JB/T 8659-1997 Calculation method of water dynamics of hot water boiler
Some standard content:
Mechanical Industry Standard of the People's Republic of China
JB/T8659—1997
Calculation Method of Hydrodynamics of Hot Water Boilers
1997—12—17 Issued
Ministry of Machinery Industry of the People's Republic of China
1998-02—01 Actual Fertilizer
The standard for calculating the hydrodynamics of hot water boilers is one of the standards for assessing the hydrodynamic characteristics. It is a design method to avoid hydrodynamic failures of hot water boilers, prevent scaling, pipe blockage and pipe burst accidents, and ensure the safe operation of hot water boilers. There are no such standards internationally or domestically.
This standard is published for the first time.
Appendices A, B and C of this standard are appendices to the standard. Appendices D, E, F and G of this standard are appendices for suggestions. This standard is proposed and managed by Shanghai Industrial Boiler Research Institute. This standard is drafted by Harbin Institute of Technology, Wuxi Boiler Factory and Shanghai University of Technology. The main drafters of this standard are: Yang Lidan, Dong Zukang, Zhuo Ning, Bao Yiling, Pang Yun, Lu Huilin, Xi Shiguang. Foreword
Cited standards
Term definitions
Basic method for calculating the pressure drop in the tube
Heat flux density distribution and reliability of the heating surface: Hydrodynamic calculation of natural circulation hot water boilers Hydrodynamic calculation of forced flow hot water boilers...·8 Computer method for hydrodynamic calculation of hot water boilers...·Appendix A (Standard Appendix)
Appendix B (Standard Appendix)
Appendix C (Standard Appendix)
Appendix D (Suggestive Appendix)
Appendix E (Suggestive Appendix)
Appendix F (Suggestive Appendix)
Appendix G (Suggestive Appendix)| |tt||Minimum safe water velocity in the tube
Specific volume and specific volume of water
Prandtl number and dynamic viscosity of water at different temperatures Examples of hydrodynamic calculations for natural circulation hot water boilers Simplified method for calculating water circulation in a simple loop of a natural circulation hot water boiler Examples of hydrodynamic calculations for forced circulation hot water boilers Hot water heating system·
1 Scope
Standards of the People's Republic of China for the machinery industry
Methods for calculating hydrodynamics for hot water boilers
JB/T8659—1997
This standard specifies the calculation and verification methods for hydrodynamic characteristics, flow resistance and hydrodynamic reliability in the heating tubes of hot water boilers. This standard is applicable to various fixed hot water boilers with water as the medium within the scope of GB/T3166-1988 "Parameter Series for Hot Water Boilers". For the water-cooled wall heating surface of shell-type horizontal externally fired water-fire tube hot water boilers and the hot water system in steam-water dual-purpose boilers, this standard can also be used to verify the hydrodynamic characteristics. This standard does not apply to hot water boilers whose water quality conditions do not meet the requirements of GB/T1576-1996 "Low-pressure boiler water quality." 2 Reference standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. At the time of publication of the standard, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest version of the following standards. GB/T15761996 Low-pressure boiler water quality
GB/T3166-1988 Hot water boiler parameter series 3 Definition of terms
3.1 Circulation mode
The flow mode of hot water boilers is generally divided into three types: natural circulation, forced flow and forced flow with natural circulation characteristics. The natural circulation mode relies on the gravity difference between the downcomer and the riser to drive the water circulation flow, and the forced flow mode relies on the head of the circulating pump to make the water flow. 3.2 Circulation loop
In a natural circulation hot water boiler, a closed system consisting of an ascending pipe and a descending pipe is called a loop: a loop formed by a single descending pipe or a group of basically identical descending pipes connected to a group of pipes with basically the same structure, position, flow direction and heat load is called a simple loop, and vice versa is called a complex loop.
3.3 Hydraulic system
The hydraulic system of a hot water boiler includes the connecting pipes, headers and heating pipe groups from the return water entering the boiler to the outlet. Under various operating conditions, the hydraulic system should maintain a single-phase medium (hot water) and should not vaporize. 3.4 Tube groups, tube bundles and pipe fittings
The heating surface composed of parallel pipes between the same inlet and outlet headers is called a tube group, and the connected bundled convection heating surface is called a tube bundle. The components in the tube group (such as throttle rings, elbows, tees, etc.) are called pipe fittings. 3.5 Flow and Tube Ring
The parallel connected heated tube sections with the same ascending, horizontal and descending flow directions in the tube group are called flow. The tube group that rises in a spiral around the furnace perimeter is called a tube ring.
