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Fusion power, which generates electricity from the heat of fusion reactions, has the potential to solve the future energy crisis; hence, methods have been developed to study fusion reactions in a f...

Rates of neutron production in deuterium-tritium (D-T) plasmas below the temperature of 100 keV have been widely studied with analytical cross sections based on nuclear physics. In the present work...

In this paper, we present the elastic solutions for the problem of an internal pressurized functionally graded thick-walled tube based on the Voigt method in Xin et al. (Int J Mech Sci 89:344–349, 2014); a transversely isotropic functionally graded thick-walled tube subjected to internal pressure is studied. It is assumed that the functionally graded tube is made up of two linear isotropic elastic materials; the matrix is reinforced by fibers with circular cross section all aligned in the circumferential direction. The volume fraction of the reinforced material is identical with our previous work (i.e., Xin et al. in Int J Mech Sci 89:344–349, 2014). By using the Mori–Tanaka method, this paper obtains the differential equation of the radial displacement and then the numerical results of the radial displacement and the stresses are deduced. The approximate analytical solutions are also derived which agree well with the numerical results on the basis of the Mori–Tanaka method. Further, both based on the Mori–Tanaka method, the results received by the present model are compared with those by a particle model for solving an isotropic inner-pressurized FGM tube problem. Finally, in the numerical part the influences of the volume fraction and the elastic moduli’s ratio on radial displacement and the stresses are discussed.

The operating parameters of task/ambient air conditioning (TAC) systems including supply air temperature (ts) and air flow rate (Qs) were reported to have critical effects on energy savings and thermally comfortable environment. Due to the existing contradictions between these two aspects, a multi-objective study should be carried out to realize consuming minimum energy and at the same time to guarantee the thermal comfort level at suitable range. Two optimization methods were adopted in this study, one is the response surface methodology (RSM), and the other is the technique for order preferences by similarity to an ideal solution (TOPSIS) method. The objective of this study was to compare the pros and cons of these two methods. It was found that the optimum operating parameters obtained using RSM method were 26 °C (ts) and 28.94 l/s (Qs), corresponding to energy consumption (Qc) of 46.89 W and PMV of 0.11; while that obtained using TOPSIS method were 26 °C (ts) and 30 l/s (Qs), corresponding to energy consumption (Qc) of 49.64 W and PMV of 0.09. Furthermore, compared with TOPSIS method, there were only 9 cases used in RSM method saving 74% of computation cost.

Mg Zn intermetallic layer on AZ31 alloy was prepared by solid–state thermal diffusion under 20 MPa pressure. The surface microstructure, microhardness and corrosion resistance of sample were investigated using X–ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM), microhardness tester and electrochemical workstation. As a result, the diffusion rate of Zn in AZ31 alloy with pressure was 10–fold higher than that of Zn without pressure, and Mg Zn intermetallic layer of 5 mm was produced at 390 °C within 2 h. The high–efficiency fabrication of Mg Zn intermetallic layer could be attributed to the increase of effective collision between Zn and Mg atoms by the application of pressure. During the fabrication procedure, microstructure evolution of Zn diffusion layer could be described as follow: Mg + Zn → Mg7Zn3 → MgZn + MgZn2. And the surface hardness as well as corrosion resistance of the sample first increased and then decreased after Zn diffusion treatment. For the first 1 h, Mg7Zn3 phase formed on AZ31 alloy, which raised the surface hardness to 220.0 HV0.2 and decreased corrosion current of AZ31 alloy about one order of magnitude in 3.5% NaCl solution. When the diffusion time was prolonged to 2 h, more complex phases (e.g., MgZn, MgZn2 and Mg7Zn3) were produced in the sample, and the voids and difference potentials among these Mg Zn intermetallic compounds led to the deterioration of surface hardness and corrosion resistance.

Due to the increased expectations on human thermal comfort in sleeping environments at a low energy consumption, task/ambient air condition system (TAC) can be the best air conditioning method when considering the immobility of a sleeping person. Previously, convection-based TAC systems for sleeping environments were developed, with an obvious inadequacy of cold-draft problem. Therefore, a new radiation-based TAC system (R-TAC) was previously developed and experimentally studied at a set of fixed design parameter for its radiant panel. Therefore, a follow-up numerical study on the effects of varying design/operating parameters of the radiant panel on indoor thermal comfort and energy saving performances has been carried out, and the study results reported in this paper. Firstly, a geometry model based on the experimental bedroom used in the previous experimental study, boundary conditions and numerical study cases are detailed. Secondly, the results of validating the numerical method using the previous experimental data are reported. Thirdly, the numerical results on indoor thermal comfort, energy saving and draft risk at different surface temperature and emissivity, area of the radiant panel, and the distance between the radiant panel and a bed are presented. The numerical results demonstrated that all the four design/operating parameters of the radiant panel can significantly affect thermal comfort and energy saving performances in the bedroom when using the R-TAC system: increasing surface temperature can lead to a higher PMV value and a higher EUC value; increasing surface emissivity and area of the radiant panel a lower PMV value and a lower EUC value; reducing the distance between the bed and the panel a lower PMV value and a higher EUC value. Finally, the DR values were at a very low level in all the study cases, indicating the cold draft problem encountered when using a convective heat transfer based TAC system for a sleeping environment can be effectively resolved when using the R-TAC system.

