Experimental evaluation of the energy efficiency of a CO2 refrigerating plant working in transcritical conditions

[EN] This work presents the experimental evaluation of the energy efficiency and optimal gas-cooler pressures of a single-stage refrigerating plant working with carbon dioxide as refrigerant in transcritical conditions. The performance of the plant was tested at three different evaporating temperatures (-0.9, -10.1 and -18.1 degrees C), for three gas-cooler refrigerant outlet temperatures (31.2, 33.6 and 40.0 degrees C) at each evaporating temperature and in a wide range of gas-cooler pressures (74.4-104.7 bar). The experimental tests enabled us to calculate accurately the optimal gas-cooler pressures and compare them with the most commonly used relations to define this value in single-stage refrigerating cycles operating with carbon dioxide in transcritical conditions. Furthermore, an analysis of the reduction in energy efficiency produced in the plant if the optimum pressure is not well defined is also presented.The authors are indebted to Frost-Trol S.A. (www.frosttrol.com) and the Spanish Ministry of Education and Science (ENE2006-09972/CON) for the economical support given to the present work and for the Grant BES-2007-16820 linked to the Ministry projectCabello, R.; Sanchez, D.; Llopis, R.; Torrella Alcaraz, E. (2008). Experimental evaluation of the energy efficiency of a CO2 refrigerating plant working in transcritical conditions. Applied Thermal Engineering. 28(13):1596-1604. https://doi.org/10.1016/j.applthermaleng.2007.10.026S15961604281

Дослідження теплообміну у щільному шарі гранульованних матеріалів при продувці

Experimental studies of heat exchange between a dense layer of granular material and a stream of heated air have been carried out. As a granular material, claydite and gravel were used in a moving and a stationary layer. Temperature curves were obtained for the air flow and the solid component at the inlet and outlet of the installation. The shape of the curves indicates presence of two distinct zones with different heating rates. It was stated that it is expedient to set the heating period in the heat accumulators with a stationary bed within the first period which is characterized by a high heating rate. When calculating duration of the heating period, it is rational to take the value of the final material temperature 10‒15 % lower than the temperature of the heating air at the inlet. It was established that the coefficient of intercomponent heat exchange depends on the gas velocity, the velocity of the bed motion, the gas temperature at the input to the installation and the process duration. It was found that the curves of the dependence of the coefficients of intercomponent heat exchange on the process duration are described by a sigma function.Intensity of heat transfer for a moving layer in the investigated region was commensurable or somewhat higher than that for a stationary layer. It was shown that claydite is the preferred material for a granular packing. The time to onset of a stationary mode for a moving claydite layer was reduced by 2.4 times in comparison with gravel layer and by 2.2 times for a stationary layer.Представлены результаты экспериментального исследования теплообмена между газовой средой и плотным слоем гранулированного материала. Определено, что при некотором приближении температуры материала к температуре воздуха на входе темп нагрева резко снижается, что следует учитывать при расчетах теплоаккумуляторов. Установлено, что изменение коэффициента межкомпонентного теплообмена во времени подчиняется уравнению класса сигмоидПредставлені результати експериментального дослідження теплообміну між газовим середовищем і щільним шаром гранульованого матеріалу. Визначено, що при деякому наближенні температури матеріалу до температури повітря на вході темп нагріву різко знижується, що слід враховувати при розрахунках теплоакумуляторов. Встановлено, що зміна коефіцієнта міжкомпонентного теплообміну в часі підпорядковується рівнянню класу сигмої

Nanostructured catalysts of the turpentine emulsion polymerization under the influence of potassium persulphate

We have revealed the catalytic activity for initiating the water-emulsion turpentine polymerization of some nanostructured materials such as Keplerate type Mo72Fe30 nanocluster polyoxometalate, nanoporous iron and nanoporous composite of intermetallic compounds Pd2In@Pd3In obtained by dealloying of equiatomic alloys Fe – Mn and Pd – In. For polyoxometalate solutions and nanoporous metal samples, respectively, the yield of sufficiently pure polyterpene resins when using the potassium persulphate initiation depends on the nature of the contact between the catalysts and substrates: solid-liquid-liquid or liquid-liquid. A system that did not contain catalysts was taken as the reaction medium for comparison. Based on the obtained data on the softening point, the molecular weight of the resin samples was determined. Infrared spectroscopy was used to identify the obtained products. In the reaction medium (mainly aqueous) after the isolation of polyterpene resins, chromatographic analysis revealed so valuable products as alpha-terpineol, which is used as an intermediate for obtaining flavors and flotation agents

Investigation of Heat Exchange in a Blown Dense Layer of Granular Materials

Experimental studies of heat exchange between a dense layer of granular material and a stream of heated air have been carried out. As a granular material, claydite and gravel were used in a moving and a stationary layer. Temperature curves were obtained for the air flow and the solid component at the inlet and outlet of the installation. The shape of the curves indicates presence of two distinct zones with different heating rates. It was stated that it is expedient to set the heating period in the heat accumulators with a stationary bed within the first period which is characterized by a high heating rate. When calculating duration of the heating period, it is rational to take the value of the final material temperature 10‒15 % lower than the temperature of the heating air at the inlet. It was established that the coefficient of intercomponent heat exchange depends on the gas velocity, the velocity of the bed motion, the gas temperature at the input to the installation and the process duration. It was found that the curves of the dependence of the coefficients of intercomponent heat exchange on the process duration are described by a sigma function.Intensity of heat transfer for a moving layer in the investigated region was commensurable or somewhat higher than that for a stationary layer. It was shown that claydite is the preferred material for a granular packing. The time to onset of a stationary mode for a moving claydite layer was reduced by 2.4 times in comparison with gravel layer and by 2.2 times for a stationary layer

Characteristic Evaluation on the Cooling Performance of an Electrical Air Conditioning System Using R744 for a Fuel Cell Electric Vehicle

The objective of this study was to investigate the cooling performance characteristics of an electrical air conditioning system using R744 as an alternative of R-134a for a fuel cell electric vehicle. In order to analyze the cooling performance characteristics of the air conditioning system using R744 for a fuel cell electric vehicle, an electrical air conditioning system using R744 was developed and tested under various operating conditions according to both inlet air conditions of the gas cooler and evaporator and compressor speed. The cooling capacity and coefficient of performance (COP) forcooling of the tested air conditioning system were up to 6.4 kW and 2.5, respectively. In addition, the electrical air conditioning system with R744 using an inverter driven compressor showed better performance than the conventional air conditioning system with R-134a under the same operating conditions. The observed cooling performance of the developed electrical air conditioning system was found to be sufficient for cooling loads under various real driving conditions for a fuel cell electric vehicle