Refrigeration Technology Research Articles

Study on physical prediction model of liquid film development and dry out point in helical tube

Helical tubes are widely used in nuclear plants, heat recovery process, refrigeration technology, etc. It is obtained the helical tubes dry out point prediction model in accordance with the experimental conditions by numerical simulation. The article is based on the physical model of the liquid membrane in the helical tube before dry out happened, establishing the analytical process of liquid film development in helical tube. The physical mechanism, thermo-hydraulic parameters that affect liquid film crushing are analyzed. The dry out point of helical tubes is predicted based on the experimental data. The result shows that the geometrical, thermo-hydraulic parameters of helical tube will affect the occurrence of the dry out point, the development process of liquid film before evaporation of spiral tube is obtained. The prediction model of dry out point is fitted to experimental data and the predicted results of evaporation point can be used to optimize during the engineering design.

The study of excess enthalpy for {ionic liquid + ethanol} binary systems as new working fluids in absorption refrigeration technology

Binary systems composed of phosphonium – based ionic liquid and water, or short-chain alcohols exhibit properties which render them suitable as candidates for working fluids in absorption refrigeration technology. This work presents the study of the excess enthalpy (HE) of mixing in ethanolic solutions of the following ionic liquids: 1-ethyl-1-methylpiperidinium dimethyl phosphate, [C1C2PIP][DMP], 1-ethyl-1-methyl-pyrrolidinium dimethyl phosphate, [C1C2PYR][DMP], N,N,N-triethyl-N-methylammonium dimethyl phosphate, [N1,2,2,2][DMP],1-hydroxyethyl-1-methylpyrrolidinium dimethyl phosphate, [C1C2OHPYR][DMP], 1-ehtyl-1-methylmorpholinium diethyl phosphate, [C1C2MOR][DEP], 1-ethyl-1-methylpyrrolidinium diethyl phosphate, [C1C2PYR][DEP], and 1-ethyl-3-methylimidazolium diethyl phosphate, [C1C2IM][DEP] is presented. The experiment was performed at temperature T = 298.15 K and under ambient pressure using isothermal titration calorimetry technique. This work presents the effect of the core structure of the cation and the effect of the carbon chain length in the anion of the ionic liquid on the HE value of the systems studied. Experimental HE values were correlated using Redlich – Kister type equation. The standard deviations for the correlation vary from σ = 9 J∙mol−1 for {[C1C2OHPYR][DMP] + ethanol} to 28 J∙mol−1 for {[C1C2IM][DMP] + ethanol} showing significant agreement between experimental and calculated values. The negative excess enthalpy of mixing over the entire composition range was found in each system which indicate stronger (IL - ethanol) interactions associated with hydrogen bond formation in this system, compared to (IL - IL) and (ethanol - ethanol) interactions. For each system, the minimum of the excess enthalpy of mixing was determined, which increases in the following series: [N1,2,2,2][DMP] (HE = −2645.9 J·mol−1) < [C1C2PYR] [DMP] < [C1C2IM][DEP] < [C1C2PYR][DEP] < [C1C2PIP][DMP] < [C1C2MOR][DMP] < [C1C2OHPYR][DMP] (HE = −881.5 J·mol−1). This characteristic is desirable from the point of view of the possibility of using these systems in absorption refrigeration technology.

Numerical simulation of a multistage magnetic refrigeration system in the temperature range of liquid hydrogen

Magnetic refrigeration is an important new refrigeration technology in the temperature range of liquid hydrogen. A multistage magnetic refrigeration system between 20 K and 80 K has been proposed, which includes three-stage active magnetic regenerators (AMRs). Based on the multistage system, a two-dimensional transient AMR model is established to research the cycle performance mechanism by considering the compressibility of helium, which has not been done before. Firstly, to simplify the simulation difficulty, the AMR model with ideal magnetocaloric materials (the constant isothermal entropy change of 5.4 J/(kg·K) at 1 T) are investigated in the temperature range between 60 K and 80 K. Some parameters including particle diameter, fluid flow fraction, and filling mass of magnetocaloric materials have been compared and analyzed. Based on the above simulation results, the AMR model with real magnetocaloric materials has been done. In the three-layer AMR, the maximum cooling power of 71.04 W at the cooling temperature of 60 K has been obtained, which is 80.17% larger than that of the one-layer AMR. Then, the cooling performance of the multistage magnetic refrigeration system has been studied. In the system, six magnetocaloric materials are filled in three-stage AMRs based on the filling method of adiabatic temperature change. With the optimal mass flow rates of each stage AMR, the maximum cooling power of 40.09 W has been obtained in the multistage system, and the corresponding thermodynamic second efficiency has been 28.14%.

