Thermal expansion

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Thermal expansion effect on the propagation of premixed flames in narrow channels of circular cross-section: Multiplicity of solutions, axisymmetry and non-axisymmetry

Thermal expansion effect on the propagation of premixed flames in narrow channels of circular cross-section: Multiplicity of solutions, axisymmetry and non-axisymmetry

The streamlines drawn in Figs. 3-5 clearly show the jump of the axial velocity through the flame front resulting from thermal expansion previously mentioned above. Contrary to the di ↵ usive-thermal modeling approach, the curva- ture of the flame is subject to the flow acceleration through the front flame which in turn alters the consumption speed and flame velocity propagation. The di ↵ erences in terms of parameters (Le, d and m) at which multiple solutions are observed here, when compared with [15], result from the e ↵ ect of thermal expansion on the flame curvature. Note that, in the present simulations, it is not possible to fix the flame propagation velocity and compute the corresponding inlet flow rate to make the two flame branches continuously recover as done in [15].

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Characterization of geometric imperfections and determination of the thermal expansion of a spherical acoustic resonator

Characterization of geometric imperfections and determination of the thermal expansion of a spherical acoustic resonator

values of radius obtained from modes TM11 and TM12 as a function of temperature; the agreement is within 15 ppm. In order to determine the thermal expansion of the resonator, the results for the two modes were fitted to a linear function of temperature. The deviations between experimental values and the fit are within ten parts per million (see fig. 4 right). It is worth noticing that, of the two modes considered, TM11 shows a higher degree of confidence. The choice of a simple functional form of the fitting function is not critical for primary thermometry measurements [6]; more realistic forms of the variations of the ratio a(T)/a(T t ) will be tested in

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A high temperature X ray diffraction study of the influence of MWCNTs on the thermal expansion of MWCNT/Ni composites

A high temperature X ray diffraction study of the influence of MWCNTs on the thermal expansion of MWCNT/Ni composites

In order to explain the observed behavior of the CTEs, we suggest three main probable lattice expansion mechanisms that could be acting in the composites during the thermal in- put. Since the expansion is measured in the Ni matrix, the lat- tice unit cells that are adjacent to pores or clusters present more free volume to expand without restraint (Fig. 4a and b). When a single CNT is in a grain border (Fig. 4c), the adja- cent unit cells also expand more that the ones inside the grain since CNTs have zero or negative thermal expansion under thermal inputs [12]. All the described mechanisms pro- duce a relaxation of the micro-stresses, which are measurable by XRD within the information volume range (0.53–0.62 mm 3 ).

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Structural masonry walls exposed to high temperatures with thermal expansion control

Structural masonry walls exposed to high temperatures with thermal expansion control

Therefore, the motivation of this work lies in the need to better understand the behavior of masonry structural walls submitted to high temperatures, previously explored in other studies such as Souza (2017), Al-Sibahy and Edwards (2013) and Ayala (2010), including the concept of internal stresses caused by the restrictions of thermal expansions, in order to understand the damage of the elements in real situations. Thus, the objective of this work is to analyze the behavior presented by small- scale masonry walls when exposed to high temperatures, axial loading and having their lateral thermal expansion restricted, in order to simulate conditions close to the reality in a fire situation.

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Structural masonry walls exposed to high temperatures with thermal expansion control

Structural masonry walls exposed to high temperatures with thermal expansion control

This study evaluates the behavior of small clay hollow-bricks walls exposed to high temperatures. Blocks measuring 14 and 19 cm thick were used, with strengths of 7 and 10 MPa. The thickness of the joints, the mortar, and the coating influence was evaluated. The temperatures of the furnace, the interior and the surface of the walls, the expansion of the blocks and the crushing of the joints were measured. It was possible to infer that the samples presented good performance, maintaining their integrity, thermal insulation, and load-bearing capacity. The restriction of the boundaries did not cause the spalling of the blocks, however, it was possible to observe the stress transfer to them in samples with rigid joint mortar. The masonry measuring 19 cm wide and the ones with coating showed better thermal performance.

