Working Pair Research Articles

Overall evaluation of single- and multi-halide composites for multi-mode thermal-energy storage

Sorption thermal-energy storage plays a critical role in addressing the mismatch between thermal-energy consumption and supply. However, the previous evaluations of sorption thermal-energy storage materials and cycles were mainly based on the equilibrium results of energy storage density. In this study, we develop evaluation models to provide an optimal working pair selection reference for single-stage sorption/resorption cycles under short- and long-term storage modes, and compare the thermal-energy storage density in the discharging stage, the effective discharging time, the temperature gradient, the exergy output during the discharge phase (ΔEdis), and the exergetic coefficient of performance (ECOP). By considering ΔEdis as a criterion, the best halides are determined to be NH4Cl and CaCl2 for single-stage sorption cycles at heat-source temperatures of 60–80 °C and 90–180 °C, respectively; however multi-halide can be a better choice when the temperature varies over optimal temperature range of single-halide, i.e., from 80 °C to 160 °C. Resorption is also analysed in this study. The results show that multi-halide is not suitable for resorption cycles because a part of the components will fail to sorb during the discharging stage. The effective reaction-temperature ranges of the resorption cycles are wider than those of the corresponding sorption cycles, whereas the performance values decrease mainly because of the larger required sorbent mass.

A centrally heated, air-coupled adsorption cooling system driven by waste heat

• Centrally heated, externally cooled adsorbent bed design presented. • Small-scale adsorption chiller with cooling duty < 100 W demonstrated. • COP of up to 0.1 and SCC of 4-80 W kg -1 predicted and experimentally demonstrated. A novel centrally heated, externally cooled (CHEC) adsorbent bed is conceptualized, modeled, and tested at a lab scale. It eliminates the need for cooling liquid lines and controls to the adsorbent bed, reducing system complexity and allowing the system to be used over a large range of thermal inputs. The reduction in complexity is achieved by using the external surface of the bed to directly transfer heat to the surrounding air. Such a system is ideal for small-scale waste heat utilization where a chiller tower cost or space prohibitive. The activated-carbon/ammonia working pair is chosen and system performance modeled over a range of waste heat temperatures. Coefficients of performance (COP) of up to 0.1 and Specific Cooling Capacities (SCC) of 4-80 W kg -1 are predicted and demonstrated experimentally for small-scale systems delivering 100 watts of cooling or less. Performance is expected to improve dramatically at larger system scales due to the larger bed-to-auxiliary thermal mass ratios. This concept trades system efficiency for reduced system complexity. It should also improve system reliability and reduce system cost by eliminating valves and pumps required for the cooling system.

Thermodynamic properties assessment of working mixtures {water + alkylphosphonate based ionic liquids} as innovative alternatives working pairs for absorption heat transformers

Based on a continuously developing portfolio of ionic liquids, the aim of this work is to evaluate the performance of new working pairs composed of {water + alkylphosphonate based IL} as alternative working pairs for absorption heat transformers. Therefore, thorough thermodynamic measurements were conducted for three alkyl phosphonate based ionic liquids and their aqueous binary systems. Experimental measurements of vapour-liquid equilibrium, heat capacity, density and excess enthalpy were measured and successfully represented using NRTL model and adequate equations. Thermal performances of single stage absorption heat transformer were numerically simulated. The influence of the temperature sources and sinks was studied. The best coefficient of performance was obtained with mixtures of water and 1-ethyl-3-methylimidazolium methylphosphonate. The typical coefficient of performance values for this mixture is found to be between 0.40 and 0.45 depending on the temperature conditions. This value is 10% lower than that observed with the classically used {water + lithium bromide} mixture. Nevertheless, {water + ionic liquid} mixture has a wider operating temperature range than conventional working pairs. The higher circulation ratio observed with the proposed mixtures may increase pumping cost.

