Cold Model Research Articles

Physical Simulation and Industrial Testing of Bottom-Blown O2-CaO Converter for Steelmaking Process

Bottom-blowing O2-CaO steelmaking technology has numerous advantages such as low iron and steel consumptions, low dust emissions, and molten steel cleanliness. Responsive to a weak stirring and high iron oxide slag in a 120-ton conventional “combined blowing” converter in a factory, a cold model of bottom-blowing O2-CaO was designed. Bottom-blowing and top-blowing parameters on the mixing effect of bottom-blowing O2-CaO converter were studied. Two symmetrical points on 0.4R trunnion connection of the bottom-blowing converter were sought as the optimum hole location. The total flow rate of bottom–blowing and top-blowing was 8.2 and 75 Nm3/h, respectively. The optimum top-blowing position was 400 mm and the optimum solid–gas ratio was found to be 9.0. The optimum scheme under laboratory conditions was converted and applied to a 120-ton bottom-blown O2-CaO converter; subsequently, hundred industrial tests were performed. The stirring strength of the molten bath was enhanced remarkably and the metallurgical effect was improved remarkably. Carbon and oxygen product of the end-point molten steel was reduced by 5.87 × 10−4 while the iron oxide content in the final slag was reduced by 1.99 pct. This laid a foundation for industrial applications of the bottom-blown O2-CaO converter steelmaking technology.

Precipitation phase uncertainty in cold region conceptual models resulting from meteorological forcing time-step intervals

Abstract Precipitation phase determination is a known source of uncertainty in surface-based hydrological, ecological, safety, and climate models. This is primarily due to the surface precipitation phase being a result of cloud and atmospheric properties not measured at surface meteorological or hydrological stations. Adding to the uncertainty, many conceptual hydrological models use a 24-h average air temperature to determine the precipitation phase. However, meteorological changes to atmospheric properties that control the precipitation phase often substantially change at sub-daily timescales. Model uncertainty (precipitation phase error) using air temperature (AT), dew-point temperature (DP), and wet-bulb temperature (WB) thresholds were compared using averaged and time of observation readings at 1-, 3-, 6-, 12-, and 24-h periods. Precipitation phase uncertainty grew 35–65% from the use of 1–24 h data. Within a sub-dataset of observations occurring between AT −6 and 6 °C representing 57% of annual precipitation, misclassified precipitation was 7.9% 1 h and 11.8% 24 h. Of note, there was also little difference between 1 and 3 h uncertainty, typical time steps for surface meteorological observations.

Numerical simulation investigations into the influence of the mass ratio of pulverized-coal in fuel-rich flow to that in fuel-lean flow on the combustion and NOx generation characteristics of a 600-MW down-fired boiler.

Numerical simulations were conducted to study the effects of the pulverized-coal bias distribution in the primary air on the coal combustion and NOx generation characteristics of a 600-MW down-fired boiler with multiple-injection and multiple-staging combustion technology. The total pulverized-coal in the primary air was kept constant, and the ratio of the pulverized-coal mass flux in the fuel-rich coal/air flow to the total pulverized-coal mass flux (RPR) was set as 60%, 70%, 80%, and 90%. By changing the RPR, the excess air coefficient of the fuel-rich flow was adjusted from 0.700 to 0.467. It was found that numerical simulation results were almost in agreement with cold modeling and in situ experimental results respectively, including the flow fields in the lower furnace at the RPR of 80% and the heating processes for the fuel-rich coal/air flow at the RPR of 90%, which verified the rationality of the numerical model and the grid. The simulation results indicated that the change of RPR has little effect on the symmetry of the flow field in the furnace. With the increase of the RPR from 60 to 90%: (1) the maximum airflow declination angle near the tertiary air slot decreased from 71 to 66°, which indicates that the downward airflow penetration depth gradually decreased; (2) the ignition distance of the fuel-rich coal/air flow decreased from 1.2 to 0.9m, and the high-temperature area in the furnace hopper decreased and the position gradually moved away from the hopper water walls; (3) the oxygen consumption rate at the initial combustion stage constantly accelerated, and the fuel NOx generation rate under the fuel-rich flow nozzle increased first and then decreased; (4) the NOx emissions at the furnace exit dropped from 778 to 662mg/m3 at 6% O2, and the carbon in the fly ash decreased from 5.87 to 5.52%. Increasing the RPR reasonably controlled the excess air coefficient of the fuel-rich flow, and realized the high-efficiency combustion in the furnace and the reduction of NOx emissions simultaneously.

