Questions about How Fluid Transfer Heat and How to Classify Heat Exchangers

1. If the hot fluid is inside the tube while the cold fluid is outside, how do the two fluid transfer heat through the wall? It includes the following three processes:
(1) Heat is transferred to the tube wall by heat fluid convection;
(2) Heat from the inner wall surface is transferred to the outer wall by heat conduction;
(3) Heat from the outer wall surface is transferred to the cold fluid by convection.
 
2. What are the requirements for the heat exchanger? The heat exchanger should meet the following requirements:
① High efficiency of heat transfer
② The pressure drop is as low as possible;
③ Reliable and expected service life
④ High product quality and safe operation
⑤ Compatibility of materials with process fluid
⑥ Convenient design and calculation, easy installation and reliable use
⑦ Easy maintenance and operation
⑧ Light weight and strong structure to withstand operating pressure
⑨ Simple manufacturing
⑩ Low price
⑪ The possibility of effective repair can be achieved for the problems existing in the repair. The heat exchanger must meet the usual requirements for operation under clean and dirty conditions as well as corrosive and non-corrosive conditions, and under specific problems. The heat exchanger must be able to accept maintenance, which often means that the selection of a structure allows for its cleaning if needed and the replacement of pipes, gaskets and any other components that are damaged by corrosion, erosion, vibration or aging, etc. This also requires the site space for the maintenance of the tube bundle, to meet the needs of the heat exchanger parts, and to facilitate the operation of inspection and monitoring.
 
3. How to classify heat exchange equipment?
In general, industrial heat exchangers are classified according to the following:
① Structure
② Heat transfer process
③ Compactness of the heat transfer surface
④ Flow pattern
⑤ Split-range situation
⑥ Fluid phase state
⑦ Heat transfer mechanism

According to their different structures, heat exchangers can be divided into:
① Tube heat exchangers, including double sleeve type, shell and tube type, coil type, etc.
② Plate heat exchangers, including gasket plate type, spiral plate type, plate and shell type, panel coil type, etc.
③ Extended surface heat exchanger, including tube fin type, plate fin type, etc.
④ Regenerator, including fixed regenerative bed type, rotary type, etc.
 
Classification according to the transfer process:
① Indirect contact type-direct transfer type, regenerative type, fluidized bed, etc.
② Direct contact type-cooling tower

The classification according to the flow pattern includes:
① Parallel flow
② Counter-current
③ Cross-flow

It can be divided into single-program and multi-program according to the classification of the division. According to the classification of fluid phase, it can be divided into gas-liquid heat exchanger, liquid-liquid heat exchanger and gas-gas heat exchanger. According to the heat transfer mechanism, it can be divided into condenser and evaporator. According to the usage, it can be classified into heat exchanger, condenser, reboiler, cooler; according to the way of heat exchange, it is divided into three types: mixed type, heat storage type and wall type.
 
Other classification methods include scraper heat exchangers.
According to "Sinopec Equipment Classification Catalog", it can be divided into:
(1) Shell and tube heat exchanger
(2) Double-tube heat exchanger
(3) Water-immersed heat exchanger
(4) Spray heat exchanger
(5) Rotary (coil) heat exchanger
(6) Plate heat exchanger
(7) Plate-fin heat exchanger
(8) Tube-fin heat exchanger
(9) Waste heat boiler
(10) Others