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Ren Liyuan = 小寬高比熱對流中高精度Nusselt數和局部溫度測量 / 任立元. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 64-66). / Text in English; abstracts in English and Chinese. / Ren Liyuan = Xiao kuan gao bi re dui liu zhong gao jing du Nusselt shu he ju bu wen du ce liang / Ren Liyuan. / Abstract (in English) --- p.i / Abstract (in Chinese) --- p.ii / Acknowledgements --- p.iii / Table of Contents --- p.iv / List of Figures --- p.vi / List of Tables --- p.ix / Chapters / Chapter I. --- Turbulent Rayleigh-Benard Convection --- p.1 / Chapter 1.1 --- Introduction of Rayleigh-Benard Convection --- p.1 / Chapter 1.2 --- The Convection Equations --- p.2 / Chapter 1.3 --- The parameters --- p.3 / Chapter 1.4 --- Background --- p.5 / Chapter 1.5 --- Synopsis of this thesis --- p.8 / Chapter II. --- Experimental Setup and Methods --- p.9 / Chapter 2.1 --- The Apparatus --- p.9 / Chapter 2.2 --- Thermistor Calibration --- p.12 / Chapter III. --- Local temperature measurements --- p.19 / Chapter 3.1 --- Introduction and motivation --- p.19 / Chapter 3.2 --- Local temperature measurements --- p.20 / Chapter 3.3 --- Temperature time series and histograms --- p.20 / Chapter 3.4 --- Mean temperature profile --- p.24 / Chapter 3.5 --- Summery --- p.35 / Chapter 3.6 --- Appendix A: Data lists for this chapter --- p.36 / Chapter IV --- Heat transport measurement --- p.39 / Chapter 4.1 --- Introduction and Motivation --- p.39 / Chapter 4.2 --- Heat transfer measurements --- p.40 / Chapter 4.3 --- Experimental uncertainties associated with high-precision measurements of Nu --- p.41 / Chapter 4.3.1 --- Cell height measurement --- p.41 / Chapter 4.3.2 --- Temperature measurement --- p.41 / Chapter 4.3.3 --- Thermal source --- p.41 / Chapter 4.3.4 --- Thermal leakage --- p.42 / Chapter 4.3.5 --- Sidewalleffect --- p.44 / Chapter 4.3.6 --- Long time measurement --- p.44 / Chapter 4.4 --- Results and discussion --- p.45 / Chapter 4.4.1 --- Experimental data --- p.45 / Chapter 4.4.2 --- Finite conductivity effect --- p.47 / Chapter 4.4.3 --- Nu dependence on Г --- p.49 / Chapter 4.4.4 --- Nu dependence on Ra --- p.50 / Chapter 4.5 --- Summary --- p.53 / Chapter 4.6 --- Appendix B: Data lists for this chapter --- p.54 / Chapter V. --- Conclusions --- p.62 / References --- p.64

Cheung Yin Har = 瑞利-柏納德湍流對流中Nusselt與縱橫比的關係以及邊界層性質的研究 / 張燕霞. / Thesis submitted in: October 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 115-119). / Text in English; abstracts in English and Chinese. / Cheung Yin Har = Ruili-Bonade tuan liu dui liu zhong Nusselt yu zong heng bi de guan xi yi ji bian jie ceng xing zhi de yan jiu / Zhang Yanxia. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgments --- p.iv / Contents --- p.v / List of Figures --- p.vii / List of Tables --- p.x / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background of turbulence --- p.1 / Chapter 1.2 --- Rayleigh-Benard convection --- p.3 / Chapter 1.3 --- Theoretical background --- p.4 / Chapter 1.3.1 --- The convection equations --- p.4 / Chapter 1.3.2 --- Characteristic parameters --- p.6 / Chapter 1.3.3 --- Reynolds equations --- p.8 / Chapter 1.4 --- Recent developments --- p.10 / Chapter 1.4.1 --- Heat transport --- p.10 / Chapter 1.4.2 --- Large scale flow and thermal plumes --- p.11 / Chapter 1.4.3 --- Boundary layers --- p.12 / Chapter 1.5 --- Motivation --- p.14 / Chapter 1.5.1 --- Nusselt measurements --- p.14 / Chapter 1.5.2 --- Boundary layer properties measurements --- p.14 / Chapter 1.6 --- Synopsis of this thesis --- p.15 / Chapter Chapter 2 --- Experimental setup and measurement techniques --- p.17 / Chapter 2.1 --- The turbulent convection system --- p.17 / Chapter 2.1.1 --- The convection cells --- p.18 / Chapter 2.1.2 --- The temperature probe --- p.21 / Chapter 2.1.3 --- The thermistors --- p.23 / Chapter 2.2 --- Particle Image