To apply the fire modelling for the fire engineer with symbolic mathematics,the key equations of a zone model were demonstrated. There were thirteen variables with nine constraints,so only four ordinary differential e...To apply the fire modelling for the fire engineer with symbolic mathematics,the key equations of a zone model were demonstrated. There were thirteen variables with nine constraints,so only four ordinary differential equations (ODEs) were required to solve. A typical fire modelling with two-room structure was studied. Accordingly,the source terms included in the ODEs were simplified and modelled,and the fourth Runge-Kutta method was used to solve the ordinary differential equations (ODEs) with symbolic mathematics. Then a zone model could be used with symbolic mathematics. It is proposed that symbolic mathematics is possible for use by fire engineer.展开更多
The cooling and heating load distribution of large area air-conditioned room such as “open” offices, shopping malls and waiting rooms is usually assumed to be even in air conditioning system design. However, it is n...The cooling and heating load distribution of large area air-conditioned room such as “open” offices, shopping malls and waiting rooms is usually assumed to be even in air conditioning system design. However, it is not the case in reality, and a low efficient air conditioning system results from this assumption. A simulation and analysis of the cooling load distribution of an office building in Hong Kong with TRANSYS software is provided in this paper. A typical office is divided into 13 zones for simulation, including external zone, medial zone and internal zone in the north, the south, the east and the west respectively and a central zone, instead of 4 directional zone. The result shows there is much cooling load difference between each zone, and more attention should be paid to uneven indoor cooling and heating load distribution to further guide the design.展开更多
To determine the oxygen concentration variation in ullage that results from dissolved oxygen evolution in an inert aircraft fuel tank,the CFD method with a mass transfer source is applied in the present study.An exper...To determine the oxygen concentration variation in ullage that results from dissolved oxygen evolution in an inert aircraft fuel tank,the CFD method with a mass transfer source is applied in the present study.An experimental system is also designed to evaluate the accuracy of the CFD simulations.The dissolved oxygen evolution is simulated under different conditions of fuel load and initial oxygen concentration in ullage of an inert fuel tank with stimulations of heating and pressure decrease.The increase in the oxygen concentration in ullage ranges from 0.82%to 5.92%upon stimulation of heating and from 0.735%to 12.36%upon stimulation of a pressure decrease for an inert ullage in the simulations.The heating accelerates the release of the dissolved oxygen from the fuel by increasing the mass transfer rate in the mass transfer source and decreasing the pressure,thereby accelerating the dissolved oxygen evolution by increasing the concentration difference between the gas and the fuel.The time constant that represents the oxygen evolution rate is independent of the initial oxygen concentration in ullage of an inert tank but depends closely on the fuel load,temperature and pressure.The time constant can be fitted using a polynomial equation relating the fuel load to temperature in the heating stimulation with an accuracy of 4.77%.Upon stimulation of a pressure decrease,the time constant can be expressed in terms of the fuel load and the pressure,with an accuracy of 5.02%.展开更多
Existed evidences show that airborne transmission of human respiratory droplets may be related with the spread of some infectious disease, such as severe acute respiratory syndrome （SARS） and H1N1 pandemic. Non-phar...Existed evidences show that airborne transmission of human respiratory droplets may be related with the spread of some infectious disease, such as severe acute respiratory syndrome （SARS） and H1N1 pandemic. Non-pharmaceutical approaches, including ventilation system and personal protection, are believed to have certain positive effects on the reduction of co-occupant＇s inhalation. This work then aims to numerically study the performances of mouth covering on co-occupant＇s exposure under mixing ventilation （MV）, under-floor air distribution （UFAD） and displacement ventilation （DV） system, using drift-flux model. Desk partition, as one generally employed arrangement in plan office, is also investigated under MV. The dispersion of 1, 5 and 10 grn droplet residuals are numerically calculated and CO2 is used to represent tracer gas. The results show that using mouth covering by the infected person can reduce the co-occupant＇s inhalation greatly by interrupting direct spread of the expelled droplets, and best performance can be achieved under DV since the coughed air is mainly confined in the microenvironment of the infected person. The researches under MV show that the two interventions, mouth covering and desk partition, achieve almost the sarae inhalation for fine droplets while the inhalation of the co-occupant is lower when using mouth covering for large droplets.展开更多
