Exergy Efficiency Values Research Articles

A detailed analysis of a novel auto-controlled solar drying system combined with thermal energy storage concentrated solar air heater (CSAC) and concentrated photovoltaic/thermal (CPV/T)

In recent years, the use of solar energy, one of the renewable energy sources, has been increasing in many areas due to its practical, environmental, and economic benefits. Besides, the drying industry is an applied area where solar energy can be implemented. Solar drying systems are used in the industry to reduce high drying costs and to obtain better quality products. In this study, a novel solar drying system was designed by combining concentrated solar air collector (CSAC) and concentrated photovoltaic/thermal system (CPV/T). In addition, the automation system has been integrated for data acquisition from the system and humidity-temperature control of the drying chamber. The SAC's inlet air was preheated by a heat exchanger using thermal energy from the PV/T. The drying system has been designed to be more useful by using phase change material in the collector. Thus, the drying process can be performed on cloudy days and after sunset. In addition, the designed system can generate electricity from the PV module to meet the electricity requirement. The mint which grows in various regions worldwide was chosen as the product to be dried in this study. Mint was dried from the first moisture content of 3.3125 g water/g dry matter to the last moisture content of 0.0625 g water/g water/g dry matter. Besides, the average overall efficiency of the system, PV module electrical efficiency, and drying efficiency were found to be 61%, 10%, and 26%, respectively. Furthermore, the average system exergy efficiency, PV module exergy efficiency, and concentrated solar air heater exergy efficiency values were calculated as 20%, 16%, and 21.9%, respectively. In the experiment, the ambient average temperature was 22 °C, while the average drying chamber temperature was 30 °C. The mint drying quality efficiency was 67% on average at this drying chamber temperature. The energy, exergy efficiency, and sustainability index of the system were calculated as 61%, 38.8%, and 1.69, respectively. Moreover, the enviro-economic cost of the system was determined to be 0.39 ¢/h.

Obtaining mathematical equations for energy, exergy and electrical efficiency: A machine learning approach

ABSTRACT In this study, in which the energy, exergy, and electrical efficiency values of the photovoltaic thermal panel are modeled with different machine learning algorithms, mathematical equations that can calculate the efficiency values have been obtained as an innovative approach. Data sets consisting of environmental parameters (temperature, wind speed, solar radiation, humidity) of the environment in which the experiments were carried out were used in the models. Thus, the effects of environmental parameters on collector efficiency values were observed, and mathematical equations were produced using these parameters with the help of the decision tree algorithm and Pace regression. In addition, environ-economic analyzes of the panels were made and the coefficient of performance values were examined. In the experiments, two data sets were obtained. With one of these data sets, the efficiency values were modeled with machine learning algorithms, and the accuracy of the mathematical equations obtained with the other data set was proven. The mean absolute percentage error values of the energy, exergy and electrical efficiency models created with the decision tree are 8.04%, 1.76%, and 1.43%, respectively. Similarly, Pace model error values are 3.83%, 2.54%, and 2.1%. The high accuracy values of the obtained efficiency equations under different experimental conditions show that these equations can be used under different conditions and in different solar energy systems.

A Genetic Algorithm approach for optimization of geothermal power plant production: Case studies of direct steam cycle in Kamojang

Indonesia has enormous geothermal potential, but it only contributes 5% to Indonesia's energy matrix. During 37 years of operation, PT. Pertamina Geothermal Energy Kamojang area has been operating to produce electricity and is currently capable of supplying and distributing electricity to the Java-Bali area with a capacity of 60 MWe. However, this can run into a decrease in the efficiency and effectiveness of system performance due to energy losses in several geothermal power plant components during energy conversion. In this case, exergy analysis at PT. Pertamina Geothermal Energy Kamojang area Unit 4 direct-dry steam cycle was done on each component and state. This aims to know the energy and exergy stream and where it happened irreversibly at the component. The biggest irreversibility value occurred at the turbine and main condenser, with a value of 21,693.890 kW and 21,688.148 kW. The total irreversibility of all systems is 58,326.201 kW, while the total exergy inlet systems is 119,308.457 kW, so the value efficiency exergy obtained is 51.13%. Based on the environment as dead state analysis, an efficiency exergy value is inversely proportional to the irreversibility value and ascending environment temperature. System optimization was done with the genetic algorithm method, with variable values at the pressure wellhead and inlet turbine for the overall exergy efficiency value. The value obtained from optimization is 11.98 bar at the wellhead and 10.023 bar at the inlet turbine, and the overall efficiency exergy increased by 51.22%.

