一、阻力比较
1、 Resistance comparison
我们在进行通风管道计算时，通常离不开流量（风量）、单位摩擦阻力、雷诺数和摩擦阻力系数这四大要素。
When we calculate the ventilation duct, we usually can not do without the four elements of flow (air volume), unit friction resistance, Reynolds number and friction resistance coefficient.
计算时，通过简化雷诺公式为
In calculation, the Reynolds formula is simplified as
Ro=vd/ν
Ro=vd/ ν
式中v为运动粘滞系数（米2/秒）
Where v is the kinematic viscosity coefficient (m2/s)
ν为风速（米/秒）
ν Is the wind speed (m/s)
d为风管内径（米）
D is the inner diameter of air duct (m)
从这一公式中也可以看，运动粘滞系数和管径一定的情况下，雷诺数越大，ν值也就越小，其动力越小。
It can also be seen from this formula that when the kinematic viscosity coefficient and pipe diameter are fixed, the larger the Reynolds number is, ν The smaller the value, the less power.
根据英国学者雷诺的实验所知，层流和率流的产生，兴流体流经的容积断面尺寸、特征速度（平均流速）和流体的粘性系数以及密度有关、见无量纲量---Ro相似准则数公式：
According to the experiment of the British scholar Renault, the generation of laminar flow and rate flow is related to the volume section size, characteristic velocity (average velocity) of the fluid flowing through and the viscosity coefficient and density of the fluid. See the dimensionless quantity - Ro similarity criterion number formula:
Ro=udP/U=ud/ν
Ro=udP/U=ud/ ν
式中：
Where:
Ro--为无量纲量（相似准则数）
Ro -- dimensionless quantity (number of similarity criteria)
u--为平均流速。
U -- mean flow velocity.
d--为特征尺寸。
D - is the feature dimension.
P--为液体的密度。
P - is the density of liquid.
U--为液体的粘性系数。
U - is the viscosity coefficient of the liquid.
ν--为特征速度。
ν-- Is the characteristic velocity.
根据公式：我们可以求证断面面积为1的矩形管和椭圆管的相似准则Ro，假设流经此管道水的平均流速u为5m/s，特征速度ν为1.13×10-6m2/s.断面形状为矩形时的相似准则数为Ro1;断面形状为椭圆形状时的相似准则数为Ro2。将已知条件代入无量纲量公式，Ro1=5×1/(1.13×10-6)>Ro2=0.5×0.5×1.28/(1.13×1)
According to the formula, we can verify the similarity criterion Ro for rectangular and elliptical pipes with a sectional area of 1 square meter. Suppose that the average velocity u of water flowing through the pipe is 5 m/s, and the characteristic velocity ν 1.13 × 10-6m2/s. When the section shape is rectangular, the number of similarity criteria is Ro1; When the section shape is elliptical, the number of similarity criteria is Ro2. Substitute the known conditions into the dimensionless formula, Ro1=5 × 1/(1.13 × 10-6)>Ro2=0.5 × zero point five × 1.28/(1.13 × 1)
我们知道，计算它们湿周的前提是要算出它们的周长，顾名思义，湿周也就是其湿润的周长，即周长。
We know that the premise of calculating their wet perimeter is to calculate their perimeter. As the name implies, the wet perimeter is also their wet perimeter, that is, perimeter.
椭圆形周长的计算公式是
The calculation formula of ellipse perimeter is
周长P=3.14×[1.5（a+b）-（a×b）1/2]
Perimeter P=3.14 × [1.5（a+b）-（a × b）1/2]
其中，a为椭圆的长半径,b为椭圆的短半径.椭圆形断面积的计算公式是:
Where, a is the long radius of the ellipse and b is the short radius of the ellipse. The formula for calculating the sectional area of the ellipse is:
S=3.14×0.5A×0.5B
S=3.14 × 0.5A × 0.5B
其中,A为椭圆的长径,B为椭圆的短径
Where, A is the major diameter of the ellipse and B is the minor diameter of the ellipse
从产品目录表中查出,一断面面积的椭圆形风管的长径A为2000mm,短径B为600mm.
According to the product catalog, the long diameter A and short diameter B of oval air duct with a sectional area of one square meter are 2000mm and 600mm respectively
则:它的四周
Then: around it
P=3.14×[1.5×(1+0.3)-(1×0.3)1/2]=4(M)
P=3.14 × [1.5 × (1+0.3)-(1 × 0.3)1/2]=4(M)
求断面面积为一的矩形风管的湿周
Calculate the wetted perimeter of rectangular air duct with a sectional area of one square meter
设它的边矩尺寸为(A×B)2000×500
Let its side moment dimension be (A × B)2000 × five hundred
即:它的湿周
That is, its wet perimeter
P=5(M)
P=5(M)
由此可见,椭圆形风管的湿周比矩形风管小20%,也就是说同样断面面积的风管,椭圆形风管的周长仅为矩形风管的80%,如果把同样断面面积的矩形风管再变革一下,设定长矩为2500mm、短矩为400mm时,它的湿周是5.8m,则比椭圆形风管大31%。所以，椭圆断面形状的空调风管湿周小。
It can be seen that the wetted perimeter of oval duct is 20% smaller than that of rectangular duct, that is to say, the circumference of oval duct is only 80% of that of rectangular duct for ducts with the same cross-sectional area. If rectangular duct with the same cross-sectional area is changed again, and the set length moment is 2500mm and short moment is 400mm, its wetted perimeter is 5.8m, which is 31% larger than that of oval duct. Therefore, the wet perimeter of the air conditioning duct with elliptical section shape is small.
Jinan ventilation pipe processing http://www.jnqsg.com For more than ten years in the industry, due to the increase of the wet perimeter, that is, the perimeter increases, which means that more materials are needed, thus increasing the cost of investment.
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