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Temperature measurement and control of analytical rotors in the ultracentrifuge
ANALYTICAL
BIOCHEMISTRY
11,
Temperature Analytical
23&245
(1965)
Measurement Rotors in the L. GROPPER
Beckman
Instruments,
Inc., Received
AND
Spinco
and Control Ultracentrifuge W.
Division,
September
22,
of
BOYD Palo
Alto,
California
1964
INTRODUCTION
This paper describes temperature studies performed on a variety of analytical rotors used in the analytical ultracentrifuge. There are a number of papers dealing with work done on the clear aluminum analytical D type rotor (l-5). The work to be described here covers not only clear aluminum An-D rotors, but black An-D, black An-E, clear An-H titanium, and black An-H titanium1 as well. Both static and dynamic tests were performed. STATIC
TESTS
Experimental Static tests were performed on the black analytical H titanium rotor and the clear aluminum analytical D rotor to determine the relationship between cell temperature and the thermistor mount assembly in the bottom of the rotor as a function of refrigeration temperature. In these studies a thermistor was placed in a modified cell housing and then into one of the rotor cell holes. Leads were t,aken from the thermistor through a specially constructed vacuum seal mounted in the third hole of the upper chamber plate of the Model E.l The leads went from the outside of the seal to a separate RTIC electronic chassis. Both the thermistor mentioned above and the one in the bottom of the rotor were calibrated in the usual manner (6). The chamber was evacuated and the refrigeration system was turned on. A Beckman linear potentiometric recorder,? which has a high impedance, was connected across pins 7 and 2 of the 12AU7 of each of the RTIC unit,s. A lo-megohm resistor was placed in series with pin 7 and a 1-pf Mylar capacitor was put in parallel between ‘Available from ’ Available from Division, Fullerton,
Beckman Beckman Calif.
Instruments, Instruments,
Inc., Spinco Division, Inc., Scientific and 238
Palo Alto, Calif. Process Instruments
TEMPERATURE
MEASUREMENT
239
the leads to the recorder. This arrangement allows the RTIC still to function in the normal manner. The standard RTIC unit which is connected to the thermistor mount in the bottom of the rotor was set to control the temperature of the rotor for various settings. The refrigeration temperature was varied, and t,he temperature of the cell and rotor was read off the RTIC units or the stripchart recorders. The correlation between the temperature indicated by the Evapotriol gage and the temperature of t.he refrigeration can was checked by putting a thermocouple on the refrigeration can and reading the temperature on a calibrated gage outside the chamber. These tests showed the can in agreement with the Evapotriol within tl”C. The heater used, as with the standard RTIC system, has a power of 18 watts. Rem1 ts Because of thermal lags in the titanium rotor, the regular RTIC unit cycled 1.2”C. The heater would cycle on and heat the rotor, and when it’ went off the thermistor in the bottom of the rotor would continue to receive heat from the rotor and would overshoot the set temperature an amount which depended on how long the heater had been on. Conversely, when the rotor cooled down, and the heater would cycle on again, the indicated temperature of the rotor would continue to drop until heat again start.ed to reach the thermistor. The time cycle was 4 to 5 min, with the length of time the heater was on depending on the refrigeration and RTIC settings. The temperature indicated by the thermistor in the cell hole did not cycle. These fluctuations were smoothed out because of the relatively longer distance of the cell from the heater and the relatively poor conductivity of t,he rotor. (The thermal conductivity of titanium is 10 to 15 t,imes less than that of aluminum.) Cycling of the aluminum rotor under the same conditions as the titanium was less than ~O.Oli”C. Again no fluctuations were noted at the cell. An additional effect, dependent on the refrigeration temperat,ure, was noted: For every 5°C change in the refrigeration setting, the temperature of the cell would be 0.6” below the temperat’ure of the thermistor at the center of the rotor with the titanium rotor. A difference of 0.37” was noted for every 5°C change in refrigeration setting with the aluminum rotor. Disconnecting the drive shaft and suspending the rotor from an insulating block on the rotor fork had no effect on these readings. It was shown, however, in another test, that heat is readily trnnsmitted through the drive shaft. This was shown by directing the air flow of a hot hair dryer onto the drive and watching the rotor temperatul~~ rise. No change in these results was observed whm very fine wire was used for the leads
