Working Pair Research Articles

Sorption based long-term thermal energy storage with strontium chloride/ammonia

Thermal energy storage takes a pivotal role in the renewable energy application and waste heat recovery through adjusting the instability and discrepancy between energy supply and demand. For the purpose of the long-duration storage application based on thermochemical sorption, SrCl2 composite materials were prepared and a demonstrative prototype has been constructed. The long-duration storage capacity of thermochemical sorption heat storage was investigated with SrCl2/NH3 as the working pair. The experimental results show that the maximum heat storage density of SrCl2/NH3 thermochemical sorption heat storage system is about 1630.8 kJ kg−1 SrCl2 (or 1386.2 kJ kg−1 composite sorbent) under the operation condition of the charging temperature of 92 °C, the condensation/evaporation temperature of −5 °C and the discharging temperature of 40 °C. The heat storage efficiency of thermochemical sorption system decreases when the discharging temperature increases, whilst the coefficient of performance is raised with the increasing discharging temperature. Under the experimental conditions, the highest values of sorption heat storage efficiency and coefficient of performance are 0.687 and 0.405, respectively. Experimental results reveal that the thermochemical sorption heat storage is an effective method for the long-duration heat storage applications. It can facilitate the large-scale solar thermal energy harvesting and the industrial waste heat recovery.

Metal-Organic Frameworks for Ammonia-Based Thermal Energy Storage.

Recently, the application of metal-organic frameworks (MOFs) in thermal energy storage has attracted increasing research interests. MOF-ammonia working pairs have been proposed for controlling/sensing the air quality, while no work has yet been reported on the immense potential of MOFs for thermal energy storage up till now. Herein, the feasibility of thermal energy storage using seven MOF-ammonia working pairs is experimentally assessed. From ammonia sorption stability and sorption thermodynamics results, it is found that MIL-101(Cr) exhibits both high ammonia sorption stability and the largest sorption capacity of ≈0.76 g g-1 . Compared with MIL-101(Cr)-water working pair, MIL-101(Cr)-ammonia working pair improves the sorption capacity by over three times with evaporation temperature lower than 8.4 °C. Due to stable ammonia sorption stability and negligible hysteresis, MIL-101(Cr) and ZIF-8(Zn) are tested at condensation/evaporation temperature of 30 °C/10 °C. The thermal energy storage density (reaching over 1200 kJ kg-1 ) and coefficient of performance of MIL-101(Cr)-based system are both higher than ZIF-8(Zn)-based one due to larger average isosteric enthalpy and cycle sorption capacity. This experimental work paves the way for developing the high efficient and stable thermal energy storage system with MOF-ammonia working pairs especially for critical conditions with low evaporation temperature and high condensation temperature.

Alkali Metal Nitrates Promoted MgO Composites with High CO2 Uptake for Thermochemical Energy Storage

Thermochemical energy storage (TCES) by means of reversible chemical reactions represents a promising strategy for harnessing renewable energy and recovering industrial waste heat. In this work, alkali metal nitrate promoted MgO composites were synthesized, and the MgO–CO2 working pair was suggested as an alternative candidate for harvesting intermediate-temperature industrial waste heat. However, it remains unclear how operating parameters would affect the heat storage density, and the long-term cycling stability of the alkali metal nitrate promoted MgO composites under harsh conditions close to practical application scenarios needs to be clarified. The objectives of this work are to expound the effects of operating parameters on TCES performance and to evaluate the long-term cycling stability of the alkali metal nitrate promoted MgO composites. With increasing NaNO3 content, the heat storage density of NaNO3–MgO increases dramatically first and then exhibits no significant change. With rising carbonation temperature, the heat storage density of the 10NaNO3–MgO composite increases first and then declines marginally, while it increases with the increasing CO2 partial pressure. Doping alkali metal nitrate eutectic mixtures adversely affects the heat storage density. 10NaNO3–MgO exhibits a high heat storage density of 2291 kJ/kg at 340 °C in 100% CO2. The 10NaNO3–MgO and 10(K–Na)NO3–MgO composites suffer a significant decline in heat storage density within 10 consecutive cycles, while 10(Li–Na)NO3–MgO retains good stability with a slight decrease of heat storage density from 1073 to 770 kJ/kg in 50% CO2. The desired 10(Li–Na)NO3–MgO is suggested as a promising material for TCES application.

