活动安排并给一张游览地的地图。在这部分，下面的表述可供参考： This paper is divided into five major sections as follows… Section one of this paper opens with…
Section three develops the second hypothesis on…
Section four shows (introduces, reveals, treats, develops, deals with, etc.)… The result of … is given in the last section. (5) 介绍一下主要结论。
(4) 和 (5) 的安排比较灵活，有时可不同时出现，甚至不出现，只介绍 (3) －本论文的目的或主要贡献及其重要性。
关于引言的功能，Raleigh Nelson有一段形象的介绍：“(it) may be thought of as a preliminary conference in which the writer and prospective reader ?go into a huddle? and agree in advance on the exact limits of the subject, the terms in which to discuss it, the angle from which to approach it, and the plan of treatment that will be most convenient to both.”
引言部分逻辑性很强。首先当然是点出问题，并使读者一下被吸引。这就必须交代为什么你选择该问题，该问题的解决状况如何，还有那些问题需要研究，你如何解决这些问题，得到了哪些有意义的结果。这些环节联系紧密、环环相扣。
引言中要引用已发表的相关文献，一般有两种引出方式：按所引文献出现的先后顺序标注，按所引文献作者的姓名的字母顺序标注。具体方式，视所投期刊要求而定。
下面通过一些例子对上面的介绍加以说明。
例1： INTRODUCTION
A variety of building materials (e.g., adhesives, sealants, paints, stains, carpets, vinyl flooring, and engineered woods) can act as indoor sources of volatile organic compounds (VOCs). Following their installation or application, these materials typically contain residual quantities of VOCs that are then emitted over time. Once installed and depending upon their properties, these materials may also interact with airborne VOCs through alternating sorption and desorption cycles (Zhao et al., 1999b, 2001). Consequently, building materials can have a significant impact on indoor air quality both as sources of and sinks for volatile compounds.
Current methods for characterizing the source/sink behavior of building materials typically involve chamber studies. This approach can b time-consuming and costly, and is subject to several limitations (Little and Hodgson, 1996). For those indoor sources and sinks that are controlled by internal diffusion processes, physically-based diffusion models hold considerable promise for prediction emission characteristics when compared to empirical methods (Cox et al., 2000b, 2001b).
The key parameters for physically-based models are the material/air partition coefficient (K), the material-phase diffusion coefficient (D), and, in the case of a source, the initial concentration of VOC in the material (C0). Rapid and reliable determination of these key parameters by direct measurements or by estimations based on readily available VOC/building material properties should greatly facilitate the development and use of mechanistic models for characterizing the source/sink behavior of diffusion-controlled materials (Zhao et al., 1999a; Cox et al., 2000a, 2001a).
Several procedures have been used to measure D and K of volatile compounds in building materials. D and K have been inferred from experimental data obtained in chamber studies (Little et al., 1994). A procedure using a two-compartment chamber has also been used for D and K measurement. A specimen of building material is installed between the two compartments. A concentration of a particular compound if introduced into the gas-phase of one compartment while the gas-phase concentration in the other compartment is measured over time. D and K are then indirectly estimated from gas-phase concentration data (Bodalal et al., 2000;
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[1]
Meininghaus et al., 2000). A complicating feature of this method is that VOC transport between chambers may occur by gas-phase diffusion through pores in the building material in addition to solid-phase Fickian diffusion, confounding estimates of the mass transport characteristics of the solid material.
A procedure based on a European Committee for Standardization (CEN) method has also been used to estimate D. A building material sample is tightly fastened to the open end of a cup containing a liquid VOC. As the VOC diffuses from the saturated gas-phase through the building material sample, cup weight over time is recorded. Weight change data can be used to estimate D. (kirchner et al., 1999). A significant drawback of this method is that D has been shown to become concentration dependent in polymers at concentrations approaching saturation (Park et al., 1989).