Abstract A86: Comparative immunophenotypic analysis of immunogenically warm and cold syngeneic tumor models at baseline and after anti-mCTLA-4 treatment

Abstract To examine how baseline tumor immunophenotyes can influence therapeutic outcome, we used the CT26 colorectal and 4T1-Luc (4T1) breast cancer models, which are immunologically warm and cold tumors, respectively. We treated tumor-bearing mice with control or anti-mCTLA-4 antibodies (anti-CTLA-4), or left them untreated, and excised tumors to measure immune cell infiltrates, TIL cytokine/granzyme B production, and activation marker expression. Baseline analysis in untreated mice revealed that CD8+ T-cell infiltrates were similar between models (5-6% of total CD45+ cells). NKT cells were reduced in CT26 (0.5% vs. 1.2%). The myeloid compartment in CT26 was mostly M2 macrophages (43% of CD45+ cells), whereas G-MDSCs dominated in 4T1 (40% of CD45+ cells). CD69 and PD-1 activation markers were expressed on >90% of CD8+ T cells from CT26 tumors compared to 4T1, which were <40% positive for both markers. Following ex vivo stimulation, the IFNγ response in CD8+ T cells was higher in CT26-derived cells. Treatment with anti-CTLA4 triggered distinct responses in the two models. Delayed tumor growth was observed in CT26 (74% TGI), but no effect in 4T1 was shown. In CT26 tumors, CD8+ T-cell and NKT cell infiltration increased, with a corresponding decrease in M2 macrophages. In 4T1 tumors, only increased NKT cell infiltration occurred. Several pharmacodynamic changes were observed in immune cell activation in CT26 but absent in 4T1. IFNγ production increased in CT26-derived CD4+ and CD8+ T cells, as well as NKT cell subsets (70%, 25%, and 17%, respectively compared to control). This included an increase in polyfunctional T cells that produced both IFNγ and TNFα. Moreover, we found that tumors with the highest frequency of IFNγ/TNFα double positive T cells had slower growth, suggesting that polyfunctional T-cell differentiation correlates with tumor growth delay. Granzyme B was 31% reduced in NKT cells in CT26. Together with increased CD107a expression on these cells, the observed granzyme B reduction was likely due to treatment-induced degranulation. Notably, a correlation between granzyme B expression and delayed tumor growth was also observed, albeit indirect. In summary, untreated CT26 tumors contained TILs that expressed high levels of CD69/PD-1 and moderately expressed IFNγ, and subsequently responded to anti-CTLA-4 treatment with increased polyfunctional T-cell recruitment, NKT cell activity, and reduced M2 macrophage infiltration. In contrast, 4T1 tumors contained low levels of both CD69/PD-1 expression and TIL cytokine expression, which is characteristic of an immunosuppressive tumor microenvironment, and did not display any remarkable response to therapy. Collectively, these results suggest baseline tumor profiles can provide insight into responsiveness to therapy and assist in model selection for preclinical research. Future studies to more broadly profile baseline TIL functional states across different syngeneic models should prove valuable during study design for targeted I/O therapy development. Citation Format: David Draper, Philip Lapinski, Stacey Roys, Scott Wise, Maryland Rosenfeld Franklin. Comparative immunophenotypic analysis of immunogenically warm and cold syngeneic tumor models at baseline and after anti-mCTLA-4 treatment [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A86.