As only about 15% of the total time of people in Hong Kong was spent outdoors, it would be more valuable if the associated effectiveness and impact of the recently proposed abatement measures could be expressed in ter...As only about 15% of the total time of people in Hong Kong was spent outdoors, it would be more valuable if the associated effectiveness and impact of the recently proposed abatement measures could be expressed in terms of the improvement in the total exposure levels. This paper uses an exposure assessment model developed from the local microenvironment concentration data together with our surveyed time activity patterns to evaluate the effectiveness of the proposed air pollution abatement policy. Prior to the enforcement of abatement measures, about 2.5% of the young group and 1.2% of the adult group having their exposure levels exceeded that defined by the current 8-hour PM10 standard (180 μg/m3). With the enforcement of abatement measures, only 0.3% of the adult group would be restored to a safe level.展开更多
The strategy of adopting cheap precursors or abundant resources,which can be obtained directly from nature,is a simple and excellent method of introducing accessible research into environmentally friendly development....The strategy of adopting cheap precursors or abundant resources,which can be obtained directly from nature,is a simple and excellent method of introducing accessible research into environmentally friendly development.Moreover,this is also an urgent requirement for the sustainable development of green technology.Herein,we introduce a simplistic and expandable method to prepare metal-free biomassderived nitrogen self-doped porous activation carbon(N-PAC) with large specific surface area(S_(BET)=1300.58 m^(2)/g).Moreover,the manufactural electrocatalysts exhibit prominent oxygen reduction reaction(ORR) performance in all PH values.As compared with the commercial Pt/C catalyst,the N-PAC/800 with a positive onset potential at 10 mA/cm^(2)(0.93 V),half-wave potential(0.87 V),and limiting current(6.34 mA/cm^(2)) bring to light excellent catalytic stability,selectivity,and much-enhanced methanol tolerance.Furthermore,the prepared electrocatalysts possess considerable hydrogen evolution reaction(HER) performance with a less onset potential of 0.218 V(acidic medium) and0.271 V(alkaline medium) respectively,which can show similar catalytic activity across the whole pH range.Such bifunctional electrocatalyst,with excellent electrocatalytic properties,resource-rich,low cost,and environmental-friendly,hold a promising application in energy conversion and reserve.展开更多
This study aims to develop a paraffin-based phase change material(PCM) emulsion with a low extent of supercooling for thermal energy storage(TES) systems to improve the cooling efficiency.Hexadecane-water emulsions we...This study aims to develop a paraffin-based phase change material(PCM) emulsion with a low extent of supercooling for thermal energy storage(TES) systems to improve the cooling efficiency.Hexadecane-water emulsions were prepared and characterized. Multi-wall carbon nanotubes(MWCNTs) were dispersed in the emulsion as a nucleating agent to reduce the supercooling. The MWCNTs were chemically modified with carboxyl groups to improve the dispersion of the tubular particles in the organic liquid. Thermal analyses of the emulsions by differential scanning calorimeter(DSC) indicated that the extent of supercooling was significantly reduced. The concentration of the nucleating agent for an effective supercooling suppression as found to be very low, in agreement with previous findings, and there appeared to be a minimum concentration for the supercooling reduction.展开更多
In view of the practical importance of the heat transfer devices in various thermal engineering fields including chemical and nuclear engineering,this study aims at developing an effective method of heat transfer enha...In view of the practical importance of the heat transfer devices in various thermal engineering fields including chemical and nuclear engineering,this study aims at developing an effective method of heat transfer enhancement by using selfrotating twisted tapes(SRTTs)and Al_(2)O_(3) nanoparticles.The effect of the selfrotating twisted tapes and Al2O3 nanoparticles on the thermal performance was comprehensively investigated in a circular pipe.The experimental results indicated the heat transfer rate was effectively improved by SRTTs in comparison of plain tube.In addition,the heat transfer multiplier with SRTTs decreased from 1.38 to 1.08 with the Reynolds number increasing from 19,322 to 64,407,while the friction factor multiplier decreased from 1.61 to 1.32.Besides,the results indicated that the employment of Al_(2)O_(3) nanoparticles and SRTTs demonstrated superior thermal performance to the single SRTTs.As Reynolds number increases from 19,322 to 64,407,the heat transfer multiplier decreased from 2.08 to 1.18 in the mass concentration of 3.0%and from 1.38 to 1.08 in mass concentration of 0.0%.Finally,the new heat transfer and friction factor correlations considering the combined effect of Al2O3 nanoparticle and SRTTs were developed within 10%deviation of experimental values.展开更多
The duct static pressure reset (DSPR) control method is a popular modern control method widely applied to variable air volume (VAV) systems of commercial buildings. In this paper, a VAV system simulation program was u...The duct static pressure reset (DSPR) control method is a popular modern control method widely applied to variable air volume (VAV) systems of commercial buildings. In this paper, a VAV system simulation program was used to predict the system performance and zone air temperature of two kinds of layouts that were applied to a typical floor of an existing building office in Hong Kong. The position where the static pressure sensor was placed should affect the zones temperature and energy consumption. The comparison of predictions of the two kinds of layouts indicates that with the same DSPR control method the layout of the air duct might influence the fan control result and energy savings.展开更多
