In recent years there has been an increasing interest in the development of high-altitude station-keeping vehicles operating in near-space environments. This new interest in near-space vehicles has resulted from a realization that such vehicles could provide unique platforms for many scientific and commercial applications. Operating in a near-space environment, however, presents substantial engineering challenges with respect to energy storage/consumption and thermal management issues.
This dissertation focuses on the fundamental issues of near-space heat transfer, thermal modeling, and thermal management of a station-keeping near-space vehicle. Near-space altitudes require that thermal modeling include multiple heat transfer mechanisms, including forced and natural convection, thermal radiation, and shell conduction.
A steady-state thermal network was first developed to analyze the relative importance of the multimode heat transfer mechanisms at near-space altitudes. The quantitative contributions of each heat transfer mode are presented in a group of dimensionless variables for an idealized near-space vehicle. A transient network model was developed to predict the temperature response within a balloonsat enclosure during its ascent into near-space altitudes. The results have been compared to the actual temperature response obtained from a near-space flight test. It has been shown that the developed transient model is able to capture the trend of the thermal response within the payload as well as the temperature extremes experienced during the flight.
The conventional no-slip condition is shown to be invalid from the middle region of near-space altitudes and above with a Knudsen number greater than 0.01. Modeling of convection heat transfer in such a rarefied environment needs to take into account the momentum and thermal interfacial discontinuity as a result of the increasing mean free path. Boundary-layer models have been developed for laminar natural convection and mixed convection from a vertical isothermal plate with first-order velocity slip and temperature jump. The boundary-layer equations are solved numerically through nonsimilarity methods. The results have revealed nonsimilar flow features within the boundary layer. The results of slip velocity, wall shear stress, and heat transfer as a function of the noncontinuum variable are also presented in this study.
|School:||The University of Alabama|
|School Location:||United States -- Alabama|
|Source:||DAI-B 70/08, Dissertation Abstracts International|
|Subjects:||Aerospace engineering, Mechanical engineering|
|Keywords:||Heat transfer, Mixed convection, Natural convection, Near-space altitudes, Space vehicles, Thermal networks|
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