Conventional Vapor Compression Refrigeration Research Articles

Membrane distillation crystallization of ammonium nitrate solutions to enable sustainable cold storage: Electrical conductivity as an in-situ saturation indicator

A novel refrigeration cycle is proposed using crystallized ammonium nitrate as a thermochemical energy storage material that is recharged with membrane distillation. Cooling is provided when needed by the dissolution of ammonium nitrate in water, an endothermic process that absorbs heat from the surroundings. The dilute solution is then concentrated to recrystallize the ammonium nitrate using membrane distillation, a thermally driven separation process capable of operating at low temperatures and high solution concentrations. Unlike conventional vapor compression refrigeration systems, this process does not rely on refrigerants with high global warming potential and could potentially utilize low-grade heat as the primary energy input rather than electricity. Membrane distillation was found to be capable of crystallizing ammonium nitrate from water at temperatures between 50 and 70 °C. The membranes tested were found to be very resistant to damage by ammonium nitrate crystallization, and performance (water flux, thermal efficiency, and rejection) was maintained even after repeated exposure to crystallization. Additionally, conductivity was found to be a reliable and consistent indicator of concentration and showed potential for use in monitoring and control systems.

Caloric Solid-State Magnetocaloric Cooling: Physical Phenomenon, Thermodynamic Cycles and Materials

Magnetic refrigeration is a promising and ecologic technology, alternative to the conventional vapor-compression refrigeration by the employment of solid-state materials as refrigerants instead of the fluid-state ones, own of vapour compression refrigeration. This emerging technology bases its operation on the MagnetoCaloric Effect (MCE), which is a physical phenomenon, related to solid-state materials with magnetic properties. For materials displaying simple magnetic ordering (i.e. paramagnetic to ferromagnetic phase transformations) a rapid increase in magnetic field causes a temperature rise in the material; likewise, a rapid reduction in the field causes cooling. This variation in temperature is called adiabatic temperature change. In 1982 the Active Magnetic Regenerative refrigeration cycle, well known as AMR cycle was introduced. The innovative idea considers a magnetic Brayton cycle but the main innovation consists of introducing the AMR regenerator concept, i.e. the employment of the magnetic material itself both as refrigerant and as regenerator. A secondary fluid is used to transfer heat from the cold to the hot end of the regenerator. Substantially every section of the regenerator experiments its own AMR cycle, according to the proper working temperature. Through an AMR one can appreciate a larger temperature span among the ends of the regenerator.

Energy conservation in vapour compression refrigeration system using vapour injection technique

In modern days, the vapour compression refrigeration system is followed in almost all air-conditioning applications. Due to the high ambient temperature during extreme summer conditions, the commercial vapour compression refrigeration system made with cost competitiveness are not in a position to meet the required indoor conditions (27°C Dry Bulb Temperature and 19°C Wet Bulb Temperature) within a stipulated time. Hence a study on the performance of vapour compression refrigeration system is needed without compromising the required indoor conditions. This paper concentrates on the use of an innovative technique called vapour injection in the rotary compressor. The rotary compressor based air-conditioning system is considered in this study as it is used widely across the world, particularly in domestic applications. This vapour injection technique meets the required indoor conditions with significantly increased cooling capacity and coefficient of performance (COP) by lowering the condensing temperature and increasing sub-cooling. A 1.5 TR vapour compression refrigeration system equipped with a rotary compressor is taken for study along with a refrigerant R22. Around 90% of heating, ventilation and air-conditioning systems in India use R22 refrigerant which is permitted to be used up to year 2030. A conventional vapour compression refrigeration system is redesigned towards injecting additional low temperature refrigerant vapour back into the compressor just before the suction port. At standard test conditions, 11.87% to 12% of higher cooling capacity is achieved with 1% to 2.5% of less power consumption which resulted in 13.3% to 15% of higher COP.

