CN105956329A - Calculation method for mechanism modeling of each channel gain of heat exchanger - Google Patents

Abstract

The present invention relates to a calculation method for mechanism modeling of each channel gain of a heat exchanger. The method is used for mechanism modeling of a heat exchanger or used for determining a value range of each channel gain during system identification and modeling. According to the calculation method, based on a process mechanism of the heat exchanger, a gain of each channel is calculated according to a structure parameter and a thermal power parameter of the heat exchanger. Compared with the prior art, the method provided by the present invention has the advantages of simpleness and high efficiency and the like.

Description

The modelling by mechanism computational methods of each channel gain of heat exchanger

Technical field

The present invention relates to a kind of heat exchanger modeling technique, especially relate to the modelling by mechanism of each channel gain of a kind of heat exchanger Computational methods.

Background technology

Heat exchanger is a kind of important industrial equipment, in chemical industry, oil, power, food and other many commercial production All it is widely used, its role is to heat cold medium or cooling thermal medium to suitable technological parameter.In order to design heat exchanger Control system, needs to set up the mathematical model of heat exchanger, and the gain of each process channel is the important parameter of heat exchanger mathematical model.

Set up the method for heat exchanger dynamic mathematical models and can be generally divided into two classes: modelling by mechanism method and system identification side Method.Modelling by mechanism method is physics, the chemistry rule followed according to heat exchanger technical process, sets up its mathematical model；System Heat exchanger is then considered as a "black box" by discrimination method, according to the inputoutput data measured, exists according to pre-determined criterion Models Sets is selected one coincide best model with data.

Use system identifying method to set up the mathematical model of heat exchanger, resolve following two problem particularly significant: 1) really Determine the structure of heat-exchanger model；2) scope of model parameter to be estimated is determined.Selecting rational model structure is to set up accurately The important prerequisite of heat-exchanger model；And determine the scope of model parameter rightly, can significantly improve parameter estimation precision and Speed.At present, the two problem is still lacked perfect solution.

Summary of the invention

Defect that the purpose of the present invention is contemplated to overcome above-mentioned prior art to exist and provide one simply, change efficiently The modelling by mechanism computational methods of each channel gain of hot device.

The purpose of the present invention can be achieved through the following technical solutions:

The modelling by mechanism computational methods of each channel gain of a kind of heat exchanger, for the modelling by mechanism of heat exchanger, or in system For determining the span of each channel gain of heat exchanger, described computational methods technique based on heat exchanger mistake during identification modeling Journey mechanism, according to structural parameters and the thermal parameter of heat exchanger, calculates the gain of each passage.

Structural parameters and the thermal parameter of described heat exchanger include: the physical parameter of heat-transfer surface, heat exchange area, heat exchange system Number；The physical parameter of hot and cold medium；The operating point parameter of heat exchanger, hot and cold rate-of flow and enthalpy.

The physical parameter of described hot and cold medium includes specific heat at constant pressure.

The feature of this computational methods heat exchanger is made defined below:

(1) the hot and cold medium of heat exchanger is single-phase, occurs without phase transformation；

(2) heat transfer type between hot and cold medium and heat-transfer surface is heat convection.

The technical process of described heat exchanger as shown in Figure 1, the process channel gain K involved by these computational methods_i(i= 1,2,3,4,5,6,7,8)、K_j(j=a, b, c, concrete meaning d) is shown in Table 1 and accompanying drawing 2.

