Total Heat Effect Research Articles

Influence of flax fibers on epoxide-amine composites: Energetics of interphase formation

Flax fibers are particularly relevant in composite fabrication due to natural availability and mechanical properties close to glass fibers. We explore flax fiber-containing epoxy-amine (DGEBA/DETA) polymers with wide industrial applicability. Flax fibers impact the glass transition temperature (DSC), with a Tg drop of 67 °C at 30 wt% loading. For deeper insight, we develop here an original mixing calorimetry approach to follow in situ DGEBA/fibers and DETA/fibers interphases. DGEBA does not interact quantitatively with flax fibers while DETA/fibers interaction is significantly exothermic and directly related to fibers content. DETA/water interaction only accounts for 25% of total heat effect. Experiments run by contacting DETA with each of the main components of flax fibers (cellulose, hemicelluloses, lignin) point out systematic exothermic effects. Considering their mean proportion in flax fibers, the sum of enthalpy contributions agrees well with the overall effect measured with entire fibers. The main contribution (58%) arises from cellulose. XRD analyses and literature considerations allow concluding on the direct implication of DETA molecules with cellulose chains, resulting in Tg decrease. This work clarifies the chemical role of flax fibers in DGEBA/DETA thermosets, down to the molecular-scale, and highlights that mixing calorimetry is a powerful tool to follow interphase formation in situ.

Reduction gas obtaining with low content of impurities by two-stage natural gas conversion

Reduction gases are widely used in the metallurgical, chemical and other industries. In this paper, the possibility of higher-quality reduction gas production using a two-stage technology is considered. It is proposed to use air conversion of natural gas with cooling and drying of the obtained products at the first stage. At the second stage, gas mixture is heated, treated in the catalyst bed, quenched and dried. It is established that the temperature of heat treatment of the gas mixture at the second stage should be at least 850–950 °C. This allows to increase the ratio (CO − H2)/CO2 in the resulting reduction gas. The minimum gas treatment temperature at the second stage is calculated depending on the pressure in the system. By overheating the gas before it enters the catalyst bed in the second stage, it is possible to compensate for the heat required for chemical reactions in temperatures above 850 °C, the total thermal effect of chemical reactions is determined. The total heat effect of chemical reactions depending on the temperature of gas heat treatment at different pressure is defined.

Parametric Analysis of Shell and Tube Heat Exchanger

The present work investigated the effect of mass flow rate, hot and cold fluid temperature on total heat transfer and effectiveness for shell and tube heat exchanger. In addition, the effect of Reynolds number and type of fluid on heat transfer coefficient and effectiveness was studied. Increasing Reynolds number by 500 from 7000, 8% increasing in heat transfer coefficient has been observed. While 7% increase in Reynolds number, effectiveness has been increases by 5%. Nusselt number change shows higher effect on effectiveness for shell side as compared to tube side. A MATLAB program has been formulated to calculate the result by changing different parameters. During experimental observation, the rate of heat transfer is 143.74 kW and effectiveness of shell and tube heat exchanger is 0.50. The optimum heat transfer through shell and tube heat exchanger had been achieved at 0.0084 m2 surface area of tube and 27 number of tube.