Simulation of Hybrid Packed Desiccant Beds for Dehumidification and Drying

<div class="section abstract"><div class="htmlview paragraph">The conventional vapor compression refrigeration cycle based air dryers are used widely for the applications of required pressure dew point temperature up to +2~3°C. However, for the industrial and pneumatic applications, the required pressure dew points are as low as -10°C, -30°C or -50°C and also up to -75°C, which is achieved by the adsorption based packed bed desiccant dryers. This paper presents the results of numerical simulation of hybrid packed desiccant beds under coupled heat and mass transfer during the adsorption and desorption phases under wide operating conditions. The bed containing a homogenous mixture of multiple desiccant types along the vertical axial direction has been investigated. A CFD code has been developed using the finite volume method which models the heat conduction and mass diffusion for these hybrid beds. The numerical results of the present model are validated with experimental data from literature and show good agreement for exit air temperature and moisture content. The improvement in moisture removal capacity, relative moisture removal efficiency, and dew point temperature or pressure dew point for these hybrid desiccant beds are investigated.</div></div>

Numerical investigations of solar-assisted hybrid desiccant evaporative cooling system for hot and humid climate

This article presents numerical investigations of the solar-assisted hybrid desiccant evaporative cooling system integrated with standard air collectors for applications under the hot and humid climatic conditions of Kuwait city. The objective is to introduce the energy-efficient and carbon-free solar-assisted hybrid desiccant evaporative cooling system to alleviate the principal problems of electricity consumption and carbon emissions resulting from the use of the conventional vapor-compression cooling systems. In the normal building, during cooling load operation, the solar-assisted hybrid desiccant evaporative cooling system can cope with the cooling load particularly sensible by evaporative cooling and latent through desiccant dehumidification. The outcomes of this work indicate that solar-assisted hybrid desiccant evaporative cooling device integrated with air collectors is capable of providing average coefficient of performance of 0.85 and has the potential to provide cooling with energy saving when compared with conventional vapor-compression refrigeration systems. It was concluded that under the intense outdoor environmental conditions (ambient air at greater than 45°C and 60% relative humidity), the delivered supply air from the evaporative cooling was nearly at 27°C and 65% relative humidity. To solve this problem, the system was assisted with conventional cooling coil (evaporator of heat pump) to supply air at comfortable conditions in the conditioned space.

Supergiant Barocaloric Effects in Acetoxy Silicone Rubber over a Wide Temperature Range: Great Potential for Solid-state Cooling

Solid-state cooling based on caloric effects is considered a viable alternative to replace the conventional vapor-compression refrigeration systems. Regarding barocaloric materials, recent results show that elastomers are promising candidates for cooling applications around room-temperature. In the present paper, we report supergiant barocaloric effects observed in acetoxy silicone rubber - a very popular, low-cost and environmentally friendly elastomer. Huge values of adiabatic temperature change and reversible isothermal entropy change were obtained upon moderate applied pressures and relatively low strains. These huge barocaloric changes are associated both to the polymer chains rearrangements induced by confined compression and to the first-order structural transition. The results are comparable to the best barocaloric materials reported so far, opening encouraging prospects for the application of elastomers in near future solid-state cooling devices.

Modeling and energy analysis of a linear concentrating photovoltaic system cooled by two-phase mechanical pumped loop system

Generally, the majority of the linear concentrating photovoltaic (LCPV) systems incorporated with active cooling systems use liquid water pump loop or conventional vapor compression refrigeration system. In this study, a new cooling system, so-called two-phase mechanical pumped loop (TMPL), is proposed to be used with LCPV system. The excess heat from photovoltaic (PV) cell is used to heat up water stored in a tank for residential purposes. The case study is Bogota in Colombia and we develop a dynamic simulation model for the LCPV-TMPL system. The design parameters of the TMPL system are the flow volumetric rate and saturation temperature of the refrigerant as well as the tube length of the condenser. Moreover, low global warming potential (GWP) refrigerants such as R1234yf and R1234ze(E) were evaluated, both showing the same performance compared to R134a. The results showed that the use of TMPL system to eliminate the generated heat of PV cell improves its temperature stability and efficiency. It also shows how the proposed model can be used to design the thermal/photovoltaic system for a local, showing also the expected performance before the system installation. In the case study region, the LCPV-TMPL system, using four PV cells with 5 m × 10 mm, produces power with an average monthly of 2 kW with a peak of 5 kW under average and peak monthly solar radiation of 400 W/m2 and 600 W/m2, respectively. The storage tank can heat up 2.2 m³ water per day from 8 °C to approximately 28 °C, in an average sense. This means that the LCPV-TMPL system could save 9000 kWh and 1900 kWh per year in electricity and thermal energies (water heating). This system can be used locally with low or medium solar radiation and cold weather.

