Efficient Refrigeration Research Articles

Research on the Application Performance of the Helmholtz High-Efficiency Wave-Elimination Chamber in Gas Wave Tubes

A gas wave refrigerator is a device that uses gas pressure to expand and refrigerate; the moving shock wave in the gas wave tube is the key to cooling. If the shock wave is reflected to the open mouth of the gas wave tube, it will heat the expanded refrigeration gas at the open end, severely reducing the refrigeration efficiency. In order to reduce this effect, a Helmholtz middle wave chamber-type gas wave tube is presented here. This study describes the performance of this structure in the gas wave refrigeration process. The refrigeration performance of the structure’s gas wave tube use was evaluated experimentally and numerically using computational fluid dynamics (CFD). The function of the middle wave elimination chamber was studied and explained: the chamber turns the reflected shock wave back to the end section of the tube and converts part of the incoming shock wave to an expansion wave, which may counteract the reflected shock wave by escaping from wave elimination chamber. The experimental results showed that the structure increased refrigeration efficiency by about 2.9% (50 Hz), 2% (40 Hz), and 2.2% (25 Hz) at the corresponding ejection frequencies, and reduced the reflected shock wave intensity by 11%, which proves the high-efficiency energy dissipation performance and the significant increase in refrigeration efficiency of the Helmholtz-type gas wave tube.

Electrolyte engineering can improve electrochemical heat engine and refrigeration efficiency

The rational engineering of electrolytes can dramatically improve electrochemical heat engines and heat pumps (refrigerators), which are emerging, low-cost, high-efficiency thermal energy conversion technologies. We discuss the key parameters that make electrolytes attractive for thermal energy conversion, provide new insight into the trade-offs, and suggest approaches to circumvent these trade-offs.

Developing low cost, efficient magnetic refrigeration down to 0.2 K

Magnetic refrigerators made of YbCu4Ni could be used for condensed matter physics, superconducting circuits, cosmic ray detectors.

Man-portable cooling garment with cold liquid circulation based on thermoelectric refrigeration

• Application of semiconductor refrigeration in cooling garment. • A new cooling garment is designed and tested in a high-temperature environment. • The cooling garment system long time running is reliable and steady. • The cooling system provides a cold water temperature of 15.7 °C. • Self-regulating heat exchange network automatically adjusts temperature balance. The use of cooling garments is emerging as an effective, convenient, and energy-efficient way to maintain thermal comfort, which is crucial for conserving physical and psychological health and for avoiding potentially life-threatening situations. Current cooling garments are generally bulky and have short operating periods, uncontrollable cooling capacity, and low effectiveness. Here, a novel man-portable cooling garment based on thermoelectric refrigeration was designed, and the heat generated by body is absorbed by capillary tube and dissipated in semiconductor refrigeration system. The coolant is circulated in the pipeline to recover residual cold energy and improve the thermal stability of the system. Several performance tests were conducted in a simulated hot environment to evaluate and to optimize refrigeration efficiency and cooling effectiveness. The results indicated that the system was capable of providing a water temperature of 15.7 °C and cooling power of 340.4 W, with a coefficient of performance of 3.40 at 100 W of electrical power and a climatic chamber at 30 °C. Additionally, the operating environment of the system significantly influenced the cooling capacity of the garment; and the cooling power of the system was significantly improved by increasing the heat dissipation capacity. The increase in electrical power was limited by constant heat dissipation capacity restrictions. The wearing trial confirmed the effectiveness of the thermoelectric cooling garment. Furthermore, our study improved the understanding of performance characteristics for the thermoelectric cooling garment, and a road map for the further development of thermoelectric cooling garments was suggested.

Varying the Cross-Sectional Area of the Regenerator for Improving the Refrigeration Efficiency at Liquid-Helium Temperatures

Varying the Cross-Sectional Area of the Regenerator for Improving the Refrigeration Efficiency at Liquid-Helium Temperatures

Design and implementation of solar powered mini refrigerator using thermoelectric cooler module

Remote areas are known for lack of conventional electrical power supply. But it is a common phenomenon to find health centres in remote areas, where vaccination campaigns are done regularly. Due to small populations, vaccines opened cannot be completely used and some usually get bad. The objective of this project is to design and implement a portable and energy efficient refrigerator for preservation of vaccines in medical centres found in remote areas where electric power supply is absent. The novelty of this work is on the use of planks, which are local materials and cheap for the construction of the frame of the refrigerator. The experimental method is used, that helps to determine the functional operation of the system and the limit to which the system functions. The main component of the refrigerator is the thermoelectric cooler module tec1-12706.The system is tested under various conditions such as simultaneous use of PV module and storage battery as source of electrical energy. The absence of cooling fan on the hot side of tec1-12706.The results show that the temperature of the system reduces from 280 C to 50c within one hour of operation. And the temperature of the hot side of the tec1-12706 module increases drastically within 15 minutes of operation if there is an absence of fan on the hot side. With this the module is easily damaged. From the literature review, the COP is maximum0.6 but the present work raises the COP to 0.7.this is done by reducing the input energy. It is then recommended that the system should not be operated without a fan attached to the hot side of the tec1 module.