Task/ambient air conditioning (TAC) system is reported to be an energy efficient technology with available methods to control thermal comfortable level for sleeping environments. Better performance in energy saving for TAC systems in sleeping environment has been demonstrated in previous studies. However, it should be noticed that the building envelope thermal load affects the indoor thermal environment and operation of the air conditioning system due to the heat transfer through the envelope. The variation of indoor thermal environment will directly affect the performance of the TAC system, especially the set of operation parameters. Therefore, an optimization study on the TAC system operation considering the effects of envelope thermal load was carried out in this paper. Firstly, a full factorial design method was used to construct the simulation case matrix. Secondly, the models of the energy consumption and thermal comfort were established using operating parameters and envelope thermal load. Thirdly, comfort surface and comfort lines were obtained to calculate the optimum operating parameters at which the energy consumption was at the lowest. Finally, the energy consumption at the optimum status was calculated. The results show that the TAC system at the optimum status can save 1.4 to 1.7 kWh each night.

The use of task/ambient conditioning (TAC) systems can help improve thermal comfort and indoor air quality, and reduce the energy consumption in bedrooms in residences or guestrooms in hotels at nighttime for sleeping. However, its operational and energy saving performances would be affected by a number of factors, such as supply air flow rate and temperature, and supply vane angles. This paper reports on optimizing numerically the operating performances of a novel bed-based TAC system. Firstly, the methods on a novel bed-based TAC system are introduced, including the experimental method and the computational method. Secondly, the numerical model is validated using the experimental results at the experimental operating conditions. Thirdly, the operating performances of the novel bed-based TAC systems at non-experimental operating conditions using the validated numerical model are optimized and the results reported. Finally, the conclusion and limitations of the study are given. The numerical study results showed that by suitably controlling its supply air flow velocity and temperature, and supply vane angle, the bed-based TAC system can be operated to maintain an acceptable level of thermal comfort without the cold draft in an occupied zone at a low energy consumption.

There has been an increasing concern on thermal comfort in sleeping environments and its associated energy use in the past few years. To improve the thermal environment and to reduce energy use of air conditioning in bedrooms, applications of task/ambient air conditioning (TAC) systems were proposed and studied previously. It’s indicated that the TAC system can be well integrated with a bed. Due to the variation of the envelope heat gain in a bedroom during night, it is necessary to study the thermal environment inside a bedroom and the energy use of a TAC system for the bedroom at varying envelope thermal loads. Therefore, this paper reports on a numerical study on a TAC system applied to a bedroom with different envelope heat gains. The influences of envelope heat gain on energy consumption of the TAC system and the indoor thermal comfort were studied in this paper. The research results show that at supply air flow rate ( Q s ) of 50 l/s, energy consumption was increased from 47.78 W to 213.11 W, and the PMV value was increased from −1.69 to −1.29 with the increase in envelope heat gain from 3.11 W to 155.6 W. To make PMV equal to zero under different envelope heat gains, linear regression models between supply air parameters and PMV were built and solved. The obtained values form curves where PMV = 0 and give a guide for operation of the TAC system. It was found that the calculation of energy consumption on these curves depends only on envelope heat gain.

An experimental and numerical study on indoor air flow and moisture transport was performed in a bedroom with a task/ambient air conditioning (TAC) system. To better evaluate the characteristics of the TAC system, a traditional full volume (FAC) air conditioning system was also investigated. In the experimental study, the horizontal stratification of temperature distribution created by the air conditioning (A/C) system and the skin (surface) temperature of thermal manikin were reported, and the results suggested an acceptable thermal stratification and a higher nonuniformity of skin temperatures at the TAC system. In the numerical study, the air temperature and velocity fields demonstrated the effect of supply air and buoyancy driven flow inside the bedroom, and the removal of moisture near the thermal manikin.

The hollow direct Z–scheme photocatalyst CdS/BiVO4 with tunable loading amount of CdS was successfully fabrication by means of hydrothermal method. The photocatalytic experiment results show that CdS/BiVO4 heterostructure possessed superior photocatalytic activity toward RhB degradation and water splitting in comparison with bare BiVO4 and CdS. Under UV–vis light irradiation, 94.7% of RhB (15 mg/L, 100 mL) was degraded and 197.2 mmol g−1 of hydrogen production rate was obtained in the present of CdS/BiVO4 with 25% CdS content within 1 h. Based on the density functional theory calculation, PL spectra testing and electrochemical analysis, it is found that the internal electric field established between BiVO4 and CdS greatly suppressed the combination of photoinduced carriers, prolonged the lifetime of electron–hole pairs and maintained sufficient redox reaction driving force for photocatalytic reaction, which endowed admirable photocatalytic performance to the CdS/BiVO4 heterostructure.

