Luca Cattani

Experimental investigation on the convective heat transfer enhancement for highly viscous fluids in helical coiled corrugated tubes

In the present analysis, the forced convective heat transfer in smooth and corrugated helical coiled tubes was experimentally studied in the Reynolds and Dean number ranges 50÷1200 and 12÷295 respectively, by adopting Ethylene Glycol as working fluid. The primary aim of the investigation is to study the combined effect of the wall curvature and of the wall corrugation in the thermal entrance region for highly viscous fluids. Two coiled tubes with a curvature ratio of about 0.06, one with smooth wall and the other with spirally corrugated wall, were investigated under the uniform heat flux boundary condition. The main conclusion is that in the Reynolds number range analyzed, both curvature and corrugation enhance the heat transfer. For Dean number values lower than about 120 the wall curvature effect prevails, and the heat transfer enhancement reflects Nusselt numbers that are approximately 2–3 times higher than the straight smooth section. For greater Dean number values, the wall corrugation instead prevails. In fact the corrugated coiled tube reaches Nusselt number values which are up to 8 times higher than the ones expected for the smooth straight tube. The smooth coiled tube shows instead thermal performances at maximum 3.6 times over the straight section.

Spatio-temporal video processing for respiratory rate estimation

In this paper, we present a wire-free, low-cost video processing-based technique for respiratory rate (RR) estimation. The proposed method blends together two recently presented techniques, with the purpose of emphasizing small movements, such as respiratory movements possibly present in a video stream, in order to detect them. Initially, the system performs a spatial decomposition of the video frames in a pyramidal representation, in which each layer contains different spatial details. The levels are then pixel-wise temporally filtered with an infinite impulse response (IIR) filter, purposely designed to extract components having a periodicity compatible with the respiratory rate. Afterwards a single motion signal is extracted from each level. Finally, the extracted signals are jointly analyzed according to the maximum likelihood (ML) criterion in order to estimate the respiratory rate. The parameters extracted by our algorithm show a good agreement with those indicated by a gold-standard polysomnographic system. Therefore, our results, although preliminary, are encouraging and show that the respiratory rate can be reliably measured and monitored by a low-cost, wire-free, video processing-based system.

Maximum-likelihood detection of neonatal clonic seizures by video image processing

In this paper we consider the use of a well-known statistical method, namely Maximum-Likelihood Detection (MLD), to early diagnose, through a wire-free low-cost video processing-based approach, the presence of neonatal clonic seizures. Since clonic seizures are characterized by periodic movements of parts of the body (e.g., hands, legs), by evaluating the periodicity of the extracted signals it is possible to detect the presence of a clonic seizure. The proposed approach allows to differentiate clonic seizure-related movements from random ones. While we first consider a single-camera scenario, we then extend our approach to encompass the use of multiple sensors, such as several cameras or the Microsoft Kinect RBG-Depth sensor. In these cases, data fusion principles are considered to aggregate signals from multiple sensors.

A wire-free, non-invasive, low-cost video processing-based approach to neonatal apnoea detection

In this paper, we present a non-invasive, low-cost, wire-free video processing-based approach to neonatal apnoea detection. Our method consists in evaluating the presence or absence of apnoea events through an innovative analysis of a motion signal extracted from a video live capturing or recording of a patient. In particular, we pre-process the video by a recently proposed selective magnification algorithm, which has the purpose of emphasizing respiratory movements. Subsequently, by relying on a motion detection method based on the difference of consecutive frames, we extract a signal representative of the “quantity” of movement. Then, since breathing is characterized by periodic movements of specific body parts (e.g., the chest), using the Maximum Likelihood (ML) criterion we detect the presence or absence of a periodic component in the motion signal, so that the presence/absence of the respiratory movements and, therefore, of apnoea episodes can be inferred. Our method is tested on a newborn with recurrent apnoea events, affected by Congenital Central Hypoventilation Syndrome (CCHS). With the proposed method, we can identify 90-100% of the apnoea events detected by polysomnography, depending on the acceptable detection delay. The results, although preliminary, are thus very promising and show that apnoea events can be identified with non-invasive, low-cost, wire-free devices.

Estimation of the local heat transfer coefficient in coiled tubes: Comparison between Tikhonov regularization method and Gaussian filtering technique

Purpose Most of the passive techniques for enhancing heat transfer inside pipes (e.g. rough surfaces, swirl-flow devices and coiled tubes) give origin to an irregular distribution of the heat transfer coefficient at the fluid–wall interface along the wall perimeter. This irregular distribution could be critical in some industrial applications, but most of the available research papers, mainly due to the practical difficulty of local measuring heat flux on the internal wall surface of a pipe, present the results only in terms of Nusselt number averaged along the wall circumference. This paper aims to study the application of inverse problem solution techniques, which could overcome this limitation. Design/methodology/approach With regard to the estimation of the local convective heat transfer coefficient in coiled tubes, two different inverse heat conduction problem solution techniques were considered and compared both by synthetic and experimental data. Findings The paper shows the success of two inverse problem solution techniques in the estimation of the local convective heat transfer coefficient in coiled tubes. Originality/value This paper fulfills an identified need because most of the available research papers present the results only in terms of average thermal performance, neglecting local behavior.

