EP2230476A2 - Temperature regulation for a microstructure evaporator for cooling liquids - Google Patents

Abstract

The control has a manipulation element for manipulating a tempering fluid flow rate at which a microstructure evaporator i.e. counter-current heat exchanger (1), is operated. A temperature detection device is provided before an inlet (11) and an outlet (12) of the heat exchanger. The manipulation element is switchable or regulatable. The detection device has a temperature sensor for measurement or a bimetal element for monitoring of a temperature. The manipulation element has a flow valve for regulating flow resistance and/or a stop valve i.e. solenoid valve (6).

Description

The invention relates to a temperature control for a microstructure evaporator for cooling liquids according to the first claim.

The tempering (heating or cooling) of fluids with heat exchangers usually takes place via a heat transfer to a fluid (liquid, vapor, gas) or to electrically operated elements such as an electric heater or Peltier elements. Alternative concepts, such as Evaporative cooling, for example, use the energy of a phase transition for heating or cooling.

The control of such processes is well developed and researched for conventional industrial equipment, and there are standard solutions for both heating and cooling, e.g. Air-operated control valves or valves with electric actuator, which are flow-regulating and well-known in the art (see for example product lines of companies such as Endress & Hauser, Jumo or other relevant manufacturers and distributors of measurement and control technology).

Due to their fine structures, microstructured heat transfer systems have a high specific heat transfer surface and a low thermal mass, which on the one hand considerably improves their efficiency, but on the other hand also extends their range of application [1, 2]. The compact design allows use in transportable applications or in the kitchen machinery sector, such as the temperature control of beverages directly by the end user.

The reduced thermal mass of the micro heat exchanger leads to very short reaction times with temperature changes. For the heating of liquids, this is usually not a disadvantage. When using a heating fluid this is electrically heated elsewhere, for example. This heating can be controlled by means of a conventional, low-cost regulator or via simple switching on and off by means of a bimetallic switch or an NTC or PTC sensor. Direct electrical heating can use similar mechanisms. Appropriate regulatory systems are known and published [3, 4]. In [3] is described how an electrically heated microstructure apparatus is operated with a conventional control mechanisms. [4] describes the use of an electrical switch for the temperature-controlled regulation of an electrical load. Corresponding PTC or NTC sensors are integrated in the meantime, for example, as overtemperature protection elements as well as cost-effective control mechanisms in devices for private consumers (eg hair dryer). Self-regulating heating elements based on PTC resistors are described eg in [5] and distributed by various manufacturers of electrical heating means (eg: David & Baader GmbH, [6])

The situation is different with the cooling of microstructured heat exchangers. If, for example, Peltier elements are attached directly to the microstructure apparatus or indirectly used for cooling a secondary fluid for cooling, simple cut-off mechanisms for the supply voltage of the Peltier elements are available for power regulation or interruptions. This is technically possible, but usually shortens the life of the Peltier elements. In addition, since Peltier elements operate with a low efficiency or with a low temperature lift and require relatively voluminous secondary cooling to dissipate the power loss, they are only of limited suitability for use with microstructured apparatuses. The rather high price of Peltier elements and the operation Required power supplies or high current sources reduces the potential applications in the home and consumer markets in addition.

A simple shutdown or interruption of operation of other cooling devices such as refrigeration compressors, as widely used in commercial refrigerators, or cooling by evaporation of a coolant, e.g. in connection with microstructured apparatuses are also technologically limited feasible. A compressor basically requires a certain start-up time and thus generates dead times during switching operations. Likewise, evaporation processes are inert in the case of changes and generally require lead times until a steady state returns. The particular advantage of a fast reaction time of microstructure devices is thus partially or completely removed. In addition, the mentioned means also cause unwanted irregularities in the cooling performance with its own dynamics.

Based on this, the object of the invention is to propose an inexpensive and reliable temperature control for a microstructure evaporator for cooling fluids, preferably liquids, which does not have the disadvantages mentioned. In particular, the scheme should meet the requirements of strong power fluctuations within a short time without significant delay. This requirement results from the task of cooling hot drinks batchwise to a defined temperature at the push of a button.

The object is achieved with a temperature control for a microstructure evaporator for cooling liquids with the features of claim 1. Advantageous embodiments of the temperature control are reproduced in the subclaims.

