DIFFUSION PUMP

Description

[0001] The invention relates to a diffusion pump.

[0002] Conventional diffusion pumps have a boiling chamber in which a heating element is located. The heating element vaporizes a propellant. Directly adjacent to the boiling chamber, a typical diffusion pump has a housing. A nozzle is located in the housing. The propellant vapor rises from the boiling chamber to the nozzle, is deflected by the nozzle into an umbrella-shaped vapor jet, and entrains diffusing gas molecules. The propellant vapor is then condensed again by a condenser. The condensed propellant returns to the boiling chamber. The entrained gas is pumped out by a vacuum pump connected to a forevacuum nozzle. This process draws gas out of a vacuum chamber, creating a vacuum in the vacuum chamber.

[0003] The diffusion process used in a diffusion pump is energy-intensive. First, the propellant must be brought to a boil or vaporize at a high temperature. This is typically achieved using electrical heating energy. However, the propellant vapor must then be condensed again. For this, the introduced heat must be dissipated. Dissipated heat is lost energy, which is removed from the overall process.

[0004] Furthermore, the diffusion process in conventional diffusion pumps is unregulated, meaning the heating element heats the propellant to a preset (temperature) value. This preset temperature is then maintained constant. Furthermore, no higher requirements are placed on the preset temperature other than that the propellant evaporates and does not undergo thermal decomposition. Cooling in conventional diffusion pumps is also unregulated, so maximum cooling is selected. With an unregulated heating element, unused heat must be dissipated through increased cooling.

[0005] Thus, known diffusion pumps are energy inefficient and are characterized by unnecessarily high energy consumption.

[0006] US 2011 / 021332 A1 describes a centrifuge comprising a rotor for receiving a sample, a rotation chamber for housing the rotor, a motor for rotating the rotor, an oil diffusion pump for reducing pressure within the rotation chamber, and a control unit for controlling the heating temperature of the oil diffusion pump to a target set temperature. The control unit changes the target set temperature from a first predetermined temperature to a second predetermined temperature lower than the first predetermined temperature after a predetermined period of time has elapsed since the start of the heating temperature control.

[0007] JP S61 10999 U describes a cooling tube wound around an outer peripheral surface of a casing and a heater mounted at a lower end portion of the casing. A thermocouple is also provided for detecting the temperature within the cooling tube or the heating vessel. A temperature controller is provided to stop the pump when each thermocouple is connected in series and the sum of the temperatures detected by the respective thermocouples is 10 to 20 °C higher than during normal operation of the diffusion vacuum pump.

[0008] The object of the present invention is to provide a diffusion pump in which energy consumption is reduced.

[0009] The problem is solved by a method according to claim 1.

[0010] A diffusion pump according to one example, in particular an energy-efficient diffusion pump, has a housing. A boiling chamber is connected to the housing, with a heating element arranged in the region of the boiling chamber. A propellant is vaporized by the heating element in the boiling chamber. A nozzle is arranged in the housing, which is connected to the boiling chamber. The propellant vapor from the boiling chamber thus reaches the nozzle and exits through the nozzle. A condenser is arranged on an inner side of the housing, in the region of the nozzle. Furthermore, a cooling system is arranged in the region of the condenser for cooling the condenser. The propellant vapor exiting the nozzle reaches the condenser and condenses at the nozzle. The condensed propellant returns to the boiling chamber of the diffusion pump. In particular, a vacuum chamber is connected to the housing, which is evacuated by the diffusion pump.

[0011] The boiling chamber is thermally separated from the housing and in particular from the condenser by an insulator. The insulator prevents heat generated by the heating element in the boiling chamber from being transferred to the condenser, as the temperature in the boiling chamber is considerably higher than the temperature of the condenser. Heat that would be transferred from the boiling chamber to the condenser if the insulator were missing would have to be dissipated by cooling the condenser in order to ensure a constant temperature in the condenser. This increases the cooling requirements for the condenser. At the same time, the dissipated heat results in energy loss, as the dissipated heat is no longer available to heat the propellant. The insulator is therefore characterized in particular by its low thermal conductivity, meaning that heat cannot be transferred from the boiling chamber to the condenser.This reduces both the energy consumption of the heating element and the cooling requirements of the condenser.