Machine learning-assisted tri-objective optimization inspired by grey wolf behavior of an enhanced SOFC-based system for power and freshwater production

In recent years paying attention to the generation of clean and sustainable power and fresh water along with having lower cost and emission has increased. In the present research, a novel scheme for generating efficient power using the flame-assisted fuel cell is introduced, which has higher efficiency than ordinary fuel cells due to increased hydrogen concentration in the flame-rich combustion chamber. The waste heat is then introduced to a multi-effect desalination unit through a heat recovery steam generation unit to generate fresh, drinkable water. In order to make the system have higher efficiency, lower cost, and lower emission, the machine learning techniques are applied to optimize the operational conditions of the system, and find out the best solution point based on the cutting-edge algorithm of the grey wolf. Also, a complete techno-economic analysis and a parametric study are necessary to figure out the best solution point based on the TOPSIS method. The results indicate that the maximum value of exergy efficiency and drinkable water generation is 67.5% and 3.4 kg/s, respectively, while the minimum energy cost is 90.1 $/MWh. Moreover, results show that for the second optimization scenario considering the drinkable water production, energy cost, and pollution index as the objectives, the net produced power, energy efficiency, exergy efficiency, and water mass flowrate improve by around 1059 kW, 5.1%, 1.3%, and 1.6 kg/s than the design condition. Besides, energy cost and emission index are reduced by about 22 $/MWh and 51.9 kg/MWh, respectively.

Proposal of novel exergy-based sustainability indices and case study for a biomass gasification combine cycle integrated with liquid metal magnetohydrodynamics

Exergy is considered a way to sustainability. Exergy-based analyses have been recently widely used for performance assessment and comparison purposes of energy systems from production to end-user while different sustainability related indices or indicators including exergetic concepts have been developed in the literature. In this regard, the present study proposed five different indices: (i) Exergetic Fuel Based Environmental Remediation Index (χ), (ii) Exergetic Product Based Environmental Remediation Index (δ), (iii) Exergetic Fuel Based Total Environmental Remediation Index (β), (iv) Exergetic Product Based Total Environmental Remediation Index (α), and (v) Improved Sustainability Index (ISI). These indices were applied to a novel Biomass-integrated Gasification Combine Cycle (BIGCC) integrated with Liquid Metal Magnetohydrodynamics (LMMHD). They allowed to perform a more complete environmental analysis by considering the exergetic cost of environmental remediation of the process. The average exergy efficiency values for the BIGCC, LMMHD and the overall system were determined as 0.491, 0.222 and 0.688 under daily ambient temperatures for a year and different air to fuel ratio (AFR) conditions, respectively. The average values for χ, β, δ, α and ISI were 1.636, 2.389, 1.949, 2.848 and 0.513, respectively.

Study of heat transfer and pressure drop for novel configurations of helical tube heat exchanger: a numerical and experimental approach

In this study, several unique tube configurations are designed and modeled to examine the thermal and hydraulic performance of a helical tube heat exchanger (HTHE) experimentally and numerically. For cold and hot side tube designs, the numerical investigation is completed using three-dimensional modeling, and the findings are confirmed using experimental data with Reynolds numbers ranging from 16,000 to 25,000. Six configurations named HTHE1, HTHE2, HTHE3, HTHE4, HTHE5, and HTHE6 are tested. The findings showed that as compared to the uniform tube distribution, the new arrangements have a greater overall heat transfer coefficient. The overall heat transfer coefficient has the highest enhancement ratio (125–185%) in the HTHE6 setup with two pathways. Additionally, it is discovered that the pressure drop rises as the Reynolds number increases. The HTHE1 configuration has the highest pressure drop values, whereas configurations with only one pass result in a greater pressure loss when compared to setups with two paths. The values of the coefficient of performance for the HTHE6 are larger than those of other forms, and the coefficient of performance decreases as the Reynolds number increases. The exergy efficiency grows with the rise of Reynolds number where the HTHE6 has the maximum value of exergy efficiency compared to other shapes. The performance of heat transfer is dramatically improved by the novel tube arrangements, although variations in pressure drop and pumping power are only a little affected.

