JPS5835278A - Heat driven engine - Google Patents

Abstract

PURPOSE:To prolong the life of an element by setting the transformation temperature and heating/cooling temperature of the energy conversion element made of a profile memory alloy so that both heating and cooling temperature are kept equal to or more than the martensite reverse transformation temperature. CONSTITUTION:Both cooling and heating sides of an energy conversion element made of a profile memory alloy of a heat driven engine are kept at or above the martensite reverse transformation completing temperature Af, thereby only an austenite phase (host phase) d and a stress inducing martensite phase c appear along the driving cycle and a heat elastic martensite phase (a) due to cooling does not appear. Accordingly, the matching disturbance due to a unistrain change from d to (a) during a temperature drop is made small, and only transformations between d and c occur during the deformation or profile recovery process (uni-stress process) of the element, thus the matching disturbance is made small and the life of the element can be prolonged.

Description

Detailed Description of the Invention The present invention relates to a thermally driven engine using a shape memory alloy as an energy conversion element. , natural thermal energy such as geothermal heat, thermal energy of hot waste water discharged from nuclear power plants, thermal power plants, chemical plants, etc. as a heating source and water as a cooling source, low temperature difference, energy to machinery or electricity It was developed for the purpose of recovering energy.

The shape memory alloy that constitutes the driving element of this thermally driven engine has the following unique properties. Namely, ■ Shape memory effect.

■　Flat elasticity effect.

■ The martensitic transformation temperature range can be controlled.

These properties will be explained in detail. The first figure is an example of a stress-strain curve of a shape memory alloy.

(The Mf point indicates the end temperature of martensitic transformation, and the Af point indicates the end temperature of martensite reverse transformation.)
At temperatures below the Az point, the deformation stress is small, and when the stress is removed, permanent strain (ε) remains, but when heated above the Az point, it returns to its original shape. Furthermore, the above-mentioned (2) transformation pseudoelastic effect is the property that even if a deformation of several percent or more is applied at degrees above the Af point, the material returns to its original shape when the load is removed, as shown by track 1b in FIG. The above properties (1) and (2) are due to martensite transformation. The temperature at which this martensitic transformation occurs is around room temperature, and the martensitic normal transformation (transformation from the parent phase to the martensitic phase)
The hysteresis of martensitic reverse transformation (change axis from martensitic phase to parent phase) is as small as a dozen degrees Celsius. The transformation temperature can be adjusted to -100°C by adjusting the composition of the shape memory alloy.
It can be controlled within the range of ~+100°C.

A thermally driven engine takes advantage of the three properties mentioned above.

FIG. 2 shows a principle diagram of a conventional heat-driven engine.

A drive element 1 made of a shape memory alloy is passed between two pulleys 2. The difference between the shape recovery stress on the heating side C and the deformation stress on the cooling side d of the drive element 1 is a normal belt 3 (a gear may be used) that is passed between the two pulleys 2.
The two pulleys 2 rotate in the same direction.

FIG. 3 represents the drive cycle of the drive element l of the thermally driven engine of FIG. 1 The driving element is deformed at a temperature below the Mf point (cooling side) and generates a driving force by recovering its shape at a temperature above the Af point (heating side). Figure 4 shows the O drive cycle shown in Figure 3 above. This is a model of changes in the atomic structure of the drive element along the

As the drive cycle passes, the atomic structure of the element changes as shown in the figure. That is, the thermoelastic martensite structure (low temperature phase) in Figure (a) → the deformed martensite structure in Figure (b) → the stress-induced martensite structure in Figure (C) → the austenite structure (matrix) in Figure (d). phase - high temperature phase) → same figure (
The cycle of structural changes from a) thermoelastic martensitic structure (low temperature phase) to... is repeated.

(a) → (b) is deformation on the cooling side, (b) → (c) isostrain change during heating, (c) → (d) is shape recovery on the JJII side, (d) → (a) is due to the isostrain change when the temperature is lowered. In this drive cycle, problems in terms of device life include internal strain due to the movement of the twin interface due to twin deformation in the process (a) → (b), or consistency between twins due to the influence of impurities. This is the accumulation of C through the thermal cycle of disturbance and change @ strain in the process of (d) → (a). These phenomena are the cause of significantly shortening the life of the drive element. The present invention has been made in consideration of the above-mentioned conventional points, and aims to obtain a long-life engine by utilizing a phase change different from that of conventional heat-driven engines.

Embodiments of the thermally driven engine according to the present invention will be described below.

As already mentioned, in the conventional thermally driven engine, the engine was constructed by cooling the drive element to below the Mf point on the cooling side and heating it above the Af point on the heating side, but in the thermally driven engine of the present invention, the driving element is cooled to below the Mf point and heated to above the Af point on the heating side. Both the side and the heating side are set to be above the Af point. Table 1 shows the transformation points of a conventional engine element and an embodiment of a T1Ni engine element according to the present invention.

As shown in Table I, the transformation point of conventional engine elements is 20 to 50°C.
If the engine element is constructed by lowering the temperature, the engine can be constructed using the same heat source as a conventional heat source (for example, hot water at 80 to 90° C.). FIG. 5 shows T1N according to the present invention shown in Table 1.
This is an example of measuring the stress-strain curve of an i-engine element.Af
This shows that even with a slight temperature difference of more than a point, there is a sufficient shape recovery stress difference, and it is possible to obtain a driving force comparable to that of conventional thermally driven engines.

FIG. 6 shows a driving cycle of an example of a thermally driven engine according to the present invention. As shown in the figure, the only phases that appear along the drive cycle are an austenite phase (mother phase) and a stress-induced martensite phase, and there is no thermoelastic martensite phase that is generated by cooling as in conventional engines.

Therefore, compared to the conventional drive cycle, there is less disturbance in the consistency between the parent phase and martensite due to phase transformation.In other words, during the deformation or shape recovery process (equal stress process) of the drive element, there is an austenite phase, a stress-induced martensite phase, and a stress-induced martensite phase. Since there is only a change in , there is little disturbance in consistency.

In other words, the austenite phase is thermally stable, and the stress-induced martensitic phase is induced only by stress, so it is stable against stress. Furthermore, the stress-induced martensite phase only changes to the thermally stable austenite phase by stress unloading, and the consistency between the austenite phase and the stress-induced martensite phase is maintained extremely well.

In addition, during the temperature rising and cooling process in the isostrictive track, the crystals only form a stable crystal arrangement at each temperature within the stress-induced martensite phase or austenite phase, and the atoms do not change as in the case of phase transformation. There is no rearrangement, and therefore there is no accumulation of internal strain that corresponds to metamorphic strain. Therefore, the life of the drive element can be extended.

Table 2 shows the thermal conditions, element form, and performance when a thermally driven engine is constructed using engine elements with the characteristics shown in Figure 5, and shows the Ω equivalents in comparison with conventional ones. According to the results shown in the table, the performance of the conventional thermally driven engine and the thermally driven engine of the present invention when using the same amount of driving elements is that the thermally driven engine of the present invention has an output of approximately A. However, the lifespan has been significantly increased by about 14 times, and the energy recovered by the drive element has increased by about 3.5 times compared to the conventional one.

Table 2Here, the drive source of conventional heat-driven engines uses a heating source such as factory wastewater and a cooling source such as water, but these two
This heating medium is relatively easy to obtain, and in other words, it is possible to drive the engine at temperatures as low as this heating medium is easily available; this is an extremely important element for a thermally driven engine. The thermally driven engine of the present invention can be achieved by immersing the drive element in a heating source such as industrial waste water as a heat medium, while cooling (d-air cooling), ie, making an air-cooled thermally driven engine possible. Since this air-cooled heat-driven engine requires cold water, the water flow path is also important, and the engine can be manufactured at low cost.) As explained above,
The thermally driven engine of the present invention, in which the driving element is operated only in the high temperature phase, has significant effects such as extending the life of the driving element, air cooling the thermally driving engine and thereby simplifying the entire device, and expanding the operating conditions of the engine. Demonstrate.

[Brief explanation of drawings]

Figure 1 is the six force-strain curve of the shape memory alloy, Figure 2 is a diagram of the principle of a thermally driven engine, Figure 3 is an illustration of the drive cycle of a thermally driven engine, and Figure 4 is an explanation of the atomic structure of the drive element. figure,
FIG. 5 shows a stress-strain curve of a shape memory alloy element according to the present invention, and FIG. 6 shows an explanatory diagram of a thermal engine engine engine according to the present invention. In the figure, 1: drive element; 2: Pulley, 3: Regular belt. Agent Patent Attorney Aihiko Fuku-m-◆ Ei (%J (c)
(d) Figure 4 0 Figure 5 Figure 6

Claims (1)

[Claims] 1. In a heat-driven engine using a shape memory alloy as an energy conversion element, the transformation point and heating/cooling temperature of the element are set so that both the heating and cooling temperatures are equal to or higher than the martensitic reverse transformation point. A thermally driven engine characterized by: 2. The heat-driven engine according to item 1, characterized in that the heating source is hot water and the cooling source is air. 3. The thermally driven engine according to item 1, wherein at least a portion of the drive cycle includes a portion where the elastic coefficient changes due to temperature change in the austenite phase region.