Refrigeration Components Research Articles

Energy efficiency enhancement of mixed refrigerant process in LNG plant

The liquefaction natural gas (LNG) process is one of the most important thermodynamic processes in the cryogenic gas industry. The operating conditions change during the compression process, throttling and heat transfer, changing the thermodynamic properties of the natural gas (NG) and refrigerants in the major equipments, including cryogenic compressors, expanders, coolers and heat exchangers. To improve the energetic efficiency of LNG plant, a thermodynamic analysis by the exergetic method was used. Energy equilibrium equations and exergy equilibrium equations of each equipment in the Air Products and Chemicals Inc (APCI) process were established. This paper is limited to the exergy analysis of the mixed refrigerant (MR) components: the axial and centrifugal compressors and the main cryogenic heat exchanger. The results show that the inlet temperature and inlet pressure of MR compressors has an impact on the evolution of the exergy efficiency. For a process MR, axial compressor is the main equipment contributing to total exergy losses.

Development and performance test of a miniature movable mixed-refrigerant liquid nitrogen generator

In order to cover long-term but small quantity liquid nitrogen requirements of laboratory or field users, a miniature movable mixed-refrigerant liquid nitrogen generator (MRLN) was developed and tested here, based on a precooled mixed-refrigerant J-T (MRJT) refrigerator. With the full air-cooled, skid-mounted structure, this MRLN was built utilizing off-the-shelf refrigeration components like commercial single-stage oil-lubricated compressors to reduce construction cost greatly. Bottled pure N2, pressure swing adsorption (PSA) unit and mini cryogenic rectification column could be employed to supply N2 in different operation modes respectively. In pure N2 mode, N2 was directly liquefied by the MRJT refrigerator. With feed N2 at 0.8 MPa, the specific power consumption (SPC) was 1.79 kWh L−1, and figure of merit (FOM) was 6.27%. The estimated SPC in PSA mode was 2.68 kWh L−1. For column mode, the SPC was 4.59 kWh L−1, with FOM of 3.38%. A closed N2 cycle could convey cooling capacity between flammable refrigerant and air. This MRLN could be a convenient and low-costing choice for some liquid nitrogen users.

Lattice Boltzmann numerical method for natural convection and entropy generation in cavity with refrigerant rigid body filled with DWCNTs-water nanofluid-experimental thermo-physical properties

In the present study, the natural convection heat transfer and total entropy generation are analyzed by utilizing Lattice Boltzmann numerical method. The simulations are performed for square cavity in presence of refrigerant rigid body. Moreover, the cavity is filled with the DWCNTs-water. The utilized nanofluid is prepared in the laboratory, and the thermo-physical properties, thermal conductivity and dynamic viscosity, of the nanofluid are measured experimentally by means of modern measuring devices. The DWCNTs-water nanofluid is obtained in different solid volume fractions of 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, and 0.5%, and thermo-physical properties are measured in all solid volume fractions and temperature range of 300–340 (K). The side walls have constant/uniform hot temperature, the top and bottom walls are insulated, and the rigid bodies are cooled with constant/uniform temperature acting like refrigerant components. Effects of different governing parameters such as four different positions of refrigerant rigid bodies, Rayleigh number and solid volume fraction on the flow structure, temperature map, Nusselt number and total/local entropy generation are obtained and discussed comprehensively. It is concluded that the array of refrigerant bodies has significant influence on the streamlines and isothermal lines. Furthermore, the average Nusselt number is highest as array is in Double Vertical form, and is lowest when the array is in Single Horizontal form. Also, the Nusselt number has direct relationship with Rayleigh number and solid volume fraction. On the other hand, the total entropy generation has direct and reverse relationship with Rayleigh number and solid volume fraction, respectively.

Model Development of Cold Chains for Fresh Fruits and Vegetables Distribution: A Case Study in Bali Province

In developing countries such as Indonesia, as much as 40% of total vegetables and fruits production becomes waste because of lack refrigeration. This condition also contributes a food crisis problem besides other factor such as, climate change and number of population. Cold chain system that will be modelled in this study is for vegetables and fruits and refrigeration system as the main devices. In future, this system will play an important role for the food crisis solution where fresh food can be distributed very well with significant low waste. The fresh food also can be kept with good quality and hygienist (bacteria contaminated). Cold Chain model will be designed using refrigeration components including, pre cooling chiller, cold room, and truck refrigeration. This study will be conducted by survey and observation di around Bali Province focus on vegetables and fruits production center. Interviews and questionnaire will be also done to get some information about the conventional distribution obstacles and problem. Distribution mapping will be developed and created. The data base of the storage characteristic of the fruits and vegetable also collected through experiment and secondary data. Depend on the mapping and data base can be developed a cold chain model that has the best performance application. The model will be can directly apply in Bali to get eligible cold chain in Bali. The cold chain model will be compared with the conventional distribution system using ALCC/LCC method and also others factor and will be weighted to get better results.