Utilization of ultra-low temperature heat by a novel cascade refrigeration system with environmentally-friendly refrigerants

From solar, geothermal and waste energy, ultra-low-grade heat of 45–60 °C is large in scale, and is still interesting challenges in converting into useful refrigeration of 7 °C. In this study, a novel cascade refrigeration system was developed to utilize 45–60 °C heat. It is composed of a novel two-stage vapor absorption refrigeration (VAR) subsystem with LiBr/H2O working pairs and a conventional vapor compression refrigeration (VCR) subsystem. The VCR subsystem employs potential R1234yf and R1234ze(E) refrigerants. The novel VAR subsystem operates by utilizing ultra-low-grade heat of renewable energy and recycling condensing heat of the VCR subsystem. Based on thermodynamic models of the novel system, its operating mechanism was theoretically investigated and discussed. The results indicate that the novel cascade system can effectively refrigerate by utilizing 45–60 °C ultra-low-grade heat. Its operation is mainly determined by the novel VAR subsystem. There are optimal Tm and Tg1 to maximize its performance. Tg2 has a greater impact on the optimal Tm and little effects on the optimal Tg1. Furthermore, it implies that an available temperature span could be obviously enlarged from 90 °C down to 45 °C. And, progress of utilizing ultra-low-grade heat of renewable energy could be promoted, beneficially.

Studies on the feasibility of adsorption cooling technologies

In the current scenario, for majority of the people and industry needs of the globe, cooling processes such as refrigeration as well as air conditioning are important and major requisites. On the other hand, the conventional vapour compression systems require high electrical energy input and employ refrigerants with negative environmental impacts like ozone layer depletion and climate change resulting from the emission of harmful gases such as CO2, Hydro fluorocarbons and Chlorofluorocarbons with the usage of conventional refrigerants. The solar energy being a renewable source is one of the key solutions to pollution problems and can be used to drive the adsorption cooling machines. With the heat source temperature of even 50° C which is obtained from the low grade energy like solar energy or waste heat energy is feasible to run the adsorption refrigeration system to reduce the operating cost. In the present work, a single bed adsorption refrigeration system is developed and tested using working pair as silica gel and water. From the experimental results, it was observed that this system can be used as alternative to the conventional vapour compression refrigeration system to produce cooling effect. However, the performance of the adsorption system studied is lower than the vapour compression refrigeration system.

A novel thermodynamic design model of a new HFO refrigerant single phase vapor jet cooling system

Vapor jet refrigeration system has been a promising research topic by far. This system bears such importance due to using low grade energy instead of the less economical high grade energy necessary for driving the conventional vapor compression refrigeration cycles despite the low COP values. The main purpose of the present work is to introduce a mathematical model to optimally size the single phase supersonic vapor ejector and to give a detailed picture on how the system operating conditions affect the main dimensions of the optimally operated ejectors. On the other hand, this paper is a predesign study of the operating conditions effect on the system performance parameters like the COP, entrainment and area ratios. The model is validated with experimental data mentioned in the literature and it gives high trusted results. Moreover, the model is general as it can be used with any refrigerant. However, the present results belong to the environment friendly hydro-fluoroolefin refrigerant (R1234yf) which will be increasingly adopted and a potential alternative for the currently used hydroflourocarbon (HFC) R134a.

