Refrigeration Mode Research Articles

Research on intelligent control of fresh air introduction based on electric vehicle air conditioning system

The high power consumption of air conditioning systems is an important reason for the significant reduction in EVs (electric vehicles) range. Reducing its energy consumption has become an urgent industry problem to be solved. In order to reduce the energy consumption of the air conditioning system, this paper proposes an intelligent control strategy for the proportion of fresh air in the cabin of EVs, taking into account the impact of factors such as the number of passengers in the cabin, ambient temperature, and humidity on demand for fresh air, and analyzes the energy-saving effect of the intelligent control strategy through simulation. The analysis found that the minimum fresh air demand in the passenger compartment is greatly affected by the number of passengers in the cabin. The developed intelligent control strategy can significantly reduce the energy consumption of air conditioning systems. The energy-saving effect in northern China is significantly better than in southern China. The actual driving range of refrigeration and heating modes can be improved by 50 and 126 km, respectively.

Otto cycles with a quantum planar rotor.

We present two realizations of an Otto cycle with a quantum planar rotor as the working medium controlled by means of external fields. By comparing the quantum and the classical description of the working medium, we single out genuine quantum effects with regard to the performance and the engine and refrigerator modes of the Otto cycle. The first example is a rotating electric dipole subjected to a controlled electric field, equivalent to a quantum pendulum. Here we find a systematic disadvantage of the quantum rotor compared to its classical counterpart. In contrast, a genuine quantum advantage can be observed with a charged rotor generating a magnetic moment that is subjected to a controlled magnetic field. We prove that the classical rotor is inoperable as a working medium for any choice of parameters, whereas the quantum rotor supports an engine and a refrigerator mode, exploiting the quantum statistics during the cold strokes of the cycle.

Dynamic simulation of DALS test facility cryoplant

Dalian Advanced Light Source (DALS) test facility program requires a 370 W cryoplant to meet the cooling requirements of four testbenches. The utilization of dynamic simulation holds significant potential for diverse applications such as process design, control logic optimization, and virtual commissioning. These applications are helpful in facilitating the subsequent stages of commissioning and operation. This paper describes the establishment of a model for the DALS test facility cryoplant based on the Ecosimpro software. The model includes the main components of the cryoplant, incorporating most control loops and sequential control strategies. The simulation encompasses three operation modes, namely liquefaction mode, refrigeration mode and fast cooldown mode. The simulation results match the Temperature-Entropy (T-S) diagram from the manufacturer well. This model will be used in the upcoming commissioning of the cryoplant for resolving challenges that may arise in future operation.

RANQUE-HILSCH VORTEX TUBE AS AN EDUCATIONAL TOOL FOR CLASSICAL THERMODYNAMICS TEACHING

A vortex or Ranque-Hilsch tube is a moving parts-free device that splits a compressed air stream into a cold and a hot stream at its two extremities. Although there exist some theoretical approaches based on internal shock and expansion waves as well as Maxwell velocity distribution, a final word on the phenomenon to explain the thermal energy splitting has not been reached yet. Nevertheless, from the classical Thermodynamics point-of-view, the conservation laws of mass and energy along with the Second Law validation applied to a control volume enveloping the vortex must be fulfilled. Consequently, such a simple device may be an outstanding tool for hands-on laboratory teaching of engineering Thermodynamics. In accordance with that, an educational laboratory test rig was conceived to carry out experiments to demonstrate the fundamental laws: mass and energy conservations, and the Second Law constraint. As a secondary goal, students can be acquainted with flow, pressure, and temperature measuring techniques, along with obtaining thermodynamic properties, computing, and data-reducing procedure as part of the testing as well. In addition, the coefficient of performance in refrigeration and heat pump operation modes can be obtained and a proper discussion of the vortex tube working principle can be fostered.