Prediction of energy and exergy performance for subcooled and superheated vapor compression refrigeration system working with new generation refrigerants

In this study, an adaptive network-based fuzzy inference system is used to facilitate the thermodynamic performance analysis of a cooling system. Adaptive network-based fuzzy inference system can extract nonlinear relationships between variables using training data and has an advantage its speed and simplicity in modeling a multivariate problem. Since the evaporator, condenser, superheating, and subcooling temperatures affect the performance of the cooling system, thermodynamic efficiencies are estimated depending on these temperatures. New generation R516A, R515A, and R515B refrigerants were used in the refrigeration system. When the estimated and actual coefficient of performance values is compared, the mean absolute percentage error values were 7.3%, 5.7%, and 6.2% for these refrigerants respectively. The mean absolute percentage error values for exergy efficiency were 4.7%, 5.9%, and 5.5% for the same refrigerants respectively. The results show that the adaptive-network-based fuzzy inference system can be successfully used in complex processes such as estimating the thermodynamic performance of the refrigeration system. Thus, this model will help engineers to predict refrigeration system performance very accurately, quickly, and easily.

Applying regression techniques to determine mathematical equations of exergy, electricity, and energy values of photovoltaic thermal collector

The highlight of this study is to produce mathematical equations that can calculate the electricity, energy, and exergy efficiency values of an air-type photovoltaic-thermal (PV-T) solar collector with the help of a regression-based artificial intelligence method. Contrary to classical predictive artificial intelligence models, the Elastic.Net regression method, which can produce a linear equation for the modeled parameter, was used. Six different data sets were obtained, with the trials carried out in two months for the PV-T efficiency values. The Elastic Net algorithm produced energy, electrical, and exergy efficiency equations with the first, third, and fifth datasets. Comparisons were made between experimental thermal efficiency ratings and the output of efficiency formulas. The other three data sets were then subjected to efficiency equations, and the results were contrasted with the experimental values. The thermal efficiency equations predicted the experimental data in the data sets 1, 3, 5 and, 2, 4, 6 with mean MAPEs of 2.9% and 4.16%, respectively. The experimental values in both group data sets have been said to be comparable to the efficiency values discovered using the equations. As a result, it is anticipated that the efficiency equations developed can be used in various experimental configurations or flat solar collectors. Additionally, prediction models were created utilizing datasets 1, 3, and 5 using the artificial neural network (ANN) technique. The best ANN network structure was obtained using different network types, training algorithms, transfer functions, and layer-neuron numbers in ANN models.

Molten carbonate fuel cell integrated hybrid system for clean and efficient power generation

Thermo-economic and environmental analyses of a hybrid power generation system were performed in this study, which included a biomass steam gasifier, an indirect heated air turbine unit, carbon dioxide separation, capture, and sequestration using a molten carbonate fuel cell, downstream waste heat recovery via organic Rankine cycle, and steam Rankine cycle. Furthermore, multi-objective optimization was performed using response surface methodology to determine the operating state at which the system delivers the highest value of exergy efficiency while also having the lowest cost of electricity. It has been found that the conceptualized system delivers its optimum output when the air compressor operates at a pressure ratio of 9.41, the temperature at the inlet of the air turbine is 1100 °C, the molten carbonate fuel cell operates at 1500 A⋅m−2 current density with 80% fuel utilization, and the heat recovery steam generator pressure is 150 bar. The optimized values of the cost of electricity and exergy efficiency have been found to be 0.0993 $/kWh and 47.46%, respectively. At the optimum condition, the plant generates 1.3 MW power with an energy efficiency of 54.5%, capturing 5052.58 tonnes of CO2 in a year, producing $0.758 million in environmental benefit. It has been found from this study that the optimized hybrid power system yields better exergy efficiency and unit cost of electricity in comparison to the existing conventional biomass-based plants available in the literature.

