Maximum Attainable Temperature Research Articles

Performance Improvement of Industrial Gas Turbine for Power Augmentation in the Nigeria Oil and Gas Sector

This paper provides a comprehensive overview of the electricity supply situation in Nigeria, focusing specifically on enhancing the performance of industrial gas turbines, GE GT13E2 (Afam Power Plant owned by FIPL) in Port Harcourt. The study encompasses two primary aspects. Firstly, it involves an examination of the nominal operating conditions of a combined cycle system and explores their dynamic performance through advanced simulations. Secondly, the research introduces a supplementary burner into the combined system and conducts a comparative analysis, considering factors such as system efficiency and power output. The power plant configurations are simulated using Gasturb14. The analysis is carried out by establishing the maximum attainable temperature in the Heat Recovery Steam Generator (HRSG), which determines the number of stages of supplementary firing that can be implemented. The results presented in this paper unveil the substantial potential for power generation with the addition of supplementary burners, indicating a remarkable increase in power output, yielding approximately 187.444 MW. However, this significant boost in power generation comes with an associated trade-off, wherein the overall system efficiency experiences a reduction. From an economic perspective, the additional power generated by the afterburner translates directly into increased revenue from electricity sales. Considering the average residential electricity rate in the U.S. as of February 2023, the calculated additional revenue from the afterburner amounted to approximately $25,641.58 per hour.

Characteristics of rice husk biochar briquettes with municipal solid waste cassava, sweet potato and matooke peelings as binders

Rice husks are not readily biodegradable making their disposal challenging due to the common disposal method of open burning which has negative environmental effects. Additionally, banana, sweet potato and cassava peelings form a large percentage of organic municipal solid waste. Therefore, this study developed rice husk biochar briquettes with organic municipal peelings waste as binders. Rice husks biochar was formed via carbonization processes in a step-down kiln at temperatures ranging between 400 and 500 °C. Organic binders were mixed with the rice husk biochar at different ratios of 10% and 15% before being compacted at a pressure ≤ 7 MPa into briquettes. Thermogravimetric results showed that the developed briquettes had high ash contents ranging from 44% to 47%. Rice husk biochar briquettes with the highest particle density were observed for briquettes with 15% cassava peel binder at 427.1 kg/m3. The highest HHV and maximum attainable flame temperature of 21.75 MJ/kg and 828.7 °C were obtained for rice husk biochar briquettes with 15% matooke peeling organic binder. For all rice husk biochar briquettes, increasing the organic peeling binder had a positive impact of reducing the ash content, while at the same time increasing the peak temperatures, thus contributing to their enhanced thermal stability.

Adiabatic Flame Temperatures for Oxy-Methane, Oxy-Hydrogen, Air-Methane, and Air-Hydrogen Stoichiometric Combustion using the NASA CEARUN Tool, GRI-Mech 3.0 Reaction Mechanism, and Cantera Python Package

The Adiabatic Flame Temperature (AFT) in combustion represents the maximum attainable temperature at which the chemical energy in the reactant fuel is converted into sensible heat in combustion products without heat loss. AFT depends on the fuel, oxidizer, and chemical composition of the products. Computing AFT requires solving either a nonlinear equation or a larger minimization problem. This study obtained the AFTs for oxy-methane (methane and oxygen), oxy-hydrogen (hydrogen and oxygen), air-methane (methane and air), and air-hydrogen (hydrogen and air) for stoichiometric conditions. The reactant temperature was 298.15 K (25°C), and the pressure was kept constant at 1 atm. Two reaction mechanisms were attempted: a global single-step irreversible reaction for complete combustion and the GRI-Mech 3.0 elementary mechanism (53 species, 325 steps) for chemical equilibrium with its associated thermodynamic data. NASA CEARUN was the main modeling tool used. Two other tools were used for benchmarking: an Excel and a Cantera-Python implementation of GRI-Mech 3.0. The results showed that the AFTs for oxy-methane were 5,166.47 K (complete combustion) and 3,050.12 K (chemical equilibrium), and dropped to 2,326.35 K and 2,224.25 K for air-methane, respectively. The AFTs for oxy-hydrogen were 4,930.56 K (complete combustion) and 3,074.51 K (chemical equilibrium), and dropped to 2,520.33 K and 2,378.62 K for air-hydrogen, respectively. For eight combustion modeling cases, the relative deviation between the AFTs predicted by CEARUN and GRI-Mech 3.0 ranged from 0.064% to 3.503%.

