Working Pair Research Articles

Thermodynamic performance analysis of a single-effect absorption refrigeration system operating with water and 1-ethyl-3-methylimidazolium-based ionic liquids mixtures

Absorption refrigeration systems (ARS) are thermally-driven technologies used to generate cold utilities. When the working pair H2O/LiBr is used in ARS, severe crystallization and corrosion problems may arise. Aiming to avoid these issues, investigations concerning ionic liquids (ILs) to replace LiBr has been conducted. This paper presents a thermodynamic performance analysis for a single-effect ARS using water and two 1-ethyl-3-methylimidazolium-based ionic liquids as absorbents: 1-ethyl-3-methyl-imidazolium ethylsulfate ([EMIM][EtSO4]) and 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([EMIM][BF4]), both not yet widely explored for this purpose. Simulations were performed using Engineering Equation Solver (EES) software. Results have shown that H2O/[EMIM][BF4] mixture is clearly unattractive. Particularly at lower temperatures in the absorber and condenser and higher temperatures in the evaporator, H2O/[EMIM][EtSO4] mixture presented COP and exergetic efficiency (ηex) profiles relatively close to those of the conventional H2O/LiBr. For an optimized case, COP and ηex were 8.2% and 19.2% greater for H2O/LiBr than for H2O/[EMIM][EtSO4] which has presented values of 0.764 and 0.114 respectively. For ηex this difference tended to decrease at higher temperatures in the generator, turning H2O/[EMIM][EtSO4] mixture competitive with H2O/LiBr at certain conditions, mainly in view of LiBr crystallization risk. The main contributions of this work regarding ARS studies is performing all the following studies simultaneously: sensitivity analysis, thermodynamic optimization and crystallization risk analysis also considering working pairs that still present some gaps in the literature.

Effect of residual air on dynamics of temperature- and pressure-initiated adsorption cycles for heat transformation

• Effect of air traces on dynamics of pressure-initiated (PI) adsorption is studied. • “Water - FAM-Z02″ and ”methanol - LiCl/silica“ working pairs are investigated. • PI adsorption is less sensitive to the air presence than temperature-initiated one. • Closed cooling cycles based on PI process are more robust against the air presence. It is well known that non-adsorbable gas, e.g. residual air, can dramatically slow down the adsorption stage of adsorption heat transformation cycles. So far, this effect has been studied for the cycles initiated by temperature change (temperature-initiated cycles). This work addresses the dynamic effect of residual air for another way of adsorption initiation, namely, by changing vapour pressure over adsorbent (pressure-initiated cycle). Comparison of the pressure- and temperature-initiated cycles is also made. The effects are studied for the working pairs “AQSOA FAM-Z02 – water” and “LiCl/(silica gel) – methanol” promising for adsorption heat transformation. The residual partial air pressure Δ P air was varied from 0 to 5 mbar. The main finding of this study is that the pressure-initiated adsorption is less sensitive to the presence of residual air than the temperature-initiated adsorption. This is especially true at a low partial air pressure Δ P air . For instance, at Δ P air ≤ 0.5 mbar, residual air has little or no effect on the pressure-initiated adsorption dynamics compared to the temperature-initiated one. A qualitative explanation of this finding is proposed. Thereby, closed adsorption heat transformation cycles based on the pressure-initiated process are more robust and resistant against the presence of residual air that could be a significant practical advantage.

Large-scale cascade cooling performance evaluation of adsorbent/water working pairs by integrated mathematical modelling and machine learning

The cooling performance of over 90 000 adsorbent/water combinations in cascaded adsorption chillers are evaluated based on experimental water adsorption isotherm by mathematical modeling, as well as efficiently predicted by machine learning models.

Screening versatile water/adsorbent working pairs for wide operating conditions of adsorption heat pumps

Computational screening of 231 adsorbent/water working pairs from experimental water adsorption isotherm database for AHPs is carried out based on effective coefficient of performance and effective temperature lift under practical working condition.