240
GROPPER
AND
BOPD
of the “cell” thermistor. Plugging the top and bottom of the cell hole with insulating material also had no observable effect. These gradients were also noted in a number of different machines where duplicate test’s were made. The temperature gradient between the center of the rotor and the cell described above with the titanium rotor was duplicated under operating conditions described below. No gradient was found with this aluminum rotor under these same subsequent checks. DYNAMIC
TESTS
Experimental The general procedure of Biancheria and Kegeles (1) was used to determine the relationship of cell temperature to the temperature indicated by the thermistor mount at t.he center of the rotor while under operating conditions. A sample of hexadecane in a cell assembly with a 3-mm aluminum centerpiece3 was used for these tests. A Model E equipped with elect,ronic speed control,’ monochromator,’ and UV scanner (7) was used for these experiments. Measurements were taken with the absorption optics and scanner at a wavelength of 390 mp. Measurements of the reference hole distances from the center of the rotor were made with a Gaertner M2001-P Coordinate Plate and Film Comparator.4 After the counterbalance had been seated in the rotor by spinning the rotor to 36,000 rpm, the rotor was placed on the stage of the comparator and the distances were measured directly. Calculations were made with a Monromatic calculator.5 The vacuum gage of the Model E was calibrated using a Kinney Measuvac McLeod gage,6 Model TD-1, connected through a “T” fitting near the Pirani element of the Model E. As no values for the Clapeyron coefficient for hexadecane could be found, it was calculated by (1) : Ap
=
where p is the average angular velocity of the liquid-solid and liquid-air the sample in the rotor, used were to = 18.5”C,
and t = t,, + KAp liquid density taken at temperature to, o is the rotor, x and x0 are the radii of rotation of the interfaces, respectively, t is the temperature of and K is the Clapeyron coefficient. The values p = 0.774 (8), and the rest of the values were
3 pw”(x’
-
x0’)
‘Kindly supplied to us by J. Vinograd. 4 Available from Gaertner Scientific Corporation, 1201 Wrightwood Avenue, Chicago, 111. ‘Available from Monroe Calculating Machine Co., Inc., Orange, N. J. 6Available from Kinney Vacuum Division of the W. T. Air Brake Co., 3529 Washington St., Boston 30, Mass.
TEMPERATURE
241
MEASUREMENT
taken from one run with a clear aluminum rotor running at 36,000 rpm at an indicated temperature of 19.5”C. Ir’ was determined in this manner to be 0.1163 X lo-‘: “K/dyne/cmz. This value was used for subsequent calculations. The assumption inherent in this procedure was that the indicated temperature of the rotor was correct. This assumption was made since variations in refrigeration temperature from -30” to + 14°C caused no change in the liquid column length of the hexadecane. Also, tests by Baldwin (3) showed agreement within 0.2 k 0.1’ of the temperature indicated by the RTIC and calculations made using diphenyl ether with a clear An-D rotor. Figure 1 shows a plot of calculated temperature vs. indicated temperature with this rotor. The maximum deviation from the theoretical straight line is *O.l”C. The precision and repeatability of the measurements made was 0.02”. Before the rotor was placed in the chamber, it was placed on the calibration stand and a reading was taken. After the rotor was placed in the chamber, a check with the RTIC was made to see that the readings on the calibration stand agreed with the indicated reading in the chamber within +2 divisions on the RTIC meter. This corresponds to kO.05”C. There was no fluctuation of the RTIC 21
.
20
.
. / . l
.
.
.
.
19 . .
q-
/, .
I8
LEAR
19
CALCULATED FIG. 1. Relationship temperature at the
cell
ALUMINUM
between using
indicated hexadecane
AN-D
ROTOR
20
TEMPERATURE
temperature for a clear
21
‘C
of RTIC aluminum
system An-D
and calculated rotor.
242
t;ROPPER
AND
L1OTI)
meter during any of the tests performed, during acceleration, deceleration, or while the rotor was at speed. A fan was used below the chamber to keep water from condensing on the out.side of the lenses on low temperature runs. Results
During all the tests reported here, t,he refrigeration unit was set to a temperature, and the RTIC system was set to control for a variety of temperatures, between 18.5” and 205°C. A plot was then made of calculated temperature, from the liquid column of the hexadecane, against the indicated temperature of the RTIC unit. Figure 2 shows a typical plot for the black aluminum An-D, black titanium An-H, and clear aluminum An-D rotors. 21 21
0 w 0t 19, . 19,
.
z
IFaG 18’
.-I818
2. Relationship cell for a number
FIG.
