JPS589096Y2 - Air temperature evaporator for low temperature liquefied gas - Google Patents

Description

[Detailed description of the invention] The present invention mainly relates to an improved structure of an air-heated evaporator that evaporates low-temperature liquefied gases such as oxygen and nitrogen by using an inexhaustible heat source, that is, the atmosphere. be.

Conventionally, in this type of air-heated evaporator, heat is passed directly from the atmosphere to the low-temperature liquefied gas or low-temperature gas (hereinafter referred to as the tube fluid) through the tube wall of the finned tube. Ice forms and grows mainly on the outer surface of the fin tube in the evaporation section (the rising section of low-temperature liquefied gas), leading to a rapid decline in performance.
Since there is a limit to long-term continuous operation, there is a drawback that a large evaporator with a rated evaporation capacity larger than the required evaporation amount must be used.

The present invention focuses on the heat transfer method, interposes a heat transfer medium between the atmosphere and the fluid inside the tube, and alleviates the temperature gradient between the atmosphere and the outer surface of the tube on the atmosphere side, thereby solving the above drawbacks and improving efficiency. The aim is to provide an air-temperature evaporator that enables long-term continuous operation.

A front view of a conventional air-heated evaporator is shown in FIG. 1, and a plan view is shown in FIG. 2.

In Figures 1 and 2, a plurality of parallel fin tubes 1 (so-called star fin tubes) each having longitudinal fins arranged in rows are connected by a bend tube 2 and then pressed to form a low-temperature liquefied gas introduction tube. The low-temperature liquefied gas entering from 3 is evaporated by the heating of the atmosphere while meandering up and down through the fin tube 1 and the bend tube 2, and is further heated and then exits from the outlet tube 4 for use.

FIG. 3 is a flowchart showing only the flow of fluid in the pipe.

In FIG. 3, arrows indicate the flow of fluid within the pipe.

FIG. 4 shows the form of heat passage between the atmosphere and the fluid in the tube in a conventional air-heated evaporator.

In Figure 4, the curve shows the temperature gradient, Ti is the fluid temperature in the pipe,
To is the atmospheric temperature outside the tube, Two is the surface temperature outside the tube, Twj
is the tube inner surface temperature, and 5 is the tube wall.

The inner and outer surface temperatures Twi and Two of the tubes depend on the heat transfer coefficient and heat transfer area determined from the physical properties of the fluid inside and outside the tube and other conditions, so naturally there is a temperature gradient when the fluid inside the tube is a low-temperature liquefied gas and a low-temperature gas. will be different.

When liquid oxygen or liquid nitrogen is inside a tube and undergoes a phase change due to the heating of the atmosphere, the temperature is extremely low, at 183°C or 196°C (atmospheric pressure), and the atmosphere outside the tube is usually 0°C to 30°C during T o. Therefore, the tube outer surface temperature T wo is sufficient to freeze moisture in the atmosphere.

Once freezing begins, the frozen area expands over time due to its insulating effect, and the thickness of the frozen layer increases, resulting in a rapid decline in the performance of the evaporator.

Depending on the atmospheric conditions, in extreme cases, most of the evaporator may become engulfed in ice and collapse.

For more details on the conventional air-temperature evaporator, please refer to
Please refer to Publication No. 1-29546.

Next, the present invention will be explained in detail according to an embodiment.

In the present invention, the heat passing method is improved in consideration of the above-mentioned drawbacks of conventional products.

A flowchart of the air-heated evaporator of the present invention is shown in FIG.

In FIG. 5, arrows indicate the flow of liquid within the tube, and the overlap between the solid line and the broken line indicates a double tube structure.

The gas heated through evaporation is supplied to the double pipe section of the evaporation section, interposed as a heat transfer medium between the low-temperature liquefied gas and the atmosphere, and heat exchanged with the low-temperature liquefied gas through the tube wall.

This heated gas, whose calorific value has been reduced by exchanging heat with the low-temperature liquefied gas, is heated again to near atmospheric temperature and exits from the outlet.

In this case, depending on the required amount of evaporation, it is of course possible to supply the gas to the evaporation section from just before the outlet pipe, or it is also possible to return a portion of the heated gas instead of returning all of it.

Furthermore, the overlap between the solid line and the broken line shown in Figure 5 is designed to be long enough for the low-temperature liquefied gas to evaporate, but in reality, some of the low-temperature liquefied gas accompanies the flow of the vaporized gas. Possibly, the double tube structure need not be limited to only the overlapping section shown in FIG. 5, ie the evaporator section.

A sectional view of the double pipe in this double pipe structure is shown in FIG.

In FIG. 6, low-temperature liquefied gas or low-temperature gas flows through the inner tube section 6, heated evaporated gas flows through the outer tube section 7, and the outside of the outer tube is the atmosphere 8.

