Search

The pressure driven membrane-based air dehumidification technology is a promising energy-efficient technology for the air conditioning systems. To promote the engineering application of membrane dehumidification technology, factor significance analysis and multi-objective optimization of dehumidification membrane module were numerically investigated. Response surface method (RSM) was adopted to design the desired simulation cases and analyze the significance of five key factors, i.e., feed velocity, water vapor permeability coefficient, filling rate, fiber length, fiber diameter, on the membrane dehumidification characteristics. The second-order regression models of the dimensionless dehumidification amount per unit area (ma*) and the dehumidification rate (γ) were established based on the analysis of variance (ANOVA). It was found that the water vapor permeability coefficient has the most significant effect on γ and ma*. However, the dehumidification coefficient of performance (COP) and the frictional coefficient (f*Re) are hardly affected by the five independent factors. An average COP of 2.523 implies a good dehumidification efficiency of membrane module. As a multi-objective optimization method, the genetic algorithm was used for the membrane module optimization. The optimal solution represented by Pareto frontier is finally obtained in terms of γ and ma*. The optimized factor-level combination can be selected from the Pareto solution set according to the actual requirements of energy consumption and dehumidification efficiency.

This study aims to improve an H-Darrieus vertical-axis wind turbine (VAWT) by imposing a novel double-deflector design. A computational fluid dynamics (CFD) model was implemented to examine the aerodynamic characteristics of the VAWT with double deflectors. Geometrics factors related to the locations of the two deflectors were considered, and the orthogonal array based on the Taguchi method was constructed for CFD simulation. The CFD results were further provided as the training data for the artificial neural network (ANN) to forecast the optimal configuration. The results indicate that the performance of a VAWT with a double-deflector design could exceed that of a bare VAWT or that of one using a single deflector. The mean power coefficient for a bare VAWT is 0.37, although it could be much higher with a proper setup using double deflectors. The prediction of ANN analysis is consistent with the result of CFD simulation, in which the difference between the ANN prediction and CFD simulation is generally less than 4.48%. The result confirms the accuracy of the prediction of the optimal VAWT performance with a double-deflector design.

This study aims to optimize the flow channel design for a proton exchange membrane electrolyzer cell (PEMEC) to minimize the pressure drop across the cell. The pattern of parallel flow channels is considered with a dual-porous layer structure sandwiched between the flow channel plate and the catalyst layer. Four geometric factors are considered in the optimization analysis, including the width of the flow channel, the depth of the flow channel, the particle diameter of the large-pore porous layer, and the particle diameter of the small-pore porous layer. Computational fluid dynamics (CFD) is used to simulate the flow field, and based on the results of the CFD simulation, the Taguchi method is employed to analyze the optimal flow channel design. The importance of the factors is further analyzed by the analysis of variance (ANOVA) method. Three inlet velocities are assigned in the Taguchi analysis, which are 0.01, 0.1332, and 0.532 m/s, and then an orthogonal array is constructed and analyzed for each inlet flow condition. It is found that the optimal combination of the factors is the depth of the flow channel 1 mm, the width of the flow channel 3 mm, the particle diameter of the large-pore porous layer 0.212 mm, and the particle diameter of the small-pore porous layer 0.002 mm. The pressure drop across the PEMEC is minimized at the condition with the optimal combination of the factors. The ANOVA analysis shows that the depth of the flow channel exhibits the most significant impact on the pressure drop, while the other factors play minor roles only.

An accurate prediction for deep-buried ground heat exchangers (DBGHEs) is the premise for efficient utilization of geothermal energy. Due to the complexity of the geological composition spanning thousands of meters, the configuration of boundary conditions plays a critical role in evaluating DBGHE thermal performance. This paper proposed a three-dimensional model of full-scale DBGHE involving both conductive and convective heat transfer in aquifuge and aquifer layers. The constant inlet temperature and constant heating power boundaries in the DBGHE domain, and the surface–bottom temperature and heat flux boundaries in the rock-soil domain were examined. It was found that the differences in the performance prediction caused by different DBGHE boundary conditions were closely related to the system’s operating time. The relative differences in heat extraction amount and average borehole temperature of 2000 m DBGHE caused by the two inlet boundaries on the 30th day were, respectively, 19.5% and 18.3%, while these differences on the 120th day were decreased to 8.4% and 9.9%, respectively. It was found that the constant inlet temperature boundary was more appropriate than the constant heating power condition for estimating aquifer effects on the performance of DBGHE. For the rock-soil domain, the results showed that the heat extraction amount of DBGHE under the heat flux boundary was 12.6%–13.6% higher than that under the surface–bottom temperature boundary. Particularly, when considering the velocity change of groundwater in the aquifer, the relative difference in heat extraction amount increments caused by the two types of rock-soil boundaries can reach 26.6% on the 120th day. It was also found that the thermal influence radius at the end of a heating season was hardly affected by either the DBGHE inlet or rock-soil domain boundary conditions.