Dynamic simulation of a solar desiccant cooling system combined with a ground source heat exchanger in humid climates

Buildings share a large amount of total energy consumption in the world, particularly in humid regions, where due to the total consumed energy and environmental issues, desiccant cooling systems have been proposed as an alternative to conventional vapor compression refrigeration systems. The present research investigated the dynamic operation of a solar desiccant cooling system coupled with a ground source heat exchanger (GSHE). Solar energy and GSHE were used as a heat source for regenerating the desiccant and a pre-cooling component, respectively. Simulations were conducted in hot-humid and moderate-humid climates. In hot-humid regions, the aim was to investigate the system operation, while the required regeneration temperatures were controlled to be below a maximum value. In moderate-humid regions, the objective was to regenerate the desiccant wheel entirely by solar energy. The effect of GSHE was evaluated on the provided thermal comfort. Moreover, the impact of desiccant wheel performance and the maximum regeneration temperature was assessed on the dehumidification of the desiccant wheel, system COP, established thermal comfort, and the solar fraction (SF). Results reveal that GSHE dramatically increased the achieved thermal comfort in both climatic conditions. Reduction in the desiccant wheel performance reduced the system COP and provided thermal comfort and daily-averaged SF. The decline in the maximum regeneration temperature decreased the established thermal comfort, but increased the system COP and daily-averaged SF.

Assessment of liquid desiccant dehumidification aided vapor-compression refrigeration system based on thermo-economic approach

This work presents the analysis of a modified liquid desiccant dehumidification incorporated vapour compression refrigeration system based on thermo-economic approach. The thermal model of the proposed system is developed and optimized by considering the co-efficient of performance and the total annual cost of the system as objectives. To focus on the liquid desiccant dehumidification subsystem, seven design variables including thermodynamic and geometric parameters are selected accordingly. The multi-objective optimization results are obtained in the form of Pareto solutions. The effect of dehumidifier height and desiccant to air mass flow rate on the optimized performance of the system is investigated. Further, the effect of design variables on the performance of the system is also examined. The results show that 51.3% of the total cooling load is handled by the desiccant dehumidifier alone. This significant sharing of heat duty by addition of liquid desiccant dehumidification to conventional vapour compression refrigeration system justifies this hybridization for humid and hotter climates. Further investigation at an optimal solution point shows that the co-efficient of performance of the hybrid system is improved up to 68.4% compared to co-efficient of performance of standalone vapour compression refrigeration system for handling the same cooling load. Also, the payback duration of the hybrid system comes out to be 1.54 years.

Energy and exergy analysis of vapor compression–triple effect absorption cascade refrigeration system

In the present work, an absorption-compression cascade refrigeration system (ACCRS) has been analyzed theoretically for low temperature cooling applications. It comprises of a triple effect H2O-LiBr series flow vapor absorption refrigeration system in higher temperature section associated with vapor compression refrigeration (VCR) system using R1234yf refrigerant in lower temperature section. The cascade system provides lower temperature i.e. 223.15–263.15 K for freeze drying, pharmaceuticals, chemical and petroleum industry at lower running cost using waste available from the exhaust of gas turbine or steam turbine to run the triple effect vapor absorption refrigeration system which reduces the overall high grade energy (electricity) consumption of the cascade system. Moreover, the use of R1234yf protects the environment from global warming and ozone depletion. Energetic and exergetic analysis have been performed for the parametric investigation of the system. An EES software based computational model has been formulated for the computation of performance parameters. The analysis determines the effect of generator temperature (448.15–473.15 K), absorber temperature (298.15–313.15 K) and evaporator temperature (223.15–263.15 K) on the energetic (COP) and exergetic (exergetic-efficiency, exergy destruction rate and exergy destruction ratio performances of the system. The results illustrate that the electricity savings of triple effect cascade system are 45.84% in comparison to conventional VCR cycle. The COP and exergetic-efficiency of VCR circuit in the cascade system boost up by 85.26% and 85.28% respectively. The COP and exergetic efficiency of triple effect cascade system are higher than that of single and double effect absorption compression cascade refrigeration systems. The system circulation pump and absorber are the sites of lowest and highest irreversibility in comparison to the other system components.

