The paper presents the construction and principle of operation of a cross-flow plate-fin heat exchanger. The two main types of matrix used in the recuperative device (for flat channels and with rectangular fins) are characterized in detail. The mathematical equations of the balances for the course of the heat and mass transfer process inside the flat channels and with the rectangular fins of the cross-flow heat exchanger were formulated. An original mathematical model of heat and mass transfer processes for a recuperative device was developed. A computer program was written using the Pascal programming environment. The program was used to conduct preliminary numerical simulations under the assumption of an 18-minute operation of the heat recovery unit. The nature of heat and mass transfer processes under condensation conditions is revealed. Three main areas of active heat and mass transfer ('dry', 'wet', and 'frost') and the limits of their formation have been identified. As the device was operated for a longer period of time, an increase in the area designated as the 'frost' zone was observed, from 11.9% to 15.6%. This was accompanied by a reduction in the area designated as the 'wet' zone, which decreased from 38.4% to 35.3%. The significant effect of frost layers on the airflow velocity inside the heat exchanger matrix was confirmed. The results demonstrated that the presence of a 'wet' area or a combined 'wet' and 'dry' area did not significantly impact the distribution of return airflow velocities.

In this paper, a process of frost accumulation inside the non-hygroscopic rotary heat exchanger depending on operating conditions is investigated. The study was based on the results of the numerical simulations conducted in the original computer program. The analysis considers both the threshold conditions of frost accumulation and the conditions of frost layer growth. For this purpose, three indicators related to frost accumulation were distinguished: a frost accumulation limit temperature, a surface of the matrix covered with the accumulated frost layer, a maximum thickness of the accumulated frost layer. The analyzes assessed the influence of operating parameters on these indicators, focusing on the return air relative humidity. It was revealed that the highest values of this parameter cause the greater thickness of the frost layer. However, the largest ‘frost’ accumulation area was created in the range of average return air relative humidity values – in the analyzed cases it was RH2i=38.5 %. The paper also includes a detailed analysis of the threshold temperature of frost accumulation. These limits of outdoor air temperature were determined for a wide range of operating parameters’ values: both airstream relative humidity and nominal temperature effectiveness. Additionally, eight probable configurations of active heat and mass transfer areas within rotary heat exchanger channels were revealed, which are related to the initiation of frost accumulation. Consequently, the locations of the initial ‘frost’ accumulation area were predicted. It was also found that the greatest impact on the frost accumulation threshold temperature has the return air relative humidity RH2i, although this influence is not unequivocal. The most unfavorable conditions regarding nominal temperature effectiveness in terms of frost accumulation are also unclear. In some cases, it was even demonstrated that an increase in the effectiveness can eliminate the ‘frost’ accumulation area.

The paper presents the course of heat and mass transfer in the fixed-bed heat exchanger. For this purpose, a previously developed original mathematical model of a fixed bed regenerator was used. On the basis of the developed model, a computer program was written and verified using experimental data. The validation results confirmed that the developed model can predict the performance of the heat exchanger. The effect of the presence of internal air leaks was analyzed for conditions of sub-zero outdoor air temperatures. Multi-variant numerical simulations carried out under low outdoor air temperature operating conditions made it possible to demonstrate many irregularities. Effectiveness variation was carried out for different thermodynamic air parameters. A maximum increase in device effectiveness (up to 0.92) was demonstrated, confirmed by the additional condensation of water vapor effect and the dominant effect of “wet” area accumulation. In the analyzed cases, a decrease in “frost” area accumulation was observed (by 10%) as the relative humidity of the return air increased. Moreover, the presence of a limiting return air relative humidity (for which the dew point temperature is equal to 0°C) was demonstrated, beyond which the non-accumulated “frost” area was partially transformed to a non-accumulated “wet” zone. A significant change in the effectiveness of the device was noticeable when the relative humidity of the return exceeds 30%, which was also confirmed by the maximum size of the “frost” area for this value (about 49%).