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Structural masonry walls exposed to high temperatures with thermal expansion control

Structural masonry walls exposed to high temperatures with thermal expansion control

This study evaluates the behavior of small clay hollow-bricks walls exposed to high temperatures. Blocks measuring 14 and 19 cm thick were used, with strengths of 7 and 10 MPa. The thickness of the joints, the mortar, and the coating influence was evaluated. The temperatures of the furnace, the interior and the surface of the walls, the expansion of the blocks and the crushing of the joints were measured. It was possible to infer that the samples presented good performance, maintaining their integrity, thermal insulation, and load-bearing capacity. The restriction of the boundaries did not cause the spalling of the blocks, however, it was possible to observe the stress transfer to them in samples with rigid joint mortar. The masonry measuring 19 cm wide and the ones with coating showed better thermal performance.

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Analysis of premixed flame propagation between two closely-spaced parallel plates

Analysis of premixed flame propagation between two closely-spaced parallel plates

Motivated by experimental observations on premixed-gas flame propagation in Hele-Shaw cells, this work analyzes quasi-isobaric flame propagation between two adiabatic parallel plates using a simple quasi-2D formulation based on averaging the flow properties across the cell gap. Instabilities associated with thermal expansion, buoyancy, viscosity change across the front and differential diffusion of thermal energy and reactants are investigated with one-step chemistry, constant heat capacity and variable transport coefficients through time-dependent computations of the flame front evolution in large domains. These insta- bilities are found to induce flame wrinkling which increases flame surface area and thus propagation speeds in ways different from those associated with freely propagating flames. The simulations are compared with experiments in Hele-Shaw cells; very good qualitative and (in some cases) quantitative agreement is found.

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Thermal denaturation of A DNA

Thermal denaturation of A DNA

Thermal measurements on A-DNA are important to test the in fl uence of the conformational form on the melting transition and the universality of models used to describe DNA thermodynamics. DNA adopting the A-form may also be an important part of the gene transcription process in vitro [4]. It is possible to have A-form in solution with high alcohol concentrations [5]. However, the DNA often takes a combination of A and B-forms, as well as molecules with B – A interfaces, so that experimental results cannot be quantitatively interpreted. A-DNA can be prepared from randomly oriented fi bers and studies of the melting process have been reported [6]. Neither DNA in solution nor in randomly oriented fi bers will give unambiguous experimental information on the spatial structure.

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Thermal processsing and quality_principl

Thermal processsing and quality_principl

The retortable pouch was developed during the 1960s in the USA, by a consortium of food packaging/processing companies working in conjunction with the US Army Natick Laboratories [98]. The retort pouch is a 3-ply multi-layer flexible pack- aging consisting mainly of polypropylene, aluminum foil and polyester. To enhance its strength, nylon has also been added as an additional layer. Pouches can withstand sterilization temper- atures up to 130 ◦ C, making it amenable to HTST operations. Coupled with its thin profile, retortable pouches allow more rapid heat transfer than cylindrical metals and glass contain- ers of equivalent volume. Commodities that have been packed in thin profile pouches include meat curries, stews, high-quality meat products, frankfurters, ready meals, gourmet sauces, corn, green beans, slice or diced carrots. Theoretical analysis and experimental measurements of Vitamin C concentration in a three dimensional pouch filled with carrot–orange soup during thermal processing at 121 ◦ C has been reported [99]. Simulated results indicated that natural convection plays an important role in the transfer of heat within the liquid product, while the slowest heating zone migrated towards the bottom of the pouch (within 30–40%) of the pouch height. The Vitamin C profile within the pouch depended on the temperature and velocity profiles within the pouch. Simpson et al. [100] developed a mathematical model for a cone-shaped and validated the model using vacuum- packed mackerel in a retortable pouch with steam/air mixture at 116.8 ◦ C. The overall heat transfer coefficient (U) expression used in validating the model for a constant temperature was: U = 1