Research on Cold Chain Logistics Path Optimization Considering Cascading Failure

Considering that the storage and transportation products in cold chain logistics are perishable and deteriorate easily, in the actual distribution process, the cascading failure of urban roads will affect the transit times and distribution costs of delivery vehicles. According to the cascading failure process under the edge failure condition, a new diversion rule is established, and then the distribution cost is associated with the transportation speed. The cold chain logistics distribution path optimization model is established, with minimal distribution costs as its objective function, and a Dijkstra-GA algorithm is developed. The Dijkstra-GA hybrid algorithm solves the model. The model is verified by simulation examples. The simulation results verify the applicability of the model and the algorithm.

Measurement of quadrupolar asymmetry in prototype rod-type radio frequency quadrupole linac for protons.

An analytical and cold model study of a prototype extended vane rod-type RFQ (radio frequency quadrupole linac) is presented. The bead-pull measurement allowed us to experimentally determine the effect of shaping of the vane-supporting posts and, most interestingly, the size of the vacuum enclosure in the dipolar and quadrupolar field asymmetry. Disk shaped beads of BaTiO3 have been tailor made for this purpose. The special shape of the beads has allowed precise measurements of frequency shifts all along the length of the RFQ. The measured quadrupolar asymmetry and dipole component at a radial distance of 7 mm from the beam axis are within ±1% for the optimized structure. Particle tracking of a 10 mA proton beam with a simulated 3D field for the optimized full scale RFQ with modulated vanes has been carried out. Simulation shows vertical and horizontal shifts of only 0.01 mm and 0.03 mm, respectively, for the accelerated beam at the exit of RFQ. The percentage of accelerated particles lying within an energy width of ±40 keV about 800 keV is increased from 86% for the original enclosure to 88% for the reduced enclosure, whereas the transmission efficiency is 100% for both the cases.

Hydrogasdynamic Regularities of Melt Blowing in “Ausmelt” Furnace by Cold Modeling Methods

This work aimed to develop the cold modeling method of melt blowing in an “Ausmelt” top submerged lance (TSL) furnace for further optimization of the working conditions of the complex to decrease copper losses with slags and increase process productivity.

Parametrized path approach to vacuum decay

We develop a new real-time approach to vacuum decay based on a reduction to a finite number of degrees of freedom. The dynamics is followed by solving a generalized Schr\"odinger equation. We first apply this method to a real scalar field in Minkowski space and compare the decay rate with that obtained by the instanton approach. The main difference is in the early-time dynamics, where the decay is faster due to the tail of the wave function. We then apply it to a cold atom model recently proposed to simulate vacuum decay experimentally. This approach will be extended to include gravity in a future work.

Development Status and Business Solution of Ultra-high Pressure Food

Ultra-high pressure food processing technology refers to the technology of sterilizing food under thousands of atmospheric pressure without destroying the properties of food raw materials. Japan is a world leader in HPP technology. Significant achievements have been made in experimental equipment, production equipment, processing, sterilization and preservation of ultra-high pressure technology. Almost all natural, safe and healthy HPP food jams and fruit juices have been commercialized. Germany, the United States, France, the United Kingdom and other countries are also unwilling to fall behind, they are scrambling to carry out research on ultra-high voltage technology and have achieved industrialization results.China’s research on food ultra-high pressure technology started late. After nearly ten years of technical digestion and research, the research results have been achieved in stages, but there is still a large gap compared with developed countries. This article outlines the application of HPP technology in food processing, briefly analyzes the development of HPP food technology in China today, and establishes a cold chain supply chain model to identify problems and propose certain countermeasures, with a view to addressing HPP technology in food and chemicals industry.

Effect of cold cap coverage and emissivity on the plenum temperature in a pilot‐scale waste vitrification melter

AbstractIntegrated computational fluid dynamics (CFD) models are being developed to model the complex physics occurring within the high‐level waste melter for vitrification of legacy tank waste at the Hanford site. This study presents a validation of the integrated CFD model by using data from two experimental runs in a pilot‐scale melter. While the model uses several simplifying assumptions (such as constant heat sinks from a cooling jacket and inleakage of ambient air, steady state feed‐to‐batch conversion heat, and a cold cap model with a simplified shape), it closely predicts the molten glass (1150°C and 1175°C) and plenum temperatures (550°C) obtained from thermocouples during two pilot‐scale tests, with an average cold cap coverage of 80%. Additional simulations were performed to explore the sensitivity of the predicted plenum temperatures to variations in cold cap coverage (fraction of melt surface covered by the glass batch) and batch emissivity. The plenum temperature was found to be in the range of 606°C when cold cap coverage decreased from 95% to 70%. Cold cap emissivity had a smaller effect, increasing the plenum temperature by as much as 179°C when cold cap emissivity increased from 0.2 to 0.8. Maintaining a high cold cap coverage without overfeeding is important for a sustained melter operation with high glass throughput. This work provides a tool for achieving that goal in terms of correlating the plenum temperature with the cold cap coverage.

Hydrodynamic Characteristics in a Cold Flow Model of Quadruple Fluidized Bed Gasifier

Quadruple fluidized bed gasifier (QFBG) is a new kind of clean power-generation system, which consists of a dual fluidized bed (DFB) gasifier and a dual fluidized bed of chemical looping. With high gasification efficiency and low carbon emissions, QFBG has attracted extensive attention. Hydrodynamic characteristics of the quadruple fluidized bed (QFB) system are the base of modeling and designing of a hot reactor. To fully understand the hydrodynamic characteristics, a cold flow model of the QFB system on a laboratory scale was designed and set up. In the cold model, operation parameters such as bubble fluidized bed velocity, riser velocity, and total solid inventory (TSI) were investigated. Meanwhile, an exclusive pressure balance equation of QFB is proposed. The QFB was also compared with DFB. The results from the experiment show that the QFB system has a positive response to the operation parameters and better solid transport capacity than the typical DFB system.

Investigation of Circulation Flow and Slag-Metal Behavior in an Industrial Single Snorkel Refining Furnace (SSRF): Application to Desulfurization

A combined method of mathematical and physical modeling was used to investigate the circulation flow and slag-metal behavior in industrial SSRF and RH. The circulation flow of molten steel was simulated by using the coupled mathematical model. The results indicate that two different circulation modes are presented separately in SSRF and RH. The incomplete exchange of molten steel was found in SSRF because of the interaction between upflow and downflow in the snorkel, while the molten steel is fully exchanged between the vacuum chamber and ladle in RH. The flow behavior of top slag in the vacuum chamber was further investigated and compared by using cold models. It was found that many slag droplets are generated in the vacuum chamber, and then dragged into ladle by downflow for both reactors. The main difference is that the majority of droplets eventually float into ladle slag in RH, while most of the slag droplets in SSRF is cycled repeatedly, which allows slag droplets to have a longer time to contact with steel. Thus, the slag-steel reaction is more adequate in SSRF. Furthermore, the industrial desulfurization tests were designed to verify the difference in the refining effect between the two kinds of droplet behavior in actual production. The results indicate that the higher desulfurization degree was realized in SSRF with less consumption of argon than that of RH.

The study of spatial dispersion effect on electromagnetic waves propagation in the warm non-uniform re-entry plasma sheath

“Communication blackout” is such a consequence that the attenuation of electro-magnetic (EM) waves becomes drastic when the frequency of EM waves is near or below the oscillation frequency of plasmas. Deep comprehension on the propagation characteristics of EM waves in the plasma sheath plays an important role in solving this issue. However, relevant works in the literature are almost based on the cold plasma sheath model, neglecting the temperature of the plasmas as well as the spatial dispersion effect. We apply COMSOL Multiphysics software to simulate and study the spatial dispersion effect in the warm plasma sheath in this paper. The mode conversion between EM waves and Langmuir waves in the warm plasmas is observed. The characteristics of field distributions in the warm plasma sheath are different from the cold plasma sheath distinctly, when the resonance between EM waves and the plasmas happens. The reflection and absorption coefficients are also influenced accordingly. The research in this paper gives an insight into EM waves propagation in the warm re-entry plasma sheath and supplies a better comprehension on the interaction between EM waves and the plasma sheath.

