The characteristics of heat exchanger for local utilization of wastewater heat under different operating conditions

Abstract

RELEVANCE. The authors research the local utilization of wastewater heat (in close proximity to the place of their formation) based on a heat exchanger. To select rational characteristics of the heat exchanger and correctly assess the potential energy effect, it is necessary to take into account the influence of the operating conditions of the device (duration of individual use of the shower, mass flow of heated and heating water, temperature of heated water at the inlet to the heat exchanger, temperature of the flow at the moment the device is turned on).THE PURPOSE. The purpose of the work is to research the dependence of the efficiency of wastewater heat utilization on the operating conditions of the heat exchanger and to identify the parameters that have the greatest impact on the effect of energy-saving measures.METHODS. Based on a verified mathematical model of the thermal operation of a recovery heat exchanger, the temperature distribution inside the flows of the heated and heating water in time is calculated (from the moment of switching on until reaching a stationary operating mode). Based on the data obtained (the temperature of the heated water at the outlet of the heat exchanger at each point in time), the absolute and relative heat savings are determined under various operating conditions.RESULTS. The influence of the non-stationary phase of the heat exchanger operation on its energy efficiency is considered. For a specific heat exchanger configuration, the time required for the device to reach a steady state of thermal operation is determined. It was revealed that the greatest influence on the relative and absolute savings of thermal energy is exerted by such operating conditions as mass flow and temperature of heated water at the entrance to the heat exchanger. The temperature of the flow at the initial moment of time has the least influence on the energy effect.CONCLUSION. The operating conditions that have the greatest impact on the effect of local wastewater heat recovery are determined. The need to take these conditions into account when designing a heat exchanger and choosing its optimal parameters has been confirmed.