JPS61285974A - Thawing of frozen material - Google Patents

Abstract

PURPOSE:To eliminate the factors to inhibit the heat transfer with condensation, by supplying low-temperature steam from outside of a closed vessel and removing the excess condensed water attached to the surface of frozen material by the ejecting force of steam. CONSTITUTION:Water supplied from the water tank 9 is heated with the heater 11 at a temperature above the boiling point of water under the pressure in the closed vessel 1 and ejected intermittently through the ejection nozzle 4 by operating the water-supply valve 8. Water is blasted in the form of a low- temperature steam toward the top of the frozen material 3 and condensed on the surface of the material 3. The condensed water deposited on the top of the frozen material is blown off by the ejecting force of the low-temperature steam. The condensed water can be effectively eliminated by this process.

Description

[Detailed Description of the Invention] Existing Technology> Is vacuum thawing the heat of fusion necessary to thaw a frozen object? This is a thawing method in which the latent heat of condensation of water vapor is supplied to a low-temperature surface in a vacuum.
In general, condensation heat transfer refers to the fact that when water vapor comes into contact with a surface such as a solid whose temperature is lower than its saturation temperature, it releases all of its latent heat as the state changes from the gas phase to the liquid phase. In an ideal state, it is approximately 107Kcal.
/m h'c, indicating an extremely high heat transfer coefficient. However, it is believed that this ideal condensation rarely occurs in reality. The reasons for this are: firstly, a liquid film formed by condensation or water droplets intervenes between the solid and the vapor, exerting an adiabatic effect, and secondly, if a non-condensable gas such as air is present, the liquid film Non-condensable gas accumulates near the point where the partial pressure of the vapor is relatively low.9, and all the diffusion within the gas molecules is required for the vapor to reach the liquid film.

Is vacuum thawing based on the absolute pressure inside the container? By lowering the saturation temperature of the steam mentioned above, metalwork and room temperature are intended to achieve condensation heat transfer at a temperature below that temperature, so it can be said that the two problems mentioned above are potentially present. Currently, most of the various methods proposed for vacuum thawing focus on the above two points? If you guessed it, there is a method to place the vacuum suction port between the multi-stage frozen bodies and exhaust the air, which is a non-condensable gas, efficiently. There is a method of placing the water source outside the vacuum chamber and supplying deaerated water after a certain degree of vacuum has been obtained to promote complete air exhaust (for example, Japanese Patent Publication No. 52-4614 (see publication). However, when these methods are applied to large-scale vacuum thawing equipment such as those for commercial use, the effort required to evacuate the entire system is much greater than the effort required to degas the water.
It can be said to be effective, but the smaller the scale, the smaller the effect.

However, the above method does not mention anything about water droplets that condense on the surface of a frozen object, and it can be said that there are still problems in this respect. The entire purpose is to eliminate factors that inhibit heat transfer, and in particular, to maximize the advantages of vacuum thawing by eliminating residual air and completely alleviating the insulation effect of condensed water droplets.

<Specific Embodiments> Hereinafter, specific embodiments of the present invention will be explained with reference to all drawings. FIG. 1 is a schematic diagram of a vacuum thawing system prototyped based on the present invention. 1 is an airtight container, 2 is a pedestal on which the whole frozen object can be frozen,
3 is a frozen object (an object to be thawed). Initially, only the frozen body is placed in the airtight container 1, and is evacuated via the exhaust pipe 5 by the vacuum pump 6. When the inside of the airtight container reaches a predetermined degree of vacuum, the exhaust valve 7 is closed and the airtight container is completely shielded from the outside. After that, the water supply pipe lOt from the water storage tank 9
At this time, the water supply pipe 9 completely passes through a heater 11 set at a predetermined temperature to raise the temperature of the water to a predetermined value. The water temperature at this time needs to be set higher than the boiling point of water at the pressure inside the airtight container 1, and it is necessary that the water vaporizes the moment it enters the airtight container. When the temperature is set to a predetermined temperature by the above-described procedure and the water is intermittently jetted from the injection nozzle 4 as the water supply valve 8 is opened and closed, the water turns into low-temperature steam gas and is jetted onto the top of the frozen body 3. Ru. Relatively speaking, the temperature of the surface of the frozen body is much lower than that of the low-temperature steam gas, and the low-temperature steam gas condenses on the surface of the frozen body 3. In addition, since the boiling point of water in the airtight container is relatively lower than that of low-temperature steam gas, the low-temperature steam gas instantly diffuses into the airtight container and reaches the surface of the frozen object, which is in the shadow of the frozen object when viewed from the injection nozzle 4. It also condenses evenly.

