Traditional Refrigeration Systems Research Articles

Theoretical Study of an Intermittent Water-Ammonia Absorption Solar System for Small Power Ice Production

This article is dedicated to the design, calculation and dimensioning of a small powered refrigeration system (132W) which produces ice bars (freezing) using solar thermal power, and resorts to an intermittent cycle absorption circuit with a water-ammonia mixture (H2O-NH3). The aim of this equipment is to minimize problems faced in places where there is no electric network to supply traditional refrigeration systems which preserve perishable products produced or stocked there, as well as drugs (vaccines), namely for specific regions of developing countries. The system developed can be divided into two parts. The intermittent cycle absorption refrigeration system uses a binary water-ammonia solution (H2O-NH3), where water is the absorber and the ammonia is the coolant and the thermal solar system. This is made up of CPC flat plate thermal collectors or vacuum tubes in which solar energy heats the water that circulates in the primary circuit. In the absorption circulation system, circulation occurs in a natural way due to the fluids affinity, and the temperature and pressure internal variations. This article shows the assumptions underlying the conception, calculation and dimensioning of the system’s construction.

EvaKuula saves Ugandan smallholder farmers’ evening milk

Smallholder dairy farmers in rural settings of sub-Saharan Africa cannot get their evening milk to markets because of several reasons. They do not have access to grid electricity to power traditional refrigeration systems that preserve their milk for market the next day. They are not able to transport at night due to safety concerns and poor road conditions, especially in the peak production rainy season, marked by high abundance of fodder. A solution involving the combination of thermization (58–63 °C for 30 s) and low-cost evaporative cooling has been shown to be effective and has been successfully tested in the hands of 30 target users in Wakiso, Kiboga, and Rakai districts of Uganda. All cooled evening milk by these farmers has successfully entered the cold chain, after assessment with the Resazurin assay, commonly used for evaluating freshness by collection centers or buyers. Based on the cooling system (EvaKuula) fabrication costs and daily evening milk sales by the early adopters, a payback period of approximately 20 months is needed for farmers to completely own the EvaKuula, in a rent-to-own business model. Work is in progress to further scale-up the EvaKuula adoption in the region.

Process Synthesis of Mixed Refrigerant System for Ethylene Plants

The refrigeration system is one of the most important and critical utility systems in the chemical and petrochemical industries. The traditional cascade refrigeration system (CRS) has been used for decades in ethylene plants. However, the mixed refrigerant system (MRS) with higher energy efficiency and less capital expenses than CRS has not widely been applied in ethylene plants. In this paper, a general methodology has been proposed for the synthesis of a tertiary refrigerant of MRS containing a mixture of methane, ethylene and propylene that can satisfy all the cooling/heating refrigeration that the traditional ethylene–propylene CRS serves in an ethylene plant. The exergy-temperature chart combined with the exergy analysis is presented to analyze comprehensively the thermodynamic nature of both CRS and MRS. Furthermore, the comparison of economic performances of these two different systems is also conducted. The efficacy of the developed MRS methodology has been demonstrated by a case study, where the ...

COP Optimization of a R134a Cross Vane Expander Compressor Refrigeration System

Cross Vane Expander Compressor (CVEC) is a newly invented expander-compressor combined unit, where it is introduced to replace the compressor and the expansion valve in traditional refrigeration system. The mathematical model of CVEC has been developed to examine its performance and it was found that the energy consumption of a conventional refrigeration system was reduced by as much as 18%. It is believed that this result can be further improved by optimizing the device. In this paper, the coefficient of performance (COP) of CVEC has been optimized under predetermined operational conditions. Several main design parameters of CVEC were selected to be the variables and the optimization was done with theoretical model in a simulation program. The theoretical model consists of geometrical model, dynamic model, heat transfer model and valve dynamics model. Complex optimization method, which is a constrained, direct search and multi-variables method, was used in the study. As a result, the optimization study suggested that with an appropriate combination of design parameters, a large COP improvement in CVEC R134a refrigeration system is possible. With a reduction of 20% in the shaft radius and 17% in inner cylinder radius, and the increase of around 16% in ports diameter, an improvement of 58% in COP can be achieved.

