Modeling and experimental study of heat transfer optimization in fractal microchannels for multilayer insulation

• The optimization heat transfer model is established based on fractal theory. • The heat transfer mechanism of interlayer microchannels in MLI is revealed. • The optimization heat transfer model is superior to the LBL model. • The influence of key factors on the insulation performance of MLI is probed. To investigate the heat transfer mechanisms in multilayer insulation, the fractal function is employed to characterize the surface topography of the multilayer insulation material. A physical model of interlayer fractal microchannels which incorporates contact regions and cavities is developed. Based on the model, the coupled relationships between gas conduction, radiation heat transfer and solid contact conduction within fractal microchannel are derived, thereby establishing an optimization heat transfer calculation model. Compared with the experimental results, the error of heat flux calculated with the optimization heat transfer model is 3.38 %, which is superior to the layer-by-layer (LBL) model. Furthermore, the temperature distribution curve obtained from the model is consistent with both experimental results and LBL model analysis. The heat flux gradually decreases as the layer count increases. The dependence of heat flux on hot and cold boundary temperatures exhibits significant nonlinear differences, in the high-temperature region, heat flux increases sharply with the fourth power of temperature, governed by radiation, whereas in the low-temperature region, it changes only slightly with its linear dependence, dominated by conduction. The heat flux follows a "U-shaped" distribution with microchannel size, with an optimal size that minimizes heat flux. As the vacuum level decreases, Gas conduction intensifies and progressively emerges as the dominant factor. Compared with the LBL model, the optimization heat transfer model maintains high accuracy across the entire vacuum level range, providing a reliable theoretical foundation and simulation tool for the design and optimization of insulation structures.