Function Of ΔT Research Articles

Effects of Overall Length and OD on Opposing Pulse-jet Cleaning for Pleated Filter Cartridges

ABSTRACT Opposing-pulse-jet technology has been proposed as a solution for regenerating filtration media by minimizing the incomplete cleaning of pleated filter cartridges. In this study, we investigated the effects of a pleated filter cartridge’s overall length and outer diameter (OD) on the performance of opposing-pulse-jet cleaning via numerical modeling. For each pleated filter cartridge, the delay time, Δt (defined as the delay in launching the secondary nozzle), was varied to analyze the intensity and the uniformity of the static pressure distribution in the core of the cartridge. It was found that two opposing jet flows collided much more intensely in the core when the length of the overall cartridge, L, was short, and the OD was small. For a given L, the pressure pulse’s performance was maximized by varying Δt. The pulse intensity and uniformity in the filter core can be represented as a bimodal (double-peaked) function of Δt. In general, the pulse intensity was greater when Δt > 0 s than when Δt < 0 s (when the secondary jet was launched before the primary jet).

466: The risk of anticipated delivery in asymptomatic women presenting with short cervix in early viability

While it is known that an asymptomatic short cervical length (CL) is an independent risk factor for spontaneous preterm birth (sPTB), it is unclear when the delivery will take place. Subsequently, management decisions such as timing of antenatal corticosteroid (ACS) administration or hospital admission may be suboptimal. Therefore, the purpose of this study was to determine the risk of anticipated delivery in asymptomatic women presenting with a short CL in early viability. A retrospective cohort study of asymptomatic women with short cervix, (CL ≤ 25mm) between 23 and 28 weeks’ gestation, at a single center from January 2015 to March 2018 was performed. Women with multiple gestations, fetal anomalies and cervical cerclage were excluded. Demographic information as well as risk factors for sPTB were collected. Cases were divided into 4 groups based on CL measurement (≤ 10mm, 11-15mm, 16-20mm, 21-25mm). The primary outcome was time interval from presentation to delivery (Δt). Secondary outcomes included delivery within 2 weeks of presentation and gestational age (GA) at delivery. Continuous variables were compared using the Kruskal-Wallis test, while categorical variables were compared using Chi-squared or Fisher’s exact test as appropriate. The Wilcoxon test for difference in survival time was used to compare GA at delivery among the 4 CL groups with data stratified based on GA at presentation. 126 pregnancies met inclusion criteria. Baseline characteristics were similar among all four groups. Primary and secondary outcomes are reported in Table 1. The probability of delivery as a function of Δt is presented in Figure 1. There was a direct correlation between shorter CL and shorter Δt (p = 0.003). Regardless of the CL at presentation, delivery within 2 weeks was uncommon (1 patient; 0.8%). As expected, the risk for sPTB in asymptomatic women with short cervix increases as the CL shortens, with CL ≤10mm associated with the highest risk. Nevertheless, regardless of the CL, delivery within 2 weeks is highly unlikely. Therefore, we suggest that the timing of administration of ACS in this population should be delayed until additional indications are present.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Positive double-pulse streamers: how pulse-to-pulse delay influences initiation and propagation of subsequent discharges

Residual charges and species created by previous streamers have a great impact on the characteristics of the next discharge. This is especially pronounced in repetitively pulsed discharges, where the physical and chemical reactions during the decay phase play a very important role. We have performed double-pulse streamer experiments in artificial air and pure nitrogen with a varying pulse delay (Δt) from 0.45 μs to 20 ms. We have observed morphological transformations of the 2nd-pulse streamer as a function of Δt and classified six typical stages by streamer length. The propagation distance of the 2nd-pulse streamer can be 66% longer than the 1st-pulse in 66.7 mbar nitrogen, while it is 37% longer in air under the same conditions. However, we find that the longer propagation distance of the 2nd-pulse streamer in N2 is not caused by a higher velocity nor by fast gas heating of previous channels under our experimental conditions, but by earlier inception which gives more time to propagate during the pulse. In air, on the other hand, the streamers initiate almost at the same time in both pulses but the inception cloud of the 2nd-pulse streamer breaks up earlier. The onset of every stage occurs at smaller Δt in air than in N2 at the same pressure. These observations imply that different mechanisms work in N2 and air, e.g. photoionization and attachment.

