[Mechanical Equipment Technology Edition] Daily Question 20171212: Refrigeration Equipment (Evaporator)
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This post was last edited by YORK Industrial Refrigeration on 2017-12-15 at 08:43. Starting from now, in order to enhance communication among users, a 【Daily Question】 activity has been launched on the Mechanical Equipment Technology forum. We hope everyone will participate actively to progress and improve together! ! ! Rewards: 3 points for active participation, 10-15 points for correct answers. This question is valid for two days; no scoring will be given after that period. Industrial refrigeration evaporators generally use shell-and-tube designs, but these shell-and-tube types come in three configurations: full-liquid type, falling-film type, and dry type. Please explain each of these three types of evaporators. Answer: Dry evaporator. In a dry evaporator, the refrigerant flows through the heat exchange tubes, while cold water flows outside these tubes. The heat exchange efficiency of such evaporators is relatively low; their heat transfer coefficient is only about twice that of tubes with no fins. However, their advantage lies in the ease of oil return and simpler control, and the amount of refrigerant required is approximately 1/2 to 1/3 of that needed in flooded-type units. Full-liquid evaporator: The operation mode of a full-liquid evaporator is exactly the opposite of that of a dry evaporator. Cold water flows through the heat exchange tubes, while the refrigerant completely submerges these tubes; after absorbing heat, it evaporates outside the heat exchange tubes. The heat transfer tubes of a full-liquid evaporator are covered with numerous pin-shaped pores, and the inner surface of the tubes features spiral protrusions to enhance heat exchange on the cold water side. This efficient heat transfer tube, which simultaneously enhances external boiling and internal heat transfer, increases its heat transfer coefficient by about 5 times compared to a plain tube. Falling film evaporator The falling film evaporator, also known as the spray evaporator, is a type of heat exchanger that is similar to the full-liquid phase evaporator, but it differs from it as well. In this type of evaporator, the refrigerant is sprayed from the upper part of the heat exchanger onto the heat exchange tubes; it forms only a thin layer of liquid refrigerant on these tubes. As a result, when the refrigerant boils and evaporates, the static head pressure is reduced, thereby improving the heat exchange efficiency. This efficiency is about 5% higher than that of units with fully filled tubes. Film evaporation is a type of flow boiling; due to the thin liquid film layer on the outer surface of the tube, there is no boiling point elevation caused by static pressure, resulting in a high heat transfer coefficient. In contrast, the bubbles generated by full-liquid evaporation (i.e., immersion evaporation) tend to accumulate on the surface of the heat exchange tubes, resulting in a decrease in heat exchange efficiency; its performance is inferior to that of falling-film evaporation. Generally speaking, falling film evaporation operates under low temperature differences, but scaling must be prevented to avoid affecting heat transfer efficiency. ================================ High-quality promotions: Mechanical equipment---Maintenance procedures for York screw compressors https://bbs.hcbbs.com/thread-1806833-1-1.html Mechanical equipment---Upgrading of York Quinton control centers https://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment---Major repairs for GEA Grauso screw compressors https://bbs.hcbbs.com/thread-1800467-1-1.html Mechanical equipment---Disassembly and maintenance of British HOWDEN screw compressors https://bbs.hcbbs.com/thread-1832529-1-1.html Mechanical equipment---Disassembly and maintenance of Japanese Maekawa MYCOM screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=
In full-fluid evaporators and falling-film evaporators, the refrigerant flows through the shell side, while the heat carrier flows through the tube side； In a dry-type evaporator, the refrigerant flows through the tube side, while the heat carrier flows through the shell side ； In a full-liquid evaporator, the liquid is introduced at the bottom of the heat exchanger, while in a falling-film evaporator, the liquid is sprayed downward from the upper part of the heat exchanger. The liquid filling volume is less in the dry type compared to the falling film type ； Film-type is less than full-liquid type ； The heat transfer efficiency is lower in dry-type systems compared to full-liquid-type systems, and it is further lower in full-liquid-type systems compared to falling-film type systems.