ТЕПЛОФИЗИЧЕСКОЕ ОБОСНОВАНИЕ ПИРОЛИТИЧЕСКОЙ ПЕРЕРАБОТКИ ВОЗОБНОВЛЯЕМОЙ БИОМАССЫ ЗА СЧЕТ ТЕПЛОТЫ РАЗЛОЖЕНИЯ

Актуальность исследования обусловлена необходимостью увеличения доли использования возобновляемых источников энергии в топливно-энергетическом балансе для снижения вредного воздействия на окружающую среду. Цель: оценка возможности пиролиза древесной биомассы и торфа за счет тепловыделения от разложения органической части сырья. Объекты: образцы торфа с двух месторождений Томской области, являющихся перспективными для разработки в энергетических целях, – Суховского и Аркадьевского, а также древесные отходы двух видов – щепа и опилки. Методы: физический эксперимент и дифференциально-термический анализ. Теплотехнические характеристики древесной биомассы определены с помощью методик ГОСТ Р 56881-2016, ГОСТ 33503-2015 и ГОСТ Р 55660-2013; теплотехнические характеристики торфа – с помощью ГОСТ 11306-2013, ГОСТ 11305-2013 и ГОСТ Р 55660-2013. Теплота сгорания сырья определена на бомбовом калориметре АБК-1 (РЭТ, Россия), элементный состав определен на анализаторе Vario Micro Cube (Elementar, Германия) с учетом содержания диоксида углерода карбонатов, устанавливаемого объёмным методом согласно ГОСТ 13455-91. Результаты. Установлены оптимальные параметры пиролитической переработки различных видов биомассы – температура пиролиза и влажность исходного сырья. Оптимальной температурой для пиролиза древесных отходов, доведенных до воздушно-сухого состояния, является 400 °C, при которой суммарный тепловой эффект максимален и составляет 36,3 кДж/кг для опилок и 78,8 кДж/кг для щепы, для суховского торфа при 500 °C суммарный тепловой эффект равен 149,7 кДж/кг. Максимальные значения влажности, обеспечивающие покрытие тепловых затрат за счет теплоты экзотермических реакций, при данных температурах пиролиза составили 10 % для древесных отходов и 14 % для суховского торфа. Величина суммарного теплового эффекта пиролиза аркадьевского торфа даже в сухом состоянии имеет отрицательное значение.

ASSESSMENT OF A POSSIBILITY OF QUALITY IMPROVING OF REDUCING GAS BY TWO STAGE NATURAL GAS CONVERSION

The analysis of the method of reducing gas obtaining by natural gas air reforming with cooling and drying of obtained products on the first stage of the process, their heat treatment in the catalyst layer, chilling and drying — on the second stage is made. It is determined that the temperature of a thermal gas treatment at the second stage of the process, shall not be less than 850–950 °C, which allows to increase the ratio (CO + H2)/CO2 in the resulting reducing gas. The values of the minimum temperature of gas processing on the second stage of the process depending on the pressure in the system are calculated. The total heat effect of chemical reactions depending on the temperature of gas heat treatment at different pressure is defined. It is shown the possibility of compensation for the heat expenditure required for the chemical reactions behavior in the temperature region above 850 °C by gas overheating in excess of the required level prior to its entering into catalyst bed on the second stage of the process. Ref. 20, Fig. 3, Tab. 1.

Kinetics of mechanical activation of Al/CuO thermite

The general aspects of the mechanical activation (MA) of Al/CuO thermite compositions based on micron-sized particles and nanopowders of the starting components have been analyzed using X-ray diffraction and hydrogen titration. The latter method has been employed to evaluate the amount of residual oxygen in CuO and Cu2O from the weight loss during heating in H2. The reactivity of the activated mixtures was assessed using DSC and TG in combination with mass spectrometric analysis. In addition, we have measured the ignition temperature, burning velocity, and brightness temperature of the reaction products. The results demonstrate that mechanical activation leads to the fragmentation of the components, mixture homogenization, and the formation of a composite, producing “weakly bound” oxygen in CuOn and causing partial reaction between the components. The total exothermic heat effect in DSC scans, burning velocity, and brightness temperature as functions of specific milling dose (D) have an extremum. The highest reactivity is observed near D = 2 kJ/g, where a sufficient defect density in the components and good mixture homogenization are ensured, but the degree of MA-induced conversion does not exceed 10%. The burning velocity then reaches 400–700 m/s, and the brightness temperature is 3400–3800 °C. The milling dose dependence of the self-ignition temperature has no extremum. The self-ignition temperature steadily decreases with increasing milling dose, even though the ignition knock “power” falls off. The use of nanoparticulate starting components does not appear reasonable.

