Measurement of thermal accommodation coefficients of steel surfaces

76 Pages·2017·1.57 MB·English

by  Wing On Ho

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Masters Theses Student Theses and Dissertations
1970
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Wing On Ho
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Ho, Wing On, "Measurement of thermal accommodation coefficients of steel surfaces" (1970). Masters
Theses. 7041.
https://scholarsmine.mst.edu/masters_theses/7041
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MEASUREMENT OF THERMAL ACCOMMODATION
COEFFICIENTS OF STEEL SURFA CES
BY
WING ON HO, 1937-
A
THESIS
submitted to the faculty of
UNIVERSITY OF MISSOURI - ROLLA
in partial fulfillment of the requirements for the
Degree of
MASTER OF SCIENCE IN MECHANICAL ENGINEERING
Rolla, Missouri
1970
Approved by
7
ii
ABSTRACT
The thermal accommodation coefficient plays an important role
in low density thermal energy transfer measurement. The object of
this investigation was to measure the thermal energy transfer between
a heated test surface and a water cooled reference surface (flat black
lacquer) consisting of two infinite concentric cylinders separated by
dry air.
Two machined and sanded steel cylinders with mean surface rough-
nesses of 25 microinches and 7. 5 microinches were used as the test
surfaces. Measurements were made in the pressure range of 1. 2 x
-6 -6
10 mm Hg. to 1. 8 x 1 0 mm Hg. and temperature range for test
cylinders of 110°- 200.2°F. in determining the emittance. The
-3 -3
pressure range was 1. 0 x 10 mm Hg. to 1 . 3 5 x 1 0 mm Hg. and the
temperature range 115.5 0 - 197. 60 F. in determining the thermal
accommodation coefficients.
The thermal accommodation coefficient for dry air on a steel
surface with an average mean surface roughness of 25 microinches
was 0. 835 (emittance was 0. 174) while for the 7. 5 microinches surface
condition, the thermal accommodation coefficient was 0. 693 (emittance
was 0. 123}.
The experimental data indicated that for the same material, the
rougher surface will have a higher value of thermal accommodation
coefficient and en1ittance. The experimental results agree closely
with those of classical theory (roughness causes more than one
iii
collision at the surface) and with some other investigators (2 & 7).
The accuracy of the results as well as the experimental deviations
are within the accepted engineering limits for this type of measurement.
iv
ACKNOWLEDGEMENT
The author gratefully acknowledges the advice, assistance and
encouragement of Dr. Ronald H. Howell, Associate Professor of
Mechanical Engineering in the successful completion of this research.
The help and cooperation of Mechanical Engineering Staff: Mr. R. D.
Smith and Mr. L. Clover were greatly appreciated.
Special gratitude is due to Dr. R. 0. McNary, Assistant Professor
of Mechanical Engineering for his valuable advice and constructive
comments on the writing of this thesis.
Thanks are due to Dr. D. C. Look. Assistant Professor of
Mechanical Engineering and Mr. Holger Chen, Ph. D. Candidate in the
Chemistry Department at the University of Missouri - Rolla for the
appreciable help they rendered.
Thanks are also due to my wife Hemeline for her encouragement
and understanding in helping to make the completion of this experiment
possible.
v
TABLE OF CONTENTS
Page
ABSTRACT-------------------------------------------------- ii
ACKNOWLEDGEMENT--------------------------------------- iv
LIST OF ILLUSTRATIONS------------------------------------ vii
LIST OF TABLES-------------------------------------------- viii
NOMENCLATURE-------------------------------------------- ix
I. INTRODUCTION-------------------------------------- 1
II. REVIEW OF LITERATURE---------------------------- 5
III. EXPERIMENTAL ANALYSIS--------------------------- 11
A. DERIVATION OF EQUATIONS--------------------- 12
B. DESCRIPTION OF APPARATUS------------------- 17
C. EQUIPMENT USED------------------------------- 19
IV. EXPERIMENTAL PROCEDURES------------------------ 24
A. MEASUREMENT OF EMITTANCE FOR THE