Detection limits of optical gas imagers as a function of temperature differential and distance

ABSTRACTOptical gas imaging (OGI) is an effective tool for detecting gas leaks from process equipment. Despite the fact that OGI has been used for leak detection for over a decade, its detection limit is an elusive performance metric and has not been systematically characterized and quantified like other detection instruments. A substantial body of research has been performed that has shed some light on the OGI detection limits and the factors that dictate the detection limits. The OGI detection limit expressed as ppm-m and ppm now can be quantified as a function of ΔT (differential temperature between the gas plume and the background), the OGI camera type, and the specific gas in question. Furthermore, the OGI detection limit expressed as grams per hour can be calculated based on the ΔT and the distance from the OGI camera to the leak location under common leak survey conditions. For the same OGI camera, the detection limit can vary by several orders of magnitude due to ΔT and distance. The present work has demonstrated how different OGI detection limits can be. More importantly, this work has, for the first time, formulated equations that can be used to determine OGI detection limits with a given set of leak detection conditions. Being able to quantify OGI detection limit and understand the variables that dictate the detection limit is a significant advancement. It will help OGI to become accepted as a mature field instrument. The variables characterized in this work should have an impact on the development of OGI leak survey protocols, such as Appendix K to Code of Federal Regulations 40 CFR Part 60 in the United States. Established detection limits will also help emission inventory for fugitive emissions when OGI is used as the sole leak detection method.Implications: Optical gas imaging (OGI) has been used for leak detection and control of fugitive volatile organic compound (VOC) emissions and methane emissions due to equipment leaks. However, detection limits of OGI have not been characterized and quantified like other detection instruments. The lack of well-understood detection limits has hindered broader applications of OGI. The work presented in this paper represents important steps that will enable OGI users and policymakers to establish (1) OGI detection limits under various conditions, (2) OGI leak survey criteria for a desired minimum detectable leak size, and (3) maximum potential emissions from the nondetect sources in emission inventory studies.

Structural Unit of Polymer Crystallization in Dilute Solution As Studied by Solid-State NMR and 13C Isotope Labeling

The nucleation and growth mechanisms of semicrystalline polymers during crystallization in dilute solutions have been debated in the past decades. Wang et al. recently reported that 13C CH3 labeled poly(l-lactic acid) (PLLA), with small weight-average molecular weight ⟨Mw⟩ = 46K g/mol (s), adopted three-dimensional nanoclusters via adjacent re-entry folding in the solution-grown crystals, and its mean size was independent of crystallization temperature (Tc) [Macromolecules 2017, 50, 6404–6414]. In this work, 13C CH3 labeled PLLA chains with middle and large ⟨Mw⟩ of 90K g/mol (m) and 326 K g/mol (l), respectively, were synthesized. Both ⟨Mw⟩ and kinetics effects on the chain-folding structures and crystal habits of the 13C CH3 labeled PLLA were systematically investigated by solid-state (ss) NMR and atomic force microscopy (AFM). s-, m-, and l-PLLAs commonly adopted faceted lozenge single crystals in dilute amyl acetate (AA) solution (0.05 wt %) under a very low supercooling, ΔT = 40 °C, but dendrites with multiple layers under a rapidly quenched condition, ΔT = ∼130 °C. By comparison of the experimental and simulated 13C–13C DQ buildup curves, it was indicated that (i) all s-, m-, l-PLLA adopted the same mean structure of the three-dimensional nanoclusters in multiple rows via adjacent re-entry structure in the lozenge shape and dendrite crystals and (ii) the mean size of the nanocluster was smaller than the nanocluster size expected from the smallest ⟨Mw⟩ used in this study. On the basis of the crystal habits as well as dimension and size of the nanoclusters, it was suggested that (i) the PLLA chains with different ⟨Mw⟩s initially adopted the same nanoclusters via folding (stage I) and (ii) the aggregation process of the nanoclusters, which was dominated by kinetics, resultantly led to the different morphological features as a function of ΔT (stage II).