Velocimetry (PIV) --- p.25 / Chapter 2.2.1 --- Image capture system --- p.27 / Chapter 2.2.2 --- Image analysis system --- p.36 / Chapter Chapter 3 --- Aspect ratio dependence of heat transport and the flow field --- p.39 / Chapter 3.1 --- Motivation for this experiment --- p.39 / Chapter 3.2 --- Heat transfer efficiency measurements --- p.40 / Chapter 3.3 --- Heat correction --- p.44 / Chapter 3.3.1 --- Temperature correction --- p.44 / Chapter 3.3.2 --- Heat current density J correction --- p.45 / Chapter 3.3.3 --- Finite conductivity of plate --- p.50 / Chapter 3.4 --- Aspect ratio dependence --- p.51 / Chapter 3.4.1 --- Without correction of finite conductivity --- p.51 / Chapter 3.4.2 --- With correction of finite conductivity --- p.59 / Chapter 3.5 --- Time-averaged velocity field --- p.65 / Chapter 3.6 --- Summary --- p.70 / Chapter Chapter 4 --- Local temperature and velocity measurements near the boundary layers --- p.71 / Chapter 4.1 --- Motivation for this experiment --- p.71 / Chapter 4.2 --- Temperature profile measurement --- p.72 / Chapter 4.2.1 --- Temperature and fluctuation profiles --- p.73 / Chapter 4.2.2 --- Thermal boundary thickness --- p.77 / Chapter 4.2.3 --- Temperature time series --- p.79 / Chapter 4.2.4 --- PDF --- p.83 / Chapter 4.3 --- Velocity profile measurement --- p.86 / Chapter 4.3.1 --- 2D velocity and fluctuation profiles --- p.86 / Chapter 4.3.2 --- Scaling properties --- p.93 / Chapter 4.4 --- Shear stress --- p.98 / Chapter 4.4.1 --- Viscous and Reynolds stresses --- p.99 / Chapter 4.4.2 --- Laminar or Turbulent? --- p.101 / Chapter 4.5 --- Summary --- p.104 / Chapter Chapter 5 --- Conclusion --- p.106 / Chapter 5.1 --- Heat flux measurement --- p.106 / Chapter 5.2 --- Boundary layers --- p.107 / Chapter 5.3 --- Perspective for further investigation --- p.108 / Appendix A Heat flux measurement for high Prandtl number --- p.109 / Chapter I. --- Experimental conditions --- p.110 / Chapter II. --- Result and discussion --- p.112 / Chapter III. --- Summary and perspective for further investigation --- p.114 / Bibliography --- p.115

Chan, Tak Shing = 粗糙表面的熱湍流對流的Nusselt數和雷諾數的測量 / 陳德城. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 63-67). / Abstracts in English and Chinese. / Chan, Tak Shing = Cu cao biao mian de re tuan liu dui liu de Nusselt shu he Leinuo shu de ce liang / Chen Decheng. / Table of Contents --- p.v / List of Figures --- p.xi / List of Tables --- p.xii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- What is turbulence ? --- p.1 / Chapter 1.2 --- Rayleigh Benard convection system --- p.3 / Chapter 1.2.1 --- Oberbeck-Boussinesq approximation and equations of Rayleigh- Benard system --- p.5 / Chapter 1.2.2 --- Some coherent structures of Rayleigh-Benard convection system --- p.7 / Chapter 1.3 --- Motivation --- p.8 / Chapter 2 --- Experimental methods and setups --- p.12 / Chapter 2.1 --- Convection cell --- p.12 / Chapter 2.2 --- Temperature measurement --- p.15 / Chapter 2.3 --- Experimental techniques --- p.16 / Chapter 2.3.1 --- Heat leakage prevention --- p.16 / Chapter 2.3.2 --- Water absorption of Dipropylene Glycol --- p.21 / Chapter 2.3.3 --- Particle Image Velocimetry --- p.22 / Chapter 3 --- Heat flux measurement --- p.25 / Chapter 3.1 --- Water Results --- p.26 / Chapter 3.1.1 --- Experimental procedures --- p.26 / Chapter 3.1.2 --- Heat leakage/ heat absorption estimation --- p.27 / Chapter 3.1.3 --- Results and discussions --- p.29 / Chapter 3.2 --- Dipropylene Glycol Results --- p.32 / Chapter 3.2.1 --- Experimental procedures --- p.32 / Chapter 3.2.2 --- Heat leakage/ heat absorption estimation --- p.33 / Chapter 3.2.3 --- Result and discussions --- p.34 / Chapter 3.3 --- More discussion --- p.41 / Chapter 4 --- Large scale circulation and Reynolds number measurement --- p.44 / Chapter 4.1 --- Flow pattern of turbulent Rayleigh-Benard convection over rough plates --- p.46 / Chapter 4.2 --- Reynolds number measurement --- p.48 / Chapter 4.2.1 --- Reynolds number determined from oscillation of temper- ature signals --- p.48 / Chapter 4.2.2 --- Reynolds number determined from velocity measurement near sidewall --- p.55 / Chapter 5 --- Conclusion --- p.61 / Chapter 5.1 --- Conclusion --- p.61 / Bibliography --- p.63

