(9) Effectiveness-NTU Method
The e-NTU method is a different approach to solving heat exchanger problems, however with similar parameters calculated and the same result is achieved. This method is also standardized by the Tubular Exchanger Manufacturers Association (TEMA) and other well-known manufacturers.
Initially, three dimensionless parameters are determined. These three parameters are related with the type of heat exchanger and the internal flow pattern. The three parameters are: Heat Capacity Rate Ratio (HCRR), Effectiveness (ε), and Number of Transfer Units (NTU).
Heat Capacity Rate Ratio (HCRR)
The dimensionless parameter Heat Capacity Rate Ratio (HCRR) is the ratio of the minimum to the maximum value of Heat Capacity Rate (HCR) for the hot and cold fluids. The HCR of a fluid is a measure of its ability to release or absorb heat. The HCR is calculated for both fluids as the product of the mass flow rate times the specific heat capacity of the …show more content…
The left curve shows a one shell / two tube pass heat exchanger and the right curve shows a two shell / four tube pass heat exchanger. These heat exchangers have corresponding CF-P-R curves shown in the discussion of the LMTD method, as displayed in figure 11. Actually, figure 11 corresponds to the same types of heat exchanger as in figure 13.
The one shell / two tube pass heat exchanger has some portion of flow that is counter flow, some is parallel flow, and some is cross flow. Each HCRR curve flattens to a maximum value of Effectiveness as was the case for the pure single pass parallel flow heat exchanger. For this configuration, the Maximum Effectiveness for a given HCRR curve is greater than that for a pure single pass parallel flow configuration.
The two shell / four tube pass heat exchanger ε-NTU curve shows that the more shells and tube passes in the heat exchanger, the more the performance approaches that of a single pass counter current heat