Variation of lubricant distribution across the radial direction in a journal bearing

A Computational Fluid Dynamics (CFD) analysis of two-phase flow was used to obtain the distribution of lubricant in a journal bearing, including inlet tube and groove. It was found that for an incomplete starting film, the oil spread-length varies along the groove depth and film thickness. The magnitude of variation was found to be independent of the inlet mass flow rate. Numerical simulations of the proposed model show that in the cavitation region the streamlets do not fill the entire film thickness. The present numerical model agrees with experimental observations.

Rubber as an advanced structural material for thermal conditioning system interfaces

In integrated launch vehicles, one of the systems responsible for successful launch preparation and support is a ground thermal conditioning system supplying low-pressure thermostatic air to the “dry” compartments and head blocks of a launch vehicle. To connect the thermal conditioning system to the launch vehicle, a special interface is used. The proper functioning of the interface is critical to the reliability of the ground equipment of the system, the launch vehicle, and the space complex as a whole. This article describes key requirements to the interfaces of the thermal conditioning system and the drawbacks of their existing designs. The article proposes a new concept of interface design, according to which the pipeline of the ground thermal conditioning system is connected to the inlet tube of the launch vehicle via a corrugated rubber hose composed of three basic parts. The hose is attached to the inlet tube of the launch vehicle with the help of a metal lock/unlock device. The proposed solution provides good air tightness, ease of operation, easy multiple connections to the launch vehicle at different angles, and an automatic disconnection at launch or a manual disconnection in the case of a cancelled launch. Using rubber, which is a high-elasticity structural material, in the manufacturing of hoses makes it possible to minimise the effort required to disconnect the interface from the launch vehicle. In a high elasticity state, rubber can absorb and dissipate mechanical energy over a wide range of temperatures, which precludes the vibration caused by the engine operation from being transmitted to the ground thermal conditioning system. The article presents the key properties of rubber used as a structural material and its features to be considered in the design of similar devices. In contrast to metal, which shows two types of deformation (elastic and plastic), rubber can exhibit three types (elastic, superelastic, and plastic). During the design of interfaces, two types of deformation were taken into account: elastic and superelastic. Experimental tests of the interface presented in the article showed its full compliance with the requirements specification.

Backflow effects on mass flow gain factor in a centrifugal pump

Previous researches has shown that inlet backflow may occur in a centrifugal pump when running at low-flow-rate conditions and have nonnegligible effects on cavitation behaviors (e.g. mass flow gain factor) and cavitation stability (e.g. cavitation surge). To analyze the influences of backflow in impeller inlet, comparative studies of cavitating flows are carried out for two typical centrifugal pumps. A series of computational fluid dynamics (CFD) simulations were carried out for the cavitating flows in two pumps, based on the RANS (Reynolds-Averaged Naiver-Stokes) solver with the turbulence model of k- ω shear stress transport and homogeneous multiphase model. The cavity volume in Pump A (with less reversed flow in impeller inlet) decreases with the decreasing of flow rate, while the cavity volume in Pump B (with obvious inlet backflow) reach the minimum values at δ = 0.1285 and then increase as the flow rate decreases. For Pump A, the mass flow gain factors are negative and the absolute values increase with the decrease of cavitation number for all calculation conditions. For Pump B, the mass flow gain factors are negative for most conditions but positive for some conditions with low flow rate coefficients and low cavitation numbers, reaching the minimum value at condition of σ = 0.151 for most cases. The development of backflow in impeller inlet is found to be the essential reason for the great differences. For Pump B, the strong shearing between backflow and main flow lead to the cavitation in inlet tube. The cavity volume in the impeller decreases while that in the inlet tube increases with the decreasing of flow rate, which make the total cavity volume reaches the minimum value at δ = 0.1285 and then the mass flow gain factor become positive. Through the transient calculations for cavitating flows in two pumps, low-frequency fluctuations of pressure and flow rate are found in Pump B at some off-designed conditions (e.g. δ = 0.107, σ = 0.195). The relations among inlet pressure, inlet flow rate, cavity volume, and backflow are analyzed in detail to understand the periodic evolution of low-frequency fluctuations. Backflow is found to be the main reason which cause the positive value of mass flow gain factor at low-flow-rate conditions. Through the transient simulations of cavitating flow, backflow is considered as an important aspect closely related to the hydraulic stability of cavitating pumping system.

