Does the temperature difference of the circulating water increase or decrease before and after scaling occurs in the heat exchanger?

A cooler is cooled by circulating water. If scaling occurs in the heat exchanger, and the heat load remains unchanged, the temperature difference between the inlet and outlet of the circulating water increases, as the thermal resistance caused by scaling increases and K decreases. With the heat transfer amount remaining constant, δtm must increase, resulting in a larger temperature difference

In the actual production process, the heat transfer amount is not constant; it decreases after scaling occurs, and as a result, the temperature of the material cooled by the heat exchanger rises. So, how does the temperature difference of the circulating water change during actual production?

In the actual production process, the heat transfer rate is not constant; it decreases after scaling occurs. As a result, the temperature of the material cooled by the heat exchanger rises. Therefore, the temperature difference of the circulating water decreases during actual production. The heat transfer rate is given by Q = m*Cp*δtm; since m and Cp remain constant, a decrease in Q leads to a decrease in δtm.

The temperature difference between the cooling water at the inlet and outlet of the heat exchanger is decreasing. Scaling leads to a reduction in the heat transfer coefficient; as the heat transfer coefficient decreases, less heat is absorbed by the cooling water, and consequently, the temperature difference between the inlet and outlet also decreases.

This post was last edited by Qingcheng Jun on 2018-5-23 at 11:39. After scaling occurs in the heat exchanger, the flow rate of the circulating water is increased to continue meeting the process cooling requirements. When an increase is made and the same cooling effect as before is achieved, it can be understood that the flow rate of the process material remains unchanged, as do the inlet and outlet temperatures. What changes is the flow rate of the cooling water and its outlet temperature; in other words, t2 decreases, and the temperature difference within the circulation water system reduces. The logarithmic mean temperature difference for heat transfer increases, compensating for the computational imbalance caused by the decrease in K. The mistake on the 4th floor was failing to understand the relationship between the average temperature difference used in heat transfer calculations and the temperature difference between the inlet and outlet of the cooling water. △Tm and t2-t1 are two different concepts; the logarithmic mean temperature difference is used because, in condensers, plate exchangers, and various other types of heat exchangers, the temperature changes. To enable more accurate selection and calculation, a relative precise value is obtained. When △T1/△T2 > 1.7, the formula △Tm = (△T1 – △T2) / ln(△T1/△T2) is applied. If △T1/△T2 ≤ 1.7, then △Tm = (△T1 + △T2) / 2. This represents the average of the integral of the temperature differences during the heat transfer process between the two fluids in the heat exchanger. During reverse flow, △T1 = T1 – t2 and △T2 = T2 – t1; during forward flow, △T1 = T1 – t1 and △T2 = T2 – t2

The temperature difference decreases; since less heat is absorbed by the circulating water, the temperature difference becomes smaller

After scaling occurs, the thermal resistance increases. If the amount of water circulating remains unchanged, the heat exchange efficiency of the same equipment will definitely decline. As a result, both the temperature difference and the amount of heat transferred will decrease, leading to an increase in the exit temperature of the process material

The core issue is the decrease in heat transfer rate; since the volume of fluid on both sides remains unchanged due to process requirements, the temperature difference decreases.