Paving 3D interconnected Cring-C3N4@rGO skeleton for polymer composites with efficient thermal management performance yet high electrical insulation

Polymer-based thermal interface materials (TIMs) with good electrical insulation property is essential in the thermal management of microelectronic devices. A common approach to increasing the polymer's low intrinsic thermal conductivity is to introduce thermally conductive fillers. In most cases, those fillers are also electrically conductive, which destroys the origin electrical insulation property. In this work, we develop a novel heterogeneous two-dimensional hybrid filler by assembling circular carbon nitride (Cring-C3N4) and graphene oxide (GO), aiming to bring the insulation property via Cring-C3N4. With an ordered 3D interconnected structure, the assembled filler shows enlarged sheet size and compact sheet stacking, which facilitates heat conduction. Additionally, the adopted ice-templated method further arranges the filler with the largest thermal conductivity reaching 4.12 W/mK. Meanwhile, it also shows a lower electrical conductivity of 3.6 × 10−7 S/m, meeting most electrical insulation required occasions. Practical heat dissipation performance tests reveal that both larger temperature change rate and maximum attainable temperature are observed for ice-templated treated composite, indicating the reduced thermal contact resistance (TCR) is responsible for the overall improved heat conduction process. This viewpoint is also supported by the practical application of the material functioning as TIMs from both experimental and simulative aspects.

Homogenization of 7075 and 7049 Aluminium Alloys Intended for Extrusion Welding

During the extrusion of aluminum alloys profiles using porthole dies, the temperature of the material in the welding chamber is one of crucial parameters determining the quality of longitudinal welds. In order to extend the permissible temperature range, the billets intended for this process should be characterized by the maximum attainable solidus temperature. Within the present work, the homogenization of AlZnMgCu alloys DC-cast (Direct Chill-cast) billets was investigated, with the aim of solidus temperature maximization. Conditions of soaking and cooling stages were analyzed. The materials were homogenized in laboratory conditions, and the microstructural effects were evaluated on the basis of DSC (Differential Scanning Calorimetry) tests and SEM/EDS (Scanning Electron Microscopy/Energy-Dispersive Spectroscopy) investigations. For all examined alloys, the unequilibrium low-melting microstructure components were dissolved during soaking, which led to the significant solidus temperature increase, in comparison to the as-cast state. The values within the range of 525–548 °C were obtained. In the case of alloy with highest Cu concentration, the application of two-step soaking was necessary. In order to take advantage of the high solidus temperature obtained after soaking, the cooling rate from homogenization must be controlled, and the effective cooling manner is strongly dependent on alloy composition. For high-Cu alloy, the solidus decreased, despite the fast cooling and the careful billets preheating being necessary.

Mathematical modeling of thermal behavior of single iron ore pellet during heat hardening oxidation

In this study, a one-dimensional generic model capable of being integrated with reactor scale models is proposed for a single pellet through solving the transient differential conservation equations. Predicted results comparison with the experimental data showed close agreement. In addition, the model was used to investigate the relevance of physical characteristics of pellet, reacting gas composition, diffusion factors, and prevailing regime. It was found that the pure magnetite pellet could achieve a temperature rise of about 245 K at oxygen concentration of 40 vol.%, whereas the maximum temperature difference inside the pellet was approximately 24 K. Moreover, increasing pellet size, the maximum attainable temperature reached a peak and then leveled out. Furthermore, by decreasing the pore diameter, the pellet size with peak temperature shifted to the smaller pellet sizes. Analyzing the numerical results also showed that for the small pellet sizes, shortening the diffusion path leads to the spreading of the reaction interface. The modeling methodology herein can be applied to any particulate processes and is not limited to the aforementioned case.