Analysis of Incomplete Film in Parallel Plates Including Inlet Tube and Groove

To clarify the realistic upstream boundary conditions of hydrodynamic bearings, the oil spread in a complex system of parallel plates including an inlet tube and axial groove is studied by the computational fluid dynamics (CFD) method. The effects of various design parameters including clearance, velocity of bottom plate, and inlet mass flowrate on oil spread-length are presented and explained. By intensive parametric study for these parameters, an empirical expression for the oil spread-length is derived. A groove with blind ends significantly increases the efficiency of the system. A comparison with experimental observation validates the present model as a proper one for accurately solving oil spread in similar systems.

Study on the Influence of Centrifugal Pump Inlet Flow Field Instability and Methods of Adjustment

The quality of centrifugal pump inlet flow field is an important factor that affecting the performance of pump. Studies have proved that the vortex in the inlet area can also bring an extra flow instability to pump, which results in a hydro-induced vibration. This phenomenon is more common and significant in the pumps with an elbow tube, which is often applied to minimize installation size, before pump inlet. Therefore, it is necessary to look into the influence of inlet flow field instability on pump performance especially the vibration performance. The methods of adjusting pump inlet flow field is also worthy of being studied in the meantime. In this study, the influence of inlet vortex on the performance of centrifugal pump with an elbow inlet tube is investigated by means of CFD analysis. The flow is significantly affected when going through the elbow tube inlet and then turbulence is generated as a result, which enters the impeller at the next moment. The turbulence brings an asymmetrical flow condition at the impeller suction area, which can intensify pressure pulsation and hydro-induced vibration. In order to reduce the turbulence, two modifications on the elbow inlet tube are investigated in this study. A specially designed vane is deployed inside the inlet tube in the MOD1, and the MOD2 is added with two splitter vanes on the basis of the MOD1. The turbulent flow in the elbow inlet tube can be reordered as it is controlled by the vanes. The difference on pump performances that the inlet vane has made is specifically simulated and compared. The flow fields of the inlet tube influenced by the vane is also investigated on the vortex distribution and velocity vector distribution. The MOD1 has a generally smaller pressure fluctuation amplitude than the prototype in the impeller inlet area while the pressure fluctuation amplitude of the MOD2 in the impeller inlet area is stronger than the prototype. It is considered as a consequence of multiple effects, which are, the rise of velocity because of flow area replacement by the vanes making the flow field less stable as well as the wake flow induced by the vanes increasing the instability of the flow field. Therefore, although the flat vanes can help adjusting the flow field, their negative influences also act in the opposite way. It is worthwhile to find the balance between the benefits and the costs in flow field stability of installing adjusting vanes. The selection of parameter, number and installation position needs to be further investigated. The numerical results of the MOD1 are also validated through experimental investigations.

Design, performance evaluation and analysis of the inlet tube of pressure sensor for chamber pressure measurement

