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Applied thermal engineering
Elservier Science Ltd.
Applied thermal engineering

Elservier Science Ltd.

1359-4311

Applied thermal engineering/Journal Applied thermal engineeringISTPSCIEI
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    Review of air disinfection approaches and proposal for thermal inactivation of airborne viruses as a life-style and an instrument to fight pandemics

    Vlaskin, Mikhail S.
    15页
    查看更多>>摘要：COVID-19 (Coronavirus Disease 2019) pandemic highlighted the importance of air biosecurity because SARS-CoV-2 is mainly transmitted from person to person via airborne droplets. Preventing infectious droplets from entering the body is one of the best ways to protect against infection. This paper reviews the transmission patterns of airborne pathogens and air disinfection methods. A particular emphasis is put on studies devoted to the thermal inactivation of viruses. These reviews reveal that air heat treatment has not been seriously considered as a possible air disinfection approach. Simple calculations show that the energy input required for thermal disinfection of human's air daily consumption is almost the same as for daily water consumption (by heat treatment from room temperature to 100 degrees C). Moreover, it is possible to organize a continuous heat recovery from the air already heated during disinfection to the inlet air, thus significantly increasing the energy efficiency. Therefore, I propose a solution for the thermal inactivation of airborne pathogens based on air heating and its subsequent cooling in a heat exchanger with heat recovery. Such a solution could be used to create mobile personal and stationary indoor air disinfectors, as well as heating, ventilation, and air conditioning systems. Thermal disinfection of air to breathe might one day be part of people's daily life like thermal disinfection of drinking water. Aside from limiting infectious disease transmission, thermal inactivation might be the basis for developing inhaled vaccines using thermally inactivated whole pathogens.
      原文链接:
    • NSTL
    • Elsevier

    Air solid packed-beds for high temperature thermal storage: practical recommendations for predicting their thermal behaviour

    Alonso, ElisaRojas, Esther
    14页
    查看更多>>摘要：An advantageous solution for thermal energy storage is an air solid packed bed that consists in a tank filled with a solid material through which an air stream passes transferring heat to the filler in charge and collecting it in discharge. Effective tools to predict the thermal behaviour are required to optimize efforts towards the technology consolidation. To contribute to it, an experimental and numerical study on an air solid packed bed is presented here including some novel assumptions. The model is based on two energy balances applied to the solid and air phase separately. It also accounts for the thermal capacity of the tank walls by means of a correction of the solid density. The effective conductivity of the solid was evaluated through two components: one for the conduction through the solid and another for the radiative heat transfer. The last one gains relevance as the system average temperature rises, although it can be neglected below 500 degrees C. Convective heat transfer coefficient was introduced according to published correlations that were adequate for the operation conditions. The model was validated with experimental results from an own facility. The most critical parameter in the system behaviour is the thermal capacity of the filler. This fact points out the need of an accurate measurement of the specific heat. Finally, the possibility of simulating this kind of systems assuming an effective medium and solving an only heat balance was proposed if the convective heat transfer coefficient between solid and air is above a limit established in 100 W/m2K. These conclusions serve as reference to optimize efforts in predicting the thermal behaviour of air solid packed beds systems.
      原文链接:
    • NSTL
    • Elsevier

    Self-adaptive cooling of chips with unevenly distributed high heat fluxes

    Li, XiuXuan, Yimin
    10页
    查看更多>>摘要：The heat load scenario of a real chip is unsteady and spatially variable and gives rise to regions of concentrated high power. Conventional liquid cooling techniques are always inadequate to tailor the flow distribution to the changing thermal environment and cool the resulting high-heat-flux regions effectively. In this work, the selfadaptive cooling for unevenly distributed high heat fluxes is proposed. It contains a matrix of microfluidic units with integrated thermal-sensitive hydrogel valves. The units are independently controlled and deliver the coolant to where it is needed. A numerical model is developed to investigate the flow and temperature distribution of the cooling unit. By introducing the self-adaptive mechanism, the near-wall flow is enhanced remarkably. Nonuniform heat fluxes of up to 460 W/cm2 are effectively dissipated by means of the developed self-adaptive cooling method. The maximum surface temperature drop amounts to 22.6 K, meanwhile the total flow rate can be reduced by nearly an order of magnitude. The microfluidic unit array adapts to local heat fluxes by reconfiguring its internal flow-channel structure automatically and thus movable hotspots are elaborately cooled. The self-adaptive cooling scheme offers both effective and smart thermal management for modern electronic devices.
      原文链接:
    • NSTL
    • Elsevier

