Conceptual Design of a Test Bench for the Measurement of Heat Transfer in Metal Foams

Kurzfassung

Metal foams have excellent thermal and structural properties, making them particularly suitable for heat dissipation applications in various industries. One of these industries is the mobility sector. In this case, the project to which the metal foam will be applied is an Eddy Current Brake (ECB). The goal is to increase the working range of the ECB by replacing one of its components with aluminum foam. This replacement is intended to extend the time required for the ECB to reach the melting point of its materials.

To do so, a conceptual design of a test bench was developed with the purpose of measuring the heat transfer characteristics of metal foams and determining whether this replacement would be successful. The new test bench is intended to imitate the behavior of the ECB. Therefore, water will flow through an electrically heated metal foam and leave the test section completely evaporated.

Some of the boundary conditions that need to be considered include voltage limits ranging from 5 to 1000 V and electrical current limits ranging from 0 to 600 A. A previously existing test bench designed for a different material was considered as a reference. Based on this design, it was hypothesized that the new cross-sectional area should be similar to the existing one of 50 mm².

The main aspects to be simulated, analyzed, and subsequently measured were the heat transfer coefficient, pressure drop, and electrical resistance of the foam. Theoretical models and correlations for these parameters were found in the literature and adapted to the desired scenario. Once the necessary modifications were made, the corresponding equations were coded in MATLAB in order to obtain the simulated values, plot the results, and determine the parameters for the test bench design.

The selected parameters were a foam density of 40 PPI, dimensions of 7 mm × 7 mm × 500 mm, a fluid inlet velocity of 0.05 m/s, and a fluid inlet temperature of 10 °C. Other parameters, such as total heat transfer, heat transfer coefficient, percentage of flow evaporation, and maximum power, were also simulated.

After these calculations, the hypothesis was confirmed. In order to comply with all boundary conditions and limitations, the required cross-sectional area was determined to be 49 mm².

Once these variables had been determined, the CAD design of the test bench was created in CATIA. The design consists of four main areas through which the fluid will flow, as well as several sensors for measuring fluid temperature, fluid pressure, and the voltage across the foam, which will be used to determine its electrical resistance.

The proper sealing of all surfaces was also considered, as well as the selection of materials capable of withstanding the demanding conditions to which the test bench will be exposed.