Patent Application
20100224346
The present invention relates inter alia to a method of controlling transfer of energy, radiation and/or mass trough or from one or more transferring elements in a fluid treatment device wherein the treatment comprises addition or subtraction of energy, heat, radiation, substances and/or the like to/from one or more fluids, preferably being liquids.
Although the present invention is applicable in a broader sense, the background of the invention is disclosed mainly with reference to heat exchangers. Other applications of the present invention comprise e.g. transfer of substances and emitting radiation to a fluid.
Today, many transferring devices, such as heat exchangers, are formed as plates or tubes where fluids with different temperatures flow on each side of the plates or tubes to generate a transferral of heat through the plates or tubes between the fluids. Such heat exchangers are designed so that the local velocities inside the heat exchangers are correlated to the flow rate (m3/h) through the exchangers in such a manner that the local velocities can not be changed without changing the flow rate through the heat exchanger.
In particular, a heat exchanger in a heat system is conventionally designed to a flow rate (m3/h) meeting a peak load condition. In partial load situations it is necessary to maintain the peak load flow rate through the heat exchanger in order to keep the velocities inside the heat exchanger high. Otherwise a reduced flow rate could result in a lower heat transferral whereby a cooling or heating requirement could not be fulfilled. Thus, if the flow rate through the heat exchanger can be reduced while keeping the heat transfer substantially constant or at a similar scale, a reduced pressure loss may be obtained in the heat systems in partial load situations.
US patent application 2003/0209343 may be seen as such an example. This reference discloses a pump system for use in a heat exchange application having a pump chamber with a fluid inlet and a fluid outlet. A rotating device is contained within the pump chamber, for causing a fluid to move across a surface to be cooled. The surface forms an integral part of the pump chamber in such a manner that the fluid as it passes through the rotating device also passes across the surface, resulting in a heat transfer between the surface and the fluid. Another aspect of the invention includes having the surface to be cooled integrally connected with the pump chamber, so that the pump chamber is separable from the surface to be cooled without disturbing the fluid circuit of the heat exchange application. A means for driving the rotating device may also be configured to drive a means for cooling the fluid. In the embodiment of FIG. 3 in US patent application 2003/0209343, it is disclosed that fluid for cooling can be led through a passageway into an impeller that has vanes for guiding the fluid across the surface to be cooled. Considering that the purpose is to design a compact and efficient pump for heat exchange application an optimum correlation or dependency between the rotational speed of the impeller and the flow rate (and effectively also the resulting cooling) may be desirable. However, it is only mentioned shortly that rotational speed of the impeller may be made dependent on inter alia the flow rate without any specific mentioning on how this dependency can be.
It has been found that conventional heat exchangers seem to suffer from the drawback that the heat transfer is strongly correlated with the flow rate of the fluids through the heat exchanger. E.g. a change in flow rate results in a change in heat transfer which in turn results in the span of operation of the given heat exchanger being limited compared to a situation where the flow through the heat exchanger is changeable without significantly changing the heat transfer.
Thus, it is an aim of the present invention to provide a method for a device by which at least the strong correlation between flow rate and the local velocities is at least mitigated so as to gain a more easily controllable transfer of e.g. heat, substance, and/or radiation.
Thus, in a first aspect the present invention relates to a method of controlling the transferral of heat, substance, radiation or the like to or from at least a first fluid in a device comprising at least one stage comprising one transferring element and a rotatable impeller, the impeller being arranged so that the first fluid flowing out of the impeller flows along a surface of the transferring element, wherein the flow of the first fluid along the surface of the transferring element comprises a spiralling flow pattern comprising a radial velocity component (Vr) and a tangential velocity component (Vt), the device further comprises one or more throttling means for throttling the flow of the first fluid through the device, wherein the rotational speed of the impeller and the throttling is mutually controlled so that:
By use of the method according to the present invention, the amount of transferral, AT, may be expressed as
AT=f
1(Vr)+f2(Vt)
wherein f1 and f2 are functions used to indicate the correlations between the tangential, Vt, and radial, Vr, velocities, respectively, and the amount transferred, AT.
The amount of transferral may be changeable by changing the rotational speed of the impeller without substantially influencing the flow rate through the device of the first fluid to be treated.
The flow rate may be changeable by changing the rotational speed of the impeller without substantially influencing the amount of transferral for the first fluid in the device.
