JP2006015323A - Microchannel evaporator and system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve heat exchange efficiency and miniaturize a microchannel evaporator.
An evaporator 1 has an evaporation liquid passage 3 between two opposing heat transfer plates 2, and a heated gas passage 4 outside the heat transfer plate 2. An evaporating liquid inlet 5 for supplying the evaporating liquid to the evaporator 1 is provided at the lower end of the evaporating liquid passage 3, and a vapor outlet 6 is provided at the upper end of the evaporating liquid passage. Evaporates while flowing from the bottom to the top of the evaporator 1. The heated gas is supplied from a heated gas inlet 7 provided at the upper end of the evaporator, and discharged from a heated gas outlet 8 provided at the lower end of the evaporator. The dimension of the passage gap s of the to-be-evaporated fluid passage 3 gradually increases from the lower side to the upper side in the gas-liquid two-phase region 11.
[Selection] Figure 1

Description

  The present invention relates to a microchannel evaporator in which a liquid passage to be evaporated is smaller than a diameter of a detached bubble and a system using the same.

  In a fuel cell, a fuel gas such as hydrogen gas and an oxidizing gas containing oxygen are electrochemically reacted through an electrolyte, and electric energy is directly taken out between electrodes provided on both surfaces of the electrolyte. In particular, a polymer electrolyte fuel cell using a polymer electrolyte has attracted attention as a power source for electric vehicles because of its low operating temperature and easy handling.

  Hydrogen can be supplied to the fuel cell by supplying hydrogen directly from a hydrogen storage device such as a high-pressure hydrogen tank or a hydrogen storage alloy tank, or by changing the fuel supplied from raw fuel such as methanol or hydrocarbons. There is a quality law. In the fuel reforming method, when the raw fuel is liquid, fuel and water are evaporated by an evaporator and led to the fuel reformer, and hydrogen is generated by a fuel reforming reaction in the fuel reformer.

As a small and highly efficient evaporator suitable for in-vehicle use, an automobile air-conditioning evaporator that evaporates a refrigerant is known (for example, Patent Document 1). According to this prior art, a laminated structure in which a pair of core plates are overlapped with a solid intermediate plate interposed therebetween. This laminated structure forms an outward flow path sandwiched between one core plate and one surface of the intermediate plate, and a return flow path sandwiched between the other core plate and the other surface of the intermediate plate. The refrigerant that is the fluid to be evaporated first flows down in the forward flow path while being heated, then moves from the forward flow path to the return flow path through the through hole in the lower part of the intermediate plate, and finally passes through the return flow path. It evaporates as it rises.
Japanese Patent No. 2786728 (page 3, Fig. 1)

  However, the conventional evaporator has a problem in that the heat exchange capability is reduced in a high heat flux region. Hereinafter, this problem will be described.

[Definition of microchannels]
In the present invention, the microchannel is defined as follows. The case where the diameter of the bubble that leaves from the heat transfer surface is larger than the channel gap is defined as a microchannel. In other words, the case where the bubbles are crushed by the wall at a stage smaller than the separation diameter to form a microlayer between the bubbles and the heating surface is defined as a microchannel.

  The detached bubble diameter varies depending on the type of liquid to be evaporated, the surface properties of the heat transfer plate, and the degree of superheat. Specifically, as shown in FIG. 12, for example, when the liquid to be evaporated is water and the titanium oxide film has high hydrophilicity, about 0.8 mm, and in the case of silicone film with high hydrophobicity, 2. The detached bubble diameter of about 5 [mm] is shown, that is, the value below that value is the gap size of the microchannel on the heated surface.

[Necessity of forming a thin liquid film on the heat transfer surface]
FIG. 13A is a graph showing the relationship between the degree of superheat and heat flux of the heat transfer surface when the gap between the heat transfer surfaces in the parallel plate evaporator is narrow (solid line) and wide (broken line). . As shown in FIG. 13 (a), when two lines intersect at a certain temperature and heat flux point and the gap between the heat transfer surfaces is narrow, the heat transfer characteristic is good in the region where the heat flux is low, In the region where the heat flux is high, the heat transfer characteristic decreases, and the critical heat flux (Critical Heat Flux) decreases accordingly. On the other hand, when the gap between the heat transfer surfaces is wide, good heat transfer characteristics are exhibited in a region where the heat flux is high, but heat transfer characteristics are degraded in a region where the heat flux is low.

  As this mechanism, there is a decrease in heat transfer coefficient due to dryout of the heat transfer surface. FIG. 13B shows changes in flow and heat transfer mode in the evaporator tube. The liquid in the evaporator tube is almost 100% liquid phase upstream (lower part in the figure), but gradually becomes a two-phase state in which bubbles increase in the liquid phase as it goes downstream (upper part in the figure). Downstream from the position (post-dryout), there is no liquid to be evaporated on the heat transfer surface, and the heat transfer surface is completely dry. In the post-dryout spray basin, there is no liquid that is always in contact with the heat transfer surface, indicating a significant decrease in heat transfer characteristics.

  FIG. 13C shows the heating heat flux and heat transfer coefficient distribution in the evaporation tube. In the figure, the heat flux increases in the order of A → B → C → D. It is shown that the region of reduced heat transfer coefficient (spray flow) moves upstream as the heat flux increases. In order to improve the decrease in the heat transfer coefficient, it is necessary to supply the liquid to be vaporized to the spray flow (post dry out) region to keep the heat transfer surface wet.

  FIG. 14 is a schematic diagram showing the boiling aspect of the microchannel in the high heat flux region. The evaporation target liquid 106 is supplied from the lower side (upstream) of the heat transfer surface 101 in the figure, and the vapor 107 is discharged from the upper side (downstream). The liquid to be evaporated 106 is heated by the heat transfer surface 101, and the liquid to be evaporated becomes a spray flow 105 above the gas-liquid interface 104.

