Refrigerant charge reduction in vapor compression refrigeration cycles via liquid-to-suction heat exchange

This short communication reports a study of the potential for refrigerant charge reduction in vapor compression refrigeration systems by means of a liquid-to-suction heat exchanger. The analysis was carried out on purely thermodynamic grounds for refrigerants of current interest, such as R134a, R22, R290, R600a and R717, assuming the cooling capacity as a constraint so that the evaporating pressure is free to vary. It was found that the minimum amount of refrigerant can be reduced depending on the thermophysical properties of the refrigerant, the working conditions, and the charge inventory.     

An experimental investigation of refrigerant mixture R32/R290 as drop-in replacement for HFC410A in household air conditioners

In the present paper, the refrigerant mixture R32/R290 (68%/32% by weight) is investigated as the drop-in replacement for R410A in household air conditioners. The GWP of it is only 22% of that of R410A. Theoretical and experimental investigations are conducted on the performance of the air conditioners working with both R32/R290 and R410A. Experimental results show that the refrigerant charge amount of R32/R290 is reduced by 30.0%–35.0%; the cooling and heating capacities are increased by 14.0%–23.7%. For further reducing charge amount and flammability, the micro-channel heat exchanger (condenser) is employed to replace the finned tube one. Compared with the R32/R290 system using finned tube heat exchanger, the R32/R290 charge amount and the power consumption are reduced by 34.1% and 0.4%, respectively; the cooling capacity and the COP are increased by 6.4% and 6.8%, respectively.     

Effect of multi pulse current treatment on microstructure and microhardness of resistance spot welded dual phase steel DP590

In this paper, microhardness and microstructural characteristics of dual phase DP590 steel resistance spot weld joint under two different welding conditions (i. e. single pulse and multi pulse) were studied. It was observed that applying multi pulse currents resulted in quasi-equiaxed grains of tempered martensite in fusion zone (FZ) of the weldment. The refinement of microstructure in fusion zone using multi pulse current treatment resulted in reduced hardness of the weld joint.     

Experimental investigation of the effect of condenser subcooling in R134a and R1234yf air-conditioning systems with and without internal heat exchanger

This paper presents an experimental study about the effect of condenser subcooling on the performance of an air conditioning system operating with R134a and R1234yf, under the same operating conditions. For both refrigerants, it has been shown that the COP undergoes a maximum as a consequence of the trade-off between increasing refrigerating effect and increasing specific compression work. At a given operating condition, the system COP increased up to 18% for R1234yf and 9% for R134a. These results confirmed the trends obtained from a previous theoretical analysis, demonstrating that a system operating with R1234yf can benefit more from the condenser subcooling than that with R134a. The experimental results also showed that the presence of an internal heat exchanger significantly reduces the COP increase due to condenser subcooling, since both improvements compete towards reducing the throttling losses. Besides the interference between IHX and condenser subcooling, the use of both simultaneously still yields a more efficient air conditioning system, especially for R1234yf.     

Impacts of layout,surface condition and alloying elements on diffusion welding of micro process devices

The formation of a monolithic part during diffusion bonding is accompanied by the diffusion of atoms across the bonding planes. At sufficient low roughness, it mainly depends on the temperature and dwell time. At the same time, the diffusion process competes against grain growth. By adjusting an appropriate level of bearing pressure, it is possible to control deformation taking into account additional parameters resulting from mechanical microstructures and the design and aspect ratio of the part. Furthermore, material properties, such as the content of alloying elements, the degree of cold work hardening and the grain size, have an impact on diffusion and deformation behavior. Also the surface condition of mating surfaces is important to diffusion kinetics and the quality of the joint. Especially passivation layers of corrosion‐resistant alloys, such as stainless steels and nickel‐based alloys, impair diffusion. In contrast to this, cold work hardening at low depth below the surface, e. g. by means of a blasting processes, may facilitate formation of a good bond and help to limit grain size. For oxide dispersion‐strengthened materials, additional impacts on diffusion bonding behavior applies.     

绕出驱动链轮处刮板输送链张力计算

绕出驱动链轮处刮板输送链张力的计算与刮板输送链的强度计算有关。根据刮板输送链在驱动链轮上不跳齿及脱链流畅的要求。将无载分支的刮板输送链的中心线视为抛物线。近似计算并确定绕出驱动链轮处刮板输送链张力。并给出了算例及测量方法。为水平埋刮板输送机的设计及安装提供理论基础。     

Sliding wear performance of metallic laser coatings against composite PTFE seals

Laser coatings are frequently used in applications where they slide against various elastomeric and polymeric seals or guide bands in different environments. Examples of such applications include hydraulics, maritime propulsion systems and components in pulp & paper industry. In this study highly corrosion resistant Inconel 625 (DIN Mat. No. 2.4856) and Thermanit 2509 super duplex stainless steel (～1.4501) coatings manufactured by novel coaxial hot‐wire laser cladding technique are tested in dry conditions at room temperature against various composite polytetrafluoroethylene (PTFE) seals. Despite only small difference in coating surface hardness, ～1.4501 and 2.4856 show significant differences in wear and friction performance against various seals. For instance, ～1.4501 is superior to 2.4856 against glass fiber and MoS₂ reinforced PTFE in terms of wear resistance and friction characteristics, whereas 2.4856 performs better against bronze reinforced PTFE seal. The reference Stellite laser coating, which is the hardest counter surface in this study, exhibits the best wear behavior against all the seal materials tested. The differences in wear performances are explained by cohesive and adhesive wear mechanisms.     

Effects of rotation speed and dwell time on the mechanical properties and microstructure of dissimilar aluminum-titanium alloys by friction stir spot welding (FSSW)

In this study, the effects of rotation speed and dwell time on the mechanical properties and microstructure of friction stir spot welded joints of dissimilar aluminum and titanium alloys were investigated. Aluminum AA6061 and titanium Ti-6Al-4 V alloys were selected as the work piece. The joint quality, mechanical behavior, and microstructural evolution in the welded regions were considerably affected by the welding parameters. The results of scanning electron microscopy showed the formation of Ti₃Al intermetallic compounds near the thermomechanical affected zone, which significantly affected the properties of the welding joint. Maximum tensile shear load was produced at 1000 min⁻¹ and 10 s dwell time. Moreover, the welding joint microhardness was improved with increasing the rotation speed.     

Characterization of corrosion behavior of aluminum welds reinforced with copper powder

This paper reports on the corrosion behavior of aluminum metal inert gas (MIG) welds reinforced with copper powder particles. Pure aluminum, AA1100 sheets, machined to a 45° v-grooved were used for this experiment. Copper powder particle reinforced samples and unreinforced samples were investigated. The corrosion behavior of the samples were investigated in 3.5 % sodium chloride (NaCl) solution, using the potentiodynamic polarization technique. The results revealed that the corrosion resistance for reinforced samples were higher than those for unreinforced samples. Hence the corrosion resistance of aluminum AA1100 welds can be improved by the addition of copper powder particle in the weld seam, and it is therefore recommended for typical industrial applications.