Generally the performance of a heat exchanger is measured by its effectiveness, but effectiveness does not provide any information. Heat exchanger analysis using effectiveness ntu method. Heat exchangers are usually analyzed using either the logarithmic mean temperature difference lmtd or the effectiveness number of transfer units. Therefore, different types of heat exchangers have different effectiveness relations. In heat transfer, effectiveness is a measure of the performance of a heat exchanger when using the ntu method. Since the calculations required for each iteration are quite lengthy, the. General expressions that can be used for determining the overall efficiency and effectiveness of heat. For example, we use a heat exchanger in refrigerator gas by cold water or air in a refrigeration system.
Heat transfer and effectiveness analysis of a crossflow. Effectiveness of parallelplate heat exchangers in thermoacoustic devices ray scott wakeland and robert m. The heart of the heat exchanger contains a fully welded circular plate pack made by pressing and cutting round plates and welding them together. Number of transfer units effectiveness method used in the design of counter flow heat exchanger. 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. Manufactured heat exchangers are found in facet of our life. Using the model, the transferred heat and effectiveness. Basic heat exchanger performance evaluation method on. The first type of a heat exchanger is called the recuperative type, in which heat are exchanged on either side of a dividing wall by fluids. Heat transfer and effectiveness analysis of a crossflow heat. An alternate method based upon heat exchanger effectiveness is more. The heating is to be accomplished by passing hot engine oil, which is at 160c, through the shell side of the exchanger. Jun 25, 2018 the results show that the singleobjective optimization at constant heat transfer rate, can be improve the performance of heat exchanger significantly and in constant heat transfer area increases the effectiveness, but it leads to increase of pump power consumption. Pdhonline course m371 2 pdh shell and tube heat exchangers.
Thus, heat exchanger has always been one of the main research topics in thermodynamics. Heat exchangers are devices that provide the transfer of thermal energy between two or more fluid streams at different temperatures. The results from effectiveness and lmtd analysis are. In contrast to the parallel flow heat exchanger, the counter flow heat exchanger can have the hottest coldfluid temperature greater than the coldest hotfluid temperatue. The detrimental effects may be characterized and appropriate allowance made in the design. The maximum value could be attained if one of the fluids were to undergo a temperature. Counter flow heat exchangers are the most efficient of the three types. Pdf a practical attempt to improve performance of heat exchanger. If outlet temperatures of a network are known we can start with static simulation, that is because effectiveness are known. Effectiveness of a heat exchanger the effectiveness. Several methods and theories have been developed to optimize the heat exchanger performance. In medicine, effectiveness relates to how well a treatment works in practice, especially as shown in pragmatic clinical trials, as opposed to efficacy, which measures how well it works in explanatory clinical trials or research. Heat exchanger effectiveness is therefore written as.
The oil provides an average convection coefficient ho 400 wm2k on the outside of the tubes. Below we illustrate the development of the effectiveness relation for the doublepipe e parallelflow heat exchanger. Effectiveness and some numericals on heat exchangers. Exchanger effectiveness the thermal performance of the exchanger can be assessed by its effectiveness. Upadhyaya2 1 department of industrial and systems engineering, university of tennessee, knoxville. Here, we analyze the heat transfer in the entire heat exchanger. A plan for increasing heat exchanger performance for shell and tube exchangers should consider the following steps. Where, qmax is the maximum possible heat transfer for the exchanger.
Development of the mathematical model definitions effectiveness. Computing the temperature distribution of both fluids, the overall effectiveness of the heat exchanger is calculated. The heat exchanger efficiency is defined as the ratio of the actual heat transfer in a heat exchanger to the optimum heat transfer rate. The concept of heat exchanger efficiency is extended to the heat exchanger networks. The results show that the singleobjective optimization at constant heat transfer rate, can be improve the performance of heat exchanger significantly and in constant heat transfer area increases the effectiveness, but it leads to increase of pump power consumption.
In the previous section we discussed heat transfer in a differential segment of the heat exchanger. T hi t ho t hi t ho t ci t co distance along the exchanger faith a. Heat exchangers are devices used to transfer heat energy from one fluid to another. Heat exchanger enhancement can be divided into both passive and active methods. Simple or composite wall of some kind divides the two. Pdf heat exchanger is a device used intensively for heat transfer form. The effectiveness of a heat exchanger is defined as. Heat exchanger fouling and estimation of remaining useful.
Effectivenessntu computation with a mathematical model. Introduction the double pipe heat exchangers are commonly used heat exchangers in commercial and industrial applications because of its. This paper presents heat transfer and effectiveness analysis based on a physical model of a crossflow heat exchanger. Basic design methods of heat exchanger, heat exchangers design, experiment and simulation, s m sohel murshed and manuel matos lopes, intechopen, doi. A shellandtube heat exchanger must be designed to heat 2. 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 basic component of a heat exchanger can be viewed as a tube with one fluid running through it and another fluid flowing by on the outside. The heat exchanger effectiveness is defined as the ratio of actual heat transfer to the maximum possible heat transfer. Heat exchanger and its types engineering solutions. Influence of fouling on heat exchanger effectiveness in a.