In a dry-type evaporator, the refrigerant flows through the heat exchange tubes, while cold water circulates outside these tubes. Such heat exchangers have a relatively low heat exchange efficiency; their heat transfer coefficient is only about twice that of tubes without fins. However, their advantage lies in the ease of oil return and simpler control, and the amount of refrigerant required is approximately 1/2 to 1/3 of that needed in a full-liquid-type unit. The falling film evaporator, also known as the spray evaporator, is a type of heat exchanger that is similar to the full-liquid evaporator, but it differs from it as well. In this type of evaporator, the refrigerant is sprayed from the upper part of the heat exchanger onto the heat exchange tubes; it forms only a thin layer of liquid refrigerant on these tubes. As a result, when the refrigerant boils and evaporates, the static head pressure is reduced, thereby improving the heat exchange efficiency. This efficiency is about 5% higher than that of units with fully filled tubes. The operation mode of a full-fluid evaporator is exactly the opposite of that of a dry evaporator: cold water flows through the heat exchange tubes, while the refrigerant completely submerges these tubes; after absorbing heat, it evaporates outside the heat exchange tubes. The heat transfer tubes of a full-liquid evaporator are covered with numerous pin-shaped pores, and the inner surface of the tubes features spiral protrusions to enhance heat exchange on the cold water side. This efficient heat transfer tube, which simultaneously enhances external boiling and internal heat transfer, increases its heat transfer coefficient by about 5 times compared to a plain tube.
Dry evaporator: In a dry evaporator, the refrigerant flows through the heat exchange tubes, while cold water circulates outside these tubes. The heat exchange efficiency of such evaporators is relatively low; their heat transfer coefficient is only about twice that of tubes without fins. However, their advantage lies in the ease of oil return and simpler control mechanisms. Additionally, the amount of refrigerant required is approximately 1/2 to 1/3 of that needed in flooded-type units. Full-liquid evaporator: The operation mode of a full-liquid evaporator is exactly the opposite of that of a dry evaporator. Cold water flows through the heat exchange tubes, while the refrigerant completely submerges these tubes; after absorbing heat, it evaporates outside the heat exchange tubes. The heat transfer tubes of a full-liquid evaporator are covered with numerous pin-shaped pores, and the inner surface of the tubes features spiral protrusions to enhance heat exchange on the cold water side. This efficient heat transfer tube, which simultaneously enhances external boiling and internal heat transfer, increases its heat transfer coefficient by about 5 times compared to a plain tube. Falling film evaporator The falling film evaporator, also known as the spray evaporator, is a type of heat exchanger that is similar to the full-liquid phase evaporator, but it differs from it as well. In this type of evaporator, the refrigerant is sprayed from the upper part of the heat exchanger onto the heat exchange tubes; it forms only a thin layer of liquid refrigerant on these tubes. As a result, when the refrigerant boils and evaporates, the static head pressure is reduced, thereby improving the heat exchange efficiency. This efficiency is about 5% higher than that of units with fully filled tubes.
Dry evaporator: In a dry evaporator, the refrigerant flows through the heat exchange tubes, while cold water flows outside these tubes. The heat exchange efficiency of such evaporators is relatively low; their heat transfer coefficient is only about twice that of tubes without any special design. However, its advantage is easy oil return and simple control. The amount of refrigerant charged is approximately 1/2 to 1/3 of that in a fully liquid-filled unit. Full-liquid evaporator: The operation mode of a full-liquid evaporator is exactly the opposite of that of a dry evaporator. Cold water flows through the heat exchange tubes, while the refrigerant completely submerges them; after absorbing heat, it evaporates outside the heat exchange tubes. The heat transfer tubes of a full-liquid evaporator are covered with numerous pin-shaped pores, and the inner surface of the tubes features spiral protrusions to enhance heat exchange on the cold water side. This efficient heat transfer tube, which simultaneously enhances external boiling and internal heat transfer, increases its heat transfer coefficient by about 5 times compared to a plain tube. Falling film evaporator: The falling film evaporator is also known as a spray evaporator. Its refrigerant is sprayed from the upper part of the heat exchanger onto the heat exchange tubes, where it forms a thin layer of cooling fluid on those tubes. In this way, when the refrigerant boils and evaporates, the pressure at the static liquid level is reduced, thereby improving the heat transfer efficiency; this efficiency is about 5 times higher than that of units with a fully filled liquid level.
In a dry-type evaporator, the refrigerant flows through the heat exchange tubes, while cold water circulates outside these tubes. Such heat exchangers have a relatively low heat exchange efficiency; their heat transfer coefficient is only about twice that of tubes without fins. However, their advantage lies in the ease of oil return and simpler control, and the amount of refrigerant required is approximately 1/2 to 1/3 of that needed in a full-liquid-type unit. The operation mode of a full-fluid evaporator is exactly the opposite of that of a dry evaporator: cold water flows through the heat exchange tubes, while the refrigerant completely submerges these tubes; after absorbing heat, it evaporates outside the heat exchange tubes. The heat transfer tubes of a full-liquid evaporator are covered with numerous pin-shaped pores, and the inner surface of the tubes features spiral protrusions to enhance heat exchange on the cold water side. This efficient heat transfer tube, which simultaneously enhances external boiling and internal heat transfer, increases its heat transfer coefficient by about 5 times compared to a plain tube. The falling film evaporator, also known as the spray evaporator, is a type of heat exchanger that is similar to the full-liquid evaporator, but it differs from it as well. In this type of evaporator, the refrigerant is sprayed from the upper part of the heat exchanger onto the heat exchange tubes; it forms only a thin layer of liquid refrigerant on these tubes. As a result, when the refrigerant boils and evaporates, the static head pressure is reduced, thereby improving the heat exchange efficiency. This efficiency is about 5% higher than that of units with fully filled tubes.
