Low-temperature Refrigeration System Research Articles

Investigation on heat recovery strategies from low temperature food processing plants: Energy analysis and system comparison

Industrial food processing plants often have significant thermal requirements at both low and high temperatures. These plants can produce a variety of products including frozen, chilled and grilled/steamed foodstuff, creating thermal demands at several temperature levels. Rapid freezing of the foodstuff at temperatures below -40 °C is required to preserve a high-quality product while steaming/grilling of foodstuff require heat above 100 °C. Heat recovery from the low-temperature refrigeration system provides an interesting opportunity to reduce the overall energy consumption of the plant. This paper presents different strategies to achieve heat recovery from a CO2/NH3 cascade refrigeration system. The low stage of the cascade features pumpcirculated CO2 circuits at -40 °C and -5 °C evaporation levels, while the high temperature stage consists of an ammonia circuit. For this investigation, a case is defined based on requirements for temperature level and heat quantity from the industry. Subsequently, different strategies for the integration and control of the energy systems are examined. Finally, the strategies are compared with selected key parameters and the results are presented. This article is a translation of the article by Ahrens MU, Selvnes H, Henke L, Bantle M, Hafner A. Investigation on heat recovery strategies from low temperature food processing plants: Energy analysis and system comparison. In: Proceedings of the 9th IIR Conference on the Ammonia and CO2 Refrigeration Technologies. Ohrid: IIF/IIR, 2021. DOI: 10.18462/iir.nh3-co2.2021.0034 Published with the permission of the copyright holder.

Comparative exergy and energy analyses of compression–absorption cascade refrigeration cycles with varied configurations and ejector implementations

This study aims to assess the feasibility and performance, as well as the exergy loss, of utilizing ejectors in absorption–compression cascade configurations for low-temperature refrigeration systems. The coefficient of performance (COP) is used to measure system efficiency, including COP.A (COP of the absorption chiller), COP.C (COP of the compression side) and COP.Ca (COP of the cascade configuration). The results highlight the importance of ejector placement on the absorption side for optimal performance. Configuration D1, with an ejector on the absorption side, demonstrates an 85% improvement in COP.A, approximately 10% in COP.C and nearly 100% in COP.Ca compared to configurations without an ejector. However, in certain cases, using an ejector on the compression side is not feasible from a second-law perspective, particularly for higher compression-side evaporator temperatures. Nonetheless, the study suggests that configuration D0, which includes an ejector on the absorption side coupled with a simple compression cycle, is applicable for these conditions and performs similarly to D1 in other temperature ranges. These findings provide valuable insights for optimizing ejector placement in absorption–compression cascade configurations and advancing the development of more energy-efficient refrigeration systems.

Investigation on solid-liquid equilibrium for binary mixtures of carbon dioxide (R744) and alkanes: Propane (R290) and isobutane (R600a)

The solid-liquid equilibrium (SLE) of binary systems containing carbon dioxide (R744) and alkanes propane (R290) and isobutane (R600a) was experimentally investigated. A novel experimental setup using the cooling curve method was designed, built and verified, enabling SLE measurements at temperatures down to 173 K. The temperature and pressure of the triple point of carbon dioxide (CO2) were measured. The results for R744 and the binary mixture of carbon dioxide and propane were in agreement with the available literature data, demonstrating the accuracy of the experimental setup. Activity coefficients were determined for the binary mixtures studied. The Schröder and Wilson equations were used to calculate solubility over various temperatures and compositions. The Wilson model produced a very accurate correlation for the studied non-ideal binary mixtures, while the Schröder equation did not provide satisfactory results. Determined activity coefficients and SLE curves should be useful for the design of low-temperature refrigeration systems operating on carbon dioxide mixtures with low global warming potential.

