B. N. Okunev

Mathematical modeling of the operation of an adsorption cooling system

A mathematical model has been constructed for the operation of an adsorption cooling system with a finned metallic adsorber using a working pair consisting of water and the CCB-1K composite sorbent (calcium chloride modified mesoporous silica gel). Optimal cycle times have been numerically calculated for a granular adsorbent bed and a compact sorbent-binder bed. The influence of the heater and condenser temperatures on the efficiency factor and cooling power of the system has been investigated. For a granular bed, the efficiency factor of such systems reaches 60.0%. For a compact bed, the specific useful cooling power can reach ∼400.0 W/kg. Possible ways of enhancing for increasing the operating efficiency of systems with a liquid heat-transfer agent are discussed.

Mathematical modeling of the operation of a solar-driven adsorption refrigerating system using a planar layer of a composite sorbent

A mathematical model is constructed of an adsorption refrigerator using a water coolant and solar radiation for the regeneration of the plane sorbent layer. On the basis of climatic data from the monitoring/observation by the Sochi City Meteorological Watch Office, numerical optimization calculations have been performed. It is shown that there is an optimal height of the sorbent layer securing the highest capacity of the plant. The optimization of the plant geometry enables a further 1.5-fold enhancement in the plant capacity. It is shown how the presence of a nonsorbing component (air) affects the plant capacity.

Analytical theory of regenerative heat transfer and study of its thermodynamic efficiency

An analytical theory of the cyclic process of regenerative heat transfer is developed. Introduction of operator-valued functions of integral operators allowed the authors to formulate an equation for determination of periodic solutions. A solution of this equation is found in a linear approximation with respect to switching times. A functional — exergic efficiency — is introduced on periodic solutions. The analytical solution obtained made it possible to study the dependence of the introduced criterion on the parameters of the system and to describe the time mode of the process in which the thermodynamic efficiency is maximum. Comparison of the analytical theory and a numerical analysis of the problem showed that upon choosing an operating mode of the apparatus that fits the maximum values of the introduced criterion, one can use results of the analytical solution at all admissible values of the switching times.

Thermodynamic Analysis of the New Adsorption Cycle “HeCol” for Ambient Heat Upgrading: Ideal Heat Transfer

Thermodynamic analysis of a new adsorption cycle recently suggested for upgrading ambient heat (the so-called “Heat from Cold” or HeCol cycle) was performed. The energy and entropy balances at each cycle stage and in each converter component were calculated for the methanol–AC-35.4 activated carbon working pair under conditions of ideal heat transfer. It is shown that useful heat can be obtained only if the ambient temperature is below a threshold temperature. The threshold temperature was calculated based on the Polanyi principle of temperature invariance and was experimentally validated. The specific useful heat can reach 200–300 J/(g adsorbent), which is of practical interest. The use of adsorbents with an abrupt change in the adsorption uptake between boundary isosters of the cycle may lead to further enhancement of the useful heat. For the HeCol cycle, the exergy losses under the conditions of ideal heat transfer are small. At low ambient temperature, the losses in the evaporator, condenser, and adsorber are comparable, whereas at higher ambient temperature the main exergy losses originate from the adsorber heating and cooling.

The dynamics of water vapor sorption on a composite sorbent in the presence of unsorbable components

Preliminary mathematical processing of the experimental data on the dynamics of water vapor adsorption on a composite adsorbent was performed. The approximate time dependence of water vapor pressure was constructed. An analytic equation describing changes in the mean temperature of adsorbent grains as a function of the duration of measurements depending on water vapor pressure was obtained, and an asymptotic approximation equation was suggested. The system under consideration was shown to pass two “diffusion” stages in the dynamics of pressure changes and changes in the mean temperature of grains. The characteristic times of the diffusion stages monotonically increased as the fraction of an unadsorbable component in the gas phase of the system grew.

An increase in thermodynamic efficiency and compactness of contact apparatuses via spatially organized structure of the active material bed

The possibility of filling the hollow input (diffuser) and output (confuser) sections of contact apparatuses by an active material is analyzed. The equation determining the distribution function of the sizes of material particles along the axis of a conelike apparatus, which provides the minimum volume of the bed of particles at the specified values of the total surface area of the interfacial contact in the bed and total flow resistance of the bed, is derived. It is shown that the change in the conventional shape of the apparatus to a construction in the form of a junction of two truncated cones filled with the active material allows one to decrease the total volume of the apparatus by 30%. The dependence of the thermodynamic efficiency and compactness of the regenerative facility on the particle size of the active material bed is numerically analyzed. The existence of a critical particle size which determines the minimum necessary volume of the bed providing high thermodynamic efficiency of the process is shown.

Influence of nonadsorbable component on the dynamics of water sorption on composite adsorbent

Experimental data are analyzed on water adsorption in the presence of a nonadsorbable component on the composite adsorbent silica gel impregnated with calcium chloride for different partial pressures of water and air. It is established that the mass-transfer mechanism inside the grain is Knudsen diffusion. It is shown that a dynamic structure is formed in the system, with increased concentration of the nonadsorbable component close to the external surface of the grain, causing externally diffusive resistance. The coefficients of heat exchange between the grain and the gas phase are defined.