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Vapour-compression water chilling machines of large capacity (megawatts of refrigeration) are extensively utilised for process cooling in the manufacturing, chemical and food industries, and for cooling hot mines. If these machines under-perform, not only may the costs of consequent losses in production be considerable, but products or working conditions may degrade or become unsafe. Performance monitoring instrumentation, including water flow meters, fitted to machines on site may be infrequently calibrated, though. Therefore, the apparent performance of a machine, indicated by the measurements in its water circuits, should be verified through independent, confirming measurements in its refrigerant circuit. For custom-built machines with screw compressors, though, there is a difficulty with so verifying apparent performance. The oil cooling load of screw compressors is large, and so must be taken into account in such verification. If the oil is cooled by water, it is easy to measure oil cooling load, but not if the oil is cooled by condensed liquid refrigerant in a thermosyphon ‘loop’, because of the two-phase flow of the refrigerant there. This research report describes a study done on a water chilling machine with a screw compressor, using ammonia as refrigerant, at KDC East Mine, Westonaria, South Africa. This study was of a proposed, alternative way of determining the oil cooling load – by measuring flows and properties in the oil circuit. The oil cooling load so determined could be independently verified by measurements in the water circuit of this machine’s oil-to-water cooler. The chief problem in determining oil cooing load from measurements in the oil circuit is that the ‘oil’ is not pure lubricant, but a solution of oil and refrigerant. Therefore the most accurate available methods of predicting the thermophysical properties of oil-ammonia solutions were identified and employed. The oil cooling load hence determined agreed within 0.43 per cent with that determined on the water side of the oil cooler. It was hence used to correct the coefficient of performance (COP) calculated from measurements in the machine’s refrigerant circuit. This corrected refrigerant-circuit COP, with the estimate of total mechanical power input to the machine, were then used to indirectly estimate the machine’s water chilling load. This indirectly estimated load compared very closely, within 1.12 per cent, to the apparent water chilling load determined from the measurements in the machine’s water circuits. It is concluded that in this study, oil cooling load could be determined with satisfactory accuracy from measurements in the oil circuit. Hence, this proposed technique offers promise of being a useful and practicable development, enabling apparent performance of such machines to be more conveniently verified than hitherto.

在近期的研究結果中, 相分離被發現發生在具非晶結構的Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅合金，而該合金的構成元素之間的有負值的混合焓。通過高分辨率透射電子顯微鏡的直接成像的方法，他們為Pd-Ni-P非晶系統相分離的發生提供了證據。 / 在這篇論文所論述的研究工作中，我們運用類似的技術來研究Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093}的合金系統從 x = 0到3.5的非晶相分離。 / 實驗結果顯示，任何在空氣中冷卻到578 K再在613K退火一小時的樣品 (乙類樣本)，非晶相分離都沒有發生。然而，在613K退火一小時而沒有經過578K和613K溫度範圍的Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093}大塊非晶金屬(丙類樣本)，卻在部分成分範圍中發生相分離。在丙類樣本中，當x>1，相分離發生；而當x≤1，相分離沒有發生。通過量度高角環形暗場影像中顯示的兩個相的平均波長，我們可得出其統計結果，而該統計結果與槓桿規則吻合。從此可見，在過冷的Pd-Ni-P熔合合金中存在著亞穩液態混溶間隙。並且這種出現在有負值混合焓的系統的亞穩液態混溶間隙，可以以短程有序的模型來解釋。 / Recently, the phase separation was found in the system of amorphous Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅ alloys which has negative heat of mixing among the constituent elements. In their work, the directly imaging method by technique of high resolution TEM provided the evidence of phase separation in amorphous Pd-Ni-P system. / In this work, by applying the similar technique of that previous studies, the alloy systems of Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093} for x = 0 to 3.5were studied for amorphous phase separation. / The experimental result showed that for any sample which was allowed to cool down in air to 578 K before thermal annealing (B-type), there was no amorphous phase separation. But for the Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093} BMG that was annealed at 613K for one hour without bypassing the temperature range between 578K and 613K (C-type), phase separation occurred with x>1 but absented when x≤1. The result of average wavelength measurement of the two phases in the HAADF images of the sample with phase separation obeyed the lever rule. This result suggested that in undercooled molten Pd-Ni-P alloys, there is a metastable liquid state miscibility gap. The formation of such miscibility gap in a system with negative heat of mixing can be explained by the model of unique short range orders. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Lau, Man Tat = 過冷鈀、鎳、磷熔化物中的亞穩液態互溶間隙 / 劉文達. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstracts also in Chinese. / Lau, Man Tat = Guo leng ba, nie, lin rong hua wu zhong de ya wen ye tai hu rong jian xi / Liu Wenda. / Abstract --- p.i / Acknowledgement --- p.iv / List of Tables --- p.vii / List of Figures --- p.viii / Chapter Chapter 1 --- : Introduction --- p.1 / Chapter 1.1 --- Amorphous metal --- p.1 / Chapter 1.2 --- Phase Separation --- p.3 / Chapter 1.3 --- Nucleation --- p.6 / Chapter 1.4 --- Spinodal Decomposition --- p.10 / Chapter 1.5 --- Objective of the project --- p.16 / Figures --- p.18 / References --- p.26 / Chapter Chapter 2 --- : Experiment --- p.27 / Chapter 2.1 --- Preparation of sample --- p.27 / Chapter 2.2 --- Differential scanning calorimetry --- p.30 / Chapter 2.3 --- Preparation of TEM sample --- p.31 / Chapter 2.4 --- Microstructural analysis --- p.33 / Figures --- p.36 / References --- p.39 / Chapter Chapter 3 --- : A metastable liquid state miscibility gap in undercooled Pd-Ni-P melts --- p.40 / Chapter 3.1 --- Introduction --- p.40 / Chapter 3.2 --- Materials and experimental --- p.41 / Chapter 3.3 --- Results --- p.44 / Chapter 3.4 --- Discussions --- p.49 / Chapter 3.5 --- Conclusions --- p.52 / Table --- p.53 / Figures --- p.54 / References --- p.75

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We have developed simple and inexpensive laser systems using grating-feedback diode lasers with electronic feedback to the injection current. These grating-feedback lasers can be continuously scanned up to 10 GHz and have a linewidth of 150 kHz. The three electronic frequency-stabilization systems we developed use polarization spectroscopy, etalon transmission and modified heterodyne signals as the frequency discriminators to drive an integrating servo control circuit. These laser systems are used for laser cooling and trapping of rubidium and atomic beam diagnostics. The rubidium D��� line at 780 nm is a strong, cycling transition that can be used for laser cooling and trapping. We use chirped cooling and Zeeman-tuned cooling to slow atoms from a thermal atomic beam. These atoms are loaded into a two-dimensional magneto-optic trap, or funnel. Using a frequency offset of the trapping lasers, the atoms are ejected from the funnel at a controllable velocity. The diode laser systems we have developed are a central component of this rubidium atomic funnel. We will use the funnel's bright, cold atomic beam as a source for matter-wave interferometry. We also developed an ionization detector to measure the flux and the spatial profile of the atomic beam when the background of scattered light makes fluorescent detection difficult. / Graduation date: 1997