Dry evaporators: In dry evaporators, the refrigerant flows through the heat exchange tubes, while cold water flows outside these tubes. The heat exchange efficiency of such evaporators is relatively low; their heat transfer coefficient is only about twice that of tubes with no fins. However, their advantage lies in the ease of oil return and simpler control. Additionally, the amount of refrigerant required is approximately 1/2 to 1/3 of that needed in flooded-type units. Full-liquid evaporator: The operation principle of a full-liquid evaporator is the opposite of that of a dry evaporator. Cold water flows through the heat exchange tubes, while the refrigerant completely submerges these tubes; after absorbing heat, it evaporates outside the heat exchange tubes. The heat transfer tubes of a full-liquid evaporator are covered with numerous pin-shaped pores, and the inner surface of the tubes features spiral protrusions to enhance heat exchange on the cold water side. This efficient heat transfer tube, which simultaneously enhances external boiling and internal heat transfer, increases its heat transfer coefficient by about 5 times compared to a plain tube. Film-type evaporator: The film-type evaporator, also known as a spray-type evaporator, is a type of heat exchanger that is similar to the full-liquid-phase evaporator, but it differs from it as well. In this type of evaporator, the refrigerant is sprayed from the upper part of the heat exchanger onto the heat exchange tubes; it forms only a thin layer of liquid refrigerant on these tubes. As a result, when the refrigerant boils and evaporates, the static head pressure is reduced, thereby improving the heat exchange efficiency. This efficiency is about 5% higher than that of units with fully filled tubes.
Dry evaporator: In a dry evaporator, the refrigerant flows through the heat exchange tubes, while cold water circulates outside these tubes. The heat exchange efficiency of such evaporators is relatively low; their heat transfer coefficient is only about twice that of tubes without fins. However, their advantage lies in the ease of oil return and simpler control mechanisms. Additionally, the amount of refrigerant required is approximately 1/2 to 1/3 of that needed in flooded-type units. Full-liquid evaporator: The operation mode of a full-liquid evaporator is exactly the opposite of that of a dry evaporator. Cold water flows through the heat exchange tubes, while the refrigerant completely submerges these tubes; after absorbing heat, it evaporates outside the heat exchange tubes. The heat transfer tubes of a full-liquid evaporator are covered with numerous pin-shaped pores, and the inner surface of the tubes features spiral protrusions to enhance heat exchange on the cold water side. This efficient heat transfer tube, which simultaneously enhances external boiling and internal heat transfer, increases its heat transfer coefficient by about 5 times compared to a plain tube. Falling film evaporator The falling film evaporator, also known as the spray evaporator, is a type of heat exchanger that is similar to the full-liquid phase evaporator, but it differs from it as well. In this type of evaporator, the refrigerant is sprayed from the upper part of the heat exchanger onto the heat exchange tubes; it forms only a thin layer of liquid refrigerant on these tubes. As a result, when the refrigerant boils and evaporates, the static head pressure is reduced, thereby improving the heat exchange efficiency. This efficiency is about 5% higher than that of units with fully filled tubes. Film evaporation is a type of flow boiling; due to the thin liquid film layer on the outer surface of the tube, there is no boiling point elevation caused by static pressure, resulting in a high heat transfer coefficient. In contrast, the bubbles generated by full-liquid evaporation (i.e., immersion evaporation) tend to accumulate on the surface of the heat exchange tubes, resulting in a decrease in heat exchange efficiency; its performance is inferior to that of falling-film evaporation. Generally speaking, falling film evaporation operates under low temperature differences, but scaling must be prevented to avoid affecting heat transfer efficiency.
