FR3026165A1 - DEVICE FOR THERMALLY TREATING A FLUID WITH REDUCED ENERGY CONSUMPTION - Google Patents

Abstract

Device for heat treatment of a fluid comprising: - a first channel (2) comprising a first wall, a second wall, a fluid supply inlet (2.1) and a fluid outlet (2.2), - a second channel (8) comprising a first wall, a second wall, a fluid supply inlet (8.1) and a fluid discharge outlet (8.2), the first wall of the first channel and the first wall of the second channel being in thermal contact, the first channel and the second channel being arranged so that the fluid flowing in the first channel circulates against the flow of the fluid flowing in the second channel; means (14) for heating the fluid flowing in the first channel; means (16) for heating the fluid flowing in the second channel; means for supplying the first and second channels with the same fluid via the supply inlets.

Description

The present invention relates to a device for the thermal treatment of a fluid, the heat treatment being intended to impose on a fluid a variation of the temperature of a fluid. controlled temperature with reduced energy consumption. In many industrial fields, it is desired to apply temperature excursions to fluids in a controlled sequence. For example, in the agri-food industry, pasteurization of milk is done by applying a rise in temperature for a given time. This time should not be less than a given time to be sure that the pasteurization is complete and should not exceed a given time to avoid changing the composition of the milk. In the chemical industry, such excursions are applied for example to cause one or more chemical reactions. Or devices of the prior art applying temperature excursions have a large installed power and energy consumption compared to the needs. DISCLOSURE OF THE INVENTION The object of the present invention is therefore to provide a heat treatment device capable of applying controlled temperature excursions to a fluid while having a reduced energy consumption. The object of the present invention is achieved by a device comprising a first channel and a second channel in thermal contact and means for applying a heat flux to the fluid flowing in each channel; the fluid to which it is desired to apply a temperature excursion flowing in the two channels against the current.

Thanks to the invention, it is possible to achieve very high or very low temperature levels and to have a reduced energy consumption. The inventors have thought to use a countercurrent heat exchanger to circulate the same fluid and make it active by providing means for applying a heat flow. They obtained a variation of the important temperature of the fluid in each channel with a reduced energy consumption. While in a countercurrent exchanger of the state of the art, a fluid to be heated or cooled circulates in a channel and a coolant providing or extracting heat respectively, circulates in the other channel. According to the invention, the thermal flows applied to the fluid in the two channels are cumulative to obtain a temporary increase in the temperature of each of the fluids. Advantageously, the exchanger is a plate exchanger, the two channels are each delimited by two plates including a plate common to the two channels through which the heat exchange between the fluids take place and the other two walls are in contact with heating means. The subject of the present invention is therefore a device for heat treatment of a fluid, comprising: at least one first channel comprising a first wall, a second wall, a fluid supply inlet and a fluid discharge outlet, at least one second channel comprising a first wall, a second wall, a fluid supply inlet and a fluid discharge outlet, the first wall of the first channel and the first wall of the second channel being in thermal contact; first channel and the second channel being arranged so that the fluid flowing in the first channel circulates against the current of the fluid flowing in the second channel, - first means adapted to apply at least one heat flow to the fluid flowing in the first channel; second means able to apply at least one heat flow to the fluid flowing in the second channel; means for supplying the first and second channels; with the same fluid through the feed inlets. Advantageously, the first and second means capable of applying a heat flux are able to vary the heat flux applied to the fluid along the direction of flow of the fluid in each of the first and second channels. In an exemplary embodiment, the first and second means capable of applying a heat flux are heating means. Preferably the device is thermally insulated from the outside.

The supply means of the first and second channels with the same fluid advantageously feed the first and second channels with the same flow rate and / or advantageously feed the first and second channels with the same fluid at the same temperature. In an exemplary embodiment, the exhaust outlet of the first channel can be connected to the supply input of the second channel. The walls are for example formed by plates, the first and second walls of the first and second channels being for example arranged substantially parallel to each other. The two second walls are advantageously formed by the same plate.

The first and second plates of each channel may be brazed or welded to define sealed channels, or a seal may be interposed between the first and second plates of each channel to define sealed channels. The present invention also relates to a heat treatment plant of a fluid comprising at least two heat treatment devices according to the present invention, the devices being thermally insulated from each other. The channels can be tightly delimited by superimposed plates.

