Increase In Initial Temperature Research Articles

Sea ice centrifugal desalination based on microwave heating

Desalinating sea ice to obtain fresh water is a new way to solve the water shortage. Centrifugal desalination (CD) is an important method for desalination of sea ice, and it is of great significance to improve desalination efficiency. Microwave heating has a significant effect on improving salt-water separation efficiency, but the effect on centrifugal desalination is still unclear. In this paper, sea ice centrifugal desalination by microwave heating (CDBMH) was designed. The four factors of the particle size of ice, initial ice temperature, relative centrifugal force and centrifugation time were selected from the key parameters of centrifugal technology and sea ice material properties, and the impact of each factor on the salinity of the melted water, the desalination rate, and the water yield rate was explored. The results showed that with the decrease of the particle size of ice, the increase of initial ice temperature, relative centrifugal force and centrifugation time, the desalination rate showed an upward trend, while the water yield rate and the salinity of the melted water gradually decreased. As a result of the CDBMH process, the desalination rate was 93.3%, and the water yield rate was 72.4%, and the salinity of the melted water was 0.4‰.

Numerical calculation of sterilization heat penetration parameters based on initial temperature and headspace in canned nonNewtonian fluid

Abstract Amount of heat penetration parameters and temperature of slowest heating zone in 3.5% starch dispersion was studied. The computational fluid dynamics software COMSOL 4.1 was used and governing equations for energy, momentum, and continuity were computed using a finite volume method. A 3.5% starch dispersion was used. The effect of 50°C and 75°C initial temperatures, and 20% and 10% headspace was investigated. It was determined that in static sterilization with headspace, the SHZ is near the interface of air–product. Increase in initial temperature and decrease in headspace leads to increase in jh. The fh of 20% headspace with 50°C initial temperature is lower in all samples. Increasing the initial temperature leads to fh increase and f2 decrease. Finally, it was demonstrated that instead of wall surface or the volume of food, the ratio of total heat surface to the volume of food is effective on its temperature pattern. Practical application The calculation of heat penetration parameters in sterilization is critical to calculate the processing time. The selection of a good temperature-time profile to destroy the goal microorganism and retaining nutritional characteristics is complex in nonNewtonian fluids. In this study, we try to numerically simulate the heat transfer and calculate the heat penetration parameters for a starch dispersion as a model fluid. These data may be applicable for starch containing or starch-based products or products with nonNewtonian behavior during sterilization.

Coupling of Magnetite Particles with Microwaves at Temperatures lower than the Curie Point

Effect of the particle size (d) and apparent density on the coupling of microwaves with Fe3O4 was investigated at temperatures lower than the Curie point, TC ≃ 585 °C. Two samples in the form of tablet with particle sizes of 45-75 μm (MT75) and <45 μm (MT45) and one sample in the form of powder with a particle size of <45 μm (MP45) were heated in multi-mode and maximum E- and H-field modes using a microwave generator at a frequency of 2.45 GHz. According to the results, an earlier temperature increase and also a higher temperature was achieved in the sample heated in the maximum H-filed mode. Regarding the incubation time in all samples, the particle size of Fe3O4 has no significant effect on the time required for the initial temperature increase in the presence of the H-field. In the maximum E-field mode, a shorter time was required for the temperature increase in the MT75 sample than MT45. At T≤Tc, magnetic loss and Joule loss are the dominant heating mechanisms in the presence and absence of the H-field, respectively. Magnetic loss is independent of the particle size whereas Joule loss which is influenced by electrical conductivity, affected by particle size. Therefore, above-mentioned effect of the particle size is attributed to the dominant heating mechanism. Also, some of the small particles seems to be transparent owing to a greater penetration depth (δ), ca. 80 μm at room temperature causing an earlier onset of temperature increase in sample with larger particle size, MT75. Moreover, microwave absorption in a sample with higher apparent density, MT45, was lower because of a higher electrical conductivity of sample in tablet form, MT45, than powder form, MP45.