[0012] Alternatively or additionally, the cooling of the diffusion pump's condenser is at least partially implemented as water cooling. The condensation heat generated at the condenser is dissipated by the water cooling.

[0013] Alternatively or additionally, the cooling of the diffusion pump's condenser is connected to the heating element via a heat pump. This transports heat generated at the condenser by the condensation of the propellant vapor to the heating element, so that the transported heat can be used to evaporate the propellant. The heat pump makes it possible to return heat energy that must be extracted from the process by the condenser to the pumping process via the heating element. This significantly reduces the process's power loss, so that both the energy required for the heating element and the demand for condenser cooling can be reduced. In particular, if the condenser is cooled by water, the provision of a heat pump can reduce the amount of water required to cool the condenser.

[0014] Alternatively or additionally, the diffusion pump has a temperature sensor that detects the condenser temperature, wherein the temperature sensor is connected to a condenser cooling control for controlling the cooling of the condenser. This allows the cooling of the condenser to be individually adapted to the existing requirements. In this case, reducing the temperature of the condenser to the lowest possible temperature is no longer necessary. By controlling the cooling of the condenser and the associated adaptation to the required condenser temperature, further energy, in particular energy for cooling the condenser, can be reduced. If the condenser is cooled by water cooling, the required amount of cooling water can be reduced by providing a temperature sensor and a condenser cooling control connected to the temperature sensor.

[0015] Alternatively or additionally, the diffusion pump has a heating element control connected to the heating element. The heating element control allows the heating element's power to be adapted to the current pumping situation. Three pumping situations are conceivable. In a first pumping situation, no or only minimal pumping of the diffusion pump is required. This pumping situation occurs particularly between two pumping processes. A second pumping situation is pumping down, in which the working pressure in the vacuum chamber is to be achieved starting from a forevacuum, in particular generated by a forevacuum pump.

[0016] The working pressure is the pressure to be generated by the diffusion pump in the vacuum chamber. The second pumping situation is characterized in particular by a high mass flow. In the third pumping situation, the working pressure in the vacuum chamber is maintained by the diffusion pump. The diffusion pump still requires pumping, but the mass flow is significantly lower than when pumping down. Depending on the current pumping situation, the heating element's heating power is adjusted by the heating element control system so that the heating power is optimally utilized and no excess heat is introduced into the diffusion pump, which would then have to be laboriously dissipated by cooling the condenser.

[0017] By applying individual, independent measures mentioned above or by combining them, an energy-efficient diffusion pump is obtained, which can significantly reduce energy consumption.

[0018] In particular, the diffusion pump is designed to generate a vacuum pressure of 10 -3< mbar, preferably 10 -6< mbar and particularly preferably 10 -9< mbar.

[0019] In particular, the insulator for thermally separating the boiling chamber from the condenser is made of PEEK, PTFE, another plastic, or a ceramic. These materials are characterized by low thermal conductivity while simultaneously ensuring high thermal stability.

[0020] Preferably, the boiling chamber is completely thermally insulated from the environment in the area of the heating element. This reduces heat loss due to the transfer of heat from the outside of the boiling chamber to the environment. In particular, the heat generated by the heating element is retained within the boiling chamber, further reducing the heating power and thus the energy required to heat the conveying medium.

[0021] In particular, the diffusion pump has a vapor barrier axially spaced from the nozzle, wherein the vapor barrier has vapor barrier cooling independent of the condenser cooling. The vapor barrier is intended to prevent propellant vapor from entering the vacuum chamber, since the propellant vapor is previously condensed at the vapor barrier. In particular, the temperature difference between the vapor barrier and the condenser is large and particularly preferably greater than 20°C. This ensures that propellant vapor that does not condense at the condenser is condensed at the vapor barrier. In particular, if the condenser cooling is designed to be variable by providing a condenser cooling control, it is preferable to design the vapor barrier cooling in such a way that constant cooling of the vapor barrier is achieved.Since the vapor barrier is a system designed to protect equipment in the vacuum chamber from damage caused by propellant vapor, it is important to ensure that the vapor barrier functions properly under all circumstances. This is achieved through constant cooling.