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This paper addresses electricity transmission planning under the new industry and institutional structure of the Mexican electricity market, which has engaged in a deep reform process after decades of a state-owned vertically-integrated non-competitive closed industry. Under this new structure, characterized by a nodal pricing system and an independent system operator (ISO), we analyze welfare-optimal network expansion with two modeling strategies. In a first model, we propose the use of an incentive price-cap mechanism to promote the expansion of Mexican networks. In a second model, we study centrally-planned grid expansion in Mexico by an ISO within a power-flow model. We carry out comparisons of these models which provide us with hints to evaluate the actual transmission planning process proposed by Mexican authorities (Prodesen). We obtain: 1) the Prodesen plan appears to be a convergent welfare- optimal planning process, and 2) incentive regulation in Mexico could further help to implement such an optimal process.

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Hypersonic plasma plume expansion in space

Hypersonic plasma plume expansion in space

The main goal of this paper is to provide a generalization of SSM of plasma plume expansion in vacuum, by establishing a single two-fluid model framework and its solutions based on variable separation. This framework, which can also be used as the starting point for the derivation of other SSM, is presented in section II. We demonstrate that rigorous self-similar solutions of the two-fluid model do not exist unless the ion axial momentum equation is simplified for hypersonic flows. The local error in this equation is measured. We focus our attention in a subset of SSM which assumes constant axial velocity along ion streamlines. The three individual models of Parks and Katz, 8 Ashkenazy and Fruchtman 9 and Korsun and Tverdokhlebova, 10

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Microstructural and Thermo-Physical Characterization of a Water Hyacinth Petiole for Thermal Insulation Particle Board Manufacture

Microstructural and Thermo-Physical Characterization of a Water Hyacinth Petiole for Thermal Insulation Particle Board Manufacture

As aforementioned, WHP pulp is comprised of the aerenchyma tissue cells, which are rich in cellulose, hemicellulose, and polyholosides, which are very hydrophilic macromolecules [53,65]. As a result, pulp WHP board had a higher water absorption capacity (1.25 times more) than staple WHP board. In the presence of water, the boards capture water and increase their volume individually by a chemical process [66,69]. For their part, the “fibre units” are comprised of microscopic tubes, such as the vessels of the xylem and phloem of the vascular bundles (Figure 4). Through these tubes, water penetrates by capillary action and remains there. In fact, the differences between capillarity and the chemical hydration process are also the reason for the thickness swelling results. As presented in Table 3, the staple WHP board had 1.75 times worse stability in dimension than pulp WHP panels. This is because, when the “fibre units” are full of water, their dimension increases. Contrarily, the pulp hydration process is a chemical process (namely, cellulose and hemicellulose hydration), and so the variability in dimension is lower. Dimensional variability must be considered, due to possible related pathologies in a building’s construction. On the other hand, water absorption capacity favours hydrothermal interior comfort. Additionally, this property could pose a problem in tropical contexts, where the relative humidity is high. Moisture content affects thermal-insulating performance where water thermal conductivity values are higher than air.

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Thermomechanical Performance of fr 4 Laminates in the Manufacturing Process of Printed Circuit Boards

Thermomechanical Performance of fr 4 Laminates in the Manufacturing Process of Printed Circuit Boards

The figure 6.27 shows some of the thermal properties considered relevant to warpage phenomena, there are low, middle and high glass transition temperature resins sys- tems, the elements at the end of the molecular chain is the factor which characterize what kind of glass transition it is. This knowledge is very useful because, engineers can gave an a idea just knowing the value of the Tg. Decomposition temperature is related with the glass transition temperature, but engineers has to pay attention in the decomposition temperature because is the temperature where the PCB starts a process of decomposition, so this study are capable to provides the methods and the knowledge to determined this property, also a typical range of decomposition tem- peratures are was presented in order to compare it with reflow process. A hole study of CTE was explained, defining CTE as one of the critical factors of warpage, it was demonstrated the difference according with the PCB area, state of the art literature was consulted showing different low CTEs but the cost of fabrication are higher that conventional materials used in Printed Circuit Boards, also the fabrication of PCB was investigated deeply and how the efficiency of this process affects PCB reliability. Time to delamination property provides the time when the PCB is exposed at high temperatures with no delaminations, the contribution was to presents the informa- tion clearly and explanied the test to know the time to delamination depending of the resin system.

