Improving efficiencies of thermal energy conversion systems is an important way to slow down global warming and mitigate climate change. Vapor absorption heat pump and refrigeration cycles are highly efficient ways of heating and cooling. These thermally activated systems also provide opportunities for the integration with a wide spectrum of low-grade and renewable heat sources, such as district heating networks, exhaust industrial heat, concentrated solar thermal energy and biomass. New fluids - ionic liquids - have been introduced into the absorption refrigeration/ heat pump field as absorbents to overcome drawbacks of traditional working fluids and to improve the energetic efficiency of systems. Some ionic liquids show high boiling points, superior thermal and chemical stabilities and strong affinities with refrigerants. Ammonia (NH3) is an environmentally friendly refrigerant with favorable thermodynamic and transport performance. Thus, studies in this thesis placed emphasis on the ammonia/ionic liquids working pairs. Studies in this thesis focus on exploring applications of ammonia/ionic liquid based vapor absorption refrigeration cycles, from a practical point of view in the refrigeration and heat pump field. By applying multi-scale evaluations covering thermodynamic and heat and mass transport aspects, it is intended to further understand the fundamentals of applying ionic liquids in heating and cooling systems. The highlights include: Assessments of equilibriummodels applied for ammonia-ionic liquid working fluids; Prediction of properties of ammoniaionic liquid fluids using molecular simulation; Collection and modeling of relevant thermophysical properties; Evaluation of the heat and mass transfer performance. Besides, concepts of using ionic liquids as absorbents with ammonia as the refrigerant in various thermodynamic cycles are analyzed and evaluated for applications in the built environment and industry... @en

Negative transport properties have always been pointed out as the key factors that hinder the application of ammonia/ionic liquids (NH3/ILs) in the absorption cycles, while heat and mass transfer of these new fluids in components have been rarely reported. The authors selected corrugated plate heat exchangers as the geometry to explore the absorption of the proposed working fluids. In this paper, a modeling method and a continuous absorption-desorption setup are introduced. Absorption process is modeled with the two-resistance theory by introducing a gas-liquid interface. Analytical heat transfer results and mass transfer from penetration theory are applied. With the model, distribution of local parameters and overall heat and mass transfer characteristics of an absorber in a cooling application are obtained. The overall heat transfer coefficient of an absorber for a refrigeration application is around 1350 W/(m2K) for the studied NH3/IL working fluids. An experimental setup is developed for further model improvement.@en

Negative transport properties have always been pointed out as the key factors that hinder the application of ammonia/ionic liquids (NH3/ILs) in the absorption cycles, while heat and mass transfer of these new fluids in components have been rarely reported. The authors selected corrugated plate heat exchangers as the geometry to explore the absorption of the proposed working fluids. In this paper, a modeling method and a continuous absorption-desorption setup are introduced. Absorption process is modeled with the two-resistance theory by introducing a gas-liquid interface. Analytical heat transfer results and mass transfer from penetration theory are applied. With the model, distribution of local parameters and overall heat and mass transfer characteristics of an absorber in a cooling application are obtained. The overall heat transfer coefficient of an absorber for a refrigeration application is around 1350 W/(m2K) for the studied NH3/IL working fluids. An experimental setup is developed for further model improvement.@en

Increasing helium use in research and production processes necessitates separation techniques to secure sufficient supply of this noble gas. Energy-efficient helium production from natural gas is still a big challenge. Membrane gas separation technology could play an important role. Herein, a novel poly(p-phenylene benzobisimidazole) (PBDI) polymeric membrane for helium extraction from natural gas with low He abundance is reported. The membranes were fabricated by a facile interfacial polymerization at room temperature. The thin and defect-free membrane structure was manipulated by the confined polymerization of monomers diffusing through the interface between two immiscible liquids. Both He/CH4 selectivity and He permeance are competitive over those of other commercial perfluoropolymers. Even at low He content of 1%, separation performance of the PBDI membrane transcended the current upper bound. The unprecedented selectivity (>1000) together with the excellent stability (∼360 h) endows PBDI membranes with a great potential for energy-efficient industrial recovery and production of this precious He resources from reservoirs with low abundance.@en