Performance enhancement of absorption refrigeration systems: An overview

The introduction of absorption refrigeration technology addressed several significant con-cerns in the domain of energy crisis, rising cost of fossil fuel, and ecological challenges aris-ing due to the excess use of traditional compression refrigeration systems. ARS (absorption refrigeration system) is gaining popularity as a result of benefits such as the use of low-grade heat sources and environmentally acceptable low-cost working fluid pairs. However, two sig-nificant hurdles to commercial success for this technology are the often too big size of the refrigeration system and the poor performance of the system. Numerous studies have been conducted in an attempt to discover methods for improving the COP (coefficient of perfor-mance) of ARS in order to get these systems more competitive in comparison to the conven-tional compression refrigeration systems. The goal of this article is to perform a review of the literature on different methods used to enhance the COP of ARSs based on cycle layout mod-ification and working pair selection as they are the promising solutions for the enhancement of the performance of ARSs. The futuristic aspect of this technology includes the introduction of new working pairs with no corrosion to the system components, including nanoparticles to increase heat transfer rate while reducing the cost of the system. Heat recovery methods should be introduced and the efficient design of various components especially the generator and absorber are to be addressed. This technology could be combined with other refrigeration technologies while utilizing the waste heat to further improve the efficiency of ARSs.

Ambient temperature, refrigerator food load, and door openings effect on a preservation performance indicator based on chicken temperature data and predictive microbiology.

Home preservation depends on the food matrix, refrigerator design/technology, consumer actions, and ambient temperature. Storing different food matrices in product-relevant refrigerator locations generating different temperature histories can be used to develop an indicator of how refrigerator technology, consumer habits, and environment conditions impact the refrigerator food preservation performance. In this study, poultry, particularly prone to spoilage reflecting its pH, nutrient availability, and high aw, was used to evaluate refrigerator preservation performance as affected by compressor technology (single [SS] and variable speed [VS]), ambient temperature (21.1°C [LT] and 32.2°C [HT]), and refrigerator load (22.5kg [RL] and 39kg [HL]). Time-temperature values collected for chicken breast stored in a drawer independently controlled at 0°C in a refrigerator set 5°C, and a Pseudomonas predictive microbiology model, were used to estimate a normalized refrigerator performance indicator (RPI). Values <1, ∼1, and >1 described excellent, good, or poor performance, respectively. A first analysis revealed that up to 54% of chicken breast temperatures were above its recommended refrigerated storage value. When ignoring variability sources, SS technology yielded RPI values ranging 0.61-0.70, whereas the more energy efficient VS compressor yielded values ranging 0.86-1.14. The higher and wider VS RPI range reflects a compressor control logic optimized for energy efficiency compliance while disregarding effects on food preservation. When considering the variability of model parameters and temperature measurements through one-sided 95% confidence intervals yielded RPI reaching 1.16. Although the independently controlled drawer preservation performance was near optimal, it can improve by considering energy use and preservation impact when optimizing the compressor speed control protocol. PRACTICAL APPLICATION: Worldwide poultry meat consumption has reached 15kg per person. Refrigeration is widely used for its safety and quality preservation. Efficiency regulations decreased the energy use of residential refrigerators by nearly tenfold even though their size increased by 50% in the last half century. In this study, we provide quantitative evidence that their preservation performance must be improved. This is particularly true for upper end units typically equipped with quieter and more energy-efficient variable speed compressors. The same methodology can be used to evaluate the preservation performance of the storage units, trucks, and display cases used for refrigerated products.

