Initial Air Temperature Research Articles

Optimization of cold startup strategy with quasi 2-D model of metal hydride hydrogen storage with fuel cell

In this work, a novel cold startup strategy is presented for a large-scale metal hydride–fuel cell system. Due to the thermal requirement of the system, when the initial temperature of metal hydride and ambient air is low, the system cannot be started because the hydrogen pressure in the metal hydrides storage system is lower than the minimal pressure required by the fuel cell. The cold startup is achieved by maintaining a part of metal hydride storage at a target temperature and using coolant control to transfer heat to the remaining cold metal hydride storage upon operation of the fuel cells. The strategy is studied numerically and a novel Quasi-2-Dimensional approach is developed to describe heat transfer within metal hydrides and validated. By the proper selection of the value of the control variable, both fast startup and immediate uninterrupted fuel cell power supply are achieved. The effect of initial conditions on the startup process is studied and the strategy consumed 30 % less energy than the alternative without control. The proposed strategy is suitable and efficient for the cold startup of large-scale metal hydride-fuel cell systems.

Experimental evaluation of localized air temperature profile and performance of serpentine copper tube heat exchanger for energy-saving crop cultivation

The objective of this study is to examine the localized air temperature profile and heat transfer performance of a serpentine copper tube heat exchanger. Particularly, the air temperature nearby the plants is controlled by the heat exchanger. The novelty of this study is to provide localized climate control only near the plants targeting periodic air temperature control with the proposed heat exchanger. This study focuses on heating and cooling for cultivation in temperate and tropical regions. In contrast to fin-and-tube heat exchangers, the serpentine heat exchanger has a simple design, provides minimal shade for plants, and is easy to maintain. This study was conducted in a laboratory. The experimental system was constructed under with the assumption that a part of actual plant cultivation was being left out. The experiments were implemented by varying the experimental operating conditions such as the inlet fluid temperature and fluid flow rate in the heat exchanger. The pressure drop in the heat exchanger was also measured. The results revealed that this heat exchanger could provide localized air temperature control. The maximum air temperature difference can be obtained at approximately 12 °C during cooling and heating from their initial air temperature even though the heat exchange is simple. The effects of decreasing the inlet fluid temperature for cooling and increasing the inlet fluid temperature for heating were more dominant than the effect of the flow rate. This simple, low-maintenance, and low-cost serpentine copper tube heat exchanger can effectively provide alternate heating and cooling for plant cultivation.

Performance optimization and evaluation of integrating thermochemical energy storage with low-temperature driven absorption heat pump for building heating: 4E analyses

A heating system achieved by combining thermochemical energy storage and absorption heat pump is proposed and verified. Based on the experimental data, a mathematical model of the zeolite/water reactor is established and verified. By setting up a micro-compressor between the evaporator and absorber, the AHP is driven by low temperature source. Based on typical days in winter, the stable operation of the system is explored, and the influence of main parameters on the charging/discharging and heating processes are analyzed. The results show that the charging and heating efficiency reached 55.11% and 73.52% during the daytime. The discharging efficiency at night reaches 88.27%. The AHP can be driven by a heat source at a minimum of 75 °C, and hot water at 48.3 °C is provided. Parameters influence analysis shows that temperature is an important factor affecting the charging process, and the initial air temperature is recommended to increase. Humidity is the biggest influencing factor in the discharging process and easily changed and controlled. By replacing electric heating, the system can allow the investment to be recovered within 6.23 years. Environmental analysis shows that the proposed system has significant benefits in terms of primary energy savings and pollutant emission reduction

Exploring the correlation and synchronicity between environmental factors and occupant thermal response in dynamic outdoor cabin environments