The solution of the problem provides a temperature control for a heat exchanger, preferably microstructure evaporator for temperature control, preferably cooling of liquids, wherein the microstructure evaporator with a tempering fluid, preferably a coolant operated. The temperature control is controlled by controlling the amount of heat transferred in the heat exchanger, i. realized a heat quantity control. In this case, manipulation of the tempering fluid flow passing through the heat exchanger or preferred microstructure evaporator takes place, for example. by tempering, throttling, control, interruption and / or bypass diversion as well as a temperature measurement on the tempering fluid for the generation of a control signal for the control.

In the context of temperature control, the manipulation of a coolant flow takes place as Temperierfluiddurchfluss by at least one flow valve for regulating a flow resistance in the coolant flow and / or at least one shut-off valve for interrupting a coolant flow.

The flow valve and / or the shut-off valve open and close regulated depending on temperature. The temperature is measured in the context of the invention at different locations.

Preferably, a control of the amount of heat transferred in the heat exchanger via the inlet temperature or the outlet temperature of the coolant at the microstructure evaporator.

Control over the inlet temperature:

The on entry into a single fluid channel, preferably evaporation passage, a heat exchanger (evaporator microstructure) _a measured temperature T correlates advantageously directly to the evaporation pressure P _steam on entry into the Evaporator passage in the heat exchanger. This results from the sum of the pressure drop ΔP over the evaporator passage of the micro heat exchanger and the pressure P _nieder in the suction line of a coolant circuit after exiting the evaporator. Accordingly, the pressure loss ΔP is calculated to: $$\mathrm{.DELTA.P}\mathrm{=}{\mathrm{P}}_{\mathrm{steam}}\mathrm{-}{\mathrm{P}}_{\mathrm{low}}$$

The pressure drop .DELTA.P is considerably larger than in corresponding macroscopic evaporators due to the microscopic dimensions, preferably between 50 and 1000 .mu.m of the cross sections of the single fluid channel. If the coolant in the micro heat exchanger fed with a quantity of heat Q _warm, which is greater than or equal to the cooling power Q _cold (required for complete vaporization heat quantity) of the circuit, the thermal treatment is completely evaporated within the individual fluid channels in the heat exchanger.

Due to the volumetric increase due to evaporation, the flow rate in the individual fluid channels increases significantly and thus causes an increase in the aforementioned pressure drop ΔP. Due to this, there is an increase in the evaporation pressure P _vapor and increase in the evaporator inlet temperature T _a .

In the event that the amount of heat supplied to the heat exchanger by the liquid to be tempered is smaller than the cooling capacity of the circuit Q _warm <Q _cold , only a portion of the tempering fluid within the individual fluid channels evaporates in the heat exchanger. Due to the higher liquid content in the tempering fluid in the evaporator, the fluid volume and thus the flow rate of the tempering fluid in the single fluid channel are also reduced. The pressure drop ΔP across the evaporator passage decreases significantly, as a result of which the evaporation pressure drops P _steam and with him the evaporation temperature at the evaporator inlet T _a .

In order to prevent freezing of the liquid to be cooled (eg water), the Temperierfluidfluss is closed via a downstream of the heat exchanger solenoid valve as soon as T _a below a threshold, which is about 2K above the freezing point of the fluid to be cooled (in water about 2 ° C. .). Exceeds the T _a measured value back to the threshold value, the solenoid valve opens the Temperierfluidfluss again, the full cooling capacity is directly available again.

Control over the outlet temperature:

A regulation of the outlet temperature T _from the temperature control fluid from the heat exchanger is advantageous if a control over measurement of the temperature T _a at the evaporator inlet due to the higher installation effort or due to the design of the micro heat exchanger (for example, in an integration of the expansion diaphragm in the micro heat exchanger) not technically possible or uneconomical. The recording of this temperature is preferably carried out directly on the tempering after leaving the evaporator passage or more cost-effective by measuring the surface temperature of the suction at the terminal micro-transformer evaporator outlet (outlet at the heat exchanger). The regulation is carried out analogously to the aforementioned temperature control over the inlet temperature, with the difference that the outlet temperature is used as a controlled variable.