Basic Research on a Magnetic Refrigeration System for Cooling to Liquid Hydrogen Temperature

Magnetic refrigeration technology is expected to be a highly efficient process at a temperature of around 20 K, which is the hydrogen liquefaction temperature. In magnetic refrigeration, a magnetic field change is applied to a magnetocaloric material (MCM) to obtain a magnetocaloric effect. In addition, since the greater the magnetic field change, the better the cooling characteristics, the magnetic field strength of permanent magnets is insufficient, and the use of superconducting coils that can generate strong magnetic fields with low power consumption is essential. We are researching and developing a static magnetic refrigeration system (SMRS) that does not have moving parts to obtain magnetic field changes, and generates them by altering the energizing current to the coil. The key to devising this system is an AC loss of the superconducting coil. In this study, we measured the AC loss under energization conditions of multiple palm-sized REBCO coils at liquid nitrogen temperature, and calculated the efficiency of the SMRS by improving the accuracy of the analysis method for evaluating the AC loss, based on the results. We report the results and discuss the technical feasibility of SMRS.

A multi-stage, first-order phase transition in LaFe11.8Si1.2: Interplay between the structural, magnetic, and electronic degrees of freedom

Alloys with a first-order magnetic transition are central to solid-state refrigeration technology, sensors and actuators, or spintronic devices. The discontinuous nature of the transition in these materials is a consequence of the coupling between the magnetic, electronic, and structural subsystems, and such transition can, in principle, cross several metastable states, where at one point, the transition takes place within the magnetic subsystem, while at another, the changes occur in the structural or electronic subsystems. To address this issue, we conducted simultaneous measurements of the macroscopic properties—magnetization, temperature change of the sample, longitudinal, and transversal magnetostrictions—to reveal the rich details of the magneto-structural, first-order transition occurring in the prototypical alloy LaFe11.8Si1.2. We found that the transition does not complete in one but in two distinct stages. The presence of the intermediate state changes the potential-energy landscape, which then impacts strongly on the width of the hysteresis associated with the first-order transition. We complement these findings with experiments on the atomistic scale, i.e., x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and Mössbauer spectroscopy, and then combine them with first-principles calculations to reveal the full complexity and two-stage nature of the transition. This new approach can be successfully extended to a large class of advanced magnetic materials that exhibit analogous transformations.

Performance analysis of adsorption refrigeration using a composite adsorbent with improved heat and mass transfer

Adsorption refrigeration is a typical environmental protection and energy-saving waste heat utilization refrigeration technology. However, improving the heat and mass transfer performance of adsorption beds is crucial to the wide-spread applications of adsorption refrigeration systems. In this paper, three types of composite adsorbents are proposed: adsorbents with improved heat transfer, improved mass transfer, and simultaneously improved heat and mass transfer. Both characteristics of adsorption and heat transfer are tested and compared. Based on the experimental results, the use of these three types of composite adsorbents in the adsorption refrigeration system is further examined. The results indicate that the silica gel (SG)/MIL-100/CF (SGMC) composite outputs the highest cooling capacity and exhibits a coefficient of performance (COP) comparable to that of a composite adsorbent with improved mass transfer. The cooling capacity and COP of the proposed SGMC system compared with those of the traditional SG–water system increase by 22% and 12.8%, respectively, and the refrigeration cycle time is shortened by 16.7%. Based on the optimal SGMC system, the impact of operation parameters is further investigated, and optimum parameters are selected to enhance the overall system performance.

Direct Conversion of Phase-Transition Entropy into Electrochemical Thermopower and Peltier Effect.

Thermocell generates thermopower from a temperature difference (ΔT) between two electrodes. The converse process of thermocells is an electrochemical Peltier effect, which creates a ΔT on the electrodes by applying an external current. The Seebeck coefficient (Se ) of the electrochemical system is proportional to the entropy change of the redox reaction; therefore, a redox system having a significant entropy change is expected to increase the Se . In this study, a thermo-responsive polymer having a redox-active moiety, poly(N-isopropyl acrylamide-co-N-(2-acrylamide ethyl)-N'-n-propylviologen) (PNV), is used as the redox species of a thermocell. PNV2+ dication undergoes the coil-globule phase transition upon the reduction to PNV+ cation radical, and a large entropy change is introduced because water molecules are freed from the polymer chains. The Se of PNV thermocell drastically increased to +2.1mV K-1 at the lower critical solution temperature (LCST) of PNV. The entropy change calculated from the increment of Se agreed with the value evaluated by differential scanning calorimetry. Moreover, the electrochemical Peltier effect was observed when the device temperature was increased above the LCST. This study shows that the large entropy change associated with the coil-globule phase transition can be used in electrochemical thermal management and refrigeration technologies. This article is protected by copyright. All rights reserved.