    Flexible Bi2Te3-based thermoelectric generator with an ultra-high power density

    You, HanLi, ZhenmingShao, YuyingYuan, Xiong...
    6页
    查看更多>>摘要：Environmental energy harvesting based on flexible thermoelectric generator (f-TEG) provides an ideal micro-power source to drive the node sensors for the Internet of Things (IoT) and wearable electronics. However, the existing flexible thermoelectric devices have some disadvantages, such as low strength, large thermal resistance, complex manufacturing processes, and low reliability. Here, we report a high-performance f-TEG with a dimension of 2 x 16 x 0.6 mm(3), encapsulating 18 pairs of thermoelectric legs with the size of 0.38 x 0.38 x 0.38 mm(3). The flexible polyimide (PI) films with patterned electrodes act as the substrates, of which the upper one is cut into blocks to ensure the generator a minimum bending radius of 4.5 mm. The f-TEG can produce an open circuit voltage of 236 mV and output power of 4.19 mW under a temperature difference of 50 K, which remain almost unchanged even after 7400 times of bending tests. The power density reaches up to 13.1 mW/cm(2) at Delta T = 50 K, and the normalized output power density is 5.26 mu W/cm(2).K-2. These results are among the best performances reported for TEGs, which opens a new avenue for flexible micro-power system design and promotes the development of the next generation self-powered sensors and charge-free electronic devices.
      原文链接:
    • NSTL
    • Elsevier

    Approach to enhance the heat transfer of valve seats through thermal analysis

    Hassan, Mohamad Aniq Syazwan MohamedRazlan, Zuradzman MohamadAbu Bakar, ShahrimanRojan, Mohd Afendi...
    19页
    查看更多>>摘要：The valve seat insert is a component of the engine cylinder head, whose primary function is to seal the combustion chamber and absorb the valve's heat, releasing it to the engine cylinder head. The valves experience high temperatures owing to high thermal loading and low heat absorption in the valve seat, which can potentially damage the engine. Therefore, the thermal characteristics of the valve seat must be optimised to increase the heat transmission between the valve and its seat. Here, three copper alloy valve seats, brass, beryllium copper, and bronze copper, were tested against the existing sintered iron valve seat, and their temperature maps were determined using actual engine operation conditions. The instantaneous heat transfer coefficients of the valves, seats, and engine cylinder head during the four-stroke cycle were evaluated using a one-dimensional thermal simulation analysis. The values obtained were used to assess the finite-element model using a three-dimensional thermal simulation in the Ansys software. The results show that the brass, beryllium-, and bronze-copper valve seats increased the overall heat flux by 4.46%, 4.16%, and 2.06%, respectively, compared to those for sintered iron. Thus, the results are essential to improve the thermal characteristics of the copper alloy valve seat imposed on the cylinder head. For validation, an experimental engine thermal survey and uncertainty magnification factors were used to validate the model. The results indicate that the maximum difference between the simulation and experimental values is 8.42%. Therefore, this approach offers a direct and comprehensible application for evaluating the temperature distribution, heat gradient, and heat flux of the cylinder head of air-cooled sparkignition moped motorcycle engines using copper alloy valve seat materials at intermediate engine speeds. Furthermore, this method is applicable as a platform for the automotive industry to improve the heat transfer of the structural parts of internal combustion engines.
      原文链接:
    • NSTL
    • Elsevier

    Energy assessment of a roof-integrated phase change materials, long-term numerical analysis with experimental validation