During the past decade research has shown that global warming may have disastrous effects on our planet. In order to limit the damage that the human race seems to be causing, it was acknowledged that substances with a high global warming potential (GWP) should be phased out. In due time, R-134a with a GWP = 1300, may probably be phased out to make way for nature friendly refrigerants with a lower GWP. One of these contenders is carbon dioxide, R-744, with a GWP = 1. Literature revealed that various Nusselt number (Nu) correlations have been developed to predict the convection heat transfer coefficients of supercritical R-744 in cooling. No proof could be found that any of the reported correlations accurately predict Nusselt numbers (Nus) and the subsequent convection heat transfer coefficients of supercritical R-744 in cooling. Although there exist a number of Nu correlations that may be used for R-744, eight different correlations were chosen to be compared in a theoretical simulation program forming the first part of this study. A water-to-transcritical R-744 tube-in-tube heat exchanger was simulated. Although the results emphasise the importance of finding a more suitable Nu correlation for cooling supercritical R-744, no explicit conclusions could be made regarding the accuracy of any of the correlations used in this study. For the second part of this study experimental data found in literature were used to evaluate the accuracy of the different correlations. Convection heat transfer coefficients, temperatures, pressures and tube diameter were employed for the calculation of experimental Nusselt numbers (Nuexp). The theoretical Nu and Nuexp were then plotted against the length of the heat exchanger for different pressures. It was observed that both Nuexp and Nu increase progressively to a maximal value and then decline as the tube length increases. From these results it were possible to group correlations according to the general patterns of their Nu variation over the tube length. Graphs of Nuexp against Nus, calculated according to the Gnielinski correlation, generally followed a linear regression, with R2 > 0.9, when the temperature is equal or above the pseudocritical temperature. From this data a new correlation, Correlation I, based on average gradients and intersects, was formulated. Then a modification on the Haaland friction factor was used with the Gnielinski correlation to yield a second correlation, namely Correlation II. A third and more advanced correlation, Correlation III, was then formulated by employing graphs where gradients and y-intercepts were plotted against pressure. From this data a new parameter, namely the turning point pressure ratio of cooling supercritical R-744, was defined. It was concluded that the employed Nu correlations under predict Nu values (a minimum of 0.3% and a maximum of 81.6%). However, two of the correlations constantly over predicted Nus at greater tube lengths, i.e. below pseudocritical temperatures. It was also concluded that Correlation III proved to be more accurate than both Correlations I and II, as well as the existing correlations found in the literature and employed in this study. Correlation III Nus for cooling supercritical R-744 may only be valid for a diameter in the order of the experimental diameter of 7.73 mm, temperatures that are equal or above the pseudocritical temperature and at pressures ranging from 7.5 to 8.8 MPa. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2010.

