Diffusion Absorption Refrigeration Research Articles

Dynamic testing and modeling of a diffusion absorption refrigeration system

This paper presents experimental investigations and modeling in dynamic or transient mode of a commercial diffusion-absorption refrigerator powered by an electric heater. The instantaneous cooling capacity is experimentally determined for different electric heater inputs. A first order transfer function with delay is found to be an adequate model of the refrigerator behavior for each heat input. The fitting quality of the model ranges between 93% and 97%. The three parameters of the model are expressed in a further step as functions of energy input to the machine in order to construct a generalized model for the machine. The steady state performances of the refrigerator are quite good predicted, with deviations in cooling capacity not exceeding 8%. The proposed generalized model could be very useful for the prediction of the transient behavior of the commercial diffusion-absorption refrigerator.

The influence of the evaporator inlet conditions on the performance of a diffusion absorption refrigeration cycle

The purity of the condensate at the evaporator inlet on the performance of a diffusion absorption refrigeration cycle is examined under three configurations of sub-cooling. Three sub-cooling configurations were studied numerically: the no sub-cooling (nSC) configuration where the condensate flows directly to the evaporator inlet without sub-cooling, the partial sub-cooling (pSC) configuration where the condensate is sub-cooled by the refrigerant heat exchanger before the evaporator inlet and the full sub-cooling (fSC) configuration where the condensate is sub-cooled both by the refrigerant heat exchanger and the evaporator. It was found that for the same heat input the pSC configuration shows the highest cooling effect at the evaporator and therefore the highest COP. The influence of the evaporator inlet condition on the triple tube gas heat exchanger was also studied. It was found that the temperature at the evaporator inlet has to be as low as possible. Finally, the influence of the purity of the vapor phase at the rectifier outlet on the cycle performance was also studied. It was found that less effort has to be invested in the purification of the hot refrigerant vapor in the rectifier.

Low-source-temperature diffusion absorption refrigeration. Part II: Experiments and model assessment

The diffusion absorption refrigeration cycle can enable passive fully thermally activated refrigeration for off-grid applications. In the accompanying paper, a new system configuration was proposed that employs alternate working fluids (NH3–NaSCN–He), a coupling-fluid heated bubble-pump generator, and an enhanced absorber. Detailed component and system level models were formulated for this design. In Part II of this work, the subject of this paper, these results are applied to implement a complete low-source-temperature (110–130 °C) passively cooled diffusion absorption refrigeration (DAR) system. Cooling was achieved at temperature ranges suitable for refrigeration (Tevap = 6 → 3 °C, COP ~ 0.06) and air-conditioning (12 → 8 °C, COP ~ 0.14). Device performance was also assessed at elevated ambient temperatures, reduced ambient air velocities, and varying system pressures. Results from this investigation agreed well with the predictions of the models developed in Part I.

Low-source-temperature diffusion absorption refrigeration. Part I: Modeling and cycle analysis

The diffusion absorption refrigeration (DAR) cycle offers a potentially fully thermally activated cooling technology. However, most implementations operate with high source temperatures, forced liquid cooling, or elevated evaporator temperatures (≳5°C). Additionally, few component design resources are available in the literature. In Part I of this investigation, a fully passive DAR design is proposed. Reduced temperature operation is enabled with alternate working fluids (NH3-NaSCN-He), a distributed heated bubble-pump generator (BPG), and an enhanced absorber. Detailed models are formulated for the BPG, condenser, evaporator, absorber, and gas circulation loop. These are integrated to yield an overall system model. System behavior is evaluated over a range of operating conditions. With the necessary and reasonably expected component performances, refrigeration COPs of 0.11–0.26 can be achieved at design conditions (Tamb = 24 °C) with low source temperatures (110–130 °C) and passive air cooling. In the accompanying paper (Part II), this refrigeration system is experimentally demonstrated, and the proposed models are evaluated.

Convective heat transfer characteristics of LiNO3–NH3 solution with low Re in a chevron plate solution cooler

What presented here is about the experimental research on the convective heat transfer characteristics of a plate-type solution cooler in a new type diffusion absorption refrigerator (DAR) in which an adiabatic spray absorber is adopted. Based on the parameters measured at stable operating status on the condition of low Reynolds number (Re), analysis on the overall heat transfer coefficient and convective heat transfer coefficient were carried out. The results show that the overall heat transfer coefficient and convective heat transfer coefficient of LiNO3–NH3 solution of the chevron plate solution cooler were in the ranges of 507.9–982.2 W/m2 °C and 634.6–1642.3 W/m2 °C, respectively. Finally, the correlation equation of the convective heat transfer coefficient of LiNO3–NH3 solution with low Re in the chevron plate solution cooler is investigated. Analysis shows that the obtained correlation equation has acceptable accuracy.

