Heat Pumps Classification

Naturally, heat flows from high-temperature to lower-temperature area. Natural heat transfer can be either conduction, convection, or radiation. Whereas, to be able to move heat from low-temperature to the higher, it requires special effort so as to combat natural heat transfer. To be able to do this effort required a special tool called heat pump.



Heat pump is a tool for moving heat energy from a heat source, to a destination medium termed “heat sink.” Heat pumps are designed to absorb heat energy from cold-temperature chambers, and throw them into hotter spaces. This tool will require an external power supply so it can move energy from a heat source to a heat sink.

One of the heat pumps that are familiar to us is air conditioning (AirCond). However, AirCond is only one example of heat pump applications that are used quite often we meet. In addition to air conditioning there are several other types of known heat pumps. The classification of heat pumps is based on different working principles. Here are the following:

Mechanical Refrigerator

The mechanical refrigerator or also known as a mechanical heat pump, uses the properties of a volatile and condensable special fluid. The special fluid as we know as refrigerant, is made to perform a cycle so that it can absorb heat in cold air, and throw it in hot air. Refrigerant is compressed to make it hotter in hot air areas, and refrigerant pressure is released to absorb heat in cold air environments.

The picture above is a simple cycle of the refrigerator system. A refrigerator system is composed of four main components: compressor, condenser, expansion valve (also called check valve, or metering device), and an evaporator. The refrigerator cycle begins with the inclusion of saturated vapor refrigerant-phase to the inlet of the compressor. Through the compressor, the refrigerant compressed to increase the pressure, while also make the temperature increased.

Thermodynamically, these hot and compressed refrigerants enter its superheater phase. This condition is a good time to remove the heat contained in the refrigerant to the cooling medium such as air or water. The heat dissipation from the refrigerant can occur not only because of fan, also because the superheater refrigerant temperature is hotter than the temperature of the cooling medium. This heat dissipation process occurs in the condenser.

One of the unique properties of the refrigerant is volatile, which means it has a low boiling point, as well as its high dew point. his property makes the refrigerant easy to reach the superheater phase when compressed, and immediately turns its phase to liquid after experiencing cooling process in the condenser. Thermodynamically, the liquid phase of this refrigerant is called liquid saturation phase. Furthermore, this liquid refrigerant will pass through an expansion valve so that the pressure drops suddenly. Decreasing the pressure of the refrigerant fluid will lead to change its phase adiabatically to steam again. This pressure drop will be followed by temperature decrease  so that it reaches a cooler temperature than the air to be cooled.



The cold refrigerant fluid, then enter the evaporator. A fan will circulate the hot air so it can pass through the evaporator grille. In this component there is heat transfer from hot air to cold refrigerant. This process will make the air circulation to cool, this air is needed in the refrigerator process to cool the room. While the fluid refrigerant will become hotter so that it returns to saturated vapor. To meet the refrigerator engine cycle, the saturated vapor of this refrigerant will re-enter the compressor and continue to cycle the system.

The mechanical refrigerator cooling system became the most common and most widely used. Starting from the refrigerator, air conditioning, air conditioning in the vehicle, or even if the cycle is used upside down, it can also be used to warm the room at the winter.

Magnetic Refrigerator

Magnetic refrigerator is a cooling technology use magnetocaloric effects. The magnetocaloric effect is a magneto-thermodynamic phenomenon in which a temperature change in a particular material occurs as a result of being exposed by changes in magnetic field values. Simply put, a material will rise in temperature when it is placed in higher magnetic fields. Similarly, the temperature of the material will also decrease when the magnetic field strength is lowered. But one thing to note is that these two concepts must occur in an isolated chamber so there is no absorption or heat release, an adiabatic process is a must. So that the increase or decrease of material temperature due to the magnetic field change is happening naturally.

Similar to a mechanical refrigerator, the magnetic refrigerator process also occurs cyclically. There are four cycles in the magnetic refrigerator process: adiabatic magnetization, isomagnetic enthalpies transfer, adiabatic demagnetization, and isomagnetic entropy transfer.