To use high-temperature waste heat generated by diesel engines for onboard refrigeration of fishing vessels, an ammonia-based double-effect vapor absorption refrigeration cycle is proposed. Non-volatile ionic liquids are applied as absorbents in the double-effect absorption system. In comparison to systems using ammonia/water fluid, the complexity of the system can be reduced by preventing the use of rectification sections. In this study, a multi-scale method is implemented to study the proposed system, including molecular simulations (the Monte Carlo method) for computing vapor-liquid equilibrium properties at high temperatures and pressures, thermodynamic modeling of the double-effect absorption cycles, and system evaluations by considering practical integration. The Monte Carlo simulations provide reasonable vapor-liquid equilibrium predictions. 1-butyl-3-methylimidazolium tetrafluoroborate is found to be the best performing candidate among the investigated commercialized ionic liquids. In the proposed cycle, the best working fluid achieves a coefficient of performance of 1.1 at a cooling temperature of −5 C, which is slightly higher than that obtained with generator-absorber cycles. Integrated with the exhaust gas from diesel engines, the cooling capacity of the system is sufficient to operate two refrigeration seawater plants for most of the engine operating modes in high-latitude areas. Thereby, the carbon emission of onboard refrigeration of the considered fishing vessel could be reduced by 1633.5 tons per year compared to the current practice. Diagrams of vapor pressures and enthalpies of the studied working fluids are provided as appendices.@en

Ionic liquids (ILs), as novel absorbents, draw considerable attention for their potential roles in replacing water or LiBr aqueous solutions in conventional NH3/H2O or H2O/LiBr absorption refrigeration or heat pump cycles. In this paper, performances of 9 currently investigated NH3/ILs pairs are calculated and compared in terms of their applications in the single-effect absorption heat pumps (AHPs) for the floor heating of buildings. Among them, 4 pairs were reported for the first time in absorption cycles (including one which cannot operate for this specific heat pump application). The highest coefficient of performance (COP) was found for the working pair using [mmim][DMP] (1.79), and pairs with [emim][Tf2N] (1.74), [emim][SCN] (1.73) and [bmim][BF4] (1.70) also had better performances than that of the NH3/H2O pair (1.61). Furthermore, an optimization was conducted to investigate the performance of an ideal NH3/IL pair. The COP of the optimized mixture could reach 1.84. Discussions on the contributions of the generator heat and optimization results revealed some factors that could affect the performance. It could be concluded that the ideal IL candidates should show high absorption capabilities, large solubility difference between inlet and outlet of the generator, low molecular weights and low heat capacities. In addition, an economic analysis of the AHP using NH3/[emim][SCN] working pair with plate heat exchangers was carried out based on heat transfer calculations. The results indicated that the NH3/IL AHP is economically feasible. The efforts of heat transfer optimization in the solution heat exchanger and a low expense of ILs can help the IL-based AHP systems to become more promising.@en

Ionic liquids (ILs), as novel absorbents, draw considerable attention for their potential roles in replacing H2O or LiBr aqueous solutions in conventional NH3/H2O or H2O/LiBr absorption chiller or heat pump cycles. In this paper, NH3/IL working pairs are proposed for implementation in parallel double effect heat pump systems. To investigate their performance, a property-prediction method, based on experimental heat capacities and the nonrandom two-liquid (NRTL) activity coefficient model for the vapor pressure, was used to estimate the thermodynamic properties for the proposed NH3/IL mixtures. Then, parallel configuration double-effect absorption heat pump cycles driven by a high-temperature heat source were analyzed by means of evaluation of the thermodynamic operating limits and performance simulations with the aforementioned properties. The ILs investigated include [Mmim][DMP], [Emim][BF4], [Hmim][BF4], [Omim][BF4], [Bmim][BF4], [Bmim][PF6], [Emim][Tf2N], [Emim][EtSO4] and [Emim][SCN]. The performance, such as the coefficient of performance, COP, and circulation ratio f, along with the environmental temperature used as heat source were compared for these ILs based pairs and the conventional ones. This work on double-effect heat pumps with NH3/ILs pairs shows that there is an optimum distribution ratio between the parallel flows and that some of the investigated mixtures have the potential to show a better performance than that of the traditional NH3/H2O pair in cooling and heating applications. @en