Experimental study on absorption characteristics of a falling film absorber with micro-scale NH3/LiNO3 liquid film

This work proposed a non-adiabatic absorber with micro-scale falling film with the working pair of ammonia/lithium nitrate. The manufacturing and structure features of the novel absorber has been presented, as well as the experimental facilities of complete absorption refrigeration system. Evaluations and characteristics of mass tansfer process of this novel absorber have been analyzed. Relationships between working conditions such as absorption pressure and cooling water temperature and absorption parameters such as absorption rate, mass transfer coefficents have also been revealed and discussed. Results of this novel micro-scale falling film absorber indicated that, it owns a relatively good performance under high-temperature cooling working condition. Regular working parameters such as absorption rates and mass transfer coefficients are much larger than previous studied adiabatic absorber with structured packing. Moreover, correlations of significant dimensionless parameters have also been concluded for the future research of this micro-scale falling film absorber. • Absorption performances of micro-scale NH 3 /LiNO 3 liquid film is proposed. • Factors of enhancements on absorption process have been comprehensively studied. • Correlations of dimensionless parameters have been established for the novel absorber. This study proposed a novel micro-scale falling film absorber with its experimental data on a complete absorption refrigeration system. Micro-scale liquid-distributor has been carefully designed and manufactured by special techniques. An experimental system for absorption refrigeration has been established to test the novel absorber. This unique absorber applies ammonia/lithium nitrate as working pair which is considered to own application potential for small-scale absorption refrigeration units. Experimental analysis has been done under various of working conditions for making contrasts. Relationships between significant working parameters and absorption parameters have been discussed. Under series of working conditions, absorption rates ranging from 1.2 to 2.6 × 10 −3 kg/(m 2 ·s) have been obtained. Approach to equilibrium factor which characterize the perfection of absorption process ranges from 0.5 to 0.98 while absorption ratio ranges from 0.02 to 0.12. With the increase of Reynolds number from 3 to 52, the mass transfer coefficient rises from 12 to 98 × 10 −6 m/s and Sherwood number ranges from about 30 to 60 respectively. According to the analysis, absorption pressure potential and cooling water temperature are two major factors which enhance the absorption intensity. Absorption pressure potential and inlet solution subcooling degree owns nearly linear relationship with parameters such as absorption rate, absorption ratio and approach to equilibrium factor. However, normalized absorption rate and approach to equilibrium factor gain negative correlations with absorption pressure potential and Reynolds number respectively. Effects of inlet solution flowing features on absorption performance are distinguished under different working condition series. In general, solution flowing intensity inside absorber is a positive factor for absorption process. All the experimental results reveal that, this micro-scale falling film absorber has its priority on absorption perfection and absorption rate for per unit of mass transfer area. Compact structure makes it more valuable for further research and application on small-scale absorption refrigeration unit with the working pair of ammonia/lithium nitrate.

Modeling and optimization of a honeycombed adsorbent bed for efficient moisture capture

Adsorption-based atmospheric water harvesting has received significant interest owing to its promise of decentralized water supply and a wide applicability. In this study, the adsorbent bed is specially designed and optimized for efficient moisture capture. A transient three-dimensional non-equilibrium model has been developed that takes both internal and external mass transfer resistances into account. It is found that the simulation results agree better with the experimental results, which indicates the reliability of the model. Then this model was applied to investigate the influence of the adsorbent bed structure, and the operating parameters on the transient distributions of the adsorbent temperature, adsorption kinetics, dynamic up-taken moisture capture, mass transfer resistance and relative capture efficiency of the adsorbent bed. ASLi30 (Activated carbon fiber + Silica gel + 30 wt% LiCl)-vapor is selected as the working pair. It has been found that generally, the effects of the air channel aspect ratio on the investigated indexes are negligibly small. A thinner layer thickness and a smaller air channel length characterize an excellent moisture capture, small vapor transport resistance and faster adsorption kinetics. By considering different parametric variations for performance optimization and the effect of operating conditions, these results provide important insights and design guidelines of adsorbent bed for efficient moisture capture.