[0022] In particular, the vapor barrier and the vacuum-side region of the condenser have a temperature of 20°C - 30°C. The high-vacuum side region is the area of the condenser facing the vacuum chamber. The low temperature of the vapor barrier and the condenser ensures reliable condensation of the propellant. However, the temperature of the condenser can be adjusted depending on the required working pressure or pumping power.

[0023] In particular, a forevacuum nozzle is arranged between the nozzle and the boiling chamber, which can be connected to a forevacuum pump. The forevacuum nozzle has a cooling system. Preferably, the cooling system, as a forevacuum support, is independent of the cooling of the condenser. Cooling the forevacuum support prevents propellant vapor from entering the forevacuum pump.

[0024] Preferably, the cooling of the pre-vacuum nozzle and / or the cooling of the vapor barrier is at least partially water cooling.

[0025] In particular, if the cooling of the condenser is at least partly water-cooled, the condenser cooling control has a thermostatic valve through which the amount of cooling water can be controlled depending on the detected condenser temperature.

[0026] In particular, the condenser cooling control system has an emergency device, which ensures minimum cooling of the condenser. Since if the condenser cooling system fails, the propellant vapor is no longer condensed and would enter the vacuum chamber uncontrollably. To prevent this, the emergency device ensures minimum cooling of the condenser. In particular, if the condenser cooling control system has a thermostatic valve, the minimum cooling is ensured by a bypass past the thermostatic valve. Just enough cooling water flows through the bypass to achieve the minimum cooling of the condenser. If the condenser cooling control system fails, cooling water continues to flow through the bypass to the condenser to cool the condenser.

[0027] In particular, an evaporator of the heat pump is connected to the cooling system of the condenser, and a condenser of the heat pump is connected to the heating element. As a result, heat removed from the propellant by the condenser is returned to the heating element. In particular, the heat pump is designed as a compression heat pump or an absorption heat pump.

[0028] In particular, it is preferred to cool the condenser both by water cooling and by a heat pump. In particular, the high-vacuum side of the condenser has water cooling, and the adjacent area of the condenser toward the heating element is connected to the heat pump.

[0029] Preferably, the heat pump is designed in several stages, whereby a higher temperature difference can be provided between the evaporator of the heat pump, which is connected to the cooling of the condenser, and the condenser of the heat pump, which is connected to the heating element.

[0030] In particular, the propellant is a silicone oil, a mineral oil, or Fomblin®. The mineral oil is preferably Diffelen®. It is preferred that the propellant used has a low evaporation enthalpy.

[0031] In water cooling, water is preferably used as the cooling fluid. However, the use of another cooling fluid is also conceivable. In this case, however, it may be necessary to circulate the cooling fluid. This requires cooling of the cooling fluid. In this case, the present invention does not reduce the amount of cooling water or cooling fluid, but rather the energy required to cool the cooling fluid pumped in the circuit. This is equivalent to reducing the required amount of cooling water.

[0032] The invention relates to a method for controlling a diffusion pump having a housing, a boiling chamber connected to the housing, a heating element arranged in the region of the boiling chamber, a nozzle arranged in the housing and connected to the boiling chamber, a condenser arranged on an inner side of the housing in the region of the nozzle, and a cooling system arranged in the region of the condenser for cooling the condenser, wherein the heating element temperature of the heating element is adjusted during the pumping process to the upper value of the boiling range of the propellant used. This prevents unnecessary heating energy from being introduced into the diffusion pump. If the temperature of the heating element is adjusted to the upper value of the boiling range of the propellant used, this ensures that the propellant, in particular its low-boiling components and its high-boiling components, can be evaporated.A higher heating element temperature is not required, so no additional energy is required. In particular, this also ensures that the propellant used is not thermally decomposed.

[0033] In particular, in addition to adjusting the heating element temperature, the condenser temperature can be detected, and a condenser cooling controller can control the condenser cooling depending on the detected condenser temperature. This allows for precise adjustment of the heat input and the required cooling capacity.