This paper tackles the issue of frost formation in non-hygroscopic rotary heat exchangers used for energy recovery from exhaust air under high-speed rotor conditions by means of numerical simulations and experimental approaches. On the basis of some idealized assumptions, a frost growth submodel is presented to predict the behavior of the rotary heat exchanger under frosting conditions. Frost formation is modeled by considering the mass diffusion of water vapor through the frost layer, taking into account supersaturation phenomena. Calculations were carried out using a three-zone model based on the modified epsilon-NTU method. The local heat transfer coefficient and the NTU calculation method resulting from the influence of the heat exchanger entrance region were also applied. The obtained correlations for the temperature effectiveness agree with the simulation data within uncertainty bounds. The results of the numerical simulations allowed us to determine the outdoor air conditions that initiated the frost accumulation phenomenon inside the thermal wheel for two values of return air relative humidity: RH2i = 20% and RH2i = 40%. In both cases, the threshold temperature for unsafe operating conditions increases with increasing relative humidity of the outdoor air. Under 'frost accumulation' operating conditions, the frost growth rate is approximately five times higher at RH2i = 40% than at RH2i = 20%. In this regard, the need to implement frost protection techniques increases significantly with an increase in relative humidity of return airflow. Further analysis conducted for the operation of a thermal wheel's operation under frosting conditions revealed that a latent heat flux contributed to the local frost density should not be neglected in a compact heat exchanger's model. Interestingly, the operation time of the rotary heat exchanger, and hence the growth of the thickness of the frost layer, has a significant influence on a local heat transfer coefficient alpha, however, it does not affect the Number of Transfer Units (NTU) visibly.

Mathematical model of dynamics of altitude distribution of natural radon isotopes in the surface atmosphere above land, parameterized by results of synchronous surface aerophysical and radonometric observations, is considered. The results of numerical solution of model equations parameterized by the observable in Borok Geophysical Observatory data are presented. The daily variations of volumetric activity of radon isotopes caused by the daily variation of the turbulent regime of the undisturbed surface atmosphere, characteristic of land of medium latitudes, are obtained.

The most important modern laser technologies include (i) the generation of colloid nanoparticles (NPs), laser ablation into a liquid (LAL-laser ablation in liquid) and (ii) surface hardening of products by laser pinning (LSP-laser shock peening). Significantly, with laser pinning, the surface to be treated is washed with water. Therefore, the physics of processes during ablation into a liquid and during pinning is common. True, the accents are different. If the ablation in the liquid actually forget about the shock wave (SW) generated by the impact, and leaving the thickness of the target, in the problem with pinning, on the contrary, the main question is about the impact. In addition, the role of water in LAL and LSP is different. In LAL, fluid contributes to the formation of NPs and adopts NPs, gently slowing them, whereas in LSP, water is needed to enhance the recoil and increase the amplitude of the hydrocarbon in the product. The complete picture, developed in the work, of course, should include both edges: the formation of ejection into the liquid as a result of ablation, i.e., LAL, and observation of the SW from the nucleation stage to its attenuation in the product volume, i.e., LSP.

In this study, we used a tethered balloon equipped with an instrumented platform to examine the altitude distribution of principal quantities of the lowest atmospheric region of the global electric circuit (GEC), radon volumetric activity, and aerosol particles concentration. Altitude soundings covered approximately 0.5 km of the lowest atmosphere and were accompanied by simultaneous ground-based measurements. This method of spaced observations allowed us to analyze the spatial and temporal changes in electrical quantities of the atmospheric boundary layer (ABL) more deeply than was possible before. Using successive balloon ascents and descents as well as holding the platform at certain heights, long-lived space charge layers were discovered and the rate of change of charge in atmospheric columns of various thickness was estimated. A charge density of small ions was determined to be enclosed in a range from -20 pC m(-3) to 30 pC m(-3) reaching the highest values with rare exceptions directly at the earth's surface. It was found that the electric field vertical profiles tend a decrease during the day most pronounced in the lower 100 m. Similar behavior is also demonstrated by radon and aerosol particle concentration profiles. Based on the results of soundings, columnar electrical resistance, electric potential, and electromotive force acting in the ABL in fair-weather conditions are quantified. These estimates show the significant contribution of the ABL to the GEC, which must be taken into account when considering it.

The paper presents an original mathematical model based on the modified epsilon-NTU method, developed for numerical simulations and analysis of coupled heat and mass transfer inside the rotary heat exchanger operating under frosting conditions. The proposed model was validated on the basis of experimental data. Positive validation results indicate that the developed model is capable to predict the behavior of the rotary heat exchanger at high rotor speed. Moreover, the nature of heat and mass transfer processes in the rotary heat exchanger under winter conditions is presented. Different variants of active heat and mass transfer zones in the regenerator channels are revealed. Schemes of safe (frost free operation without a frost area accumulation) and unsafe operation (with a presence of frost area accumulation) of the device are discussed. Three methods of protecting the heat exchanger against frost are presented and analyzed. The influence of rotor speed on frost formation inside the matrix of rotary heat exchanger is discussed. For analyzed cases the increase in rotor speed by 65% results in an increase in heat exchanger effectiveness (from 0.70 to 0.87) with simultaneous decrease in the size of the frost area accumulation (Delta(X) over bar1) from 0.22 to 0.07. The 68% decrease in the rotor speed was accompanied by a decrease in the heat exchanger effectiveness (up to 0.58) with complete elimination of the frost area accumulation. A similar effect was also observed when the outdoor air temperature slightly increased (from -15 degrees C to -13.5 degrees C) while maintaining constant efficiency (0.70) of the heat exchanger. (C) 2020 Elsevier Ltd. All rights reserved.