Heat transfer characteristics of a binary thin liquid film in a microchannel with constant heat flux boundary condition

Thin film evaporation of multi-component fluids in microchannels is important in many industrial applications, which requires comprehensive modeling of the transport mechanisms in the liquid, gas and solid phases. This paper presents a numerical study on the heat transfer characteristics of a binary thin liquid film in a microchannel with constant heat flux boundary condition, using the enhanced Young-Laplace equation that considers the effect of disjoining pressure for binary fluids. Effects of temperature, microchannel size, and non-condensable gas on the binary thin film heat transfer was analyzed. The results show that the thin film contribution to the total heat transfer rate reduces when the initial temperature increases, but the difference between them decreases as the microchannel size reduces. Size effect can be prominent when the characteristic microchannel size is smaller than 10 μm. When the microchannel size decreases, the cumulative heat transfer rate across the interface of the solution decreases, while the thin film contribution to the total heat transfer rate increases obviously. The non-condensable gas deteriorates the cumulative heat transfer rate, but the deterioration reduces under the high temperature condition as compared to that under the low temperature condition. Comparison of the results shows that the temperature and microchannel size have the greatest effect on the heat transfer followed by the non-condensable gas. This can be efficiently utilized for heat transfer enhancement and thermal design in applications involving phase-change heat transfer of multi-component fluids in microchannels.

Mechanism of carbon deposits removal from supported Ni catalysts

Catalyst deactivation due to carbon deposition is a major issue in all reforming technologies. Because of the significant economic cost of catalyst replacement, catalyst regeneration is increasingly attracting attention. The regeneration mechanism of Ni catalysts, with respect to carbon removal, was investigated on support materials prepared by one-pot synthesis. The supports were classified based on their redox functionality: Al2O3, MgAl2O4 show no redox properties in contrast to MgFe0.09Al1.91O4 and CeZrO2 that have redox functionality.A Temporal Analysis of Products (TAP) setup was used to investigate the isothermal regeneration mechanism of Ni catalysts at 993 K by O2. Different mechanisms were distinguished depending on the redox functionality of the support material. Two consecutive steps occur on the support that have no redox properties (Al2O3 and MgAl2O4): metallic Ni is oxidized to form NiO (oxidation step), resulting in an initial local temperature increase of 50–60 K in total, enabling metal particle migration to carbon that was initially separated from the metal and subsequent oxidation through NiO lattice oxygen (reduction step). On the other hand, the mechanism of carbon removal by O2 from Ni catalysts on supports with redox properties does not require particle migration. Two parallel contributions are proposed: 1) Ni metal is oxidized to form NiO, where after lattice oxygen of NiO is used for the oxidation of carbon that is deposited upon the metals, 2) carbon oxidation through lattice oxygen that is provided by the support. No dependency of the carbon gasification mechanism on the exposed fraction of the metal (particle size in the nanoscale) or on the structure of the deposited carbon was concluded.

Experimental study of thermal-crack characteristics on hot dry rock impacted by liquid nitrogen jet

Liquid nitrogen jet fracturing is a novel stimulation technology, which is expected to be suitable for hot dry rock (HDR) reservoirs. Due to the large temperature difference between hot rock and cryogenic fluid, a great number of thermal cracks would be created during fracturing process, which is conductive to improve the penetration capacity of formation. In this study, a set of experiments were conducted to investigate the characteristics of thermal cracks. In these experiments, granite specimens with temperatures ranging from 200 ℃ to 300 ℃ were impacted by the low-pressure liquid nitrogen jet. The complexity and connectivity of cracks were quantitatively analyzed by a fractal method. The permeability and ultrasonic velocity of the granite specimens were tested in order to evaluate the damage conditions caused by thermal stress. Additionally, scanning electron microscope was adopted to analyze the microscopic characteristics of the thermal cracks. The results show that the heating process has a slight effect on thermal-crack generation compared with the liquid-nitrogen impact. The cracks mainly concentrate in the region near the impingement surface, due to the large temperature gradient there. The impacted rock breaks as the effects of tensile stress and shear stress. With an increase of initial rock temperature, the number of thermal cracks increases, and a more complex crack-network is formed in each specimen. Transient pulse evaluation and ultrasonic velocity measurements indicate that the impact of liquid nitrogen jet can improve the permeability and cause the damage of hot rock noticeably. This study demonstrates the important effect of thermal stress on crack generation during liquid nitrogen jet fracturing for HDR reservoirs, and the results shed light on the exploitation of HDR energy.

