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.

Effectiveness of Parallel Flow Microchannel Heat Exchangers With External Heat Transfer and Internal Heat Generation

2008 ◽  
Author(s):  
B. Mathew ◽  
H. Hegab
Keyword(s):  
Heat Transfer ◽  
Ambient Temperature ◽  
Heat Generation ◽  
Heat Exchangers ◽  
Internal Heat ◽  
External Heat ◽  
Internal Heat Generation ◽  
Parallel Flow ◽  
External Heat Transfer ◽  
The Individual

In this paper the thermal performance of balanced parallel flow microchannel heat exchangers subjected to external heat transfer and internal heat generation have been numerically analyzed. The governing equations were numerically solved to obtain the axial temperatures of the fluids. The effectiveness of each fluid was determined using the inlet and outlet temperatures obtained from the numerical analysis. Moreover, the heat transferred between the individual fluids and the ambient as well as that between the fluids were numerically determined. The effectiveness depended on NTU, ambient temperature, thermal resistance between the ambient and the fluids, and the internal heat generation. When NTU is zero, the effectiveness depends only on the internally generated heat. At a particular ambient temperature and NTU the effectiveness of the hot and cold fluids degraded and improved, respectively, with increase in the internally generated heat. On the other hand with increase in ambient temperature the effectiveness of the hot and cold fluids decreased and increased, respectively, for a specific amount of heat generation. The model developed in this paper has been validated using existing models which consider the individual effect of external heat transfer and internal heat generation on the performance of parallel flow microchannel heat exchangers.

Effectiveness of Counter Flow Microchannel Heat Exchangers Subjected to External Heat Transfer and Internal Heat Generation

2009 ◽  
Author(s):  
B. Mathew ◽  
T. J. John ◽  
H. Hegab
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Ambient Temperature ◽  
Heat Generation ◽  
Internal Heat ◽  
External Heat ◽  
Internal Heat Generation ◽  
Counter Flow ◽  
External Heat Transfer ◽  
The Individual

The effect of external heat transfer and internal heat generation on the thermal performance of a balanced counter flow microchannel heat exchanger is theoretically analyzed in this paper. External heat transfer occurs due to the thermal interaction between ambient and the fluids. Internal heat generation takes into account the heat generated inside the channels due to the conversion of pumping power into heat. One-dimensional governing equations for both fluids were developed and solved to obtain the axial temperatures. The governing equations were solved using a 2nd order finite difference scheme. The effectiveness of the fluids is dependent on NTU, the ambient temperature, the thermal resistance between the individual fluids and the ambient and the pumping power. With increase in ambient temperature the effectiveness of the hot and cold fluid decreased and improved, respectively. On the other hand, reductions in the ambient temperature always lead to the improvement and degradation of the hot and cold fluid effectiveness, respectively. Depending on the ambient temperature, the thermal resistance between the individual fluids and the ambient increased or decreased the effectiveness of the fluids. Internal heat generation always reduced and improved the hot and cold fluid effectiveness, respectively. The combined effect of external heat transfer and internal heat generation on the effectiveness of the fluids depends on the net amount of heat gained/lost by the individual fluids. The effectiveness of a microchannel counter flow heat exchanger is found to be better than of a parallel flow heat exchanger subjected to the same set of external conditions. The model developed in this paper has been verified using existing models that consider each of these effects individually.

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.

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.

Effectiveness-NTU Relationship for a Counterflow Heat Exchanger Subjected to an External Heat Transfer

2004 ◽  
Vol 127 (9) ◽  
pp. 1071-1073 ◽  
Author(s):  
Gregory F. Nellis ◽  
John M. Pfotenhauer
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Exchanger ◽  
Numerical Model ◽  
Analytical Solution ◽  
Convenient Method ◽  
Process Engineering ◽  
External Heat ◽  
External Heat Transfer ◽  
External Heat Flux

This paper presents the analytical solution for the effectiveness of a counterflow heat exchanger subjected to a uniformly distributed, external heat flux. The solution is verified against conventional ε-NTU relations in the limit of zero external heat flux. This situation is of interest in applications such as cryogenic and process engineering, and the analytical solution provides a convenient method for treating differential elements of a heat exchanger in a numerical model.

Numerical Simulation of Manifold Microchannel Heat Exchanger

2016 ◽  
Author(s):  
Muhammad Ansab Ali ◽  
Tariq S. Khan ◽  
Ebrahim Al Hajri
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Transfer Rate ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Water Mixture ◽  
Microchannel Heat Exchanger ◽  
Compact Size

The quest to achieve higher heat transfer rate, smaller size and minimum pressure drop is a main area of focus in the design of heat exchangers. Plate heat exchangers are one of viable candidates to deliver higher heat duties but still have a drawback of higher pressure drop due to long restricted flow path. Motivated by demand of miniaturization and cost reduction, a novel design of tubular microchannel heat exchanger for single phase flow employing ammonia water mixture is proposed. Numerical simulation of unit fluid domain is conducted in ANSYS Fluent. Parametric study of the different flow geometries is evaluated in terms of Nusselt number and pressure drop. The salient features of the design include ultra-compact size with higher heat transfer rate and acceptable pressure drop.

Development of a Microchannel Heat Exchanger for Aerospace Applications

2012 ◽  
Author(s):  
Hal Strumpf ◽  
Zia Mirza
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
State Of The Art ◽  
Design And Optimization ◽  
Microchannel Heat Exchanger ◽  
Aerospace Applications ◽  
Accurate Design ◽  
Adjustment Factors

Honeywell Aerospace has been developing microchannel heat exchangers for aerospace use. These heat exchangers offer significant reduction in volume and some reduction in weight compared to state-of-the-art aerospace heat exchangers constructed using offset plate and fin interupted surfaces. A microchannel heat exchanger was designed based on the requirements and available envelope for an aerospce liquid-to-air heat exchanger presently in service. The new micochannel heat exchanger was fabricated and a full testing campaign was undertaken to validate the design approach and generate appropriate adjustment factors for pressure drop and heat transfer. Based on this correlated model, the heat exchanger was re-sized for the required conditions. This updated design shows a significant reduction in size compared to the existing heat exchanger. In addition, Honeywell now has a validated approach enabling accurate design and optimization of microchannel heat exchangers for diverse problem conditions.

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