A Constant-Wall-Temperature Model for Prediction of Thermal Performance of Gas-to-Gas Counter-Flow and Parallel-Flow Microchannel Heat Exchangers

2011 ◽  
Author(s):  
Kohei Koyama
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Difference Method ◽  
Heat Exchangers ◽  
Parallel Flow ◽  
Counter Flow ◽  
Partition Wall ◽  
Transfer Rates ◽  
Flow Configuration ◽  
Microchannel Heat Exchanger

Thermal performances of gas-to-gas counter-flow and parallel-flow microchannel heat exchanger have been investigated. Working fluid used is air. Heat transfer rates of both heat exchangers are compared with those calculated by a conventional log-mean temperature difference method. The results show that the log-mean temperature difference method can be employed to a parallel-flow configuration whereas that cannot be employed to a counter-flow configuration. This study focuses on the partition wall which separates hot and cold passages of the microchannel heat exchanger. The partition wall is negligibly thin for a conventional-sized heat exchanger. In contrast, the partition wall is thick compared with channel dimensions for a microchannel heat exchanger. A model which includes the effect of the thick partition wall is proposed to predict thermal performances of the microchannel heat exchangers. The heat transfer rates obtained by the model agree well with those obtained by the experiments. Thermal performances of the counter-flow and parallel-flow microchannel heat exchangers are compared with respect to one another based on temperature of the partition wall. The comparison results show that thermal performances of the counter-flow and parallel-flow microchannel heat exchangers are identical. This is due to performance degradation induced by the thick partition wall of the counter-flow microchannel heat exchanger. This study reveals that the thick partition wall dominates thermal performance of a gas-to-gas microchannel heat exchanger.

Performance Evaluation of Parallel Flow Microchannel Heat Exchanger Subjected to External Heat Transfer

2007 ◽  
Author(s):  
B. Mathew ◽  
H. Hegab
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
External Heat ◽  
Parallel Flow ◽  
External Heat Transfer ◽  
Microchannel Heat Exchanger ◽  
External Heating ◽  
Wide Range ◽  
The Individual

In this paper the effect of constant external heat transfer on the performance of a two fluid balanced parallel flow microchannel heat exchanger is analyzed. A mathematical model is developed for predicting the effectiveness-NTU relationship of both the fluids. Theoretical analysis is presented for various cases of external heating over a wide range of NTU. External heating improved the effectiveness of the cold fluid but degraded the effectiveness of the hot fluid while external cooling produced the opposite changes in the effectiveness of the coolants. The extent of improvement or degradation depended on the level of external heating/cooling. A term referred to as performance factor is used to assess the degree of improvement or degradation of the effectiveness of the individual fluids. Experiments conducted on two microchannel heat exchangers by subjecting the coolants to 5% and 10% external heating have been presented in this paper. The experimental value of NTU varied from 0.42 to 1.76. Good agreement is observed between the theoretical predictions and experimental results. The results presented in this paper are nondimensional; thus they can be utilized irrespective of the dimensions of parallel flow microchannel heat exchangers as well as the type of coolant.

Heat Exchange Characteristics of a Gas-Gas Counterflow Microchannel Heat Exchanger

2008 ◽  
Author(s):  
K. Koyama ◽  
Y. Asako
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchange ◽  
Transfer Rate ◽  
Rectangular Cross Section ◽  
Working Fluid ◽  
Partition Wall ◽  
Transfer Rates ◽  
Pressure Losses ◽  
Microchannel Heat Exchanger

Heat exchange characteristics of a gas-gas counterflow microchannel heat exchanger have been investigated experimentally. The microchannel has a rectangular cross section with 200 μm high and 300 μm wide. Working fluid is air. Reynolds number in the hot passage ranges from 127 to 381, and that in the cold passage ranges from 25 to 381. Temperatures and pressures at inlets and outlets of the heat exchanger have been measured to obtain heat transfer rates and pressure losses. The heat exchange and the pressure loss characteristics of the tested microchannel heat exchanger are discussed. Since the partition wall of the heat exchanger is thick comparing with the microchannel dimensions, a simple heat exchange model, the wall temperature of which is constant, is proposed to predict the heat transfer rate. The predicted heat transfer rates are compared with those of the experimental results and both results agree well.