Heat exchanger enhancement must always satisfy the primary goal of providing a cost advantage relative to the use of a conventional heat exchanger6. Industrial heat exchangers are much less complex although the technological civilization makes them no less vital. If heat exchanger effectiveness is known, one can readily obtain q from equations 14 and 15. 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. The two most common heat exchanger design problems are those of rating and sizing. 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. Common example the classic example of a heat exchanger is found in an. Heat exchanger fouling and estimation of remaining useful life tutpol ardsomang1, j. After that, the outlet temperatures can be obtained from the energy balance. Heat exchangers are devices that facilitate the exchange of heat between two fluids with high effectiveness and low investment and low maintenance cost. When the area of a heat exchanger is known and the outlet temperatures of both streams are to be determined, an iterative calculation using equation 3. Chemical engineering calculations to assist process, plant operation and maintenance engineers. Effectivenessntu curves for tubular heat exchangers.
Heat exchanger fouling and estimation of remaining useful life. The moisture transfer efficiency for an heat recovery unit can be calculated as. Efficiency and effectiveness of heat exchanger series. Optimizing the performance of the heat exchanger results in efficient utilization of energy with reduction in total volume and the weight of the heat exchanger. Doublepipe heat exchanger, overall heat transfer coefficient, ntu, effectiveness. In this section, economic simulation of a sample hen was performed to monitor e of all hes. T lm,cf where determine correction factor f based on heat exchanger type and stream temperatures pay attention to symbols t versus t t is always the temperature of the tube side fluid. Correcting flaws in construction and piping that may have a detrimental effect on heat transfer and pressure drop may be the solution. Effectiveness improvement and optimization of shellandtube. Other factors that should be addressed include fouling potential, reliability and safety. Effectiveness and lmtd correction factor of the cross flow. A heat exchanger uses to exchange heat or heat energy from one medium to another. Effectiveness and efficiency analysis of parallel flow and. Effectiveness and lmtd correction factor of the cross flow exchanger.
Since the heat transfer occurs across the smaller tube, it is this. 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. Effectiveness of heat exchanger depends on the convection heat transfer coefficient of the fluid. Economic simulation of a sample heat exchanger network. Automobiles are equipped with heat exchangers called as radiators and all electronic and electrical equipment must be provided with heat exchanger for cooling. Heat exchanger effectiveness is defined as the ratio of the actual amount of heat transferred to the maximum possible amount of heat that could be transferred with an infinite area. Effectivenessntu computation with a mathematical model for. Influence of fouling on heat exchanger effectiveness in a polyethylene plant 6. Keoliana the pennsylvania state university, graduate program in acoustics and applied research laboratory, p. The effectiveness of a heat exchanger depends on the geometry of the heat exchanger as well as the flow arrangement. Two common methods are used to calculate the effectiveness, equations and graphical.
Simulation of heat exchangers and heat exchanger networks. Two types of flow arrangement are possible in a doublepipe heat exchanger. Chapter 5 heat exchangers faculty of engineering and. For calculation of heat exchanger performance, if only the inlet temperatures are known, it is preferable to use the effectivenessnumber of transfer units. 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.
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. The term heat exchanger applies to all equipment used to transfer heat between two streams. Heat exchangers are devices that regulate efficient heat transfer from one fluid to another. Folding of passages to achieve a more satisfactory heat exchanger size envelope is a viable approach even at relatively high heat exchange effectiveness. The heat exchanger efficiency is a very essential keypoint while selecting a right heat exchanger for your job. In medicine, effectiveness relates to how well a treatment works in practice, especially as shown in pragmatic clinical trials. Heat exchanger effectiveness heat transfer articles. In parallel flow, both the hot and cold fluids enter the heat exchanger at the same end and move in the same direction, as shown in figure 1.
Pdf this paper provides the solution to the problem of defining thermal efficiency for heat exchangers based on the second law of. Combining each of these resistances in series gives. A third type of heat exchanger is a plate and shell heat exchanger, which combines plate heat exchanger with shell and tube heat exchanger technologies. However, the term is commonly used to equipment in which two process streams exchange heat with each other. Another approach introduce the definition of heat exchanger effectiveness, which is a dimensionless with ranging between 0 to1. A simulation elementbyelement model discretizes the whole heat exchanger into smaller ones along the tube fluid path based on a local effectiveness concept. Jeter1 abstract a unified and somewhat simplified although complete presentation of the performance of the most common cross flow heat exchanger is presented. With a plate type heat exchanger, the heat penetrates. 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. This tedious procedure can be simplified by the definition of heatexchanger effectiveness. Effectiveness and overall heat transfer coefficient o. Heat exchangers 73 individual thermal resistances of the system. Effectiveness improvement and optimization of shelland.
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