[0034] In a further development of the method according to the invention, the condenser cooling control ensures that the condenser temperature is always kept below the condensation temperature of the propellant, thus ensuring that the vapor pressure of the propellant is always lower than the working pressure of the diffusion pump. Thus, it is not necessary to bring the condenser temperature to the lowest possible temperature by cooling the condenser. Instead, the method individually adjusts the condenser temperature, which can change, in particular, depending on the required working pressure. This significantly reduces the amount of cooling water required.

[0035] In a further development of the method according to the invention, the heating element temperature is adjusted during the pumping process to the upper value of the boiling range of a propellant used. A pumping process encompasses both pumping out the vacuum chamber and maintaining the working pressure in the vacuum chamber. By adjusting the heating element temperature to the upper value of the boiling range, the lowest possible heating output is achieved while simultaneously ensuring reliable evaporation of the propellant. The boiling range of the propellant used encompasses the range in which low-boiling and high-boiling components of the propellant evaporate. If the temperature is adjusted to the upper value of the boiling range of the modified propellant, both the low-boiling and high-boiling components of the propellant evaporate.

[0036] In a further development of the method according to the invention, the heating element temperature is adjusted during the pumping process to the required suction power of the pump. Increasing the heating element temperature, in particular, increases the suction power of the diffusion pump. This is particularly necessary when pumping out the vacuum chamber, since in this pumping situation, a high suction power is required to quickly reach the working pressure in the vacuum chamber.

[0037] In a further development of the method according to the invention, the heating element temperature is reduced between pumping cycles. If pumping of the diffusion pump is not required, the heating element temperature can be reduced to save energy. In particular, the heating element temperature is reduced between pumping cycles by at least the value of the boiling range of the propellant used. If the heating element temperature is below the boiling range of the propellant used, little or no propellant is evaporated, so that no pumping effect is achieved and, at the same time, considerable heating power can be saved. Of course, the heating element temperature can be further reduced between pumping cycles, although the propellant must then first be heated up, which is energy-intensive, for the next pumping cycle.Also, below a certain temperature, gas accumulates in the propellant, so that the propellant must first be degassed before the next pumping process begins.

[0038] In a further development of the method according to the invention, the condenser temperature is adjusted simultaneously when the heating element temperature is reduced. This occurs particularly between pumping processes. However, the condenser temperature can also be adjusted simultaneously with the heating element temperature while maintaining the working pressure in the vacuum chamber, so that an optimal diffusion process can be maintained, with the diffusion pump operating in an energy-efficient manner. Preferably, the condenser temperature is increased when the heating element temperature is reduced. However, this only occurs as long as the vapor pressure of the propellant at the increased condenser temperature is lower than the working pressure of the diffusion pump.

[0039] In a further development of the method according to the invention, a diffusion pump designed as described above is used in the method.

[0040] Furthermore, an example relates to the use of a heat pump with a diffusion pump. The heat pump is preferably developed as described above. Particularly preferably, the diffusion pump is also developed as described above.

[0041] The invention is explained in more detail below using preferred embodiments with reference to the accompanying drawings.

[0042] They show: Figure 1A schematic representation of a diffusion pump according to a first example, Figure 2a schematic representation of the pumping process based on pump-specific variables, Figure 3a schematic representation of a diffusion pump according to a second example and Figure 4a schematic representation of a diffusion pump according to a third example.

[0043] The diffusion pump according to one example comprises a housing 10 having a flange 12 at its high-vacuum end, with which the housing 10 can be connected to a vacuum chamber (not shown). The housing 10 is connected to a boiling chamber 14 having a heating element 16. The heating element 16 vaporizes a propellant 18, which rises in the diffusion pump and exits through the two nozzles 20, 22 into the housing. Any gas particles present are entrained by the propellant vapor. The propellant vapor reaches a condenser 24, which is arranged on the housing 10 in the region of the nozzles 20, 22. The condenser 24 has a cooling system 26. In the illustrated embodiment, the cooling system 26 is a water cooling system with a supply line 27 and a discharge line 25.

[0044] The propellant vapor condenses at the condenser 24 and returns to the boiling chamber 14.

[0045] A forevacuum port 28, which can be connected to a backing pump (not shown), is arranged between the condenser 24 and the boiling chamber 14. Gas conveyed by the propellant vapor is extracted via the forevacuum port 28 by the backing pump.

