Mechanical Engineering - Research Publications
Permanent URI for this collection
Search Results
1 - 7 of 7
-
ItemAn ice thermal storage computer model(Elsevier, 2001-12-01)In hot humid countries such as Thailand, air conditioning plant is installed in most commercial and industrial buildings. A conventional air conditioning system, which is normally operated when cooling is required, is the most favored option. Ice thermal storage on a large scale, used to provide a cool reservoir for use in peak periods, is however an attractive financial option for large buildings to supply coolness. There are two means of operating ice thermal storage systems, namely full storage and partial storage. In this paper, a computer model has been developed in order to compare energy use in conventional air cooling systems and ice thermal storage systems. Under Thailand electricity tariff rates, the results from the simulations show that the full ice thermal storage can save up to 55% of the electricity cost required for cooling per month when compared with the conventional system. It is also found that using full storage option can reduce the total energy consumption by 5% for the selected building.
-
ItemBenefits of cool thermal storage in Thailand(RERIC, 2001-06-01)The use of thermal storage on a large to provide a cool reservoir for use in peak periods is an attractive financial option for large hotels, hospitals or office blocks. This enables the refrigeration plant to operate more effectively and to be completely or partially shut down during peak periods when the demand can be met in full or in part from the cool store. In this paper an overview is given of the power generation capacity and costing structure in Thailand and a typical load profile is presented to illustrate the advantages to be gained by shifting plant operation to off-peak periods. Specific load calculations have been utilized to demonstrate the cost savings possible by incorporation of such a cool thermal storage system into a traditional refrigeration and air conditioning plant for a major hotel complex.
-
ItemEffects of changing aspect ratio through a wind tunnel contraction(American Institute of Aeronautics & Astronautics, 2001)No abstract.
-
ItemExperimental study of wall boundary conditions for large-eddy simulation( 2001)An experimental investigation was conducted to study the wall boundary condition for large-eddy simulation (LES) of a turbulent boundary layer at R = 3500. Most boundary condition formulations for LES require the specification of the instantaneous filtered wall shear stress field based upon the filtered velocity field at the closest grid point above the wall. Three conventional boundary conditions are tested using simultaneously obtained filtered wall shear stress and streamwise and wallnormal velocities, at locations nominally within the log region of the flow. This was done using arrays of hot-film sensors and x-wire probes. The results indicate that models based on streamwise velocity perform better than those using the wall-normal velocity, but overall significant discrepancies were found for all three models. A new model is proposed which gives better agreement with the shear stress measured at the wall. The new model is also based on the streamwise velocity but is formulated so as to be consistent with `outer-flow' scaling similarity of the streamwise velocity spectra. It is therefore expected to be more generally applicable over a larger range of Reynolds numbers at any first-grid position within the log region of the boundary layer.
-
ItemEvolution and structure of sink-flow turbulent boundary layers( 2001)An experimental and theoretical investigation of turbulent boundary layers developing in a sink-flow pressure gradient was undertaken. Three flow cases were studied, corresponding to different acceleration strengths. Mean-flow measurements were taken for all three cases, while Reynolds stresses and spectra measurements were made for two of the flow cases. In this study attention was focused on the evolution of the layers to an equilibrium turbulent state. All the layers were found to attain a state very close to precise equilibrium. This gave equilibrium sink flow data at higher Reynolds numbers than in previous experiments. The mean velocity profiles were found to collapse onto the conventional logarithmic law of the wall. However, for profiles measured with the Pitot tube, a slight ‘kick-up’ from the logarithmic law was observed near the buffer region, whereas the mean velocity profiles measured with a normal hot wire did not exhibit this deviation from the logarithmic law. As the layers approached equilibrium, the mean velocity profiles were found to approach the pure wall profile and for the highest level of acceleration Π was very close to zero, where Π is the Coles wake factor. This supports the proposition of Coles (1957), that the equilibrium sink flow corresponds to pure wall flow. Particular interest was also given to the evolutionary stages of the boundary layers, in order to test and further develop the closure hypothesis of Perry, Marusic & Li (1994). Improved quantitative agreement with the experimental results was found after slight modification of their original closure equation.
-
ItemOn the different contributions of coherentstructures to the spectra of a turbulent round jetand a turbulent boundary layer(Cambridge University Press, 2001)This paper examines and compares spectral measurements from a turbulent round jetand a turbulent boundary layer. The conjecture that is examined is that both flows consist of coherent structures immersed in a background of isotropic turbulence. In the case of the jet, a single size of coherent structure is considered, whereas in the boundary layer there are a range of sizes of geometrically similar structures. The conjecture is examined by comparing experimental measurements of spectra for the two flows with the spectra calculated using models based on simple vortex structures.The universality of the small scales is considered by comparing high-wave number experimental spectra. It is shown that these simple structural models give a good account of the turbulent flows.
-
ItemOn the role of large-scale structures in wall turbulence(American Institute of Physics, 2001-03)Recent experimental and computational studies by Adrian and co-workers, such as Adrian et al. [J. Fluid Mech. 422, 1 (2000)] and Zhou et al. [J. Fluid Mech. 387, 353 (1999)], have proposed that a dominant structure in wall turbulence is the organization of hairpin vortices in spatially correlated packets or trains of vortices. In this study this scenario is investigated using the attached eddy model of Perry and Marusic [J. Fluid Mech. 298, 361 (1995)] by calculating structure angles, two-point velocity correlations and autocorrelations and comparing them to experimental measurements across a zero-pressure-gradient turbulent boundary layer. The results support the conclusion that spatially coherent packets are a statistically significant structure for Reynolds stresses and transport processes in the logarithmic region of the flow.