Using ice slurry as secondary refrigerant for charge reduction in industrial facilities

This work analyses warming impact and electricity cost in farm milk cooling facilities when direct expansion systems are replaced by ice slurry based secondary refrigeration systems. The environmental improvement obtained has been assessed by comparing the TEWI values obtained using ice slurry with those obtained using a direct refrigeration facility. Economical effects have also been assessed by evaluating power consumption and taking into account the feasibility of benefiting from reduced electricity rate by producing and accumulating ice slurry during off-peak hours

Heat exchanger performance modeling using ice slurry as secondary refrigerant

Ice slurry is well known as a biphasic secondary refrigerant that presents several potential advantages compared to single phase secondary refrigerants. These potential advantages can be summarized in the ability to use the thermal storage and the high cooling capacity given by the latent heat. Theoretically, these features should allow important energy savings in secondary refrigerant distribution loop. However, an accurate evaluation of these energy savings requires the knowledge of the thermal and rheological performance of the refrigerant studied. Based on the experimental model developed by the authors for brine based ice slurry, a theoretical analysis of heat exchangers performance is presented in this work in order to calculate the potential energy savings associated to its use. The influence of ice concentration, mass flow rate, heat exchanger length and cooled fluid temperature over pumping power and heat transfer rate is studied. The ratio between heat transfer rate and pumping power is used as the evaluation parameter, which allows us to find the most favourable operation conditions for ice slurry flow. In order to assess the improvement obtained using ice slurry, results for ice slurry are compared to those obtained for carrier fluid at same inlet temperature.This research has been partially financed by the project DPI2007-66551-C02-01 grant from the “Dirección General de Industria, Mº de Ciencia y Tecnología”, the project 2I05SU0029 grant of the “Secretaría General de la Consejería de Educación y Cultura de la C.A. de la Región de Murcia” and the HRS Spiratube Company, Murcia (Spain)

Effects of the aeration on the fluid dynamic behaviour of a multi-zone activated sludge system

Conventional wastewater treatment plants (WWTP) are necessary to modify the wastewater properties in order to make it acceptable for a safe discharge into the environment or a certain reuse purpose. Biological oxidation is the most important of the processes involved in conventional WWTP. Organic substances dissolved in the water are removed by means of bacteria presented in the biological reactor. Air is necessary to enable the reduction of the organic content of the water by the bacteria. Bubbles of air are introduced into the reactor through air diffusers. Air diffusers can account up to 70% of WWTP total energy consumption. So a deep understanding of the dynamic behaviour of the flow is necessary for optimizing the process and saving energy. A numerical analysis of the effects of the aeration in the fluid dynamics behaviour of a real multi-zone activated sludge reactor is carried out. The purpose is to identify and analyse the changes originated in the velocity field by the aeration. A numerical modelling of the activated sludge system located in San Pedro del Pinatar (Murcia, Spain) is developed throughout a general-purpose computational fluid dynamics (CFD) code. The multiphase flow is simulated with a Euler–Lagrange approach; modelling the bubbles as discrete phase. Two simulations, one with aeration and the other without it, are carried out. The numerical results show that the aeration has a notable effect in the performance of the reactor. Changes in velocity field, stagnant zones, residence time distribution or even free surface level originated by the aeration in the reactor are studied. In general, the aeration reduced the amount of stagnant volume in the reactor. However, when the aeration is activated, some re-circulating zones are formed, reducing the residence time in the reactor.The researcher team of the present work acknowledges the contribution of the company ESAMUR, owner of the biological reactor studied, which provided the experimental data necessary for the development of the numerical model presented

Dimensional analysis and experimental study of pressure drop and heat transfer for Na-Cl ice slurry in pipes