Performance investigation of regenerative total heat exchanger with periodic flow

This study proposes a new regenerative type of the periodic total heat exchanger system, which consists of four centrifugal fans and two fixed wheels. The total heat exchanger, which operates periodically to replace the rotation of the fixed wheel in conventional design, can save more energy from motors. The fixed wheels alternately store and release energy using the heat and moisture storage materials of aluminum and silica gel. The operation periods are 2 min, 3 min, 4 min, 6 min, and 8 min. The results show that under the temperature and humidity ratio differences of 10 °C and 4g/kg between indoors and outdoors, the operating period of 3 min has the best performance of sensible heat effectiveness, latent heat effectiveness, and total heat effectiveness. When the temperature and humidity differences increase, the optimal operating period becomes shorter. In order to increase heat effectiveness, adding another high temperature and low moisture air for regeneration in the total heat exchanger increases the latent heat effectiveness, but the sensible heat effectiveness decreases.

Experimental and theoretical investigation of regenerative total heat exchanger with periodic flow for air-conditioning systems

This study experimentally investigates the theoretical performance of the periodic total heat exchanger. The total heat exchanger has a double flow-circuit heat exchange function for periodic positive- and reverse-directional pumping. The operating period parameters are 2 minutes, 3 minutes, 4 minutes, 6 minutes, and 8 minutes. Under the temperature and humidity ratio differences, 10 °C and 4 g kg−1, the operating period of 3 min results in optimal performance of sensible heat effectiveness, latent heat effectiveness, and total heat effectiveness. This study also proposes the lumped system, with dimensionless analysis assumption applied to the whole, and solves it in a one-dimensional model involving the heat and mass transport equations. The dimensionless operating period dominates latent heat effectiveness, while the latent heat effectiveness decreases when the dimensionless operating period increases.

Synthesis and thermal analysis of a Ni(II) complex of nicotinamide

Nickel(II) bisnicotinamide sulfate was synthesized, isolated, and studied by means of FTIR spectroscopy, thermogravimetry, and differential scanning calorimetry with simultaneous mass-spectrometry analysis of pyrolysis products. The order the molecules are evolved from the coordination compound during thermal treatment is determined. The total heat effects of the processes involved in pyrolysis are estimated.

Construction and Effect of New Mechanical Structure in Traditional Nitroguanidine Propellants

ABSTRACTIn order to improve the mechanical properties of nitroguanidine propellants, spheroidized nitroguanidine (SNGu) was mixed up with needle-shaped NGu (NSNGu) at different mass ratios. The results from tensile/compression tests showed that the addition of SNGu could improve compression properties of nitroguanidine propellants. At the NSNGu to SNGu ratio of 8:2, compression properties of the propellants exhibit an excellent promotion with the maximum increase of 25.2% at −40°C comparing against the value of the traditional propellants. Meanwhile, tensile properties of the new propellants at the same ratio were nearly equal to those of traditional propellants. The impacts of the morphology of NGus on the distribution density and orientation of the NGus were investigated by scanning electron microscopy (SEM). The aforementioned mechanical behavior of nitroguanidine propellants could be well explained by the results of closed-bomb tests. The difference of the total heat effect observed in the Differential Scanning Calorimeter (DSC) tests of the two NGus was calculated to be only 1.5%.

A study of p-xylylene polymerization kinetics using high-vacuum in situ differential scanning calorimetry

The polymerization kinetics of p-xylylene in condensed state was studied by in situ non-isothermal DSC measurements, using a custom-made heat-flux calorimeter integrated into a vacuum vapor deposition polymerization reactor. The temperature range (−110 to −75°C) and the total heat effect (Q=86±8kJmol−1) of the polymerization reaction were found to be almost identical to the values previously measured ex situ with a commercial Perkin Elmer DSC7 calorimeter. The differential isoconversional method by Friedman was applied for the kinetics analysis. The effective activation energy exhibits variation with the degree of conversion in the range from 30kJmol−1 to 50kJmol−1 indicating the complexity of the reaction mechanism. To evaluate the reaction model f(α) a model-free method based on the use of the compensation effect has been employed. The calculated f(α) values are adequately fitted to the Avrami–Erofeev A2 model in the conversion degrees interval of 20–80%. The discrepancy observed at the end of the reaction is probably due to diffusion control of the reaction, whereas the complexity of the reaction mechanism can be a reason of the discrepancy at low degrees of conversion.

