Zanshe Wang

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.

Revisit of Wind Flows between Wind Tunnels and Real Canyons – The Viewpoint of Reynolds Dynamic Similarity

Wind tunnel test and numerical simulation are two powerful methods to study air flows and pollutant dispersions around urban buildings environment. As commonly known, the development of a successful numerical model should be firstly validated by experimental results, usually by wind tunnel data [1,2], a numerical model is ultimately needed to simulate the air flows and pollutant dispersions in real street canyons [3]. It is obvious that wind tunnel models and real canyons are of different scales. The scaling effects for wind tunnel tests have already been investigated on some simple models, such as single building and normal street canyon with the aspect ratio near 1.0 (AR, denoted by building height, H, over road width, W) [4,5]. But the scaling effects on the flows around complex buildings or in real street canyons still need to be examined. In wind tunnel test, air is often used as the experimental fluid. The air velocities in the wind tunnels are several metres per second, rarely more than 20m s 1 [5,6], which are similar to the velocities in the real canyon environment. But wood blocks with height of several centimetres, subject to the experimental conditions, are adopted for the street canyon models, following that the dimensions of wood blocks are about two orders of magnitudes smaller than the real buildings. Thus, the wind tunnel experiments only satisfy the geometric similarity, but miss the Reynolds dynamic similarity in nature. On the other hand, the numerical simulations of turbulent flows with high Reynolds numbers often demand large computing resources, so that the downscaling model is always used to simulate the air flows and pollutant dispersions in urban street canyons. In such cases, building models are set in several centimetres and incoming wind velocities are given similar to the real background wind velocities; this treatment is the same as the wind tunnel test [7,8]. This means that the downscaling simulations would just satisfy the geometric similarity, but miss the Reynolds dynamic similarity. The downscaling modelling was based on the Townsend’s ‘‘Reynolds number similarity’’ hypothesis [9] and determined by the critical Reynolds numbers [1,10]. The Townsend’s hypothesis is that, in the absence of thermal and Coriolis effects and for a specified flow system whose boundary conditions are expressed non-dimensionally in terms of a characteristic length, L, and velocity, UR, the flow structure is similar with all sufficiently high Reynolds numbers. Based on the ‘‘Reynolds number similarity’’ hypothesis, the critical Reynolds numbers are only determined by the representation of minor changes in flow structures or wind profiles, in which actually the wind

Advances in the Fine Scale Simulation of Urban Wind Environment

This work gives a review of studies on the air flow and pollutant dispersion in the fine scale environment of the urban street canyon. The affecting factors on the air flow and pollutant dispersions in urban street canyons are illustrated by analyzing the street canyon physical model and boundary conditions. The building layouts along the street and the variations in the ambient wind velocities and directions could contribute an impact on the basic air flow within urban street canyons, while the atmospheric instabilities inside the street canyons, the vehicle induced turbulence, and tree plantings could affect the turbulence and pollutant distributions inside the street canyons, especially under weak-wind conditions. In the case of the street canyons with high aspect ratio (building height H over street width W), Reynolds number would be related to the vortex structure. The current empirical or semi-empirical models are lacking of careful description of the street canyon’s real geometries and atmospheric conditions, which had often resulted in large errors in the simulated or forecasted results. Based on the computational fluid dynamic (CFD) method, further development of numerical models should focus on the integrated model, taking account of canyon’s real geometries and the real atmospheric conditions.

ANALYSIS ON MEMBRANE HEAT EXCHANGER APPLIED TO ABSORPTION CHILLER

A novel membrane heat exchanger was proposed and analyzed. It was expected that the novel heat exchanger could be applied to the lithium bromide absorption chiller. Polyvinylidene fluoride hollow fiber module was adopted as the solution heat exchanger. The hot feed solution from the generator flowed into the lumen side of the membranes while the cold feed solution from the absorber flowed away from the shell side. Heat transfer and mass transfer occurred simultaneously in the membrane module, and only water vapor could diffuse across the membrane pore due to the water vapor pressure difference between the inside and outside of the membrane. Mathematical equations of the heat and mass transfer processes in the membrane heat exchanger were built, and the parallel flow process and the counter flow process were compared by numerical simulation. The simulation results show that the counter flow process was the better flow mode because the mean temperature difference was larger and the mass transfer was more steadily from the lumen side to the shell side. The heat caused by water vapor mass transfer may account for one-third of the total heat transfer. As a result, the membrane heat exchanger not only reinforced the heat recovery but also enlarged the deflation range and reduced the circulation rate and the heat loads of the generator and absorber. Eventually, the coefficient of performance of the heat exchanger was increased.

Application of the Geometry of Conjugate Curves to the Design of Internal-Meshing Rotary Compressors

The internal-meshing rotary compressor can be applied to the CO2 transcritical refrigeration cycle due to its simple structure, self-balanced initial mass, and high pressure endurance. Because of the different fluids transmitted by compressor and pump, the design method of the internal meshing rotary pump cannot be entirely and directly employed. In order to simplify the further study of the internal-meshing rotary compressors, the essential profile equations for the inner and outer rotors are derived and explicitly formulated based on the equidistant curve of curtate epicycloid and the multi-section circular arc, respectively. Then, the relationship between the meshes of the inner and outer rotors, the position of the instantaneous center, the meshing range of the tooth tip arc, and the modification of the profiles are discussed. These basic geometric theories are expected to lay the principles for the design of the compressor of interest.