The effect of lithium bromide on the performance of ammonia-water absorption-resorption heat pump system

Ammonia absorption-resorption heat pump (ARHP) has lower operating pressure than the absorption heat pump, and it can also make full use of low-grade heat in the heating process. But the low coefficient of performance (COP) limits the applications of ammonia ARHP. Lithium bromide, as the third working medium, is added to the traditional ammonia-water working pair to improve the performance of the system. In this paper, COPs of NH3-H2O-LiBr ternary working fluid ARHP systems under different operating temperatures are studied by a simulation model established in Aspen Plus. The operating temperature parameters ranges of the ternary ARHP are compared with those of the binary ARHP. The simulation results indicate that the COP of the ternary system is greatly influenced by the concentration of lithium bromide, and it improves up to 21% at TGen = 100 °C, TDes = 5 °C, TAbs = TRes = 40 °C, and PH/PL = 1.5/0.48 MPa. Besides, when lithium bromide is added to the binary ARHP, the minimum values of TGen and TDes are reduced to 87 °C and 3 °C, respectively. In contrast, the maximum values of TAbs and TRes are increased to 47.5 °C compared with the binary system. The NH3-H2O-LiBr ternary working fluid makes the low-grade heat reused by the ARHP more efficiently.

Thermodynamic and kinetic investigations of the SrBr2 hydration and dehydration reactions for thermochemical energy storage and heat transformation

The potential of thermochemical energy storage and heat transformation has been soundly highlighted in literature. For applications in the temperature range from approximately 150 °C to 300 °C, the inorganic salt strontium bromide, which reacts with water vapor in an exothermic reaction, is a promising candidate:SrBr2 (s) + H2O (g) ⇌ SrBr2·H2O (s) + ΔRH.This chemical reaction offers a specific energy density of 291 kJ/kgSrBr2 (or 81kWh/t). The feasibility of a thermochemical energy storage and heat transformer based on the SrBr2/H2O working pair has already been successfully demonstrated on a 1 kW scale in a lab-scale storage unit. Here, we report on the steam pressure-dependent reaction temperatures of the dehydration and hydration reactions as well as the reaction rate and the cycle stability of the reactive system over 100 reaction cycles using thermogravimetric analysis. For distinct operating points, e.g. running the hydration reaction at 180 °C and 69 kPa, specific thermal powers up to 4 kW/kg SrBr2 were experimentally determined. Running the dehydration reaction at 210 °C and 5 kPasteam pressure showed specific thermal powers of 2.5 kW/kg of SrBr2·H2O, thus proving the suitability of SrBr2/H2O as thermochemical working pair for high-power storage applications. Our results provide fundamental material-related data for the design of high-power reactor modules as well as for numerical studies on the potential of thermochemical energy storage and heat transformation based on SrBr2/H2O.

Comparative performance analysis of a combined cooling system with mechanical and adsorption cycles

This article aims to analyze comparatively the performance of a combined refrigeration system consists of an upper section (adsorption chiller) and a lower section (vapor compression chiller (VCC)). The arrangement of the adsorption cooling chiller (ACC) depends on two adsorption beds that use silica gel/water as a working pair. The beds are driven by heat comes from outside heat sources with low-grade temperatures ≤100 °C. Whereas in the bottom section, different types of refrigerants (R410A, R152A, R1234yf, R1270, and R32) have been utilized to be driven by the mechanical compressor. This paper focuses on the evaluation of the refrigerants in VCC and the working pair in ACC by means of coefficient of performance (COP) and energy-saving ratio (ES) in this refrigeration system. The computed results reveal that the refrigerants show the same behavior while calculating the COP of the combined system and the VCC in the combined system, with the high values reached up to 0.5 and 8.8 for R152A, respectively. Meanwhile, the energy-saving reached up to 65.3%. The increase ratio (IR) of the COP of the VCC is also calculated with the highest value reached up to 188%. The effects of the ambient air temperature, the heat source temperature, the cycle time and the evaporation temperature on the system performance and the required mass of adsorbent in the adsorption beds are investigated for the design of ACC-VCC combined system.