scholarly journals Execution of a Smart Prediction Tool to Evaluate Thermal Performance in a heat exchanger by using Single Elliptical Leaf Strips with altered Angle

2019 ◽  
Vol 8 (11) ◽  
pp. 123-131
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Industrial Applications ◽  
Generalized Regression Neural Network ◽  
Prediction Tool ◽  
Pressure Drops ◽  
Transfer Rates ◽  
Mass Flow Rates

Heat exchangers are prominent industrial applications where engineering science of heat transfer and Mass transfer occurs. It is a contrivance where transfer of energy occurs to get output in the form of energy transfer. This paper aims at finding a solution to improve the thermal performance in a heat exchanger by using passive method techniques. This experimental and numerical analysis deals with finding the temperature outlets of cold and hot fluid for different mass flow rates and also pressure drop in the tube and the annular side by adding an elliptical leaf strip in the pipe at various angles. The single elliptical leaf used in experiment has major to minor axes ratios as 2:1 and distance of 50 mm between two leaves are arranged at different angular orientations from 0 0 to 1800 with 100 intervals. Since it’s not possible to find the heat transfer rates and pressure drops at every orientation of elliptical leaf so a generalized regression neural network (GRNN) prediction tool is used to get outputs with given inputs to avoid experimentation. GRNN is a statistical method of determining the relationship between dependent and independent variables. The values obtained from experimentation and GRNN nearly had precise values to each other. This analysis is a small step in regard with encomiastic approach for enhancement in performance of heat exchangers

scholarly journals Thermal Analysis of the Effects of Multifaceted Conditions on Performance of Shell-and-Tube Heat Exchanger

2021 ◽  
Vol 6 (1) ◽  
pp. 69-75
Author(s):  
Taiwo O. Oni ◽  
Ayotunde A. Ojo ◽  
Daniel C. Uguru-Okorie ◽  
David O. Akindele
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Parallel Flow ◽  
Hot Water ◽  
Inlet Temperature ◽  
Fiber Glass ◽  
Counter Flow ◽  
Tube Heat Exchanger ◽  
Shell And Tube ◽  
Flow Configurations

A shell-and-tube heat exchanger which was subjected to different flow configurations, viz. counter flow, and parallel flow, was investigated. Each of the flow configurations was operated under two different conditions of the shell, that is, an uninsulated shell and a shell insulated with fiber glass. The hot water inlet temperature of the tube was reduced gradually from 60 oC to 40 oC, and performance evaluation of the heat exchanger was carried out. It was found that for the uninsulated shell, the heat transfer effectiveness for hot water inlet temperature of 60, 55, 50, 45, and 40 oC are 0.243, 0.244, 0.240, 0.240, and 0.247, respectively, for the parallel flow arrangement. For the counter flow arrangement, the heat transfer effectiveness for the uninsulated shell are 2.40, 2.74, 5.00, 4.17, and 2.70%, respectively, higher than those for the parallel flow. The heat exchanger’s heat transfer effectiveness with fiber-glass-insulated shell for the parallel flow condition with tube hot water inlet temperatures of 60, 55, 50, 45, and 40 oC are 0.223, 0.226, 0.220, 0.225, and 0.227, respectively, whereas the counter flow condition has its heat transfer effectiveness increased by 1.28, 1.47, 1.82, 1.11, and 1.18%, respectively, over those of the parallel flow.

