Evaporator Types and Principle of Operation
Evaporator in a cooling system in which the liquid evaporates and this order is Refrigerant device that extracts heat from its environment. In other words, the evaporator is a refrigerant.
Evaporator operating principle can summarize briefly as follows. through the direct or Refrigerant tank from the condenser and direct ekspansiyonl in the system (dry type) expansion valve, capillary tube or similar pressure reducing element after expansion as the adiabatic evaporator liquid-falling in the form of vapor mixture Refrigerant the most part is liquid. Evaporator Refrigerant evaporates in the heat until, given a little more heat before giving the suction side and anger come to between 3-8 ° C superheated steam case has a lot of benefits. On top of the fluid can cause big damage to the compressor can be shown to come Refrigerant compressors. In liquid flooded type evaporator Refrigerant liquid present in case the evaporator and a liquid evaporating portion by heat – steam resolving agent (surge tank) to a compressor in the vapor state after bears passed and the liquid portion. Refrigerant liquid level control feeding the evaporator (float, magnetic, etc.) are made with a valve. Refrigerant liquid ayıştırıc liquid accumulated in the tank again sent to the evaporator and the cooling benefit. Direct or liquid must also arranged in each of running on Refrigerant evaporator pressure, condenser pressure on the side, relative to the pressure in the condenser side is much lower. Therefore, the evaporator side of low-pressure side of the system is called.
The structure of the evaporator; Refrigerant’s will provide the best and quick evaporation, cooling medium (air, water, brine, etc.) by providing a good heat transfer the heat, take in a high yield and Refrigerant the inlet and outlet pressure difference (losses) should be designed in a manner to keep to a minimum. However, the latter of which is generally contrary to the first two. That is to say, a good heat transfer and more indented and more easily wetted inner and outer surfaces of the necessary conditions for a good evaporation (capillarity more) increases the pressure loss of this situation requires that. For these reasons, wanting extensive experience and attention evaporator design also requires a way of working is often referred to trial. This work will cool factor is foremost in directing the type and location of the substance (liquid, solid, gas). Also, Refrigerant heat while shopping and in which case the volume of meat as well evaport move brings significant design changes occur. Here, pass outside of the act in a pipe coil the Refrigerant and the substance to be cooled tubes or vice versa it is said that the first of these usually dry direct ekspansiyonl evaporator, the latter is applied to the liquid carry-type evaporators.
In case of passing through the pipe when Refrigerant, the inside film coefficient of increasing the flow rate and therefore is expected an effect in the direction of increasing the heat transfer, but this will reduce the flow rate to be increased Refrigerant when pressure losses and reduce the capacity.Here, the values that both factors together into consideration and passage of the state bulundurup thermal capacity is appropriate should be determined.
Evaporator types can be divided into three main groups according to the characteristics of the application:
– The evaporators used to cool the gaseous substance (usually air)
– Substances in the case of liquid refrigerant evaporators (water, brine, antifreeze, methylene glycol, chemical fluid, etc.)
– Solids evaporators cooling (ice, ice rink, metals, etc.)
Evaporator Structure and Types
Air Cooled Evaporators
In this type of evaporator, the air heat transmission coefficient is low and to compensate for this purpose to increase the air passage surface of the fins will generally be added. It forced the fans to increase the air speed of the transition to further increase the coefficient of thermal film provided an air movement. However, the addition of wings, putting both motor-driven fan pratikman may not be possible in any application. For example, household refrigerators and commercial types of small-capacity cabinet (butcher cabinet, such as window type cabinets) or even like a small cold storage rooms in the gravity-type or natural convection air circulation evaporators he mentioned are used.Gravity type, channel tube heat transmission coefficient in the evaporator, 2-10 kcal / h. ° cm2 between changing (copper pipe – aluminum for wing manufacture) and the fin density increases or as the number of rows of tubes in the vertical direction increases heat transmission coefficient is closer to the lower value.