A thermochemical heat and cold control strategy for reducing diurnal temperature variation in the desert

The significant diurnal temperature variation has become a severe challenge restricting comfortable human survival in the summer desert. Thermochemical heat and cold control technology, which owns the characteristics of large thermal energy storage/release capacity and excellent heat-cold combined storage/supply performance, makes an attractive method to solve the challenge. Herein, we propose a thermochemical heat and cold control strategy based on the working pair of manganese [email protected] natural graphite treated with sulfuric acid/ammonia (MnCl2@ENG-TSA/NH3) for reducing diurnal temperature variation in the summer desert. The system converts the thermal energy into chemical energy for storage by efficiently harvesting solar energy during the daytime, while the chemical energy transforms into thermal energy and cooling capacity for heating supply and refrigeration at night. The effective thermal energy charge in the daytime and thermal energy discharge at night are about 3011.48 and 1411.60 kJ with the oil temperature of solar collector and heating supply temperature of 175 °C and 40 °C as well as the ambient temperature of 30 °C and 10 °C. Moreover, the thermal energy charge density, thermal energy release density, and thermal storage efficiency of the system are as high as 941.09 kJ kg−1, 450.49 kJ kg−1, and 47.87%. Additionally, the system's effective cooling capacity, specific cooling capacity, and coefficient of performance (COP) are approximately 965.40 kJ, 301.68 kJ kg−1, and 0.383. The control system possesses strong heating supply ability and refrigeration ability because the temperature difference of heating supply and refrigeration can reach up to 16.99 °C and 3.03 °C at night, respectively. Therefore, this strategy can significantly improve indoor thermal comfort and reduce building energy consumption in the desert, having potential promotion value for efficient recovery and medium-low temperature thermal energy across time and space.

Manipulating Pore Topology and Functionality to Promote Fluorocarbon-Based Adsorption Cooling

ConspectusWith the worldwide demand for refrigeration and cooling expected to triple, it is increasingly important to search for alternative energy resources to drive refrigeration cycles with reduced electricity consumption. Recently, adsorption cooling has gained increased attention since energy reallocation in such systems is based on gas adsorption/desorption, which can be driven by waste/natural heat sources. Eco-friendly sorption-based cooling relies on the cyclic transfer of refrigerant gas from a high to low energy state by the pseudocompression effect resulting from adsorption and desorption. The driving force for energy transfer relies on heat rather than electricity. The performance of a sorption chiller is primarily influenced by this cyclic sorption behavior, which is characterized as the working capacity of the porous sorbent. Thus, increases in this working capacity directly translate to a more compact and efficient cooling system. However, a lack of highly effective sorbent/refrigerant pairs lowers cooling performance and therefore has limited applicability. To this end, synthetic metal-organic frameworks (MOFs) and covalent organic polymers (COPs) possess higher porosity and greater tunability leading to more substantial potential benefits for adsorption, compared to traditional sorbent materials. Similarly, hydrofluorocarbon refrigerants have more favorable applicability given the ease of operation above atmospheric pressures due to suitable saturated vapor pressures and boiling points. For these reasons, our work focuses on an ongoing strategy to promote sorption cooling via improvements in the sorbent/refrigerant pair. Specifically, we target the interaction of hydrofluorocarbon refrigerants with MOF/COP materials at a molecular level by interpreting the host-guest chemistry and the role of framework pore topology. These molecular-level differences translate to cooling performance, which is described herein. These strategies include engineering framework porosity (i.e., pore size, pore volume) by using elongated organic linkers and stereochemistry control during synthesis; manipulating the sorbate/sorbent interaction by introducing functional moieties or unsaturated metal centers to enhance working capacities in narrow pressure ranges; varying pore topology/morphology to impact adsorption isotherm behavior; and leveraging defective sites within the frameworks to further enhance adsorption capability. This atomic level understanding of sorbate-sorbent interactions is conducted using various in situ experimental techniques such as synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, in situ Fourier transform infrared spectroscopy, and direct sorption energies determinization with calorimetry. Moreover, the experimentally studied interactions and the corresponding adsorption mechanism are corroborated by computational studies using density functional theory (DFT) and grand canonical Monte Carlo (GCMC) simulations. Using this approach, we have made strides toward engineering designed frameworks with precise molecular control to target refrigerant molecules and thereby enhance the performance of desired working pairs for sorption-based cooling.

