To address the challenges of high energy consumption and elevated global warming potential (GWP) associated with refrigerants in -86 ℃ ultra-low temperature medical freezers, this study investigates a 568 L freezer employing a single-stage mixed-refrigerant J-T refrigerator. Two ternary hydrocarbon mixtures (R600a/R170/R1150 and R601a/R290/R1150) were experimentally evaluated as environmentally friendly alternatives to the conventional fluoride-containing mixture (R600a/R23/R14/R50). The refrigeration performance of the 2 hydrocarbon blends was analyzed without changing the system components; capillary, compressor and charge adjustments were made for R601a/R290/R1150 with the aim of reducing the refrigeration temperature, compressor discharge temperature and system energy consumption. Experimental results demonstrated that, without system modifications, R600a/R170/R1150 achieved a refrigeration temperature of approximately -60 ℃, whereas R601a/R290/R1150 attained -70 ℃. After reduction of the capillary tube inner diameter and replacement of the compressor with one suitable for R290, R601a/R290/R1150 achieved a refrigeration temperature of -87.3 ℃. Compared to R600a/R23/R14/R50, this configuration reduced the maximum discharge temperature by 11.4 ℃ and energy consumption by 32.9%. However, the pull-down time to -81 ℃ increased from 246 min to 404 min. Further adjustments by increasing compressor speed and refrigerant charge shortened the cooling time to 298 min while reducing energy consumption by 28.9%. These findings confirm that R601a/R290/R1150 not only achieves sub -86 ℃ refrigeration temperatures but also exhibits superior energy efficiency and environmental benefits. Therefore, this hydrocarbon mixture presents a viable eco-friendly alternative for ultra-low temperature freezer applications.

To address the lack of sufficient validation for the thermodynamic design methods of intermediate fluid vaporizers (IFV) and the inadequacy of research on IFV heat transfer testing technologies, a fully structured IFV test prototype was developed. Additionally, an IFV supercritical vaporization heat transfer performance test system was established using liquid nitrogen as the working medium. Laboratory tests on IFV supercritical heat transfer and flow performance were conducted. The results show that the root mean square deviation of gas-phase temperature measurement points in the experimental system is within 1 ℃, and the deviation for liquid-phase measurement points is within 0.1 ℃, demonstrating good temperature uniformity across the measurement points. The thermal balance error of the working medium on both the hot and cold sides is within 5%, indicating that the prototype and testing system are reasonably designed. For IFV boiling heat transfer, the Cooper criterion is found to be overly optimistic under conditions of low wall superheat. Instead, the Mostinsk criterion is recommended, with an additional 10% design margin. The error between the corrected heat transfer coefficient calculations and the experimental measurements is less than 5%. Under experimental conditions, the measured average condensation heat transfer coefficient is approximately 20% lower than the calculated value based on segmented calculations. The causes of weakened condensation in the intermediate medium are analyzed, and improvement suggestions are proposed from the perspectives of structure optimization, heat transfer design and commissioning and installation. This research provides experimental and validation support for the design of IFV supercritical heat transfer systems and serve as a reference for the engineering design of IFV products.

An integrated semiconductor air conditioner for electrical cabinet is designed, and the effects of input current (6~11 A), ambient temperature (20~35 ℃), temperature difference between inside and outside the cabinet (0~40 ℃) and air volume at the hot end on the refrigeration performance of the cabinet semiconductor air conditioner are studied by using the calibrated room calorimeter method. The experimental results indicate that when the ambient temperature is 26 ℃ and the temperature difference between the inside and outside of the box is 20 ℃, the optimal working current of the semiconductor air conditioner is 8 A (36 V), and the refrigeration capacity is the largest (213 W). When the current is 8 A (36 V), with the increase of ambient temperature (20~35 ℃), the cooling capacity and COP increase by 13.9% and 11.9%, respectively. With the increase of temperature difference (0~40 ℃) inside and outside the box, the refrigeration capacity and COP both increase significantly (108~340 W, 0.38~1.21), and the increase of heat exchange capacity is the main reason for the increase of refrigeration capacity. When the air volume of the hot-end fan is increased from 108.63 m³/h to 156 m³/h, the cooling capacity increased by 4.02% and the COP increased by 1.50%. It can provide reference for the design optimization of new cabinet semiconductor air conditioning.