If the heat transfer fluid in the micro heat exchanger via the fluid to be cooled, preferably a liquid, an amount of heat supplied which exceeds the cooling capacity of the circuit Q _warm > Q _cold , the tempering fluid evaporates completely until Exit from the individual fluid channels (evaporator passage). There is an overheating of the tempering in the gaseous region; the temperature at the Temperierfluidaustritt T _off is then significantly greater than 0 ° C. In the example, a refrigerant R134A was used for this, but other tempering fluids are also possible and practical, such as R744 or R600a.

If, on the other hand, too little heat is supplied via the fluid to be cooled (Q _warm <Q _cold ), the tempering fluid does not evaporate completely within the individual fluid passages (evaporator passage). Non-evaporated tempering fluid evaporates in this case immediately after exiting the evaporator passage upon entry into the suction line and therefore directly cools the suction line and the temperature sensor T _from .

As the switching value for the closing of the solenoid valve, a value of about T _of <1 ° (for aqueous fluids to be temperature) has to be chosen in order to prevent freezing.

The invention includes use of the temperature control for cooling preferably in microstructured heat exchangers of hot beverages, preferably freshly brewed hot drinks such as coffee or tea, or other beverages such as hot beverages. Milk drinks, which are to be cooled on request, preferably immediately after a heat treatment (cold drink on demand).

The invention further includes a use of the temperature control for a temperature, preferably cooling in chemical processes or processes in which, for example due to an exothermic reaction or a heating time-dependent different temperatures occur or different amounts of heat must be removed controlled to ensure a stable experimental design or Temperaurkonstanz ,

The invention also includes use of the temperature control for temperature control of smaller air conditioners in e.g. portable devices in the electronics and IT sector or in the automotive sector, in which strong power fluctuations and thus also large fluctuations of the waste heat occur and are exchanged with heat exchangers of small dimensions.

The invention also includes a method for controlling the temperature of a microstructure evaporator for cooling liquids, wherein the microstructure evaporator is operated with a tempering fluid flow (coolant flow). For temperature control, this tempering fluid flow through the heat exchanger is set in the manner mentioned by at least one means for manipulating the tempering fluid flow into mass flow, volume flow, pressure and / or temperature.

• Fig.1 eine Ausführung mit Bypassleitung um den Mikrostrukturverdampfer sowie einem Magnetventil im Kühlmittelhauptstrom,
• Fig.2 eine Ausführung mit regelbarem Durchlassventil im Kühlmittelhauptstrom vor dem Mikrostrukturverdampfer sowie
• Fig.3 eine Ausführung mit regelbarem Durchlassventil im Kühlmittelhauptstrom nach dem Mikrostrukturverdampfer.

The invention will be explained in more detail below with exemplary embodiments and the following figures. Show it

• Fig.1 an embodiment with a bypass line around the microstructure evaporator and a solenoid valve in the coolant main stream,
• Fig.2 a version with adjustable passage valve in the main coolant flow upstream of the microstructure evaporator and
• Figure 3 an embodiment with adjustable passage valve in the main coolant stream after the microstructure evaporator.

Fig.1 to 3 give embodiments with countercurrent heat exchanger 1 as a microstructured evaporator again. This is on the one hand for the temperature control of fluids with high temperature differences. In addition, it has a parallel guidance of a plurality of individual fluid channels for liquid 3 to be tempered and temperature control medium 4 (two fluid channel fractions), whereby the same tempering conditions prevail in each of the fundamentally identically designed fluid channels per fluid channel fraction. Consequently, a liquid to be tempered in the main stream 2 after branching into a plurality of individual fluid channels in these in contrast to a cross-flow heat exchanger in principle also experiences an identical thermal loading.

In contrast, a cross-flow heat exchanger represents a component which can be produced economically. A use is then advantageous and therefore desirable if the tempering fluid only passes through small temperature changes when it passes through the heat exchanger. This is the case when the tempering medium undergoes an isothermal phase transition from liquid to gaseous or vice versa and the phase transition of the liquid to be tempered additionally extracts or supplies heat. This embodiment is therefore particularly suitable for evaporative coolers.

A first embodiment ( Fig.1 ) provides a bypass line 5 for a coolant as Temperierfluid to the microstructure evaporator (countercurrent heat exchanger 1 ) before. The diversion of the coolant into the bypass line takes place with the aid of a temperature-controlled solenoid valve 6 , which is preferably inserted in the coolant line 13 between branch 7 to the bypass line 5 and microstructure evaporator, ie in the coolant stream 8 before entering the microstructure evaporator. The temperature is - as described above - measured in the tempering (coolant) directly at the inlet 11 or directly at the outlet 12 of the heat exchanger, or alternatively at the liquid outlet 14 on the heat exchanger 1 in the main stream 2 and as a controlled variable of a control (control electronics), not shown for the control used the solenoid valve 6 . In the control system, the measured temperature is compared with an adjustable threshold value and the solenoid valve is either closed or opened in the event of overshoot or undershoot. A measurement At the liquid outlet 14 has the advantage that the temperature is measured directly on or in the liquid to be tempered and thus this is particularly accurate temperature controlled. However, in order to prevent the liquid from freezing when the liquid is stationary, the temperature of the tempering fluid at the inlet or outlet must also be monitored.

The branch 7 is preferably designed as a flow switch so that it passes the coolant flow with the solenoid valve 6 fully open in the heat exchanger and only when it flows the same coolant flow into the bypass line. The parallel to the bypass line 5 coolant flow through the heat exchanger between junction 7 and the introduction 16 is the main coolant flow and corresponds to Fig.1 the coolant line 13.

If a division of the coolant flow in bypass line 5 and coolant line 13 with continuously adjustable mass flow ratio for continuous temperature control, ie heat quantity control required, a continuously adjustable valve (eg slide valve) or a continuously adjustable aperture is provided.

It is basically within the scope of the invention and can be combined with all illustrated embodiments, a valve or aperture with a temperature detection with regulation by a temperature-dependent control panel, ie a component without additional possibly required power supply of a scheme to replace, preferably a bimetal a slide over a bimetallic flexure against a preset spring force to be closed or opened. The combination of two different bimetal flexural elements for opening or closing the aperture in opposite operation is conceivable. This control panel is preferably arranged directly at the inlet 11 or directly at the outlet 12 of the heat exchanger.

The heating or cooling potential in the coolant flow in the bypass line can be used, for example, by a further heat exchanger 9 for further uses. In particular, in a domestic appliance (so-called consumer machine) for the production of hot and cold drinks, the cooling capacity can be used indirectly via an additional secondary cooling circuit or directly for cooling the fresh water reservoir or accessory components such as cups, cups or other vessels. Another possibility is the direct pre-cooling of the liquid to be cooled, for example, to reduce or prevent degradation (in the case of water: algae). This represents a decisive hygienic advantage over simple bearing components.

The second and third embodiment acc. Fig.2 respectively. Figure 3 disclose alternative temperature controls without a bypass line. The cooling capacity of the coolant flow 8 (here equivalent to the main coolant flow) is manipulated by means of a temperature-controlled orifice 10 (flow valve) or a solenoid valve 6, alternatively also the aforementioned continuously temperature-dependent control orifice, by the height of the mass flow of the tempering fluid (coolant). The height of the mass flow determines the height of the introduced through the coolant through the heat exchanger 1 heat flow and thus directly to be transferred in the heat exchanger to the main stream 2 heat output.

In addition (or in principle also alternatively) to the aforementioned volumetric flow regulations, a manipulation of the cooling capacity of the heat exchanger can in principle also be carried out by means for temperature control 15 of the tempering fluid before it enters the heat exchanger (cf. Figure 3 ). Here, in particular, electrical elements such as Peltier elements are suitable for a cooling or resistance heating element for heating, which are preferably preferably continuously controllable in their performance via the aforementioned regulation in their performance.

Particularly advantageous is the use of a downstream of the heat exchanger solenoid valve ( Figure 3 ), which is controlled by a temperature sensor at the inlet 11 or outlet 12 of the heat exchanger 1 .

The fast switching times of a solenoid valve of the aforementioned type make it possible to obtain the advantages of the very short heat conduction path lengths of the tempering fluid in the coolant stream 8 to the tempering liquid in the main stream 2 and therefore very short heat transfer reaction times of micro heat transfer for very rapid cooling due to the small channel dimensions of the individual fluid channels. It is thus possible to always set the necessary cooling capacity at a very low cost with variable flow rate of the fluid to be tempered, without having to switch a cooling source (cooling compressor, Peltier element). As a result, dead times or control delays are excluded and the advantages of the micro-heat exchangers can be fully utilized. Conventional control systems are too slow for these micro heat exchangers or evaporators usual very short reaction times or technically very complicated and therefore expensive.