This paper is devoted to the jubilee of I.M. Khalatnikov, the founder and the first director of the Landau Institute for Theoretical Physics of the Russian Academy of Sciences. I.M. Khalatnikov organized a first-class institute the studies at which cover a broad spectrum of research directions. The plasma and lasers department of the Institute conducts research on plasma physics problems, laser–matter interaction, questions pertaining to laser applications, and hydrodynamics problems. Much attention is given to solid-state physics with an emphasis on the behavior of matter in extreme conditions under intense laser irradiation. A number of new results are presented: the behavior of metals in two-temperature states (when the temperature of the electron subsystem of a metal is much greater than the temperature of the ion subsystem due to ultrafast laser heating); determining the boundaries of existence of a single-wave propagation mode of elastoplastic shock waves in ductile metal crystals; the formation of a laser torch from target materials and liquids under metal laser ablation of a metal into the surrounding liquid; the physical–mechanical consequences (melting, capillarity, recrystallization) of nonuniform (along the irradiated surface) energy dissipation caused by the interference of plasmon–polariton and laser electromagnetic fields.

This paper focuses on the influence of geometrical parameters of the rotary heat exchanger on its operation under high-speed rotor conditions. Proposed mathematical model of heat recovery wheel is based on a structure of the counter-flow heat exchanger model. After implementation of a numerical method on the modified α-model, the computer simulations were conducted. They allowed considering the distribution of the active heat and mass transfer zones (“ dry, ” “ wet ” and “ frost ”) on the matrix channel surface depending on the outdoor air conditions for different variants of rotor size. The obtained results indicate that the increase in the wheel’s depth leads to the increase in temperature effectiveness of heat recovery (from 0.667 to 0.814). Moreover, it was also established that the threshold temperature under which the frost is accumulated on the core surface also rises with the rotor depth (from − 10.7 to −9.6 °C). It was concluded that under certain outdoor air temperature conditions ( t 1 i > –10.7 °C, for rotor depth equal to 0.40 m), the mass transfer rate of the condensed water vapor in the channels of the return air side is equal to the evaporation mass transfer rate in the channels of the supply air side, and hence, the temperature efficiency reaches the same value level as under “ dry ” operating conditions. It was established that only under frost accumulation conditions, the increased temperature effectiveness is observed.

In this study theoretical analysis of the heat and mass transfer in counter-flow recuperators used for energy recovery in air handling units (AHU) under sub-zero outdoor air temperature operating conditions is presented. The most probable variants of year-round heat exchanger operation performance, which characterized by existence of three active heat and mass transfer zones (“dry”, “wet”, “frost”), and effect of the latent heat of water vapour condensation on the realization of these variants was determined. It was established, that the frost tends to take place with increasing temperature effectiveness of the heat exchanger. Two main techniques of the frost prevention (preheating and bypassing the outdoor airflow) were described and analysed. The values of critical outdoor temperatures and outdoor-to-return airflow rate ratio were determined on the base of parametric frosting limits analysis conducted under different inlet return airflow conditions. The comparison of the heat recovery efficiency and additional energy consumption for the air treatment in the AHU is presented.

The paper presents an analysis of heat and mass transfer processes occurring inside the rotary heat exchanger operating under high-speed rotor conditions for different values of the airflow rate. For this purpose the original mathematical α-model was used. Conducted computer simulations allowed to determine the influence of Number of Transfer Units (NTU) of airflow on the temperature effectiveness as well as on the distribution of different active heat and mass transfer zones: “dry”, “wet” and “frost”. It was found that the increase of the values of NTU strictly affects the increase of the effectiveness of heat recovery. Another issue emerging from this study is the fact that in the certain range of low values of NTU there is no “dry” area created. It was established that at low values of NTU (NTU≈1) “frost” area extremum and sharp drop in the “frost” area accumulation are observed.

In this study, four arrangements of the desiccant system with different Maisotsenko Cycle (M-Cycle) heat and mass exchangers (counter-flow and cross flow heat and mass exchangers) were selected for a comparative study. The proposed system is able to obtain high thermal COPs (up to 4.9) due to effective pre-cooling of the airflow with a highly effective evaporative heat and mass exchanger. The performance of the systems was analyzed numerically with ε–NTU models developed by the authors for moderate climatic conditions. To compare selected systems, different performance indicators were considered. These are the thermal COP (Coefficient of performance), the ERR (Energy Efficiency Ratio), and the humidity ratio decreases. The results show that the desiccant system with two counter-flow heat and mass exchangers (marked as System A) achieves highest humidity ratio decrease, as well as the highest thermal COP. In terms of the EER, factor for system with counter-flow and cross flow heat and mass exchanger (marked as System B) achieves highest effectiveness. There is a slight difference between COP values obtained by System A and System B. That is why it was concluded that System B is a solution which needs more analysis to be done to maximize this desiccant system potential.

