DE102011006165A1 - Cooling device with adjustable evaporation temperature - Google Patents

Abstract

The invention relates to a cooling device for cooling a test sample, comprising at least two cooling cascade stages, each comprising at least one refrigerant line, a compressor (1.1, 2.1), an expansion throttle (1.4, 2.4), an evaporator (6, 7) and a condenser (3, 6), which is characterized in that an additional expansion throttle is arranged between the evaporator (7) of the last cooling cascade stage and the compressor (2.1) of the last cooling cascade stage. This is a simple way to adjust the cooling temperature, being dispensed with cold-adjusting valves, as they are complicated and expensive.

Description

The invention relates to a cooling device for cooling a measurement sample, comprising at least two cooling cascade stages, each of which comprises at least one refrigerant line, a compressor, an expansion throttle, an evaporator and a condenser.

Devices which exhibit such properties are, for example, the NMR90 from Millrock Technology, Kingston, NY, USA, the ULSP90 from ULSP bv, Ede, NL and the FTS XR Air Jet from Rototec Spintec GmbH, Biebesheim, D.

In various analytical methods, it is necessary to cool the samples to be analyzed. In selected cases, such as nuclear magnetic resonance spectroscopy or x-ray crystallography, this is often done by placing the sample in a cold gas stream (cooling gas), preferably nitrogen or helium.

This cold gas stream can be realized, for example, by evaporating liquid gases or by cooling a warm gas by means of heat exchangers immersed in liquid gas. However, a complex logistics for the procurement or production and storage of these liquefied gases must be operated.

Alternatively, the cooling of the warm gas can also be carried out by means of a refrigerant cycle. In this case, in a cyclic process, a suitable refrigerant in a compressor is brought to a higher pressure and thereby heated, cooled in a heat exchanger under heat given the pressure prevailing at the pressure condensing temperature (deprived) and liquefied under release of further heat, by a suitable throttle relaxes a lower pressure and re-evaporated in a second heat exchanger while absorbing heat from the gas to be cooled at the low evaporation temperature.

To set the desired cooling temperature, arrangements of refrigerant circuit processes with adjustable evaporating pressure with variable throttle between the first (refrigerant condenser) and second heat exchanger (refrigerant evaporator) are known. This arrangement is technically complicated when the cycle to be varied already works in a cascade of cycle processes with a very low condensation temperature and thus this adjustable throttle also becomes very cold.

For this reason, it is currently largely unnecessary to set the desired cooling temperature. For example, this applies to the devices of the companies Broker (type "BCU-X"), ULSP type "90 Immersion Probe Cooler" and Milrock type "NMR90 sample cooler". Alternatively, the cooled to a fixed set temperature gas flow is heated with a built-in heater to a desired, higher temperature. An example of this are the devices of the company RototecSpintec FTS "XR Air-Jet Cooler".

Object of the present invention is therefore to provide a simple way to adjust the cooling temperature, which is to be dispensed with cold valves, as they are complicated and expensive.

This object is achieved in a surprisingly simple yet effective manner in that an additional expansion throttle is arranged between the evaporator of the last cooling cascade stage and the compressor of the last cooling cascade stage.

In the inventive cooling device, the evaporated refrigerant after the second heat exchanger (evaporator) is relaxed again. As a result, the entire relaxation between high-pressure and low-pressure side of the compressor is divided into two partial relaxations, wherein the intervening pressure in the evaporator is influenced by the adjustable throttle of the second partial relaxation. The evaporation of the refrigerant takes place under provision of the desired cooling capacity in the second heat exchanger, which lies between the two throttles, at the evaporation temperature of the refrigerant at this pressure which can be influenced, and thus the cooling temperature can likewise be influenced.

In contrast to the commonly used method, it is thus avoided that the throttle itself must be adjustable, which would be possible with a circuit to be varied in a cascade of cycles with a very low condensing temperature and thus low throttle temperature only with great technical effort.

Another advantage of this invention results from the fact that at higher desired temperature and thus higher desired evaporation pressure in the second heat exchanger by the necessary stronger relaxation at the second throttle results in a lower suction pressure in the compressor, resulting in this lower power consumption. In contrast, a cold-adjustable throttle between the first and second heat exchanger when setting a higher evaporation temperature and thus a lower cooling power requirement would cause a higher suction pressure and thus a greater power consumption of the compressor.

A particularly advantageous embodiment is characterized in that the additional expansion throttle is designed in two stages as a parallel arrangement of a bypass valve and an invariable expansion throttle. In this way, a variable expansion throttle is created with simple and inexpensive means.

Alternatively, the additional expansion throttle is designed as a variable, adjustable expansion throttle.

A further advantageous embodiment is characterized in that the evaporator of the last cooling cascade stage is designed as a heat exchanger, that a cooling gas enters the heat exchanger through a gas inlet, gives off heat and exits through a gas outlet from the heat exchanger, and that the cooled cooling gas passed to the measurement sample will be to cool this. Due to this structure, the heat exchanger is at the same time a transfer line for the cooling gas and the device can be designed to be simple and space-saving.