Thermodynamic analysis of thermochemical energy storage system based on AB5 type hydride pairs

The present study deals with the performance analysis of thermochemical energy storage system based on four different working pairs, namely LaNi4.85Sn0.15-MmNi4.6Al0.4, LaNi4.75Sn0.25-MmNi4.6Al0.4, LaNi4.65Sn0.35-MmNi4.6Al0.4 and LaNi4.55Sn0.45-MmNi4.6Al0.4. The first law and second law performance parameters are considered to evaluate the performance of the energy storage system. The temperature of heat storage and heat recovery for the four different working pairs are in the range of 93–140 °C and 105–165 °C respectively. Recovering the heat at higher temperature than that of storage is called heat upgradation. Highest degree of heat upgradation is 24 °C, and it is obtained for the working pair of LaNi4.55Sn0.45-MmNi4.6Al0.4. The theoretical highest energy storage density and COP are 129 kJ/kg and 0.54 respectively for the working pair of LaNi4.65Sn0.35-MmNi4.6Al0.4. From the second analysis, the lowest exergy loss and highest second law efficiency are 2.57 kJ and 96.4% respectively for the working pair of LaNi4.75Sn0.25-MmNi4.6Al0.4. Based on the first law analysis, the working pair, LaNi4.65Sn0.35-MmNi4.6Al0.4, is taken as best pair and based on the second law analysis, the working pair, LaNi4.75Sn0.25-MmNi4.6Al0.4, is taken as best pair. However, suitable working pair need to be selected based on the type of application.

Performance Analysis of an Adsorption Refrigeration System Working on Activated Carbon/Methanol Pair Using Finned Tube Type Adsorber Bed

Adsorption refrigeration, being a unique and eco-friendly technology, has gained popularity over conventional refrigeration systems. The present study is aimed at developing an annular finned tube adsorber model which serves as a thermal compressor in adsorption refrigeration systems. The mathematical model is addressed numerically using finite difference discretization method and explicit scheme was used for the solution. The generalized model has been simulated for activated carbon–methanol working pair. The system has an optimum cycle time of 1800s. It was found to have a highest refrigeration capacity of 260.66 kJ/kg at a regeneration temperature of 393 K and evaporator temperature of 283 K. The highest COP (Coefficient of Performance) achieved by the system is 0.3706 at a regeneration temperature of 353 K and evaporator temperature of 283 K. A highest SCP (Specific Cooling Power) of 144.8 W/kg was obtained at an evaporator temperature of 283 K and regeneration temperature of 393 K.

Performance analysis on a hybrid compression-assisted sorption thermal battery for seasonal heat storage in severe cold region

Sorption thermal battery has revealed vast potential of heat utilization to address the issue of long-term energy storage. A hybrid compression-assisted sorption thermal battery is presented for solar energy utilization, which aims to solve the mismatch of heat storage and supply in cold region. Thermodynamic performance of the hybrid sorption thermal battery in cold region is analyzed by using MnCl2–SrCl2 and MnCl2–CaCl2 working pairs and then compared with that of basic sorption type with internal heat recovery. It is demonstrated that when ambient temperature in winter ranges from −30 °C to -5 °C, energy and exergy efficiencies of hybrid thermal battery using different working pairs increase from 0.74 to 0.865 and 0.25 to 0.43, respectively. Energy efficiency of hybrid thermal battery is almost twice higher than that of basic type with internal heat recovery. For different operating parameters, mass ratio and global conversion rate have a larger influence on thermal performance than isentropic efficiency of compressor. Although energy storage density per salt of basic sorption thermal battery is a bit higher than that of hybrid type, the density per reactor of hybrid compression-assisted thermal battery could be improved by 50%, which indicates a good system compactness in real application.

