This is the basis for one of the most powerful tools in heat exchanger analysis, the effectiveness ntu approach. To design or to predict the performance of a heat exchanger, it is essential to. Using the model, the transferred heat and effectiveness. They will also calculate the number of tubes needed for a shell and tube heat exchanger and to calculate the pipe length needed for a double pipe heat exchanger.
Design analysis and calculation of tube type heat exchanger design. Chemical engineering calculations to assist process, plant operation and maintenance engineers. This reduced performance can also be quantified as the reduced effectiveness of heat transfer. How to calculate the efficiency of a heat exchanger quora. Calculations are carried out using data in table 1 and 2 as a base. For calculation of heat exchanger performance, if only the inlet temperatures are known, it is preferable to use the effectivenessnumber of transfer units. In your heat transfer text book you will find these effectivenessntu relationships for a variety of heat exchangers in both equation form and graphically. Heat transfer and effectiveness analysis of a crossflow. Heat exchanger effectiveness heat transfer articles. A procedures manual was created for the doublepipe heat exchanger. For example, efficiency is related to heat exchanger effectiveness fakheri through 8. Lets take a counterflow heat exchanger with 80% effectiveness.
Liquid liquid exchanger ashell and tube exchanger of following configuration is considered being used for oil cooler with oil at the shell side and cooling water at the tube side. Mar 22, 2016 the effectivenessntu method the log mean temperature difference lmtd method discussed in section 234 is easy to use in heat exchanger analysis when the inlet and the outlet temperatures of the hot and cold fluids are known or can be determined from an energy balance. In your heat transfer text book you will find these effectiveness ntu relationships for a variety of heat exchangers in both equation form and graphically. The general effectiveness method appears to be first publicized by london and seban 1942.
Heat exchanger effectiveness and outlet temperature. Each heat exchanger is a bespoke product, designed by iteration and consultation with customers to provide optimal cost and performance i. Energy performance assessment of heat exchangers bureau of energy efficiency 59 4. Basic heat exchanger performance evaluation method on otec.
Jul 08, 2019 efficiency in this case is termed effectiveness and is the ratio of temperature difference. Ntu method, which simplifies the algebra involved in predicting the performance of complex. Effectiveness and lmtd correction factor of the cross flow. It is called a doublepipe exchanger because one fluid flows inside a pipe and the other fluid flows between that pipe and another pipe that surrounds the first. Another approach introduce the definition of heat exchanger effectiveness.
It is therefore possible to heat or cool fluids or gases which have minimal energy levels. Heat exchanger problem calculation lmtd and effectiveness. To analyze the effectiveness of the heat exchanger 9. You can compare the current heat transfer rate to the original rated. How to calculate the efficiency or effectiveness of a. A shellandtube heat exchanger must be designed to heat 2. How to calculate the efficiency of a shell and tube heat. Two important problems in heat exchanger analysis are i rating existing heat exchangers and ii sizing heat exchangers for a particular application. Correcting flaws in construction and piping that may have a detrimental effect on heat transfer and pressure drop may be the solution. Therefore, the comprehensive performance evaluation method of a heat exchanger for otec. What is heat exchanger analysis performance calculation. This is the basis for one of the most powerful tools in heat exchanger analysis, the effectivenessntu approach. In a cross flow heat exchanger heat is transferred directly from the outlet air to the makeup air through the separating walls in the heat exchanger.
Make a more detailed estimate of the overall heat transfer coefficient, u, based on the preliminary heat exchanger configuration. Optimizing the performance of the heat exchanger results in efficient utilization of energy with reduction in total volume and the. In this section, economic simulation of a sample hen was performed to monitor e of all hes. Here, we will cite only those that are immediately useful for design in shell and tube heat exchangers with sensible heat transfer on the shellside. E1mnl032a design and rating of shell and tube heat. Download the excel spreadsheet templates in this article to make preliminary heat exchanger design calculations. Calculate the required heat transfer area based on values needed. Heat exchangers are commonly used in industry, and proper design of a heat exchanger depends on many variables. Ntu method relates the effectiveness to the number of transfer units ntu of the heat transfer process and the ratio of the heat capacity rates c, defined as. Heat transfer and effectiveness analysis of a crossflow heat. Combining each of these resistances in series gives.
Two common methods are used to calculate the effectiveness, equations and graphical. For example, we use a heat exchanger in refrigerator gas by cold water or air in a refrigeration system. Shell and tube heat exchangers basic calculations pdh online. Basic heat exchanger performance evaluation method on. Measured results are compared to the deltae model that is often used in the design of conventional thermoacoustic devices, and possible. The heat capacitance rate is defined in terms of mass flow rate. However, energy effectiveness of the shell and tube heat exchanger can be increased by using metal oxide nanofluids, and better performance can be achieved by maintaining higher mass flow rates of shell side fluid and lower mass flow rates for tube side fluid. Calculation of overall heat transfer coefficient u. The basic design equation and overall heat transfer coefficient the basic heat exchanger equations applicable to shell and tube exchangers were developed in chapter 1. Heat exchangers have wide applications in modern industries. What is the difference between heat exchangers effectiveness. Lmtd can be calculated by using the following formula, where. Heat exchanger effectiveness ntu method if more than one of the inlet and outlet temperature of the heat exchanger is unknown, lmtd may be obtained by trial and errors solution.
When condensation is experienced in the exhaust of an aahx, additional heat transfer occurs that improves the performance of the device. A heat exchanger uses to exchange heat or heat energy from one medium to another. A plan for increasing heat exchanger performance for shell and tube exchangers should consider the following steps. With a plate type heat exchanger, the heat penetrates the surface, which separates the hot medium from the cold one very easily. The ufactor is defined by an expression analogous to newtons law of cooling. Optimisation of plateplatefin heat exchanger design. Fin efficiency model for heat exchanger the possible heat transfer q k. Efficiency analysis of heat exchangers and heat exchanger.