In order to solve gas dynamic noise of Roots vacuum pump due to gas pulsation, return cavity models of four different structures, such as constant rectangular, expanding rectangular, constant depth arc and expanding arc cavities, were designed. The effects of return cavity structure on exhaust pressure, flow rate and internal flow field were analyzed by using the RNG k- εturbulence model and dynamic mesh method, and were verified by experiment. The research results show that the return cavity can increase the pressure of primitives volume in the pump chamber, which effectively suppresses high-pressure gas backflow and improve pressure and flow fluctuation at the outlet. Meanwhile, it can cause lower volumetric flow at inlet. When the inlet pressure is 30~76 kPa, compared with other three return cavities, the fluctuation amplitude of exhaust pressure and flow rate are the lowest at the outlet of constant depth rectangular return cavity (1.31~6.97 kPa and 0.39~1.48 m³/s, respectively). The research results can provide a theoretical basis for noise reduction and structural optimization of the Roots vacuum pump.

In order to improve the phenomenon of piston ring eccentric wear in oil-free lubricated wobble plate compressors, for wobble plate compressors under two typical types of anti-rotation structures, the motion models of the ball hinge on wobble plate and the connecting rod were constructed, and the optimization design method of cylinder distribution radius based on genetic algorithm with the optimization objective of minimizing the average tilting angle of the connecting rod in the motion period was proposed. The study shows that the best distribution circle radius of cylinder is the same for each phase under the bevel gear anti-rotation structure; and the best distribution circle radius corresponding to cylinder in each phase is different for each phase under the roller-straight groove anti-rotation structure, but the mean value can be used as a uniform distribution circle radius, and at this time the effect on the average tilting angle of the connecting rod in each phase is extremely small, less than 5‰; When the tilting angle of the wobble plate is 25° or less, the optimal design values of the cylinder distribution circle radius of the wobble plate compressor under the two types of anti-rotation structures are almost the same. By applying this optimization design method to a variety of existing wobble plate mechanisms, the average tilting angle of the connecting rod is reduced by nearly 21.4%~28.6%, and the peak piston lateral force is reduced by nearly 19.5%~49.6%. This optimization design method can effectively improve the eccentric wear phenomenon of piston ring.

To investigate the influence of a non-parallel rotor blade tip clearance structure on a compressor, this paper studies the effects of different rotor blade tip clearance values on compressor performance and flow field structure and identifies the optimal clearance value. Based on the design clearance value and the optimal clearance value, three expansion clearance distribution schemes were proposed to analyze their effects on compressor performance and flow field structure. The research results indicate that when the rotor tip clearance is set to 0.5τ, the stability margin improvement of the compressor is relatively large, and the performance of the compressor is superior near the stall point. The flow field structure near the stall point is relatively good, and 0.5τ clearance (P2) is considered the optimal clearance value. If the parallel gap distribution is changed to the expansion gap distribution D1, D2 and D3 schemes, the low-energy fluid vortex near the rotor pressure surface is significantly weakened. For the low-speed zone near the trailing edge of the blades, it is further blown away, improving the flow structure and increasing the stall margin. Compared with the baseline scheme, the D1, D2 and D3 schemes improve the stall margin by 1.6%, 1.9% and 2.4%, respectively. The total pressure ratio and efficiency stability margins are improved by 3.18%, 8.56% and 6.20%, respectively. The stability margin improvement rate is increased by 0.59%, 1.45% and 1.55%, respectively. The results provide insights into optimizing the clearance distribution structure for axial flow compressors.

Aiming at the issue that the conventional volute profile fails to completely enclose the impeller, the imPact of the profile's incompleteness on the fan's performance is explored, and a novel profile design approach is proposed. This method commences from the tongue and designs the Archimedes spiral around the impeller for an entire cycle to guarantee the uniformity and full development of the airflow within the volute. Through CFD simulation, the influence of the variation of the envelope angle on the flow field, efficiency, and noise characteristics of the fan is determined. The results indicate that when the envelope angle is gradually increased to the shape line encomPassing the impeller, the efficiency of the centrifugal fan is significantly enhanced and the operational noise is reduced. Under the design condition, the total pressure efficiency is elevated by 7.67% and the noise is decreased by 3.89 dB. A new line design method with complete impeller envelopment can notably improve the fan's performance and holds significant guiding value for the fan design.

