U.S. patent application number 10/768165 was filed with the patent office on 2005-08-04 for intake cross-sheets for gas chromatographic oven.
Invention is credited to Miller, Sammye.
Application Number | 20050166663 10/768165 |
Document ID | / |
Family ID | 34274913 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050166663 |
Kind Code |
A1 |
Miller, Sammye |
August 4, 2005 |
INTAKE CROSS-SHEETS FOR GAS CHROMATOGRAPHIC OVEN
Abstract
An apparatus, system and method reduce the cool down time of GC
ovens by supplying larger volumes of air through oven intake ducts.
The system and method provide intake cross-sheets in an oven intake
duct to reduce airflow spin, increasing the flow rate of fresh air
into the GC oven and reducing the overall cool-down time of the GC
oven. In addition, because the improved airflow allows the oven
wall temperature to quickly match the oven air temperature, the
noise in the temperature signal may be reduced. As a result, the GC
oven can reach an equilibrium "ready" state faster. Furthermore,
the utilization of the cross-sheets may allow for flexibility in
the design of a fast GC oven--specifically in the location and
shape of the intake duct--without loss of performance. This
flexibility may become increasingly significant as GC ovens
continue on the trend of becoming smaller and faster.
Inventors: |
Miller, Sammye; (New Castle,
DE) |
Correspondence
Address: |
AGILENT TECHNOLOGIES, INC.
Legal Department, DL429
Intellectual Property Administration
P.O. Box 7599
Loveland
CO
80537-0599
US
|
Family ID: |
34274913 |
Appl. No.: |
10/768165 |
Filed: |
February 2, 2004 |
Current U.S.
Class: |
73/23.42 ;
219/399; 73/23.41 |
Current CPC
Class: |
G01N 30/30 20130101;
G01N 2030/3084 20130101 |
Class at
Publication: |
073/023.42 ;
073/023.41; 219/399 |
International
Class: |
G01N 030/30; G01N
030/42; F27D 007/02; F27D 009/00 |
Claims
1. An oven intake for a gas chromatographic (GC) oven, comprising:
an intake duct having a convergent geometry to accommodate a small
oven, the intake duct having one or more intake fans that supply
airflow to the GC oven, wherein the airflow originates from the one
or more intake fans and flows through the intake duct into the GC
oven; and one or more cross-sheets positioned inside the intake
duct parallel to a direction of the airflow flowing into the GC
oven, wherein the one or more cross-sheets reduce spin of the
airflow originating from the one or more intake fans and help guide
the airflow through the intake duct into the GC oven.
2. The oven intake of claim 1, wherein the intake duct has a
non-uniform cross-section.
3. The oven intake of claim 1, wherein each of the one or more
cross-sheets has a converging shape that conforms to the convergent
geometry of the intake duct.
4. The oven intake of claim 1, wherein each of the one or more
cross-sheets is secured to the intake duct by riveting one or more
metal tabs.
5. The oven intake of claim 1, wherein the number of cross-sheets
positioned inside the intake duct to guide the air-flow through the
intake duct is one of: two, three or four.
6. The oven intake of claim 1, wherein one cross-sheet is installed
off center with respect to an axis of spin of the airflow to guide
the airflow through the intake duct.
7. The oven intake of claim 1, wherein the one or more cross-sheets
are positioned proximately to the one or more intake fans inside
the intake duct.
8. The oven intake of claim 1, wherein the one or more intake fans
are axial boxer fans located at one end of the intake duct.
9. The oven intake of claim 1, wherein the intake duct has a
conical shape.
10. The oven intake of claim 1, wherein the one or more
cross-sheets reduce frictional losses of the airflow flowing into
the GC oven, introduce a larger volume of air to the GC oven, and
reduce a cool-down time of the GC oven.
11. The oven intake of claim 1, wherein two cross-sheets are placed
in an "=" configuration at one-third and two-thirds of a width of
the intake duct.
12. The oven intake of claim 1, wherein the spin of the airflow
originates from a source other than the one or more intake
fans.