Thermodynamic performance analysis of a low-temperature absorption refrigeration system in a proton exchange membrane fuel cell refrigerated vehicle

To utilize the waste heat of a proton exchange membrane fuel cell (PEMFC), an absorption refrigeration system (ARS) with a novel low-temperature working pair LiBr- 1-Butyl-3-methylimidazolium Bromide ([BMIM]Br) /C2H5OH is proposed for cooling in the refrigerated vehicle. The thermodynamic performance of the ARS using LiBr-[BMIM]Br/C2H5OH is investigated under various operating conditions and compared with that using the conventional working pair LiBr/H2O. The efficiency performance of the PEMFC refrigerated vehicle using ARS and vapor compression refrigeration system (VCRS) are also studied and compared under different operating conditions. The results show that the ARS achieves the maximum coefficient of performance (COP) of 0.86 and the generation temperature is reduced to 65.45 °C with LiBr-[BMIM]Br/C2H5OH a decrease around 15% in comparison to LiBr/H2O. Comprehensive efficiency of the stack coupled with ARS is up to 85% due to recovery its waste heat. Under identical output power and cooling capacity of the refrigerator vehicle, the stack coupled with a VCRS has a comprehensive efficiency of 70% and requires a larger power scale. Thus, the stack coupled with ARS using LiBr-[BMIM]Br/C2H5OH has a great significance for enhancing the performance, enlarging the mileage, and reducing the cost of the refrigerator vehicle.

Analysis of defrosting system failure of ship low temperature cold storage

The frosting of the evaporator of the ship’s low-temperature cold storage will affect the heat exchange performance of the evaporator operation, the stability of the low-temperature cold storage of the ship’s food security and the effect of food refrigeration. Therefore, the evaporator coil of the low-temperature cold storage needs to be defrosted regularly. The low-temperature refrigeration system of a ship adopts the defrosting mode of electric heating. The lower the temperature of the low-temperature warehouse, the more important the thermal effect of defrosting is. This paper puts forward a technical innovation scheme for the design of the ship’s cold storage and the defrosting control mode, which can provide a reference for the design of the ship’s low-temperature refrigeration system and the defrosting of the low-temperature cold storage.

Thermo-economic analysis of absorption-compression hybrid cooling systems with parallel subcooling and recooling for small scale low-grade heat source and low temperature application

The consumption of low temperature refrigeration systems goes up dramatically due to the fast development of cold chain. In this regard, developing the absorption-compression hybrid cooling systems and employing the low-grade heat to save the compressor work is effective to address the above-mentioned issue. However, one of the main obstacles associated with such solution lies in small scale heat source vs. large heat consumption, which remarkably lowers the amount of energy saving. Consequently, a novel layout, absorption-compression hybrid cooling system with parallel subcooling and recooling, is proposed to deal with the above-mentioned problem. Comparative study is performed to display the advantage of the proposed facility at first. Subsequently, exergy analysis and parametric analysis of the proposed layout are implemented to derive design and operation criteria. Finally, the economic analysis of proposed system is carried out to assess the feasibility. It is found that the compressor power of the novel system is 9.3% and 10.45% less than that of two-stage vapour compression chiller and absorption-compression cascade layout, respectively. Moreover, the payback period of proposed layout is 3.67 years. The paper is favorable to enhance the energy saving of refrigeration system which is associated with small scale low-grade heat source and low temperature application.

Performance Evaluation of Modified Low-Temperature Cascade (MLTC) Type Refrigeration System

An experimental investigation was carried out to study the performance evaluation of Modified Low-Temperature Cascade (MLTC) system, based on two-stage cascade type refrigeration system using the combination of R404A/R23 refrigerants. This system was developed using chilled water (CHW) in the condenser of high-temperature circuit (HTC) and pre-cooler (PC) in the low-temperature circuit (LTC). Isentropic compression efficiency is computed in this work and used here as an important parameter. Performance of MLTC system was compared with or without the introduction of PC into LTC. System’s coefficient of performance (COP) has also been compared with using CHW, cooling tower water (CTW), normal water (NW) into the HTC condenser. It has also been shown that COPs of the system are significantly affected by slight variation in the LTC and HTC evaporating temperatures. Presented parameters and comparisons are likely to help in developing a low-temperature (LT) refrigeration system with higher efficiency for industrial and other applications.

