<p>In modern gas turbines parts of combustion chamber and turbine section are under heavy heat load, for example, the rotor inlet temperature is far higher than the melting point of the rotor blade material. These high temperatures causes thermal stresses in the material, therefore it is very important to cool the components for safe operation and to achieve desired component life. But on the other hand the cooling reduces the turbine efficiency, for that reason it is vital to understand and optimize the cooling technique.</p><p>In this project Thermochromic Liquid Crystals (TLCs) are used to measure distribution of heat transfer coefficient over a scaled up combustor liner section. TLCs change their color with the variation of temperature in a particular temperature range. The color-temperature change relation of a TLC is sharp and precise; therefore TLCs are used to measure surface temperature by painting the TLC over a test surface. This method is called Liquid Crystal Thermography (LCT). LCT is getting popular in industry due to its high-resolution results, repeatability and ease of use.</p><p>Test model in present study consists of two plates, target plate and impingement plate. Cooling of the target plate is achieved by impingement of air coming through holes in the impingement plate. The downstream surface of the impingement plate is then cooled by cross flow and re-impingement of the coolant air.</p><p>Heat transfer on the target plate is not uniform; areas under the jet which are called stagnation points have high heat transfer as compare to the areas away from the center of jet. It is almost the same situation for the impingement plate but the location of stagnation point is different. A transient technique is used to measure this non-uniform heat transfer distribution. It is assumed that the plates are semi-infinitely thick and there is no lateral heat transfer in the plates. To fulfill the assumptions a calculated time limit is followed and the test plates are made of Plexiglas which has very low thermal conductivity.</p><p>The transient technique requires a step-change in the mainstream temperature of the test section. However, in practical a delayed increase in mainstream temperature is attained. This issue is dealt by applying Duhamel’s theorem on the step-change heat transfer equation. MATLAB is used to get the Hue data of the recorded video frames and calculate the time taken for each pixel to reach a predefined surface temperature. Having all temperatures and time values the heat transfer equation is iteratively solved to get the value of heat transfer coefficient of each and every pixel of the test surface.</p><p>In total fifteen tests are conducted with different Reynolds number and different jet-to-target plate distances. It is concluded that for both the target and impingement plates, a high Reynolds number provides better overall heat transfer and increase in jet-to-target distance</p><p>decreases the overall heat transfer.</p>

In modern gas turbines parts of combustion chamber and turbine section are under heavy heat load, for example, the rotor inlet temperature is far higher than the melting point of the rotor blade material. These high temperatures causes thermal stresses in the material, therefore it is very important to cool the components for safe operation and to achieve desired component life. But on the other hand the cooling reduces the turbine efficiency, for that reason it is vital to understand and optimize the cooling technique. In this project Thermochromic Liquid Crystals (TLCs) are used to measure distribution of heat transfer coefficient over a scaled up combustor liner section. TLCs change their color with the variation of temperature in a particular temperature range. The color-temperature change relation of a TLC is sharp and precise; therefore TLCs are used to measure surface temperature by painting the TLC over a test surface. This method is called Liquid Crystal Thermography (LCT). LCT is getting popular in industry due to its high-resolution results, repeatability and ease of use. Test model in present study consists of two plates, target plate and impingement plate. Cooling of the target plate is achieved by impingement of air coming through holes in the impingement plate. The downstream surface of the impingement plate is then cooled by cross flow and re-impingement of the coolant air. Heat transfer on the target plate is not uniform; areas under the jet which are called stagnation points have high heat transfer as compare to the areas away from the center of jet. It is almost the same situation for the impingement plate but the location of stagnation point is different. A transient technique is used to measure this non-uniform heat transfer distribution. It is assumed that the plates are semi-infinitely thick and there is no lateral heat transfer in the plates. To fulfill the assumptions a calculated time limit is followed and the test plates are made of Plexiglas which has very low thermal conductivity. The transient technique requires a step-change in the mainstream temperature of the test section. However, in practical a delayed increase in mainstream temperature is attained. This issue is dealt by applying Duhamel’s theorem on the step-change heat transfer equation. MATLAB is used to get the Hue data of the recorded video frames and calculate the time taken for each pixel to reach a predefined surface temperature. Having all temperatures and time values the heat transfer equation is iteratively solved to get the value of heat transfer coefficient of each and every pixel of the test surface. In total fifteen tests are conducted with different Reynolds number and different jet-to-target plate distances. It is concluded that for both the target and impingement plates, a high Reynolds number provides better overall heat transfer and increase in jet-to-target distance decreases the overall heat transfer.