Parametric design optimization and thermodynamic analysis of plate fin heat exchanger for helium liquefaction system

The plate-fin heat exchanger is one of the most important components of helium liquefaction system as it recovers cold energy from helium gas in the cold box. Because of larger heat transfer surface area and compact geometrical configuration, plate-fin heat exchangers are widely used. The design of heat exchanger using helium as a cryogenic fluid needs high thermodynamic performance with minimum pressure drop which particularly requires the optimization of dimensional array and its geometrical configurations. In this regard, a parametric investigation was performed to compute the effective geometrical parameters and its effect on thermodynamic (effectiveness and log-mean temperature difference) performance has been discussed in detail. The present study aims to design optimization and thermodynamic performance evaluation of plate-fin type heat exchangers used in helium liquefaction systems. The developed helium liquefaction model has been simulated for the most critical liquefier with and without liquid nitrogen precooling, mixed mode, and refrigeration mode. Each component of the liquefaction model has been technically and thermodynamically analyzed and, in particular, four plate-fin heat exchangers have been considered and designed accurately using Aspen EDR®. Initially, the sensitivity analysis was carried out to characterize the most significant geometrical parameters (fin thickness, height, number and arrangement of layers, frequency, and fin type) and their effect on thermodynamic performance and pressure drop. After that, the artificial intelligence model was used to determine the optimal range of such geometrical variables in which the heat exchanger has maximum effectiveness and log mean temperature difference. Finally, the operating conditions obtained from cycle modeling and optimized geometrical datasets have been applied in commercial simulation software Aspen EDR® for plate-fin heat exchangers design. Finally, a comparative thermodynamic analysis has been carried out to determine the performance of all the designed heat exchangers operating at four different modes (boundary conditions).

Design and construction of a refrigerator-cooled adiabatic calorimeter for heat capacity measurement in liquid helium temperature region.

Heat capacity is a fundamental thermodynamic property of a substance. Although heat capacity values and related thermodynamic functions are available for many materials, low-temperature heat capacity measurements, especially for novel materials, can still provide valuable insights for research in physics, chemistry, thermodynamics, and other fields. Reliable low-temperature heat capacity data are typically measured using classical adiabatic calorimeters, which use liquid helium as the refrigerant to provide a cryogenic environment for heat capacity measurements. However, liquid helium is not only expensive but also not easy to obtain, which greatly limits the application of adiabatic calorimetry. In this work, an accurate adiabatic calorimeter equipped with a Gifford-MacMahon refrigerator was designed and constructed for measuring the heat capacity of condensed matter in the temperature range from 4 to 100K. The Gifford-MacMahon refrigerator was utilized to provide a stable liquid helium-free cryogenic environment. A simple mechanical thermal switch assembly was designed to facilitate switching between the refrigeration mode and the adiabatic measurement mode of the calorimeter. Based on the measurement results of standard reference materials, the optimized repeatability and accuracy of heat capacity measurements were determined to be within 0.8% and 1.5%, respectively. The heat capacity of α-Fe2O3 nanoparticles was also investigated with this device. Furthermore, this adiabatic calorimeter only requires electricity to operate in the liquid helium temperature range, which may significantly advance the research on low-temperature heat capacity based on adiabatic calorimetry.

Histological examination of skin tissue in the porcine animal model after application of a new monopolar radiofrequency.

This study aims to evaluate the safety of the radiofrequency device and its efficacy in various treatment and refrigeration modes. Four4-weekBama miniature pigs were used in this study, and four repeated treatment sites were selected on the pig's abdomen, each site consisting of 6 different treatment and cooling modes, with radiofrequency device (YouMagic; WE Medical Technology Co., Ltd.) administered every 3-5 s for a total of five treatments. The handheld infrared thermometer (HIKMICRO; Hangzhou Hikmicro Sensing Technology Co., Ltd.) was used to monitor the surface temperature of skin. Twenty minutes after the completion of treatment, a biopsy of the treatment and control area was performed on the pigs using a 4-mm biopsy punch. One-month after the treatment, samples were obtained using surgical scalpels. After that we used proper staining to estimate the therapeutic efficacy. At last, SPSS and Image J were used to proceed to the next step of analysis. During the therapy, no side effects were observed apart from mild transient erythema caused by the heating of skin temperature, staining of biopsy samples taken 20 min after treatment showed no serious damage of dermis. After 1 month of treatment, it can increase collagen I and elastin production. In addition, increases in energy setting at a standard pass number also increased the expression of collagen I. Meanwhile, we also found an increase in the thickness of the dermal layer among all treatment groups. The new monopolar radiofrequency instrument possesses excellent therapeutic safety. After 1 month of treatment, it can increase collagen I and elastin production in 2-month-old Bama miniature pigs.

