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KUKLA, R, VITĚZ, T., TRAVNICEK, P., SEDLAK, P.: Calculation of cooling curve of the combustion boiler refractories lining with use of an experimental device. Acta univ. agric. et silvic. Mendel. Brun., 2012, LX, No. 3, pp. 111–116 The aim of the work was modeling of cooling process dynamics of a combustion boiler and designing of the method, which is suitable for calculation of cooling time in a large scale of temperature. Methods were verifi ed with the use of referential combustion boiler with heat output of 130 kW. This boiler burned mixture of waste sawdust and shavings originating in the course of production of wooden furniture. For these purposes specialized experimental device has been used. Cooling curves were measured in interval from 380 °C to 50 °C and were described by using of polynomial function. The cooling time was calculated by using of polynomial function in full temperature scale for cooling of combustion boiler refractories lining, from 700 °C to 50 °C. cooling curve, combustion boiler, refractories lining, heat transfer coeffi cient Measurment and evaluating of cooling curves is an integral part of the fi eld of metalography. This issue is described in scientifi c works (Chen et. al., 2006; Li et al., 2008). In practise there is necessary to know the cooling dynamics of other materials that is not associated with a signifi cant change in the crystalline as in the case of metallic materials. It includes metallic materials for example. Typical cases are heat devices such as combustion boilers for solid fuels. In this case the biggest amount of heat energy is accumulated in a refractory lining, which consists from a heat ressistant material such as fi re clay. According to information given by producer of this material the temperature resistance of fi re clay is about 1400 °C. Measurment of a cooling dynamics is very important for maintenance of heat devices and for planing of temporary shutdown of heat devices. If the course of cooling dynamics is knowed, the temporary shutdown can be planned precisely, which means considerable fi nancial savings. Accurate cooling dynamics measurment of large heat devices is technically and fi nancially demanding. Endeavour of authors were to design a method, which is fi nancially accetable and measured values relevant for practice. For this purpose experimental device, which proved success in experimental determination of temperatures of the inner wall of the combustion chamber of the boiler for the purpose of verifi cation of a CFD model have been used. This experimental device has been designed at the Department of Agricultural, Food and Evironmental Engineering at Mendel University in Brno (Travnicek et al., 2011). For the purpose of testing of new method, the materials, which are commonly used as refractory lining in the combustion chamber of reference boiler with heat output of 130 kW, have been used. The bases of refractory lining have been two layers of fi re clay and one layer of porous insulating material with the trade name – Peril. MATERIAL AND METHODS The basis for the experimental device was a layer of lining material (fi re clay) and insulation layer consisting of porous material, Peril. Both these materials are used in the reference device. The fi rst layer from the fi re clay measures 112 R. Kukla, T. Vitěz, P. Travnicek, P. Sedlak 130 mm and second layer from Peril measures 65 mm. These layers of materials have been subsequently insulated by using of mineral wool ( = 150 kg·m−3;  = 0,049 W·m−1·K−1) and placed on a resistance heater with heat output of 1200 W (Fig. 1). Temperatures of the inner and outer surfaces of the layer have been measured in the time interval of 1 second by two T-type thermoelectric couples with measurement range from −200 °C to 400 °C. The typical deviation was ± 1 °C while the maximum deviation was ± 1.5 °C. Measured values were compiled by measuring transducer ADAM (Fig. 2) and subsequently evaluated. Further measured values were saved into the fi le by user real time application, which was created in ControlWeb so wate environment (Fig. 3). The fi rst layer of refractory lining was heated to the temperature 380 °C. When required temperature was reached, the electric heater was turned off . Temperatures of inner and outer side of refractories lining were measured for a period of twelve hours. Measured values were evaluated by using of Microso Excel and Matlab so ware. A erwards values were plotted into graphs which were interspersed by tendentious curves. Then the function of tendentious curve and the determination coeffi cient were calculated. Grubbs’ test for outliers was executed, as well. Measurments of values were executed in atmospheric temperature 23 °C and barometric pressure 99 600 kPa. Experiment was repeated threetimes. The fi nal values were averaged. RESULTS AND DISCUSSION First of all basic physical properites of materials used for refractory ligning of boiler have been defi ned. The important physical property is heat transmission coeffi cient. The dependence of the heat transmission coeffi cient on the temperature was converted into a chart on the basis of the data sheets pertaining to individual materials used for isolation of the boiler. The dependence of the heat transmission coeffi cient on the temperature for the fi re clay is shown in Fig. 4. The dependence of heat transmission coeffi cient on the temperature for the insulation material (Peril) is shown in Fig. 5. Both the fi gures document the fact, that the function characterizing the respective dependence is exponential. The determination coeffi cient applicable to the function characterizing the 1: Experimental device The calculation of cooling curve of the combustion boiler refractories lining with use of an experimental device 113 dependence of heat transmission coeffi cient on the temperature for the fi re clay was R2 = 0.99 and for the Peril was R2 = 0.97. The experimental device performed measurement in the temperature range from 25 °C to 400 °C. In total, more than 64 000 values were recorded and evaluated. The cooling dynamics of inner wall is shown in Fig. 6. The outer surface cooling dynamics of the boiler is shown in Fig. 7. The following stage of measurement was supposed to comprise heating of a layer of material using a gas burner in order to determine cooling dynamics from temperature 700 °C. This temperature is commonly achieved in cobustion boiler for combusting of biomass (Travnicek et al., 2011; Lavric et al., 2004; Novozhilov et al., 1996). However, due to safety reasons the experiment was terminated (the propane-butane cylinder was overheated). Aborting of experiment 2: External modules for data collection 3: Graphical user interface for experimental measurment and data collection 114 R. Kukla, T. Vitěz, P. Travnicek, P. Sedlak was executed in temperature of 400 °C. However it was proved that progress of this curve is acorrding to scientifi c work (Travnicek et al., 2011). The calculation showed that curve trend, which defi ned the dynamics of inner refractory lining cooling was given by polynomial function: y = 7 × 10−16 × x4 − 6 × 10−11 · x3 + 2 × 10−6 × x2 − − 0.0369x + 381.34 (1) The trend of this curve is shown in Fig. 6. Coeffi cient of determination of this curve was R2 = 0.9998. It was necessary to express roots of polynomial functions for y = 700. In this way we have obtained the time, which is necessary for refractory lining cooling from temperature 700 °C to temperature 50 °C. A er calculation of roots is obvious that absolute value of the real root is x = 6 166. This value idicated, how long does it take to cool refractory lining from temperature 700 °C to temperature 380 °C. From experimental measurement it is obvious, that combustion chamber have been cooled down from temperature y = 1.2095e0.0001x R2 = 0.9999 1.2 1.22 1.24 1.26 1.28 1.3 1.32 1.34 1.36 0 200 400 600 80