Research of forces acting on the skip turn angles in the structures of the rope-profile guides

The study of combustion processes at high temperatures is associated with two main problems. The first of them is to determine composition and amount of possible combustion products, and to clarify thermodynamic properties of the mixture under various combustion conditions. The second problem is to determine amount of heat released during combustion and maximum attainable temperature of combustion or work which can be obtained if to apply the established simplifications and under the conditions in which combustion occurs. Great importance is given to predicting temperature indicators in the fire site when performing work in mine conditions on extinguishing and assessing the development of fires in mines. These indicators are important for the actual assessment of the state of the environment in the focus of its extinguishing, since they are control indicators for determining the cooling of the rocks of the massif and, ultimately, indirectly assess the fact of an extinct fire. In the article, the authors present a method for calculating parameters of the process of solid fuel combustion, which is based on the results of theoretical and experimental studies in the field of the theory of combustion of dusty fuel. By this method, the following parameters of combustion process are calculated: theoretical air consumption required for combustion of a unit of fuel quantity; volume of combustion products; composition of combustion products; enthalpy of combustion products at required temperatures and excess air; and calorimetric and theoretical temperatures of solid fuel combustion. By using the known dependences, the forecast of the temperature in the fire zone is substantiated for further development of new and improvement of existing methods. Some proposals developed for improving the estimates of the parameters of the state of the rock massif in the process of extinguishing a fire are considered. It is proposed, for example, as preventive measures, while determining indicator gases and evaluating their dynamics, to take additionally samples of coal before a fire and gradually heat them in laboratory conditions in muffle furnaces until the coal ignites, whereupon to evaluate their dynamics according to a laboratory experiment; then, when a fire occurs, it is possible to determine its real state by the dynamics of changes in the factually measured indicator gases. This proposal is not normative and requires further development, industrial verification and discussion. Keywords: coal particles, temperature forecast, area of fire, heat exchange, air, atmospheric composition.

Modeling of processes occurred during heating and ignition of coal particles in methane-air mixture in the area of fire

The study of combustion processes at high temperatures is associated with two main problems. The first of them is to determine composition and amount of possible combustion products, and to clarify thermodynamic properties of the mixture under various combustion conditions. The second problem is to determine amount of heat released during combustion and maximum attainable temperature of combustion or work which can be obtained if to apply the established simplifications and under the conditions in which combustion occurs. Great importance is given to predicting temperature indicators in the fire site when performing work in mine conditions on extinguishing and assessing the development of fires in mines. These indicators are important for the actual assessment of the state of the environment in the focus of its extinguishing, since they are control indicators for determining the cooling of the rocks of the massif and, ultimately, indirectly assess the fact of an extinct fire. In the article, the authors present a method for calculating parameters of the process of solid fuel combustion, which is based on the results of theoretical and experimental studies in the field of the theory of combustion of dusty fuel. By this method, the following parameters of combustion process are calculated: theoretical air consumption required for combustion of a unit of fuel quantity; volume of combustion products; composition of combustion products; enthalpy of combustion products at required temperatures and excess air; and calorimetric and theoretical temperatures of solid fuel combustion. By using the known dependences, the forecast of the temperature in the fire zone is substantiated for further development of new and improvement of existing methods. Some proposals developed for improving the estimates of the parameters of the state of the rock massif in the process of extinguishing a fire are considered. It is proposed, for example, as preventive measures, while determining indicator gases and evaluating their dynamics, to take additionally samples of coal before a fire and gradually heat them in laboratory conditions in muffle furnaces until the coal ignites, whereupon to evaluate their dynamics according to a laboratory experiment; then, when a fire occurs, it is possible to determine its real state by the dynamics of changes in the factually measured indicator gases. This proposal is not normative and requires further development, industrial verification and discussion. Keywords: coal particles, temperature forecast, area of fire, heat exchange, air, atmospheric composition.

Unsteady Heat Conduction Study During Underground Coal Gasiflcation For Constructing an In-situ Pyrolysis Project.(Dept.M)