Over the last few years, many works have been developed to study the influence of some factors like the mass flow, pipe diameter or ice contents on the pressure drop characteristics and heat transfer process when using ice slurry as liquid secondary refrigerant. Nevertheless, most of these works present results of great scientific interest, but hardly applicable to different situations to those of test conditions and therefore they have a limited interest when approaching the design of practical ice slurry installations. Based on the dimensional analysis, the work reported in this paper try to determine which are the variables that explain the thermal and hydraulic behaviour of ice slurry, to fix the influence of these variables and to present the results so that they can be used as a tool of design for ice slurry applications. Experimental studies were performed to clarify the thermal and hydraulic characteristics of ice slurry with a 3% sodium chloride-water solution flowing in circular pipes. A number of experiments have been carried out to investigate the characteristics of flowing ice slurry for various pipes diameter, ice mass fraction, flow velocity and ice crystal size, and the non-dimensional values have been obtained from the pressure drop (via Fanning factor) and the heat transfer (via Nusselt number). Experimental data on friction factor are plotted on a Moody diagram. Experimental values of Nusselt number are plotted also versus Reynolds number and others parameters. Both data collection has been compared with other researcher’s results, showing the most cases a good level of agreement

Application of ramp limitation regulations for smoothing the power fluctuations from offshore wind farms

This paper deals with the smoothing regulation strategies for reducing the effects of the wind farm power fluctuations. Concretely, realistic available power is obtained from an aggregated simulator of an offshore wind farm, developed and validated in previous papers. Being curtailed the power through positive ramp limitation and through a delta constraint linked with a negative ramp limitation. Then, the smoothing of the fluctuations is compared for an equivalent energy cost. Showing the reduction in the reserve requirements and ramping rates the power system needs for compensating them.The financial support provided by “Junta de Comunidades de Castilla-La Mancha”—PBC08-0275-3945— and “Ministerio de Educación y Ciencia” —ENE2006-15422-C02-01/ALT and ENE2006-15422-C02-02/ALT— is gratefully acknowledged

Lost Cities, Recovered Cities: Technology in the Service of the Past

[ES] Las ciudades son entes vivos que cambian casi a diario sin que sus habitantes sean conscientes de ello. Se olvida el estado previo a las grandes transformaciones y los ciudadanos se acostumbran a la nueva imagen urbana. En cien años una ciudad puede cambiar completamente su apariencia e incluso su esencia. Este es el caso de Granada, donde su centro histórico fue profundamente modificado a lo largo del siglo XIX. Estos cambios han sido estudiados por un proyecto de análisis y reconstrucción de la ciudad histórica. El trabajo abarca, desde el Rey Chico, bajo la Alhambra, hasta Puerta Real, restituyendo la imagen de la ciudad hacia 1831, apoyándose en los grabados y descripciones de los viajeros románticos, en los planos de alineaciones previos a las transformaciones y en las fotografías antiguas.[EN] Cities are living entities that change almost daily but its people are aware of it. They forget the state before the great changes and people become accustomed to the new urban image. In a hundred years a city can completely change its appearance and even its essence. This is the case of Granada, where its historic center was heavily modified during the nineteenth century. These changes have been studied by a project analyzing and virtually rebuilding the historic city. The work ranges from the Rey Chico, below the Alhambra palace, to Puerta Real, restoring the image of the city around 1831, based on the engravings and descriptions of romantic travelers, on the previous alignments and transformations in old pictures.Fernández Ruiz, JA.; Gómez Robles, L. (2013). Ciudades perdidas, ciudades recuperadas. La tecnología al servicio del pasado. Virtual Archaeology Review. 4(9):48-57. https://doi.org/10.4995/var.2013.4247OJS485749Archivo del Patronato de la Alhambra y Generalife (APAG). Colección de Grabados/0051. Signatura antigua: 756. Plataforma de Granada por Ambrosio de Vico, Maestro mayor de la insigne Iglesia de Granada, 1590- 1613.ICOMOS (2008): Carta Ename para la interpretación de lugares pertenecientes al patrimonio cultural. http://www.enamecharter.org/index.htmlFERNÁNDEZ SALINAS, V. M. (1994): Los centros históricos en la evolución de la ciudad europea desde los años setenta, en Eria, Revista Cuatrimestral de Geografía. nº 34, pp. 121-131.LOWENTHAL, D. (1985): El pasado es un país extraño. Madrid: Akal, 1998

TokenTLB+CUP: A Token-Based Page Classification with Cooperative Usage Prediction

