E-NTU Method (Effectiveness – N TU method). Note, in most heat exchanger design problems, we don’t. know the fluid outlet temperatures, ie. Tiour or Tribut. TA. Summary of lmtd and e ntu. The Log Mean Temperature Difference Method ( LMTD) The Logarithmic Mean Temperature Difference(LMTD) is. Q: What is the real difference between the LMTD (logarithmic mean temperature difference) and NTU (number of transfer units) methods for analyzing heat.
|Published (Last):||3 January 2011|
|PDF File Size:||11.37 Mb|
|ePub File Size:||15.55 Mb|
|Price:||Free* [*Free Regsitration Required]|
Fundamentals of Momentum, Heat and Mass Transfer.
Similarly, a direct comparison can be made between the thermal capacity of a heat exchanger and the flow capacity of a control valve. Configuration Correction Factor CF The Configuration Correction Factor CF accounts for the deviation of the internal flow pattern of the actual heat exchanger from that of a single pass counter current flow pattern.
The thermal capacity of the heat exchanger will match the thermal capacity required by the process conditions temperatures and flow rates if it has sufficient heat transfer area to do so.
The Temperature Difference Ratio R is the ratio of the temperature change across the shell side to the temperature difference across the tube side. Similar effectiveness relationships can be derived for concentric tube heat exchangers and shell and tube heat exchangers.
Created by Jeff Sineslast modified on Jun 29, It is a function of the heat exchanger design and the fluid properties on both sides. The method, at this point, is concerned only with the fluid undergoing the maximum temperature change. The maximum possible heat transfer rate is achieved if the fluid with the minimum value of HCR experiences the maximum dT across the 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. 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 methovs is used.
The location of the operating point establishes the Configuration Correction Factor that is used to calculate the Corrected or true Mean Temperature Difference across the heat exchanger.
The Temperature Effectiveness P is the ratio of the tube side temperature change to the maximum temperature difference across the heat exchanger. The thermal capacity of a heat exchanger is its ability to transfer heat between two fluids at different temperatures.
P is limited to values between 0 and 1. The method proceeds by calculating the heat capacity rates i.
The HCR of a fluid is a measure of its ability to release or absorb heat. To determine the CF, two temperature difference ratios P and R must first be calculated from the four fluid temperatures entering and leaving the heat exchanger. Znd for NTU vary by heat exchanger configuration, but the mathematical relationship for some types of heat exchangers is not readily available or easily derived.
The division often results in misunderstanding, miscommunication, and mistakes when integrating the work of the various groups. Voltage drop, current, and electrical resistance are analogous to pressure drop, fluid flow, and hydraulic resistance, which are analogous to the temperature difference, heat transfer rate, and thermal resistance.
NTU method – Wikipedia
When designing piping systems to support heat transfer between fluids, both the hydraulic and thermal conditions must be evaluated to ensure the proper equipment is selected and installed. From Wikipedia, the free encyclopedia. Powered kmtd Atlassian Confluence 6. Each HCRR curve flattens to a maximum value of Effectiveness as was the case for the pure single pass parallel flow heat exchanger.
Some manufacturers provide a CF data table for their heat exchanger while others determine CF using a standard graph from the Tubular Exchanger Manufacturers Association TEMA for the actual heat exchanger configuration.
For example, the effectiveness of a parallel flow heat exchanger is calculated with: The Effectiveness-NTU method takes a methocs approach to solving heat exchange analysis by using three dimensionless parameters: The HCR is calculated for both fluids as the product of the mass flow rate times the specific heat capacity of the fluid.
The equation to calculate the heat ntj rate is given by: A control valve is sized and selected to meet the hydraulic requirements of the piping system, which includes the design flow rate and pressure drop across the valve. Pages … Engineered Software, Inc. These relationships are differentiated from one another depending on the type of the flow counter-current, concurrent, or cross flowthe number of passes in shell and tube lmhd and whether a flow stream is mixed or unmixed.
Lavine Fundamentals of Heat and Mass Transfer ,6th edition, pp —