Table of Contents
Open Access
Heat transfer augmentation procedures, such as Heat Transfer Enhancement and Intensification, are commonly used in heat exchanger systems to enhance thermal performance by decreasing thermal resistance and increasing convective heat transfer rates. Swirl-flow devices, such as coiled tubes, twisted-tape inserts, and other geometric alterations, are commonly used to create secondary flow and improve the efficiency of heat transfer. This study aimed to explore the performance of a heat exchanger by comparing its performance with and without the use of twisted-tape inserts. The setup consisted of a copper inner tube measuring 13 mm in inner diameter and 15 mm in outer diameter, together with an outer pipe measuring 23 mm in inner diameter and 25 mm in outer diameter. Mild steel twisted tapes with dimensions of 2 mm thickness, 1.2 cm width, and twist ratios of 4.3 and 7.2 were utilised. The findings indicated that the heat transfer coefficient was 192.99 W/m²°C when twisted-tape inserts were used, while it was 276.40 W/m²°C without any inserts. The experimental results closely aligned with the theoretical assumptions, demonstrating a substantial enhancement in heat transfer performance by the utilisation of twisted-tape inserts. The study provides evidence that the utilisation of twisted-tape inserts resulted in a nearly two times increase in the heat transfer coefficient, hence demonstrating their efficacy in augmenting heat transfer.
Open Access
The last decades have offered new challenges to researchers worldwide through the problems our planet is facing both in the environment protection field and the need to replace fossil fuels with new environmentally friendly alternatives. Bioenergy as a form of renewable energy is an acceptable option from all points of view and biofuels due to their biological origin have the ability to satisfy the new needs of humanity. By releasing some non-polluting combustion products into the atmosphere, biofuels have already been adopted as additives in traditional liquid fuels, being intended mainly for internal combustion engines of automobiles. The current work proposes an extension of biofuels application in combustion processes specific to industrial furnaces. This technical concern is not found in the literature, except for achievements of the research team involved in this work, which has performed previous investigations. A 51.5 kW-burner was designed to operate with glycerine originating from triglycerides of plants and animals, mixed with ethanol, an alcohol produced by the chemical industry recently used as an additive in gasoline for automobile engines. Industrial oxygen was chosen as the oxidizing agent necessary for the liquid mixture combustion, allowing to obtain much higher flame temperatures compared to the usual combustion processes using air. Mixing glycerine with ethanol in 8.8 ratio allowed growing flame stability, accentuated also by creating swirl currents in the flame through the speed regime of fluids at the exit from the burner body. Results were excellent both through the flame stability and low level of polluting emissions.
Open Access
Open Access
In order to meet the guidance, publicity and commercial functions, various types of billboards have become important permanent facilities in the airport terminal, which are distributed all over the terminal. The advertising materials inside billboards have certain fire hazards, and there is a lack of research on the fire risk of advertising materials at present. Therefore, it is necessary to study the fire risk of advertising materials in airport terminal. Taking PVC board, a commonly used advertising material, as the research object, Pyrosim was used to model and analyze its fire, and the characteristics of fire spread, smoke flow, and distribution of combustion products such as CO and CO2 in the terminal building were obtained. This study explores the fire combustion characteristics of advertising materials in civil airport terminals, providing a basis for fire prevention management in civil airport terminals.
Open Access
The location of the heat of adsorption term in microscopic mathematical models is closely related to how we perceive this parameter. The heat of adsorption term may accordingly be included either only in the thermal energy equation or only in the boundary condition at the ambient-adsorbent interface. In this study, adsorbents with different properties, namely, NaA, NaX, SAPO-34 zeolites and a metal organic framework (MOF) were selected to demonstrate the extent of variation of the results obtained when the two different approaches were used, considering adsorption heat pumps utilizing adsorbent coatings. It was determined that using heat of adsorption in mathematical models in different forms had some effects on the results, varying according to the adsorbent used. Relatively long cycle durations due to high coating thicknesses and mass transfer limitations favored the proximity of the results obtained by using different models. Some correlation was present between Lewis/Fourier numbers and the differences between the results obtained by using different models; differences more commonly decreased as Lewis/Fourier numbers increased. A primary factor leading to the differences was related to the boundary condition at the ambient-adsorbent interface, determining the surface temperature and concentration and governing the concentration distribution in the adsorbent layer. Characteristics of water adsorption isotherms of the adsorbents, including their regeneration temperatures, had notable impact on this factor. MOF and SAPO-34 adsorbents, with relatively low regeneration temperatures, exhibited the highest differences between the models, considering the adsorption stage and whole cycle.
