Terry J. Hendricks

Surface Structure Enhanced Microchannel Flow Boiling

We investigated the role of surface microstructures in two-phase microchannels on suppressing flow instabilities and enhancing heat transfer. We designed and fabricated microchannels with well-defined silicon micropillar arrays on the bottom heated microchannel wall to promote capillary flow for thin film evaporation while facilitating nucleation only from the sidewalls. Our experimental results show significantly reduced temperature and pressure drop fluctuation especially at high heat fluxes. A critical heat flux (CHF) of 969 W/cm2 was achieved with a structured surface, a 57% enhancement compared to a smooth surface. We explain the experimental trends for the CHF enhancement with a liquid wicking model. The results suggest that capillary flow can be maximized to enhance heat transfer via optimizing the microstructure geometry for the development of high performance two-phase microchannel heat sinks.

Cost Scaling of a Real-World Exhaust Waste Heat Recovery Thermoelectric Generator: A Deeper Dive

Cost is equally important to power density or efficiency for the adoption of waste heat recovery thermoelectric generators (TEG) in many transportation and industrial energy recovery applications. In many cases, the system design that minimizes cost (e.g., the

TEMPERATURE-STAGED THERMAL ENERGY STORAGE ENABLING LOW THERMAL EXERGY LOSS REFLUX BOILING IN FULL SPECTRUM SOLAR ENERGY SYSTEMS

/W value) can be very different than the design that maximizes the system’s efficiency or power density, and it is important to understand the relationship between those designs to optimize TEG performance-cost compromises. Expanding on recent cost analysis work and using more detailed system modeling, an enhanced cost scaling analysis of a waste heat recovery TEG with more detailed, coupled treatment of the heat exchangers has been performed. In this analysis, the effect of the heat lost to the environment and updated relationships between the hot-side and cold-side conductances that maximize power output are considered. This coupled thermal and thermoelectric (TE) treatment of the exhaust waste heat recovery TEG yields modified cost scaling and design optimization equations, which are now strongly dependent on the heat leakage fraction, exhaust mass flow rate, and heat exchanger effectiveness. This work shows that heat exchanger costs most often dominate the overall TE system costs, that it is extremely difficult to escape this regime, and in order to achieve TE system costs of

Full spectrum hybrid photovoltaics and thermal engine utilizing high concentration solar energy

1/W it is necessary to achieve heat exchanger costs of

Development of Multi-Physics Dynamics Models for High-Frequency Large-Amplitude Structural Response Simulation

1/(W/K). Minimum TE system costs per watt generally coincide with maximum power points, but preferred TE design regimes are identified where there is little cost penalty for moving into regions of higher efficiency and slightly lower power outputs. These regimes are closely tied to previously identified low cost design regimes. This work shows that the optimum fill factor Fopt minimizing system costs decreases as heat losses increase, and increases as exhaust mass flow rate and heat exchanger effectiveness increase. These findings have profound implications on the design and operation of various TE waste heat recovery systems. This work highlights the importance of heat exchanger costs on the overall TEG system costs, quantifies the possible TEG performance-cost domain space based on heat exchanger effects, and provides a focus for future system research and development efforts.

Thermoelectric heat recovery from glass melt processes

The efficiency of solar power collection is increased by adding a thermal energy storage stage to a sunlight concentrator and thermodynamic power generator system. The thermal energy storage includes tubes or capsules made of a phase change material that stores thermal energy in different temperature stages through a working fluid. The stored thermal energy is directed to the thermodynamic generator during off-sun periods.

Next-generation radioisotope thermoelectric generator study

We describe a Hybrid full spectrum solar system (FSSS) that utilizes the full spectrum available from the sun. It is designed to convert the full solar spectrum into useful electrical energy by using both photovoltaics energy conversion and thermal energy conversion combined with thermal energy storage (TES) in order to operate around-the-clock even when solar energy is not available. It is composed of a parabolic dish concentrator and a hybrid high temperature photovoltaics and thermal engine. The target efficiency of the overall system is over 35% with the AM1.5D solar spectrum as a power input.

Heat Exchanger Performance Impacts on Optimum Cost Conditions in Thermoelectric Energy Recovery Designs

An analytic approach is demonstrated to reveal potential pyroshock-driven dynamic effects causing temporary power losses in the Thermo-Electric (TE) module bars of the Mars Science Laboratory (MSL) Multi-Mission Radioisotope Thermoelectric Generator (MMRTG). This study utilizes high-fidelity finite element analysis with SIERRA/PRESTO codes to estimate wave propagation effects due to large-amplitude suddenly-applied pyroshock loads in the MMRTG. A high fidelity model of the TE module bar was created with ∼30 million degrees-of-freedom (DOF). First, a quasi-static preload was applied on top of the TE module bar, then transient tri-axial displacement inputs were simultaneously applied on the preloaded module. The applied displacement inputs were derived from measured acceleration signals during MMRTG shock qualification tests performed at the Jet Propulsion Laboratory. An explicit finite element solver in the SIERRA/PRESTO computational environment, along with a 3000 processor parallel super-computing framework at NASA-AMES, was used for the simulation. The simulation results were investigated both qualitatively and quantitatively. The predicted shock wave propagation results provide detailed structural responses throughout the TE module bar, and key insights into the dynamic response (i.e., loads, displacements, accelerations) of critical internal spring/piston compression systems, TE materials, and internal component interfaces in the MMRTG TE module bar. They also provide confidence on the viability of this high-fidelity modeling scheme to accurately predict shock wave propagation patterns within complex structures. This analytic approach is envisioned for modeling shock sensitive hardware susceptible to intense shock environments positioned near shock separation devices in modern space vehicles and systems.