Papers by Keyword: Refrigeration

Abstract: This work analyzes a shape memory alloy Stirling heat engine through an integrated thermal, mechanical, and materials approach. It builds on our previously published framework by generalizing behavior of shape memory alloys (SMA) beyond the nanoscale and extends it to elastocaloric applications, where mechanical work can be used to induce the stress-induced phase transformation. Parallels between stress-strain and enthalpy-temperature behavior underline this extension. Heat engine performance is evaluated in terms of torque and speed, and consideration is given to fatigue service life. Heat transfer and transformation energetics are examined with implications for heat engine performance. The resulting work supports shape memory alloy based heat engines and refrigerators for thermal management in space applications.

Abstract: As renewable energy elucidation, the solar refrigeration of fruits such as date palm is a storage alternate to preserve food in healthy parameters of conditioning. This statistical and numeric study investigates the energy gain cost case around the diverse dimensions’ models of positive cold stores (02, 04, and 06 cold rooms), concerning energetic disparity and numerous financial fluctuations of the applied systems. The results of computation and analysis regarding panels of construction, equipment, consumption, and maintenance for classic, absorption, and adsorption refrigeration systems that conserve dates palm into these three cold stores. In the end, the comparison of technical and economic elements in tables and figures by enumerating their advantages and inconveniences. Classic Bitzer, Absorption WFC SC 5, and Adsorption AG ACS 15 and 08 are models in which their evaluation is relating to their costs. In Biskra, these results mean that adsorption chiller termed AG ACS (15 plus 08) is illustrious by its parameters of simplicity, lifespan, safety, and security, valued to 1147.5 €/m² and median cost up ten years of using is 92972 €.

Abstract: The effect of super-chilling at -2°C compared with ice storage at 0°C on flavor quality changes of turbot (Psetta maxima) was investigated. Changes in total volatile basic nitrogen (TVB-N), sensory attributes and volatile compounds were periodically examined for 20 days. Results demonstrated that super-chilling retarded the increases of TVB-N values and maintained better sensory quality compared to the ice storage. Additionally, GC-MS analysis showed super-chilling could more effectively maintain the characteristic volatiles responsible for fresh fish flavor and reduce the contents of putrid compounds such as TMA and acetic acid.

Abstract: Nowadays, developing solar cooling technologies, especially ejector refrigeration system, has become preferable to scientific researchers. Exergy analysis is a technique in which the basis of evaluation of thermodynamic losses follows the second law rather than the first law of thermodynamics. An experimental exergy analysis of a solar-driven dual parallel-connected ejector (DPE) refrigeration system was conducted using water as working fluid. Saturated steam with 2 bar and 120oC was provided by heat–pipe evacuated tube solar collector with an assistant of an electric heater. The saturated stream was used as a motive flow for the ejectors. The exergy destruction and exergetic efficiency of the main components of the DPE refrigeration system were determined and compared with those when using a single ejector (SE) under same operating conditions. It was found that the most irreversibilities of both systems occurred at the solar collector, electric boiler and ejectors, respectively. Also, the total irreversibility (Exergy destruction) of the system when using DPE was lower than using a SE. In additions, the exergetic efficiency of the ejector, evaporator, and overall system when using DPE were increased by 21%, 10%, and 27%, respectively. The system thermal ratio (STR) and coefficient of performance (COP) of the system using DPE compared with SE were increased by 20% and 23%, respectively.

Abstract: This work explores the utilization of alternative refrigerants to the conventional silica gel + water adsorption pair for the adsorption chiller cycle. Water as the working fluid in the cycle limits the cooling temperatures to above 0°C due to its triple point. The activated carbon Maxsorb III is thus considered as the adsorbent due to its high micro-porous characteristics which lead to higher uptake values. The isotherms of this adsorbent with natural refrigerant Propane, n-butane as well as refrigerants HFC-134a, R507a and R-32 are fitted to the Dubinin-Astakhov equation and the parameters tabulated. With these isotherms, the performances of these pairs with respect to their Specific Cooling Effects (SCE) are compared for assorted cooling temperature, ambient temperature and waste temperature requirements. It was found that the natural refrigerant propane exhibits the most favorable operational conditions when the required cooling temperature is below 0°C. A mathematical model is thus developed to predict the cycle of the propane cycle and is found to show a good fit to the experimental results.