CLEAR
AL,UMINUhl AL,UMINUM
AN-D
A
BLACK
TITANIUM
AN-H
X BLACK
ALUMINUM
AN-D
IS IS CALCULATED
the
l
between of rotors
20 TEMPERATURE
indicated temperature with the refrigeration
21 “C
and calculated temperature system at 14” to 15°C.
at
The refrigeration was set at between 14’ and 15°C in all these cases. As stated previously, the refrigeration setting had no effect on the calculated temperature of the clear aluminum rotor; all other rotors showed an offset whose degree was dependent on the rotor material, its finish, and the refrigeration setting. Figure 3 shows a series of plots for the black aluminum An-D rotor for different refrigeration settings. The
TEMPERATURE
243
MEASUREMENT
/
BLACK
ALUMINUM
I8
AN-D
of refrigeration
,/’
.
REFRIGERATION
n
REFRldERATlON
-1 “C 4 “C
A REFRIGLRATION
10 “C
x
14 “C
REFRIG’ERATION
19 CALCULATED
FIG. 3. Effect
i
ROTOR
20
21
TEMPERATURE
setting
“c
on temperature
of the
cell.
shortness of the plot with the refrigeration set at -1°C was because above 18.77’ the temperature of the rotor could not be controlled, as the heater was on all the time. The refrigeration system was cooling the rotor down more than the heater could cope with. Table 1 shows the relationship of the indicated temperature taken at the center of the rotor to the temperature calculated at the cell as a function of the refrigeration setting. Clear titanium An-H, black aluminum An-D, and black aluminum An-E rotors all showed the same relation to TABLE RELATIONSHIP TEMPERATURE
OB INDICATED CALCULATED
REFRIGERATION
(The
Al. Al. Al. Ti. Ti.
of temperature
Range
Rotor
Clear Black Black Clear Black
range
An-D An-D An-E An-H An-H
1
TEMPERATURE TAKEN AT CELL AS A FUNCTION
OF ROTOR CH.\NGE
5°C
at which “C
18.5”
to 20.5”C.)
Di5erence between calculated temperature and indicated temperature for every 5°C change in refrigeration setting
to +lri”
None
to
14”
-0.1”
1.5” to 15” -1” to 10” 10” to 15”
-0.1” -0.1” -1.0”
-30” -1”
TO IN
SETTING
at the cell was from
of refrigeration settings experiments were made,
AT CENTER OF EVERY
244
GROPPER
AND
BOYD
refrigeration setting. There is thus a temperature gradient across the rotor when the RTIC unit is used to cont,rol the temperature. This is more severe in titanium rotors because of the relatively poor heat conduction of this material as compared to aluminum. It was found that, if the refrigeration temperature is set so that there is little cycling of the RTIC unit, then the temperat,ure of the cell would be the same as the temperature of the thermistor, except in the case of the black titanium rotor, which showed a gradient in all cases. In these runs it was found that the optimum temperature of the refrigeration system was from 4.5” to 8.5”C lower than the desired control temperature. It must be remembered that this figure will probably be good only for this machine, with its present drive and at a speed of 36,000 rpm. The picture for black rotors was not all dark, however: first, a lower temperature could be obtained with them and, second, the response t.o changes in control temperatures was much faster than with clear rotors. Other Studies Checks of the adiabatic cooling (2) were made on a number of titanium and aluminum rotors. These tests were made without use of refrigeration and relied on the RTIC to indicate temperature changes in the rotor. Temperatures of the aluminum rotors varied from 0.5” to 1.5”C cooling during acceleration to 60,000 rpm. This variation of adiabatic cooling occurred not only among rotors, but also during the life of any one rotor. It is assumed that this variation was dependent on which phase of the metal stress curve the rotor was on. Three titanium rotors were tested, two cooled 0.3”C when accelerated to 68,000 rpm and 0.2”C on acceleration to 60,000. The third cooled 0.5”C on acceleration to 60,000 rpm. About 10 min was allowed to elapse at speed for any temperature gradients in the rotor to equilibrate; no further cooling of the rotors was noted, however, after the first few minutes at speed. Acceleration time for the titanium rotor was 12-15 min to 68,000 rpm, and deceleration time with maximum braking rate was about 17 min. For the acceleration tests, the Variac was adjusted so that the current to the drive was between 13 and 15 amp. Above 55,000 rpm the Variac was at its maximum setting, and the current to the drive fell off steadily to about 9 amp at 68,090. The titanium rotor, since it is stronger than aluminum rotors, distorts less at high speeds. This is particularly noted in the cell holes, which apparently do not e1ongat.e as much as those of aluminum rotors. The consequence is that cell components remain in their original shape longer with titanium rotors, while those used with aluminum rotors become elongated. The latter parts, once distorted, often will not fit into the titanium rotor (9).
