JPS649560B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to improvements in heat exchangers.

For example, when generating electricity using geothermal heat or waste heat,
In the heat exchangers 1a to 1f shown in FIG. 1, by flowing hot water or other high-temperature fluid H into the heat transfer tube 2 and flowing a low-temperature fluid L such as Freon on the outside of the heat transfer tube, the heat between the two fluids can be reduced. The exchange is performed, and the evaporated freon and the like are used to drive a power generation turbine.

When heat exchange is performed by such counterflow of high temperature fluid H and low temperature fluid L, as shown in Fig. 2,
The temperature T _H of the high temperature fluid gradually decreases, while the temperature T _L of the low temperature fluid gradually increases and becomes constant after reaching the evaporation temperature. However, the temperature difference between the two fluids is relatively large at the point when each fluid enters the heat exchanger, but the temperature difference gradually decreases and becomes very small at an intermediate pinch point. The amount of heat exchanged is significantly reduced.

In order to solve this problem, it would be possible to increase the overall heat transfer coefficient of the heat exchanger, but this would result in a significant increase in cost. Since the pressure loss of the flowing high-temperature fluid and low-temperature fluid increases, it becomes necessary to increase the pump output for supplying these fluids, which is rather negative in terms of economic efficiency.

The present invention provides an effective means for increasing the heat exchange capacity of such a heat exchanger, and is characterized in that the heat exchange amount is significantly increased by a slight increase in the pump output. It is something.

That is, in the heat exchanger of the present invention, a high-temperature fluid and a low-temperature fluid flow in countercurrents inside and outside a heat transfer tube, and the low-temperature fluid is evaporated by heat exchange between the two fluids.
This is characterized in that a means for increasing the heat transfer coefficient is applied only to the heat transfer tube near the pinch point.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In the heat exchanger according to the present invention, as shown in FIG. The heat transfer coefficient of the heat exchanger tube only in the vicinity of the point is increased by appropriate means. Various known means can be used to increase the heat transfer coefficient, such as making the heat transfer surface rough, and the range in which the heat transfer coefficient can be increased is determined by increasing the pressure of the fluid in the heat exchanger. Losses will increase and the power of the pumps for supplying hot and cold fluids will increase, but the increase in power of these pumps will be sufficiently smaller than the increase in output of turbines etc. obtained by increasing the amount of heat exchange. Within the range.

Figure 2 shows an ordinary heat exchanger in _which the heat transfer coefficient _of heat transfer tubes has not been partially improved.
h of hot water flows, while the inlet temperature as a cold fluid.
T _H in is 25℃, outlet temperature T _L v is 84℃, flow rate W _L is
Indicates the temperature T _H and T _L of the high-temperature fluid and low-temperature fluid when 2039 t/h of Freon is flowed, and the heat transfer area dA/dQ required to exchange unit heat.
In this case, the pinch temperature ΔT _P is
The electrical output P obtained when the turbine is driven by heat-exchanged freon at 9.36℃ is 1.063×
10 ⁴ KW.

On the other hand, in FIG. 3, the heat transfer coefficient of the heat exchanger tube 2b in the heat exchanger 1a and the heat exchanger tubes in the heat exchangers 1b and 1c of FIG. Heat tube 2a and heat exchanger 1d
This shows the case where hot water and Freon are flowed under the same temperature conditions with the heat transfer coefficient at ~1f unchanged; in this case, the Freon flow rate W _L
is increased to 2216t/h, and the output obtained when driving the turbine is 1.155×10 ⁴ KW.
Therefore, an increase in output of about 900KW can be obtained compared to the case shown in Fig. 2 above.

FIG. 4 shows the output a of the heat exchangers 1a to 1f in FIG.
This shows the output b when the heat transfer coefficient is increased sequentially up to the 1f heat transfer tube, and the slope in the left half of the output b curve is steep, that is, the increase in output due to the improvement in the heat transfer coefficient is significant within that range. This shows that the partial improvement in heat transfer coefficient in the heat exchanger of the present invention is extremely effective.

As described above, according to the heat exchanger of the present invention, the amount of heat exchanged can be significantly increased with a relatively simple configuration without any particular increase in cost.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a heat exchanger for explaining the present invention, Figures 2 and 3 are characteristic diagrams of a conventional heat exchanger and the heat exchanger of the present invention, and Figure 4 is a diagram of heat exchanger tubes. It is a graph showing changes in output when changing the range in which the heat transfer coefficient is increased. 1a to 1f... Heat exchanger, 2... Heat exchanger tube.

Claims (1)

[Claims] 1. In devices that flow high-temperature fluid and low-temperature fluid in countercurrents inside and outside the heat exchanger tube, and evaporate the low-temperature fluid through heat exchange between the two fluids, means are applied to increase the heat transfer coefficient only in the heat exchanger tube near the pinch point. A heat exchanger characterized by: