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.

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.

scholarly journals The Effects of Internal Heat Generation or Absorption on Mixed Convection in a Lid-Driven Rectangular Cavity using Finite Volume Method

CFD letters ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 38-54
Author(s):  
Norhaliza Abu Bakar ◽  
Rozaini Roslan ◽  
Mohd Kamalrulzaman Md Akhir
Keyword(s):  
Heat Transfer ◽  
Heat Generation ◽  
Heat Exchangers ◽  
Internal Heat ◽  
Heat Transfer Process ◽  
Internal Heat Generation ◽  
Flow And Heat Transfer ◽  
Horizontal Cavity ◽  
Heat Generation Or Absorption ◽  
Volume Method

Mixed convection heat transfer in cavities is a significant phenomenon in numerous engineering fields, such as nuclear reactors, solar energy storage, and heat exchangers. Despite acknowledging that a square is a basic shape found in these systems, not all the figures are geometrical. Less attention was given to the rectangle cavity even though it could be found in these systems. Various internal reactions could occur inside the systems, especially in geothermal heat exchangers. Therefore, this research aims to analyze the effect of internal heat generation or absorption in a two-dimensional (2D) horizontal cavity to the fluid flow and heat transfer process numerically. The vertical walls are well insulated. Meanwhile, the top and bottom walls are kept at and , respectively, where . The top wall moves at a constant speed from left to right. The finite volume method (FEM) and SIMPLE algorithm are employed to discretize the governing equations. Next, the algebraic equations are solved iteratively using the tri-diagonal matrix algorithm (TDMA). The influences of heat generation or absorption parameters are investigated in terms of the flow, heat transfer, and Nusselt number. The numerical results are plotted in the form of streamlines and isotherms. It is found that the presence of heat generation or absorption has a significant effect on the fluid flow and heat transfer process in the horizontal cavity. Overall, for internal heat generation, the heat transfer rate decreases, while the opposite pattern can be observed for the case of internal heat absorption. However, for Ri = 10.0, as the heat generation's value increases from 2 to 4, the heat transfer rate is the same.

Heat Transfer on Nanofluid Flow With Homogeneous–Heterogeneous Reactions and Internal Heat Generation

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Raj Nandkeolyar ◽  
Peri K. Kameswaran ◽  
Sachin Shaw ◽  
Precious Sibanda
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Heat Generation ◽  
Internal Heat ◽  
Internal Heat Generation ◽  
Heterogeneous Reactions ◽  
Transfer Coefficients ◽  
Transfer Characteristics ◽  
Fluid Properties

We investigated heat and mass transfer on water based nanofluid due to the combined effects of homogeneous–heterogeneous reactions, an external magnetic field and internal heat generation. The flow is generated by the movement of a linearly stretched surface, and the nanofluid contains nanoparticles of copper and gold. Exact solutions of the transformed model equations were obtained in terms of hypergeometric functions. To gain more insights regarding subtle impact of fluid and material parameters on the heat and mass transfer characteristics, and the fluid properties, the equations were further solved numerically using the matlab bvp4c solver. The similarities and differences in the behavior, including the heat and mass transfer characteristics, of the copper–water and gold–water nanofluids with respect to changes in the flow parameters were investigated. Finally, we obtained the numerical values of the skin friction and heat transfer coefficients.

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