In accordance with a previously proposed strategy for characterizing homogeneous, diffusion-controlled, indoor sources and sinks (Little and Hodgson, 1996), the objectives of this study were to (1) develop a simple and rapid experimental method for directly measuring the key equilibrium and kinetic parameters, (2) examine the validity of several primary assumptions upon which the previously mentioned physically-based models are founded and (3) develop correlations between the O and K, and readily available properties of VOCs.
例2[2]： 1. Introduction
Liquid desiccant cooling systems have been proposed as alternatives to the conventional vapor compression cooling systems to control air humidity, especially in hot and humid areas. Research has shown that a liquid desiccant cooling system can reduce the overall energy consumption, as well as shift the energy use away from electricity and toward renewable and cheaper fuels (Oberg and Goswami, 1998a). Burns et al. (1985) found that utilizing desiccant cooling in a supermarket reduced the energy cost of air conditioning by 60% as compared to conventional cooling. Oberg and Goswami (1998a) modeled a hybrid solar cooling system obtaining an electrical energy savings of 80%, and Chengchao and Ketao (1997) showed by computer simulation that solar liquid desiccant air conditioning has advantages over vapor compression air conditioning system in its suitability for hot and humid areas and high air flow rates.
Use of liquid desiccants offers several design and performance advantages over solid desiccants, especially when solar energy is used for regeneration (Oberg and Goswami, 1998c). Several liquid desiccants are commercially available: triethylene glycol, diethylene glycol, ethylene glycol, and brines such as calcium chloride, lithium chloride, lithium bromide, and calcium bromide which are used singly or in combination. The usefulness of a particular liquid desiccant depends upon the application. At the University of Florida, Oberg and Goswami (1998a,b) conducted a study of a hybrid solar liquid desiccant cooling system using triethylene glycol (TEG) as the desiccant. Their experimental work concluded that glycol works well as a desiccant. However, pure triethylene glycol does have a small vapor pressure which causes some of the glycol to evaporate into the air. Although triethylene glycol in nontoxic, any evaporation into the supply air stream makes it unacceptable for use in air conditioning of an occupied building. Therefore, there is a need to evaluate other liquid desiccants for hybrid solar desiccant cooling systems. Lithium chloride (LiCl) is a good candidate material since it has good desiccant characteristics and does not vaporize in air at ambient conditions. A disadvantage with LiCl is that it is corrosive. This paper presents an experimental and theoretical study of aqueous lithium chloride as a desiccant for a solar hybrid cooling system, using a packed bed dehumidifier and regenerator.
A number of experimental studies have been carried out on packed bed dehumidifiers using salt solutions as desiccants. Chung et al. (1992, 1993), and Chen et al. (1989) used lithium chloride (LiCl); Ullah et al. (1998), Kinsara et al. (1998) and Lazzarin et al. (1999) used calcium chloride (CaCl2); while Ahmed et al. (1997) and Patnaik et al. (1990) used lithium bromide (LiBr). Other experiments for absorbers using LiCl were carried out by Kessling et al. (1998), Kim et al. (1997) and Scalabrin and Scaltriti (1990).
The moisture that transfers from the air to the liquid desiccant in the dehumidifier causes a dilution of the
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desiccant resulting in a reduction in its ability to absorb more water. Therefore, the desiccant must bee regenerated to its original concentration. The regeneration process requires heat which can be obtained from a low temperature source, for which solar energy and waste energy from other processes are suitable. Different ways to regenerate liquid desiccants have been proposed. Hollands (1963) presented results from the regeneration of lithium chloride in a solar still. Hollands focused his study on the still efficiency, concluding that lithium chloride can be regenerated in a solar still with a daily efficiency of 5 to 20% depending on the insolation and the concentration of the desiccant. Ahmed Khalid et al. (1998) presented an exergy analysis of a partly closed solar generator to compare it with the solar collector reported previously. Ahmed et al. (1997) simulated a hybrid cycle with a partly closed-open solar regenerator for regeneration the weak solution. They found that the system COP is about 50% higher than that of a conventional vapor absorption machine. Leboeuf and Lof (1980) presented an analysis of a lithium chloride open cycle absorption air conditioner which utilizes a packed bed for regeneration of the desiccant solution driven by solar heated air. In this case, the air temperature ranged from 65 to 96oC while the desiccant temperature ranged from 40 to 55 oC. Lof et al. (1984) conducted experimental and theoretical studies of regeneration of aqueous lithium chloride solution with solar heated air in a packed column. In this case, air at a temperature of 82 to 109 oC was used to regenerate the desiccant at an average temperature of 36 oC.