The operation mode of a full-fluid evaporator is exactly the opposite of that of a dry evaporator: cold water flows through the heat exchange tubes, while the refrigerant completely submerges these tubes; after absorbing heat, it evaporates outside the heat exchange tubes. The heat transfer tubes of a full-liquid evaporator are covered with numerous pin-shaped pores, and the inner surface of the tubes features spiral protrusions to enhance heat exchange on the cold water side. This efficient heat transfer tube, which simultaneously enhances external boiling and internal heat transfer, increases its heat transfer coefficient by about 5 times compared to a plain tube. The falling film evaporator, also known as the spray evaporator, is a type of heat exchanger that is similar to the full-liquid evaporator, but it differs from it as well. In this type of evaporator, the refrigerant is sprayed from the upper part of the heat exchanger onto the heat exchange tubes; it forms only a thin layer of liquid refrigerant on these tubes. As a result, when the refrigerant boils and evaporates, the static head pressure is reduced, thereby improving the heat exchange efficiency. This efficiency is about 5% higher than that of units with fully filled tubes. Film evaporation is a type of flow boiling; due to the thin liquid film layer on the outer surface of the tube, there is no boiling point elevation caused by static pressure, resulting in a high heat transfer coefficient. In contrast, the bubbles generated by full-liquid evaporation (i.e., immersion evaporation) tend to accumulate on the surface of the heat exchange tubes, resulting in a decrease in heat exchange efficiency; its performance is inferior to that of falling-film evaporation. Generally speaking, falling film evaporation operates under low temperature differences, but scaling must be prevented to avoid affecting heat transfer efficiency. In a dry-type evaporator, the refrigerant flows through the heat exchange tubes, while cold water circulates outside these tubes. Such heat exchangers have a relatively low heat exchange efficiency; their heat transfer coefficient is only about twice that of tubes without fins. However, their advantage lies in the ease of oil return and simpler control, and the amount of refrigerant required is approximately 1/2 to 1/3 of that needed in a full-liquid-type unit. Film evaporation is a type of flow boiling; due to the thin liquid film layer on the outer surface of the tube, there is no boiling point elevation caused by static pressure, resulting in a high heat transfer coefficient. In contrast, the bubbles generated by full-liquid evaporation (i.e., immersion evaporation) tend to accumulate on the surface of the heat exchange tubes, resulting in a decrease in heat exchange efficiency; its performance is inferior to that of falling-film evaporation. Generally speaking, falling film evaporation operates under low temperature differences, but scaling must be prevented to avoid affecting heat transfer efficiency.
The operation mode of a full-fluid evaporator is exactly the opposite of that of a dry evaporator: cold water flows through the heat exchange tubes, while the refrigerant completely submerges these tubes; after absorbing heat, it evaporates outside the heat exchange tubes. The heat transfer tubes of a full-liquid evaporator are covered with numerous pin-shaped pores, and the inner surface of the tubes features spiral protrusions to enhance heat exchange on the cold water side. This efficient heat transfer tube, which simultaneously enhances external boiling and internal heat transfer, increases its heat transfer coefficient by about 5 times compared to a plain tube. The falling film evaporator, also known as the spray evaporator, is a type of heat exchanger that is similar to the full-liquid evaporator, but it differs from it as well. In this type of evaporator, the refrigerant is sprayed from the upper part of the heat exchanger onto the heat exchange tubes; it forms only a thin layer of liquid refrigerant on these tubes. As a result, when the refrigerant boils and evaporates, the static head pressure is reduced, thereby improving the heat exchange efficiency. This efficiency is about 5% higher than that of units with fully filled tubes. Film evaporation is a type of flow boiling; due to the thin liquid film layer on the outer surface of the tube, there is no boiling point elevation caused by static pressure, resulting in a high heat transfer coefficient. In contrast, the bubbles generated by full-liquid evaporation (i.e., immersion evaporation) tend to accumulate on the surface of the heat exchange tubes, resulting in a decrease in heat exchange efficiency; its performance is inferior to that of falling-film evaporation. Generally speaking, falling film evaporation operates under low temperature differences, but scaling must be prevented to avoid affecting heat transfer efficiency. In a dry-type evaporator, the refrigerant flows through the heat exchange tubes, while cold water circulates outside these tubes. Such heat exchangers have a relatively low heat exchange efficiency; their heat transfer coefficient is only about twice that of tubes without fins. However, their advantage lies in the ease of oil return and simpler control, and the amount of refrigerant required is approximately 1/2 to 1/3 of that needed in a full-liquid-type unit. Film evaporation is a type of flow boiling; due to the thin liquid film layer on the outer surface of the tube, there is no boiling point elevation caused by static pressure, resulting in a high heat transfer coefficient. In contrast, the bubbles generated by full-liquid evaporation (i.e., immersion evaporation) tend to accumulate on the surface of the heat exchange tubes, resulting in a decrease in heat exchange efficiency; its performance is inferior to that of falling-film evaporation. Generally speaking, falling film evaporation operates under low temperature differences, but scaling must be prevented to avoid affecting heat transfer efficiency.