In the present context, throttling is equivalent to suppression. Because flow in a pipe is driven by pressure difference, throttling accordingly necessitates to create a counter-pressure on the exit side, or to lower the entry pressure. The throttling means may therefore comprise throttling valves, one or more dedicated cavities for throttling, a diaphragm, a narrowing of a pipe with the first fluid, a counter flow, or viscosity controlling means. By physically blocking or positioning of obstacles, the kinetic energy of the flow is passively transferred into counter-pressure. An active way of throttling could be to provide the counter-pressure by a dedicated pump therefore, though this consumes energy. As a special case, the liquid properties may be changed to create a throttling effect, e.g. by electrorheology.
The tangential velocity may be increased or decreased by increasing or decreasing the rotational speed of the impeller. An increase or a decrease of the rotational speed of an impeller may give rise to a pressure increase/decrease which may increase/decrease the radial velocity component and thereby the flow rate through the device. The flow rate is considered as being correlated with the radial velocity component and only slightly correlated, if at all, with the tangential velocity component in the present invention. Typically, the change of the tangential velocity due to the change of rotational speed of the impeller is so large that the change of the flow rate may be neglected.
Although the spiralling flow pattern may be generated by stationary flow guides, the invention has the particular advantage that the impeller(s) generates the spiralling flow pattern.
However, if it is aimed at increasing or decreasing the tangential velocity without affecting the radial velocity component, a throttling may be applied to compensate for the increase/decrease in pressure due to the increase/decrease in rotational speed of the impeller.
Thus, the present invention is considered to provide a method by which the local velocities inside a device, e.g. being a heat exchanger, may be changed without changing the flow rate through the device, thereby enabling a change in e.g. heat transferring without changing the flow rate through the device.
The present invention and in particular preferred embodiments thereof will now be disclosed in greater details with reference to the enclosed figures in which:
FIG. 1.a is a schematic cross sectional view of a first embodiment of a device according to the present invention; FIG. 1.b shows schematically a spiralling flow of fluid leaving the impeller in FIG. 1.b; FIG. 1.c. is a schematic graph of the head-flow characteristic for a typical impeller demonstrating the working principle of the present invention, and FIG. 1.d. is graph showing the friction loss for a pump as a function of the flow through for demonstrating the advantages of the present invention.
The fluid to be treated flows into the device through the inlet element 6 and flows towards a rotating impeller 3. The fluid to be treated leaves the impellers and flows along a surface of one of the transferring elements 2, towards the rim of the transferring element 2, and through the passage between the rim of the transferring element 2 and the inner surface of the casing 5. Alternatively or in combination to the passage between the rim and the casing 5, one or more penetrations could be provided in the transferring elements 2 through which the fluid may flow.
Due to the presence of the floor element 8, fluid flows 5 towards the second impeller after the passage between the rim and the casing. After passage of the second impeller 3, the fluid flows along the surface of the second transferring element 2 towards the rim, through the passage between the rim and the casing 8, and finally towards the outlet element 7 through which the fluid leaves the device 1. The flow path is illustrated schematically with arrows.
A transferring element 2 may be a heat transferring element through which heat is conducted to or from the fluid to be treated, a mass transferring element through which mass is transferred to or from the fluid to be treated, a radiation element through or from which radiation to be emitted to the fluid is emitted, or combinations thereof. The flow pattern of the fluid to be treated while flowing along the surface of the transferring element 2 is a spiralling flow pattern comprising, as indicated in FIG. 1.b, a radial velocity component Vr in the radial direction of the transferring element 2 and a tangential velocity component Vt in the tangential direction of the transferring element 2. A velocity component normal to the Vr and Vt may of course be present. The flow pattern on the underside (with respect to the orientation in the figure) will typically also comprise a spiralling motion, but it may differ from the one on the top side. Vr is correlated with the flow rate (m3/h) through the device and depends inter alia on the pressure loss through the device 1. Vt is correlated with the rotational speed of the impellers. It should be mentioned that the pressure loss and the rotational speed of the impellers may be correlated.
Transfer of e.g. energy and substance from the fluid to the transferring elements 2 (or vice versa) is governed inter alia by the boundary flow at the surface of the transferring elements 2 and the residence time—or the flow rate—of the fluid to be treated while the fluid flows along the surfaces of the transferring elements 2. Similarly, if radiation is emitted to the flow along the surface of the transferring elements 2 from the transferring elements 2, inter alia the boundary layer flow and the residence time governs the dose emitted to the fluid to be treated.
In connection with at least a swirling flow past a transferring element 2 (as discussed in connection with
Amount transferred=K*residence time
where “amount transferred” is the amount transferred from the fluid to be treated and to the transferring elements (or vice versa), and K is expressed in terms of:
K[ε/m2s].