Secondary air distribution in a 600 MWe multi-injection multi-staging down-fired boiler: A comprehensive study

Multi-injection multi-staging combustion technology was designed to provide high boiler efficiency together with low pollutant emissions when employing hard-to-burn coal, and showed good application prospects. In this technology, to achieve the first staged air and more flexible combustion regulation on the arches, the secondary air employs a more complicated distribution surrounding the coal/air flows. This design concept significantly affects the flow and combustion characteristics of the actual boiler. Elucidating the underlying mechanisms by which the various secondary air parameters affect the boiler operation requires a comprehensive analysis of the secondary air distribution on the arches. In this work, small-scale cold modeling tests combined with industrial-scale trials using two actual 600 MWe down-fired boilers were conducted. The results show that the secondary air distribution can significantly affect the near-burner flow and mixing as well as the decay of the downward airflow velocity. High velocity secondary air, especially the secondary air surrounding the fuel-rich flow, evidently promotes the advanced mixing of fuel-rich and fuel-lean flows. Increasing the secondary air flux around the fuel-rich flow and raising the secondary air velocity decrease the pulverized coal heating rate, while a decreased inner secondary air velocity advances the coal ignition. Adjusting the secondary air also greatly affects the downward flame depth and the unburnt coal proportion in the near wall region of the furnace hopper, such that the flame kernel location and the temperatures near the hopper wall are modified. In addition, NOx formation can be accelerated by a high secondary air flux near the fuel-rich flow or a large contact area between the secondary air and the fuel-rich flow.

Identification, functional prediction, and key lncRNA verification of cold stress-related lncRNAs in rats liver

Cold stimulation reduces the quality of animal products and increases animal mortality, causing huge losses to the livestock industry in cold regions. Long non-coding RNAs (lncRNAs) take part in many biological processes through transcriptional regulation, intracellular material transport, and chromosome remodeling. Although cold stress-related lncRNAs have been reported in plants, no research is available on the characteristic and functional analysis of lncRNAs after cold stress in rats. Here, we built a cold stress animal model firstly. Six SPF male Wistar rats were randomly divided to the acute cold stress group (4 °C, 12 h) and the normal group (24 °C, 12 h). lncRNA libraries were constructed by high-throughput sequencing (HTS) using rat livers. 2,120 new lncRNAs and 273 differentially expressed (DE) lncRNAs were identified in low temperature environments. The target genes of DElncRNA were predicted by cis and trans, and then functional and pathway analysis were performed to them. GO and KEGG analysis revealed that lncRNA targets were mainly participated in the regulation of nucleic acid binding, cold stimulation reaction, metabolic process, immune system processes, PI3K-Akt signaling pathway and pathways in cancer. Next, a interaction network between lncRNA and its targets was constructed. To further reveal the mechanism of cold stress, DElncRNA and DEmRNA were extracted to reconstruct a co-expression sub-network. We found the key lncRNA MSTRG.80946.2 in sub-network. Functional analysis of key lncRNA targets showed that targets were significantly enriched in fatty acid metabolism, the PI3K-Akt signaling pathway and pathways in cancer under cold stress. qRT-PCR confirmed the sequencing results. Finally, hub lncRNA MSTRG.80946.2 was characterized, and verified its relationship with related mRNAs by antisense oligonucleotide (ASO) interference and qRT-PCR. Results confirmed the accuracy of our analysis. To sum up, our work was the first to perform detailed characterization and functional analysis of cold stress-related lncRNAs in rats liver. lncRNAs played crucial roles in energy metabolism, growth and development, immunity and reproductive performance in cold stressed rats. The MSTRG.80946.2 was verified by network and experiments to be a key functional lncRNA under cold stress, regulating ACP1, TSPY1 and Tsn.

