It is the smallest difference between the temperatures of the cold and hot streams. For example, if you heat a cold fluid from 80°C up to 100°C using a hot fluid at 105°C, the approach temperature of the heat exchanger is 105-100 = 5°C. The lower approach, the higher heating area. Thus, it is the difference in temperature between the cooling medium inlet temperature and the process fluid discharge temperature.
- Rated Approach Temperature is from a heat exchanger manufacturer and is dependent on stated pressures, temperatures, and volumetric flowrates
- Measured Approach Temperature is utilized in IIoT and equipment servicing to alert to increased inefficiencies across the heat exchanger, and need for service or repair
Air compressor’s approach temperature is how effectively the coolers will cool the compressed air before discharging to the main plant piping. The approach temperature is a reference point on how close the compressed air discharge temperature is to the ambient temperature. Most air-cooled compressors have an approach to ambient temperature listed as 10°F (-12°C), 15°F (-9.4°C), or higher; it all depends on the size of the compressor and the rated design conditions. The stated approach temperature is most likely at the cooler design conditions, not the actual conditions.