Actual Refrigeration Research Articles

Active noise control of refrigerator based on cascaded notch feedback algorithm

Refrigerators bring convenience to people, but the noise they produce can also affect people’s lives. Refrigerator noise is dominated by low-frequency noise, and the active noise control method is more effective for this kind of noise. However, the existing active noise control methods for refrigerators do not take into account factors such as the limited space and complex structure of the refrigerator compressor room, and external interference signals will be introduced to affect the noise reduction performance during the error signal collection. Given that, this paper proposes the cascade notch feedback algorithm, which can well reduce the influence of external interference signals to better achieve the refrigerator noise reduction. The algorithm consists of the cascaded notch filtering algorithm and the feedback algorithm. The cascade notch filtering algorithm is formed by cascading the adaptive notch filtering algorithm, which is used to deal with the main frequency and harmonic noise generated by the refrigerator. The feedback algorithm consists of a robust algorithm for dealing with external interference signals introduced during error signal collection. The simulation experiment proves that the algorithm has advantages in terms of noise reduction and computational cost compared with the adaptive notch filtering algorithm and the improved algorithm. The experimental test platform is set up to carry out the actual refrigerator noise reduction experiments under different conditions. The algorithm has the effect of noise reduction under different robust algorithms.

Advanced model for a non-adiabatic capillary tube considering both subcooled liquid and non-equilibrium two-phase states of R-600a

Previous empirical correlations have largely failed to predict the mass flow rate variations of R-600a during the transient pull-down operation of household refrigerators. This shortcoming is attributed to the fact that these correlations were developed for specific thermodynamic states of the refrigerant at the capillary inlet, whereas the thermodynamic state varies during transient operations, particularly involving non-equilibrium two-phase states. To address these limitations, a novel model has been developed. This model comprises two distinct sub-models corresponding to the refrigerant state at the capillary tube inlet: one for the subcooled liquid state and the other for the non-equilibrium two-phase state. These sub-models are integrated to account for the transitions in the thermodynamic state of R-600a at the capillary inlet. The integrated model demonstrates excellent agreement with observed variations in the R-600a mass flow rate during the pull-down operation of actual refrigerators. The mean absolute percentage error between the measured and estimated mass flow rates is approximately 10 % over the entire period of pull-down operations tested under various environmental conditions.

Effect of lubricating oil on non-azeotropic refrigerant in flow boiling: an entropy generation analysis

ABSTRACT Entropy generation analysis is a useful method for studying the relationship between heat transfer and pressure drop in flow boiling. The flow boiling process in an actual refrigeration system is inevitably affected by oil. Therefore, the effect of oil on entropy generation needs to be investigated. A new non-azeotropic ternary refrigerant mixture, R447A, was selected as working fluid. Subsequently, flow boiling entropy generation models of R447A with and without oil were established. The effects of individual parameters on entropy generation were investigated. The entropy generation per unit tube length under different conditions was proposed as the benchmark for comparison. The results show that there is an optimal mass flux corresponding to minimum entropy generation per unit tube length at a specific oil concentration, and optimal mass flux decreases with increasing oil concentration. The tube diameter also affects the optimal mass flux of the fluid with oil, which increases with decreasing tube diameter and is smaller than that without oil for the same diameter tube. When the oil concentration is 0–4.95%, the total entropy generation exhibits a decreasing trend. Therefore, within the scope of this research, the addition of oil is beneficial for reducing the entropy generation of heat exchangers.

Computationally-efficient optimization of the remanence angles of permanent magnet circuits for magnetic refrigeration

Permanent magnets are used in many engineering fields, but their high cost and restricted availability demand optimization techniques to generate high magnetic fields over large areas with minimal material. This paper advances an optimization technique for magnetic circuits composed of NdFeB and iron wedges. The remanence angles of each magnetized block are optimized to generate a desired magnetic waveform in the air gap, a critical parameter of the magnetocaloric cooling response in magnetic refrigerators. An advantage of the proposed method is that the number of finite element simulations is twice the number of magnetized blocks, often capped due to cost reasons. Therefore, the method can fully optimize a given geometry in a few minutes. Two-dimensional and three-dimensional models are developed and compared, and the full three-dimensional model is used to design the magnetic circuit for an actual magnetic refrigerator, capable of achieving 1.1T in the high field region. An encouraging agreement is observed between the modeling results and the local experimental magnetic field measured within the air gap. The most significant deviations between simulated and measured values, never higher than 40%, are observed in the region where the magnetic field gradient is the steepest and are likely caused by manufacturing imperfections that are hard to control, such as magnetization magnitude and direction deviations and localized self-demagnetization. Deviations between experimental data and numerical results smaller than 20% are observed in the high field region.