The study of dynamic characteristics on a novel air source heat pump coupled with liquid-storage gas-liquid separator under non frosting and refrigeration conditions

Air source heat pump is widely used for heating as it has high efficiency and environmentally friendly advantages, but there is frosting issue in low temperature and high humidity conditions. In order to improve the performance of air source heat pump (ASHP) when its evaporator is subject to frosting, a novel ASHP system coupled with liquid-storage gas-liquid separator was proposed in previous work, which was conducted at a constant temperature. However, the environment temperature is variable during the actual operation, the influence mechanism of the temperature change on the dynamic characteristics of the system and operation characteristics is still unclear. Therefore, experimental method is employed in this work, the aim is to investigate the dynamic performance of the novel ASHP in heating and refrigeration modes in actual environment, including suction/exhaust pressure, suction/exhaust temperature, inlet/outlet water temperature, the coefficient of performance (COP) etc. to improve the adaptability of the heat pump unit. The results indicate that the COP is 2.78–3.49 when the ambient temperature is 6.5–12.5 °C under the heating condition. Also, in refrigeration mode, the COP of the system is 3.28–3.04 under the ambient temperature of 22∼38 °C. This study shows that the novel ASHP has a good dynamic performance during heating/cooling operation in the actual environment. Also, some suggestions for improvement are put forward to solve the existing problems in this work.

Multi-objective particle swarm optimization algorithm for data acquisition and system characteristics research of phase change thermal storage heat pump water heaters

In order to understand the multi-objective particle swarm optimization algorithm for data collection and system characteristics research of heat pump water heaters, the author proposes a multi-objective particle swarm optimization algorithm for data collection and system characteristics research of phase change thermal storage heat pump water heaters. The author first introduced the working principle of the phase change heat storage heat pump water heater, and then conducted a comparative experimental study on the performance of two types of heat pump water heater systems using pure paraffin phase change heat storage and water storage. They compared and analyzed the heat storage process, condensation heat recovery rate of the heat storage box, and comprehensive energy efficiency coefficient of the system under the refrigeration and heat recovery mode of the two types of heat pump water heater systems, on this basis, measures were proposed to improve the performance of pure paraffin phase change thermal storage hot water systems. At long last, the examination of exploratory information shows that the Rx of the water warm capacity framework is around 6% higher than that of the stage change warm capacity framework, and the framework COPt is likewise 20% higher than that of the stage change warm capacity framework, from this, it tends to be seen that the stage change heat capacity box has unfortunate intensity move proficiency, prompting a lessening in the presentation of the intensity siphon water radiator framework. Contrasted and customary water stockpiling heat siphon boiling water frameworks, unadulterated paraffin stage change capacity heat siphon high temp water frameworks lessen the volume of the intensity stockpiling tank, and the framework works somewhat flawlessly during the intensity stockpiling process. However, the system?s overall energy efficiency is impacted by the heat storage tank?s poor heat exchange effect and relatively low condensation heat recovery rate. The intensity move of the intensity stockpiling box can be upgraded by finning the winding curls in the intensity stockpiling box, embedding aluminum foil, adding extended graphite, and different measures to further develop the buildup heat recuperation rate, subsequently working on the general execution of the framework.

Experimental research and energy saving analysis of an integrated data center cooling and waste heat recovery system

To better make use of the waste heat in distributed data centers, a new design of integrated waste heat recovery system that can meet different needs including heating for users and data center cooling is introduced. The system can switch among different operation modes including waste heat recovery mode, natural cooling mode, composite cooling mode and refrigeration mode based on the ambient temperature. The integrated waste heat recovery system is experimented in the enthalpy-difference laboratory, and the experimental results show well consistency compared with the modeling results. The operation strategies to switch among different modes are determined based on the experimental and modeling results. The paper introduced PUE (Power Usage Effectiveness) and ERE (Energy Reuse effectiveness) to comprehensively evaluate the cooling and energy reutilization effectiveness of the system. According to the evaluation result, the integrated waste heat recovery system has well performed energy effectiveness, environmental and economic effect. The ERE values of using the integrated waste heat recovery system in Chinese typical climate cities including Harbin, Beijing, Xi'an, Shanghai and Guangzhou are 0.87, 1.02, 1.04, 1.17 and 1.29 respectively. Using this system at 96 kW distributed data center instead of CRAC (computer room air conditioning) system can save 152.7 MWh electricity, 56.4 tons of standard coal, and 244.7 tons of CO2 emission in Beijing annually. The payback periods of this new system in different climate regions in China are all within 3 years.