Underground coal gasification (UCG) Is a potential coal utilization technology, receiving renewed interest around the world. In the last .five years there has been Increasing Interest In tile world energy and mining Industry for tile development of a new operating underground coal gasification systems to generate synthetic gas from underground coal seams. In this paper, the problem of unsteady heat conduction In the underground coal and rock layers during underground gasification Is considered. The heating of coal results In releasing considerable amount of gases mainly hydrogen and methane which would be collected and pumped through pipelines for use in different Industrial applications. In the present analysis, a spherical type heat source having a surface temperature of (1000OC, 1500OC, 1750OC and 2000OC) is used for heating the coal layer for achieving tile pyrolysis process. The differential equations describing the unsteady heat conduction in both coal and rock layers are solved numerically using the discretization method (control volume formulation). A computer program Is constructed for calculating the temperature fields and the gasified volumes of mineral coal as well as the heating velocity in the coal seams. In the experimental part, a model of an underground coal layer Is constructed. To validate the numerical model, an electrical spherical heat source Is Inserted directly into the coal layer for heating. The temperature distribution In coal layer is measured In different locations using the Thermocouples. The results show that the temperature profiles and the maximum attainable temperature in the coal seams depend on the time and the surface temperature of the heating reactor. Furthermore, the gasified volume of coal increase with the increase of both the surface temperature of the heating source and the running time. It is found also that the heating velocity in the underground coal. Lies between the mean value (2 to 10-3 K/min.) and increase with the time to reach a maximum value, after this it decrease to approach zero at the steady-state conditions. This study indicates that geometry, position, surface temperature and distribution of heating sources are very important parameters which should be carefully chosen for realizing an efficient pyrolysis of underground coal and avoiding thereby the combustion of a part of the coal seams. The analysis indicated that the best temperature is between (700-800oC) at which the high efficiency of pyrolysis process, the analysis might be useful in constructing an in-situ pyrolysis project for utilizing the underground coal seams.

Thermo-chemical manifold reduction for tabulated chemistry modeling. Temperature and dilution constraints for smooth combustion reactors

New scenarios for energy systems pointed out the importance of designing innovative combustion systems. In this context, high levels of internal dilution and preheating show interesting features related to low emissions, smooth temperature gradients, absence of visible flame and large fuel and load flexibility. Those characteristics are very difficult to obtain simultaneously with conventional combustion processes in the same device.The large-scale utilization of such novel concepts relies on the developments of proper modeling tools that should consider the multiple physical phenomena involved under distributed ignition. A challenging modeling aspect is related to the strong coupling between fluid-dynamics and kinetic time scales that implies the use of detailed mechanisms. Moreover, the heat transfer mechanisms and the heat loss at walls play key roles.In this context, tabulated chemistry methods are viable solutions to represent the thermo-chemical pattern in combustion systems with internal recirculation. However, the identification of adequate controlling variables for these systems is not trivial. In fact, in addition to mixture fraction and progress variable, an internal dilution and a heat loss parameter must be considered, leading to a 4-dimensional thermo-chemical manifold, with an inherent increase of computational costs.In this work a novel tabulation procedure is proposed in order to represent such comprehensive manifold taking into account the primary role of the internal recirculation on system reactivity.Moreover, a reduction of the thermo-chemical manifold was carried out by exploiting active interconnections between experiments and computations and embedding physical and process constraints based on measurable quantities obtained from experiments. These constrains are related to minimum ignition and maximum attainable process temperatures, heat loss through the surroundings and recirculation rate. The reliability of the proposed approach was assessed by comparing the reduced manifolds to the measured data for a cyclonic burner operating under massive internal dilution levels.

A three-dimensional ring-array concentrator solar furnace

A single ring-array concentrator solar furnace unit was firstly modeled analytically, and then optimized numerically by ZEMAX® and ANSYS® software, reaching a temperature of 3778 K, nearly equivalent to that of a medium size solar furnace with 3.14 m2 collection area. A novel three-dimensional ring array concentrator solar furnace was subsequently proposed and analyzed. It consisted of five single ring array concentrators, forming a compact box-shaped solar furnace with an opening at the rear side for an easy access to a common focal spot in the center. Based on the edge-ray principle of non-imaging optics, 30,960 solar concentration ratio was analytically calculated for this solar furnace, leading to significantly enhanced thermal and optical efficiencies. The temperature performance of the three-dimensional ring-array concentrator furnace as a function of receiver size and collector area was analyzed numerically and compared to that of the medium size solar furnace. For a 5.68 mm diameter spherical receiver and large collection area varying from 3.14 m2 to 100 m2, 1.1 times gradual enhancement in the maximum attainable temperature was calculated for the ring array concentrator furnace. More importantly, its average and minimum temperatures were significantly improved by 870 K and 1140 K, respectively, as compared to that of the medium size solar furnace. In addition, the three-dimensional ring-array concentrator also presented a significant tracking error compensation capacity in relation to that with the medium size solar furnace.