English

Cross vane expander compressor (CVEC) is a newly invented expander-compressor combined unit, where it is introduced to replace the compressor and the expansion valve in traditional refrigeration system. The mathematical model of CVEC has been developed to examine its performance and it was found that the energy consumption of a conventional refrigeration system was reduced by as much as 18%. It is believed that this result can be further improved by optimizing the device. In this paper, the coefficient of performance (COP) of CVEC has been optimized under predetermined operational conditions. Several main design parameters of CVEC were selected to be the variables and the optimization was done with theoretical model in a simulation program. The theoretical model consists of geometrical model, dynamic model, heat transfer model and valve dynamics model. Complex optimization method, which is a constrained, direct search and multi-variables method, was used in the study. As a result, the optimization study suggested that with an appropriate combination of design parameters, a large COP improvement in CVEC R134a refrigeration system is possible. With a reduction of 20% in the shaft radius and 17% in inner cylinder radius, and the increase of around 16% in ports diameter, an improvement of 58% in COP can be achieved. Key words: Coefficient of performance (COP), cross vane expander-compressor, simulation, optimization.

Investigation on air flow patterns of evaporative cooling and dehumidification process for a hybrid refrigeration system

In this paper, two different air flow patterns (close-pattern and open-pattern) are studied to achieve the optimum configurations of a hybrid refrigeration system, in which the refrigerant is subcooled by evaporative cooling of dry air dehumidified by the liquid desiccant. With different ambient air ratios (Ramb), full return air (Ramb = 0) is used in the close-pattern; full ambient air (Ramb = 1) and mix air (0 < Ramb < 1) are chosen in the open-pattern respectively. Comparisons of the close-pattern and open-pattern are made under typical climate condition and extremely humid climate condition. Both of the close-pattern and open-pattern (Ramb = 1) show much higher COP than the traditional refrigeration system, with the maximum COP improvement 12.3% and 9.8%, respectively. Under typical climate condition, the open-pattern (Ramb = 0.3) is suggested, the regenerator size has little influence on the system performance and the optimum mass flow ratio of ambient air to solution (ṁamb/ṁs) is between 0.5 and 2 in the regenerator; under extremely humid climate condition, the close-pattern is proposed, the optimum ṁamb/ṁs is 0.4 and larger regenerator size is suggested. In addition, the latent and sensible heat capacities in the indirect evaporative cooler are illustrated. These findings will be beneficial for the system design and optimization.

Thermoplastic filled with magnetocaloric powder

Abstract Magnetic refrigeration is an innovative and promising alternative to traditional refrigeration systems. This technology does not require refrigeration gases and offers a high thermodynamic efficiency, reducing the global environmental impact associated with the process. However, the production of magnetocaloric components used as regenerators in magnetic refrigeration systems is a significant challenge. This work consists of developing an innovative process to obtain magnetocaloric components by powder injection or extrusion moulding. A component containing up to 91.5 wt.% magnetocaloric powder was obtained using a gas atomised magnetocaloric powder La–Fe–Si alloy patented by Erasteel. The powder is first mixed with a thermoplastic polymer to obtain a “ready to shape” feedstock. Then, the feedstock is either injected or extruded to obtain the magnetocaloric component. Characterisations of the thermo-physical and mechanical properties are carried out during all stages of processing, from pure powder to injected parts. A study on the modification of the Curie temperature as a result of dehydrogenation was performed during each processing stages. Good processability was demonstrated for the highly loaded feedstock and conservation of the magnetocaloric properties during the process. Finally, the process does not induce any mass loss and allows the production of stable pieces containing a giant magnetocaloric effect.