Gas membrane separation technology is widely applied in different industry processes because of its advantages relating to separation performance and economic efficiency. It is usually difficult and time consuming to determine the suitable membrane materials for specific industrial separation processes through traditional experimental research methods. Molecular simulation is widely used to investigate the microscopic morphology and macroscopic properties of materials, and it guides the improvement of membrane materials. This paper comprehensively reviews the molecular-level exploration of the dominant mechanism and influencing factors of gas membrane-based separation. The thermodynamics and kinetics of polymer membrane synthesis, the molecular interactions among the penetrated gases, the relationships between the membrane properties and the transport characteristics of different gases in the composite membrane are summarized and discussed. The limitations and perspectives of the molecular simulation method in the study of the gas membrane separation process are also presented to rationalize its potential and innovative applications. This review provides a more comprehensive reference for promoting the materials’ design and engineering application of the gas separation membrane.

The development of electric vehicles plays an important role in the field of energy conservation and emission reduction. It is necessary to improve the thermal performance of battery modules in electric vehicles and reduce the power consumption of the battery thermal management system (BTMS). In this study, the heat transfer and flow resistance performance of liquid cold plates with serpentine channels were numerically investigated and optimized. Flow rate (m˙), inlet temperature (Tin), and average heat generation (Q) were selected as key operating parameters, while average temperature (Tave), maximum temperature difference (ΔTmax), and pressure drop (ΔP) were chosen as objective functions. The Response Surface Methodology (RSM) with a face-centered central composite design (CCD) was used to construct regression models. Combined with the multi-objective non-dominated sorting genetic algorithm (NSGA-II), the Pareto-optimal solution was obtained to optimize the operation parameters. The results show that the maximum temperature differences of the cold plate can be controlled within 0.29~3.90 °C, 1.11~15.66 °C, 2.17~31.39 °C, and 3.43~50.92 °C for the discharging rates at 1.0 C, 2.0 C, 3.0 C, and 4.0 C, respectively. The average temperature and maximum temperature difference can be simultaneously optimized by maintaining the pressure drop below 1000 Pa. It is expected that the proposed methods and results can provide theoretical guidance for developing an operational strategy for the BTMS.

Intraocular surgery is tabooed in retinoblastoma management, due to the concern of lethal extraocular spread. We reviewed the outcomes of consecutive children with intraocular retinoblastoma diagnosed at 29 Chinese centers between 2012–2014. We compared the outcomes of three categories of treatment: eye salvage including tylectomy (Group I), eye salvage without tylectomy (Group II), and primary enucleation (Group III). A total of 960 patients (1243 eyes) were diagnosed: 256 in Group I, 370 in Group II, and 293 in Group III; 41 patients abandoned treatment upfront. The estimated 5-year overall survivals (OS) were, for Group I, 94%, for Group II 89%, and for Group III 95%. The estimated 5-year disease-specific survivals (DSS) were, for Group I, 96%, for Group II 90%, and for Group III 95%. Patients in Group I had a significantly higher 5-year DSS than patients in Group II (p = 0.003) and not significantly different than patients in Group III (p = 0.367). Overall survival was not compromised by the inclusion of tylectomy in eye salvage therapy compared to eye salvage without tylectomy or primary enucleation. Disease-specific survival was better when tylectomy was included in eye salvage treatments. Tylectomy as part of multimodal treatment may contribute to the care of retinoblastoma patients with chemotherapy-resistant tumor, eyes with concomitant ocular complications, or at the risk of treatment abandonment.

A hybrid air-conditioning system has been proposed by integrating an indirect evaporative pre-cooling unit. In the proposed system, the room exhaust air is employed in the indirect evaporative cooler (IEC) to pre-condition the ambient intake air. The mathematical formulation has been judiciously established for the pre-cooling IEC. The validation of the numerical model has been conducted by comparing the simulated results with the experimental data in terms of the outlet temperature and the heat flux along the heat exchanger surface. The pre-cooling performance of the IEC is theoretically investigated for the climate in representative cities selected from five different climate zones. The psychrometric illustration of the air conditioning variation has indicated that the ambient air can be pre-cooled and pre-dehumidified through the IEC. The possibility of water vapor condensation depends on the humidity ratio of the ambient intake air. The simulation result demonstrates the capability of the pre-cooling IEC to fulfill part of the cooling load of the ambient intake air resulting in a marked energy saving potential.

