Gas separation: apparatus – Chromatography type apparatus
Reexamination Certificate
1999-07-30
2001-06-19
Spitzer, Robert H. (Department: 1724)
Gas separation: apparatus
Chromatography type apparatus
C095S087000, C096S102000, C210S198200
Reexamination Certificate
active
06248158
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for the provision of a controlled thermal environment, and, more particularly, for an oven housing module suitable for effecting thermal control of a component located therein.
BACKGROUND OF THE INVENTION
Modern analytical instruments are particularly susceptible to performance variations due to the thermal sensitivity of certain components that operate within the analytical instrument. The temperature of one or more components of an analytical instrument is typically controlled by locating the component in a temperature-controlled environment, or thermal zone. The temperature of the thermal zone is typically effected by an electrically-powered heating device or cooling device, or a combination of such devices.
One particular type of analytical instrument is a chromatograph. The basic components of a chromatograph include an injection port for introducing a sample of matter to be examined into a stream of carrier fluid, a separation column attached to the injection port that causes some of the constituents of the sample to elute at different times, and a detector for producing a signal indicative of the presence of the constituents being eluted. A signal processing section may be employed for integrating the signal so as to provide information as to the quantity of each constituent.
In the typical gas chromatograph, the temperature controlled zone is provided within an oven cavity. The injection port and detector are attached to respective pneumatic fittings on the oven housing, and the separation column, usually mounted on a basket, is attached between the pneumatic fittings and located within the oven cavity. The oven housing typically comprises a fast-cooling flap and an enclosure having several insulated oven housing walls. A heating element and a stirring fan located in the oven cavity respectively heats and stirs the air contained within the oven cavity so as to minimize temperature gradients therein that could adversely affect the performance of the chemical process occurring within the column. During a typical sample analysis, the heating element is operated so as to increase the temperature of the oven from a minimum initial value to a final value. Before introduction of the next sample into the column, the temperature of the oven is usually returned to its initial value.
The conventional chromatograph is typically constructed for operation of one or more capillary columns that are wound on 5 inch (or larger) diameter baskets. Additional components may also be designed for operation within the thermal zone. A large oven cavity (typically over one thousand cubic inches) is often built to accommodate the foregoing requirements. The typical oven cavity housing is constructed of an inner wall of thin stainless-steel surrounded by some type of soft insulation, which in turn is surrounded by an outer casing of structural sheet metal.
High resolution gas chromatography requires that the oven temperature be varied from an initial temperature to a final temperature, according to a precisely controlled profile, as known in the art. After the oven reaches its final temperature, the analysis is considered to be complete. However, to begin a new analysis, the oven must be cooled to a predetermined initial temperature. Cooling is typically accomplished by opening a vent in the rear of the oven cavity. This method of cooling is inefficient and usually results in a long cooling cycle due to the recirculation of considerable amounts of heated air.
The entire oven cavity is subject to these repeated patterns of heating and cooling. Accordingly, with repeated cycling of the heating unit, fan, and other such devices, a large amount of energy is generated and dissipated, and thus the chromatograph consumes a considerable amount of power.
In some applications, the temperature control system may be expected to produce an especially fast oven temperature ramp rate. However, such a rate causes the temperature control system to consume an even greater amount of electrical current, one which is beyond the amperage typically available from a single mains socket (e.g., over 15 amps). Oven designs that are capable of programmed temperature ramp rates beyond 60 degrees centigrade per minute will therefore require a voltage supply that exceeds 120 volts AC.
Furthermore, the time required for heating and cooling the oven cavity is too long. The time required to cool the oven will reduce the throughput of the instrument and the overall efficiency of the oven is not optimal.
Accordingly, the conventional chromatograph is best suited for use in the laboratory, or similar settings, where sufficient space and electrical power are available. There have been attempts to reduce the size and complexity of a chromatograph so as to be practical outside of the laboratory. Such miniaturization has not been fully realized, due in part to the power demands put on the system by an inefficient oven, and due to the large size and large thermal mass that is presented by the typical oven housing.
There is accordingly an unresolved need for a more compact, reliable, and energy efficient system for providing the requisite control of a thermal zone, so as to effect,inter alia, faster analysis, in an analytical instrument.
SUMMARY OF THE INVENTION
We have determined that the energy efficiency of a thermal zone in an analytical instrument is improved by use of a compact oven cavity in an oven housing module wherein a fan and a fast cooling flap are provided, wherein the fast cooling flap may be operated for opening at least one side of the oven cavity to ambient conditions, such that heated cavity air may be rapidly exhausted from the oven cavity.
In a preferred embodiment, the oven module features an enclosure body formed of rigid insulating material that encloses the oven cavity in which is the desired thermal zone. This novel oven housing module has less thermal mass and accordingly retains less heat than the conventional oven housing, so as to reduce not only the the amount of heating or cooling required for temperature control of a component positioned therein, but also the time required for effecting thermal changes, thus accomplishing a much faster analysis.
The thermal response of the oven module, that is, the time necessary for adjusting the temperature of the thermal zone by a temperature control assembly is greatly improved. Accordingly, temperature changes according to an oven temperature profile (e.g., ramp rate) may be accomplished faster and more efficiently than found in the prior art.
In a particularly preferred embodiment of the invention, the oven housing module includes, in the enclosure body, a fast-cooling flap constructed of rigid insulating material, wherein the enclosure body exhibits a size and shape sufficient to enclose the oven cavity and define therein a thermal zone, whereby the oven housing module impedes heat transfer between the thermal zone and ambient conditions. The body includes an interior surface which faces the thermal zone. The oven housing module includes an oven vent assembly and an oven fan assembly having a fan. The oven cavity in the enclosure body is shaped so as to provide a thermal envelope about the component, whereby the envelope corresponds to the volume occupied by the component located in the thermal zone and includes a marginal volume disposed about the component so as to permit a primary air flow to be directed by the fan around the component for efficient temperature control of the component.
In one aspect of the invention, the fast cooling flap, adjustment of the fast-cooling flap position alters the primary air flow about the component so as to draw a secondary flow of ambient air rapidly across the oven walls and through the volume occupied by the component, and then directed out of the oven cavity, whereby such efficient circulation of the primary air flow through the thermal zone effects very rapid cooling of the component, the cavity air, and the wallsof the oven cavity.
In another as
Abdel-Rahman Mahmoud F.
Firor Roger L.
Agilent Technologie,s Inc.
Spitzer Robert H.
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