In this study, the application potential of desiccant cooling system with indirect evaporative precooling is analyzed for moderate climatic conditions. Wrocław (Poland) was selected as a representative city. On the base of summer season weather parameters different system running modes were proposed such as cooling and dehumidification mode (Mode 1) and only cooling mode (Mode 2). The average month Thermal and Electrical COP were established for selected climatic conditions. It was concluded that proposed system allows to cool the air without occurrence of condensation in Mode 2 with high average monthly electrical COP (COPel = 62.2 in August). On the other hand when dehumidification is needed, system operates in Mode 1 and obtains relatively high average Thermal COP values (COPth = 2.2).

The statistics of crimes in the field of computer information using malware were studied. The analysis of modern types of malicious software is presented in the paper. The trends of the malware market of the anonymous segment of the Internet are indicated.

In this study, two different indirect evaporative coolers operating with a desiccant wheel are compared theoretically: System A with the regenerative Maisotsenko Cycle (M-Cycle) unit and System B with the cross-flow M-cycle unit. Each system component performance was simulated using the original ε-NTU model. The influence of selected operational factors, such as inlet air temperature, humidity and regeneration air temperature for two system configurations was analysed and compared. It was established, that System B obtains higher cooling capacities and is more sensitive on ambient air humidity changes than System A.

This paper presents a numerical study of a novel, multi-stage desiccant air conditioning system designed for moderate climates. The proposed system is based on multi-stage cooling process through the Maisotsenko Cycle (M-Cycle), regenerative heat and mass exchangers (pre-cooling and post-cooling) combined with a desiccant wheel. The performance of the system was analysed numerically with original epsilon-NTU models and it was compared with a typical solution based on a desiccant wheel and the Maisotsenko cycle. It was found that multi-stage system obtains lower supply airflow temperatures and higher moisture content decrease in desiccant wheel as compared to typical M-Cycle desiccant system. Moreover, this solution allows a decrease in the regeneration airflow temperature to 40 degrees C maintaining the same or lower supply airflow temperature in moderate climatic conditions. Using multi-stage cooling, the proposed system was able to attain a thermal COP (defined as amount of cooling capacity obtained by the unit divided by required heating capacity) of up to 4.0. Due to this performance the proposed system has high application potential in moderate climates.

Boundary conditions required for numerical solution of the Boltzmann kinetic equation (BKE) for mass/heat transfer between evaporation and condensation surfaces are analyzed by comparison of BKE results with molecular dynamics (MD) simulations. Lennard-Jones potential with parameters corresponding to solid argon is used to simulate evaporation from the hot side, nonequilibrium vapor flow with a Knudsen number of about 0.02, and condensation on the cold side of the condensed phase. The equilibrium density of vapor obtained in MD simulation of phase coexistence is used in BKE calculations for consistency of BKE results with MD data. The collision cross-section is also adjusted to provide a thermal flux in vapor identical to that in MD. Our MD simulations of evaporation toward a nonreflective absorbing boundary show that the velocity distribution function (VDF) of evaporated atoms has the nearly semi-Maxwellian shape because the binding energy of atoms evaporated from the interphase layer between bulk phase and vapor is much smaller than the cohesive energy in the condensed phase. Indeed, the calculated temperature and density profiles within the interphase layer indicate that the averaged kinetic energy of atoms remains near-constant with decreasing density almost until the interphase edge. Using consistent BKE and MD methods, the profiles of gas density, mass velocity, and temperatures together with VDFs in a gap of many mean free paths between the evaporation and condensation surfaces are obtained and compared. We demonstrate that the best fit of BKE results with MD simulations can be achieved with the evaporation and condensation coefficients both close to unity.

This paper investigates application potential of the maisotsenko cycle (M-Cycle) evaporative air coolers in air conditioning systems in moderate climate (Poland is used as an example). Cross-flow M-Cycle heat and mass exchanger (HMX) was chosen as the most representative unit for this type of application. Analysis is based on the computer simulations performed during the peak day in summer (day when the highest cooling loads occur) and assumptions used in Polish standards for air conditioning systems. The obtained results show that evaporative cooling through Maisotsenko cycle has high application potential and allows to generate significant energy savings in compare to the systems equipped with standard heat recovery devices. The most favorable application for the M-Cycle in moderate climate is displacement ventilation, where proposed unit is able to cover almost all energy required by the air conditioning system.