# LMTD AND NTU METHODS PDF

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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P is limited to values between 0 and 1. Configuration Correction Anv 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.

As with any engineering problem, there are various ways to approach a solution when sizing and selecting a heat exchanger or analyzing its ad performance. Fundamentals of Momentum, Heat and Mass Transfer.

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. 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.

Lmrd 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. Created by Jeff Sineslast modified on Jun 29, This page was last edited on 17 Octoberat Piping systems are built to transport fluid to do work, transfer heat, and make a product.

The Temperature Difference Ratio R is the ratio of the temperature change across the shell side to the temperature difference across the tube side. The Effectiveness-NTU method takes a different approach to solving heat exchange analysis by using three dimensionless parameters: The greater the value of NTU, the larger the heat transfer surface area A required to meet the process conditions. Retrieved from ” https: For this configuration, the Maximum Effectiveness for a given HCRR curve is greater than that for a pure single pass parallel flow configuration.

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## NTU method

Lavine Fundamentals of Heat and Mass Transfer ,6th edition, pp — 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. 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.

Resulting in less heat transfer and higher outlet fluid temperatures, which leads to off-quality production, exceeding environmental limits, or creating safety hazards that require mitigation. 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.

Equations 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 equation to calculate the heat transfer rate is given by:. Effectiveness is dimensionless quantity between 0 and 1.

The Nhu of a fluid is a measure of its ability to release or absorb heat. 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.

A properly sized heat exchanger must have some abd capacity to account for fouling that will occur during operation but significant oversizing results in higher capital and unnecessary installation costs for thermal capacity.

The method, at this point, is concerned only with the fluid undergoing the maximum temperature change. 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. The other fluid would change temperature more quickly along the heat exchanger length.

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### NTU method – Wikipedia

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.

Similar to the LMTD method, the heat exchanger will operate at this thermal capacity as long as it has sufficient heat transfer area at these operating conditions, taking into account the fouling factor. The method proceeds by calculating the heat capacity rates i. The thermal capacity of a heat exchanger is its ability to transfer heat between two fluids at different temperatures.

The control valve is slightly over-sized to ensure sufficient capacity to deliver the required flow. 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. 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.

To understand the difference between these two methods, we need to understand the key terminology and the equations used in each solution method. Similar effectiveness relationships can be derived for concentric tube heat exchangers and shell and tube heat exchangers. 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.

The Temperature Effectiveness P is the ratio of the tube side temperature change to the maximum temperature difference across the heat exchanger.

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.