  1. Adiabatic Magnetization
    A magnetocaloric material, which acts as a refrigerant, is placed in an isolated chamber. Furthermore, the chamber is subjected to a magnetic field so that the atoms refrigerant material repositioned. This condition results in magnetic entropy and the material’s heat capacity being reduced. Because the system is isolated so that there is no heat transfer (adiabatic), and the total value of the entropy is not reduced, the temperature of the refrigerant material will naturally increase.
  2. Isomagnetic Enthalpy Transfer
    The second condition, with a fixed system induced by an unchanged magnetic field (isomagnetic), the heat contained by the refrigerant is cooled by the cooling fluid. The cooling fluid can be either gas or liquid. The cooling medium commonly used in this system is helium gas. The magnitude of the fixed magnetic field remains to prevent the refrigerant atoms from being re-positioned to their original position when the heat is absorbed by the cooling fluid. After the heat of the refrigerant is fully absorbed by the cooling fluid, the coolant fluid is subsequently removed from the system.
  3. Adiabatic Demagnetization
    Furthermore, the refrigerant material is re-insulated to keep no heat coming out or entering the system (adiabatic). In such conditions, the magnetic field value is lowered so that the thermal energy of the material creates a magnetic moment to overcome the change of magnetic field. This process is what makes the refrigerant temperature down. The energy transfer (and entropy) occurs from the thermal entropy to the magnetic entropy, indicating a change in the magnetic field of the system.
  4. Isomagnetic Entropy Transfer
    The next cycle process is to keep the magnetic field of the system unchanged (isomagnetic), to keep the refrigerant material unheated. Then made thermal contact between the environment or air to be cooled, with refrigerant material that is in cold conditions. Since the refrigerant temperature is cooler than the air the environment wants to cool, there is heat transfer from the hot air to the refrigerant. This process will lower the air temperature so that there is a temperature equilibrium between the two. Next, the cycle process starts at the beginning.The magnetic refrigerator technique is well suited to produce very cold environmental temperatures. Compared with conventional mechanical refrigerators, magnetic refrigerators tend to be safer, less noisy, simpler, higher cooling efficiency, and certainly environmentally friendly because they do not use harmful refrigerant materials such as CFCs in the process of mechanical refrigerators that damage ozone.

    An example of a material that has a high magnetocaloric effect and is suitable for use as a refrigerant, is gadolinium (Gd) material and its compound mixtures. The gadolinium temperature rises as it enters a certain magnetic field, and the temperature will drop too if it leaves the magnetic field. The gadolinium compounds commonly used for refrigerants include Gd5Si2Ge2, Gd5 (SixGe1-x) 4, as well as a mixture of Gd-Bi-Sb (Gadolinium-Bismuth-Antimony) composition.

Thermo-electric Refrigerator

The thermo-electric cooling system is incorporated into a solid material heat engine using the Peltier effect (also known as thermo-electric effect) to create a heat flow between two different materials. This thermo-electric effect transfers heat from one side of the material to the other, by consuming electrical energy.

Two semiconductor materials with different electron densities are used as the main components of the thermo-electric heat engine. Two materials called the n-type and p-type are arranged in parallel, but are interconnected in series in an electrical circuit. Both of them then flanked by two material heat conductor on each side. When the voltage is applied to the free end of each semiconductor, there will be DC current flow across the system, and result in a temperature difference. One side of the plate will be cooler than the surrounding area so it will absorb the heat. The heat is absorbed for the next flow to another side plate that is hotter than the surrounding room, so that heat can be discharged to the heat sink.



The thermoelectric heat has a lower thermal efficiency than mechanical refrigerator. The thermo-electric system is only capable of achieving thermal efficiency of 10-15% only. Far enough when compared with conventional mechanical coolers that can achieve efficiencies up to 40-60%. Thermo-electric refrigerator is only capable of producing a temperature differential of 70 degrees only. Materials commonly used as a thermo-electric semiconductors include bismuth telluride, lead telluride, silicon germanium, and a mixture of bismuth-antimony.

Termo-acoustic Refrigerator

The last known model of heat pump is to use sound. Slightly odd indeed, but the sound that comes out of a speaker can be used to cool the room temperature if treated with the right way and tools. Thermo-acoustic refrigerator uses sound properties to be able to compress and stretch the air. Through this principle, the compressed air will rise in temperature, while the pressure dropped air will also fall in temperature. So if a proper system is made by using this phenomenon, an inverse Brayton cycle can be made.

