SU147010A1 - The method of determining the flow of heat brought by the flow of the heated medium - Google Patents

Description

Methods are known for determining the heat consumption allowed by the flow of a heated medium, with correction for specific gravity, heat content, flow coefficient, expansion coefficients of the medium, as well as a restriction device and a pipeline. Devices are also known for carrying out such methods in which the multiplication of the quantities included in the heat consumption equation is carried out by converting them into electrical quantities, followed by multiplying and recording the results of the multiplication with an electric meter. Such methods and devices are complex and ineffective.

In the proposed method, the values of specific gravity, heat content and consumption coefficient are entered into the expression for determining the heat consumption by the flow of the heated medium in the form of products of a constant coefficient by two factors, one of which depends only on temperature, the other only on pressure, and expansion coefficients and a tapering device with a pipeline are introduced into the same expression as the product of constant coefficients and factors, depending on temperature and pressure, respectively, which is achieved Niemi in the apparatus for performing the method of potentiometric flow sensors, pressure and temperature are connected to multiplier-del.itelnuyu scheme. This makes it possible to increase the accuracy of determining the heat flux of the heated medium and simplify the introduction of a correction to the change in these values due to a change in temperature and pressure.

The drawing shows a basic electrical-dividing circuit explaining the described method.

The heat consumption by the method of taking into account the heat coefficient and the flow rate of the heat transfer medium (steam, gas) by the pressure drop across the restriction device is generally determined by the following relationship:

Q G.i Kia.E.Kt.d.i I / AT, kcal hour, (1)

No. 147010-2 -

where G is the actual flow rate of the coolant, kg / h;

i - heat content of the heat carrier in working condition, i.e.

with actual pressure and temperature, kcal / kg; Ki is a coefficient depending on the medium filling the differential pressure gauge, the medium contained in the impulse piping; a - coefficient of discharge; S - correction factor for the expansion; Kt- correction factor for thermal expansion of the material

constriction and pipeline;

d is the diameter of the opening of the narrowing device at a temperature of 20 °, mm; h - pressure drop across the restriction device, measured by a differential pressure gauge, mm Hg. v .; 7 - the specific gravity of the coolant corresponding to its state

before narrowing device, kg / m.

The heat content i is a complex function of the temperature and pressure of the heat transfer medium.

The specific gravity of dry gases and steam is expressed by the equation

T That (2)

where That is the specific weight of the coolant at the design pressure PO and the calculated temperature Go, for example, adopted in the calculation of the restriction device,

P is the actual pressure of the heat carrier before the restriction device, kg / cm; T is the actual temperature of the coolant before narrowing

device, ° K;

K is the coefficient characterizing the deviations of the coolant from the laws for an ideal gas, or the compressibility factor. The specific gravity, y, is a complex function of the temperature and pressure of the heat transfer medium, since the compressibility coefficient K in expression (2) also depends on temperature and pressure.

With a properly selected tapering device, the coefficients of the cues in most cases, the measurement of heat consumption remains almost constant.

The equation of heat consumption () with correction in all quantities depending on the parameters of the heat transfer medium (pressure and temperature), in general, will be echoed: Q where Co, EO, L / o - GO - Unified

p 7

P, - T-K l ± lj .G ,. , kcal / h, (3) о So Kt.V That is, the values of the coefficients G, 8, Kt at the calculated temperature tu and the pressure PQ adopted in the calculation of the restriction device; value of coolant flow without correction, measured by a differential pressure gauge, kg / h. constant values, expression (3) will be overwritten: Q /Cz.a.e. Dg; GO./Y, (4). (5)

The values of expression (4), depending on both the temperature and the pressure of the heat transfer medium, namely, t, /, a, can be conditionally presented as follows:

    (. "G / .g (6)

 it p ip t: kcal1k1 (7)

where, 4, are constant coefficients;

,, w., p is the corresponding value of m. - for any

pressure P and design temperature / o, i.e.

7. /, a f (P) with / const;

 in ,, t, - according to the value of t. /, e: at any temperature / and the design pressure PO, i.e.