[EN] Discerning the private or shared condition of the data accessed by the applications is an increasingly decisive approach to achieving efficiency and scalability in multi- and many-core systems. Since most memory accesses in both sequential and parallel applications are either private (accessed only by one core) or read-only (not written) data, devoting the full cost of coherence to every memory access results in sub-optimal performance and limits the scalability and efficiency of the multiprocessor. This paper introduces TokenTLB, a TLB-based page classification approach based on exchange and count of tokens. Token counting on TLBs is a natural and efficient way for classifying memory pages, and it does not require the use of complex and undesirable persistent requests or arbitration. In addition, classification is extended with Cooperative Usage Predictor (CUP), a token-based system-wide page usage predictor retrieved through TLB cooperation, in order to perform a classification unaffected by TLB size. Through cycle-accurate simulation we observed that TokenTLB spends 43.6% of cycles as private per page on average, and CUP further increases the time spent as private by 22.0%. CUP avoids 4 out of 5 TLB invalidations when compared to state-of-the-art predictors, thus proving far better prediction accuracy and making usage prediction an attractive mechanism for the first time.This work has been jointly supported by the MINECO and European Commission (FEDER funds) under the project TIN2015-66972-C5-1-R and TIN2015-66972-C5-3-R and the Fundacion Seneca-Agencia de Ciencia y Tecnologia de la Region de Murcia under the project Jovenes Lideres en Investigacion 18956/JLI/13.Esteve Garcia, A.; Ros Bardisa, A.; Robles Martínez, A.; Gómez Requena, ME. (2018). TokenTLB+CUP: A Token-Based Page Classification with Cooperative Usage Prediction. IEEE Transactions on Parallel and Distributed Systems. 29(5):1188-1201. https://doi.org/10.1109/TPDS.2017.2782808S1188120129

Analysis of heat transfer phenomena during ice slurry production in scraped surface plate heat exchangers

Heat transfer during ice slurry production in a scraped surface plate heat exchanger (SSPHE) has been experimentally investigated. By using a 7 wt. % sodium chloride brine, a wide range of operating conditions has been tested: scraping velocities from 0.1 to 0.8 s−1 and logarithmic temperature differences from 0.5 to 2.5 °C. Two different PEEK scraper arrangements have been used, mounted on the driving arms: rigid scrapers and surface adaptable scrapers, pushed by torsion springs. Heat transfer coefficients and ice production rate were measured under batch operating mode. Experimental results shown dependence of the nucleation onset with the scraping speed and the wall supercooling degree. Global nucleation only occurred for high velocities and low supercooling degrees, appearing only on the wall for the other cases. A decrease of the heat transfer coefficient of 1.5 times for increasing logarithmic temperature differences is reported, as a consequence of the ice layer growth with a low effect of the scraping speed. The use of adaptable scrapers provide heat transfer coefficient augmentations from 2 to 4-fold with respect to the rigid configuration

Ice slurry production in plate heat exchanger with subcooled scraped surface. Póster

Ice slurries consist of aqueous solutions in which small ice crystals are present. One of the main advantages of ice slurries compared with the storage and usage of common ice is the easiest transport capacity, being possible to pump it. Due to their high cooling capacity and constant cooling temperature, the use as refrigerant offers the major benefit of ice slurries. In this work ice slurry is produced in an innovative scraped-surface plate heat exchanger (SSPHE): a 28 liters capacity tank with a total heat transfer area of 10m2m-3 crystallizer volume. The heat transfer surface is continuously scraped by four rotating blades and cooled underneath by a flow of calcium chloride solution in water. The coolant solution is subsequently cooled by the expansion of a flow of R507 refrigerant in a compact evaporator

Production of ice slurry in a scraped-surface plate heat exchanger.

The present work presents experimental results of the production of ice slurry in an innovative scraped-surface plate heat exchanger (SSPHE). It consists of a 28 liters capacity tank with a total heat transfer area of 10m2m-3 crystallizer volume. The scraper consists of four rotating PEEK blades that are driven by a vertical shaft connected to an electrical motor. The heat transfer surface is cooled underneath by a foow of calcium chloride solution in water. The coolant solution is subsequently cooled by the expansion of a flow of R507 refrigerant in a compact evaporator. Sodium chloride brine with a concentration of 5% is the base solution for the generation of ice slurries of about 20% of ice content in a batch process