1,721,099 research outputs found
Experiments on natural convection in water-cooled ribbed channels with different aspect ratios
No full textNatural convection heat transfer in vertical ribbed channels, using water as working fluid, has been experimentally studied. The investigation encompassed a large range of the channel aspect ratio, defined as the ratio between channel spacing and channel height, while the wall-to-fluid temperature difference was kept fixed. The measurement of local heat transfer coefficient was facilitated by a non-intrusive diagnostic tool, the schlieren technique, whose use for the quantitative study of liquid flows is rarely documented in the literature. Results provided an insight into the nature of free convection heat transfer from ribbed channels, whose geometry is significant in such several engineering devices as electronic equipment. It was found that a general reduction of heat transfer performance, relative to that of a flat vertical surface or a smooth vertical channel, was induced by the presence of ribs, within the range of the parameters investigated. Local and heat transfer characteristics were sensitive to changes in interplate spacing for small channel aspect ratios. Experimental data, recast in dimensionless form, were in excellent agreement with those obtained by this author in a previous research performed for aircooled channels, using the same experimental technique, the same geometric parameters of the ribbed surface, and a similar Rayleigh number
An experimental study on the transient thermal response of an electronic equipment box for UAV remote sensing applications
No full textAn experimental study of the thermal behavior of an electronic equipment box under transient conditions is presented. The box consists of a cabinet designed to contain electronic devices (such as infrared and visible cameras, hyperspectral sensors, etc.) carried on UAV systems and thermal control has to be assured only for the short duration (15-20 mins) of each flight. Different cooling systems have been considered, including forced convection of external ambient air and use of storage units (cold gel packs) inside the box. The best cooling solution was obtained by a mixed active/passive technique consisting in placing cold gel packs inside the box in combination with the internal ventilation, without any air exchange with external environment
Heat transfer in rectangular channels with transverse and V-shaped broken ribs
No full textRepeated ribs are used on heat exchange surfaces to promote turbulence and enhance convective heat transfer. Applications include fuel rods of gas-cooled nuclear reactors, inside cavities of turbine blades, and internal surfaces of pipes used in heat exchangers. Despite the great number of literature papers, only few experimental data concern detailed distribution of the heat transfer coefficient in channels with rib turbulators. This issue was tackled by means of the steady-state liquid crystal thermography: a pre-packaged liquid crystal film was glued onto the heated surface, and the colour map was taken by a video-camera at the steady state of a given experiment. After calibration tests to assess the colour-temperature relationship had been performed, local heat transfer coefficients were obtained by applying custom-made software to process the digitised colour images. Liquid crystal thermography was applied to the study of heat transfer from a rectangular channel (width-to-height ratio equal to five) having one surface heated at uniform heat flux and roughened by repeated ribs. The ribs, having rectangular or square sections, were deployed transverse to the main direction of flow or V-shaped with an angle of 45 or 60 degree relative to flow direction. The effect of continuous and broken ribs was also considered. Local heat transfer coefficients were obtained at various Reynolds numbers, within the turbulent flow regime. Area-averaged data were calculated in order to compare the overall performance of the tested ribbed surfaces and to evaluate the degree of heat transfer enhancement induced by the ribs with respect to the smooth channel
La tomografia ottica per la ricostruzione di campi termici tridimensionali
No full textDescrizione dei metodi di ricostruzione tomografica di campi termici tridimensionali da dati sperimentali (proiezioni
Natural convective heat transfer in vertical channels with low-thermal-conductivity ribs
No full textThe effect of repeated horizontal protrusions on the free-convection heat transfer in a vertical, asymmetrically heated, channel has been experimentally investigated. The protrusions have a square section and are made of a low-thermal-conductivity material. Experiments were conducted by varying the number of the protrusions over the heated surface (whose height was held fixed) and the aspect ratio of the channel. The convective fluid was air and the wall-to-ambient air temperature difference was set equal to 45 K. The local heat transfer coefficient was obtained by means of the schlieren optical technique.
The protrusions were found to significantly alter the heat transfer distribution along the heated surface of the channel, especially in the vicinity of each obstacle. For the ranges of parameters studied, the addition of low-conductivity protrusions leads to a decrease in the average heat transfer coefficient, as compared to that for the smooth surface, in the 0-7% range for the largest channel aspect ratio and in the 18-43% for the smallest channel aspect ratio
Studio sperimentale dello scambio termico per convezione naturale in un sistema di piastre verticali sfalsate
No full textUn modello per la previsione della prestazione nella gara di maratona in base ad alcuni parametri di allenamento
No full textHeat transfer and pressure drop in a rectangular channel with diamond-shaped elements
No full textHeat transfer and pressure drop experiments were performed for a rectangular channel equipped with arrays of diamond-shaped elements. Both in-line and staggered fin arrays were considered, for values of the longitudinal and transverse spacings, relative to the diamond side, from 4 to 8 and from 4 to 8.5, respectively. The height-to-side ratio of the diamonds was 4.0. Liquid crystal thermography was used to determine the heat transfer coefficients on the surface of the channel (endwall) on which the fins were mounted. Local variations in heat transfer coefficients induced by the arrangements of the diamond-shaped elements were measured and discussed. Correlations giving the average Nusselt number for each fin configuration as a function of the Reynolds number were developed. Thermal performance comparisons with data for a rectangular channel without fins showed that the presence of the diamond-shaped elements enhanced heat transfer by a factor of up to 4.4 for equal mass flow rate and by a factor of up to 1.65 for equal pumping power
Forced convection heat transfer from a surface with diamond-shaped elements having low/high thermal conductivity
No full textHeat transfer from arrays of staggered diamond fins has been experimentally investigated by means of liquid crystal thermography and standard thermocouple / heating foil technique. The arrays present the diamonds either with high or low thermal conductivity. Local (per-module or spanwise averaged) heat transfer coefficients have been reconstructed and, when possible, separated to infer the individual contribution of diamond and endwall
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