Energy, exergy, economic, environmental and sustainability (4ES) analyses of a wastewater source heat pump system for district heating applications based on real operational data

In recent years, worldwide interest in utilizing the heat energy from wastewater (WW) has increased significantly, concurrently with establishing policies and strategies for the sustainable management of WW. This study evaluated the 4ES performance of a photovoltaic-thermal powered WW source heat pump system for district heating applications with a series of Engineering Equation Solver (EES) simulations based on 20 different cases using actual data. The results indicated that the WW might have an energy rate potential of up to 25470 kW and an exergy rate potential of up to 2263 kW in January in a Koppen-Geiger-classified Dfb (warm-summer humid continental) climate. The highest and lowest exergy efficiency values ranged from 2.85 % to 98.24 % and from 74.80 % to 94.54 %, respectively for the employed components and the entire system. The environmental and sustainability studies utilized these simulated results to derive environmental effect factor (EEF) and exergy based-sustainability index (ExSI) values in the ranges of 0.58x10-5 to 4.95x10-5 and 3.97 to 18.32, respectively. In addition, the levelized cost of energy (LCOE) was modeled to be between 0.0801 ¢/kWh and 0.1341 ¢/kWh. In terms of sustainability, the proposed system demonstrated superior performance than the most common heating solution on the market (i.e. natural gas-fired heating system).

Development and investigation of a pollutants emission reduction process from a coal-gasification power plant integrated with fuel cell and solar energy

Abstract Even though coal resources are the most abundant among fossil fuels, coal-fired plants release large amounts of greenhouse gases into the atmosphere. In this regard, reducing environmental challenges and crises caused by coal burning can be a promising option to reduce today's crises in the energy field. The integration of coal-fired plants with renewable-driven energy systems can simultaneously improve thermodynamic performance and reduce pollutants emission rates. This article presents the thermodynamic and pollutant emission investigations of a new coal-fired plant coupled with a linear Fresnel solar collector (LFSC)-driven solar unit, a parabolic trough solar collector (PTSC)-driven solar unit, a high-temperature fuel cell stack (molten carbonate fuel cell stack [MCFCS]) and a heat recovery system (based on the steam turbine and gas turbine-based power cycles). The plant is able to produce electricity and hot water (HW). The main structure of the offered plant is based on coal, whereas, is coupled with renewables-based cycles to mitigate environmental impacts. The plant could generate ~ 207 MW of power and 3728 m3/h of HW. In such conditions, the energy efficiency of 73.1% and exergy efficiency of 44.18% could be achievable. Further, the emitted gas rates of the plant were nearly 403 tons/h. A comprehensive comparison is also presented for the plant's behavior under different types of coal (petcoke and anthracite). In addition, a two-function optimization is developed to determine the maximum value of exergy efficiency and the minimum value of total pollutants emission rate.

Conceptual design and evaluation of a hybrid energy system based on a tri-level waste heat recovery: an approach to achieve a low-carbon cogeneration system

Abstract The exhaust waste heat of the fossil-fired power plants and some power generation technologies (such as fuel cells) is a rich source of recoverable thermal energy. Meanwhile, the effective use of the fuel cell's exhaust waste heat in the downstream processes and units can improve the thermodynamic superiority, reduce the environmental impacts caused by the release of waste heat in the environment and enhance the attractiveness and sustainability of the energy process. Here, the multi-variable analysis (thermodynamic, economic and environmental assessments)/optimization of a low-carbon cogeneration process (power and cooling capacity production system) are proposed and investigated. The proposed cogeneration process works under waste heat from the exhaust of a fuel cell, an ejector refrigeration cycle and an organic Rankine cycle (ORC)-driven tri-stage waste heat recovery system. A bi-objective optimization is based on identifying the maximum value of exergy efficiency and the minimum value of the total cost of the system. To highlight the advantages, the behavior of the considered cogeneration process is compared with a system that works under a compressor refrigeration cycle and a single-stage waste heat recovery system (as a reference process). According to the results, the considered process can provide approximately 10% higher exergy efficiency compared to the reference process. Moreover, the overall cost of the considered process can be about 20% lower compared to the reference process. The amount of emitted CO2 from the proposed process can be mitigated by nearly 11 thousand tons compared to the reference process.

Performance analysis and exergy assessment of an inertance pulse tube cryocooler

The world is facing the problems of the energy crisis. Thermal analysis and energy conservation of the engineering devices help to improve their performance. This paper conducted an experimental investigation for the performance analysis and exergy assessment of an Inertance Pulse Tube Cryocooler (IPTC) that uses working fluid -helium operated between 80 K cold end side temperature and room temperature.The variation of the different performance parameters like the effect of charge pressure, pulse tube volume, pulse tube length, etc., and its effect on the refrigerating effect isdescribed graphically. Exergy analysis involves the use and concepts of energy andexergy balances, enthalpy, entropy, and exergy calculations at various stages in thesystem. Exergy analysis identifies the zones of key exergy destruction that occurs insidethe system, which afterward can be subjected to its minimization to amend the systemperformance. The actual exergy efficiency value calculated for the overall system is 21.30 %. The decreasing order of exergy efficiency among the different components is acompressor (38.79 %), a hot end heat exchanger (6.19 %), regenerator, pulse tube andinertance tube (6 %), and cold end heat exchanger (2.70 %).