Process development and exergy cost sensitivity analysis of a novel hydrogen liquefaction process

A novel hydrogen liquefaction process including a single mixed refrigerant cycle is proposed and investigated by energy, conventional and advanced exergy and exergoeconomic analyses methods. The proposed liquefaction process can produce 130 tons liquid hydrogen per day. Results of energy analysis reveals that 7.646kWh/kgLH2 power is consumed to liquefy the hydrogen from 21 bar to 25 °C. Exergy analysis indicates that exergy efficiency of the proposed hydrogen liquefaction process is almost 32%, which is higher than Ingolstadt operating hydrogen liquefaction plant with exergy efficiency of 21.28%. Also, the power consumption of proposed hydrogen liquefaction plant is less than its kind between other similar conceptual processes. Based on the advanced exergy analysis, most part of the exergy destruction rates of the compressors, heat exchangers and air cooler are endogenous, while the dominant part of irreversibilities of the turbo expanders is exogenous. Effect of mole fraction of the mixed refrigerant components on performance of the process is investigated. Also, sensitivity of exergy destruction cost rate and exergoeconomic factor to operating variables of the proposed hydrogen liquefaction process is investigated and discussed. Results of the analyses show that maximum exergy destruction cost rate of the process components is 2265.26 $/h, which most of it is endogenous and unavoidable.

Design Construction and Performance of 10W Thermoacoustic Refrigerators

In this paper, the construction and performance of the 10[Formula: see text]W cooling power thermoacoustic refrigerators designed for a temperature difference of 120 K at 3% drive ratio are discussed. The construction and assembly procedure of the optimized thermoacoustic refrigerator components viz. spiral stack, heat exchangers, 0.28[Formula: see text]-taper, small diameter tube and divergent section with hemispherical end (TSDH) and 0.24[Formula: see text]-taper and divergent section with hemispherical end (TDH) resonator designs and loudspeaker found in the published literature, and instrumentation are discussed. The performance of the 0.28[Formula: see text]-TSDH, and 0.24[Formula: see text]-TDH resonator designs, and the uncertainties involved in the experimental measurements are discussed. Both the resonator designs show good behavior. A decent low temperature of [Formula: see text]11.3[Formula: see text]C and [Formula: see text]8.7[Formula: see text]C at 10[Formula: see text]W cooling power is achieved at the cold heat exchanger for the 0.28[Formula: see text]-TSDH and 0.24[Formula: see text]-TDH resonator designs, respectively. The comparative analysis of the experimental results with the theoretical and DeltaEC results is discussed.

A study on the use of dual mixed refrigerant in a cascade dual mixed refrigerant cycle

In this article, a precooling cycle was used to reduce the power consumption and improve the heat transfer efficiency of a mixed refrigerant cycle. Propane precooling and mixed refrigerant precooling are two common precooling methods. The cascade dual mixed refrigerant cycle, which involves mixed refrigerant precooling and has a specific power consumption 10.9% lower than that of propane precooling, has been widely used. In order to analyze the relationships among precooling temperature, mixed refrigerant composition, and specific power consumption, the specific power consumption of a cascade dual mixed refrigerant cycle was investigated. A mixed refrigerant cooling temperature of 223 K, a precooling mixed refrigerant comprising C2H6–C5H12, and a subcooling mixed refrigerant comprising N2 and CH4–C3H8 yielded optimal results. In addition, a mixed refrigerant component ratio optimization model was established for the dual mixed refrigerant cycle. The results indicated that the optimum mixed refrigerant component ratios corresponded with the lowest levels of specific power consumption. Furthermore, by studying the effects of the feed gas pressure and temperature on the mixed refrigerant component ratios, the optimal operating conditions of the cascade dual mixed refrigerant cycle were determined to be 5.0 MPa and 298 K.