Carbon‐Methanol Based Adsorption Heat Pumps: Identifying Accessible Parameter Space with Carbide‐Derived Carbon Model Materials

AbstractIn adsorption heat pumps, the properties of the porous adsorbent and the refrigerant determine the performance. Major parameters for this working pair are the total uptake of the adsorptive, its kinetics, and the heat transfer characteristics. In the technical application despite powdered adsorbents, thin consolidated layers of the adsorbent can be attractive and obtained by a binder‐based approach but likely result in competing material properties. Thus, for a process optimization, the accessible parameter space and interdependencies have to be known and were deduced in this work for model porous carbons (carbide‐derived carbons derived from TiC and ZrC) and methanol as well as the addition of different amounts of boron nitride, silver, and graphite as heat‐conductive agents and the use of two binders.

Efficiency of the Lamm–Honigmann thermochemical energy storage

The Lamm–Honigmann-process is a flexible thermo-chemical energy storage and converter that can be charged and discharged arbitrarily with both heat and electrical power. In this paper, an approximation for the theoretical round-trip efficiency is given for various process configurations. The goal is to predict the process efficiency and storage capacity in dependence of the temperatures of heat sink and source and some easily accessible working fluid properties, namely heat capacities, latent heat of evaporation of the pure working fluid, heat of ab-/adsorption or reaction enthalpy of the working fluid pair, and the boiling point elevation, respectively.The derived approximations are verified by comparing with a detailed calculation using enthalpy data of the working fluid pairs LiBr/H2O and H2O/NH3. The results show a good agreement (deviation less than 11%). The round trip efficiencies are almost independent of temperature and it can be concluded that from a thermodynamic point of view the single stage storage and conversion process should be driven with low temperature heat, e.g. industrial waste or solar thermal heat, and the pure electrical storage process should be driven near ambient temperature to reduce heat losses to the environment.The method is recommended for checking usefullness of further working pairs and is applied exemplary to the adsorption systems Zeolite/H2O and Silica gel/H2O.

THE INFLUENCE OF SITUATIONAL CHARACTERISTICS AND DISPOSITIONS ON THE WORK-FAMILIES-CULTURE CONFLICT (WFCC)

Purpose of this research to examine the role of the coping strategy variable as a moderating variable with the relationship between the WFCC (Work Family-Culture Conflict) and satisfaction to determine the magnitude of the influence of situational characteristics and the size of disposition on the WFCC. The population in this study was a pair of workers who were married and living in one house, and came from the main family who lived in urban areas. The sampling of this research was determined using the purposive sampling method. All hypotheses refer to the theory used as a guideline in examining the role of dichotomous conflicts, especially the WFC (work Family-Conflict). Thus, this research is in a position to use theories and models that are not yet strong in theory to be applied to the conflicting role of trichotomy, namely the WFCC.There are four variables that have been shown to influence the WFCC. These variables are work relationship, family time discipline, family support, and relationship in religious practice. Originality is theoretically described by the expansion model in accordance with abundance theory, ecological system theory, role stress theory, theory of social learning, social cognitive theory, gender role theory, social identity theory, and theories about family systems.

Evaluating the performance of a coated tube adsorber for adsorption cooling

Abstract Adsorption cooling (AC) is an environmentally friendly alternative to conventional vapor compression cooling. In this paper, the performance of a coated tube adsorber suitable for AC systems is numerically evaluated. The developed adsorber uses silica gel-water as adsorbent-adsorbate working pair. A numerical model is used to analyze the influence of several governing parameters such as the evaporator, condenser and regeneration temperatures, cycle time, metal-adsorbent heat transfer coefficient, metal tube diameter, coating thickness and heat transfer fluid (HTF) velocity on the adsorber's performance. It is confirmed that increasing the evaporator temperature results on a performance increase whereas increasing the condenser temperature hindrances the system's performance. A regeneration temperature close to 70 oC results on the highest cooling coefficient of performance (COPc). The cycle time can be used as a system-controlling parameter to tune the COPc and the specific cooling power (SCP). The adsorber performs better when the regeneration time is 35% shorter than the adsorption time. The maximum COPc occurs when the metal-adsorbent heat transfer coefficient reaches values of 100 W.m-2.K-1. The SCP greatly increases until this coefficient reaches 350 W.m-2.K-1. The adsorbent coating thickness severely influences the performance of an AC system. It was found that the maximum COPc corresponds to a coating thickness of 1.75 mm and, the smaller the coating thickness the smaller the SCP. The metal tube's diameter and the HTF's velocity mainly influence the SCP since they have direct impact on the heat transfer rate exchanged between the HTF and the adsorbent material.

