Performance Of Absorption Refrigeration System Research Articles

Vapor-liquid equilibrium for dimethyl ether and three imidazolium ionic liquids as working pairs in absorption-refrigeration cycle

To overcome the shortcomings of traditional working pairs of H2O/LiBr and NH3/H2O, the combination of dimethyl ether (DME) and ionic liquids (ILs) have been studied recently. The solubilities of DME in [HMIM][BF4], [HMIM][PF6] and [HMIM][Tf2N] were firstly measured and correlated using NRTL equation. The thermodynamic performance of absorption refrigeration system (ARS) using those working pairs are compared with R152a/[HMIM][Tf2N], R1234ze(E)/[HMIM][Tf2N] and other DME/IL pairs which include [BMIM][BF4], [BMIM][PF6] and [BMIM][Tf2N]. Under the studied condition Tg/Ta/Tc/Te = 325–370 K/300 K/300 K/278 K, the maximum COPs of DME/[HMIM][Tf2N], DME/[BMIM][PF6] and R152a/[HMIM][Tf2N] in ARS are 0.592, 0.531 and 0.648, respectively, while that of R1234ze(E)/[HMIM][Tf2N] is only 0.345. DME/[BMIM][PF6] performs best at Tg = 350 K, but at Tg = 340 K, DME/[HMIM][Tf2N] shows better performance. The difference of optimal Tg between them is about 10 K. It shows that ARS of using DME/[HMIM][Tf2N] can utilize lower-grade waste heat. Our studies prove that DME/ILs are good choices to balance the environmental protection property and energy efficiency improve.

Performance Prediction for a Marine Diesel Engine Waste Heat Absorption Refrigeration System

The output of the absorption refrigeration system driven by exhaust gas is unstable and the efficiency is low. Therefore, it is necessary to keep the performance of absorption refrigeration systems in a stable state. This will help predict the dynamic parameters of the system and thus control the output of the system. This paper presents a machine-learning algorithm for predicting the key parameters of an ammonia–water absorption refrigeration system. Three new machine-learning algorithms, Elman, BP neural network (BPNN), and extreme learning machine (ELM), are tested to predict the system parameters. The key control parameters of the system are predicted according to the exhaust gas parameters, and the cooling system is adjusted according to the predicted values to achieve the goal of stable cooling output. After comparison, the ELM algorithm has a fast learning speed, good generalization performance, and small test set error sum, so it is selected as the final optimal prediction algorithm.

Numerical investigation on thermal performance of absorption refrigeration system using MWCNT nanoparticle-enhanced 1-hexyl-3-methylimidazolium cation-based ionic liquids

• Specific heat of HMIM cation based four different ionic liquids were investigated experimentally. • Increase concentration in the MWCNT nanoparticle enhanced ionic liquid improves the COP of the ARS. • The largest COP is presented by 1 wt% MWCNT [HMIM][Pf 6 ] NEIL, followed by 1 wt% MWCNT [HMIM][Tf 2 N] NEILs. In this investigation, the thermal performance of single-stage absorption refrigeration systems (ARSs) utilizing different MWCNT nanoparticle-enhanced 1-hexyl-3-methylimidazolium (HMIM) cation-based ionic liquids with R1234yf refrigerant were analyzed. The specific heats of the various MWCNT nanoparticle-enhanced [HMIM] cation-based ionic liquids were obtained experimentally at a temperature and a concentration of 303–383 K and 0–1 wt%, respectively, and were subsequently used for modeling the solubility and absorption refrigeration cycle. As a result, the maximum specific heats of all considered ionic liquids were examined at the highest temperature of 383 K. The solubility order of R1234yf refrigerant from highest to lowest was [HMIM][Bf 4 ], [HMIM][Pf 6 ], [HMIM][TfO], and [HMIM][Tf 2 N] RTILs. In addition, the maximum COPs of the ARSs were achieved at the temperature and concentration of 363 K and 1 wt%, respectively, which were 0.205, 0.242, 0.286, and 0.259 for the [HMIM][Bf 4 ], [HMIM][TfO], [HMIM][Pf 6 ], and [HMIM][Tf 2 N] MWCNT NEILs, respectively. By applying the proposed system could be simplified at high-temperature applications and prevent undesirable side effects of conventional working pairs such as metal incompatibility, toxicity, and chemical instability.