Experimental and numerical study on performance of hybrid refrigeration system that combines vapor compression and thermoelectric systems

As high-quality food preservation has become an important aspect of daily life, a need has developed for domestic household refrigerators with a wide refrigeration temperature range. The temperature range of domestic household refrigerators is generally above −20 °C. In this study, a hybrid refrigeration system that combined vapor compression refrigeration (VCR) and a thermoelectric refrigerator (TER) is investigated for the freezer compartment of a domestic refrigerator with a volume of 0.018 m3. Although an additional 99.5 W of electrical power is consumed, a lower temperature of −38.1 °C is experimentally achieved in the deep freezer compartment of a compact VCR–TER system, with no noise or mechanical parts. In contrast, a temperature of only −8.8 °C is obtained in a typical VCR system. A three-dimensional numerical model is applied to study the performance of the finned heat sink of the TER using FLUENT. The effects of the fin height and fin pitch on the thermal resistance and pressure drop are investigated. The results show that the thermal resistance decreases with an increase in the fin height and increases with an increase in the fin pitch. An optimized finned heat sink with a fin height of 50 mm is obtained, which has a thermal resistance of 0.05 °C/W. It has a higher cooling capacity of 53.6 W than the heat sink with the original fin height of 30 mm. The VCR–TER system has potential application to low-temperature domestic refrigeration systems with a small size and small cooling capacity.

A novel hybrid dual-temperature absorption refrigeration system: Thermodynamic, economic, and environmental analysis

The applications of multi-evaporator and low temperature refrigeration systems are growing rapidly, highlighting the necessity of developing new configurations that can be economically and environmentally attractive. In this study, a hybrid dual-evaporator absorption refrigeration system for refrigerating and freezing applications is proposed and evaluated from thermodynamic, economic, and environmental viewpoints. In the proposed system, two compressors were employed between the evaporators and absorbers to increase the absorbers pressure to a higher level. The detailed parametric study results demonstrated that only employing a compressor between the higher temperature evaporator and absorber is beneficial improving the coefficient of performance (COP) significantly. However, the economic results showed that the compressor should be implemented carefully because in most design and operating conditions, the required capital and operating costs outweigh the COP improvement. Under specified design conditions, integrating the second compressor with a pressure ratio of 2.5 significantly increased the COP from 0.404 to 0.624 while it caused an increase in the unit production cost of cooling (UPCC) from $0.211/ton-hr to $0.228/ton-hr. The use of flue gas as a heat input was found to have excellent potential to improve the economic and environmental performance of the system. A detailed comparison with a dual-temperature transcritical carbon dioxide refrigeration cycle from the literature demonstrated that, under similar conditions, the system of this study has a substantially lower UPCC than the system in the literature ($0.211/ton-hr and $0.110/ton-hr for the steam and waste heat driven systems against $0.457/ton-hr). Overall, the proposed system (with and without the compressor) of this study showed an excellent potential for dual-temperature refrigeration applications.

Investigating potential benefits of a salinity gradient solar pond for ejector refrigeration cycle coupled with a thermoelectric generator

Extraction of thermal heat from a salinity-gradient solar pond (SGSP) as a way of accumulating solar energy, stockpiling and taking merit of it for medium and low temperature demands is presented as an interesting topic in recent decades. This reliable supply of heat can be used for low-temperature refrigeration systems to yield cooling load for residential applications. For this purpose, theoretical investigation of ejector refrigeration cycle (ERC) driven by a SGSP is carried out to produce cooling output. Also, thermoelectric generator (TEG) is used as a potential device replacing condenser of the ERC for the sake of bolstering performance of the fundamental system by producing power, using heat from SGSP. To express viscosity effect of refrigerant through different components of ejector, available numerical correlations are used and it is demonstrated that this deliberation highly increases the accuracy of ejector mathematical modeling. An extensive thermodynamic evaluation on the basis of the mass-, energy-, and exergy-based balance relations for disparate constituents of the introduced system is executed and the outcomes are corroborated with those of experiential approaches. Moreover, performance of the integrated system is optimized by maximizing energy efficiency as well as exergy efficiency for an optimal solar pond. At the optimum mode, the outcomes of modeling portrayed that the introduced system can culminate in furnishing cooling capacity of 9.216 kW and net electricity of 1.026 kW, respectively, at lower convective zone (LCZ) temperature of 359.7K, LCZ's thickness of 1.003m, non-convective zone of 1.339m, upper convective zone of 0.102m, and solar pond area of 189,476m2. Under this optimum condition, the energy and exergy efficiencies are evaluated around 28.26% and 29.95%, respectively, using R245fa as working fluid in the ERC. In the optimal scenario, the ERC should be designed with primary pressure of 0.49 MPa, secondary pressure of 0.098 MPa, mass entrainment ratio of 0.3046, nozzle efficiency of 96.77%, mixer efficiency of 95.52%, and diffuser efficiency of 76.7%.