The ability and efficiency of today’s gas turbine engines are highly dependent on development of cooling technologies, among which film cooling is one of the most important. Investigations have been conducted towards discovering different aspects of film cooling, utilizing both experiments and performing CFD simulations. Although, investigation by using CFD analysis is less expensive in general, the results obtained from CFD calculations should be validated by means of experimental results. In addition to validation, in cases like simulating a turbine vane, performing CFD simulations can be time consuming. Therefore, it is essential to find approaches that can reduce the computational cost while results are validated by experiments. This study has shown the potential for reduced models to be utilized for investigation of different aspects of film cooling by means of CFD at low turn-around time. This has been accomplished by first carrying out CFD simulations and experiments for an engine-like setting for a full vane. Then the computational domain is reduced in two steps where all results are compared with experiments including aerodynamic validation, heat transfer coefficient and film effectiveness. While the aerodynamic results are in close agreement with experiments, the heat transfer coefficient and film effectiveness results have also shown similarities within the expected range. Thus this study has shown that this approach can be very useful for e.g. early vane and film cooling design.

The present work seeks to investigate the thermal hydraulic (heat transfer and fluid dynamics) behavior of supercritical (Sc) fluids at both the fundamental and applied levels. The thermal hydraulics of these fluids is not very well known although they have been used in various applications. There are drastic changes in the thermal and hydraulic properties of fluids at supercritical conditions. There has been a lot of focus to effectively utilize these properties changes in many applications such as heat exchangers. This work focuses on studying the forced convective heat transfer of Sc-CO2 in a series of mini semi-circular horizontal tubes and a zig-zag shaped horizontal channel. The problems were investigated numerically by second-order finite volume method using a commercial software FLUENT. Three dimensional Computational Fluid Dynamics (CFD) models were developed to simulate the flow and heat transfer for three different geometries – a single semi-circular channel, a series of nine parallel semi-circular channels and a zig-zag channel. Grid and accuracy refinement studies were carried out to assess numerical errors. All the computational meshes developed for this study incorporated the first node cell within the viscous sub-layer i.e. y <1. Since the flow is turbulent, an appropriate choice of turbulence model is highly desirable. Henceforth, various turbulence models were used to study their impact on the heat transfer solution for these problems. The present numerical work focuses on improving the CFD model and methodologies in order to capture the experimental data of the heat transfer spike at the super critical conditions. Local and average heat transfer coefficients near the critical point were determined from measured wall temperatures and calculated local bulk temperatures. The numerical results are compared with the experiments. The numerical predictions do not convincingly agree with the experiments. This could be because of the incapability of turbulent models to capture the flow physics accurately due to the rapid changes in the fluid properties near critical conditions.

This thesis presents the experiment study results on the local heat transfer coefficients for air jet impinging on a flat rectangle board. A transient thermochromatic liquid crystal technique is used to visualize and record isotherms on an impingement surface. The parameter studied include Reynolds number¡]Re=108,142,170¡^,jet height from the rectangular board¡]H/D=0.086,0.172,0.259,0.345,0.431,0.52¡^, and size of outlet¡]B/D=1.45,1.86,2.41¡^. The correlation of average Nusselt number is curve-fitted with Re,H/D and B/D . According to the present study,heat transfer is best when the Reynolds number is large,the jet height is small,and the outlet area is large .

In the present study, the local heat transfer coefficient over the surface of the tube row of a fin-and-tube heat exchanger is to measure. The test cases including the tube row arrangement of staggered and in-line, Reynolds number range of 2000 to 9000, and transverse tube pitch of S=2.0D, 2.5D and 2.8D, are studied and discussed. Experimental models of heat exchangers are constructed according to similarity principles. Complete distribution of local heat transfer coefficients are measured over the full surface of the tube row of a fin-and-tube heat exchanger by the transient heat transfer method with thermochromic liquid crystal used as the surface thermometer. And using micro video camera assembled in the experimental system to obtain the experimental image. Software, LCIA(Liquid Crystal Image Analysis), is used to obtain the temporal history of the surface temperature used to determined the local heat transfer coefficient. The results show that the heat transfer coefficient over the surface of the fin tube row increases with the Reynolds number. And the heat transfer coefficient for staggered cases is larger than that for in-line cases. The heat transfer coefficient on the surface of the tube row with transverse tube pitch S=2.0D is similar to the case with S=2.5D, and is larger than the case with S=2.8D. Therefore, there should exist an optimum geometry of the plate fin for a fin-and tube heat exchanger.

Nowadays, the filling and solidification of macro-scale injection mouldings can be predicted using commercial CAE software. For micro-injection moulding, the conventional tools do not work for all process conditions. The reasons might be the lack of high quality database used in the simulation and the improperly specified boundary conditions which do not reflect the real state in the cavity. Special aspects like surface tension or "size dependent" viscosity might also be responsible for the inaccuracy of the simulations. In this paper, those aspects related to the boundary conditions were taken into consideration, especially the thermal contact behaviour and the melt compression in the barrel which affects not only the temperature of the melt due to the compression heating, but also reduces the actual volume rate in the cavity. It can be shown that the heat transfer coefficient between the melt and the mould wall has a significant influence on the simulation results. In combination with precise material data and considering the reduction of the volume rate due to the melt compression in the barrel, the heat transfer coefficient may be quantified by means of reverse engineering. In general, it decreases when either the cavity thickness or the injection speed increases. It is believed that a pressure dependent model for the heat transfer coefficient would be more suitable to describe the thermal contact behaviour in micro injection moulding. The melt compression in the barrel affects definitely the filling behaviour and subsequently the heat transfer in the cavity as well, which is especially true for micro parts of high aspect ratio.

