远古以来，人类就习惯于用天然热源和自然通风来干燥物料，完全受自然条件制约，生产能力低下。随生产的发展，它们逐渐为人工可控制的热源和空气除湿机所代替。近代空气干燥机开始使用的是间歇操作的固定床式空气干燥机。19世纪中叶，洞道式空气干燥机的使用，标志着空气干燥机由间歇操作向连续操作方向的发展。回转圆筒空气干燥机则较好地实现了颗粒物料的搅动，干燥能力和强度得以提高。
Since ancient times, people have been used to using natural heat sources and natural ventilation to dry materials, which are restricted by natural conditions and have low productivity. With the development of production, they are gradually replaced by artificial controllable heat sources and air dehumidifiers. The modern air dryer starts with a stationary bed air dryer that operates intermittently. In the middle of the 19th century, the use of the tunnel air dryer marked the development of air dryer from intermittent operation to continuous operation direction. The rotary cylinder air drying machine can realize the agitation of granule materials better, and the drying capacity and strength can be improved.

 

 
　　一些行业则分别发展了适应本行业要求的连续操作空气干燥机，如纺织、造纸行业的滚筒空气干燥机。20世纪初期，乳品生产开始应用喷雾空气干燥机，为大规模干燥液态物料提供了有力的工具。40年代开始，随着流化技术的发展，高强度、高生产率的沸腾床和气流式空气干燥机相继出现。而冷冻升华、辐射和介电式空气干燥机则为满足特殊要求提供了新的手段。60年代开始发展了远红外和微波空气干燥机。
Some industries have developed continuous air drying machines, such as the roller air drying machines in textile and paper industries, which are suitable for the industry. In the early 20th century, dairy production began to apply spray air dryer, which provided a powerful tool for mass drying of liquid materials. Since the 1940s, with the development of fluidization technology, high-intensity, high-productivity boiling bed and air flow air dryer have appeared successively. And freezing sublimation, radiation and dielectric air dryer provide new means to meet special requirements. Since the 1960s, far infrared and microwave air drying machines have been developed.

 

 
　　干燥过程需要消耗大量热能，为了节省能量，某些湿含量高的物料、含有固体物质的悬浮液或溶液一般先经机械脱水或加热蒸发，再在空气干燥机内干燥，以得到干的固体。
Drying process needs to consume a large amount of thermal energy, in order to save energy, high content of some of the wet material, suspending liquid containing solid material or solution by mechanical dehydration or heating evaporation first commonly, to dry in the air dryer, to get dry solids.

 

 
　　干燥的目的是为了物料使用或进一步加工的需要。如木材在制作木模、木器前的干燥可以防止制品变形，陶瓷坯料在煅烧前的干燥可以防止成品龟裂。另外干燥后的物料也便于运输和贮存，如将收获的粮食干燥到一定湿含量以下，以防霉变。由于自然干燥远不能满足生产发展的需要，各种机械化空气干燥机越来越广泛地得到应用。
The purpose of drying is for the use of materials or for further processing. If the drying of wood before making wood and wood, can prevent the deformation of products, the drying of ceramic blank in the calcining can prevent the product from cracking. In addition, the dry materials are also easy to transport and store. If the harvested grain is dried to a certain amount of moisture, it can be used to prevent mildew. Since natural dryness is far from being able to meet the needs of production development, various mechanized air dryers have been widely used.

 

 
　　在干燥过程中需要同时完成热量和质量(湿分)的传递，保证物料表面湿分蒸汽分压(浓度)高于外部空间中的湿分蒸汽分压，保证热源温度高于物料温度。
In the drying process needs to be done at the same time in the transfer of heat and mass (moisture), ensure material surface moisture vapor partial pressure (concentration) than the wet steam pressure, in the outer space guarantee the temperature of heat source temperature is higher than the material.

 

 
　　热量从高温热源以各种方式传递给湿物料，使物料表面湿分汽化并逸散到外部空间，从而在物料表面和内部出现湿含量的差别。内部湿分向表面扩散并汽化，使物料湿含量不断降低，逐步完成物料整体的干燥。
The heat transfer from the hot heat source to the wet material in a variety of ways, the surface moisture of the material is vaporized and dispersed to the outer space, thus the moisture content of the material surface and the interior is different. The internal moisture is diffused to the surface and vaporized, so that the moisture content of the materials is continuously reduced, and the overall drying of the materials is gradually completed.

 

 
　　物料的干燥速率取决于表面汽化速率和内部湿分的扩散速率。通常干燥前期的干燥速率受表面汽化速率控制;而后，只要干燥的外部条件不变，物料的干燥速率和表面温度即保持稳定，这个阶段称为恒速干燥阶段;当物料湿含量降低到某一程度，内部湿分向表面的扩散速率降低，并小于表面汽化速率时，干燥速率即主要由内部扩散速率决定，并随湿含量的降低而不断降低，这个阶段称为降速干燥阶段。
The drying rate of materials depends on the diffusion rate of surface vaporization rate and internal moisture. The drying rate is controlled by surface evaporation rate. Then, as long as the external conditions of the dry conditions are constant, the drying rate and surface temperature of the material are stable, which is called the constant speed drying stage. When the material moisture content down to a certain extent, the internal moisture to the surface of the diffusion rate is reduced, and vaporization rate is less than the surface, the drying rate is mainly determined by the internal diffusion rate, and decrease with the decrease of moisture content, this phase is called the falling rate drying stages.