On the growth orientation of twin-related faceted dendrites

The growth orientation of twin-related faceted silicon dendrites depends on the undercooling ΔT in the melt, which cannot be explained by the existing models. We propose a model to explain the growth behavior showing that the re-entrant corners would lead to the growth of 〈112〉 dendrites, while the 〈110〉 branch is due to continuous growth. Such a selection could be determined by the velocity ratio Vre-entrant/Vridge that is a function of ΔT. An analytical expression for this ratio is derived and compared to the experimental observations.

Reconstructing CO2 concentrations in basaltic melt inclusions using Raman analysis of vapor bubbles

Melt inclusions record valuable information about pre-eruptive volatile concentrations of melts. However, a vapor bubble commonly forms in inclusions after trapping, and this decreases the dissolved CO2 concentration in the melt (glass) phase in the inclusion. To quantify CO2 loss to vapor bubbles, Raman spectroscopic analysis was used to determine the density of CO2 in bubbles in melt inclusions from two Cascade cinder cones near Mt. Lassen and two Mexican cinder cones (Jorullo, Parícutin). Using analyses of dissolved CO2 and H2O in the glass in the inclusions, the measured CO2 vapor densities were used to reconstruct the original dissolved CO2 contents of the melt inclusions at the time of trapping. Our results show that 30–90% of the CO2 in a melt inclusion is contained in the vapor bubble, values similar to those found in other recent studies. We developed a model for vapor bubble growth to show how post-entrapment bubbles form in melt inclusions as a result of cooling, crystallization, and eruptive quenching. The model allows us to predict the bubble volume fraction as a function of ΔT (the difference between the trapping temperature and eruptive temperature) and the amount of CO2 lost to a bubble. Comparison of the Raman and modeling methods shows highly variable agreement. For 10 of 17 inclusions, the two methods are within ±550ppm CO2 (avg. difference 290ppm), equivalent to ±~300bars uncertainty in estimated trapping pressure for restored inclusions. Discrepancies between the two methods occur for inclusions that have been strongly affected by post-entrapment diffusive H+ loss, because this process enhances bubble formation. For our dataset, restoring the CO2 lost to vapor bubbles increases inferred trapping pressures of the inclusions by 600 to as much as 4000bars, highlighting the importance of accounting for vapor bubble formation in melt inclusion studies.

Development of bond strength model for CFRP-to-concrete joints at high temperatures

Abstract Because of temperature sensitivity of the adhesives used in the interface, temperature variations may significantly affect the bond behavior of carbon fiber reinforced polymer (CFRP) to concrete joints. An analytical solution is used in this work to derive the two-parameter bond–slip relationship of CFRP to concrete bonded joints at high temperatures. The values of the key parameters at elevated temperatures can be directly calculated from the expressions for the strength and the stiffness of CFRP to concrete joints. Considering the effect of the free end slip on the bond behavior, a simplified formula of the peak load for a given joint is presented. Based on regression analyses of existing test data, it is found that the normalized value of interfacial bond property at elevated temperatures should be a function of ΔT (service temperature subtracts glass transition temperature). The proposed bond strength-temperature model here represents the test data well, despite the large scatter.

Exploring the effect of different time resolutions to calculate the rainfall erosivity factor R in Calabria, southern Italy

AbstractThe rainfall erosivity factor R of the Universal Soil Loss Equation is a good indicator of the potential of a storm to erode soil, as it quantifies the raindrop impact effect on the soil based on storm intensity. The R‐factor is defined as the average annual value of rainfall erosion index, EI, calculated by cumulating the EI values obtained for individual storms for at least 22 years. By definition, calculation of EI is based on rainfall measurements at short time intervals over which the intensity is essentially constant, i.e. using so‐called breakpoint data. Because of the scarcity of breakpoint rainfall data, many authors have used different time resolutions (Δt = 5, 10, 15, 30, and 60 min) to deduce EI in different areas of the world. This procedure affects the real value of EI because it is strongly dependent on Δt. In this contribution, after a general overview of similar studies carried out in different countries, the relationship between EI and Δt is explored in Calabria, southern Italy. The use of 17 139 storm events collected from 65 rainfall stations allowed the calculation of EI for different time intervals ranging from 5 to 60 min. The overall results confirm that calculation of EI is dependent on time resolution and a conversion factor able to provide its value for the required Δt is necessary. Based on these results, a parametric equation that gives EI as a function of Δt is proposed, and a regional map of the scale parameter a that represents the conversion factor for converting fixed‐interval values of (EI30)Δt to values of (EI30)15 is provided in order to calculate R anywhere in the region using rainfall data of 60 min. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Characteristic Evaluation on Cooling Performance of Thermoelectric Modules.