To improve the cabin thermal environment and explore advanced automotive air-conditioning control methods, it is essential to understand the key factors affecting occupant thermal response as well as the synchronicity of the thermal response to environmental changes in outdoor conditions. Given the current gaps in research, this study conducted outdoor experiments in summer to analyze the correlation and synchronicity between the cabin thermal environment and occupant thermal sensation as well as facial skin temperature. Results showed that, during the cooling phases of experiments with high initial cabin air temperatures, occupant thermal sensation improved significantly within 7 min. After 15 min, facial skin temperature and thermal sensation reached quasi-steady states. Thermal sensation was primarily influenced by air temperature, followed by solar radiation, and exhibited significant synchronicity with changes in these factors. When the air temperature stabilized at around 26 °C, every 200 W/m2 of solar radiation exposure increased the thermal sensation unit during the 40-min experiment period. Cheek and nose skin temperatures were significantly correlated with air temperature and solar radiation, and were sensitive to environmental changes, synchronizing with changes in air temperature and relative humidity. Further analysis showed the feasibility of using cheek and nose skin temperatures to characterize the occupant thermal sensation in a cabin. Additionally, this study found sex differences in the occupant thermal response in a cabin. The results provide insight into the key optimization parameters for comfort-oriented cabin thermal environment design and offer support for future air conditioning control in cabins based on thermal imaging.

Experimental Study of Influence of Initial Air Temperature on Characteristics of Combustion of Diesel Fuel Atomized by Jet of Superheated Steam

Experimental Study of Influence of Initial Air Temperature on Characteristics of Combustion of Diesel Fuel Atomized by Jet of Superheated Steam

Enhancing the electricity and desalinated water production from solar chimney power plants through integration with nuclear power plants: A case study in Jordan

A new energy generation system combining a solar chimney power plant (SCPP) with a nuclear power plant (NPP) cooling tower has been developed and assessed in Irbid, Jordan. The surplus hot air from the NPP is directly routed into the SCPP collector, increasing the initial air temperature and boosting the air profile of the SCPP, improving the air velocity inside the chimney and boosting electricity and water production. The integration of these two systems (SCPP+NPP) has shown significant improvements in electricity and water production compared to a standalone SCPP. The integrated system provides reliable electricity production throughout the day (24/7), thanks to the contribution of heat from the NPP side. Key results include a maximum electricity production rate of about 238 kW at approximately noon, twice the productive value of a conventional SCPP. The average monthly water and electricity production increased from 9.44 ktons and 25.73 MWh in the SCPP to 22.96 ktons and 63.81.64 MWh in the integrated system. The SCPP+NPP system peaks electricity production of 69.4 MWh in December, underscoring the positive influence of the added nuclear heat. While March emerges as the month of the maximum of water production (25.6 ktons) in the SCPP+NPP system, the SCPP water production peaks at 14.9 ktons in July. The results also show that the integrated system demonstrates a remarkable monthly electricity and water production of 63.81 MWh and 22.96 ktons, surpassing the standalone SCPP's production (25.73 MWh and 9.44 ktons), respectively. These results demonstrate this innovative solution's potential for optimizing excess heat produced by the NPP and the potential to revolutionize the energy industry.

Modeling the cooling effect of urban green spaces: The neglected control variables of ‘soil moisture’ and ‘biotope types’

Cooling by plant evapotranspiration (ET) is a prominent ecosystem service provided by urban green spaces (UGSs). UGSs counteract the warming of cities during heat waves. This study presents a GIS model to quantitatively assess the cooling intensity (CI) of UGS units (biotope types) during heat waves at the landscape scale. We conceptualize the CI as a physical index based on the ET of UGSs. Cooling intensities are calculated using the ambient temperature, biotope types, soil characteristics, and initial soil water conditions at the beginning of a heat wave as inputs. We calibrated and validated the model against the surface temperature in the city of Bochum, Germany, based on the thermal band of an orthorectified and calibrated atmospheric-, temperature- and emissivity-corrected mosaic from an airborne hyperspectral scanner. The Nash-Sutcliffe efficiency coefficient of the calibrated model is 0.75. The initial soil water content in the urban area affected the modeled CI by up to 2.6 K, and under the same transpiration rate, whether the initial ambient air temperature was 27 or 37 °C had effects of up to 2 K on the CI. The CI increased by up to 1 K with area size up to 2.5 ha. The purpose of the model was to evaluate and compare the CI of current and planned spatial patterns of land units to mitigate urban heat islands. The similar range of the goodness-of-fit criteria of the uncalibrated model compared to the calibrated model indicated the robustness and transferability of the model.