Explosion characteristics of a methane/air mixture at low initial temperatures

In this paper, the explosion characteristics of a methane-air mixture at low initial temperatures (up to 113 K) and elevated pressures were measured. Various parameters, such as explosion pressure, rate of the explosion pressure rise, combustion duration and flame development duration were obtained for the initial temperature range of 123–273 K. The results indicated that the maximum explosion pressure and the maximum rate of explosion pressure rise reached peak values at the equivalence ratio of 1.1. With the increase in initial pressure, the maximum explosion pressure increased significantly, and the maximum rate of explosion pressure rise increased linearly because of a larger density of the flammable mixture within the explosion vessel. With the decrease in the initial temperature the maximum explosion pressure increased monotonically, whereas the effect of initial temperature on the maximum rate of explosion pressure rise was negligible because of two opposing aspects: an increase in the amount of flammable mixture and a decrease in the flame propagation speed. Both the combustion duration and the flame development duration increased with the increase in initial pressure and decreased with the increase in initial temperature. Finally, at an equivalence ratio of 1.0, two empirical correlations were obtained to calculate the combustion duration and the flame development duration.

Effects of aqueous phase recirculation in hydrothermal carbonization of sweet potato waste

Aqueous phase recirculation was investigated in hydrothermal carbonization of sweet potato waste at 220 °C for 60 min. The result showed that the aqueous phase reuse significantly increased the hydrochar yield. The lower H/C and O/C ratios indicated that decarboxylation reaction was promoted. The CC vibration of the benzene backbone became intense, suggesting the occurrence of aromatization and polymerization reactions. Thus, the carbon content and HHV were improved. After recirculation, hydrochar showed a decrease in combustion ignition temperature whereas an increase in pyrolysis initial decomposition temperature. The burnout temperatures in combustion and terminated temperature in pyrolysis both showed an increase trend. The hydrochars obtained from the recirculation step possessed lower emissions of NOX or SO2 than that from reference step. The pyrolysis emission result showed that more high thermal stability components were formed during recirculation step. Overall, aqueous phase recirculation was a feasible way to improve hydrothermal carbonization process.

Effect of particle size and apparent density on the initial stages of temperature increase during the microwave heating of Fe3O4

Effect of the particle size and apparent density on the time required for the initial temperature increase during the microwave heating of Fe3O4 was investigated to clarify the mechanism of interaction between the magnetite powder and microwave at temperatures lower than the Curie point of Fe3O4 (585 °C). Samples in the form of powders and briquettes (density, 3.3 g/cm3) with particle sizes of 75–150 μm, 45–75 μm, and < 45 μm were heated in multi-mode and maximum E- and H-field modes using a microwave generator at a frequency of 2.45 GHz. Results reveal that the microwave absorption capability of a sample with higher apparent density is lower because of its higher electrical conductivity, which causes a shallower penetration depth. Further, the effect of the particle size on the microwave heating of Fe3O4 at temperatures higher than the Curie point is different in the presence and absence of a strong electric field. This is attributed to a change in the heating mechanism from dielectric loss in the presence of the E-field to Joule loss in its absence. At temperatures lower than the Curie point, some of the small particles would be transparent owing to a greater penetration depth of the microwaves, which causes an early onset of temperature increase in the magnetite sample with a larger particle size. Moreover, the mechanism for the formation of spark and plasma during the microwave-induced heating is discussed by applying a novel approach to analyse the interactions between the powdery materials and microwaves.