Background The prevalence of ocular abnormalities of newborn in China has seldom been reported. To report the implementation of digital imaging in ocular screening of all newborns in multiple centres in China and to describe the abnormal findings of fundus examination, we did the cross-sectional study. Methods Fundus examinations were performed on newborns within the 42 days after birth using a RetCam wide-field digital imaging system. Digital images of the posterior pole, superior, nasal and temporal retinal fields of each participant were taken. All newborns were from eights centres across China from January 2009 to July 2017. Results A total of 199 851 newborns were included in the study. We detected 18 198 (9.11%) abnormal cases. The most frequent abnormality was severe retinal haemorrhage (RH) found in 12 810 cases (6.41%). The other anomalies included familial exudative vitreoretinopathy, retinopathy of prematurity, abnormal fundus pigmentation, subconjunctival haemorrhage, choroidal coloboma, idiopathic retinal venous tortuosity, exudative changes and other anomalies with uncertain identities. Conclusion This large-scale study of newborn fundus examination showed a relatively high prevalence of ocular abnormalities. Hundreds of neonates with rare disorders that severely impair ocular health were also detected at an early age. The long-term impact of other anomalies including RHs on the ocular system should be investigated by a perspective study. Our study suggested that fundus examination of newborns can play a beneficial role in ocular health. [ABSTRACT FROM AUTHOR]

Biomass hot blast stove is one energy source which is aimed to provide clean hot air, it is widespread and has great potential for being generated from biomass. Under the equal condition of heating load between biomass hot blast stove and natural gas blast stove, this paper investigated the economic feasibility and adaptability of a method that using biomass hot blast stove instead of natural gas blast stove. Based on the technological process and the design parameters demand such as air supply temperature, heating capacity, air flow volume of the existed natural gas hot blast stove heating project, the mathematical model and some indexes for evaluating the technical and economic feasibility of the biomass heating way were established, the difference of the technical maturity, initial investment, annual operating cost, operation maintenance, operational risk and allowance policy within the two heating way were comparative analysed, the sensitivity of factors influencing annual total investment of the biomass hot blast stove was analysed. The results show that, the ratio represented by QZs/QZt of annual total investment between biomass hot blast stove and natural gas hot blast stove was only 0.56 under the equal heating load, the sensitivity of factors influencing annual total investment of the biomass hot blast stove was the biomass fuel, and the many problems about biomass hot blast stove like the technology is still immature, operational risk is relatively large, policy direction is unclear, regional differences and other factors were existence. If the operation of the biomass hot blast stove is safety and the biomass fuel of the biomass hot blast stove is plenty, we will recommend using biomass hot blast stove when the ratio of QZs/QZt was less than 1, and using natural gas blast stove when the ratio of QZs/QZt was more then 1. [ABSTRACT FROM AUTHOR]

The ancient architectures of tower buildings type are representative in ancient architectures in Beijing, and compared with other types of ancient architectures, they are characterized by long distance from ground, high height of building itself, and large inner space. For the ancient architectures of tower buildings type, a proposal using floor-type fan coil air-conditioner for control of physical environment is suggested, and simulation calculation for indoor temperature field for one ancient architecture of tower building in Beijing is done using CFD software, with calculation content comprising the indoor temperature field and velocity field when the system is used in summer. The result shows that: adopting floor-type fan coil air-conditioner for summer conditions and adjusting blast amount of fan coil and blasting parameters can make air temperature agreeable and comfortable. [ABSTRACT FROM AUTHOR]

Fog and haze weather has seriously affected many important aspects of human life and physical fitness. In order to improve air quality, local government has transformed coal-fired heating into clean energy heating in Beijing rural areas. This paper introduces three typical clean energy heating systems which are low temperature air source heat pump (LTASHP), thermal storage heater (TSH) and wall-mounted gas furnace (WGF), researches and tests the practical operation situation of three heating systems in the field. To compare technical and economic feasibility of three heating systems, the paper takes such residence where energy-saving standard of building palisade structure is approximately 50% as the research object, and establishes technical and economic mathematical analysis models, compares primary energy consumption and carbon dioxide emissions of three heating systems. This paper adopts annual cost approach, comprehensively takes into account power capacity increasing tariff and gas pipe network construction fee, and compares initial investment, operation cost and annual cost of three heating systems respectively from the perspective of users and government. The results show that LTASHP is the most energy-saving and its annual cost is lowest in the three heating systems. LTASHP is the most suitable alternative solutions to coal-fired heating in the three heating systems in rural Beijing. [ABSTRACT FROM AUTHOR]