[0046] To prevent heat from the heating element 16 from being lost, the boiling chamber 14 is completely surrounded by insulation 30. This prevents heat from the boiling chamber 14 from being released into the environment. This reduces the required heating power of the heating element 16.

[0047] A heating element control 32 is connected to the heating element 16, by means of which the heating power of the heating element can be adapted to the respective pumping situation.

[0048] A temperature sensor 34 is arranged in the area of the condenser 24 to detect the condenser temperature T c . The condenser temperature T c is measured at the condenser surface. The temperature T c of the condenser 24 can also be detected via the temperature of the cooling water in the discharge line 25. The temperature sensor is connected to a condenser cooling control, which is designed as a thermostatic valve 36. The thermostatic valve 36 can be used to adjust the cooling water flow V through the cooling system 26 of the condenser 24 depending on the detected surface temperature T c of the condenser 24.

[0049] To ensure that a minimum cooling of the condenser 24 is always achieved, the condenser cooling control system includes an emergency device, which is provided as a bypass 38 to the thermostatic valve 36. In the event of a failure of the condenser cooling control system, cooling water continues to be directed through the bypass 38 to the cooling system 26 of the condenser 24, so that the propellant vapor continues to condense. The emergency device is particularly necessary in the event of a power failure or sudden shutdown of the diffusion pump and ensures that the minimum cooling of the condenser 24 allows the diffusion pump to be shut down properly without propellant vapor entering the vacuum chamber.

[0050] The pumping process is controlled by the Figure 2explained in detail, although this is a schematic representation and does not represent exact values. In particular, the example is not limited to the pumping process shown, as an exemplary pumping process is shown. Figure 2 The pressure p 60, the coolant flow V 62, the heating element temperature T 64, the vapor pressure of the propellant 66 and the condenser temperature T c 67 are shown for the different pumping situations. The left vertical axis of the diagram describes the pressure for line 60 and line 66, whereas the right vertical axis describes the temperature for lines 64 and 67 and the coolant flow for line 62. On the horizontal axis of the diagram the Figure 2 the different pumping situations are shown.

[0051] In region 68, there is little or no pumping action. The pressure in the vacuum chamber is p 0 . This situation occurs between pumping cycles and especially during standby operation.

[0052] In the second region 70, a pressure reduction from the initial pressure p 0 to the working pressure p 1 takes place by pumping down. During pumping down 70 of the vacuum chamber, the heating power and accordingly the temperature T of the heating element 16 are increased to their maximum value T max in order to increase the suction power of the diffusion pump. In order to compensate for the increased heat input by the heating element 16, the cooling water quantity V for cooling the condenser 24 is increased. In this case, it is not necessary for the condenser temperature T c in region 70 to reach a minimum T c,min. The coolant flow V through the condenser 24 can be controlled such that the condenser temperature T c drops continuously from its initial value T c,0 to the working value T c,1.

[0053] Once the working pressure p 1 is reached in the vacuum chamber, the heating element control adjusts the temperature T of the heating element 16 to the upper value of the boiling range of the propellant used. The temperature T of the heating element 16 is reduced from its maximum value T max , which is necessary for quickly reaching the working pressure p 1 in range 70, to the value T 1 . This continues to ensure a pumping effect, since T 1 in particular is greater than T 0 , so that unnecessary heat input is prevented. The reduction in the heating power from T max to T 1 of the heating element 16 simultaneously results in the flow rate of cooling water V being reduced from V max to V 1 by the condenser cooling control in the form of the thermostatic valve 36. This increases the surface temperature of the condenser 24 to T c,1 or the final condenser temperature T c,1 is reached.However, an increase in the surface temperature of the condenser T c is only provided if the vapor pressure 66 of the propellant at the increased temperature remains below the working pressure p 1 of the vacuum chamber, as in . Fig. 2 shown.

[0054] Between two pumping operations 68, the temperature T of the heating element 16 is reduced below the lower value of the boiling range of the propellant used. As a result, no or very little propellant 18 is evaporated. A pumping action is neither required nor achieved with a reduced heating power of the heating element 16. Simultaneously with the reduction of the temperature T of the heating element 16 to T 0 between two pumping operations, the coolant flow V of the cooling system 26 of the condenser 24 is reduced to V 0 by the thermostatic valve 36.

