EXERGIC ASSESSMENT OF EFFICIENCY OF HEAT APPLICATION FOR SELF-HEATING OF WATER BY MEANS OF FIRE ENGINE’S PUMP

Introduction. Efficiency of heat-insulating covering of the pump filled by water being self-heated for the purpose of ice-forming decrease inside fire hoses was investigated. Technique of the experiment. The object under research was the centrifugal pump PN-40UV of water tender ATs-3,2-40(433114) which operating time has made 186 hours at the resource of the unit equal to 1100 hours. The demountable cover according to the patent of the Russian Federation ¹ 68324 consisted of two heat-insulating layers from half-woolen blankets and one heat-reflecting layer from metallized half-linen fabrics with layers of air between them. The temperature of the air and the initial temperature of water in the pump made accordingly (51) and (201) °Ñ. Electronic potentiometer EPP-09 was used. Chromel-coppel thermocouples were placed on the axis of the pump sucker and in its collector. The average volumetric temperature of the system was defined as the average arithmetic based on indications of these devices. For determination of capacity of idling of the pump, frequency of rotation of the driving wheel and size of the twisting moment was measured. Results of research. The calculated model which adequately describes the process is received and it can be applied, for example, to determination of time of self-heating of water up to the set temperature depending on an ambient temperature, and also from capacity of idling of the pump. Exergic efficiency of preliminary self-heating of water in the pump for powers of free running 14,0 and 23,5 kWt (frequency of rotation of the pump impeller accordingly 1900 and 2700 revolutions per minute) was calculated. It was established that the efficiency of the process of preliminary self-heating of water by the pump before its flow into the hose line is not high and it is in the range of 3,3…7,5 %. The share of exergy of warmth reflected by the surface of the pump into the environment is 0,027…0,126 %. The maximum share of exergy loss during the conversion of work into warmth is 0,94…0,88. Aside from that, 1,74…3,92 % of warmth is spent on heating of pump elements. Of this amount of warmth the pump covering absorbs more than 81 % of exergy of the reflected warmth, the pump impeller absorbs more than 7 % by the shaft, by spindle valves and also by oil in the oil bath — all in all, more than 10 %. Conclusions. 1. The investigated design of heat insulation of pump PN-40UV in an insignificant degree forces preliminary self-heating of the water which is in a special unit, before it flows into the hose line as exergy losses of the heat reflected by external surfaces of the fire pump in the environment, are rather insignificant. However, during the further operation of the pump at a fire, the presence of heat insulation will allow to provide the increased attendant heating of extinguishing liquid that is necessary for its flow with required intensity during the whole period of firefighting. 2. The share of exergy of useful work of a specialty unit, necessary for self-heating of water, increases in the course of time of warming up and with the rise of its temperature. 3. Application of heat-insulating covering of internal surfaces of pump's elements will allow to redirect the certain share of heat on the increased self-heating of water in the specialty unit. 4. Application of exergic method of analysis gives an opportunity to systemically and fully estimate the degree of perfection of thermodynamic processes in systems of fire vehicles as it gives all-round representation about character of use of power resources and about specific weight of losses in its various elements.