Laboratory investigation of the efficiency optimization of an inclined two-phase closed thermosyphon in ambient cool energy utilization

Abstract Some environmental and engineering problems are associated with permafrost thaw or degradation due to the releasing of CO2, the reducing of soil strength and the change of hydrologic processes. How to control the geothermal to approach these problems in cold regions is an important issue. Two-phase closed thermosyphons (TPCTs) are simple and efficient energy exchangers that are used in low-temperature refrigeration systems. In this study, a series of experiments were carried out to explore the geotemperature control process of a TPCT in an air-TPCT-soil system by storing renewable ambient cool energy. To enhance the control efficiency of the TPCT, we considered different operating conditions, with inclination angles of 90°, 70°, and 50°. The results indicate that the TPCT can cool the surrounding soil by selectively capturing the ambient energy due to its thermal semi-conductor effect. The inclination angle can change the efficiency of the TPCT, which should be accounted in engineering design. Under the experimental conditions, the geotemperature control efficiency of the TPCT with an inclination angle of approximately 70° was the optimal. The results of this study could provide a basis for the design of TPCTs used in cool energy utilization and other energy storage applications.

Comparison of the biogas upgrading methods as a transportation fuel

Abstract The aim of this study is investigating and analyzing the water scrubbing, cryogenic separation, amine scrubbing and caustic wash biogas upgrading processes. In order to comparing the upgrading processes, input condition is supposed to be fixed for all of the processes. The results of this study indicate that although amine scrubbing process consumes less power but the required hot utility is higher than other upgrading methods. In the cryogenic process, high pressure operating condition needs high compression power. This process also needs low temperature refrigeration system. Water wash process is a simple and economic method which has acceptable separation efficiency, but caustic wash is more efficient than other methods and its energy consumption is reasonable.

Theoretical investigation on performance improvement of a low-temperature transcritical carbon dioxide compression refrigeration system by means of an absorption chiller after-cooler

A Transcritical Carbon dioxide Compression (TCC) refrigeration system is a suitable tool to provide low-temperature refrigeration, but with a low COP. To improve the performance of a TCC, different combinations of Liquid Suction Heat Exchanger (LSHE), after-cooler and two-stage compression are embedded into the system configuration. The cooling load of the after-cooler is provided by an Absorption Chiller (ABSC) and the required heating energy to run the ABSC is recovered from the hot refrigerant leaving the compressors of the TCC. Eleven modified configurations are proposed and modeled in detail by EES software and energy and exergy analyzes are performed for each configuration. The results showed that the two-stage compression is a suitable method to upgrade the TCC system performance from both first and second laws of thermodynamics view point. The COP of a typical two-stage TCC is calculated to be 207% higher than its single-stage counterpart, in an evaporator temperature of −50 °C. It is also concluded that the combination of a two-stage compression TCC and a single-effect LiBr ABSC, performs with the highest performance. This combination increases the TCC system performances for about 4 and 2 times compared to single-stage and two-stage TCCs, respectively. A parametric study also revealed that well-calculated operating conditions are fundamental in design of TCCs to gain the highest performance.

Energy and Exergy Analysis for Low-Temperature Refrigeration System for Biogas Upgrading

Low-temperature refrigeration system for biogas upgrading has been developed by the Cryo Pur company based on cooling biogas in three steps: removing most of the water content at -40°C, removing siloxanes and SVOCs at -85 °C and frosting CO2 at temperatures varying from -90 °C to -120°C. This process transforms biogas containing typically 60% methane, 35% CO2, 5% water vapor in methane containing 2.5% of CO2. This paper studies how a single low-temperature refrigeration system is able to cool biogas with an indirect system using low-temperature heat-transfer fluids. The exergy study defines the exergy losses and served as guidance for the energy/pinch analysis that is used for the design of the heat-exchanger series and the appropriate heat recovery. An optimal system could save up to 40% of the electric consumption of the refrigeration system.