These computational methods specifically include following steps:

Cold medium in heat exchanger application quality conservation law respectively and law of conservation of energy can obtain:

D_cs,in-D_cs,out=0 (1)

D_cs,inH_cs,in-D_cs,inH_cs,out+Q_cs=0 (2)

In formula (1) and formula (2), D is rate-of flow, and H is medium specific enthalpy, and Q is heat exchange amount；Lower footnote cs represents cold medium, In represents entrance, and out represents outlet；

Formula (1) is substituted into formula (2), and will obtain after formula (2) linearisation:

C_p,cs(T_cs,in-T_cs,out)|₀ΔD_cs,in+C_p,csD_cs|₀ΔT_cs,in+ΔQ_cs=C_p,csD_cs|₀ΔT_cs,out (3)

In formula, C_pFor specific heat at constant pressure, T is temperature；Lower footnote 0 represents operating point；

And then obtain K_cComputing formula:

$K_c=\frac{{\mathrm{\ΔT}}_{cs,out}}{{\mathrm{\ΔQ}}_{cs}}=\frac{1}{C_{p,cs}{D}_{cs}{|}_0}---\left(4\right)$

The quantity of heat convection in formula (2) calculates according to Newton cooling formula:

Q_cs=α_csA(T_w-T_cs,out) (5)

In formula, α is the coefficient of heat transfer, and A is heat exchange area；Lower footnote w represents heat-transfer surface；

Formula (5) and formula (1) are substituted into formula (2), and takes hot-face temperature T_wConstant, will obtain after formula (2) linearisation:

C_p,cs(T_cs,in-T_cs,out)|₀ΔD_cs,in+C_p,csD_cs|₀ΔT_cs,in=(C_p,csD_cs+α_csA)|₀ΔT_cs,out (6)

And then obtain K₁And K₂Computing formula:

$K_1=\frac{{\mathrm{\ΔT}}_{cs,out}}{{\mathrm{\ΔD}}_{cs,in}}=\frac{C_{p,cs}(T_{cs,in}-T_{cs,out}){|}_0}{(C_{p,\mathrm{cs}}{D}_{cs}+{\mathrm{\α}}_{cs}A){|}_0}---\left(7\right)$

$K_2=\frac{{\mathrm{\ΔT}}_{cs,out}}{{\mathrm{\ΔT}}_{cs,in}}=\frac{C_{p,cs}{D}_{cs}{|}_0}{(C_{p,\mathrm{cs}}{D}_{cs}+{\mathrm{\α}}_{cs}A){|}_0}---\left(8\right)$

Take hot-face temperature T_wConstant, will obtain after formula (5) linearisation:

ΔQ_cs=-α_csAΔT_cs,out (9)

And then obtain K_aComputing formula:

$K_a=\frac{{\mathrm{\ΔQ}}_{cs}}{{\mathrm{\ΔT}}_{cs,out}}=-{\mathrm{\α}}_{cs}A---\left(10\right)$

Thermal medium side is deduced accordingly, obtains the computing formula of following gain:

$K_b=\frac{{\mathrm{\ΔT}}_{hs,out}}{{\mathrm{\ΔQ}}_{hs}}=\frac{1}{C_{p,hs}{D}_{hs}{|}_0}---\left(11\right)$

$K_3=\frac{{\mathrm{\ΔT}}_{hs,out}}{{\mathrm{\ΔD}}_{hs,in}}=\frac{C_{p,hs}(T_{hs,in}-T_{hs,out}){|}_0}{(C_{p,hs}{D}_{hs}+{\mathrm{\α}}_{hs}A){|}_0}---\left(12\right)$

$K_4=\frac{{\mathrm{\ΔT}}_{hs,out}}{{\mathrm{\ΔT}}_{hs,in}}=\frac{C_{phs}{D}_{hs}{|}_0}{(C_{p,hs}{D}_{hs}+{\mathrm{\α}}_{hs}A){|}_0}---\left(13\right)$

$K_d=\frac{{\mathrm{\ΔQ}}_{hs}}{{\mathrm{\ΔT}}_{hs,out}}={\mathrm{\α}}_{hs}A---\left(14\right)$

Formula (11) is in formula (14), and lower footnote hs represents thermal medium；

According to Fig. 2, obtain K₅To K₈Computing formula:

K₅=K₁K_aK_b (15)

K₆=K₂K_aK_b (16)

K₇=K₃K_dK_c (17)

K₈=K₄K_dK_c (18)。

Compared with prior art, present invention is primarily based on the technical process mechanism of heat exchanger, join according to the structure of heat exchanger Number and thermal parameter, can calculate the gain of each passage, and result of calculation has for the scope determining each channel gain of heat exchanger There are stronger directive function and practical value.