Numerical study of CO2-enhanced coalbed methane recovery

Although CO2-enhanced coalbed methane (CO2-ECBM) recovery has been comprehensively investigated, fewer scholars have taken the effect of temperature into account, which brought a large deviation for the study of the influence of CO2-ECBM. In this work, a hydraulic-mechanical-thermal coupled model of CO2-ECBM is established, it combines binary gases (CO2 and CH4) infiltration and diffusion, where non-isothermal adsorption is also considered. The effect of injection pressure and reservoir initial temperature on CO2-ECBM was simulated by the finite element simulation software COMSOL Multiphysics, results show that: the injection of CO2 into coalbed has a good effect on enhancing the production of CH4, and both the CO2 storage rate and CH4 production rate increase with the increase of injection pressure. The effect of initial reservoir temperature on CO2-ECBM is obvious. Since the amount of adsorbed gas in coal decreases with the increase of temperature, the CO2 storage rate and CH4 production rate decrease with the increase of initial reservoir temperature. In the gas extraction process without CO2 injection, the variation of permeability is competition result of two types of factors: the coal matrix shrinkage caused by temperature reduction and gas desorption increase, the other is the coal matrix expansion caused by gas pressure decrease, so the permeability follows the rule of first decreasing and then increasing with the extraction time. The injection of CO2 has a great influence on the permeability of coalbed, adsorption of CO2 by the coal matrix causes the permeability to drop rapidly.

Minimum ignition energy for the CH4/CO2/O2 system at low initial temperature

In this paper, the minimum ignition energy (MIE) for methane in an atmosphere of CO2/O2 is measured at 0.1–0.7 MPa and 183–273 K using a gas explosion experimental device that is able to withstand a temperature as low as 113 K. Effects of initial temperature (T0) and initial pressure (P0) on MIE are studied via experiment and a simple theoretical analysis. Results indicate that in our experimental setup, the sensitive conditions of MIE are an equivalence ratio of 1 and an electrode gap of 1 mm. Under low initial temperature, the trends in MIE with respect to initial pressure and temperature in an atmosphere of CO2/O2 are similar to those in an atmosphere of N2/O2. With an increase in initial pressure and temperature, MIE gradually decreases. MIE has a linear correlation with the reciprocal of the square of the initial pressure and the reciprocal of the initial temperature. At low initial temperature, P0 has a large impact on MIE, whereas at low initial pressure, MIE is more sensitive to initial temperature. At the same initial temperature and pressure, MIE in an atmosphere of CO2/O2 is about 1.2 times larger than that in an atmosphere of N2/O2 atmosphere. CO2 is more dilute than N2 in accordance with large heat capacities and small thermal conductivities.

Numerical study of multi-branch horizontal well coalbed methane extraction

ABSTRACTAlthough multi-branch horizontal well coalbed methane (CMB) extraction has been comprehensively investigated, fewer scholars have taken the effect of temperature into account, which brought a large deviation for the study of multi-branch horizontal well parameter design. In this work, the hydraulic-mechanical-thermal coupled model of multi-branch horizontal well CMB extraction was established. In order to verify the accuracy of the model and study the effect of temperature on CMB extraction, a series of numerical simulations based on engineering geological conditions and drilling arrangement parameters of 24307 face of Shaqu Mine were made, results show that: The CH4 production rate of both field data and numerical simulation result have the same changing tendency, and the difference between the simulation result and the actual value is not big. In multi-branch horizontal well CMB extraction process, the matrix shrinkage caused by temperature reduction and methane desorption dominates, the permeability continues to increase. Due to the effect of temperature on the amount of gas adsorbed by coal, the CH4 production decreases with the increase of initial reservoir temperature, and the permeability of coalbed increases with the increase of temperature.

Fourier and non-Fourier bio-heat transfer models to predict ex vivo temperature response to focused ultrasound heating

Although predicting temperature variation is important for designing treatment plans for thermal therapies, research in this area is yet to investigate the applicability of prevalent thermal conduction models, such as the Pennes equation, the thermal wave model of bio-heat transfer, and the dual phase lag (DPL) model. To address this shortcoming, we heated a tissue phantom and ex vivo bovine liver tissues with focused ultrasound (FU), measured the temperature response, and compared the results with those predicted by these models. The findings show that, for a homogeneous-tissue phantom, the initial temperature increase is accurately predicted by the Pennes equation at the onset of FU irradiation, although the prediction deviates from the measured temperature with increasing FU irradiation time. For heterogeneous liver tissues, the predicted response is closer to the measured temperature for the non-Fourier models, especially the DPL model. Furthermore, the DPL model accurately predicts the temperature response in biological tissues because it increases the phase lag, which characterizes microstructural thermal interactions. These findings should help to establish more precise clinical treatment plans for thermal therapies.