Economic Practicability of the Implementation of the Mine Refrigeration Technology for Normalization of Thermal Conditions

Economic Practicability of the Implementation of the Mine Refrigeration Technology for Normalization of Thermal Conditions

Improved piezoelectric, ferroelectric, pyroelectric and electrocaloric properties of Sm-substituted PMN-PT

This study reports the processing and characterization of Pb0.96Sm0.025[Mg1/3Nb2/3]0.70Ti0.30O3 (Sm-PMN-PT) polycrystalline ceramics for solid-state refrigeration technologies. The composition illustrated maximum polarization of nearly 40 μC/cm2 at 293 K for an applied electric field of 17.5 kV/cm and piezoelectric coefficients d33 ∼ 146 pm/V under application of 10 kV/cm. It also showed a pyroelectric coefficient −4610 µC/m2/K1 in the temperature range 340 – 370 K. In contrast to parent PMN-PT, the composition showed above room-temperature ferroelectric transition offering an appealing change in polarisation and better suitability from a device viewpoint. Due to this, the present study explored Sm-PMN-PT for an electrocaloric effect (ECE) using Maxwell relations. Our calculations suggest a maximum ECE entropy (|∆S|) and temperature (|∆T|) changes of 0.55 J/Kg.K and 0.7 K for a broad temperature range of 20 K (390–410 K), respectively.

Electrocaloric effect of (Ba1-xSrx)(HfxTi1-x)O3 lead-free ferroelectric ceramics with phase structure regulation

Electrocaloric (EC) refrigeration is a new type of solid-state refrigeration technology based on the electrocaloric effect (ECE), which has the advantages of environmental protection, high efficiency, easy integration and miniaturization. In this paper, Sr2+ and Hf4+ are doped into the A and B sites of BaTiO3 (BT), respectively. By adjusting the proportional composition, the multicritical point is constructed to improve the adiabatic temperature change (ΔT), and the relaxor ferroelectrics are formed to broaden the working temperature span (Tspan). The effect of doping content on the crystal structure, surface morphology, dielectric, ferroelectric and electrocaloric properties of ceramics is studied systematically. The phase diagram of (Ba1-xSrx)(HfxTi1-x)O3 (BSHT) ceramics is established, and (Ba0.9Sr0.1)(Hf0.1Ti0.9)O3 (BSHT10) is at the multicritical point. It has the most excellent comprehensive electrocaloric performance, with ΔTmax obtained 1.2 K and Tspan (ΔT ≥ 0.9 ΔTmax) reached 45 °C under 50 kV/cm, indicating its potential as a lead-free bulk ceramic material for EC refrigeration applications.

Energetic and exergetic analysis of a Vapour compression refrigeration test rig in varying concentrations of (TiO2-SiO2/MO) hybrid nano-lubricants and R600a refrigerant charges

ABSTRACT Every residential refrigerator employs a Vapor Compression Refrigeration (VCR) technology. The performance of a VCR system is mostly determined by the input power and refrigeration effect. In present study, effects of varying concentrations of TiO2-SiO2/MO hybrid nano-lubricant (0.1, 0.2, 0.3, and 0.4 g/L), and mass charge of refrigerant R600a (80, 100, and 120 g) investigated by the authors. The performance parameters of the VCR test rig optimized at 0.2 g/L of hybrid nano-lubricant concentration using 100 g mass charge of R600a refrigerant. At this optimum condition, the percentage increase in coefficient of performance was 37.83% compared to the pure lubricant using 80 g mass charge of R600a refrigerant. The percentage reduction in input power at optimum condition was 13.46% compared to pure lubricant case using 80 g R600a, refrigerant mass charge. The maximum value of second law efficiency and the least value of exergy lost were found at 0.2 g/L concentration of hybrid nano-lubricant using 100 g charge of R600a refrigerant, with values of 77% and 96.90W, respectively. In conclusion, performance of VCR test rig altered when the concentrations of hybrid nano-lubricant and refrigerant mass concentrations changed.