Experimental investigation on the phase behavior of DME/ [P6,6,6,14][Cl] and thermodynamic analysis for absorption refrigeration system

Dimethyl ether (DME), as an environmental-friendly alternative refrigerant, has received broadly attention. Phosphonium-based ionic liquids with good thermophysical properties are regarded as promising absorbents in absorption refrigeration systems. In this work, the measurement of solubility behavior to DME in trihexyltetradecylphosphonium chloride ([P6,6,6,14][Cl]) was carried out from 278.15 K to 348.15 K by means of isochoric saturation method. Non-random two liquid (NRTL) model and Krichevsky-Kasarnovsky (K-K) model were used to correlate the experimental data. The absolute average relative deviation between experimental liquid mole fraction and calculated values was 0.739% and 1.517% for NRTL model and K-K model respectively. Based on the solubility results, the performance of single-effect absorption refrigeration cycle used DME/[P6,6,6,14][Cl] pairs was analyzed, and further compared with other working pairs composed of [P6,6,6,14][Cl].

КОМУНІКАТИВНО-ЗОРІЄНТОВАНИЙ ПІДХІД ДО ВИВЧЕННЯ ЧАСТИН МОВИ СТУДЕНТАМИ ФАХОВОГО КОЛЕДЖУ

The role of communicative-activity approach in the process of mastering English by students on the basis of a professional college is described. The importance of focusing the English language course on the development of skills and abilities to produce their own statements in the personal and professional spheres is noted. The emphasis is placed on the content of this approach through the prism of the development of the speed of speech activity and the formation of speech patterns and structures. The orientation of the communicative-oriented approach to the formation of communicative competence, which determines the students' worldviews, the system of value orientations, the development of professional and critical thinking is considered. Six principles of the organization of educational activity of students studying English are allocated. The importance of the principle of communicative-personal organization of educational activity for realization of communicative orientation of the educational process is determined. The effectiveness of the use of game, active and interactive methods, group, pair and individual forms of work as ways to implement a communicative-oriented approach during English language learning is noted. The active role of the teacher in directing the discussion, debate or dispute in the right direction during the classroom classes using interactive methods is highlighted. The emphasis is placed on the effectiveness of modeling a communicative situation close to real life using professional vocabulary and mastering certain socio-cultural aspects. The classification of parts of speech is considered and the presence of a specific set of grammatical properties and basic syntactic functions is noted. The importance of role-playing games in the study of parts of speech by students of a professional college is considered. The examples of effective grammar games are given: ball games, dice, gifts, etc. The emphasis is placed on the effectiveness of the communicative-oriented approach in the study of parts of speech.

Thermophysical properties of R32/advanced PVE mixture and parametric analysis on oil transport characteristic of compressor suction line

Advanced PVE was developed as the coupled lubricant oil for the alternative refrigerant R32 and R32/PVE will be a potential working pair of R32 refrigeration systems. This paper presented modeling study of physical properties of PVE lubricant oil with viscosity grade 68 and R32/PVE mixture. Thermal conductivity, specific heat and surface tension of PVE oil were measured experimentally. New calculation models for properties of pure oil were developed based on the experimental data. Moreover, the solubility, miscibility and viscosity of R32/PVE mixture were also well correlated with the new correlations. Further, a parametric analysis was performed to study oil transport and retention characteristics in compressor suction line, based on the force balance method. A new consolidated database for oil retention was amassed from six existing literatures, including 187 data points. A new correlation for oil retention was established by incorporating influence factors derived from the parametric analysis. The validation result showed that the oil retention correlation exhibits satisfactory prediction accuracy, which achieved mean absolute error of 14.43% and 87.70% of data fell within ±30% error bands. The property models and oil retention correlation could serve as tools to accurately predict oil retention amount of suction line with R32/PVE mixture.

