Ravi Kumar, Akhilesh Gupta, B. ChatterjeeAbstract:Abstract The Rewetting phenomenon was experimentally investigated for the hot horizontal stainless steel surface of 0.25 mm thickness and 800 ± 10 °C initial surface temperature. The round water jet of 2.5 mm diameter at 22 ± 1 °C temperature was injected through a sharp edge nozzle. The investigation was done for the stagnation point to 12 mm (≈5d) radial distance and jet Reynolds number varied in the range of 5000–24,000. The Rewetting phenomena during the transient cooling was accessed on the basis of Rewetting temperature, wetting delay, wetting speed and maximum surface heat flux. It has been observed that with rise in jet Reynolds number, the Rewetting performance increased for the entire measured spatial locations. However, for downstream region the surface Rewetting has been delayed and occurred at the reduced surface temperature as compared to the stagnation region. The maximum surface heat flux is the highest at the stagnation point and in a range of 2.1–2.45 MW/m2. The correlation developed for the wetting front speed predicts 85 percent of experimental data within an error band of ±20 percent and the correlation for maximum surface heat flux predicts 90 percent of experimental data within an error band of ±10 percent.
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Rewetting of a hot horizontal surface through mist jet impingement cooling
International Journal of Heat and Mass Transfer, 2013Co-Authors: Chitranjan Agrawal, Ravi Kumar, Akhilesh Gupta, O F P Lyons, Darina B MurrayAbstract:Abstract An experimental investigation has been carried out to study the Rewetting behaviour of a hot horizontal stainless steel surface during the mist jet impingement cooling. The experiments have been performed to study the Rewetting behaviour for three different initial surface temperatures viz. 255, 355, 565 °C. An axis-symmetric nozzle has been used to develop the mist jet of constant flow rate. The variation in surface temperature has been acquired up to 20 mm downstream spatial locations away from the stagnation point. It has been observed that unlike liquid jet impingement cooling the rise in surface initial temperature increases the Rewetting temperature and the wetting delay increase with rise in the initial surface temperature but the Rewetting velocity reduces. Further, the maximum surface heat flux is the highest at 20 mm spatial location for 565 °C initial surface temperature. Whereas, at the stagnation point, the maximum surface heat flux is not affected by the change in surface initial temperature.
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effect of jet diameter on the Rewetting of hot horizontal surfaces during quenching
Experimental Thermal and Fluid Science, 2012Co-Authors: Chitranjan Agrawal, Ravi Kumar, Akhilesh Gupta, B. ChatterjeeAbstract:Abstract A horizontal stainless steel surface of 0.25 mm thickness and at 800 ± 10 °C initial temperature was cooled by a round water jet. The water jet at 22 ± 1 °C temperature impinged onto the hot surface through tube type nozzles of 250 mm length. The experiments were performed for the jet diameters in the range of 2.5–4.8 mm and the jet Reynolds number remained within 5000–24,000. The transient cooling performance of the test surface was determined on the basis of Rewetting temperature, wetting delay and the Rewetting velocity. A rise in the Rewetting temperature and the Rewetting velocity has been observed with the increase in jet diameter and jet Reynolds number, leading to decline in the wetting delay. The results of the steady state cooling are in agreement with the findings of other investigators. The correlations have also been developed to evaluate the stagnation and the local Nusselt number for the steady state cooling condition. These correlations predict 80% experimental data within an error band of ±10%.
Noah Fierer - One of the best experts on this subject based on the ideXlab platform.
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a proposed mechanism for the pulse in carbon dioxide production commonly observed following the rapid Rewetting of a dry soil
Soil Science Society of America Journal, 2003Co-Authors: Noah Fierer, Joshua P SchimelAbstract:The rapid Rewetting of a dry soil often yields a pulse in soil CO 2 production that persists for 2 to 6 d. This phenomenon is a common occurrence in surface soils, yet the mechanism responsible for producing the CO 2 pulse has not been positively identified, We studied the effects of a single drying and Rewetting event on soil C pools, to identify which specific C substrates are mineralized to produce the observed pulse in respiration rates. We labeled two soils with C-glucose and measured the enrichment and pool sizes of the released CO 2 , extractable biomass C, and extractable soil organic matter (SOM-C) throughout a drying and Rewetting cycle. After Rewetting, respiration rates were 475 to 370% higher than the rates measured before the dry down. The enrichment of the released CO 2 was 1 to 2 times higher than the enrichment of the extractable biomass C pools and 10 to 20 times higher than the enrichment of the extractable organic C, suggesting that the CO 2 pulse was generated entirely from the mineralization of microbial biomass C. However, there was no evidence of substantial microbial cell lysis on Rewetting. We hypothesize that the pulse of CO 2 is generated by the rapid mineralization of highly enriched intracellular compounds as a response by the microbial biomass to the rapid increase in soil water potentials. The drying and Rewetting process also releases physically protected SOM, increasing the amount of extractable SOM-C by up to 200%. The additional SOM-C rendered soluble by the Rewetting event did not contribute substantially to the Rewetting CO 2 pulse. Overall, the rapid Rewetting of a dry soil can influence soil C cycling in the short-term, by increasing the microbial mineralization of cytoplasmic solutes, and in the longer-term, by decreasing the total amount of SOM physically protected within microaggregates.