3.6 Subcooled Boiling
When the average temperature of the fluid cross section in the heated tube is lower than the saturation temperature at that pressure, the boiling phenomenon near the wall is called subcooled boiling. 3.7 Hydrodynamic Characteristics
The relationship between pressure drop and flow is called hydrodynamic characteristics, and the above relationship expressed in a graph is called a hydrodynamic characteristic curve. The hydrodynamic characteristics of a single-phase medium of a hot water boiler are generally single-valued, that is, one pressure corresponds to one and only one flow rate. However, some tube groups with special flow may have multiple values. Approved by the Ministry of Machinery Industry on December 17, 1997
Implementation on February 1, 1998
3.8 Comprehensive hydrodynamic characteristic curve
JB/T8659--1997
When each circuit in the pipe group is composed of parallel connected pipes with different heating or inlet medium temperatures, the curve represented by the hydrodynamic characteristic curves is called the comprehensive hydrodynamic characteristic curve. 4 Basic method for calculating the pressure drop in the pipe
4.1 Explanation of symbols
A-—pipe flow cross-sectional area, m\;
A. Pipe flow cross-sectional area, m\;
A,——pipe flow cross-sectional area, m\;
A2-—pipe flow cross-sectional area, m;
A. Cross-sectional area of side branch flow (as shown in Figures 19 and 20), m2; Aj
Cross-sectional area of collecting pipe flow (as shown in Figures 19 and 20), m2; Adk
Total area of porous plate, m2;
Ab——Cross-sectional area of straight branch flow (as shown in Figures 19 and 20), m2b——Length of the extended end of the pipe (as shown in Figure 6), m; b.
Side length of filter mesh hole, m;
Wet perimeter of a pipe section, m;
ChShape coefficient when flowing in annular sleeve; C,——Correction coefficient of spiral tube (obtained from Figure 1); Resistance correction coefficient of welded elbow (obtained from Table 15); Cw
Outer diameter of inner ring of annular sleeve, m;
Inner diameter of inner pipe of 180° circular turn (as shown in Figure 13), m; —Equivalent diameter of pipe (da=4A/C.), m; dai
Flow diameter of the reduced gate valve, m;
Inner diameter of the outer cylinder of the filter, m;
Inner diameter of the inlet pipe of the filter, m;
Inner diameter of the outlet pipe of the filter, m;
Inner diameter of the outlet pipe of the filter, m;
Inner diameter of the perforated cylinder inside the filter, m;
Inner diameter of other types of filters, m;
Inner diameter of the outer cylinder of the mixer, m;
Mixer Side inlet pipe inner diameter, m;
mixer front inlet pipe inner diameter, m;
mixer side inlet pipe inner diameter, m
mixer rear outlet pipe inner diameter, m
- mixer internal perforated cylinder inner diameter, m; dj - throttling ring opening diameter, m;
header inner diameter, m;
pipe inner diameter, m;
annular casing equivalent diameter (d,D-d), m; dm-throat diameter of the reduced gate valve, m;
dsk-diameter of the reduced gate valve, m;
D——inner diameter of the outer ring of the annular sleeve, m; nominal diameter of the valve, m;
cross-sectional area of the pipe, m2;
JB/T 8659-1997
fgl-ratio of the opening area of the first opening zone of the perforated cylinder inside the filter to the unopened area; f2-ratio of the opening area of the second opening zone of the perforated cylinder inside the filter to the unopened area; fhi
The ratio of the opening area of the first opening zone of the perforated cylinder inside the mixer to the unopened area; the ratio of the opening area of the second opening zone of the perforated cylinder inside the mixer to the unopened area; G-—mass flow rate of water, kg/s;
The first inlet flow rate of the mixer, kg/s;
The second inlet flow rate of the mixer, kg/s;
The third inlet flow rate of the mixer, kg/s;
Gk4—Mixer outlet flow rate, kg/s;
Filter inlet flow rate, kg/s;
-Filter first outlet flow rate, kg/s;
Filter second outlet flow rate, kg/s;
Gravity acceleration, m/s;
Calculate the height difference of the pipe section; the depth of the 180° circular turn (as shown in Figure 13), m; the absolute roughness of the inner wall of the pipe, m;
K—the coefficient of the gentle bend (see Table 13);
l——the length of the pipe, m2;
the conical depth of the 50°~60° expansion hole in the boiler drum (as shown in Figure 2(d)), m; l;——the length of the throttling ring, m;
l——the length of the perforated cylinder inside the filter, m;
