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