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Characteristic curve of helium pool boiling
The results o f an experimental investigation on helium pool boiling over a wide range o f temperature differences covering nucleate, transition, and film regions are presented. Heating surfaces under investigation were made o f different materials and were processed with various degrees o f roughness. Helium boiling curve on stainless steel has an anomalous character: heat flux in the transition region increases when temperature difference rises and there is no nucleate boiling zone on the surface with the lowest degree o f roughness. A comparative analysis o f the results presented with available data is also carried out.
Characteristic curve of helium pool boiling V . A . Grigoriev, V . V .
K l i m e n k o , Y u . M . Pavlov, Y e . V . A m e t i s t o v , and A . V . K l i m e n k o
In the past few years various investigators have paid a great deal of attention to heat transfer on helium boiling. This is not just a chance occurrence as cooling with liquid helium is one of the most effective methods and in a number of cases the only method o f intensive heat removal over a specified temperature range. Particular interest has been shown in relation to studies of applied superconductivity. For pool boiling under free convection it should be noted that most of the available data are referred to the nucleate boiling region, the most important one from the practical point of view. 1 -a In this region the great scatter in the results from various authors is probably explained not only by different experimental conditions but also by the complexity of experimenting with helium. Nevertheless it appears to be possible to single out a group of factors which mainly influence the process of helium nucleate boiling. These are thermal material properties, roughness, and heating surface orientation, the latter is probably influential at very low heat fluxes or, on the contrary, at some critical ones. 2 The data on helium film boiling are quite few in number 9 -12 and mainly relate to cylindrical surfaces of very small diameter. For the helium boiling transition region, there are no practical data available (the data of references 13 and 14 cannot apparently be taken into account as the appropriate experimental sections were not equipped with special devices able to fix the points of a transition region). In addition to references 13 and 14 the data on nucleate and film boiling regions on the same heating surface were probably obtained only in reference 15. Our aim was to obtain the complete curves of boiling on the materials with substantially different thermal properties and various roughness of heating surface in order to reveal the influence of the specified parameters on film and transition regions, the positions of transition points, and also to check the available data for a nucleate region. The non-stationary experimental procedure similar to that described in reference 16 was used by us to reproduce the boiling curve in all three regions. Additional tests using the stationary procedure were also carried out. Boiling took place under atmospheric pressure on the horizontally placed butt-end surfaces of the cylindrical rods, 8 mm in diameter, made of copper M1 and stainless steel XI8H9T. Heating surface roughness varied from 6/am (in The authors are with the Moscow Power Engineering Institute, 105835, Krasnokasarmennaya street 14, Moscow. Received 5 November 1976.
CRYOGENICS. MARCH 1977
most experiments) to 0.7/am. To measure the surface temperature and the heat flux five thermocouples C u - ( C u + Fe) with the thermoelectrodes 0.1 mm in diameter were placed along the vertical axis of the specimen. These thermocouples were described in reference 19 and they had quite high sensitivity ( 1 2 - 1 7 / a V K -1 ) over all the temperature range studied. The cold thermocouple junctions were placed directly in liquid helium. The temperature difference between the heating surface and the helium bath was determined by the extrapolation of the temperature distribution along the vertical extent of the specimen; the heat flux being calculated from Fourier's law. The thermal conductivity of the copper specimen was experimentally determined at helium and nitrogen temperatures and over the range 4 . 