| The operating principle of a heat pump dryer |
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| 2025-8-26 publish |
The heat pump dryer (also known as the heat pump dryer) is a highly efficient and energy-saving drying equipment. Its operating principle is similar to that of an air conditioner or a refrigerator, but the purpose is opposite. It does not dry items by directly heating with electric heating tubes, but ingeniously "transfers" heat, thus having a very high energy efficiency.
Its core operating principle can be summarized as follows: Based on the reverse Carnot cycle, it utilizes the phase change cycle of the refrigerant (coolant) to recover the heat from the moist air and reuse it for heating, while simultaneously discharging the moisture.
Now let's elaborate on its working principle and key components step by step.
I. Four Core Components and Circulation
The heat pump dryer mainly consists of four core components to form a closed refrigerant circulation system:
Compressor: The "heart" of the system, it compresses the low-temperature and low-pressure gaseous refrigerant into high-temperature and high-pressure gaseous refrigerant.
Condenser (Condenser) : the "heater" of the system. The high-temperature and high-pressure refrigerant gas releases heat here, heating the dry air flowing through the condenser, cooling itself and condensing into a medium-temperature and high-pressure liquid.
Throttling device (Expansion Valve) : Usually a capillary tube or electronic expansion valve. It causes the medium-temperature and high-pressure liquid refrigerant to throttle and reduce pressure, instantly turning it into a low-temperature and low-pressure mist-like liquid (mixed with a small amount of gas).
Evaporator (Evaporator) : the "heat absorber" and "dehumidifier" of the system. The low-temperature and low-pressure mist-like refrigerant here absorbs the heat of the moist air flowing through the evaporator, causing the air temperature to drop sharply. The water vapor in it condenses into water droplets and is discharged (moisture is released). The refrigerant absorbs heat by itself and evaporates into a low-temperature and low-pressure gas, then returns to the compressor to complete one cycle.
Simple memory: Compressor compresses → condenser releases heat → Throttle valve reduces pressure → evaporator absorbs heat.
Ii. Air Circulation and Drying Process (Double Circulation System)
There are actually two cycles inside a heat pump dryer: the refrigerant cycle (as mentioned above) and the air cycle. The two interact to complete the drying.
Heating and drying stage (air is heated) :
The indoor air is drawn into the dryer by the fan.
Air first flows through the condenser. At this time, the condenser is releasing a large amount of heat, and the air is heated into dry hot air (the temperature rises, the absolute moisture content remains unchanged, and the relative humidity decreases).
This dry and hot air is blown into the drying chamber (such as the clothes inside the drum), taking away the moisture from the clothes and turning them into moist and hot air.
Cooling and dehumidification stage (air is dehumidified) :
The hot and humid air carrying a large amount of moisture then flows through the evaporator.
At this time, the temperature of the evaporator is extremely low. When the hot and humid air meets the cold fins of the evaporator, the temperature drops sharply below the dew point. The water vapor in the air condenses into water droplets and drips onto the water collection tray or is discharged through the drain pipe.
Meanwhile, the heat of the air itself is absorbed by the refrigerant in the evaporator, the air is cooled and its water content is greatly reduced, turning into dry cold air.
Energy recovery and recycling
This dry and cold air then flows through the condenser again, is reheated and turns back into dry and hot air.
This cycle repeats itself, forming a closed air circulation that constantly "draws" out the moisture from the clothes and dissolves it, while the majority of the heat is retained within the system, achieving efficient energy utilization.
The entire process can be understood as:
The evaporator is a "dehumidifier", responsible for converting moisture into water and discharging it away.
The condenser is the "heater", responsible for providing the heat required for drying.
The compressor provides power to drive the entire energy transfer process.
Iii. Main Advantages (Compared with Traditional Electric Heating Drying)
Ultra-high energy efficiency: Its core lies in "transporting" heat rather than "generating" it. Generally, one unit of electrical energy can transport 3 to 4 units of heat from the air, and the coefficient of performance (COP) is much higher than 1 (the COP of ordinary electric heating is about 0.95). It saves 50% to 70% energy compared with traditional electric heating drying.
Low-temperature care: The drying temperature is usually between 40℃ and 60℃, which belongs to low-temperature drying. It is more friendly to the fabric of clothes (such as wool, silk, down), and is less likely to shrink, deform or be damaged.
Safety: There is no risk of high-temperature open flames with electric heating wires, making the heating process safer.
Uniform and thorough: The gentle wind force and temperature ensure that the clothes are dried more evenly, preventing them from being dry on the outside and wet on the inside.
Summary
The heat pump dryer is like a "heat transporter". It extracts heat and moisture from the moist air, discharges the moisture, and reuses the recovered heat for drying. This cycle repeats itself, achieving an efficient and energy-saving drying effect. This is a very ingenious technology that conforms to the concept of sustainable development.
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