  The gas-liquid interface 104, which is an interface between the wet region (upstream from the dryout position) 102 of the heat transfer surface 101 and the spray flow region 103, moves downward (upstream) as the heat flux increases, and is efficient as heat transfer. The wet region 102 of the heat transfer surface that can be used for the heat transfer surface is limited, and the heat exchange efficiency of the entire heat transfer surface is reduced. In order to improve the heat exchange efficiency, it is necessary to increase the ratio of the wet region 102 having a high heat transfer coefficient in the heat transfer surface.

FIG. 15 is a schematic diagram of photographs of boiling states in heat fluxes of (a) 9 [kW / m ² ], (b) 14 [kW / m ² ], and (c) 19 [kW / m ² ]. It has become. As shown in FIG. 15, the wetting area of the heat transfer surface is reduced as the heat flux increases.

  FIG. 16A shows the heat transfer coefficient corresponding to the quality of the liquid to be evaporated, and FIG. 16B shows the heat flux corresponding to the quality of the liquid to be evaporated. As shown in FIG. 16 (a), the heat transfer surface maintains the wet (wet) region where the quality is lower than the dry-out point A (the quality of this point A is Xa). It is necessary to improve the transmission rate. Further, as shown in FIG. 16B, the heat flux at the boundary between the region before dryout and the region after dryout decreases to the right with respect to the increase in quality. The heat flux for the quality Xa is qca, and it is necessary to control the heat flux to be smaller than this.

  In order to solve the above problems, the present invention is directed to a microchannel evaporator in which the gap dimension of the liquid passage to be evaporated is smaller than the diameter of the separation bubble, and the liquid passage to be evaporated is installed vertically, The gist is that the gap size in the gas-liquid two-phase region is the minimum gap size that satisfies the critical heat flux or less with respect to quality.

  According to the present invention, since the thin liquid film of the liquid to be evaporated is formed on the heat transfer surface in contact with the gas-liquid two-phase region of the liquid to be evaporated, the heat transfer surface in contact with the gas-liquid two-phase region always has a heat transfer coefficient. The heat exchange efficiency of the microchannel evaporator can be improved, and the microchannel evaporator can be reduced in size.

  Next, with reference to the drawings, embodiments of a microchannel evaporator (also simply referred to as an evaporator) according to the present invention will be described in detail. Although not particularly limited, the evaporator according to the present invention is suitable for an evaporator that evaporates water or a hydrocarbon-based raw fuel and supplies it to a fuel reformer for a fuel cell.

  FIG. 1A is a cross-sectional view, FIG. 1B is a conceptual diagram of a vaporized liquid passage, and FIG. 1C is a conceptual diagram of a heated gas passage, illustrating basic structural units of an evaporator according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the evaporator 1 in this embodiment is an evaporator in which a space between two opposing heat transfer plates 2 serves as an evaporation target liquid passage 3. The outside of the heat transfer plate 2 is a heated gas passage 4. When actually configuring the evaporator, it is preferable to have a configuration in which a plurality of basic structural units shown in this figure are arranged in parallel.

  An evaporating liquid inlet 5 for supplying the evaporating liquid to the evaporator 1 is provided at the lower end of the evaporating liquid passage 3, and a vapor outlet 6 is provided at the upper end of the evaporating liquid passage. Evaporates while flowing from the bottom to the top of the evaporator 1. On the other hand, the heated gas is supplied from a heated gas inlet 7 provided at the upper end of the evaporator and discharged from a heated gas outlet 8 provided at the lower end of the evaporator. Therefore, the evaporator according to the first embodiment is a counter-flow evaporator in which the flow direction of the liquid to be evaporated and the flow direction of the heating gas are opposed to each other. During the operation of the evaporator 1, the inside of the liquid passage 3 to be evaporated becomes a liquid phase region 10, a gas-liquid two phase (boiling two phase) region 11, and a gas phase region 12 in order from the bottom.

  The dimension of the passage gap s of the evaporated fluid passage 3 gradually increases from the lower side to the upper side in the gas-liquid two-phase region 11.

  The heat transfer plate 2 can be made of a corrosion-resistant metal material such as stainless steel, titanium, titanium alloy, or the like.

  Furthermore, by forming a film of titanium oxide or the like on the surface of the heat transfer plate 2 that contacts the liquid to be evaporated and performing a hydrophilic treatment, it becomes possible to obtain a larger capillary pressure and a penetrating power to the heating surface. The critical heat flux can be improved.

  In the first embodiment, it is assumed that the mass flow rate of the heating gas is sufficiently larger than the mass flow rate of the liquid to be evaporated, and the temperature of the heating gas is substantially unchanged between the heating gas inlet 7 and the heating gas outlet 8.

FIG. 2 is a diagram illustrating a change in the passage gap s of the liquid passage 3 to be evaporated in the gas-liquid two-phase region 11 in the evaporator according to the first embodiment. The horizontal axis in FIG. 2 indicates the quality, which is the ratio of the gas phase mass flow rate to the total mass flow rate of the liquid to be evaporated, and the vertical axis indicates the heat flux or critical heat flux qc [kW / m ² ]. If the quality is 0, the total mass flow rate of the liquid to be evaporated is a liquid, that is, a liquid phase, and if the quality is 1, the total mass flow rate of the liquid to be evaporated is a gas, that is, a gas phase (vapor single phase).

  The gas-liquid two-phase region 11 in FIG. 1 can be considered as a region where the quality at the lower end is 0, the quality at the upper end is 1, and the middle is a region where the quality gradually increases.

With such quality as the horizontal axis, the vertical axis indicates the critical heat flux, and the passage gaps s _A , s _B , s _C (s _A > s _B > s in the parallel plate type microchannel evaporator) The correlation between the quality X and the critical heat flux q _C in _C ) is shown in FIG.

