Abstract The present investigation is performed by repeated experiments to simulate the impingement cooling heat transfer in leading-edge region of gas turbine with thermochromic liquid crystals. The experiments was studied on a rotating square duct without crossflow effect from three different rotational speeds of 0, 30 and 60 rpm. The study covered jet Reynolds number 7000 to 9000 and the rotational speeds from 0 to 60 rpm. Results are presented and focused on the effect of three different rotational speeds. Nusselt number values increased (up to 14%) with Reynolds number. However, Rotation induced coriolis and centrifuged forces and decreased the Nusselt number values about 9% which is quite coincided with those of previous studies.

This experimental study contains two points; part1 – turbine blade heat transfer under low Reynolds number flow conditions, and part 2 – trailing edge cooling and heat transfer. The effect of unsteady wake and free stream turbulence on heat transfer and pressure coefficients of a turbine blade was investigated in low Reynolds number flows. The experiments were performed on a five blade linear cascade in a low speed wind tunnel. A spoked wheel type wake generator and two different turbulence grids were employed to generate different levels of the Strouhal number and turbulence intensity, respectively. The cascade inlet Reynolds number based on blade chord length was varied from 15,700 to 105,000, and the Strouhal number was varied from 0 to 2.96 by changing the rotating wake passing frequency (rod speed) and cascade inlet velocity. A thin foil thermocouple instrumented blade was used to determine the surface heat transfer coefficient. A liquid crystal technique based on hue value detection was used to measure the heat transfer coefficient on a trailing edge film cooling model and internal model of a gas turbine blade. It was also used to determine the film effectiveness on the trailing edge. For the internal model, Reynolds numbers based on the hydraulic diameter of the exit slot and exit velocity were 5,000, 10,000, 20,000, and 30,000 and corresponding coolant – to – mainstream velocity ratios were 0.3, 0.6, 1.2, and 1.8 for the external models, respectively. The experiments were performed at two different designs and each design has several different models such as staggered / inline exit, straight / tapered entrance, and smooth / rib entrance. The compressed air was used in coolant air. A circular turbulence grid was employed to upstream in the wind tunnel and square ribs were employed in the inlet chamber to generate turbulence intensity externally and internally, respectively.

The effects on heat transfer in a two-dimensional parallel plate channel with sixteen porous baffles in a staggered arrangement with a uniform heat flux heating applied to the top and bottom walls has been numerically investigated. Developing Flow (DF) was considered for this study. The Brinkman-Forchheimer-extended Darcy model was used for modeling the heat transfer and fluid flow through the porous baffles. The flow was assumed to be laminar. A finite volume based method in conjunction with the SIMPLEC algorithm was used to solve the model equations. Calculations were made by varying several independent parameters such as Reynolds number (Re), Darcy number ⎞ (Da), thermal conductivity ratio ⎛⎜ k e kf ⎠⎟ , baffle thickness ( * ) , non-dimensional w ⎝ baffle spacing ( * ) , and non-dimensional baffle height ( * ) . w The results of the study established that porous baffles out perform solid baffles from a pressure drop point of view. However, porous baffles under perform solid baffles from a heat transfer point of view. The ratio representing increase in heat transfer per unit increase in pumping power (heat transfer performance ratio) was found to be less than unity for all cases. Increasing the Darcy number was found to produce less desirable heat transfer enhancement ratios. Increasing the non-dimensional baffle spacing (d/w) and the baffle aspect ratio (H/w) were found to enhance heat transfer.

The goal of this study is to design and analyze a sandwich composite panel with lightweight graphite foam core and carbon epoxy face sheets that can function as a radiator for the given payload in a satellite. This arrangement provides a lightweight, structurally efficient structure to dissipate the heat from the electronics box to the surroundings. Three-dimensional finite element analysis with MSC Visual Nastran is undertaken for modal, dynamic and heat transfer analysis to design a radiator panel that can sustain fundamental frequency greater than 100 Hz and dissipate 100 W/m2 and withstand launch loads of 10G. The primary focus of this research is to evaluate newly introduced graphite foam by Poco Graphite Inc. as a core in a sandwich structure that can satisfy structural and thermal design requirements. The panel is a rectangular plate with a cutout that can hold the antenna. The panel is fixed on all the sides. The objective is not only to select an optimum design configuration for the face sheets and core but also to explore the potential of the Poco foam core in its heat transfer capacity. Furthermore the effects of various parameters such as face sheet lay-up, orientation, thickness and material properties are studied through analytical models to validate the predictions of finite element analysis. The optimum dimensions of the sandwich panel are determined and structural and thermal response of the Poco foam is compared with existing aluminum honeycomb core.