For the problem of serious exhaust loss of miniature oil-free scroll air compressor with asymmetric working chambers, the design method of the exhaust port was given according to the inner volume ratio. The effects of the internal flow field characteristics and performance variations of the scroll compressor with asymmetrical chambers under different clearances and altitude were analyzed by CFD method and verified experimentally. The results show that the new exhaust port can reduce the amount of over-compression by 17.85% and reduce exhaust losses. When the radial clearance increases from 10 μm to 30 μm, the compressor volumetric efficiency decreases from 89.68% to 16.02% and the isentropic efficiency decreases from 78.69% to 32.84%. Experimental results on main performance such as flow and power etc. show that the maximum error between the experimental mass flow rate and the simulation result is 9.09%, and the maximum error of the power at an exhaust pressure of 0.26 MPa is 8.90%. The relevant results are of reference significance for reducing the exhaust loss of scroll compressors with asymmetric working chambers.

In order to provide theoretical guidance for pipeline layout and optimized operation in engineering design, and reduce building operation energy consumption, the variations in local resistance coefficients, fluid motion states, and viscous dissipation of elbows under different pipe diameters and velocities were compared by the method of combining the experiments and numerical simulation, and the groove method was utilized to optimize the components of the elbows. The results reveal that as the pipe diameter increases, the influence of deformed components on the fluid within the elbow gradually decreases, and the area of the low-velocity zone in both the turning section and downstream straight pipe section gradually decreases. At an inlet velocity of 1.1 m/s, elbows of varying diameters exhibit deviations from the established power function law regarding local resistance coefficients. Specifically, elbows ranging from DN40 to DN65 demonstrate nearly identical resistance coefficients, as do those from DN100 to DN125. This phenomenon is attributed to the internal fluid dynamics and stress distribution within the elbows. Using the aforementioned theoretical study for component optimization, adding grooves in the separation area of the material wall can reduce the local resistance loss of the elbow, reduce the range of low-velocity areas, and reduce mechanical energy consumption as well. In the elbow with added grooves, the optimization of local resistance is most significant at a smaller inlet flow rate of v=0.5 m/s, the local resistance is reduced by 63.96%. These research findings offer valuable insights for the design layout and structural optimization of elbows in engineering applications.

Cavitation in engine fuel pumps has a significant impact on the safety and life of the engine. Through a comprehensive overview of domestic and international research results on cavitation in engine fuel pumps, we have systematically summarized the reasons for the formation of cavitation in fuel pumps, the factors affecting it, the research methods and the current status of the development of cavitation, and introduced the two major factors affecting the generation and development of internal cavitation in fluid machinery, namely, the geometrical form of the objects in which cavitation occurs and physical factors (such as pressure, temperature, etc.). And for the research and observation of the cavitation phenomenon in this component of the method for organization and division, and gives the study of cavitation phenomenon in the fluid machinery and reduce the impact of the cavitation of the new program, for the optimization of the engine fuel pump to provide a direction.

The research foundation for carbon emission evaluation, certification and accreditation technology of refrigeration and air conditioning equipment in China is relatively weak. In order to provide ideas for the study of life cycle carbon emission evaluation methods for refrigeration and air conditioning equipment, this article provides a detailed review and analysis of relevant standards and literature on carbon emission accounting and evaluation at home and abroad. The results show that for refrigeration and air conditioning equipment, there is a lack of technical standards for carbon emission accounting at home and abroad, and it is necessary to develop a life cycle carbon emission accounting method based on the characteristics of refrigeration and air conditioning equipment; the calculation methods for carbon emissions at different stages of the lifecycle of different products have certain similarities and differences, mainly determined by the availability of data and the operability of the methods; it is necessary to establish a universal lifecycle carbon emission assessment method. With the application of new materials and technologies, the improvement of product energy efficiency, and regional energy efficiency differences, the technical assessment method should have a certain degree of inclusiveness and openness. The research results can provide reference for China to formulate carbon emission accounting methods for refrigeration and air conditioning equipment.