  If the gap size is the same, the smaller the quality, the larger the ratio of the liquid, and a larger amount of heat is transferred from the heat transfer plate, so the critical heat flux tends to increase. If the gap size is increased, the gap is held in the gap. The amount of liquid to be evaporated increases and the critical heat flux tends to increase.

Here, as viewed from the reference passage gap s _B , when the passage gap is increased, the critical heat flux increases, and the rate of increase is larger when the quality is smaller. Conversely, when the passage gap is decreased, the critical heat flux is decreased, and the rate of the decrease is larger when the quality is smaller.

In this embodiment, the mass flow rate of the heating gas is sufficiently larger than the mass flow rate of the liquid to be evaporated, and the temperature of the heating gas is almost unchanged between the heating gas inlet 7 and the heating gas outlet 8. The heat flux given to the liquid to be evaporated from the heat transfer plate through the heat transfer plate is constant regardless of the quality, and is shown by a broken line in FIG. The broken line indicating the heat flux and the line indicating the limit heat flux of the passage gap s _B intersect with each other with quality X _B. This is because the critical heat flux is supplied at the position of the evaporator quality X _{B in} the passage gap s _B , and in the region of quality X _B or higher, the supplied heat flux exceeds the critical heat flux. Since it changes from dry to dry and the heat transfer coefficient decreases, the heat flux rapidly decreases as shown by the alternate long and short dash line.

In this embodiment, in order to avoid such a decrease in heat flux, in the region where the quality X is X _B or more, the passage gap is set to s _{B + 1_case1} , as the quality increases to X _{B + 1} , X _{B + 2} , X _{B + 3} . _{s B +} 2_case1, to expand and _{s B +} 3_case1. Thus without heat flux also increases quality from X _B exceeds the limit heat flux, it is possible to obtain the maximum heat transfer coefficient.

Similarly, in the following areas Quality X is X _B, As the quality decreases and _{X B-1, X B-} 2, the heat transfer also by reducing the passage gap _{s B-1_case1,} and _{s B-2_case1} The surface can be maintained in a wet state. Thus in heat flux also decreases quality from X _B maintains the critical heat flux, it is possible to obtain the maximum heat transfer coefficient.

  As described above, in the counter-flow microchannel evaporator, the passage gap s of the liquid passage to be evaporated with respect to the quality X is set to the minimum gap dimension that satisfies the critical heat flux or less. Since a thin liquid film of the liquid to be evaporated is formed on the heat transfer surface in contact with the gas-liquid two-phase region, the heat transfer surface in contact with the gas-liquid two-phase region can always be maintained in a state with a high heat transfer coefficient, The heat exchange efficiency of the microchannel evaporator can be improved, and the microchannel evaporator can be reduced in size.

  FIGS. 3A and 3B are (a) a sectional view, (b) a vaporized liquid passage conceptual diagram, and (c) a heated gas passage conceptual diagram for explaining basic structural units of an evaporator according to a second embodiment of the present invention.

  The configuration of the evaporator 1 itself according to the second embodiment is a counter flow type in which the flow direction of the liquid to be evaporated and the flow direction of the heating gas are opposed to each other, similarly to the configuration of the evaporator according to the first embodiment. However, the present embodiment is an embodiment in which the mass flow rate of the heating gas is not negligible compared to the mass flow rate of the liquid to be evaporated, and the temperature of the heating gas decreases from the heating gas inlet 7 to the heating gas outlet 8. .

  FIG. 4 is a diagram showing a change in heat flux from the heated gas to the liquid to be evaporated side (broken line) and the limit heat flux in each passage gap in the present embodiment. As shown by the broken line in FIG. 4, the heat flux is small where the quality is small, and the heat flux is large where the quality is large. This is because where the quality of the heated gas is high, the temperature of the heated gas is high, and the temperature difference between the heated gas and the liquid to be evaporated is large, so the heat flux is large, and where the quality is small, the temperature of the heated gas is reduced. This is because the heat flux is small because the temperature difference between the heated gas and the liquid to be evaporated is small.

In FIG. 4, the broken line indicating the heat flux given to the liquid to be evaporated from the heated gas and the line indicating the limit heat flux of the passage gap s _B intersect with each other with quality X _B. This is because the critical heat flux is supplied at the position of the evaporator quality X _{B in} the passage gap s _B , and in the region of quality X _B or higher, the supplied heat flux exceeds the critical heat flux. Since it changes from dry to dry and the heat transfer coefficient decreases, the heat flux rapidly decreases as shown by the alternate long and short dash line.

In this embodiment, in order to avoid such a decrease in heat flux, in the region where the quality X is X _B or higher, the passage gap is set to s _{B + 1_case2} , as the quality increases to X _{B + 1} , X _{B + 2} , X _{B + 3} . _{s B +} 2_case2, to expand and _{s B +} 3_case2. Thus without heat flux also increases quality from X _B exceeds the limit heat flux, it is possible to obtain the maximum heat transfer coefficient.

Similarly, in the following areas Quality X is X _B, As the quality decreases and _{X B-1, X B-} 2, the heat transfer also by reducing the passage gap _{s B-1_case2,} and _{s B-2_case2} The surface can be maintained in a wet state. Thus in heat flux also decreases quality from X _B maintains the critical heat flux, it is possible to obtain the maximum heat transfer coefficient.

  As described above, in the counter-flow microchannel evaporator, the passage gap s of the liquid passage to be evaporated with respect to the quality X is set to the minimum gap dimension that satisfies the critical heat flux or less. Since a thin liquid film of the liquid to be evaporated is formed on the heat transfer surface in contact with the gas-liquid two-phase region, the heat transfer surface in contact with the gas-liquid two-phase region can always be maintained in a state with a high heat transfer coefficient, The heat exchange efficiency of the microchannel evaporator can be improved, and the microchannel evaporator can be reduced in size.