ll——the length of the first opening area of the perforated cylinder inside the filter, m; lg2——the length of the second opening area of the perforated cylinder inside the filter, m; lh
the length of the perforated cylinder inside the mixer, m;
l hl—the length of the first opening area of the perforated cylinder inside the mixer, m; l h2-the length of the second opening area of the perforated tube inside the mixer, m; Lg-the length of the outer tube of the filter, m;
the distance between the end inlet of the filter and the side outlet, m; the length of the outer tube of the mixer, m;
Lhl-the distance between the end inlet of the mixer and the side inlet, m; M-the mass of water, kg;
the ratio of the number of outlet pipes to the number of inlet pipes of the header (n-the number of outlet pipes/the number of inlet pipes); n;-ratio (see Article 4.5.17 of this standard); △P-the total pressure drop of the flow in the pipe, Pa; ||t t||△Pzw—weighted pressure difference, Pa;
△Pta
—flow resistance loss, Pa;
△P. Friction resistance loss, Pa;
△Pjb—local resistance loss, Pa;
P, Prandtl number of water;
Q—flow rate in the side branch pipe, kg/s;
Q;—flow rate in the collecting pipe, kg/s;
r—flange radius of the large diameter downcomer, m;
R-bending radius of the elbow, m;
R. Reynolds number of water (R.=pWd./μ); R, radius of the spiral pipe, m;
V——volume of water, m;
W-flow rate of water, m/s;
W. Water flow rate, m/s;
Mass flow rate of water, kg/(m2·s);JB/T8659—1997
Water flow rate (as shown in Figures 18, 19, and 20), m/s;Water flow rate (as shown in Figures 18, 19, and 20), m/s;Water flow rate, m/s;
Water flow rate in the side branch pipe (as shown in Figures 19 and 20), m/s;Water flow rate in the collecting pipe (as shown in Figures 19 and 20), m/s;Medium flow rate in the nozzle hole, m/s;
Average water flow rate, m/s;
Water flow rate in the straight branch pipe (as shown in Figures 19 and 20), m/s;α—Angle of the oblique inlet of the pipe tip (as shown in Figure 7), (°);β--Angle of the chamfered inlet of the pipe (as shown in Figure 8), ();0-
Cross section Gradually expand (reduce) the angle (as shown in Figure 11), (); — bending angle of the elbow (as shown in Figure 12), (°); wall thickness, m;
— coefficient (see Table 12);
β--- water density, kg/m";
P1-— water density, kg/m\;
water density, kg/m;
Ppi average water density, kg/m;
入——— friction resistance coefficient;
入,—— friction resistance coefficient
入2——— friction resistance coefficient;
converted friction resistance coefficient (入=入/d.), 1/m; 入-- friction resistance coefficient of a circular cross-section pipe with the equivalent diameter of annular sleeve as the diameter; 入
friction resistance coefficient of the medium flowing in the annular sleeve; In - Friction resistance coefficient of the medium when flowing in the spiral tube; In - Friction resistance coefficient of the straight tube with the same inner diameter as the spiral tube; Zone
Dynamic viscosity of water, Pa·s;
Resistance coefficient;
. - Slow bend coefficient (see Table 14);
. ——- Outlet resistance coefficient;
Resistance coefficient of porous plate;
- Resistance coefficient of valve;
s Resistance coefficient of other types of filters;
JB/T8659---1997
g1 - Resistance coefficient corresponding to the flow velocity at the first outlet of the filter (as shown in Figure 28); x2 - Resistance coefficient corresponding to the flow velocity at the second outlet of the filter (as shown in Figure 28); h - Resistance coefficient corresponding to the flow velocity at the first inlet of the mixer (as shown in Figure 27); Sh2—resistance coefficient corresponding to the flow velocity at the second inlet of the mixer (as shown in Figure 27); h3—resistance coefficient corresponding to the flow velocity at the third inlet of the mixer (as shown in Figure 27); ,—inlet resistance coefficient;
Sst—resistance coefficient of the tee;
ZA—total area of the holes in the porous plate, m
t—coefficient (see Table 26);
β—angle of the Y-shaped tee (as shown in Figure 19), (°); Q—filter mesh diameter, mm;
pore diameter of the first opening area of the perforated cylinder inside the filter, mm; g2—pore diameter of the second opening area of the perforated cylinder inside the filter, mm; Qm—pore diameter of the first opening area of the perforated cylinder inside the mixer, mm; ①h2—pore diameter of the second opening area of the perforated cylinder inside the mixer, mm; —coefficient (see Tables 10 and 11).