The theories of transient heat transfer in doublepipe heat exchangers were explained and followed by literature correlations. The optimum thermal design of a shell and tube heat exchanger involves the. The lmtd correction factor, the heat exchanger effectiveness, and heat exchanger efficiency are all derived from the same basic set of equations and therefore can be related to each other. In this work, experimental study and numerical simulation on heat transfer and pressure drop characteristics where performed at the shell side of a helically baffled heat exchangers. The two most common heat exchanger design problems are those of rating and sizing. To calculate q, we need both inlet and outlet temperatures.
This tedious procedure can be simplified by the definition of heatexchanger effectiveness. Evaluation of design results and adjustment to meet process specification with respect to heat transfer and pressure drop ensure that the final design and consideration meet process requirement at lowest possible cost. Introduction for calculation of heat exchanger performance, if only the inlet temperatures are known, it is preferable to use the effectivenessnumber of transfer units. Rating calculation for plate heat exchanger effectiveness and pressure drop using existing performance data article pdf available in chemical engineering research and design 803.
The hot source is at 210deg c and the cold end at 10deg c for a difference of 200deg c. Influence of fouling on heat exchanger effectiveness in a polyethylene plant 6. Effectiveness and efficiency analysis of parallel flow and. This is one of the common type of heat exchanger, a combination of shell and tube as shown in the figure, this shell and tube exchanger consists of a number of tubes mounted inside a cylindrical shell in which tubes runs parallel to shell. In a parallel flow heat exchanger, the two fluid streams hot and cold flow through the heat exchanger in the. Effectivenessntu curves for tubular heat exchangers. The concept of heat exchanger efficiency provides a new way for the design and analysis of heat exchangers and heat exchanger networks. The heating is to be accomplished by passing hot engine oil, which is at 160c, through the shell side of the exchanger. The heat exchanger effectiveness is defined as the ratio of actual heat transfer to the maximum possible heat transfer. Another approach introduce the definition of heat exchanger effectiveness, which is a dimensionless with ranging between 0 to1. Reason for heat exchangers a heat exchanger is a piece of equipment built for efficient heat transfer from one medium to. If outlet temperatures of a network are known we can start with static simulation, that is because effectiveness are known. This analysis is very well known and is universally adopted as one of the preferred methods of presenting and conducting heat exchanger analysis. A heat exchanger follows this principle in its endeavour to reach equalisation.
The first presentation is the conventional heat exchange effectiveness method. Estimate the pressure drop across the heat exchanger. The transfer of heat takes place through the surface of the tubes. This medium may be heat transfer from liquid to liquid, liquid to gas or gas to liquid and this will depend on application and requirements. R sekulib university of kentucky introduction a heat exchanger is a device that is used for transfer of thermal energy enthalpy between two or more fluids, between a solid surface and a fluid, or between solid particulates and a. Influence of fouling on heat exchanger effectiveness in a. Heat exchangers are devices that facilitate the exchange of heat between two fluids with high effectiveness and low investment and low maintenance cost. Presume that the exit temperature of water is not to. A procedure for use of the equipment and the software was outlined.
The heat exchanger effectiveness is defined as the ratio of the actual heat transfer rate to the maximum possible. The average fin temperature t f is close to the wall temperature t w as increase of the thermal conductivity. Shell and tube heat exchangers page 4 of 30 mnl 032a issued 29 august 08, prepared by j. Correcting flaws in construction and piping that may have a detrimental effect on. Heat exchanger analysis heat exchanger calculation. Heat exchangers 73 individual thermal resistances of the system. The oil provides an average convection coefficient ho 400 wm2k on the outside of the tubes. Simulation of heat exchangers and heat exchanger networks. T 1 t 2 what if the outlet temperatures are unknown.
Optimisation of plateplate fin heat exchanger design kunpeng guo the university of manchester 2015 abstractphd thesis with increasing global energy consumption, stringent environmental protection legislation and safety regulations in industrialised nations, energy saving has been put under high priority. Since the heat exchanger must operate on an hcrr curve within the region defined by the hcrr 0 and hcrr 1. Fire the boiler as per instructions in the boiler manual. When a heat exchanger has been in operation for a while, its performance decreases for a variety of reasons such as, fouling, scaling, corrosion etc. Heat exchanger analysis using effectiveness ntu method. If the overall heat transfer coefficient is expected to be 1. The doublepipe heat exchanger is one of the simplest types of heat exchangers. If it is too high, revise the heat exchanger configuration until the pressure drop is acceptable. Economic simulation of a sample heat exchanger network. Latent heat when moisture in the outlet air condensates in the heat exchanger.
The effectiveness of a heat exchanger is defined as the ratio of actual beat transfer to the maximum possible heat transfer. Difference between the effectivenessntu and lmtd methods. Heat exchanger effectiveness 2374 2 the maximum possible temperature change in any of the fluid flows would be th,in tc,in. This paper discusses the design and surface enhancement considerations that lead to optimal heat exchanger designs. Viscosity and specific heat of nanofluids are responsible for these phenomena. Effectiveness of heat exchanger the concept of effectiveness is applied to the heat transfer process in a heat exchanger. Reason for heat exchangers a heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another hot and cold fluid.434 1378 832 986 1428 1460 857 243 468 144 543 755 1114 969 1225 1417 1294 96 707 833 945 430 1477 966 145 1633 720 562 1003 697 1185 617 1201 979 1481 567 301 1331 76 898 1210