Ground-coupled heat pumps(GCHP)are commonly used in residential heating system.To mitigate the boreholes temperature dropping with operating time,a new exhaust-air recharging system is developed.The new recharging sys...Ground-coupled heat pumps(GCHP)are commonly used in residential heating system.To mitigate the boreholes temperature dropping with operating time,a new exhaust-air recharging system is developed.The new recharging system can be used in three operational modes.In this paper,a ground-coupled heat recovery ventilation(HRV)model is discussed.A thermal model is set up to find the optimal brine flow rate and heat transfer allocation ratio between exhaust and supply coils for maximum heat recovery efficiency.Contrary to the conventional liquid-loop HRV systems,the brine temperature entering the exhaust coil never goes blow zero(0℃),and hence defrosting is needless in the ground-coupled HRV system.This can make the ground-coupled HRV system over 20% more efficient than a conventional HRV system at low outdoor temperatures.展开更多
The expression of the Maxwell magnetic monopole was employed to correlate the space to space projection that gives rise to the Gell-Mann standard model, and space to time projection which gives the leptons;and how doe...The expression of the Maxwell magnetic monopole was employed to correlate the space to space projection that gives rise to the Gell-Mann standard model, and space to time projection which gives the leptons;and how does it correlate to the Perelman mappings from the homogeneous 5D manifold to the Lorentz 4D manifold, together with correlating the physical consequences caused by the breaking of the Diagonal Long Range Order [DLRO] of the monopoles quantum states affected by the motion of massive particles in the Lorentz 4D boundary of the 5D manifold, which leads to gravitons and the gravity field via the General Relativity covariant Riemannian 4D curvatures metric equation.展开更多
A summary of the homogeneous 5D universe model is expressed in the Dirac second-order quantized representation for the magnetic monopoles, identified in terms of the Higgs Bosons, and through systematic ordered excita...A summary of the homogeneous 5D universe model is expressed in the Dirac second-order quantized representation for the magnetic monopoles, identified in terms of the Higgs Bosons, and through systematic ordered excitations of the Higgs vacuum obtained the non-homogeneous 4D Lorentz manifolds filled with masses, corresponding to making space dimension reduction projections, and thus realization of Newtonian gravity, followed by the 3D space symmetry breaking into 2D × 1D that produces the Perelmann-entropy and Ricci-Flow mappings, resulting in the realization of Poincare spheres, represented by nucleus such as Carbon 12, all the way to stars, and matter filled discs, such as stars in galaxies and 2D carbon-based molecular structures like nitrogenous bases. Finally, the forming of RNAs and DNAs, then life forms.展开更多
The technological advances in Lithium-ion batteries have created many new applications, including electric vehicles. In this short note, we shall explain in simple terms the basic physics why and how it is possible to...The technological advances in Lithium-ion batteries have created many new applications, including electric vehicles. In this short note, we shall explain in simple terms the basic physics why and how it is possible to have high energy capacity in Lithium-ion batteries. However, heating has been a common problem and without appropriate design, they might give fire and explosion as reported.展开更多
The main objectives were to (1) calculate the total volatile organic compounds (TVOCs) inhalation dose, (2) analyze the proportions of human’s inhaled contaminant dose from different sources, and (3) present a newly ...The main objectives were to (1) calculate the total volatile organic compounds (TVOCs) inhalation dose, (2) analyze the proportions of human’s inhaled contaminant dose from different sources, and (3) present a newly defined ratio of relative inhalation dose level (RIDL) to assess indoor air quality (IAQ). A user defined function based on CFD (computational fluid dynamics) was developed, which integrated human motion model with TVOCs emission model in a high sidewall air supply ventilation mode. Based on simulation results of 10 cases, it is shown that the spatial concentration distribution of TVOCs is affected by human motion. TVOCs diffusion characteristic of building material is the most effective way to impact the TVOCs inhalation dose. From the RIDL index, case A-2 has the most serious IAQ problem, while case D-1 is of the best IAQ.展开更多
The combined use of dry cooling(DC) system and dedicated ventilation(DV) system to decouple cooling and dehumidification process for energy efficiency was proposed for subtropical climates like Hong Kong. In this stud...The combined use of dry cooling(DC) system and dedicated ventilation(DV) system to decouple cooling and dehumidification process for energy efficiency was proposed for subtropical climates like Hong Kong. In this study, the energy performance and condensation risk of the use of DCDV system were examined by analyzing its application in a typical office building in Hong Kong. Through hour-by-hour simulation using actual equipment performance data and realistic building and system characteristics, it was found that with the use of DCDV system, the annual energy consumption could be reduced by 54% in comparison with the conventional system(constant air volume with reheat system). In respect of condensation risk, it was found that the annual frequency of occurrence of condensation on DC coil was 35 h. Additional simulations were conducted to examine the influence of different parameters on the condensation risk of DCDV system. Measures to ensure condensate-free on DC coil were also discussed.展开更多
