MEASUREMENT ERROR INFLUENCE ON MASS AND HEAT TRANSFER COEFFICIENTS
ANALYSIS OF MEASUREMENT ERRORS INFLUENCE
ON EXPERIMENTAL DETERMINATION
OF MASS AND HEAT TRANSFER COEFFICIENTS
MEASUREMENT ERROR INFLUENCE ON MASS AND HEAT TRANSFER COEFFICIENTS
Floarea Pop, Cornelia Croitoru, Mihai Culcer, Mariana Iliescu,
Gheorhge Titescu, Ioan Stefanescu, Marius Peculea1
National Institute of Research-Development for Cryogenic and Isotopic Technologies ICSI Ramnicu Valcea, Romania,
1Romanian Academy, Bucharest
The paper analyses the influence of measurement errors of temperatures and concentrations at experimental determination of the mass and heat transfer coefficients. Calculus model for these coefficients, data obtened on the water distillation experimental plant, calculus model for measurement errors and the results of effected studies regarding measures errors influence are presented.
On experimentaal determination of mass and heat transfer coefficients have been used the relations
(1)
(2)
The experimental column, with inner diameter of 108 mm have been equipped with B7 structured packing, on a hight of 14 m. This column offers the possibility to measure vapour temperatures and concentrations in 12 points, figure 1. The quantities that have been measured are: temperatures, pressures, flow rate and isotopic concentrations. For errors propagation analysis were used just parameters measured on each packing stratum, vapour temperature, isotopic concentration respective, values presented in table 1. Isotopic concentrations were determinated by densimetry, measurement errors being of 0.02%. Tempeartures were measured with Fe-Co thermocouples, that have 0.1OC measurement errors. For the variaton of these parameters with packing hight, have been used aproximate relations. For each packing stratum were calculated mass and heat transfer coefficients, using relations (1) and (2). These values are presented also in table 1.
Maximum errors at experimental determination of mass and heat transfer coefficients were calculated with relation:
(3)
Partial derivatives on calculates using the next relation:
(4)
Using relation (4) were calculated maximum errors possible errors at experimental determination of the mass and heat transfer coefficients. These values are also presented in table 1.
Table 1
Measured and calculated values
Nr. strat / x / t / Ky exp / eKy / Kt exp / eKt0,59 / 53,3 / kmol/m3.s / kW/m3.grd
1 / 1.11 / 53.3 / 4.94E-02 / 1.42E-03 / 9.80E+00 / 9.87E-01
2 / 1.95 / 55.1 / 2.05E-01 / 1.40E-03 / 1.95E+00 / 1.56E-01
3 / 4.0 / 57.4 / 1.86E-01 / 2.52E-03 / 1.58E+00 / 1.31E-01
4 / 6.38 / 61.2 / 1.55E-01 / 3.78E-03 / 2.44E+00 / 8.78E-03
5 / 10.21 / 61.4 / 1.60E-01 / 7.28E-03 / 5.75E-01 / 5.19E-01
6 / 15.8 / 63.85 / 1.47E-01 / 2.06E-02 / 7.77E-01 / 2.09E+00
7 / 29.52 / 62.8 / 1.35E-01 / 1.56E-02 / 1.34E+00 / 1.71E+00
8 / 41.76 / 63.8 / 1.24E-01 / 4.59E-02 / 5.20E+00 / 8.69E+00
9 / 51.46 / 62.2 / 1.15E-01 / 1.97E-02 / -1.40E+01 / 2.84E+00
10 / 72.55 / 65.8 / 1.05E-01 / 1.44E-02 / -1.46E+00 / 6.60E-01
Figures 2 and 3 show sugestivly how large are the errors that can appear on experimental determinations.
The column having pelliculiar boiler, durring the experiments appeared superheatings of the column bottom. This ending effect have not been taken into consideration on the coefficients calculus, fact emphasised by negative values of heat transfer coefficient. In the same area measurement errors are the bigest. Being used in design, it is very important to know with high precisione the these transfer coefficients. Large errors on determination can lied to under or overestimation of packing performances. If the under estimation lieds to increasing of investment costs, overestimation lieds to decreasing of production capacity.
References
[1] F. Pop, M. Peculea, C. Croitoru, Experimental Determination of the Height of Transfer Unit at the Hydrogen Isotopic Distillation on Ordered Packing, B7 Type, Revue Roumaine de Chimie, nr. 2, 1999
[2] Tiron M., Prelucrarea statistica si informationala a datelor de masurare, Editura Tehnica, Bucuresti, 1976
[3] C. Croitoru, F. Pop, Gh. Titescu, M. Culcer, M. Iliescu, Experimentari asupra transferului de masa si caldura in coloane echipate cu umplutura ordonata tip B7, Raport de cercetare, INC-DTCI ICSI Rm. Valcea, 2001