A new recuperator is now being introduced for small and micro-turbine applications. These applications are characterized by low pressure ratios, exhaust gas temperatures that are suitable for use with stainless steel, and a limited allowance for leakage that does not impair the performance. However high reliability is required, because microturbines typically experience 4000 start/stop cycles during their life, and have to be totally reliable when supplying electricity for applications that are independent of the grid. Recuperated gas turbines have a history of expensive installations, prone to cracking under thermal shocks. The ACTE recuperator has been specifically designed for reliablity, compactness and low cost. This paper shows how these seemingly conflicting requirements are met in the ACTE design.

The present paper focuses on the development steps of heat exchangers dedicated to single room ventilation unit with heat recovery (SRVHR) by proposing a numerical approach. A methodology is suggested in order to determine the best trade-off between hydraulic and thermal performance given a specific geometry. The methodology consists in a mapping of the coefficient of performance (COP) of the unit. The latter is defined as the ratio between recovered heat and the fan energy use, given a specific indoor/outdoor temperature difference. However, the energy performance should not be the only criterion to be taken into account in the frame of the design steps of a heat recovery exchanger: technical, economic and acoustic aspects should also be considered. This numerical methodology is illustrated by means of a real example of a newly developed heat exchanger dedicated to a SRVHR. The optimization is first performed while using a semi-empirical model (based on the use of correlations and on a spatial division of the studied heat exchanger). The semi-empirical model allows for the creation of a COP map in order to identify the most effective geometry parameters for the heat exchanger. The decision concerning the final geometry is made accounting for the so-called technical, economic and acoustic considerations. A discussion on some parameters needed for the COP establishment is also proposed.

No abstract

Recently, interest in spiral heat exchangers has grown for high temperature, high cycling applications, especially in the gas turbine industry. Air and gas flow distribution in heat exchangers is known to play a major role in their pressure drop performance and effectiveness. Modelling this distribution is needed to optimise the primary surface geometry. This optimisation has been applied to the ACTE spiral recuperator and resulted in smaller and lighter recuperators thanks to a better use of the metal. A specific CFD code was developed and used to investigate different ‘state of the art’ flow configurations and hydraulic diameters. The best of these was then adapted to ACTE’s manufacturing technology. The model has been validated by pressure drop, velocity profile and effectiveness measurements. The improved geometry consists of a primary surface cross-corrugated pattern for both air and gas flows (see fig. 4 and 5). The pattern includes a central zone with a half angle of 30° for counterflow and two lateral zones with a half angle of 45° for fluid distribution and collection. The corrugations are not strictly sinusoidal but include a flat area that allows welding the two sheets together. The sheet pair (or “doublet”) is thus made resistant to ballooning. It is also used to hoop the annular heat exchanger.

The present paper describes the design improvement of a single-room ventilation unit. This ventilation system presents many advantages, however, several drawbacks exist. The first one is the acoustic disturbance. As the facilities are directly installed within the rooms, the fans' noise may create discomfort. Furthermore, in the cold or temperate climates, condensation or frost may appear. A dedicated management should then be implemented. Finally, as the system is not centralized, communication between the different units is required to ensure the global system efficiency. A team of several industrial partners and research institutes tackles the above-mentioned issues in the frame of the "Silenthalpic" project. The project is split in three major tasks. To correctly reduce the sound emission level (i), a spectral analysis of the noise emitted by an existing unit was undertaken, revealing that frequencies under 1 kHz are mainly responsible for the noise disturbance. From this analysis, active and passive solutions for noise reduction are envisaged, showing encouraging trends. The next research aspect is the exchanger of the ventilation unit (ii). The constituting material is a new porous membrane allowing the humidity transfer (vapor or liquid). This specific exchanger is numerically modelled to predict its performances. The last considered problematic is the optimization of the ventilation and control strategies for the specific case of decentralized units (iii), taking advantage of sensors and recent communication technologies like IOT (Internet Of Things) to establish communication between decentralized units and ensure their consistent control. The association of the three aspects presented here should then lead to versatile and efficient ventilation systems.