T, 1, a / (/) with P const.

If we present the values of y, /, and according to the proposed method with the design parameters of the heat carrier / o, PO, then the values of the coefficients Lz, K ,, Ks

  1 1 J, 9)

AZ - ,,,

K, ..- .., (10)

i.p g "kcal kg

No. 147010

a i; / C5 - a, Yar, (§)

where / o is the value of the heat content of the coolant at the design parameters t ,,. Ru, / -scal / kg.

The value of the coefficient K, in the fields (1), (3), (4), declined 1m only on temperature, and the value of the coefficient e practically depends on the pressure and the value of the flow of the measured coolant.

The method of representing the specific gravity of the coolant (steam, gases) gives a much smaller error in comparison with expression (2), if we assume in it the coefficient K is constant.

From expressions (6), (7), (8) it can be seen that with deviations from the calculated value of temperature only or pressure tag1, the proposed / presentation method y, /, and the error does not contribute at all. The values of y, /, and are divided into za co-factors, each of which depends only on the temperature or only on the pressure of the heat carrier, which makes it possible to introduce a correction to the heat consumption value on the changes in the specific weight y, tenlo content /, coefficients a, e, Kt is separate but at the temperature and pressure of the heat transfer medium, and also allows you to significantly simplify the calculation of cxejM automatical correction.

No 147010 4 Taking into account (6), (7), (8), expression (4) in general will rewrite Q K, t, p p, t 3 / С, 0 „. 1 kcal1, ac (12)

where K, K, UK, K, K, -

For the cases of measuring the heat consumption, when the values of the coefficients a, e in equations (3), (4) can be taken constant, the expression (12) takes the form

 G, - itop ipoi Ki Y ,, t, (14)

where ;, expression f.p- it. is a function of coolant pressure

,,; (i) (16)

Expression - L; 1 Tp "/ is a function of heat carrier temperature

PofKfp ,, ((17)

The values of expressions (16) and (17) are known at any temperature and pressure. They are calculated based on the table values of the corresponding quantities included in these expressions.

The admission of an insignificant additional error of dependence (16), (17) within the limits of correction input, can be presented;

, r. -KR (1 ")

p „A, ip t} 77-) With account for expressions (18), (19), equation (12) takes the form:

Apply; to the equation (14), the expressions (18), (19), respectively, are written

h ..

o o o o o - (15)

  To about

A10 g A PC,., - / b, r

A multiply-dividing scheme that reproduces the relationship described by equation (20) or (23) is shown in the drawing.

The voltage UQ is proportional to the actual heat consumption,

,,.,.,"..one"" )

where is the ballast resistance, Rp is the variable resistance of the sensor; R ,, i is the resistance of a rheostat sensor of a primary or secondary instrument - pressure gauge: Rf is a resistance thermometer - heat carrier temperature sensor; Rao - variable resistance of the sensor, proportional to the flow rate of the coolant without correction; RO- compensation resistance; / o / - resistance of the rheostat sensor of the secondary device - flow meter; U is the supply voltage; Uoo-voltage, proportional to the flow of the coolant without correction,

- relative displacement of the variable resistance engine Roo.

3 - + Ran RD Ran, pc

Ri-rrp +

load factor resistance RaoRn Ri + Rpn + Rt, ohm (27)

The expression in square brackets (24) characterizes the error of the potentiometer loaded with resistance RH. To reduce this error at relatively small values of RH resistance, you can change the scale of power supply, its voltage (by s), and limit the displacement of the variable resistance motor R by resistance RO.

