Аналіз та розрахунки ексергетичного коефіцієнта корисної дії швидкісних водо-водяних теплообмінників для гарячого водопостачання

Abstract

Exergy efficiency is the most precise and correct characteristic of effectiveness of thermodynamic systems. A procedure for calculating the exergy efficiency (EE) for both individual elements of heat exchangers and for the whole structure has been developed. On the basis of known thermal engineering data, single-stage and two-stage heat exchangers are calculated. It is established that the exergy efficiency of single-stage heat exchangers changes within the limits of 0.74...0.77, and the two-stage ones – 0.84 ...0.86 and practically do not depend on the design and method of connection to the pipelines of the heating network. The loss of exergy in high-speed heat exchangers from the physical point of view can be explained by the change in temperature (specific heat capacity) during heat exchange and removal of heating flows outside the hot water supply system. An increase in the exergy efficiency value is possible due to an increase in the number of heat exchange sections, but from a practical point of view it is not practical and a deeper cooling of the heat-carrier can cause a violation of the temperature mode of the heating systems. The transition to group and individual heat supply systems limits the use of high-speed heat exchangers for hot water supply and their use is advisable in heat networks with powerful sources of heat generation, for example from a combined heat and power plant or an industrial heating boiler house. For the effective use of thermal energy in the preparation of hot water supply it is desirable to use heat exchangers-mixers of heat flows, which transforms anergy of flows to the exergy of hot water. For the individual hot water supply, the electrical boilers are more efficient . Using the exergy method for heat and mass exchange systems by exergy efficiency makes possible not only the engineering estimation of effectiveness of heat exchange but more detailed research of the processes.