Thermodynamics of one and two-qubit nonequilibrium heat engines running between squeezed thermal reservoirs

Quantum heat engines form an active field of research due to their potential applications. There are several phenomena that are unique to the quantum regime, some of which are known to give these engines an edge over their classical counterparts. In this work, we focus on the study of one and two-qubit finite-time Otto engines interacting with squeezed thermal baths, and discuss their important distinctions as well as the advantage of using the two-qubit engine. In particular, the two-qubit engine offers an interesting study of the interplay between the degree of squeezing and that of the coherence between the two qubits. We find that the two-qubit engine generally yields higher power than its one-qubit counterpart. The effective temperature of the squeezed baths can be calculated both for the one and two-qubit engines, and they tend to show an exponential growth with increase in squeezing parameters $r_h$ and $r_c$. It is also observed that by tuning the squeezing parameters, the machine can be made to work either in the engine or in the refrigerator mode. Additional effects due to the change in the inter-qubit separation have been studied.

Experimental energy evaluation of R516A and R513A as replacement of R134a in refrigeration and air conditioning modes

This paper presents the experimental energy behavior of R516A and R513A compared to R134a as baseline refrigerant in refrigeration and air conditioning temperatures. The comparative is made in an evaporating temperatures range of 261 K to 285 K with step 4 K increases, taking condensing temperatures of 308 K, 313 K, and 318 K. Results show that the best energy performance was reached by R134a while the worst were for R513A in all experimental tests, here R516A shows the smallest difference respect to R134a being just 5.4%. Also, R134a showed lower values in discharge pressure respect to its replacements, while R516A exhibited the lower discharge temperatures. R513A showed lower useful superheating for refrigeration applications, while R516A achieved the minor useful superheating for air conditioning temperatures only below R134a. Finally, R513A reached the higher value of volumetric refrigeration capacity for air conditioning temperatures at 308 K condensing temperature. All results were obtained considering the optimal refrigerant mass charge which were 682 g, 655 g, and 632 g for R134a, R513A and R516A, respectively.

Experimental study on reliable operation strategy for multi-split backplane cooling system in data centers

The composite air-conditioning system combined heat pipes and vapor compression, which can utilize natural cooling sources effectively, has been widely used in data centers recently. The common energy-saving strategy is to make the best use of the natural cooling sources according to outside ambient temperature. However, existing studies indicate that the cooling failure problem often occurs in the mechanical refrigeration mode due to incorrect control strategy, when the outdoor ambient temperature is lower and natural cooling capacity is insufficient. Thus, taking the multi-split backplane cooling system used in the data center as an object, the reason for the cooling failure under the condition of lower outside ambient temperature is investigated through theoretical analysis and experimental study. Results indicate that system energy consumption will decrease as condensing pressure decreases, but lower condensing pressure may cause insufficient refrigerant problems at the most unfavorable terminal. To solve the problem, a reliable operation control strategy based on variable condensing pressure is proposed and validated by experiments, and results indicate that a maximum of 12% energy consumption can be saved with the decrease of condensing pressure. Finally, the determination for condensing pressure setpoint is provided, and it is pointed out that how to determine optimal condensing pressure setpoint is worthy of further study in the consideration of energy efficiency and cooling effect meantime.

Josephson quantum spin thermodynamics

A 1D Josephson junction (JJ) loop, doped with a spin-flipper and attached to two thermal reservoirs is shown to operate as a heat engine, or a refrigerator, or a Joule pump or even as a cold pump. When operating as a quantum heat engine, the efficiency of this device exceeds that of some recent Josephson heat engine proposals. Further, as a quantum refrigerator, the coefficient of performance of this device is much higher than previously proposed JJ based refrigerators. In addition, this device can be tuned from engine mode to refrigerator mode or to any other mode, i.e., Joule pump or cold pump by either tuning the temperature of reservoirs, or via the flux enclosed in the JJ loop. In presence of spin flip scattering we can tune our device from engine mode to other operating modes by only changing the enclosed flux in JJ loop without changing the temperatures of the reservoirs. This is potentially an advantage with respect to other proposals. This makes the proposed device much more versatile as regards possible applications.