When the low-temperature steam condenses in this way, the latent heat of condensation is released and the entire frozen body is thawed, but at the same time, a large amount of condensed water adheres to the surface of the frozen body, and the rate of heat conduction to the frozen body gradually decreases. This is mainly due to the presence of condensed water between the steam and the steam, and it is essential to effectively eliminate this condensed water to improve the thawing speed. Condensed water that adheres to the sides or bottom of the frozen body falls naturally due to gravity, but water droplets that condense on the top of the frozen body are left alone. This device focuses on this point and utilizes the power of low-temperature steam gas that is intermittently ejected from the condensate water injection nozzle on the top of the frozen body to blow away the condensed water that accumulates on the top of the frozen body. are being effectively eliminated.

The process up to this point will be explained again using the pressure change curve inside the airtight container shown in FIG. 2 and the state temperature change curve inside the airtight container shown in FIG. 3.

Point a in FIG. 2 is a state in which the frozen body 3 is placed in the airtight container l and is under atmospheric pressure immediately after f-. From here vacuum pump 6
Evacuation is started, and the absolute pressure inside the airtight container 1 gradually decreases to around 1 to 5 torr, and when it reaches point b, the exhaust valve 7 is closed and the vacuum pump 6 is stopped. After that, the water supply valve 8 is opened and the hot water is introduced into the airtight container 1 through all the nozzles 4, and because the temperature of the hot water is higher than the boiling point of water at the pressure inside the container, it is rapidly vaporized.
The pressure on the yen also rises rapidly and reaches the zero point.

Thereafter, the water supply valve 8 is closed and water vapor begins to condense on the surface of the frozen body, so that the pressure inside the airtight container 1 gradually decreases again and reaches point d. The temperature changes within the airtight container during the process up to this point are as shown in a to d of FIG. That is, in the evacuation process a-b, the remaining gas in the airtight container apparently expands adiabatically, and the temperature decreases. b
= Since steam is ejected at e, the appearance increases rapidly due to the above adiabatic compression and the latent heat of the steam. In c-d, the temperature gradually decreases as steam condenses on the surface of the frozen body. In this manner, when the pressure inside the airtight container is reduced to a predetermined value again, the water supply pulp 8 is fully opened and steam is ejected again. The frozen object is thawed by repeating the above process several times, but if the water droplets on the surface of the frozen object are not removed by the steam gas mentioned above, each state value inside the container is as shown in Figures 2 and 2. Fluctuations like the one shown by the broken line in Figure 3? On the other hand, if all the water droplets on the surface of the frozen body are removed according to the present invention, the result will be as shown by the solid line in the figure, and the amount of water vapor condensed on the surface of the frozen body will be large.

<Effects of the Invention> As described above, the present invention supplies low-temperature steam from the outside of an airtight container and utilizes the full jetting power of the steam to eliminate excess condensation adhering to the surface of frozen objects during vacuum thawing. Water can be removed completely effectively, and as a result, there are more opportunities for the frozen body to thaw due to condensation heat transfer, which is the most important feature of vacuum thawing, and the overall thawing time can be shortened by a wide range. It is possible to achieve remarkable effects.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of a vacuum thawing device used in the present invention, Fig. 2 is an explanatory diagram of pressure changes in an airtight container, and Fig. 3 is an explanatory diagram of temperature changes in an airtight container. 3
: Frozen body, 4: Injection nozzle, 6: Vacuum pump, 11: Heater. Agent Patent attorney Aihiko Fukushi (and 2 others) Shiguya (p
)

Claims (1)

[Claims] 1. The frozen object is sealed in an airtight container, the air inside the container is removed to create a vacuum state, and the steam saturation temperature is kept low to increase the partial pressure of water vapor in the container, which is necessary to thaw the frozen object. In a thawing method in which heat supply is controlled so that condensation heat transfer is dominant, low-temperature steam is supplied into the airtight container, and condensed water adhering to the surface of the frozen body is removed by the jetting force of the steam. A method for thawing a frozen body.