A novel hydrogen liquefaction process configuration with combined mixed refrigerant systems

A novel large-scale plant for hydrogen liquefying is proposed and analyzed. The liquid hydrogen production rate of the proposed plant is 100 tons per day to provide the required LH2 for a large urban area with 100,000–200,000 hydrogen vehicles supply. In the pre-cooling section of the process, a new mixed refrigerant (MR) refrigeration cycle, combined with a Joule–Brayton refrigeration cycle, precool gaseous hydrogen feed from 25 °C to the temperature −198.2 °C. A new refrigeration system with six simple Linde–Hampson cascade cycles cools low-temperature gaseous hydrogen from −198.2 °C to temperature −252.2 °C. The process specific energy consumption (SEC) is 7.69kWh/kgLH2 which minimum value is 2.89kWh/kgLH2 in ideal conditions. The exergy efficiency of the system is 39.5%, which is considerably higher than the existing hydrogen liquefier plants around the world. However, assuming more efficiency values for the equipment can improve it. The energy analysis specifies that coefficient of performance (COP) of the process is 0.1710 which is a high quantity of its kind between other similar processes. Effect of various refrigerant components concentration, discharge pressure of the high pressure compressors of the pre-cooling section, and hydrogen feed pressure on the process COP, exergy efficiency, and SEC are investigated. After that, a new MR will be offered for the cryogenic section of the plant. The system improvements are considerable comparing to current hydrogen liquefying plants, therefore, the proposed conceptual system can be used for future hydrogen liquefaction plants design.

Reliability and availability analysis of a 10 kW@20 K helium refrigerator

A 10 kW@20 K helium refrigerator has been established in the Technical Institute of Physics and Chemistry, Chinese Academy of Sciences. To evaluate and improve this refrigerator’s reliability and availability, a reliability and availability analysis is performed. According to the mission profile of this refrigerator, a functional analysis is performed. The failure data of the refrigerator components are collected and failure rate distributions are fitted by software Weibull++ V10.0. A Failure Modes, Effects & Criticality Analysis (FMECA) is performed and the critical components with higher risks are pointed out. Software BlockSim V9.0 is used to calculate the reliability and the availability of this refrigerator. The result indicates that compressors, turbine and vacuum pump are the critical components and the key units of this refrigerator. The mitigation actions with respect to design, testing, maintenance and operation are proposed to decrease those major and medium risks.

Relationship between composition of mixture charged and that in circulation in an auto refrigerant cascade and a J-T refrigerator operating in liquid refrigerant supply mode

The composition of the refrigerant mixture in circulation during steady state operation of J-T and allied refrigerators is not the same as that charged due to liquid hold up in the heat exchangers and phase separators, as well as the differential solubility of different refrigerant components in the compressor lubricating oil. The performance of refrigerators/liquefiers operating on mixed refrigerant cycles is dependent on the mixture composition. It is therefore important to charge the right mixture that results in an optimum composition in circulation during steady state operation. The relationship between the charged and circulating composition has been experimentally studied in a J-T refrigerator operating in the liquid refrigerant supply (LRS) mode and an auto refrigerant cascade refrigerator (with a phase separator) operating in the gas refrigerant supply (GRS) mode. The results of the study are presented in this work. The results show that the method presented earlier for J-T refrigerators operating in GRS mode is also applicable in the case of refrigerators studied in this work.

Investigations into air and refrigerant side heat transfer coefficients of finned-tube CO2 gas coolers

Gas coolers are heat rejection heat exchangers in vapour compression refrigeration systems that use carbon dioxide (CO2) as refrigerant. The design of gas coolers has a significant influence on the performance of CO2 refrigeration systems as it determines to a large extent the gas cooler/condenser pressure and the power consumption of the system. This paper investigates local refrigerant and air heat transfer coefficients in plain fin-and-tube gas cooler coils using Computational Fluid Dynamics (CFD) modelling. The aims were to provide insights into the variation of the local heat transfer rates in the coil and determine the influence of a) design enhancements such as the use of slit fins and b) to develop correlations for overall refrigerant and air heat transfer coefficients to be used in CO2 refrigeration component and system modelling. The results from the model which was validated against experimental measurements showed that a horizontal slit on the fin between the first and second row of tubes can lead to an increase in the heat rejection rate of the gas cooler by between 6% and 8%. This in turn can lead to smaller heat exchanger heat transfer area for a given heat rejection capacity or lower high side pressure and higher efficiency for the refrigeration system. The results and heat transfer correlations developed are a valuable resource for researchers and manufacturers of CO2 and other heat exchanger coils that experience a wide variation in refrigerant temperature during the gas cooling process.

