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.
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Pages … Engineered Software, Inc. The Effectiveness-NTU method takes a different approach to solving heat exchange analysis by using three dimensionless parameters: Improperly sized equipment, whether the equipment is a pump, control valve or heat exchanger, results in additional capital and maintenance costs, off-quality production, environmental excursions, and potentially increase safety risks. Fundamentals of Momentum, Heat and Mass Transfer.
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.
Similarly, a direct comparison can be made between the thermal capacity of a heat exchanger and the flow capacity of a control methids. Lavine Fundamentals of Heat and Mass Transfer ,6th edition, pp — Powered by Atlassian Confluence 6.
The equation to calculate the heat transfer rate is given by: The method, at this point, is concerned only with the fluid undergoing the maximum temperature change. The required thermal capacity UA needed to achieve the heat transfer rate established by the temperatures and flow rates is calculated from the Heat Transfer Rate and the Corrected Mean Temperature Difference.
The relationship between these three parameters depends on the type of heat exchanger and the internal flow pattern.
The division often results in misunderstanding, miscommunication, and mistakes when integrating the work of the various groups. 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 meethods the value of NTU, the larger the heat transfer surface area A required to meet the process conditions. Similar to the LMTD method, the heat exchanger will operate at this thermal capacity as long as it has sufficient heat ane area at these operating conditions, taking into account the fouling factor.
The NTU is a function of the Effectiveness and HCRR established by the process temperatures and flow rates and is indicative of the size of the heat exchanger needed.
Each HCRR curve flattens to a maximum value of Effectiveness as was ntj case for the pure nhu pass parallel lmts heat exchanger. The thermal capacity of a heat exchanger is its ability to transfer heat between two fluids at different temperatures.
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 exchangers and whether a flow stream is mixed or unmixed.
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.
Summary Piping systems are built to transport fluid to do work, transfer heat, and make a product. Corrective action would require the purchase and ntj of a properly sized heat exchanger, causing additional downtime for installation. The method proceeds by calculating the heat capacity rates i. Wiley, New York F. 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.
Resolved comments Export to PDF. If the selected heat exchanger jtu undersized, the design heat transfer conditions will not be achieved. After calculating P and R, CF is then determined graphically using the location of the P value on the appropriate R curve. The equation to calculate the heat transfer rate is given by:.
Both methods share common parameters and concepts and will arrive at the same solution to heat exchanger thermal capacity. Piping systems are built to transport fluid to do work, transfer heat, and make a product.
To define the effectiveness of a heat exchanger we need to find the maximum possible heat transfer that can be hypothetically achieved in a counter-flow heat exchanger of infinite length.
The control valve is slightly over-sized to ensure sufficient capacity to deliver the required flow.
Equations for NTU vary by heat exchanger configuration, but the mathematical relationship for some types of metthods exchangers is not readily available or easily derived. Temperature Effectiveness P The Temperature Effectiveness P is the ratio of the tube side temperature change to the maximum temperature difference across the heat lmtr. Similarly, a heat exchanger is sized and selected to meet the thermal requirements of the system, which includes the design heat transfer rate at a true mean temperature difference across the heat exchanger.
NTU method – Wikipedia
As with any engineering problem, there are various ways to approach a solution when sizing and selecting a heat exchanger or analyzing its thermal performance. Created by Jeff Sineslast modified on Jun 29, The Temperature Difference Ratio R is the ratio of the temperature change across the shell side to the temperature difference across the tube side.
From Wikipedia, the free encyclopedia. The HCRR is limited to values between 0 and 1. Evaluating both the hydraulic and thermal conditions of a system can be a daunting task for any engineer and is often divided into different groups who specialize in a specific field.