Analytical Study of Nonstationary Modes in Recuperative Heat Exchangers

2020 ◽  
pp. 60-71
Author(s):  
A.A. Aleksandrov ◽  
V.A. Akatev ◽  
M.P. Tyurin ◽  
E.S. Borodina ◽  
O.I. Sedlyarov
Keyword(s):  
Heat Exchanger ◽  
Stationary State ◽  
Heat Carrier ◽  
Heat Exchangers ◽  
Stationary Mode ◽  
Dimensionless Time ◽  
Counter Flow ◽  
Direct Flow ◽  
Output Section ◽  
Flow Heat

Recuperative heat exchanger transient operation modes during the start-up were considered in order to identify the time for establishing the stationary mode. This is important in carrying out technological processes that require constancy in values of certain parameters ensuring both product quality and process safety. The research was carried out using the analytical method for direct-flow and counter-flow heat exchangers. It was demonstrated that stationary state establishment in the direct-flow heat exchangers occurs immediately after the heat carrier gets into the apparatus. It should be noted that the entire apparatus reaches the stationary mode, when the slower heat carrier arrives at the apparatus output section. In case of a heat exchanger with the heat carrier counter-flow, it was found out that at the moment of the less heated heat carrier appearing at the apparatus output section, it was having the highest temperature. Then the temperature was decreasing, and after passing its minimum was beginning to oscillate along a curve with the damping amplitude. In the case under consideration, the stationary process started, when the dimensionless time value was ϕ ≥ 0.5. The indicated solution was obtained under assumption that thermal and physical characteristics were constant in time and space. It was assumed that total heat capacity of the heat exchanger heat transferring wall was infinitesimal. This assumption is valid with an error of up to 1 % at Fo ≥ 100, which is the case in most practical cases. For apparatuses under study, a formula was also obtained for the time required to reach the stationary state

A Transient Model for Parallel Flow and Counter Flow Heat Exchangers

2013 ◽  
Author(s):  
K. Abbasi ◽  
M. Del Valle ◽  
A. P. Wemhoff ◽  
A. Ortega
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Transient Behavior ◽  
Parallel Flow ◽  
Thermal Mass ◽  
Dimensionless Time ◽  
Internal Wall ◽  
Counter Flow ◽  
Thermal Capacitance ◽  
Flow Heat

The transient and steady-state response of single pass constant-flow (concentric parallel flow, concentric counter flow) heat exchangers was investigated using a finite volume method. Heat exchanger transients initiated by both step-change and sinusoidally varying hot stream inlet temperatures were investigated. The wall separating the fluid streams was modeled by conduction with thermal mass; hence the heat exchanger transient behavior is dependent on the thermal mass of the fluid streams as well as the internal wall. The outer wall is approximated as fully insulating. The time dependent temperature profiles were investigated as a function of heat exchanger dimensionless length and dimensionless time for both fluids. It was found that the transient response of the heat exchanger is controlled by a combination of the residence time and thermal capacitance of the fluid streams, the overall heat transfer coefficient between the fluid streams, and the thermal capacitance of the internal wall.

Effectiveness-NTU Relations for Heat Exchangers With Streams Having Significant Kinetic Energy Variation

2003 ◽  
Vol 125 (2) ◽  
pp. 377-387 ◽  
Author(s):  
Gregory F. Nellis
Keyword(s):  
Heat Exchanger ◽  
Kinetic Energy ◽  
Differential Equations ◽  
Heat Exchangers ◽  
Parallel Flow ◽  
Temperature Profiles ◽  
Cryogenic Temperatures ◽  
Cold Side ◽  
Counter Flow ◽  
Flow Heat

Effectiveness-NTU equations are derived for counter and parallel-flow heat exchangers with fluids having high velocities. In this case, the change in the kinetic energy occurring within the heat exchanger will significantly affect the temperature profiles. The effectiveness is found to depend on the usual non-dimensional variables that compare the heat exchanger conductance to the hot- and cold-side capacity rates and on four additional nondimensional quantities that reflect the magnitude and distribution of the kinetic energy on the hot and cold-sides of the heat exchanger. The governing differential equations are derived, nondimensionalized, and solved analytically for the case of an exponentially distributed kinetic energy. Graphical solutions are presented and interpreted for several cases. The solutions are applied to a particular case involving high velocities within a counter-flow heat exchanger used to produce cryogenic temperatures.