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Effect of N, N'-diallyl-phenylphosphoricdiamide on ease of ignition, thermal decomposition behavior and mechanical properties of poly (lactic acid)

Effect of N, N'-diallyl-phenylphosphoricdiamide on ease of ignition, thermal decomposition behavior and mechanical properties of poly (lactic acid)

Based on the results of thermal decomposition kinetics shown in 3.2.2, the addition of PO AA did not change the main thermal decomposition path of PLA. However, it might impact the elementary reactions [47,48]. On one hand, phosphorus containing acids formed during the thermal decomposition of PO AA posi tively catalyzed most random tranester fi cation (R1 and some R2 reactions) in PLA matrix. Under such catalyzed reactions, at the earlier thermal decomposition behavior, PLA/PO AA produced more oligomers than that of PLA. On the other hand, phosphorus containing acids showed negative effect on cis elimination reac tion (R3) in PLA matrix. Some tranester fi cation reactions which produced carboxylic acid compounds (c) also suffered negative effect. As a result, the depression of cis elimination and some tra nester fi cation reactions reduced the production of c, d and f during the early thermal decomposition. This inference was favor of the reduction of absorbance of carbonyl compounds showed in Fig. 4

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Mecanismos para la inversión y remuneración de la transmisión de energía eléctrica

Mecanismos para la inversión y remuneración de la transmisión de energía eléctrica

From the economic point of view, oligopolistic models are able to describe these issues. For example, in the case of inter- connected systems, the capacity of a transmission line decreases with the increase in the injection capacity of generation, which creates conflicts in the planning of the design capacity of trans- mission lines and the indivisibility of investments. In turn, from the social point of view, the capacity of a line should be maxi- mized, which leads to a conflict of interest between the gener- ators. In addition, the behavior of the transmission owner, de- pendent on the payment of congestion, shows a low-capacity response. In practice, neither the lines are funded strictly by these rents nor can a minimum capacity rent fully finance their costs. Additionally, it creates a dilemma in regard to whether the market structure reflects the necessary investments in capacity and the timing thereof, that is whether the expansion should be proactively done [1]. It creates a problem between the antici- pated expansion of transmission lines and the inclusion of new generation. This kind of behavior brings a high degree of un- certainty because, although from the social viewpoint it is more efficient, anticipation carries a cost and risk as to whether or not to build power generation [2], [3].

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Free flowing, transparent gamma alumina nanoparticles synthesized by a supersonic thermal plasma expansion process

Free flowing, transparent gamma alumina nanoparticles synthesized by a supersonic thermal plasma expansion process

prominent lines of atomic aluminium at 394 and 396 nm and atomic oxygen at 777/844 nm along with all the major lines of argon were clearly identi fi ed. This indicates the proper decom- position of the reactants injected into the nozzle. Fig. 5 shows the variations in the plasma temperature with oxygen fl ow rates in different plasma currents. It is observed that the calculated plasma temperature increases with increase in plasma current and at constant plasma current, the temperature decreases as more oxygen is injected into the injection section. This explains the observation that the relative intensity of the aluminium peaks with respect to the argon decreases with higher oxygen fl ow rate. In a previous communication we had measured the effective quenching rate across the nozzle under almost similar conditions which was found to be in the range of 10 6 e 10 7 K per second [15]. In the present investigation the gas phase atomic aluminium, at the reactant injection section, react with the oxygen to form the material of our interest, which undergoes a rapid cooling while expanding through the nozzle into the low pressure sample collection chamber. Unlike the typically turbulent gas mixing quenching in conventional plasma assisted processes, the super- sonic expansion produces a uniform cooling pro fi le [15]. This rapid but also uniform cooling has ensured homogeneous condensation of meta-stable g -alumina nanoparticles with a narrow size distribution without being mixed with other impurity phases. Higher temperature or pressure in the plasma tail on the other hand promotes collision and hence the particle