Modelado del evaporador de un sistema difusión-absorción: análisis energético y efecto sobre el diseño de un frigobar

En este artículo se presenta como aportación, el desarrollo del modelado de un evaporador que forma parte de un sistema de refrigeración difusión-absorción de pequeña capacidad volumétrica (frigobar). El modelo es basado en fundamentos físicos y correlaciones empíricas, además, se involucran parámetros geométricos de interés como la longitud y el diámetro del evaporador. Se realiza un análisis experimental para obtener los comportamientos térmicos del evaporador bajo tres posiciones del termostato; a través de estos resultados se lleva a cabo la validación del modelo, arrojando errores marginales por debajo del 10%. En base a la buena confiabilidad mostrada por el modelo, este se aplica para la simulación energética del sistema global. Entre los resultados relevantes se pueden conseguir reducciones en la longitud del evaporador sin alterar la capacidad frigorífica y el desempeño energético del sistema experimental, representando esto una oportunidad para los fabricantes en extender su análisis a los diferentes equipos que forman un sistema de difusión-absorción en la búsqueda de mejoras energéticas y condiciones de diseño óptimas.

Investigation the effects of different heat inputs supplied to the generator on the energy performance in diffusion absorption refrigeration systems

This study aims to investigate experimentally the effects of three different heat inputs supplied to generator on the energy performance of the diffusion absorption refrigeration system. To achieve this goal, a conventional diffusion absorption refrigeration system, in which electrical resistance as heat input is employed, is taken a model, which is experimentally scrutinized under different heat inputs, 62, 80 and 115 W, but at the same ambient temperatures and the same filling rate of three-component working fluid. In the analyses, the energy losses rejected to ambient from rectifier, condenser, absorber, solution heat exchanger as well as other components such as solution tank and pipes, the energy gain by evaporator and also energy performance is investigated. While the highest energy performance is calculated for DAR-62 W system as 0.36, the lowest energy performance is calculated for DAR-115 W system as 0.30.

Performance investigation of a diffusion absorption refrigeration system using nano-size alumina particles in the refrigerant

In this study, the effects of the passive heat transfer improvement method of coupling ammonia/water with nano-size alumina (Al2O3) particles were examined in regard to the heat performance of a diffusion absorption refrigeration system (DARS). Adding nanoparticles into the fluid leads to significant improvement in heat transfer since the surface area and heat capacity of the fluid increase due to the high surface area of the nanoparticles. In this study, cooling/absorption fluid mixtures with Al2O3 nanoparticles and their impact on system energy and exergy performance were assessed. The results of experiments indicated that the system with nanoparticles provided better absorption of heat from the generator and faster evaporation of the cooler from the cooling/absorption fluid. Addition of alumina nanoparticles to DARS improved the system's coefficient of performance (COP) and exergetic coefficient of performance (ECOP) by 55.56% and 22.8%, respectively, and reduced the circulation ratio (f) by 51.72%.

Investigation of Flow and Heat Transfer Characteristics in Two-Phase Flow Through Evaporator of Diffusion Absorption Refrigerator (DAR)

The application of the cooling system becomes very important for a comfortable and almost all public buildings in Indonesia using the cooling system. The cooling system is commonly requires considerable electrical power to drive the compressor used for the vapor compression cooling system in operation. Different with the diffusion absorption refrigeration system, all cycles in the system are occurred by natural circulation where the refrigerant is pressurized (partial) lower in the evaporator is obtained with the aid of an inert gas that can be either hydrogen or helium, which is mixed with the refrigerant gas, but not also react. The study was conducted by flowing the refrigerant at the evaporator copper tube passes that are part of a diffusion absorption refrigeration machine. Long dimension of passes evaporator is 2.38875 m. The method used in this study is the experimental and numerical approach, which is using Multiphase Flow Fluent CFD 6.3. simulation to validate the experimental observations of flow.Through this study, the fenonena happened to be validated by experimental observations numerically. Also can be seen flow characteristics of refrigerant flowing along the evaporator and heat transfer phenomena that occur.

Development of binary nanoemulsion to apply for diffusion absorption refrigerator as a new refrigerant

Binary nanoemulsion is defined as the nanoemulsion of which base fluid is a binary mixture such as NH3/H2O solution. The objectives of this paper are to estimate the effect of nano-sized oil droplets on the performance of a diffusion absorption refrigerator (DAR) and to find the relationship between the dispersion stability and COP (coefficient of performance) enhancement of the DAR system. The concentration and ratio of oil and surfactants are considered as the key parameters. N-decane oil is added into NH3/H2O solution to make the binary nanoemulsions, and C12E4 (Polyoxyethylene lauryl ether) and TWEEN20 (Polyoxyethylen sorbitan monolaurate, C58H114O26) are used as the surfactants for stable dispersion. The dispersion stability of binary nanoemulsions is evaluated by the droplet size measurement and Tyndall effect analysis. It is found that the binary nanoemulsion fluid increases the COP of the DAR system as high as 15% compared with that of the base fluid refrigerator.