Modeling of Recuperative Heat Exchanger in a Joule-Thomson Cooler

2001 ◽  
Author(s):  
Kim Choon Ng ◽  
Jinbao Wang ◽  
Hong Xue
Keyword(s):  
Heat Conduction ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Cooling System ◽  
Experimental Measurements ◽  
Temperature Dependent ◽  
Counter Flow ◽  
Flow Heat ◽  
Temperature Dependent Properties ◽  
Recuperative Heat Exchanger

Abstract To develop effective heat exchangers for miniature and micro Joule-Thomson (J-T) cooling system, the performance of a recuperative heat exchanger is analyzed and evaluated. The evaluation is based on a theoretical model of the Hampson-type counter-flow heat exchanger. The effect of the pressure and temperature-dependent properties and longitudinal heat conduction are considered. The results of the numerical simulation are validated with the corresponding experimental measurements. The performance of the heat exchanger on effectiveness, flow and various heat conduction losses as well as liquefied yield fraction are analyzed and discussed. The simulation model provides a useful tool for miniature J-T cooler design.

Differential Methods for the Performance Prediction of Multistream Plate-Fin Heat Exchangers

1992 ◽  
Vol 114 (1) ◽  
pp. 41-49 ◽  
Author(s):  
B. S. V. Prasad ◽  
S. M. K. A. Gurukul
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Performance Prediction ◽  
Heat Exchangers ◽  
Loss Functions ◽  
Computer Algorithms ◽  
Counter Flow ◽  
Flow Heat ◽  
Differential Methods ◽  
Section Level

Use of traditional methods of rating can prove inaccurate or inadequate for many plate-fin heat exchanger applications. The superiority in practical situations of differential methods, based on dividing the heat exchanger into several sections and a step-wise integration of the heat transfer and pressure loss functions, is discussed. Differential methods are developed for counterflow, crossflow, and cross-counter-flow heat exchangers. The methods developed also avoid iterations at the section level calculations. Design of computer algorithms based on these methods is outlined. Two computer programs developed using the methods are presented and the results for a few typical cases are discussed.

Analysis of Two Fluid Four-Channel Heat Exchanger Using Finite Element Method

2015 ◽  
Vol 813-814 ◽  
pp. 658-662
Author(s):  
Kavadiki Veerabhadrappa ◽  
Dhanush Dayanand ◽  
Darshan Dayanand ◽  
Vinayakaraddy ◽  
K.N. Seetharamu ◽  
...  
Keyword(s):  
Finite Element ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Element Model ◽  
Counter Flow ◽  
Transfer Rates ◽  
Heat Exchanger Design ◽  
Dimensional Parameters ◽  
Flow Heat ◽  
Two Fluid

The development of heat exchangers from two streams to multi-stream passage arrangement becomes a key problem for heat exchanger design. In this paper, a new design is developed for multi-stream (four-channel) heat exchanger. Multi-channel heat exchangers are extensively used in refrigeration and air conditioning, chemical industries, milk pasteurization, cryogenics industries and energy-recovery applications due to their higher heat transfer rates. The focus of this study is to determine the performance of four-channel counter flow heat exchanger. The hot and cold fluids are assumed to recirculate and exchange heat between them. Finite element model of the heat exchanger is developed based on the detailed geometry and the specific working conditions with the help of which effectiveness of the four-channel heat exchanger is computed. Non-Dimensional parameters are introduced which makes the analysis more versatile. The effectiveness is computed for different values of NTU and heat capacity ratio.

Thermal Efficiency of the Cross Flow Heat Exchangers

2006 ◽  
Author(s):  
Ahmad Fakheri
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Rate ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Cross Flow ◽  
Algebraic Expression ◽  
Counter Flow ◽  
Optimum Heat ◽  
Flow Heat

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 optimum heat transfer rate, qopt, is given by the product of UA and the Arithmetic Mean Temperature Difference, which is the difference between the average temperatures of hot and cold fluids. The actual rate of heat transfer in a heat exchanger is always less than this optimum value, which takes place in an ideal balanced counter flow heat exchanger. It has been shown that for parallel flow, counter flow, and shell and tube heat exchanger the efficiency is only a function of a single nondimensional parameter called Fin Analogy Number. The function defining the efficiency of these heat exchangers is identical to that of a constant area fin with an insulated tip. This paper presents exact expressions for the efficiencies of the different cross flow heat exchangers. It is shown that by generalizing the definition of Fa, very accurate results can be obtained by using the same algebraic expression, or a single algebraic expression can be used to assess the performance of a variety of commonly used heat exchangers.

