Heat transfer equipment is found to be useful in a wide range of industries. They can be broadly defined as equipment used for transfer of heat from a hot medium to cold medium. Heat exchanger design and structure of heat transfer equipment varies a lot depending on the application where they are used and the heat transfer media involved.
Efficiency of heat transfer equipment
Some fundamental parameters governing the efficiency of heat transfer.
1. Temperature difference- High temperature difference between the involved media ensures efficient heat transfer by increasing the heat flux.
2. Nature of fluid- 流体特性，例如viscosity, conductivity,densityplay critical role in热交换器效率and determination of heat transfer coefficient.
3.流动类型- 通常，参与传热的介质是连续流动的。这些流可以彼此平行（共流流），彼此相反（逆流流）或彼此近似垂直（交叉流）。两种介质之间的温度差异随沿流动长度的位置而变化。反电流流通过确保高度温度差（通过LMTD测量）提供最佳效率。
4. Surface area- 可用于热能转移的高表面积意味着对同一热通量的热能更有效地转移。通过在传热表面上使用鳍来实现传热区域的增强。
5. Turbulence- 高湍流意味着通过流体中的对流更轻松地传热。由于传热对流比传导更有效地传热方式，因此湍流可用于提高传热效率。
Difference types of heat exchangers
Differenttypes of heat transfer equipmentor heat exchangers are widely used in the process industry. Selection of a specific exchanger type depends on several factors -
- 主要目标——例如,加热或cooling down a particular 'process fluid'
- 可用的公用事业 - 例如，空气，冷水，蒸汽，热水，电力，燃料等
- Type of hot and cold fluids - Are they liquid or gaseous? What is the operating pressure for both of them?
- Available space, for compact and concealed spaces special compact heat exchangers may be needed
- Flow rates of both hot and cold steams
- Required heat transfer rate
- 如何和冷液的化学组成 - 设计可能的腐蚀
Commercial factors in design of heat transfer equipment
There are some other factors as well, which are not related to heat transfer but still govern the design of heat exchangers.
1. Capital costs -Large heat exchangers can perform heat transfer for even very small temperature differences, but they come at a higher cost.
2.运营成本- In shell and tube exchangers, small diameter tubes can be used to increase the surface area available for heat transfer. But, small diameter also means higherpressure drop across the tubes导致更高的运营成本。
3. Materials- Depending on the type of fluid and itscorrosiveness, a suitable material has to be chosen for construction of a heat exchanger, even if does not assure maximum heat transfer. Moreover, in a壳和管热交换器, you can have different materials for the shell and tube sides. Generally, it is a good practice toput corrosive fluid on tube side, so you can have tubes with better corrosion resistant material.
4. Fluid phase- Different types of exchangers are used for different phases of fluid and even phase changes e.g. condensers, boilers, air cooled exchangers etc.
More examples of heat transfer equipment
- HVAC systems- Heating, Ventilation and Air Conditioning systems are responsible for the heating and cooling (via air conditioning) of indoor air, to maintain a comfortable indoor temperature. Thus HVAC systems are built with different kinds of heat transfer equipment. Ventilation is the other important element of HVAC.
