Fatigue Limit Reliability Analysis for Notched Material with Some Kinds of Dense Inhomogeneities Using Fracture Mechanics

This study proposes a quantitative method for predicting fatigue limit reliability of a notched metal containing inhomogeneities. Since the fatigue fracture origin of the notched metal cannot be determined in advance because of stress nonuniformity, randomly distributed particles, and scatter of a matrix, it is difficult to predict the fatigue limit. The present method utilizes a stress-strength model incorporating the “statistical hardness characteristics of a matrix under small indentation loads” and the “statistical hardness characteristics required for non-propagation of fatigue cracks from microstructural defects”. The notch root is subdivided into small elements to eliminate the stress nonuniformity. The fatigue limit reliability is predicted by unifying the survival rates of the elements obtained by the stress-strength model according to the weakest link model. The method is applied to notched specimens of aluminum cast alloy JIS AC4B-T6 containing eutectic Si, Fe compounds and porosity. The fatigue strength reliability at 107 cycles, which corresponds to the fatigue limit reliability, is predicted. The fatigue limits of notch root radius ρ = 2, 1, 0.3, and 0.1 mm are obtained by rotating-bending fatigue tests. It is shown that the fatigue limits predicted by the present method are in good agreement with the experimental ones

Experimental Investigation of Relative Humidity Effect on the Thermal Conductivity of Desiccant Material

Study on effective thermal conductivity (ETC) of desiccant materials is getting attention in the literature in order to optimize the operating parameters of close and open cycle adsorption cooling systems. In addition, it is an important parameter to enhance the performance of adsorption heat pump and adsorption cooling systems (AHP/ACS). Most of the desiccant materials are porous in nature, therefore, results in different ETC at different operating conditions i.e. temperature and humidity. In order to find the more precise performance expression, the combined effect of desiccant porosity, temperature and relative humidity (RH) should be considered. In this regard, many empirical and theoretical models have been presented for the estimation of ETC. Models developed in the literature are characterized by a single value at a particular temperature irrespective of humidity. Hence this study experimentally investigates the relative humidity effect on the thermal conductivity of the commercially available desiccant material i.e. AQSOA-Z05.The levels of RH were investigated in the range of 8% to 100%. The results showed that ETC of oven dry adsorbent material was 0.066 W/mK whereas it increased from 0.067-0.089 W/mK at RH of 8-100%, respectively. The ETC values increase due to the phenomena of pores filling by water vapor adsorption. It also showed that pore filling incorporate the change in the mean free path and it varied from 6.93-0.55μm at RH range 8-100%, respectively. Consequently, an empirical correlation has been presented which can predict the effective thermal conductivity at different levels of RH

Theoretical and Experimental Analysis of Desiccant Air Conditioning System for Storage of Agricultural Products

The study emphasizes on the use of desiccant air conditioning (DAC) system for the storage of agricultural products. The chilling sensitivity of the tropical fruits and vegetables makes this system more promising for their optimal storage. The desiccant air conditioning system assisted by Maisotsenko cycle evaporative cooler is proposed in the study to achieve the latent and sensible load of air conditioning. In this regard, the dehumidification evaluation of the honeycomb like polymer based hydrophilic desiccant blocks are carried out by the means of an open-cycle experimental unit. The representative ideal storage zones of three temperature and relative humidity compatible groups of fruits and vegetables are established on the psychrometric chart on the basis of published data. The ideal DAC cycle analysis is accomplished at low regeneration temperature (55°C) for case-I (T = 31°C; RH = 21%) and case-II (T = 13°C; RH = 70%). The dehumidification analysis of the desiccant blocks recommended the time ratio between regeneration and dehumidification modes as 1:1 and 2:3 for the case-I and case-II respectively. The suggested time ratios ensure the dehumidification of the process air up to 2 g/kg of dry air and 4 g/kg of dry air in case-I and case-II respectively. The COP of the system was calculated as 0.90-0.43 and 0.55-0.25 at 30-90 minutes dehumidification with regeneration heat supplies of 1.7-2.3 kW and 2.5-3.5 kW in case-I and case-II respectively. The promising dehumidification by the desiccant blocks resulted in achieving the latent load itself followed by flat plate heat exchanger and Maisotsenko cycle evaporative cooler to achieve the sensible load. However, in case of high sensible loads hybrid DAC system is being recommended in this study

ER stress response mechanisms in the pathogenic yeast Candida glabrata and their roles in virulence