Evaluation of thermal and rheological characteristics of CNT-PAG nanolubricant for the development of energy efficient refrigeration systems

The addition of nanoparticles is one of state of the art methods to enhance the thermophysical and heat transfer characteristics of cooling and lubricating fluids. Exploring the energy-saving potentials of novel material Carbon Nano Tube (CNT) as a lubricant additive is the primary focus of this study. The thermal and rheological properties of Poly Alkylene glyco l (PAG)-CNT nanolubricant at different volume fractions are investigated to pose as an energy-efficient alternative lubricant in vapour compression refrigeration systems. Furthermore, genetic algorithm-based regression correlations are proposed to predict the thermal conductivity and viscosity of the nanolurcant. The results show that the CNT has the potential to improve the thermophysical and rheological characteristics of the lubricant. Experimental results show that the presence of tubular-shaped CNT particles enhances the thermal and rheological characteristics of the colloidal suspension. The proposed regression models exhibit excellent agreement with the experimental data. Studies revealed that the potentials of CNT-PAG nanolubricant as an alternative lubricant for refrigerant compressors is excellent and will eventually improve the energy efficiency and overall performance of refrigeration systems and which in turn leads to the development of energy-efficient HVAC systems.

Characterization of cooling equipment in the food industry: Case study of the Colombian meat, dairy, and fruit and vegetable sectors

The food industry contributes to environmental impacts through the intensive use of energy. Therefore, it is important to understand the characteristics of cooling systems as a material service to develop strategies to decrease their environmental impacts and improve productivity. This study analyses three food sectors in Colombia that use refrigerant systems based on the requirements of the quality, processing and preservation of products and material service in emerging economies, where it is important to determine the baseline technology level and identify beneficial system innovations. This paper provides an overview of the value chains, production levels and trends, cooling systems, material services and maintenance processes for three sectors using qualitative and quantitative methods and different knowledge sources, including a survey and previous studies related to refrigeration in the food industry. The results show that the infrastructure most used is a cold chamber or cold storage, followed by refrigerators and the equipment used in the refrigeration systems, including compressors, condensers, evaporators and, to a lesser extent, chillers, on which preventive and corrective maintenance is performed every three to four months. The equipment and accessories largely come from the United States, Europe and China, and purchasing decisions are based on price. The results also indicate that it is important that decision makers in these three sectors increase their awareness and knowledge of cooling equipment and its environmental impacts with the aim of improving productivity and decreasing pollution. In particular, material services that require resources such as energy and other materials should be more environmentally friendly. Based on these findings, the government could design different instruments for technological change. The majority of cooling systems in the three sectors have been in operation for over 10 years. Thus, in a country where agricultural diversity and export capacity are key contributors to development and economic growth in rural areas, strategies to implement cold chain systems that are less polluting and more productive are essential. The findings of this study are important for establishing actions for change and technology transfer and promoting the modernization of the agricultural market through exports. It is important to ensure an effective cold chain utilizing environmentally friendly and efficient refrigeration systems, which may provide access to new markets for natural and fresh food products.

Enhancement of magnetocaloric effect in all-d-metal Heusler Mn52.6Ni30.5Co7.8Ti9.1/PVA/PET flexible composite by mechanical strains

The prominent enhancement of magnetocaloric effect (MCE) and the extension of effective magnetic refrigeration temperature region near room temperature (RT) are urgent needs for efficient and clean refrigeration technologies. Here, we report that a flexible composite is made up of all-d-metal Heusler ferromagnetic shape memory alloys (FSMAs) Mn52.6Ni30.5Co7.8Ti9.1 (Mn-Ni-Co-Ti) ribbon and polyethylene terephthalate (PET) substrate with polyvinyl alcohol (PVA) coating, exhibiting a tunable martensitic transformation (MT) by applying mechanical strains and accompanying a remarkably enhanced MCE near RT. The MT temperature of the Mn-Ni-Co-Ti/PVA/PET flexible composite obviously shifts, leading to the bidirectional control of the magnetization difference (ΔM) with the increase of tensile/compressive strains. Especially, the magnetic entropy change (ΔSM) and refrigeration capacity (RC) are remarkably improved under the tensile strain (ε = 6.0%) state. As a result, the MCE can be controlled and the effective magnetic refrigeration temperature region can be expanded by adjusting the mechanical strains in the Mn-Ni-Co-Ti/PVA/PET flexible composite, which is beneficial to improve the refrigerating efficiency in promising applications of magnetic devices.