TEMPERATURE
245
MEASUREMEKI
CONCLUSION
Temperature tests with various rotors were performed. The most accurate temperature indication of the ccl1 occurs with clear rotors. For low temperature runs, below 4”C, black rotors must be used. The refrigeration system should be set so that the RTIC heater comes on as little as possible, yet does go on (i.e., about 10% of the time). It is worthy of note that the temperature gradients found during these studies arc in a direction which would tend to stabilize the cell contents against convection. REFERENCES 1. 2. 3. 4.
BIANCHERIA, A., AND KEGELES, G., J. Am. Chem. Sot. WAUGH, D. F., AND YPHANTIS, D. A., Rev. Sci. Znstr. BALDWIN, R. L., Biochem. 1.65, 503 (1957). PEDERSEN, Ii. O., J. Phys. Chem. 62, 1282 (1958). BAUER, J. H., AND PICKELS, E. G., J. Exptl. Med. 65,
76,3737 (1954). 23, 609 (1952).
5. 565 (1937). 6. Spinco Division, Beckman Instruments, Inc., Model E Instruction Manual. 7. BOYD, W., AND GROPPER, L., unpublished data. 8. LANGE, N. A., ed., “Handbook of Chemistry,” p. 571. 9th ed. Handbook Publishers, Sandusky, Ohio, 1956. 9. BALDWIN, R. L., private communication.
BIOCHEMISTRY
11,
Temperature Analytical
23&245
(1965)
Measurement Rotors in the L. GROPPER
Beckman
Instruments,
Inc., Received
AND
Spinco
and Control Ultracentrifuge W.
Division,
September
22,
of
BOYD Palo
Alto,
California
1964
INTRODUCTION
This paper describes temperature studies performed on a variety of analytical rotors used in the analytical ultracentrifuge. There are a number of papers dealing with work done on the clear aluminum analytical D type rotor (l-5). The work to be described here covers not only clear aluminum An-D rotors, but black An-D, black An-E, clear An-H titanium, and black An-H titanium1 as well. Both static and dynamic tests were performed. STATIC
TESTS
Experimental Static tests were performed on the black analytical H titanium rotor and the clear aluminum analytical D rotor to determine the relationship between cell temperature and the thermistor mount assembly in the bottom of the rotor as a function of refrigeration temperature. In these studies a thermistor was placed in a modified cell housing and then into one of the rotor cell holes. Leads were t,aken from the thermistor through a specially constructed vacuum seal mounted in the third hole of the upper chamber plate of the Model E.l The leads went from the outside of the seal to a separate RTIC electronic chassis. Both the thermistor mentioned above and the one in the bottom of the rotor were calibrated in the usual manner (6). The chamber was evacuated and the refrigeration system was turned on. A Beckman linear potentiometric recorder,? which has a high impedance, was connected across pins 7 and 2 of the 12AU7 of each of the RTIC unit,s. A lo-megohm resistor was placed in series with pin 7 and a 1-pf Mylar capacitor was put in parallel between ‘Available from ’ Available from Division, Fullerton,
Beckman Beckman Calif.
