Views:0 Author:Site Editor Publish Time: 2020-05-07 Origin:Site
Heat exchangers often use the terms "heat transfer and accumulation" and "heat transfer coefficient" of the heat exchanger, which is a customary name with a specific meaning. Because the surface area on both sides of the heat exchanger partition may be different, the so-called "heat transfer area of the heat exchanger" actually refers to the surface area of one side of the agreement. The surface area of the wall surface in contact is called the heat transfer area of the heat exchanger, and the heat flux accumulated with respect to the heat transfer per unit time, unit product, and unit temperature difference is called the heat transfer of the heat exchanger. Product, so the heat transfer coefficient is also relative to the product on the agreed side. It is convenient to use "heat transfer accumulation" and "heat transfer coefficient" in the heat exchanger structure and estimation. In the heat transfer analysis of the converter, the heat transfer thermal resistance 1 / (KA) is used. The calculation formula of the thermal resistance of the plate heat exchanger is as follows:
1 / KA = 1 / AW (1/1 + yF1 + 8 / h + yF2 + 1/2)
Where, K——heat transfer coefficient, W / m2C
A——surface area, m2
AW——flat wall area, m2
8—Sheet thickness, m2 C / W
yF——Fouling coefficient, m: C / W.
Subscripts: 1-the side in contact with fluid 1; 2-the side in contact with fluid 2.
1. For the turbulent state, the heat transfer laws of plates with different shapes can generally be summarized as follows,
Nu = CRcPrm (u / Hw) P
In the formula, the feature size in Nu and Re is the equivalent diameter d, d = 4Wb / (2W + 2b)
W——plate width, m;
b——Slab spacing, m
The approximate range of c, n, m, p values are as follows:
c = 0.15 ~ 0.40, n = 0.65 ~ 0.85
m = 0.30 ~ 0.45 (usually 1/3), p = 0.05 ~ 0.20
The Reynolds number of Linsuke is about 10 ~ 400, depending on the shape of the plate.
Nu = C (RePrd / L) n (u / pw) p
In the formula, the range of c, n, p values is generally c = 1.86 ~ 4.50, n = 0.25 ~ 0.33, p = 0.1 ~ 0.2 (usually 0.14)
L——Slab length, m.
Because the shape of the plate is complicated, the heat transfer law obtained from the test must be determined as the basis for the heat transfer calculation of the plate heat exchanger.