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influence of drying Rewetting frequency on soil bacterial community structure
Microbial Ecology, 2003Co-Authors: Noah Fierer, Joshua P Schimel, Patricia A HoldenAbstract:number of drying–Rewetting cycles. At the end of the 2-month incubation we extracted DNA from soil samples and characterized the soil bacterial communities using the terminal restriction fragment length polymorphism (T-RFLP) method. We found that drying–Rewetting regimes can influence bacterial community composition in oak but not in grass soils. The two soils have inherently different bacterial communities; only the bacteria residing in the oak soil, which are less frequently exposed to moisture stress in their natural environment, were significantly affected by drying–Rewetting cycles. The community indices of taxonomic diversity and richness were relatively insensitive to drying–Rewetting frequency. We hypothesize that drying–Rewetting induced shifts in bacterial community composition may partly explain the changes in C mineralization rates that are commonly observed following exposure to numerous drying–Rewetting cycles. Microbial community composition may influence soil processes, particularly in soils exposed to a significant level of environmental stress.
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effects of drying Rewetting frequency on soil carbon and nitrogen transformations
Soil Biology & Biochemistry, 2002Co-Authors: Noah Fierer, Joshua P SchimelAbstract:Soil drying and Rewetting impose a significant stress on the soil microbial community. While wetting events are common in most environments, the short and long-term effects of soil Rewetting on microbial processes have not been well studied. Furthermore, it is not clear if stress history is important to consider when modeling microbial controls on ecosystem dynamics. In this experiment, we manipulated the frequency of soil Rewetting events during 2 months to determine how stress history influences the response of soil microbial communities to Rewetting events. Two soils were collected from the Sedgwick Ranch Natural Reserve in Santa Ynez, CA, one from an annual grassland, the other from underneath an oak canopy. Soils were incubated in the lab and went through either 0, 1, 2, 4, 6, 9, or 15 drying–Rewetting cycles over 2 months. Soil moisture content was adjusted so that the average moisture content over the course of the incubation was the same for all samples, compensating for the number of drying–Rewetting cycles. Soils were analyzed for respiration rate, substrate utilization efficiency, nitrification potential, microbial biomass, and NH4+ and NO3− concentrations. Total CO2 loss during incubation significantly increased with number of Rewetting events for oak soils but not for grass soils, where a large number of Rewetting events decreased total CO2 loss. Exposure to frequent drying–Rewetting events decreased the amount of CO2 released upon Rewetting and dramatically increased the activity of autotrophic nitrifier populations. For up to 6 weeks after the last drying–Rewetting cycle, respiration rates in soils exposed to a history of drying–Rewetting events were substantially lower than their non-stressed controls. In all cases, the effects of the Rewetting stress were greater in oak than in grass soils. The results indicate that drying–Rewetting events can induce significant changes in microbial C and N dynamics and these effects can last for more than a month after the last stress. The frequency of drying–Rewetting stress events has important ecosystem-level ramifications and should be incorporated into models of soil microbial dynamics.
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Effects of drying–Rewetting frequency on soil carbon and nitrogen transformations
Soil Biology & Biochemistry, 2002Co-Authors: Noah Fierer, Joshua P SchimelAbstract:Soil drying and Rewetting impose a significant stress on the soil microbial community. While wetting events are common in most environments, the short and long-term effects of soil Rewetting on microbial processes have not been well studied. Furthermore, it is not clear if stress history is important to consider when modeling microbial controls on ecosystem dynamics. In this experiment, we manipulated the frequency of soil Rewetting events during 2 months to determine how stress history influences the response of soil microbial communities to Rewetting events. Two soils were collected from the Sedgwick Ranch Natural Reserve in Santa Ynez, CA, one from an annual grassland, the other from underneath an oak canopy. Soils were incubated in the lab and went through either 0, 1, 2, 4, 6, 9, or 15 drying–Rewetting cycles over 2 months. Soil moisture content was adjusted so that the average moisture content over the course of the incubation was the same for all samples, compensating for the number of drying–Rewetting cycles. Soils were analyzed for respiration rate, substrate utilization efficiency, nitrification potential, microbial biomass, and NH4+ and NO3− concentrations. Total CO2 loss during incubation significantly increased with number of Rewetting events for oak soils but not for grass soils, where a large number of Rewetting events decreased total CO2 loss. Exposure to frequent drying–Rewetting events decreased the amount of CO2 released upon Rewetting and dramatically increased the activity of autotrophic nitrifier populations. For up to 6 weeks after the last drying–Rewetting cycle, respiration rates in soils exposed to a history of drying–Rewetting events were substantially lower than their non-stressed controls. In all cases, the effects of the Rewetting stress were greater in oak than in grass soils. The results indicate that drying–Rewetting events can induce significant changes in microbial C and N dynamics and these effects can last for more than a month after the last stress. The frequency of drying–Rewetting stress events has important ecosystem-level ramifications and should be incorporated into models of soil microbial dynamics.
