Table of Contents
What is the significance of the term NTU in a heat exchanger?
The Number of Transfer Units (NTU) Method is used to calculate the rate of heat transfer in heat exchangers (especially counter current exchangers) when there is insufficient information to calculate the Log-Mean Temperature Difference (LMTD).
What are the advantages of effectiveness-NTU method over LMTD method in the analysis of heat exchangers?
The LMTD method is convenient for determining the overall heat transfer coefficient based on the measured inlet and outlet fluid temperatures. The ε-NTU method is more convenient for prediction of the outlet fluid temperatures if the heat transfer coefficient and the inlet temperatures are known.
How are the exit temperatures determined with the help of effectiveness-NTU method?
NTU method formula:
- R (specific heat ratio) = CminCmax.
- And, NTU = UACmin.
- Where, R = CminCmax.
- and, NTU = CUACmin.
- ∴ R = CminCmax=Cmin∞ C min C max = C min ∞ =0.
- ∴R=CminCmax=1.
- ∴ɛ=QactualQmax.
- R = CminCmax C min C max =62500189000 = 0.3306.
How do you calculate NTU in heat exchanger?
- Determine Cr as: Cr = Cmin / Cmáx.
- Calculate NTU using the relationship: NTU = U x A / Cmin
- With the values of NTU and Cmin, use the ε formula or curves of the respective heat exchanger to calculate ε.
When effectiveness and NTU method is used instead of LMTD method?
In heat exchanger analysis, if the fluid inlet and outlet temperatures are specified or can be determined by simple energy balance, the LMTD method can be used; but when these temperatures are not available The NTU or The Effectiveness method is used.
What is the significance of effectiveness of heat exchanger?
Calculating heat exchanger effectiveness allows engineers to predict how a given heat exchanger will perform a new job. Essentially, it helps engineers predict the stream outlet temperatures without a trial-and-error solution that would otherwise be necessary.
Under what condition the effectiveness NTU method is preferred over LMTD method as a method of analysis of heat exchanger?
c. When the heat transfer surface area A of the heat exchanger is known, but the outlet temperatures are not, the effectiveness-NTU method is the preferred method.
What is the physical significance of NTU in mass transfer?
The number of transfer units (NTU) required is a measure of the difficulty of the separation. A single transfer unit gives the change of composition of one of the phases equal to the average driving force producing the change. The NTU is similar to the number of theoretical trays required for trayed column.
What is NTU reading?
NTU stands for Nephelometric Turbidity unit, i.e. the unit used to measure the turbidity of a fluid or the presence of suspended particles in water. The higher the concentration of suspended solids in the water is, the dirtier it looks and the higher the turbidity is.
What does higher NTU mean?
What is NTU in heat and mass transfer?
The number of transfer units (NTU = UA/(mcp)) itself is a combination of overall heat transfer coefficients, transfer area, fluid flow rate and heat capacity. It summarizes these dimensional parameters into one dimensionless parameter. The performance becomes a monotone function of this dimensionless parameter.
What is NTU method of heat transfer?
Effectiveness – NTU Method. As heat is transferred from one fluid to another fluid in a heat exchanger one fluid will rise in temperature while the other fluid falls in temperature. In the introduction article on heat exchangers the heat transfer between the two fluids was expressed as the following equation.
What is the effectiveness of NTU method?
Effectiveness – NTU Method. One method that can be used to take this into consideration is the Log Mean Temperature Difference (LMTD). However, this method requires you to know what the input and output temperature of the fluid is. Another method that can be used is the effectiveness NTU method.
What is the difference between LMTD and NTU analysis?
In heat exchanger analysis, if the fluid inlet and outlet temperatures are specified or can be determined by simple energy balance, the LMTD method can be used; but when these temperatures are not available The NTU or The Effectiveness method is used.
What does NTU stand for?
The Number of Transfer Units (NTU) Method is used to calculate the rate of heat transfer in heat exchangers (especially counter current exchangers) when there is insufficient information to calculate the Log-Mean Temperature Difference (LMTD).