Investigating the fuel type influence on the thermo-economic performance of absorption refrigeration systems: a comparative study

Investigating the fuel type influence on the thermo-economic performance of absorption refrigeration systems: a comparative study

Absorption Refrigeration Systems Based on Ammonia as Refrigerant Using Different Absorbents: Review and Applications

The interest in employing absorption refrigeration systems is usually related to electricity’s precariousness since these systems generally use thermal rejects for their activation. The application of these systems is closely linked to the concept of energy polygeneration, in which the energy demand to operate them is reduced, which represents their main advantage over the conventional vapor compression system. Currently, the solution pairs used in commercial absorption chillers are lithium bromide/water and ammonia/water. The latter pair has been used in air conditioning and industrial processes due to the ammonia operation’s low temperature. Few review papers on absorption chillers have been published, discussing the use of solar energy as the input source of the systems, the evolution of the absorption refrigeration cycles over the last decades, and promising alternatives to increase the performance of absorption refrigeration systems. There is a lack of consistent studies about designing requirements for absorption chillers, so an updated review covering recent advances and suggested solutions to improve the use and operation of those absorption refrigeration systems using different working fluids is relevant. Hence, this presents a review of the state-of-the-art of ammonia/absorbent based absorption refrigeration systems, considering the most relevant studies, describing the development of this equipment over the years. The most relevant studies in the open literature were collected to describe this equipment’s development over the years, including thermodynamic properties, commercial manufacturers, experimental and numerical studies, and the prototypes designed and tested in this area. The manuscript focuses on reviewing studies in absorption refrigeration systems that use ammonia and absorbents, such as water, lithium nitrate, and lithium nitrate plus water. As a horizon to the future, the uses of absorption systems should be rising due to the increasing values of the electricity, and the environmental impact of the synthetic refrigerant fluids used in mechanical refrigeration equipment. In this context, the idea for a new configuration absorption chiller is to be more efficient, pollutant free to the environment, activated by a heat substantiable source, such as solar, with low cost and compactness structure to attend the thermal needs (comfort thermal) for residences, private and public buildings, and even the industrial and health building sector (thermal processes). To conclude, future recommendations are presented to deal with the improvement of the refrigeration absorption chiller by using solar energy, alternative fluids, multiple-effects, and advanced and hybrid configurations to reach the best absorption chiller to attend to the thermal needs of the residential and industrial sector around the world.

Visual experimental research on the effect of nozzle orifice structure on R124–DMAC absorption process in a vertical bubble tube

A visual experimental platform for R124–DMAC bubble absorption in a vertical tube absorber was designed and built for this research. The bubble behaviors, flow pattern characteristics and distributions are observed and the bubble absorption heights (BAHs) were measured when the two kinds of different structure nozzles (single-orifice or multi-orifice nozzle) were applied in the absorber. The results showed that the BAH will heighten with increases of vapor flow rate and nozzle flow area. Based on visual experimental observations, the BAH or bubble absorption performance was significantly affected by the velocity of vapor from the nozzle rather than by the nozzle structure. The proportion of slug flow in BAH or the BAH can be decreased by using a multi-orifice nozzle in the absorber under the same flow area condition. However, the flow resistance of the vapor through the nozzle will increase, which has a negative action on the performance of absorption refrigeration systems. So, using multi-orifice nozzle does not improve the absorption performance of the bubble absorber under the same nozzle flow resistance condition.

Influence of two internal irreversibilities on the new thermo-ecological criterion for three-heat-source refrigerators

Irreversibility is a phenomenon that affects much the performance of absorption refrigeration systems. Internal irreversibility is produced by the dissipation of the working fluid. This paper studies and analyzes the effect of two internal irreversibilities parameters (the internal irreversibility parameter for generator–absorber assembly and the internal irreversibility parameter for condenser–evaporator assembly) on the optimal ecological performances of an irreversible three-heat-source absorption refrigerator based on the ECOP criterion. The results obtained show that the internal irreversibility parameter for condenser–evaporator assembly affects more the ecological performance of the system than the internal irreversibility parameter for generator–absorber assembly. This is of importance to the optimal design and performance improvement of absorption refrigeration cycles.