[0055] Figure 3shows a second example. Identical parts are designated by the same reference numbers. Even though this is an alternative example, the individual features for saving the required energy in a diffusion pump from the first example can still be combined with those of the second example, provided these features are not mutually exclusive.

[0056] In the second example, the cooling system 26 is connected to a heat pump 40, which has a condenser 41 and an evaporator 39. Cooling water flows from the cooling system 26 to a reservoir 42 on the housing 10 of the diffusion pump. From the reservoir 42, the still warm cooling water flows to the heat pump 40, which extracts heat from the cooling water. This reduces the temperature of the cooling water. The thus cooled cooling water is fed to the cooling system 26 via a feed pump 44 through the thermostatic valve 36 or the bypass 38. The thermal energy extracted from the cooling water by the heat pump is fed to the heating element 16 via a heating circuit. Thus, the heat dissipated by the cooling system 26 is used to heat the propellant 18 by the heating element 16.The heat dissipated by the cooling system 26 thus does not represent a power loss, and at the same time, the energy required to be supplied externally to the heating element 16, for example, in the form of electrical energy, can be reduced. The heat pump 40 is particularly designed as a compression heat pump. In particular, it may be advantageous to reverse the flow direction so that the cooling water first releases its thermal energy in the heat pump 40 and then reaches the reservoir 42. From there, the cooling water is pumped to the cooling system 26 by the feed pump 44.

[0057] In Figure 4 A third example is shown, with identical parts designated by identical reference numbers. Features of the previous examples can be combined with the third example to reduce the energy consumption of the diffusion pump, as long as the features are not mutually exclusive.

[0058] In the third example, the high-vacuum side region 46 is designed as a water cooling system 26. A vapor barrier 48 is also provided, which has a water cooling system. The region 50 of the condenser 24, which adjoins the heating element 16, is connected to a heat pump 40, so that heat from the region 50 is supplied to the heating element 16 via the heat pump 40, thereby heating the propellant 18. Additionally, a controllable thermostatic valve can also be arranged in the heat exchanger circuit, which can be controlled in particular by the temperature sensor 34 or an additional temperature sensor arranged in the region 50.

[0059] In particular, the boiling chamber 14 is thermally separated from the housing 10 by an insulator 52. Heat generated by the heating element 16 does not reach the housing 10 due to the insulator 52 and therefore does not need to be dissipated via the cooling system 26 or the heat pump 40. This further reduces the energy consumption of the diffusion pump. The insulator 52 has a low thermal conductivity.

Claims

1. A method for controlling a diffusion pump comprising a housing (10), a boiling chamber (14) connected to said housing (10), a heating element (16) arranged in the area of said boiling chamber (14), a nozzle (20, 22) arranged in said housing (10) and connected to said boiling chamber (14), a condenser (24) arranged at an inner surface of said housing (10) in the area of said nozzle (20, 22), and a cooling system (26) configured for cooling said condenser (24) and arranged in the area of said condenser (24), characterized in that during the pumping process the heating element temperature is adjusted to the upper value of the boiling range of the propellant (18) used.

2. The method according to claim 1, wherein the condenser temperature is measured and the cooling system (26) of the condenser (24) is controlled by a condenser cooling system regulator depending on the measured condenser temperature.

3. The method according to any one of claims 1 or 2, wherein the condenser cooling system regulator keeps the condenser temperature constantly below the condensation temperature of a propellant (18) and the vapor pressure of said propellant (18) is always lower than an operating pressure of the diffusion pump.

4. The method according to any one of claims 1 to 3, wherein the heating element temperature is adjusted to the required suction capacity of the diffusion pump during the pumping process.

5. The method according to one of claims 1 to 4, wherein the heating element temperature is reduced between pumping processes.

6. The method according to claim 5, wherein between pumping processes the heating element temperature is reduced by at least the value of the boiling range of the propellant (18) used.

7. The method according to any one of claims 1 to 6, wherein during a reduction of the heating element temperature the condenser temperature is adjusted at the same time.