JP2003269820A - Drying method and cold air dryer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To defrost an evaporator in a short time of period to resume drying in view of a state where defrosting is required since the evaporator is frosted when setting a drying temperature low in the case of drying with a cold air dryer, and if it takes a long time to defrost it, drying time becomes long and drying efficiency is lowered. <P>SOLUTION: A required circuit and control equipment are added to make the evaporator usable as a condenser, and the condenser usable as the evaporator by switching a refrigerant circuit. A by-pass circuit is provided in front of the evaporator so that drying air does not pass through the evaporator in course of being operated as the condenser during defrosting operation. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dryer and a dryer, which is a so-called cold air dryer or heat pump dryer, which dries an object using a refrigerator.

[0002]

2. Description of the Related Art In this method of drying, when the drying temperature is set low, when the drying air is cooled and dehumidified by the evaporator, the fins of the evaporator are frosted and heat exchange is not performed. There is. In this case, the frost on the fins of the evaporator is melted by heating it with an electric heater or by stopping the operation of the refrigerator and applying air for drying.

[0003]

When the electric heater is used, the electric heater must be installed for that purpose, and the electric bill and maintenance cost are required. If only the air for drying is applied, defrosting will take time and the drying efficiency will deteriorate. The present invention reduces such waste, is low cost, is efficient,
It is intended to quickly defrost.

[0004]

[Means for Solving the Problem] In a drying method in which a drying air is cooled and dehumidified by using a refrigerator, and an object is dried by heating to an appropriate temperature, when a frost is formed on an evaporator, a circuit of a refrigerant is removed. Defrosting is performed by switching and using the evaporator as a condenser and the warming condenser as an evaporator. In the dryer of the type that cools and dehumidifies the drying air using a refrigerator and heats the product to an appropriate temperature to dry the product, the refrigerant discharged from the compressor
Reheat circuit that returns to the compressor through the heating condenser, drying expansion valve, and evaporator, and cooling circuit that returns to the compressor through the outdoor condenser, drying expansion valve, evaporator, evaporator, and defrost Expansion valve, defrosting circuit returning to the compressor through the heating condenser, and opening / closing means for controlling the flow of the refrigerant in each of these circuits, a sensor for operating these opening / closing means, an operating device and a check means. A dryer having

In order to further improve the defrosting efficiency, a bypass circuit for drying air that comes out from the front of the evaporator and enters between the evaporator and the condenser for heating is provided, and this detour circuit is opened during defrosting. Most of the drying air passes through this bypass circuit. A bypass circuit for the drying air that comes out from the front of the evaporator and enters between the evaporator and the condenser for heating, a damper that switches this circuit, and a device that operates this are provided.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an example of a refrigerant reheat circuit of a dryer according to the present invention, and shows a refrigerant flow during a reheat operation. The on-off valve 21 is closed and the on-off valve 22 is opened for the refrigerant compressed by the compressor 1 to become a high-temperature and high-pressure gas.
It flows to the four-way valve 3 and is guided to the heating condenser 4 by opening and closing the valve in the four-way valve. Here, heat is applied to the drying air, and the refrigerant itself is cooled and liquefied. The liquefied refrigerant is used for the check valve 5
1 flowed through the branch circuit in front of it, and the check valve 5
2 and 53 are blocked by the on-off valve 23 and enter the drying expansion valve 6. Here, the high pressure is released, the evaporator 7 takes heat from the drying air to vaporize it, and returns it to the compressor 1.

If the reheat operation is continued, the temperature of the drying air rises above the appropriate temperature for drying, so if the temperature rise exceeds the limit, the cooling operation starts. FIG. 2 shows the flow of the refrigerant in the cooling circuit. The refrigerant that has been cooled by the compressor 1 and has become a high-temperature and high-pressure gas is guided to the outdoor condenser 8 because the open / close valve 21 is open and 22 is closed, where heat is exchanged with the outdoor air. It is cooled and liquefied. The liquefied refrigerant is blocked by the check valves 52, 54 and the opening / closing valve 23, guided to the drying expansion valve 6, released from the pressure, and discharged from the drying air in the evaporator 7 in the same manner as in the reheat operation. It takes heat and vaporizes, and returns to the compressor.