4.2 Calculation of pressure drop in pipe
4.2.1 Calculation of total pressure drop in pipe
The total pressure drop △P of hot water flowing in pipe is calculated as follows: AP=△Pzw+△Pla
△Pid=△Pm+△Pijb
4.2.2 Calculation of gravity pressure difference
The pressure difference caused by different vertical elevations when hot water flows in pipe is called gravity pressure difference, and its value is calculated as follows: APzw=±hgp
△P takes positive value when hot water flows upward, and takes negative value when hot water flows downward. 4.2.3 Calculation of friction resistance loss
The friction resistance loss AP of hot water is calculated as follows: ·2
△Pm入
or △Pm=入.
4.2.4 Calculation of local resistance loss
The local resistance loss △Pi is calculated as follows: APi
4.3 Characteristic parameters
4.3.1 Calculation of mass flow rate
The mass flow rate of the medium flowing through the unit flow cross-section of the pipe is called the mass flow rate W., and its value is calculated as follows: Wm=
When the flow cross-sectional area of the pipe remains unchanged, regardless of whether it is heated or not, the mass flow rate of each section of the pipe is the same during stable flow. 4.3.2 Calculation of water velocity
The velocity W of water flowing through a unit flow cross section of a pipe can be calculated as follows: (1)
4.3.3 Calculation of average water velocity
JB/T 8659--1997
When the water velocity in the pipe changes, the average water velocity W can be calculated as follows: Wei
4.3.4 Calculation of water density
The mass of water per unit volume is called the density of water. When the density at any point in the water is the same, it is a uniform fluid. The density β of a uniform fluid is calculated as follows:
: (10)
The density of water decreases with increasing temperature and increases slightly with increasing pressure. The density value of water within the parameter range of a hot water boiler can be determined according to 8.3.1.
4.3.5 Calculation of the average density of water
When the water temperature or pressure in the tube changes and the water density changes, the average density of water βp can be calculated as follows: +p2
4.3.6 Reynolds number R of water
Reynolds number R of water is calculated as follows:
4.3.7 Prandtl number P of water
For Prandtl number P of water at different temperatures, see Appendix C. 4.4 Friction resistance coefficient bzxz.net
4.4.1 Friction resistance coefficient when medium flows in a circular cross-section tube (11)
When medium flows in a circular cross-section tube, depending on the value of Reynolds number R and the relative roughness d./k value of the inner wall of the tube, the relationship between the friction resistance coefficient and the Reynolds number R can be divided into laminar flow zone, transition zone and turbulent flow zone. The turbulent flow zone can be further divided into turbulent smooth zone, flow transition zone and turbulent complete zone (also called self-modeling zone). For carbon steel pipes and pearlite alloy steel pipes, the absolute roughness k of the inner wall of the pipe is taken as 0.00008m, i.e. 0.08mm; for austenitic steel pipes, the absolute roughness k of the inner wall of the pipe is taken as 0.00001m, i.e. 0.01mm; for cast iron pipes, the absolute roughness k of the inner wall of the pipe is taken as 0.00025m, i.e. 0.25mm. 4.4.1.1 The friction resistance coefficient in the laminar flow zone (R. ≤ 2300) is calculated as follows: -
4.4.1.2 Transition zone (2300
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