THEORETICAL ANALYSIS ON THE PREDICTION OF PERFORMANCE COEFFICIENT OF TWO-STAGE CASCADE REFRIGERATION SYSTEM USING VARIOUS ALTERNATIVE REFRIGERANTS
This paper presents a comparison of the refrigerants CFC-12, HCFC-22, CFC-502, and their alternatives, such as HFC-134a, HFC-152a, HFC-404A, HFC-407C, HC-290, HC-600a, R717 (ammonia), and three mixtures composed of HFC-134a, HFC-152a, HC-600a, and HC-290. A theoretical performance study on a cascade refrigeration system was performed using two refrigeration cycles connected through a heat exchanger in the middle working as an evaporator for the high-pressure cycle and a condenser for the low-pressure cycle. The condensing temperatures varied between 40 and 60 °C, the evaporating temperatures varied between -50 and -10 C, and the heat exchanger temperature was kept constant at 1 °C. The refrigerants in both cycles are assumed to be same at first. The alternative refrigerants of HFC-152a and R717 had higher coefficients of performance (COPs) than other refrigerants and also low refrigerant charge rates for all operating conditions in the case study, according to the results of the theoretical analysis. The effects of the investigated refrigerants on the depletion of the ozone layer, increase in global warming, and flammable and toxic characteristics were considered and alternative refrigerant mixtures that may be suggested were determined. It was found that refrigerant blends of HC290/HC600a (55/45 by wt%), as a nonazeotropic mixture, and HFC-152a/HFC-134a (14/86 by wt%) and HFC-134a/HC600a (82/18 by wt%), as azeotropic mixtures, gave lower performance coefficients (COPs) and required lower refrigerant charge rates than their base pure refrigerants in the analysis. The separate usage of the refrigerants R717 and HFC-152a for the highand low-pressure sections of the cascade system, respectively, were found to be the best combination in terms of the analysis for the determination of coefficients of performance (COP) and refrigerant charge rates. The results of this study are of technological importance for efficient design when the industrial systems are assigned to utilize various alternative refrigerants.
Testing of a hydrocarbon mixture in domestic refrigerators
Performance of a propane/isobutane (R-290/R-600a) mixture was investigated in domestic refrigerators. Thermodynamic cycle analysis indicated that the R-290/R-600a mixture in the composition range of 0.2 to 0.6 mass fraction of R-290 yields an increase in the coefficient of performance (COP) of 1.7% to 2.4% as compared to R-12. For the actual performance tests, two refrigerator units (299 liters and 465 liters, respectively) were used. For both units, all refrigeration components remained the same throughout the tests, except that the length of the capillary tube and the amount of charge were changed for the mixture. Each refrigerator was fully instrumented with more than 20 thermocouples, 2 pressure transducers, and a digital watt/watt-hour meter. For each unit, both an energy consumption test and a no-load pull-down test were performed under the same conditions. The experimental results obtained with the same compressor indicated that the R-290/R-600a mixture at 0.6 mass fraction of R-290 showed a 3% to 4% increase in energy efficiency and a faster cooling rate as compared to R-12. The R-290/R-600a mixture showed a shorter compressor on-time and lower compressor dome temperatures than R-12. In conclusion, the proposed hydrocarbon mixture seems to be an appropriate candidate to replace R-12 from themore » viewpoint of energy conservation.« less
Impacts of climate and land use changes on flood risk management for the Schijn River, Belgium
Abstract Flooding is the most common natural disaster in Europe. Modern flood risk management relies not only infrastructure development but also on governmental and non-governmental actors applying legal, economic and communicative water management instruments. Within the European Union (EU), flood management closely relies on policy set at the EU and national levels. It is now recognized that a sound understanding of climate change is required in addition to current management by taking into account land use change and socio-political context, as climate and land use changes have major impacts on hydrological responses. This paper investigates the hydrological behavior due to urbanization under current and future climate scenarios of high summer and high winter rainfall for 20 sub-catchments of the Schijn River, located in the Flanders region near Antwerp, Belgium. As urbanization increases and existing rainfall-runoff models neglecting the specific behavior of urban runoff, a hydrological model was developed based on a basic reservoir concept and applied to the existing rainfall-runoff model (PDM) flow to examine the specific urban contribution. Results revealed that peak flow for urban runoff and the total peak flow (i.e. rural and urban runoff) were significantly higher (i.e. ranges from 200% to 500%) than the existing rainfall-runoff model (PDM) flows, because of faster and more peaked urban runoff response. The impact of climate change on current and future conditions was also assessed by estimating peak flows with respect to return periods from the flood frequency curve. The predicted peak flow of high summer future climate scenario was significantly higher (i.e. ranges from 200% to 250%) than that of the current climatic condition for this region. Furthermore, hourly peak flow and daily volume ratios of 100-year return period for the highest, lowest and average impervious area were projected for the time horizon of the year 2100. It is concluded that climate change impacts contribute the most in producing peak flow in coming years, while increased urbanization takes the second place for both hourly and daily values. Results on urbanization effect and climate change impact assessment are useful to the water managers for spatial planning, emergency planning and insurance industry.