MODELING OF BOILING TWO-PHASE FLOW IN THE BUBBLE PUMP OF DIFFUSION-ABSORPTION REFRIGERATION CYCLES

ABSTRACT This work presents a numerical model developed to simulate steady-state refrigerant flow along a tube of a bubble pump at operating conditions of interest for diffusion-absorption refrigeration systems. The flow is considered one-dimensional, and non-metastable flow is neglected. The two-fluid model was employed to simulate the two-phase flow, considering the hydrodynamic nonequilibrium between the liquid and the vapor phases. Comparisons were made for void fraction versus vapor quality using the homogeneous model, the Rouhani and Axelsson drift model, and the Zivi annular model. The results show a great similarity among the values achieved in the present work and those calculated using the Rouhani and Axelsson and Zivi correlations. On the basis of the numerical simulations, a detailed description of the flow characteristics was obtained. The influence of the heat source on the flow characteristics was numerically examined.

Energetic analysis of a diffusion–absorption system: A bubble pump under geometrical and operational conditions effects

This paper presents an analytical model of the bubble pump in a commercial diffusion–absorption refrigerator. Moreover, the energetic analysis achieved is integrated with a heat transfer model and coupled to a thermodynamic model to evaluate the cooling capacity and the coefficient of performance of the refrigeration system, based on geometrical and operational parameters such as heat input, diameter ratio and bubble tube length as well as the ammonia fraction at the inlet of the bubble pump. The results show that the cooling capacity and COP are mainly influenced by geometrical parameters, such as diameter ratio and tube length of the bubble pump, and slightly influenced by the heat input supplied to the bubble pump. The strong concentration range, which is also considered in this work, is a parameter that does not affect the cooling capacity and COP. Moreover, the results reveal that the lowest cooling capacity and COP are obtained when the refrigerator operates at the manufacture design conditions. An increase in cooling capacity and COP of about 150% can be obtained when the diameter ratio is expanded up to 1.5 when comparing with the original configuration. It is expected that these results help researchers and manufacturers extend their analysis to increase the energy performance in diffusion–absorption refrigeration systems.

Effect of insulation on the energy and exergy performances in Diffusion Absorption Refrigeration (DAR) systems

In this study, the effect of insulation on the energy and exergy performances of DAR systems was investigated. A DAR system with the insulated generator-bubble pump (DAR1) was compared with a DAR system having the insulated generator-bubble pump, solution heat exchanger and partial-insulated rectifier (DAR2) experimentally and both components of the DAR1 and the DAR2 systems were insulated by rock wool. In the analyses, the energy losses rejected to ambient from rectifier and condenser, the energy gain (heat gain) by evaporator and also energy performance and exergy performance were calculated. While energy and exergy performances of DAR1 system were determined as 0.35 and 0.095, respectively, the performance values of DAR2 system were calculated as 0.44 and 0.115. As a consequence, the insulation of solution heat exchanger and the insulation of a part of rectifier in the DAR system increased the energy performance by 26% and the exergy performance by 21%.

Improving the thermal performance of diffusion absorption refrigeration system with alumina nanofluids: An experimental study

In this study, the effect of the passive heat transfer improvement method of ammonia/water couple with alumina (Al2O3) particles in nano-size were examined in diffusion absorption coolers regarding to the heat performance of the system. Adding nanoparticles into fluid leads to significant improvement in heat transfer since the surface area and heat capacity of the fluid increase due to nanoparticles. Therefore, in this study cooling/absorption fluid mixtures with Al2O3 nanoparticles and their impact on system performance were assessed. The results of experiments indicated that the system with nanoparticles provided better absorption of heat from the generator and faster evaporation of the cooler from the cooling/absorption fluid. The connection units of the heat transfer in the system were investigated considering the effect of fluids containing nanoparticles. It was observed that the operation time of the system was reduced due to shorter heat transfer periods. Consequently, it resulted in obtaining desired temperature faster.

Review of diffusion–absorption refrigeration technologies

A review of diffusion–absorption refrigeration technologies has been done in this work in order to promote their main characteristics in terms of the refrigeration process, their applications, work fluids, current trends and limitations, among others. Over 70 publications in the field were analyzed concluding that diffusion–absorption technology represents a complementary and viable alternative in the field of refrigeration technologies for small cooling capacity, due to an increase in the current demand of refrigeration and air-conditioning devices.