Optimization mathematical model of a contact air cooler for a mine turbocompressor

Purpose. Establishing the dependencies of rational parameters of turbocompressor contact air coolers on the operating mode and initial conditions. Methodology. The methods of analytical research, mathematical modeling, physical modeling, and mathematical statistics were used in the study. Findings. As a result of the research, an optimization mathematical model of the mine turbocompressor air cooler was developed, which allows establishing its rational parameters depending on the initial conditions and operating modes of the turbocompressor. The adequacy of the theoretical studies was proved on a specially designed experimental setup. The obtained dependences make it possible to minimize the theoretical flow rate at the inlet to the uncooled section of the turbocompressor, which reduces the specific energy consumption for the compressed air production. Originality. For the the first time, a method has been developed for determining the rational parameters of contact air coolers when the initial temperature of water, air, and air pressure changes, which allows developing a methodology for the constructive calculation of the contact cooling system of mine turbocompressors. Practical value. Compressed air is widely used in all industries. It is one of the most common energy carriers in industrial enterprises, and the devices associated with its distribution and processing are an energy-intensive complex industrial energy system; the level of its perfection depends on the performance of technological processes that use compressed air. Compressed air is widely used in the mining industry (ore mining and fuel production). Compressed air is produced by turbocompressors. To increase the efficiency of the compressor, compressed air coolers are used. A significant weakness of the standard compressor cooling system is the rapid contamination of the heat exchange surfaces of air coolers with scale layers, which leads to a decrease in their efficiency and an increase in the specific energy consumption for compressed air production. This disadvantage is not found in the Venturi tube – centered droplet separator contact air coolers. As a result of the study, the dependencies were obtained and used to develop a methodology for the constructive calculation of contact air coolers for a mine turbocompressor.

Absolute heat sources as a method to check the accuracy of temperature prediction in underground structures within cryolithozone

Forecasting the thermal regime of mine workings and the surrounding rock mass is a necessary element of the design of underground structures in cryolithic zone. This is particularly necessary when substantiating and selecting reliable methods and means of rock supporting, in order to ensure safe operation of underground structures during the entire standard service life. Changes in the temperature of discontinuous permafrost rocks in the range of negative values (below the ice point in the rock) can lead to a decrease in their strength characteristics, and consequently to a decrease in the stability of workings. The aim of the research was to compare two ways of considering absolute heat sources (point sources and sources uniformly distributed along the length of a mine working) when forecasting the thermal regime in mine workings of underground structures. The dependencies used to determine temperature differences in various methods of considering absolute heat sources were established. For the sake of generality, the dependencies were produced in dimensionless (criterial) form. The variants were calculated, and the results are presented in the form of graphs. The aim is to visually present the influence of the method of heat sources when considering the accuracy of air temperature prediction in an underground facility. Key qualitative and quantitative features of the formation of thermal regime in workings at different methods of considering absolute heat sources were established. It was shown in particular that during the transition from a negative temperature in a working to a positive one, incorrect consideration of the action of absolute heat sources can lead to an almost 30 % (1.26 times) difference (i.e., error) in the calculated depth of thawing of discontinuous rocks. It was also established that at a positive temperature, when the initial air temperature in a structure is more than 7.5 oC, there is no fundamental difference in engineering calculations results depending on the method of considering of absolute heat sources.