The present invention also relates to a heat treatment process so as to apply at least one temperature excursion to a fluid comprising the steps of: - circulating against the current in two channels in thermal contact the same fluid, - apply to each channel distinctly a heat flow. The two channels are advantageously supplied by the same fluid with the same flow rate and / or by the same fluid at the same temperature. In one exemplary embodiment, the fluid leaving one of the channels flows in the other of the channels. A variation of the thermal flows can be applied to each channel. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be better understood on the basis of the following description and the attached drawings in which: FIG. 1 is a diagrammatic sectional view of an exemplary embodiment of the heat treatment device; FIG. 2 is a schematic cross-sectional view of a variant of the heat treatment device of FIG. 1; FIGS. 3A and 3B are graphical representations of the variation of temperature of the fluid along the two channels of the device according to FIG. for devices having a heat exchange coefficient equal to h = 1 kW / m2 / K and h = 10 kW / m2 / K respectively; - Fig. 4 is a cross-sectional view of an exchange facility 5 is a graphical representation of the temperature variation of the fluid along the two channels of a countercurrent heat exchanger of the state of the art, exchanged having a heat exchange coefficient equal to h = 0.001 kW / m2 / K.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS In the present application, the term "temperature excursion" means an increase or decrease in temperature over a given time. In the following description the device according to the invention will be described mainly in an application in which the fluid is heated. But the device applying fluid cooling is not beyond the scope of the present invention. FIG. 1 shows a schematic representation of an embodiment of a device for heat treatment of a fluid comprising a first channel 2 delimited by two longitudinal walls 4, 6 in the form of plates connected to each other. the other in a sealed manner by their side edges, and a second channel 8 defined by two longitudinal walls 4, 12 in the form of plates connected to each other in a sealed manner by their lateral edges, the plate 4 common to both channels allows a heat exchange between the fluids flowing in each of the channels 2, 8. The fluid may be a liquid, a mixture of liquid, gas or a gas mixture. The heat treatment device also comprises means 14 capable of applying a heat flux for heating the fluid flowing in the first channel 2, the means 14 are mounted on or in the outer face of the wall 6.

The thermal treatment device also comprises means 16 capable of applying a heat flux to heat the fluid flowing in the second channel 8, the means 16 are mounted on or in the outer face of the wall 12. Preferably, a thermal insulator ( not shown) is provided around the means applying the heat flow to control the direction of heat flow to the channels 2, 8. For example, the thermal insulation may be a plastic material, a ceramic such as zirconia, glass .. ., a mineral material. These thermal insulators are generally also electrical insulators. In this example the thermal insulation is also in the form of a plate.

The first channel has a feed end 2.1 and a discharge end 2.2. The second channel 8 has a feed end 8.1 and a discharge end 8.2.

The supply end 2.1 of the first channel 2 and the supply end 8.1 of the second channel 8 are such that the flow of fluid in the first channel and the flow of fluid in the second channel have opposite directions. The fluids circulate against the current. The circulation of the fluid in the two channels is for example provided by a pump.

Alternatively, the two channels could be delimited each by two plates, two of the plates being in thermal contact. Furthermore, preferably the fluid to which it is desired to apply a temperature excursion flows in the first 2 and second 8 channel with the same flow.

Preferably, the plates have a small thickness to allow heat exchange. The materials of the plates are then chosen so that they offer good mechanical strength, good resistance to temperature, corrosion. The plates are for example metal, such as copper or aluminum, metal alloy, plastic material, ceramic material.

The material advantageously has good corrosion resistance, such as stainless steel or a copper-nickel alloy. The means for applying the heat flux to the fluid are, for example, electric heating means by Joule effect, for example heating wire type. Other heating means can be envisaged for example by induction or means using a coolant. Preferably the device has the structure of a plate heat exchanger. The plates can be brazed or welded together. In another example, a peripheral seal is provided between each pair of plates. The plates may advantageously be corrugated to improve heat exchange.

The typical operation of the heat treatment device will now be described. The two channels are fed with the fluid to be heated, preferably with the same flow rate.

