# 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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It is a function of the heat exchanger design and the fluid properties on both sides. Therefore the effectiveness is given by:. 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 ane 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. 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. 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 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. In heat exchanger analysis, if the fluid inlet and outlet temperatures are specified or can be determined by simple energy lmgd, the LMTD method can be used; but when these temperatures are not available Anx NTU or The Effectiveness method is anr.

Engineering Analogies Analogies are often made between concepts in many engineering disciplines. Similar effectiveness relationships can be derived for concentric tube heat exchangers and shell and tube heat exchangers.

The other fluid would change temperature more quickly along the heat exchanger length. 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.

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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 relationship between these three parameters depends on the type of heat exchanger and the internal flow pattern. By using this site, you agree to the Terms of Use and Privacy Policy. The HCR is calculated for both fluids as the product of the mass flow rate times the specific heat capacity of the fluid.

Each HCRR curve flattens to a maximum value of Effectiveness as was the case for the pure single pass parallel flow heat exchanger. For example, the effectiveness of a parallel flow heat exchanger is calculated with: 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.

Analogies are often made between concepts in many engineering disciplines. P is limited to values between 0 and 1. 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. Views Read Edit View history.

### NTU method – Wikipedia

A properly sized heat exchanger must have some excess capacity to account for fouling that will occur during operation but significant oversizing results in higher capital and unnecessary installation costs for thermal capacity. Retrieved from ” https: The thermal capacity of a heat exchanger is its ability to transfer heat between two fluids at different temperatures. Similarly, a direct comparison anf be made between the thermal capacity kethods a heat exchanger and the flow capacity of a control valve.

The method, at this point, is concerned only with the fluid undergoing the maximum temperature change. The Temperature Effectiveness P is the ratio of the tube side temperature change to the maximum temperature difference across the heat exchanger.

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

Similarly, methds heat exchanger is sized and selected nt meet the thermal requirements of the system, which includes the design heat transfer rate at a true mean temperature difference across the heat exchanger.

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

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. 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 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.

Lavine Fundamentals of Heat kmtd Mass Transfer ,6th edition, pp — If the selected heat exchanger is undersized, the design heat transfer conditions will not be achieved.

## NTU method

Pages … Engineered Software, Inc. 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. The equation to calculate the heat transfer rate is given by: Therefore the effectiveness is given by: Wiley, New York F.

From Metjods, the free encyclopedia. The HCRR is limited to values between 0 and 1.

Configuration Correction Factor CF The Configuration Correction Factor Methodw 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 heat exchanger will operate at this thermal capacity as long as it has sufficient heat transfer area at these operating conditions, including a factor for fouling. The equation to calculate the heat transfer rate is given by:.

Summary Piping systems are built to transport fluid to do work, transfer heat, and make a ntuu.

For example, for a pure single pass counter current flow heat exchanger: The HCR of a fluid is a measure of its ability to release or absorb heat.

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