Applied Mechanics and Materials Vol. 818

Abstract: Several features of heat transfer on enclosing surfaces are discussed including temperature distributions in a room heated by a floor heater. Numerical analyses on radiative and convective heat transfer were carried out against several partial floor heating. Partial floor heating produces different types of temperature distribution between the heated and non-heated places, which is a remarkable characteristics found out in this study. In the heated places, the temperature distribution is almost the same as that of typical floor heating. However, in the non-heated places, air temperature differs by 6 °C (3.6 °Difference) between a point near the floor surface and a point well above that. Heating efficiency of partial heating slightly depends on the set place as well as its Area. Moreover, convective heat exchange constitutes approximately half of the total heat exchange

Abstract: In this paper, single phase model was used to investigate the effect of base fluid in enhancing the heat transfer for forced convection flow of SiO₂ in microtube. Four different types of base fluid such as water, ethylene glycol, engine oil and glycerin were used in this investigation. Reynolds number used was ranged from 10 to 120. The results are presented in terms of axial and wall temperature along the tube radius and tube axis, axial velocity and Nusselt number. The result shows that the glycerin has the highest Nusselt number followed by engine oil, ethylene glycol then water.

Abstract: The characteristics of two-phase flow boiling of R-290 are required for replacing R-22 that has been phased-out. The present study focuses on experimental pressure drop for R-22 and R-290. The experiment was run with heat flux of 5.09 kW/m² to 19.03 kW/m², mass flux of 114.91 kg/m²s to 751.74 kg/m²s and saturation temperature of 4.77°C to 18.12°C. The present result showed that pressure drop was affected by heat flux, mass flux and saturation temperature. Lower mass flux, heat flux and saturation temperature results in lower pressure drop. The pressure drop of R-290 is lower than that of R-22. Among the existing pressure drop prediction methods, Lokhart-Martinelli (1949) gives the best prediction for the present pressure drop data.

Abstract: This paper introduces a novel two-sleeve rotary compressor (TSRC) concept. The compressor mechanism is basically that of a rotary motion whereby the novelty lies in the usage of two rotating sleeves and a secured vane that has one end fixed to an outer sleeve and the other end to a rotor, respectively. The paper introduces the working principle and thermodynamic model of the TSRC compressor. The swept volume, the delivered pressure, the work and the power of the TSRC are formulated and analyzed. The compressor configuration and thermodynamic analysis are based on the 174 cm³.rev^-1 swept volume with R134a as the compressed gas. The thermodynamic analysis reveals that the TSRC will perform well as refrigerant compressor and can be reliably adopted for refrigeration and air-conditioning applications.

Abstract: Today the use of fatty acids as heat storage substance is growing. The use of several types of fatty acids such as oleic acid, palmitic acid, and stearic acid as heat storage materials has been studied. But, ricinoleic acid from castor oil has not been studied yet. This study was conducted to ascertain the characteristics of ricinoleic acid as a heat storage material.Methyl ricinoleic was obtained through transesterification of castor oil by methanol with sodium methoxide catalyst. Methyl ricinoleic was then hydrolyzed using sodium hydroxide in ethanol to produce ricinoleic acid. Ricinoleic acid was identified by FTIR (Fourier Transform Infrared Spectrophotometer) test standard ASTM E 1252-07 and its chemical composition was determined by Gas Chromatography-Mass Spectrometry (GC-MS). The identification of the type, amount, and environment of hydrogen in the compound was determined by Nuclear Magnetic Resonance (NMR). The analysis on characteristics, that is, transition and melting temperatures of material was performed by DSC (Differential Scanning Calorimetry) test standard ASTM D 3419-08.Based on the results of FTIR, GC-MS, ¹H-NMR, dan ¹³C-NMR tests, the spectra that were obtained indicated that the test substances were methyl and ricinoleic acid 70.349%. And, the results of DSC tests indicated that the characteristics of ricinoleic acid absorbed and released latent heat at the temperature from 8.58°C and absorbed sensible heat at the temperature from-7.17°C to 8.58°C.