Energy and exergy analyses of the diffusion absorption refrigeration system

This paper describes the thermodynamic analyses of a DAR (diffusion absorption refrigeration) cycle. The experimental apparatus is set up to an ammonia–water DAR cycle with helium as the auxiliary inert gas. A thermodynamic model including mass, energy and exergy balance equations are presented for each component of the DAR cycle and this model is then validated by comparison with experimental data. In the thermodynamic analyses, energy and exergy losses for each component of the system are quantified and illustrated. The systems' energy and exergy losses and efficiencies are investigated. The highest energy and exergy losses occur in the solution heat exchanger. The highest energy losses in the experimental and theoretical analyses are found 25.7090 W and 25.4788 W respectively, whereas those losses as to exergy are calculated 13.7933 W and 13.9976 W. Although the values of energy efficiencies obtained from both the model and experimental studies are calculated as 0.1858, those values, in terms of exergy efficiencies are found 0.0260 and 0.0356.

Micro distributed energy system driven with preheated Croton megalocarpus oil – A performance and particulate emission study

As a carbon neutral biofuel, the cold pressed Croton megalocarpus oil (CMO) has the nature of easy production without any further chemical process, but suffers for its high viscosity and poor atomisation if being applied on the compression-ignition (CI) engine generator. A micro distributed energy system comprised of a modified 6.5kWe CI engine generator and an engine exhaust driven diffusion absorption refrigerator has been set up for domestic application, which applies both diesel and CMO. To minimise the negative impact of fuel properties of CMO, the temperature before injection has been elevated with the trace heater and the waste heat from the engine. The performance of the preheated CMO up to 90°C on the engine generator system reflects an improvement of the atomisation and combustion in the cylinder compared to the non-preheated CMO. The particulate emission test reveals the similarity of both the total number and the total weigh of the particulates emitted from the engine generator system running on diesel and CMO in 90°C.

An enhanced model for the design of Diffusion Absorption Refrigerators

A steady state description of the thermal pump driving the Diffusion Absorption Refrigerator was integrated in the model previously proposed by the same authors. The thermal pump allows the DAR cycle to be activated, moving the strong mixture and separating the refrigerant from the weak one. So, the design parameters play a primary role in the DAR cycle performance in terms of COP. The enhanced model results were validated on a prototype built coupling a domestic 750 W-magnetron on a small purposely modified commercial DAR to activate the thermal pump. A maximum mismatch of 2.32% in the weak mixture mass flow rate and lower than 5% in COP between the predicted and measured data were found.The microwaves activated thermal pump produced a distinct reduction in the starting transient time of the refrigerator and for this reason it can be proposed as a valid candidate to be used as a rapid cooler in small refrigeration applications.

Performance analysis of a diffusion absorption refrigeration cycle working with TFE–TEGDME mixture

The binary mixture of TFE–TEGDME has good thermo-physical properties and been investigated by many absorption chiller and heat pump researchers. However, few studies have been reported on the diffusion absorption refrigeration (DAR) system using TFE–TEGDME as the working fluid. The present article numerically investigates the potential of TFE–TEGDME used in the DAR system with two cooling mediums, viz. water (32°C) and air (35°C). It is found that with the absorber effectiveness of 0.8, the optimum generation temperature for the air-cooled TFE–TEGDME DAR system is around 170°C, and the corresponding coefficient of performance (COP) is up to 0.45. In comparison, the performance of the water-cooled system is better with a lower optimum generation temperature around 130°C and a higher COP reaching 0.56. Parametric studies are also conducted to analyze the effects of the cooling medium, generation temperature, evaporation temperature and absorber effectiveness on the system performance. Finally, the performance of the TFE–TEGDME and NH3–H2O DAR cycles is compared in terms of the COP and circulation ratio. Overall, it can be concluded that the TFE–TEGDME mixture is a good working fluid for the DAR cycle.

Research Progress of Diffusion Absorption Refrigeration Technology

Compared with the gas-compressed refrigeration system, the diffusion absorption refrigeration cycle has no moving part and the associated noise and vibration. It can be operated without any electric input and driven by various energy sources, has no the problem of the substitute of CFC, furthermore it has positive significance in energy conservation, off peak, environmental protection, and promoting the use of gas. So it has broad application prospects as a kind of absorption refrigeration mode. In the development of diffusion absorption refrigeration technology, the performance of diffusion absorption refrigeration system has been improved and enhanced continuously. The paper presents and discusses the recent research progress of diffusion absorption refrigeration which contains design of bubble pump, adjustment and optimization of operation parameters, utilization of low-grade thermal energy and selection of working medium. The research direction of diffusion absorption refrigeration in the future is suggested.