Performance Analysis and Identification of an Indirect Photovoltaic Thermal Dryer with Aluminum Oxide Nano-Embedded Thermal Energy Storage Modification

In the current paper, different thermal energy storage unit-integrated photovoltaic thermal (PVT) air collectors with and without nanoparticles have been designed, fabricated and tested. Aluminum oxide nanoparticles have been integrated into the thermal storage unit to increase the performance of the PVT collector. The developed collectors have been tested in a drying application at two different mass flow rates. The major goals of this work are upgrading the performance of the PVT air collector by employing a nano-embedded thermal energy storage unit and analyzing the impacts of using nanoparticles in the latent heat storage unit in the PVT collector on the drying performance of the system. The drying time was reduced by approximately 15–22% by employing nanoparticles in the thermal storage unit. Moreover, overall exergy efficiency values were obtained in ranges of 12.49–14.67% and 13.64–16.06%, respectively, for modified and unmodified PVT air collectors. It should be indicated that the overall energy and exergy efficiencies of the PVT air collectors were improved in the ranges of 6.91–6.97% and 9.20–9.47%, respectively, by using nanoparticles in the thermal energy storage unit. The combination of increasing the flow rate and integrating nanoparticles into the storage unit improved the overall exergetic efficiency of the PVT air collector by 28.58%. The mean exergetic efficiency of the drying room was between 48.33 and 54.26%. In addition to the experimental analysis, dynamic models for thermal and exergy efficiencies of developed collectors were constructed by employing the system identification method.

Concentrated solar powered agricultural products dryer: Energy, exergoeconomic and exergo-environmental analyses

Only energy-efficient and sustainable drying processes can ensure a long-term and safe storage of agricultural products. Therefore, in this study, a multi-conical solar concentrating system is proposed for drying of various agricultural products. This paper focuses on multiple aspects of performance including energy, exergo-economic and exergo-environmental performance analyses. Copper oxide/water nanofluid was used as a heat transfer medium and the drying characteristics of green pumpkin and carrot slices were studied as samples application. It was found that the proposed multi-conical solar dryer showed a significant improvement in the thermal performance, and the drying time which takes to reach the set drying temperature was reduced by 40% related to the conventional solar dryers. In addition, the inside temperature of the dryer was well maintained at the set temperature for 10 h. Using multi-conical solar dryer, the average values of exergy efficiency and exergy loss were found to be 38.08% and 0.61 kW, respectively. In context of economic and environmental analyses, the energy payback time and CO2 mitigation for the expected lifetime of CuO nanofluid based solar dryer were 4.38 years and 13.41 tons, respectively, and with water as a heating medium these values were found to be 7.65 years and 10.39 tons, respectively. The performed assessments revealed that the nanofluid powered multi-conical solar drying system is highly efficient for drying of agricultural products at an industrial scale.

Techno-economic analysis and optimization of a proposed solar-wind-driven multigeneration system; case study of Iran

This paper performs a thermo-economic assessment of a multi-generation system based on solar and wind renewable energy sources. This system works to generate power, freshwater, and hydrogen, which consists of the following parts: the solar collectors, Steam Rankine subsystem, Organic Rankine subsystem, desalination part, and hydrogen production and compression unit. Initially, the effects of variables including reference temperature, solar radiation intensity, wind speed, and solar cycle mass flow rate, which depend on weather conditions and affect the performance of the integrated system, were investigated. The thermodynamic analysis results showed that the overall study's exergy efficiency, the rate of hydrogen and freshwater production, and total cost rate are 33.3%, 7.92 kg/h, 1.6398 kg/s, and 61.28 $/h, respectively. Also, the net power generation rate in the Steam and Organic Rankine subsystems and wind turbines are 315 kW, 326.52 kW, and 226 kW, respectively. The main goal of this study is to minimize the total cost rate of the system and maximize the exergy efficiency and hydrogen and freshwater production rate of the total system. The results of optimization showed that the exergy efficiency value improved by 20.7%, the hydrogen production rate increased by 1%, and the total cost rate value declined by 2%. Moreover, the optimum point is similar to a region in Hormozgan province, Iran. So, this region is proposed for building the power plant.

