Heat transfer theory the natural laws of physics always allow the driving energy in a system to. Chapter 7 comparison of heat exchangers heat exchangers may be classified according to their flow arrangement. For example, the heat transfer coefficient in the fluid can be calculated from general correlations according to fluid flow. Optimal design of an airtoair heat exchanger with cross. Pdf heat exchanger lab experiment chemical engineering. Double pipe heat exchanger design with counterflow or.
When hot gas flows over the heat transfer surface through flow passages. Engineering flow and heat exchange octave levenspiel. Thermal analysis of double pipe heat exchanger by changing. Cross flow heat exchanger mixedunmixed example book problem 11. If the heat exchanger is located at the inlet or discharge of a blower with a pulsating flow, such as a roots type rotary lobe blower, the heat exchanger must be protected from the pulsation by a chambered silencer. Fluid engine oil sea water inlet temperature, c 65 20 outlet temperature, c 55 25 heat. In a few heat exchangers, the fluids exchanging heat are in direct contact. Geometry is also needed to calculate the heat transfer area. The oil provides an average convection coefficient ho 400 wm2k on the outside of the tubes. Praveen babuc a, anna university of technology tiruchirappalli, pattukkottai campus, raja madam 614 701, tamilnadu, india. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact.
John richard thome ltcm sgm epfl heat transfer heat exchanger design 1er mars 2008 6 41 the cross. They made it clear that the heat transfer rate of the spiral heat exchanger is more than that of the other types of heat exchangers 6. Design and construction of a spiral heat exchanger. Our main focus is to increase the efficiency of the parallel flow heat exchanger and on the basis of this, decide the shape and size of the heat exchanger. Lesson30 numerical problems related to heat exchanger. But of the three, the counter flow heat exchanger design is the most efficient when comparing heat transfer rate per unit surface area. Two types of flow arrangement are possible in a doublepipe heat exchanger. That means that given an infinitely long heat exchanger and 0 and 100 fluids, the eventual temperature of both the hot and the cold will reach 50. Because each of the plates has a very large surface area, the plates provide each of the fluids with an extremely large heat transfer area. In parallel flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. However, there are applications where parallel flow has its benefits, such as when limiting the transfer of heat is recommended.
Shell and tube heat exchangers, the most common liquidtoliquid heat exchanger, are used commonly in large buildings as a part of the hvac system. A heat exchanger is a heat transfer device that exchanges heat between two or more process fluids. Heat exchangers are used in both cooling and heating processes. Dns of turbulent channel flow with conjugate heat transfer. Pdf design and development of parallel counter flow. Introduction to engineering heat transfer these notes provide an introduction to engineering heat transfer. A common application of this type of heat exchanger is to use steam to. It is referred to as a laminar flow heat exchanger if the surface area density is above about 3000 m2m 3 914 ft2ft3, and as a micro heat exchanger if the surface area density is above about 10,000 m2m 3 3050 ft2ft3. A heat exchanger is a device in which energy is transferred from one fluid to another across a solid surface. Crossflow, parallel flow, and counterflow heat exchanger configurations are three examples. Various types of fins and attachments are illustrated in fig.
Approximate equations for the design of cross flow heat. The design of parallel flow heat exchanger is advantageous when two fluids are required to be. Heat is transferred from the warm fluid through the wall of the inner tube the socalled heating surface to the cold fluid. Design and development of parallel counter flow heat exchanger. Heat exchanger the purpose of a heat exchanger is just thatto exchange heat. What is parallelflow and counterflow heat exchanger. Methods of increasing thermal efficiency of a counter flow. The heat exchanger must be isolated from system vibrations using flexible piping connections and isolation pads on the mounting feet.
The heating is to be accomplished by passing hot engine. In the counter flow setup, the fluids are travelling along the heat exchanger in opposite directions. July 2016, volume 3, issue 7 jetir issn23495162 jetir16070 journal of emerging technologies and innovative research jetir. Experimental and cfd study of a helical coil heat exchanger using water as fluid 88 thermometers were used to measure the tube and coil side fluid temperature. 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. There is no change of phase either of the fluid during the heat transfer. Heat exchangers are typically classified according to flow arrangement and type of construction. Cross flow heat exchanger provide compact design of heat exchanger. A heat exchanger can have several different flow patterns. New heat exchangers have been designed for emerging thermal engineering. Log mean temperature difference lmtd me mechanical.
The hot and cold fluids alternate between each of the plates. Hemmat of mechanical engineering, shahid bahonar university of kernlan, iran abstract the single phase flow and thermal performance of a double pipe heat. Compared to a traditional plate design it is also possible to use thinner plates at high pressures. This heat exchanger consists of two concentric pipes of different diameters. The diagram above shows a shell and tube heat exchanger. These heat exchangers are submerged in low temperature water and the ambient air is streamed by fan with 0. In general, parallel flow heat exchangers considered less efficient than counter flow heat exchangers in terms of transferring heat from one fluid to another. Approximate equations for the thermal calculation of these flow arrangements with arbitrary numbers of passes are proposed. Take a single pass shell and tube exchanger and look at how the temperature changes as we go along the length of it in small segments. Heat exchanger effectiveness 2374 2 the maximum possible temperature change in any of the fluid flows would be th,in tc,in. Pdf thermal analysis of multipass cross flow heat exchanger. Parallel flow heat exchanger the figure below shows a schematic of a parallel flow heat exchanger along with temperature distribution for the hot and cold fluids.
Mar 06, 20 finds the length of a concentric, parallel flow heat exchanger using an overall heat transfer coefficient and the log mean temperature. The overall heat transfer coefficient of the exchanger is 300 wm2 k, and the area for heat transfer is 15. A synopsis of the various heat transfer models together with their conditions of. In counter flow heat exchangers the fluids enter the exchanger from. 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 figure 4.
Many researchers have investigated the characteristics of heat transfer and flow of the crosscorrugated heat exchangers to enhance the heat. The inlet temperature of cooled fluid has insignificant impact on heat exchanger effectiveness. Other articles where parallelflow heat exchanger is discussed. This flow chart indicates all the models available in cctherm and shows the default selections. E1mnl032a design and rating of shell and tube heat. The inner pipe is a suction pipe of the pump in which hot hydrocarbon flows and in outer annulus cold crude oil passes from opposite direction. Convective heat transfer from the outer tube wall to the outside fluid. Asee 2014 zone i conference, april 35, 2014, university of. What is application of parallel flow heat exchanger.
A test is conducted to determine the overall heat transfer coefficient in an automotive radiator that is a compact cross flow watertoair heat exchanger with both fluids air and water unmixed. The fluids can flow in the same direction through the equipment. Furthermore, the surface area of the heat exchanger is proportional to the amount of heat that can be transferred and is the most indicative cost component of a heat exchanger wilcox, 2009. Criterial equations for convective heat transfer in the boundary layer. Next, we will analyze the parallel flow heat exchanger for steady state flow. A shellandtube heat exchanger must be designed to heat 2.
Shellandtube heat exchangers funke warmeaustauscher. Designing steps for a heat exchanger ijert journal. Crosscounterflow configurations with one fluid unmixed throughout are important flow arrangements for the design of aircoolers and extended surface exchangers. The flow in a heat exchanger can be arranged as parallel flow, counter flow, and cross flow. Aug 28, 2017 you can see that using linear flow, the most you can ever heat or cool to is the midpoint of the differential. Multipass cross flow heat exchanger can be easily manufactured compare to parallel and counter flow heat exchanger. Therefore, all of the commercial simulators include models for heaters, coolers, heat exchangers, fired heaters,and air coolers towler and sinnott, 20. The alternative channels maximises the heat transfer surface in a compact manner. Parallel flow heat exchangers brazed plate, water to air. If the overall heat transfer coefficient is expected to be 1. Therefore, the results of the heat transfer and the pressure drop characteristics in function of changing the flow of working fluids are presented below. This is fairly efficient at first but quickly runs out of steam pun intended. But particularly the counter flow heat exchanger design is. Parallel and counter flow designs heat exchangers although ordinary heat exchangers may be extremely different in design and construction and may be of the single or twophase type, their modes of operation and effectiveness are largely determined by the direction of the fluid flow within the exchanger.
