Continued on next page To see other variants and accessories, please enter the webcode on our website. webcode 549 KNOWLEDGE DIRECT HEATING IN THE VACUUM DRYING OVEN Different heating concepts are possible in the vacuum drying process: Air jacket heating on the one hand and direct plate heating on the other hand. Since there is no air to conduct the heat in vacuum processes, direct contact between heater and charge is recommended to achieve good results. For this reason, direct heating in the vacuum drying oven has some advantages compared to traditional air jacket heating: In vacuum drying, it provides for short heating and process times and optimum vacuum drying results thanks to the direct contact to the heating elements (thermal shelves). Good heat transfer, short heating times, excellent temperature distribution values, and precise control of the parameters are major criteria for users of vacuum drying ovens. Memmert direct heating in Memmert vacuum drying ovens, for example, meets all these requirements. In these ovens, the direct heaters are cured on to the bottom of the thermal shelves, protected by an aluminium or stainless steel cover plate. In most cases, shelves for vacuum ovens are by default made of surface-finished anodised aluminium or stainless steel to ensure optimum temperature distribution in the vacuum on all separately heated levels. In particular for applications with highly corrosive materials, stainless steel plates should be used. Some vacuum oven manufacturers offer thermal shelves with dedicated Pt100 temperature sensors placed inside the thermal shelf in direct vicinity to the charge. A special connector is provided between each shelf and the rear wall so that the thermal shelves can be removed as required and plugged in on different levels. This also significantly uses the energy consumption. Since the charge is in direct contact with the heating, heat loss is avoided and the charge is heated directly via the thermal shelf. The separate control circuits react precisely to different charge volumes and the humidity of the material and evenly maintain the setpoint temperature. The benefits of direct heating compared to air jacket heating: high energy efficiency and accurate temperature values. Directly heated thermal shelves at Memmert Good to know: To get premium results from your vacuum drying oven, combine it with a speedcontrolled vacuum pump. If another vacuum pump or a central vacuum supply is connected, vacuum control will be effected fully automated via solenoid valves. Thermal shelves made of aluminium (W.St. 3.3547) or stainless steel (W.St. 1.4404) Silicone heating pad (with housing) Integrated Pt100 temperature sensor Connector for heater and temperature sensor
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