Thermophysical properties and water sorption characteristics of 1-ethyl-3-methylimidazolium acetate ionic liquid and water binary systems

Non-corrosive ionic liquids with negligible vapor pressure are potential substitutes for traditional absorbents used in absorption refrigeration chillers. In this study, we aimed to investigate the thermophysical properties and water sorption characteristics of the 1-ethyl-3-methylimidazolium acetate ([EMIm]Ac) ionic liquid and water binary systems. Density, thermal conductivity, specific heat capacity, viscosity, and surface tension were determined at various [EMIm]Ac mass fractions in the 20–100% range, as well as at various temperatures. In addition, mathematical relationships between the measured thermophysical properties and the studied variables (temperature and mass fraction) were developed. The water sorption and desorption performance were investigated for the [EMIm]Ac aqueous solution. Modified two-step sorption mechanism and linear desorption kinetics were proposed for the absorption and desorption process, respectively. These properties are helpful for the calculation and evaluation of the performance of the absorption and desorption based on the [EMIm]Ac/water working pair.

Experimental investigation of oil retention and pressure drop of R32/PVE oil mixture in compressor suction line

R32/PVE oil mixture has become a popular working pair of commercial refrigeration/heat pump systems in recent years. This paper presented experimental study of oil retention and pressure drop characteristics of R32/PVE VG68 mixture in the compressor suction lines. The test samples were two smooth copper pipes of horizontal and vertical flow orientations with 10.7mm inner diameter. The oil retention in suction lines were measured based on remove-and-weight technique (RWT). Three conditions of saturation temperature and superheat degree (7.5/12, 7.5/6 and 10/12°C) were tested, in order to obtain different thermophysical and transport properties. Refrigerant mass flux and nominal oil mass fraction (OMFno) were varied with the ranges of 90−230 kg•m−2·s−1 and 1−5%, respectively. The influences of refrigerant mass flux, oil mass fraction, mixture viscosity and flow configuration on oil retention and pressure drop were investigated. The results showed that the oil retention amount tends to increase with the increases of actual oil mass fraction (OMFact) and mixture kinematic viscosity ratio and the decrease of refrigerant mass flux. Two consolidated databases for oil retention and pressure drop of suction lines, which involved five working pairs, were collected from the existing literatures to perform a comparison. Finally, based on analysis of oil transport mechanism, a new dimensionless parameter called oil retention impact factor was proposed to characterize the difficulty of oil transport, which integrated the influences of geometric dimension, working pairs and operation parameters. It showed relatively satisfactory relationship with the oil retention data from the amassed database and the present study.

Experimental Study on Heat Transfer and Adsorption Cooling Performance of MIL-101/Few Layer Graphene Composite

MIL-101 is a promising metal-organic frameworks (MOFs) material in adsorption chiller application due to its high adsorption capacity for water and excellent adsorption/desorption cyclic stability. Few layer graphene (FLG) as the thermal conductive additive was added into MIL-101 to improve inferior heat transfer of MIL-101 in the adsorption cooling process. The heat transfer characteristic of MIL-101/FLG adsorber and the adsorption cooling performance of the MIL-101/FLG-water working pair were studied. Results show that thermal conductivity of MIL-101/20%FLG composite is 5.79-6.54 times that of MIL-101. Adding FLG is conducive to the formation of heat transfer channels in MIL-101/FLG adsorber and the rapid removal of adsorption heat. The heating and cooling rate of MIL-101/FLG adsorber is ~2.2 times that of MIL-101 adsorber. Under typical adsorption water chiller conditions, the specific cooling power (SCP) and coefficient of performance (COP) of the MIL-101/FLG-water working pair is 72.2–81.0 W kg−1 and 0.187–0.202, respectively, at desorption temperatures of 70 °C and 90 °C, which is 1.43–1.56 times higher than the MIL-101-water working pair. The excellent structural and adsorption/desorption cyclic stability of MIL-101/FLG composite is verified after 50 consecutive cycles. It can provide a promising adsorbent candidate (MIL-101/FLG composite) in adsorption water chiller process.