Abstract: Environment and energy problems over the world have motivated researchers to develop energy systems more sustainable, having as one of the possible alternative the use of solar energy as source for cooling systems. Adsorption refrigeration systems are regarded as environmentally friendly alternatives to conventional vapour compression refrigeration systems, since they can use refrigerants that do not contribute to ozone layer depletion and global warming. In this paper a performance comparison between a solar continuous adsorption cooling system without mass recovery process and solar continuous adsorption cooling system with mass recovery process is carried out. Silica-Gel as adsorbent and water as refrigerant are selected. The results show that the adsorption refrigeration machine driven by solar energy can operate effectively during four months and is able to produce cold continuously along the 24 hours of the day. The importance of the mass recovery is proved in this study by increasing the coefficient of performance and the cooling capacity produced. For the same cooling capacity produced, the required number of solar collectors with mass recovery system is lower than the required number of solar collectors in the case of the refrigeration unit without mass recovery. For the same cooling capacity the system with mass recovery process allowed lower generation temperature.

Abstract: A vortex tube offers an alternative cooling with advantages of simplicity and compact. Using a natural refrigerant, a vortex tube enclosure cooling is environmentally benign. In this paper, the performance of a vortex tube enclosure cooling, VTEC, is investigated experimentally. The VTEC system comprises of the vortex tube cooling, an enclosure with a volume space of 0.045 m³, an air compressor, a compressed air storage tank and a compressed air line. The VTEC system is tested for its efficiency and cooling potential in the laboratory. An operating condition is controlled by a pressure regulator for an inlet air pressure of 3 bars, for energy saving, and a cold flow rate is adjusted by a needle valve near the hot exit of a vortex tube for the cold fraction between 0 and 1. Accordingly, the analysis of experimental data shows the maximum isentropic efficiency of the vortex tube enclosure cooling is 0.37 at the cold mass fraction of 0.45. Air temperature in the enclosure is about 13°C in average.

Abstract: The coefficient of performance (COP), the volumetric refrigeration capacity and the pressure ratio of refrigeration cycle were studied in a refrigeration-type compressed-air dryer using environmentally friendly refrigerants R410A and R407C and compared with those using R22. Study indicates that under the working condition of a refrigeration-type compressed-air dryer, COP using R410A is 3% higher than that using R407C, the volumetric refrigeration capacity using R410A is 50 percentage points higher than that using R407C and the pressure ratio of R410A is 10% less than that of R407C. COP using R410A equals 96% of that using R22 and the volumetric refrigerating capacity equals 147% of that using R22. COP using R407C is equal to 93% of that using R22 and the volumetric refrigerating capacity is equal to 97% of that using R22. R410A is a more appropriate alternative to R22 than R407C in a refrigeration-type compressed-air dryer.

Abstract: The coefficient of performance (COP), the volumetric refrigeration capacity and the pressure ratio of the refrigeration cycle were calculated for a refrigeration-type compressed-air dryer using natural environmentally friendly refrigerants R717, R290 and R610a and compared with those using R22. Study shows that in the working condition of a refrigeration-type compressed-air dryer the COP and volumetric refrigeration capacity using R717 are 5% and 11% higher than those using R22 respectively and COP using R290 is equal to 98% of COP using R22 and the volumetric refrigeration capacity is equal to 85% of that using R22. Although COP using R600a is 2% higher than that using R22, the volumetric refrigeration capacity is much lower than that using other refrigerants above mentioned. R717 and R290 are recommended as appropriate substitute refrigerants for R22 in a refrigeration-type compressed-air dryer.

Abstract: In this article is presents a short analyze of a solar cooling systems using absorption and adsorption chillers. We try to pick the optimum dimension for the principal equipment of a cooling system for a holiday house place in Mediterranean climate using TRNSYS software.