Real-Time Construction of Thermal Model Based on Multimodal Scene Data

In commercial buildings, the total consumption of central air conditioning accounts for about 40%–50%. However, at present, the initial design value of building Heating Ventilation and Air Conditioning (HVAC) is usually far greater than the actual refrigeration value of refrigeration demand, which will lead to great energy consumption waste. Moreover, the operation of HVAC affects the thermal comfort of users, so it is necessary to establish a thermal model for the scene to control. The thermal model describes the temperature of the scene in different environments. So it is very important to design a thermal model to calculate the scene in real time. Because the flow of people, the opening of windows, the ventilation of the scene and other parameters influence the change of thermal state in the scene environment, these parameters are complicated to model. Human disturbance will lead to the instability of the state of the scene environment. The inconsistency of its thermal model will lead to energy allocation tracking strategies in different regions. To solve this problem, We propose a thermal model for building thermal comfort using a multimodal analysis framework. This paper analyzes multiple temperature and humidity sensors and area image by multimodal combination and processes the image and sensor data by combining CNN and LSTM. Our results show that when the thermal model analyzed by this method is deployed in a building in the south of China, the MSE accuracy of the local effect of temperature field prediction reaches 99%, and its AMAX reaches 94%, so the running stability of the model in the scene is high. In addition, the research shows that the thermal model analysis framework can make the Internet of Things (IoT) in buildings more intelligent, and it can be combined with this thermal model to improve human comfort, make it easier to deploy in each hot zone, and have a better overall energy-saving effect.

Visualization and Measurement of Swirling Flow of Dry Ice Particles in Cyclone Separator-Sublimator

The dry ice sublimation process of carbon dioxide (CO2) is a unique, environmentally friendly technology that can achieve a temperature of −56 °C or lower, which is a triple point of CO2 in CO2 refrigeration systems. In this study, a cyclone separator-evaporator was proposed to separate dry ice particles in an evaporator. As an initial step before introducing the cyclone separator-evaporator into an actual refrigeration system, a prototype cyclone separator-evaporator was constructed to visualize dry ice particles in a separation chamber. A high-speed camera was used to visualize the non-uniform flow of dry ice particles that repeatedly coalescence and collision in a swirl section. Consequently, the dry ice particle size and the circumferential and axial velocities of dry ice were measured. The results show that the equivalent diameter of the most abundant dry ice particles in the cyclone separation chamber is 2.0 mm. As the inner diameter of the separation section decreases, dry ice particles coalesce and grow from an equivalent diameter of 4 mm to a maximum of 40 mm. In addition, the comparison of the experimental and simulation results shows that the drag force due to CO2 gas flow is dominant in the circumferential velocity of dry ice particles.

Investigation of Heat Transfer and Pressure Drop for R744 in a Horizontal Smooth Tube of R744/R404A Hybrid Cascade Refrigeration System—Part 1: Intermediate Temperature Region

In this study, the evaporation heat transfer characteristics of an intermediate temperature of R744 in a smooth horizontal tube, when operating as an indirect refrigeration system (IRS) among hybrid cascade refrigeration systems (HCRSs), are evaluated. Studies on the characteristics of intermediate-temperature evaporation heat transfer under the operating conditions of evaporators used in actual refrigeration systems, such as IRS, cascade refrigeration systems, and HCRS, used in supermarkets are lacking. Thus, this study provides basic data on the characteristics of evaporation heat transfer of R744 in the evaporators of refrigerators used in supermarkets. The tube employed to the evaporation experiment in this study was a horizontal smooth copper tube with a length of 8000 mm and an inner diameter of 11.46 mm. The experimental variables were measured over a wide range of mass flux of 200–500 kg/(m2·s), heat flux of 10–40 kW/m2, and saturation temperature of −40–0 °C. The main results are summarized as follows: (1) The application of Kandlikar’s correlation formula at an evaporation temperature of −20 °C in an IRS helps in a good prediction of the R744 evaporation heat transfer coefficient. (2) The pressure drop according to the heat and mass flux showed the same heat transfer coefficient trend, but the pressure drop at saturation temperature was different from the trend of heat transfer coefficient.

