What Is a Tube Shield?

The fume hood is a device installed at the outlet of the water heater's flue gas, which is used to reduce the influence of the downwind on the combustion performance of the burner; it is conducive to the easy escape of smoke when the smoke is discharged and the flue is blocked. ^[1]

The smoke exhaust hood is composed of a cover body and an upper and a lower part of the cover. The cover body is composed of three parts.

Umbrella hood

This type of exhaust hood is mainly used to remove dirty heat from dishwashing basins, dishwashers and small single cooking equipment. It is usually installed above the equipment and generally does not have filtering and purification devices. The cross section of the umbrella cover used in the kitchen is mostly rectangular. Its characteristics are simple structure, easy to manufacture, good ventilation when the air volume is reasonable, and it is a necessary equipment in the kitchen.

Oil mesh fume hood

This is the most commonly used type of fume hood in the kitchen. The horizontal projection surface of the hood is rectangular, and the cross-section is like an umbrella hood with a half side. The length is determined by the number of stoves and the length of the display. The height is 550 mm, the width is generally 1250 mm, and the total width of the leading-edge air supply device is about 1500 mm. The inside of the hood is equipped with a labyrinth filter oil filter at an angle of 60 °, which has a certain ability to filter oil fume, and is often used in the kitchen of a general restaurant.

The technical parameters of the commonly used oil mesh fume hood are shown in the following table:

Resistance / Pa	Hood / mm			Supply fresh air pipe / mm				Applicable cooker depth / mm	Fan power / kW
	long	deep	high	long	deep	high	Wind blow
<100		6000	1250	550	6000	550	350	<1000	4
<100		6000	1450	550	6000	550	350	<1300	5.5

Water hood

The water equipped with the washing liquid is pressurized by a water pump and sent to a hood for spraying into a fan shape. The oily gas from the lower part of the hood is decontaminated and purified during contact with the fan-shaped water surface, and the water is separated by a gas-liquid separation fan and flows. Back to the water tank. This is the basic working principle of the water hood. The water transport hood has a complete set of automatic control systems such as sewage, water, washing liquid, and circulation, which is very convenient to operate and use. After the hood is purified, the gas degreasing rate can reach about 90%, and the pipeline is no longer polluted. Due to the isolation of water mist, this hood also has a certain fire prevention function.

The technical parameters of commonly used water hoods are shown in the following table:

Resistance / Pa	Hood / mm			Supply fresh air pipe / mm
	long	deep	high	long	deep	high	Water pump	Power / kW
<120	<4600	1350	685	618	527	1950	single	1.1
<120	<9200	1350	685	618	527	1950	double	2.2

Impinging stream fume purification fume hood

This device is a patented product. It uses the principle of impinging flow. Its core technology is an active high-speed gas-liquid contact device. This equipment has the characteristics of high mass transfer coefficient, small size, high purification efficiency and low energy consumption. Its oil fume purification efficiency can reach more than 95%. The gas-liquid contact mechanism without mechanical power and control device in the reaction box in the system is an oil fume purification device with high purification efficiency, lowest operating cost and smallest volume among existing oil fume purification equipment. The technical data of impinging fume purification fume hood is shown in the following table:

Dimensions	Handling air volume	Purification efficiency	Equipment resistance	Moisture content of outlet flue gas
1200mm × 650mm × 500mm	3000	<95%	120Pa	> 8%

When selecting such equipment, the number of reaction boxes should be calculated according to the length of the fume hood, and all the reaction boxes should be arranged in the hood in order, and the equipment such as the exhaust duct, water inlet pipe, drain pipe, control box and so on should be connected. ^[3]

Smoke extraction hoods that use natural smoke are required to be able to generate a certain amount of suction in order to exhaust all the smoke that should be removed and the ambient air that is sucked in. If the flue gas flow is unstable, or there is little difference between the severity of the flue gas and the surrounding air, it is reasonable to use a natural exhaust hood.

(1) Determination of the shape and size of the exhaust hood of the horizontal smoke emission source

The cross-sectional shape of the exhaust hood mouth is as similar as possible to the horizontal projection of the smoke emission source.

The contraction angle of the exhaust hood should be equal to or less than 60 °, and the maximum should not be greater than 90 °. In order to reduce the height of the fume hood, the long side of the rectangular fume hood can be set in sections.

The fume hood cover should have a vertical edge (skirt edge) with a certain height, and the height of the vertical edge

(

Is the cover area).

The section size of the hood is calculated as follows:

(1) The absorption rate of oil fume should be greater than 95%, and the same diversion containment device should be adopted.

(2) The enclosure structure should be equipped with hinged inspection doors to facilitate sanitary cleaning and observation.

(3) The equipment is all made of stainless steel, and all joints are waterproof, steam-proof, and oil-proof.

(4) The windshield is embedded in the suspended ceiling, with a stainless steel decorative plate between the two. It is made of stainless steel with a thickness of 1.2mm.

(5) All covers are made of stainless steel with a thickness greater than 1.0mm.

(6) The ventilation pipe is made of 1.0 galvanized sheet and is equipped with a stainless steel iron air volume regulating valve.

(7) The lighting equipment is splash-proof, waterproof, and recessed, and is distributed every 1000mm distance. All wires should be placed in conduits and connected with junction boxes. Illumination device is greater than or equal to 600 lux, using energy-saving zhiguang tube lights, unified power interface.

(8) The vertical plate of the wind hood is equipped with a self-discharging device that surrounds the whole. The discharge tank is easy to clean oil fume and steam. The discharge pipe is made of stainless steel.