The expression (24) can be rewritten

 -C-KP -. In (28)

In order for the error from the load resistance Ron not to exceed the allowable value of Zdoc, for example + 0.1%, the following relationships must be met:

- 17Л2 Ron, ohm (32)

Expression (28) is proportional to expressions (20), (23)

,, GO -j- / К ,, q. in. (33)

When calculating the scheme, the resistance of the thermometer of resistance Rt of standard calibration is used; at the same time, i, R ,, ii, Ran, Ro- 5 - № 147010 are to be determined

,

Si + ffpn - | - Rf

  0,37 Ron, ohm (29)

0 0.08 (30)

C 0.982. (31)

AI -t- ArP + A, 8 t

No. 147010-6 If one accepts a linear approximation of the curve described by the heat consumption equation as a function of temperature change, and also assumes that the direct equation takes the values of the actual heat consumption, ,,,, P, temperature TI and T2 correspond to their lower ( Ti) at the upper (G2) limits of the input correction for temperature, then the equation approximating the direct is written (passing through two given points)

Q 2Qp, A Q / .Л.Qp..t, -Qpnf, j. kcal

Tchi-riri- T

/ 2 -. - G, hour

Substituting in expression (34) the value (12) at I fо, we obtain in general form:

O, K G (1, / ... o 1--.

P1 - - i

. Pot-,, / | g, p..t, G /, 1 / | ° jPiA t -.- pnt ViA. . j j Гз - TIт, TI

where a ,,; a ,, j.j Л:,; ; ..; Oud ,,; v, /. respectively, the values of these values at the design pressure Pn and temperatures

t, (t,) and / 2 ().

The change in heat flow Qy ,,, due to the change in temperature T in equation (35) must correspond to the change in voltage UQ in the discharge (20) due to change in resistance of the thermometer Rf. For this, it is necessary that the slope of the approximation straight line described by equation (35 ) was numerically equal to the relative change in the load resistance of the RH circuit due to the change in Rt, i.e.

, Kt, i-pj, t, - V ... / iL- I PJ, t,, 0.

T rt G

J - J IJ 2 - J 1

where, R., are, respectively, the resistance values of the thermometer at TI and TZ.

Expression (36) implies the value of the scale factor of the resistance factor Kzo connecting the resistance of the circuit with ordinate Qpijf to equation (35) with temperature.

 -...., .... (- /

p, A t, Vu /, Tr,; /, - y-p., t; t, p, t, v.,. kcal: hour

The value of the load resistance R (at temperature 1) or RH, (at TZ) is determined from expression (35) by substituting into it the value of the scale factor Lao instead of the scale coefficient of flow.

kcal.h (35)

this instead of T is substituted by Gg or TI, respectively.

, By known RH., Or. Pr.imen consumption of heat Rpn where

R, -P-K, -P, ohm. (44)

The values of the resistances RD / -R and Ro are determined based on the known resistance P., and the permissible error.-I from the load on the potentiometer Ran. With a, the inO, V / o zones and Rol and PO are determined by expressions (29), (32).

When the value of RH changes (due to a change in P (), an additional error occurs (the coefficient C changes in equation 28). However, this error is insignificant and can be compensated for by decreasing the quality of the compensation resistance PO) the internal resistance of the power supply of the measuring circuit can be used.

- 7 - .Ko 147010

(38)

Pp // Rc K. 1 -. 1 /, ohm (39) or ", determine the value of" (pri 7 "), ,, Ch-." Ozh (40) Ln,, - /, - g-, OW (41), similar transformations with respect to the equation in depending on pressure P, we obtain, Ω (42). / y, J Par.-A-oR. / T / „; n“., - p, ,, 1 / Tz ;; - v (p. t; P, / is the pressure measurement limit of the pressure sensor, ago; Pb P2 - the lower and upper limits of the input of the correction pressure, ata, respectively. Resistance value R is determined from the expression: ", - K, -Krp , ohm. (43) The resistance value of the pressure sensor / ,, at any pressure is determined: Y, LH g, ip.t,, 00-,, VA Pi

No. 147010-8 For most cases of measuring heat consumption, the coefficients a and S remain almost constant. In this case, expressions (38), (42) take the form

R ..-, AN. - - ::: -

KRP 5 5

P 1i 2fj

M g,

The remaining circuit elements are calculated by expressions (40), (41), (43), (44), (29), (32).

