Condenser Types and Numerical Analysis

In this presentation, we delve into the fundamentals of condensers, exploring their various types and the principles governing their operation. From basic definitions to complex numerical analyses, this slide deck offers a comprehensive overview for students, engineers, and enthusiasts alike.

1. Welcome To Heating, Ventilation, Air Conditioning and Refrigeration Engineering Topic : Thermal Design of Refrigeration System Components Condenser Cooling Tower R.S . KOLHE ME (HEAT POWER) BE (MECHANICAL)

2. Thermal Design of Refrigeration System Components Compressor : Characteristic curves of reciprocating & Centrifugal compressors, sizing of reciprocating compressor Evaporator : Standards & Codes, Performance analysis of Dx evaporator, Condenser : Standards & Codes, air-cooled condenser, shell & tube condenser and evaporative condenser. Expansion Devices : Standards & Codes, Operating Characteristics, Liquid Charge in the Sensing Bulb , Hunting of Thermostatic Expansion Valve Cooling Tower : Types & design of cooling towers, cooling tower thermal performance, tower Efficiency .

3. Introduction : The condenser is an important device used in the high pressure side of a refrigeration system . Its function is to remove heat of the hot vapour refrigerant discharged from the compressor . The hot vapour refrigerant consists of the heat absorbed by the evaporator and the heat of compression added by the mechanical energy of the compressor motor. The heat from the hot vapour refrigerant in a condenser is removed first by transferring it to the walls of the condenser tubes and then from the tubes tothe condensing or cooling medium. The cooling medium may be air or water or a combination of the two.

4. Working of a Condenser

5. Factors Affecting the Condenser Capacity Material. Since the different materials have different abilities of heat transfer, therefore the size of a condenser of a given capacity can be varied by selecting the right material. It may noted that higher the ability of a material to transfer heat, the smaller will be the size of condenser Amount of contact. The condenser capacity may be varied by controlling the amount contact between the condenser surface and the condensing medium. This can be done by varying the surface area of the condenser and the rate of flow of the condensing medium over condenser surface . Temperature difference . The heat transfer capacity of a condenser greatly depends upon the temperature difference between the condensing medium and the vapour refrigerant. As temperature difference increases, the heat transfer rate increases and therefore the condenser capacity increases.

6. Heat Rejection Factor The load on the condenser per unit of refrigeration capacity is known heat rejection factor. The load on the condenser (Qc) is given by

7. Classification of Condensers According to the condensing medium used, the condensers are classified into the following three groups : 1. Air-cooled condensers, 2. Water-cooled condensers, and 3. Evaporative condensers.

8. Air-Cooled Condensers An air-cooled condenser is one in which the removal of heat is done by air. It consists steel or copper tubing through which the refrigerant flows . The size of tube usually ranges from 6 mm to 18 mm outside diameter, depending upon the size of condenser. Generally copper tubes are used because of its excellent heat transfer ability . The condensers with steel tubes are used in ammonia refrigerating systems.

9. Types of Air-Cooled Condensers Natural convection air-cooled condensers . In natural convection air-cooled condenser, the heat transfer from the condenser coils to the air is by natural convection. As the air comes in contact with the warm condenser tubes, it absorbs heat from the refrigerant and thus the temperature of air increases. The warm air, being lighter, rises up and the cold air from below rises to take away the heat from the condenser. This cycle continues in natural convection air-cooled condensers . Since the rate of heat transfer in natural convection condenser is slower, therefore they require a larger surface area as compared to forced convection condensers . The natural convection air-cooled condensers are used only in small-capacity applications such as domestic refrigerators, freezers , water coolers and room air-conditioners. Natural convection air-cooled condensers Forced convection air-cooled condensers

10. Forced convection air-cooled condensers In forced convection air-cooled condensers. the fan (either propeller or centrifugal) is used to force the air over the condenser coils to increase its heat transfer capacity. The forced convection condensers may be divided into the following two groups : (a) Base mounted air-cooled condensers, and ( b) Remote air-cooled condensers.