Thermal Performance Evaluation of the Variation of Condenser Dimensions for Foodstuffs Transportation Cooling Systems

The process of sending food using transportation requires a refrigeration system to keep the product fresh. Unsuitable temperatures will cause the transported products to often experience damage so that they are rejected in the mark. To achieve this, it is done through testing using a condenser with several variations of dimensions for a room temperature of 5oC. The dimensions of condenser-1 are (W 23 x H 14) inch2 x 19 mm, condenser-2 is (W 23 x H 14) inch2 x 26 mm, and condenser-3 is (W 23 x H 14) inch2 x 44 mm. The test results show that condenser-3 produces a faster cooling time compared to condenser-2 and condenser-1. Cooling time for condenser-3 is 1160 minutes, while condenser-2 and condenser-1 are 1560 minutes and 1860 minutes, respectively. Condenser-3 provides the lowest compression work of 42.131 kJ/kg compared to condensers 2 and 1, respectively 42.931 kJ/kg, and 46.147 kJ/kg. This has an impact on the COP value, namely condenser-3, condenser-2, and condenser-1 each of 3.437, 3.233, and 2.845. COP at condenser-3 occurs the highest. These results indicate that the largest condenser dimension gives the most optimum thermal performance results. An efficient refrigeration system has low compression work and high COP.

Experimental Study on the Stability and Transient Behavior of a Closed-Loop Two-Phase Thermosyphon (CLTPT) Charged with NOVEC 649

Currently, the growing need for efficient refrigeration resources in the industrial sector has led to an increasing interest in finding technologies with a higher heat removal potential and better cooling performance. Along these lines, two-phase liquid cooling appears to be a very interesting solution, with the CLTPT (closed-loop two-phase thermosyphon) being one of the leading alternatives. Most works in the scientific literature study loop thermosyphons that work in flow boiling conditions in steady state. The present paper analyzes the transient thermal behavior of a pool boiling CLTPT gravitational channel as a passive cooling system using NOVEC 649 as working fluid. The evaporator works with two submerged cylindrical heaters that represent different heat sources located in different positions. The initial transient behavior and consequent instabilities of a laboratory-scale facility were studied, followed by a stability analysis for various power inputs. Parameters such as temperature and pressure along the experimental setup were monitored, and the effects of internal pressure and room conditions were also tested. The results show some instabilities in the process to start the flow circulation and a relative stability and quick adaptation to changes when circulation is reached. The temperature in the evaporator chamber was highly homogeneous during the whole process; however, the temperature changes in the riser and the loop top were delayed with respect to the evaporator zone. The analysis shows several pressure and temperature raises before the vapor flux reaches the condenser. When the flow circulation is established, the system becomes highly stable and thermally homogeneous, decreasing the thermal resistance when increasing the power input. The stability analysis also showed that, when the system reaches the steady state, the changes in the power input produce a transient increase in the pressure and temperature of the fluid, followed by a quick decrease of the previous steady state values. The heat transfer analysis in the evaporator shows a higher heat flux on the upper heater caused by the buoyancy flow that rises from the lower heater. It was also observed that the lower heater reaches the CHF point with a lower heat flux.

Effect of Physical Properties of a Gas on the Refrigeration Temperature Drop of Vortex Tubes Used in Oil and Gas Fields.

The composition of natural gas can vary considerably across different oil and gas fields. Such compositional variation is primarily reflected in the distinctive physical properties of natural gas. However, during practical application in an oil and gas field, a refrigeration temperature drop in a vortex tube is often observed because vortex tubes generally have low intrinsic refrigeration efficiencies. When vortex tubes are applied in oil and gas fields, the utilization of the oil pressure of a natural gas wellhead is often desirable to avoid excessive energy usage from external devices. In this study, a numerical model of a vortex tube was developed, executed, and validated through laboratory experiments. The refrigeration temperature drop values of 12 gases with distinctive physical properties at a total inlet pressure of 0.3 MPa, an inlet temperature of 300 K, and a cooling mass flow ratio of 0.5 were analyzed. The importance of different physical properties was ranked based on the gray correlation method. Additionally, the synergetic effects of the physical properties on the refrigeration temperature drop were analyzed via regression fitting. The results indicate a significant impact of the gas physical properties on the refrigeration temperature drop in the vortex tube. The maximum and minimum refrigeration temperature drop obtained for different gases can differ by up to 16 K. Furthermore, the refrigeration temperature drop in the vortex tube does not change monotonically with any physical property. Instead, it depends on the synergetic effect from the physical properties, which have different levels of influence on it.

