Measurements of Oil Retention in a Microchannel Condenser for AC Systems

In a refrigeration cycle, a small portion of the compressor oil circulates with the refrigerant flow through the cycle components, while most of the oil stays in the compressor. The presence of the lubricant affects the performance of heat exchangers by increasing the pressure losses and adding a thermal resistance to the heat transfer exchange process. The oil effects on microchannel heat exchangers are unique due to their relatively small scale geometry and manifold configuration. In this paper, oil retention in a microchannel type condenser was measured and its effects on heat transfer and pressure drop characteristics are presented. The heat exchanger was a 2 passes, aluminum louvered-fin type condenser that consisted of multiports rectangular microchannels with hydraulic diameter of 0.06 inch (1.7 mm). The refrigerant and oil flow rates were varied and actual operating conditions of an air conditioning condenser for R410A systems were replicated in laboratory. The refrigerant R410A and Polyolester oil mixture was studied at saturation temperature from 85 to 130 °F (29 to 54 °C) and two refrigerant mass flux that are common for a 4 ton nominal capacity AC system for residential applications. Oil mass fraction (OMF) in circulation with the refrigerant was varied from 0.5 to 5.6 in wt.%. The results indicated that at OMFs of 0.5 wt.% to 1 wt.%, which are common ranges in typical air conditioning systems, the oil retention in the microchannel condenser was less than 5% of the microchannel condenser internal volume for all saturation temperatures and all mass fluxes studied in this work. The oil retained in the condenser increased if the OMF increases and it was measured up to 23% of the total microchannel condenser internal volume when the OMF was 5.4 wt. %. The superheated vapor refrigerant section of the condenser held small amount of oil due to high refrigerant vapor superficial velocities inside the microchannel tubes. At OMFs of 0.5 wt. % the heat transfer capacity of the coil was the same of that of oil free conditions. At high saturation temperature of 130 °F (54 °C). and high mass flux, the heat transfer capacity of the coil decreased as the OMF increased and some penalization of refrigerant-side heat transfer rate was observed at OMFs as low as 1 wt. %. If OMF increased then the heat transfer capacity of the heat exchanger was penalized by up to 9% and the pressure drops across the condenser was augmented up to 19% with respect to the oil free case

La teodicea social de Adam Smith

Sostengo que existen dos tensiones en el sistema de ideas de Smith: la primera se da entre el postulado de un orden del universo nouménico invisible y los principios imaginarios por medio de los cuales conectamos los fenómenos; el segundo es una tensión entre el orden nouménico del mundo en el que convergen el 'ser' y el 'deber ser', y los distintos órdenes parciales que pueden reconstruirse en los fenómenos sociales, que dejan lugar a la irracionalidad y la injusticia. Mi primera propuesta es que esas tensiones son tensiones dialécticas en un sistema unitario presentadas rapsódicamente. Mi segunda tesis afirma que la pregunta que queda sin respuesta en el sistema en el ámbito moral es una cuestión 'metafísica' y 'teológica', a saber, el problema del mal; como consecuencia, también sostengo que Smith no era secularista, sino un agnóstico o un fideista post-escéptico, que se tomó en serio la pregunta de Bayle: ¿por qué los hombres son malos e infelices? Su ética privada de la prudencia, la justicia y la benevolencia, y su ética pública de la libertad, la justicia y la igualdad, eran modestas propuestas para enfrentarse al problema del mal social en nuestro mundo imperfecto.-----I argue the existence of two tensions in Smith's system of ideas: the first is that between the postulate of an invisible 'noumenical' order of the universe and the imaginary principles by means of which we connect the phenomena; the second is a tension between the noumenical order of the world where 'is' and 'ought' converge, and the various partial orders that may be reconstructed in social phenomena that leave room for irrationality, and injustice. My first claim is that these tensions are dialectical tensions in a unitary, albeit rhapsodically presented in writing. My second claim is that, the system’s unanswered question in the moral domain is a 'metaphysical' and 'theological' question, namely the problem of evil; by implication, I contend also that Smith was no secularist, but instead a post-sceptical fideist or agnostic, who took Bayle's question: "why are men wicked and unhappy?" quite seriously. His private ethics of prudence, justice, benevolence and his public ethics of liberty, justice, equality were modest proposals for coping with the problem of social evil in our imperfect world