The aim of this work is to develop a performance evaluation system for thermoelectric cooling modules. We describe the design of such a system, composed of a vacuum chamber with a heat sink along with a metal block to measure the absorbed heat Qc. The system has a simpler structure than existing water-cooled or air-cooled systems. The temperature difference between the cold and hot sides of the thermoelectric module ΔT can be accurately measured without any effects due to convection, and the temperature equilibrium time is minimized compared to a water-cooled system. The evaluation system described here can be used to measure characteristic curves of Qc as a function of ΔT, as well as the current-voltage relations. High-performance thermoelectric systems can therefore be developed using optimal modules evaluated with this system.

Fractional Approach for Estimating Sap Velocity in Trees

Abstract In the context of fractional calculus (FC), this paper is devoted to model thermal processes in trees based on the measurement of the temperature difference (ΔT) between sensors located above and below a heater inserted in the tree trunk. By evaluating several temperature curves taken from real trees of different species, the current approach shows that the temperature in each probe can be successfully described by the two-parameter Mittag- Leffler function Eα,β. Then, a simple methodology is followed to derive a novel expression of the heat-pulse velocity (v) as a function of ΔT and the parameter α of the mentioned Eα,β function. Experimental results are given to validate the goodness of the current proposal.

Distinguishing Positional Uncertainty from True Mobility in Single-Molecule Trajectories That Exhibit Multiple Diffusive Modes

Although imperfect spatial localization in single-molecule object tracking experiments has long been recognized to induce apparent motion in an immobile population of molecules, this effect is often ignored or incorrectly analyzed for mobile molecules. In particular, apparent motion due to positional uncertainty is often incorrectly assigned as a distinct diffusive mode. Here we show that, due to both static and dynamic contributions, positional uncertainty does not introduce a new apparent diffusive mode into trajectories, but instead causes a systematic shift of each measured diffusion coefficient. This shift is relatively simple: a factor of σ²/Δt is added to each diffusion coefficient, where σ is the positional uncertainty length scale and Δt is the time interval between observations. Therefore, by calculating the apparent diffusion coefficients as a function of Δt, it is straightforward to separate the true diffusion coefficients from the effective positional uncertainty. As a concrete demonstration, we apply this approach to the diffusion of the protein fibrinogen adsorbed to a hydrophobic surface, a system that exhibits three distinct modes of diffusion.

Stress induced deformation in the solidification of undercooled Co80Pd20 alloys

Substantial undercooling ΔT up to 415K was achieved for Co80Pd20 melt applying molten glass denucleation combined with cyclic superheating. The as-solidified structure as function of ΔT was described concisely. On this basis, dense-regular fault (DRF) ribbons were detected provided if a critical undercooling is surpassed. An integrated analysis of the DRF formation with a model calculation [16] for shrinkage-stress developed in the coherent dendrite network upon rapid solidification was then performed. This confirms that the as-formed DRF originates from a stress-induced deformation, which also plays an important role in understanding the grain refinement occurring upon rapid solidification of undercooled melts.

Microstructural Transitions in Commercial Fe-Ni–Based Soft-Magnetic Alloys Quenched from Undercooled Liquid Droplets

Liquid droplets of three commercial Fe-Ni–based alloys were undercooled to different temperatures by electromagnetic levitation and quenched. Discontinuous changes in the grain size and microstructure as a function of melt undercooling (ΔT) were observed in all three alloys. At ΔT 155 K, the equiaxed grains with a substructure of spherical elements returned. The critical undercoolings at which the microstructural transitions occur (ΔT * 1 = 80 K and ΔT * 2 = 155 K) show good agreement with those for similar binary systems. The results were successfully described by calculating the time needed for breakup of the primary dendrites as a function of ΔT and comparing this to the time during which the sample temperature is above the solidus due to recalescence.