The main components of thermo-acoustic refrigerators include sound sources (speakers), hot and cold heat exchangers flanking a regenerator or stack (a section composed of small parallel spaces), as well as a resonator chamber. The components are arranged in a long tube room with the speakers at one end. When the stack is placed at the correct distance inside the resonator, a temperature difference will be created on both sides of the stack. If both sides of the stack are paired with heat exchangers, then heat transfer will be created.

The inverse thermodynamic cycle of Brayton from this cooling machine is:

Adiabatic compressed gas. The air will rise in pressure at the same time the temperature along with the sound frequency resonance that occurs. The temperature in this room is now higher than the temperature of the heat exchanger metal pile.

Isobaric heat transfer. The heat will move from the compressed air to the heat exchanger plate. The process of heat transfer occurs under no pressure changes.

Adiabatic expansion. Stack will expand the air so that the pressure back down. This pressure drop will simultaneously lower the air temperature so that it is lower than the plate temperature.

Isobaric heat transfer. After the air temperature drops, heat exchanger heat will move into the air without any change of pressure, so that the air temperature will return to room temperature.

References: Wikipedia: Heat Pump, Wikipedia: Magnetic Refrigeration, Wikipedia: Thermoelectric Cooling, Wikipedia: Thermoacoustic Hot Air Engine

Positive Displacement Pumps Classification

Positive displacement pump has more variation than dynamic pump. Generally it is divided into two large groups, rotary pump and reciprocating pump. Both are still divided into various types of pumps again. And here are the pumps:

  1. Positive Displacement Rotary Pump


    This rotary type moves the working fluid through a rotary mechanism by make a vacuum effect so it can suck the working fluid from the inlet side, and move it to the outlet side. If there is air trapped inside the rotary pump, it will naturally discharge the air, thereby reducing the need to vent the air trapped inside the pump manually.

    Here are all kinds of rotary pumps:

    • Internal Gear Pump

    This pump uses two gears as a working fluid driver inside the pump casing. One gear drives and the other becomes driven. The driving gear is inside the driven gear. For more details please see the following picture.

     

    Internal Gear Pump

    And here is the process whereby the working fluid is pumped by this internal gear pump.

     

    Internal Gear Pump Working Principle

    The working fluid enters through the pump inlet toward the outer gear rotated by the inner gear. The fluid moves toward the outlet side as a result of the drive from the outer gear. Furthermore the inner gear goes into the sidelines of the outer gear to push the working fluid to exit through the outlet side of the pump.

    • External Gear Pump

    Same with the internal gear pump, this external gear pump –or typically called gear pump–  also uses two gears as its main component. What distinguishes is that both gears are in parallel positions, and the driving gear is not inside the driven gear.

     

    Gear Pump
    • Screw Pump

    Screw pump was first developed by Archimedes. This why a screw pump also called Archimedes Screw Pump. Single screw rotor was used to move water from the river at lower point to the rice fields for irrigation purposes.

     

    Screw Pump

    The screw pump design has evolved into several types such as twin-rotor, triple-rotor, and 5-rotor. The differences is in the number of the screw. Here is a screw pump video with twin-rotor.

    The working principle of screw pump with multi-rotor is when working fluid entering through the inlet side of the pump, moved by the rotor screw through the sidelines of the outer side. Upon reaching the outlet side, the fluid will be pushed out of the pump.

    • Progressive Cavity Pump

    This type of pump is the development of a screw type pump. The working principle was first introduced by Rene Moineau in the 1930s. The pump consists of both helical rotor and stator, but the stator designed to have a spiral pitch distance which is 2 times larger than the pitch of the rotor. The progressive cavity pump rotor is connected to the shaft driven by an electric motor. Among the shafts with the rotor is connected by flexible coupling which when the shaft rotates, this clutch moves to follow the movement of the rotor and shaft. For more details please note the following animation.

    Progressive Cavity Pump (Source: Wikipedia)

    Spiral design of the rotor and stator form a cavity (cavities) in it, which is when the rotor cavity as if it moved toward the pump outlet. This space is the space to move the working fluid.