In the subtropics, air conditioning (A/C) for a bedroom in residential buildings commonly serves to provide an appropriate indoor thermal environment at nighttime for sleeping. During daytime when A/C is not provided, a large amount of thermal energy can be stored in the thermal mass in its envelope components, in particularly its external walls. The energy stored would be gradually released, contributing significantly to the total space cooling load in the bedroom at nighttime. Therefore, this paper reports a simulation study on the impacts of daytime external envelope heat gain/storage on the nighttime cooling load in a hypothetic west-facing bedroom and the related mitigation measures in the subtropical Hong Kong. The study results showed that, among all envelope components, the west-facing external wall contributed most significantly to the total nighttime cooling load, because of its direct exposure to solar radiation, thus the heat gain and storage in its thermal mass. In addition, adding an air gap in the west-facing external wall can reduce remarkably the hourly total nighttime cooling load for the first hour (21:00–22:00) and the total cooling load for the 10-h A/C period. However, while varying the width of either the air gap or inside/outside concrete layers would not reduce cooling load further, ventilating mechanically the air gap can further increase the cooling load reduction and improve the flatness of load variation profile at the expense of consuming additional electrical energy. Finally, adhering aluminum foil to both sides of the air gap can further remarkably reduce nighttime cooling load, and improve the flatness of the load variation profile.

In this paper, the mechanical responses of a thick-walled functionally graded hollow cylinder subjected to uniform magnetic field and inner-pressurized loads are studied. Rather than directly assuming the material constants into some certain function forms as displayed in previous researches, we firstly give the volume fractions of different constituents of the FGM cylinder and then determine the expressions of material constants. By the use of the Voigt method the corresponding analytical solutions of displacements in radical direction, the strain and stress components and the perturbation magnetic field vector are derived by the following. In numerical part, the influences of volume fraction on displacement, stain and stress components and the magnetic perturbation filed vector are investigated; indicated by the results, we can conclude that the Poisson's ratio has a significant effect on the FGM cylinder's mechanical behaviors. Moreover, by some appropriate choices of the material constants it can be found that the obtained results in this paper can reduce to some special cases given in previous literatures., 31 pages, 14 figures and 50 conferences

A novel Proportional-Derivative (PD)law based Fuzzy Logic Controller (PFC) for a variable speed (VS) direct expansion (DX) air conditioning (A/C) system has been developed. There were two coupled control loops in this controller, i.e., varying supply fan speed to control indoor dry-bulb temperature ( T db ), and compressor speed indoor wet-bulb temperature ( T wb ). To weaken the coupling effect between the two loops, fuzzy logic principles were deployed. Furthermore, a PD law was used instead of a Proportional-Integral-Derivative (PID) law, in the PFC, which helped simplify not only calculation but also the structure of the PFC. The controller developed was validated by carrying out the controllability tests with the experimental conditions covering the normal operational range of a VS DX A/C system. The experimental results of the controllability tests suggested that the novel PFC developed is capable of realizing the simultaneous control of indoor temperature and humidity satisfactorily, in terms of control accuracy and sensitivity.

When the surface temperature of the outdoor coil in an air source heat pump (ASHP) unit is lower than both freezing point of water and the air dew point, frost can be formed and accumulated over outdoor coil surface. Frosting affects the energy efficiency, and periodic defrosting therefore is necessary. Reverse cycle defrosting is currently the most widely used defrosting method. A previous related study has indicated that during reverse cycle defrosting, downwards flow of the melted frost over a multi-circuit outdoor coil could affect the defrosting performance, without however giving detailed quantitative analysis of the effects. Therefore an experimental study on the effects has been carried out and a quantitative analysis conducted using the experimental data. In this paper, the detailed description of an experimental ASHP unit which was specifically built up is firstly reported. This is followed by presenting experimental results. Result analysis and conclusions are finally given.

Because of the increased expectations on thermal comfort and indoor air quality in sleeping environments at a low energy consumption, it is necessary to develop new air conditioning systems applied to sleeping environments. In recent years, a large number of studies on task/ambient air conditioning (TAC) have been carried out due to its excellent ventilation and energy saving performance. However, compared to full volume air conditioning (FAC), there exists an inadequacy on thermal control for TAC because cooled air is directly delivered to the space around a human body. Hence, the TAC and FAC systems have their own pros and cons in aspects of thermal, ventilation and energy saving performances, and the position of a supply outlet in an air conditioning (A/C) system significantly influences its operating performances. Therefore, a study on the performance evaluations of an A/C system installed in an experimental bedroom with its supply outlet positioned at five different heights has been carried out, and the study results are presented in this paper. The study results suggested that overall speaking, the A/C system performed the best at a supply air temperature of 23 °C, an air flow rate of 50 L/s and a fresh air flow rate of 13 L/s at H1100 setting, among all study cases. On the other hand, the A/C system performed the best at H800 setting among the five height settings.