Study of Flow Behaviour in Vertical Centrifugal Casting

In centrifugal casting processes, flow of fluid layers determines the quality of the cast. However flow visualization is not possible, as mould and molten metal are opaque in nature. Therefore many research workers have resorted to understand the flow visualization process by carrying out simulation studies. Literature survey indicates that earlier investigators have studied the melt flow in horizontal centrifugal casting process by conducting cold modeling experiment using horizontal transparent mould and fluids of different viscosity. However it appears that there is no published information available in the area of influence of various parameters in the case of vertical centrifugal casting process. Therefore in this research work the cold modeling experimentation on fluids of different viscosity like water, Glycerin and SAE 90 rotated in a transparent mould at a constant room temperature had been conducted with an objective of understanding the influence of rotational speed and aspect ratio on flow patterns of different fluids subjected to vertical axis rotation. Later the flow behavior had been studied by numerical simulation through Ansys fluent software. Further for the purpose of comparison, casts of paraffin wax at different rotational speeds had been obtained and the trend of variation of the lift with the variation of rotational speed had been compared with the trend predicted using cold modeling studies and using Ansys software. From cold modeling studies it can be concluded that of the dimensional accuracy of fluid cylinder in terms of lift had been increased with increase in viscosity. The possibility of formation of complete fluid cylinder increases with increase in rotational speed and mould diameter. Howvere, at aspect ratio of 1.0 the formation of complete fluid cylinder had not been obtained.The trend of result observed in CFD study was found to be similar to the trend of results observed in cold modeling study. The study of actual paraffin cast confirmed the result obtained in cold modeling and CFD.

A comparative study of non-thermal parameters of the X-class solar flare plasma obtained from cold and warm thick-target models; error estimation by Monte Carlo simulation method

The electron transport and relaxation in the non-thermal plasma of solar flare are often described by cold thick-target model. Recently introduced warm thick-target model however is also found to be more consistent for describing it and hence provide the accurate estimate of parameters of non-thermal solar flare plasma. In this study, we evaluate the consistency of cold and warm thick-target models by estimating non-thermal parameters viz., low-energy cutoff (${E_{c}/E_{wc}} $), kinetic power of non-thermal electrons (${P _{nth}/P_{wnth}} $) and non-thermal energy (${E_{nth}/E_{wnth}} $), along with standard error (SE) and their linear statistical analysis with respect to flare duration (${t _{f}}$). We further evaluate the accuracy of these parameters using Monte Carlo simulation data in $2 \sigma $ limits. We found that cold thick-target model gives high values of mean and SE of the estimated parameters compare to warm thick-target model those were also found consistent with the Monte Carlo data (in both cases). Here, we also found that the variation of ${E_{c}/E_{wc}} $ and ${P _{nth}/P_{wnth}} $ with respect to ${t_{f}} $ give a negative/positive and positive values of correlation coefficient ($r$) and slope ($b$) respectively which account for upper and lower limits of ${E_{c}/E_{wc}} $ and high and slow rate of thermalization of non-thermal electrons. Our results show that the warm thick-target model is more consistent model compare to cold thick-target model that could also lead a multi-temperature component in the thermalized plasma.

Protective effect of ferulic acid on human umbilical vein endothelial cell model of cold stress

Context: Ferulic acid (FA) is an active principle derived from the traditional Chinese medicine Angelica sinensis, which has been used for the treatment of cardiovascular and cerebrovascular diseases in China for many years. However, a thorough understanding of effects on vascular function by FA has not been investigated. Aims: The aim of the present study was to investigate the potential mechanism of FA by suppressing Transient receptor potential cation channel subfamily M member 8 (TRPM8) channels and regulating endothelial nitric oxide (NO) pathway to ameliorate cold explore injury in human umbilical vascular endothelial cells (HUVECs). Subjects and Methods: The effects of cold exposure and FA on cell viability were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and lactate dehydrogenase (LDH) assay. Quantitative polymerase chain reaction and Western blot were utilized to detect TRPM8, hypoxia-inducible factor-alpha (HIF-1α), endothelin-1 (ET-1), inducible NO synthase (iNOS), endothelial NO synthase (eNOS) messenger RNA, and protein expression in HUVECs. Enzyme-linked immunosorbent assay method was used to detect the concentration of ET-1 in culture supernatants of HUVECs. Results: Cold exposure at 18°C had no significant effect on cell morphology but increased secretion of LDH and ET-1 and the expression of TRPM8, HIF-1α, iNOS, and ET-1. Treatment with FA decreased all of these changes. The levels of NO and eNOS decreased in cold stress model, while FA treatment attenuated the cold-induced decrease of NO and eNOS. Conclusion: Cold stress can cause an increase in vasoconstrictors such as TRPM8 and ET-1 and reducing cell viability, but FA can prevent cold stress-related cardiovascular disease by regulating the expression of these substances in cells.