A novel method and operation strategy for the improved performance of an absorption heat transformer

Recently, waste heat recovery in industry applications of absorption heat transformers has developed rapidly. Due to the instability of the heat source and constantly changing heat load, it is difficult to adjust and control an absorption heat transformer to meet the needs of heat supply and heat consumption. Thus, the dynamic performance caused by thermal inertia and solution concentration inertia becomes increasingly important. A dynamic model of a vertical falling-film absorption heat transformer using LiBr/H2O as the working pair is established in this paper and validated by experimental data. The simulation results show that there is a contradiction at different stages of equipment operation. Less solution reserved in the system is more advantageous during start-up and load changing, but reserving less solution is opposite under internal and external fluctuations. Thus, a system improvement method and operational strategy are proposed to resolve this contradiction. The improved system has a faster temperature stabilization speed and higher total Coefficient of performance (COP) under start-up, load changing, and operating condition fluctuations. The stabilization time for start-up and load changing processes can be reduced by 43.8%, and a 20 kW absorption heat transformer can save about 212.2 kJ for each load changing operation.

Organizational and educational peculiarities of teaching speech adaptation to future English language teachers

The article reveals organizational and educational peculiarities of effective developing of future English language teachers’ speech adaptation skills in English Practice classes aimed at the third-year students of foreign languages departments. The suggested subsystem of professionally oriented activities and the model of the teaching process for developing speech adaptation skills have been described. The main conditions for successful implementation of the methodology of teaching speech adaptation have been specified. The organizational forms of teaching and the sequence of teaching stages within one unit of activities have been defined. The introductory stage is connected with developing the system of declarative knowledge about speech adaptation. Basic diagrams, tables and receptive-analytical activities are offered to systemize the educational information. The stage of pedagogical interaction practice includes two sub-stages: 1) doing communicative professionally oriented activities after work with each of three subgroups of activities within one unit of activities; 2) students’ taking part in microteaching. During the stage of reflection the observation tables are filled in, then students take part in written self-assessment and reflective discussion. The peculiarities of using individual, pair, group and front modes of classroom work have been analyzed. The ways of monitoring the learning process, assessment criteria and controlling methods of speech adaptation skills development level have been clarified. The quantity and distribution of academic hours for classroom and self-study work have been suggested.

Molecular dynamics simulation of diffusion and interaction of [bmim][Tf2N] + HFO-1234yf mixture

Understanding of the interaction and thermophysical properties of HFO and ionic liquid mixture at the micro level is helpful for the molecular design of the new working pair of HFO + ionic liquid for absorption refrigeration. In this work, the densities, viscosities, thermal conductivities and diffusion coefficients of HFO-1234yf and [bmim][Tf2N] are firstly calculated using molecular dynamics simulation method and compared to the results in literature in order to verify the reliability of our method. Then, the density, energy, diffusion coefficient and radial distribution function of the liquid mixture of HFO-1234yf and [bmim][Tf2N] are calculated and analyzed. The dissolution of HFO-1234yf in ionic liquid is found to increase the diffusion coefficients of [bmim] and [Tf2N]. [bmim] and [Tf2N] both play important role in the absorption of HFO-1234yf.