Abstract: This paper proposes an approach for the detection of the single line to ground fault on a unit generator-transformer, based on the extraction of statistical parameters from wavelet transform based neural network. In the simulation, the current and voltage signals were found decomposed over wavelet analysis into several approximations and details. The simulation of the unit generator-transformer was carried out using the Sim-PowerSystem Blockset of MATLAB. The statistical parameters analysis involved measurement of the dispersion factors (range and standard deviation) of wavelet coefficients. Regarding the pattern recognition of neural networks performance, the accuracy of SLG-fault detection of neural networks was 97.45 %. The results indicated that dispersion factor feature of wavelet transforms was accurate enough in distinguishing a single line to ground-fault and normal condition for a unit generator-transformer.

Abstract: Voltage sag and harmonics are the most frequent power quality problems faced by industrial and commercial customers today. Situation has been aggravated by modern sensitive industrial equipments which introduce system harmonics due to their inherent V-I characteristics. In this paper, proportional integral (PI) control technique based dynamic voltage restorer (DVR) is implemented in power distribution system to suppress voltage sag and harmonics under linear, non-linear and induction motor load conditions. Real-time power distribution system and DVR test models are built in Matlab/Simulink software. Simulation results exhibit excellent PI control approach with effective performance yielding excellent voltage regulation.

Abstract: Polymeric material such as low density polyethylene (LDPE) has been used for decades as insulating material. Any polymeric material will experience degradation after prolonged application of high electrical stresses. Deeper understanding of the long term electrical degradation of the insulating material is necessary to predict the life of high voltage cable. Electroluminescence method (EL) is used to detect the breakdown voltages of thin film LDPE. This method utilizes a Peltier cooled electron multiplying charge coupled device (EMCCD) camera to detect the breakdown of the sample. Statistical distribution of the AC breakdown voltages of 100μm virgin and aged LDPE has been analysed. Comparison for the best fitted distribution was made for Weibull distribution and Johnson SB distribution using Anderson-Darling (A2) goodness-of-fit and Kolmogorov-Smirnov (D) goodness-of-fit (GOF). Johnson SB is rarely used in high voltage engineering application. The probability density function (PDF) and the cumulative density function (CDF) for both distributions are defined in this article. The statistical parameters used are estimated based on Maximum Likelihood Estimation (MLE) for both distributions. Based on the statistical analysis, it is observed that Johnson SB provide better fitting than Weibull distribution with lower fitting error and that 3-parameter Weibull is much better fitting than 2-parameter Weibull distribution for most cases. It is also found that the median breakdown voltage of LDPE samples decreases with increasing aging temperature.

Abstract: Distribution and power transformer is the essential part of electrical power transmission system. Abnormalities occur at the transformer can be interpreted and analysed to get the cause of faults, thus it can be further studied for monitoring ageing and condition of the transformer. A lot of studies have been done to detect as many abnormalities that can possibly arise in a transformer. For inexperienced user, it can be a bit of overwhelming to choose which studies that they can refer to. Numerous techniques and methods has been used for transformer monitoring till date and still being improved which includes: Common Electrical Tests, Power and Dissipation Factor Measurement, Partial Discharge (PD) Analysis, Frequency Response Analysis (FRA), Dielectric Response Analysis (DRA), Dissolved Gas Analysis (DGA), Dielectric Breakdown Voltage, Oil Resistivity, and Karl Fischer Titration. These techniques and methods are developed to monitor and analyse the common part of transformer which are winding, core, bushing, insulation oil, and insulation paper. This paper reviews the current improved techniques and methods in transformer monitoring according to the technology, accuracy, complexity, and cost for the past five years. A few methods and techniques can be appointed to each of classified user as a beginner, intermediate and competent. Finally, this paper suggests more improvement to be studied on the existing established methods. Some of the techniques can be combined to create a better accuracy and efficiency for fault identification, ageing estimation and condition monitoring.