The Shell and Tube Heat Exchanger Efficiency and Its Relation to Effectiveness

2003 ◽  
Author(s):  
Ahmad Fakheri
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Rate ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Counter Flow ◽  
Tube Heat Exchanger ◽  
Optimum Heat ◽  
Flow Heat ◽  
Shell And Tube

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 optimum heat transfer rate, qopt, is given by the product of UA and the Arithmetic Mean Temperature Difference, which is the difference between the average temperatures of hot and cold fluids. The actual rate of heat transfer in a heat exchanger is always less than this optimum value, which takes place in a balanced counter flow heat exchanger. It is shown that for parallel flow, counter flow, and shell and tube heat exchanger the efficiency is only a function of a single nondimensional parameter called Fin Analogy Number. Remarkably, the functional dependence of the efficiency of these heat exchangers on this parameter is identical to that of a constant area fin with an insulated tip. Also a general algebraic expression as well as a generalized chart is presented for the determination of the efficiency of shell and tube heat exchangers with any number of shells and even number of tube passes per shell, when the Number of Transfer Units (NTU) and the capacity ratio are known. Although this general expression is a function of the number of shells and another nondimensional group, it turns out to be almost independent of the number of shells over a wide range of practical interest. The same general expression is also applicable to parallel and counter flow heat exchangers.

scholarly journals Optimization procedure of a new type counter–flow heat exchanger

2021 ◽  
Vol 2116 (1) ◽  
pp. 012093
Author(s):  
R Karvinen
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Optimization Procedure ◽  
Multi Objective Optimization ◽  
Counter Flow ◽  
Overall Heat Transfer Coefficient ◽  
Different Types ◽  
New Type ◽  
Flow Heat

Abstract Plenty of studies exist in books and archival journals dealing with different types of heat exchangers. In the paper an analytical approach to evaluate the overall heat transfer coefficient of a new type heat exchanger is presented. Derived equations are applied to multi-objective optimization of a very large economizer of a recovery boiler, when the exchanger mass and size should be small but simultaneously heat transfer rate high.

scholarly journals ANALISA PERFORMANSI HEAT PUMP MENGGUNAKAN COUNTER FLOW HEAT EXCHANGERS

2016 ◽  
Vol 2 (2) ◽  
Author(s):  
Kusnandar Kusnandar ◽  
Kusnandar Kusnandar
Keyword(s):  
Heat Exchanger ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Coefficient Of Performance ◽  
Counter Flow ◽  
Heating And Cooling ◽  
Flow Heat

Heat pump is a device that can be make heat and cool , which is functions as a cooling evaporator can be replaced to be a heating condenser. With adding a heat exchanger in the heat pump can provide better effect of heating and cooling. In this experiment, the heat pump using type hydrocarbon refrigerantand type friendly refrigerant to the environment, one of refrigerant isR-290. From the results that obtained value Coefficient Of Performance (COP) in the heat pump that uses a counter flow heat exchanger is 4.8 while the heat pump that does not use a counterflow heat exchanger obtained COP of 4.1. Efficiencies increase in the heat pump without using counter flow heat exchanger is 74%, otherwise the efficiency decrease of the heat pump using heat pump is 85%.

Exergy Transfer Effectiveness on Heat Exchanger

2006 ◽  
Author(s):  
Shuang-Ying Wu ◽  
Xiao-Feng Yuan ◽  
You-Rong Li ◽  
Wen-Zhi Cui ◽  
Liao Quan
Keyword(s):  
Heat Transfer ◽  
Heat Capacity ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Cross Flow ◽  
Counter Flow ◽  
Temperature Heat ◽  
Relevant Variables ◽  
Flow Heat ◽  
Exergy Transfer

In this paper, the concept of exergy transfer effectiveness is put forward firstly and the expressions involving relevant variables for the exergy transfer effectiveness, the heat transfer units number and the ratio of cold and hot fluids heat capacity rate have been derived for the high and low temperature heat exchangers. Taking the parallel flow, counter flow and cross flow heat exchangers as examples, the numerical results of exergy transfer effectiveness are given and the comparison of exergy transfer effectiveness with heat transfer effectiveness is analyzed.

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