How to select duct heater

As the product field of duct heaters continues to expand, duct heaters are now involved in various fields, and there are many transformation cases. There are more and more power station boiler transformation heaters, drying room transformation air heaters, tunnel furnace transformation, coal-to-electricity, mine, sand and gravel transformation, etc. The following editor will take you to look at several groups of duct heater cases. Because duct heaters are mainly used in industry, the final selection is generally different according to temperature requirements, air volume requirements, size, material, etc., and the price is also different. Generally, the selection can be based on the following 5 points: 1. Power selection The power is selected to meet the calorific value required by the heating medium. It is the first choice to ensure that the heater can achieve the heating purpose and operate normally. Since the thermal efficiency of electric heaters is close to 100%, it can be considered that the power of electric heaters is the calorific value. The calculation and selection of power should consider the following three points: (1) From the initial state, the heating medium is heated to the set temperature (working temperature) according to the specified time requirements; (2) Under working conditions, the calorific value is sufficient to maintain the medium temperature; (3) There should be a certain safety margin, generally 1.2.

Obviously, the larger power selected from (1) and (2) and multiplied by the safety margin is the power to be selected.

II. Wind speed design

The measurement of wind pressure, wind speed and air volume in the air duct can be completed by instruments such as Pitot tubes, U-type pressure gauges, inclined micromanometers, and hot-bulb anemometers. Pitot tubes and U-type pressure gauges can test the total pressure, dynamic pressure and static pressure in the air duct. The measured total pressure can be used to know the working condition of the fan, the resistance of the ventilation system, etc. The measured dynamic pressure of the air duct can be converted into the air volume of the air duct. The hot-bulb anemometer can also be used to directly measure the wind speed in the air duct and convert the wind speed into the air volume in the air duct.
1. Connect the fan and ventilation duct.

2. Use a steel coil to measure the diameter of the air duct or the dimensions of the rectangular air duct.

3. Determine the measurement point location based on the diameter or dimensions of the rectangular air duct.

4. Drill a 12mm diameter circular hole in the air duct at the test location.

5. Mark the measurement point location on the Pitot tube or hot-bulb anemometer.

6. Connect the Pitot tube and U-type pressure gauge with latex tubing.

7. Insert the Pitot tube or hot-bulb anemometer vertically into the air duct at the measurement hole to ensure the measurement point is correctly positioned. Pay attention to the orientation of the Pitot tube probe.

8. Directly read the total pressure, dynamic pressure, and static pressure in the air duct on the U-type pressure gauge, and the wind speed in the air duct on the hot-bulb anemometer.

III. Electric Heating Tube Requirements

1. Heating Time: Under the test voltage, the time it takes for the component to heat from ambient temperature to the test temperature should not exceed 15 minutes.

2. Rated Power Deviation: Under fully heated conditions, the deviation of the component's rated power should not exceed the following specified range: for components with a rated power of 100W or less, the deviation is ±10%. For components with a rated power greater than 100W, the deviation is +5% to -10% or 10W, whichever is greater.

3. Leakage Current: Cold leakage current and leakage current after water pressure and sealing tests should not exceed 0.5 mA. Hot leakage current at operating temperature should not exceed the calculated value in the formula, but should not exceed 5 mA. I = 1/6 (tT × 0.00001), where I is the hot leakage current in mA, t is the heating length in mm, and T is the operating temperature in °C. When multiple components are connected in series to a power supply, the leakage current test should be conducted on the entire group.
4. Insulation Resistance: During factory inspection, the cold insulation resistance should be no less than 50 MΩ. The hot insulation resistance at operating temperature should be no less than the calculated value in the formula, but should not be less than 1 MΩ. R = (10 - 0.015T) / t × 0.001, where R is the hot insulation resistance in MΩ, t is the heating length in mm, and T is the operating temperature in °C.

5. Dielectric Withstand Voltage: Components should withstand the specified test conditions and test voltage for 1 minute without flashover or breakdown.

6. Power On/Off Capacity: The component should withstand 2000 power on/off cycles under specified test conditions without damage.

7. Overload Capacity: The component should withstand 30 cycles of overload testing under specified test conditions and input power without damage.

8. Heat Resistance: The component should withstand 1000 cycles of heat resistance testing under specified test conditions and test voltage without damage.

IV. Cabinet Appearance
1. The cabinet consists of: inner chamber, outer insulation layer, bell mouth, upper cover, and machine feet.

2. Materials: Carbon steel, 304 stainless steel, 201 galvanized sheet.

3. Thickness: 1mm, 1.5mm, 2mm, 3mm

4. Inner Chamber Dimensions: Ensure adequate space for the heating element. If the heating element cannot fit, the wattage must be increased. If the inner chamber is too large, there may be dead spots where air cannot reach, and the lifespan of the heating element may be shortened under the same conditions.

5. Flange Types: Square, Round, Rectangular

Reducing Diameter: For inconsistent interface diameters, square to round, round to square, square to square, or round to round.

Center-to-Center Height: The center-to-center distance between the inlet and outlet. The hot air interface on the other side is the outlet of the duct heater.

V. Electrical Appliances and Other Components

Junction Box: Copper busbars, hoses, cables, plastic and metal cable clamps

Distribution Cabinet: Simple, standard, microcomputer LCD, artificial intelligence

Temperature Control: Temperature Probe, Temperature Controller

Temperature Probe: One thermocouple is located in the junction box, the other at the outlet. This one is crucial.

Insulation Requirements: Thickness for optimal insulation. Generally, 50mm is recommended, while larger ones are 80-100mm.

Accessories: Heating tubes, flanges, metal gaskets, asbestos gaskets, screws and nuts