In response to the complex internal structure and numerous components of enclosed compressors, the precise positioning and identification of resonant components are extremely difficult, which limits the efficient control of vibration and noise performance of vortex compressors. In order to rapid identify the noise sources of compressor, a acoustic and vibration coupling simulation analysis method for vortex compressor is proposed in this paper. The finite element simulation technology is employed to simulate the working process of the compressor rotor system, then the upper and lower support reaction forces are obtained. Add the forces inside the shell to calculate the surface vibration characteristics of the shell. Then LMS. Virtual. Lab software is used for acoustic simulation to clarify the noise characteristics radiated from the shell, while the experiment is also carried out to obtain the compressor noise spectrum. The results show that the measured noise spectrum is in good agreement with the simulation results. And the sound pressure level of compressor is 75.2 dB (A) with an error of about 2.4 dB (A) compared to simulation results. 824 Hz and 1 940 Hz are the main noise sources of the compressor, corresponding to the moving vortex and stator shell components, respectively. Combined with the sound source recognition system, it can also be seen that the main sound source position of the compressor is also consistent with the simulation results. The research results can provide theoretical basis and technical reference for the localization and optimization of noise sources in enclosed scroll compressors.

Addressing the issues inherent in traditional aerodynamic design methods for blades—such as reliance on designer experience, long development cycles, and difficulty in ensuring design precision—this study applies an optimal surrogate model optimization method to the impeller optimization of a centrifugal blower. By parameterizing the design of a small centrifugal blower and using the Advanced Latin Hypercube Sampling (ALHS) method to sample 36 parameters from the meridional profile, inlet and outlet blade angles, and blade surface twist angle, 200 sets of blower performance data were constructed through numerical simulations. Based on this data, the optimal surrogate model (MOP) was employed to identify the 9 parameters that most significantly impact blower performance. Subsequently, an evolutionary algorithm (EA) was utilized to iteratively compute the optimal values of these 9 parameters, with the objective of maximizing isentropic efficiency and constraining the inlet-outlet pressure difference. A comparative analysis of the flow fields before and after optimization was conducted. The results demonstrate that the optimized blower suppressed tip leakage flow, reducing the tip leakage flow rate by 10% compared to the original model. At the mid-span of the impeller (at 55% of the meridional streamline), the maximum fluid velocity along the blade height decreased from 101.66 m/s to 82.06 m/s after optimization, and the velocity variation ΔV reduced from 53.52 m/s to 40.74 m/s, indicating reduced flow losses. Additionally, the maximum pressure at the impeller outlet increased from 115.37 kPa to 116.19 kPa. The optimal surrogate model effectively filters out non-critical input parameters during the optimization process, thereby reducing optimization costs and time. The findings of this research provide a reference for the optimal design of centrifugal blowers.

To address the vibration issue caused by the rubbing between the floating oil ring and the shaft in the thrust bearing of the steam turbine, the working principle, working characteristics, leakage rate, and structural relationship of the floating oil ring were analyzed. The results revealed that the clearance between the floating oil ring and the shaft at the oil inlet was reasonably arranged, allowing the floating oil ring to operate freely without jamming. However, the upper assembly gap between the floating oil ring and the shaft at the outlet was relatively small, and the anti-rotation adjusting pressure plate and bush groove upper and side clearances were insufficient. Consequently, the running oil ring, which was clamped on the shaft, could not float freely, resulting in high vibration caused by rubbing. After optimizing the design, the clearance of the floating oil ring at the oil inlet and the upper part and side of the groove of the anti-rotation adjusting pressure plate and tile sleeve was adjusted to 0.10 mm to 0.30 mm, and the floating oil ring was lifted and installed to ensure free floating without rubbing. Additionally, the assembly clearance should be controlled at 0.05 mm, and the clearance between the top of the floating oil ring and the shaft should be maintained at 0.55~0.76 mm to ensure that the floating oil ring operates stably. The vertical deviation of flatness is also limited to no more than 0.03 mm. The results show that by addressing the free-floating clearance of the floating oil ring and correcting the alignment deviation, the rubbing issue between the floating oil ring and the shaft is effectively resolved. This study provides a reference for solving vibration problems in the thrust bearing of steam turbines caused by floating oil ring rubbing.