2 - 7 7 K. it was calculated by the linear (in logarithmic scale) interpolation of the data obtained. The stainless steel thermal conductivity was taken in accordance with the data in reference 17. The error in the wall temperature and heat flux determination was on average as follows: for a film region - 2 and 13%, for a transition region - 6 and 13%, for a nucleate region 27 and 29% respectively. In our experiments the rate of the specimen temperature change varied from approximately 0.01 K s -1 in the largest part of a film region to about 1 K s-I in the transition and nucleate regions. According to a recently published work, 18 the rate of cooling on boiling on the horizontal surface has quite a weak influence on the position of a boiling curve, so the data obtained must approximately correspond with the results of the stationary experiment under identical conditions. The results are shown in Figs 1 and 2. It can be seen from Fig. 1 that the heating surface material substantially influences both the nucleate and the transition regions of boiling. But as distinct from other liquids (see for instance reference 16) the heat transfer intensity on a copper surface in both regions appears to be higher than that on the stainless steel one. It becomes possible due to the fact, that the value ofqcr, for stainless steel is less than that of qcr2, and, as a result, the transition boiling curve has no negative slope, as usual, but a positive one. The anomalous nature of the transition boiling is explained by the fact that the first crisis on the stainless steel surface having a stressed thermodynamic nature takes place substantially at the original part of the nucleate boiling curve. Such a boiling curve is often observed at pressures close to the critical ones (see, for instance reference 20) but in our experiments Ps/Pc = 0.45. In all other cases the boiling curves on various metals are adequate to the previous obtained accuracy: with increasing values ofx/ock of the
155
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o
I0o
o
8 6 4
~ •
t o"
•
2
~-,
oE
°~° •
t
t
o
t,o~,
"4
2 10-2 8 6 4
Metal
o
-
t
Non-stationary Stationary
Copper • Copper Stationary ( accordingto referencel)
f
-
Method
• Copper
o Stainless steel Stainless steel z~ Stainless steel
44
I I II
Non-stationary Stationary
Stationary /°clc°lrdling t°l referlencle~ I 1 I I II 4 6810 o 2 4 6810 2 4 6 8102 A T, K
I
4 6 810 -I 2
at the atmospheric pressure (0.47 K), after that fdm boiling conditions take place. Similar data on helium are obtained for the first time. Apparently such a result must be explained by the substantial increase in the temperature difference of the incipient boiling on the heating surface made o f the material with the small value of x/pck and processed with low surface roughness. In this connexion it should be noted that studies made before did not reveal such an effect, as they dealt either with roughened heating surfaces ~ or with the materials with substantially large values of X/pck: silver,3 copper, 2']2 bronze, tin, 13 and platinum. 4 As would be expected, over the range of micro-irregularity magnitudes and the values of ~/pck o f the surface material investigated we did not show the influence of the factors mentioned on the film boiling intensity. The high accuracy data obtained by us coincide with the data on boiling o f the horizontal copper disc 15.2 mm in diameter obtained by Cummings and Smith; la our data covering a much wider temperature range.
Fig. 1 Helium boiling on different metals; horizontal surface 8 m m in die, roughness 7/~m
Conclusions
material the heat transfer intensity in the nucleate region increases, the values of ATeq and qcr2 decreases. Both the data o f reference 1 obtained by the stationary method on identical specimens and those obtained using our apparatus are plotted in Fig. 1. Good agreement was obtained from reference 1 with the data; the small deviation of the data on copper can be explained by the various values of the specimens (0.068 W s 1/2 cm -2 K -l and 0.019 W s ~/2 cm -2 K -~ in this work). The results obtained by the various methods, are in agreement with the conclusions made in reference 18; that is, they practically coincide.
2. Helium boiling on stainless steel has an anomaly - no part of the characteristic curve has a negative slope; there is no nucleate boiling zone on the surface with a low degree of roughness.
It follows from Fig. 2 that the reduction in the heating surface roughness o f stainless steel to 0.7/~m brings about the complete disappearance of the boiling nucleate region. The incipience o f boiling takes place at temperature differences o f the order of 0.6 K, and it corresponds in much the same way to the helium limiting superheating temperature
1. The thermal properties of the heating surface substantially influence helium nucleate and transition boiling.
3. Over the range of the thermal properties of the material and heating surface roughness investigated it was found that the heating surface roughness does not influence the helium film boiling region.
