Heat Transfer Characteristics of Jet Array Impingement at Low Streamwise Spacing

The present work studies the effect of low streamwise jet-to-jet spacing and uneven spanwise jet-to-jet spacing on target wall heat transfer coefficient in impingement cooling systems. Temperature sensitive paint alongside constant flux heaters were used to gather heat transfer data on the target wall. Two different geometries have been tested with varying jet-to-jet spanwise distance. The streamwise jet spacing was set to 3 jet diameters, the spanwise jet spacing was set to 3, 8 and 13 jet diameters while the jet-to-target spacing was set to 3 jet diameters. The tests were run at three average jet Reynolds numbers of 10,000, 13,000 and 16,000. Results show little effect of crossflow on the target wall heat transfer. Nusselt number profiles are compared to the Florschuetz prediction, the area averaged Nusselt number matches closely; however, the Florschuetz correlation shows a decreasing trend in Nusselt number as a function of streamwise distance while the data shows a Nusselt number profile that remains relatively constant as a function of streamwise distance, x. To better understand the flow physics behind this trend, a CFD run was set up using the v2-f turbulence model for all cases. Computational and experimental results display a strong similarity of their heat transfer trends. The crossflow is seen to not be able to reattach behind each jet due to their proximity to one another. Copyright © 2013 by ASME

Heat Transfer Characteristics Of Jet Array Impingement At Low Streamwise Spacing

The present work studies the effect of low streamwise jet-to-jet spacing and uneven spanwise jet-to-jet spacing on target wall heat transfer coefficient in impingement cooling systems. Temperature sensitive paint alongside constant flux heaters were used to gather heat transfer data on the target wall. Two different geometries have been tested with varying jet-to-jet spanwise distance. The streamwise jet spacing was set to 3 jet diameters, the spanwise jet spacing was set to 3, 8 and 13 jet diameters while the jet-to-target spacing was set to 3 jet diameters. The tests were run at three average jet Reynolds numbers of 10,000, 13,000 and 16,000. Results show little effect of crossflow on the target wall heat transfer. Nusselt number profiles are compared to the Florschuetz prediction, the area averaged Nusselt number matches closely; however, the Florschuetz correlation shows a decreasing trend in Nusselt number as a function of streamwise distance while the data shows a Nusselt number profile that remains relatively constant as a function of streamwise distance, x. To better understand the flow physics behind this trend, a CFD run was set up using the v2-f turbulence model for all cases. Computational and experimental results display a strong similarity of their heat transfer trends. The crossflow is seen to not be able to reattach behind each jet due to their proximity to one another. Copyright © 2013 by ASME

Evaluation of left ventricular dimension and systolic function by standard transthoracic echocardiography before and 24-hours after percutaneous closure of patent ductus arteriosus in 120 dogs

One hundred and twenty dogs were enrolled to value the effect of loading condition changes on left ventricular volumes before and 24-hours after the patent ductus arteriosus (PDA) occlusion by Amplatzer Canine Duct Occluder (ACDO) using standard echocardiography. The animals were divided in pure breed (n. 94) and mixed breed (n. 26); subsequently, the pure breed dogs were divided on the basis of the size of the breed of belonging in 3 groups (small size n. 36; medium size n. 8; large size n. 50). Moreover, the animals were divided in three classes based on their age: until 6 months; 6-12 months; over 12 months. A significant reduction of all the examined parameters (left ventricle internal diameter at end-diastole-LVIDd; left ventricle internal diameter at end-systole-LVIDs; end-diastolic volume-EDV; end-systolic volume-ESV; end-diastolic volume index-EDVI; end-systolic volume index-ESVI; fractional shortening-FS) was observed after ductal closure. Twenty-four hours after the closure, the evaluation of the relative percentage difference (RPD) of the echocardiographic parameters showed a significant reduction, higher in small size breed than in large size breed dogs. No significant difference related to breed size was observed only for RPD_FS variable. A significant interaction effect, between breed size and age classes, was observed only for RPD_EDVI (F = 3.39; p = 0.039). Until six months of age there was no significant difference in RPD_EDVI reduction, but over 6 months a significant reduction between small size and large size breed dogs at 24-hours from the occlusion was observed. In conclusion, our data seem to indicate that small breed dogs show a greater tolerance to congenital volume overload than large breed dogs, and this finding could be justify a delay of PDA closure in order to simplify the interventional procedure

Echocardiographic Evaluation of Left Ventricular Dimension and Systolic Function Before and 24 Hours after Percutaneous Closure of Patent Ductus Arteriosus in 120 Dogs

One hundred and twenty dogs were enrolled to value the effect of loading condition changes on left ventricular volumes before and 24 hours after the patent ductus arteriosus (PDA) occlusion by ACDO using standard echocardiography. The animals were divided in pure breed (n=94) and mixed breed (n=26); subsequently, the pure-breed dogs were divided on the basis of the size of the breed of belonging in 3 groups (small size n=36; medium size n=8; large size n=50). Moreover, the animals were divided in three classes based on their age: until 6 months; 6–12 months; over 12 months. A significant reduction of all the examined parameters (LVIDd, LVIDs, EDV, ESV, EDVI, ESVI, FS) was observed after ductal closure. The evaluation of the relative percentage difference (RDP) of the echocardiographic parameters showed at 24 hours after the closure, a significant reduction higher in small size breed than in large size breed dogs. No significant difference related to breed size was observed only for RPD_FS variable. A significant interaction effect, between breed size and age classes, was observed only for RPD_EDVI (F=3.4; p=0.039). Until six months of age there was no significant difference in RPD_EDVI reduction, but over 6 months a significant reduction between small size and large size breed dogs at 24 hours from the occlusion was observed. In conclusion, our data seem to indicate that small-breed dogs show a greater tolerance to congenital volume overload, and for this reason it could be possible to delay the PDA closure of a few months, allowing weight gain that makes easier the interventional procedure. On the other hand, the large-breed dogs should be submitted to ductal closure as soon as possible, in order to avoid an excessive LV wall stress