    Elawady, NahedBekheit, MaherSultan, Ahmed A.Radwan, Ali...
    19页
    查看更多>>摘要：Achieving the concept of energy efficient building (EEB) is a promising direction for global energy saving. The incorporation of phase change materials (PCM) in the building structure is one of the new techniques recently applied in EEB. However, many recent investigations used short-term analysis of roof integrated PCM. Therefore, long-term thermal behavior of building roof containing PCM layer is investigated in this study. The roof with and without PCM layer are compared at variable outside weather conditions. Enthalpy-porosity model along with a simplified thermal model are developed and simulated using ANSYS-Fluent. The enthalpy-porosity model is essential to capture the melting behavior inside the PCM layer, while the simplified model is the appropriate model for long-term simulation. The two models are compared and validated with the experiments conducted in this study and with data in the literature. Roof with three different PCMs and three thicknesses are evaluated. Long term simulation is conducted for both roof with and without PCM in hot summer season of Aswan city, Egypt. The results showed that using PCM in the roof structure decreases the indoor heat flux and attains an indoor wall temperature closer to the indoor air temperature requirements. Further, the larger thickness of the PCM, the better performance. Based on four months' simulation, the average predicted indoor wall temperature reached 32.5 C and 29.4 C for the roof without and with PCM respectively. Furthermore, around 40% decrease in the total energy gain in four summer months is attained due to the use of 40 mm of RT31-PCM in the roof structure.
      原文链接:
    • NSTL
    • Elsevier

    The multi-field coupling effect of fuel injection duration on gas exchange stability for a free piston engine generator

    Yuan, ChenhengLiu, DongZeng, Shan
    11页
    查看更多>>摘要：Free piston engine generator (FPEG) is a new energy conversion plant to substitute for conventional combustion engine. However, the fluctuation of gas exchange is a key problem to induce the FPEG to run unsteadily and restrict its engineering application. This paper presents a study to explore the multi-field coupling effect of fuel injection duration on the gas exchange stability of a diesel compression-ignition, direct-injection, looped scavenging FPEG. A full-cycle gas exchange model of the FPEG is carried out by coupling the zero-dimensional dynamics, multi-dimensional combustion model and scavenging model, and an iterative calculation method is proposed for numerical simulation of the model. Meanwhile, the effect of injection duration schedule lasting from 0.50 ms to 0.80 ms on the scavenging and gas exchange is analyzed. The results show that the shorter injection duration brings about higher fresh trapping efficiency due to its faster reciprocating frequency which reduces the available time for fresh gas to flow out of the cylinder during gas exchange process, and the trapping efficiency is 41.3 % and the operating frequency achieves 36.6 Hz in the injection duration of 0.5 ms condition. However, the influence of injection duration on exhaust gas cleaning is opposite, and the scavenging efficiency varies in positive correlation with the injection duration, because the long injection leads to low motion velocity and causes the exhaust port to be opened and closed slowly, which provides long exhaust time of the residual burned gas in the cylinder. The maximum scavenging efficiency occurs in the injection duration of 0.8 ms condition and features with 97.9%. Suggesting, relatively high scavenging efficiency and trapping efficiency can be obtained at the same time under appropriate injection duration condition.
      原文链接:
    • NSTL
    • Elsevier

    Rapid die preheating using a high-power infrared lamp array

    Maldonado, LuisShi, CarlSinclair, CollinVian, Corey...
    13页
    查看更多>>摘要：High pressure die casting (HPDC) is a highly violent process that causes significant wear on the die from chemical attacks and from repeated cycling at high pressure and temperature. In practice, HPDC dies are usually preheated by injecting aluminum into the die as warm-up shots. Although warm-up shots transfer heat into the die at a high rate, the warm-up shots are often rejected as scrap due to defects caused by the lower-than-optimal die temperature. The present work aims to develop an auxiliary heating system using an array of high-power, electric infrared lamps to preheat an HPDC die. The potential advantage of this method is a reduction in scrap material and a reduction in thermal cycles on the casting die. Experiments were conducted to quantify the heating rate for various infrared electric heater configurations. A numerical model was also developed to simulate the radiation heat transfer from the lamp array to the die. The model was validated against experiments and subsequently used to optimize the configuration of the heater. The heating system was improved by adding a small radiation shield to minimize hot spots on protruding surfaces while still maintaining a fast heating time. The validated numerical model can be used in the future to develop custom heater solutions for different die geometries.
      原文链接:
    • NSTL
    • Elsevier