Process synthesis for cascade refrigeration system based on exergy analysis

Refrigeration system holds an important role in chemical/petrochemical processes. The traditional cascade refrigeration system (CRS) used in ethylene plants contains multiple refrigerants working at multiple temperature/pressure levels. In this study, a general methodology is developed for the optimal process synthesis of a CRS based on exergy analysis. This procedure involves four stages: (1) refrigeration system exergetic analysis; (2) optimization model development for simultaneous synthesis of refrigeration system and heat exchanger network (HEN); (3) HEN configuration; and (4) final solution validation. The exergy–temperature chart is used to comprehensively analyze a CRS. A mathematical model is presented to minimize total compressor shaft work of the HEN‐considered CRS, where multiple recycling loops satisfying all cooling/heating demands are simultaneously addressed. The optimal solution is examined by rigorous simulations to verify its feasibility and consistency. The efficacy of the developed methodology is demonstrated by a case study of a propylene CRS in an ethylene plant. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2471–2488, 2015

Experimental Study of Single Bed Silica Gel-water Adsorption Chiller

Adsorption refrigeration system are of significance to meet the need for cooling requirements such as ice making , food preservation and also it can works on solar energy or waste heat. Adsorption refrigeration system has various advantages over traditional refrigeration system. This covers the performance of commonly used adsorption pair. A model is constructed for the experimental investigation of single bed silica gel/water adsorption chiller. This paper includes the working principles of the adsorption system and includes sorption refrigeration cycle, it also mentioned the properties of the adsorption pairs.

Experimental investigation of the performance of a single-stage auto-cascade refrigerator

Auto-refrigerating cascade (ARC) systems possess many advantages comparing with traditional cascade refrigeration systems. This work proposed a novel ternary mixture, R600a/R23/R14, for ARC systems for 190 K applications. The performance of the ternary mixture and the influences of compositional ratio and bypass scheme were assessed in a modified domestic cooler. The results demonstrated the feasibility of the proposed R600a/R23/R14 ternary mixture as an environmental benign alternative for ARC systems. The performance varied little within a certain composition range and a mass ratio of 35/30/35 for R600a/R23/R14 mixture was recommended. It also showed that the two bypass schemes, which can regulate more effectively the refrigerant compositions, were better than the conventional hot-gas bypass approach. The variation of the evaporator temperature suggested the presence of local dryout at high heat loads (i.e., larger than the design value), which should be carefully prevented.

Application on Evaporative Cool Technique in Garment Workshop in Hot-humid Area

The paper researches the application situation of evaporating cooling technique in clothing workshop located at the hyperthermia and humidity condition through analyzing a clothes factory with a direct evaporative cooling air condition in Xiamen. The temperature, humidity and comfort of clothing workshop are researched while the outdoor temperature is 35°C. It is also compared the initial investment, energy consumption and power usage with traditional mechanical refrigeration system. The result shows that the direct evaporative cooling system improves the thermal environment of workshop more efficient than the traditional mechanical refrigeration system.

Application of Cold Water Cycle for Indoor Cooling System

A small indoor cooling system through cold water circulation is introduced in this paper. The system mainly includes cooling pool, cold water circulation equipment, indoor heat exchanger, temperature measurement equipment and induction controlling equipment. The indoor cooling is achieved by heat transfer between the natural underground water of lower temperature and indoor air of higher temperature, and it is different from the traditional compression refrigeration system in which a great amount of electric energy is consumed while the refrigerant is compressed. Compared with the ordinary air conditioning system, this system has obvious advantages on economy, application potential and energy conservation in rural developing areas.

Preliminary study of a novel R718 refrigeration cycle with single stage centrifugal compressor and two-phase ejector

The paper describes the investigations of a novel R718 refrigeration cycle with single stage centrifugal compressor and two-phase ejector as a second stage compression device. The limitations of the R718 centrifugal stage pressure ratio, connected with small molecular mass of the water and high isentropic exponent, result on high impeller peripheral speed, high Mach number and high discharge temperature. Reynolds number is low and dimensions of the compressor stage are large. The complex thermal and flow phenomena inside two-phase ejector flow field are investigated and performance characteristics are estimated. Although efficiency of the concept of compression with hydraulic pump and two-phase ejectors is lower, the integration of two-phase ejectors in the R718 centrifugal unit results in low cost high capacity refrigeration system with high energy efficiency, competitive with traditional refrigeration systems by environmental, technical and economical reasons.