References
1 2 3 4 5 6 7
@
2 6
o
4
o
o
o oQ
2
# "
6
~
4
00 o
2
o° 6 4 2
0
Stainless steel
4
~ I ~i
i I
~lbleI
i~ ~1 I
4 6
Roughness 07/.~m/Non-
Roughness 7Fm )stationary
Roughness 0.7p.m~ 7p.m / St°ti°nary
Roughness I
810 -I
I
2
I
I II
4 6 810° 2 4 6 810 AT, K
I
2
I
I tl
I
4 6 810 z 2
Fig. 2 Influence of roughness on heat transfer on helium boiling; horizontal surface 8 m m in die, stainless steel
156
Grigoriev, V.A., Pavlov, Yu.M., Ametistov, Ye.V. Proc 5th International Heat Transfer Conference, Tokyo, Vol 4 (1974) 45 Jergel, M., Stevenson, R. Int J Heat and Mass Trans 14 (1971) 2099 Reeber, M.D. JAppl Phys 34 (1963) 481 Lyon, D.N. Advances in Cryogenic Engineering 10 (1965) 371 Dorey, A.P. Cryogenics 5 (1965) 46 Dinaburg, L.B. Cryogenics 11 (1971) 238 Boissin, J.C., Thibault, J.J., Roussel, J., Faddi, E. Advances in Cryogenic Engineering 13 (1968) 607 Efferson, K.R. JAppl Phys 40 (1969) 1995 Frederking, T.H.K. AIChE J 5 (1959) 403
8 9 10 Grassman, P., Karagonnis, A. Proc 5th International Conference on Low Temperature Physics and Chemistry (1958) 41 11 Frederking, T.H.K., Wu, Y.V., Clement, B.W. AIChE J 12 (1966) 238 12 Frederking, T.H.K., Chapman, R.C., Wang, S. Advances in Cryogenic Engineering 10 (1965) 353 13 Cummings, R.D., Smith, J.L. Liquid Helium Technology (Paris, 1966) 88 14 Butler, A.P., James, G.B., Maddock, BJ., Norris, W.T. fat J Heat and Mass Trans 13 (1970) 106 15 Gonchatov, I.N., Su, H.S., Chovanec, F. Cryogenics 10 (1970) 316 16 Grigoriev, V.A., Pavlov, Yu.M., Ametistov, Ye.V., Klimenko, V.V., Klimenko, A.V. Izvesti]a vuzov MV i SSO SSSR, Energetika, No 3 (1975) 72 17 Malkov, M.P. et ai Spravochnik po fiziko-tekhnicheskim osnovam Kriogeniki (Energia, 1973) 18. Grigotiev, V.A,, Klimenko, V.V., Pavlov, Yu.M., Ametistov, Ye.V.
ICEC6, presented at Grenoble (1976) 19 Beilin, V.M., Levin, 1.Ya., Medvedova, L.A., Orlova, M.P., Rogel'berg, I.L. Prib i Tekh Exper No 6 (1972) 215 20 Nikolayev, G.P., Makarov, Ye.N. Teploflsika vysokih temperatur 12 (1974) 1058
C R Y O G E N I C S . MARCH 1977
Characteristic curve of helium pool boiling V . A . Grigoriev, V . V .
K l i m e n k o , Y u . M . Pavlov, Y e . V . A m e t i s t o v , and A . V . K l i m e n k o
In the past few years various investigators have paid a great deal of attention to heat transfer on helium boiling. This is not just a chance occurrence as cooling with liquid helium is one of the most effective methods and in a number of cases the only method o f intensive heat removal over a specified temperature range. Particular interest has been shown in relation to studies of applied superconductivity. For pool boiling under free convection it should be noted that most of the available data are referred to the nucleate boiling region, the most important one from the practical point of view. 1 -a In this region the great scatter in the results from various authors is probably explained not only by different experimental conditions but also by the complexity of experimenting with helium. Nevertheless it appears to be possible to single out a group of factors which mainly influence the process of helium nucleate boiling. These are thermal material properties, roughness, and heating surface orientation, the latter is probably influential at very low heat fluxes or, on the contrary, at some critical ones. 2 The data on helium film boiling are quite few in number 9 -12 and mainly relate to cylindrical surfaces of very small diameter. For the helium boiling transition region, there are no practical data available (the data of references 13 and 14 cannot apparently be taken into account as the appropriate experimental sections were not equipped with special devices able to fix the points of a transition region). In addition to references 13 and 14 the data on nucleate and film boiling regions on the same heating surface were probably obtained only in reference 15. Our aim was to obtain the complete curves of boiling on the materials with substantially different thermal properties and various roughness of heating surface in order to reveal the influence of the specified parameters on film and transition regions, the positions of transition points, and also to check the available data for a nucleate region. The non-stationary experimental procedure similar to that described in reference 16 was used by us to reproduce the boiling curve in all three regions. Additional tests using the stationary procedure were also carried out. Boiling took place under atmospheric pressure on the horizontally placed butt-end surfaces of the cylindrical rods, 8 mm in diameter, made of copper M1 and stainless steel XI8H9T. Heating surface roughness varied from 6/am (in The authors are with the Moscow Power Engineering Institute, 105835, Krasnokasarmennaya street 14, Moscow. Received 5 November 1976.
