Autonomous capillary microfluidic devices with constant flow rate and temperature-controlled valving

In this paper, we report on a capillary microfluidic device with constant flow rate and temperature-triggered stop valve function. It contains a PDMS channel that was grafted by a thermo-responsive...

PERAMALAN UNTUK PERENCANAAN PRODUKSI STOP VALVE TIPE TX277S MENGGUNAKAN METODE PERAMALAN DERET WAKTU (TIME SERIES) DI PT. XYZ

Untuk menghadapi kondisi persaingan industri manufaktur yang ketat perusahaan dituntut agar bisa memenuhi permintaan konsumen dengan cepat dan tepat tanpa mengesampingkan efisiensi. Peramalan akan suatu permintaan pasar sangatlah penting, karena sebagai acuan perencanaan produksi sebelum order diterima dari konsumen. Time series adalah suatu metode peramalan yang cukup banyak digunakan dalam peramalan permintaan. Model peramalan rata-rata bergerak menggunakan MA(4) didapat nilai sebesar 1361,72. Model peramalan rata-rata bergerak menggunakan MA(5) didapat nilai MAD sebesar 1440. Model peramalan pemulusan eksponensial dengan nilai ES (α = 0,8) didapat nilai MAD yaitu 1158,3. Model peramalan pemulusan eksponensial dengan nilai ES (α = 0,95) didapat nilai MAD yaitu 1248,75. Dari model peramalan yang digunakan, nilai MAD yang paling rendah adalah model ramalan pemulusan eksponensial menggunakan ES (α = 0,8) yaitu 1158,3. Berdasarkan model peramalan pemulusan eksponensial dengan ES (α = 0,8), maka dapat diperoleh nilai peramalan untuk bulan Mei 2020 yaitu 1158,3. Kata Kunci: Peramalan permintaan, Time Series, MAD

Fluid dynamic forces in the main steam pipeline of thermal power plant upon stop valves closure

A steam turbine trip is followed by a prompt closure of stop valves in front of the turbine and consequently to a pressure rise in the main steam pipeline. This steam hammer transient leads to the generation of intensive fluid dynamic forces that act along the pipeline axis and induce additional dynamic loads on the main steam pipeline. It is a common practice to assume a simultaneous closure of all stop valves in the safety analysis of the main steam pipeline. In the present paper computer simulations and analyses of the fluid dynamic forces are performed for several scenarios that take into account the possibility of delayed closure of the stop valve in front of the turbine. The influence of the failure of the steam by-pass line opening is considered too. The results show that the delay of the stop valve closure increases the maximum intensity of fluid dynamic force in the pipeline segment in front of the stop valve and decreases the intensity of fluid dynamic forces in segments along the pipeline. The failure of the by-pass line to open leads to prolonged steam pressure and fluid dynamic forces oscillation in pipeline segments. The simulations were performed with the in-house computer code based on the method of characteristics for the solving of the hyperbolic system of PDE that represent the mass, momentum and energy balance equations of the 1-D, compressible and transient fluid-flow. The obtained results are a support to safety analyses of thermal power plants under transient conditions.

Analysis of reliability of design of stop valve of steam turbin

The stop valve is one of the «critical» elements of the steam turbine installation, the heating conditions of which determine the reliability of the power unit as a whole. The stop valve for cogeneration steam turbines of subcritical parameters of "UTZ" is unified for familiesT-110/120-130, T-185/210-130/15, ПT-140/165-30/15, P-100-130/15. The sequence of analysis of the valve design is presented for conditions, where only the static temperature and steam pressure at the inlet to the valve, the steam flow rate at the outlet of it, the restrictions for movement during heating are known. The results of the analysis of calculations of unsteady gas-thermodynamic and stress-strain state of the valve during the heating of the main steam line of the turbine T-110/120-130 from the cold state according to the standard instructions are shown. The calculations were carried out by the finite element method using a three-dimensional geometric model of the valve body with a slit filter. The height of the holes in the slit filter is 3.5 mm. The equations of the Nusselt criterion for the flange, the steam box, the lower half of the steam box and the fairing when using computers with limited computing resources are presented. It is shown that the peak of the maximum stresses occurs at the initial stage of the stop valve warming up on the inner (heated) surface of the stop valve body in the area of the flange and the cover. The maximum equivalent stresses are 300 MPa. The comparison of calculated temperatures and temperatures measured during the start-up at the CHP is presented; the temperature difference does not exceed 5–6%. It is proposed to analyze the stop valve reliability with a sequence given in this article in the design of new stop valves with significant differences from the existing prototypes.