Performance analysis of type 1 and type 2 hybrid absorption heat pump using novel working pairs

In this study, cooling and heating cycle performance analysis is carried out for alternative absorption working fluids using R32, R1234ze (E), and R1234yf, which have gained attention due to regulations on high global warming potential (GWP) refrigerants. The hybrid cycle operates heating and cooling simultaneously because the type 1 and the type 2 cycles are combined sharing the generator and condenser. It is found that the cooling COPs are in the order of R32/DMAC > R32/[hmim][Tf2N] > R1234ze(E)/[hmim][Tf2N] > R1234yf/[hmim][Tf2N]. In the heating mode which occurs in the type 2, the R32/DMAC pair shows the highest COP at the lowest circulation ratio. Therefore, the R32/DMAC pair is selected as the working fluid for the type 1 and type 2 hybrid absorption heat pumps. The conditions of the high temperature absorber are very sensitive to the split ratio. The maximum system COP of 0.617 is achieved when the generator split ratio is 0.80 and the condenser split ratio is 0.96 without the superheating. It is found that the maximum cooling COP is enhanced up to 0.325 and the maximum heating COP is up to 0.562, and it can be used properly for combined heating and cooling systems.

New environment friendly working pairs of dimethyl ether and ionic liquids for absorption refrigeration with high COP

To overcome the limitations of absorption refrigeration system brought by commercial working pairs of NH3/H2O and H2O/LiBr for the utilization of low-grade heat, a new class of working pairs consisting of dimethyl ether (DME) and ionic liquids (ILs) are developed. The solubilities of DME in three ILs [BMIM][BF4], [BMIM][PF6] and [BMIM][Tf2N] were firstly measured and correlated. Then, COPs of the single-effect absorption refrigeration system (ARS) and absorption-compression hybrid refrigeration system (ACRS) using DME/IL were calculated under different conditions. The maximum COP of ARS using the three DME/IL working pairs can be up to 32.0% larger than that using NH3/H2O, while the maximum COP of ACRS using the three DME/IL working pairs can be up to 38.3% larger than that using NH3/H2O under studied conditions. The three DME/IL working pairs also show much better cooling performance than HFC/IL and HFO/IL working pairs which are R152a/[HMIM][Tf2N] and R1234ze(E)/[HMIM][Tf2N]. In ACRS, DME/ILs can drop the optimal generation temperature in ARS by more than 10 K. DME/ILs are very promising alternative absorption refrigeration working pairs due to the high COP, wide applicability and environmental friendliness.

Preparation and direct photothermal property of reduced graphene oxide @copper foam cured MIL-101 for solar adsorption cooling process

Since the energy and environment issues, a renewable and sustainable solar adsorption cooling technology has attracted extensive attention. In order to improve the energy conversion efficiency in the solar adsorption cooling technology, a novel reduced graphene oxide (rGO) @copper foam cured MIL-101 (CFCM) composite with direct illumination property was explored in this paper. The preparation process and photothermal desorption performance of rGO@CFCM were studied. A solar adsorption cooling system with rGO@CFCM-water working pair was designed and constructed. Temperature characteristic curve of rGO@CFCM adsorber, the specific cooling power (SCP) and solar coefficient of performance (SCOP) of rGO@CFCM-water working pair were investigated. The results show that the rGO@CFCM with the carbon/oxygen ratio of 5.43, amount of rGO of 1.6 g m−2, thickness of copper foam of 10 mm owns great photothermal heating rate and desorption performance for water. The heating rate of rGO@CFCM is 0.90 ℃ min−1 with desorption percentage of water of 84.36% and energy conversing efficiency of 0.7573 under the irradiation intensity of 2 kW m−2 within 60 min. The light-to-heat conversion performance of rGO@CFCM composite is significantly improved through the addition of rGO. Even if 20 sets of adsorption/photothermal desorption, the adsorption capacity of rGO@CFCM for water still keep stable. SCP and SCOP of the rGO@CFCM-water adsorption cooling system is 85.38 W kg−1 and 0.163 at evaporation temperature of 17 ℃, respectively. It provides basic data for solar adsorption cooling technology.