In any thermodynamic system, the conditions of the working fluids and parameters of the physical equipment define the overall performance of the system. In a liquid desiccant cooling system, variables such as air and desiccant flow rate, air temperature and humidity, desiccant temperature and concentration are of great interest for the performance of the dehumidifier. The mass ratio of air to desiccant solution MR=mair/msol is an important factor for absorber efficiency and system capacity. Previous studies have reported the performance of packed bed absorbers and regenerators with MR between 1.3 and 3.3. The range of MR varies with the type of absorber/regenerator, but in general better results are obtained for small MR.
For simulation purposes, validated models are required for modeling the absorber in a liquid desiccant system. Models using lithium chloride have been descried by Khan and Martinez (1998), Ahmed et al. (1997) and Kavasogullare et al. (1991). Due to the complexity of the dehumidification process, theoretical modeling relies heavily upon experimental data. Oberg and Goswami (1998b) developed a model for a packed bed liquid desiccant air dehumidifier and regenerator with triethylene glycol as liquid desiccant which was validated satisfactorily by the experimental data. The present study uses a modified version of the mathematical model developed by Oberg and Goswami to compare the experimental results of a packed bed dehumidifier and regenerator using lithium chloride as a desiccant.
例3[4]
Introduction
The measure of success of an air conditioning system design is normally assessed by the thermal conditions provided by the system in the occupied zones of a building. Although the thermal condition of the air supply may be finely tuned at the plant to offset the sensible and latent heat loads of the rooms, the thermal condition in the room is ultimately determined by the method of distributing the air into the room. Fanger and Pedersen [1] have shown that the thermal comfort in a room is not only affected by how uniform the air temperature and air velocity are in the occupied zone (the lower part of a room to a height 2m) but also by the turbulence intensity of the air motion and the dominant frequency of the flow fluctuations. There environmental parameters which have profound influence on comfort, are influenced by the method used to diffuse the air into the room. In addition to the supply air velocity and temperature, the size and position of the diffuser in the room have a major influence on the thermal condition in the occupied zone [2].
In air distribution practice, ceilings and walls are very common surfaces which are used for diffusing the air jet so that when this penetrates the occupied zone its velocity would have decayed substantially. Thus the
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occurrence of draughts is minimized. The region between the ceiling and the occupied zone serves as an entrainment region for the jet which causes a decay of the main jet velocity as a result of the increase in the mass flow rate of the jet.
There are sufficient information and design guides [3, 4] which may be applied for predicting room conditions produced by conventional air distribution methods. However, where non-conventional methods of air supply are employed or where surface protrusions or rough surfaces are used in a wall-jet supply, the design data is scarce. The air distribution system designer has to rely on data obtained from a physical model of the proposed air distribution method. Modifications to these models are then made until the desired conditions are achieved. Apart from being costly and time consuming, physical models are not always possible to construct at full scale. Air distribution studies for the design of atria, theatres, indoor stadiums etc. can only be feasibly conducted with reduced scale models. However, tests carried out in a model should be made with dynamic and thermal similarity if they are to be directly applied to the full scale. This normally requires the equality of the Reynolds number, Re, and the Archimedes number, Ar, [5, 6] which is not possible to achieve in the model concurrently.
The other problem which is often encountered in air distribution design is the interference to the jet from rough surfaces and surface-mounted obstacles such as structural beams, light fittings etc. Previous studies [7, 8] have shown that surface-mounted obstacles cause a faster decay of the jet velocity and when the distance of an obstacle from the air supply is less than a certain value called “the critical distance”, a deflection of the jet into the occupied zone takes place. This phenomenon renders the air distribution in the room ineffective in removing the heat load and, as a result, the thermal comfort in the occupied zone deteriorates. Here again there is a scarcity of design data, particularly for non-isothermal air jets.