Open Access
The effective drainage radius of coal seam is an important basis for the spacing of pre-drainage gas boreholes. To quickly and accurately determine the effective drainage radius, a new method was proposed. For the coal face where the desorbable gas content before mining has met the standard, the compliance of mine gas drainage rate was used as the basis to determine the effective drainage radius. The fluid-structure interaction model was constructed, numerical simulation of coal seam gas drainage was carried out by using COMSOL software, and the model was validated by combining the field test results. The results show that the new method has the advantage of short cycle. With the extension of drainage time, the increase of effective drainage radius gradually decreases, and finally reaches a relatively stable limit value, which conforms to the Langmuir function. The average error between numerical simulation and field test values of effective drainage radius is 4.9 %, which proves that the model is reliable. This model can accurately predict the effective drainage radius under different coal seam gas contents and drainage times. The research results provide a new mean for determining the effective drainage radius of coal seam and the layout of gas drainage boreholes.
Open Access
This research introduces a novel framework integrating stochastic finite element
analysis (FEA) with advanced circular statistical methods to optimize heat pump efficiency
under material uncertainties. By modeling directional variability in thermal conductivity
using both uniform and Von Mises distributions, the study highlights the superiority of the
Von Mises distribution in providing consistent and efficient thermal performance. The Von
Mises distribution, known for its concentration around a mean direction, demonstrates a
significant advantage over the uniform distribution, resulting in higher mean efficiency and
lower variability. The findings underscore the importance of considering both stochastic
effects and directional consistency in thermal systems, paving the way for more robust and
reliable design strategies.
Open Access
Biomass energy is abundant, clean, and carbon dioxide neutral, making it a viable alternative to fossil fuels in the near future. The release of syngas from biomass thermochemical treatments is particularly appealing since it may be used in a variety of heat and power generation systems. When a syngas with low tar and contaminants is required, downdraft gasifiers are usually one of the first gasification devices deployed. It is time-consuming and impractical to evaluate a gasification system's performance under multiple parameters, using every type of biomass currently available, which makes rapid simulation techniques with well-developed mathematical models necessary for the efficient and economical use of energy resources. This work attempts to examine, through model and experimentation, how well a throated downdraft gasification system performs when using pretreatment biomass feedstock that has been characterized.
For the analyses, peanut shell (PS), a biomass waste easily obtained locally, was used. The producer gas generated with 9 mm PS pellets had a composition of 17.93% H2, 24.43 % CO, 12.47 % CO2, and 1.22 % CH4 on a wet basis at the value of 0.3 equivalency ratio and 800 °C gasification temperature. The calorific value was found to be 4.96 MJ/Nm3. The biomass feedstock PS is found to be suitable for biomass gasification in order to produce syngas.
Open Access
With the wide application of the Internet and smart systems, data centers (DCs) have become a hot spot of global concern. The energy saving for data centers is at the core of the related works. The thermal performance of a data center directly affects its total energy consumption, as cooling consumption accounts for nearly 50% of total energy consumption. Superior power distribution is a reliable method to improve the thermal performance of DCs. Therefore, analyzing the effects of different power distribution on thermal performance is a challenge for DCs. This paper analyzes the thermal performance numerically and experimentally in DCs with different power distribution. First, it uses Fluent simulate the temperature distribution and flow field distribution in the room, taking the cloud computing room as the research object. Then, it summarizes a formula based on the computing power distribution in a certain range by the numerical and experimental analysis. Finally, it calculates an optimal cooling power by analyzing the cooling power distribution. The results shows that it reduces the maximum temperature difference between the highest temperature of the cabinet from 5-7k to within 1.2k. In addition, the cooling energy consumption is reduced by more than 5%.
Open Access
It is proposed to use angular descriptors (in polar and Euler coordinates or quaternions), as well as radiation patterns of many variables, in HF radiofrequency and microwave thermal analysis of anisotropic systems.
Combining thermal analysis with monitoring of electrical properties in the radio frequency range in contactless cells has long been a canonical direction of physicochemical analysis – orthodox / conventional from both thermodynamic and electrochemical positions. Having begun more than half a century ago in the USSR [1], research in the field of high-frequency thermoelectrometry (as recorded by JCTA) demonstrated applicability in dozens of different applications of the analysis of binary and ternary systems [2-4] and eutectic anomalies [5], solubility polytherms [6,7], crystallization and dehydration of crystallohydrates [8], melting and solidification processes [9], as well as thermal decomposition reactions [10,11]. This method was also used to study polymorphism [12] and isomerism [13], including cis-trans isomerism and cis-trans transitions [14]. By probing a cell (or rather its contents) with a field with a frequency from units to hundreds of megahertz, or by scanning this range when switching from one mode to another, a thermographer inevitably passes the ranges of effective HF (high frequency) / radio frequency and microwave absorption by the substances being analyzed. With sufficient power, it is possible not only to identify, but also to modify processes in a cell with an external field. This shifts the problem of controlling such processes from the area of competence of high-frequency thermal analysis to the area of microwave calorimetry [15], in contrast to microwave measurements in thermal analysis [16], which not only probes a heated body with a field, but also heats it as a detector with a field.
