This thesis describes the development and validation of a look-up table capable of predicting heat transfer to water flowing vertically upward in a circular tube in the trans-critical pressure range from 19 to 30 MPa. The table was based on an extensive and screened experimental database and its trends were smoothened to remove unrealistic scatter and physically implausible discontinuities. When compared to other prediction methods, the present look-up table approximated the experimental data closer in values and trends. Moreover, unlike existing prediction methods, the table applies not only to normal heat transfer conditions but also to conditions with heat transfer deterioration and enhancement. A separate multi-fluid look-up table for trans-critical heat transfer was also developed, which besides the existing water database incorporated new measurements in carbon dioxide; the latter were collected at the University of Ottawa supercritical flow loop under conditions of interest for the current Super-Critical Water-Cooled Reactor designs, for which few water data were available in the literature. Existing fluid-to-fluid scaling laws were tested and two additional sets of scaling laws were proposed, which are applicable not only to the supercritical pressure region, but also to the high pressure subcritical region. The multi-fluid table is applicable to water at conditions of normal and abnormal heat transfer, but its applicability to model fluids is restricted to the normal heat transfer mode.

This thesis processes design of hot water heater. It was done thermal, hydraulic and basic strength calculations in the work and from their outcomes was set up a design of heat exchanger, which was afterwards modelled and drawn. In the beginning of the work is reader introduced to heat exchanger types and characteristics and also to its thermal processes. Then the work continues with thermal design of the heat exchanger, where the most important outcome is heat transfer surface with other geometric parameters, followed by hydraulic design, where pressure loss on water side was calculated. The calculations are finished up by basic strength design, calculating thickness of shell and tube walls. The thesis is ended with evaluation of computed design and description of its basic features.

Vita. / Digitized by Kansas Correctional Industries

Call number: LD2668 .T4 1984 V46 / Master of Science

Carbon Nanotubes (CNTs) have great potentials for Field Electron Emission (FEE) and Flow Boiling Heat Transfer (FBHT) applications. However, their weak adhesion on metallic substrates limits the development of CNTs in both applications. Diamond has high thermal conductivity and develops strong bonding with CNTs. The development of a diamond interlayer between CNTs and substrates is a feasible approach to address the adhesion problems. The purpose of this research was to develop a new CNT-based materials with a diamond interlayer for FEE and FBHT applications by focusing on four objectives: (1) enhancement of diamond thin film adhesion on a Cu substrate, (2) improvement of the CNT FEE stability, (3) reduction of the CNT FEE turn-on field, and (4) investigation of the FBHT performance of CNT based structures. The CNTs and diamond thin films in this thesis were prepared by Microwave Plasma enhanced Chemical Vapor Deposition (MPCVD) and Hot Filament enhanced Chemical Vapor Deposition (HFCVD). The structure and chemical states of the diamond films and CNTs were characterized by Scanning Electron Microscopy (SEM), cross-sectional Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Raman spectroscopy, synchrotron based X-ray Absorption Spectroscopy (XAS). To deposit diamond thin films on a Cu substrate with sufficient adhesion strength, a sandblasting pretreatment and alloying with a tiny amount of Al were investigated. The adhesion of diamond thin films to substrates was evaluated by Vickers micro-hardness indentation. The FEE stability and turn-on field were measured by a Keithley 237 high voltage measuring unit. The FBHT property of the structures was tested repeatedly at different flow velocities to explore the dependence of heat transfer performance on certain parameters, including the flow patterns, Critical Heat Flux (CHF), and stability. The results show that sandblasting pretreatment increases the surface roughness and surface defect density, thereby increasing diamond nucleation density and adhesion to the Cu substrate. Al alloying appears to inhibit the formation of graphite at the interface between diamond and the Cu substrate, which improves the chemical bonding between diamond and the Cu substrate and increases the adhesion strength between them. The FEE testing results show that ultra-high FEE stability (more than 5000 minutes) was achieved for the CNTs with a diamond interlayer. This is attributed to the good contact at the diamond-CNT and diamond-substrate interfaces. The main factors that affect the CNT FEE turn-on field were also studied. By optimizing the structure, an FEE turn-on field of 5.1 V/μm was achieved and an emission barrier model for CNTs with a diamond interlayer on Cu substrate was used to explain the results. FBHT testing was done on CNTs with different structures and the results show that high heat transfer efficiency can be achieved on CNTs with a diamond interlayer at low mass fluxes.