  5A is a sectional view, FIG. 5B is a conceptual diagram of a liquid to be evaporated, and FIG. 5C is a conceptual diagram of a heated gas path, illustrating basic structural units of an evaporator according to a third embodiment of the present invention.

  As shown in FIG. 5, the evaporator 1 according to the present embodiment is an evaporator in which a space between two opposing heat transfer plates 2 serves as an evaporation target liquid passage 3. The outside of the heat transfer plate 2 is a heated gas passage 4. When actually configuring the evaporator, it is preferable to have a configuration in which a plurality of basic structural units shown in this figure are arranged in parallel.

  An evaporating liquid inlet 5 for supplying the evaporating liquid to the evaporator 1 is provided at the lower end of the evaporating liquid passage 3, and a vapor outlet 6 is provided at the upper end of the evaporating liquid passage. Evaporates while flowing from the bottom to the top of the evaporator 1. On the other hand, the heated gas is supplied from a heated gas inlet 7 provided at the lower end of the evaporator and discharged from a heated gas outlet 8 provided at the upper end of the evaporator. Therefore, the evaporator of the present embodiment is a parallel flow type evaporator in which the flow direction of the liquid to be evaporated and the flow direction of the heated gas are parallel. During the operation of the evaporator 1, the inside of the liquid passage 3 to be evaporated becomes a liquid phase region 10, a gas-liquid two phase (boiling two phase) region 11, and a gas phase region 12 in order from the bottom.

  The dimension of the passage gap s of the evaporated fluid passage 3 gradually decreases from the lower side to the upper side in the gas-liquid two-phase region 11.

  The heat transfer plate 2 can be made of a corrosion-resistant metal material such as stainless steel, titanium, titanium alloy, or the like.

  Furthermore, by forming a film of titanium oxide or the like on the surface of the heat transfer plate 2 that contacts the liquid to be evaporated and performing a hydrophilic treatment, it becomes possible to obtain a larger capillary pressure and a penetrating power to the heating surface. The critical heat flux can be improved.

  In this embodiment, the mass flow rate m [g / s] of the heated gas is not negligible compared to the mass flow rate of the liquid to be evaporated, and the temperature of the heated gas decreases from the heated gas inlet 7 to the heated gas outlet 8. This is an example.

  FIG. 6 is a diagram showing a change in heat flux from the heated gas to the liquid to be evaporated side (broken line) and the limit heat flux in each passage gap in the present embodiment. As shown by the broken line in FIG. 6, the heat flux is large where the quality is small, and the heat flux is small where the quality is large. This is because where the quality of the heated gas is high, the temperature of the heated gas is high, and the temperature difference between the heated gas and the liquid to be evaporated is large, so the heat flux increases, and where the quality is large, the temperature of the heated gas decreases, This is because the heat flux is small because the temperature difference between the heated gas and the liquid to be evaporated is small.

In FIG. 6, the broken line indicating the heat flux given to the liquid to be evaporated from the heated gas and the line indicating the critical heat flux of the passage gap s _B intersect with each other with quality X _B. This is because the critical heat flux is supplied at the position of the evaporator quality X _{B in} the passage gap s _B , and in the region below the quality X _B , the supplied heat flux exceeds the critical heat flux. Since it changes from dry to dry and the heat transfer coefficient decreases, the heat flux rapidly decreases as shown by the alternate long and short dash line.

In this embodiment, in order to avoid such a decrease in the heat flux, in the region where the quality X is X _B or less, the passage gap is set to s as the quality decreases and decreases to X _B-1 and X _{B-2. B-1_case3,} to expand and _{s B-2_case3.} Thus without heat flux also decreases quality from X _B exceeds the limit heat flux, it is possible to obtain the maximum heat transfer coefficient.

Similarly, in the region where the quality X is X _B or higher, the heat transfer surface is reduced even if the passage gap is reduced to s _{B + 1_case3} , s _{B + 2_case3} , s _{B + 3_case 3 as} the quality increases to X _{B + 1} , X _{B + 2} , X _{B + 3.} The wet state can be maintained. Thus in heat flux also increases quality from X _B maintains the critical heat flux, it is possible to obtain the maximum heat transfer coefficient.

  In this way, in the co-flow microchannel evaporator, the vapor gap s of the liquid passage to be evaporated with respect to the quality X is set to the minimum gap dimension that satisfies the critical heat flux or less, so that the liquid vapor passage Since a thin liquid film of the liquid to be evaporated is formed on the heat transfer surface in contact with the gas-liquid two-phase region, the heat transfer surface in contact with the gas-liquid two-phase region can always be kept in a high heat transfer rate state. The heat exchange efficiency of the microchannel evaporator can be improved, and the microchannel evaporator can be reduced in size.

  7A is a cross-sectional view illustrating a basic structural unit of an evaporator according to a fourth embodiment of the present invention, FIG. 7B is a conceptual view of a liquid passage to be evaporated, FIG. 7C is a conceptual view of a heated gas passage, and FIG. FIG.

  As shown in FIG. 7, the evaporator 1 in the present embodiment is an evaporator in which a space between two opposed heat transfer plates 2 serves as an evaporation target liquid passage 3. The outside of the heat transfer plate 2 is a heated gas passage 4. When actually configuring the evaporator, it is preferable to have a configuration in which a plurality of basic structural units shown in this figure are arranged in parallel.

  An evaporating liquid inlet 5 for supplying the evaporating liquid to the evaporator 1 is provided at the lower end of the evaporating liquid passage 3, and a vapor outlet 6 is provided at the upper end of the evaporating liquid passage. Evaporates while flowing from the bottom to the top of the evaporator 1. On the other hand, the heated gas is supplied from a heated gas inlet 7 provided at the right end of the evaporator and discharged from a heated gas outlet 8 provided at the left end of the evaporator. Therefore, the evaporator of the present embodiment is a cross-flow type evaporator in which the flow direction of the liquid to be evaporated and the flow direction of the heated gas are orthogonal. During the operation of the evaporator 1, the inside of the liquid passage 3 to be evaporated becomes a liquid phase region 10, a gas-liquid two phase (boiling two phase) region 11, and a gas phase region 12 in order from the bottom.

  In the gas-liquid two-phase region 11, the dimension of the passage gap s of the evaporated fluid passage 3 gradually decreases from the lower side to the upper side and gradually decreases from the right side to the left side. I am doing.

  The heat transfer plate 2 can be made of a corrosion-resistant metal material such as stainless steel, titanium, titanium alloy, or the like.

  Furthermore, by forming a film of titanium oxide or the like on the surface of the heat transfer plate 2 that contacts the liquid to be evaporated and performing a hydrophilic treatment, it becomes possible to obtain a larger capillary pressure and a penetrating power to the heating surface. The critical heat flux can be improved.

  FIG. 8 shows the position LL on the upstream side of the heating gas, the position MM on the center of the evaporator 1, and the position NN on the downstream side of the heating gas of the evaporator 1. It is a figure which shows the change (broken line) of the heat flux from heated gas to the to-be-evaporated liquid side, and the limit heat flux in each passage gap.

  In the present embodiment, the heat flux transmitted from the heating gas of the evaporator to the liquid to be evaporated is large at the position LL on the upstream side of the heating gas, the position MM on the midstream side, and the position NN on the downstream side. As the process proceeds to, it decreases with a decrease in temperature of the heated gas. In the present embodiment, as in the first embodiment, the mass flow rate of the heated gas is sufficiently larger than the mass flow rate of the liquid to be evaporated, and the temperature of the heated gas is almost unchanged between the heated gas inlet 7 and the heated gas outlet 8. Therefore, the heat flux given to the liquid to be evaporated from the heated gas through the heat transfer plate is constant regardless of the quality, and is shown by a broken line in FIG.

In FIG. 8, the broken line indicating the heat flux given to the liquid to be evaporated from the heated gas at the position MM and the line indicating the critical heat flux of the passage gap s _B intersect with each other with the quality X _B. This is because the critical heat flux is supplied at the position of the quality X _B of the passage gap s _B , and in the region below the quality X _B , the supplied heat flux exceeds the critical heat flux. Since it changes and the heat transfer coefficient decreases, the heat flux decreases rapidly as in Example 2, although not shown.

In the present embodiment, in order to avoid such a decrease in heat flux, in the region where the quality X at the position MM is equal to or higher than X _B , the passage increases as the quality increases to X _{B + 1} , X _{B + 2} , X _{B + 3.} The gap is expanded to s _{B + 1} , s _{B + 2} and s _{B + 3} . Thus without heat flux also increases quality from X _B exceeds the limit heat flux, it is possible to obtain the maximum heat transfer coefficient. In the region where the quality X is X _B or less, the heat transfer surface is reduced even if the passage gap is reduced to s _B-1 and s _{B-2 as} the quality decreases to X _B-1 and X _B-2. Can be maintained in a wet state. Thus in heat flux also decreases quality from X _B maintains the critical heat flux, it is possible to obtain the maximum heat transfer coefficient.

Similarly, the broken line indicating the heat flux given to the liquid to be evaporated from the heated gas at the position LL of the evaporator 1 and the line indicating the limit heat flux of the passage gap s _A intersect with each other with the quality X _A. . This is critical heat flux is supplied at a position of the quality X _A of the passage gap s _A, the following areas Quality X _A, the heat flux supplied exceeds the critical heat flux, heat transfer surface to dry the wet Since it changes and the heat transfer coefficient decreases, the heat flux decreases rapidly as in the second embodiment although not shown.

In order to avoid such a decrease in heat flux, in the region where the quality X at the position LL is X _A or higher, the passage gap is expanded as the quality increases to X _{A + 1} , X _{A + 2} , X _{A + 3} . As a result, even if the quality increases from X _A , the maximum heat transfer coefficient can be obtained without the heat flux exceeding the critical heat flux. In the region where the quality X is X _A or less, the heat transfer surface can be maintained in a wet state even if the passage gap is reduced as the quality decreases to X _A-1 and X _A-2. . Thus in heat flux also decreases quality from X _A maintains the critical heat flux, it is possible to obtain the maximum heat transfer coefficient.

  In the present embodiment, the same processing as that performed at the positions LL and MM is performed in the entire region of the evaporator 1, so that the quality of the entire region of the gas-liquid two-phase region 11 of the evaporator 1 is improved. It is set as the minimum passage gap dimension of the liquid passage to be evaporated which is equal to or less than the critical heat flux.

  In this way, in the cross-flow type microchannel evaporator, the passage gap s of the liquid passage to be evaporated with respect to the quality X is set to the minimum gap dimension that satisfies the critical heat flux or less, so that Since a thin liquid film of the liquid to be evaporated is formed on the heat transfer surface in contact with the gas-liquid two-phase region, the heat transfer surface in contact with the gas-liquid two-phase region can always be maintained in a state with a high heat transfer coefficient, The heat exchange efficiency of the microchannel evaporator can be improved, and the microchannel evaporator can be reduced in size.

  FIG. 9A is a sectional view, FIG. 9B is a conceptual diagram of a vaporized liquid passage, and FIG. 9C is a conceptual diagram of a heated gas passage, illustrating a basic structural unit of an evaporator according to a fifth embodiment which is a modification of the second embodiment. is there. The difference between the evaporator of the present embodiment and the evaporator of Embodiment 2 is that the passage gap s is gradually narrowed in the gas phase region 12 of the liquid passage 3 to be evaporated. Since the other configuration is the same as that of the second embodiment, the same components are denoted by the same reference numerals and redundant description is omitted. As a result, it is possible to prevent the liquid droplets to be evaporated from being discharged from the vapor outlet 6.

  Note that, as in the fifth embodiment, gradually reducing the passage gap s in the gas phase region 12 of the vaporized liquid passage 3 can be applied not only to the second embodiment but also to other embodiments.

  FIG. 10 shows a sixth embodiment in which the heating gas is meandered by providing a plurality of folded portions in the heating gas passage 4 by the partition walls 9 in the cross flow type evaporator of the fourth embodiment shown in FIG. Since other configurations are the same as those of the fourth embodiment, the same components are denoted by the same reference numerals and redundant description is omitted.

  In the fourth embodiment, the boundary line between the gas phase region 12 and the gas-liquid two-phase region 11 and the boundary line between the gas-liquid two-phase region 11 and the liquid-phase region 10 are inclined. Compared to Example 4, these boundaries can be kept more parallel to the heated gas flow direction. Thereby, there exists an effect that the superheat degree of the steam produced | generated from the edge part of the steam outlet 6 can be made more uniform.

  FIG. 11 is an embodiment 7 in which the heating gas is meandered by providing a plurality of folded portions in the heating gas passage 4 by the partition wall 9 in the cross flow type evaporator of the embodiment 4 shown in FIG. The difference from the sixth embodiment is that the heating gas inlet 7 is set in the vicinity of the vaporized liquid inlet 5 and the heating gas outlet 8 is set in the vicinity of the vapor outlet 6. As a result, the liquid phase region 10 having the highest critical heat flux is heated from the hottest portion of the heated gas, so that the passage gap s of the liquid passage 3 to be evaporated can be made narrower than that of the sixth embodiment, and the evaporator There is an effect that the shape of 1 can be further downsized. Since other configurations are the same as those of the fourth embodiment, the same components are denoted by the same reference numerals and redundant description is omitted.

  This embodiment will be described with reference to FIGS. FIG. 17 is a (a) cross-sectional view, (b) a vaporized liquid passage conceptual diagram, and (c) a heated gas passage conceptual diagram for explaining a basic structural unit of an eighth embodiment of the evaporator according to the present invention. 18 shows the critical heat flux characteristics under the inlet conditions of pure water and hot gas as the liquid to be evaporated in the evaporator shown in FIG. 17, and FIG. 19 shows the inlet conditions of pure water and the boiling region based on the characteristics of FIG. FIGS. 20 to 22 show the flow patterns of the heating gas when controlled based on the map of FIG. 19, respectively.

  As shown in FIG. 17, the evaporator 1 according to the present embodiment is an evaporator in which a space between two opposed heat transfer plates 2 serves as an evaporation target liquid passage 3. The outside of the heat transfer plate 2 is a heated gas passage 4. When actually configuring the evaporator, it is preferable to have a configuration in which a plurality of basic structural units shown in this figure are arranged in parallel.

  An evaporating liquid inlet 5 for supplying the evaporating liquid to the evaporator 1 is provided at the lower end of the evaporating liquid passage 3, and a vapor outlet 6 is provided at the upper end of the evaporating liquid passage. Evaporates while flowing from the bottom to the top of the evaporator 1. On the other hand, the heated gas is supplied from a heated gas inlet 7 provided at the lower end of the evaporator and discharged from a heated gas outlet 8 provided at the upper end of the evaporator. Therefore, the evaporator of the present embodiment is a parallel flow type evaporator in which the flow direction of the liquid to be evaporated and the flow direction of the heated gas are parallel. During the operation of the evaporator 1, the inside of the liquid passage 3 to be evaporated becomes a liquid phase region 10, a gas-liquid two phase (boiling two phase) region 11, and a gas phase region 12 in order from the bottom. The dimension of the passage (microchannel) gap s of the fluid passage 3 to be evaporated is a constant dimension in the entire region of the evaporator 1.

  Next, the map in FIG. 19 will be described with reference to FIGS. 17 and 18.

  In Example 8, as shown in FIG. 17, a co-flow type evaporator with a constant microchannel gap (s) is used, and the conditions at the pure water inlet are the mass flow rate mw [g / s] and the temperature Tw [K]. The conditions at the heating gas inlet are mass flow rate mg [g / s] and temperature Tg [K]. 18 is different depending on the microchannel gap s as described above, and shows a higher characteristic as the gap s is larger.

For example, the relationship between the quality and heat flux when the gap is s _B will be described below. First, when the mass flow rate at the high temperature gas inlet is mg2 and the temperature is Tg2, the heat flux between the high temperature gas and the liquid to be evaporated changes as shown by the broken line with the change in quality, and the gap s in the quality from zero to one. It is below the critical heat flux characteristics of _B. Similarly, in the case of (mg2, Tg1) and (mg1, Tg2) (each one-dot chain line), it is below the critical heat flux characteristic of the gap s _B as described above. These indicate that a thin liquid film can be formed and efficient heat exchange is possible.

  On the other hand, in the case of (mg2, Tg3) and (mg3, Tg2) (each broken line), as the quality increases, the heat flux of the hot gas and the liquid to be evaporated intersects the critical heat flux characteristics, and then the dryout region As a result, the heat flux decreases significantly. As a result, the heat exchange rate deteriorates.

  The above results are summarized in FIG. 19 in relation to the (mg, Tg) conditions at the hot gas inlet and the boiling region (dry out, wet). In this map, the pure water inlet condition is (mw [g / s] Tw, [K]). Note that the map in FIG. 19 is used to determine whether or not to move to the dryout region, and to determine quantitative ΔTg and Δmg for shifting to the wet region when it is determined to shift to the dryout region. Used for. Further, in the line for distinguishing the dry out region and the wet region in FIG. 19, mw [g / s] and Tw [K] are changed in the range of use, and the heat flux characteristic with respect to the quality obtained by experiment or calculation is the critical heat flux characteristic. Is created by plotting the conditions of mw [g / s] and Tw [K] in contact with.