Accompanying drawing explanation

Fig. 1 is heat exchanger technical process schematic diagram；

Fig. 2 is heat exchanger each channel gain calculated relationship figure.

Detailed description of the invention

The present invention is described in detail with specific embodiment below in conjunction with the accompanying drawings.

Embodiment

The technical process of heat exchanger, as it is shown in figure 1, hot and cold medium respectively flows through the different passages of heat exchanger, is passed through simultaneously Heat-transfer surface carries out heat exchange.The purpose of heat exchanger technique, or utilize thermal medium to heat cold medium, or utilize cold Jie Matter cooling thermal medium.The feature of the heat exchanger considered is made defined below:

(1) the hot and cold medium of heat exchanger is single-phase, occurs without phase transformation.

(2) heat transfer type between hot and cold medium and heat-transfer surface is heat convection.

Table 1 lists the process channel that heat exchanger is main.From the technical process mechanism of heat exchanger, according to heat exchanger Structural parameters and thermal parameter, can calculate the gain of these passages.Fig. 2 gives the calculated relationship figure of each channel gain.

Table 1

The present invention proposes the computational methods of heat exchanger each process channel gain, the method be embodied as step For:

Obtain structural parameters and the thermal parameter of heat exchanger.Desired parameters mainly has: the physical parameter of heat-transfer surface, heat-transfer surface Long-pending, the coefficient of heat transfer；The physical parameter of hot and cold medium, such as specific heat at constant pressure；The operating point parameter of heat exchanger, hot and cold rate-of flow And enthalpy, etc..

According to formula (4), formula (7), formula (8), formula (10) and formula (11) to formula (18), calculate each process channel of heat exchanger Gain K_i(i=1,2,3,4,5,6,7,8).

Claims (5)

1. modelling by mechanism computational methods for each channel gain of heat exchanger, for the modelling by mechanism of heat exchanger, or distinguish in system For determining the span of each channel gain of heat exchanger when knowing modeling, it is characterised in that described computational methods are based on heat exchange The technical process mechanism of device, according to structural parameters and the thermal parameter of heat exchanger, calculates the gain of each passage.

The modelling by mechanism computational methods of each channel gain of a kind of heat exchanger the most according to claim 1, it is characterised in that institute Structural parameters and the thermal parameter of the heat exchanger stated include: the physical parameter of heat-transfer surface, heat exchange area, the coefficient of heat transfer；Hot and cold Jie The physical parameter of matter；The operating point parameter of heat exchanger, hot and cold rate-of flow and enthalpy.

The modelling by mechanism computational methods of each channel gain of a kind of heat exchanger the most according to claim 2, it is characterised in that institute The physical parameter of the hot and cold medium stated includes specific heat at constant pressure.

The modelling by mechanism computational methods of each channel gain of a kind of heat exchanger the most according to claim 1, it is characterised in that should The feature of computational methods heat exchanger is made defined below:

(1) the hot and cold medium of heat exchanger is single-phase, occurs without phase transformation；

(2) heat transfer type between hot and cold medium and heat-transfer surface is heat convection.

The modelling by mechanism computational methods of each channel gain of a kind of heat exchanger the most according to claim 1, it is characterised in that should Computational methods specifically include following steps:

Cold medium in heat exchanger application quality conservation law respectively and law of conservation of energy can obtain:

D_cs,in-D_cs,out=0 (1)

D_cs,inH_cs,in-D_cs,inH_cs,out+Q_cs=0 (2)

In formula (1) and formula (2), D is rate-of flow, and H is medium specific enthalpy, and Q is heat exchange amount；Lower footnote cs represents cold medium, in generation Table entry, out represents outlet；