Cool Air-Gas Mixtures with Combustible Gas Admixtures Steady Flameless Combustion Delay Time on Platinum Particle (Wire)

The proposed work shows analytical way to find a build-up time (induction period) for a mode of steady flameless catalytic combustion on metallic wire for cool air-gas mixtures with combustible gaseous admixtures using as an example flameless combustion of air-gas mixtures with hydrogen admixture of a platinum wire. Steady flameless combustion is observable after an induction period due to increase of initial catalyst temperature exceeding critical point of ignition which depends on particle diameter and combustible gaseous admixture content. Total time of build-up time is split into two stages, being the time of catalytic reaction proceeding in transient and diffusion stages, respectively. Effects of combustible gas ratio, catalyst wire diameter and excess of initial temperature compared with point of ignition upon particular stages duration and induction period are illustrated.

Kinetics and thermodynamics of NPX adsorption by γ-FeOOH in aqueous media

Naproxen (NPX) is a common PPCPs in wastewater treatment plants which is influenced by the coexistence on its photodegradation. Most research on reasons for NPX photodegradation has focused on the soluble substances in water mainly, and the adsorption effect of solid particles is less. The effects of initial concentration, temperature, and pH on the adsorption of NPX on γ-FeOOH were studied. It was found that the equilibrium time of γ-FeOOH adsorbed NPX was 240 min. The increase of initial concentration and temperature were favorable for the adsorption. The optimal adsorption pH was 7.0, and the adsorption capacity attained 28.05 mg·g−1. It was learned, through model fitting, that the adsorption reaction was in accordance with the Laggenren quasi-second-order kinetic model; the internal diffusion process was the control step, where the adsorption was close to the Langmuir isothermal adsorption model. The thermodynamic calculation showed that ΔG < 0, ΔH < 0, ΔS < 0, which inferred that the adsorption was a spontaneous, endothermic, and entropy increasing process, which is the common action of chemical bond forces and static electricity.

Thermal, mechanical properties and shape memory performance of a novel phthalide-containing epoxy resins

A novel phthalide-containing aromatic amine (PBMI-DDE) was synthesized by Michael addition of 3,3-bis[4-(4-maleimidophenoxy)phenyl]phthalide (PBMI) and 4,4′-diaminodiphenylether (DDE), its chemical structure was confirmed by nuclear magnetic resonance (NMR) spectrometer and Fourier transform infrared (FTIR) spectrometer. A serial of phthalide-containing epoxy resins were prepared with the PBMI-DDE/DDE blends in different molar ratios as curing agents. The cure behavior, thermal and mechanical properties, and shape memory performance of the cured resins were carefully characterized using differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), dynamic mechanical analyses (DMA), universal material testing machine and notched Izod impact test, respectively. DMA and TGA thermograms show the glassy storage modulus and the initial decomposition temperature increase while the rubbery storage modulus and the glass transition temperature are reduced as PBMI-DDE content increases. The investigations of mechanical properties exhibit a complicated trend with increasing PBMI-DDE content, and the epoxy resin with an equal molar ratio of PBMI-DDE/DDE has a maximum mechanical strength. The fracture morphology investigated by scanning electron microscope (SEM) indicates the existence of hole defects in the cured products with higher PBMI-DDE content. The shape memory performance of these fully cured epoxy networks is improved with PBMI-DDE content, and the shape fixity ratio (Rf) and shape recovery ratio (Rr) of the pure PBMI-DDE cured epoxy resins are both lager than 95% with a deformation strain above 12%.

KINETICS AND ISOTHERM ANALYSIS OF Cd2+ REMOVAL FROM AQUEOUS SOLUTIONS BY ION EXCHANGE PROCESS

In the present study, Dowex HCR-S/H, cationic resin was used as a resin for the removal of cadmium from aqueous solutions. The experiments were carried out in a batch vessel. Subsequent experiments were performed as a function of initial solution pH, resin dosage, agitation time, initial Cd2+ concentration, solution temperature and agitation speed. Ion exchange rate increased with the increase in initial cadmium concentration, stirring speed and temperature. The Langmuir, Freundlich, Elovich, Temkin, Khan, Sips, Toth, Koble-Corrigan and the Radke-Prausnitz isotherm models were tested for their applicability. It was found that the Sips equation appears to fit the equilibrium data. The ion exchange data obtained at various temperatures were applied to pseudo first-order, pseudo second-order, intra-particle diffusion and Elovich models. Pseudo-second-order rate equation was able to provide realistic description of ion exchange kinetics. Intra-particle diffusion process was identified as the main mechanism controlling the rate of the metal exchange. Thermodynamic activation parameters such as .G*, .S* and .H* of the ion exchange of Cd2+ on Dowex HCR-S/H cationic resin were also calculated.