Investigating the effect of nanoparticle on thermo-economic optimization of fin and tube heat exchanger

In this paper, the effects of Al2O3 nanoparticles suspended in the water-based fluid on the thermo-economic properties of a fin and tube heat exchanger are studied using fast and elitism nondominated sorting genetic algorithm. Nine design parameters are selected as design parameters, and the total annual cost and effectiveness are considered as the two objective functions. First, the effect of nanoparticle on the total annual cost versus effectiveness is obtained at different cold side mass flow rates, and the results are compared with the base fluid. The results show that nanoparticles have a significant influence on the total annual cost and effectiveness in a lower cold side mass flow rates. Next, the heat exchanger volume versus effectiveness for the optimum points is measured at different cold side mass flow rates. It is demonstrated that, adding Al2O3 nanoparticle to the base fluid for the fixed value of effectiveness, decreases the heat exchanger volume, and this reduction is more significant in the lower mass flow rates. The pressure drop and total heat transfer surface area versus effectiveness for the optimum points are also obtained with and without nanoparticle. An increase in the tube side pressure drop is revealed in the nanofluid. In addition, due to the increase in the overall heat transfer coefficient, the lower heat transfer surface area is required for the fixed value of effectiveness. Finally, variations of objective functions versus particle volumetric concentration for five typical optimum points are estimated. It is concluded that an optimal value for the volumetric concentration can be obtained, in which the effectiveness is highest.

Ceramic Monolith Heat Exchanger - A Theoretical Study and Performance Analysis

A ceramic monolith heat exchanger has been learnt for finding out heat transfer performance and effectiveness on computing numerically and ξ-NTU method. In entire domain computation numerically has been performed along with fluid region in rectangular ducts of exhaust gas side, ceramic core and rectangular duct fluid region in air side with the air exhaust in direction of cross flow. Additionally, the heat exchanger has been examined for estimating the functionality via ξ-NTU technique that is conventional along numerous Nusselt number links for rectangular duct flow for the literature. Based on the research, it has been performed on the ceramic heat exchangers and on the ceramic materials and the demand in utilizing the ceramic materials in heat exchangers. Then the recuperator is modeled by using GAMBIT and it is analyzed using FLUENT. The effectiveness and the heat transfer rate are also calculated. Then those outcomes have been assessed along the experimental data. By comparison of both functionality by computing numerically and the ξ-NTU technique, the efficiency by ξ-TU technique has been identified to be nearest to product by the numerical computation among the associative of 2.15% when Stephan's Nusselt number association has been adapted to the ξ-NTU technique within numerous connections. The total heat transfer and effectiveness by ξ-NTU method relative errors utilizing five Nusselt number correlations from literature have been lesser than 14.5% comparative to numerical computation. Associated to Nusselt number correlations, the entire heat transfer utilizing ξ-NTU technique with Stephan's correlation is highly nearest to numerical computation. For that reason, the exit temperature by ξ-NTU method with Stephan's correlation simulates within 1.2% of the relative error for exhaust exist temperature and 0.45% for the air exit temperature assessed against the numerical computation. Overall heat transfer coefficient's relative errors by ξ-NTU technique utilizing five Nusselt number correlations for the literature have been more than 17.5% to that on computing numerically.

Avoiding Buffer Interference in ITC Experiments: A Case Study from the Analysis of Entropy-Driven Reactions of Glucose-6-Phosphate Dehydrogenase.

