Efficiency of the Air Heater in a Heat Recovery System at Different Thermophysical Parameters and Operational Modes of the Boiler

We have examined, for the plate heater included in a heat recovery system of the boiler plant, the influence of its thermophysical parameters on the losses of exergetic power under different operational modes of the heating boiler. A procedure for the calculation of losses in a given heat recovery unit is based on an integrated approach that combines exergetic methods with the methods of thermodynamics of irreversible processes. A mathematical model includes a differential equation of the exergy balance and an equation of thermal conductivity for an air heater under boundary conditions of the third kind. The differential equation of exergy balance has been solved jointly with the equation of thermal conductivity. The result of solving them is the obtained estimation dependences for determining the losses of exergetic power associated with the processes of heat transfer.We have calculated losses of exergetic power in the examined heat recovery units at a change in the coefficient of thermal conductivity of the plate, in the heat transfer coefficient from flue gases and an operational mode of the boiler. The derived dependences on a thermal conductivity coefficient for the considered operating modes of the boiler have two distinct sections, along the first of which there is a relatively small increase in the losses of exergetic power while reducing the coefficient of thermal conductivity, along the second ‒ the loss of exergetic power in a heat recovery unit increase relatively sharply. For the considered sequence of regimes of the boiler a transition from its maximum heat output to the minimal one is accompanied by a decrease in the losses of exergetic power. A similar character is also demonstrated by the dependence on a thermal conductivity coefficient of the relative contribution of losses of exergetic power in the heat transfer processes to their totals in a heat recovery unit. In this case, there are minor differences in the relative contribution of these losses under different operational modes of the boiler. The heat transfer coefficient from the side of flue gases within a framework of a single operating mode of the boiler affects less significantly, compared to the thermal conductivity coefficient of the material of a heat exchange surface, the losses of exergetic power in the heat transfer processes. We have established regions of change in the thermal conductivity coefficient, as well as operational modes of the boiler, in the range of which the losses of exergetic power in a heat recovery unit are minima

Establishment of Regularities of Influence on the Specific Heat Capacity and Thermal Diffusivity of Polymer Nanocomposites of A Complex of Defining Parameters

This paper reports a series of experimental studies to establish regularities of the integrated effect exerted on the specific heat capacity of polymer nanocomposites by such factors as the temperature regime of their production, the value of the mass fraction of the filler, and the temperature of the composite material. The studies were conducted for nanocomposites based on polypropylene filled with carbon nanotubes. When obtaining composites, the method of mixing the components in the melt of the polymer was used. During the studies, the temperature of nanocomposites varied from 295 to 455 K, the mass fraction of the filler ‒ from 0.3 to 10 %. The basic parameter of the technological mode for obtaining composite materials, the value of overheating the polymer melt relative to its melting point, varied in the range of 10...75 K. It is shown that the temperature dependence of the specific heat capacity of the considered composites is sensitive to changes in the overheating of the polymer melt only in the region maximum values of the specific heat capacity. Concentration dependences of the specific heat capacity of the considered nanocomposites at different values of their temperature and the level of overheating of the polymer melt have been built. The studies have been carried out to identify the effects of the influence of the above parameters on the coefficient of thermal diffusivity of nanocomposites. It has been established, in particular, that an increase in the level of overheating the polymer could lead to a very significant increase in the coefficient of thermal diffusivity, which is all the more significant the higher the proportion of filler and the lower the temperature of the composite material. It is shown that the level of overheating the polymer melt relative to its melting point is a parameter that can be used as the basis for the creation of polymer composite materials with specified thermophysical properties