Xiaojun Shi

Analysis of a combined cycle power plant integrated with a liquid natural gas gasification and power generation system

An analysis of a novel liquefied natural gas (LNG) gasification and power generation system integrated with a combined cycle power plant is presented in this article. In the proposed combined cycle, low-temperature waste heat can be efficiently recovered and the cold energy of the LNG can be fully utilized. The latent heat of the spent steam of the steam turbine vaporizes the LNG. The conventional combined cycle and the proposed combined system are simulated using the commercial process simulation package IPSEpro and both energy and exergy analyses are conducted. A parametric analysis has been performed for the proposed combined system to evaluate the effects of several key factors on the performance. The results show that the net electrical efficiency and the total work output of the proposed combined cycle can be increased by 3.8 per cent and 15.6 MW above those of the conventional combined cycle while delivering 33.59 kg/s of natural gas (at 4.3 °C, 0.3 MPa) and saving 0.4 MW of electrical power by removing the need for sea water pumps.

Flow and Heat Transfer Characteristics in Rotating Two-pass Channels Cooled by Superheated Steam

Abstract In a modern gas turbine, using superheated steam to cool the vane and blade for internal convection cooling is a promising alternative to traditional compressor air. However, further investigations of steam cooling need to be performed. In this paper, the three-dimensional flow and heat transfer characteristics of steam are numerically investigated in two-pass square channels with 45° ribbed walls under stationary and rotating conditions. The investigated rotation numbers are 0 and 0.24. The simulation is carried out by solving the Reynolds averaged Navier-Stokes equations employing the Reynolds stress turbulence model, especially considering two additional terms for Coriolis and rotational buoyancy forces caused by the rotating effect. For comparison, calculations for the air-cooled channels are done first at a Reynolds number of 25 000 and inlet coolant-to-wall density ratio of 0.13. The results are compared with the experiment data. Then the flow and heat transfer in steam-cooled channels are analyzed under the same operating conditions. The results indicate that the superheated steam has better heat transfer performance than air. Due to the combined effect of rotation, skewed ribs and 180° sharp turn, the secondary flow pattern in steam-cooled rotating two-pass channels is quite complex. This complex secondary flow pattern leads to strong anisotropic turbulence and high level of anisotropy of Reynolds stresses, which have a significant impact on the local heat transfer coefficient distributions.

Experimental Study on Comparison of Cooling Effectiveness Between Steam and Air for a Gas Turbine Nozzle Guide Vane

An experimental investigation of the cooling performance for a gas turbine vane with internal passages is conducted on a linear turbine cascade consisting of three nozzle guide vanes with a chord length of 126mm and a blade height of 83 mm. Measurements of temperature and static pressure distribution are implemented on the center guide vane, which is internally cooled by air or steam flowing radially through five smooth channels. The main objective of this investigation is to receive more information on the temperature of vane surface, and to compare the cooling effectiveness between air and superheated steam. The experiments are performed for a variety of exit Mach numbers, exit Reynolds number, coolant-to-mainstream mass flow ratio, and coolant-to-mainstream temperatures ratio. The experimental results show, that at coolant-to-mainstream mass flow ratio 0.08 and coolant-to-mainstream temperatures ratio 0.61, the average surface temperature of steam cooled vane decreases about 25% and the corresponding average cooling effectiveness is 52%, while for the air cooled vane, it is 18% and 42%, respectively. Therefore the coolant steam has much better cooling performance than air. Furthermore, the cooling effectiveness at the middle chord region of vane is much higher than that at the leading and trailing region, as is expected. Consequently, this leads to great temperature gradient and thermal stresses at the leading and trailing region, where the internal convective cooling method has insufficient cooling ability. Therefore, besides convective cooling method, more complicated cooling configuration may be necessitated. NOMENCLATURE

Experimental investigation on heat transfer and friction characteristics of ribbed rectangular channels using steam as coolant

Heat transfer and friction characteristics of steam flow in ten different rectangular channels with ribs on two opposite walls have been investigated experimentally in this article. To simulate the actual geometry and heat transfer structure of gas turbine blade/vane internal cooling passage, each of the test channels was made by welding four stainless steel plates. The aspect ratio of these steam-cooled channels was 1/4, 1/2, 1, 2 and 4. The rib angle-of-attack was 30°, 45°, 60° and 90°. The Reynolds number range was 10,000–80,000. The pitch-to-rib height ratio (p/e) was kept at 10. The rib height to hydraulic diameter ratios (e/D) were 0.078 for W/H = 0.25 and 0.047 for W/H = 2, 1 and 0.5. The results show that the highest heat transfer accompanied by the highest friction factor occurred at the rib angle α = 60°. The effect of rib angle on the f/f0 and the Nu/Nu0 values is reduced gradually with the channel aspect ratio ranging from 4 to 1/4. When the aspect ratio varies from 0.25 to 4, the Nu values increase 35% and the f/f0 values increase 4.7 times. Semi-empirical correlations of heat transfer and friction are developed to account for channel aspect ratio, rib angle and Reynolds number.

Experimental study on the effect of coolant on the thermal characteristics of gear grinding machine under load

It is very important to reduce the thermal deformation of machine tools for modern precision machining because the machining error induced by the thermal deformation is up to 75% of the total errors. In this paper a special measurement system was established for a five-axis gear grinding machine and the effect of coolant on thermal behaviour of the machine tool during various grinding processes has been studied experimentally. The results show that the coolant has a strong influence on the thermal behaviour. This is mainly because the coolant absorbs a large amount of cutting heat and the uneven flows of coolant on the bed surface increase the temperature gradient of the machine tool. In addition, coolant atomisation leads to higher ambient temperature inside the machine tool housing. The measured thermally induced errors increase with the increase of the coolant temperature. Although coolant causes the machine tool temperature increase, it can also positively affect the thermal behaviour if coolant is controlled to flow correctly and stabilise the machine tool temperature. In order to further reduce the thermal error, controlling coolant flow has to be considered in earl design stages.

Experimental and numerical study of an integrated air- and steam-cooled gas turbine vane

This paper proposes a new cooling method which integrates steam and air for gas turbine vane cooling with the aim to solve the problem of a very high thermal load at the trailing edge region of a steam-cooled gas turbine vane. The influence of coolant inlet conditions on the temperature and cooling effectiveness distribution of the experimental vane surface has been investigated in a hot wind tunnel test facility with a three-vane cascade. The test vane external aerodynamic and heat transfer were investigated experimentally and numerically. Two improved arrangement of cooling working fluid flow direction were designed to reduce the temperature gradient along the vane height. The following conclusions can be made: the thermal load at the trailing edge region is reduced for this integrated air and steam cooled gas turbine vane; the surface temperature uniformity is improved. Under an optimal thermal physical parameters of the cooling fluids, the cooling effectiveness of the trailing edge region and the leading edge region are 50% and 55%, respectively; the cooling effectiveness of the mid chord region is the highest and reaches 67%; The cooling method and structure have more influence on the cooling effectiveness compared with the cooling fluids inlet conditions.