The study on the influence of glycols on the vapor pressure, density and dynamic viscosity of lithium bromide aqueous solution

This paper is a continuation of our comprehensive research on finding the most effective additive to the conventional {lithium bromide + water} system, which is commonly used in absorption refrigeration technology. Serious disadvantages of commercially used working pairs in absorption refrigeration make it necessary to modify them. Such modification can be carried out by finding and characterizing new additives to conventional systems that will improve the operation of the refrigerator, which this work relates to. The addition of a chemical compound to such a system is one of the possibilities to improve the properties of the working pair, increase the efficiency of the absorption refrigerator and eliminate their main disadvantages. The main disadvantage of {lithium bromide + water} system is the crystallization of this salt. In recent years, many compounds have been proposed as additives to this conventional system to improve the functioning of the absorption aggregate. Based on the results obtained in our previous research, we selected substances that most effectively affected the solubility of lithium bromide in water. In this work, tests on ethylene glycol, diethylene glycol, triethylene glycol, and glycerol (additive to LiBr mass fraction w2 = 0.3) which were added to the binary {LiBr (Boryta, 1970) [1] + water (Iyoki et al., 1990) [2]} system were performed. Measurements of vapor pressure, dynamic viscosity and liquid density were carried out over a wide range of temperatures and composition. Experimental VLE data were predicted using the conductor-like screening for real solvents model, COSMO-RS. Empirical equations were used to correlate dynamic viscosity and density data. Based on the comparison of results obtained in the case of ternary systems to the properties of a conventional binary system, the effect of the additive on physicochemical properties was characterized and the possibility of potential application of such new ternary systems in absorption refrigeration technology was determined.

Utilization of ultra-low temperature heat by a novel cascade refrigeration system with environmentally-friendly refrigerants

From solar, geothermal and waste energy, ultra-low-grade heat of 45–60 °C is large in scale, and is still interesting challenges in converting into useful refrigeration of 7 °C. In this study, a novel cascade refrigeration system was developed to utilize 45–60 °C heat. It is composed of a novel two-stage vapor absorption refrigeration (VAR) subsystem with LiBr/H2O working pairs and a conventional vapor compression refrigeration (VCR) subsystem. The VCR subsystem employs potential R1234yf and R1234ze(E) refrigerants. The novel VAR subsystem operates by utilizing ultra-low-grade heat of renewable energy and recycling condensing heat of the VCR subsystem. Based on thermodynamic models of the novel system, its operating mechanism was theoretically investigated and discussed. The results indicate that the novel cascade system can effectively refrigerate by utilizing 45–60 °C ultra-low-grade heat. Its operation is mainly determined by the novel VAR subsystem. There are optimal Tm and Tg1 to maximize its performance. Tg2 has a greater impact on the optimal Tm and little effects on the optimal Tg1. Furthermore, it implies that an available temperature span could be obviously enlarged from 90 °C down to 45 °C. And, progress of utilizing ultra-low-grade heat of renewable energy could be promoted, beneficially.

Adsorption characteristics and cooling/heating performance of COF-5

Adsorption-driven heat pumps (AHPs) powered by low-grade waste heat and solar energy are promising to reduce the energy consumption for cooling and heating. Seeking novel high-performing adsorbents of AHPs is the key to improve their cooling/heating performance. Very recently, the potential use of covalent-organic frameworks (COFs) adsorbents of AHPs has won increasing research interests. However, the adsorption cooling/heating performance of COFs under varying working conditions is still unexplored. In this study, COF-5 was synthesized and tested to obtain the adsorption isotherms of ethanol working fluid. For comparison, three commonly used metal-organic frameworks (MOFs), including Cu-BTC, MIL-101(Cr), and ZIF-8, were also investigated. The cooling/heating performance of COF-5/ethanol and MOF/ethanol working pairs was evaluated by mathematical modelling based on the basic thermodynamic cycle of AHPs. The results demonstrated that COF-5 with the high coefficient of performance for cooling/heating (COPC/COPH) under wide temperature lift (ΔTlift) outperformed MOFs, especially for cooling.

Design of surface profile of pairs of friction unit

To control the processes of friction and wear in the working pairs of the friction unit, it is necessary to study the behavior of the materials of the friction unit during contact interaction, accompanied by the combined action of temperature and dynamic loads. Numerous studies are devoted to the study of the influence of the chemical composition on the friction process of friction units, as well as the creation of new materials for brake units. There are practically no works devoted to the influence of nanogeometry of the surfaces of contact pairs of friction units on contact pressure. In this case, from an uneven distribution of contact pressure over the friction surface, strong heating can occur, which results in the formation of burns, thermal spots and foci of microcracks.

