Xilian Luo

Primitive environment control for preservation of pit relics in archeology museums of China.

Immovable historical relics in some archeology museums of China suffer deterioration due to their improper preservation environment. The existing environmental control systems used in archeology museums are often designed for the amenities of visitors, and these manipulated environments are often inappropriate for the conservation of abiotic relics. This paper points out that the large open space of the existing archeology museum could be a cause of deterioration of the relics from the point of view of indoor air convective flow. The paper illustrates the need to introduce a local pit environmental control, which could reintegrate a pit primitive environment for the preservation of the historical relics by using an air curtain system, orientated to isolate the unearthed relics, semiexposed in pits to the large gallery open space of the exhibition hall.

Desiccation cracking of earthen sites in archaeology museum – A viewpoint of chemical potential difference of water content

Unearthed relics and earthen sites are historical evidence of our cultural heritage. Many of them are referred to as immobile cultural relics since both the relics-in-itself and their surroundings are our historic heritage of past emperor’s burial with significant historical importance such that they cannot be moved into indoor-display museums. Researchers have studied the specific environmental specifications to establish the desired steady temperature, humidity and air quality for collections and visitors in indoor-display museums. However, due to the unique exhibition characteristics, the conservation of earthen sites is still a challenge to environmental scientists and technologists, and how to effectively protect these ancient sites has been a major concern globally. Archaeology museum is developing advanced techniques to prevent weathering of relics caused by the sun, wind and rain. The in-situ relics in archaeology museum are far from being well preserved because of the lack of understanding of site conservation and the impact of indoor micro-climatic conditions. Many of them are suffering deteriorations or even ruins due to improper preservation environment adopted for maintenance of relics. Among the hazards that unearthed relics are facing with, desiccation cracking is the most common and problematic. The drying layer of the earthen site in the Banpo museum (Xi’an, China) is thicker than 0.4m (see Figure 1(a)). The same phenomena are also found in the Emperor Qin’s Terra-Cotta Warriors and Horses Museum (see Figure 1(b)), the water content of the earthen site decreased from 15% to 22% in 1994 when it was excavated to less than 5% now, such that serous shrinkage and cracking occurred on the surface of the site. To upgrade the conservation of the relics in archaeology museums, great efforts have been made in recent years, e.g. maintenance of a high relative humidity (RH) and space division in the exhibiting hall have been implemented in archaeology museum as a part of the preservation regime. The underground exhibiting hall of Hanyangling Museum (Xi’an, China) is such a modern archaeology museum (see Figure 1(c)). It exhibits partially exposed pits containing pottery figurines in the co-burial grave of the fourth Emperor (188–141 B.C.) and Queen of Han Dynasty, China. The enclosed space for relics’ domain is being maintained at about 24 C in summer and 16 C in the winter. Moreover, the RH has been maintained at a level higher than 95% to prevent the drying of unearthed relics and sites. However, the water content of the earthen site in the exhibiting hall still decreased from over 15% when it was excavated in 2006 to around 4% in 2009. In addition to the desiccation cracking, gypsum was found to deposit on the surface of relics due to the transport mechanism by which the carbonates were diffused and migrated with moisture across the air-relic-topsoil complex interfaces. The carbonates would react with the penetrating SO2 from the ambient atmosphere to form sulphates (see Figure 1(d)). The reason why desiccation cracking occurs in high humidity environment is not entirely clear. The conservation protocol, i.e. space division and maintaining a high RH as a preservation regime, has been considered by archaeologists as an approved practice and therefore the protocol was applied to new archaeology museums; however, cracking still persists in the terracotta relics and earthen sites. The desiccation cracking of unearthed relics and excavated sites in these archaeology museums seems to be a spontaneous process even though the RH of the atmospheric environment was at approximately the ceiling value (100%). In order to clarify the mechanism of moisture migration behind the desiccation cracking phenomenon and to verify whether a high RH is adequate to prevent the desiccation cracking of unearthed in-situ relics, the chemical potential analysis

Efficacy of an air curtain system for local pit environmental control for relic preservation in archaeology museums

Indoor environmental control has been proven to be a critical consideration for preserving in situ unearthed relics in archaeology museum. An air curtain system has been proposed to separate the local environment of funerary pit from its large-space exhibition hall. The isolation efficiency of the air curtain is formulated by using stream function method in this study. The geometrical dimensions and jet flow parameters were investigated in this study through the theoretical formula, to determine their effects on the isolation efficiency and suitable operation mode, respectively. An experimental setup was constructed to investigate the performance and validate the feasibility of an air curtain system for preservation of historical terracotta figurines in their semi-exposed pits in the exhibition hall. The experimental results showed that the air curtain system could be orientated to isolate the relics or buried treasures unearthed in pits from the large open space of the exhibition hall. These results have significant implications for protecting the relics from deterioration in a control environment of a national museum and will contribute towards sustainable protocol for long-term preservation of unearthed relics in archaeology museums.

