Plate-and-Frame Exchangers Plate-and-frame exchangers assemblies of pressed corrugated plates on a frame. Gaskets in grooves around the periphery contain the fluids and direct the flows into and out of the spaces between the plates. Close spacing and the presence of the corrugations result in high coefficients on both sides several times those of shell-and-tube equipment and fouling factors are low. The accessibility of the heat exchange surface for cleaning makes them particularly suitable for fouling services and where a high degree of sanitation is required, as in food and pharmaceutical processing. Operating pressures and temperatures are limited by the natures of the available gasketing materials, with usual maxima of 300 psig and 400℉.
Since plate-and-frame exchangers are made by comparatively few concerns, most process design information about them is proprietary but may be made available to serious, engineers. Friction factors and heat transfer coefficients vary with the plate spacing and the kinds of corrugations. Pumping costs per unit of heat transfer are said to be lower than for shell-and-tube equipment. In stainless steel construction, the plate-and-frame construction cost is 50%~70% that of the shell-and-tube.
Spiral Heat Exchangers In spiral heat exchangers, the hot fluid enters at the center of the spiral element and flows to the periphery; flows of the cold liquid is countercurrent, entering at the periphery and leaving at the center. Heat transfer coefficients are high on both sides, and there is no correction to the log mean temperature difference because of the true countercurrent action. These factors may lead to surface requirements 20% or so less than those of shell-and-tube exchangers. Spiral types generally may be superior with highly viscous fluids at moderate pressures.
板式换热器
板式换热器由压制成型的波纹板片组装而成。密封胶垫安装在板片四周的凹槽内，起密封以及导流的作用。板式换热器板间距很小，同时波纹状的板片更易形成湍流，因此板式换热器的传热系数要比管壳式换热器高很多，污垢系数也更小。板式换热器可以拆开清洗，因而更适用于易结垢的工况以及对卫生条件要求比较高的工况，如食品、医药行业。换热器的操作压力和操作温度由密封胶垫的材质决定，最大操作压力一般为300psig左右，做大操作温度一般在400℉左右。
由于板式换热器原理较简单，因此大部分的设计资料都在各个生产厂家手中。不同板型的摩擦系数和传热性能是不同的。每个传热单元数对应的泵送成本要比管壳式换热器低。对于不锈钢板材的板式换热器，其成本大概是管壳式换热器的50%~70%。
螺旋板式换热器
螺旋板式换热器中热流体由内向外流动，冷流体由外向内流动，因此流动方式为逆流。螺旋板式换热器两侧传热膜系数都很高，而且由于流动方式纯逆流，因此对数平均温差无需做修正。同一工况下，螺旋板式换热器要比管壳式换热器面积小20% 左右。对于常压下粘度较高的流体的换热，螺旋板式换热器可能是更好的选择。