Some design features of CO2 two-rolling piston expander

Improving the efficiency of trans-critical CO2 heat pump systems becomes one of the investigative focuses of the development of refrigeration technologies. The use of expander can improve the efficiency of trans-critical CO2 cycles, and make it near to that of traditional refrigeration systems. On the basis of the previously developed single-cylinder rolling piston expander, a new two-rolling piston expander is designed and produced. The design process and its working principles are introduced, and a trans-critical CO2 water–water heat pump system is used to test its efficiency. Results of the tests show that under working conditions the rotating speed of the expander ranges from 850 to 1000 rpm, and its efficiency ranges from 28% to 33%. Analysis of the problems that appeared in the expander is made to further improve its efficiency.

Numerical analysis of three direct cooling systems using underground energy storage: A case study of Jinghai County, Tianjin, China

Three kinds of ground source energy system used as heat sink directly for cooling the buildings in summer are presented, which are underground water system, ground heat exchange system and underground sink system, respectively. Correspondingly, three numerical models are established. Based on a rural housing in Jinghai County, Tianjin, the simulated operating results of three systems are analyzed and compared. The applied size parameters for direct cooling system (DCS) were coincident with traditional compression refrigeration system. The results indicate that the outlet water temperature of the double-wells circulating system remains stable and the system operation effect is satisfied. Hence, it is recommended as a prior way for DCS to give long-term, safe and stable operation. However, the outlet water temperature of the U-shaped tube system easily exceeds 23°C after 10 days of running, which is the maximum temperature limit for DCS due to heat transfer effect. This is not recommended. The feasibility of using an underground sink for DCS depends on reasonable analysis of the adaptability between the building cooling load and the cooling capability of the sink. Because of economical and ecological reasons, it is still recommended as an auxiliary cooling system.

EFECTO DEL ALMACENAMIENTO EN ATMÓSFERA CONTROLADA SOBRE LA CALIDAD POSCOSECHA Y NUTRICIONAL DEL TOMATE

The objective of the present work was to determine the effect of Controlled Atmosphere (CA) storage on the postharvest quality and nutritional content of tomato (Solanum lycopersicum L.) ‘Imperial’. Mature green fruit were stored at 12 °C under refrigeration (ambient air, AIR) or CA (4 kPa O2 + 96 kPa N2) at 12 °C for up to 21 days before being transferred to air at 23 °C for up to 12 days. Three fruits were taken per treatment after zero, four, eight and 12 days of ripening at 23 °C to evaluate external color, firmness, soluble solids content (SSC), CO2 and ethylene production rates, and ascorbic acid, β-carotene and lycopene content. CA storage delayed the loss of firmness and ascorbic acid degradation. It also decreased CO2 and ethylene production rate, β-carotene and lycopene synthesis, delaying red color development and ripening. The results indicate that storage of tomato fruit under CA extends the shelf life and the marketing period compared with traditional refrigeration systems.

A performance comparison of vapour-compression refrigeration system using various alternative refrigerants

A theoretical performance study on a traditional vapour-compression refrigeration system with refrigerant mixtures based on HFC134a, HFC152a, HFC32, HC290, HC1270, HC600, and HC600a was done for various ratios and their results are compared with CFC12, CFC22, and HFC134a as possible alternative replacements. In spite of the HC refrigerants' highly flammable characteristics, they are used in many applications, with attention being paid to the safety of the leakage from the system, as other refrigerants in recent years are not related with any effect on the depletion of the ozone layer and increase in global warming. Theoretical results showed that all of the alternative refrigerants investigated in the analysis have a slightly lower performance coefficient (COP) than CFC12, CFC22, and HFC134a for the condensation temperature of 50 °C and evaporating temperatures ranging between − 30 °C and 10 °C. Refrigerant blends of HC290/HC600a (40/60 by wt.%) instead of CFC12 and HC290/HC1270 (20/80 by wt.%) instead of CFC22 are found to be replacement refrigerants among other alternatives in this paper as a result of the analysis. The effects of the main parameters of performance analysis such as refrigerant type, degree of subcooling, and superheating on the refrigerating effect, coefficient of performance and volumetric refrigeration capacity are also investigated for various evaporating temperatures.