The polyethylene glycol (PEG-1000) was selected as phase change material (PCM) and the expanded perlite (EP), the granular activated carbon(GAC), the powdered activated carbon (PAC) and the expanded graphite (EG) were selected as porous adsorption materials. The composite phase change material (CPCM) was prepared by the physical adsorption method. The composite phase change materials compound with the polyethylene glycol and the expanded graphite were picked by comparing and analyzing the adsorption capacity of such four types of porous materials. And then the composite building material for thermal storage mixed with the CPCM and the cement, water-reducer, early strength agent was prepared in the pressure condition of -0.05Mpa and the constant temperature condition of 70°C. Its thermal physical properties, the structural stability and the compression resistance capability of different quality proportion specimens were experimental researched. The results show that such composite building materials with CPCM appears light density, high thermal conductivity, large heat storage capacity and good stability, and its compression resistance capability can satisfy the requirement of ordinary mortar building material. [ABSTRACT FROM AUTHOR]

This study focuses on the heat transfer between the vertical concentric tubes buried underground and the medium-deep rock-soil geothermal energy. The numerical simulation based on an in-house FORTRAN computation program was performed to analyze the mechanism of heat exchange underground. The program was shown to predict the test results of outlet water temperature and heat gain very well under the corresponding operating conditions when engineering data of an actual geothermal well were obtained to validate the numerical scheme. The effects of inlet water temperature and flow rate on the heat exchanger performance were also analyzed in detail. The comparison indicated that the present numerical scheme is able to predict the heat transfer performance of extremely long ground-coupled heat exchanger subject to various geothermal conditions. [ABSTRACT FROM AUTHOR]

The sewage flow rate of the urban drainage system is relatively large and generally stable, its sewage temperature range varies relatively lightly and maintains 10~15? in winter. The sewage in the drainage system can be the low grade thermal source for building heating and cooling. Sewage source heat pump technology can efficiently extract or discharge the amount of heat from the sewage in the drainage system for building heating or cooling. The field test of the actual operation thermal performance of the sewage source heat pump were carried out and investigated. The sewage source heat pump system were continuously measured for 72 hours. Based on the test datum, the average COP of the heat pump was 4.5. The relationship between energy consumption of system and energy consumption of transportation are analyzed. The analysis shows that the pump of this system cannot match the load change well and the use of variable frequency pump can improve the energy efficiency of the system. Before the use of the sewage source heat pump system, the traditional coal-fired boiler and air-cooled chiller are the heating and cooling system of this building. Compared with the traditional coal-fired boiler and air-cooled chiller, the advantages of sewage source heat pump system in energy saving, economy and environmental protection are analyzed. The results show that: Compared with the original system, direct heat exchange type sewage source heat pump system can save 53% of the primary energy consumption, reduce the annual operating cost by 11%, increase the initial investment by a factor of 14.3%, and the payback period of incremental investment is about 4.7 years. This method not only has better energy saving, saving capital benefit, but also can reduce the local pollutant emission, and has better environmental emission reduction benefits. [ABSTRACT FROM AUTHOR]

The lithium ion battery has been widely applied in the fields of electric vehicles and electronic products due to its advantages of high power density, long lifespan and low self-discharging, etc. In this study, two lithium ion batteries are adopted to explore the effects of different thermal conditions on battery's performance. One of thermal conditions makes battery close to adiabatic condition similar to the thermal condition of battery pack without any thermal management system. Another thermal condition is constant temperature condition employed to simulate the thermal condition of battery pack with thermal management system. The experimental results show that (i) next chargeable capacities of these batteries are dependent on the previous dischargeable capacities for all thermal conditions; (ii) dischargeable capacities of these batteries markedly decrease with the increase of the discharge rates under 20°C constant temperature condition; (iii) dischargeable capacities are independent on discharge rates under close to adiabatic condition because the obvious battery temperature rise can offset the adverse effects of higher discharge rates on battery's performance. Although higher battery temperature is conductive to weaken or eliminate the adverse effects of higher discharge rates, excessively high temperature can also accelerate battery aging and easily cause battery thermal runaway, which indicates that it is necessary for battery pack with thermal management system to control thermal conditions of batteries. [ABSTRACT FROM AUTHOR]