It is important that a passage for heated evaporated gas is formed around the inner tube all around, so in principle it is necessary that the inner tube and outer tube do not come into contact with each other. .

However, it is permissible to form fins on the outer circumferential surface of the inner tube and/or the inner circumferential surface of the outer tube, and to bring the tips of the fins into contact with the circumferential surface of the mating O tube so that both tubes support each other. Therefore, it is preferable to achieve stability as a structure through this.

FIG. 7 shows the form of heat passage in this double tube structure.

In Figure 7, Tj is the fluid temperature inside the tube, To is the atmospheric temperature outside the tube,
Ts is the heat transfer medium temperature, Twlo is the outer surface temperature of the tube on the atmospheric side,
Twls is the inner surface temperature of the tube on the heat transfer medium side, Tw2s is the outer surface temperature of the tube on the heat transfer medium side, and Tw2j is the inner surface temperature of the tube on the fluid side of the tube, the outer tube wall 9, and the inner tube wall 10.

Here, by flowing the heated gas, the temperature gradient of the atmosphere-side tube outer surface temperature Tw1o is relaxed compared to the conventional method, and the temperature Tw1o becomes relatively close to the tube-outside atmospheric temperature To.

In other words, unlike conventional evaporators, the atmosphere and the fluid inside the tube do not directly exchange heat through the tube wall, but by interposing a heat transfer medium, the C8 gradient between the atmosphere outside the tube and the outside surface of the tube is alleviated. , allowing heat to pass from the atmosphere to the heat transfer medium to the fluid in the pipe, significantly preventing the formation and growth of ice.

FIG. 8 is a graph showing the relationship between the evaporation capacity Q and the continuous use time H of the conventional evaporator 11 and the evaporator 12 of the present invention, both of which have the same rated evaporation capacity.

From Fig. 8, it can be seen that the evaporation capacity of the evaporator of the present invention is smaller than that of the conventional evaporator until the short time Ho immediately after the start of operation, which depends on the double tube structure of the evaporator of the present invention, but after Ho, the conventional evaporator loses heat due to freezing. The resistance monotonically increases with the passage of time, and the evaporation capacity monotonically decreases accordingly.

- In the evaporator devised by the secondhand book, the effect of the double tube structure is extremely significant, and the evaporation capacity decreases over time with a gentle curve.

For example, in the conventional evaporator, the continuous operating time is Hl for the evaporation amount Q1, whereas in the evaporator of the present invention, H2 (>
It can be seen that there is a significant increase in Hl).

This means that when operating continuously for long periods of time, with conventional evaporators, it is necessary to use a large evaporator with a large rated evaporation capacity in anticipation of the extreme decrease in evaporation capacity due to freezing. In this evaporator, by interposing a heat transfer medium in the outer tube part of the double tube, the occurrence and growth of ice is significantly prevented. It has been shown that the purpose can be sufficiently distantly related, and it can be said to be of extremely great industrial value, as it allows for effective use of energy and various cost reductions.

[Brief explanation of drawings]

FIG. 1 is a front view of a conventional evaporator, FIG. 2 is a plan view of FIG. The figure is a flow chart of the evaporator of the present invention, Figure 6 is a cross-sectional view of a double tube, Figure 7 is a diagram of the heat passage form of the evaporator of the present invention, and Figure 8 is a conventional evaporator and an evaporator of the present invention. It is a graph showing the performance of. DESCRIPTION OF SYMBOLS 1... Fin pipe, 2... Bend pipe, 3... Inlet pipe, 4... Outlet pipe, 5... Pipe wall, 6... Inner pipe, 7...
...Outer tube, 8...Atmosphere, 9...Outer tube wall, 10...
Inner tube wall, 11... conventional evaporator, 12... evaporator of the present invention.

Claims (1)

[Scope of utility model registration request] Aluminum with rows of longitudinal fins or
A large number of extruded aluminum alloy fin tubes are arranged vertically in parallel, and the low temperature liquefied gas introduction tube is connected to the lower end of the fin tube of the low temperature liquefied gas rising section which becomes the evaporation section of the liquefied gas. The upper end of the fin tube is connected to the upper end of the fin tube in the evaporative gas descending section, and the fin tubes are connected so that the fluid passage for heating the evaporated gas meanders up and down sequentially. In the device, the fin tube in the rising section is formed of a double tube consisting of an inner tube and an outer tube, with the inner tube section serving as a passage for the low-temperature liquefied gas, and the outer tube section serving as a passageway for the heated evaporated gas. An air-heating type evaporator for low-temperature liquefied gas, characterized in that the evaporated gas is connected to the fluid passage for heating the evaporated gas so as to serve as a passage through which a portion of the evaporated gas is circulated.