Date of Award
2015
Document Type
Open Access Master's Thesis
Degree Name
Master of Science in Mechanical Engineering (MS)
Administrative Home Department
Department of Mechanical Engineering-Engineering Mechanics
Advisor 1
Amitabh Narain
Committee Member 1
V.C Rao Komaravolu
Committee Member 2
Sunil Mehendale
Abstract
Contemporary cooling applications necessitate the use of mm-scale shear driven flow condenser designs which also need to ensure substantial heat transfer rates for a wide range of flow conditions. Some modern shear driven flow condensers must meet the requirements of small size and large heat flux removal capability for variety of flow conditions. For this, effective estimates of heat transfer rate correlations and correlations for estimating the length of the annular regime are essential. Existing heat transfer correlations are built based on semi-empirical approaches which are primarily supported by large data sets, which are often mixed with insufficient explanation and also do not exhibit a direct relation to flow physics based modelling of condensing flows. Typical heat transfer correlations primarily eliminate the dependency of heat transfer coefficient on the method of cooling imposed on the cooling surface of the condenser. These correlations are typically reported in terms of vapor quality, on which the heat transfer coefficient depends. Correlations based on quality instead of physical distance are preferred because the rest depends on the "method of cooling". The energy balance equation is then used to obtain a spatial variation of vapor quality along the length of the condenser. However, in fundamental physics based approaches, heat transfer coefficients are significantly dependent on thermal boundary conditions. This study focuses on bridging the knowledge gap between the semi-empirical approaches of typical correlations in literature and the direct flow physics based fundamental results from theory, computation and experiments. This study further explains the equivalency of physics based modelling to typical approach under certain conditions.
An important factor that needs vigilant observation on typical heat transfer correlations is the obscurity associated with the application of flow regime maps for internal condensing flows. Heat transfer rate is strongly influenced by the type of flow, but several heat transfer correlations are presented that cover several different flow regimes. This means correlations approach and data have to be good enough to accommodate significant variations in the correlated values of the heat transfer rates among different flow regimes. Flow regime maps in literature are also inaccurate because the assembled data from different experiments are examples of data on thermal boundary conditions and the downstream physical distances and quality where transitions are observed. This is believed to be true as these flow regime map data are not properly non-dimensionalized or have not been differentiated by suitable flow physics, further exacerbating their use for different flow applications. The key objective of this study (primarily restricted to shear driven annular flow regimes) is to establish the need for heat transfer correlations which are fundamentally (based on flow physics) constructed and compare their predictions with these obtained from correlations and flow regime maps existing in literature. This study also provides a basic structure for creating similar new correlations for various other flow types and regimes. For annular flows this is done by using two numerical tools, one which is highly efficient but in an approximate flow simulation tool (A Quasi 1-D Simulation tool [2]) and a nearly exact 2-D steady/unsteady simulation tool [3].
Recommended Citation
Ravikumar, Siddharth, "ELEMENTARY ASSESSMENTS AND SIMULATIONS BASED PROPOSALS FOR NEW HEAT TRANSFER CORRELATIONS AND FLOW REGIME MAPS FOR ANNULAR/STRATIFIED REGIME OF SHEAR DRIVEN INTERNAL CONDENSING FLOWS", Open Access Master's Thesis, Michigan Technological University, 2015.