Terry W. Simon

Measurements Over a Film-Cooled, Contoured Endwall With Various Coolant Injection Rates

This paper presents the results of a study of film coverage for coolant injection through an axisymmetric, contoured endwall of a high-pressure turbine first stage vane row. Tests are done on a low speed, linear cascade. The injection is either through a single slot upstream of the leading edges of the vanes or through two slots, one upstream of the other. Because the contouring begins upstream of the leading edges, injection is in an accelerating flow region. The effects of such injection on the secondary flows within the vane cascade are inferred by means of contours of dimensionless temperature. These thermal measurements are made by slightly heating the injection stream above the main flow temperature and documenting the temperatures inside the coolant-mainstream mixing zone. The thermal results are complemented with three-component, hot-wire measurements taken near the exit plane. Performance with different injection rates is discussed. The secondary flow seems to affect the cooling flow strongly when the momentum of the injected flow is small, compared to the main flow momentum. As a result, coolant coverage is non-uniform, with most of the coolant accumulating near the suction side of the passage. As the injection momentum is increased, some pressure-side accumulation of coolant is observed. However, non-uniformity still exists, with a lesser amount of coolant in the central region and more near the suction and pressure surfaces. For the same ratio of coolant to mainstream mass flow rates, cooling through a single slot seems to give more cooling towards the pressure side than does cooling through two slots. With the same mass flow rate, the one-slot case has higher injection momentum than does the two-slot case. This indicates that momentum flux is an important parameter in establishing the distribution of the coolant within the passage.Copyright

Boiling incipience and nucleate boiling heat transfer of highly-wetting dielectric fluids from electronic materials

An experimental study of pool boiling was conducted using cylindrical heater surfaces of platinum, silicon, silicon dioxide, and aluminum oxide. They were immersed in FC-72 and R-113, saturated at 1-a.t.m. pressure. The effects of fluid and surface material on boiling incipience and on the nucleate boiling curve was investigated. A probabilistic representation was used to present the incipience wall superheat values, which scattered widely for ostensibly identical runs. The difference in incipience wall superheat values between those with FC-72 and R-113 was significant, but the surface material effect on boiling incipience was small. The surface material effect was more pronounced in the nucleate boiling regime than on the incipience process. >

Optimal trajectories for a liquid piston compressor/expander in a Compressed Air Energy Storage system with consideration of heat transfer and friction

For a Compressed Air Energy Storage (CAES) approach to be viable, the air compressor/expander must be sufficiently powerful and efficient. Since efficiency is governed by heat transfer, there is a generally a tradeoff between efficiency and compression/expansion time (or power). In this paper, we determine Pareto optimal compression/expansion profiles for a liquid piston air compressor/expander that maximizes efficiency (power) for a given power (efficiency). Compared to previous works, a numerical optimization approach is proposed that allows for more general heat transfer model, the consideration of the viscous friction, and system limitations in the optimization. The resulting optimal profiles are compared to other trajectories. At compression ratio of 10, the optimal profile results in 10%-40% increase in power density relative to other methods. Optimal geometries that trades off friction and heat transfer improvement can also be determined using this method.

Fluid Selection and Property Effects in Single- and Two-Phase Immersion Cooling

A bslruct-The governing equations for liquid and two-phase heat transfer are used to derive fluid figures of merit (FOM’s) for forced and natural convection, boiling incipience, and critical heal flux in both pool and flow boiling modes. These FOM’s can he used to evaluate and compare the thermal performance of several candidate immersion cooling fluids. In addition, the governing equations are used to determine the sensitivities of thermal performance to fluid property values.

Heat transfer—a review of 1984 literature

Synthese bibliographique et bibliographie des publications mondiales sur le transfert de chaleur en 1984

Optimal Control Experimentation of Compression Trajectories for a Liquid Piston Air Compressor

Air compressor is the critical part of a Compressed Air Energy Storage (CAES) system. Efficient and fast compression of air from ambient to a pressure ratio of 200-300 is a challenging problem due to the trade-off between efficiency and power density. Compression efficiency is mainly affected by the amount of heat transfer between the air and its surrounding during the compression. One way to increase heat transfer is to implement an optimal compression trajectory, i.e., a unique trajectory maximizing the compression efficiency for a given compression time and compression ratio. The main part of the heat transfer model is the convective heat transfer coefficient (h) which in general is a function of local air velocity, air density and air temperature. Depending on the model used for heat transfer, different optimal compression profiles can be achieved. Hence, a good understanding of real heat transfer between air and its surrounding wall inside the compression chamber is essential in order to calculate the correct optimal profile. A numerical optimization approach has been proposed in previous works to calculate the optimal compression profile for a general heat transfer model. While the results show a good improvement both in the lumped air model as well as Fluent CFD analysis, they have never been experimentally proved. In this work, we have implemented these optimal compression profiles in an experimental setup that contains a compression chamber with a liquid piston driven by a water pump through a flow control valve. The optimal trajectories are found and experimented for different compression times. The actual value of heat transfer coefficient is unknown in the experiment. Therefore, an iterative procedure is employed to obtain h corresponding to each compression time. The resulted efficiency versus power density of optimal profiles is then compared with ad-hoc constant flow rate profiles showing up to %4 higher efficiency in a same power density or %30 higher power density in a same efficiency in the experiment.

Iterative optimal and adaptive control of a near isothermal liquid piston air compressor in a compressed air energy storage system

The power density and efficiency of high compression ratio (~200:1) air compressors/expanders are crucial for the economical viability of a Compressed Air Energy Storage (CAES) system such as the one proposed in [1]. There is a trade-off between power density and efficiency that is strongly dependent on the heat transfer capability within compressor/expander. In previous papers, we have shown that the compression or expansion trajectory can be optimized so that for a given power, the efficiency can be optimized and vice versa. Theoretically, for high compression ratios, the improvement over ad-hoc trajectories can be significant- for example, at the same efficiency of 90%, the power can be increased by 3-5 folds [2], [3], [4], [5]. Yet, the optimal trajectories depend on the heat transfer coefficient profile that is often unknown. In this paper, we focus on the experimental study of an iterative control algorithm to track a compression trajectory that optimizes the efficiency-power trade-off in a liquid piston air compressor. First, an adaptive controller is developed to track any desired compression trajectory characterized by the temperature-volume profile. The controller adaptively estimates the unknown heat transfer coefficient. Second, the estimated heat transfer coefficient from one iteration is then used to estimate the optimal compression trajectory for the next iteration. As the estimate of the heat transfer coefficient improves from one iteration to the next, the quality of the estimated optimal trajectory also improves. This leads to successively improved efficiency. The experimental results of optimal trajectories show up to 2% improvement in compression efficiency compared to linear trajectories in a same power density.

Fluid selection and property effects in single- and two-phase immersion cooling (of electronic components)

The governing equations for liquid and two-phase heat transfer are used to derive fluid figures-of-merit (FOMs) for liquid-forced and natural convection, boiling incipience, and critical heat flux in both pool and flow boiling modes. These FOMs are given to help evaluate and compare the thermal performance of several candidate immersion cooling fluids. In addition, the governing equations are used to determine the sensitivities of thermal performance to fluid property values.<<ETX>>