Optimization of modified single mixed refrigerant process of natural gas liquefaction using multivariate Coggin’s algorithm combined with process knowledge

The optimization of a mixed refrigerant liquefaction process is a challenge because of its non-linear characteristics with stringent multiple process constraints. This study proposes a novel hybrid approach for the optimization of a newly developed, modified single mixed refrigerant process of natural gas liquefaction targeted for offshore applications. This contribution focuses on interpreting the geometric pattern of a plot of the temperature difference between the hot and cold composite curves in a cryogenic heat exchanger to understand the profound effects of the flow rates of the individual refrigerant components and the operating pressure on the liquefaction efficiency. From this, an effective method to generate a proper initial approach temperature profile was developed to ensure robust convergence of the main optimization step. An enhanced coordinate descent methodology was implemented in the main optimization procedure to accelerate the optimization of the modified single mixed refrigerant liquefaction process. The proposed knowledge-inspired hybrid optimization approach showed a robust convergence on determining the optimal design condition. The total energy requirement for natural gas liquefaction cycle was reduced by 21.9% compared to the base case. The proposed methodology can be extended directly to solve optimization problems for other mixed refrigerant based natural gas liquefaction processes.

Experimental Validation of On-Field Measurement Method for a Heat Pump System with Internal Heat Exchanger

Determining the on-field heating capacity and coefficient of performance (COP) of residential air-to-air heat pumps (HPs) is problematic, given that measuring accurately the enthalpy and, specifically, the mass flow rate of air is challenging. This paper validates a promising on-field performance measurement method for HPs with an internal heat exchanger (IHX) as vapor injection system using experimental data obtained from air-to-water heat pump prototype in several operating conditions. The method is based on refrigerant fluid measurements and component energy/mass balances. Nonintrusive sensors, such as surface temperature sensors, are used to estimate pressure and refrigerant mass flow rate in different types of heat pump systems, including air-to-air. Obtained results compared with intrusively measured reference values in steady-state conditions are in good agreement, suggesting that a comprehensive performance analysis can be conducted in already-installed high efficiency residential IHX air-to-water HPs, as well as internal heat exchanger air-to-air HPs.

EFFECT OF COLD STORAGE USING SOLAR ENERGY ON QUAILTY OF POMEGRANATE FRUITS

This study aims to evaluate a cold storage system using solar energy of pomegranate fruits (cv. Wonderful) for storage period 50 days under storing temperatures of (5 oC) and relative humidity of 90 -95 %. The storage process was done using two refrigeration systems one of them is a refrigerator driven by solar energy, the other one driven using electrical energy. The component of refrigerator driven by solar energy consists, two parallel photovoltaic cells (PV), two batteries, an inverter, and cables, In addition to refrigerator unit. Testing the PV system showed that, nine hours discharge time for one battery is available during connected to the cold storage. So it is necessary to use two batteries connected in series to be suitable for refrigerator driven power and Egyptian conditions, and can therefore run the cooling system throughout the day without interruption. The percentage of weight loss, hardness, and total soluble solid (TSS) for pomegranate fruits using refrigerator driven using photovoltaic cell were 8.46 %, 11.18 kgf, and 15.80% respectively; Meanwhile cold storage driven by electrical energy, these parameters were 8.79 %, 10.41 kgf, and 15.71% respectively. Operating cost using solar energy achieved the lowest cost compare with using electrical energy, therefore, can rely on the use of solar energy instead of electrical energy to operate the refrigeration unit. From the above results, pomegranate fruit inside PV driven refrigerator has a good quality compared with pomegranate fruit inside electrically driven refrigerator.

Application of investigation techniques to identify an arson fire

Determining the cause of an arson fire is the most difficult part of fire investigation. In this study, the researcher used various clues and several pieces of fire debris collected from the actual fire site to conduct a series of experiments and analyses in sequence, starting from metallographic analysis to inductively coupled plasma optical emission spectrometry and then a thermal analysis experiment to determine the cause of a fire. It was found that when the temperature was elevated at a rate of 2 °C/min, polyurethane (PU) foam, a structural component of refrigerators, started thermal decomposition. At about 130 °C, the thermal decomposition accelerated, and eventually at 384 °C, about 4883.33 J/g of maximum heat was released. In the end, remaining debris was about 4.96%. Therefore, the combustion of PU foam is an ultrafast type of combustion reaction. The content as well as the experimental procedure of the study is useful for fire investigators in determining the cause of arson fires.