A Numerical Study on the Effect of Oil Lubricant on the Heat Transfer and Efficiency of a Vapour Compression Refrigeration System

The involvement of oil lubricants in vapour compression refrigeration (VCR) systems could adversely influence the flow, heat transfer and efficiency of refrigeration. A numerical model for a VCR system using linear compressor, R1234yf, and POE oil is developed in this study to investigate the effect of oil lubricant on the flow and heat transfer as well as the system performance including cooling capacity and coefficient of performance (COP). The proposed model is validated by measurements of a prototype oil-free VCR system with most of the simulated data falling within ± 20 % of measurements. The evaporator heat transfer coefficient, cooling capacity, and COP for the system from the proposed model show a negative correlation with oil circulation rate (OCR). The COPs and pressure losses for oil-free system are 15-28% higher and 36-60% lower than that of oil-lubricated system respectively.

Exploiting the thermal and rheological potentials of graphene-PAG nanolubricant for the development of energy efficient refrigeration systems

The addition of nanoparticles is one of state of the art methods to enhance the thermophysical and heat transfer characteristics of cooling and lubricating fluids. Exploring the energy-saving potentials of novel material graphene as a lubricant additive is the primary focus of this study. The thermal and rheological properties of Poly Alkylene glycol(PAG)-graphene nanolubricant at different volume fractions are investigated to pose as an energy-efficient alternative lubricant in refrigeration systems. Moreover, genetic algorithm based regression correlations are proposed to predict the thermal conductivity and viscosity of the graphene-PAG nanolubricant. The results show that the addition of graphene nanoplatelets to the oil has the potential to improve the thermophysical characteristics of the lubricant. The presence of platelet shaped nano graphene particles enhance the thermal and rheological characteristics of the colloidal suspension. The proposed regression models exhibit excellent agreement with the experimental data. Thermal and rheological studies revealed that the application of graphene-PAG nanolubricant is an option to improve the energy efficiency and overall performance of HVAC systems.

Enhanced room temperature electrocaloric effect in lead-free relaxor ferroelectric NBT ceramics with excellent temperature stability

Solid-state refrigeration based on electrocaloric effect (ECE) is a high efficiency and eco-friendly refrigeration technique, which has attracted increasing attention. However, it is still a challenge to realize a large adiabatic temperature change (∆T) accompanied by wide operating temperature range (Tspan). Herein, enhanced room temperature ECE was realized in lead-free (1-x)Na0.5Bi0.5TiO3-xSr0.85Bi0.10TiO3 (NBT-xSBT) by a synergistic effect of forming relaxor ferroelectric and constructing multilayer ceramic capacitor (MLCC). It is found that the maximum ∆T of NBT-0.50SBT ceramic is 0.31 K at 80 kV/cm, and Tspan is up to 60 K. To further improve the breakdown strength (BDS), NBT-0.50SBT MLCC was fabricated by a tape-casting method. A large ECE of MLCC reached 2.59 K at 60 °C with excellent temperature stability from 35 °C to 95 °C. These results indicate that NBT-based material is a promising electrocaloric material for solid-state cooling applications.

Numerical simulation and experimental study on marine cabin's ventilation for reefer containers

In global refrigerated transportation, marine reefers play an extremely important role. Considering the high freight cost and harsh surroundings of the decks during the voyage, reefer containers are always loaded into cabins for safe and economical purpose. However, under severe environment conditions in cabin, the refrigeration efficiency of reefer units was greatly affected, because of the weak ventilation and low heat exchange capacity. In order to find a more scientific and reasonable way to ventilate the cabin of reefer containers, two different ventilation modes, that is, air supply and air exhaust, were experimented and simulated. The temperature distribution was analyzed in a typical reefer cabin with 14.4 m (in length) × 23.2 m (in width) × 16.85 m (in height). Compared with two contrary ventilation modes, the temperature distribution in the cabin at steady state was simulated and analyzed. The results show that, the temperature of the cabin under the air exhaust condition was about 4K lower than that under the air supply condition. But with higher heat dissipation efficiency, the air exhaust condition sacrifices the uniformity of the temperature in the cabin. A relatively uniform temperature distribution and airflow field were obtained under air supply condition. Therefore, considering the heat dissipation effect of the container and the uniformity of airflow distribution, the air supply method was recommended. The two ventilation modes were compared in detail in this paper, and the results provide a reference for ventilation design of reefer container vessels.