Taking public transit facilities (PTFs) is the major transport style in Hong Kong. Human exposure to indoor air pollutants may cause adverse health effects to the passengers. Exposure assessment on air pollutants is i...Taking public transit facilities (PTFs) is the major transport style in Hong Kong. Human exposure to indoor air pollutants may cause adverse health effects to the passengers. Exposure assessment on air pollutants is important for the control of human diseases caused by indoor air pollution. In this paper, the indoor PM10, CO and CO 2 levels in various PTFs, such as public bus, subway, railway and ferry in Hong Kong, were mea- sured. Combining with the time budget survey of Hong Kong population,the human exposures were calculated through Monte-Carlo simulation.展开更多
With a self-similar parameter b（At） = Hi/λi, where At is the Atwood number, Hi and λi are the a.mplluae and wavelength of bubble （i = 1） and spike （i = 2） respectively, we derive analytically the solutions to ...With a self-similar parameter b（At） = Hi/λi, where At is the Atwood number, Hi and λi are the a.mplluae and wavelength of bubble （i = 1） and spike （i = 2） respectively, we derive analytically the solutions to the buoyancy-drag equation recently proposed for dynamical evolution of Rayleigh-Taylor and Richtmyer-Meshkov mixing zone. Numerical solutions are obtained with a simple form ofb（At）--- 1/（1 ＋ At） and comparisons with recent LEM （linear electric motor） experiments are made, and an agreement is found with properly chosen initial conditions.展开更多
A novel experimental setup was developed to study the heat extraction of geothermal heat exchanger(GHE)in different operational modes under adiabatic and isothermal boundaries.The experimental setup consists of a sand...A novel experimental setup was developed to study the heat extraction of geothermal heat exchanger(GHE)in different operational modes under adiabatic and isothermal boundaries.The experimental setup consists of a sand trunk,a tailored water chiller,a natural cold source unit,two water boxes containing hot water and cool water,and a data acquisition system.The experimental results indicate that the volume flow rate of the entering water is a main factor affecting the heat extraction;furthermore,the heat extraction value per meter pipe decreases gradually along the heat extraction pipe and increases with the increase of the incoming water volume flow rate.Therefore,this novel experimental setup may be helpful to further study the operation performance of GHE in different types of soil.展开更多
Side branch Helmholtz resonators (HRs) are widely used to control low frequency tonal noise in air duct system. The passive Helmholtz resonator only works effectively over a narrow frequency range around resonance fre...Side branch Helmholtz resonators (HRs) are widely used to control low frequency tonal noise in air duct system. The passive Helmholtz resonator only works effectively over a narrow frequency range around resonance frequency. Changes in the exciting frequency and temperature will decrease the noise reduction performance. Many studies have been conducted on incorporating a Helmholtz resonator with active noise control to tuning the resonance frequency of HRs. The objective of this study is to study the effect of flow on the semi active Helmholtz resonator for duct noise control. Owing to a low Mach number air flow, the discontinuity condition at the joint is analytically formulated according to the conservation of the momentum and mass of air flow. Based on the transfer function at the junction, a controller function is proposed to tune the semi-active Helmholtz resonator under flow condition.展开更多
In this paper, we briefly go over the homogeneous 5D model field theory: from the 5D space-time inception, to its quantum field solutions given in terms of Higgs vacuum, filled with magnetic monopole bose fields of al...In this paper, we briefly go over the homogeneous 5D model field theory: from the 5D space-time inception, to its quantum field solutions given in terms of Higgs vacuum, filled with magnetic monopole bose fields of all energies. Then through the space dimension reduction projections, the Gell-Mann standard model was obtained as well as a quantum to Classical connection was made via introducing Bose distribution to the monopoles to obtain the Perelman entropy and Ricci Flow mappings. This provided us a picture to the creation of Astronomical objects, from galaxies to stars and planets. This method of splitting the monopole energy into ranges is extended to show that below the basic rest mass range of the electron and Quark, it still can be applied to explaining for the creation of the chemical elements periodic table. But perhaps the most interesting is in the lowest hundreds of Hz energy range, obtained from yet another 3 fold space symmetry breaking, into 2D × 1D, producing bio nitrogenous bases composed of 3 Carbon 12 in hexagon structures, due to preservation of the 1D monopole standing waves of this low frequencies. From that by imposing gauge changes the monopole states into DNA spectra. Since such spectra states retain the DLRO, it induces formation of charge carriers periodicity in a spherical bio cell.. It was then argued that due to cell’s surface proteins, the structure must contain partial filled VB, with “p” state hole density, and empty CB, separated from VB by a positive band gap. Such band structures resemble known HTC Cuprate ceramics. Since the HTC goes through a Superconductivity transition via the simultaneous bose exciton condensation, providing a Coulomb pressure, which reduces the band gap substantially, and induces the ODLRO transition of the hole density. The same obviously applies to the bio cells. Because of the near continuous exciton levels generated, a matching to the DNA spectra then can always occur by selective choices of proteins on the cell surface. Judging from a numerical study, we did years ago on YBCO, with doping. We found with a large enough VB hole density, the exciton induced superconducting gap can easily lead to <em>T</em><em>c</em> in the room temperature range. In fact by EMF excitation can increase the exciton pressure and trigger the ODLRO transition <em>T</em><em>c</em> upward. In fact, numerical results then suggest there do exist coherent EMF spectra from three key elements: Water, Carbon and Hydrogen, together with Oxygen, as studied over the years by numerous people, starting from Schr<span style="white-space:nowrap;">ö</span>dinger to most recently Geesink.展开更多