Algebra air circulation (forced convestio’s) evaporators can provide higher capacity with less heat transfer area and is always preferred when the application duruu have my permission. Our country erfos (airforce) such coolers unit refrigerant known as he is described and air movement mostly axial / propeller type sometimes radial / centrifugal (channel air transmission and excessive pressure loss exists) is provided with a fan. These devices are cooling, cooling coil (evaporator) are the air vent and the outer casing with hair dripping pan occur. Air fans, blowers and the absorbent can be placed so that it runs in shape.
Cooler unit name, which defines a complete cooling with fans. However, forced air circulation is more generic definition. Indeed, no fans, air conditioning is provided in an integral manner, for example by a power plant cooling coil (evaporator) is calculated again as forced air circulation are designed. Forced air movement evaporators can be divided into 3 main groups;
– Low-speed chillers (air speed 1-1.5 m / s)
– Medium fast cooler (2.5-4 m / s)
– High-speed chillers (4-10 m / s)
More air movement in the objectionable practices (flower storage, air movement such as meat cutting room 1 m / s. Still need to be under) low speed cooling should be used. Medium speed coolants and general cooling applications are the most commonly used device. High-speed cooling in the case of rapid cooling required, for example in shock tunnel and provides a convenient way of cooling in particular the rapid cooling process. The most accurate account of the evaporation temperature of the air flow of the unit cooler, “the room is heard / total” heat rate there and here by going room apparatus dew point (room apparatusdew point) psychometric diagram is provided with the detection on. This type of account is always done in air conditioning applications, but not much choice in the cooling unit is applied, because the sensible heat ratio is often to determine the real value of force. Instead, it is possible to utilize an approximate value given in the table below.
Table 3.1: Room-evap. The average room temperature, humidity levels can be kept aware
In a chilled volume, it is undoubtedly the evaporator where the surface temperature is lowest.Therefore, the room humidity is high enough level, passing through the room starts to condense moisture in havasıevaporat will fall below the dew point temperature. Even with the evaporator surface temperature is below 0 ° C, this moisture will freeze. Ileevaporasyo rt room temperature by keeping the difference below certain limits is possible to keep the relative humidity at a certain level.The table above gives the value for a mediocre room or closet.
Water Cooled Evaporators
The evaporators are typically water-cooled ice rink, the ice-making equipment, building and food industry in general cooling evaporators used in the brine cooling system.
Buildings are air handling and fan coil unit devices to be used in the production of cold water. Thanks to their high efficiency and low operating costs are preferable to other air conditioners due to the long lasting work opportunities. Three types of chillers are used. These;
– Air-cooled water chillers
– Water-cooled water chillers
– Condenserless type water chillers
Air Cooled Water Chillers
It is designed to operate in ambient conditions are industrial air conditioning and cold water producing device. The compressor crankcase heater, compression and suction valves are available with electronic motor thermistor to avoid overheating. Apart from this evaporator, the condenser, the condenser fan, the cooling circuit consists of electrical panels.
Condenserless Type Water Chillers
In cases where it is not appropriate to use other cooling chiller used independent of the condenser cooling. chiller again in the presence of the moving gas or high ambient temperatures can be used.Also important is the level of sound and instruments to be used in places occupying much of the space.
Water Cooled Water Chillers
Water cooled chillers are high capacity. These devices to operate at the same ambient conditions, generally in the machine room placed on the building. where there is significant volume of the air-cooled water chillers are preferred. In addition, the location of the high cooling capacity of the air-cooled water chillers, bulky volume, if desired water-cooled water chillers are used with smaller size.
Shell & Tube Evaporators
Shell & Tube evaporator water-cooled cold water producer groups in the water or glycol solution and the cooling of the heat pump is used for hot water production.
Shell & Tube evaporator cooling water or ethylene dipropylene UNITERM solutions (the brine) circuit element used for cooling. 1-2 compressor circuit are manufactured as well as 3 and compressor circuit Dörken standard production. From 2 kW up to 600 kW are produced as standard. Removable tube bundle that provides cleaning and maintenance. All products in the water input and output connections other than that, the thermostat connections, drain pipe and freeze control connection is available. Evaporators are subjected to a leak test pressure of 30 bar