Total improvement of the heat transfer efficiency is up to 15%. Mar 09, 2016 the overall heat transfer coefficient u is constant throughout the heat energy. Flow in a doublepipe heat exchanger can be cocurrent or countercurrent. The effectiveness is determined as a function of heat exchanger size for sets of fixed operating conditions. A double pipe heat exchanger consists of one pipe inside another. The major types of heat exchanger include double pipe, shelltube, plate and shell, plate fin, and phase change heat exchangers. 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. The thermal efficiency of the heat exchanger with a larger surface area was measured to 82. In this exercise the students will 1 operate a tubeinshell heat exchanger and 2 analyze heat exchanger performance by the lmtd and ntu methods.
The overall heat transfer characteristics of a double pipe heat exchanger. The results of heat transfer experiments show that the shellside heat transfer coefficient of the improved heat exchanger increased by 18. The third edition of engineering flow and heat exchange is the most practical textbook available on the design of heat transfer and equipment. Material and flow information are needed to calculate the heat transfer coefficients and.
Plate type heat exchanger consists of plates instead of tubes to separate the hot and cold fluids. This book is an excellent introduction to realworld applications for advanced undergraduates and an indispensable reference for professionals. In the sizing problem, an appropriate heat exchanger type is selected. Criterial equations for convective heat transfer in channels 10. It can be operated as a parallel flow or as a counterflow heat exchanger. Gpx plate heat exchanger gpx heat exchangers are of a gasketed plate pack design. Eccentric an off centered shaft mount or eccentric design is recommended for viscous and sticky products. The wet heat exchanger has a higher effectiveness in counter flow than parallel flow. Pfx plate and frame heat exchanger hvac fluid flow. Experimental study on parallel and counter flow configuration. There is no loss of heat to the surroundings, due to heat exchanger being perfectly. However ordinary heat exchangers might be extremely dissimilar in design and construction and might be of the single or twophase kind, their modes of operation and efficiency are largely established by the direction of the fluid flow inside the exchanger. The specific heats c p and mass flow rates of both fluids is constant. The theory behind heat transfer plate heat exchangers.
Thermal analysis of heat exchangers with parallel flow the efficiency of the heat exchanger with parallel flow of working fluids is calculated by the expression. Types of heat exchangers shell and tube, plate type. Therefore, it can produce the most effective performance from the compact size. Concentric for most applications the shaft is mounted in the center of the heat transfer tube, or concentric. You can see that using linear flow, the most you can ever heat or cool to is the midpoint of the differential. Experiment regarding heat exchanger concurrentcountercurrent flows at same rate and different rates. A variety of highintensity heat transfer processes are involved with combustion and chemical reaction in the gasi. Heattransfer characteristics of wet heat exchangers in. The rating program is shown schematically in figure 4. Heat exchangers, cross flow introduction the cross flow exchanger is probably the dominant heat exchanger type in overall usage. The simplest heat exchanger is one for which the hot and cold fluids move in the same or opposite directions. Comparison of heat exchanger types each of the three types of heat exchangers parallel, cross and counter flow has advantages and disadvantages. How lmtd of counter flow heat exchanger is greater than.