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Studies on a supersonic thermal plasma expansion process for synthesis of titanium nitride nanoparticles

Studies on a supersonic thermal plasma expansion process for synthesis of titanium nitride nanoparticles

However, the thermal plasma assisted techniques often produce broad particle size distribution and serious inter-particle agglomera- tion. We have demonstrated in the recent past that these typical problems associated with conventional plasma techniques can be avoided in a supersonic plasma jet based reactor con fi guration, which can produce narrow size dispersion because of uniform tem- perature pro fi le of the expanded plasma jet, and less agglomeration due to the directed supersonic velocity of the particles embedded in the plasma [13 – 15]. The plasma jet was accelerated to supersonic velocity in the fi rst place by connecting the discharge zone (plasma torch) to the particle nucleation region (sample collection chamber) through a converging nozzle and maintaining an appropriate pres- sure difference across the same. We have also demonstrated that a non equilibrium electron population could have charged up the nano-particles all negatively after nucleation in this system, thereby curbing unwanted coagulation among particles and ensuring better particle size distribution [14]. We had reported synthesis of free- fl owing, blue-black stoichiometric TiN particles by this reactor con fi g- uration by injecting NH 3 and TiCl 4 to the relatively hotter zone of the

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REGIONALISMO, EL: EXPANSION DEL CONCEPTO DE ASOCIACION LATERAL

REGIONALISMO, EL: EXPANSION DEL CONCEPTO DE ASOCIACION LATERAL

event, although the Round went further than had originally been anticipated, there was much frustration at its slow pace, prompting many countries to take a ‘sub-globalist’ route. The creation of MERCOSUR in 1991 by Argentina, Brazil, Paraguay and Uruguay (see box), and the expansion of the US-Canada free trade area to include Mexico in 1993 and form the North American Free-Trade Agreement (NAFTA) were both examples of regionalism as a subset of global tariff-cutting. In global negotiations, moreover, regionalism also encourages the formation of collective negotiating positions, likely to have more weight in the overall balance.

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The change in activity of R. arenarum (nocturnal to diurnal) during the reproductive period implies a thermal benefit that allows the toads to increase call performance. The call is strongly related to the body temperature (Duellman &Trueb 1986, Wells 2001). During BP, the principal activity of male toads is to call for females. While spending long periods of time calling, mobility is reduced and obtaining food is more difficult. Quiroga (pers. comm.) observed that during reproductive periods toads have prolonged fasts, in which the stomach contains only their own skin. In others bufonid toads, this behavior (ingesting their own skin) is well known and is apparently related with energy budget (Weldon et al. 1993). Although feeding is scarce during the reproductive period of R. arenarum, it appears that there is a physi- ological or behavioral mechanism that allows the adjustement of the optimum thermal range for reproduction. It is possible that R. arenarum uses stored fat, as do Elachistoclaeis bicolor, Rhinella fernandezae, and Leptodactylus lati- nasus. In these species, evidence shows an inverse relationship between the somatic index of the testicles and amount of body fat (Martori et al. 2005). Females prefer males with greater total sound energy in terms of calling rate, call duration, and loudness (Gerhardt 1994, Schwartz 2001). These attributes of calling activity impose a high energetic cost for male toads (Wells 2001). In this framework, R. are- narum gains energy from the environment dur- ing the day (basking for calling), to compensate for these energetic costs and to ultimately increase reproductive success.

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