Keeping Your Compressor Healthy: Developing the Right Lubricant Formulation is the Key

Selecting the correct compressor lubricant is crucial to the duration of the compressor and the refrigerant systems’ useful life. However, developing an optimized lubricant for a refrigeration system requires a multitude of screenings and tests. The compatibility and stability of the lubricant with the refrigerant and compressor components needs to be examined at various accelerated conditions. The lubricant and refrigerant working viscosity must be determined at various refrigerant concentrations, temperatures and pressures as the diluted refrigerant in the lubricant has a significant effect on the viscosity. The correct lubricant formulation needs to be investigated for optimal performance. A compressor lubricant can provide many benefits to a refrigeration system such as bearing durability, sealing, and increased efficiency. Sometimes it is necessary to formulate the lubricant in order to optimize system performance. Specifically, this study investigated anti-wear properties of different oil additives to create a more robust refrigeration system. Many different additives and concentrations were considered and screened. Pending a successful screen test; these different additives’ anti-wear properties were analyzed using bench top tribology tests. To reduce uncertainty and provide more in-situ results the different additives were operated in a refrigerant compressor on a gas-loop testing apparatus. Oil samples were taken periodically during the test duration for analysis. Lastly, upon test completion the compressors were dismantled and the parts were examined to determine the effectiveness of the anti-wear additives.

Wireless sensors system for the chillers fault diagnostic based on characteristic Petri net modelling

The chillers are important refrigeration components of building air-conditioning systems and their operational status is directly related to the building's HVAC system performance and stability. The issue of fault diagnosis of chillers has received wide attention. This paper will feature Characteristic Modelling Technology in fault diagnosis for chillers and modelling with fuzzy Petri net technique. Using fuzzy Petri nets knowledge representation and inference algorithm for matrix operations describes the characteristic parameters of chiller fault indication and relationships. Using the proposed diagnostic systems can take full advantage of the information resources of characteristic parameters for fault diagnosis, and according to chiller efficiency indexes of COP a comprehensive diagnosis of fault diagnosis and chiller can run efficiently. The test results of plant running show the feasibility and accuracy of the fault diagnostic system.

Magnetic Shielding Effect on Halbach Cylinder used in Magnetic Refrigerators

The system for producing magnetic field constitutes an important component of magnetic refrigerator. Many researchers have directed significant effort to increase the magnetic field intensity, because the magnetocaloric effect at the Curie temperature increases with the power of 2/3 of the magnetic field. In this study, we report the simulation of the magnetic field intensity at polar axis of a Halbach cylinder (HC) by i) changing the length and thickness of the HC, ii) having with or without gap of the HC, and iii) surrounding the HC with a soft magnet shell, acting as a shielding. We simulated the field distribution of a HC with a finite size. Furthermore, the detailed numerical results of the magnetic field distribution and its dependence on shielding are presented in this study.

Shape optimization of compressor supporting plate based on vibration modes

In typical household refrigeration systems, the compressor is structurally connected to the cabinet through an assembly composed of rubber mounts and a steel support plate, usually called base-plate. This plate works as a vibration energy path from the compressor to other refrigerator components, and its dynamic behavior must be known in order to avoid the coincidence of resonances and operational frequencies , a situation in which the energy flow is maximized. One way to design a support that satisfies this requirement is to optimize the shape of the plate, locating its structural modes as far as possible from the operational frequency and first harmonics. In this work, the Finite Element Method (FEM) is used to solve the eigenvalue problem and to parameterize the optimization procedure, which is based on positioning of the nodes of a design region (the plate) in a FEM simplified model. Due to the large number of variables, a gradientbased method is adopted. The objective of the methodology is to maximize the difference between two adjacent eigenvalues near the fundamental operation frequency of the compressor, in order to obtain a large and effective bandgap. A geometrical constraint is imposed to the problem and it is represented by a maximum allowed deformation of the plate. The gradients needed are obtained using elementary stiffness and mass matrices information. The obtained results show that the procedure leads to a new shape which ensures the desired dynamic characteristics for the support plate.

DESIGN AND OPTIMIZATION OF A LOUDSPEAKER DRIVEN 10-W COOLING POWER THERMOACOUSTIC REFRIGERATOR

The design and optimization procedure for a loudspeaker driven 10-W cooling power thermoacoustic refrigerator components with a temperature difference of 120 K has been discussed using the linear thermoacoustic theory. The resonator losses are proportional to surface area and the optimum diameter ratio of small and large resonator tubes for minimum heat loss for a quarter-wavelength hemispherical ended resonator design is discussed. The hemispherical ended resonator design is further analytically optimized to increase COP, cooling effect at cold heat exchanger and power density by decreasing total resonator surface area and volume. An alternate convergent-divergent resonator design is proposed which is found to be more efficient compared to previous published designs. Resonator designs are tested with DeltaEC software, which predicts a lowest temperature of -48°C and -47°C for the improved hemispherical and convergent-divergent resonator designs, respectively. Theoretical results are in good agreement with DeltaEC results.