Session K.pdf - Clarkson University

gested. The material is composed on the basis of astringent bitumen with electrical conductiveand inert additions (electrical conductive bitumen – ECB) (license application№ 2002118348, priority of 08.07.2002, the positive resolution for license presentationof 08.01.2004). The principle of the material action is as follows: the resistance is retainedquite small till the temperature reaches the value, above which the resistancegrows quickly with the temperature growth. As this takes place, the resistance growth ismuch quicker than the growth of the temperature and the reduction of the current intensityassists it. It leads to the reduction of the heater consumed power. By contrast in caseof the system cooling the resistance lowers and the heating grows.Fig. 4. The dependence of ECB resistivity from the heating temperatureSo more intensive heating takes place in the more cooled areas, which leads to the constanttemperature of the whole system. Owing to such a self-regulation of the electricalcharacteristics of the material no special electrical systems of regulation are needed toheat the well. Furthermore in this case the overheating of neither the most active elementin the heater or the well itself is impossible. The recommended maximum temperatureof the active heating ECB element is +90 °C. One more advantage of the proposedmaterial is the fact that the latter can be used in the wide range of moisture contentup to the using it in water without changing its electrical parameters. One of thepossible heaters with ECB consists of six active heating elements of 100x200x40 mm insize and with nominal power 0,25 kWt, connected in series and placed in the metal box.Such a heater is of 650x270x50 mm in size and has a power 1,5 kWt and operates at thevoltage 220 V. Except ECB active heating CRM elements made of astringent phosphatecan be used in the heaters. Such a heater consists of 10 active elements connected in seriesof 650x270x50 mm in size, has the power 1,0 kWt and the operating voltage 220 V.The recommended maximum temperature of the active heating element of this type is100 °C. The It is worth noting that using CRM allows creating the heaters operating inthe wide voltage range. The arrangement of the heating elements in the heater can bedifferent. For ensuring both electrical and hydro isolation special mastic is poured intothe heater box. The exterior heater surface is covered with anticorrosive coating. It isrecommended to connect the heaters across since in this case even if one or more heatersfail the whole system continues operating. The warming up system of the collectorwell is to be automatically switched on as the water temperature at the end of the deliveringpipe is –0,01 °С and switched off as it is +5 °С.342