11. The base mounted air-cooled condensers , using propeller fans, are mounted on the same base of compressor, motor, receiver and other controls. The entire arrangement is called as condensing unit . ln small units, the compressor is belt-driven from the motor and the fan requires to force the air through the condenser is mounted on the shaft of the motor. The use of this type of compressor for indoor units is limited up to 3 kW capacity motor only. These condensing units are used on packaged refrigeration systems of 10 tonnes or less . The remote air-cooled condensers are used on systems above 10 tonnes and are available to 125 tonnes . The systems above 125 tonnes usually have two or more condensers. These condensers may be horizontal or vertical. They can be located either outside or inside the building

12. Water-Cooled Condensers A water-cooled condenser is one in which water is used as the condensing medium. They always preferred where an adequate supply of clear inexpensive water and means of water disposal available . These condensers are commonly used in commercial and industrial refrigerating units. water-cooled condensers may use either of the following two water systems : 1. Waste water system, or 2. Recirculated water system.

13. Water-cooled condenser using waste water system . Water-cooled condenser with recirculating water system.

14. Types of Water-Cooled Condensers 1. Tube-in-tube or double-tube condensers 2. Shell and coil condensers 3. Shell and tube condensers .

15. Tube-in-tube or double-tube condensers The tube-in-tube or double-tube condenser consists of a water tube inside a large refrigerant tube. In this type of condenser , the hot vapour refrigerant enters at the top of the condenser . The water absorbs the heat from the refrigerant and the condensed liquid refrigerant flows at the bottom. Since the refrigerant tubes are exposed to ambient air, therefore some of the heat is also absorbed by ambient air by natural convection . Counter flow system . Parallel flow system.

16. Shell and coil condensers . A shell and coil condenser, consists of one or more water coils enclosed in a welded steel shell. The shell and coil condenser may be either vertical or horizontal . In this type of condenser, the hot vapour refrigerant enters at the top of the shell and surrounds the water coils. As the vapour condenses , it drops to the bottom of the shell which often serves as a receiver. Most vertical type shell and coil condensers use counter-flow water system as it is more efficient than parallel-flow water system . Since the water coils are enclosed in a welded steel shell, therefore the mechanical cleaning of these coils is not possible. The coils are cleaned with chemicals. The shell and coil condensers are used for units up to 50 tonnes capacity .

17. Shell and tube condensers The shell and tube condenser consists of a cylindrical steel shell containing a number of straight water tubes. The tubes are expanded into grooves in the tube sheet holes to form a vapour tight fit. The tube sheets are welded to the shell at both the ends. The removable water boxes are bolted to the tube sheet at each end to facilitate cleaning of the condenser. The intermediate supports are provided in the shell to avoid sagging of the tubes . In this type of condenser, the hot vapour refrigerant enters at the top of the shell and condenses as it comes in contact with water tubes. The condensed liquid refrigerant drops to the bottom of the shell which often serves as a receiver.

18. Evaporative Condensers The evaporative condensers, uses both air and water as condensing mediums to condense the hot vapour refrigerant to liquid refrigerant. These condensers perform the combined functions of a water-cooled condenser and a cooling tower. In its operation, the water is pumped from the sump to a spray header and sprayed through nozzles over the condenser coils through which hot vapour refrigerant from the compressor is passing. The heat transfers from the refrigerant through the condensing tube walls and into the water. At the same time, a fan draws air from the bottom side of the condenser and discharged out at the top of the condenser

19. Cooling Tower A cooling tower is an enclosed tower like structure through which atmospheric air circulates cool large quantities of warm water by direct contact . A spray pond consists of a piping and spray nozzle arrangement suspended over an outdoor open reservoir or pond. It can also cool large quantities of warm water. The cooling towers and spray ponds, used for refrigeration and air-conditioning systems, cool the warm water pumped from the water-cooled condensers. Then the warm water can be used again and again to cool the condenser . The principle of cooling the water in cooling towers and spray ponds is similar to that of evaporative condensers, i.e. the warm water is cooled by means of evaporation.

20. Capacity of Cooling Towers and Spray Ponds The amount of evaporation of water, in turn, depends upon the following factors : 1 The amount of water surface exposed to the air 2. The length of the exposure time 3 . The velocity of air passing over the water droplets formed in cooling towers , and 4. The wet bulb temperature of the atmospheric air

21. Types of Cooling Towers The cooling towers are mainly divided, according to their method of air circulation, into the following two groups : Natural draft cooling towers, and Mechanical draft cooling towers . In natural draft cooling towers, the air circulates through the tower by natural convection whereas in Mechanical draft cooling towers the air is forced through the tower by mean fans blowers.