Air distribution problems, such as those discussed here, are most suitable for numerical solutions which, by their nature, are good design optimization tools. Since most air distribution methods are unique to a particular building a rule of thumb approach is not often a good design practice. For this reason, a mock-up evaluation has so far been the safest design procedure. Therefore, numerical solutions are most suitable for air distribution system design as results can b readily obtained and modifications can be made as required within a short space of time. Because of the complexity of the air flow and heat transfer processes in a room, the numerical solutions to these flow problems use iterative procedures that require large computing time and memory. Therefore, rigorous validation of these solutions is needed before they can be applied to wide ranging air distribution problems.
In this paper a review is given of published work on numerical solutions as applied to room ventilation. The finite volume solution procedure which has been widely used in the past is briefly described and the equations used in the k-ε turbulence model are presented. Numerical solutions are given for two- and three-dimensional flows and, where possible, comparison is made with experimental data. The boundary conditions used in these solutions are also described.
3.3 如何写论文的展开部分(Approach), 结果和讨论(Results and Discussion)
3.3.1 材料和方法部分
对于以实验为主的研究论文，该部分往往位于论文展开部分的前面。
对于实验，描述应尽可能详细。详细的程度应使别的研究者可以重复你的实验，对难以重复的实验可评价你的实验。
这一部分经常采用小标题，如：subjects, apparatus, experimental design, and chemical synthesis。 在这一部分，你应当说明：(1) 你所用的材料和化学药品的名称；(2)实验条件；(3)实验仪器；(4)实验方法和步骤。
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3.3.2 原理和理论模型部分
对于理论分析和数值计算为主的研究论文，该部分往往位于论文展开部分的前面。
一般首先用数学方法描述所讨论的问题，如列出控制方程、边界条件和初始条件。为简化问题并突出问题本质，常需对问题进行合理假设。这部分会引入一些方程、格式、边界条件和初始条件，下面通过一些例子说明其经常采用的表达方式。
例1[5]
DEVELOPMENT OF MODEL
The model assumes that VOCs are emitted out of a single uniform layer of material slab with VOC-impermeable backing material, and a schematic of the idealized building material slab placed in atmosphere is shown in Fig.1. The governing equation describing the transient diffusion through the slab is
?C(x,t)?t?D?C(x,t)?x22 （1）
where C(x,t) is the concentration of the contaminant in the building material slab, t is time, and x is the linear distance. For given contaminant, the mass diffusion coefficient D is assumed to be constant. The initial condition assumes that the compound of interest is uniformly distributed throughout the building material slab, i.e.,
C(x,t)?C0for0?x?L, t=0 （2）
where L is the thickness of the slab, and C0 is the initial contaminant concentration. Since the slab is resting on a VOC-impermeable surface, the boundary condition of the lower surface of the slab is
?C(x,t)?t?0,t?0,x?0 (3)
A third boundary condition is imposed on the upper surface of the slab (Fig.1)
?D?C(x,t)?x?hm(Cs(t)?C?(t)),t?0,x?L. (4)
where hm is the convective mass transfer coefficient, m/s；Cs(t) is the concentration of VOC in the air adjacent to the interface; mg m-3; C?(t) is the VOC concentration in atmosphere, mg m-3. It should be mentioned that almost all the physically based models in the literature assumed Cs(t)= C?(t), i.e. implied that hm is infinite, (Dunn, 1987; Clausen et al., 1991; Little et al., 1994). Obviously, the case assumed is a special case of equation (4). Besides, equilibrium exists between the contaminant concentrations in the surface layer of the slab and the ambient air, or (Little et al., 1994)
C(x,t)?KCs(t),t?0,x?L. (5)
where K is the so-called partition coefficient.
x C?(t) Cs(t) C(L,t) C(x,t) building material ?m(t)air interface L
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