Formula (1) is substituted into formula (2), and will obtain after formula (2) linearisation:

C_p,cs(T_cs,in-T_cs,out)|₀ΔD_cs,in+C_p,csD_cs|₀ΔT_cs,in+ΔQ_cs=C_p,csD_cs|₀ΔT_cs,out (3)

In formula, C_pFor specific heat at constant pressure, T is temperature；Lower footnote 0 represents operating point；

And then obtain K_cComputing formula:

$K_c=\frac{{\mathrm{\ΔT}}_{cs,out}}{{\mathrm{\ΔQ}}_{cs}}=\frac{1}{C_{p,cs}{D}_{cs}{|}_0}---\left(4\right)$

The quantity of heat convection in formula (2) calculates according to Newton cooling formula:

Q_cs=α_csA(T_w-T_cs,out) (5)

In formula, α is the coefficient of heat transfer, and A is heat exchange area；Lower footnote w represents heat-transfer surface；

Formula (5) and formula (1) are substituted into formula (2), and takes hot-face temperature T_wConstant, will obtain after formula (2) linearisation:

C_p,cs(T_cs,in-T_cs,out)|₀ΔD_cs,in+C_p,csD_cs|₀ΔT_cs,in=(C_p,csD_cs+α_csA)|₀ΔT_cs,out (6)

And then obtain K₁And K₂Computing formula:

$K_1=\frac{{\mathrm{\ΔT}}_{cs,out}}{{\mathrm{\ΔD}}_{cs,in}}=\frac{C_{p,cs}(T_{cs,in}-T_{cs,out}){|}_0}{(C_{p,\mathrm{cs}}{D}_{cs}+{\mathrm{\α}}_{cs}A){|}_0}---\left(7\right)$

$K_2=\frac{{\mathrm{\ΔT}}_{cs,out}}{{\mathrm{\ΔT}}_{cs,in}}=\frac{C_{p,cs}{D}_{cs}{|}_0}{(C_{p,\mathrm{cs}}{D}_{cs}+{\mathrm{\α}}_{cs}A){|}_0}---\left(8\right)$

Take hot-face temperature T_wConstant, will obtain after formula (5) linearisation:

ΔQ_cs=-α_csAΔT_cs,out (9)

And then obtain K_aComputing formula:

$K_a=\frac{{\mathrm{\ΔQ}}_{cs}}{{\mathrm{\ΔT}}_{cs,out}}=-{\mathrm{\α}}_{cs}A---\left(10\right)$

Thermal medium side is deduced accordingly, obtains the computing formula of following gain:

$K_b=\frac{{\mathrm{\ΔT}}_{hs,out}}{{\mathrm{\ΔQ}}_{hs}}=\frac{1}{C_{p,hs}{D}_{hs}{|}_0}---\left(11\right)$

$K_3=\frac{{\mathrm{\ΔT}}_{hs,out}}{{\mathrm{\ΔD}}_{hs,in}}=\frac{C_{p,hs}(T_{hs,in}-T_{hs,out}){|}_0}{(C_{p,hs}{D}_{hs}+{\mathrm{\α}}_{hs}A){|}_0}---\left(12\right)$

$K_4=\frac{{\mathrm{\ΔT}}_{hs,out}}{{\mathrm{\ΔT}}_{hs,in}}=\frac{C_{phs}{D}_{hs}{|}_0}{(C_{p,hs}{D}_{hs}+{\mathrm{\α}}_{hs}A){|}_0}---\left(13\right)$

$K_d=\frac{{\mathrm{\ΔQ}}_{hs}}{{\mathrm{\ΔT}}_{hs,out}}={\mathrm{\α}}_{hs}A---\left(14\right)$

Formula (11) is in formula (14), and lower footnote hs represents thermal medium；

Obtain K₅To K₈Computing formula:

K₅=K₁K_aK_b (15)

K₆=K₂K_aK_b (16)

K₇=K₃K_dK_c (17)

K₈=K₄K_dK_c (18)。