From dust devil to sustainable swirling wind energy.

Dust devils are common but meteorologically unique phenomena on Earth and on Mars. The phenomenon produces a vertical vortex motion in the atmosphere boundary layer and often occurs in hot desert regions, especially in the afternoons from late spring to early summer. Dust devils usually contain abundant wind energy, for example, a maximum swirling wind velocity of up to 25 m/s, with a 15 m/s maximum vertical velocity and 5 m/s maximum near-surface horizontal velocity can be formed. The occurrences of dust devils cannot be used for energy generation because these are generally random and short-lived. Here, a concept of sustained dust-devil-like whirlwind is proposed for the energy generation. A prototype of a circular shed with pre-rotation vanes has been devised to generate the whirlwind flow by heating the air inflow into the circular shed. The pre-rotation vanes can provide the air inflow with angular momentum. The results of numerical simulations and experiment illustrate a promising potential of the circular shed for generating swirling wind energy via the collection of low-temperature solar energy.

Performance comparison of capillary mat radiant and floor radiant heating systems assisted by an air source heat pump in a residential building

The radiant heating system assisted by an air source heat pump has been widely applied in China for its effective energy conservation, high comfort performance and flexible utilization. Because the coefficient of performance of the system is strictly controlled by the supply water temperature heated by the air source heat pump, an efficient radiant terminal with low-temperature supply water is of significance to the coefficient of performance. In this research, the energy-saving feature of the capillary mat radiant heating system was first proved theoretically based on the influence of the heat transfer temperature difference on the coefficient of performance of the air source heat pump. In order to compare the performances of the capillary mat radiant and floor radiant heating systems, an experiment platform of two different radiant terminals assisted by an air source heat pump was established in a residential building in Xi’an, China. Experimental results showed that, to satisfy the indoor heating requirements, the supply and return water temperatures ought to be 35.0℃ and 30.9℃, respectively, and for the capillary mat radiant heating system, 43.9℃ and 38.8℃, respectively, for the floor radiant heating system. However, the electricity consumption of the capillary mat radiant heating system is 45% less than that of the floor radiant heating system. Thus, our study validated the energy-saving potential of the capillary mat radiant heating system assisted by an air source heat pump.

Simulation of Eccentric-Shaft Journal Microbearing by DSMC

Many micromachines use rotating shafts and other moving parts which carry a load and need fluid bearings for support. Most of them operate with air or water as the lubricating fluid. The present study analyzes air microbearing represented as an eccentric cylinder rotating in a stationary housing. The fluid mechanics and operating characteristics of microbearing are different from their larger cousins. The small length-scale may invalidate the continuum approximation in Navier-Stokes equations, and slip flow, rarefaction, compressibility and other unconventional effects may have to be taken into account. Surface effects dominate in small devices due to a high surface-volume ratio. In this study, two-dimensional eccentric-shaft journal microbearings with different eccentricities are simulated by direct simulation Monte Carlo (DSMC) code incorporated with a Volume-CAD software. The diffuse reflection model and Cercignani-Lampis-Lord (CLL) model are applied to model the molecule-surface interaction by considering the accommodation coefficients of shaft wall and housing wall separately. The distribution of mean free path in the flow field indicates that the continuum model may break down and it is necessary to carry our molecular modeling. Calculation results show that at high eccentricity and high accommodation coefficient on the housing wall (ACO) the flow may develop a recirculation region. However, the accommodation coefficient on shaft wall (ACI) does not have any effect on the occurrence of recirculation and the size of recirculation zone. There is antisymmetry of the pressure about a vertical axis, which produces a pressure force on the shaft wall. The influence of ACI to isobars is larger than that of ACO. The shear stress profile on shaft wall is big at low ACI. At the region of short clearance between the shaft wall and housing wall, it is also influenced by the surface condition of housing wall and may even change its direction at low ACO. The pressure profile is reduced in amplitude as the ACI increases, but it is enhanced a little with the increase of ACO. The ACO has great impact on the viscous force in the case of big eccentricity. With the increase of ACI, the viscous force decreases. The pressure force is high at large eccentricity. The influence of ACO to pressure force is insignificant, but the pressure force fall is enormous when ACI increases, especially for large eccentricity. The total force decreases markedly at high eccentricity when ACI increases. The ACO almost has no impact on the total force. The torque increases with ACO, but decreases with ACI. The eccentricity also has great impact on the torque, and the microbeaing may have large torque at high eccentricity. The method developed in this paper would be very useful for designing and evaluating journal microbearing.Copyright