Colossal Elastocaloric Effect in Ferroelastic Ni-Mn-Ti Alloys.

Energy-efficient and environment-friendly elastocaloric refrigeration, which is a promising replacement of the conventional vapor-compression refrigeration, requires extraordinary elastocaloric properties. Hitherto the largest elastocaloric effect is obtained in small-size films and wires of the prototype NiTi system. Here, we report a colossal elastocaloric effect, well exceeding that of NiTi alloys, in a class of bulk polycrystalline NiMn-based materials designed with the criterion of simultaneously having large volume change across phase transition and good mechanical properties. The reversible adiabatic temperature change reaches a strikingly high value of 31.5K and the isothermal entropy change is as large as 45 J kg^{-1} K^{-1}. The achievement of such a colossal elastocaloric effect in bulk polycrystalline materials should push a significant step forward towards large-scale elastocaloric refrigeration applications. Moreover, our design strategy may inspire the discovery of giant caloric effects in a broad range of ferroelastic materials.

Magnetocaloric effect in Gd60Al25(NiCo)15 bulk metallic glass

Magnetic cooling technology is a very promising alternative to conventional vapor compression refrigeration systems. Searching for suitable magnetocaloric materials with improved properties is a key issue in this field. In this work, we report thermal, magnetic and magnetocaloric properties of the Gd60Al25(NiCo)15 bulk metallic glass. A completely amorphous sample of 3 mm in diameter is successfully fabricated by a vacuum suction casting method. The alloy demonstrates the distinct glass transition and near-eutectic melting. Magnetic measurements reveal ferromagnetic ordering in the BMG at about 91 K. We have found a field-induced magnetic transition in the glass, which provides a table-like behavior for the magnetic entropy changes. Due to this metamagnetic effect, the BMG demonstrates excellent magnetocaloric effect over a wide temperature range. The values of relative cooling power (RCP) and the full width of half maximum of magnetic entropy change (ΔTFWHM) under a magnetic field of 5 T are 890 J × kg−1 and 141 K, respectively. All that makes this glass a promising candidate for magnetic refrigeration applications working at liquid‑nitrogen temperatures.

Optimization of the Design Parameter for Standing Wave Thermoacoustic Refrigerator using Genetic Algorithm

Standing wave thermoacoustic refrigerator has a potential of replacing conventional vapor compression refrigeration system due to several factors. Firstly, this green technology does not contain any harmful chemicals or ozone depletion refrigerant. In fact, it uses the sound wave to generate the cooling effect. Thus, it is friendly to the environment. Besides, this technology is affordable, lightweight and easy to be constructed too. However, it has a low coefficient of performance compared to conventional refrigerator with the same cooling capacity. Recently, there is no noticeable breakthrough in the research of this technology. In this study, genetic algorithm is used to optimize the design parameters of the standing wave thermoacoustic refrigerator system to achieve the highest coefficient of performance. Multi-Objective Genetic Algorithm is used to provide the performance trend of a standing wave thermoacoustic refrigerator system. There are five normalized parameters which will undergo optimization using genetic algorithm, namely normalized stack length, normalized stack center position, blockage ratio, drive ratio and normalized gas thermal penetration depth. The results show that the highest COP that can be achieved by a thermoacoustic refrigerator system (working gas = air, temperature = 300 K and pressure = 1 atm) is 4.8904. The coefficient of performance is about 120.3 % higher than the previously published data. A standing wave thermoacoustic refrigerator prototype is built based on the optimized results obtained from genetic algorithm, whereby the system is operating under no load condition. It is found that the experimental results agree well with the optimization results.

