Very comprehensive - how to select air duct heaters?

Due to the fact that the air duct heater is mainly used in industry, the final selection is generally based on temperature requirements, air volume requirements, size, material, and other factors, and the price also varies. Generally, the selection can be based on the following 5 points:

1, Power selection

The selection of power is to meet the required heat generation of the heating medium and is the preferred choice to ensure that the heater can achieve its heating purpose and operate normally. Due to the thermal efficiency of the electric heater being approximately 100%, it can be assumed that the power of the electric heater is the heat generated.

The calculation and selection of power should consider the following three factors:

(1) From the initial state, heat the medium to the set temperature (working temperature) according to the specified time requirements;

(2) Under operating conditions, the heat generated is sufficient to maintain the medium temperature;

(3) There should be a certain safety margin, generally taking 1 2.

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

 

2, Wind speed design

The measurement of air duct pressure, wind speed, and air volume can be achieved through pitot tubes Use instruments such as U-shaped pressure gauges, inclined micro pressure gauges, and hot ball anemometers to complete the task. Bi Tuo Tuo The U-shaped pressure gauge can measure the total pressure, dynamic pressure, and static pressure inside the air duct. The measured total pressure can indicate the working condition of the fan and the resistance of the ventilation system. The measured dynamic pressure of the air duct can be used to convert the air volume of the air duct. The hot ball anemometer can also be used to directly measure the wind speed inside the air duct, and the air volume inside the duct can be converted from the wind speed.

 

1. Connect the fan and ventilation duct

2. Use steel coils to detect the diameter of air ducts or the size of rectangular air ducts

3. Determine the measurement point position based on the diameter or size of the rectangular air duct

4. Drill a circular hole with a diameter of 12mm on the air duct at the location

5. Mark the measurement point position on a pitot tube or hot bulb anemometer

6. Connection between pitot tube and U-shaped pressure gauge using latex tube

7. A pitot tube or hot ball anemometer is inserted vertically into the air duct at the measuring hole to ensure the correct position of the measuring point, and attention is paid to the direction of the pitot tube probe.

8. Directly read the total pressure, dynamic pressure, and static pressure inside the air duct on a U-shaped pressure gauge, and directly read the wind speed inside the air duct on a hot ball anemometer.

3, Requirements for electric heating tubes

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

2. Rated power deviation: Under sufficient heating conditions, the deviation of the rated power of the component should not exceed the range specified below. For components with a rated power of less than or equal to 100W, it is ± 10%. For components with a rated power greater than 100W, it is+5%~-10% or 10W, whichever is greater.

3. Leakage current: The cold leakage current, as well as the leakage current after water pressure and sealing tests, should not exceed 0.5mA. The hot leakage current at operating temperature should not exceed the calculated value in the formula, but the maximum should not exceed 5mA, I=1/6 (tT × 0.00001), I - Hot leakage current mA t - Heating length mm, When multiple components are connected in series to the power supply at a working temperature of ℃, a leakage current test should be conducted on this group of components as a whole.

 

 

4. Insulation resistance: During factory inspection, the cold insulation resistance should not be less than 50M Ω, and the hot insulation resistance at working temperature should not be lower than the calculated value in the formula, but the minimum should not be less than 1M Ω, R=(10-0.015T)/t x 0.001, R - Thermal insulation resistance M Ω, T - heating length mm, T - Working temperature ℃.

5. Insulation and withstand voltage strength: The component should be maintained for 1 minute under the specified test conditions and test voltage without flashover or breakdown.

6. Ability to withstand power on and off: Components should be able to undergo 2000 power on and off tests under specified test conditions without damage.

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

8. Heat resistance: The component should withstand 1000 cycles of heat resistance testing under the specified test conditions and test voltage, rather than occurring.

4, Appearance of the box

 

1. The box is divided into: inner chamber, outer insulation layer board, horn mouth, upper cover plate, and machine foot

2. The materials are divided into: carbon steel, stainless steel 304, 201 galvanized sheet

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

4. Inner bore size: attention should be paid to the placement of electric heating tubes. If they cannot be arranged properly, the power of the electric heating tubes should be increased. If they are too large, there may be blind spots that cannot be blown by wind, and the lifespan of the electric heating tubes may be affected under the same conditions.

5. Types of flanges: square, circular, rectangular

Variable diameter type: Inconsistent interface diameter, square to circle, circle to square, square to square, and circle to circle diagrams

Center to center height: The center to center height of the air inlet and outlet, where the other side's hot air interface is the outlet of the air duct heater

5, Electrical and other parts

 

Junction box: copper bar, hose, cable, plastic metal cable clamp

Distribution cabinet: simple, ordinary, microcomputer LCD artificial intelligence

Temperature control: temperature measuring probe, temperature controller

 

Temperature measuring probe: One thermocouple is inside the junction box and the other is at the air outlet, which is very important

Insulation requirements: How thick is the insulation degree, usually 50mm, and the larger volume is 80-100mm

Spare parts: heating tubes, flanges, metal gaskets, asbestos gaskets, screws and nuts