基金Project(PolyU B-Q01e) supported by the Research Project "Onsetting of Internal Fire Whirls in Buildings and Associated Safet Provision"
文摘To apply the fire modelling for the fire engineer with symbolic mathematics,the key equations of a zone model were demonstrated. There were thirteen variables with nine constraints,so only four ordinary differential equations (ODEs) were required to solve. A typical fire modelling with two-room structure was studied. Accordingly,the source terms included in the ODEs were simplified and modelled,and the fourth Runge-Kutta method was used to solve the ordinary differential equations (ODEs) with symbolic mathematics. Then a zone model could be used with symbolic mathematics. It is proposed that symbolic mathematics is possible for use by fire engineer.
文摘The cooling and heating load distribution of large area air-conditioned room such as “open” offices, shopping malls and waiting rooms is usually assumed to be even in air conditioning system design. However, it is not the case in reality, and a low efficient air conditioning system results from this assumption. A simulation and analysis of the cooling load distribution of an office building in Hong Kong with TRANSYS software is provided in this paper. A typical office is divided into 13 zones for simulation, including external zone, medial zone and internal zone in the north, the south, the east and the west respectively and a central zone, instead of 4 directional zone. The result shows there is much cooling load difference between each zone, and more attention should be paid to uneven indoor cooling and heating load distribution to further guide the design.
基金financially supported by NSFC-Civil Aviation Joint Research Fund,China(No.U1933121)Scientific Research Program Funded by Shaanxi Provincial Education Department,China(No.19JK0374)+2 种基金the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(No.KYCX19_0198)the Fundamental Research Funds for the Central UniversitiesPriority Academic Program Development of Jiangsu Higher Education Institutions。
文摘To determine the oxygen concentration variation in ullage that results from dissolved oxygen evolution in an inert aircraft fuel tank,the CFD method with a mass transfer source is applied in the present study.An experimental system is also designed to evaluate the accuracy of the CFD simulations.The dissolved oxygen evolution is simulated under different conditions of fuel load and initial oxygen concentration in ullage of an inert fuel tank with stimulations of heating and pressure decrease.The increase in the oxygen concentration in ullage ranges from 0.82%to 5.92%upon stimulation of heating and from 0.735%to 12.36%upon stimulation of a pressure decrease for an inert ullage in the simulations.The heating accelerates the release of the dissolved oxygen from the fuel by increasing the mass transfer rate in the mass transfer source and decreasing the pressure,thereby accelerating the dissolved oxygen evolution by increasing the concentration difference between the gas and the fuel.The time constant that represents the oxygen evolution rate is independent of the initial oxygen concentration in ullage of an inert tank but depends closely on the fuel load,temperature and pressure.The time constant can be fitted using a polynomial equation relating the fuel load to temperature in the heating stimulation with an accuracy of 4.77%.Upon stimulation of a pressure decrease,the time constant can be expressed in terms of the fuel load and the pressure,with an accuracy of 5.02%.
基金funded by Research Grant Committee of the Hong Kong SAR government (RGC No. PolyU5265/08E)
文摘Existed evidences show that airborne transmission of human respiratory droplets may be related with the spread of some infectious disease, such as severe acute respiratory syndrome （SARS） and H1N1 pandemic. Non-pharmaceutical approaches, including ventilation system and personal protection, are believed to have certain positive effects on the reduction of co-occupant＇s inhalation. This work then aims to numerically study the performances of mouth covering on co-occupant＇s exposure under mixing ventilation （MV）, under-floor air distribution （UFAD） and displacement ventilation （DV） system, using drift-flux model. Desk partition, as one generally employed arrangement in plan office, is also investigated under MV. The dispersion of 1, 5 and 10 grn droplet residuals are numerically calculated and CO2 is used to represent tracer gas. The results show that using mouth covering by the infected person can reduce the co-occupant＇s inhalation greatly by interrupting direct spread of the expelled droplets, and best performance can be achieved under DV since the coughed air is mainly confined in the microenvironment of the infected person. The researches under MV show that the two interventions, mouth covering and desk partition, achieve almost the sarae inhalation for fine droplets while the inhalation of the co-occupant is lower when using mouth covering for large droplets.