Supported ionic liquid-like phases based on CMS/DVB with different NR3 cations as catalysts for the chlorosilanes disproportionation

The variety of catalysts based on macroporous supported ionic liquid-like phases using chloromethyl styrene cross-linked with divinylbenzene (CMS/DVB) and different NR3 cations was investigated for disproportionation of trichlorosilane in a continuous-flow reactor. To determine the optimal conditions for conducting a complex catalytic process, the primary task is to determine the thermodynamical equilibrium state of the reaction system. Increase in the concentration of DCS in the system occurs from 5 to 10%, which in turn is promising in terms of considering DCS as the main precursor for the processes of epitaxial silicon growth. In addition, the maximum attainable temperature is thermodynamically optimal for the process. In the first stage, the thermal stability of the catalyst supports was determined using evolved gas analysis and all samples have a similar thermal stability 475 К. All samples have been carefully studied by SEM, AFM, EGA and nitrogen physisorption. To compare the catalytic activity of different catalytic systems on the basis of macroporous supports modified by different tritic ammonium functional groups with the subsequent activation, the kinetics of the TCS disproportionation on the catalyst sample having the highest catalytic activity was studied. The results obtained indicate that the introduction of acceptor substituents increases catalytic activity in the disproportionation of TCS. To assess the feasibility of using dichlorosilane (DCS) as a raw material for the creation of semiconductor structures, the kinetics of thermal decomposition of DCS in a mixture with hydrogen was studied at a temperature of 1200–1500 K. According to the obtained kinetic results, the activation energy of the process is determined, which is in the temperature range of 1220–1320 K and the concentration of DCS in hydrogen 9–28.6 mol.%, is 112.9 kJ/mol. Activation energy value indicates the kinetical mode of the thermal decomposition.

Tuning the heat transfer medium and operating conditions in magnetic refrigeration

A new experimental test bed has been designed, built, and tested to evaluate the effect of the system’s parameters on a reciprocating Active Magnetic Regenerator (AMR) near room temperature. Bulk gadolinium was used as the refrigerant, silicon oil as the heat transfer medium, and a magnetic field of 1.3 T was cycled. This study focuses on the methodology of single stage AMR operation conditions to get a high temperature span near room temperature. Herein, the main objective is not to report the absolute maximum attainable temperature span seen in an AMR system, but rather to find the system’s optimal operating conditions to reach that maximum span. The results of this research show that there is a optimal operating frequency, heat transfer fluid flow rate, flow duration, and displaced volume ratio in any AMR system. By optimizing these parameters in our AMR apparatus the temperature span between the hot and cold ends increased by 24%. The optimized values are system dependent and need to be determined and measured for any AMR system by following the procedures that are introduced in this research. It is expected that such optimization will permit the design of a more efficient magnetic refrigeration system.

Illustrations of Efficient Solar Driven Organic Reactions

The article covers some of the important prior art on solar-mediated organic transformations. It additionally highlights recent initiatives from our laboratory toward use of concentrated solar radiation to drive thermochemical and photo-thermochemical organic reactions. Solar radiation (800-1000 W m-2) comprises a continuum of photons of various wavelengths – from ultraviolet (uv) to visible (vis) to infrared (IR) – covering a part of the electromagnetic spectrum. In the context of organic synthesis, uv-vis radiation helps drive reactions via the excited state of substrate or reagent while IR radiation can provide thermal energy. Single sun exposure limits the photon flux and maximum attainable temperature. On the other hand, concentrated radiation provides higher photon flux and also helps generate higher temperatures. This assists in speeding up reactions and/or conducting reactions at larger scale. A laboratory scale solar photo-thermochemical reactor in V-trough configuration was developed that generated reaction temperatures up to 80 °C besides providing ca. two fold higher photon flux. It was used successfully to conduct a variety of photo-thermochemical bromination reactions in efficient manner. Benzylic bromination of p-methylstyrene-based inter-polymer film was also carried out successfully. Tandem reactions were also developed for the synthesis of more complex molecules such as oxazole derivatives from simple building blocks. The reactions presumably occurred via intermediate formation of halo derivatives. Radiation from parabolic dish concentrators provide still higher levels of concentration of solar radiation. These were used to drive useful thermochemical processes such as the energetically uphill conversion of dicyclopentadiene to cyclopentadiene (Cp) and further downstream processes such as Diels-Alder synthesis of a norbonadiene derivative from Cp. A continuous process of production of β-bromostyrene from cinnamic acid was also explored using radiation from a parabolic trough. Concentrated radiation was additionally employed for distillation of a variety of organic solvents. Keywords: Solar driven synthesis, bromo derivatives, oxazole derivatives, -bromostyrene derivatives, solar energy storage, continuous process.