For the purposes of the description, the fluid flowing in the first channel 2 is designated F1 and the fluid flowing in the second channel 8 is designated F2, but it is the same fluid. Fluid F1 and F2 at the inlet of each of the channels are at the same temperature. In an example of operation, the fluids F1 and F2 are for example pumped simultaneously into the same reservoir of fluid to be heated and discharged simultaneously into a heated fluid reservoir. The two reservoirs can be confused, for example to apply several excursions to the fluid. The heating means 14, 16 are activated so as to inject identical thermal powers in each of the fluids F1, F2 flowing in each channel 2, 8. For this, a heat flow is imposed through the walls 4, 12. D On the output side 2.2, 8.2 of the channels, the fluids F1 and F2 have an outlet temperature corresponding to the thermal balance, the temperature varying axially in a linear manner. On the other hand, because of the heat exchange between the fluids through the plate 4, the temperature of each of the fluids varies parabolically through a maximum that occurs in the second half of the channels. In the absence of heat exchange between the channels, the temperature of the fluid in each of the channels varies linearly. With the type of fluid and flow imposed, the maximum temperature of the excursion depends on the heat exchange between the two channels and the power injected and is all the higher as the exchanges are important and the power injected is important. It is possible to determine the temperature variations in each of the channels. After calculation, we obtain; The temperature Tp (z) in the first channel varies according to the relation Tp (z) = az (1 + 13 (1_, - z) + Te.

The temperature Ts (z) in the second channel varies according to the relation Ts (z) = z) (1 + 13z) + Te. with a = w1 (qmxCp) 13 = h x P (qm x Cp).

With Lc the length of the channels along which the heat exchange takes place, z the longitudinal position in the channel according to the representation of Figure 1, z = 0 corresponding to the input of the first channel 2. h the exchange coefficient local thermal on an exchange perimeter P, qm the fluid flow, Cp the thermal capacity of the fluid, Te the inlet temperature, wl the imposed linear power. It can be seen that the temperature variation for each of the fluids F 1, F 2 follows a parabolic variation. In FIGS. 3A and 3B, a graphical representation of the variations of the temperatures Tp (z) and Ts (z) of the fluids Fi and F2 respectively as a function of the axial position z in the channels in the heat treatment device according to FIG. invention of Figure 1 taking: Lc = 10 m, P = 1m, qm = 0.5 kg / s, Te = 30 ° C, wl = 1 kW / m and Cp = 4000 J / kg / K, and h = 1 kW / m2 / K (FIG. 3A) and h = 10 kW / m2 / K (FIG. 3B). In FIG. 5, a graphical representation of the variations of the temperatures T'p (z) and T'5 (z) of the fluids Fi and F2 respectively as a function of the axial position z in the channels in a heat exchanger can be seen in FIG. the current being Lc = 10 m, P = 1m, qm = 0.5 kg / s, Te = 30 ° C, w1 = 1 kW / m and Cp = 4000 J / kg / K, and h = 0.001 kW / m2 / K. FIGS. 3A and 3B show the appearance of the maximum temperature at the same axial positions in the two channels. The temperature excursion is about 60 K in the device whose temperature variations are shown in Figure 3A and about 8 ° C in the device whose temperature changes are shown in Figure 3B. In addition, the output temperatures Tp (Lc) and Ts (0) are higher than the input temperatures Tp (0) and Ts (Lc) respectively. In a countercurrent exchanger without power injection, it can be seen in FIG. 5 that the same temperatures are reached at the output, but there is no temperature excursion. As indicated above, it is possible to envisage to make several fluid temperature excursions, the excursions being identical or different. The effectiveness of the device can be defined by the ratio of the effective increase in temperature of the liquid to that of the power injected.

This ratio is expressed by ri = (qmxCp + hxS) 2 / (4xqmxCpxhxS) With h: exchange coefficient between channels 2 and 8, S (= Lc * P): exchange surface between channels 2 and 8 , qm mass flow rate in each channel, Cp heat capacity of the fluid. i tends to 1/2 + hxS / (4xqmxCp) when the product hxS is large in front of qmxCp. The term hxS / (qmxCp) is a coefficient of efficiency of the exchange between the channels 2 and 8 in terms of axial temperature increase that is noted Cet. We can then write that i tends to 1/2 + 1 / 4xCet.

For example, for channels 2 and 8 of 1m wide (P = 1m) and 10m long (Lc = 10m) with a flow rate qm of 0.5 kg / s of liquid water, a coefficient of exchange h of 1.104 W / m2 / K and a linear power of 1 kW / m, the actual increase in temperature of the liquid is 60 K (Figure 3B) whereas it would be only 5 K by the only power injected (Figure 5), an efficiency of 12.

In the case where the device would apply a negative temperature excursion, i.e. a cooling peak, the heating means would be replaced by cooling means, for example formed by cold coolant circulations or by Peltier cells. Alternatively, the discharge end of the first channel is connected to the end of the second channel, so the fluid goes back and forth in the device. In this variant, the maximum temperature of the excursion peak appears at the end of each of the channels. In Figure 2, we can see an alternative embodiment in which the device has a circular cross section. It has a first central channel 302, surrounded by a second annular channel 308. The heating means of the first channel are for example formed by a wire suspended in the first channel and the heating means 316 are in contact with the outer wall of the second channel 308. The passage sections of the first and second channels are determined from preferably so that the channels have the same exchange coefficients.

