【導讀】和新型殼程結(jié)構的匹配與高效換熱器的開發(fā)進展。闡述了最近換熱器技術：計算流體。力學和傳熱促進技術等的發(fā)展狀況,指出了今后換熱器發(fā)展的方向。在工業(yè)生產(chǎn)中，凡用來實現(xiàn)冷熱流體熱量交換的設備，統(tǒng)稱為換熱器。工、煉油、原子能、建筑、機械、交通等許多技術領域中均有廣泛的應用。傳熱的基本方式有熱傳導、對流和輻射3種，因此在換熱器中，熱量總是從熱流。他高溫流體等；起冷卻作用的冷流體又稱冷卻介質(zhì)，如空氣、冷凍水、冷凍鹽水等。放熱而下降，冷流體的溫度由于吸熱而上升。適應于各種換熱條件，換熱器有多種形。藝具體情況，才能進行合理選型和正確的設計?；瘋鳠嵩菪韫苡糜谡哿鳁U換熱器,節(jié)省換熱面積接近60%,效果十分顯著。前,螺旋植桿折流桿換熱器在桂林化工廠已系統(tǒng)化生產(chǎn)。近年來,桂林化工機械廠、縮放管其擴展段得到有效的利用,收縮段還利用了流體粘附。槽孔折流柵板換熱器工業(yè)應用操作運行的結(jié)果表明具有明顯的強化傳熱效果。

　　

【正文】 in two ways: first by raising the temperature of the receiving stream or bodyofwater above the range that can support the aquatic habitat。 and second by causing a reduction in the dissolved oxygen content of the receiving stream, affecting the kinds of aquatic anisms that can live there. Steps that can be taken to reduce the impact of thermal pollution on the receiving bodyofwater include the following: 1. Use of a holding pond large enough to dissipate the energy of the heated water into the atmosphere, prior to discharge. 2. Use of an evaporative cooling tower prior to discharge. 3. Use of aircooled heat exchangers to reduce the temperature of the waste heated water prior to discharge. 4. Find industrial uses for the waste heated water such as using it with heat exchangers to provide heat for buildings or other processes [5]. Thermal pollution of air from industrial stack emissions is not a practical problem since it does not harm natural habitat. However, if the exhaust air (gas) temperature from the industrial stack is sufficiently high, it is quite mon to employ some waste heat recovery exchangers to recover thermal energy and save the fuel cost [6]. In some cases, in colder climates, solid waste incinerators need to reheat the stack gases in the winter to prevent the creation of fog by condensation of water vapor to avoid people39。s misconception that the emissions are polluting the surrounding environment. In many applications, both material and thermal pollution of air and water is founded such as hot dirty air or water streams. 4. Air pollution prevention from VOCs Volatile anic pounds (VOCs) are precursors (when bined with NOx) to the ozone problem. Some of the VOCs (or effluent contaminants and odor) are: anic solvents, phenols, aldehydes, oil mists, phthalic anhydride, sulphides, mercaptans, odors, and sewage gases. Some of the applications in which VOCs generated are as follows: general 23 manufacturing (wire enameling facilities, paint bake ovens, glass 174。ber curing), phenols and solvent adhesive tape and label curing ovens, sandpaper curing ovens, rubber processing, asphalt blowing, petroleum processing, paper and pulp mills, paint spraying, printing, phenolic coating, laminating, converting, flexible packaging, oil refining, sewage plants, scrap salvaging, metal decorating, food processing and chemical processing. In order to prevent the generation of VOCs, or reduce them, an evaluation of the process must be performed. This includes characterization of the total gas flow rate, VOCs concentration, position, temperature, pressure, solid suspension, humidity, etc. All these parameters will enter in the final selection of the technical solution. There is no universal process for the VOCs treatment, but rather a bination of two or more individual techniques. Five main methodologies can be identified (see Fig. 2) for the VOCs prevention or treatment: biofiltration, high temperature oxidation, adsorption, absorption and condensation. The last three technologies allow recovery and possible recycling of the VOCs. For a more prehensive description of these techniques, refer to Corbitt [7], Ruddy and Caroll [8] or Le Cloirec [9] Heat exchangers are directly involved in condensation processes and are used for energy recovery as services for cooling/heating the streams in all other methods used for the VOCs removal. In the following subsections, we will describe the function of these heat exchangers in the processes, and the main parameters that affect their selection. From an economic viewpoint, the annual operating cost of the process (electricity, gas, nitrogen, etc.) ranges from 5 to 30% of the total investment cost of the process equipment (that include heat exchangers, fans, controls, burners, etc.). Therefore, adopting pact heat exchangers and enhanced technologies is cost e€ ective, as they have lower energy consumption than conventional heat exchangers. The payback time can be less than one year for such enhanced equipment. Furthermore, the reduced volume of the equipment will allow developing skidmounted units. 24 . Biofiltration Biofiltration is a relatively new technology, which uses the microanisms in post todestroy objectionable pollutants in exhaust air from a facility. In applying the technology, the exhaust air is passed through a biofilter system filled with a medium that is essentially the same as a gardener39。s post pile. The microanisms in the medium depose the pollutants in the exhaust, similar to the action that breaks down posted leaves and grass clippings into a soil conditioner. The biofiter39。s action requires no energy other than electricity to operate the fan, which circulates the exhaust air through the system. If successful this can be a considerable advantage over a conventional system such as a thermal oxidizer, which requires nonrenewable resources. While several hundreds of these post technology systems are already in use in Europe, experience has been limited and variable in the United States. An attempt, a few years ago, by one pany to use a biofilter to control odorous solvent vapors from a manufacturing operation was not successful. Biofilters are sensible to temperature, on one hand, the rate of reaction increases with the temperature and on the other the solubility of the VOC decreases. Furthermore, if the temperature of the biofilter remains too longer, the active microanism can be affected and loose its efficiency. In most of the bioreactors the temperature is kept between 108C and 408C. In case that the reaction is exothermic it may be required to cool down the air before 25 blowing. The most simple technique used is to spray water, which has the double advantage of cooling the air stream and of increasing the humidity (which is favorable for biodegr