文摘As only about 15% of the total time of people in Hong Kong was spent outdoors, it would be more valuable if the associated effectiveness and impact of the recently proposed abatement measures could be expressed in terms of the improvement in the total exposure levels. This paper uses an exposure assessment model developed from the local microenvironment concentration data together with our surveyed time activity patterns to evaluate the effectiveness of the proposed air pollution abatement policy. Prior to the enforcement of abatement measures, about 2.5% of the young group and 1.2% of the adult group having their exposure levels exceeded that defined by the current 8-hour PM10 standard (180 μg/m3). With the enforcement of abatement measures, only 0.3% of the adult group would be restored to a safe level.
基金supported by the National Natural Science Foundation of China(Nos.21673290,U1662103)Science Foundation of China University of Petroleum,Beijing(No.2462017YJRC027)the Strategic Cooperation Technology Projects of CNPC and CUPB(No.ZLZX2020-04)。
文摘The strategy of adopting cheap precursors or abundant resources,which can be obtained directly from nature,is a simple and excellent method of introducing accessible research into environmentally friendly development.Moreover,this is also an urgent requirement for the sustainable development of green technology.Herein,we introduce a simplistic and expandable method to prepare metal-free biomassderived nitrogen self-doped porous activation carbon(N-PAC) with large specific surface area(S_(BET)=1300.58 m^(2)/g).Moreover,the manufactural electrocatalysts exhibit prominent oxygen reduction reaction(ORR) performance in all PH values.As compared with the commercial Pt/C catalyst,the N-PAC/800 with a positive onset potential at 10 mA/cm^(2)(0.93 V),half-wave potential(0.87 V),and limiting current(6.34 mA/cm^(2)) bring to light excellent catalytic stability,selectivity,and much-enhanced methanol tolerance.Furthermore,the prepared electrocatalysts possess considerable hydrogen evolution reaction(HER) performance with a less onset potential of 0.218 V(acidic medium) and0.271 V(alkaline medium) respectively,which can show similar catalytic activity across the whole pH range.Such bifunctional electrocatalyst,with excellent electrocatalytic properties,resource-rich,low cost,and environmental-friendly,hold a promising application in energy conversion and reserve.
基金Supported by the Research Grant Council of the Hong Kong SAR government(GRF PolyU 5241/11E)
文摘This study aims to develop a paraffin-based phase change material(PCM) emulsion with a low extent of supercooling for thermal energy storage(TES) systems to improve the cooling efficiency.Hexadecane-water emulsions were prepared and characterized. Multi-wall carbon nanotubes(MWCNTs) were dispersed in the emulsion as a nucleating agent to reduce the supercooling. The MWCNTs were chemically modified with carboxyl groups to improve the dispersion of the tubular particles in the organic liquid. Thermal analyses of the emulsions by differential scanning calorimeter(DSC) indicated that the extent of supercooling was significantly reduced. The concentration of the nucleating agent for an effective supercooling suppression as found to be very low, in agreement with previous findings, and there appeared to be a minimum concentration for the supercooling reduction.
文摘In view of the practical importance of the heat transfer devices in various thermal engineering fields including chemical and nuclear engineering,this study aims at developing an effective method of heat transfer enhancement by using selfrotating twisted tapes(SRTTs)and Al_(2)O_(3) nanoparticles.The effect of the selfrotating twisted tapes and Al2O3 nanoparticles on the thermal performance was comprehensively investigated in a circular pipe.The experimental results indicated the heat transfer rate was effectively improved by SRTTs in comparison of plain tube.In addition,the heat transfer multiplier with SRTTs decreased from 1.38 to 1.08 with the Reynolds number increasing from 19,322 to 64,407,while the friction factor multiplier decreased from 1.61 to 1.32.Besides,the results indicated that the employment of Al_(2)O_(3) nanoparticles and SRTTs demonstrated superior thermal performance to the single SRTTs.As Reynolds number increases from 19,322 to 64,407,the heat transfer multiplier decreased from 2.08 to 1.18 in the mass concentration of 3.0%and from 1.38 to 1.08 in mass concentration of 0.0%.Finally,the new heat transfer and friction factor correlations considering the combined effect of Al2O3 nanoparticle and SRTTs were developed within 10%deviation of experimental values.