  Next, the configuration and operation of the system using the evaporator of this embodiment will be described with reference to FIGS. 23 (a) to 23 (c).

  Each of the systems shown in FIGS. 23 (a) to 23 (c) uses an evaporator body 1, a superheater 21, a heating gas inlet 31 as a system, and a three-way valve for switching the heating gas flow path. Provided with valves 32, 33 and 34, and a heated gas outlet 35 as a system.

  The system shown in FIG. 23A is a system that supplies heating gas in parallel to the superheater 21 and the evaporator main body 1 when the mass flow rate of the heating gas is equal to or higher than a specified value.

  The system of FIG. 23B is a system characterized in that when the temperature of the heated gas is equal to or higher than the specified temperature, the heated gas is supplied to the superheater 21 and then supplied to the evaporator body 1.

  23C, when the mass flow rate and temperature of the heating gas are higher than the specified value, the heating gas is supplied in parallel to the superheater 21 and the evaporator main body 1, and the heating gas discharged from the superheater 21 is further supplied. It is a system characterized in that it is supplied to the evaporator body 1.

  In addition, the location described with the thick line in the figure shows the flow of gas, and the black portion of the three-way valve is the direction in which the gas flow is closed. This embodiment is composed of two heat exchangers. One is an evaporator main body 1 using a microchannel evaporator intended to be used in the wet region, and the other is a superheater 21 for generating superheated steam. The gas that has passed through the heat exchanger 1 or 21 is supplied to a hydrogen generation element to an ATR (Auto Thermal Reactor) (not shown). Further, in a normal state (in the case of Wet Rigion) not described below, the superheater 21 is bypassed and supplied. FIG. 23 (a) corresponds to FIG. 20, FIG. 23 (b) corresponds to FIG. 21, FIG. 23 (c) corresponds to FIG. 22, and FIGS. Is. Further, the configuration diagrams shown in FIGS. 23A to 23C are examples, and do not limit the present invention.

  Next, specific control will be described with reference to FIGS. 19 to 22. 20 shows the case where the condition (mg3, Tg2) in the A direction in FIG. 19 is changed to the condition (mg2, Tg2) direction, and FIG. 21 shows the condition (mg2) from the condition (mg2, Tg3) in the B direction in FIG. , Tg2), and FIG. 22 shows the case of changing from the condition (mg3, Tg2) in the C direction to the condition (mg2, Tg1) in FIG.

  In FIG. 20, the heated gas supplied under the conditions (mg3, Tg2) is supplied to the evaporator main body 1 under the conditions (mg2, Tg2) and to the superheater 21 under the conditions (Δmg, Tg2). The heated gases discharged from the evaporator main body 1 and the superheater 21 merge and are sent to the ATR. The heated gas discharged from the evaporator main body 1 may be passed through the superheater 21.

  In FIG. 21, the heated gas supplied under the conditions (mg2, Tg3) is supplied to the superheater 21 under the conditions (mg2, Tg3), and the temperature of the superheater 21 decreases by ΔTg. mg2, Tg2). The heated gas discharged from the evaporator main body 1 is sent to the ATR. Note that the heated gas discharged from the evaporator body 1 may pass through the superheater 21 again.

  In FIG. 22, the heated gas supplied under the conditions (mg3, Tg2) is supplied to the evaporator main body 1 under the conditions (Δmg, Tg2) and to the superheater 21 under the conditions (mg3-Δmg, Tg2). The The heated gas discharged from the superheater 21 is supplied to the evaporator body 1 at a temperature (Tg2−ΔTg) and sent to the ATR. The heated gas discharged from the evaporator main body 1 may be passed through the superheater 21.

  Thus, in the present embodiment, the following effects can be obtained.

  Keeping the heat transfer surface in a wet state with a narrow gap having a uniform cross section makes it possible to maintain a high heat transfer coefficient in a vaporizer-liquid two-phase region with a smaller evaporator volume. A highly efficient and compact evaporator can be realized.

  Although the gap s is constant in the eighth embodiment, it may be changed as in the first to seventh embodiments.

  In addition, in the present invention, the vertical arrangement of the liquid passage to be evaporated means an angle at which the heat transfer characteristics of the left and right heat transfer surfaces forming the microchannel are not greatly lost due to the inclination, for example, about vertical ± 20 degrees. The angle up to is included.