Instruments, Instruments,
Inc., Spinco Division, Inc., Scientific and 238
Palo Alto, Calif. Process Instruments
TEMPERATURE
MEASUREMENT
239
the leads to the recorder. This arrangement allows the RTIC still to function in the normal manner. The standard RTIC unit which is connected to the thermistor mount in the bottom of the rotor was set to control the temperature of the rotor for various settings. The refrigeration temperature was varied, and t,he temperature of the cell and rotor was read off the RTIC units or the stripchart recorders. The correlation between the temperature indicated by the Evapotriol gage and the temperature of t.he refrigeration can was checked by putting a thermocouple on the refrigeration can and reading the temperature on a calibrated gage outside the chamber. These tests showed the can in agreement with the Evapotriol within tl”C. The heater used, as with the standard RTIC system, has a power of 18 watts. Rem1 ts Because of thermal lags in the titanium rotor, the regular RTIC unit cycled 1.2”C. The heater would cycle on and heat the rotor, and when it’ went off the thermistor in the bottom of the rotor would continue to receive heat from the rotor and would overshoot the set temperature an amount which depended on how long the heater had been on. Conversely, when the rotor cooled down, and the heater would cycle on again, the indicated temperature of the rotor would continue to drop until heat again start.ed to reach the thermistor. The time cycle was 4 to 5 min, with the length of time the heater was on depending on the refrigeration and RTIC settings. The temperature indicated by the thermistor in the cell hole did not cycle. These fluctuations were smoothed out because of the relatively longer distance of the cell from the heater and the relatively poor conductivity of t,he rotor. (The thermal conductivity of titanium is 10 to 15 t,imes less than that of aluminum.) Cycling of the aluminum rotor under the same conditions as the titanium was less than ~O.Oli”C. Again no fluctuations were noted at the cell. An additional effect, dependent on the refrigeration temperat,ure, was noted: For every 5°C change in the refrigeration setting, the temperature of the cell would be 0.6” below the temperat’ure of the thermistor at the center of the rotor with the titanium rotor. A difference of 0.37” was noted for every 5°C change in refrigeration setting with the aluminum rotor. Disconnecting the drive shaft and suspending the rotor from an insulating block on the rotor fork had no effect on these readings. It was shown, however, in another test, that heat is readily trnnsmitted through the drive shaft. This was shown by directing the air flow of a hot hair dryer onto the drive and watching the rotor temperatul~~ rise. No change in these results was observed whm very fine wire was used for the leads
240
GROPPER
AND
BOPD
of the “cell” thermistor. Plugging the top and bottom of the cell hole with insulating material also had no observable effect. These gradients were also noted in a number of different machines where duplicate test’s were made. The temperature gradient between the center of the rotor and the cell described above with the titanium rotor was duplicated under operating conditions described below. No gradient was found with this aluminum rotor under these same subsequent checks. DYNAMIC
TESTS
Experimental The general procedure of Biancheria and Kegeles (1) was used to determine the relationship of cell temperature to the temperature indicated by the thermistor mount at t.he center of the rotor while under operating conditions. A sample of hexadecane in a cell assembly with a 3-mm aluminum centerpiece3 was used for these tests. A Model E equipped with elect,ronic speed control,’ monochromator,’ and UV scanner (7) was used for these experiments. Measurements were taken with the absorption optics and scanner at a wavelength of 390 mp. Measurements of the reference hole distances from the center of the rotor were made with a Gaertner M2001-P Coordinate Plate and Film Comparator.4 After the counterbalance had been seated in the rotor by spinning the rotor to 36,000 rpm, the rotor was placed on the stage of the comparator and the distances were measured directly. Calculations were made with a Monromatic calculator.5 The vacuum gage of the Model E was calibrated using a Kinney Measuvac McLeod gage,6 Model TD-1, connected through a “T” fitting near the Pirani element of the Model E. As no values for the Clapeyron coefficient for hexadecane could be found, it was calculated by (1) : Ap
=
where p is the average angular velocity of the liquid-solid and liquid-air the sample in the rotor, used were to = 18.5”C,
and t = t,, + KAp liquid density taken at temperature to, o is the rotor, x and x0 are the radii of rotation of the interfaces, respectively, t is the temperature of and K is the Clapeyron coefficient. The values p = 0.774 (8), and the rest of the values were
3 pw”(x’
-
x0’)
‘Kindly supplied to us by J. Vinograd. 4 Available from Gaertner Scientific Corporation, 1201 Wrightwood Avenue, Chicago, 111. ‘Available from Monroe Calculating Machine Co., Inc., Orange, N. J. 6Available from Kinney Vacuum Division of the W. T. Air Brake Co., 3529 Washington St., Boston 30, Mass.
