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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Resulting in less heat transfer and higher outlet fluid temperatures, which leads to off-quality production, exceeding environmental limits, or creating lmtdd hazards that require mitigation. To understand the difference between these two methods, we need to understand the key terminology and the equations used in each solution method.
The maximum possible heat transfer rate is achieved if the fluid with abd minimum value of HCR experiences the maximum dT across the heat exchanger. Fundamentals of Momentum, Heat and Mass Transfer. 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.
Each HCRR curve flattens to a maximum value of Effectiveness as was the case for the pure single pass parallel flow heat exchanger. A control valve is sized and selected to meet the hydraulic requirements of the piping system, which includes the design flow rate and andd drop across the valve. 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.
When designing piping systems to support heat transfer between fluids, znd the hydraulic and thermal conditions must be evaluated to ensure the proper equipment is selected and installed.
Resolved comments Export to PDF. Effectiveness is dimensionless quantity between 0 and 1. The HCRR is limited to values between 0 and 1.
NTU method – Wikipedia
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 emthods. The HCR is calculated for both fluids as the product of the mass flow rate times the specific heat lmt of the fluid. This page was last edited on 17 Octoberat 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.
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. The thermal capacity UA required to achieve the heat transfer rate is determined by re-arranging the NTU equation after determining the value of NTU for the particular heat exchanger configuration. Similarly, a direct comparison can be made between the thermal capacity of a heat exchanger and the flow capacity of a control valve.
For example, for a pure single pass counter current flow heat exchanger:. 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 method proceeds by calculating the heat capacity rates i. The division often results in misunderstanding, miscommunication, and mistakes when integrating the work of the various groups. Corrective action would require the purchase and installation of a properly sized heat exchanger, causing additional downtime for installation. 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.
Retrieved from ” https: For example, for a pure single pass counter current flow heat exchanger: Analogies are often made between concepts in many engineering disciplines. It is a function of the heat exchanger design and the fluid properties on both sides.
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. Views Read Edit View history. The Temperature Effectiveness P is the ratio of the tube side temperature change to the maximum 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. Hence in this special case nru heat exchanger behavior is independent of the flow arrangement. 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 thermal capacity of a heat exchanger is its ability to transfer heat between two fluids at different temperatures. 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 mtehods but when these temperatures are not available The NTU or The Effectiveness method is used.
Engineering Analogies Analogies are often made between concepts in many engineering disciplines. 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. Summary Piping systems are built to transport fluid metods do work, transfer heat, and make a product.
Therefore the effectiveness is given by:. The method, at this point, is concerned only with the fluid undergoing the maximum temperature change. The greater the value of NTU, the larger the heat transfer surface area A required to meet the process conditions.