1. Field of the Invention
The present invention relates to heat-accumulating microcapsule dispersion, and more particularly to a microcapsule dispersion including, in a stably dispersed state in heat transfer fluid medium, a number of heat-accumulating microcapsules each having a microcapsule shell accommodating therein organic compound functioning a heat accumulating material in association with a phase change thereof. The heat-accumulating microcapsule dispersion may be used as heat transfer medium employed in e.g. an air-conditioning system such as a local area air-heating system or an indoor air-cooling system.
2. Description of the Related Art
There is known heat-accumulating microcapsule dispersion of the above-noted type including, in a stably dispersed state in water, a number of heat-accumulating microcapsules made of e.g. melamine resin having microcapsule shell accommodating therein heat-accumulating material such as tetradecane, paraffin wax or the like.
For manufacturing such heat-accumulating microcapsule dispersion as above, the heat-accumulating material and prepolymer of melamine resin are polymerized with each other while being dispersed and emulsified in water. As a result, there is obtained the dispersion in which heat-accumulating microcapsules each having a core formed mainly of the heat-accumulating material covered with a capsule outer layer microcapsule shell of the resin coating are dispersed in a stable manner in the water.
The heat-accumulating microcapsule dispersion of the above-noted type has a greater viscosity than e.g. water alone, because the dispersion includes the microcapsules dispersed therein. And, this viscosity tends to increase with use of the dispersion.
On the other hand, as for the heat-accumulating capacity, the dispersion has a higher capacity than the heat transfer fluid medium alone. Then, in order to obtain a certain fixed amount of heat transfer capacity, this is possible simply by circulating a smaller amount of dispersion in a circulating passage provided between a heat receiving end and a heat supplying end. That is, even if the diameter of the pipe constituting this passage is reduced, the same amount of heat transfer capacity may be obtained.
As shown in FIG. 2, the heat-accumulating microcapsule dispersion described above is responsible for transferring heat between a heat-receiving end heat exchanger and a heat-supplying end heat exchanger. Then, in order to allow the heat exchange to take place efficiently, one will encounter the problem of the heat transfer performance between the dispersion and the inner wall of the passage constituting the heat exchanging passage in which the dispersion runs.
In general, the heat transfer rate under such environment as above is a function of the Reynolds number which represents flow conditions of fluids. A smaller Reynolds number results in lower heat transfer rate.
The above will be described more specifically with reference to FIG. 6. In this FIG. 6, the horizontal axis represents the Reynolds number: Re of the dispersion flow, while the vertical axis represents the heat transfer rate: hi between the passage wall and the dispersion. An alternate long and short dashed line indicates the relationship between the Reynolds number: Re of water conventionally employed and the heat transfer rate: hi. A white round dot chain line indicates the relationship for the conventional dispersion including the conventional heat-accumulating microcapsules (the microcapsule has a volume average particle diameter smaller than 5 .mu.m and exhibits a particle distribution pattern as depicted in FIG. 4) dispersed in water.
Referring further to the same figure, the mark: Reynolds (near 10000), denotes a typical Reynolds number obtained with a system operation using water alone as the operational medium. The further mark: Renew (near 1250), denotes a typical Reynolds number obtained with a system operation using dispersion including microcapsules dispersed therein in a stable manner.
As may be understood from this FIG. 6, in the case of the use of water alone or the conventional microcapsule, the heat transfer rate decreases with decrease in the Reynolds number. The heat transfer rate: hiold, of the case using water alone at Reold, is significantly higher than the heat transfer ratio: hinew of the case using the conventional microcapsule dispersed at Renew. In this respect, there is room for improvement.
That is to say, in case the heat-accumulating capsule is used as being stably dispersed in the heat transfer fluid medium in order to secure a certain heat transfer amount, it is desired to increase the heat transfer rate between this dispersion and the wall of the heat exchanging passage through which the dispersion is caused to flow.
Accordingly, in view of the above-described drawbacks of the conventional art, a primary object of the present invention is to obtain heat-accumulating microcapsule dispersion which can provide a higher heat transfer rate between this dispersion and the member constituting the passage through which the dispersion is caused to flow.