Structural, magnetic and magnetocaloric properties of the Gd2Fe17-xCrx (x = 0, 0.5, 1 and 1.5) compounds

We have investigated the effect of the substitution of iron by chromium on the structural, magnetic and magnetocaloric behaviors of Gd2Fe17-xCrx (x = 0, 0.5, 1 and 1.5). The Rietveld analysis of the X-ray powder diffraction refinement showed that this substitution leads to an increase of the unit-cell volume. All the compounds show a ferromagnetic to paramagnetic transition at the Curie temperature (TC) from the variation of magnetization vs. temperature. Upon Cr substitution, the Curie temperature decreases from 475 K for x = 0 to a value of 452 K for x = 1.5. Arrott plot analyses were applied for verifying the order of the magnetic transition in this system, which was found to be of second order. Besides, the magnetocaloric effect for the Gd2Fe17-xCrx (x = 0, 0.5, 1 and 1.5) compounds was evaluated by the magnetic entropy change and the related Relative Cooling Power (RCP). In the vicinity of TC, |-ΔSM| reached a maximum value of 1.14 J kg−1 K−1, 1.71 J kg−1 K−1, 2.45 J kg−1 K−1 and 3.40 J kg−1 K−1, although the RCP was found to be 18 J kg−1, 31.9 J kg−1, 42.5 J kg−1 and 51.2 J kg−1 for x = 0, 0.5, 1 and 0.15, respectively in a magnetic applied field of 1.56 T. These results reveal that the Gd2Fe17-xCrx (x = 0, 0.5, 1 and 1.5) compounds are attractive materials that could be used as active refrigerants for the magnetic refrigeration and heat pumping technology above room temperature.

Performance potential and optimal configuration study for low-GWP R161-DMETEG single-stage absorption refrigeration system via pinch technology

New low-GWP R161-DMETEG mixture showed its high feasibility as an alternative working pair to overcome shortcomings of traditional ones. Its internal heat recovery capacity significantly influences operating performances. To systematically explore its ideal performance potentials and heat integration principles of the traditional single-stage absorption refrigeration system (SSARS), this paper conducted the internal heat recovery optimization and derived optimal systems by establishing an approach via pinch technology as a comprehensive planning. The ideal optimal system for maximum heat recovery under different conditions was derived initially using problem tables and Q-T graphical methods. Among all DMETEG-based fluids, R161-DMETEG exhibits the highest average performance potential of approximately 0.677 and an ideal performance improvement of 108%. Subsequently, a new configuration, called MFD-SSARS, was derived using the gird method. Its actual performances and economic feasibility under different parametrical conditions and control strategies were further explored. MFD-SSARS achieves COPs between SSARS and the ideal potential, and it can flexibly adjust internal heat recovery according to varying conditions to stimulate the performance potential. MFD-SSARS maximumly improvs COPs by approximately 65.953% relative to SSARS, reaching 96.167% of its potential under basic conditions. Despite its higher total capital costs than SSARS, it showed the lowest payback period of 2.23 years, thus proving the economic feasibility. Overall, the adopted environment-friendly working pair with designed high-performance configuration of this work serves as a technical solution to overcome current limitations of traditional absorption refrigeration technologies.

A single long NiTi tube compressive elastocaloric regenerator: experimental results

Elastocaloric cooling is an environmentally friendly alternative to the current vapor-compression refrigeration technology, and the development of an efficient operation strategy is significant for its commercialization. In this article, the cooling performance including the temperature span, specific cooling power, and coefficient of performance for a novel single long NiTi tube compressive elastocaloric regenerator (tube outer diameter 5 mm, wall thickness 1 mm, and initial length 305 mm) was comprehensively characterized under different operation parameters (operation cycle time, loading/unloading time, heat transfer fluid timing, flow time, and utilization). The single long NiTi tube compressive elastocaloric regenerator achieved maximum temperature span, specific cooling power, and coefficient of performance of 5.7 K, 135 W·kg−1, and 4.7, respectively under an applied strain of 2.5%. It was found that the most important factors for obtaining a good cooling performance of the single long NiTi tube compressive elastocaloric regenerator were a short operation cycle time, a proper heat transfer fluid timing, and a proper heat transfer fluid utilization. The dependences of the temperature span on the cycle time and heat transfer fluid utilization factor were in agreement with the existing experimental data for a parallel plate tensile elastocaloric regenerator. A thinner tube wall thickness and advanced cross-section geometry for the regenerator may further improve the cooling performance of the compressive elastocaloric regenerator.

