A NOVEL THERMAL CONDUCTIVITY MEASUREMENT
OF FLUIDS WITH CHANGING AND ANISOTROPIC STRUCTURE
DUE TO SHEARING FLOW
[Thermal Conductivity Apparatus with Computerized Data Acquisition]

NATIONAL SCIENCE FOUNDATION (NSF) FINAL PROJECT REPORT
NSF-CTS Award No. 9523519

The objectives of this project were to employ an innovative method to measure the fluid thermal conductivity while in shearing flow, and to determine its dependence on the shearing itself, contrary to the current state-of-the-art of measuring thermal conductivity under the condition of motionless fluid. It is known that some fluid structure could be affected by shearing (becoming fiber-like, non-uniform and non-isotropic), particularly for high molecular polymeric solutions or other rheologically complex non-Newtonian fluids. Therefore, it is important to measure the thermal conductivity corresponding to actual fluid structure while undergoing shearing flow.

A concentric-cylinders apparatus was developed to provide controlled heat transfer in the radial direction, orthogonal to the circumferential fluid velocity. Therefore, the fluid velocity component in the direction of heat flow is zero, thus virtually preserving pure conductive heat transfer mode. The measurement and control are accomplished and integrated by using a computerized data acquisition system and a comprehensive virtual instrument, developed using the LabVIEW application software.

It was found that the thermal conductivity of a Newtonian fluid, such as distilled water, was virtually independent of the fluid motion. However, for non-Newtonian fluids such as 1000 and 2000 wppm aqueous polyacrylamide (Praestol) solutions, there was up to a 10-20% increase of thermal conductivity in the operating shear rate range (40£ g [1/sec] £ 510) at 27° C.

Publications resulting from this award:

1. Kostic, M., "Data Acquisition and Control Using LabVIEW® Virtual Instrument for An Innovative Thermal Conductivity Apparatus," Virtual Instrumentation in Education Conference (at MIT and UCB) June 1997, also NIWeek 97 Annual Conference, National Instruments, Austin, TX, August 1997.
2. Tong H., "A Novel Thermal Conductivity Measurement of Fluids with Changing and Anisotropic Structure Due to Shearing Flow," MS Thesis, Northern Illinois University, 1997.
3. Kostic, M., "Instrumentation with Computerized Data Acquisition for an Innovative Thermal Conductivity Apparatus." ASEE 1997 Annual Conference, American Society for Engineering Education, 1997.
4. Kostic, M. and H. Tong, "Innovative Thermal Conductivity Apparatus for Testing of Complex Fluids," Manuscript in preparation for journal publication, Northern Illinois University, DeKalb, IL, 1997.
5. H. Tong and M. Kostic, "Thermal Conductivity Measurement of Polyacrylamide Solutions While in Shearing Flow - The First Results," Manuscript in preparation for journal publication, Northern Illinois University, DeKalb, IL, 1997.

Due to special circumstances, extended project time and additional support by the University, the emphasis was on developing, fabricating, and heavily instrumenting and computerizing the apparatus [see Ref. 1-4]. A graduate thesis was defined based on this project and successfully completed [2]. The College relocation to a new and modern building and related demand on everybody's time was slowing the work rate on this project but also providing additional resources and additional funding for developing and fabricating the apparatus. The Engineering College and ME Department's decision to invest in and develop computerized data acquisition and the PI's extensive involvement in that area were crucial in developing the apparatus beyond the proposed scope of this small project [1, 3, 4]. On the other hand, after spending a lot of time and resources on apparatus development, calibration and testing [2], the remaining limited time was used on thorough investigation of thermal conductivity of a rather limited number of non-Newtonian fluids, namely 1000 and 2000 wppm aqueous polyacrylamide (brand name Praestol, by Stockhausen) solutions [5]. It was found that the thermal conductivity of these solutions was increasing with the shear rate as hypothesized. However, the increase was moderate, up to 10-20%, in the operating shear rate range (40£ g [1/ sec] £ 510) at 27° C, as compared with up to 50-70% corresponding increase reported by Lee and Irvine, Jr. : (1) Lee, D. L., "Thermal Conductivity Measurements of Non-Newtonian Fluids in a Shear Field," Ph.D. Thesis, State Univ. of New York, Stony Brook,1995; (2) Lee, D.L. and Irvine, Jr., T.F., "Shear Rate Dependent Thermal Conductivity Measurements of Non-Newtonian Fluids," a manuscript prepared for "Experimental Thermal and Fluid Science Journal," 1996. These are the only reported results for similar fluids and under similar testing conditions known to the PI. It has to be stated that Lee's measurements were performed under much less rigorous conditions than the current measurements, and are not confirmed by other independent studies. Further and comprehensive research under well-controlled conditions and using the concomitant methods are necessary to resolve the existing hypothesis and discrepancies.

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