Bruno Agostini

Flexible two-phase thermosyphon for power electronic cooling

A two phase thermosyphon system for power electronic cooling is presented. The designed evaporator can house multiple power electronics modules, it collects the generated vapor to a common flexible tube that drives the vapor to a plate heat exchanger condenser. The system was tested and simulated for a total power loss of 12.5 kW. The condenser was installed at a distance of 3 m from the evaporator enabling flexibility from a customer side concerning location and distance where the heat is finally dumped to ambient. The evaporator is a novel design and it consists of a bottom liquid collector (i.e. it is a pool of liquid constantly feeding the evaporator channels) and a two-phase mixture collector at the top evaporator that collects the discharged two-phase flow and separates the liquid part from the vapor allowing the vapor to travel without liquid to the condenser. The system works with gravity driven circulation. Thermal performances of the system are presented and compared to the simulation results of a dedicated two-phase code developed by ABB. The total power dissipation investigated ranges between 5 and 12.5 kW. This is attained by three power modules Econopack Plus from Infineon. The condensation is provided by means of a water cooled plate heat exchanger. Results will be presented for a cooling water temperature of 38 and 50 °C. The working fluid was refrigerant R245fa.

Compact Air-to-Air Thermosyphon Heat Exchanger

Outdoor cabinets containing power electronics components need to be cooled effectively and at the same time protected from outside air, which may contain moisture and various kinds of dirt that would reduce the reliability of the electronics. Air-to-air heat exchangers are widely used in the industry as they are cost-competitive and easy to install and maintain. On the other hand, they are inefficient and bulky. ABB holds a patent on a cost-effective modular compact thermosyphon-based air-to-air heat exchanger for power electronics cabinets. This technology uses numerous multiport extruded tubes with capillary-sized channels disposed in parallel to achieve the desired compactness. The heat exchanger is made of a stack of thermosyphon units to cope with the required heat loads. The experimental performance of this novel power electronics cooling system with R134a was measured for a single unit and a stack of thermosyphons. The influence of different parameters such as the heat load, fluid filling ratio, air temperature, and flow rate were investigated. A numerical model was developed in order to predict the performance of the thermosyphon unit and stack for various and changing operating conditions. Prediction shows good agreement with the experimental results.

Modeling of a Gravity Driven Two-Phase Loop

This paper proposes an analytical based numerical model of a small channel gravity driven two-phase loop. This model is based on the solving of the mass, momentum and energy conservation equations. Suitable correlations and models are used to calculate the pressure drop, void fraction and heat transfer coefficient in the successive sections of the thermosyphon. Then residuals of these conservation equations are evaluated and minimized with a minimization algorithm. The first simulations show as expected the existence of an optimal filling around 50%, the influence of the heat load and the coolant temperature. This model will enable us to predict the heat transfer performances in a gravity driven two-phase loop with various and changing operating conditions.Copyright