Date of Award


Degree Name

Doctor of Philosophy


Mechanical Engineering


Md. Mahamudur M. Rahman


Nowadays, one of the most talked-about subjects in space exploration is cryogenic heat pipes. These heat pipes are made in a way that allows them to operate without the need for additional power or energy. Evaporated vapor and condensed liquid can be moved by buoyancy forces or capillary forces that are subject to gravity because of the phase shifts of the working fluids moving inside. The cooling solution typically entails a phase transition from liquid to vapor, which can dissipate larger heat fluxes because of the fluid's high latent heat of vaporization. Recent developments in additive manufacturing and micro-nano structures open new possibilities and future directions for deep space applications and spacecraft cooling. These advanced micro-structured surfaces are highly capable of carrying fluids freely onto the structure, as the main conveyance method is capillary pressure, which is generated within the wick structure of the heat pipe. Also, these micro-structured cryogenic heat pipes can be a potential solution to actively deposit sublimated water vapor on a cold plate during thermal mining of icy regolith mixtures. Therefore, the design and development of an efficient cryogenic heat pipe is required. Under the National Aeronautics and Space Administration (NASA), the UTEP Aerospace Center team is developing an advanced thermal mining technology that integrates vapor extraction from lunar icy regolith, transportation of vapor through ionization and electrostatic field, and recapture of sublimated vapor on an engineered cold plate that consists of an additively manufactured cryogenic heat pipe to absorb vapor deposition heat flux and an intermittent ice delamination thin film heater [1].Heat pipes can be classified in several ways, considering operating temperature ranges, such as cryogenic, ambient, or liquid metal, by wicking structure: arterial or composite, or by function: micro-heat pipes, variable conductance heat pipes, or thermal diodes. In most cases, they consist of three sections, i.e., evaporator, adiabatic, and condenser. Heat pipes can be manufactured and fabricated in various ways in this modern era. In this study, additively manufactured cryogenic heat pipe is chosen, as substrate material, surface roughness associated with various fabrication methods plays a significant role in the heat transfer and recent studies indicate that additively manufactured samples give better results as the surfaces contain more porosity and roughness which leads to better heat transfer. To verify and justify this myth, both additively manufactured and conventional CNC machined micro-structured different material samples were manufactured, and thin film evaporation and condensation testing were executed. For cryogenic fluid, Liquid Nitrogen was selected because of its availability and cost-effectiveness. Also, the characterization of the micro-pillar dimension and so, the effect of spacing, and the effect of height of the micro-pillar structure were studied. Four different materials Ti-64, Stainless Steel 304, Aluminum 6061, and Copper 101 were selected for both manufacturing processes. Depending on the additive manufacturing design restrictions, the width of the micro-pillar sample was fixed at 400 µm. The micro-pillar wall-to-wall spacing was varied from 400 µm, 500 µm, and 600 µm. In both thin film evaporation and condensation testing, it is seen that the additively manufactured samples were showing 10-20% increased heat flux values in both evaporation and condensation test. Besides, an optimum micro-pillar spacing of 500 µm was achieved for a fixed 600 µm height samples for both of segment. The study also found that increasing micro-pillar heights increases the heat flux values exclusively. The micro-pillar height was varied between 600 µm, and 800 µm. With the increased height of the micro-pillar samples, up to ~104% CHF increased value was achieved in the thin film evaporation testing of LN2 on micro-pillars having wall-to-wall spacing of 600 µm. ~20% increased CHF values were achieved on the condensation experiments as the micro-pillar height was increased from 600 µm to 800 µm, where the micro-pillars wall-to-wall spacing was 500 µm. In both cases, an optimum height for the existing design still needed to be examined. The effect of different materials was observed and a correlation between the thermal diffusivity of the material and the heat flux values was explained for the micro-structured cryogenic heat pipe. This study concluded that comparatively lower thermal conductive materials give better heat transfer rate in the field of engineered capillary driven heat pipes. In both thin film evaporation and condensation experiments, it is seen that the trend is quite the same. Among the four different materials, Ti-64SS-304>Al-6061>Cu-101. Depending on the findings of the thin film evaporation and film condensation testing, a complete cryogenic heat pipe model was established by considering both analytical and theoretical analysis. After completing the prototype design, the cryogenic heat pipe was manufactured, and using the prototype heat pipe, preliminary ice collection testing was successfully executed




Recieved from ProQuest

File Size

154 p.

File Format


Rights Holder

Mahadi Hasan

Available for download on Friday, December 19, 2025