CRYOGENICS. MARCH 1977
most experiments) to 0.7/am. To measure the surface temperature and the heat flux five thermocouples C u - ( C u + Fe) with the thermoelectrodes 0.1 mm in diameter were placed along the vertical axis of the specimen. These thermocouples were described in reference 19 and they had quite high sensitivity ( 1 2 - 1 7 / a V K -1 ) over all the temperature range studied. The cold thermocouple junctions were placed directly in liquid helium. The temperature difference between the heating surface and the helium bath was determined by the extrapolation of the temperature distribution along the vertical extent of the specimen; the heat flux being calculated from Fourier's law. The thermal conductivity of the copper specimen was experimentally determined at helium and nitrogen temperatures and over the range 4 . 2 - 7 7 K. it was calculated by the linear (in logarithmic scale) interpolation of the data obtained. The stainless steel thermal conductivity was taken in accordance with the data in reference 17. The error in the wall temperature and heat flux determination was on average as follows: for a film region - 2 and 13%, for a transition region - 6 and 13%, for a nucleate region 27 and 29% respectively. In our experiments the rate of the specimen temperature change varied from approximately 0.01 K s -1 in the largest part of a film region to about 1 K s-I in the transition and nucleate regions. According to a recently published work, 18 the rate of cooling on boiling on the horizontal surface has quite a weak influence on the position of a boiling curve, so the data obtained must approximately correspond with the results of the stationary experiment under identical conditions. The results are shown in Figs 1 and 2. It can be seen from Fig. 1 that the heating surface material substantially influences both the nucleate and the transition regions of boiling. But as distinct from other liquids (see for instance reference 16) the heat transfer intensity on a copper surface in both regions appears to be higher than that on the stainless steel one. It becomes possible due to the fact, that the value ofqcr, for stainless steel is less than that of qcr2, and, as a result, the transition boiling curve has no negative slope, as usual, but a positive one. The anomalous nature of the transition boiling is explained by the fact that the first crisis on the stainless steel surface having a stressed thermodynamic nature takes place substantially at the original part of the nucleate boiling curve. Such a boiling curve is often observed at pressures close to the critical ones (see, for instance reference 20) but in our experiments Ps/Pc = 0.45. In all other cases the boiling curves on various metals are adequate to the previous obtained accuracy: with increasing values ofx/ock of the
155
•o" o
o
I0o
o
8 6 4
~ •
t o"
•
2
~-,
oE
°~° •
t
t
o
t,o~,
"4
2 10-2 8 6 4
Metal
o
-
t
Non-stationary Stationary
Copper • Copper Stationary ( accordingto referencel)
f
-
Method
• Copper
o Stainless steel Stainless steel z~ Stainless steel
44
I I II
Non-stationary Stationary
Stationary /°clc°lrdling t°l referlencle~ I 1 I I II 4 6810 o 2 4 6810 2 4 6 8102 A T, K
I
4 6 810 -I 2
at the atmospheric pressure (0.47 K), after that fdm boiling conditions take place. Similar data on helium are obtained for the first time. Apparently such a result must be explained by the substantial increase in the temperature difference of the incipient boiling on the heating surface made o f the material with the small value of x/pck and processed with low surface roughness. In this connexion it should be noted that studies made before did not reveal such an effect, as they dealt either with roughened heating surfaces ~ or with the materials with substantially large values of X/pck: silver,3 copper, 2']2 bronze, tin, 13 and platinum. 4 As would be expected, over the range of micro-irregularity magnitudes and the values of ~/pck o f the surface material investigated we did not show the influence of the factors mentioned on the film boiling intensity. The high accuracy data obtained by us coincide with the data on boiling o f the horizontal copper disc 15.2 mm in diameter obtained by Cummings and Smith; la our data covering a much wider temperature range.