Experimental investigation of the temperature field of a frost-penetration tunnel based on a whole life cycle laboratory test

Temperature field evolution plays an essential role in anti-freezing design of frost-penetration tunnels, for which temperature data measured throughout the whole life cycle (100 years) are lacking. The spatial and temporal temperature evolution of a frost-penetration tunnel during the whole life cycle was investigated by using a laboratory test. The test model was designed following some basic fundamental assumptions and similarity principles. The proposed test model was validated using typical cases of the long-term evolution of the temperature fields in cold region tunnels. The evolution features, formation mechanisms and influencing factors were deeply discussed. Experimental results of the model test indicate that a frost-penetration phenomenon occurs in tunnels with positive ground temperature and negative mean annual air temperature. Under negative mean annual air temperature, the freezing circle develops radially towards the surrounding rock and simultaneously develops longitudinally along the tunnel after the tunnel breakthrough. The unfrozen surrounding rock freeze yearly and can develop into permafrost. The primary impact factor of frost penetrations is the positive initial ground temperature and negative mean annual air temperature. The mean annual air temperature has an insignificant effect on the annual temperature amplitude of the surrounding rock, whereas the annual air temperature amplitude has a negligible effect on the mean annual temperature.

Characterization of the Thermoelectric Coolers and Fatty Acid as a Phase Change Material of the Portable Box Cooler

The utilization of portable box coolers (PBC) for traditional fishermen is quite popular in Indonesia. However, pure water's cooling medium is still limited to ice. With the development of PCM technology, the utilization of fatty acids began to be used. Likewise, the use of thermoelectric coolers (TEC) directly on PBCs has also been widely developed. In this study, a combination of utilization of PCM based on fatty acids, namely lauric acid, myristic acid, and stearic acid has been carried out with the addition of a TEC to PBC. The concentration of each use of fatty acids in pure water was 5 mg/L, and the use of pure water was also tested as a comparison. The PBC design was developed for this research and given a load of 5 watts lamps in each test. The study was carried out in two stages, firstly, the use of PCM without the use of TEC, and the second study was the combination of the use of PCM which was added with the use of a TEC. The results showed that using a fatty acid solution was able to maintain the air temperature in the PBC longer than using only pure water. The use of stearic acid solution produces the best performance which can be seen from the time it takes to maintain the air temperature in the PBC is the longest to reach the initial air temperature, which is 1,160 minutes, followed using myristic acid solution for 1,120 minutes, while the use of the lauric acid solution is only able to maintain air temperature in PBC for 1080 minutes. This can be caused by the melting point of stearic acid being higher than the use of myristic acid and lauric acid. However, these results show that they are better than pure water, which can only reach 900 minutes to maintain air temperature in PBC. Adding a TEC to PCM from fatty acids could extend the time to maintain the air temperature in the PBC by about 40 minutes. These results indicate that the use of these fatty acids as PCM media can work significantly in thermal energy storage.

Determination of Energy-Saving Drying Modes in Vibrofluidized Bed Apparatus

The traditional pectin production technology is highly energy-intensive and environmentally unsafe. One of the possible ways to improve the technological process of pectin production is to dry directly the petine hydrolyzate before it is precipitated with ethyl alcohol. The most effective method of drying pectin hydrolyzate is drying in a vibrofluidized layer of an inert material, which provides high productivity in terms of evaporated moisture per unit volume of the chamber and the quality of the resulting dry product. This paper proposes a method for optimizing the drying process of pectin hydrolyzatein the apparatus of a vibrofluidized layer of an inert material, which makes it possible to determine the values of regime parame- ters at which the drying process proceeds with minimal costs for thermal and electrical energy. The technique is based on the experimentally obtained relationship between the specific productivity of the drying unit and the following operating parameters of the drying process: the air velocity in the drying chamber, the initial air temperature, the specific load related to the area of the gas distribution grid, the initial concentration for dry substances. On the basis of this experimental dependence, the criteria for assessing the reduced costs for heat and electric energy are formalized. A complex criterion for optimizing the drying process in a vibrofluidized bed is formulated, the minimization of which makes it possible to increase the efficiency of the drying process. Restrictions on the ranges of variation of the operating parameters of the drying process are formulated as well. The posed problem of optimization of the drying process in a vibrofluidized bed is solved numerically using the method of sequential quadratic programming and recommendations are formulated on the values of operating parameters for conducting the process in the optimal mode.