The Effect of Fe Addition on the Curie Temperature and Magnetic Entropy of the Gd45Co50Al5 Amorphous Alloy.

The new magnetic refrigeration (MR) technology, which uses the magnetocaloric effect (MCE) of materials for refrigeration, has shown apparent advantages over the compression refrigeration of freon and other gases. Therefore, how to obtain materials with excellent magnetic entropy change near room temperature is of great significance for the realization of MR. In order to achieve high Tc of a Gd-based amorphous alloy, Gd45Co50Al5 amorphous alloy with good room temperature MCE was selected, and a series of Gd45Co50-xFexAl5 (x = 2, 5, 10) amorphous alloys were prepared by adding Fe instead of Co. In this paper, the effect of Fe addition on the Curie temperature, and the magnetic entropy change in the alloys, were studied thoroughly. The results show that the Curie temperature is increased to 281 K by adding 5% Fe elements, which is mainly related to the enhanced 3d-3d interaction of transition elements caused by Fe addition, and the maximum value of magnetic entropy change is 3.24 J/(kg·K) under a field of 5 T. The results are expected to provide guidance for further improving the room temperature MCE of Gd-based amorphous alloys.

Absorption-compression hybrid refrigeration analysis and application for energy conservation of cryogenic separation in propane dehydrogenation

Cryogenic separation is an energy extensive process in chemical industries and compression refrigeration (CR) is the most common refrigeration technology with huge energy consumption and carbon emission. Based on the principle and thermodynamic analysis of absorption refrigeration (AR) and CR, this paper puts forward serial AR-CR combined absorption-compression hybrid refrigeration (ACHR) technology as a substitution for traditional CR to conserve both power consumption and carbon emission. Industrial propane dehydrogenation is employed and the ACHR is introduced to accomplish the cryogenic separation by refrigerating temperature and load division. The phase transition of refrigerated streams encompassed by AR is crucial to the performance of ACHR. When the inter-connected temperature is determined to be 6 °C, the optimal refrigeration scenario is obtained. Through partial substitution of AR driven by waste heat for CR, the results show that the hybrid refrigeration can save 48.73% of power consumption and 110.8 GW h of energy per year, which is equivalent to the annual reduction of 39.8 kt standard coal and 0.12 Mt carbon emission. This work demonstrated that absorption-compression hybrid refrigeration is prospective in energy consumption and emission reduction industrially.

Biomass power plants

Biomass power plants

Giant magnetocaloric effect in the Co-doped Tb5Si2Ge2 by establishing magnetostructural coupling

The magnetostructural coupling materials exhibit excellent magnetocaloric properties, making them ideal candidates for magnetic refrigerants. Tb5Si2Ge2 reveals diverse phase transition behaviors, but its structural and magnetic phase transitions are decoupled, which restricts its potential applications in magnetic refrigeration technology. Here, we demonstrate that upon the addition of Co into the Ge site of Tb5Si2Ge2, the compound can obtain a strong magnetostructural coupling between the structural and the magnetic transition, which can significantly improve the magnetocaloric properties. It is observed that the magnetic entropy change under a magnetic field change of 5 T is increased from − 18.30 Jkg−1K−1 to − 31.34 Jkg−1K−1 after adding the magnetic element Co into the compound. The temperature-averaged entropy change (TEC) at the working range of 3 K under 1 T is also improved 2.1 times, exhibiting an enhanced low-field magnetocaloric performance. In addition, theoretical calculations show that a large lattice entropy change of 21.5 Jkg−1K−1 can be achieved after the magnetostructural transformation in the Co-doped compound. The results demonstrate that Co doping can be used to construct a stable magnetostructural transition, transforming Tb5Si2Ge2 into an excellent magnetic refrigerant.