     

    Progressive Cavity Pump Parts

    Progressive cavity pumps can be used in various types of working fluids, from dilute fluids to high-viscosity fluids. However, this pump does not match the solid particles. For operational purposes, this pump needs to be carried out a priming process as well as discharge of air trapped (venting) in it before operating. It aims to extend the life of the pump.

    • Rotary Lobe Pump and Rotary Piston Pump

    The rotary lobe pump is similar to a gear pump, it’s just using a kind of lobe-shaped rotor. There are two lobe rotor inside the pump casing, which are both driven by a driving source and arranged by gear that is outside the body of the pump so that the rotor rotates in rhythm. The rotation of the rotor gives rise to empty space so that the fluid can enter into it and move to the outlet side. On the outlet side the two rotor lobes meet so close the existing cavity and push the working fluid out through the pump outlet.

    Rotary Lobe Pump


    Rotary piston pump is the development of a rotary lobe pump. The rotary piston pump rotors are designed in such a way that the pump cavity volume becomes wider. In addition to the pump outlet side, the pump rotor no longer “squeezes” the working fluid out as in the rotary lobe pump, but the rotary piston pump rotation shape will push the fluid out to the outlet side of the pump.

     

    Rotary Piston Pump
    • Vane Pump

    This rotary pump uses a cylinder in the rotor section, a spring-mounted cylinder base connected to the pump rotor. The rotor axis is not aligned with the pump casing axis, so that when the rotor rotates, the rotor cylinder will follow the shape of the casing and push the working fluid to the outlet.

    Vane Pump
    • Peristaltic Pump

    The last rotary type is a peristaltic pump. This type of pump uses a working principle similar to the peristaltic movement of the esophagus. This pump uses a kind of elastic hose as a working fluid conduit. The hose is pressed by the rotor with the tip of the roller to form a push motion.

     

    Peristaltic Pump (Source: Wikipedia)

    Peristaltic pumps were initially widely used in laboratories only, but along with the development of rubber technology, current peristaltic pumps can be used for “heavy” materials including solid materials.

  2. Positive Displacement Reciprocating Pump
    The reciprocating pump uses a piston that moves back and forth as its working component, and directs the working fluid flow to only one direction with the help of a check valve. This positive displacement pump has a widespread work cavity during fluid sucking, and will push it by narrowing down the working cavity. With the help of check valve to regulate fluid flow direction, there will be harmonic pumping process.

    The reciprocating pump consists of several types:

    • Piston Pump

    This pump uses a piston to suck and push the working fluid. The number of pistons depends on the manufacturer’s design that adapts to the system requirements. The less number of pistons in the pump, the flow of water out will be more unstable. To obtain a stable fluid flow can be used pressure relief valve or pump with more pistons.

     

    • Plunger Pump

    This type of pump is similar to a piston pump. What distinguishes is not using a piston, the pump that drives the fluid does not fully fill the cylinder room. For more details see the picture of the difference between the piston pump with the following plunger pump.



    • Diaphragm Pumps

    The pump is also similar to the piston pump but the pump component that performs the back and forth motion is the diaphragm connected to the crank of the drive. The diaphragm will move forward and backward to create changes in the space cavity inside the pump. With the help of check valve then the fluid flow of work can occur.

     

    Diaphragm pumps generally operate at lower pressures than piston or plunger pumps. However, because of its unique design, the diaphragm pump can continue to operate even when there is no fluid flowing in it. And automatically when the working fluid is available again, this pump can naturally primed and vented.

    • Swashplate Pump

    The last type of pump we will discuss is a swashplate pump. This pump is the development of the piston pump. Some pistons are arranged parallel to the one end connected with the upright plate, while the other end is connected to the sloping plate. As the pump shaft rotates the parallel piston-piston rotates to produce a movement back and forth. To better understand this type of pump, let’s consider the following animated video.

    What is interesting about this pump is that the fluid flow discharge can be greatly changed. This can be done by altering the angle of the slope of the plate connected to the pump pistons.

Pumps Classification

In general, pumps are classified into two major groups, the dynamic pump and positive displacement pump. These two big groups are divided into few more.