文摘The duct static pressure reset (DSPR) control method is a popular modern control method widely applied to variable air volume (VAV) systems of commercial buildings. In this paper, a VAV system simulation program was used to predict the system performance and zone air temperature of two kinds of layouts that were applied to a typical floor of an existing building office in Hong Kong. The position where the static pressure sensor was placed should affect the zones temperature and energy consumption. The comparison of predictions of the two kinds of layouts indicates that with the same DSPR control method the layout of the air duct might influence the fan control result and energy savings.
文摘Ground-coupled heat pumps(GCHP)are commonly used in residential heating system.To mitigate the boreholes temperature dropping with operating time,a new exhaust-air recharging system is developed.The new recharging system can be used in three operational modes.In this paper,a ground-coupled heat recovery ventilation(HRV)model is discussed.A thermal model is set up to find the optimal brine flow rate and heat transfer allocation ratio between exhaust and supply coils for maximum heat recovery efficiency.Contrary to the conventional liquid-loop HRV systems,the brine temperature entering the exhaust coil never goes blow zero(0℃),and hence defrosting is needless in the ground-coupled HRV system.This can make the ground-coupled HRV system over 20% more efficient than a conventional HRV system at low outdoor temperatures.
文摘The expression of the Maxwell magnetic monopole was employed to correlate the space to space projection that gives rise to the Gell-Mann standard model, and space to time projection which gives the leptons;and how does it correlate to the Perelman mappings from the homogeneous 5D manifold to the Lorentz 4D manifold, together with correlating the physical consequences caused by the breaking of the Diagonal Long Range Order [DLRO] of the monopoles quantum states affected by the motion of massive particles in the Lorentz 4D boundary of the 5D manifold, which leads to gravitons and the gravity field via the General Relativity covariant Riemannian 4D curvatures metric equation.
文摘A summary of the homogeneous 5D universe model is expressed in the Dirac second-order quantized representation for the magnetic monopoles, identified in terms of the Higgs Bosons, and through systematic ordered excitations of the Higgs vacuum obtained the non-homogeneous 4D Lorentz manifolds filled with masses, corresponding to making space dimension reduction projections, and thus realization of Newtonian gravity, followed by the 3D space symmetry breaking into 2D × 1D that produces the Perelmann-entropy and Ricci-Flow mappings, resulting in the realization of Poincare spheres, represented by nucleus such as Carbon 12, all the way to stars, and matter filled discs, such as stars in galaxies and 2D carbon-based molecular structures like nitrogenous bases. Finally, the forming of RNAs and DNAs, then life forms.
文摘The technological advances in Lithium-ion batteries have created many new applications, including electric vehicles. In this short note, we shall explain in simple terms the basic physics why and how it is possible to have high energy capacity in Lithium-ion batteries. However, heating has been a common problem and without appropriate design, they might give fire and explosion as reported.
基金Projects(2006BAJ02A08, 2006BAJ02A05) supported by the National Science and Technology Pillar Program Project during the 11th Five-Year Plan PeriodProject(2007-209) supported by the Excellent Youth Teacher of Ministry of Education of China
文摘The main objectives were to (1) calculate the total volatile organic compounds (TVOCs) inhalation dose, (2) analyze the proportions of human’s inhaled contaminant dose from different sources, and (3) present a newly defined ratio of relative inhalation dose level (RIDL) to assess indoor air quality (IAQ). A user defined function based on CFD (computational fluid dynamics) was developed, which integrated human motion model with TVOCs emission model in a high sidewall air supply ventilation mode. Based on simulation results of 10 cases, it is shown that the spatial concentration distribution of TVOCs is affected by human motion. TVOCs diffusion characteristic of building material is the most effective way to impact the TVOCs inhalation dose. From the RIDL index, case A-2 has the most serious IAQ problem, while case D-1 is of the best IAQ.
基金Supported by Competitive Earmarked Research Grant of Hong Kong Government(CERG No.522709)
文摘The combined use of dry cooling(DC) system and dedicated ventilation(DV) system to decouple cooling and dehumidification process for energy efficiency was proposed for subtropical climates like Hong Kong. In this study, the energy performance and condensation risk of the use of DCDV system were examined by analyzing its application in a typical office building in Hong Kong. Through hour-by-hour simulation using actual equipment performance data and realistic building and system characteristics, it was found that with the use of DCDV system, the annual energy consumption could be reduced by 54% in comparison with the conventional system(constant air volume with reheat system). In respect of condensation risk, it was found that the annual frequency of occurrence of condensation on DC coil was 35 h. Additional simulations were conducted to examine the influence of different parameters on the condensation risk of DCDV system. Measures to ensure condensate-free on DC coil were also discussed.