Thermal conductivity measurement of oil in Water (O/W) nanoemulsion and oil in H 2O/LiBr (O/S) binary nanoemulsion for absorption application

Binary nanoemulsions, oil-droplet suspensions in binary solution (H 2O/LiBr), are developed to enhance the heat and mass transfer performance of absorption refrigeration systems. In this study, a novel four-step method is used to prepare the stable oil-in-binary solution (O/S) emulsion. To stabilize the nanoemulsions in a strong electrolyte, four different polymers are used as a steric stabilizer. The droplet size and the thermal conductivity of binary nanoemulsions are measured by the dynamic light scattering method and the transient hot-wire method, respectively. It is found that the measured thermal conductivities of the oil in water (O/W) nanoemulsion and binary nanoemulsion (O/S) with a stabilizer enhance up to 6.4 and 3.6%, respectively compared with the Maxwell’s model. It is also found that GA (Gum Arabic) gives the highest thermal conductivity enhancement. It is finally confirmed that the initial stable condition of the O/S nanoemulsion can be recovered by the re-dispersion in actual absorption systems.

Thermal conductivity enhancement of binary nanoemulsion (O/S) for absorption application

Binary nanoemulsions, oil-droplet suspensions in binary solution (H2O/LiBr), are developed to enhance the heat and mass transfer performance of absorption refrigeration systems. In this study, a novel four-step method is proposed to prepare the stable oil-in-binary solution (O/S) emulsion. To stabilize the nanoemulsions in a strong electrolyte, a polymer (Gum Arabic) is used as a steric stabilizer. The droplet size and the thermal conductivity of binary nanoemulsions are measured by the dynamic light scattering method and the transient hot-wire method, respectively. It is concluded that the ratio of 2:1 (oil:surfactant) is the best condition to obtain the distribution stability. It is also found that the measured thermal conductivity of the binary nanoemulsion with a stabilizer enhances up to 3.6% compared with the estimated one from the Maxwell’s model. It is finally proposed that the thermal conductivity of the binary nanoemulsion could be enhanced by adding nano-sized droplets of n-decane oil, which has a lower thermal conductivity than that of the base fluid.

Theoretical study on the effect of operating conditions on performance of absorption refrigeration system

In this study, a detailed thermodynamic analysis of the water/lithium bromide absorption refrigeration cycle is performed. The influences of operating temperature and effectiveness of heat exchanger on the thermal loads of components, coefficients of performance (COP c , COP) and efficiency ratio ( η ) are investigated. It is concluded that the COP c and COP values increase with increasing generator and evaporator temperatures but decrease with increasing condenser and absorber temperatures. The η value varies with these temperatures. Also, the effects of solution and refrigerant heat exchangers on the performance, efficiency ratio of the system and fluid temperatures are compared. As a result, it is found that the solution heat exchanger (SHE) has more effect on the investigated parameters than the refrigerant heat exchanger (RHE). While the SHE increases the COP value up to a maximum 44%, the RHE has an effect of only 2.8%.

Effect of heat exchangers on performance of absorption refrigeration systems

Effect of heat exchangers on performance of absorption refrigeration systems

Effect of heat exchangers on performance of absorption refrigeration systems

In this study, the effect of heat exchangers on the system performance in an aqua–ammonia absorption refrigeration system has been investigated. For this purpose, the thermodynamic performance of the system is analysed, and the irreversibilities in the thermal processes have been determined for three different cases. These cases are: both of the heat exchangers are included in the system, only the refrigerant heat exchanger is included in the system and only the mixture heat exchanger is included in the system. It is assumed that the ammonia concentration at the rectifier outlet is independent of the other parameters, constant and equal to 0.999. The coefficient of performance, exergetic coefficient of performance, circulation ratio ( f) and non-dimensional exergy loss of each component of the system are calculated separately. After these calculations, some graphics indicating the change of the variables with the system parameters have been plotted.