Glass transition-related thermorheological complexity in polystyrene melts

The relaxation-modulus G(t) functional forms covering the whole time range are given by incorporating a stretched exponentialfor the structural- (glassy-) relaxation process into the extended reptation theory (ERT; forentangled systems) or the Rouse theory (for entanglement-free systems). The creep complianceJ(t) curves of two entangled (A and B) and one entanglement-free (C)polystyrene samples (Plazek) as well as the viscoelastic spectraG*(ω) of fourentanglement-free polystyrene samples (Inoue et al) have been quantitatively analyzed in terms of thegiven G(t) functional forms. In such quantitatively successful analyses, the ERT or the Rouse theory works asthe frame of reference in both the line shape and timescale. The thermorheological complexity in theJ(t) curves is explained naturally and precisely by the temperature dependence of theenergetic-interaction-derived structural relaxation being stronger than that of theentropic ERT or Rouse dynamics in a simple way. Structural-relaxation timesτS (= 18s′K′) of all thestudied samples are equally well separated into two decoupled quantities: the structural-growth parameters′ and thefrictional factor K′ (for the Rouse–Mooney or Rouse modes of motion). The separation is fundamentally a clean-cut process:s′ is determined entirelyby the line shape of J(t) or G*(ω) while K′ is calculated from the timescale shifting factor obtained from the superpositionof the calculated curves onto the measured. The glassy-relaxation strengthAGf and the stretchingparameter β extracted from the J(t) and G*(ω) results over the glassy-relaxation region are in good agreement. The glass-transition temperatureTg is defined ascorresponding to τS = 1000 s for allthe studied samples. The τS, s′ and K′ data points of samples A, B and C extracted from theirJ(t) curves individually fall closely on the same curves when expressed as a function ofΔT = T−Tg, revealinga Tg-related universality within the polystyrene system, entangled or not. The revealeduniversality confirms the previously derived conclusion that the ERT and the Rouse theoryhave the same footing at the Rouse-segmental level. Representing important physicalfeatures of the universality, the length-scale of the structural relaxation increases asΔT diminishes andreaches the value of ∼3 nm at ΔT = 0 (or at Tg) for all three samples, A, B and C. Extracted from theG*(ω) results,the τS, s′ and K′ data of samples with molecular weights just below and well below entanglement molecular weightMe (13 500) are found to deviate more from the respective universal curves withdecreasing molecular weight. Deviation is estimated to start occurring atMw = 12 000.

Growth Rate of Frost Heave in Helium and Mass Transport in Solid 4He

Frost heave phenomena have been studied in 4He on porous vycor glass, in which 4He in the pores remained supercooled fluid below the bulk melting temperature, Tm. When we cool a bulk solid at T below Tm on the vycor, the bulk solid sucks the supercooled liquid in the pores and grows. We measured the maximum frost heave pressure over bulk melting pressure, Pm, as a function of ΔT=Tm−T. When temperature was suddenly lowered, the frost heave pressure increased in time to a next equilibrium pressure and we measured the time constant and derived the frost heave rate. The frost heave rate was measured as a function of temperature and decreased very rapidly as temperature was lowered. We propose models to explain the mass transport in solid either by vacancy or by amorphous solid between bulk solid 4He and vycor. From measured temperature dependence of the rate in comparison with our model, we conclude the frost heave rate is determined by mass flow in solid 4He due to thermally-activated vacancy diffusion.

In situ observation and analysis of crystal growth process of GdBCO superconductive oxide

To clarify the nucleation and growth process of 123 crystals, growth of faceted Gd123(GdBa2Cu3O7−δ) crystals was observed in situ on MgO(100) by using a high temperature optical microscope with zoom lens (×50–500). Gd123 crystals nucleated and grew at each undercooling (ΔT=30,35,40,45K). Growth rate (u) and incubation time (tinc) for nucleation were obtained from the relationship between time and position of faceted interface. u was approximated by a function of ΔT: u=AgpΔTr2/η(T), where Agp is a constant, Agp=1.0×10−5. Nucleation rate (Iv) was obtained from the relationship between time and number of nucleated crystals. Iv was approximated by an exponential function: Iv={An/η(T)}exp(-B/ΔTr2), where An and B are constants, An=1.3×107, B=2.7×10−3. The nucleation and growth process of Gd123 crystals were expressed quantitatively by the above equations.