The optimal step locations for high-performance adsorption heat pumps under various working conditions

Adsorption heat pumps (AHPs) driven by solar energy or waste heat outperform traditional vapor compression heat pumps, because they greatly reduce the primary energy consumption and greenhouse emissions. However, the low coefficient of performance (COP) limits the wide application of AHPs. It is known that adsorbent-based working pairs with stepwise adsorption isotherm are favorable for the COP of AHPs. Nevertheless, the optimal step locations that are the favorable steps in adsorption isotherms of working pairs for COP under adsorption heating, cooling and ice making working conditions have not been explored. In this work, the correlations between the optimal step locations, working conditions and COP was investigated by theoretical analysis and mathematic modelling based on ideal stepwise adsorption isotherms. It was found the predicted optimal step locations for adsorption heating was smaller than those for adsorption cooling and ice making. It was also revealed that the evaporation temperature was more evidently correlated with the optimal step locations as well as COP. Moreover, it is favorable for COP when the loading average enthalpy of adsorption is close to the enthalpy of vaporization of working fluids. This study may guide the choosing and designing of high-performing working pairs for AHPs under various working conditions.

An Experimental Investigation on Hybrid Nano fluid with Vegetable Oils as a Cutting Fluid using Minimum Quantity Lubrication

Hard machining plays a vital role in traditional machining for high productivity and for complex jobs. In this type of machining cutting, fluid has major factor property of cutting fluid to minimize the friction and to reduce the temperature at machining area. In the traditional approach, most of the time industries using mineral oils for lubrication or as cutting fluid in machining but a due large amount of using of mineral oils a large amount of oxidation happens which is toxic and harmful to workers. To overcome these effects experiment is done by using vegetable oil with the addition of nanoparticles which enhanced the properties of cutting fluid. The experiment is done on Mild Steel with working pair of Al2O3 and MoS2 nanoparticles in palm oil. Output is taken from this experiment in parameters like cutting forces, surface temperature, tool temperature, and surface roughness. This method gives better results than dry machining.

Thermodynamic characterization of {1-ethyl-1-methyl-pyrrolidinium dimethylphosphate, [C1C2PYR][DMP], or 1-hydroxyethyl-1-methylpyrrolidinium dimethylphosphate, [C1C2OHPYR][DMP] (1) + ethanol (2)} binary systems

In this work, {1-ethyl-1-methylpyrrolidinium dimethylphosphate, [C1C2PYR][DMP], or 1-hydroxyethyl-1-methylpyrrolidinium dimethylphosphate, [C1C2OHPYR][DMP] (1) + ethanol (2)} binary systems were studied as an alternative working pair for the absorption heat pump cycle. It is well known that the knowledge of the thermodynamic properties of the working fluid used plays a key role in the coefficients of performance values, and thus in the efficiency of the apparatus. Therefore, in this work thermodynamic and physicochemical characteristics of ethanol solutions of two dimethylphosphate-based ionic liquids are presented. The isothermal VLE was measured by an ebulliometric method within a temperature range from T = (328.15 to 348.15) K with an increment of 10 K and pressures up to 90 kPa. Experimental VLE data have been successfully correlated using the NRTL equation using temperature-dependence parameters. Additionally, experimental VLE data were tested for thermodynamic consistency using the Van Ness test. The liquid density and dynamic viscosity were determined as a function of IL's mole fraction over a wide composition range at temperature from T = (293.15 to 338.15) K with an increment of 5 K at ambient pressure. For the correlation of physicochemical properties, empirical equations were applied. From experimental density data, the excess molar volumes were determined and correlated using the Redlich – Kister type equation. Additionally, thermophysical properties of pure ILs including glass transition temperature, heat capacity at glass transition, temperature and enthalpy of (solid + solid) phase transition as well as temperature and enthalpy of melting were determined using differential scanning calorimetry (DSC) technique. Data presented in this work, compared to the available literature data for ethanolic solutions of other dimethylphosphate-based ILs, allows discussing the impact of the IL's cation structure on the presented physicochemical and thermodynamic properties. In addition, the data presented in this work were compared to data for a water solution of lithium bromide, commercially used in absorption refrigeration technology.