A preferred interval-like activation and interruption of the coolant flow through the valve also reduces the risk of frost for the liquid to be cooled in the individual fluid channels for the liquid 3 to be tempered.

The use of a heat exchanger 1 downstream temperature-controlled solenoid valve ( Figure 3 ) also allows the use of a cost additional fixed orifice before entering 11 in the heat exchanger (eg evaporator) or the direct integration of this throttle function in the micro heat exchanger, since the flow control is done exclusively via the solenoid valve. A complicated and expensive control panel is still possible, but no longer mandatory.

The downstream of the solenoid valve behind the heat exchanger acc. Figure 3 has opposite the execution in Fig.2 with upstream solenoid valve, especially in evaporative cooling a significant advantage. Since the Temperierfluidfluss is blocked only after exit 12 from the evaporator passage, the evaporation pressure D increases _ampf within the Einzelfluidkanälen (evaporation passage of the Mikrowärmeübertragers). As a result, the evaporation temperature in the entire micro heat exchanger increases, so that further cooling and thus freezing of the liquid passage to be cooled is physically excluded. The system regulates itself independently.

If this is not the case and the Temperierfluidkreislauf is interrupted via an upstream valve before entering the evaporator, it would be initially to a further cooling of the component, since Temperierfluidreste would be sucked at further decreasing evaporation pressure and thereby further decreasing evaporation temperature from the micro heat exchanger. It can be assumed that the fluid to be cooled freezes. A more complex regulation would be necessary to prevent this.

For a responsive and simple temperature control, which precludes freezing, therefore, a downstream switching of the solenoid valve or a diaphragm as proposed is advantageous.

Literature:

1. [1] Schubert et al .: Microstructure Devices for Applications; Thermal and Chemical Process Engineering, Microscale Thermophys. Eng., Vol.5, No.1, 17-39 ,
2. [2] Brandner et al.: Microstructure Heat Exchanger Applications; Laboratory and Industry Heat Transfer Engineering, vol. 28, No. 8-9, Aug. 2007, 761-771
3. [3] Brandner et. al. : Fast Temperature Cycling in Microstructure Devices; Chemical Eng. J., 101 / 1-3, 2004, 217-224
4. [4] EP 0 208 318 A2
5. [5] http://de.wikipedia.org/wiki/Heizelement, as of 20.02.2009
6. [6] http://dbk-group.de/eng/Produktbereiche/Heizkomponenten-aggregate/PTC-Heizelemente, as of 20.02.2009

LIST OF REFERENCE NUMBERS

1

Counterflow heat exchanger

2

main power

3

Single fluid channel for liquid to be tempered

4

Single fluid channel for temperature control medium

5

bypass line

6

magnetic valve

7

diversion

8th

Coolant flow

9

heat exchangers

10

cover

11

entry

12

exit

13

Coolant line

14

liquid outlet

15

Means for tempering

16

introduction

Claims (8)

Temperature control for a microstructured evaporator ( 1 ) for cooling liquids ( 2 ), wherein the microstructure evaporator is operated with a tempering fluid flow ( 8 ) comprising at least one means ( 5, 6, 10, 15 ) for manipulating the tempering fluid flow. Temperature control according to claim 1, characterized in that a temperature detection in Temperierfluiddurchfluss before entry ( 11 ) or after exit ( 12 ) are provided from the microstructure evaporator and the means for manipulation by the temperature can be switched or regulated. Temperature control according to claim 2, characterized in that the temperature detection comprises a temperature sensor for measuring or a bimetallic element for monitoring a temperature. Temperature control according to one of the preceding claims, characterized in that the means for manipulation comprise at least one flow valve ( 10 ) for regulating a flow resistance and / or at least one shut-off valve for interrupting the Temperierfluiddurchflusses. Temperature control according to claim 4, characterized in that the shut-off valve is a solenoid valve ( 6 ) in the Temperierfluiddurchfluss. Temperature control according to claim 5, characterized in that the solenoid valve ( 6 ) in the Temperierfluiddurchfluss the microstructure evaporator ( 1 ) is connected downstream. Temperature control according to one of the preceding claims, characterized in that the means for manipulation comprise a bypass line ( 5 ) for the tempering fluid. Temperature control according to claim 7, characterized in that the bypass line comprises means ( 9 ) for a further use of heat.

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