Process analysis and control flow design of the 1kW @ 4.5K helium refrigerator for NNBI

A helium cryogenic system with a cooling capacity of 1kW@4.5K was designed in order to support the NNBI(Negative ion based Neutral Beam Injection system) test facility, cryopumping test facility and beam source test facility, which consists of a helium compressor with its storage and recovery system, 1kW@4.5K helium refrigerator, a cryogenic distribution valve box, cryogenic transfer lines and a helium Dewar, etc. Based on the SIMATIC S7-1500H PLC, the cryogenic control system can realize seven major operational modes, including the independent refrigeration mode and independent liquefaction mode, etc. On the basis of process analysis, the control flow of the NNBI helium cryogenic system in each operational modes was designed and will be presented in this paper. It will direct the control system to realize automatic control in multiple operational modes.

Dynamic performance of a multi-mode operation CO2-based system combining cooling and power generation

The CO2-based combined cooling and power generation system (CCP) is considered as a promising solution for waste heat recovery due to its multiple energy outputs, environmental protection, and compactness. In this work, for waste heat recovery in refrigerated trucks, a dynamic simulation model of a multi-mode CO2-based CCP system is established in Matlab/Simulink and the experimental data verifies the dynamic simulation model well. The effect of engine heat source, condenser cooling water, and operation mode on the dynamic behavior of the CCP system is analyzed. The results show that the power output will slightly improve when switching from integrated refrigeration and power mode to full power mode. In addition, exhaust gas temperature, flue gas flow, and condenser cooling water temperature are the main disturbance factors affecting the operation of the CCP system. Moreover, in the case of sufficient condenser cooling water, the correlation between the power sub-cycle and the refrigeration sub-cycle of the CO2-based CCP system is weak, so the two sub-cycles can be controlled independently. The preliminary results presented in this paper will be helpful for the future design and the development of control strategies for the CO2-based CCP system.

Smart temperature difference management in summer desert enabled by ammonia-based resorption cycle

Diurnal temperature difference management driven by solar energy is one of the essential and attractive strategies in summer desert. However, the conventional phase-change thermal energy storage way possesses inherent drawbacks of serious heat dissipation, low heat storage efficiency, single-mode thermal energy storage, etc. Herein, we report a smart temperature difference management (STDM) strategy based on the ammonia-based resorption cycle of MnCl2@expanded natural graphite (ENG) treated with sulfuric acid and CaCl2@ENG composite sorbents for adjusting indoor diurnal temperature variation in summer desert. In midday refrigeration mode, the desorption reaction of MnCl2 and the sorption reaction of CaCl2 occurs by harvesting sunlight during the forenoon, subsequently the resorption reaction of MnCl2 taking place to discharging cooling capacity at midday. In the night heating supply mode, the resorption process of MnCl2 happens to discharging thermal energy, but the desorption process during the afternoon is similar to the forenoon. Amplifiable composite sorbents own high ammonia sorption capacity up to 0.540 g∙g−1 and 0.915 g∙g−1 contributed by strong ammonia complexation reaction. Based on these sorbents, the STDM device realizes cold and heat charging/discharging via the multistep ammonia desorption/sorption process of MnCl2 and CaCl2 composite sorbents in closed structures driven by solar energy in summer desert. Importantly, the lab-scale STDM device exhibits high heating supply performance of 213.65 kJ∙kg−1 (SHE), 49.86% (ηh), 8.2 °C (△Th), 40.67 min (th) at night and high refrigeration performance of 163.6 kJ∙kg−1 (SCE), 0.344 (COPc), 3.88 °C (△Tc), 33.5 min (tc) at midday. Our approach offers a prospective low-carbon route for efficient temperature difference management in summer desert.