Isothermal titration calorimetry (ITC) is a label-free technique that allows the direct determination of the heat absorbed or released in a reaction. Frequently used to determining binding parameters in biomolecular interactions, it is very useful to address enzyme-catalyzed reactions as both kinetic and thermodynamic parameters can be obtained. Since calorimetry measures the total heat effects of a reaction, it is important to consider the contribution of the heat of protonation/deprotonation that is possibly taking place. Here, we show a case study of the reaction catalyzed by the glucose-6-phosphate dehydrogenase (G6PD) from Leuconostoc mesenteroides. This enzyme is able to use either NAD(+) or NADP(+) as a cofactor. The reactions were done in five buffers of different enthalpy of protonation. Depending on the buffer used, the observed calorimetric enthalpy (ΔH(cal)) of the reaction varied from -22.93 kJ/mol (Tris) to 19.37 kJ/mol (phosphate) for the NADP(+)-linked reaction, and -11.67 kJ/mol (Tris) to 7.32 kcal/mol or 30.63 kJ/mol (phosphate) for the NAD(+) reaction. We will use this system as an example of how to extract proton-independent reaction enthalpies from kinetic data to ensure that the reported accurately represent the intrinsic heat of reaction.

Hydrodeoxygenation, decarboxylation and decarbonylation reactions while co-processing vegetable oils over a NiMo hydrotreatment catalyst. Part I: Thermal effects – Theoretical considerations

The presented work covers theoretical considerations regarding the total heat effects associated with vegetable oil hydroconversion to form n-paraffinic diesel fuel biocomponents relative to the process conditions. The hydroconversion of fatty acid triglycerides is a highly exothermic process. The hydrodeoxygenation, decarboxylation and decarbonylation of fatty acids are the basic reactions occurring during this process. The hydrodeoxygenation and decarboxylation reactions are exothermic, while decarbonylation exhibits a relatively modest endothermic effect. A similar situation applies to the secondary reactions: rWGSR – reverse water gas shift reaction (endothermic) and CO methanation (strongly exothermic). The contribution of each reaction depends on the process conditions, particularly the hydrogen pressure. Theoretical considerations suggest that the total heat effect in the reactor should be similar under different pressure conditions. The heat effects connected to a particular hydroconversion reaction (main and secondary) may compensate one another.

Hydrodeoxygenation, decarboxylation and decarbonylation reactions while co-processing vegetable oils over NiMo hydrotreatment catalyst. Part II: Thermal effects – Experimental results

Two paraffinic feedstocks containing 20 vol.% of significantly different vegetable oils (olive or corn oil) were subjected to hydroconversion over a commercial NiMo catalyst under two different pressures (3.0 or 6.0MPa), at 320°C, with liquid hourly space velocity (LHSV) of 1.0h−1 and hydrogen/feedstock ratio equal to 300Nm3/m3.Changes in the hydroconversion pressure significantly affect the contribution of the major (hydrodeoxygenation, decarboxylation and decarbonylation) and secondary reactions (strongly exothermic methanation and endothermic reverse water gas shift reaction (rWGSR)). Nevertheless, the total heat effect in the reactor did not differ significantly.The heat effects changed noticeably when different vegetable oils were used as feedstocks. It was found that the differences in the total heat effects noted during hydroconversion for the two vegetable oils depend on the unsaturated fatty acid contents.

Performance investigation of Automobile Radiator operated with Al2O3 based nanofluid

In this study, effect of adding Al2O3 nanoparticle to base fluid (mixture of EG+Water) in Automobile radiator is investigated experimentally. Radiators are compact heat exchangers optimized and evaluated by considering different working conditions. The cooling system of a Automobile plays an important role in its performance, consists of two main parts, known as radiator and fan. Improving thermal efficiency of engine leads to increase the engine's performance, decline the fuel consumption and decrease the pollution emissions. For this purpose, an experimental setup was designed. Effects of fluid inlet temperature, the flow rate and nano particle volume fraction on heat transfer are considered. Results show that Nusselt number, total heat transfer, effectiveness and overall heat transfer coefficient increases with increase , nano particle volume fraction , air Reynolds number and mass flow rate of coolant flowing through radiator.

