Date of Award

6-2019

Degree Name

Doctor of Philosophy

Department

Mechanical and Aerospace Engineering

First Advisor

Dr. Claudia Fajardo-Hansford

Second Advisor

Dr. Parviz Merati

Third Advisor

Dr. HoSung Lee

Fourth Advisor

Dr. Christopher Cho

Keywords

transitional flows, heat transfer, low-Reynolds

Abstract

Turbulent flows are intrinsic to most fluid-based engineering systems, including internal combustion engines. In these devices, mixing, scalar transport and heat transfer are both critical for proper operation and challenging to model. In previous work, Kreun et al. [1] modeled a pre-heated intake manifold of a Diesel engine for cold-start simulations. Accurately predicting the heat transfer at the intake port proved to be a challenging task. Existing heat transfer correlations yielded predictions which were (at best) within 20% of the measured values. The discrepancy was attributed to a mismatch between the range of applicability of existing heat transfer models and cold-cranking conditions. This is because the intake runners are typically not long enough for the flow to fully develop and cranking speeds are not high enough to induce a wholly turbulent gas flow. Accurately predicting heat transfer in non-fully developed, transitional flows remains a difficult task. While several empirical correlations have been developed for turbulent, fully-developed flow at 𝑅𝑒>104, many applications rely on flows in transition, spanning a range of 2300<𝑅𝑒<104, as well as low Reynolds number turbulent flows. In this regime, most of the correlations are based on interpolated values with very limited direct measurements. Hence, there is a need for accurate heat transfer correlations based on direct velocity and temperature measurements for transitional and low Reynolds numbers turbulent flows.

To address this need, simultaneous flow-field/heat transfer measurements were conducted to develop correlations for calculating the Nusselt number (hence the convective heat transfer coefficient) for low-Reynolds number flows, and under steady-state constant heat flux conditions. Measurements of temperature and velocity were conducted for combined entry, which refers to a simultaneously (thermally and hydrodynamically) developing flow. Three experimental configurations were investigated: uniform, tripped flow, and ninety-degree entrance. These conditions were explored both to test the range of applicability of the developed correlations and to replicate conditions that might be found in reciprocating internal combustion engine runners. Experimental results were correlated in terms of the governing dimensionless numbers to develop an accurate model for heat transfer for the targeted regime and pipe lengths.

Access Setting

Dissertation-Open Access

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