13. A system for providing intake cross-sheets for a gas
chromatographic (GC) oven, comprising: an intake duct having a
convergent section to accommodate the GC oven located at one end of
the intake duct; one or more intake fans located remotely from the
GC oven at an opposite end of the intake duct, the one or more
intake fans supplying airflow to the GC oven; and one or more
cross-sheets positioned inside the intake duct parallel to a
direction of the airflow flowing into the GC oven, wherein the one
or more cross-sheets reduce spin of the airflow originating from
the one or more intake fans and reduce frictional losses of the
airflow flowing into the GC oven.
14. The system of claim 13, wherein each of the one or more
cross-sheets has a converging shape that approximates the
convergent section of the intake duct.
15. The system of claim 13, wherein two cross-sheets are positioned
inside the intake duct to guide the airflow through the intake
duct.
16. The system of claim 13, where the one or more cross-sheets are
positioned proximately to the one or more intake fans inside the
intake duct.
17. (canceled)
18. A method for cooling an oven, comprising: providing one or more
cross-sheets inside an intake duct parallel to a direction of
airflow flowing into the oven, wherein the intake duct has a
convergent geometry to accommodate the oven and has one or more
intake fans located remotely from the oven, and wherein the one or
more intake fans supply airflow for the oven; and enabling the one
or more cross-sheets to reduce spin of the airflow originating from
the one or more intake fans and reduce a cool-own time of the oven,
wherein each of the one or more cross-sheets has a converging shape
that conforms to the convergent geometry of the intake duct.
19. The method of claim 18, further comprising positioning two
cross-sheets inside the intake duct to help guide the airflow
through the intake duct.
20. The method of claim 18, further comprising positioning the one
or m re cross-sheets proximately to the one or more intake fans
inside the intake duct.
Description
TECHNICAL FIELD
[0001] The technical field relates to a gas chromatographic oven,
and, in particular, to oven cooling efficiency.
BACKGROUND
[0002] Gas chromatography (GC) is a physical method for the
separation, identification, and quantification of chemical
compounds. A sample mixture is injected into a flowing neutral
carrier stream and the combination flows through a tube or
chromatographic column. The inner surface of the column is coated
or packed with a stationary phase. As the sample mixture and
carrier stream flow through the column, the components within the
mixture are retained by the stationary phase to varying degrees
depending on the relative volatility of the individual components
and on their respective affinities for the stationary phase.
Different chemical compounds are retained for different times by
the stationary phase. When the individual mixture components are
released into the carrier stream by the stationary phase, the
components are swept towards the column outlet to be detected and
measured by a detector. The specific compounds in the components of
the mixture can be identified and their relative concentrations
determined by measuring peak retention times and peak areas,
respectively.
[0003] A current trend in chromatography is towards improving
sample cycle time to increase customer throughput. Cycle time
includes sample injection time, oven heating time, sample
separation time, and oven cooling or equilibration time. To
decrease sample residence time, ovens are increasingly becoming
more powerful (higher wattage coils) and smaller (lower thermal
mass). As the size of the oven shrinks, often the ductwork for the
oven's intake and exhaust becomes more complex in order to fit in
smaller places or to be located more remotely from the oven.
[0004] A geometry that is utilized in small and fast GC ovens
includes one or more axial boxer intake fans connected to an intake
duct of convergent geometry. The intake fans supply fresh air to
the GC oven through the converging intake duct. The use of a
converging intake duct allows larger intake fans located remotely
from a small oven to be used during cool-down. However, further
improvements can be made to this system to cool the oven more
quickly.
SUMMARY
[0005] An oven intake for a gas chromatographic (GC) oven includes
an intake duct having a convergent geometry to accommodate a small
oven. The intake duct has one or more intake fans that supply
airflow to the GC oven. The airflow originates from the one or more
intake fans and flows through the intake duct into the GC oven. The
oven intake further includes one or more cross-sheets positioned
inside the intake duct parallel to a direction of the airflow
flowing into the GC oven. The one or more cross-sheets reduce spin
of the airflow originating from the one or more intake fans and
guide the airflow through the intake duct into the GC oven.