Full-coverage or effusion cooling is commonly used in the thermal management of gas turbine combustion systems. The combustor environment is characterised by highly turbulent free-stream conditions and relatively large turbulent length scales. This turbulent flow field is predominantly created by the upstream fuel injector for lean burn systems. In rich burn systems the turbulent flow field is augmented further by the addition of dilution ports. The available evidence suggests that large energetic eddies interact strongly with the injected coolant fluid and may have a significant impact on the film-cooling performance. The desire to create compact low-emission combustion systems with improved specific fuel consumption, has given rise to a desire to reduce the quantity of air used in wall cooling, and has led to the need for improved cooling correlations and validated computational methods. In order to establish a greater understanding of effusion cooling under conditions of very high free-stream turbulence, a new laboratory test facility has been created that is capable of simulating representative combustor flow conditions, and that allows for a systematic investigation of cooling performance over a range of free-stream turbulence conditions (up to 25% intensity, integral length scale-to-coolant hole diameter ratios of 26) and coolant to mainstream density ratios (??_c/??_??? ???2). This thesis describes this new test facility, including the method for generating combustor relevant flow conditions. The hot side film cooling performance of cylindrical and fanned hole effusion has been evaluated in terms of adiabatic film-cooling effectiveness and normalised heat transfer coefficient (HTC) and heat flux reduction (HFR). Infrared thermography was employed to produce spatial resolved surface temperature distributions of the effusion surface. The analysis of this data is supported by fluid temperature field measurements. The interpretation of the data has established the impact of turbulence intensity, integral length scale and density ratio on the mixing processes between free-stream and coolant flows. Elevated levels of free-stream turbulence increase the rate of mixing and degrade the cooling effectiveness at low blowing ratios whereas at high blowing ratios, where the coolant detaches from the surface, a modest increase has been observed under certain conditions; this is due to the turbulent transport of the detached coolant fluid back towards the wall. For angled cylindrical hole injection the impact of density ratio as an independent parameter was found to be relatively weak. Adiabatic effectiveness data gathered at DR's of 1 - 1.4 scaled reasonable well when plotted against momentum flux ratio. This suggests data collected at low DR's can be scaled to engine representative DR's. The investigation of shaped cooling holes found fanned effusion has the potential to dramatically improve film effectiveness. The diffusion of the flow through a fanned exit prevented jet detachment at blowing ratios up to 5, increasing spatially averaged effectiveness by 89%.

This thesis describes the development of the computer program UT Fire, which serves as a preprocessor for the computer program SAFIR2007. SAFIR2007, developed at the University of Liege in Belgium, conducts heat transfer analysis and structural response analysis for structures subjected to fire. The preprocessor UT Fire was developed to allow a simplified graphical interface for input to the heat transfer portion of SAFIR 2007. This thesis provides step by step instructions on the use of UT Fire and illustrates its use through a series of detailed examples. / text

As the fluidic devices are miniaturized to improve portability, the friction of the microchannel becomes intrinsically high and a high pumping power will be required to drive the fluid. Since the pumping power delivered by portable devices is limited, one method to reduce this is to render the surface to become slippery. This can be achieved by roughening up the microchannel wall and form a bed of air pockets between the roughness elements, which is known as the superhydrophobic Cassie-Baxter state. While the study on superhydrophobic microchannels are focused mainly in maximizing the friction reduction effects and maintaining the stability of the air pockets, less attention has been given to characterizing the microchannel friction under a metastable state, where partial flooding of the micro-textures may be present, and under heated conditions, where the air pockets are trapped between the micro-textures. In order to quantify the frictional characteristics, microchannels with micron-sized trenches on the side walls were fabricated and tested under varying inlet pressures and heating conditions. By measuring the hydrodynamic resistance and comparing with numerical simulations, results suggest that (1) the air-water interface behaves close to a no-slip boundary condition, (2) friction becomes insensitive to the wetting degree once the micro-trenches become highly wetting, (3) the fully wetted micro-trench may be beneficial over the de-wetted ones in order to achieve friction reduction effects and (4) heating the micro-trenches to induce a highly de-wetting state may actually be detrimental to the microchannel flow due the excessive growth of the air layer. As part of the future work to characterize heat transfer in superhydrophobic microchannels, a rectangular microchannel with microheaters embedded close to the side walls was fabricated and the corresponding heat transfer rates were measured through dual fluorescence thermometry. Results suggested that significant heat is lost through the environment despite the high thermal resistance of the microchannel material. An extra insulation is suggested prior to characterizing the convective heat transfer coefficients in the superhydrophobic microchannel flow. / text

No description available.

Due to their efficient heat and mass transfer potential, impinging jets have received attention in various applications. Heat transfer and flow characteristics of rectangular turbulent impinging jets issued from a 24:1 aspect ratio and 24:1 contraction ratio nozzle were investigated experimentally and numerically. In the heat transfer measurements; a thin stainless-steel foil was utilized to obtain iso-flux boundary conditions on the impingement surface. The target plate was free to translate in the lateral direction and the heat transfer distributions were determined at 0 ≤ x/W ≤ 20 with the micro-thermocouples placed underneath the foil. The measurements were conducted for Re(j) = 8900 − 48600 at nozzle-to-target spacing of 0.5 ≤ H/W ≤ 12.0. Both semi and fully confined jets were investigated. Heat transfer coefficients at Re(j) = 28100, 36800, 45600 and H/W = 4.0 were determined by using adiabatic-wall temperatures and the distributions were compared with those of the wall shear stress. Off-center peaks were observed at high Re(j) and low H/W. Since the wall distributions are susceptible to nozzle-exit conditions, velocity and turbulence profiles at the nozzle-exit were measured for the velocity range of interest. Additionally, near-wall mean velocity and turbulence profiles were determined at Re(j) = 21500 and 36800 at H/W = 4.0 to have a better understanding of the secondary peaks in the wall distributions. Numerical computations were performed by using several different turbulence models (k − ω, k − ε, V 2F and Reynolds stress models). In wall-bounded turbulent flows, near-wall modeling is crucial. Therefore, the turbulence models eliminating wall functions such as the k − ω and V 2F models may be superior for modeling impingement flows. The numerical results showed reasonable agreement with the experimental data for local heat transfer and skin friction coefficient distributions. The occurrence of the secondary peaks was predicted by the k − ω and V 2F models, and for a few cases with the low-Re-k − ε models. Near-wall measurements along with the computed profiles were used to describe the “secondary peak” phenomena. It was shown that the increase in turbulence production in the wall-streamwise direction enhances turbulent momentum and heat transport in the wall-normal direction which lead to secondary peaks in the wall distributions. The possibility of improving surface heat transfer with fully-developed jets was also explored numerically as a case study.