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The present paper deals with experimental measurements performed within a heat exchanger devoted to the thermal rotating machineries. The device is based on a rotor-stator system scaled from an industrial rotary kiln. The thermal recovery system is able to capture the heat losses while the kiln wall is cooled. The inner moving wall-to-air heat exchanges measured through the insulated external shell are compared to the values established in various flow conditions similar to the present geometry. The thermal convection regimes are distinguished according to the different forces exerted on the fluid air motion: the buoyancy forces being compared to the inertial effects combining the centrifugal and the axial motions. General scaling relationships devoted to the natural, mixed and forced convection regimes are proposed in an extended range of the Richardson numbers.

Pavement material production requires a highly intensive energy processing related to the drying and the heating of granular materials within a rotary kiln. Thus, a better prediction of thermophysical parameters of bituminous concrete materials during their transformation is required to improve the processes in order to reduce their environmental impact. The present paper deals with accurate thermodynamics balance in a mix-asphalt plant. We report input and output mass flows captured within an instrumented flight rotary kiln devoted to a large range of asphalt materials. Hot-mix (Tmaterials ∼170°C), warm-mix (Tmaterials ∼120°C) and Recycled Asphalt Products (so-called RAP) are compared. Computation of the macroscopic energy balance exhibits an averaged energy flux source equal to about 7 MW, the major amount being connected to the power gas burner. The heat sink related to the drying is different according to the formulation, RAP particles having non-negligible moisture content. In situ temperature sensor...

International audience; We propose a minimal model aiming to describe heat transfer between particles (i.e. grains) and gases in a model of flighted rotary kilns. It considers a channel in which a convective gas interacts with a granular suspension and a granular bed. Despite its simplicity it captures the main experimental findings in the case of dilute suspension of heavy grains typical of what can be observed in many industrial rotary kilns. Energy balance between each phase takes into account the main heat transfer mechanisms between the transverse granular motion and the convective gas. In the absence of radiation heat transfer, the model predicts exponential variations of the temperatures characterized by a length which depends on the granular and gas heat flow rates as well as on the exchange areas. When radiation is taken into account, the model can be solved numerically. For this case, the temperature variations can be fitted by stretched exponentials whose parameters are found to be independent of the studied phases. Finally, an efficiency criterion is proposed to optimize the length of the system.

International audience; The advancement on the physical heat transfer model in granular system is crucial for the energy process efficiency development such as flights rotary kiln encountered in many industrial areas. The present paper is devoted to a coupled thermal-granular model development applied to that process. Based on the exchange surfaces estimation governing the heat transfer phenomena, the granular motion distribution is calculated in the kiln cross-section. The granular volume fraction is accurately obtained in a dilute regime characterized by one active phase (curtain area) and a granular dense regime characterized by two passive phases (within a bed and the loaded flights). A suitable energy balance, where the fully heat transfer phenomena are considered, is established in an elementary volume and integrated along the kiln. The numerical results are compared to a set of experiments performed in an industrial flights rotary kiln applied to the hot-mix asphalt materials manufacture. The relative errors reach less than 5% on the gases and materials temperature. Finally, a set of simulations is carried out in order to analyze the role played by the rotational speed and flights in the frame of a suitable energy diagnostics for future process design. (C) 2014 Elsevier Ltd. All rights reserved.