JPS6241594A - Evaporator - Google Patents

Abstract

PURPOSE:To disturb the temperature boundary layer in the vicinity of the surface of a heat transfer pipe, to reduce the overheat degree and to increase the heat transfer performance by applying a voltage between the heat transfer pipe and a plurality of metal wire electrodes disposed at an interval without contacting the outer periphery of the heat transfer tube, thereby forming an electric field. CONSTITUTION:A plurality of metal wire electrodes 12 are disposed at the outer periphery of a heat transfer tube 11 to extend in parallel at a suitable interval without making contact with the outer periphery of the heat transfer tube 11 and further along the longitudinal direction of the heat transfer tube 11. An electrode supporter 13 is wound around the electrodes 12 in the longitudinal direction thereof. When a heating medium flows within the heat transfer tube 11 and a non-conductive medium such as Flon or the like flows on the outside of the tube, the medium outside the tube boils up by the heat from the medium on the heating side and generates air bubbles. In such a state, when a voltage is applied between the heat transfer tube 11 and the electrode 12 to form an electric field, the boiling of the medium on the tube outside is suppressed, and generated air bubbles are rapidly reduced whereby the surface temperature of the heat transfer tube 11 is lowered and approached to the temperature of the medium on the tube outside and thus the heat transfer is promoted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a technique for improving the heat transfer performance of a heat transfer tube for an evaporator, particularly a flooded evaporator.

2. Prior Art Conventional heat transfer tubes for evaporators include a smooth tube 1 as shown in FIG. 4 and a finned tube 2 as shown in FIG. A non-conductive medium flows, and this medium outside the tube boils due to heat from the heating medium side, producing bubbles.

Problems to be Solved by the Invention Conventional heat exchanger tubes for evaporators made of smooth tubes or finned tubes as described above, however, have a large degree of superheating (the difference between the heat exchanger tube surface temperature and the medium saturation temperature). , there is a problem of poor heat transfer performance.

In other words, Figure 6 is a graph showing the heat transfer performance of a smooth tube.
The horizontal axis represents the superheat degree Δt, and the vertical axis represents the heat flux (exchanged heat amount per unit area) q. Since the surface area of the finned tube is larger than that of the smooth tube, the heat transfer performance is almost the same, but the amount of heat exchanged per unit length is larger than that of the smooth tube.

However, as can be clearly seen from FIG. 6 in the case of a smooth tube, the degree of superheating Δt is required to be 10°C or more for the heat flow type S 10' kcal 7m''h, and therefore, the present invention solves this problem. This was done in order to solve the conventional problems, and the purpose is to improve the heat transfer performance of heat transfer tubes in order to improve the performance of the evaporator.

Means for Solving the Problems The present invention provides an evaporator using a medium with low conductivity, in which a plurality of metal wire electrodes are spaced apart from each other on the outer periphery of a heat transfer tube without contacting the heat transfer tube. The electrodes are arranged parallel to each other and extend in the longitudinal direction of the heat exchanger tube, and means for applying a voltage between these electrodes and the heat exchanger tube to form an electric field is arranged.

Operation In such an evaporator, therefore, by creating an electric field between the heat exchanger tube and the metal wire electrode, the temperature boundary layer near the surface of the heat exchanger tube is disturbed, thereby reducing the degree of superheating and improving the conduction. Thermal performance is increased.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings.

In FIGS. 1 and 2, 11 is a heat exchanger tube for an evaporator, 12 is an electrode made of, for example, a metal wire with an outer diameter of 1 cm or less, 13 is an electrode support that also serves as a reinforcing wire, and 14 is a high-voltage power source.

The plurality of metal wire-electrodes 12 are arranged on the outer periphery of the heat exchanger tube 11 at intervals of, for example, less than 5 mm without contacting the heat exchanger tube, and at intervals of, for example, less than the circumferential length of the heat exchange tube. Preferably, they are arranged parallel to each other at equal intervals and extending along the longitudinal direction of the heat exchanger tube. The electrode supports 13 are wound around the metal wire electrodes 12 at intervals of, for example, 50 to 100 B in the longitudinal direction of the metal wire electrodes 12, and the high voltage power source 14 connects the metal wire electrodes 12 and the heat exchanger tubes through the electrode supports 13. 11 to form an electric field by applying a voltage between them.

Next, its effect will be explained.

When no voltage is applied between the heat exchanger tube 11 and the metal wire electrode 12 and no electric field is formed, a heating medium flows inside the heat exchanger tube 11, and a non-conductive medium such as fluorocarbon flows outside the tube. As it flows, this outside-tube medium boils due to heat from the heating medium side, creating bubbles.

In this state, when a voltage is applied between the heat exchanger tube 11 and the metal wire electrode 12 to form an electric field, boiling of the medium outside the tube is suppressed, and the number of bubbles generated is rapidly reduced. As a result, the surface temperature of the heat transfer tube 11 decreases and approaches the temperature of the medium outside the tube, promoting heat transfer.

That is, due to the electric field (unequal electric field) formed between the heat exchanger tube 11 and the metal wire electrode 12, the temperature boundary layer near the surface of the heat exchanger tube is disturbed, and the layer thickness becomes thinner, which is necessary for boiling. Since a certain degree of superheating is not obtained, the generation of bubbles is suppressed, thereby promoting convective heat transfer and increasing heat transfer performance.

Effects of the Invention As detailed above, according to the present invention, an electric field is generated by applying a voltage between a heat exchanger tube and a plurality of metal wire electrodes arranged at intervals without touching the outer periphery of the heat exchanger tube. By forming a heat exchanger, it is possible to disturb the temperature boundary layer near the surface of the heat exchanger tube, reduce the degree of superheating, and increase heat transfer performance.

FIG. 3 shows an example of the effect of an electric field when experimenting on a flat plate. Heat flux q is 5000kcal/m
If we pay attention to the temperature around 2 hours, we can see that there are many boiling bubbles when the voltage is OKV, but when the voltage is applied and the voltage is 26KV just before discharge, bubbles are only seen on a small part of the surface of the heat exchanger tube. The superheat degree PΔt is 115~
As a result, since the heat transfer coefficient=q/Δt as described above, the heat transfer performance increases by 5 to 6 times.

[Brief explanation of drawings]

FIG. 1' is a partial side view showing an example of a heat exchanger tube used in the evaporator of the present invention, and FIG. Figure 3 is a graph for explaining its heat transfer performance, Figures 4 and 5 are partial side views showing two sides of a conventional heat exchanger tube for an evaporator, and Figure 6 is a graph for explaining the heat transfer performance. 3 is a graph showing the heat transfer performance of the smooth tube shown in FIG. 11... Heat exchanger tube, 12... Metal wire electrode, 13... Electrode support, 14... High voltage power supply. 411 Figure 2 Figure 31!1 Figure 4 Figure 6 m fever l7LAt(”c)

Claims (1)

[Claims] In an evaporator that uses a medium with low conductivity, a plurality of metal wire electrodes are placed on the outer periphery of the heat exchanger tube at intervals without touching the heat exchanger tube, and parallel to each other at intervals and along the longitudinal direction of the heat exchanger tube. An evaporator comprising means for applying a voltage between the electrodes and the heat transfer tube to form an electric field.