In the examples described the channels are rectilinear but it will be understood that any channel shape is conceivable such as for example a spiral shape. In Figure 4, we can see an installation comprising a plurality of heat exchange devices according to the invention, the devices being superimposed. The installation comprises a plurality of channels 2,8, 102, 108, 202, 208 ... delimited by superposed plates. The plurality of channels is distributed in pairs. Each pair is thermally insulated from the other pairs by a thermal insulator 20, 120, 220 and each channel of each pair has a heating means 14, 16, 114, 116, 214, 216. For example all the channels 2.8, 102 , 108, 202, 208 are supplied in parallel from the same fluid.

The thermal insulation between the pairs of plates can also be an electrical insulator according to the type of means for applying the heat flow implemented. Alternatively, it is possible to connect the channels for example 2 and 102, the installation then has the behavior of two devices in series.

It is conceivable to make a plurality of channels in each other on the basis of the variant of FIG. 2, channel pairs being thermally insulated from each other in a manner similar to the variant of FIG. besides its very simple realization presents a great adaptability. Indeed, it is enough to modify the electric power or the flow to modify the temperature excursion.

Alternatively, it may be provided to vary axially the injected power to adjust the kinetics of temperature increase of the fluid. In another variant, it may be provided to cancel the exchange between channels, for example, to obtain a temperature plateau. The heat exchange can be interrupted by an insulating wall zone or by separating the fluids as exchanger outlet. If the flow rates in the two channels are different, the temperature changes are different, within the limits of the differences between channels. The present invention applies to all technical fields in which it is desired to apply a heat treatment to a fluid in the form of a temperature excursion having a maximum or a minimum of temperature, for example in the food industry and the food industry. chemical industry.15

Claims (13)

REVENDICATIONS1. Device for heat treatment of a fluid, comprising: at least one first channel (2) comprising a first wall, a second wall, a fluid supply inlet (2.1) and a fluid discharge outlet (2.2); at least one second channel (8) comprising a first wall, a second wall, a fluid supply inlet (8.1) and a fluid discharge outlet (8.2), the first wall of the first channel and the first wall of the second channel being in thermal contact, the first channel and the second channel being arranged so that the fluid flowing in the first channel circulates against the current of the fluid flowing in the second channel, - first means (14) adapted to applying at least one heat flow to the fluid flowing in the first channel, - second means (16) capable of applying at least one heat flow to the fluid flowing in the second channel, - feed means of the first and second av channels ec the same fluid through the power inputs. 2. heat treatment device according to claim 1, wherein the first (14) and second (16) means capable of applying a heat flux are adapted to vary the heat flow applied to the fluid along the flow direction of the fluid in each of the first (2) and second (8) channels. 3. heat treatment device according to claim 1 or 2, wherein the first (14) and second (16) means adapted to apply a heat flow are heating means. 4. heat treatment device according to one of claims 1 to 3, wherein the supply means of the first and second channels with the same fluid are able to feed the first (2) and second (8) channels with the same debit. 5. Heat treatment device according to one of claims 1 to 4, wherein the supply means are adapted to simultaneously supply the first (2) and second (8) channels with the same fluid at the same temperature. 6. Heat treatment device according to one of claims 1 to 5, wherein the discharge outlet (2.2) of the first channel (2) is connected to the supply inlet (8.1) of the second channel (8). . 7. Heat treatment device according to one of claims 1 to 6, wherein the walls are formed by plates, the first two walls of the first and second channels being arranged substantially parallel to each other and the two second walls. being formed by the same plate. 8. Installation for thermal treatment of a fluid comprising at least two heat treatment devices according to claim 1 to 7, the devices being thermally insulated from each other. 9. Heat treatment process so as to apply at least one temperature excursion to a fluid comprising the steps of: - circulating against the current in two channels in thermal contact the same fluid, - apply to each channel separately a heat flow. 10. Heat treatment process according to claim 9, wherein the two channels are fed by the same fluid with the same flow rate. 11. Heat treatment process according to claim 9 or 10, wherein the two channels are fed by the same fluid at the same temperature. 12. Heat treatment process according to claim 9 or 10, wherein the fluid exiting from one of the channels flows in the other channel. 13. Heat treatment process according to one of claims 9 to 12, wherein a variation of thermal flows is applied along the channels.