Characteristics of Homogeneous Nucleation Boiling in Ethanol during Rapid Linear Boundary Heating

The characteristics of homogeneous boiling in ethanol subjected to rapid heating with a linearly increasing boundary temperature condition have been studied by applying a theoretical model. A finite liquid control volume or cluster at the liquid boundary hasbeen considered in this model where energy is stored due to external heating while some energy is consumed due to bubble nucleation and subsequent growth. A particular state of liquid heating has been defined as the boiling explosion condition when massive scale vaporization causes the liquid sensible energy to decrease. As the size of liquid cluster, two different length scales have been adopted such as, size of a critical vapor embryo (2rc) and thermal penetration depth ▪. For ethanol heating with initial and boundary conditions identical to those reported in the literature, the model predicts the time of the homogeneous boiling explosion with reasonable agreement with the experiments with the liquid cluster size being assumed to be that of a critical vapor embryo (2rc); while the consideration of the thermal penetration depth ▪ results in late prediction of the occurrence of boiling explosion. However, the temperature at the boiling explosion essentially corresponds to the same for both sizes of the liquid cluster. The obtained results have been presented and discussed in terms of the average liquid temperature rise inside the liquid cluster, maximum attainable cluster temperature and time to reach the boiling explosion condition for a wide range of boundary heating rates (10-109 K/s).

An Indirect Passive Solar Dryer for Drying

A solar drying system designed on the principles of convective heat flow, constructed from local materials was employed in drying yam (Dioscorea Alata). A glass collector having an efficiency of about 0.63 was used along with an absorber for absorbing the heat energy. The drying chamber consisted of drying trays. A chimney fitted at the top centre of the drying chamber enhanced airflow. Air passing through the collector heated up and dried the foodstuff in the drying chamber. The latitude of Ilorin is 8.26oN and the collector angle could be varied . 56o C, 41o C and 71o C were obtained as the maximum attainable temperatures for the drying chamber, ambient and collector respectively. Two samples of yam chips, each weighing 1560g and having an average size of 1cm thick, were dried both inside the dryer and outside the dryer within its surrounding. The initial moisture content of the yam was 70.3% (wet basis) and its final moisture content was 9% (wet basis).The result was compared to natural sun drying. It was observed that the drying time was reduced from 52 hours for sun drying to 45 hours for solar drying. The total cost of the construction was 6, 105 Naira.

Homogeneous nucleation boiling during jet impingement quench of hot surfaces above thermodynamic limiting temperature

What happens in the early stages of jet impingement quenching, when the surface temperature remains well above the thermodynamic limiting temperature for stable solid–liquid contact, is not clearly understood yet. The footage of the boiling and flow phenomena of this period of quenching reveals that the jet impacts on the surface due to hydrodynamic force and immediately splashes away violently, because of explosive boiling or boiling explosion that leaves the surface dry again. It is speculated that, a repetition of wetting and drying of the surface continues until the surface is cooled enough down to allow stable solid–liquid contact. However, neither high speed visual observation nor temperature measurement can help us to find out any concrete and quantitative explanation of the above mentioned wetting and drying phenomena of the surface as it takes place within a very short time. In the present study, we focused on the event of explosive boiling due to homogeneous nucleation that occurs when a liquid jet comes in contact with a very hot surface during jet impingement quenching. Assuming the liquid jet as 1-D semi-infinite solid during its brief contact with the solid, the authors proposed a model based on the concept of 1-D semi-infinite heat conduction and that of molecular theory of homogeneous nucleation boiling. In this model, a characteristic liquid cluster at the boundary is considered and the corresponding energy balance is obtained by accounting two parallel competing processes that take place inside the cluster, namely, transient external heat deposition and internal heat consumption due to bubble nucleation and associated growth. Results obtained are presented in terms of the liquid temperature escalation within the cluster, the limit of maximum attainable liquid temperature and the time necessary to reach the temperature limit at the boiling explosion. From the present model, the temperature at which homogeneous nucleate boiling takes place during quenching of carbon steel with water (20 °C) at atmospheric pressure can be obtained to be higher than 335 °C which might be regarded as the lower limit of surface temperature for homogeneous nucleate boiling. This lower limit of surface temperature for homogeneous nucleate boiling depends on the ratio of thermo-physical properties of the solid and the liquid, namely, β = ( ρ c λ ) s / ( ρ c λ ) l . As the precontact temperatures of the hot surface increases above the lower limit, the interface temperature between the solid and the liquid increases and the time at which homogeneous nucleation boiling appears is greatly shortened.

