FLOW BOILING IN MINICHANNELS UNDER NORMAL, HYPER AND MICROGRAVITY: LOCAL HEAT TRANSFER ANALYSIS USING INVERSE METHODS

摘要

The objective presented in this paper is here to provide basic knowledge on the systems of biphasic cooling in mini and microchannels during hyper and microgravity. The experimental activities are performed in the frame of the MAP Boiling project founded by ESA. The main aspect of this paper is to present the use of inverse methods to estimate local flow boiling heat transfers coefficient in minichannels. To observe the influence of gravity level on the fluid flow and to take data measurements, an experimental setup is designed with two identical channels; one for the visualization and the other one for the acquisition of data. These two devices enable us to study the influence of gravity on the temperatures and pressures measurements. The two minichannels are modeled as a rectangular rod made up of three materials; a layer of polycarbonate (λ=0.2 W·m{sup}(-1)·K{sup}(-1)) used as insulator, a cement rod (λ=0.83 W·m{sup}(-1)·K{sup}(-1)) instrumented with 21 K-type thermocouples and in the middle a layer of inconel (λ=10.8 W·m{sup}(-1)·K{sup}(-1)) in which the minichannel is engraved. Pressures and temperatures measurements are carried out simultaneously at various levels of the minichannel. Above the channel, we have a set of temperatures and pressures gauges and inside the cement rod, 5 heating wires providing a power of 11 W. The K-type thermocouples sensors enable us to acquire the temperature in various locations (x, y and z) of the device. With these temperatures and the knowledge of the boundary conditions, we are able to solve the problem using inverse methods and to obtain local heat flux and local surface temperatures on several locations. All the results on hydrodynamics and pressure drop will be provided in a second paper in the same congress.