TEMPERATURE
241
MEASUREMENT
taken from one run with a clear aluminum rotor running at 36,000 rpm at an indicated temperature of 19.5”C. Ir’ was determined in this manner to be 0.1163 X lo-‘: “K/dyne/cmz. This value was used for subsequent calculations. The assumption inherent in this procedure was that the indicated temperature of the rotor was correct. This assumption was made since variations in refrigeration temperature from -30” to + 14°C caused no change in the liquid column length of the hexadecane. Also, tests by Baldwin (3) showed agreement within 0.2 k 0.1’ of the temperature indicated by the RTIC and calculations made using diphenyl ether with a clear An-D rotor. Figure 1 shows a plot of calculated temperature vs. indicated temperature with this rotor. The maximum deviation from the theoretical straight line is *O.l”C. The precision and repeatability of the measurements made was 0.02”. Before the rotor was placed in the chamber, it was placed on the calibration stand and a reading was taken. After the rotor was placed in the chamber, a check with the RTIC was made to see that the readings on the calibration stand agreed with the indicated reading in the chamber within +2 divisions on the RTIC meter. This corresponds to kO.05”C. There was no fluctuation of the RTIC 21
.
20
.
. / . l
.
.
.
.
19 . .
q-
/, .
I8
LEAR
19
CALCULATED FIG. 1. Relationship temperature at the
cell
ALUMINUM
between using
indicated hexadecane
AN-D
ROTOR
20
TEMPERATURE
temperature for a clear
21
‘C
of RTIC aluminum
system An-D
and calculated rotor.
242
t;ROPPER
AND
L1OTI)
meter during any of the tests performed, during acceleration, deceleration, or while the rotor was at speed. A fan was used below the chamber to keep water from condensing on the out.side of the lenses on low temperature runs. Results
During all the tests reported here, t,he refrigeration unit was set to a temperature, and the RTIC system was set to control for a variety of temperatures, between 18.5” and 205°C. A plot was then made of calculated temperature, from the liquid column of the hexadecane, against the indicated temperature of the RTIC unit. Figure 2 shows a typical plot for the black aluminum An-D, black titanium An-H, and clear aluminum An-D rotors. 21 21
0 w 0t 19, . 19,
.
z
IFaG 18’
.-I818
2. Relationship cell for a number
FIG.
CLEAR
AL,UMINUhl AL,UMINUM
AN-D
A
BLACK
TITANIUM
AN-H
X BLACK
ALUMINUM
AN-D
IS IS CALCULATED
the
l
between of rotors
20 TEMPERATURE
indicated temperature with the refrigeration
21 “C
and calculated temperature system at 14” to 15°C.
at
The refrigeration was set at between 14’ and 15°C in all these cases. As stated previously, the refrigeration setting had no effect on the calculated temperature of the clear aluminum rotor; all other rotors showed an offset whose degree was dependent on the rotor material, its finish, and the refrigeration setting. Figure 3 shows a series of plots for the black aluminum An-D rotor for different refrigeration settings. The
TEMPERATURE
243
MEASUREMENT
/
BLACK
ALUMINUM
I8
AN-D
of refrigeration
,/’
.
REFRIGERATION
n
REFRldERATlON
-1 “C 4 “C
A REFRIGLRATION
10 “C
x
14 “C
REFRIG’ERATION
19 CALCULATED
FIG. 3. Effect
i
ROTOR
20
21
TEMPERATURE
setting
“c
on temperature
of the
cell.
shortness of the plot with the refrigeration set at -1°C was because above 18.77’ the temperature of the rotor could not be controlled, as the heater was on all the time. The refrigeration system was cooling the rotor down more than the heater could cope with. Table 1 shows the relationship of the indicated temperature taken at the center of the rotor to the temperature calculated at the cell as a function of the refrigeration setting. Clear titanium An-H, black aluminum An-D, and black aluminum An-E rotors all showed the same relation to TABLE RELATIONSHIP TEMPERATURE
OB INDICATED CALCULATED
REFRIGERATION
(The
Al. Al. Al. Ti. Ti.
of temperature
Range
Rotor
Clear Black Black Clear Black
range
An-D An-D An-E An-H An-H
1
TEMPERATURE TAKEN AT CELL AS A FUNCTION
OF ROTOR CH.\NGE
5°C
at which “C
18.5”
to 20.5”C.)