Characteristics of CO2-ionic liquids/PEG200 as new working pairs for absorption-compression refrigeration system

Absorption-compression refrigeration system using CO2-Ionic Liquids (ILs) as working pairs could avoid the high operating pressure in transcritical CO2 refrigeration cycle. This work proposed using PEG200 as the additive to improve the physical properties of the pure ILs, making the absorption-compression refrigeration system being more efficient and less corroded. The effects of PEG200 on the CO2-ILs absorption and desorption, the viscosity and the corrosion behavior on stainless steel were investigated experimentally. Results show that PEG200 has positive effect on these key parameters at temperature of 293.15 K to 343.15 K and pressures up to 10.0 MPa. The addition of PEG200 to [emim][FAP] could increase the CO2 solubility by 10.17% maximally, reduce the viscosity by 24.43% maximally, and accelerate the desorption rate. The CO2 solubility increases with the pressure increasing, and decreases with the temperature increasing. The viscosity of the mixed solvent decrease with the increase of the temperature and pressure. The addition of PEG200 to [emim][Tf2N] effectively weakens the corrosion on the 316L stainless steel, the corrosivity of ILs/PEG200 is less than that of the pure ILs. This work shows ILs with PEG200 added have better physical properties as the CO2 absorbent, providing a new approach of selection for CO2 absorption.

Facing the Storm: Our First Annual Faculty of Color Writing Retreat as a Microcosm for Being a Black Woman in the Academy

In this article, four Black woman scholars explore their experiences in academia through the shared event of a writing retreat. This piece follows the rich storytelling history of Black women scholars who have carved out spaces where they can tell their truths. This work pairs narrative inquiry and autoethnography to address the question: How do Black women faculty create and navigate spaces to promote their success within academia?

Non-isothermal pore change model predicting CO2 adsorption onto consolidated activated carbon

Accurate simulation and detailed description of the dynamics of the adsorption process play a significant role in forecasting the performance of new materials when used in various adsorption systems, like cooling/heating. The activated carbon (AC) consolidation allows improving the heat transfer rate inside the adsorption/desorption bed and compacting the systems. There are numerous mathematical models in literature for gas adsorption onto granular AC. But for consolidated AC, because of the absence of macropores, most assumptions that work well for granular AC may lead to significant discrepancies. Therefore, the present research proposes a new mathematical model for gas (CO2) adsorption onto consolidated adsorbent, a non-isothermal pore change model. The model takes into account the porosity and permeability changes due to the adsorption. The validation of the developed model is performed via comparison with the results obtained experimentally and numerically using an isothermal model. The effective Knudsen diffusion coefficient for the working pair is evaluated from porosity data. The rate of adsorption or mass transfer coefficient is estimated using the van't Hoff plot. The study results could be applied in the development of waste heat-driven cooling systems employing consolidated composite material as the adsorbent. The proposed mathematical model is also applicable for many other working pairs.