During the past decade research has shown that global warming may have disastrous effects on our planet. In order to limit the damage that the human race seems to be causing, it was acknowledged that substances with a high global warming potential (GWP) should be phased out. In due time, R-134a with a GWP = 1300, may probably be phased out to make way for nature friendly refrigerants with a lower GWP. One of these contenders is carbon dioxide, R-744, with a GWP = 1. Literature revealed that various Nusselt number (Nu) correlations have been developed to predict the convection heat transfer coefficients of supercritical R-744 in cooling. No proof could be found that any of the reported correlations accurately predict Nusselt numbers (Nus) and the subsequent convection heat transfer coefficients of supercritical R-744 in cooling. Although there exist a number of Nu correlations that may be used for R-744, eight different correlations were chosen to be compared in a theoretical simulation program forming the first part of this study. A water-to-transcritical R-744 tube-in-tube heat exchanger was simulated. Although the results emphasise the importance of finding a more suitable Nu correlation for cooling supercritical R-744, no explicit conclusions could be made regarding the accuracy of any of the correlations used in this study. For the second part of this study experimental data found in literature were used to evaluate the accuracy of the different correlations. Convection heat transfer coefficients, temperatures, pressures and tube diameter were employed for the calculation of experimental Nusselt numbers (Nuexp). The theoretical Nu and Nuexp were then plotted against the length of the heat exchanger for different pressures. It was observed that both Nuexp and Nu increase progressively to a maximal value and then decline as the tube length increases. From these results it were possible to group correlations according to the general patterns of their Nu variation over the tube length. Graphs of Nuexp against Nus, calculated according to the Gnielinski correlation, generally followed a linear regression, with R2 > 0.9, when the temperature is equal or above the pseudocritical temperature. From this data a new correlation, Correlation I, based on average gradients and intersects, was formulated. Then a modification on the Haaland friction factor was used with the Gnielinski correlation to yield a second correlation, namely Correlation II. A third and more advanced correlation, Correlation III, was then formulated by employing graphs where gradients and y-intercepts were plotted against pressure. From this data a new parameter, namely the turning point pressure ratio of cooling supercritical R-744, was defined. It was concluded that the employed Nu correlations under predict Nu values (a minimum of 0.3% and a maximum of 81.6%). However, two of the correlations constantly over predicted Nus at greater tube lengths, i.e. below pseudocritical temperatures. It was also concluded that Correlation III proved to be more accurate than both Correlations I and II, as well as the existing correlations found in the literature and employed in this study. Correlation III Nus for cooling supercritical R-744 may only be valid for a diameter in the order of the experimental diameter of 7.73 mm, temperatures that are equal or above the pseudocritical temperature and at pressures ranging from 7.5 to 8.8 MPa. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2010.

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D.Ing.

M.Ing. / Heat pump water heaters (HPWHs) have been identified as a viable replacement for electrical resistance heaters due to their high efficiency and reliability. Heat exchangers are a crucial part of HPWHs, and play a vital role in improving the system's coefficient of performance (COP). Experimentally analysing a heat exchanger is usually a slow and highly labour intensive practice since vast amounts of data have to be logged and mathematically manipulated to obtain results. A lot of time and money could be saved, if this process were to be automated. The first objective of this study was to develop a software program capable of calculating the heat transfer correlation constants of a tube-in-tube heat exchanger using the modified Wilson plot technique from data obtained through water-to-water experimentation at different flow rates and temperatures. The data was to be captured by using data acquisition equipment capable of measuring temperature from several Ptl 00-type temperature sensors, pressure transducers as well as Coriolis flow meters, all within a few seconds, thus giving virtually steady-state measurements. The second objective of this study was to develop a software package, capable of capturing and manipulating data from a HPWH system using the same tube-in-tube heat exchanger and using R-22 as refrigerant. The software package had to be capable of capturing all the required experimental data from the system and calculate the local and average heat transfer coefficients on-line and display it to the user. It also had to capture it in the form of a spreadsheet data file for further manipulation. The success of the software package would depend on the results achieved, as well as the time saved with its implementation. To verify the results, the output of the program was compared with the findings of various other researchers. It was found that the output of the program compared well with the results obtained by other researchers, both for the average heat transfer coefficient as well as the local heat transfer coefficients. The time taken for a full set of data was as little as 30 minutes, compared to many hours previously needed to achieve stable results. The software package has thus succeeded in fulfilling its objective to reduce the time taken to achieve accurate results during heat transfer experimentation.