The value of the scale factor Kz in the expression (33), which relates the heat consumption Q to the output voltage UQ of the circuit, is determined from equations (33) and (28) at t and PO.

gg, jj- -gppkkl

/ Sy, (Eop-L, 9 / o CGI, “d -,, (47) from where l-„ - 0.73. C-

where Oop is the measurement limit for the sensor flow rate (i.e., the measurement limit of the secondary instrument - flow meter), kg / h; Qon - heat consumption corresponding to Sop, kcal / hour; Кц max - maximum mixing of the engine of the potentiometer Ran (according to expressions (25), (29) is 0.73).

The difference between the heat consumption determined by the expression (33) with regard to the actual heat consumption (expression 3), referred to the actual heat consumption, is the error 0 of the measuring circuit. As a result of mathematical transformations we get

("O- 1 / That,;

  1-t-77 77 / t - V °

where l Rp Rp -R ,, om. (50)

 /, - / ,, om. (51)

(46)

/.hour Ggfi

 1 ± P

 R kLaHas

- 9 - № 147010

Expression

/ a g „L. g

a o -} / - - 1 100.% (52)

 and in Kf 1 V 7 /

in equation (49) is the error in the measurement of heat consumption by a flow meter differential pressure meter due to the deviation of the parameters of the coolant from the calculated ones in the absence of a correction circuit.

The largest errors in the expression (49) are obtained when the values of the parameters of the coolant correspond to the limits of the input correction, i.e. at t ti; f I, P P2- With this, depending on the accepted limits for entering the correction, the unequal maximum errors of both signs can be obtained. In order to obtain equal errors, it is necessary to choose the coefficient K2i in such a way that a certain error соответствующего of the corresponding sign was assumed for the design parameters of the coolant:

where i h i. absolute values of the largest errors of different signs) h) I calculated by the expression (49) for various combinations of changes in the parameters of the coolant corresponding to the limits of the input correction (/ tz, P}, P-i) The sign of the error V is always opposite to the sign of norpeniHOSTI 3

Taking into account the value of Bo expression (48) will take the form:

K.,., L: J 1 -. Finally, the heat consumption is expressed through the LQ voltage of the measuring circuit:

0 f; Q.A, fl-) -. . ,. ,,

- lOO-Jo7H.r./; (

taking into account (53) the maximum error of the measuring circuit due to the deviation of the parameters of the coolant from the calculated ones within the correction input will be:

.i ... o: o - (56)

The values are not computed for the values of temperature and pressure of the heat transfer medium corresponding to the limits of the input correction g; Р Р) at various combinations of deviations.

To take into account the additional error from the load of the Koi potentiometer, it is necessary to add the value 0.1, which is accepted when the circuit is drawn, to the error values calculated by expression (56).

In the multiplication-dividing scheme, instead of rheostatic heat flow and pressure sensors, 1 non-contact induction sensors and linear rotators can be used: 1sec are transformers, which significantly increases the reliability of ycTpoiicTBa.

% (53)

1 cal: h. Aas. (B4)

 100, in

No. 147010

Subject invention

Claims (2)

1. The method of determining the heat flow brought by the flow of the heated medium, with correction for specific gravity, heat content, flow coefficient, expansion coefficients of the medium, as well as the restriction device and the pipeline, is also distinguished by the fact that, in order to increase the accuracy of determining the heat of the heated pool environment and simplify the input of a correction to the change of the indicated values due to changes in temperature and pressure, specific gravity, heat content and flow coefficient are entered into the expression to determine the heat consumption flow m of the heated medium in the form of products of a constant coefficient by two factors, one of which depends only on temperature, the other only on pressure, and the coefficients of expansion of the medium and the restriction device with the pipeline are introduced into the same expression as a product of constant coefficients by factors , depending respectively on temperature and pressure. 2. A device for carrying out the method according to claim 1, from that, in order to increase the measurement accuracy of heat consumption with automatic correction of changes in specific gravity, consumption coefficient, heat content, as well as the coefficient of expansion of the heated medium and a constricting device with a pipeline due to a change in temperature and pressure of the flow of the heated medium, in it the potentiometric flow, pressure and temperature sensors are connected in a multiplication-division circuit. and - ten