Investigation on Moisture and Salt Transport in Heterogeneous Porous Media of Relics-Soil in Archaeology Museum

The unearthed relics in archaeology museum are usually being presented to the public as still partly connected to their primitive environment. Migration of moisture may cause the carbonate from the soil being deposited on the relic’s surface and some carbonates would react with the penetrating SO2 to form sulphates, which will change the relics’ primitive form and material properties. In this research, experiments were carried out to clarify the migration mechanism of water and salt in a soil-relic-atmosphere coupling environment. The research results show that there existing a one-way transport of moisture from the soil-relics to the air even though the relative humidity approximates to 100%. Meanwhile, the effects of soil properties, air temperature, relative humidity and salt concentration on the transports of moisture and salt are identified.

Numerical and Experimental Investigation on Thermal Management of an Outdoor Battery Cabinet

Many forms of electronic equipment, of necessity, must be located in an outdoor environment. Such equipment in typical form may be battery packs or telecom-equipment. It is essential that these facilities be protected from a wide range of ambient temperatures and solar radiation. To this end, cabinet enclosures with proper thermal management have been developed to house such electronic equipment in a highly weather tight manner, especially for battery cabinet. Often the batteries are of a lead-acid construction which is known to be adversely affected by temperature extremes in terms of battery performance and life. Therefore, it is important to maintain the cabinet temperature ideally for ensuring battery stability and extending battery lifespan. In this paper, physical and mathematical models are established to investigate the flow field and temperature distribution inside an outdoor cabinet, which contains 24 batteries with two configurations of two-layer and six-layer respectively. The cabinet walls are maintained at a constant temperature by a refrigeration system and the ambient temperature is up to 50 °C according to the practical situation. The flow field and temperature distribution are analyzed with and without consideration of solar radiation. An experimental facility is then developed to measure the battery surface temperatures and to validate the numerical simulation. The differences between the CFD and experimental results are within 2%, which confirms the CFD model.

Effect of boundary conditions on the performances of gas-lubricated micro journal bearing

As significant components of micromechanics, gas-lubricated microbearings are more prevalent for their special advantages than other types. The fluid dynamics of the microbearing is different from their larger cousins due to the noncontinuum effect and surface-dominated effect, which may make the Navier-Stokes equations invalid. In this paper, by considering the accommodation coefficients on journal (? i) and that on bearing (? o) separately, the microbearings with different bearing numbers under the assumption of large L/D (length to diameter) are simulated using direct simulation Monte Carlo (DSMC) program incorporated with a Volume-CAD software. The diffuse reflection model and Cercignani-Lampis-Lord (CLL) model are applied to model the molecule-surface interaction. The flow field characteristics, as well as the performances of gas-lubricated journal bearings including load-carrying capacity, attitude angle and bearing drag are obtained. The results reveal that ?i and ?o have different effects to flow field characteristics and bearing performances. The bearing number has significantly impact on the bearing performances. The method developed in this paper would be very useful for designing and evaluating the gas-lubricated journal microbearing.

Cylindrical Couette Flow of a Rarefied Gas From Macro- to Micro-Scales

The cylindrical Couette flow of a rarefied gas from macro- to micro-scales, in the case where the inner cylinder is rotating whereas the outer cylinder is at rest, is extensively investigated by direct simulation Monte Carlo (DSMC) code incorporated with a Volume-CAD software. The generalized soft sphere (GSS) model is applied to an intermolecular collision calculation. The diffuse reflection model and Cercignani-Lampis-Lord (CLL) model are used to model the molecule-surface interaction by considering the accommodation coefficients on inner cylinder (ACI hereafter) and outer cylinder (ACO hereafter) separately. The contents in this paper include following three aspects: I the flow field characteristics and force and torque on inner cylinder for eccentric Couette flow between different scales with same non-dimensional parameters (accommodation coefficients, eccentricity-clearance ratio, Knudsen number and Reynolds number) are compared; the flow field characteristics for different scales are same; with the increase of the scale, the total force on the inner cylinder increases slightly, while the torque is proportional to the scale; II the velocity profiles in concentric Couette flow under different non-dimensional parameters are studied; the result shows that the phenomenon of inverted velocity profile in the concentric Couette flow is only induced by a smooth outer cylinder; the non-dimensional tangential velocity, as well as its gradient is high at low Reynolds number; the Knudsen number has great impact on the tangential velocity profile, and the velocity profile may not be inverted in the case of low Knudsen number; III the flow field characteristics in eccentric Couette flow under different non-dimensional parameters are obtained; the recirculation zone may not appear when Knudsen number is high; the position of its center may be different depending on Reynolds number; with the increase of Reynolds number, the compressibility effect becomes important; stratified distribution of the density becomes obvious at low Knudsen number.Copyright