Performance analysis of an ejector-assisted two-stage evaporation single-stage vapor-compression cycle

• An ejector-assisted 2-stage evaporation 1-stage vapor-compression cycle is proposed. • New cycle works for different refrigerants, especially for CO 2 transcritical cycle. • Energy savings depend on reasonable design and variable operating conditions. For actual vapor-compression refrigeration or heat pump systems with variable-temperature heat reservoirs, two-stage evaporation cycle is an efficient way to improve the coefficient of performance (COP). However, its application is limited because the two-stage evaporation cycle requires two individual suction pressures carried out by two cylinders or two compressors. To solve this problem, a two-stage evaporation cycle with a common single-stage compressor is proposed. An ejector is applied to lift the lower evaporation pressure up to the higher evaporation pressure or the compressor suction pressure. A thermodynamic model is developed to analyze its performance. Numerical results indicate that the COP of the novel cycle is 12.1% higher than the ejector cycle, 6.9% higher than the two-stage evaporation cycle and 22.0% higher than the basic refrigeration cycle under rated operating conditions. The exergy analysis indicates that TSEC-E can reduce 49.6% exergy loss of expansion process and 21.5% exergy loss of heat transfer process in evaporators in comparison with the basic refrigeration cycle. Although TSEC-E is applicable with various refrigerants, particularly it is more effective for CO 2 transcritical cycle. Moreover, performance improvement of the novel cycle under variable operating conditions is numerically investigated.

Performance prediction of a new solar-driven electrochemical refrigerator

A new solar-driven electrochemical refrigerator model is proposed by integrating a dye-sensitized solar cell with a thermally regenerative electrochemical refrigerator. Considering various irreversible losses within the dye-sensitized solar cell, thermally regenerative electrochemical refrigerator as well as between them, mathematical formulas for the performance parameters of dye-sensitized solar cell and thermally regenerative electrochemical refrigerator as well as the solar-driven electrochemical refrigerator are derived. Based on the energy balance equation, the electric current relation between the dye-sensitized solar cell and the thermally regenerative electrochemical refrigerator are derived. The maximum cooling rate density and maximum coefficient of performance of the solar-driven electrochemical refrigerator could reach 800.47 W m−2 and 0.8, respectively. There exists an optimum thin film thickness of DSSC to optimize the system performance. A larger photoelectron absorption coefficient, specific charge capacity, isothermal coefficient or regenerative efficiency positively improves the solar-driven electrochemical refrigerator performance. However, a larger Schottky barrier, internal resistance of TRER and temperature difference between hot and cold heat reservoirs is unfavorable for the solar-driven electrochemical refrigerator performance. The obtained results may offer some guidance for the design and optimization of such an actual refrigerator.

Condensate drainage on slit or louvered fins in microchannel heat exchangers for anti-frosting

When the condensate isn’t removed in time, it is easy to cause frosting, which limits the application of microchannel heat exchangers (MCHE). Although some methods can measure well about improving the condensate drainage performance of the MCHE, the quantitative value of drainage amount can not be given in the operation condition of one actual refrigeration system. The objective of this study included developing a test facility to investigate condensate drainage in MCHE, and study condensing in MCHE to valuate different condensate detecting methods. In the present study, condensate drainage was experimentally investigated on louvered and slit fins in MCHE for anti-frosting. Experimental data of drainage amount, the moist air pressure drop across the test sample and the heat capacity of the MCHE were recorded. The calculation formula for drainage amount was set up. The rate of condensate drainage from the experimental system is mainly a function of the velocity with the dew point temperature and the dry bulb temperature of the moist air unchanged. The calculation value and the test value of the drainage amount were compared for four different structures MCHE with slit or louvered fins. The research result shows that for the given brine flow conditions, the rate of condensate drainage is mainly influenced by the air velocity, the calculation formula predictions of the condensate drainage agree well with the test measurement results, and the maximum deviation is 12%.This study provides reference for the application of micro channel evaporator.

Experimental investigation of the effect of solid-gas two-phase flow in CO2 cascade refrigeration system

ABSTRACT The dry ice sublimation process of CO2 is a unique technique in which temperature ranges below the triple point of −56 °C can be achieved in a CO2 refrigeration system. However, during the evaporation process of the actual refrigeration system, the dry-ice blockage maybe happens in the evaporator, which causes a risk of system failure in the suction of the compressor. In order to overcome this problem, in this study, an ultra-low temperature CO2 cascade refrigeration system with a novel tapered evaporator/sublimator was designed and constructed. The novel evaporator/sublimator included a swirl promoter, which induces the swirling flow of solid-gas two-phase flow. Experiments were conducted for the investigation of solid-gas two-phase flow heat transfer characteristics in the evaporator/sublimator. According to the experimental results, it is verified that the CO2 refrigeration system can operate consistently and steadily without dry ice blockage in the evaporator/sublimator. In addition, the dry ice particles are uniformly distributed along the inner wall of the evaporator/sublimator by the installation of the swirl promoter, and the heat transfer coefficient is considerably improved.