ε is e.g. Q (heat) or m (mass). ε is correlated to gradients of e.g. temperature, concentration or the like primarily in the boundary layer close to the surface of the transferring element 2, and ε/m2 of K is considered to be correlated with Vt alone. The residence time/flow rate is considered to be correlated with Vr alone.
Thus, as Vr and Vt are considered as being non-correlated, the amount transferred may be expressed as:
Amount transferred=f1(Vr)αf2(Vt)
f1 and f2 are functions used to indicate the correlations between the tangential and radial velocities and the amount transferred. Thus, in accordance with the present invention, the amount transferred may be changed by changing the rotational speed of the impeller without influencing the flow rate through the treatment device of the fluid to be treated.
While the above considerations reflect a somehow ideal situation, an increase of e.g. the impeller speed will have a tendency to increase the total pressure of the fluid during its passage through the impellers. This increase in total pressure may, if no other measures are incorporated in the treatment device 1, result in a higher flow rate giving a lower residence time. In order to take this into account, throttling of the flow of the fluid to be treated may be applied e.g. by a throttling valve 6a and 7a arranged in the inlet element 6 and/or in the outlet element 7. Furthermore, one or more flow sensors are typically arranged in connection with the throttling valve(s) for determining the actual flow rate through the treatment device so that if e.g. an increase in rotational speed of the impellers give rise to an unwanted increase in flow rate, the device may be throttled so as to decrease the flow rate.
It should be mentioned that when throttling is applied, the control method may comprise a step of increasing/decreasing throttling while maintaining the rotational speed of the impellers.
FIG. 1.c. is a schematic graph of the head-flow characteristics w1 and w2 for a typical impeller demonstrating a working principle of the present invention. The curve P indicates the pump curve. On the horizontal scale the flow, Q, is indicated, whereas the vertical scale indicates the head or a corresponding measure total pressure. If an impeller 3 is initially operated at specific flow Q2, and it is desired to lower the flow to the flow Q1, there are two ways of doing this:
Firstly, it is possible to simply lower the flow Q through the impeller by reducing the rotational speed (of the impeller) 3 as indicated by solid arrow A. However, this has the disadvantage that when following the working curve w1 the corresponding head will be somewhat reduced at the lower flow Q1.
Secondly, is possible to use throttling for lowering the flow to the value Q1 as indicated by arrow B. This has the disadvantage that will typically be a relatively large pressure loss needed to compensate for the additional head (and thereby energy loss) by this process B.
The present invention facilitates that the flow rate Q and the throttling are mutually controlled so that the radial velocity component (Vr) and the tangential velocity component (Vt) are substantially independent with the result that the flow rate Q can be changed (from Q2 to Q1) with a comparatively smaller change (increase or decrease) of the head. This is indicated by the arrow C.
The present invention facilitates that the flow rate Q and the throttling are mutually controlled so that the radial velocity component (Vr) and the tangential velocity component (Vt) are substantially independent with the result that the flow rate Q can be changed with a comparatively smaller change (increase or decrease) of the cross flow velocity, i.e, velocity across the transferral surface and thereby a comparatively smaller change in the transfer rate to or from the surface. Even more preferably, the change of the cross flow velocity and/or the transfer rate could be substantially unchanged. For instance, the flow rate could be changed a factor at least of 10×, or at least a factor of 5×, or at least a factor of 2.5×, without substantially changing the resulting cross flow velocity or transferral rate. Compared to hitherto known solutions, this is unprecedented to the best of the applicant's knowledge.
FIG. 1.d. is graph showing the friction loss for a typical pump as a function of the flow (horizontal scale) for demonstrating the advantages of the present invention. The two values indicated on the curve, 2370 RPM and 1230 RPM, are the rotational speed of the impeller given as the number of rotations per minute (RPM) at the two end point situations. The pump is operated to create a constant turbulence level. The turbulence is proportional to the velocity, V, of the fluid, and it is given by the Reynolds number, Re, as:
Re=V/(d·ny),
where d is a typical distance between the active surfaces of the pump, ny is the viscosity, and V is the velocity, which is given by:
V=sqrt(Vr̂2+Vt̂2).
From the graph of FIG. 1.d, it is evident that a pump with an impeller is most advantageously operated at the optimum value for lowest power loss at a specific ratio of the tangential velocity component (Vt) and radial velocity component (Vr) and: Vt/Vr. With the present invention, this can be more easily achieved because the pump can be operated in a manner so that that the radial velocity component (Vr) and the tangential velocity component (Vt) are substantially independent.