[0006] A system for providing intake cross-sheets for a GC oven
includes an intake duct having a convergent section to accommodate
the GC oven located at one end of the intake duct. The system
further includes one or more intake fans located remotely from the
GC oven at an opposite end of the intake duct. The one or more
intake fans supply airflow to the GC oven. The system further
includes one or more cross-sheets positioned inside the intake duct
parallel to a direction of the airflow flowing into the GC oven.
The one or more cross-sheets reduce spin of the airflow originating
from the one or more intake fans and reduce frictional losses of
the airflow flowing into the GC oven.
[0007] A method for cooling an oven includes providing one or more
cross-sheets inside an intake duct parallel to a direction of
airflow flowing into the oven. The intake duct has a convergent
geometry to accommodate the oven and has one or more intake fans
located remotely from the oven. The one or more intake fans supply
airflow for the oven. The utilization of the one or more
cross-sheets reduces spin of the airflow originating from the one
or more intake fans and reduces a cool-down time of the oven.
DESCRIPTION OF THE DRAWINGS
[0008] The preferred embodiments of a system and method for
providing intake cross-sheets for a gas chromatographic (GC) oven
will be described in detail with reference to the following
figures, in which like numerals refer to like elements, and
wherein:
[0009] FIG. 1 illustrates an exemplary oven intake with a
converging intake duct and an intake fan;
[0010] FIG. 2 illustrates a cutaway side view of the exemplary oven
intake of FIG. 1 without cross-sheets showing the potential
tendency for airflow spin;
[0011] FIG. 3A illustrates a front view of the exemplary oven
intake of FIG. 1 with the intake fan;
[0012] FIG. 3B illustrates another front view of the exemplary oven
intake of FIG. 1 without the intake fan;
[0013] FIG. 4 illustrates a cutaway top view of the exemplary oven
intake of FIG. 1 showing the location of cross-sheets inside the
intake duct;
[0014] FIG. 5 illustrates an exemplary cross-sheet used in the
exemplary oven intake of FIG. 1 to improve airflow speed; and
[0015] FIG. 6 illustrates a cutaway side view of the exemplary oven
intake of FIG. 1 showing the direction of airflow into a GC
oven.
DETAILED DESCRIPTION
[0016] Current small and fast gas chromatographic (GC) ovens may
use a converging intake duct to connect remotely located larger
intake fans to a small oven. However, a converging geometry
downstream of an axial flow fan generally sustains airflow spin
induced by the axial flow fan that can lead to significant
frictional losses. This effect, in the specific case of conical
geometry, is discussed in Bleier, Frank, Fan Handbook: Selection,
Application, and Design, McGraw-Hill, 1998 (pp 1.09-1.11), but may
be extended to include all geometry of convergent shape. The
induced friction greatly reduces the speed of the airflow and the
volume of fresh air flowing into the oven from the intake fans.
[0017] An apparatus, system and method reduce the cool down time of
GC ovens by supplying larger volumes of air through oven intake
ducts. The system and method provide intake cross-sheets in an oven
intake duct to disrupt and reduce airflow spin, increasing the flow
rate of fresh air into the GC oven and reducing the overall
cool-down time of the GC oven. In addition, because the improved
airflow allows the oven wall temperature to quickly match the oven
air temperature, the noise in the temperature signal may be
reduced. As a result, the GC oven can reach an equilibrium "ready"
state faster. Furthermore, the utilization of the cross-sheets may
allow for flexibility in the design of a fast GC oven--specifically
in the location and shape of the intake duct--without loss of
performance. This flexibility may become increasingly significant
as GC ovens continue on the trend of becoming smaller and
faster.
[0018] FIG. 1 illustrates an exemplary oven intake 100 with a
converging intake duct 120 and an intake fan 140 located upstream
at one end of the converging intake duct 120. The intake fan 140
may be an axial boxer fan. The intake fan 140 supplies fresh air to
a GC oven (not shown) located remotely from the intake fan 140 at
an opposite end of the converging intake duct 120. As shown in FIG.