Città e crisi globale: clima, sviluppo e convivenza

Il collasso del sistema finanziario mondiale ha scosso le certezze che hanno indirizzato mercati e politiche dagli anni ’80, quando la crisi delle città appariva al suo apice. In questo periodo, le politiche delle città hanno progressivamente acquisito maggior visibilità tra le priorità nazionali. I contributi sollevano questioni e riflessioni che affrontano i seguenti temi: 1. Le metropoli nel cambiamento climatico: ambiente, energie e paesaggi 2. Progetti urbani, mobilità sostenibile e mercato immobiliare 3. Teorie e pratiche per l’urbanistica per il XXI secolo 4. Conflitti e convivenza negli spazi pubblici 5. Innovazione, competitività e sviluppo territoriale 6. Politiche abitative ed emergenze metropolitane 7. La crisi a Mezzogiorno: trasformazioni e sfi deThe collapse of the world financial system shook the certainties that have addressed politichedagli markets and '80s, when the crisis of the city looked at its peak. During this period, the policies of the city hannoprogressivamente gained more visibility among the priorities nazionali.I contributions raise questions and reflections that address the following issues: 1. The metropolis in climate change: environment, energy and paesaggi2. Urban projects, sustainable mobility and market immobiliare3. Theories and practices for planning for the twenty-secolo4. Conflict and coexistence in the spaces pubblici5. Innovation, competitiveness and development territoriale6. Housing policies and emergencies metropolitane7. The crisis in the South: transformations and challenges o

Mediterranean radiocarbon offsets and calendar dates for prehistory

A single Northern Hemisphere calibration curve has formed the basis of radiocarbon dating in Europe and the Mediterranean for five decades, setting the time frame for prehistory. However, as measurement precision increases, there is mounting evidence for some small but substantive regional (partly growing season) offsets in same-year radiocarbon levels. Controlling for interlaboratory variation, we compare radiocarbon data from Europe and the Mediterranean in the second to earlier first millennia BCE. Consistent with recent findings in the second millennium CE, these data suggest that some small, but critical, periods of variation for Mediterranean radiocarbon levels exist, especially associated with major reversals or plateaus in the atmospheric radiocarbon record. At high precision, these variations potentially affect calendar dates for prehistory by up to a few decades, including, for example, Egyptian history and the much-debated Thera/Santorini volcanic eruption

The sensory pain of Dante's Inferno - Semantics of chronic pain in patients with narcolepsy.

To examine the semantics of chronic pain in narcolepsy and to compare with the poem Inferno, from Dante Alighieri. A cross-sectional study, in which type 1 (n=33) and type 2 (n=33) patients (hypocretin-1 quantification in cerebrospinal fluid), were studied at Departamento de Psicobiologia - Universidade Federal de São Paulo (Brazil). We assessed pain descriptors in the Present Rating Index (PRI) from McGill Pain Questionnaire. There was no significant difference in PRI between narcolepsy groups. In both groups, the most frequent words had a sensory dimension: throbbing, jumping, and tugging. Multiple correspondence analysis revealed the predominance of sensory descriptors and the deficiency of affective descriptors in these groups. A study that interpreted the poem Inferno, from Dante Alighieri, as McGill Pain Questionnaires descriptors suggested a contribution of the sensory dimension in pain of possibly narcolepsy patients, similar as in our results

Excursion to the valley of the Torrente Tiepido

The morphological evolution of the Torrent Tiepido (Province of Modena) is described. Following intense gravel excavation from its riverbed, this watercourse has been subject to accelerated erosion which has caused several problems to bridges and hydraulic structures. The remedial measures carried out in order to control this man-induced erosional process are discussed