Methodology to calculating the temperature around an evaporating droplet using a set of thermocouples

A new approach is proposed to calculating the gas/vapor temperature field in the immediate vicinity of a droplet using a set of thermocouples. The schemes used in the experiments are based on convective and combined droplet heating. The air temperature during droplet heating was varied in the range of 100–500 °C, and the droplet radii from 1 mm to 1.7 mm. The paper describes data processing algorithms and methods for calculating the gas/vapor temperature field around a droplet using three to five series of measurements and shows the advantages of this approach over non-contact optical techniques. We also determine the applicability range of the proposed method for temperature field calculation and the limits of systematic and random measurement error variation. The instantaneous droplet radius and the initial air temperature around it are shown to be the main factors influencing the gas/vapor temperature distributions around an evaporating droplet. The experimental data are compared to earlier research findings. The results indicate that reliable gas/vapor temperature fields around evaporating liquid droplets can be obtained even with inexpensive equipment.

Sensitivity analysis of a louvered micro-channel evaporator

Most of the reported optimizations of micro-channel evaporators focus on specific variables, their priority has not been revealed. In the present study, a numerical model for a louvered micro-channel evaporator is established. The operating patterns under different cases are first revealed. Then, sensitivity analysis of operational and structural parameters is analyzed; sensitivity coefficients are additionally revealed to enumerate the priority. The results indicate that the influence mechanism and sensibility of different operating factors are distinct. The log-mean temperature difference (LMTD) increases first and then decreases with the air speed while the overall heat transfer coefficient increases first and then decreases with the inlet dryness. In other cases, the LMTD, heat transfer rate, entropy generation, and overall heat transfer coefficient display positive or negative variation trends with the operating factors. On the whole, the air speed, initial air temperature, and mass flow rate of the refrigerant play positive roles while the cross-sectional size and inlet dryness play opposite roles in determining the heat transfer performance. Of which, the heat transfer rate is positively determined by the initial air temperature with the maximum value of 0.85 while negatively determined by the inlet dryness with the value of −0.23; the overall heat transfer coefficient is positively determined by the air speed with the value of 0.83 while negatively determined by the cross-sectional size with the maximum value of −0.41. The mass flow rate of the refrigerant makes no difference in determining the heat transfer performance.

A Numerical-Hierarchical Framework for Predicting Volume Changes in Expansive Soils under Variable Surface and Weather Conditions

This research developed a numerical-hierarchical framework that captured surface conditions and climate parameters. Volume changes under distinct scenarios of surface boundary, antecedent moisture, and meteorological parameters were predicted using a coupled seepage-deformation model. Risk was hierarchically based on expert judgment for surface scenarios (Stage-I indices) and normal distribution for antecedent moisture and atmospheric parameters scenarios (Stage-II indices). Results indicated seasonal volumetric changes with minor variations of −5 mm from January to April, a steady settlement of −17 mm by June, and a gradual heave of +8 mm by December. All Stage-I indices showed similar trends such that the fluctuations were highest for vegetation, followed by slope, then by cover, and lowest for loading. Volume changes gradually reduced with depth and diminished at 3.1 m. Similar seasonal and profile trends were generally found for most Stage-II indices. Nonetheless, different trends under wet and dry conditions were observed for initial water content, precipitation, and air temperature. For the datum scenario, risk was non-existent till February, increased to 2.3 by June, diminished by October, and rose back to 1.0 by December. Similar values of cyclic variations in risk were found in most urban facilities. Volume changes were found to be two times higher in parks, insignificant for roads, half for five story buildings, and one-fourth for pipes under roads. Among the Stage-II indices, risk for the initial water content inhibited seasonal variations whereas that for precipitation was about half with a wider distribution; all the other indices showed about one-third the values. Under a higher occurrence probability of 0.129, a magnified risk was observed for all the indices such that the most critical were the initial water content and precipitation.