Di5erence between calculated temperature and indicated temperature for every 5°C change in refrigeration setting
to +lri”
None
to
14”
-0.1”
1.5” to 15” -1” to 10” 10” to 15”
-0.1” -0.1” -1.0”
-30” -1”
TO IN
SETTING
at the cell was from
of refrigeration settings experiments were made,
AT CENTER OF EVERY
244
GROPPER
AND
BOYD
refrigeration setting. There is thus a temperature gradient across the rotor when the RTIC unit is used to cont,rol the temperature. This is more severe in titanium rotors because of the relatively poor heat conduction of this material as compared to aluminum. It was found that, if the refrigeration temperature is set so that there is little cycling of the RTIC unit, then the temperat,ure of the cell would be the same as the temperature of the thermistor, except in the case of the black titanium rotor, which showed a gradient in all cases. In these runs it was found that the optimum temperature of the refrigeration system was from 4.5” to 8.5”C lower than the desired control temperature. It must be remembered that this figure will probably be good only for this machine, with its present drive and at a speed of 36,000 rpm. The picture for black rotors was not all dark, however: first, a lower temperature could be obtained with them and, second, the response t.o changes in control temperatures was much faster than with clear rotors. Other Studies Checks of the adiabatic cooling (2) were made on a number of titanium and aluminum rotors. These tests were made without use of refrigeration and relied on the RTIC to indicate temperature changes in the rotor. Temperatures of the aluminum rotors varied from 0.5” to 1.5”C cooling during acceleration to 60,000 rpm. This variation of adiabatic cooling occurred not only among rotors, but also during the life of any one rotor. It is assumed that this variation was dependent on which phase of the metal stress curve the rotor was on. Three titanium rotors were tested, two cooled 0.3”C when accelerated to 68,000 rpm and 0.2”C on acceleration to 60,000. The third cooled 0.5”C on acceleration to 60,000 rpm. About 10 min was allowed to elapse at speed for any temperature gradients in the rotor to equilibrate; no further cooling of the rotors was noted, however, after the first few minutes at speed. Acceleration time for the titanium rotor was 12-15 min to 68,000 rpm, and deceleration time with maximum braking rate was about 17 min. For the acceleration tests, the Variac was adjusted so that the current to the drive was between 13 and 15 amp. Above 55,000 rpm the Variac was at its maximum setting, and the current to the drive fell off steadily to about 9 amp at 68,090. The titanium rotor, since it is stronger than aluminum rotors, distorts less at high speeds. This is particularly noted in the cell holes, which apparently do not e1ongat.e as much as those of aluminum rotors. The consequence is that cell components remain in their original shape longer with titanium rotors, while those used with aluminum rotors become elongated. The latter parts, once distorted, often will not fit into the titanium rotor (9).
TEMPERATURE
245
MEASUREMEKI
CONCLUSION
Temperature tests with various rotors were performed. The most accurate temperature indication of the ccl1 occurs with clear rotors. For low temperature runs, below 4”C, black rotors must be used. The refrigeration system should be set so that the RTIC heater comes on as little as possible, yet does go on (i.e., about 10% of the time). It is worthy of note that the temperature gradients found during these studies arc in a direction which would tend to stabilize the cell contents against convection. REFERENCES 1. 2. 3. 4.
BIANCHERIA, A., AND KEGELES, G., J. Am. Chem. Sot. WAUGH, D. F., AND YPHANTIS, D. A., Rev. Sci. Znstr. BALDWIN, R. L., Biochem. 1.65, 503 (1957). PEDERSEN, Ii. O., J. Phys. Chem. 62, 1282 (1958). BAUER, J. H., AND PICKELS, E. G., J. Exptl. Med. 65,
76,3737 (1954). 23, 609 (1952).
5. 565 (1937). 6. Spinco Division, Beckman Instruments, Inc., Model E Instruction Manual. 7. BOYD, W., AND GROPPER, L., unpublished data. 8. LANGE, N. A., ed., “Handbook of Chemistry,” p. 571. 9th ed. Handbook Publishers, Sandusky, Ohio, 1956. 9. BALDWIN, R. L., private communication.