Airside performances of finned eight-tube heat exchangers

For applications in the relatively low temperature refrigeration systems with large constant temperature bath, the present work performed the experimental studies on the airside performances of the staggered finned eight-tube heat exchangers with large fin pitches. The airside heat transfer coefficients and pressure drops for three fin types and two fin pitches are obtained and analyzed. The heat transfer enhancement with louver fins is 11–16 % higher than the flat fins and that with sinusoidal corrugated fins is 1.1–3.4 % higher than the flat fins. Higher Re brings larger enhancement for various fins. Fin pitches show weak influence on heat transfer for eight tube rows. However, effects of fin pitch on heat transfer for both the sinusoidal corrugation and the louvered fin are larger than the flat fins and they are different from those for N ≤ 6. Airside Colburn j factor are compared with previous and it could be concluded that the airside j factor is almost constant for finned tube heat exchangers with eight tubes and large fin pitches, when Re is from 250 to 2500. The results are different from previous studies for fewer tube rows.

Thermodynamic investigations of Zeotropic mixture of R290, R23 and R14 on three-stage auto refrigerating cascade system

The zeotropic mixture of environment friendly refrigerants (hydrocarbons and hydrofluorocarbons) being the only alternatives for working fluid in low temperature refrigeration system. Hence, three-stage auto refrigerating cascade system was studied for the existence using four combinations of three-component zeotropic mixture of six different refrigerants. The exergy analysis confirmed the existence of three-stage auto refrigerating cascade system. The performances of the system like coefficient of performance, exergy lost, exergic efficiency, efficiency defect, and the evaporating temperature achieved were investigated for different mass fractions in order to verify the effect of mass fraction on them. In accordance with the environmental issues and the process of sustainable development, the three-component zeotropic mixture of R290/R23/R14 with the mass fraction of 0.218:0.346:0.436 was performing better and hence can be suggested as an alternative refrigerant for three-stage auto refrigerating cascade system operating at very low evaporating temperature in the range of ?97?C (176 K), at coefficient of performance of 0.253 and comparatively increased exergic efficiency up to 16.3% (58.5%).

Energy and exergy analysis of a two-stage cascade refrigeration system

A noble integration of a cascade refrigeration system with a two-stage compression chiller is proposed. The compression and the absorption systems have a cascade inter-cooler/evaporator, and the compression system has two compressors working in series. The compressors can be either reciprocating or screw type. This system runs by a driving unit which can be a micro-turbine or a solid oxide fuel cell. The system components are modeled and analyzed through the energy and exergy approaches. The performance parameters of the systems and the second law efficiency are calculated in different operating conditions. The results show that the maximum irreversibilities happen in the generator and the first-stage compressor, and the total destruction is higher when a micro-gas turbine is used as the prime mover. It appears that by using reciprocating compressors, energy and exergy are consumed up to 260% and 188% more efficiently in the proposed system compared to a traditional single-stage compression refrigeration system. The two latter parameters would be 53.7% and 29.2% in case of using screw compressors. Practical application: So much of our lives rely on refrigeration, from the food that we eat to the transportation and processing of vital resources. Industrial refrigeration systems such as gas compression, oil and gas processing, petrochemicals, power generation, carbon capture and food processing and storage are dependent on low-temperature refrigeration systems. Multi-stage refrigeration cycle is a conventional approach to provide low temperature for industrial processes. The proposed cascade system can reduce the energy consumption of a two-stage refrigeration system, using the waste heat from an industrial process. The first and second law analysis of the proposed system approves the upgrade in energy and exergy efficiencies of this system.

Design of a mechanical subcooling system device for increasing a low temperature refrigeration system’s capacity

El subenfriamiento mecánico se emplea para incrementar el coeficiente de desempeño de cualquier ciclo de refrigeración,especialmente en las aplicaciones de baja temperatura. Cuando es necesario reconfigurar un cicloexistente, un dispositivo de subenfriamiento mecánico permite una gran flexibilidad para encontrar un puntoespecífico de operación, ya sea un sistema combinado con un mejor coeficiente de desempeño (COP) y una mayorcapacidad de refrigeración o un sistema combinado de la misma capacidad que trabaja por menos tiempo y unmejor COP. Las simulaciones corridas en Aspen HYSYS® permiten estudiar tantos casos posibles como puedenpresentarse para lograr un diseño óptimo en el sistema reconfigurado, teniendo en cuenta la restricciones querepresentan cada uno de los componentes existentes en el sistema principal.