EXPERIMENTAL RESEARCHES ON SOME SPECIES AND VARIETIES OF FRUITS AND VEGETABLES SUBJECTED TO DEHYDRATION TREATMENTS

The main objective of the work is the study of the process of dehydration of fruits and vegetables, using two different types of equipment for dehydration: convective dryer, equipped with drying trays; microwave field dehydration instalation, with continuous flow. In the case of the convective dryer, the divided products will be placed evenly on the drying trays and the following specific parameters of the dehydration process will be determined: the initial and final humidity of the products; initial and final air temperature; the initial and final humidity of the air. In the case of microwave dehydration equipment, the divided products will be placed in a uniform layer on the conveyor belt, which moves at a constant speed of 4.5 cm/min. The following parameters will be measured: the mass of the sample; the amount of water evaporated in the measuring interval; the final mass of the sample; the final humidity at the end of the dehydration cycle. The results obtained in the case of using the convective dryer with drying trays indicate that the measured values fall perfectly within the admissibility range imposed by the technology,regarding all the studied parameters. In the case of using the dehydration installation with microwaves, the dehydration process is very intense, producing rapid heating of the product to over 600 C0, in approx. 5 min., in its entire volume, which leads to the inactivation of oxidative enzymes and reduces the risk of thermal browning and caramelization.

Control of modes of energy-saving vibro-drying devices

This paper proposes a method for optimizing the drying process of pectin hydrolyzate in the vibrofluidized bed of inert material, which allows to determine the values of the parameters of the regime at which the drying process continues with minimal costs for thermal and heat. It is based on the experimentally obtained relationship between the specific productivity of the drying equipment and the following parameters of the drying process: air movement speed in the drying chamber, initial air temperature, specific load depending on the drying area, gas distribution network , the initial concentration of dry matter. A complex criterion for the optimization of the vibrofluidized drying process has been developed, its minimization allows to increase the efficiency of the drying process. Restrictions on the ranges of changing the parameters of the drying process have been developed.

ОБҐРУНТУВАННЯ КОМПЛЕКСНИХ ЗАХОДІВ ОХОРОНИ ПРАЦІ ШАХТАРІВ ЗА ФАКТОРАМИ ЯКОСТІ РУДНИКОВОГО ПОВІТРЯ

The results of an analytical-experimental study related to the actual task of substantiating comprehensive measures for occupational safety of miners in deep coal mines on the factors of mine air quality based on the study of hydrodynamic air conditioning processes, which is especially important for the development of autonomous and energy-saving means of ensuring miners' occupational safety standards, are presented. Purpose. The goal is to substantiate and analytically study the main thermodynamic characteristics of the process of hydraulic mine air conditioning for the development of functional modules of mine air conditioners with variable indicators of rational capacities that satisfy the specific conditions of miners' workplaces in deep coal mines. Methodology. The general research methodology is based on a systematic approach to the analysis of hydraulic and thermodynamic processes, which include a complex of analytical study of the mixture of air with water droplets with substantiation and development of a mathematical model in the working volume of the air conditioner, analysis of experimental laboratory and industrial data by methods of mathematical statistics, as well as generalization regarding the determination of regularities of the main characteristics of the thermodynamic process of hydrodynamic conditioning of mine air. The results. The enthalpy and humidity indicators of the mine air have been analytically determined for the study of the energy state of the active component of the working body of the flow of a mixture of air and water droplets; diagrams of the assessment of the essence of the change in the thermodynamics of the working mixture in the hydrodynamic air conditioner have been obtained, as well as the energy characteristic of the change in the relative humidity of the air during its cooling with a change in the pressure and temperature of the working mixture in the multi-chamber ejector of the hydrodynamic air conditioner. Scientific novelty. For the first time, thermodynamic indicators of the state of the working mixture of thermopotential air and droplet water before and after conditioning, as well as indicators of changes in enthalpy, humidity and temperature of the mine air in the hydrodynamic conditioner, have been determined analytically. The practical significance of the results of the presented research is that, on the basis of energy characteristics, it becomes possible to calculate the necessary initial temperatures of water (in the range of 1.0°C-20°C) supplied to the hydrodynamic air conditioner and the initial air temperature (for limits of 30-50°C), which is a technical condition for the development of an ejector module of a hydrodynamic conditioner for a specific local working area of a deep coal mine.