Influence of key parameters on the performance of a helium cryogenic system in refrigeration and liquefaction modes

At present, medium-scale helium cryogenic system is commonly based on modified Claude cycle with two expanders in series. In this study, considering the minimum allowable heat exchanger temperature difference (MHTDamd), the influence of key parameters (including compressor discharge pressure (Pcd) , temperature at the inlet of expander1 (Tin-EXP1) and temperature at the inlet of Joule-Thomson valve (Tin-JT)) on the system performance (including refrigeration capacity (RC)/liquefaction rate (LR), specific energy consumption (SEC) and total UA of the heat exchangers (UAtotal)) of the helium cryogenic system is investigated and analyzed in refrigeration and liquefaction modes, respectively. The results show that in refrigeration and liquefaction modes, the optimal ranges of Pcd, Tin-EXP1, and Tin-JT are within 8 ∼ 10 bar, 30 ∼ 45 K and 5.2 K ∼ 7.2 K, respectively. Furthermore, the constraint relation between UAtotal and SEC is obtained. By using genetic algorithm (GA), it is found that keeping constraint SEC within 100%∼115% of the chosen SEC from the optimal range can achieve a relatively economic trade-offs between SEC and UAtotal. In the end, a comparison of T-S diagram obtained from design and experimental values in refrigeration and liquefaction modes is carried out, respectively. The maximum temperature deviation is within 5%, which verifies the accuracy of the calculation models. The optimized results in this study are also applicable to the same processes with mass flow rate of compressor lower than 100 g/s.

Multi-mode analysis and comparison of four different carbon dioxide-based combined cooling and power cycles for the distributed energy system

To meet the diversified demand of power and cooling for the distributed energy system, this paper proposes two combined cooling and power (CCP) systems combining the supercritical carbon dioxide cycles with a carbon dioxide ejector refrigeration cycle, which can switch between full power mode (Mode-P), combined cooling and power mode (Mode-PR), and full refrigeration mode (Mode-R) according to the energy demands of users. In the proposed CCP systems, the recompression cycle and modified dual-stage compression cycle are used to replace the regenerative cycle and basic dual-stage compression cycle in two reference systems respectively. The mathematical models of systems are established and verified. Detailed parametric analysis is conducted to investigate the effects of key parameters on the performances of proposed systems and reference systems. Moreover, the modified systems and reference systems are optimized and compared at three modes. Multi-mode analysis is also applied to study the ability of the four CCP systems to convert power into cooling. Finally, detailed exergy analysis and thermoeconomic analysis are performed for the optimal system. The results show that the modified systems can achieve higher exergy efficiency by recovering partial waste heat before the pre-cooler. Under the refrigeration condition (the evaporation temperature is 0 ℃), the exergy efficiencies of the modified single-stage compression (M−S) system are 13.71% and 14.08% higher than those of the reference system at Mode-P and Mode-R, respectively. The cooling capacities of the systems at Mode-PR and Mode-R are positively correlated with their power outputs at Mode-P. The M−S system has the best multi-mode performance owing to its highest exergy efficiency (64.01%) at Mode-P, minimal energy loss at Mode-PR, and the maximum cooling capacity to heat input ratio (1.714 at 0 ℃ and 0.964 at −20 ℃) at Mode-R. Under the freezing condition (the evaporation temperature is −20 ℃), the single-stage compression systems generally perform better than the dual-stage compression systems. During the process of switching from Mode-P to Mode-R, the total product unit cost of the M−S system increases from 12.24 $·GJ−1 to 44.74 $·GJ−1 under the refrigeration condition and from 12.24 $·GJ−1 to 38.15 $·GJ−1 under the freezing condition.

Colored radiative cooling: How to balance color display and radiative cooling performance

Radiative cooling, which aims at cooling objects by radiating heat into the outer space through the atmosphere window, has garnered wide interests since it is a passive refrigeration mode without extra energy consumption. However, most of the proposed structures, to maximize the cooling performance, are in white color, which may limit their practical applications due to some aesthetic consideration. To reveal the competing role between color display and radiative cooling performance, we take a metal-dielectric-metal (MDM) colored radiative cooler structure as representative to explore how the structure parameters influence the cooling performance and color display respectively, and clarify the key parameters for the desired performance. Moreover, the reflectance of the colored radiative cooler is identified as peak- and valley-types to clarify the color display performance. The Spearman rank order correlation coefficients between radiative cooling performance and the CIE-LCH color space parameters (lightness, chroma, and hue) are calculated, revealing that the lightness plays a dominant role. The present study is expected to reveal the competing role of radiative cooling power and color display, and trigger the practical applications of radiative cooling technologies.