A modelling and experimental study of nucleate boiling for application to IC engines.
2014-01-14T12:33:47Z (GMT) by
This thesis describes the development of experimental and predictive techniques for analysing boiling heat transfer for internal combustion engine cooling systems. Environmental and packaging requirements are placing increasing demands on the emission and power density characteristics of internal combustion engines. To meet these demands, boiling heat transfer is proposed as a means of achieving higher heat transfer rates than is possible with conventional forced convection. A novel experimental method developed using electrically heated indium tin oxide (ITO) coated glass in conjunction with a bubble image analysis system allowed new boiling data to be obtained. This allowed the study of boiling from a new perspective with higher data analysis rates than was possible in previous reported work. It also enabled, for the first time, direct, non-contact measurement of bubble/liquid void fraction. The data from these experiments was compared with predictions from a computational fluid dynamics (CFO) package known as CFX-4. The predictions for the percentage of the heated surface covered in vapour were shown to be strongly dependent on the bubble diameter and nucleation site density submodels. These values were in turn demonstrated to be dependent on the surface finish of the heated surface. ITO coated glass was successfully implemented for the study of boiling heat transfer. The data from this work allowed a new evaluation of the predictive abilities of the CFO boiling models. The standard default bubble diameter and site density submodel equations, whose lack of universal applicability has been demonstrated, were replaced with new empirically based equations that provided more accurate predictions. As a result, a new design methodology for practical application of nucleate boiling to rc engme cooling galleries was proposed. This method introduced an experimental stage early in the design process to obtain bubble diameter and site density data for when boiling occurs on the surface to be used in the finished product. These data provide empirically based submodels for use in CFO subroutines. These ensure that more accurate results can be obtained than would be possible with the standard default submodel equations.