A thin shell of ionized gas as the explanation for infrared excess among classical Cepheids

Context. The infrared (IR) excess of classical Cepheids is seldom studied and poorly understood despite observational evidence and the potential for its contribution to induce systematics on the period-luminosity (PL) relation used in the calibration of the extragalactic distance scale. Aims. This study aims to understand the physical origin of the IR excess found in the spectral energy distribution (SED) of 5 Cepheids: RS Pup (P = 41.46d), ζ Gem (P = 10.15d), η Aql (P = 7.18d), V Cen (P = 5.49d) and SU Cyg (P = 3.85d). Methods. A time series of atmospheric models along the pulsation cycle were fitted to a compilation of data, including optical and near-IR photometry, Spitzer spectra (secured at a specific phase), interferometric angular diameters, effective temperature estimates, and radial velocity measurements. Herschel images in two bands were also analyzed qualitatively. In this fitting process, based on the SPIPS algorithm, a residual was found in the SED, whatever the pulsation phase, and for wavelengths larger than about 1.2 μm, which corresponds to the so-determined infrared excess of Cepheids. This IR excess was then corrected from interstellar medium absorption in order to infer the presence (or absence) of dust shells and was, ultimately, used in order to fit a model for a shell of ionized gas. Results. For all Cepheids, we find a continuum IR excess increasing up to approximately −0.1 magnitudes at 30 μm, which cannot be explained by a hot or cold dust model of CircumStellar Environment (CSE). However, a weak but significant dust emission at 9.7 μm is found for ζ Gem, η Aql and RS Pup, while clear interstellar clouds are seen in the Herschel images for V Cen and RS Pup. We show, for the first time, that the IR excess of Cepheids can be explained by free–free emission from a thin shell of ionized gas, with a thickness of ≃15% of the star radius, a mass of 10−9−10−7M⊙ and a temperature ranging between 3500 and 4500 K. Conclusions. The presence of a thin shell of ionized gas around Cepheids must be tested with interferometers operating in the visible or mid-IR, or using radio telescopes. The impact of such CSEs of ionized gas on the PL relation of Cepheids also calls for further investigation.

Design of a 1 t/h Biomass Chain Boiler and ιts Fuel Adaptability Analysis

The arch is an important component of a biomass boiler. Initial arch design of most boilers is generally gained through manual computation, thus resulting in uncertain reasonability of flue gas flow. Moreover, biomass fuels in the market have instable characteristics, which influence the utilization of biomass energies considerably. To address the problems concerning reasonable flue gas flow caused by the collaborative design of arch and air staging and the combustion adaptability of fuels, a cold modeling experiment of a 1 t/h biomass boiler under different staged air distribution ratios when the rear arch coverage varies was conducted using Fluent software in this study after thermal performance computation and initial structural design of grate and furnace. Furthermore, a boiler performance test based on main fuels and a combustion adaptation test of auxiliary fuels were also performed. The experiments show that the best flue gas flow in the furnace is achieved when the rear arch coverage is 60% and the primary–secondary air distribution ratio is 4:6. The mean boiler efficiency and the mean boiler heat output are 81.26% and 715.76 kW/h by using Pinus koraiensis pellets, wood–straw mixed pellets, and cotton straw briquettes as main fuels; and the tested pollutant emissions are in compliance with the limits of the national standard. The results of the combustion adaptation test reveal that the excessive particle size, the high ash content and the relatively low calorific value of biomass molded fuels are all against the combustion of biomass boilers. Fuel upgrading based on washing process and other methods is suggested. This study can provide references to the performance optimization of traditional small-scale biomass chain heating boilers.