Influence of initial bed temperature on bed performance of an adsorption refrigeration system

The study deals with the complete dynamic analysis (numerical and practical) of an existing adsorption refrigeration system. The adsorption refrigeration setup is available at Indian School of Mines (Dhanbad, India), Mechanical engineering department. The system operates with activated carbon (as an adsorbent) and methanol (as refrigerant).Numerical model is established base on energy equation of the heat transfer fluid (water) and transient heat and mass transfer equations of the adsorbent bed. The input temperature of heat source is 90?C, which is very low compared to other low-grade energy input refrigeration system. The thermo-physical properties of an adsorptive cooling system (using activated carbon?methanol pair) are considered in this model. In this analysis influence of initial bed temperature (T1) on the bed performances are analysed mathematically and experimentally. The simulation and practical results of this system show that the cycle time decreases with increase in initial bed temperature and the minimum cycle time is 10.74 hours (884 minutes for practical cycle) for initial bed temperature of 40?C. Maximum system COP and specific cooling capacity are 0.436 and 94.63 kJ/kg of adsorbent under a condenser and evaporator temperatures of 35?C and 5?C, respectively. This analysis will help to make a comparison between simulated and experimental results of a granular bed adsorption refrigeration system and also to meet positive cooling needs in off-grid electricity regions.

Removal of polyacrylate in aqueous solution by activated sludge: Characteristics and mechanisms

Abstract The aim of this study is to evaluate the removal potential of polyacrylate in aqueous solution by activated sludge. Batch experiments investigated the effects of contact time, pH value, temperature, and concentration of adsorbate on polyacrylate removal by activated sludge to evaluate the isotherms, kinetics, thermodynamics, and mechanisms. The materials were characterized by N2 adsorption-desorption isotherms, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FT-IR). The experimental results indicate that more than 90% of polyacrylate was removed by activated sludge in a short time. The adsorption capacity increase with the increase in initial polyacrylate concentration and temperature. Increasing pH value resulted in a decrease in adsorption capacity. The adsorption process fitted well to Langmuir isotherm and pseudo-second-order kinetic models. Thermodynamic parameters indicate that the adsorption of polyacrylate onto activated sludge was feasible, spontaneous, and endothermic. The results of kinetics, thermodynamics, SEM-EDS, and FT-IR showed that surface binding, hydrophobic interaction, and hydrogen bond force may play a major role in the removal process. Microbial community structure analysis by 16S rRNA gene revealed that short-term exposure with polyacrylate had a little negative impact on the activated sludge microorganisms. A better understanding of polyacrylate adsorption onto activated sludge is essential for improving predictions of the fate and transport of polyacrylate in waste water treatment process.

Application of ethylenediamine hydroxypropyl tamarind fruit shell as adsorbent to remove Eriochrome black T from aqueous solutions – Kinetic and equilibrium studies

ABSTRACTEthylenediamine Hydroxypropyl Tamarind Fruit Shell (EDAHP-TFS) was synthesized to remove Eriochrome Black T (EBT) from aqueous solutions. Maximum adsorption occurred at pH 2.0 and equilibrium time 2 h. Adsorption increased with increase in initial concentration and temperature. Adsorption kinetics obeyed the pseudo-second-order model and indicates a partial ion exchange, followed by the complexation mechanism. Lower E# (4.48 kJ/mol) represents film diffusion as the rate-limiting step. EBT removal followed the Sips isotherm model with a maximum adsorption capacity of 0.237 mmol/g at 30ºC. Isosteric heat of adsorption (ΔHi) decreased with increase in surface loading, indicating heterogeneous adsorption sites. Desorption studies were carried out and 96.4% recovery was achieved at pH 11.0.