Microwave thermal analysis [17] includes methods of differential thermal analysis [18], adapted to the microwave region, and can be implemented on a chip for calorimetric measurements directly during the processes of phase transformations on the chip. The principle of coupling thermal analysis in situ with microwave irradiation inducing phase transitions or reactions in the system cannot be considered non-canonical: there are known works from twenty years ago on the determination of sol-gel transitions and gelification under the influence of a microwave field using differential scanning calorimetry methods [20], as well as the experiments on thermal analysis of vegetable oils during heating and biodiesel precursors during microwave-mediated technology for its production [21,22]. In the work of Schick [23], the methods of fast scanning and high-frequency or alternating-current thermal analysis are equated to the “temperature-modulated calorimetry” (it should be noted that the standard methods of thermal modulation in scanning calorimetry are not high-frequency; even in multi-frequency methods implemented on a chip, except from the very special cases, the upper limit of modulation is in the region of hundreds of hertz or even less [24]). The improvement of the mesurement capabilities in scanning fluid calorimeters, nanocalorimeters, and on-chip calorimeters is a consequence of the peculiarities of the heat transfer in the laminar (microfluidic) layer and capillary / size effects, as well as the subcritical heat capacity phenomena [25-27]. However, the question arises: the effect of which of the modulation variables in the microwave field is critical for microwave modulation [28] calorimetry and microwave heating in it?
It is known that due to the uneven distribution of waves in space, the heating in devices for microwave sample preparation is uneven. It is also known that the amplitude of these waves is different at different distances from the sample and depends on the angle from the center of the direction of propagation of the wave packet (if we take its directionality as the coordinate axis). The directivity coefficient (as the ratio of the square of the field strength of a given directionality to the average value of its "isotropic" strength) clearly affects the efficiency of the effect at the projection point of a given axis. In this case it is possible to reduce the problem of optimization and spatial-angular normalization of measurements in radio-frequency or microwave thermal analysis to the problem of determining and taking into account the radiation patterns of the radiation sources affecting the sample and the radiation patterns of its own surface as a so-called "detector" on the one hand, and the reference microwave detector, using which the metrological accounting of the microwave power is carried out (in agreement or not with the sample location as a “detector”) on the other hand. Neglecting the non-thermal effects of microwaves, one can use a smaller set of variables than when analyzing them during the measurements. When taking into account the thermal effects, we should inevitably make a correction for the energy dissipation in a medium that can be heterogeneous and anisotropic or texture-oriented in space. If in the general case it seems obvious that the effect is proportional to the microwave energy contribution to a given zone, then in the case of reaction-diffusion effects in microwave-induced self-organization [29,30] (as well as in the analysis of heterogeneous biological structures with their inherent compensation and adaptation effects) this simplified scheme is not optimal, and much depends on the electrical and magnetic properties of the sample itself [1,4].
Thus, it is firstly necessary to find out, what types of radiation patterns are physically adequate to the induced and measured processes. By the field strength or by power / power flux density does the process occur, and are they suitable criteria in the case of comparative in situ microwave thermal analysis? In some cases it is advisable to consider separately from the amplitude radiation pattern, but in colocalization with it, its equiphase visualizations - phase radiation patterns representing the dependence of the initial field phase on the spatial angles. It is obvious that the processes will occur synchronously only at the points at which at a given time moment the field phase is the same (they form the equiphase surface - visualization of the wave front). We propose to consider the difference in the directional factors / variables acting on the processes in the system and characterizing it in situ simultaneously as: the difference in the mechanisms induced in the system; differentiation of the methodological approaches (for example, high-frequency thermal analysis can analyze the phase and electrical properties at high frequencies without heating the medium, and in microwave thermal analysis microwave heating at certain frequencies is inevitable, and the task of analyzing electrophysical properties is not set); the difference in the analysis descriptors, which are the field strength or its density, the directivity coefficient, the surface utilization coefficient, as well as the phase and angular characteristics. From the formal mathematical point of view, the directivity coefficient is a dimensionless value determined in decibels, therefore, the radiation pattern is invariant to the analyzed variables. It is also possible to compare the directogram or radiation pattern with the susceptibility diagram of the analyte material or detector, so that their topological overlap will determine the areas of analysis efficiency and the areas of intensity of microwave-induced processes in the medium, and the metrological variables or analysis descriptors and the influencing factors must coincide.
Open Access
This paper proposes to apply a microfluidic chip combining DSC, DTA, and PCR-like functions for studying synthesis and selection of precursors of the genetic code carriers at hydrothermal conditions including those in natural high frequency fields (such as magnetosphere emission, atmospherics, auroras and lightings).
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