    Electro-osmotic regeneration and its behavior in a dehumidification application

    Zhou, XingCai, ShanshanLuo, XuLuo, Xiaobing...
    19页
    查看更多>>摘要：Based on the electro-osmotic regeneration of solid desiccants, this paper proposes an improved dehumidification fin with a silica gel-based composite and internal cooling fins to investigate the potential for the application of air dehumidification. In order to solve the problems existed in the current literature, such as the poor structural stability of the hygroscopic sheet, the effect of Joule heat and the operation modes, series tests were present in this study to provide foundation for the reasonable design of the dehumidifying fins and the determination of the suitable working conditions. This paper first introduced the fabrication method and basic performance tests, including adsorption and stability tests. Based on the behavior of adsorption and the stability of the structure, the types of composites and relevant contents were optimally selected to fabricate a hygroscopic sheet and dehumidification fin. Subsequently, electro-osmotic tests were applied to the hygroscopic sheet to investigate the main factors that affect the electro-osmotic procedures in the sample sheet. The results indicated the hygroscopic sheet with particle sizes of 0.1-0.2 mm and a voidage of 60.75% exhibited the best performance when an electric field with an intensity of 3.92 V/mm. Dehumidification tests were further applied to the optimal selected sample fin installed in the air duct for the effects of dehumidification rate, Joule heat effect, operation modes, and energy consumption. Results show that under the two different conditions set, the dehumidification rate of the dehumidification fin with the above structure can reach 974.19 and 950.24 g/m(2).h, respectively, and the corresponding energy consumption is 770.35 and 726.93 kg/m(2).kWh, respectively. The theoretical specific moisture extraction rate (SMER) of the proposed fin could be more than twice that of other dehumidification methods.
      原文链接:
    • NSTL
    • Elsevier

    Performance enhancement of a double pass solar air heater by using curved reflector: Experimental investigation

    El-Said, Emad M. S.Gohar, Mohammed A.Abdelaziz, Gamal B.Ali, Aml...
    14页
    查看更多>>摘要：In this research, a double pass solar air heater with a corrugated absorber plate and built-in external reflector is adopted to improve its thermo-hydraulic performance. The proposed solar air heater is tested with five tilt angles: 0 degrees, 5 degrees, 10 degrees, 15 degrees and 20 degrees. Data obtained from the proposed heater are compared with the conventional design without reflector under a typical seven air flow rates 11, 13, 15, 17, 20 and 25 l/s. The measured results are reported based on some parameters such as thermal, exergy, thermo-hydraulic efficiencies, cost heat unit and temperature differences. The heater with external reflector improves the performance parameters when compared with the conventional heater. Also, the air flow rate has a strong effect on enhancement of the thermal and thermo-hydraulic efficiencies and production cost. The energy input configuration has been shown to be the superior effect on the enhancement of heater performance than the others effects. The maximum effectiveness and achieved average temperature differences for proposed heater were 0.74 and 26.5 degrees C, respectively. The maximum improvements in average thermal and thermo-hydraulic efficiencies for proposed heater were 19.33% and 19.84% respectively. The maximum value and enhancement ratio of average exergy efficiency for proposed heater was 1.14% and 27.01% respectively. The minimum cost heat unit is achieved using proposed heater estimated by about 0.0047 $ and maximum 93.11% reduction. The optimum values of the performance parameters of the proposed heater under study are obtained when the mass flow rate of flowing air and tilt angle are 25 l/s and 20 degrees respectively. The current study is considered as an attempt to open the research way to new design depends on maximize utilization of the available solar energy.
      原文链接:
    • NSTL
    • Elsevier