Experimental research on a new solar pump-free lithium bromide absorption refrigeration system with a second generator

This paper is concerned with experimental research on a new solar pump-free lithium bromide absorption refrigeration system with a second generator. By using the second generator together with a lunate thermosiphon elevation tube, the required minimum driving temperature of the heat source is only 68 °C compared to above 100 °C in traditional absorption refrigeration systems. Based on the horizontal-tube falling-film method, the performance of the absorber can be enhanced by the second generator due to an increase in the differential concentration of the solution between the inlet and the outlet of the absorber and an increase in the temperature difference between the inlet and the outlet of the cooling water in the absorber. The yield of condensate with the second generator open is increased by 68% compared to that with the second generator closed. The performance of the evaporator is significantly improved due to the increase in temperature drop of the chilled water and the decrease in the outlet temperature of the chilled water. This leads to an improvement of the performance of the overall refrigeration system. The maximum coefficient of performance (COP) approaches 0.787.

Experimental study on an absorption refrigeration system at low temperatures

The heat-driven auto-cascade absorption refrigeration cycle can be used at low temperatures, and a novel auto-cascade absorption refrigeration system is proposed to gain better performances with a refrigerating temperature as low as −50 °C. The new system uses a mixture of R23 + R32 + R134a/DMF as its working pair and its characteristic study is carried out under different operational conditions. It has successfully obtained a refrigerating temperature of −47.2 °C under the generating temperature of 163 °C. This refrigerating temperature is far lower than that of a traditional absorption refrigeration system with the same working pair, and it is also lower than that of an auto-cascade absorption refrigeration system using R32 + R134a/DMF as its working pair. From the experimental results, it is clearly seen that this new system shows a rapider lowering rate of refrigerating temperature than that of an auto-cascade absorption refrigeration system using R23 + R134a/DMF as its working pair. The results of experimental analyses imply that this new absorption refrigeration system can be used in the deep-freezing as low as −50 °C by utilizing low-potential thermal power. Its potential of industrial application might be greater than that of an auto-cascade absorption refrigeration system using R23 + R134a/DMF as its working pair in the future.

Heat transfer measurements on ammonia forced convection boiling in vertical tubes

Abstract This paper tackles a subject of present interest. It contributes to the promotion of small capacity refrigerating systems working with ammonia – an ecologically and highly efficient refrigerant – as an alternative to the traditional commercial refrigeration, heat pumps and air-conditioning systems working with CFC refrigerants. Since a literature survey showed that available theoretical methods have not been sufficiently experimentally validated, the authors focused on constructing a test facility, namely a test loop, assisted by a data acquisition system. Experiments have been run in order to develop a data bank for the heat transfer of ammonia inside an electrically heated tube. The local heat transfer coefficient for boiling ammonia was measured in 10 different locations along the tube and the flowing regime was visualized in three locations, using segments of glass tube. Sequences of computerized collected data (from pressure transducers, thermocouples, platinum RTD temperature sensors, and an ultrasound flowmeter) were treated with a digital filtration. A comparison between theoretical and experimental results indicated that the Steiner–Taborek and Gungor–Winterton correlations make the best predictions for the local heat transfer coefficient of boiling ammonia. In addition, the authors experimentally determined the fluid coefficient to be used in Kandlikar's correlation in order to extend its applicability to ammonia boiling. It is shown the influence that the main parameters have on the boiling process, over a range of the input parameters. Both the developing of the two-phase flow mechanisms and the heat transfer coefficients characterizing ammonia boiling inside tubes, are strongly influenced by those parameters.