Verification of Combined Main Steam Valve Pressure Distribution and Vibration Characteristics With Downscale Model Test on Air Condition

In order to enhance the efficiency and reduce the manufacturing cost of steam turbine, combined main steam valve consisting of main stop valve and control valve in the same casing has been developed. Combined main steam valve with improved flow path at internal structure will reduce pressure loss. A downscale model test on air condition was conducted to verify pressure distribution characteristics. Experimental result and numerical result obtained by computational fluid dynamics (CFD) showed reasonable agreement in pressure loss and static pressure at each flow point within the design operation range. Main stop valve (SV) and control valve (CV) vibration characteristics tests were performed simultaneously for the stability verification of governing operation from start up to full load. We confirmed that CV aerodynamic added damping ratio was positive under all measured condition of CV stroke and pressure ratio, and self-excited vibration was not generated. We also confirmed that pressure fluctuation acting on main stop valve body was sufficiently small within the operation range. Meanwhile, in the case where pressure ratio or CV stroke deviated from the operation range, pressure fluctuation around main stop valve increased. Based on CFD result and detailed analysis of experimental result, it was found that steam flow along valve seat separates periodically, which revealed the mechanism of increasing pressure fluctuation around main stop valve. By reflecting on these results, the reliability of new combined main steam valve has substantially been enhanced.

Pendokumentasian Kegagalan pada Peralatan Main Liquid Fuel Pump GTG 1.1 dan Accessories Gear Train GTG 1.1 dengan Menggunakan Metode FMEA (Failure Mode & Effect Analysis)

Perawatan suatu asset perusahaan merupakan salah satu aktivitas atau tindakan utama yang dilakukan dengan tujuan meningkatkan keselamatan kerja serta menekan biaya pengeluaran dari suatu perusahaan. Suatu perusahaan dapat dikatakan maju apabila kondisi pemasukan dari perusahaan tinggi dan pengeluaran kecil. Hal ini berkaitan dengan aktivitas dari perawatan suatu asset. Perawatan yang tidak sesuai memicu kerusakan atau timbulnya modus kegagalan dari suatu asset. Besarnya tingkat kerusakan dan perawatan yang kurang sesuai memberikan peluang akan terjadinya kerusakan baik yang dapat diperbaiki maupun yang harus diganti. Tingginya frekuensi suatu asset yang mengalami kerusakan yang mengharuskan untuk dilakukan pergantian mempengaruhi kondisi keuangan dari perusahaan tersebut. Disamping hal tersebut kerusakan pada suatu asset juga dapat mempengaruhi proses produksi yang berlangsung pada suatu perusahaan tersebut. Maka agar masalah tersebut teratasi salah satu solusi yang mampu mengatasi atau mengurangi tingkat kerusakan pada suatu asset yaitu melakukan perawatan yang sesuai. Pada penelitian ini akan dilakukan analisa terkait kondisi suatu asset yang rawan akan mengalami suatu kerusakan dengan menggunakan metode failure mode & effect analysis (FMEA). pada metode ini akan diidentifikasi mode kegagalan yang terjadi pada asset yang terkait. Proses identifikasi tersebut maka akan diberikan penilaian sesuai kondisi asset dilapangan. Dengan nilai tersebut maka dapat digunakan untuk memprioritaskan asset yang akan dilakukan tindakan perawatan. Hasil dari Penelitian ini didapatkan besar dari frekuensi terkecil excitation transformer (PPT) GTG 1.1, protection relay GTG 1.1, liquid fuel stop valve GTG 1.1, load compartment GTG 1.1 dengan memiliki frekuensi sebesar 52.3 minggu/ kegagalan.

Structure and Characteristics of the Metal of the Cr-Ni-Mo-Mn-Si-Ti-Nb System Obtained by Surfacing with a Flux-Cored Wire Alloyed by Boron Carbide

This study explores structure and characteristics of the nickel-chrome steel of the Cr-Ni-Mo-Mn-Si-Ti-Nb-B doping system obtained by surfacing with a flux-cored wire alloyed by boron carbide. It has shown that the deposited metal has a composite structure consisting of a supersaturated with alloyed elements solid solution with an austenite-martensitic matrix and a eutectic component (Mo, Cr, Fe, Nb)2B in the form of sections along the boundaries of former austenite grains. Because of the significant content of ferrite-forming elements in the process of crystallization, a metastable δ-ferrite is formed in the weld metal in the form of differently oriented interlayers between the martensite rails. As a result of aging of such a deposited metal at 500 °C for 2 hours, the metastable ferrite undergoes decay at the interphase boundaries α/δ with the formation of the σ phase, which represents sharpened plates with the size of 300÷550 nm. Moreover, aging leads to hardening of the matrix by finely dispersed carboboride and intermetallic phases (Cr, Mo, Fe, Nb, Ti)23(С,В)6, (Fe, Cr, Si)2(Mo, Ti) и (Ni, Fe)3Ti, causing high levels of hardness and wear resistance. The usage of this wire as a surfacing material allows to increase significantly the operability and reliability of the stop valve parts, which work on abrasion in contact with corrosive medium.