1, the section of the intake duct 120 that is connected to the
intake fan 140 has an approximately square cross-section 190. The
intake duct 120 then converges to a rectangular cross-section 195
extending to the GC oven. As an example, an intake duct on an
Agilent 6850GC oven is a duct of approximately 92 mm square
cross-section (to accommodate a 92 mm boxer fan), that converges to
a rectangle of 35 mm.times.92 mm cross-section (to fit behind the
keyboard and display of a GC). The intake duct 120 may or may not
have a conical shape.
[0019] FIG. 2 illustrates a cutaway side view of the exemplary oven
intake 100 without cross-sheets showing the potential tendency for
airflow spin 210. The intake duct 120 is shown with a convergent
geometry 165. The intake fan 140 supplies airflow in the direction
180. The airflow flows through the converging intake duct 120 and
into the GC oven in the direction 185. An intake flap 250 directs
the airflow direction 185. Because the intake duct 120 has a
non-uniform converging cross-section, the spin 210 induced by the
axial intake fan 140 about an axis 170 may be sustained through the
length of the intake duct 120. Airflow spin 210 may originate from
a source other than the intake fan 140. The spin 210 may increase
the effective distance the airflow travels, which in turn increases
the frictional losses the airflow experiences due to interaction
with the intake duct wall. This increased friction decreases the
airflow flowing into the GC oven. To increase the velocity and
volume of the airflow flowing into the GC oven, one or more
cross-sheets 110 (shown in FIG. 3B) may be added to the intake duct
120 to reduce the airflow spin 210.
[0020] FIG. 3A illustrates a front view of the exemplary oven
intake 100 with, the intake fan 140. FIG. 3B illustrates another
front view of the exemplary oven intake 100 without the intake fan
140. Two cross-sheets 110 are shown in FIG. 3B. The cross-sheets
110 are located inside the intake duct 120 near the intake fan 140,
such as 2 cm from the fan 140, and parallel to the direction of the
airflow. The cross-sheets 110 shown here are trapezoidal in shape,
with bases slightly undersized from 35 mm and 92 mm, to approximate
the convergent section of the oven intake 100. However, other
shapes and sizes of cross-sheets may be employed. The cross-sheets
110 may be secured to the intake duct wall by riveting metal tabs
115. If only one cross-sheet is used, the cross-sheet may be placed
off-centered, for example, at one-third of the width of the intake
duct 120 or one-third the diameter of the intake fan 140, to
disrupt the spin 210. Additional cross-sheets may be used. For
example, additional cross-sheets may be added alongside the
cross-sheets 110 shown. One, two, three or more may be added. Also,
cross-sheets may be added orthogonal to or at right angles to the
cross-sheets 110 shown. A preferred embodiment is two cross-sheets
placed in an "=" configuration at one-third and two-thirds of the
width of the intake duct 120 or intake fan 140 diameter. Other
arrangements of cross-sheets are possible with the same beneficial
effect.
[0021] FIG. 4 illustrates a cutaway top view of the exemplary oven
intake 100 showing the location of the cross-sheets 110 inside the
intake duct 120. The intake fan 140 supplies airflow in the
direction 180. The airflow flows through the converging intake duct
120 into the GC oven. As noted above, the intake fan 140 may induce
airflow spin 210 about an axis 170. The utilization of the
cross-sheets 110 disrupts 220 the tendency for the airflow to
maintain spin 210 so that the airflow is guided 230 through the
intake duct 120 to reach the GC oven. As a result, the frictional
losses may be reduced because the distance over which any piece of
fluid interacts with the intake duct wall is reduced. The reduced
frictional losses may lead to increased airflow speed and
consequently more fresh air flowing into the GC oven during
cool-down. The cross-sheets 110 preferably are located close to the
intake fan 140 to guide the airflow as soon as possible, such as 2
cm from the intake fan 140.
[0022] FIG. 5 illustrates an exemplary cross-sheet 110 used in the
exemplary oven intake 100 to improve airflow speed. The metal tabs
115 are riveted to secure the cross-sheets 110 to the intake duct
wall. Other methods of securing, for example, screws, bolts, etc.,
may be used. The cross-sheets 110 shown in FIG. 5 has a converging
shape 160 that conforms to and approximates the intake duct's
convergent geometry 165.
