A heat pipe is an efficient phase change device which enables to dissipate heat from a required source with a minimal temperature drop. Common applications which utilize its performance are electronic cooling, heat recovery systems, waste management, vehicle thermal management and more. There are no unique dimensions for a heat pipe. Each case demands its own solution according to physical limitations. A heat pipe`s performance is dependent on the working fluid and physical structure compatability as well as its shape. The heat capacity limitations are capillary limit, viscous limit, sonic limit, boiling limit and entrainment limit. Those are mostly affected by the vapor space diameter and the working fluid properties. The authors have performed a theoretical optimization of a negative inclination copper-water heat pipe with an internal composite wick structure, which consists of two different mesh wicks. This structure enables to overcome the gravitational force up to a certain level and prevent the heat pipe`s dry out. The optimization introduced a new ratio (LR) between coarse mesh wraps and fine mesh wraps of the wick structure. In this case it has been found that the heat capacity of the heat pipe is limited by the capillary, boiling and entrainment limits. Thus it can be concluded that these limits are dependent on the new introduced ratio. Performance verification tests are in progress in order to confirm the theoretical optimization.
