During the development of flight tests of a spacecraft, heat exchange occurs among the many physically separated subsystem surfaces through the phenomenon of thermal radiation. Considering the increasing complexity of the geometrical forms and shapes in the design of such systems, the monitoring and control of the radiative heat fluxes taking place in the multi-reflecting, absorbing and emitting heat transfer environment are very critical. Because the analytical solution of thermal radiation in such geometrically complex three-dimensional systems is not practical, extensive numerical modelling techniques are widely used to predict radiative heat fluxes on the many thermally active surfaces. From experience, it is found that this can be very difficult and not at all commensurate with fast feedback unless the analysis is from a simple system layout. Considering that a relatively new approach dedicated to the basic analysis of radiative heat flux has been developed by the heat transfer community as a numerical approximation called the Discrete Ordinates Method (DOM), a first question did arise in terms of how well an enhanced and more comprehensive formulation based on this concept would fulfil the task of achieving faster results whilst still accurately predicting radiative heat transfer in three-dimensional, more complex geometries.

<p> The results of an investigation of the micro-climate of a sweet corn canopy is reported at two stages in its development. The purpose of the experiment was to study the height dependence and diurnal variations of the net radiation, sensible and latent heat fluxes, and the turbulent transfer mechanism. Only daytime data were used.</p> <p> The depletion of net radiation in the canopy was studied within the framework of the exponential model. A new model for estimating net radiation in the canopy is developed. The pattern of the sources and sinks and the apparent turbulent transfer coefficient for sensible and latent heat in the canopy space are reported.</p> / Thesis / Doctor of Philosophy (PhD)

This study presents the numerical analysis of steady laminar flow heat transfer in a horizontal rectangular duct with differential heating on the vertical walls. Three heating configurations: one uniform wall temperature (CS1) and two linearly varying wall temperature cases (CS2 and CS3) are analysed. The study considers the combined effects of natural convection, forced convection and radiation heat transfer on the overall heat transfer characteristics. Air, which is assumed to be a non-participating medium, is chosen as the working fluid. A computational fluid dynamics solver is used to solve a set of governing equations for a range of parameters.For chosen duct aspect ratios, the numerical model simulates the flow and heat transfer for two main effects: buoyancy and radiation heat transfer. Buoyancy effect is represented by Grashof number, which is varied from 2,000 to 1,000,000. The effect of radiation heat transfer is examined by choosing different wall surface emissivity values. The weak and strong radiation effect is represented by the emissivity values of 0.05 and 0.85 respectively. Three duct aspect ratios are considered - 0.5, 1 and 2. The heat transfer characteristics of all the above heating configurations - CS1, CS2, and CS3 are analysed and compared. The numerical results show that, for all heating configurations and duct aspect ratios, the overall heat transfer rate is enhanced when the buoyancy effect increases. Since buoyancy effect induces natural circulation, this circulation is therefore the main mechanism that enhances heat transfer. Radiation heat transfer is found to significantly influence convection heat transfer in high Grashof numbers.

An experimental activity was performed to observe and study the effects of graphite dispersion and deposition on thermal hydraulic phenomena in a Reactor Cavity Cooling System (RCCS). The small scale RCCS experimental facility (16.5cm x 16.5cm x 30.4cm) used for this activity represents half of the reactor cavity with an electrically heated vessel. Water flowing through five vertical pipes removes the heat produced in the vessel and releases it in the environment by mixing with cold water in a large tank. PIV technique was used to study the velocity field of the air inside the cavity. A set of 52 thermocouples was installed in the facility to monitor the temperature profiles of the vessel and pipes walls and air. 10g of a fine graphite powder (particle size average 2 [mu]m) were injected into the cavity through a spraying nozzle placed at the bottom of the vessel. Temperatures and air velocity field were recorded and compared with the measurements obtained before the graphite dispersion, showing a decrease of the temperature surfaces which was related to an increase in their emissivity. The results contribute to the understanding of the RCCS capability in case of an accident scenario.

In order to maximize the e ciency of power generation in concentrated solar power systems (CSP) it is de- sired to achieve as high a tempera- ture in the receiver as possible due to the use of the Sterling cycle to gen- erate power. This report investigates three di↵erent geometries for cavity receivers in CSP systems; cylindrical, conical and truncated conical. The goal has been to minimize the heat loss due to radiation. This was achieved through mathematical mod- eling with the help of MATLAB. Five di↵erent cases with regards to oper- ating temperature and proportions of the receiver where investigated for each of the three chosen geometries. It was found that the conical geometry minimized this heat loss in all except one case.