Shape Memory Alloys (SMA) are a group of metallic alloys that have the ability to return to some previously defined shape or size when subjected to an appropriate thermal cycling procedure. In recent years there has been a lot of research on the development of small, light and, yet, powerful actuators for use in areas like robotics, prosthetics, biomimetics, shape control and grippers. Many of the miniaturized conventional actuators do not have sufficient power output to be useful and SMAs can be used advantageously here. The widespread use of SMAs in actuators is limited by their low bandwidth. Use of SMAs in two-way actuators requires that they undergo thermal cycling (heating and cooling). While SMAs can be heated quickly by resistive heating, conventional convection cooling mechanisms are much slower as the exothermic austenitic to martensitic phase transformation is accompanied by the release of significant amount of latent heat. While a number of cooling mechanisms have been studied in SMA actuator literature, most of the cooling mechanisms involve unidirectional forced convection. This may not be the most effective method. Oscillating flow in a channel can sometimes enhance heat transfer over a unidirectional flow. One possible explanation for this heat transfer enhancement is that the oscillatory flow creates a very thin Stokes viscous boundary-layer and hence a large time-dependent transverse temperature gradient at the heated wall. Therefore heat transfer takes place at a large temperature difference, thereby enhancing the heat transfer. In this work, the heat transfer from an SMA actuator under an oscillating channel is investigated and is compared to steady, unidirectional flow heat transfer. Oscillating flow is simulated using a finite volume based method. The resulting velocity field is made use of in solving the heat transfer problem using a finite difference scheme. A parametric study is undertaken to identify the optimal flow conditions required to produce the maximum output for a given geometry of the SMA actuator. The latent heat of transformation of the SMA is accounted for by means of a temperature dependent specific heat.

Mass transfer experiments were conducted to study the thermal performance characteristics of blockages with round and elongated holes, positioned in a 12:1 rectangular channel. Naphthalene sublimation technique was adopted to conduct experiments with four different blockage configurations, flow rates corresponding to Reynolds numbers (based on channel hydraulic diameter) of 7,000 and 17,000, and at three blockage locations. The hole area to channel area ratio for all four blockage configurations was the same at 0.196. The hole width was half the channel height, and the distance between consecutive blockages was twice the channel height. Average heat transfer, local heat (mass) transfer and overall pressure drop results were obtained. The thermal performance for a particular blockage configuration was measured in terms of the heat transfer enhancement and the friction factor ratio. Heat transfer enhancement was measured as a ratio of average Nusselt number on the blockage surface to the Nusselt number for a thermally fully developed turbulent flow in a smooth channel. Results indicate that this ratio ranged between 3.6 and 12.4, while the friction factor ratio varied between 500-1700. The blockage configuration with round holes was found to yield best thermal performance, while the configuration with largest hole elongation was nearly equal in thermal performance. In order to compare different blockage configurations, an average value of upstream and downstream side thermal performances was used. A general downward trend in Nusselt number ratio with elongation of holes was observed on the upstream side and a reverse trend was observed on the downstream side. An upward trend in the Nusselt number ratio with blockage hole elongation on the downstream side of a blockage was primarily due to jet reversal from the downstream blockage and its impingement on the downstream surface of the upstream blockage. Local experiments were performed to compare against the results from average experiments and also to gain insights into the flow behaviour. There was good agreement between the results from local and average mass transfer experiments. The average variation in Nusselt number ratio between local and average mass transfer experiments was about 5.06%.