Analysis of hybrid compression absorption refrigeration using low-GWP HFC or HFO/ionic liquid working pairs

Absorption refrigeration systems (ARS) are the leading alternative for reducing the electricity costs associated with compression refrigeration systems. However, classical pairs based on NH3/H2O and H2O/LiBr have drawbacks that limit their practical application. In this work, we analyze 16 pairs of refrigerant gases and ionic liquid sorbents based on two low global warming potential (GWP) hydrofluorocarbons (HFCs), R32 and R134a, and two novel hydrofluoroolefins (HFOs), R1234ze(E) and R1234yf, using the low-viscosity ionic liquids [C2mim][BF4], [C2mim][OTf], [C2mim][SCN], and [C2mim][Tf2N]. We provide new data and modeling of the vapor-liquid equilibria of R1234ze(E) with [C2mim][OTf], [C2mim][SCN] and [C2mim][Tf2N]. ARS performance in single-effect (SE-ARS) and compression-assisted absorption refrigeration (CA-ARS), in terms of coefficient of performance (COP, ECOP), solution circulation factor (f), and the thermal and electrical contribution to the total COP, is evaluated through energy and exergy analyses. The results showed that CA-ARS performs better even at lower generator temperatures. In addition, HFCs returned a better performance than HFOs because of their higher solubility in ILs. The working pair R32/[C2mim][Tf2N] gave the best results, COP = 0.74 and f = 5.4 at 328 K in the desorber, and a maximum ECOP of 0.41 at 318 K. Furthermore, the HFO R1234ze(E), with a lower working pressure and negligible GWP, is also a promising option for CA-ARS. In conclusion, we consider that ARS with the HFC or HFO/IL pairs examined in this study shows outstanding potential as a more energy efficient system compared to compression systems, when an inexpensive energy source is available.

Structure-Property Correlation of Hierarchically Porous Carbons for Fluorocarbon Adsorption.

Although traditional commercially available porous carbon-fluorocarbon working pairs have shown promising applicability for adsorption cooling, advancements in engineered carbons may further improve the performance. Moreover, insights into structure-property relationships that target higher sorption capacities within these synthesized carbons may guide such materials' future design. We utilized hierarchically porous carbons (HPCs), synthesized with colossal microporous and mesoporous content characterized by high surface areas (up to 2689 m2/g) and pore volume values (up to 10.31 cm3/g) toward fluorocarbon R134a adsorption. This unique pore topology leads to exceptional R134a uptake, ∼250 wt %, outperforming the highest uptake carbon material to date, Maxsorb III (∼220 wt %). Material characterizations reveal that the outstanding R134a capacity may be attributed to textural properties and oxygen-terminated functional groups more than graphitization of the material. Most importantly, HPCs are efficiently utilized in a two-bed model chiller device, where the performance shows excellent working capacity (105 wt %, ∼2 times the value of reported carbon materials/R134a). Fluorocarbon adsorption on HPCs also displays fast kinetics (equilibrium time: ∼2 min) mainly driven by physical adsorption (Qst: ∼27 kJ/mol), characteristic of swiftly reversible behavior adsorption-desorption behaviors. This work provides a fundamental understanding of the applicability of HPCs/R134a working pair for adsorption cooling.