It is (a) sectional drawing explaining the structure of Example 1 of the microchannel type evaporator which concerns on this invention, (b) Evaporative liquid channel | path conceptual diagram, (c) Heating gas channel | path conceptual diagram. It is a figure explaining the limit heat flux and heat flux with respect to quality in Example 1. It is (a) sectional drawing explaining the structure of Example 2 of the microchannel type evaporator which concerns on this invention, (b) Conceptual drawing of a to-be-evaporated liquid channel | path, (c) It is a conceptual diagram of a heating gas channel | path. It is a figure explaining the limit heat flux and heat flux with respect to quality in Example 2. FIG. It is (a) sectional drawing explaining the structure of Example 3 of the microchannel evaporator which concerns on this invention, (b) Conceptual figure of a to-be-evaporated liquid channel | path, (c) It is a conceptual diagram of a heating gas channel | path. It is a figure explaining the limit heat flux and heat flux with respect to quality in Example 3. It is (a) sectional drawing explaining the structure of Example 4 of the microchannel type evaporator which concerns on this invention, (b) Evaporable liquid channel | path conceptual diagram, (c) Heating gas channel | path conceptual diagram. It is a figure explaining the limit heat flux with respect to the quality in Example 4, and a heat flux. It is (a) sectional drawing explaining the structure of Example 5 of the microchannel type evaporator which concerns on this invention, (b) Conceptual figure of a to-be-evaporated liquid channel | path, (c) It is a conceptual diagram of a heating gas channel | path. It is (a) sectional drawing explaining the structure of Example 6 of the microchannel evaporator which concerns on this invention, (b) Conceptual drawing of a to-be-evaporated liquid channel, (c) It is a conceptual diagram of a heating gas channel | path. It is (a) sectional drawing explaining the structure of Example 7 of the microchannel type evaporator which concerns on this invention, (b) Conceptual drawing of a to-be-evaporated liquid channel | path, (c) It is a conceptual diagram of a heating gas channel | path. It is a figure which shows the surface property of a heat-transfer surface, and the diameter of the isolation | separation bubble by superheat degree. (A) The figure explaining the relationship between the superheat degree and heat flux of a microchannel type evaporator, (b) The figure explaining the change of the flow and heat transfer mode in an evaporation pipe, (c) Heating heat flux and heat transfer distribution It is a figure explaining a relationship. It is a figure explaining the boiling aspect of the microchannel in a high heat flux area | region. (A) 9 [kW / m ² ], (b) 14 [kW / m ² ], (c) 19 [kW / m ² ] each of which is a photograph of the state of boiling in each heat flux. is there. (A) It is a figure which shows the heat transfer coefficient with respect to the quality of a gas-liquid two phase, (b) Critical heat flux (CHF) with respect to the quality of a gas-liquid two phase. It is (a) sectional drawing explaining the structure of Example 8 of the microchannel type evaporator which concerns on this invention, (b) Conceptual drawing of a to-be-evaporated liquid channel | path, (c) It is a conceptual diagram of a heating gas channel | path. It is a figure explaining the limit heat flux with respect to the quality in the evaporator of Example 8, and a heat flux. It is a figure which shows the relationship between the entrance conditions of a pure water based on the characteristic of FIG. 18, and a boiling area. It is a figure which shows the heating gas flow pattern (case A) in the system provided with the evaporator and the superheater. It is a figure which shows the heating gas flow pattern (case B) in the system provided with the evaporator and the superheater. It is a figure which shows the heating gas flow pattern (case C) in the system provided with the evaporator and the superheater. (A) Heating gas flow pattern of case A, (b) Heating gas flow pattern of case B, (c) Heating gas flow pattern of case C.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Evaporator 2 ... Heat-transfer plate 3 ... Evaporated liquid channel 4 ... Heated gas channel 5 ... Evaporated liquid inlet 6 ... Steam outlet 7 ... Heated gas inlet 8 ... Heated gas outlet 9 ... Partition

Claims (12)

In a microchannel evaporator where the gap dimension of the liquid passage to be evaporated is smaller than the diameter of the detached bubble,
The evaporated liquid passage is installed vertically,
The microchannel evaporator according to claim 1, wherein the gap size in the gas-liquid two-phase region of the liquid passage to be evaporated is a minimum gap size that satisfies a critical heat flux or less with respect to quality.   2. The microchannel evaporator according to claim 1, wherein a gap dimension of the liquid passage to be evaporated is gradually changed depending on a position in the evaporator.   3. The microchannel evaporator according to claim 2, wherein a gap dimension of the evaporating liquid passage is gradually changed in a flow direction of the evaporating liquid.   3. The microchannel evaporator according to claim 2, wherein the gap size of the vapor phase single phase region of the liquid passage to be evaporated is gradually reduced in the flow direction of the liquid to be evaporated. The flow of the liquid to be evaporated and the flow of the heated gas are counterflows,
4. The microchannel evaporator according to claim 3, wherein the gap dimension in the gas-liquid two-phase region of the vaporized liquid passage is gradually increased in the flow direction of the vaporized liquid. The flow of the liquid to be evaporated and the flow of the heated gas become a parallel flow,
4. The microchannel evaporator according to claim 3, wherein the channel gap in the gas-liquid two-phase region of the vaporized liquid passage is gradually reduced in the flow direction of the vaporized liquid. The flow of the fluid to be evaporated and the flow of the heated gas become a cross flow,
3. The microchannel evaporator according to claim 2, wherein the channel gap of the liquid to be evaporated is gradually changed in the flow direction of the hot gas.   8. The microchannel evaporator according to claim 7, wherein the heating gas is meandered by providing a plurality of folded portions in the heating gas passage. The flow of liquid to be evaporated and the flow of heated gas are co-current flow,
By controlling the mass flow rate and / or temperature of the heated gas using a map of the mass flow rate and temperature of the heated gas corresponding to the mass flow rate and temperature of the liquid to be evaporated,
The microchannel evaporator according to any one of claims 1 to 4, wherein a thin liquid film is formed on the heat transfer surface of the liquid to be evaporated. A microchannel evaporator according to any one of claims 1 to 4,
A superheater for further heating the steam from the microchannel evaporator to generate superheated steam,
In the microchannel evaporator, the flow of the liquid to be evaporated and the flow of the heating gas become a parallel flow,
A system using a microchannel evaporator, wherein a heating gas is supplied in parallel to the superheater and the microchannel evaporator when the mass flow rate of the heated gas is equal to or greater than a specified value. A microchannel evaporator according to any one of claims 1 to 4,
A superheater for further heating the steam from the microchannel evaporator to generate superheated steam,
In the microchannel evaporator, the flow of the liquid to be evaporated and the flow of the heating gas become a parallel flow,
A system using a microchannel evaporator, wherein the heating gas is supplied to the superheater after being supplied to the superheater when the temperature of the heating gas is higher than a specified value. A microchannel evaporator according to any one of claims 1 to 4,
A superheater for further heating the steam from the microchannel evaporator to generate superheated steam,
When the mass flow rate and temperature of the heating gas are not less than the specified value, the heating gas is supplied in parallel to the superheater and the microchannel evaporator,
A system using a microchannel evaporator, wherein the heated gas discharged from the superheater is supplied to the microchannel evaporator.