Performance of Parallel-Flow Gas-to-Gas Micro-Double-Tubes-Heat Exchangers

2009 ◽  
Author(s):  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Koichi Suzuki
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Circular Tube ◽  
Steel Tube ◽  
Parallel Flow ◽  
Bulk Temperature ◽  
Stainless Steel Tube ◽  
Cross Sectional ◽  
Partition Wall ◽  
Annular Tube

Heat transfer performance of two-stream parallel-flow gas-to-gas micro-double-tubes-heat exchangers was investigated numerically. The flow passages of the micro- double-tubes-heat exchanger are a circular tube for hot passage and a concentric annular tube for cold passage. A circular tube of r = 50 μm and a concentric annular tube of ri = 51 μm and ro = 71 μm with an identical cross-sectional area were chosen and the selected length was 20mm, respectively. Then, the partition wall is assumed to be a stainless steel tube with 1 μm in thickness. Numerical methodology is based on the arbitrary-Langrangian-Eulerian method. Computations were performed for wide flow range to find the effects of capacity ratio on the heat transfer characteristics of gas-to-gas micro-double-tubes-heat exchangers. The results are presented in form of temperature contours, bulk temperature, total temperatures and heat flux variation along the length. Also, the effectiveness and the number of transfer units approach and the estimation of the heat exchange rate were discussed.

The Effectiveness-NTU Relationship of Microchannel Counter Flow Heat Exchangers With Axial Heat Conduction

2007 ◽  
Author(s):  
B. Mathew ◽  
H. Hegab
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Microchannel Heat Exchanger ◽  
Axial Temperature ◽  
Axial Heat ◽  
Relationship Of ◽  
End Wall ◽  
Axial Heat Conduction

In this paper the effect of axial heat conduction on the thermal performance of a microchannel heat exchanger with non-adiabatic end walls is studied. The two ends of the wall separating the coolant are assumed to be subjected to boundary condition of the first kind. As the end walls are not insulated heat transfer between the microchannel heat exchanger and its surroundings occur. Analytical equations have been formulated for predicting the axial temperature of the coolants and the wall as well as for determining the effectiveness of both fluids. The effectiveness of the fluids has been found to depend on the NTU, axial heat conduction parameter and end wall temperatures. The heat transfer through the end walls have been expressed in nondimensional terms. The nondimensional heat transfer from both ends of the wall also depends on the axial heat conduction parameter and temperature gradient at the end walls. A new parameter, performance factor, has been proposed for comparing the variation in effectiveness due to axial heat conduction coupled with heat transfer with the effectiveness without axial heat conduction. The effectiveness of both the hot and cold fluid for several cases of end wall temperatures and axial heat conduction parameter are analyzed in this paper for better understanding of heat transfer dynamics of microchannel heat exchangers.

Arithmetic Mean Temperature Difference and the Concept of Heat Exchanger Efficiency

2003 ◽  
Author(s):  
Ahmad Fakheri
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Rate ◽  
Temperature Difference ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Arithmetic Mean ◽  
Counter Flow ◽  
Mean Temperature ◽  
Optimum Heat

In this paper, it is shown that the Arithmetic Mean Temperature Difference, which is the difference between the average temperatures of hot and cold fluids, can be used instead of the Log Mean Temperature Difference (LMTD) in heat exchanger analysis. For a given value of AMTD, there exists an optimum heat transfer rate, Qopt, given by the product of UA and AMTD such that the rate of heat transfer in the heat exchanger is always less than this optimum value. The optimum heat transfer rate takes place in a balanced counter flow heat exchanger and by using this optimum rate of heat transfer, the concept of heat exchanger efficiency is introduced as the ratio of the actual to optimum heat transfer rate. A general algebraic expression as well as a chart is presented for the determination of the efficiency and therefore the rate of heat transfer for parallel flow, counter flow, single stream, as well as shell and tube heat exchangers with any number of shells and even number of tube passes per shell. In addition to being more intuitive, the use of AMTD and the heat exchanger efficiency allow the direct comparison of the different types of heat exchangers.

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.

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