Chapter 6 technology institute of HAVC from usst INDUSTRIAL VENTILATION TUTORIAL 王丽慧

Chapter 6 the ventilation pipe’s design and calculation 1.This chapter mainly elaborates the design principle and calculation methods of ventilation pipe 2.The purpose of design calculation under the prerequisite requirements of air distribution, reasonable duct layout and size, make the system of the integrated optimal initial investment and running costs.

The first section: Duct in the air flow resistance 1.Duct air flow resistance has two kinds: frictional resistance (frictional resistance and local resistance 2.The formula of frictional resistance

Hydraulic radius calculation For circular duct (1) the hydraulic radius The first section: Duct in the air flow resistance

（ 2 ） Frictional resistance （ 3 ） Frictional resistance The use of line diagram: known flow rate, pipe diameter, flow velocity, resistance from two of the four parameters, can use the picture the rest of the two parameters are obtained. But should pay attention to when the actual conditions of use and the conditions of the line diagram is not at the same time, should be revised. The first section: Duct in the air flow resistance

The use of line diagram: Line diagram is in a certain pressure, temperature, air density, kinematic viscosity, wall roughness situation, attention should be paid to: 1) the density and viscosity correction 2) air temperature and atmospheric pressure 3) tube wall roughness correction The first section: Duct in the air flow resistance

Rectangular duct friction resistance (1)the flow velocity equivalent diameter According to the flow velocity equivalent diameter of DV of rectangular duct and the actual velocity v, can use the line diagram to check than friction of rectangular duct (2) flow equivalent diameter

According to the rectangular duct flow equivalent diameter of DL and the actual flow, L can use the line diagram to check than friction of rectangular duct. 2. Local resistance Produce: when the air through the section change of pipe fittings, flow to the changes of pipe fittings and flow pipe fittings can produce local resistance. Local resistance calculation

When the design to reduce the local resistance, usually the measures taken 1. The elbow: circular duct bend radius of curvature of the general should be greater than 1 ~ 2 times the pipe diameter. Rectangular right-angle bend should set a deflector. 2. T: avoid even the appearance of ejector. Pay attention to the main and branch pipe connection, reduce the Angle. Try to keep the tubes and the flow rate of the dry tube is equal. 3. The exhaust pipe exports: reduce the exhaust of the riser exit velocity, dynamic pressure loss to reduce exports 4. The pipe connection and fan: try to avoid in the takeover of local vortex. The first section: Duct in the air flow resistance

the second section: Pressure distribution within the duct As shown in the figure below the ventilation system, analysis the system pressure distribution in the flue

The main characteristic: 1) fan air pressure is equal to the full differential pressure at the inlet and outlet of the fan; Duct resistance and export pressure loss, the sum of the duct is equal to the total resistance. 2) fan inhaled total pressure and static pressure are negative, negative pressure at the entrance of the fan's largest; Fan out of total pressure and static pressure are generally positive, in the biggest export positive pressure fan. 3) each parallel branch pipe resistance are always equal. 4) when the pressure big all over pressure, static pressure is negative, the opening place will be out of the air inhaled air rather than pressure. the second section: Pressure distribution within the duct

Thinking: calculate the value of each point total pressure, static pressure value and the dynamic pressure value, mark them, in point connection, the pressure inside the duct distribution can be obtained. 1 the second section: Pressure distribution within the duct

2 ： 3 ： 4 ： the second section: Pressure distribution within the duct

5 （ the entrance of fan ）： 11(the duct import) the second section: Pressure distribution within the duct

6 （ the entrance of fan ）： Put in the total pressure of any of the above points, and according to the frictional resistance and duct length into linear relationship, connecting the points total pressure distribution curve. Each point total dynamic pressure, reduce to this point, the static pressure at various points is to draw the static pressure distribution curve. The flow of air in the tube the second section: Pressure distribution within the duct

10 ： 9 ： 8 ： 7 ： the second section: Pressure distribution within the duct

The third section: The hydraulic calculation of ventilation pipes Objective: to determine the section of the pipe diameter (or section size) and resistance, and guarantee the system meet the requirements of air distribution, determine the type and power consumption of the fan. Duct hydraulic calculation methods: assume that velocity of pressure loss of the (common), average method, the static pressure after wisely. The characteristics of the three methods and applicable

Assume that the velocity calculation steps and methods of the methods are as follows: 1. Map system shaft side, the section number, length and air flow. To determine the reasonable air flow rate 3. According to each duct of air volume and select the velocity determine the section size of each section, calculation of frictional resistance and local resistance. 4. And even the line resistance balance. (1) adjust the branch pipe diameter The third section: The hydraulic calculation of ventilation pipes

(2) increase the air volume The third section: The hydraulic calculation of ventilation pipes

(3) regulating valve 5. Calculate the total resistance system 6. Select the fan (1) according to the nature of the conveying gas, the system of air volume and resistance to determine the type of fan. (2) considering leakage and pressure calculation is not accurate, press to choose the type fan. The third section: The hydraulic calculation of ventilation pipes

(3) when the fan working under non-standard state, press the type conversion of fan performance parameter selection fan The third section: The hydraulic calculation of ventilation pipes

The forth section :uniform air duct design calculations The design principle of uniform air supply pipes 1. The flow rate of the static pressure difference to produce 2. The velocity of air within the duct

3. The orifice flow direction: 4. The orifice of the actual flow rate: The forth section :uniform air duct design calculations

5. Orifice outflow air volume 6.Mean velocity The forth section :uniform air duct design calculations

Achieve uniform air supply can take measures Realize the basic conditions of uniform air supply 1. Keep the side hole static pressure is equal 2. Keep the side hole flow coefficient is equal 3. Increase the flow Angle alpha Side hole when the supply air path coefficient of local resistance and local resistance coefficient of side hole The calculation method of uniform air supply duct The forth section :uniform air duct design calculations

The fifth section:The relevant issues in the design of ventilation pipes The classification principles of system Duct layout A standard system, the choice of section shape and pipes 1. Rectangular duct and the resistance ratio of the same area of circular duct

2. The pipe standard 4. Duct material choice 5. Duct insulation 6. Into the air outlet 7. The explosion and fire The fifth section:The relevant issues in the design of ventilation pipes

The sixth section: Pneumatic conveying pipeline calculation of the system The characteristics of the pneumatic conveying system Classification: suction type compression type hybrid circulating 1. The pumping system (negative pressure pneumatic conveying system) has simple structure, convenient operation and maintenance, transportation distance is restricted, system work under negative pressure. 2. Delivery system

Pneumatic conveying system of pipeline resistance computation System resistance including 1. The device resistance 2. The air and the acceleration of boring resistance 3. The floating resistance material 4. Improve resistance materials The frictional resistance of the transporting pipe 6. Bending resistance 7. Separator resistance 8. The resistance of the other components The sixth section: Pneumatic conveying pipeline calculation of the system