Issues related to 1.4 and 1.5 in TSG R0004-2009

Brief explanation: A shellless coil heat exchanger refers to a type of heat exchanger that consists of double tubes; in it, a fine tube carries one type of fluid, while another type of fluid flows between this fine tube and the outer thick tube. A cooling coil refers to a type of heat exchange device in which a large array of cooling tubes is submerged in an open or non-pressurized cooling tank.

It consists of a concentric inner tube and an outer tube. Hot and cold fluids flow in the gaps between the inner tube and the outer sleeve, thereby exchanging heat. The inner tubes are connected in series using U-tubes, while the sleeves are connected at both ends with straight tubes. The shell-and-tube heat exchanger has a simple structure, a large heat transfer area, is easy to clean, and convenient for disassembly and assembly; with an appropriate flow rate, it can operate in pure counterflow mode, resulting in a high heat exchange rate.

Although the ultra-high pressure tubular reactor is not a heat exchanger, the reaction tube also features a similar water-cooled jacket structure.

There’s no need to explain shell-and-tube heat exchangers; everyone is very familiar with them. Let me talk only about the cooling coils: Cooling coils are a type of evaporator used to cool air. It is widely used in low-temperature refrigeration chambers, where the refrigerant flows through and evaporates within the cooling coils, while the air to be cooled, acting as a heat transfer medium, undergoes natural convection outside the coils. 　　 The greatest advantage of cooling exhaust pipes is their simple structure, which makes them easy to manufacture, and they cause less drying out of unpackaged foods stored in the warehouse. However, the heat transfer coefficient of the exhaust pipe is low, and defrosting is difficult to operate, which hinders automation. For seamless steel tubes used in ammonia direct cooling systems, plain tubes or finned tubes are employed ； For Freon systems, coil-type or sleeve-type copper tube finned tube assemblies are generally used. 1. Coiled tube type exhaust pipe: Gravity feeding or ammonia pump feeding is both possible for the coiled tube type jacking pipe ； Single-row and double-row coiled tube wall coils can be used in ammonia pump feeding systems with liquid entering from below and exiting from above, as well as in gravity-fed systems. Individual coiled tube coils can also be used in ammonia pump feeding systems with liquid entering from above and exiting from below, as well as in thermal expansion valve feeding systems. 　　 The advantages of the coiled tube exhaust pipe are its simple structure, ease of fabrication, small liquid storage capacity, and wide applicability. Its main drawback is that the vapor generated in the lower section of the exhaust pipe cannot be removed promptly; it must travel through the entire length of the pipe before being discharged. As a result, the heat transfer coefficient is low, and the resistance to vapor-liquid two-phase flow is high. 2. U-shaped tube arrays: Common U-shaped tube arrays are composed of two or four layers of smooth, seamless steel tubes. 　　 The advantages of U-shaped top-mounted coils are uniform frosting, ease of fabrication and installation, and low liquid filling volume, which accounts for about 50% of their volume. They are suitable for gravity-fed liquid supply systems as well as ammonia refrigeration systems with ammonia inlet at the bottom and outlet at the top, and are widely used in cold storage facilities. However, it occupies a large amount of effective space in the warehouse, and the pipes on the upper layer are difficult to defrost.