J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983). Moreover, engineers also use the logarithmic mean temperature difference (LMTD) to determine the temperature driving force for heat transfer in heat exchangers. Inserting the above values into the heat transfer Equation (2-2) for parallel flow heat exchanger yields the following result. 2) You may not distribute or commercially exploit the content, especially on another website. Fakheri, A. ISBN: 978-2759800414. Heat Exchanger Analysis – Performance Calculation. Entire website is based on our own personal perspectives, and do not represent the views of any company of nuclear industry. | Feedback Our Privacy Policy is a legal statement that explains what kind of information about you we collect, when you visit our Website. { Get links to your website. Engineering Forum The heat exchanger is designed to foster contact between materials in a conduit network, with one material exchanging heat … The general equation of heat load Main purpose of this project is to help the public learn some interesting and important information about engineering and thermal engineering. Although many manufacturers of heat exchangers believe they’ve fully optimized their products, technological advances will make the process never-ending. Heat Exchanger Companies Suppliers The mention of names of specific companies or products does not imply any intention to infringe their proprietary rights. In a cross-flow, in which one system, usually the heat sink, has the same nominal temperature at all points on the heat transfer surface, a similar relation between exchanged heat and LMTD holds, but with a correction factor. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1. For shell & tube heat exchangers, the overall heat transfer rate is defined as. The reason for the combination of the various types is to maximize the efficiency of the heat exchanger within the restrictions placed on the design. https://doi.org/10.1115/1.2739620. Engineering Toolbox Heat Transfer. A second method to achieve multiple passes is to insert baffles on the shell side of the heat exchanger. The layer of deposits represents additional resistance to heat transfer and causes the rate of heat transfer in a heat exchanger to decrease. Regenerative heat exchangers are usually found in high temperature systems where a portion of the system's fluid is removed from the main process, and then returned. Advertise directly with us. Efficiency = Actual out put / Output of the ideal system. Heat exchanger efficiency is calculated by comparing between the real and perfect performance. A ratio of (Q/rated duty) will tell you how effectively your exchanger is working. That should give you a good idea of how much heat transfer would be possible with each of them. (November 16, 2006). Williams. Efficiency of any system has to be calculated based on the performance of some ideal system. There is no simple answer. The heat transfer rate is mostly governed by the product UA, which is the product of surface area and heat transfer coefficient. Efficiency comparison between shell/tube and plate/frame heat exchangers, efficiency definitions:Heat exchanger efficiency definitions2 The following exercise demonstrates how the higher log mean temperature of the counter flow heat exchanger results in a larger heat transfer rate. Theodore L. Bergman, Adrienne S. Lavine, Frank P. Incropera. Heat exchangers are commonly used in industry, and proper design of a heat exchanger depends on many variables. For that reason, we don't have a practical definition for 'ideal heat exchanger'. Here is a list of equations governing the design of a shell & tube exchanger. These terms and methods, which are widely used to select an appropriate heat exchanger, are described below. Pinch point is the location in heat exchanger where the temperature difference between hot and cold fluid is minimum at that location. Please enable cookies on your browser and try again. Disclaimer where, LMTD is the logarithmic mean temperature difference. else DFM DFA Training (adsbygoogle = window.adsbygoogle || []).push({}); Engineering Calculators Co; 1st edition, 1965. Advertising Center Choosing the Right Heat Exchanger for Your Needs DOE Fundamentals Handbook, Volume 1 and 2. This process is automatic. Nuclear and Particle Physics. Given the inherent mathematical and mechanical problems associated with choosing the right heat exchanger, it is exceedingly necessary to consult a professional. A regenerative heat exchanger is one in which the same fluid is both the cooling fluid and the cooled fluid, as illustrated in Figure 7. Since we don't have an ideal heat exchanger to compare with, we cannot use the traditional concept of efficiency for heat exchangers. The overall heat transfer coefficient, U, is related to the total thermal resistance and depends on the geometry of the problem. The U-factor is defined by an expression analogous to Newton’s law of cooling. The rate of flow of oil is 1 kg/s. One common classification is regenerative or nonregenerative. A heat exchanger with higher efficiency may cost you more money at purchasing, but will definitely save money in running and payback in not long run; an inefficient heat exchanger might be cheaper at purchasing, but will consume much more energy in running and cost you double or three times more money in energy consumption in running, which must be much more than you saved at heat exchanger purchasing. May 2016. Training Online Engineering It explains how we use cookies (and other locally stored data technologies), how third-party cookies are used on our Website, and how you can manage your cookie options. Therefore the log mean temperature for a counter flow heat exchanger is larger than the log mean temperature for a similar parallel or cross flow heat exchanger. What is Example - Calculation of Heat Exchanger - Definition, What is Plate Heat Exchanger - Definition, What is Flow Boiling – Forced Convection Boiling – Definition, What is Regenerative Heat Exchanger – Definition. Addison-Wesley Pub. The efficiency of a counter flow heat exchanger is due to the fact that the average T (difference in temperature) between the two fluids over the length of the heat exchanger is maximized, as shown in … If so, give us a like in the sidebar. A heat exchanger typically involves two flowing fluids separated by a solid wall. 18. If the fluids pass each other only once, the heat exchanger is called a single-pass heat exchanger. The ideal heat exchanger transfers the maximum amount of heat, equal to the product of UA and arithmetic mean temperature difference, and generates the minimum amount of entropy, making it the most efficient and least irreversible heat exchanger. Metal Advertising To further examine the economic viability, you can also compare the ratio of (UA/cost). 5 Heat Exchangers The general function of a heat exchanger is to transfer heat from one fluid to another. The larger the LMTD, the more heat is transferred. A corrosion-resistant material must retain elasticity when dealing with high temperatures and pressure, and continuous contractions and expansions. The concept of heat exchanger efficiency provides a new way for the design and analysis of heat exchangers and heat exchanger networks. Calculating heat exchanger efficiency For any system, efficiency is normally calculated by comparing the actual performance with ideal performance. These direct the shell side fluid back and forth across the tubes to achieve the multi-pass effect. This can be seen by comparing the graphs in Figure 3, Figure 4, and Figure 5. The science of thermodynamics is universally concerned with the relationship between heat and temperature, and energy and work. In this equation only the definition of mean temperature difference has been made more specific. Consider a parallel-flow heat exchanger, which is used to cool oil from 70°C to 40°C using water available at 30°C.