Introduction: On Learning, Freedom, and Democracy

Introduction: On Learning, Freedom, and Democracy

Thermodynamic Analysis of a Combined Single Effect Vapour Absorption System and tc-CO2 Compression Refrigeration System

Transcritical CO2 refrigeration system is coupled with the single effect vapour absorption with LiBr-water as a working pair having an objective to enhance the performance of low temperature transcritical refrigeration system while using natural working pair and to reduce the electricity consumption to produce low temperature refrigeration. The high grade waste heat rejected in the gas cooler of tc-CO2 compression refrigeration system (TCRS) is utilized to run the single effect vapour absorption system (SEVAR) to enhance the energy efficiency of the system. The gas cooler in the transcritical CO2 system is having heat energy at high temperature and pressure, which is utilized to run the vapour absorption system, while the other refrigerant heat exchanger provides subcooling to further enhance the performance. The combined cycle can provide refrigeration temperature at different levels, to use it for different applications. Energetic and exergetic analysis have been done to analyze the combined system to compute the performance parameters and the irreversibilities occurring in different components to further increase the performance. The combined system is optimized for various heat rejection and refrigeration temperatures. The COP of the combined system has been enhanced by to 24.88% while the enhancement in exergetic efficiency (ηex) is observed as 10.14% respectively over tradition transcritical CO2 compression refrigeration system, with -10°C as an evaporation (TCRS cooling) temperature and exit temperature of gas cooler T4 being 40°C. Doi: 10.28991/HIJ-2021-02-02-02 Full Text: PDF

Reduction and equalization of thermal loading of contact pairs of the friction unit

Controlling the processes of interaction of the working pairs of the friction unit is possible when solving the problem of determining the parameters of influence. As the main criterion of the process, it is necessary to highlight the temperature on the surface of the friction unit. This paper presents a method for modeling the magnitude and distribution of temperature over the surface of a metal friction element depending on the nanogeometry of the surface profile of contact pairs of friction units. The ability to control the process of interaction of contacting pairs of the friction unit will further predict the life of the part and avoid such phenomena as burns and the formation of foci of microcracks.

Towards high-performance sorption cold energy storage and transmission with ionic liquid absorbents

The shortcomings of conventional working pairs in thermal energy storage and transmission based on absorption cycle have become major obstacles for practical application. Ionic liquids (ILs) are promising alternatives, while only few ILs have been evaluated with enumeration method, by which it is difficult to create a short-term breakthrough. In this study, a prediction framework is established via relating the fundamental thermodynamic properties (absorbing ability and excess enthalpy) with cycle performance (COP and energy density) in order to clarify the maximum potential of this technology and the desirable properties of potentially interesting working fluids. A comprehensive investigation of promising IL absorbents in thermal storage/transmission has been carried out by the framework. Then, theoretical analysis shows that an optimal region with both high COP and high energy density (between 31.00 kJ/mol to 37.00 kJ/mol) could be reached, indicating 57% of improvement in energy density is possible (the highest level at current stage is 23.52 kJ/mol). To pursue the optimal performance, strong affinity between the species and decreasing trend of excess enthalpy during generation are found to be key roles. Such a theoretical framework could be further extended to the fluids design and screening of absorption thermal energy storage/transmission, as well as other related technologies.

Optimisation of Operation of Adsorption Chiller with Desalination Function

The demand for electricity is growing rapidly along with economic development and increasing population. At present, its production is mainly based on non-renewable sources, which has negative impacts on the environment and contributes to global warming. A large proportion of the produced electricity is consumed by refrigeration equipment. Climate change and the progress of civilisation are additionally increasing the demand for cooling, with increasing electricity consumption as a consequence. One of the options for obtaining eco-friendly cooling is the use of adsorption chillers. These devices are powered by low-temperature heat and their operation only requires a small amount of electrical energy. The source of low-temperature heat can be, e.g., waste heat generated in many industrial processes. Its use allows one to increase energy efficiency and achieve additional financial benefits. However, adsorption chillers are characterised by low coefficients of performance. This paper presents possibilities to improve their performance. It also presents the results of tests carried out on a three-bed adsorption chiller with desalination function. The aim of the investigation was to determine the effect of the cycle time on the coefficient of performance (COP) and specific cooling power (SCP). The working pair was silica gel and water. The results confirmed the effect of the duration of adsorption and desorption on the COP and SCP of the adsorption chiller. Increasing the duration of the cycle led to an increase in the COP.