Abstract
This article presents a comprehensive set of experimental and computational methods aimed at determining heat transfer regimes in superfluid helium-4, evaluating thermal resistance at various temperatures, and developing a scalable model for analyzing the performance of an ultracold neutron (UCN) converter. The results obtained constitute an essential part of the scientific foundation required for the development and optimization of modern UCN sources, which operate on the principle of neutron thermalization through inelastic interactions with the medium. This study is fundamental in nature and is oriented toward addressing strategically important problems in neutron physics, such as refining the neutron lifetime and searching for the neutron electric dipole moment. These challenges are crucial for advancing our understanding of nucleosynthesis and the formation of matter in the early Universe. The advancement of heat transfer models in cryogenic environments, particularly in superfluid helium, plays a key role in ensuring the stability and efficiency of UCN sources. The paper discusses approaches to the metrological verification of thermal parameters and provides recommendations for applying the results in future engineering and design developments.