Model for boiling explosion during rapid liquid heating

The process of rapid liquid heating with a linearly increasing boundary temperature condition has been simulated by applying the analytical solution of 1D semi-infinite heat conduction in association with the molecular theory of homogeneous nucleation boiling. A control volume having the size of a characteristic critical cluster at the liquid boundary is considered, and the corresponding energy balance equation is obtained by considering two parallel competing processes that take place inside the control volume, namely, transient external energy deposition and internal energy consumption due to bubble nucleation and subsequent growth. Depending on the instantaneous rate of external energy deposition and boiling heat consumption within the control volume, a particular state is defined as the boiling explosion condition in which bubble generation and growth cause the liquid sensible energy to decrease. The obtained results are presented in terms of the average liquid temperature rise within the control volume, maximum attainable liquid temperature before boiling explosion and the time required to achieve the condition of boiling explosion. The model is applied for the case of water heating at atmospheric pressure with initial and boundary conditions identical to those reported in the literature. Model predictions concerning boiling explosion are found to be in good agreement with the experimental observations. The boiling explosion condition as predicted by the present model is verified by comparing the heat flux across the liquid–vapor interface with the corresponding limit of maximum possible heat flux, q max , max , at the time of boiling explosion. A comparative study between the actual heat flux and the limit of maximum heat flux, q max , max , at the time of boiling explosion for different rates of boundary heating indicates that, with much higher boundary heating rates, it is possible to heat the liquid to a much higher temperature before theoretical instantaneous boiling explosion occurs.

Flame aerosol synthesis and characterization of pure and carbon coated titania nano powder

Carbon coated titanium dioxide (TiO 2) nano powder has been synthesized by combustion of TiCl 4 precursor in a laminar diffusion flame using inexpensive liquid petroleum gas (LPG) as a fuel, air as an oxidant, nitrogen gas as a carrier, and characterized with regard to phase(s), surface area, carbon content, morphology and optical absorption. The product is shown to contain both the anatase and rutile phases and exhibits (i) decrease in rutile content, (ii) increase in BET specific surface area, and (iii) increase in the amount of carbon (soot) present with increase in fuel flow rate. Further, the maximum attainable temperature depends on carbon content and determines the phase content and morphology of nano powder, e.g. spherical particles result and display reduced agglomeration when carbon content is more. The rutile phase essentially emerges by transformation of the anatase phase, formed initially with lattice parameters somewhat smaller than the bulk due to oxygen deficiency. On the other hand, use of oxygen (instead of air) leads to formation of spherical particles (average diameter ∼104 nm) of a pure anatase phase (as transformation to rutile phase is totally suppressed) with lattice parameters, a=3.776(5) Å, c=9.507(5) Å, close to bulk.

Simple Procedure for Optimal Scale-up of Fine Chemical Processes. II. Nitration of 4-Chlorobenzotrifluoride

In this work, a simple and general procedure for optimally scaling-up exothermic semibatch processes has been applied to the analysis of a nitration reaction performed in the agrochemical industry for the production of an important class of herbicides. Such a reaction is performed in indirectly cooled semibatch reactors in which the species to be nitrated is added to a mixture of sulfuric and nitric acid, forming a heterogeneous (liquid−liquid) system. Adiabatic calorimetric experiments performed in an ARC equipment showed that the reaction in question belongs to the most critical class of exothermic reaction processes, for which maximum attainable temperature due to synthesis reaction (MTSR) is, at the same time, higher than system decomposition temperature and lower than boiling temperature of the reaction mass. It has been verified, through reaction calorimetry experiments (performed in an RC1 equipment), that the optimization−scale-up procedure previously developed allows, with minimum calculation and experimental effort, both for a selection, at laboratory scale, of operating conditions characterized by a rapid coreactant consumption and for their safe scale-up, maximizing industrial reactor productivity.