The absolute roughness of the ventilation pipe has a direct influence on the technical parameters of the ventilation pipeline, which mainly affects the wind speed and pressure loss.
The material with high absolute roughness limits the increase of wind speed. When the wind speed increases, the resistance increases according to the square of the speed, and it will be consumeda larger energy. In piping design, reducing pressure loss means reducing energy consumption, on the contrary, the large the pressure loss, the more the fan load and power consumption increases.And large pressure loss would cause smoke exhaust is not smooth and cannot be discharged. To make the air flow, it is necessary to analyze and calculate the whole pipeline, such as flowing smoothly, discharging the smoke and saving energy.
There are many kinds of materials available for the ventilation pipe. As the kitchen exhaust contains dirty oil and water, and is adjacent to high temperature heat source, it is easy to fire. Therefore, the pipeline should have the characteristics of non-leakage, non-combustion and corrosion resistance. The most widely used are sheet metal, such as galvanizing steel and stainless steel. The composite material are also used for ventilation pipes. The material selection of the pipe depends on the characteristics of the ventilation gasand kitchen condition. The characteristics of ventilation gas are mainly the differences of oil smoke, hot gas, steam, exhaust gas and fresh air. The differencefor the kitchen condition is on internal, outdoor, firefighting, strength, installation method and sanitation and environmental protection requirements, cold rolled plate and cast steel pipe smoke exhaust pipe are mainly used forsmoke chimney in high-altitude outdoor. Metal sheet, such as galvanized sheet and stainless-steel sheet, is corrosion-resistant, easy to seal, non-flammable, non-oil permeable, smooth surface and low friction resistance, which meets the requirements of health, environmental protection and food safety, so it is widely used. The average absolute roughness of brick concrete flue is dozens of times of that of metal plate, and it has the disadvantage of oil and smoke leakage. It is not convenient for construction and transformation, and has been gradually replaced by metal flue.
In order to prevent flue fire, the exhaust pipe needs to clean up the dirty oil regularly. Due to most kitchens use the strong alkali heat treatment method to clean up the dirty oil, the galvanized plate flue will rust and leak after several times of treatment, which greatly reduces the efficiency of the smoke exhaust system. To this end, now many kitchens are using stainless steel plate flue, especially the closed flue which is not easy to reform and repair, should choose stainless steel plate flue.