This paper describes a properties-optimization work for the working fluids in NH3 / ionic liquid (ILs) based single-effect absorption heat pumps. The optimum parameters of the IL can be used as criteria in screening task-specified ILs, which play the role of absorbents, in absorption heat pumps. First, a 8-parameter thermodynamic model to calculate performances of a single-effect absorption heat pump cycle was proposed, which is based on the non-random two-liquid (NRTL) activity coefficient model for the vapor pressure and a linear function for the heat capacity. Then, experimental data on the vapor-liquid equilibrium (VLE) of solutions and heat capacities of the pure ILs were reviewed and fitted to obtain ranges of those parameters. Within certain limits, the values of parameters were optimized in the following step using the above proposed mode. The objective is a maximum system performance. The optimized ILs have low molecular weights, low specific heats and have high absorption capabilities.@en

Monte Carlo (MC) simulations in ensembles with a fixed chemical potential or fugacity, for example the grand-canonical or the osmotic ensemble, are often used to compute phase equilibria. Chemical potentials can be computed either with an equation of state (EoS) or from molecular simulations. The accuracy of the computed chemical potentials depends on the quality of the (critical) parameters used in the EoS and the applied force field in the simulations. We investigated the consistency of both approaches for computing fugacities of the industrially relevant gases CO2, CH4, CO, H2, N2, and H2S. The critical temperature (Tc), pressure (Pc), and acentric factors (ω) of these gases are computed from MC simulations in the Gibbs ensemble. The effect of cutoff radius and tail corrections on the computed values of Tc, Pc, and ω is investigated. In addition, MC simulations in the Gibbs ensemble are used to compute the VLE of the 15 possible binary systems comprising the gases CO2, CH4, CO, H2, N2, and H2S, and the ternary systems CO2/CH4/H2S and CO2/CO/H2. Binary interaction parameters (kij) of these natural/synthesis gas mixtures are obtained by fitting the Peng-Robinson (PR) EoS to the binary VLE data from the MC simulations. The computed properties from the MC simulations are compared with the PR EoS, the GERG EoS, and experimental results. The MC results show that including tail corrections in the simulations is crucial to obtain accurate critical properties. The force fields used for the gases can reproduce the fugacities of the gases within 5% of the experimental data. The dew-point curves of all the 15 binaries were predicted correctly by the MC simulations, but the bubble-point curves for the systems H2/CO, CH4/H2, H2S/N2, and H2S/CO significantly deviate from the experiments.@en

Unfavorable transport properties have always been pointed out as the key factors that hinder the application of ammonia/ionic liquids (NH 3 /ILs) in absorption cycles, while heat and mass transfer of these new fluids in components have been rarely reported. In this study, a corrugated plate heat exchanger is selected as the geometry for exploring the absorption of NH 3 in the proposed NH 3 /ILs working fluids. The process is studied making use of a semi-empirical framework: experimental data is needed to determine unknown information of heat and mass transfer, and a numerical model is developed making use of frequently applied theories. In addition, relevant transport properties of the NH 3 /ILs working fluids are modeled based on collected experimental data. The proposed model is used to study the heat and mass transfer performance during the absorption of NH 3 vapor into NH 3 /ILs fluids. Distribution of local parameters and overall heat and mass transfer characteristics are obtained. The performance of absorption of NH 3 into different working fluids is investigated as well. The overall heat transfer coefficient is found around 1.4 kW/(m 2 ·K) for the most promising working fluid NH 3 /[emim][SCN]. @en