From FIG. 1.d., it should also be noted that the rotational speed of the impeller could be changed with about a factor of 2×, while still maintaining a substantially unchanged cross flow velocity or transferral rate according to the present invention.
In the following, a number of embodiments will be disclosed, which embodiments have proved to be particularly useful when applying the above disclosed controlling strategy.
An application of the present invention is for heat exchangers wherein a fluid is either cooled or heated by heat transferral from another fluid having a different temperature, at least where the heat transferral begins. FIG. 2.a and FIG. 2.b show an embodiment of a transferring element in the form of a heat transferring element 2. The heat transferring element 2 is seen obliquely from above and from below, respectively; “above” and “below” refers to the orientation of the heat exchanging unit in
The flow path of the first fluid through the heat exchanger unit 1 is illustrated by a broken line in
The flow path of the second fluid is illustrated schematically in
The impeller 3 induces energy to the second fluid which makes it flow towards the rim 35 of the heat transferring element 2. From here it flows into the space partly defined by the guide plate 36 (not shown in
The figures described above show that the first and second fluids flow in opposite overall directions, i.e. upwards and downwards with respect to the figures. It is however also possible within the scope of the invention to have the two fluids flowing in the same overall direction.
Thus, by applying the control method outlined above, the heat transfer coefficient may be changed by varying the rotational speed of the impeller thereby varying at least the tangential velocity of the second fluid. The flow rate through the device may be further controlled by throttling e.g. by arranging a throttling valve at the outlet and/or inlet of the heat exchanger unit.
The heat transferring elements 2 are arranged inside the intermediary casing element 22 which is shaped as a cylinder with open ends. The inlet and outlet pipes 15, 16 leading the first fluid to and from the heat transferring elements 2 extend through the wall of the first casing element 21 as indicated in
The second casing element 23 comprises an inlet 19 for the second fluid as indicated on
The heat exchanger unit shown in
In preferred embodiments of the invention, the casing is a pressure carrying casing adapted to resist the pressure difference between the pressure of the fluids in the heat exchanger unit 1 and the ambience pressure, i.e. the pressure outside the heat exchanger unit 1.
If desired, it is possible within the scope of the invention to ensure that the pressure of the second fluid is increased inside the heat exchanger unit 1 before it flows through the heat transferring elements 2. Such an increase in pressure can e.g. be established as illustrated in
Connection stubs 32 leading fluid from one channel 31 to another channel 31 located upstream of a neighbouring channel are provided; these may, as shown in the figure, be arranged on some of the elements or be separate pieces to be fitted into a mating connection provided in the elements 2. Each heat transferring element 2 abuts the casing at the rims 33. The rims 33 are preferably sealed to the casing.
The flow paths of the two fluids are indicated
The second fluid flows into the heat exchanger unit via an inlet stub from above and via a connection stub 32 to an impeller 3. After the impeller 3, the second fluid flows in a swirling motion into a channel 31 towards a connection stub leading fluid to a next channel 31. The fluid flows through the next channel 31 towards and through a connection stub 32 leading the fluid to an impeller 3. The pattern may be repeated a number of times by stacking more heat transfer elements, before the second fluid flows out of the unit through an outlet stub.
As can be realised from
The embodiment shown in
Also in this embodiment, the heat transfer unit comprises inlet and outlet stubs through which the fluid flows into and out of the unit 1. In the figure, the flow paths of the three fluids are indicated. As in
When the impellers 3 are arranged on two or more shafts 27, the shafts 27 may be driven by the same or different motors 26.
In another embodiment the present invention relates to a filtering device. In this embodiment the transferring elements 2 are disc-shaped mass transferring elements as shown in
Such transferring elements 2 may take the place of the heat transferring elements shown in the previous figures and in such cases the openings 38 of the channels 37 are connected to a flow channels guiding the fluid with particles to a pump. The fluid to be filtered is pumped through the filtering device by arranging impellers 3 at the central penetration 38 as disclosed in connection with the heat transferring device shown e.g. in
Also in connection with the mass transferring elements 2 and the impellers, the flow along the surfaces of the mass transferring elements 2 is a spiralling motion comprising a tangential velocity component and a radial velocity component. The mass transfer through the mass transferring elements 2 is correlated with the pressure difference between the pressure of the fluid flow along the outer surface of the mass transferring elements 2 and the pressure in channels 37, and the radial as well as the tangential velocities of the fluid along the outer surface of the mass transferring elements 2. Thus, by utilising the control method of controlling the tangential and radial velocities by the speed of the impellers and, if applied, a throttling the mass transfer may be controlled.
