1、 Resistance comparison

我們在進(jìn)行通風(fēng)管道計(jì)算時，通常離不開流量（風(fēng)量）、單位摩擦阻力、雷諾數(shù)和摩擦阻力系數(shù)這四大要素。

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.

計(jì)算時，通過簡化雷諾公式為

In calculation, the Reynolds formula is simplified as

Ro=vd/ν

Ro=vd/ ν

式中v為運(yùn)動粘滯系數(shù)（米2/秒）

Where v is the kinematic viscosity coefficient (m2/s)

ν為風(fēng)速（米/秒）

ν Is the wind speed (m/s)

d為風(fēng)管內(nèi)徑（米）

D is the inner diameter of air duct (m)

從這一公式中也可以看，運(yùn)動粘滯系數(shù)和管徑一定的情況下，雷諾數(shù)越大，ν值也就越小，其動力越小。

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.

根據(jù)英國學(xué)者雷諾的實(shí)驗(yàn)所知，層流和率流的產(chǎn)生，興流體流經(jīng)的容積斷面尺寸、特征速度（平均流速）和流體的粘性系數(shù)以及密度有關(guān)、見無量綱量---Ro相似準(zhǔn)則數(shù)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--為無量綱量（相似準(zhǔn)則數(shù)）

Ro -- dimensionless quantity (number of similarity criteria)

u--為平均流速。

U -- mean flow velocity.

d--為特征尺寸。

D - is the feature dimension.

P--為液體的密度。

P - is the density of liquid.

U--為液體的粘性系數(shù)。

U - is the viscosity coefficient of the liquid.

ν--為特征速度。

ν-- Is the characteristic velocity.

根據(jù)公式：我們可以求證斷面面積為1的矩形管和橢圓管的相似準(zhǔn)則Ro，假設(shè)流經(jīng)此管道水的平均流速u為5m/s，特征速度ν為1.13×10-6m2/s.斷面形狀為矩形時的相似準(zhǔn)則數(shù)為Ro1;斷面形狀為橢圓形狀時的相似準(zhǔn)則數(shù)為Ro2。將已知條件代入無量綱量公式，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)

我們知道，計(jì)算它們濕周的前提是要算出它們的周長，顧名思義，濕周也就是其濕潤的周長，即周長。

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.

橢圓形周長的計(jì)算公式是

The calculation formula of ellipse perimeter is

周長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為橢圓的長半徑,b為橢圓的短半徑.橢圓形斷面積的計(jì)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為橢圓的長徑,B為橢圓的短徑

Where, A is the major diameter of the ellipse and B is the minor diameter of the ellipse

從產(chǎn)品目錄表中查出,一斷面面積的橢圓形風(fēng)管的長徑A為2000mm,短徑B為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

則: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)

求斷面面積為一的矩形風(fēng)管的濕周

Calculate the wetted perimeter of rectangular air duct with a sectional area of one square meter

設(shè)它的邊矩尺寸為(A×B)2000×500

Let its side moment dimension be (A × B)2000 × five hundred

即:它的濕周

That is, its wet perimeter

P=5(M)

P=5(M)

由此可見,橢圓形風(fēng)管的濕周比矩形風(fēng)管小20%,也就是說同樣斷面面積的風(fēng)管,橢圓形風(fēng)管的周長僅為矩形風(fēng)管的80%,如果把同樣斷面面積的矩形風(fēng)管再變革一下,設(shè)定長矩為2500mm、短矩為400mm時,它的濕周是5.8m,則比橢圓形風(fēng)管大31%。所以，橢圓斷面形狀的空調(diào)風(fēng)管濕周小。

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.

濟(jì)南通風(fēng)管道加工http://www.369ba.com從事行業(yè)十幾年，由于濕周的增大，也就是周長增大，周長增大意味著所需材料增多，從而投資的成本增加。

Jinan ventilation pipe processing http://www.369ba.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.