JP3347768B2 - Mixed-media plug-flow evaporator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaporator for a mixed medium when a heat cycle is constituted by using a mixed medium comprising two or more components having different boiling points.

[0002]

2. Description of the Related Art In a thermal cycle using a mixed medium as a working fluid, it is intended to increase the amount of recovered heat without changing the evaporation pressure by changing the evaporation temperature.

One example of a heat recovery apparatus using a non-azeotropic mixed medium is a binary power generation system. Referring to the binary power generation system shown in FIG. 4, the evaporator (2), the steam engine (4), the condenser (6) and the medium pump (8) are connected in series to form a closed loop (10). . The working fluid circulating in the closed loop (10) first evaporates by removing heat from the heat source fluid in the evaporator (2), and the generated steam is supplied to the steam engine (4). This steam expands in the steam engine (4) and serves to drive the generator (12). The steam discharged from the steam engine (4) is deprived of heat by the cooling water in the condenser (6) and condensed. The condensate is sent again to the evaporator (2) by the circulation pump (8).

[0004] The binary cycle is basically a Rankine cycle. When the working fluid is a single medium, as shown in FIG. 5, "-" and "-" in the TS diagram show isothermal changes, respectively. However, when a mixed medium such as a mixture of Freon R123 and R22 is used as the working fluid, the saturation temperature changes even at the same pressure, as shown in FIG. Go down. This forms a Lorentz cycle and improves system efficiency.

[0005]

In the Lorentz cycle, as shown in FIG. 6, (TH ₁ -TH ₂ ) = (Te ₁ -Te ₂ )
It is optimal to design the system so as to satisfy the following condition. In the case of a mixed medium, however, low-boiling components tend to evaporate first in the evaporator, and since vapor has a higher flow velocity than liquid, most of it evaporates and rises immediately after heating, and later evaporates. Only high-boiling components which are difficult to perform are left. In this case, there is no change in evaporation temperature as in the case of evaporation of a single medium, so that the characteristics of the mixed medium cannot be utilized.

Accordingly, an object of the present invention is to provide an evaporator capable of evaporating a mixed medium without deteriorating its characteristics.

[0007]

According to the present invention, the medium evaporating space of the evaporator is made almost vertical and the cross section is made narrow so that a plug flow is formed and liquid is entrained in the united foam. .

[0008]

By making the medium evaporation space almost vertical and narrowing its cross section, a plug flow is formed as shown in FIG. The liquid accompanies the bubble and moves in the vapor flow direction, and the moving speed of the gas and liquid is kept equal to the outlet of the evaporator (V _V =
_VL ). As a result, low-boiling components at the gas-liquid interface during movement,
An equilibrium state is created by the mass transfer of the high-boiling components, and a shift in the equilibrium state of the gas-liquid is reduced, so that a smooth evaporation temperature change is realized. It should be noted that reference symbol a in FIGS.
To d represent liquids or vapors in the state indicated by the corresponding reference numerals a to d in the vapor-liquid equilibrium diagram of FIG.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments shown in the drawings will be described below.

In the case of a plate heat exchanger, as shown in FIG. 1, a plurality of heat transfer plates (21) are vertically arranged at predetermined intervals, and a heat transfer plate (21) is provided between the heat transfer plates (21). The medium evaporation space (22) and the heating fluid passage (23) adjacent to each other via (21) are alternately formed. Medium evaporation space (22)
The distance between the opposing surfaces of the pair of heat transfer plates (21) facing each other is set to be small, preferably 2 to 10 mm.

The multi-tube evaporator supplies a heating fluid to the outside of the tube group to make the inside of each tube a medium evaporation space, and conversely supplies a heating fluid to the inside of each tube to provide an outside of the tube. As a medium evaporation space. In the case of in-tube evaporation, although not shown, the heat transfer tubes are disposed vertically, and the inner diameter of each heat transfer tube is small, preferably 2 to 10 mm. In the case of out-of-tube evaporation, as shown in FIG. 2, a number of heat transfer tubes (24) into which a heating fluid is supplied are arranged vertically or horizontally (the latter is shown in the figure), and partitions (25) are formed in the tube group. The medium evaporating space (26) extending vertically is formed. Then, the distance between the opposing surfaces of the facing partition (25) is set to be small, preferably 2 to 10 mm. The mixed medium is supplied from the liquid inlet (28) below the shell (27) and flows into each medium evaporation space (26), and the generated steam is supplied to the vapor outlet (2) above the shell (27).
9) taken out.