Purpose In Aerospace applications, the inlet tubes are used to mount strain gauge type pressure sensors on the engine under static test to measure engine chamber pressure. This paper aims to focus on the limitations of the inlet tube and its design aspects to serve better in the static test environment. The different sizes of the inlet tubes are designed to meet the static test and safety requirements. This paper presents the performance evaluation of the designed inlet tubes with calibration results and the selection criteria of the inlet tube to measure combustion chamber pressure with the specified accuracy during static testing of engines. Design/methodology/approach Two sensors, specifically, one cavity type pressure sensor with the inlet tube of range 0-6.89 MPa having natural frequency of the diaphragm 17 KHz and another flush diaphragm type pressure sensor of the same range having −3 dB frequency response, 5 KHz are mounted on the same pressure port of the engine under static test to study the shortcomings of the inlet tube. The limitations of the inlet tube have been analyzed to aid the tube design. The different sizes of inlet tubes are designed, fabricated and tested to study the effect of the inlet tube on the performance of the pressure sensor. The dynamic calibration is used for this purpose. The dynamic parameters of the sensor with the designed tubes are calculated and analyzed to meet the static test requirements. The diaphragm temperature test is conducted on the representative hardware of pressure sensor with and without inlet tube to analyze the effect of the inlet tube against the temperature error. The inlet tube design is validated through the static test to gain confidence on measurement. Findings The cavity type pressure sensor failed to capture the pressure peak, whereas the flush diaphragm type pressure sensor captured the pressure peak of the engine under a static test. From the static test data and dynamic calibration results, the bandwidth of cavity type sensor with tube is much lower than the required bandwidth (five times the bandwidth of the measurand), and hence, the cavity type sensor did not capture the pressure peak data. The dynamic calibration results of the pressure sensor with and without an inlet tube show that the reduction of the bandwidth of the pressure sensor is mainly due to the inlet tube. From the analysis of dynamic calibration results of the sensor with the designed inlet tubes of different sizes, it is shown that the bandwidth of the pressure sensor decreases as the tube length increases. The bandwidth of the pressure sensor with tube increases as the tube inner diameter increases. The tube with a larger diameter leads to a mounting problem. The inlet tube of dimensions 6 × 4 × 50 mm is selected as it helps to overcome the mounting problem with the required bandwidth. From the static test data acquired using the pressure sensor with the selected inlet tube, it is shown that the selected tube aids the sensor to measure the pressure peak accurately. The designed inlet tube limits the diaphragm temperature within the compensated temperature of the sensor for 5.2 s from the firing of the engine. Originality/value Most studies of pressure sensor focus on the design of a sensor to measure static and slow varying pressure, but not on the transient pressure measurement and the design of the inlet tube. This paper presents the limitations of the inlet tube against the bandwidth requirement and recommends dynamic calibration of the sensor to evaluate the bandwidth of the sensor with the inlet tube. In this paper, the design aspects of the inlet tube and its effect on the bandwidth of the pressure sensor and the temperature error of the measured pressure values are presented with experimental results. The calibration results of the inlet tubes with different configurations are analyzed to select the best geometry of the tube and the selected tube is validated in the static test environment.

ANALISIS EFISIENSI KINARJA ECONOMIZER DI PT. PLN (PERSERO) KALIMANTAN SELATAN-TENGAH SEKTOR PLTU ASAM – ASAM

Electrical energy is the dominant energy needed for human life. One source of electricity income is Steam Power Plant (PLTU). With an installed capacity of 4 x65 MW for public transportation, each unit of acid acid plant has one boiler with 1 economizer as a means of boiler efficiency enhancer by absorbing hot flue gas. To avoid it then in need of maximum care to components of economizer. To see the effectiveness of the economizer it is necessary to observe the economizer. This study aims to analyze the effectiveness of the economizer. From the results of the boiler efficiency study from March 27, 2017 to April 10, 2017 with a total average efficiency in the analysis of 81.93%. With the highest efficiency on date On March 29, 2017 the efficiency calculated was 83.42% at 02:00. And the lowest on April 2, 2017, an 80.32% efficiency at 09:00. The factor that influences the efficiency ratio is the temperature difference between the incoming gas gas furnace (T_ (h, i)), exit (T_ (h, o)) and the feed water inlet tube temperature (T_ (c, i)). The research obtained the highest heat transfer coefficient that is equal to 1.647,1 Btu/h.ft2 at 227,4°C on 27/03/2017 and the lowest that is equal to 1.636,91 Btu/h.ft2 at 233°C on 28/03/2017 Keywords: Economizer, Feed Water Tube, Flue Gas, Koefisien Heat Transfer, Heat transfer