Recuperates continuous heat flow hot and cold fluid are separated by a wallshell and tube heat exchangers 2. Designing steps for a heat exchanger reetika saxena 1 m. Difference in counter heat exchanger and parallel flow heat. When heat is transferred form hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by. Regenerators periodic heat flow hot and cold fluid alternately occupy the space of the heat exchanger g. University, moradabad abstract distillation is a common method for removing dissolved solids and to obtain pure water for drinking and for the purpose like battery water, electroplating etc. The experiments are carried out once the steady state has reached. The many types of heat exchangers can be characterized. Heat exchangers with cocurrent flow of the two streams are not very often seen because of the obvious reason that it is possible to do more heat exchange if the two streams are put in countercurrent flow, providing the same heat exchange area, w.
The overall heat transfer characteristics of a double pipe. Experimental study on parallel and counter flow configuration of a shell and helically coiled tube heat exchanger using al 2 o 3 water nanofluid p. It provides optimum heat transfer and flow conditions for a wide variety of fluids, with a builtin selfcleaning effect, while keeping the overall size of the unit to a. Heat exchanger can transfer energy between two liquids or between liquid and air. Some actual heat exchangers are a mixture of cross flow and counter flow due to design features that force the flow paths to wind back and forth. A counterflow heat exchanger will require less heat exchange surface area than a parallel flow heat exchanger for the same heat transfer rate and the same inlet and outlet temperatures for the fluids.
Tm is the log mean temperature difference given as t t. For examples, cross flow exchangers are ubiquitous in heating, ventilating, and air conditioning hvac systems not only as cooling and dehumidification coils but also as heating coils and aircooled condensers. Effectiveness and lmtd correction factor of the cross flow. If the flow rate, specific heat and temperature difference on one side are known, the heat load can be calculated. A heat transfer model selection flow chart is presented in the appendix iv to assist in this procedure. Why counter flow heat exchangers are more efficient. Same design features as the chx heat exchanger except chxs is all stainless steel construction, 2 12 diameters. Heat exchangers have widespread industrial and domestic applications.
A heat exchanger can also be operated in counterflow, in which the two fluids flow in parallel but opposite directions. Therefore the log mean temperature for a counter flow heat exchanger is larger than the log mean temperature for a similar parallel or. The heat recovery from hot fluid is used to increase the temperature of cold fluid. A more detailed description of aircooled heat exchanger geometries is given refs. On the diagram above the cold fluid, highlighted in blue, is travelling right to left where as the warm fluid, shown in red and amber, travels left to right. Higher flow capacity thanks to the noncircular ports, the. Effectiveness and efficiency analysis of parallel flow and. Design a double pipe heat exchanger with bare inner multitubes that can be used to cool engine oil with cold sea water.
Steady state flow is a valid assumption for steady operating conditions and temperatures. Some common examples are parallel low heat exchangers, in. Heat exchanger efficiency 4 has also been defined on the basis of efficiency of a fin of a constant area with its tip insulated, as a a f tanhf 3 where f a is the heat exchanger number and is expressed as, 2 ntu1 r f a for counter flow heat exchanger fand for parallel flow 2 ntu1 r a where ntu is the number of transfer units. For efficiency, heat exchangers are designed to maximize the surface area of the wall between the two fluids, while minimizing resistance to fluid flow through the. Temperature difference leads to heat transfer and heat transfer changes the temperature difference. For example, the heat transfer coefficient in the fluid can be calculated from general correlations according to fluid flow pattern and phases present.
In any heat exchanger there must be a fluid that requires a change in energy heating or cooling and a fluid. The gas goes through various cleanup and pipedelivery processes to get to our stoves. The heat transfer processes involved in these stages are generally less intense. July 2016, volume 3, issue 7 jetir issn 2349 5162 numerical. Made by faculty at the university of colorado boulder. A heat exchanger is a system used to transfer heat between two or more fluids. If the overall heat transfer coefficient is 1500 wm2k, determine.
Comparison of heat exchanger types parallel heat exchanger. The power consumption was logged during the test in order to predict how the. Combining each of these resistances in series gives. Thermal analysis of multipass cross flow heat exchanger. Heat exchangers 73 individual thermal resistances of the system. Heat transferheat exchangers wikibooks, open books for an.
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