As shown in FIG. 3, in the case of a double tube heat exchanger in which the medium evaporation space (32) is provided between the inner and outer tubes (30, 31), the inner and outer tubes (30, 31) are connected. In addition to being arranged vertically, the outer diameter of the inner pipe (30) is made closer to the inner diameter of the outer pipe (31) to reduce the gap, preferably to 2 to 10 mm.

In each of the embodiments, the medium evaporation space (22, 2
6, 32) extend vertically, i.e. in the natural flow direction of the steam, and have a narrow cross-section, i.e., a cross section perpendicular to the flow direction of the steam, of 2 to 10 mm. Thus, a form of plug flow evaporation is created in which the liquid moves with the coalesced foam. The reason why the interval is 2 to 10 mm is that the conditions under which united bubbles are formed vary depending on the amount of steam (volume). The amount of steam is determined by the degree of wall superheat, pressure, concentration, temperature, and medium type, and the interval between the cross sections is appropriately selected according to these. Since a normal evaporator is used in the nucleate boiling region, a range of 2 to 1 mm is preferable in this range.

In a liquid-filled evaporator, if the entire medium evaporation space is filled with liquid, coalesced bubbles are unlikely to grow, and a gas-liquid mixed phase is formed. It is not constant (FIG. 7B). Therefore, as shown in FIG. 7 (a), the simulated liquid level is determined by the communication pipe (33), and the simulated liquid level is kept relatively low so that the plug flow can be easily formed.
In other words, the simulated fluid level is kept relatively low to the extent that a plug flow is formed.

[0015]

According to the present invention, since the medium evaporation space of the evaporator is made almost vertical and the cross section is made narrow, a plug flow is formed so that the liquid is entrained in the united foam. The equilibrium state is created by the mass transfer of low-boiling and high-boiling components at the gas-liquid interface during the movement, and the shift in the equilibrium state of the gas-liquid is reduced. And a smooth evaporation temperature change is realized.
Therefore, the advantage of the mixed medium that increases the amount of recovered heat without lowering the evaporation pressure can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment applied to a plate heat exchanger.

FIG. 2 is a cross-sectional view showing an embodiment applied to a multi-tube heat exchanger.

FIG. 3 is a sectional view showing an embodiment applied to a double tube heat exchanger.

FIG. 4 is a block diagram of a binary power generation system.

FIG. 5 is a TS diagram of a Rankine cycle.

FIG. 6 is a TS diagram of a Lorentz cycle.

FIG. 7 is a schematic diagram showing a comparison of evaporation modes in a medium evaporation space.

FIG. 8 is a vapor-liquid equilibrium diagram of a mixed medium in an evaporator.

[Explanation of symbols]

 22, 26, 32 Medium evaporation space

Continued on the front page (72) Inventor Kio Yamazaki 3-4-6, Hirano-cho, Chuo-ku, Osaka-shi, Osaka Inside Hisaka Works Co., Ltd. (72) Inventor Kazuo Hiroto 2-1-1 Watanabe-dori, Fukuoka City, Fukuoka Prefecture No. 82 Inside Kyushu Electric Power Co., Inc. (72) Manabu Yoshida 2-1-2, Watanabe-dori, Fukuoka City, Fukuoka Prefecture No. 82 Inside Kyushu Electric Power Co., Ltd. (72) Shinji Ega 2-1-2, Watanabe Dori, Fukuoka City, Fukuoka Prefecture No. Kyushu Electric Power Co., Inc. (56) References JP-A-3-100307 (JP, A) JP-A-1-302098 (JP, A) JP-A-59-104086 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F25B 39/02 F01K 25/10 F28F 13/06 F25D 7/00 F28D 9/00

Claims (1)

(57) [Claims] 1. A mixed-medium plug-flow evaporator characterized in that a medium evaporation space is made substantially vertical and a cross section is made narrow to form a plug flow so that liquid is entrained in a united foam. .