Absorption behavior for R1234ze(E) and R1233zd(E) in [P66614][Cl] as working fluids in absorption refrigeration systems

The absorption-cycle technology driven by low-grade thermal energy has attracted significant attention. Hydrofluoroolefins refrigerant and ionic-liquid absorbent have been currently proposed as the promising candidates to traditional NH 3 /H 2 O and H 2 O/LiBr working pairs. The properties of refrigerant/absorbent pairs have a vital impact on the efficiency of an absorption-refrigeration cycle, especially the solubility of the gaseous refrigerant in an absorbent. In this work, solubilities were measured for two new working pairs (R1234ze(E)/[P 66614 ][Cl] and R1233zd(E)/[P 66614 ][Cl]) by an isochoric saturation method at the temperature range from 283.15 to 343.15 K. Solubilities increase with the increase of pressure and decrease with increase of temperature. To assess solubility model of refrigerant/IL pairs, the Krichevsky-Ilinskays (KI) equation and Nonrandom Two-Liquid (NRTL) model were used to correlate the new data. From the results, we found that the NRTL model could provide smaller deviations than KI equation. In contrast with the existing IL, the [P 66614 ][Cl] has the highest solubility. Furthermore, the enthalpy, entropy, and Gibbs energy of dissolution were estimated.

Electrical conductivity of concentrated LiBr Ethylene-Glycol and water ternary system

LiBr/H2O as working pair in absorption chiller is widely used in the absorption refrigeration system, and the electrical conductivity is used as secondary properties as an empirical relation with temperature and concentration as a simple method to measure the concentration. In this paper, another working pair Carrol/H2O is chosen, more suitable for air-cooled cycles. Carrol contains ethylene glycol and LiBr with a mass ratio at 4.5:1 and has advantages of low risk of crystallization and reduce the LiBr charge. The working range for the LiBr/H2O solution is temperature 25-80°C, at concentration 50–64%, in term of Carrol/H2O system, the temperature range is 25-80°C, concentration range is 50%-75%. The electrical conductivity will be measured according to the working range and a typical used solution extracted from an absorption chiller prototype will also be measured to compare with the experimental result.

A Parametric Examination of the Factors Affecting the Performance of a Diffusion Absorption Refrigeration System

Abstract Despite being identified nearly a century ago, the diffusion absorption refrigeration (DAR) cycle has received relatively little attention. One of the strongest attractions of the DAR cycle lies in the fact that it is thermally driven and does not require high value work. This makes it a prime candidate for harnessing low-grade heat from solar collectors, or the waste heat from stationary generators, to produce cooling. However, to realize the benefits of the DAR cycle, there is a need to develop an improved understanding of how design parameters influence its performance. In this vein, this work developed a new, validated, parametric model that can be used by designers and practitioners to examine the performance of the DAR cycle for a range of operating conditions. The results showed that the cycle’s performance was particularly sensitive to several factors: the rate of heat added and the temperature of the generator, the effectiveness of the gas and solution heat exchangers, the mass flowrate of the refrigerant and the type of the working fluid. It was shown that it can deliver good performance at low generator temperatures if the refrigerant mass fraction in the strong solution is made as high as possible. Moreover, it was shown that a H2O–LiBr working pair could be useful for achieving cooling at low generator temperatures.

Performance of thermochemical adsorption heat storage system based on MnCl2-NH3 working pair

As a leading technology of heat storage, thermochemical adsorption heat storage has become a hot research direction in the world because of its high heat storage density, which can realize cross season heat storage and combined cold and heat storage. In this study, a thermochemical adsorption heat storage system with MnCl2-NH3 as working pair is constructed. MnCl2@expanded graphite composite adsorbent has been prepared by adding expanded graphite (EG) to suppress the expansion and agglomeration of chemical salts, and 3.78 kg MnCl2@EG are filled in the chemical reactor. The heat storage performance of the MnCl2-NH3 thermochemical adsorption heat storage system is experimentally tested. The optimal heat storage performance was obtained when the charging, discharging and condensation/evaporation temperature is 174 °C, 50 °C and 20 °C, respectively. The corresponding total heat storage density is 3211.56 kJ/kg MnCl2 (or 2729.82 kJ/kg consolidated composite material) with the total heat storage efficiency 0.939. The experimental results revealed that MnCl2@EG composite exhibits the superior heat storage performance and could be a promising thermochemical adsorption heat storage material. The thermochemical adsorption heat storage could be used for harvesting the solar thermal energy in large scale and recovering the industrial waste heat.