Annals of Warsaw University of Life Sciences - SGGW.

48 M. Sojak, Sz. GłowackiFigure 3 presents diagrams of localrelative and absolute errors determiningaccuracy of calculations on water contentof models (1) and (2) compared to valuescalculated from measurements.is not acceptable, which is pointed outby absolute and relative error valuescalculated in relation to measurementresults. Error values of both modelsincrease along with an increase inδ [%]60504030201000 100 200 300 4000-0,3 0,0 0,3τ [min]Δ [−]FIGURE 3. Diagrams of local relative (δ) and absolute (∆) errors for water content calculations of modelI (thin line) and II (thick line) of drying period for pumpkin chips of Justynka variety for slice thickness5 mm, temperature 80°C, drying medium speed 1.2 m·s –1 and coefficients: N = 1.6, b = 0.056u [kg . kg -1 ]8642The value of relative error was takenas 0.3 kg·kg –1 , assuming that this valuedetermines the range of water content,where models (1) and (2) can be regardedas verified; this value should not beexceeded.The time τ cr after which the driedsamples achieve water content 2 kg·kg –1was determined basing on formulaeapproximating results of measurements.It was found that changes in dryingspeed can be described with a linearequation of large value of correlationcoefficient. It results in the value of Ncoefficient in model (1) equal to 2. Thevalues of this coefficient, for which themodel of I drying period is regarded asverified are presented in Table 1.The models of changes in watercontent (1) and (2) are highly dependenton coefficient N. If its value is taken as 3,the accuracy of drying process modelingcoefficient N values (Fig. 4).The carried out logical analysis ofmodels (I) and (II) with considerationto equation (3) showed the sufficientaccuracy of modeling the drying processfor values of drying shrinkage values bincluded in interval [0,0; 0,1];it is provedby relative and absolute error valuesfor both models, calculated in relationto measurement results. However, thisaccuracy calculated for b values includedin interval (0,1; 1,0] can not be accepted,basing on the relative and absolute errorvalues (Fig. 5).In Table 1 there are presented valuesof particular drying parameters and modelcoefficients of drying periods I and II,for which these models were consideredas verified. Additionally, the percentcontent of dried matter was included forparticular varieties of pumpkin fruits.