Force Field based Monte Carlo (MC) simulations are conducted to predict the performance of an absorption heat pump cycle involving NH3/ionic liquid (IL) (refrigerant/absorbent) as working pair. To investigate the thermodynamic performance of the cycle, various properties such as the enthalpy of absorption, heat capacity, and solubility of refrigerant in the absorbent are required. As an alternative to experiments, MC simulations are used to predict the required properties. The simulations are performed at temperatures ranging from 303 K to 373 K and pressures ranging from 4 to 16 bar. The thermodynamic performance parameters such as the coefficient of performance, COP, and the circulation ratio, f, of NH3 paired with [emim][Tf2N] are investigated using MC simulations and compared to results obtained from correlated experimental data, showing a reasonable agreement. MC simulations could be used as an inexpensive alternative for preliminary design considerations involving potential working pairs for absorption heat pump cycles in the absence of available experimental data.@en

This paper assesses the performance of vapor–liquid equilibrium (VLE) models in ionic liquid based absorption cycles with natural refrigerants. Frequently used equation-of-state (EOS) based models, activity coefficient based models, and generic Clausius–Clapeyron relations are evaluated. Working pairs considered are H2O/[emim][DMP] and NH3/[bmim][BF4]. Firstly, experimental VLE data of those working pairs are correlated by using the models. Mixing enthalpies are then estimated using the models and corresponding correlated parameters. Performances of the different models in reproducing VLE data and estimating mixing enthalpies are compared with each other. Subsequently, total enthalpies and thermodynamic performances of absorption refrigeration cycles are predicted based on the different models. The assessment reveals that the RK-EOS and the NRTL model perform best in reproducing VLE data. In addition, the RK-EOS and the UNIFAC model show the best performance in estimating mixing enthalpies. Hence, the RK-EOS is recommended in correlating VLE data and estimating mixing enthalpies in absorption cycles.@en

The energy separation and the increase of heating effect and the decrease of cooling effect in the vortex tube with various gases, such as R41, R32, R23, R290, R134a, R1234yf, was studied in the numerically simulated. The pressure field and temperature field and velocity field of the vortex tube were analyzed with R41. The results show that the R41 in the vortex tube, the cold and hot performance will best, the maximum temperature difference what be between cool area and hot area is 5.2 K. The numerical results show that flow motion inside the vortex tube presents extraordinary complicated behavior; The flow inside the vortex tube exist an outer region of quasi-free vortex flow and an inner region of quasi-forced vortex flow; there are the parallel flow, reverse flow and secondary flow in the vortex tube, The interface between parallel flow and reverse flow is that the energy separation place in the vortex tube.@en

The energy separation and the increase of heating effect and the decrease of cooling effect in the vortex tube with various gases, such as R41, R32, R23, R290, R134a, R1234yf, was studied in the numerically simulated. The pressure field and temperature field and velocity field of the vortex tube were analyzed with R41. The results show that the R41 in the vortex tube, the cold and hot performance will best, the maximum temperature difference what be between cool area and hot area is 5.2 K. The numerical results show that flow motion inside the vortex tube presents extraordinary complicated behavior; The flow inside the vortex tube exist an outer region of quasi-free vortex flow and an inner region of quasi-forced vortex flow; there are the parallel flow, reverse flow and secondary flow in the vortex tube, The interface between parallel flow and reverse flow is that the energy separation place in the vortex tube.@en

Ionic liquids (ILs), as novel absorbents, draw considerable attention for their potential roles in replacing water or LiBr aqueous solutions in conventional NH3/H2O or H2O/LiBr absorption refrigeration and heat pump cycles. In this paper, to investigate the absorption heat pump using ILs, a prediction method, based on non-random two-liquid (NRTL) activity coefficient model for the vapor pressure and Redlich–Kwong equation of state (RK EOS) for mixing heat, was used to estimate thermodynamic properties for the proposed NH3/IL solutions. Then, single effect absorption heat pump cycles with NH3 as refrigerant and IL as absorbent were analyzed by thermodynamic simulations based on the aforementioned properties. Some of the ILs used including [mmim][DMP], [emim][BF4], [hmim][BF4] and [omim][BF4], have not been previously reported in absorption cycles with NH3. The performance parameters such as coefficient of performance (COP) and circulation ratio (f) of them were then compared along with the reported ILs by Yokozeki and Shiflett (2007 a & b) including [bmim][PF6], [hmim]Cl, [emim][Tf2N], [bmim][BF4], [emim][Ac], [emim][EtSO4], [emim][SCN] and [DMEA][Ac].@en

