通風(fēng)管道沿程局部阻力的計算

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當(dāng)空氣流動斷面變化的管件（如各種變徑管、風(fēng)管進出口、閥門）、流向變化的管件（彎頭）流量變化的管件（如三通、四通、風(fēng)管的側(cè)面送、排風(fēng)口）都會產(chǎn)生局部阻力。

When the air flow section changes tube parts (such as all kinds of variable diameter pipes, air pipes, inlet and outlet, valves), pipes that flow to change (elbow) flow rate of pipe fittings (such as three way, four way, side pipe and air outlet) will produce partial resistance.

局部阻力按下式計算：

Local resistance press formula:

Z=ξν2ρ/2

V 2 P /2 Z=.

ξ――――局部阻力系數(shù)。 局部阻力在通風(fēng)、空調(diào)系統(tǒng)中占有較大的比例，在設(shè)計時應(yīng)加以注意，為了減小局部阻力，通常采用以下措施：

Zeta -- local resistance coefficient. Local resistance occupies a large proportion in ventilation and air conditioning systems. Attention should be paid to the design of local resistance. In order to reduce local resistance, the following measures are usually adopted.

1. 彎頭 布置管道時，應(yīng)盡量取直線，減少彎頭。圓形風(fēng)管彎頭的曲率半徑一般應(yīng)大于（1~2）倍管徑；矩形風(fēng)管彎頭斷面的長寬比愈大，阻力愈??；矩形直角彎頭，應(yīng)在其中設(shè)導(dǎo)流片。

When the 1. elbow is arranged, the line should be taken as far as possible to reduce the elbow. The radius of curvature of the circular duct elbow generally should be greater than (1~2) times the diameter; rectangular duct elbow section length to width ratio is, the smaller the resistance; rectangular elbow, should be set up in the deflector.

2. 三通 三通內(nèi)流速不同的兩股氣流匯合時的碰撞，以及氣流速度改變時形成的渦流是造成局部 阻力的原因。為了減小三通的局部阻力，應(yīng)注意支管和干管的連接，減小其夾角；還應(yīng)盡量使支管和干管內(nèi)的流速保持相等。

2. the collision of the two - strand air flow with different flow velocity in the three pass and three through, and the eddy formed when the velocity of the air flow is changed is the cause of the local resistance. In order to reduce the local resistance of the three pass, attention should be paid to the connection of the branch pipe and the dry pipe to reduce the angle of the pipe; the flow rate in the pipe and the dry pipe should be kept as equal as possible.

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