Aggregation, Dividend Irrelevancy, and Earnings‐Value Relations*

AbstractIn this paper I show that the aggregation of operating and financial income imposes three conditions on earnings‐based value functions. These three conditions provide a shortcut way to identify dividend irrelevant value functions. For example, consider any value function Vt of book value bt, earnings xt, and dividends dt. The aggregation conditions imply that Vt must be of the form Vt = (1 − k)bt + k [f xt − dt]. f is the permanent earnings capitalization factor and undetermined weight k may be any function of Δt ≡[φxt − dt] − bt. The Ohlson 1995 model is the special case when k is constant. But generally k does not have to be constant to maintain dividend irrelevancy. Whenk varies with Δt, Vt is nonlinear in earnings. Hence, this result specifies how Vt may be nonlinear in earnings in settings with limited liability or production or abandonment options and still be dividend‐irrelevant.An even more remarkable feature of this result is that it holds whether accounting is clean surplus or not. One must conclude that accounting‐based valuation properly builds from accounting aggregation and Δt, and not from the clean surplus relation and abnormal earnings as many now believe.

Effect of spurt duration on the heat transfer dynamics during cryogen spray cooling

Although cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic surgery, optimization of the current cooling approach is needed to permit the safe use of higher light doses, which should improve the therapeutic outcome in many patients. The objective of this study was to measure the effect of spurt duration (Δt) on the heat transfer dynamics during CSC using a model skin phantom. A fast-response temperature sensor was constructed to record the changes in surface temperature during CSC. Temperature measurements as a function of Δt at two nozzle-to-skin distances (z = 50 and 20 mm) were performed. The average surface heat fluxes (q) and heat transfer coefficients (h) for each Δt were computed using an inverse heat conduction problem algorithm. It was observed that q undergoes a marked dynamic variation during the entire Δt, with a maximum heat flux (qc) occurring early in the spurt (5–15 ms), followed by a quick decrease. The estimated qc vary from 450 to 600 kW m−2, corresponding to h maxima of 10 and 17–22 kW m−2 K−1 for z = 50 and 20 mm, respectively. For z = 50 mm, spurts longer than 40 ms do not increase the total heat removal (Q) within the first 200 ms. However, for z = 20 mm, Δt longer than 100 ms are required to achieve the same Q. It is shown that the heat transfer dynamics and the time it takes to reach qc during CSC can be understood through classic boiling theory as a transition from transient to nucleate boiling. Based on the results of this model skin phantom, it is shown that spurts longer than 40 ms have a negligible impact on both q and Q within clinically relevant cooling times (10–100 ms).

Contact angles for evaporating liquids predicted and compared with existing experiments

The stationary meniscus of an evaporating, perfectly wetting system exhibits an apparent contact angle Θ which vanishes with the applied temperature difference ΔT, and is maintained for ΔT &gt; 0 by a small-scale flow driven by evaporation. Existing theory predicts Θ and the heat flow q∗ from the contact region as the solution of a free-boundary problem. Though that theory admits the possibility that Θ and q∗ are determined at the same scale, we show that, in practice, a separation of scales gives the theory an inner and outer structure; Θ is determined within an inner region contributing a negligible fraction of the total evaporation, but q∗ is determined at larger scales by conduction across an outer liquid wedge subtending an angle Θ. The existence of a contact angle can thus be assumed for computing the heat flow; the problems for Θ and q∗ decouple. We analyse the inner problem to derive a formula for Θ as a function of ΔT and material properties; the formula agrees closely with numerical solutions of the existing theory. Though microphysics must be included in the model of the inner region to resolve a singularity in the hydrodynamic equations, Θ is insensitive to microphysical detail because the singularity is weak. Our analysis shows that Θ is determined chiefly by the capillary number Ca = μlVl/σ based on surface tension σ, liquid viscosity μl and a velocity scale Vl set by evaporation kinetics. To illustrate this result of our asymptotic analysis, we show that computed angles lie close to the curve Θ = 2.2Ca1/4; a small scatter of ±15% about that curve is the only hint that Θ depends on microphysics. To test our scaling relation, we use film profiles measured by Kim (1994) to determine experimental values of Θ and Ca; these are the first such values to be published for the evaporating meniscus. Agreement between theory and experiment is adequate; the difference is less than ±40% for 9 of 15 points, while the scatter within experimental values is ±25%.