Thermal performance enhancement of a periodic total heat exchanger using energy-storage material

A periodic total heat exchanger is a double flow circuit heat exchange device, which is improved by a membrane-based energy recovery ventilator with two additional fans to change the flow direction. Similar to membrane-based energy recovery ventilators, the deficiency of latent heat effectiveness poses a problem. Thus, this paper investigates the usage of energy-material in the periodic total heat exchanger to enhance the device performance. Three types of energy-storage materials, activated carbon, aluminum, and a mixture of activated carbon and aluminum are respectively installed and experimentally investigated. The results show that adding activated carbon to the device increases the latent heat effectiveness by 17.3%. Also, installing aluminum results in an increment of 15.1% on the sensible heat effectiveness. Finally, among the three types of energy-storage materials, the device with activated carbon has the best performance, with an increment of the total heat effectiveness of up to 11.7%.

Heat transfer from a vertical fin array by laminar natural convection and radiation—A quasi‐3D approach

AbstractA quasi‐3D numerical model is developed to study the problem of laminar natural convection and radiation heat transfer from a vertical fin array. An enclosure is formed by two adjacent vertical fins and vertical base in the fin array. Results obtained from this enclosure are used to predict heat transfer rate from a vertical fin array. All the governing equations related to fluid in the enclosure, together with the heat conduction equation in both fins are solved by using the Alternating Direction Implicit (ADI) method for getting the temperatures along the height of the fin and the temperature of the fluid in the enclosure. Separate analysis is carried out to calculate the heat transfer rates from the end fins in the fin array. A numerical study has been carried out for the effect of fin height, fin spacing, fin array base temperature, and fin emissivity on total heat transfer rates and effectiveness of the fin array. The numerical results obtained for an eight‐fin array show good agreement with the available experimental data. Results show that the fin spacing is the most significant parameter and there exists an optimum value for the fin spacing for which the heat transfer rate from the fin array is maximum. Correlations are presented for predicting the total heat transfer rate, average Nusselt number, and effectiveness of the fin array. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.20360

The toxic effect of cadmium on pure microbes using a microcalorimetric method and a biosensor technique

A microcalorimetric technique based on microbes heat-output was explored to evaluate the effect of Cd (II) on Bacillus subtilis and Candida humicola. The power-time curves of the growth metabolism of Bacillus subtilis and Candida humicola and the effect of Cd (II) on it were studied by using a TAM III microcalorimeter, ampoules method at 28°C. For the evaluation of toxic effect on pure micro-organisms, the maximum peak-heat output power (P max) in the growth phase, the growth rate constants (k), the log phase heat effects (Q log), and the total heat effect (Q T) for Bacillus subtilis and Candida humicola were determined. Dissolved oxygen and biochemical oxygen demand (BOD) were evaluated by a biosensor. Cadmium has been regarded as the essential biological trace element. Cd (II) solutions of different concentration have different effects on Bacillus subtilis and Candida humicola growth metabolism. The higher concentrations of Cd (II) inhibit the growth of Candida humicola (1600–3200 μ g·mL−1), Bacillus subtilis (240–480 μg·mL−1); the lower concentrations can promote the growth of both micro-organism. The values of cell dry weight is also showed in conformity in the cell dry weight changes to the micro-organisms' growth time. Comparison of growth curves of two micro-organisms showed that both the trends of biochemical oxygen demand were exhibiting regressive changes with the passage of time during their generation times (t G). Results from ultraviolet spectrophotometer and precision pH meter all showed that the control growth curves were visioning same trends with the thermodynamic curves of micro-organisms measured by microcalorimeter.