Heat insulation is the process of blocking the transfer of thermal energy between objects at different temperatures. Heat transfer occurs due to conduction, convection, or radiation, as well as any combination of these three mechanisms. Fibrous insulations can completely suppress the convective mode of heat transfer for most applications, and also help to reduce the conductive and radiative modes to some extent. In this study, an attempt has been made to computationally predict the effects of microstructural parameters (e.g., fiber diameter, fiber orientation and porosity) on the insulation performance of fibrous materials. The flexible simulation method developed in this work can potentially be used to custom-design optimal multi-component fibrous insulation media for different applications. With regards to modeling conductive heat transfer, a computationally-feasible simulation method is developed that allows one to predict the effects of each microstructural parameter on the transfer of heat across a fibrous insulation. This was achieved by combining analytical calculations for conduction through interstitial fluid (e.g., air) with numerical simulations for conduction through fibrous structures. With regards to modeling radiative heat transfer, both Monte Carlo Ray Tracing and Electromagnetic Wave Theory were implemented for our simulations. The modeling methods developed in this work are flexible to allow simulating the performance of media made up of different combinations of fibers with different materials or dimensions at different operating temperatures. For example, our simulations demonstrate that fiber diameter plays an important role in blocking radiation heat transfer. In particular, it was shown that there exists an optimum fiber diameter for which maximum insulation against radiative transfer is achieved. The optimum fiber diameter is different for fibers made of different materials and also depends on the mean temperature of the media. The contributions of conduction and radiation heat transfer predicted using the above techniques are combined to define a total thermal resistance value for media with different microstructures. Such a capability can be of great interest for design and optimization of the overall performance of fibrous media for different applications.

In the electronics the quality, reliability, operational speed, device density and cost of circuits are fundamentally determined by carriers. If it is necessary to use better material than plastic carrier, it has to be made of ceramics or glass-ceramics. This study dealt with the ceramic based carrier production system. The types of the raw ceramics fired at low temperature (below 1000&deg / C) are called Low Temperature Co-Fired Ceramics (LTCC). In this study, a comprehensive thermal model is described for the high temperature oven which belongs to a Low Temperature Co-fired Ceramic (LTCC) substance production line. The model includes detailed energy balances with conduction, convection and radiation heat transfer mechanisms, view factor derivations for the radiative terms, thermocouple balances, heating filaments and cooling mechanisms for the system. Research was conducted mainly on process development and production conditions along with the system modeling of oven. Temperature control was made in high temperature co-firing oven. Radiation View Factors for substrate and thermocouples are determined. View factors between substrate and top-bottom-sides of the oven are calculated, and then inserted into the energy balances. The same arrangement was made for 3 thermocouples at the bottom of the oven. Combination of both expressions gave the final model. Modeling studies were held with energy balance simulations on MATLAB. Data analysis and DOE study were held with JMP Software.

A negative index material (NIM), which possesses simultaneously negative permittivity and permeability, is an emerging material that has caught many researchers attention after it was first demonstrated in 2001. It has been shown that electromagnetic waves propagating in NIMs have some remarkable properties such as negative phase velocities and negative refraction and hold enormous promise for applications in imaging and optical communications. This dissertation is centered on investigating the unique aspects of the radiative properties of NIMs. Photon tunneling, which relies on evanescent waves to transfer radiative energy, has important applications in thin-film structures, microscale thermophotovoltaic devices, and scanning thermal microscopes. With multilayer thin-film structures, photon tunneling is shown to be greatly enhanced using NIM layers. The enhancement is attributed to the excitation of surface or bulk polaritons, and depends on the thicknesses of the NIM layers according to the phase matching condition. A new coherent thermal emission source is proposed by pairing a negative permittivity (but positive permeability) layer with a negative permeability (but positive permittivity) layer. The merits of such a coherent thermal emission source are that coherent thermal emission occurs for both s- and p-polarizations, without use of grating structures. Zero power reflectance from an NIM for both polarizations indicates the existence of the Brewster angles for both polarizations under certain conditions. The criteria for the Brewster angle are determined analytically and presented in a regime map. The findings on the unique radiative properties of NIMs may help develop advanced energy conversion devices. Motivated by the recent advancement in scanning probe microscopy, the last part of this dissertation focuses on prediction of the radiation heat transfer between two closely spaced semi-infinite media. The objective is to investigate the dopant concentration of silicon on the near-field radiation heat transfer. It is found that the radiative energy flux can be significantly augmented by using heavily doped silicon for the two media separated at nanometric distances. Large enhancement of radiation heat transfer at the nanoscale may have an impact on the development of near-field thermal probing and nanomanufacturing techniques.

The development and advancement of microelectronics technology have been dramatically. The time and cost, for research and optimization of process and equipment, can be saved by using flow simulation. The governing equations of flow field, inside chemical vapor deposition (CVD) reactor, are constructed, dispersed, and solved by grid mesh and numerical method. At present, rapid thermal process (RTP) is becoming more important and popular for thin-film depositing technology. In this thesis, vertical type single wafer RTCVD reactor in poly-silicon thin-film depositing process is analyzed by numerical method. Several operating process parameters, such as: (a) the gap between shower head and wafer surface, (b) gas inlet velocity in shower head, and (c) operating pressure inside chamber of reactor, are considered for discussion and analysis of steady or unsteady phenomenon in three steps of thin-film depositing process, including (¢¹) heating for wafer, (¢º) deposition in steady state, (¢») cooling after deposition etc.. As shown in the results, each operating parameters performs different relations and phenomenon in these steady and unsteady steps: Operating pressure can affect the activity of chemical reaction strongly in unsteady or steady region. Larger gap between wafer and shower head causes less influence by flow effects or buoyancy. And also, radiation heat transfer, which is adopted by RTCVD process, can decrease the influence of some parameters on flow field.

Thesis (M.S.)--University of Wisconsin--Madison, 1962. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 12).