The maintenance of endoplasmic reticulum (ER) homeostasis is critical for numerous aspects of cell physiology. Eukaryotic cells respond to the accumulation of misfolded proteins in the ER (ER stress) by activating the unfolded protein response (UPR), an intracellular signaling pathway that adjusts the folding capacity of the ER. Recent studies of several pathogenic fungi have revealed that the UPR is important for antifungal resistance and virulence; therefore, the pathway has attracted much attention as a potential therapeutic target. While the UPR is highly conserved among eukaryotes, our group recently discovered that the pathogenic yeast Candida glabrata lacks the typical fungal UPR, but possesses alternative mechanisms to cope with ER stress. This review summarizes how C. glabrata responds to ER stress and discusses the impacts of ER quality control systems on antifungal resistance and virulence

Performance Evaluation of Heat Pump Cycle using Low GWP Refrigerant Mixtures of HFC-32 and HFO-1123

Hydro-fluorocarbons (HFCs) have been widely used as working fluids (refrigerants) in air-conditioning and refrigeration systems. At the 1997 Kyoto Conference (COP3), a worldwide agreement was obtained to regulate the production and use of HFCs exhibit high global warming potential (GWP). In the above situation, Hydro-fluoro Olefins (HFOs) having extremely low GWP values such as HFO-1234yf, HFO-1234ze(E), HFO-1123, has attracted attentions. In this study, the performance of heat pump cycle using low GWP refrigerant mixtures of HFC-32 and HFO-1123 is evaluated experimentally. The experimental system is a water heat source vapor compression cycle, mainly composed of an inverter-controlled & hermetic-type scroll compressor (cylinder volume: 11 cm3), an oil separator, a double-tube-type condenser (heat transfer tube; inner grooved , OD 9.53 mm, ID 7.53 mm, total length 7.2 m), a liquid receiver, a solenoid expansion valve, and a double-tube-type evaporator (heat transfer tube; inner grooved , OD 9.53 mm, ID 7.53 mm, total length 7.2 m). Tested compositions of mixtures of HFO-32/HFO-1123 are 58/42 mass% (GWP=393) and 42/58 mass% (GWP=285). These mixtures are tested for the heating and the cooling modes. In the heating mode, the heat sink water temperatures at the inlet and outlet of condenser are kept at 20 ˚C and 45 ˚C, respectively, and the heat source water temperatures at the inlet and outlet of evaporator are kept at 15 ˚C and 9 ˚C. Then, the heating load is varied from 1.6 kW to 2.6 kW. Similarly, in the cooling mode, the water temperature at the inlet and outlet are kept at 30 ˚C and 45 ˚C in condenser, and at 20 ˚C and 10 ˚C in evaporator. Then, the cooling load is varied from 1.4 kW to 2.4 kW. The conventional refrigerant R410A is also tested as the reference. In both modes of heating and cooling, the COP of HFO-32/HFO-1123 mixture (58/42 mass%) is almost the same as that of R410A, while the COP of HFO-32/HFO-1123 mixture (42/58 mass%) is a little lower than that of R410A. By analyzing the irreversible loss of the heat pump cycle based on the second low analysis, the losses of both mixtures in condenser and evaporator are slightly smaller than that of R410A, while the losses of both mixtures in compressor are slightly higher than that of R410A. This result reveals that tested mixtures of HFO-32/HFO-1123 are available to use as the alternative of R410A if the design of compressor and heat exchangers are optimized

Optimized Performance of One-Bed Adsorption Cooling System

Adsorption cooling system can be driven by solar energy or waste heat, so it will effectively reduce fossil fuel consumptions when total system is well-designed. On the other hand, the system tends to have a large size, which will be an obstacle to install adsorption cooling systems to small to medium scale cooling demands, such as automobiles, houses, or shops. The study was aiming at the reduction of system size of adsorption cooling systems for refrigeration and air-conditioning applications. To simplify the system, we investigated one-bed configuration of adsorption cooling system. In general, one-bed adsorption cooling system would result in a large temperature fluctuation at chilled water outlet. To overcome that drawback and to maximize the cooling capacity, the cycle time, namely, pre-heating, desorption, pre-cooling, and adsorption times, of one-bed adsorption cooling system was optimized. In case of two-bed adsorption cooling system, two adsorbers operates in reverse phase each other, which means that the degree of freedom for cycle time optimization is two. In case of one-bed adsorption cooling sytem, four processes can be independently optimized. In our study, activated carbon-ethanol pair was chosen as the adsorbent-refrigerant pair because of a high adsorption capacity of activated carbons against ethanol. Using adsorption isotherms and kinetic data of activated carbon-ethanol pair measured by our research group, a lumped parameter model of one-bed adsorption cooling system was developed. The four parameters of cycle time were optimized using global optimization method, and the optimal time settings were effectively found. The results showed the effect of cycle time optimization on the cooling performance of one-bed adsorption cooling system