Effects of Oil Wettability on the Performance of a Cyclone-Type Oil Separator

The effects of oil wettability on the performance of a cyclone-type oil separator was studied through in situ experimentation and in a real refrigeration system. Based on previous research, the geometry of the oil separator in the present study was designed with an oil recovery device installed at its bottom to mount it on the actual refrigerator. The performance of the oil separator without surface treatment was predicted by applying design correlations proposed in the open literature, which were then compared with the experimental data. Through surface treatment, oleophilic or oleophobic properties were given to the inner wall and helix of the oil separator, and its performance was measured in a real refrigeration system. Oil wettability had a great effect on the performance of the oil separator, and in order to obtain high separation efficiency, oleophilic properties were found to be advantageous not only in the inner wall but also in the helix.

Improving defrosting performance by controlling frost distribution to match defrosting heat distribution in frost-free household refrigerators

In the defrosting process of most of existing frost-free refrigerators, major part of the heat generated by electric heater cannot be absorbed by the frost, resulting in the raise of the energy consumption. The objective of this study is to present a new method to improve the energy efficiency in the defrosting process. Based on the idea of making the frost absorb most of the heat generated by electric heater, a new method of defrosting is proposed, and its principle is to make the defrosting process at different locations complete simultaneously by optimizing the frost mass distribution on the evaporator. In this method, the defrosting heat distribution on evaporator surface, the required frost mass distribution, the required air flow distribution and the structure of return air duct are determined, respectively. Application of this method in an actual household refrigerator shows that the defrosting efficiency is improved by 29.8%.

Nonlinear Dissipation Heat Devices in Finite-Time Thermodynamics: An Analysis of the Trade-Off Optimization

Abstract:The nonlinear dissipation heat devices are proposed by means of generalizing the low-dissipation heat devices to the quadratic order case. The dimensionless formulas of the output (input) power and the efficiency (coefficient of performance) for the nonlinear dissipation heat engines (refrigerators) are derived in terms of characteristic parameters for heat devices and the dimensional analysis. Based on the trade-off criterion, the optimal performance of the nonlinear dissipation heat devices is discussed in depth, and some system-specific properties for the nonlinear dissipation heat devices under the trade-off optimization are also uncovered. Our results may provide practical insight for designing actual heat engines and refrigerators.

Trade-off optimization for low-dissipation heat engine with generic heat transfer process

The heat transfer process inevitably occurs in the operation of real heat engine. In this article, a low-dissipation heat engine with generic heat transfer process is proposed based on the low-dissipation Carnot model. The formulas for the power and the efficiency of heat engine with generic heat transfer law are derived, and the low-dissipation heat engine performance is also optimized by the trade-off optimization method, which offers a unified scheme to understand the behaviors of heat engines with generic heat transfer processes. Furthermore, the characteristics of the power as well as the efficiencies for thermal engines with the different heat transfer processes are discussed in detail, and it is found that the power and the efficiency without heat transfer process are independent of heat leak, but are related to contact time, heat dissipation and Carnot efficiency. The power output of heat engine monotonically increases as Carnot efficiency increases, but the large contact time ratio and the large dissipation ratio make it difficult to provide the big power output. When the heat leak is absent and () is fixed, the efficiency of heat engine decreases (increases) with the increase of (). It is noted that the heat transfer process greatly influences the performance of heat engine, and /C versus displays the similar properties under three heat transfer laws. It is clearly shown that /C versus shows the transition from the monotonic decrease to monotonic increase with increasing, but /C versus is opposite to the former, and the maximum value of /C also shifts rightwards with the increase of . Additionally, the corresponding efficiency of heat engine diminishes significantly as m decreases and n increases. When heat engines are dominated by different heat transfer laws, the curves of versus C are consistent as C is relatively large or small, but it is observed that there exist the evident differences among three characteristic curves in the middle regime. The relatively large or small will also lead to the reduction of the working regime where heat engine can function normally. Our results are very helpful in understanding the design principle and the optimization mechanism for actual thermal engines and refrigerators.