At the normal drying temperature, the above two kinds of refrigerants may flow repeatedly, but when the drying temperature becomes low, the water content in the drying air is further cooled to the fins of the evaporator. It freezes. For this reason, heat exchange is not performed and cooling dehumidification of the drying air becomes impossible, so defrosting is necessary. FIG. 3 shows the flow of the refrigerant in the defrosting circuit according to the present invention. The refrigerant compressed by the compressor 1 into a high-temperature and high-pressure gas goes to the four-way valve because the on-off valve 21 is closed and 22 is open, and is guided to the evaporator 7 by opening and closing the valve in the four-way valve, and the evaporator 7 It heats and melts the frost adhering to it, and some of it also heats the drying air, cooling itself and liquefying. Then, the check valves 53, 54, and the on-off valve 24 prevent the expansion air for defrosting 9 from releasing the pressure, and the condenser 4 for heating removes heat of vaporization from the drying air and returns to the compressor. .

FIG. 4 shows the flow of the drying air in the portion related to the bypass circuit during the drying operation (reheating, cooling). Since the bypass circuit damper 10 is closed, it is shown that the entire amount of drying air passes through the evaporator to the heating condenser. FIG. 5 shows the flow of drying air in the portion related to the bypass circuit during the defrosting operation. Since the bypass circuit damper is open, it indicates that the drying air tries to pass through the bypass more than in the evaporator with high air resistance, and the amount of drying air passing through the evaporator decreases, As a result, the temperature of the evaporator rises and the defrosting speed increases.

[0010]

When an electric heater is used for defrosting, the electric heater must be attached for that purpose, which increases equipment costs, electricity costs, maintenance costs, and the like. When stopping the operation of the refrigerator and relying solely on the air from the blower, no equipment investment is required for that purpose, but the defrosting time and the drying time will be long, and the equipment efficiency will be poor.

On the other hand, according to the present invention, the frost on the fins of the evaporator is directly and efficiently and quickly melted by the heat of condensation of the refrigerant in the evaporator. The fact that a part of the melted frost evaporates at the time of frost to increase the dehumidification load is the same as the present situation, but according to the present invention, the condenser also functions as an evaporator during defrosting to perform dehumidification. Therefore, the drying efficiency is high. Further, by providing the bypass circuit, most of the drying air flows avoiding the evaporator, so that the temperature rise of the evaporator becomes faster and the defrosting time becomes shorter.

[Brief description of drawings]

FIG. 1 is a drawing showing an example of a refrigerant circuit according to the present invention and a flow of a refrigerant during reheat operation in the circuit by arrows. The thick hollow arrow indicates the flow of drying air. (same as below)

FIG. 2 is a diagram showing a flow of a refrigerant during a cooling operation in the same circuit.

FIG. 3 is a diagram showing a flow of a refrigerant during a defrosting operation in the same circuit.

FIG. 4 is a view showing a flow of drying air when a bypass circuit damper is closed during a reheat or cooling operation.

FIG. 5 is a drawing showing a flow of drying air when a bypass circuit damper is opened during a defrosting operation.

[Explanation of symbols]

1 compressor 21-24 open / close valve 3 four-way valve 4 Heating condenser 51-54 Check valve 6 Expansion valve for drying 7 evaporator 8 outdoor condenser 9 Expansion valve for defrost 10 Bypass circuit damper

Claims (4)

[Claims] 1. A method of drying, wherein a drying air is cooled and dehumidified by using a refrigerator and heated to an appropriate temperature to dry an object, and when frost is formed on the evaporator, the refrigerant circuit is switched to change the refrigerant circuit. Is used as a condenser, and a heating condenser is used as an evaporator to perform defrosting. 2. In a dryer of a type in which a drying air is cooled and dehumidified by using a refrigerator and heated to an appropriate temperature to dry an object, a refrigerant discharged from a compressor is a condenser for heating and an expansion for drying. Reheat circuit returning to the compressor via the valve and evaporator, outdoor condenser, expansion valve for drying, cooling circuit returning to the compressor via evaporator, evaporator, expansion valve for defrosting, condenser for heating A defrosting circuit that returns to the compressor via the opening and closing means for controlling the flow of the refrigerant in each of these circuits, a sensor for operating these opening and closing means, an operating device, and a check means. . 3. A bypass circuit for drying air, which comes out from the front side of the evaporator and enters between the evaporator and the heating condenser, is provided. During defrosting, the bypass circuit is opened to remove most of the drying air. The drying method according to claim 1, wherein the drying method is performed through the bypass circuit. 4. A bypass circuit for drying air which comes out from the front side of the evaporator and enters between the evaporator and the heating condenser, a damper for switching the circuit, and a device for operating the bypass circuit. The dryer according to claim 2.