Ionic liquid (IL)-NH3 double-effect absorption systems are proposed to utilize the high-temperature exhausted gas (250-500 oC) from engines with the purpose of delivering the required refrigeration of the fishing vessel. In this work, practical concerns on the stabilities, toxicities and viscosities of IL-based fluids have been discussed. Monte Carlo (MC) methods have been applied to extend the vapor-liquid equilibrium properties of selected IL-NH3 working pairs to high-temperature conditions. Additionally, a case study based on a specific fishing vessel has been carried out to investigate the economic feasibility of the proposed systems.@en

Ionic liquid (IL)-NH3 double-effect absorption systems are proposed to utilize the high-temperature exhausted gas (250-500 oC) from engines with the purpose of delivering the required refrigeration of the fishing vessel. In this work, practical concerns on the stabilities, toxicities and viscosities of IL-based fluids have been discussed. Monte Carlo (MC) methods have been applied to extend the vapor-liquid equilibrium properties of selected IL-NH3 working pairs to high-temperature conditions. Additionally, a case study based on a specific fishing vessel has been carried out to investigate the economic feasibility of the proposed systems.@en

Excess enthalpy is crucial in investigating absorption refrigeration and heat pump cycles. Apart from a direct measurement, it can be estimated from vapor-liquid equilibrium (VLE) data by using thermodynamic models. Models which can be used are equation-of-state (EOS) based model, activity-coefficient based methods, and generic Clausius-Clapeyron relation. This paper assesses the performance of different models in the excess enthalpy prediction of natural refrigerants/ILs pairs for absorption cycles. First, the fundamental theories on excess enthalpy prediction with different thermodynamic models are introduced. Then, the VLE data of two working pairs are fitted and used to estimate excess enthalpy by these models. The predicted results are compared with measured ones for the pair H2O/[emim][DMP]. The influence of fitted parameters on the excess enthalpy prediction is also discussed. The assessment reveals the predicted excess enthalpies have quite large deviations compared with the measured values. UNIFAC and Redlich-Kwong EOS models perform best with relatively smaller errors. @en

For absorption refrigeration, it has been shown that ionic liquids have the potential to replace conventional working pairs. Due to the huge number of possibilities, conducting lab experiments to find the optimal ionic liquid is infeasible. Here, we provide a proof-of-principle study of an alternative computational approach. The required thermodynamic properties, i.e., solubility, heat capacity, and heat of absorption, are determined via molecular simulations. These properties are used in a model of the absorption refrigeration cycle to estimate the circulation ratio and the coefficient of performance. We selected two ionic liquids as absorbents: [emim][Tf2N], and [emim][SCN]. As refrigerant NH3 was chosen due to its favorable operating range. The results are compared to the traditional approach in which parameters of a thermodynamic model are fitted to reproduce experimental data. The work shows that simulations can be used to predict the required thermodynamic properties to estimate the performance of absorption refrigeration cycles. However, high-quality force fields are required to accurately predict the cycle performance.@en

Absorption refrigeration and heat pump cycles, especially for the promising double-effect absorption heat pump systems, are drawing considerable attention because they can make effective use of higher temperature heat from concentrated solar energy and exhaust gases. Ionic liquids (ILs), novel and tailor-made absorbents, can be used with natural refrigerants as working pairs for absorption refrigeration cycles. This paper presents a preliminary work to select an appropriate model (from equation of state (EOS) or activity coefficient-based methods) to describe the vapour-liquid equilibrium properties of the binary systems between natural refrigerants and ILs. First, different thermodynamic models are reviewed. Then, some experimental vapour-liquid-equilibrium data from literature of ILs based mixtures are fitted with different models (Redlich-Kwong EOS with mixing rule, NRTL and UNIFAC models). The fitted interaction parameters and fitting quality of each model are listed for comparison. Finally, the applicability of each model is estimated by taking into account both its precision and its simplicity. @en