文摘Taking public transit facilities (PTFs) is the major transport style in Hong Kong. Human exposure to indoor air pollutants may cause adverse health effects to the passengers. Exposure assessment on air pollutants is important for the control of human diseases caused by indoor air pollution. In this paper, the indoor PM10, CO and CO 2 levels in various PTFs, such as public bus, subway, railway and ferry in Hong Kong, were mea- sured. Combining with the time budget survey of Hong Kong population,the human exposures were calculated through Monte-Carlo simulation.
文摘With a self-similar parameter b（At） = Hi/λi, where At is the Atwood number, Hi and λi are the a.mplluae and wavelength of bubble （i = 1） and spike （i = 2） respectively, we derive analytically the solutions to the buoyancy-drag equation recently proposed for dynamical evolution of Rayleigh-Taylor and Richtmyer-Meshkov mixing zone. Numerical solutions are obtained with a simple form ofb（At）--- 1/（1 ＋ At） and comparisons with recent LEM （linear electric motor） experiments are made, and an agreement is found with properly chosen initial conditions.
基金Sponsored by the National Natural Science Foundation of China (Grant No. 50378024)
文摘A novel experimental setup was developed to study the heat extraction of geothermal heat exchanger(GHE)in different operational modes under adiabatic and isothermal boundaries.The experimental setup consists of a sand trunk,a tailored water chiller,a natural cold source unit,two water boxes containing hot water and cool water,and a data acquisition system.The experimental results indicate that the volume flow rate of the entering water is a main factor affecting the heat extraction;furthermore,the heat extraction value per meter pipe decreases gradually along the heat extraction pipe and increases with the increase of the incoming water volume flow rate.Therefore,this novel experimental setup may be helpful to further study the operation performance of GHE in different types of soil.
文摘Side branch Helmholtz resonators (HRs) are widely used to control low frequency tonal noise in air duct system. The passive Helmholtz resonator only works effectively over a narrow frequency range around resonance frequency. Changes in the exciting frequency and temperature will decrease the noise reduction performance. Many studies have been conducted on incorporating a Helmholtz resonator with active noise control to tuning the resonance frequency of HRs. The objective of this study is to study the effect of flow on the semi active Helmholtz resonator for duct noise control. Owing to a low Mach number air flow, the discontinuity condition at the joint is analytically formulated according to the conservation of the momentum and mass of air flow. Based on the transfer function at the junction, a controller function is proposed to tune the semi-active Helmholtz resonator under flow condition.
文摘In this paper, we briefly go over the homogeneous 5D model field theory: from the 5D space-time inception, to its quantum field solutions given in terms of Higgs vacuum, filled with magnetic monopole bose fields of all energies. Then through the space dimension reduction projections, the Gell-Mann standard model was obtained as well as a quantum to Classical connection was made via introducing Bose distribution to the monopoles to obtain the Perelman entropy and Ricci Flow mappings. This provided us a picture to the creation of Astronomical objects, from galaxies to stars and planets. This method of splitting the monopole energy into ranges is extended to show that below the basic rest mass range of the electron and Quark, it still can be applied to explaining for the creation of the chemical elements periodic table. But perhaps the most interesting is in the lowest hundreds of Hz energy range, obtained from yet another 3 fold space symmetry breaking, into 2D × 1D, producing bio nitrogenous bases composed of 3 Carbon 12 in hexagon structures, due to preservation of the 1D monopole standing waves of this low frequencies. From that by imposing gauge changes the monopole states into DNA spectra. Since such spectra states retain the DLRO, it induces formation of charge carriers periodicity in a spherical bio cell.. It was then argued that due to cell’s surface proteins, the structure must contain partial filled VB, with “p” state hole density, and empty CB, separated from VB by a positive band gap. Such band structures resemble known HTC Cuprate ceramics. Since the HTC goes through a Superconductivity transition via the simultaneous bose exciton condensation, providing a Coulomb pressure, which reduces the band gap substantially, and induces the ODLRO transition of the hole density. The same obviously applies to the bio cells. Because of the near continuous exciton levels generated, a matching to the DNA spectra then can always occur by selective choices of proteins on the cell surface. Judging from a numerical study, we did years ago on YBCO, with doping. We found with a large enough VB hole density, the exciton induced superconducting gap can easily lead to <em>T</em><em>c</em> in the room temperature range. In fact by EMF excitation can increase the exciton pressure and trigger the ODLRO transition <em>T</em><em>c</em> upward. In fact, numerical results then suggest there do exist coherent EMF spectra from three key elements: Water, Carbon and Hydrogen, together with Oxygen, as studied over the years by numerous people, starting from Schr<span style="white-space:nowrap;">ö</span>dinger to most recently Geesink.