[0023] FIG. 6 illustrates a cutaway side view of the exemplary oven
intake 100 showing the direction 185 of airflow into the GC oven.
As stated above, the intake fan 140 supplies airflow in the
direction 180. The airflow is guided 230 by the cross-sheets 110
located inside the intake duct 120 directly in front of the intake
fan 140. The guided airflow flows through the converging intake
duct 120 into the GC oven in the direction 185. The utilization of
the cross-sheets 110 reduces the airflow spin 210 induced by the
intake fan 140 and sustained by the convergent geometry 165 of the
intake duct 120, increasing the flow rate and volume of fresh air
into the GC oven.
[0024] The overall cool-down time of the GC oven may be reduced as
the flow rate of fresh air into the GC oven is increased. Also, the
noise in the temperature signal may be reduced because the improved
airflow allows the oven wall temperature to quickly match the oven
air temperature. As a result, the GC oven can reach an equilibrium
"ready" state faster. In addition, the utilization of the
cross-sheets 110 may allow for flexibility in the design of a fast
GC oven without loss of performance. For example, converging intake
ducts may be used to allow larger intake fans located remotely from
a small oven to be used during cool-down without suffering
frictional losses induced by the airflow spin 210.
[0025] The following experiments illustrate the benefit of using
the cross-sheet 110, specifically measured as the flow rate of air
exhausted from the GC oven into open air.
[0026] One type of experiment is a battery of airflow measurements.
In this experiment, an oven without insulation or support, such as
an Agilent 6850 inner oven, is equipped with an axial fan 140 and
one or more cross-sheets 110. The cross-sheets are placed in
various locations in the oven intake duct 120. The oven stirring
fan is not present in this experiment. The oven is sealed with a
plastic cover.
[0027] The flow rate of air exhausted from the oven is measured
using both a vane anemometer and a hot-wire anemometer. An
anemometer is an instrument for measuring and indicating airspeed.
Because the airspeed varies over the cross-section of the oven's
exhaust duct (not shown), four points are taken to generate an
average velocity. The experiment is performed at room temperature
and under standard pressure. Table 1 illustrates the results of
this experiment.
1TABLE 1 Airspeed (m/s) Number of Airspeed (m/s) Hot-wire
Cross-Sheets Vane Anemometer Anemometer 0 3.300 3.1725 1 3.475 N/A
2 3.650 3.450 3 3.675 3.425
[0028] Although some discrepancy exists over absolute values
between the vane anemometer and the hot-wire anemometer, the trend
is evident. The airspeed increases with the presence of the
cross-sheets 110. For this particular application little if any
improvement is shown when using more than two cross-sheets 110. As
a result, the preferred number of cross-sheets is two.
[0029] For the special case of one cross-sheet, the cross-sheet is
off-centered, for example, at one-third of the width of the intake
duct, to generate the beneficial result illustrated in Table 1. If
the cross-sheet is centered along the width of the intake duct, the
cooling time actually increases.
[0030] A second type of experiment is more application specific.
This experiment compares the cooling profile of GC ovens, such as
Agilent 6850GC prototype ovens, that are equipped with one or more
cross-sheets 110 with the same GC ovens without the cross-sheets
110. Table 2 illustrates the cool-down time of an Agilent prototype
oven, which is geometrically similar to a standard Agilent 6850GC
oven with the exception of the wall material. In addition, a more
efficient intake fan 140 is used in this experiment, and the
observed benefit of two cross-sheets 110 is apparent as shown below
in Table 2.
2TABLE 2 Prototype Oven with More Efficient Fan Cross-sheets?
Cool-down Time (min) No 4.07 Yes 3.40
[0031] As shown in this experiment, the addition of two
cross-sheets 110 inside the intake duct 120 reduces the cool-down
time of the GC oven by more than 16%.
[0032] While the system and method for providing intake
cross-sheets for a GC oven have been described in connection with
an exemplary embodiment, those skilled in the art will understand
that many modifications in light of these teachings are possible,
and this application is intended to cover variations thereof.
* * * * *