Environmental/Economic assessment and multi-aspect optimization of a poly-generation system based on waste heat recovery of PEM fuel cells

In the present study, a novel poly-generation system is introduced and studied from energy, exergy, economic and exergy-economic standpoints. In the proposed configuration, the waste heat of proton exchange membrane (PEM) fuel cells is recuperated by an organic Rankine cycle (ORC). Also, an LNG subsystem is chosen as a heat sink medium for the ORC. In this study, the impact of system irreversibilities on the environment is considered as part of the exergoenvironmental analysis, which is a relatively new type of study. In the considered system, PEM fuel cells are responsible for output power while the output power of the ORC and LNG subsystem is transmitted to a trans-critical CO2 compression refrigeration subsystem and a reverse osmosis desalination unit for cooling and freshwater production. A sensitivity analysis is done to assess the effect of changes in PEM fuel cells temperature, PEM fuel cells pressure, current density, and condensation temperature of ORC on the output parameters. Considering the just-mentioned parameters as design variables, the results of two-objective optimization reveals that the exergy efficiency and net present value are calculated to be 22.67 % and 56.61 M$, correspondingly. At the optimum point, the proposed system can produce 1214 kW power, 1116 kW cooling, 161.1 kW heating, and 6 kg/s freshwater. Also, exergoenvironmental index and sustainability index were obtained as 0.5472 and 2.256 at the optimum point.

4E investigation of solar-driven RO and RRO osmotic desalination systems from water, energy, and environment relevance perspective: a comparative approach

In this paper, two osmotic desalination systems, namely, plug reverse osmosis (RO) and recirculation reverse osmosis (RRO) systems integrated with solar and organic Rankine cycle (ORC), have been presented. These systems are modeled and optimized from energy, exergy, economic, and environmental perspectives. The objective functions are the concentration disposal index (CDI) and unit cost of the product (fresh water) (UPC). The results show that the RO cycle has an optimal configuration grounded on max (CDI) and min (UPC). At identical UPC, the environmental effects of the RO system were less than those of the RRO. This is attributed to higher recovery with increasing temperature of discharged water into the sea in a smaller area and at a higher rate. For the RO system, the values for CDI, exergy efficiency, and fresh water production are 0.193, 45.6%, and 13.1 m3/h for R245ca fluid. Also, the share of RO and RRO in the total TAC costs is 19.44% and 17.33%, respectively. The R245ca working fluid is selected for both cycles, which is more productive than the other fluids. The results show that more than 50% recovery is achieved for the SW30HR-320 membrane at the optimum for the RO system.

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.

Drying kinetics and energy-exergy analysis of an experimental heat pump dryer utilized horseshoe heat recovery heat pipes for drying different grapes

In this study, nine different seeded and seedless grape cultivars (Vitis spp) were dried in a closed circuit heat pump-drying (HPD) system. The system’s drying performance was determined for each grape cultivar, and exergy analysis was performed. The evaporator efficiency increases when the external condenser is in the “on” position. This revealed that when the system reached the desired drying temperature, the longer the external condenser stayed in the “on” position, the more moisture can be drawn from the product. The heat pump highest coefficient of performance total (COPtotal,hp) and system coefficient of performance total (COPtotal,sys) were found to be 3.714 and 3.035, respectively, in the external condenser “on” position. The highest exergy efficiency values of compressor, condenser, TXV, evaporator and drying cabined were found to be 68 %, 75.41 %, 92.43 %, 77.35 % and 78.28 % respectively, when the external condenser “on” position. The highest exergy efficiencies were determined 75.75 %, 69.81 %, 87.5 %, 86.65 % and 80.46 % respectively, when the external condenser “off” position. The experiments of were evaluated in order to study the drying characteristics in HPD system. The changes in moisture ratio during the drying process were compared by six thin-layer drying models and then assessed in terms of various statistical criteria like root-mean-square-error (RMSE), diminished chi-square (χ2), and determination constant(R2). Fick’s second law of diffusion was used to obtained diffusivity of effective-moisture values, and they were found to range between 4.715 × 10–11 and 1.280 × 10-10 m2/s.