 

 
　　空气干燥机可按操作过程、操作压力、加热方式湿物料运动方式或结构等不同特征分类。按操作过程，空气干燥机分为间歇式(分批操作)和连续式两类;
Air dryer can be classified according to operation procedure, operation pressure, heating mode wet material movement or structure. According to the operation process, the air dryer is divided into intermittent (batch) and continuous type;

 

 
　　按操作压力，空气干燥机分为常压空气干燥机和真空空气干燥机两类，在真空下操作可降低空间的湿分蒸汽分压而加速干燥过程，且可降低湿分沸点和物料干燥温度，蒸汽不易外泄，所以，真空空气干燥机适用于干燥热敏性、易氧化、易爆和有毒物料以及湿分蒸汽需要回收的场合;
According to the operating pressure, air dryer can be divided into normal pressure air drying machine and vacuum air dryer, operation can reduce the moisture of the space in the vacuum steam partial pressure and speed up drying process, and can reduce moisture boiling point and material drying temperature, steam is not easy to leak, so the vacuum air drying machine is suitable for drying heat sensitive, easy oxidation, explosive and toxic materials, and moisture vapor recovery situation;

 

 
　　按加热方式，空气干燥机分为对流式、传导式、辐射式、介电式等类型。对流式空气干燥机又称直接空气干燥机，是利用热的干燥介质与湿物料直接接触，以对流方式传递热量，并将生成的蒸汽带走;传导式空气干燥机又称间接式空气干燥机，它利用传导方式由热源通过金属间壁向湿物料传递热量，生成的湿分蒸汽可用减压抽吸、通入少量吹扫气或在单独设置的低温冷凝器表面冷凝等方法移去。这类空气干燥机不使用干燥介质，热效率较高，产品不受污染，但干燥能力受金属壁传热面积的限制，结构也较复杂，常在真空下操作;辐射式空气干燥机是利用各种辐射器发射出一定波长范围的电磁波，被湿物料表面有选择地吸收后转变为热量进行干燥;介电式空气干燥机是利用高频电场作用，使湿物料内部发生热效应进行干燥。
According to heating method, air dryer is divided into flow type, conduction type, radiant type, dielectric type and so on. The air dryer is also known as direct air drying machine. It is a direct contact between the hot drying medium and wet materials to transfer heat by convection, and the generated steam is carried away. Conduction type air dryer, also known as indirect air dryer, it USES the conduction way by heat transfer heat to the wet material through metal partition, the generated moisture vapor available vacuum suction and ventilation with a small amount of purge gas or in a separate set of low-temperature condensation on the condenser surface method. This kind of air dryer does not use the drying medium, the heat efficiency is higher, the product is not polluted, but the drying ability is limited by the heat transfer area of the metal wall, the structure is also more complex, often in the vacuum operation; The radiant air dryer is the electromagnetic wave that USES various radiators to emit a certain wavelength range, which is selectively absorbed by the wet material surface and then converted into heat to dry. Dielectric air drying machine is used to use high frequency electric field to dry the heat effect inside the wet material.

 

 
　　按湿物料的运动方式，空气干燥机可分为固定床式、搅动式、喷雾式和组合式;按结构，空气干燥机可分为厢式空气干燥机、输送机式空气干燥机、滚筒式空气干燥机、立式空气干燥机、机械搅拌式空气干燥机、回转式空气干燥机、流化床式空气干燥机、气流式空气干燥机、振动式空气干燥机、喷雾式空气干燥机，以及组合式空气干燥机等多种。
According to the way of wet materials, air dryer can be divided into fixed bed type, agitating type, spray type and combination. According to the structure, air dryer can be divided into the van air dryer, air drying machine, roller conveyor type air dryer, vertical air drying machine, the mechanical agitation type air drying machine, rotary air drying, fluidized bed type air drying machine, pneumatic air dryer, vibration type air dryer, spray dryer, air and combined type air dryer, etc.

 

 
　　空气干燥机的未来发展将在深入研究干燥机理和物料干燥特性，掌握对不同物料的最优操作条件下，开发和改进空气干燥机;另外，大型化、高强度、高经济性，以及改进对原料的适应性和产品质量，是空气干燥机发展的基本趋势;同时进一步研究和开发新型高效和适应特殊要求的空气干燥机，如冷冻除湿机、转轮除湿机和空气冷冻干燥机等。
The future development of air dryers will be studied in depth to study the drying mechanism and the drying characteristics of the material, master the optimal operating conditions for different materials, and develop and improve the air dryer. In addition, the development of air drying machine is the basic trend of the development of air drying machine, with the development of large scale, high strength, high economy and improving the adaptability of raw materials and the quality of products. In the meantime, we will further study and develop new and efficient air drying machines, such as freezing dehumidifiers, wheel dehumidifiers and air freeze drying machines.

 

 
　　空气干燥机的发展还要重视节能和能量综合利用，如采用各种联合加热方式，移植热泵和热管技术，开发太阳能空气干燥机等;还要发展空气干燥机的自动控制技术、以保证最优操作条件的实现;另外，随着人类对环保的重视，改进空气干燥机的环境保护措施以减少粉尘和废气的外泄等，也将是需要深入研究的方向。
The development of air dryer should also pay attention to the comprehensive utilization of energy saving and energy, such as the use of various combination heating methods, transplanting heat pump and heat pipe technology, developing solar air dryer, etc. The automatic control technology of air dryer is also developed to ensure the optimal operating conditions. In addition, with the emphasis on environmental protection, the improvement of environmental protection measures of air dryer to reduce the leakage of dust and exhaust gas will also need to be further studied.