Inverse estimation of the local heat transfer coefficient in curved tubes: a numerical validation

Wall curvature represents one of the most used passive techniques to enhance convective heat transfer. The effectiveness of wall curvature is due to the fact that it gives origin to the centrifugal force: this phenomenon induces local maxima in the velocity distribution that locally increase the temperature gradients at the wall by then maximizing the heat transfer. This fact brings to a significant variation of the wall temperature and of the wall heat flux along the circumferential coordinate. The convective heat transfer coefficient is consequently not uniformly distributed along the tubes perimeter and is characterized by higher values at the extrados wall surface in comparison to the ones at the intrados wall surface. Therefore, for predicting the overall performance of heat transfer apparatuses that involve the use of curved tubes, it becomes important to know the local distribution of the convective heat transfer coefficient not only along the axis of the heat transfer section, but also on the internal tubes surface along the cross section circumference. The present paper is intended to the assessment of a procedure developed to evaluate the local convective heat transfer coefficient, along the circumferential coordinate, at the internal wall of a coiled pipe.

Monitoring infants by automatic video processing

A unified approach to contact-less and low-cost video processing for automatic detection of neonatal diseases characterized by specific movement patterns is presented. This disease category includes neonatal clonic seizures and apneas. Both disorders are characterized by the presence or absence, respectively, of periodic movements of parts of the body-e.g., the limbs in case of clonic seizures and the chest/abdomen in case of apneas. Therefore, one can analyze the data obtained from multiple video sensors placed around a patient, extracting relevant motion signals and estimating, using the Maximum Likelihood (ML) criterion, their possible periodicity. This approach is very versatile and allows to investigate various scenarios, including: a single Red, Green and Blue (RGB) camera, an RGB-depth sensor or a network of a few RGB cameras. Data fusion principles are considered to aggregate the signals from multiple sensors. In the case of apneas, since breathing movements are subtle, the video can be pre-processed by a recently proposed algorithm which is able to emphasize small movements. The performance of the proposed contact-less detection algorithms is assessed, considering real video recordings of newborns, in terms of sensitivity, specificity, and Receiver Operating Characteristic (ROC) curves, with respect to medical gold standard devices. The obtained results show that a video processing-based system can effectively detect the considered specific diseases, with increasing performance for increasing number of sensors.

Video simulation of apnoea episodes

This paper presents a video simulator of apnoea episodes. A simple Continuous-Time Markov Chain (CTMC) model, describing the apnoea statistical behaviour, is combined with a properly designed video processing tool to insert apnoea episodes in the video recording of a normally breathing patient. In particular, the simulator has been applied to videos of newborns in order to simulate respiratory arrests. The obtained video streams are processed through a previously developed video processing-based system for automatic detection of apnoeas. Because of the rarity of apnoeas and the consequent limited availability of video recordings, the use of this simulator can be very helpful to test and design algorithms for detection of apnoea events. The presented results show that these events can indeed be simulated by the proposed video processing method in an accurate and reliable fashion. The proposed simulation approach can thus be very helpful for the implementation of innovative video-based, non-invasive monitoring systems or telemedical devices for in-home care.

Passive techniques for the enhancement of convective heat transfer in single phase duct flow

This review presents the main results of the experimental campaign on passive techniques for the enhancement of forced convective single phase heat transfer in ducts, performed in the last years at the Laboratory of the Industrial Engineering Department of the University of Parma by the Applied Physics research group. The research was mainly focused on two passive techniques, widely adopted for the thermal processing of medium and high viscosity fluids, based on wall corrugation and on wall curvature. The innovative compound heat transfer enhancement technique that couples together the effect of wall curvature and of wall corrugation has been investigated as well. The research has been mainly focused on understanding the causal relationship between the heat transfer surface modification and the convection enhancement phenomenon, by accounting the effect of the fluid Prandtl number. The pressure loss penalties were also evaluated. The principal results are presented and discussed.

Experimental investigation on the convective heat transfer enhancement in tubes with cross-helix profile wall corrugation

Wall corrugation is a popular heat transfer enhancement technique since it acts as a disturbance source in the flow that significantly enhances the thermal performance of the tube section with a limited pressure drop augmentation if compared to other passive techniques, such as the ones based on insert devices. In the hereby presented study nine pipes characterised by a cross-helix type corrugation were tested: this kind of corrugation, that was obtained by rolling twice the same tube with two helical corrugations evolving along opposite directions, showed a performance that exceeded the single helix-type corrugation behaviour and moreover presented an earlier transition to unstable regime. In the analysis the effect of the cross-helix type corrugation profile on the forced convection heat transfer mechanism was experimentally investigated in the Reynolds and Prandtl number range 25÷1000 and 115÷150 respectively. In particular, the effect of both the corrugation depth and the corrugation pitch were analysed. The results were compared with other types of wall corrugation and with the predictions for the smooth tube in order to point out the achieved heat transfer enhancement.