Дослідження впливу основних режимних параметрів на ексергетичний ККД конвективної сушильної установки

Mathematical model is proposed for the numerical study of exergy losses in a chamber convective drying unit and the determination of the Impact of the main mode parameters during convective drying on the exergy coefficient of the useful effect of the convective drying unit. The mathematical model is implemented in the MathCad environment. The SKRR-400 intermittent chamber dryer for drying agricultural products with a one-time load of 400 kg was chosen as the object of the study. The components of exergy losses, which have the greatest influence on the thermodynamic perfection of the drying plant, are determined, and the ways of reducing their specific weight in the exergy balance are indicated. Numerical studies of the effect on the exergetic efficiency coefficient of the dryer of such parameters as the ambient temperature, the temperature of the coolant at the entrance to the drying installation, the temperature of the coolant at the outlet of the drying installation — spent coolant, the temperature of the steam condensate in the heater have been carried out. A numerical experiment showed that with the increase in the initial air temperature, the useful specific exergy consumption for moisture evaporation decreases and the change the prominence of the dryer performance does not affect the total exergy losses. It is established that the energy or exergetic and thermal efficiency factors of the dryer differ significantly . According to the calculations, the exergetic.efficiency of the chamber dryer, which reflects its thermodynamic perfection, does not exceed 14.5 %. Comparison of exergetic.efficiency with the energy or thermal efficiency of SKRR-400 type dryer showed that the thermal efficiency of dryers is significantly higher (50,4 % versus 14,5 %). It is hypothesized that this is due to the fact that thermal efficiency does not take into account the phenomena of irreversibility of heat and mass transfer processes. It was established that losses with waste coolant in the exergy balance make up 8 %, and in the thermal balance — 33,2 %. According to the results of the numerical experiment, it is shown that increasing the efficiency of drying units can be achieved by improving their heating devices and reducing their losses.

EXERGY ANALYSIS OF AN OPEN-MODE ADSORPTIVE HEAT STORAGE UNIT BASED ON COMPOSITE ADSORBENT ‘SILICA GEL – CRYSTALLINE HYDRATE’

Exergy analysis of an open-mode adsorptive heat storage unit has been performed when a composite ‘silica gel – crystalline hydrate’ used as an adsorbent. The crucial factors affecting the exergy efficiency factor are stated to be temperature and initial humidity of airflow supplied to the inlet of adsorbent layer, temperature of external air and methods of air flow humidification. Procedure of calculation of the operating characteristics of an open-mode adsorptive heat storage device was further developed. The suggested procedure involves determination of adsorption, specific adsorption heat and final airflow temperature, useful heat, heat inputs for operating heat storage device and its efficiency factor, then exergy recovered, exergy supplied and exergy efficiency are calculated. Exergy efficiency depends on characteristics of flow of humid air fanned into the adsorbent layer such as temperature and initial absolute humidity which strongly affect the adsorption and final airflow temperatures. Increase of initial temperature of the humid air leads to decreasing of the exergy efficiency. Maximal values of exergy efficiency are determined at the absolute humidity and temperatures of initial airflow within the ranges of 0.03 – 0.04 kg/m3 and 20 – 30ºC, respectively. These characteristics are corresponded to the maximal airflow temperatures after passing through the adsorbent layer which meet to the Sanitary Regulations. Dependence of exergy efficiency vs. external air temperature and initial airflow temperature is shown. The exergy efficiencies of the open-mode adsorptive heat storage unit with steam and ultrasonic humidification were compared. Ultrasonic humidification is shown to allow increasing the exergy efficiency by 7 % against steam humidification. The obtained results can be used when energy-efficient heat and ventilation systems for residential premises developed.