Giant room temperature electrocaloric effect in a layered hybrid perovskite ferroelectric: [(CH3)2CHCH2NH3]2PbCl4

Electrocaloric effect driven by electric fields displays great potential in realizing highly efficient solid-state refrigeration. Nevertheless, most known electrocaloric materials exhibit relatively poor cooling performance near room temperature, which hinders their further applications. The emerging family of hybrid perovskite ferroelectrics, which exhibits superior structural diversity, large heat exchange and broad property tenability, offers an ideal platform. Herein, we report an exceptionally large electrocaloric effect near room temperature in a designed hybrid perovskite ferroelectric [(CH3)2CHCH2NH3]2PbCl4, which exhibits a sharp first-order phase transition at 302 K, superior spontaneous polarization (>4.8 μC/cm2) and relatively small coercive field (<15 kV/cm). Strikingly, a large isothermal entropy change ΔS of 25.64 J/kg/K and adiabatic temperature change ΔT of 11.06 K under a small electric field ΔE of 29.7 kV/cm at room temperature are achieved, with giant electrocaloric strengths of isothermal ΔS/ΔE of 0.86 J·cm/kg/K/kV and adiabatic ΔT/ΔE of 370 mK·cm/kV, which is larger than those of traditional ferroelectrics. This work presents a general approach to the design of hybrid perovskite ferroelectrics, as well as provides a family of candidate materials with potentially prominent electrocaloric performance for room temperature solid-state refrigeration.

Investigation of Parameters Affecting the Efficiency of Thermoelectric Refrigerator

The efficiency of thermoelectric refrigerator was investigated by two thermoelectric cooling (TEC 1-12709) at outside insulator box with cooling side at inside box and rejected heat at outside box by heat sink and fan. We applied electrical current 0.5 – 2 A for 15 minutes at room temperature and found that the inside thermoelectric refrigerator box showed a lowest temperature decreasing at center from 26.49 °C to 19.32 °C and at surface of TEC from 25.70 °C to 7.05 °C. The highest coefficient of performance (COP) is 0.10 by parallel connection.

Analysis of the performance of air blast freezer by using hydrofluorocarbon and hydrocarbon refrigerants

The air blast freezer has been used as a freezing method in the fish processing units before being frozen for a long time in cold storage. For this reason, the use of hydrocarbon refrigerants that are more environmental friendly has become a demand and a central issue in the future. This paper presents a performance analysis of using R290 and R600a as a drop-in replacement to R404A and R507A. The system performance analysis is based on the evaporation temperature variation using CYCLE_D-HX software with the condensation temperature maintained constant. The important quantities analyzed are mass flow rate, pressure ratio, temperature discharge, heat released, power consumption, coefficient of performance and refrigeration efficiency. The results show that at minimum evaporation temperature, system performance using R290 and R600a is on average ±14% higher compared to R404A and R507A. R290 has characteristics that are closer to R404A and R507A so it is more suitable to replace the two refrigerants compared to R600a. However, this is a performance analysis that can lead to higher performance than normal conditions.

The enhancement effect and competition behavior of a flash evaporation system with a continuous DC glow discharge plasma

The transient plasma kinetic has been proved to be able to significantly improve the refrigerant efficiency of vacuum flash evaporation. Here we explore the flash evaporation cooling enhancement effect induced by a continuous glow discharge plasma, generally exists in vacuum, but the heat deposition is more severe than a transient plasma source. Several controlled groups with different discharge currents, which determine the thermal deposition rates, are subjected to an oscilloscope, CCD, and optical emission spectroscopy (OES) for diagnosis of plasma and Infrared Radiation (IR) thermography, vacuum gauge, and electronic balance for thermal and evaporative properties to reveal the influence of plasma characteristics on flash evaporation cooling. The characterization results of plasma show that the translational temperature increases with current while the rotational temperature and electron density are almost independent of current. Compared to plasma-free, the plasma generally leads to a significant increase in the maximum temperature drop (ΔTmax), but the effect increases with current from 0.95 to 3.07 mA and decreases at 3.87 mA. The behavior is attributed to the competition between the positive effect of evaporative cooling enhancement resulted from particle kinetic and the negative effect of joule heat itself. This has also led to that the system presents a best cooling enhancement efficiency defined by the increased ΔTmax per unit watt due to plasma, (ΔTmax(I)−ΔTmax(Plasma−free))/P, at the current of 2.01 mA for our cases. In conclusion, the continuous DC glow discharge plasma has been demonstrated to be useful to enhance flash evaporation cooling.