The advantages of the invention are particularly effective when the cooling device is part of a nuclear magnetic resonance spectrometry apparatus, since the cooled gas stream is heated to the desired temperature and less cooled for higher temperatures and therefore less heating, which simplifies the scheme ,

The cooling device according to the invention may alternatively also be part of an apparatus of X-ray spectroscopy. Especially in X-ray crystallography, the measurement samples often have to be cooled.

Alternatively, the cooling device according to the invention is also advantageous if it is part of an apparatus of the EPR.

Further advantages of the invention will become apparent from the description and the drawings. Likewise, the features mentioned above and those listed further can be used individually or in any combination. The embodiments shown and described are not to be understood as exhaustive enumeration, but rather have exemplary character for the description of the invention.

It shows:

1 a schematic representation of an embodiment of the inventive cooling device.

In the 1 An exemplary cooling device according to the invention includes a first cooling cascade stage with compressor 1.1 , Safety pressure switch 1.2 , Filters 1.3 , Relaxing throttle 1.4 , and pressure balance vessel 1.5 and a second cooling cascade stage with compressor 2.1 , Safety pressure switch 2.2 , Filters 2.3 , Relaxing throttle 2.4 , and pressure balance vessel 2.5 ,

For example, a combined air heat exchanger with blower 5 serves as a liquefier 3 for the first cooling cascade stage and as a desuperheater 4 for the second cooling cascade stage.

A heat exchanger 6 serves as an evaporator for the first cooling cascade stage and as a condenser for the second cooling cascade stage.

An evaporator (heat exchanger) 7 , exemplified as a transfer line of the cooling gas, serves as an evaporator for the second cooling cascade stage to provide the desired cooling capacity, in which the cooling gas from entry 7.1 to the exit 7.2 to be led.

The inventive setting of the desired temperature by changing the evaporation pressure of the refrigerant in the second stage of a cooling cascade shown here by way of example is carried out by a variable throttle on the return path of the refrigerant from the evaporator 7 to enter the compressor 2.1 , Shown is this variable throttle in 1 exemplified by an invariable expansion throttle 2.6 and a bypass valve 2.7 to bypass this throttle. This results in open bypass valve 2.7 a lower release pressure and with a closed bypass valve a higher expansion pressure in the evaporator 7 and thus a lower or higher evaporation temperature. Instead of the invariable relax throttle 2.6 and the bypass valve 2.7 Alternatively to the example shown, a variable throttle in the form of an adjustable needle valve can also be used.

Although here the invention has been shown on a cooling device according to the principle of the compression refrigeration machine with two-stage cooling cascade, the adjustability of the evaporation temperature by a variable throttle between the refrigerant evaporator and the compressor inlet is also possible with single-stage cooling devices according to this principle as well as in cooling cascades with more than two steps.

LIST OF REFERENCE NUMBERS

1.1

Compressor of the first cooling cascade stage

1.2

Safety pressure switch of the same

1.3

Filter the same

1.4

Relaxing throttle of the same

1.5

Equalizing vessel of the same

2.1

Compressor of the second cooling cascade stage

2.2

Safety pressure switch of the same

2.3

Filter the same

2.4

Relaxing throttle of the same

2.5

Equalizing vessel of the same

2.6

Relaxing throttle for setting a higher evaporation pressure of the second cooling cascade stage

2.7

Bypass valve to bypass the expansion throttle 2.6 for setting a lower evaporation pressure of the second cooling cascade stage

3

Condenser of the first cooling cascade stage

4

Desuperheater of the second cooling cascade stage

5

Fan for condenser 3 and desuperheater 4

6

Heat exchanger as the evaporator of the first and condenser of the second cooling cascade stage

7

Heat exchanger as an evaporator of the second cooling cascade stage for providing the cooling power by cooling a gas

7.1

Entry of the gas to be cooled

7.2

Exit of the cooled gas

Claims (7)

Cooling device for cooling a test sample, having at least two cooling cascade stages, each comprising at least one refrigerant line, a compressor ( 1.1 . 2.1 ), a relax throttle ( 1.4 . 2.4 ), an evaporator ( 6 . 7 ) and a liquefier ( 3 . 6 ), characterized in that between the evaporator ( 7 ) of the last cooling cascade stage and the compressor ( 2.1 ) of the last cooling cascade stage an additional expansion throttle is arranged. Cooling device according to claim 1, characterized in that the additional expansion throttle two-stage as a parallel arrangement of a bypass valve ( 2.7 ) and an invariable relax throttle ( 2.6 ) is executed. Cooling device according to claim 1, characterized in that the additional expansion throttle is designed as a variable, adjustable expansion throttle. Cooling device according to one of the preceding claims, characterized in that the evaporator ( 7 ) of the last cooling cascade stage is designed as a heat exchanger that a cooling gas by a gas inlet ( 7.1 ) enters the heat exchanger, gives off heat and by a gas outlet ( 7.2 ) exits the heat exchanger again and that the cooled cooling gas is passed to the sample to cool it. Cooling device according to one of claims 1 to 4, characterized in that the cooling device is part of a nuclear magnetic resonance spectroscopy apparatus. Cooling device according to one of claims 1 to 4, characterized in that the cooling device is part of an apparatus of X-ray spectroscopy. Cooling device according to one of claims 1 to 4, characterized in that the cooling device is part of an apparatus of the EPR.

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