Film cooling is used in gas turbine engines to cool turbine components. Cooler air is bled from the compressor, routed internally through turbine vanes and blades, and exits through discrete holes, creating a film of coolant on the parts’ surfaces. Cooling the turbine components protects them from thermal damage and allows the engine to operate at higher combustion temperatures, which increases the engine efficiency. Shaped film cooling holes with diffuser exits have the advantage that they decelerate the coolant flow, enabling the coolant jets to remain attached to the surface at higher coolant flow rates. Furthermore, the expanded exits of the coolant holes provide a wider coolant distribution over the surface. The first part of this dissertation provides data for a new laidback, fan-shaped hole geometry designed at Pennsylvania State University’s Experimental and Computational Convection Laboratory. The shaped hole geometry was tested on flat plate facilities at the University of Texas at Austin and Pennsylvania State University. The objective of testing at two laboratories was to verify the adiabatic effectiveness performance of the shaped hole, with the intent of the data being a standard of comparison for future experimental and computational shaped hole studies. At first, measurements of adiabatic effectiveness did not match between the labs, and it was later found that shaped holes are extremely sensitive to machining, the material they are machined into, and coolant entrance effects. In addition, the adiabatic effectiveness was found to scale with velocity ratio for multiple density ratios and mainstream turbulence intensities. The second part of this dissertation measures heat transfer coefficient augmentation (hf/h0) at density ratios (DR) of 1.0, 1.2, and 1.5 using a uniform heat flux plate and the same shaped hole geometry. In the past, heat transfer coefficient augmentation was generally measured at DR = 1.0 under the assumption that hf/h0 was independent of density ratio. This dissertation is the first study to directly measure the wall and adiabatic wall temperature to calculate heat transfer coefficient augmentation at DR > 1.0. The results showed that the heat transfer coefficient augmentation was low while the jets were attached to the surface and increased when the jets started to separate. At DR = 1.0, hf/h0 was higher for a given blowing ratio than at DR = 1.2 and DR = 1.5. However, when velocity ratios are matched, better correspondence was found at the different density ratios. Surface contours of hf/h0 showed that the heat transfer was initially increased along the centerline of the jet, but was reduced along the centerline at distances farther downstream. The decrease along the centerline may be due to counter-rotating vortices sweeping warm air next to the heat flux plate toward the center of the jet, where they sweep upward and thicken the thermal boundary layer. This warming of the core of the coolant jet over the heated surface was confirmed with thermal field measurements. / text

Computations were run to study heat transfer coefficient augmentation with film cooling for a simulated gas turbine blade leading edge. The realizable k-[epsilon] turbulence model (RKE) and Shear Stress Transport k-[omega] turbulence model (SST) were used for the computational simulations. RKE computations completed at a unity density ratio were confirmed to be consistent with experimental measurements conducted by Yuki et al.(1998) and Johnston et al. (1999) whereas SST computations exhibited significant discrepancies. Moreover the effect of the density ratio on heat transfer coefficient augmentation was studied because experimental measurements of heat transfer coefficient augmentation with film cooling are generally constrained to unity density ratio tests. It was shown that heat transfer coefficient augmentation can be simulated using unity density ratio jets, but only when scaled with the momentum flux ratio of the coolant jets. / text

Direct contact condensation of steam injected into water is a special mode of condensation where condensation occurs on the interface between steam and water. This type of condensation forms an essential part of various industrial applications and correct prediction and modelling of the condensation behaviour is crucial to obtain an optimised design of such devices. While present prediction models for direct contact condensation are valid for a limited range of flow conditions only, the work presented in this thesis provides improved models for direct contact condensation. The models are developed in the form of diagrams and include: a condensation regime diagram, for predicting the condensation behaviour, a steam plume length diagram, for predicting the penetration distance of steam into water, and a heat transfer coefficient diagram. These models are derived using a wide range of data and therefore provide more accurate predictions compared with alternative models available in literature. In contrast to present models, the derived models presented in this work are constructed using an additional physical parameter to describe the process. The diagrams are validated against independent experiments and demonstrate close agreement. Furthermore, the predictions from the condensation regime diagram and steam plume length diagram are self-consistent. The models developed in this study are capable of predicting condensation behaviour for a wide range of initial conditions and can be used in conjunction with computational fluid dynamics techniques for direct contact condensation.