Performance Analysis of a Cascading Adsorption Cycle Powered by High-Temperature Heat Sources for Low-Temperature Cooling in Hot Climates

Abstract Cascade adsorption refrigeration technology using high-temperature driving heat is a very promising option for low-temperature cooling applications due to the large temperature difference between the heat source and the cold distributed. The present work carried out a feasibility and parametric study in order to analyze the functioning of a cascading adsorption cycle using the working pair zeolite/ammonia in beds operating at high temperatures and activated carbon/ammonia in those operating at low temperatures. At the nominal thermal conditions, namely, heating, condensing, and evaporating temperatures of 280 °C, 35 °C, and (−5) °C, respectively, the coefficient of performance (COP) and the specific refrigerating capacity (SCP) of the cycle were 0.53 and 67.1 W/kg. When the driving temperature is varied from 260 °C to 320 °C, the COP increases by 57% and the SCP by 36%. The performance of the cascading adsorption cycle at negative evaporating temperatures is very satisfactory.

Wide applicability of analogical models coupled with hysteresis effect for halide/ammonia working pairs

As the effective way for utilizing low-grade thermal energy, chemisorption technologies have been widely researched by establishing various phenomenological models and analogical models. But the existing kinetic models have the disadvantages of complexity or narrow adaptability, and they also cannot adapt to the serious hysteresis phenomena found in recent years. In order to obtain wide-adaptable kinetic models of halide/ammonia for material level, in this paper the sorption and desorption kinetics which consider hysteresis effects of halide/ammonia with MnCl2/NH3 and CaCl2/NH3 as representative working pairs are studied. Results show that the fitting parameters of the three-parameter models are unstable, while the two-parameter linear model is a relatively reliable candidate model with the recommended reaction rates (ks/kd) and reaction orders (m) varying widely for different halides (MnCl2 and CaCl2), different reaction stages (Ca4-8 and Ca2-4) and different reaction directions (sorption and desorption). The validation of model presents that the established linear model considering hysteresis effect could adapt to different halide/ammonia working pairs and predict the kinetic property. Furthermore, the model adaptability to large scale occasions is researched through the experiments with 200 g composited sorbent in a sorption reactor, which indicate that the established kinetic models and parameters can simulate the total reaction time accurately with the deviation of 10.4% and 3.9% under 0 °C and 10 °C evaporating temperature, respectively.

Parametric Investigation of a Trigeneration System with an Organic Rankine Cycle and Absorption Heat Pump Driven by Parabolic Trough Collectors for the Building Sector

This article presents a simulation study which focuses on the thermodynamic analysis of a solar-driven trigeneration system for heating, cooling, and electricity production. The system uses parabolic trough collectors operating with Therminol VP-1 for feeding an organic Rankine cycle operating with toluene and an absorption heat pump operating with a LiBr–H2O working pair. The collecting area is selected at 100 m2 and the storage tank at 4 m3. The system is studied parametrically in order to examine the impact of various parameters on the system energy efficiency, system exergy efficiency, electricity production, heating production, and cooling production in the simple payback period of the investment. The examined parameters are the following: solar beam irradiation level, solar beam irradiation angle, superheating degree in the turbine inlet, pressure level in the turbine inlet, heat source temperature level, generator temperature level, and the heat input in the generator. For the nominal case of a 15 kW generator input, the electricity production is 6.3 kW, the heating production 11.5 kW, and the cooling production 10.7 kW. The system energy efficiency is 40.7%, while the system exergy efficiency is 12.7%. The financial investigation of the investment proved that it is viable with the simple payback period to be 8.1 years in the nominal case and it can be reduced to 7.8 years with an optimization procedure. Lastly, it has to be said that the examined system is found to be a viable configuration which is an ideal choice for application in the building sector. The analysis was conducted under steady-state conditions with a model developed using Engineering Equation Solver (EES).