22. Natural Draft Cooling Towers Atmospheric natural draft (spray type ) cooling towers: The atmospheric natural draft (spray type) cooling tower, consists of a box-shaped structure with louvers. The louvers allow the atmospheric air to pass through the tower, but slant down towards the inside of the tower to retain water in it . The framework and louvers are usually made of steel. The size of the cooling tower depends upon the capacity of the unit . The atmospheric natural draft ( spray type ) cooling towers should be located in the open space or on the roof of a building where the air can blow freely through them .

23. Natural Draft Cooling Tower. In this type of cooling tower, warm water from the condenser is pumped to a spray header provided at the top of a tower. It is sprayed down into the tower through the nozzles . Since the heat transfer from water from air is dependent upon the surface of water exposed to the air stream, therefore spray nozzle having finer spray pattern is essential for good performance of the cooling tower . It may be noted that the finer spray exposes more water surface to air . However, if the spray is too fine, too much water is blown away. The water spray blown away by the air is called drift. The drift increases water loss in the tower, but does not affect the cooling action

24. Atmospheric N atural draft (splash deck type) cooling tower. The atmospheric natural draft (splash deck type ) cooling tower, is similar to a spray type cooling tower except that it contains decking ( also called fill) made. from redwood hollow tiles , ceramic, metal sheets or plastic. Many splash deck towers do not employ nozzles . The water splashes on the decking from the holes in the bottom of a water box on the top of a tower, as shown in Fig. The objective of decking is to increase the rate of heat transfer, by exposing a large amount of wetted surface to the air. The decking also helps to break up the water into small droplets and slows down the fall of water to the bottom of tower . This type of cooling tower is 20 to 30 per cent more efficient than the spray type for the same size and same quantity

25. Mechanical Draft Cooling Towers The mechanical draft cooling towers are similar to atmospheric natural draft cooling towers except that the fans are used to force the air through them. These towers may use either propeller or centrifugal fans . Advantages 1. The mechanical draft cooling towers are smaller in size than natural draft cooling tower of the same capacity, because the large volume of forced air increases the cooling capacity. 2. The cooling capacity of mechanical draft cooling towers can be controlled by the amount of forced air . 3. The mechanical draft cooling towers can be located inside the building because they do not depend upon atmospheric air. Disadvantages 1. The mechanical draft cooling towers require additional power to operate the fans. 2. The maintenance of fans, motors and controls increases the operating cost. The mechanical draft cooling towers may be either forced draft or induced draft

26. Forced Draft Cooling Towers In the forced draft cooling tower , a fan forces the air through the tower. In its operation, the warm water from the condenser is sprayed at the top of the tower through the spray nozzles . The air is forced upward through the tower by the propeller fan provided on the side near the bottom of the tower as shown in the figure . The condenser warm water is cooled by means of evaporation . The effectiveness of the cooling tower may be improved by increasing the height of the tower, area of water surface exposed to air or the velocity of air. The air velocities from 75 to 120 m/min is recommende with a flow of 90 to 120 m3 I min per tonne of refrigeration capacity

27. Forced Draft Cooling Towers

28. Induced Draft Cooling Towers In the induced draft cooling tower, the fan sucks the air through the tower . The induced draft cooling towers are similar to forced draft cooling towers except that the fans are located at the top instead of at the bottom and draw the air upward through the tower.

29. Moist air is heated from 20 o C to 65 o C by hot water whose temperature changes from 95 o C to 75 o C. Determine the true mean temperature difference if the heat exchanger is of the following type: (a) pure counterflow , (b) pure parallel flow, (c) average temperature difference

30. EXAMPLE 2: Determine the length of tubes in a two-pass 10 TR shell-and-tube R22 water cooled condenser with 52 tubes arranged in thirteen columns as shown in Figure . The heat rejection ratio is 1.2747. The condensing temperature is 45 o C. The water inlet and outlet temperatures are 30 o C and 35 o C respectively. The tube inner and outer diameters are 14.0 and 16.0 mm respectively . The average properties of the refrigerant and water are as follows:

31. References 1 ) REFRIGERATION AND AIR CONDITIONING BY R.S.KHURMI

32. Have a Good Day 40