REFERENCE SURFACE--------------------------- 24
B. MEASUREMENT OF THE THERMAL ACCOMMO
DATION COEFFICIENT FOR THE REFERENCE
SURF ACE---------------------------------------- 25
C. MEASUREMENT OF EMITTANCE AND THE
THERMAL ACCOMMODATION COEFFICIENT FOR
STEEL SURFA CES-------------------------------- 26
V. DISCUSSION------------------------------------------- 27
A. REFERENCE SURFACE VALUES------------------- 27
B. ROUGH SURFACE MEASUREMENTS---------------- 30
C. ACCURACY OF RESULTS-------------------------- 36
vi
Page
VI. CONCLUSIONS AND RECOMMENDATIONS------------- 41
VII. BIBLIOGRAPHY------------------------------------- 43
VITI. VITA----------------------------------------------- 45
IX. APPENDICES--------------------------------------- Al
A. EXPERIMENTAL DATA------------------------ Al
B. SA.t\1PLE CALCULATIONS---------------------- Bl
C. DATA CORRECTIONS-------------------------- Cl
vii
LIST OF ILLUSTRATIONS
Figures Page
1. Low Density Thermal Conduction Model-------------------- 15
2. Assembly of Test Unit----------------------------------- 18
3. McLeod Gage Installation--------------------------------- 21
4. Wiring Diagram-------... --------------------------------- 23
5. Emittance of Black Painted Cylinder----------------------- 28
6. Thermal Accommodation Coefficient of Black Painted
Cylinder------------------------------------------------ 29
7. Emittance of Steel Cylinder with Surface Roughness of 25
Nlicroinches--------------------------------------------- 31
8. Emittance of Steel Cylinder with Surface Roughness of 7. 5
Microinches--------------------------------------------- 32
9. Thermal Accommodation Coefficient of Steel Cylinder with
Surface Roughness of 25 Microinches----------------------- 33
10. Thermal Accommodation Coefficient of Steel Cylinder with
Surface Roughness of 7. 5 Microinches---------------------- 34
11. Conduction Data for Black Painted Surface------------------ 37
12. Conduction Data for Steel Surface with Surface Roughness of
25 Microinches and Black Painted Surface------------------ 39
13. Conduction Data of Steel Surface with Surface Roughness of
7. 5 Microinches and Black Painted Surface----------------- 40
viii
LIST OF TABLES
Table Page
I. Comparison of Measured Values of the Thermal
Accommodation Coefficient-------------------------------- 9
II. Experimental Results Compared to Other Investigations------ 35
III. Maximum Experimental Deviations from Average Values----- 36
IV. Radiation Test on Black Surface--------------------------- A2
V. Conduction Test on Black Surface-------------------------- A5
VI. Radiation Test on Steel Surface with Surface Roughness of
25 Microinches------------------------------------------ A8
VII. Conduction Test on Steel Surface with Surface Roughness of
25 N.licroinches------------------------------------------ AlO
VIII. Radiation Test on Steel Surface with Surface Roughness of
7.5 Microinches----------------------------------------- Al2
IX. Conduction Test on Steel Surface with Surface Roughness of
7.5 Microinches----------------------------------------- A14
X. Heat Transfer at Steel End-------------------------------- Cl
XI. Heat Transfer at Aluminum End--------------------------- Cl
XII. Vapor Pressure and Outgassing Rates of Rubber------------ C2
ix
NOMENCLATURE
2
A Surface area, FT
26
A Avogadro's number, 2. 73 x 10 /LB-MOL
0
a Absorptivity
D Diameter of gas molecule, FT
2
e Emissive power, BTU/HR/FT
F Fraction of energy or viewing factor
i, j Number of integers
K Thermal Conductivity, BTU/HR/FT/°F
k Specific heat ratio
L Length of inner cylinder, FT
M Molecular weight of gas molecules
M Molecular weight of air
0
n Number of molecules per unit volume
p Gas pressure, mm Hg.
p Gas pressure, LB /FT2
Total heat transfer, BTU /HR
Radiative heat transfer, BTU /HR
Conductive heat transfer, BTU /HR
r Radius of inner cylinder, FT
1
r Inner radius of outer cylinder, FT
2
2
R Radiative heat transfer per unit area, BTU /HR/ FT
. 0
R Un1versal Gas Constant, 1545.3 FT-LB/LB-M:JL- R
0
Degree Farenheit (temperature unit)