Experimental evaluation and field trial of low global warming potential R404A replacements for commercial refrigeration

R404A refrigerant is widely used for various refrigeration applications ranging from centralized refrigeration systems for supermarkets to transport refrigeration for truck/trailer. Various environmental regulations have been proposed in the United States and Europe that phase out the use of high global warming potential refrigerants like R404A (global warming potential = 3943) in these applications. This article presents an evaluation of two low global warming potential R404A replacements: A nonflammable refrigerant R448A with global warming potential of 1273 and a mildly flammable refrigerant R455A with global warming potential of 146. Tests carried out with a commercially available R404A self-contained freezer showed that the compressor run time of R448A and R455A are similar to R404A due to similar capacity. The 24-h energy consumption of the compressor is 9% lower for R448A and 6% lower for R455A compared to R404A. Tests were also performed with R448A in a commercially available walk-in freezer/cooler. R448A matches the capacity with 4 to 8% higher efficiency compared to R404A. This indicates that R448A and R455A can reduce both the direct and indirect emissions significantly in these systems. Finally, this study presents the performance results conversion of an actual supermarket refrigeration system from R404A to R448A, which resulted in energy savings from about 9 to 20% depending on outdoor ambient temperature.

Improving thermodynamic performance of refrigerator condenser using nanoparticles

Data about the effect of nanoadditives on the work of heat exchangers of small refrigerator in the literature are practically absent. It is difficult to find technical solutions aimed at improving the efficiency of small refrigerators. Thus, work on further research of small refrigerators with nanofluids as the working body becomes actual. Reduce the electricity consumption of refrigerator is possible by improving the efficiency of heat exchange systems. New heat transfer fluids with better thermodynamic characteristics are one option to improve heat transfer. An important achievement in the study of heat transfer fluids is the use of a colloidal mixture of primary coolant liquid and metal particles with the size of 1-100 nm. Initial versions of colloidal solutions, such as microfluids, resulted in formation of a precipitate, causing erosion of the friction surfaces of metal parts. Nanofluids are unconnected monoparticles located in the base fluid. Their use can increase the heat transfer more than 50% in actual refrigerators of heat exchangers even when the relative amount of nanoparticles is less than 0,3 %. The paper compares the parameters of the condenser of small refrigerating machine using pure refrigerant and nanoparticle additives. Further, a comparison of theoretical calculation and experimental data of the condenser are conducted. The experiment revealed that the use of nanoadditives increases the heat transfer coefficient by 16 % in comparison with the pure refrigerant, which makes them promising means of improving the efficiency of the refrigerator without requiring structural changes.

Ecological optimization and coefficient of performance bounds of general refrigerators

An analysis of COP and its bounds at maximum ecological criterion for general refrigerators is conducted. For generality, both the non-isothermal heat transfer processes and the internal dissipations are considered. Under different situations, the COP under the maximum ecological criterion have been studied systematically. And the general upper and lower bounds of the optimal COP have been obtained. Furthermore under maximum ecological criterion, the COP of general endoreversible refrigerators have also been studied. And the COP bounds of different kinds of refrigerators have been analyzed. As actual refrigerators may not operate under the condition of maximum COP or maximum cooling load, but operate under the maximum ecological condition which indicates the best compromise between the refrigeration rate and the loss of refrigeration rate. This paper could provide a practical insight for designing and operating actual refrigerators.

Unified trade-off optimization for general heat devices with nonisothermal processes.

An analysis of the efficiency and coefficient of performance (COP) for general heat engines and refrigerators with nonisothermal processes is conducted under the trade-off criterion. The specific heat of the working medium has significant impacts on the optimal configurations of heat devices. For cycles with constant specific heat, the bounds of the efficiency and COP are found to be the same as those obtained through the endoreversible Carnot ones. However, they are independent of the cycle time durations. For cycles with nonconstant specific heat, whose dimensionless contact time approaches infinity, the general alternative upper and lower bounds of the efficiency and COP under the trade-off criteria have been proposed under the asymmetric limits. Furthermore, when the dimensionless contact time approaches zero, the endoreversible Carnot model is recovered. In addition, the efficiency and COP bounds of different kinds of actual heat engines and refrigerators have also been analyzed. This paper may provide practical insight for designing and operating actual heat engines and refrigerators.

2P1-E08 ハンドアームと自律走行車の連携による冷蔵庫への横付けと開扉動作の実装

We aim to develop a home service robot which can take foods or drinks to users. The robot should be able to move to a refrigerator and open the door even if the actual refrigerator's pose is slightly different from the environmental map which has been created beforehand. In this paper, we focus on two functions of the robot: approaching the front of the refrigerator correctly and opening the door by pulling the door ' s handle. We propose a method of determining a goal pose of the robot according to an actual environment by recognition of a refrigerator ' s pose. This paper shows an implementation of these functions by cooperation of vehicle motion and hand-arm operation using ROS.