View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by University of Saskatchewan's Research Archive CONVECTIVE MASS TRANSFER BETWEEN A HYDRODYNAMICALLY DEVELOPED AIRFLOW AND LIQUID WATER WITH AND WITHOUT A VAPOR PERMEABLE MEMBRANE A Thesis Submitted to the College of Graduate Studies and Research in Partial Fulfillment of the Requirements for the Degree of Master of Science in the Department of Mechanical Engineering University of Saskatchewan Saskatoon By Conrad Raymond Iskra © Copyright Conrad Raymond Iskra, March 2007. All rights reserved. PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a Postgraduate degree from the University of Saskatchewan, I agree that the Libraries of this University may make it freely available for inspection. I further agree that permission for copying of this thesis in any manner, in whole or in part, for scholarly purposes may be granted by the professor who supervised my thesis work or, in his absence, by the Head of the Department or the Dean of the College in which my thesis work was done. It is understood that any copying or publication or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and to the University of Saskatchewan in any scholarly use which may be made of any material in my thesis. Requests for permission to copy or to make other use of material in this thesis in whole or part should be addressed to: Head of the Department of Mechanical Engineering University of Saskatchewan Saskatoon, Saskatchewan, S7N 5A9 i ABSTRACT The convective mass transfer coefficient is determined for evaporation in a horizontal rectangular duct, which forms the test section of the transient moisture transfer (TMT) facility. In the test facility, a short pan is situated in the lower panel of the duct where a hydrodynamically fully developed laminar or turbulent airflow passes over the surface of the water. The measured convective mass transfer coefficients have uncertainties that are typically less than ±10% and are presented for Reynolds numbers (ReD) between 560 and 8,100, Rayleigh numbers (RaD) between 6,100 and 82,500, inverse Graetz numbers (Gz) between 0.003 and 0.037, and operating conditions factors (H*) between -3.6 and -1.4. The measured convective mass transfer coefficients are found to increase as ReD, RaD, Gz and H* increase and these effects are included in the Sherwood number (ShD) correlations presented in this thesis, which summarize the experimental data. An analogy between heat and mass transfer is developed to determine the convective heat transfer coefficients from the experimentally determined ShD correlations. The convective heat transfer coefficient is found to be a function of ShD and the ratio between heat and moisture transfer potentials (S*) between the surface of the water and the airflow in the experiment. The analogy is used in the development of a new method that converts a pure heat transfer NuD (i.e., heat transfer with no mass transfer) and a pure mass transfer ShD (i.e., mass transfer with no heat transfer) into NuD and ShD that are for simultaneous heat and mass transfer. The method is used to convert a pure heat transfer NuD from the literature into the NuD and ShD numbers measured in this thesis. The results of the new method agree within experimental uncertainty bounds, while the ii results of the traditional method do not, indicating that the new method is more applicable than the traditional analogy between heat and mass transfer during simultaneous heat and mass transfer. A numerical model is developed that simulates convective heat and mass transfer for a vapor permeable Tyvek® membrane placed between an airflow and liquid water. The boundary conditions imposed on the surfaces of the membrane within the model are typical of the conditions that are present within the TMT facility. The convective heat and mass transfer coefficients measured in this thesis are applied in the model to determine the heat and moisture transfer through the membrane. The numerical results show that the membrane responds very quickly to a step change in temperature and relative humidity of the air stream. Since the transients occur over a short period of time (less than 1 minute), it is feasible to use a steady-state model to determine the heat and mass transfer rates through the material for HVAC applications. The TMT facility is also used to measure the heat and moisture transfer through a vapor permeable Tyvek® membrane. The membrane is in contact with a water surface on its underside and air is passed over its top surface with convective boundary conditions. The experimental data are used to verify the numerically determined moisture transfer rate through the Tyvek® membrane. The numerical model is able to determine the mass transfer rates for a range of testing conditions within ±26% of the experimental data. The differences between the experiment and the model could be due to a slightly different mass transfer coefficient for flow over Tyvek® than for flow over a free water surface. iii ACKNOWLEDGMENTS I wish to thank my supervisor, Professor Carey J. Simonson, for his guidance, knowledge and inspiration throughout my undergraduate and graduate program at the University of Saskatchewan. I give thanks to my committee members (Professor R.W. Besant and Professor David Sumner) for their input in making this thesis a success. I would like to thank my Mom and Dad and family for their love and support. Appreciation is also extended to the University of Saskatchewan, CFI and NSERC SRO for their financial support. iv DEDICATION I dedicate this work to my parents, Raymond and Elaine Iskra, my sister, Mrs. Sherry Gibson and her loving family. TABLE OF CONTENTS page PERMISSION TO USE....................................................................................................i ABSTRACT......................................................................................................................ii ACKNOWLEDGMENTS ..............................................................................................iv DEDICATION..................................................................................................................v TABLE OF CONTENTS................................................................................................vi LIST OF FIGURES ........................................................................................................ix LIST OF TABLES ........................................................................................................xiv NOMENCLATURE.......................................................................................................xv 1. INTRODUCTION........................................................................................................1 1.1 Introduction .............................................................................................................1 1.2 Convective Mass Transfer Coefficient....................................................................1 1.2.1 Literature Review...........................................................................................3 1.3 Convective Mass Transfer with a Permeable Membrane........................................7 1.3.1 Literature Review.........................................................................................11 1.4 Research Objectives ..............................................................................................14 1.5 Thesis Overview....................................................................................................15 2. EXPERIMENTAL FACILITY AND INSTRUMENTATION..............................16 2.1 Introduction ...........................................................................................................16 2.2 Apparatus and Procedure.......................................................................................16 2.2.1 Network of the Apparatus ............................................................................18 2.2.2 Test Section..................................................................................................20 2.2.3 Bottom Surface of the Test Section..............................................................22 2.2.4 Data Acquisition...........................................................................................23 2.2.5 Hydrodynamically Fully Developed Flow...................................................24 2.3 Measurements and Calibration of Instruments......................................................30 2.3.1 Temperature Sensors ....................................................................................30 2.3.2 Relative Humidity Sensors...........................................................................33 2.3.3 Gravimetric Load Sensors............................................................................35 2.3.4 Orifice Plate..................................................................................................36 2.3.5 Pressure Transducer .....................................................................................39 vi 3. DATA ANALYSIS .....................................................................................................41 3.1 Introduction ...........................................................................................................41 3.2 Transient