Heat pump is a simple system which is configured by compressor, expansion valve and heat exchanger. Among the configuration, compressor is heart of heat pump and performance of the compressor affect performance of the heat pump. There are a lot of kinds of compressor and they are selected corresponding to their capacity, temperature and used purpose.
For KENKI DRYER which is a heat pump type self-heat recuperation dryer, selection of compressor is the most important for building a system.

compressor heat pump sludge dryer  KENKI DRYER 10/07/2020


A device which suck gases in, increase pressure of the gases and discharge from outlet is called ventilator or compressor. They are classified into ventilator/fan and compressor based on their maximum pressure of discharged air, and blower is included in compressor recently although it is midway between ventilator and fan.

Ventilator/FanMaximum discharge pressure is less than 111.4kPa when suction pressure is the same as atmospheric pressure.

Maximum discharge pressure is 111.4kPa or more and less than 202.6kPa when suction pressure is the same as atmospheric pressure.

Maximum discharge pressure is 202.6kPa or more when suction pressure is the same as atmospheric pressure.

Reference Site: Wiki Compressor

Classification of compressor


Turbo typeCentrifugal type
Axial type
Positive displacementRoots type




Turbo typeCentrifugal type 
Axial type 
容積式 Reciprocating typePiston type
Diaphragm type
Rotary typeScrew type
Scroll type



Expansion valve


Expansion valve of heat pump decreases gas pressure by adiabatic expansion and lowers gas temperature by evaporation. Evaporation starts at expansion valve and it is done further by heat exchanger at heat transfer process which is a next process. Compressing process, which is a next process of heat exchange, can be done smoothly when the vaporization is done thoroughly during the processes between expansion valve and heat exchanger.
Expansion valve lowers gas temperature by absorbing surrounding heat while it changes state of liquid contained in gas into gas state by decreasing gas pressure with adiabatic expansion. By transferring this heat at heat exchanger used in next process, the state transition is done further. Heat at this step is called heat of evaporation or heat of vaporization and adiabatic compression which is next process can be smoothly done at compressor by utilizing these heats sufficiently.
Configuration of this expansion valve is simple and temperature is lowered by narrowing paths where gas goes through and decreasing pressure. At expansion valve, narrowness of valve needs to be adjusted to make heat transfer done enough at heat exchanger in the next process. However, pressure and amount of gas fed into expansion valve is not always constant and expansion valve needs to be adjusted each time according to the fluctuation. This adjustment can be done automatically with no manual operation, and there are many automatic expansion valve can be seen in market and are in use already.

expansion valve heat pump sludge dryer Kenki dryer 10/07/2020


Heat exchanger


Heat pump is a system which generates heat by changing state of gas without additional heat supplied from outside and uses the heat with heat transfer. Heat generated by compression or expansion of gases can be utilized by being transferred at heat exchanger. For example, air conditioner lowers temperature by expanding gas and decreasing its pressure, then generates cool air by transferring heat at heat exchanger. Also, it rises temperature by compressing gas and increasing its pressure, then generates worm air by transferring heat at heat exchanger.
Heat exchanger in heat pump is a device which utilize heat generated by expansion and compression by transferring it. Expansion and compressing process can be done smoothly when heat generated in heat pump is used efficiently by heat transfer at heat exchanger.
At heat pump process, gases which is evaporated at expansion valve is evaporated more thoroughly by heat transfer at heat exchanger. By evaporating gas as much as possible with the heat transfer at heat exchanger, condensation and liquefaction at compressors which is a next process can be done smoothly. On the other hand, gases condensed and liquefied at compressor is compressed and liquefied more in heat transfer with heat exchanger. Evaporation of gas at expansion valve can be done smoothly as next process when gas is condensed and liquefied thoroughly.
These processes are repeated at heat pump and the heat generated by state change of gas can be utilized without being supplied heat from outside. Compared with conventional heat utilization with fossil fuel such as oils, it is a system which has better heat efficiency, can save energy and emit very small amount of CO2 , therefore, it is a system whose environment load is extremely small.


heat pump heat exchanger heat pump sludge dryer KENKI DRYER 10/07/2020



Heat pump dryers