Exergy and energy analysis of three stage auto refrigerating cascade system using Zeotropic mixture for sustainable development

The Zeotropic mixture of environment friendly refrigerants (HC’s and HFC’s) being the only alternatives for working fluid in low temperature refrigeration system and hence three stage auto refrigerating cascade (ARC) system was studied for the existence using two combinations of (R290/R23/R14, R1270/R170/R14) three component Zeotropic mixture of five different refrigerants. The exergy analysis confirmed the existence of three stage ARC system. The performances of the system like Coefficient of Performance (COP), exergy lost, exergic efficiency, efficiency defect and the evaporating temperature achieved were investigated for different mass fractions in order to verify the effect of mass fraction on them. In accordance with the environmental issues and the process of sustainable development, the three component Zeotropic mixture of R290/R23/R14 with the mass fraction of 0.218:0.346:0.436 was performing better and hence can be suggested as an alternative refrigerant for three stage ARC system operating at very low evaporating temperature in the range of 176K (−97°C) at COP of 0.253 with 58.5% exergic efficiency (comparatively 22.6% increased value).

캐스케이드 냉동시스템과 2단 압축 1단 팽창식 냉동 시스템의 성능 비교

<TEX>$-30^{\circ}C{\sim}-50^{\circ}C$</TEX> 범위의 저온 증발온도를 얻기 위해서는 2단 압축 1단 팽창식 냉동 시스템이나 캐스케이드 냉동 시스템이 필요하다. 하지만 이러한 냉동시스템의 성능 비교에 대한 연구 결과는 대단히 부족한 실정이다. 본 논문은 R744-R404A용 캐스케이드 냉동시스템과 R404A용 2단 압축 1단 팽창식 냉동 시스템의 성능을 서로 비교한 것이다. <TEX>$-30^{\circ}C{\sim}-50^{\circ}C$</TEX>의 증발온도 범위에서 2단 압축 1단 팽창식 냉동시스템의 성능계수가 캐스케이드 냉동시스템 보다 약 36%~57% 정도 높다. 하지만, 2단 압축 1단 팽창식 냉동 시스템의 경우 증발온도와 압축효율 감소시에 성능계수의 변화가 커서 안정적이지 못하다. 특히, 압축효율 감소시에 성능계수가 크게 감소하는데, 이는 장기간 냉동 시스템의 사용시에 단점이 될 수 있다. 반면, R744-R404A용 캐스케이드 냉동 시스템은 자연냉매를 사용하여 친환경적이며, 고온과 저온 사이클에 사용되는 냉매의 적절한 선택에 의해서 다양한 온도영역에서 고효율 냉동 시스템을 구성할 수 있다. 위의 결과로부터, 성능과 환경적인 측면을 고려하여 용도에 따라 적합한 저온 냉동시스템을 선택하는 것이 좋으리라 판단된다. In order to obtain a low evaporation temperature ranging from <TEX>$-30^{\circ}C{\sim}-50^{\circ}C$</TEX>, a cascade refrigeration system and two-stage compression one-stage expansion refrigeration system is required. However, the research results of performance comparison of these refrigeration system are very scarce. This paper were compared the performance characteristics of R744-R404A cascade refrigeration system and R404A two-stage compression refrigeration system. The COP of R404A two-stage compression refrigeration system is about 36~57% greater than that of R744-R404A cascade refrigeration system in the range of evaporation temperature of <TEX>$-30^{\circ}C{\sim}-50^{\circ}C$</TEX>. But R404A two-stage compression refrigeration system is unstable because COP is significantly changed when evaporating temperature and compressor efficiency decreased. In particular, when compressor efficiency decreased, COP is significantly decreased. In this case, not efficient for long-term use. Whereas R744-R404A cascade refrigeration system using natural refrigerants. Therefore, it is environmentally friendly. And this system is high-efficiency refrigeration system. The reason it can be configured by selecting the suitable refrigerant at high-temperature side and low-temperature side. From the above results, select the appropriate low temperature refrigeration system by considering the environmental and performance aspects.