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.
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.
查看更多>>摘要：In this study, state-of-the art deep neural networks to train and predict the heat transfer in building structures were proposed. Today, many of studies analyze thermal energy performance of buildings by analytical or numerical methods. Although building energy performance can be predicted effectively by finite element method, it is still time-consuming to calculate and solve the heat transfer problem. Moreover, expert engineer is required and complicate process to set simulation model is essential. In this work, a novel deep-learning method, which was pre-trained by the thermal simulation data, was developed to predict the thermal behavior of building structures in a fast time without complicated process. Heat transfer simulations of the slab wall building structure depending on its thermal properties and geometries were carried out to get training datasets for deep learning. The database of thermal simulation results was used for deep learning training. The image of temperature and heat flow distribution was trained by convolutional encoding-decoding network and the value of total heat loss through building and thermal bridge coefficient was trained by multi-layer perceptron. After train completed, the thermal behavior could be predicted in a second by just feeding information such as blueprint image and thermal properties of constructions into deep-learning architecture. There was no need to set a new simulation model at each time which consumes time and effort for modeling, meshing and calculating. With the developed network, the prediction of thermal behavior with high accuracy was possible in a super-fast time.
查看更多>>摘要：A novel porous artery structure is proposed and experimentally validated to enhance the pool boiling heat transfer performance based on the concept of "phase separation and modulation". In the experiment, multiple rectangular arteries are formed in the bottom of a porous structure, and a thin copper microporous layer is placed between the heating surface and the rectangular arteries. Compared with conventional porous structures, this novel porous artery structure can effectively improve the pool boiling heat transfer performance due to i) increased nucleation site density, ii) improved liquid replenishment by capillarity, and iii) effective liquid/vapor phase separation. Experimental results show that comparing with boiling heat transfer on a plain surface, a 200% higher in CHF, and a 144% higher in heat transfer coefficient (HTC), together with a 59% lower in superheat at the onset of nucleate boiling (ONB) are obtained for this new structure. In addition, the effects of the top and bottom microporous layer thickness and the artery depth on the pool boiling heat transfer performance are investigated, and the inherent physical mechanisms are analyzed.
查看更多>>摘要：Experimental research was conducted to observe the frost growth under forced convection and cryogenic conditions (-180 degrees C). A laser was installed as a light source to investigate the frost microscopically, and the frost film and frost seed were observed on the test surface. The process of frost growth under cryogenic conditions was classified into four periods and it was compared with those under general-low temperature conditions. The frost coverage factor was defined based on the pixel intensity of the frost image, and the shape of the frost layer could be visualized using the frost coverage factor. The heat flux of the test surface was compared with the frost coverage factor, and it decreased by 40% when the frost coverage factor was 1. Therefore, the frost coverage factor can be used as a useful index to evaluate the heat transfer performance of the heat exchanger operating under cryogenic conditions.
查看更多>>摘要：An accurate heat and mass transfer model of a tumble drum has not been developed yet owing to complicated random motions of clothes in the tumble drum. In this study, heat and mass transfers of water from clothes to air, including the heat loss in the tumble drum of a clothes dryer, are measured with the temperature, humidity, airflow rate, and water content of clothes. The mass transfer rate increases as the air temperature, airflow rate, and water content of clothes increase; however, it decreases with an increase in the relative air humidity. The mass transfer rate enhancement is dominated by the increase in the temperature over the airflow rate; the increased temperature from 40 degrees C to 80 degrees C results in an increase in the mass transfer rate of 196%-238%, and the increased volumetric airflow rate from 2.5 CMM to 3.1 CMM leads to an increase in the mass transfer rate of 21%-23%. The heat loss in a tumble drum increases as the air temperature increases and continues to increase as the relative air humidity and water content of clothes decrease. Furthermore, although the heat loss is linearly proportional to the difference between the temperatures of ambient air and clothes, it has an insignificant relationship with the airflow rate. In addition, the prediction models of heat and mass transfers of water and heat loss in the tumble drum are developed using artificial neural network, exhibiting optimal agreements with the measured data. The developed prediction models can be used to optimize the tumble drum dryer, considering energy efficiency and short drying time.
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.
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.
查看更多>>摘要：Variable refrigerant flow (VRF) systems faults are inevitable due to installation errors, degradation, and other reasons. It is of great value to quantitatively understand the impact of faults on VRF systems performance and to clarify the changing trends of variables under different types of faults through experiments. In particular, the experimental analysis of simultaneous faults situations is helpful to improve the fault detection and diagnosis technology of VRF systems. There have been some previous experimental studies on the impact of faults, but none of them concerns modern VRF systems and their simultaneous faults. This paper presents results from a laboratory study of a VRF system with different types of faults. It provides the first published results of combinations of triple simultaneous faults, in addition to previously untested types of double simultaneous faults. The quantitative impact of the three crucial performance parameters, e.g. cooling capacity, system power, and COP, of the system under different faults has been analyzed. In addition, the quantitative influence and variation trend of system parameter variables during single fault and simultaneous fault are summarized. Results show that the outdoor fouling fault has the greatest impact, which can cause a 47.6% COP drop and 80.27% cooling capacity reduction. The influence of the simultaneous fault on the variable trend is superimposed and offset, but the trend influence of some faults also has a dominant characteristic.
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.
NSTL
Elsevier