When a duct-type electric heater is used for air heating, the surface temperature of the electric heating tube is directly related to the cross-sectional flow rate of the air duct. If the flow rate is too low, heat cannot be carried away in time, and the tube wall temperature may approach the allowable upper limit of the material; if the flow rate is too high, the outlet temperature rise will be insufficient, and additional power compensation will be required. During selection, the power density must be calculated based on the air volume, target temperature rise, and allowable tube wall temperature. The DJR-60 offers three structural forms: low-temperature, medium-temperature, and high-temperature. The low-temperature type uses a lower power density, the medium-temperature type increases the load per unit area, and the high-temperature type uses high-temperature-resistant alloy tubes together with a built-in over-temperature control device.
Different media have different requirements for the shell material and surface load of the electric heating tube. When heating air, the tube wall temperature is significantly affected by the flow rate, and carbon steel or stainless steel tubes can be used; when heating oil, the surface load must be controlled to avoid local carbonization of the oil, and a lower power density is usually used; when heating water, the effect of scale on heat transfer must be considered, and tubes with anti-scale coatings can be used; when heating chemical media, stainless steel, titanium tubes, or PTFE sleeves should be selected according to the corrosiveness of the medium. The DJR-60 can adjust the tube material and power density configuration according to the medium type.
In terms of structure, the duct-type electric heater uses steel plates to support the electric heating tubes to reduce vibration caused by airflow. An over-temperature control device is installed in the junction box, which cuts off the power supply when the temperature exceeds the set value. On this basis, the DJR-60 allows the junction box protection rating to be selected as IP54 or higher according to the on-site environment, and the connection between the electric heating tubes and the frame uses a detachable structure for easy single-tube replacement. For air ducts with large vibration, additional intermediate support points can be added.
The DJR-60 is suitable for heating air, oil, water, chemical media, hot-pressing molds, as well as melting salt, alkali, and low-melting-point alloys. During selection, the following must be clarified: medium type, working temperature, ambient temperature, air volume or medium flow rate, power supply voltage (commonly 380V), allowable tube wall temperature, and protection rating. For duct heating, the duct cross-sectional dimensions and interface form must also be provided.
During installation, ensure that the effective heating zone of the electric heating tube is fully immersed in the medium or located within the airflow of the air duct to avoid dry burning. The junction box should avoid high-temperature areas and leave space for maintenance. Regularly check whether the over-temperature control device operates normally, and clean scale or carbon deposits on the surface of the electric heating tubes. When replacing electric heating tubes, select them according to the original model and power density; it is not recommended to arbitrarily increase the surface load.