Dynamic Pump

Dynamic pump is divided into several kinds, centrifugal pumps, axial pumps, and special-effect pumps. These pumps generate high fluid velocity by converting velocity into pressure through the changes of cross-sectional fluid flow. This type of pump has lower efficiency than positive displacement pump, but has lower cost in maintenance. Dynamic pumps can also operate at high speeds and high flow discharge.

  1. Centrifugal Pump


  2. Centrifugal pump composed of an impeller with inlet channel in the middle. With this design, when the impeller rotates, fluid flows into the pump casing around the impeller as a result of centrifugal force. This casing decreases the fluid flow velocity while impeller rotation speed remains high. The fluid velocity is converted into pressure by the casing so that the fluid can reach its outlet point. Centrifugal pump has some advantages include smooth operation in pumps, uniform pressure at pump discharge, low cost, and can work at high speeds so that further applications can be connected directly with steam turbines or electric motors. The use of centrifugal pumps in the world reaches 80% because of its suitable use to cope with large amounts of fluid than positive-displacement pumps.

    Centrifugal Pump
  3. Axial Pumps
  4. Axial pump is also called propeller pump. This pump produces most of the pressure and lifting force from the propeller. These pumps are widely used in drainage and irrigation systems. Single-stage vertical axial pumps are more commonly used, but sometimes two-stage axial pumps are more economical to implement. Horizontal axial pumps are used for large fluid flow discharge with small pressure and usually involve the siphon effect in the flow.

    Axial Pump
  5. Special-Effect Pump
  6. This type of pump used in industries with certain conditions. This type of pump are jet-eductor, gas lift, hydraulic ram, and electromagnetic.

    Jet-eductor pump is using venturi effect of a convergent-diverging nozzle to convert pressure energy from moving fluid to motion energy to create a low pressure area, than can suck fluid on the suction side.

    Injector Pump

    Gas Lift Pump is a way to lift fluid inside a column by injecting a certain gas causing the drop of hydrostatic weight from the fluid so that the reservoir can lift it to the surface.

    The hydraulic ram pump is a cyclic water pump using hydropower.

    And an electromagnetic pump is a pump that drives metal fluids by using electromagnetic forces.

    Electromagnetic Pump


Positive Displacement Pump

Positive displacement pumps are devided into reciprocating and rotary pumps. The positive displacement pump works by assigning a certain force to the fixed fluid volume from the inlet side to the pump outlet point. The advantages of using this type of pump is that it can produce a larger power density, and also provides fluid displacement that is fixed/stable in every turn.

  1. Reciprocating Pumps
  2. At this type of pump, a certain amount of fluid volume enters the cylinder through the inlet valve at entry step and then pumped out under positive pressure through the valve outlet in a step forward. The fluid coming out of the reciprocating pump, pulsating and can only change when the pumping speed changes. This is because the volume of the inlet side is constant. This type of pump is widely used for pumping sediment and sludge.

    Reciprocating Pump

    Metering Pump is included in the reciprocating pump type. This pump can varied the fluid pressure discharge as needed. Metering pumps typically used to pump additives inserted into a particular fluid stream.

    Metering Pump
  3. Rotary Pump
  4. Is a pump that drives the fluid by using the principle of rotation. The vacuum is formed by the rotation of the pump and then sucks the incoming fluid. The advantage of this type is its high efficiency because it naturally removes air from its flow pipe, and reduces the user’s need to manually remove the air.

    This pump weakness is, because of its natural design, the clearence between the swivel blade and the follower blade should be as small as possible. It’s also has requirement to rotate at low and stable speed. If the pump is working at a very high speed, then the working fluid can eroded the pump blades.

    Rotary pumps can be classified into several types:

    • Gear pumps – a simple rotary pump where the fluid is pressed using two gears.
    Gear Pump
    • Screw pumps – These pumps use two threads that meet and rotate to produce the desired fluid flow.
    Screw Pump
    • Rotary Vane Pump – has the same principle as a scroll compressor, which uses a rotating cylindric rotor to produce a certain fluid pressure.
    Rotary Vane Pump

    More details about the various positive displacement pumps, you can open the following article.