Research is performed to assess the viability of applying the least squares model to one-dimensional heat transfer and Euler-Bernoulli Beam Theory problems. Least squares models were developed for both the full and mixed forms of the governing one-dimensional heat transfer equation along weak form Galerkin models. Both least squares and weak form Galerkin models were developed for the first order and second order versions of the Euler-Bernoulli beams. Several numerical examples were presented for the heat transfer and Euler- Bernoulli beam theory. The examples for heat transfer included: a differential equation having the same form as the governing equation, heat transfer in a fin, heat transfer in a bar and axisymmetric heat transfer in a long cylinder. These problems were solved using both least squares models, and the full form weak form Galerkin model. With all four examples the weak form Galerkin model and the full form least squares model produced accurate results for the primary variables. To obtain accurate results with the mixed form least squares model it is necessary to use at least a quadratic polynominal. The least squares models with the appropriate approximation functions yielde more accurate results for the secondary variables than the weak form Galerkin. The examples presented for the beam problem include: a cantilever beam with linearly varying distributed load along the beam and a point load at the end, a simply supported beam with a point load in the middle, and a beam fixed on both ends with a distributed load varying cubically. The first two examples were solved using the least squares model based on the second order equation and a weak form Galerkin model based on the full form of the equation. The third problem was solved with the least squares model based on the second order equation. Both the least squares model and the Galerkin model calculated accurate results for the primary variables, while the least squares model was more accurate on the secondary variables. In general, the least-squares finite element models yield more acurate results for gradients of the solution than the traditional weak form Galkerkin finite element models. Extension of the present assessment to multi-dimensional problems and nonlinear provelms is awaiting attention.

This paper starts from the single tube condensation theory of shell side inferred by Nusselt , and then analyzes the coefficient of heat transfer of the shell side and the overall heat transfer coefficient of the tube bundle. Referring to the overall heat coefficient of surface condensers and the calculation means of pressure decrease, the HEI, the most exploited one in the commerce is used by combining the basic theory of condenser heat transfer based on the Delphi function language to develop a set of assistant designing software. The software can be used to evaluate the performance of condensers, calculate the sizes of tube materials, and predict the pressure of condensers when the different tube materials are used. When the units are in using, this software also can calculate the cleanliness factor and determine the suitable time to clean the condenser tubes. There are four common used tube materials to compare their performance. They are Al- Brass tubes, 70-30 Cu-Ni tubes, Sea-Cure tubes and Ti tubes. This paper use the software to analyze the performance of the heat transfer of these four different kinds of tube materials and also to calculate the sizes of tubes .And use research papers to analyze the reason of anti-corrosion of these four. In addition, the HEI method can analyze the anti-vibration ability of these four. After comparing with all the performance of the tube materials, and then choosing the best tube material to provide an example for condenser design of new electricity plants or for old electricity plants to change the tube materials.

The Purpose of this thesis is to experimentally demonstrate an inversion analysis technique, developed by Dr. Jay Frankel (UTK), that utilizes transient temperature data from probes embedded at known locations in a material. This allows one to determine thermal properties (thermal diffusivity and thermal conductivity) of the material, surface temperature, and the surface heat flux as they change with time. Dr. Frankel’s inversion method can be used to determine surface temperature and heat flux of a one-dimensional semi-infinite slab based on the transient data from one or two embedded probes, if the thermal conductivity and thermal diffusivity of the material are known. Frankel’s theory suggests that the thermal properties of the material can be determined if transient data from two thermocouple (TC) probes at known locations and the heat flux at the surface are known. This thesis investigates finding the thermal properties and surface temperature of materials using a two embedded thermocouple approach. As an initial check to the inversion analysis, the theoretical temperature solution for a one-dimensional semi-infinite slab was used. This validated that the analysis could converge to the constant thermal properties for the theoretical material. An experiment was run again to provide data for the materials copper and aluminum. Using a real material is fundamentally different from using theoretical determined (analytical) data, because the thermal properties for a real material vary with temperature. Since the inversion analysis converged to a constant solution for the theoretical temperatures, it was believed that the real material will converge to a solution. However, it was seen that the thermal diffusivity for the real materials never converged to the expected value. Although, when a constant handbook value for the thermal diffusivity is used to calculate the thermal conductivities from the experimental temperature data collected from the internal probes, the inversion analysis resulted in good agreement with experiment.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2002. / Includes bibliographical references (leaves 145-150). Also available in electronic version. Access restricted to campus users.