Theoretical investigation on the performance of a modified refrigeration cycle with R170/R290 for freezers application

This study presents a modified vapor compression refrigeration cycle (MVRC) with zeotropic mixture R170/R290 for freezers. Different from the conventional vapor compression refrigeration cycle (CVRC), two separators and corresponding capillary tubes are employed into MVRC to achieve partial-condensation separation and flash separation for a composition shift effect, respectively. MVRC can provide the cycle performance improvement due to the composition shift effect of zeotropic mixture. The mathematical model based on energetic and exergetic methods is developed to evaluate the cycle operating performance of MVRC and compare with that of CVRC. The results show that MVRC is more promising for low-temperature cooling system over CVRC. Under the given operation condition, the cycle performance improvement of MVRC over CVRC in terms of coefficient of performance (COP), volumetric cooling capacity and exergy efficiency can reach up to 12.7%, 32.6% and 20%, respectively. The performance characteristics of the proposed cycle demonstrate its potential advantages for application in the freezers.

Experimental study on a hybrid photo-thermal and radiative cooling collector using black acrylic paint as the panel coating

Radiative cooling is treated as a promising clean alternative for cooling energy harvesting by dissipating heat to the sky mainly at night in a passive manner. Yet the cooling flux of a stand-alone radiative cooling system is far below a conventional vapor compression refrigeration system, which hinders its wider application. If the nocturnal radiative cooling process acts as an auxiliary function of the solar collector, the aforementioned limitation of radiative cooling technique can be addressed. Therefore, a dual-functional collector which can offer heat in daytime and cooling energy in nighttime was proposed in this study. This hybrid photo-thermal and radiative cooling collector used the cheap and accessible black acrylic paint as the panel coating. A photo-thermal and radiative cooling prototype was manufactured and investigated experimentally in heating and cooling modes. Results showed that the thermal efficiency at zero-reduced temperature and cooling efficiency at zero-dimensionless temperature difference were 63.0% and 58.3%, respectively under clear sky condition. Besides, the collector achieved a net radiative cooling flux of 55.1 W/m2 in a clear night. Moreover, the hybrid system gathered a daily heat of 8.64 MJ during a consecutive 8 h, and a nightly cooling energy of 0.99 MJ in a consecutive 11.5 h.

Performance improvement of ejector expansion refrigeration cycles employing a booster compressor using different refrigerants: Thermodynamic analysis and optimization

A novel ejector-expansion refrigeration cycle (EERC) is proposed, analyzed and optimized in this paper. Assuming a constant-pressure mixing model for ejector simulation, a detailed and comprehensive thermodynamic analysis, based on the first and second laws, is conducted and the system performance is investigated for six proper refrigerants. The proposed system is then optimized considering the exergy efficiency as the objective function and a comparison is made with the standard EERC and conventional vapor compression refrigeration system at the optimized conditions. The results indicated that, among the six investigated refrigerants, R1234ze is the best one for which the proposed system has 5.7% and 15.5% higher exergy efficiency values than the standard EERC and conventional vapor compression refrigeration cycle, respectively, at condensing temperature of 40 ∘C and evaporation temperature of 5 ∘C. Also, it is concluded that for higher condensing and lower evaporating temperatures the value of performance improvement is higher.

Nanoconfinement-Induced Giant Electrocaloric Effect in Ferroelectric Polymer Nanowire Array Integrated with Aluminum Oxide Membrane to Exhibit Record Cooling Power Density.

The electrocaloric effect (ECE) offers a unique mechanism to realize environmentally friendly and highly efficient solid-state cooling that completely differs from the conventional vapor-compression refrigeration. Here a new class of hybrid films composed of ferroelectric polymer nanowire array and anodic aluminum oxide (AAO) membrane is reported, which displays pronounced ECE driven by relatively low electric fields. Under confinement and orientation of AAO channels on the crystallization of the polymer, the polymer nanowire array shows substantially enhanced ECE that is about three times that of the corresponding thin films. Simultaneously, the integrated AAO membrane forms thermally conducting channels for the polymer nanowires, enabling the efficient transfer of cooling energy and operation of the EC materials under high frequencies, which are unattainable based on the currently available EC structures. Consequently, the integrated polymer nanowire-AAO hybrid film exhibits the state-of-the-art cooling power density, outperforming the current ferroelectric polymers, ceramics, and composites. This work opens a new route for the development of scalable, high-performance EC materials for next-generation refrigeration.