Optimization study of using PTC for human body heating dissipation

A better knowledge of the human body heat loses mechanisms is important for both diminishing the number of deaths during the surgical procedures of the patients under effect of full anaesthesia and increasing the efficiency of the Heating, Ventilation and Air Conditioning (HVAC) systems. For these studies it is necessary to manufacture a human body mannequin having its surface temperature maintained on a value close to the real human body temperature. A number of PTC (Positive Temperature Coefficient) thermistors placed on the entire external surface of the mannequin can be used for this purpose. This paper presents a study of the transient heating regime and the stability of the maintained temperature, performed on these devices

Structure tourbillonnaire des jets lobés et pouvoir de mélange

Le contrôle passif des jets turbulents est un moyen de mélange peu coûteux qui intéresse un large domaine industriel. Il est montré qu'une buse lobée droite, permet l'amélioration du mélange du jet issu de celle-ci, par rapport à un jet circulaire de référence. Une buse lobée de même plan de soufflage et à lobes inclinés, s'avère plus performante que la précédente. L'analyse de la dynamique tourbillonnaire, montre que les structures azimutales des jets lobés ne sont pas annulaires comme dans un jet circulaire, mais discontinues en raison du cisaillement de l'écoulement transversal généré par la variation du rayon de courbure de la frontière de la buse. Il s'en suit un épanouissement des structures longitudinales aux points de discontinuités expliquant probablement le gain d'induction dans le jet lobé droit. L'inclinaison des lobes et des creux accentue le cisaillement de l'écoulement transversal et l'auto-induction des structures longitudinales en devient plus importante

Thermal comfort models for indoor spaces and vehicles—Current capabilities and future perspectives

International audienceThroughout this paper, we reviewed the most popular thermal comfort models and methods of assessing thermal comfort in buildings and vehicular spaces. Most of them are limited to specific steady state, thermally homogenous environments and only a few of them address human responses to both non-uniform and transient conditions with a detailed thermo-regulation model. Some of them are defined by a series of international standards which stayed unchanged for more than a decade. The article proposes a global approach, starting from the physiological reaction of the body in thermal stress conditions and ending with the model implementation. The physiological bases of thermal comfort are presented, followed by the main thermal comfort models and standards and finishing with the current methods of assessing thermal comfort in practice. Within the last part we will focus mainly on thermal manikin experimental studies, and on CFD (computational fluid dynamics) numerical approach, as in our opinion these methods will be mostly considered for future development in this field of researc

Intelligent control of HVAC systems. Part I: Modeling and synthesis

This is the first part of a work on intelligent type control of Heating, Ventilating and Air-Conditioning (HVAC) systems. The study is performed from the perspective of giving a unitary control method to ensure high energy efficiency and air quality improving. To illustrate the proposed HVAC control technique, in this first part it is considered as benchmark problem a single thermal space HVAC system. The construction of the mathematical model is performed only with a view to obtain a framework of HVAC intelligent control validation by numerical simulations. The latter will be reported in a second part of the study

Dynamique tourbillonnaire et entraînement dans la région initiale d'un jet rond et d'un jet Marguerite à bas Reynolds

L’étude présente l’influence de la dynamique tourbillonnaire sur l’induction dans la région initiale de deux jets rond et lobé. L’entrainement du jet rond est modulé à la fréquence de passage des structures de K-H. Dans le jet lobé, la géométrie introduit un cisaillement transversal et des discontinuités de la structure de K-H conduisant au libre développement des structures longitudinales. Il en résulte un taux d’entrainement non corrélé au passage des structures de K-H et de niveau plus grand

Passive control of jet flows using lobed nozzle geometries

Passive control of the entrainment phenomenon in the turbulent jets is a mixing enhancement economical method of wide interest in the industrial field. A lobed nozzle without lobes inclinations allows improving mixing in the generated flow compared to a reference circular jet. A second lobed nozzle, having the same exit plane geometry but with inclined lobes intensifies, in a considerable manner, the entrainment which reaches up to four times the one in the reference circular jet. The lobed jets vortical dynamics analysis shows that the azimuthal structures are not annular like in the case of a circular jet, but discontinuous, due to the shear of the transverse flow induced by the curvature variation of the exit plane. The streamwise structures development at the discontinuities locations is probably explaining the entrainment benefit observed in the lobed jet without inclination angles. The lobed jet issued from the second nozzle presents like the first lobed jet, discontinuous azimuthal structures, but its remarkable induction benefit is not merely owed to the previous phenomenon. The intensification and organisation of the streamwise vorticity field into large scale structures, resulting in a consequent mixing enhancement, are connected to the increased shear produced by the lobes inclinations

Impinging jets – a short review on strategies for heat transfer enhancement

In industrial applications, heat and mass transfer can be considerably increased using impinging jets. A large number of flow phenomena will be generated by the impinging flow, such as: large scale structures, large curvature involving strong shear and normal stresses, stagnation in the wall boundary layers, heat transfer with the impinged wall, small scale turbulent mixing. All these phenomena are highly unsteady and even if nowadays a substantial number of studies in the literature are dedicated, the impinging jets are still not fully understood due to the highly unsteady nature and more over due to great difficulty of performing detailed numerical and experimental investigations

A state of the art regarding urban air quality prediction models

Urban pollution represents an increasing risk to residents of urban regions, particularly in large, over-industrialized cities knowing that the traffic is responsible for more than 25% of air gaseous pollutants and dust particles. Air quality modelling plays an important role in addressing air pollution control and management approaches by providing guidelines for better and more efficient air quality forecasting, along with smart monitoring sensor networks. The advances in technology regarding simulations, forecasting and monitoring are part of the new smart cities which offers a healthy environment for their occupants

Cross and clover shaped orifice jets analysis at low Reynolds number

The jet coming from a cross-shaped orifice with an open center has been shown in the past, to provide substantial increase in the near field convective transport-mixing, in comparison to a classical round orifice jet. Detailed information has been reported in previous works on the role played in the jet mixing enhancement by the crow of vortices composed of counter-rotating pairs of secondary streamwise structures which are developing in orifice’s troughs. A trough in the cross-shaped jet generates a local shear like the one generated by a triangular tab in a square jet. In the present study we are interested by the modification of local shears in the troughs of the cross-shaped jet, when orifice geometry is modified, such as the center of the orifice becomes closed, leading to a clover-shaped orifice. The general motivation is to understand the effect of using a set of combination of longitudinal structures, themselves produced by the superposition of local shear regions, in mixing performance of a cross jet. It is shown that lower entrainment rates in the clover jet is a results of a additional internal crown of vortices which opposes the external one due to inner shears generated by closing the center of the orifice

Special Issue “Urban Sustainability and Resilience of the Built Environments”

Urbanization and the development of urban areas are profoundly altering the relationship between society and the environment [...