Fig. 1 Helium boiling on different metals; horizontal surface 8 m m in die, roughness 7/~m
Conclusions
material the heat transfer intensity in the nucleate region increases, the values of ATeq and qcr2 decreases. Both the data o f reference 1 obtained by the stationary method on identical specimens and those obtained using our apparatus are plotted in Fig. 1. Good agreement was obtained from reference 1 with the data; the small deviation of the data on copper can be explained by the various values of the specimens (0.068 W s 1/2 cm -2 K -l and 0.019 W s ~/2 cm -2 K -~ in this work). The results obtained by the various methods, are in agreement with the conclusions made in reference 18; that is, they practically coincide.
2. Helium boiling on stainless steel has an anomaly - no part of the characteristic curve has a negative slope; there is no nucleate boiling zone on the surface with a low degree of roughness.
It follows from Fig. 2 that the reduction in the heating surface roughness o f stainless steel to 0.7/~m brings about the complete disappearance of the boiling nucleate region. The incipience o f boiling takes place at temperature differences o f the order of 0.6 K, and it corresponds in much the same way to the helium limiting superheating temperature
1. The thermal properties of the heating surface substantially influence helium nucleate and transition boiling.
3. Over the range of the thermal properties of the material and heating surface roughness investigated it was found that the heating surface roughness does not influence the helium film boiling region.
References
1 2 3 4 5 6 7
@
2 6
o
4
o
o
o oQ
2
# "
6
~
4
00 o
2
o° 6 4 2
0
Stainless steel
4
~ I ~i
i I
~lbleI
i~ ~1 I
4 6
Roughness 07/.~m/Non-
Roughness 7Fm )stationary
Roughness 0.7p.m~ 7p.m / St°ti°nary
Roughness I
810 -I
I
2
I
I II
4 6 810° 2 4 6 810 AT, K
I
2
I
I tl
I
4 6 810 z 2
Fig. 2 Influence of roughness on heat transfer on helium boiling; horizontal surface 8 m m in die, stainless steel
156
Grigoriev, V.A., Pavlov, Yu.M., Ametistov, Ye.V. Proc 5th International Heat Transfer Conference, Tokyo, Vol 4 (1974) 45 Jergel, M., Stevenson, R. Int J Heat and Mass Trans 14 (1971) 2099 Reeber, M.D. JAppl Phys 34 (1963) 481 Lyon, D.N. Advances in Cryogenic Engineering 10 (1965) 371 Dorey, A.P. Cryogenics 5 (1965) 46 Dinaburg, L.B. Cryogenics 11 (1971) 238 Boissin, J.C., Thibault, J.J., Roussel, J., Faddi, E. Advances in Cryogenic Engineering 13 (1968) 607 Efferson, K.R. JAppl Phys 40 (1969) 1995 Frederking, T.H.K. AIChE J 5 (1959) 403
8 9 10 Grassman, P., Karagonnis, A. Proc 5th International Conference on Low Temperature Physics and Chemistry (1958) 41 11 Frederking, T.H.K., Wu, Y.V., Clement, B.W. AIChE J 12 (1966) 238 12 Frederking, T.H.K., Chapman, R.C., Wang, S. Advances in Cryogenic Engineering 10 (1965) 353 13 Cummings, R.D., Smith, J.L. Liquid Helium Technology (Paris, 1966) 88 14 Butler, A.P., James, G.B., Maddock, BJ., Norris, W.T. fat J Heat and Mass Trans 13 (1970) 106 15 Gonchatov, I.N., Su, H.S., Chovanec, F. Cryogenics 10 (1970) 316 16 Grigoriev, V.A., Pavlov, Yu.M., Ametistov, Ye.V., Klimenko, V.V., Klimenko, A.V. Izvesti]a vuzov MV i SSO SSSR, Energetika, No 3 (1975) 72 17 Malkov, M.P. et ai Spravochnik po fiziko-tekhnicheskim osnovam Kriogeniki (Energia, 1973) 18. Grigotiev, V.A,, Klimenko, V.V., Pavlov, Yu.M., Ametistov, Ye.V.
ICEC6, presented at Grenoble (1976) 19 Beilin, V.M., Levin, 1.Ya., Medvedova, L.A., Orlova, M.P., Rogel'berg, I.L. Prib i Tekh Exper No 6 (1972) 215 20 Nikolayev, G.P., Makarov, Ye.N. Teploflsika vysokih temperatur 12 (1974) 1058
C R Y O G E N I C S . MARCH 1977