Further to a previous experimental study on the inherent operational characteristics of an experimental variable speed (VS) direct expansion (DX) air conditioning (A/C) system at only two inlet air states, an experimental study using the same experimental VS DX A/C system at six different inlet air states to the DX A/C system has been carried out and the study results are presented in this paper. The results suggested that different inlet air states to a DX A/C system influenced the operational characteristic of the system, in terms of the Inherent Correlation (IC) between its output total cooling capacity (TCC) and Equipment sensible heat ratio (SHR). Therefore, a further data processing method was developed using regression, by which the ICs of the VS DX A/C system at non-test inlet air states can be predicted with adequate accuracy. This has therefore paved way to developing advanced control strategies for indoor thermal environment (i.e., air temperature and humidity) based on the known or predicted ICs within the possible operating ranges of inlet air temperature and humidity to the DX A/C system, for better control accuracy and energy efficiency.

To provide better indoor thermal comfort and indoor air quality in sleeping environments and to achieve greater energy saving, it is necessary to develop new air conditioning systems applied to sleeping environments. In recent years, a large number of studies have been carried out on the task/ambient air conditioning (TAC). To address a number of the inadequacies in a previous related study for a novel bed-based TAC system for sleeping environments, a ductless bed-based TAC system has been developed and its thermal, ventilation and energy saving performances have been experimentally evaluated, by comparing them with those of a full volume air conditioning (FAC) system. Firstly, an experimental setup at two different settings, a ductless bed-based TAC setting and a FAC setting, is presented. Secondly, the methods for measuring air dry-bulb and wet-bulb temperatures, air velocity and CO2 concentrations are reported and six groups of experimental conditions detailed. Finally, experimental results of thermal, ventilation and energy saving performances at the two settings are presented and analyzed. The experimental results demonstrated that using the ductless bed-based TAC could lead to a better ventilation performance and energy saving performance, but a poor thermal performance in terms of a higher draft risk than using the FAC system. It was possible to reduce the draft risk, while still maintaining an acceptable energy saving performance, by selecting a proper supply air temperature and air flow rate as well as a proper supply vane angle.

External wall insulation plays an important role in building energy consumption through affecting cooling and heating energy uses. In this paper, a study on the effects of external wall insulation thickness on annual cooling and heating energy uses under different Chinese climates is reported. Firstly, two indexes: Energy Gain Ratio (EGR) and Relative Variation Ratio (RVR) of the sum of annual cooling and heating energy uses, to assess the effects of external wall insulation thickness on energy saving potential are introduced. Secondly, a model space having four different exterior zones facing four different orientations in an office building is presented and the settings of the model space described. Lastly, the simulated annual cooling and heating energy uses for the four different exterior zones at different external wall insulation thicknesses under three different climates in China, Guangzhou, Shanghai and Beijing, are reported. The results suggested that energy saving was significant by increasing the external wall insulation thickness in exterior zones facing all orientations under Beijing’s climate, since the heating energy use was dominant and can be reduced remarkably with the increase in insulation thickness. Under Shanghai’s climate, increasing external wall insulation thickness to over 26 mm would not reduce the sum of annual heating and cooling energy uses in the south-facing exterior zone, but would help save energy in exterior zones facing the other three orientations. For all exterior zones under Guangzhou’s climate, it was, however, hardly possible to reduce the sum of annual heating and cooling energy uses by increasing the external wall insulation thickness.

Because of their excellent performance in local thermal environmental control, task/ambient conditioning (TAC) systems have attracted increasingly more research attention. However, the current applications of TAC systems are mainly for daytime activities, but seldom for nighttime. In fact, TAC systems may be best applied to a sleeping environment, since the subjects to be served by a TAC system are immobile during sleep. Therefore, there is a strong need for studying the operational and energy saving performance of TAC systems when applied to sleeping environments. This paper reports on an experimental study on evaluating the operational and energy saving performance of a novel bed-based TAC system. The experimental results and their analysis demonstrated that the use of the novel bed-based TAC system can help achieve energy saving, compared with the use of a full volume air conditioning (FAC) system. Considering the experimental limitations, the energy saving potential of the novel bed-based TAC system if used in an actual bedroom was studied through a theoretical analysis. It demonstrated that the novel bed-based TAC system would help achieve significant energy saving when used in real buildings.