Alternatively, the heat transferring elements shown in e.g.
In a further embodiment, the control method relates to emitting radiation and in particular ultra violet radiation to a fluid. Such an embodiment is shown schematically in
The treatment section is cylindrical along its length axis (vertical with respect the orientation of
A radiation source 41 is arranged inside a source shield 42. The radiation source 41 is preferably a UV radiation source emitting UV radiation, and the source shield 42 is preferably a tubular member being penetrable to UV radiation; it is preferably made of quarts. The radiation source 41 and the source shield 42 are arranged tangentially to the floor elements as shown in
The floor elements 39, 40 are of two different shapes. The floor element 39 leaves a passage open between its rim and the outer casing 18, and the floor element 40 is sealed at its rim to the casing 18 and comprises a central penetration to allow fluid to flow towards and into an impeller 3. The configuration is therefore similar to the configuration shown in
During the fluid's passage through the treatment section, the fluid flows in close vicinity of the UV source located in the source shield 42. Furthermore, the floor elements 39, 40 are preferably made of a material being penetrable to UV radiation, e.g. made of quarts, so that the radiation may penetrate—depending on the damping characteristics of the fluid—to regions of the treatment section not located in direct proximity of the source shield 42. The treatment section is designed so that a number of connected channels are defined by the floor elements 39, 40 where the channels 44 are direct exposure channels into which the source emit radiation directly, and where the channels 43 are indirect exposure channels into which the source emits radiation indirectly as the radiation has passed through one or more floor elements 39, 40. In this respect, the source is considered to emit directly into the channels 44 although the source is shielded by the source shield 42.
It should be noted that whether or not an indirect exposure channel receives radiation depends inter alia on the damping characteristics of the fluid; if, e.g. the fluid damps the radiation to a high degree, the radiation may not penetrate the fluid and into an indirect exposure channel. However, the treatment section is designed so that when the damping from the fluid is insignificant, the radiation from the UV source will extend into the indirect exposure channels 43.
The fluid out of the impellers 3 flows in a spiralling flow pattern as disclosed in connection with the above embodiments. In the embodiment the radiation shield with radiation source is considered to be a transferring element according to the present invention. Furthermore, when the one or more the floor elements 39, 40 are transparent to radiation emitted from the radiation source, these elements are also considered to be transferring elements according to the present invention, as these elements are considered as transferring radiation to the fluid. Thus, the fluid past the radiation shield and thereby past the radiation source—and the transferring elements if made of a radiation penetrable material—flows also in a spiralling flow pattern comprising a radial velocity component Vr and a tangential velocity component Vt. The control method according to the present invention may be applied to control the radial and tangential velocities.
The control method indicated above has the advantage that the magnitude of the radial and tangential velocity components may be controlled independently of each other. By using this control method, the flow rate through the device may e.g. be increased or decreased while maintaining the magnitude of the tangential velocity component. Alternatively the magnitude of the tangential velocity component may be increased without changing the flow rate. By utilising the control method the advantages may be obtained that fouling on the source may be removed, and tailing effects (where particles shadow for each other) may be made smaller by increasing the tangential velocity component.
The control method may comprise use of information on the relationship between the rotational velocity of the impellers and the transferral of e.g. heat, substance or radiation. This information may include quantitative or qualitative information on the correlations with the tangential velocity of the fluids, which correlation may depend on the physical properties of the fluids. The information may e.g. be gained from experiments or from computer simulations. It is typically stored in a database or other computer readable medium from where it can be retrieved by the control system used in the application of the control method according to the present invention. It may also be stored in a way which makes manual interaction necessary as a part of the control method. The control method may comprise control of the velocity of the impellers related to one fluid or to two or more fluids. The control method may additionally or alternatively comprise control of one or more throttling means, e.g. throttling valves.
In the above embodiments, the radial and tangential velocities may be viewed as being in the plane parallel to the surface of the transferring elements.
Recirculation may be applied to one or more of the fluids flowing through devices according to preferred embodiments of the present invention. Such recirculation may be embodied by leading all or a fraction of the fluid flowing out of an outlet of a device to an inlet of the device.
| Number | Date | Country | Kind |
|---|---|---|---|
| PA 2007 01536 | Oct 2007 | DK | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DK2008/050260 | 10/24/2008 | WO | 00 | 5/20/2010 |