The radiant cooling air conditioning system has been widely applied, due to its features of better thermal comfort and efficient energy-saving. Most of the research on radiant cooling air conditioning system tends to concentrate on its cooling performance and energy-saving potential. However, the design methods of radiant cooling air conditioning system to guide its engineering application are rare. On the basis of the simplified human thermal balance equation and the linear relationship between the sensible heat loss and human thermal comfort achieved in our previous studies, the cooling performance of cooled surface is analyzed and then the method for determining the area of cooled surface is proposed in this paper. The numerical model is validated by experimental data and the calculation methods of cooled area are investigated with different boundary conditions. In addition, the PMV values in different heights and around human body are analyzed in detail. The results show that the calculation methods on account of the features of cooled surface could accurately predict the cooled area to maintain human thermal comfort under different conditions. Therefore, it is possible to determine the area of cooled surface in view of the relationship between human thermal comfort and thermal balance. This study could provide the guidelines for both the assessment of human thermal comfort and the system design of radiant cooling air conditioning system. [ABSTRACT FROM AUTHOR]

Subglacial water bodies are critical components in analyzing the instability of the Antarctic ice sheet. Their detection and identification normally rely on geophysical and remote sensing methods such as airborne radar echo sounding (RES), ground seismic, and satellite/airborne altimetry and gravity surveys. In particular, RES surveys are able to detect basal terrain with a relatively high accuracy that can assist with the mapping of subglacial hydrology systems. Traditional RES processing methods for the identification of subglacial water bodies mostly rely on their brightness in radargrams and hydraulic flatness. In this study, we propose an automatic method with the main objective to differentiate the basal materials by quantitatively evaluating the shape of the A-scope waveform near the basal interface in RES radargrams, which has been seldom investigated. We develop an automatic algorithm mainly based on the traditional short-time Fourier transform (STFT) to quantify the shape of the A-scope waveform in radargrams. Specifically, with an appropriate window width applied on the main peak of each A-scope waveform in the RES radargram, STFT shows distinct and contrasting frequency responses at the ice-water interface and ice-rock interface, which is largely dependent upon their different reflection characteristics at the basal interface. We apply this method on 882 RES radargrams collected in the Antarctic’s Gamburtsev Province (AGAP) in East Antarctica. There are 8822 identified A-scopes with the calculated detection value larger than the set threshold, out of the overall 1,515,065 valid A-scopes in these 882 RES radargrams. Although these identified A-scopes only takes 0.58% of the overall A-scope population, they show exceptionally continuous distribution to represent the subglacial water bodies. Through a comprehensive comparison with existing inventories of subglacial lakes, we successfully verify the validity and advantages of our method in identifying subglacial water bodies using the detection probability for other basal materials of theoretically the highest along-track resolution. The frequency signature obtained by the proposed joint time–frequency analysis provides a new corridor of investigation that can be further expanded to multivariable deep learning approaches for subglacial and englacial material characterization, as well as subglacial hydrology mapping.

Characterizing acoustic waveguide channels is becoming important for the development of communication and signal processing applications across diverse fields ranging from urban water supply systems to oil and gas distribution pipeline networks. These applications include sonar and transmission systems in support of leak detection, blockage location, sensing, monitoring, and signaling for example. In this paper, we provide experimental results and models for the wideband channel characterization of acoustic waveguides formed from gas and water pipelines over the 1-50 kHz frequency band. Experimental results are provided for two straight pipe systems comprising an acrylic pipe filled with air and a steel pipe filled with water. A mode-based analytical model for predicting acoustic wave propagation in rigid and elastic pipes is proposed with deterministic and stochastic characteristics both considered. Good matching is demonstrated between the model predictions and experimental results in terms of dispersion curves, channel spectrograms, and delay spread. A key finding is that acoustic waveguides filled with water should be treated as elastic pipes, and they have significantly different characteristics from those filled with gas, which can usually be treated as rigid pipes. Furthermore for the steel-water waveguide pipeline, link budget calculations and noise power spectral density measurements reveal that a communication range of more than 50 m can be obtained.

This paper reports the results of an experimental investigation on the heat transfer performance of metal foam as a heat sink subjected to oscillating flow. The measured pressure drops, velocities, and surface temperatures of oscillating flow through aluminum 40 PPI foam are presented in detail. The calculated cycle-averaged local temperatures and Nusselt numbers for different kinetic Reynolds numbers were analyzed. The variation of total heat transfer rate with a kinetic Reynolds number suggests that oscillating flow at relative low frequency has a substantial effect on heat transfer enhancement in a metal foam heat sink. A comparison of the length-averaged Nusselt numbers between oscillating and steady flows indicates that higher heat transfer rates can be obtained in metal foams subjected to oscillating flow. The relation between pumping power and total heat transfer rates for the oscillating flow cooling system was also analyzed with a view to designing a novel heat sink using metal foam. The results show that high heat transfer performance of metal foam heat sinks subject to oscillating flow can be obtained with moderate pumping power. [ABSTRACT FROM AUTHOR]