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6 results on '"Altwieb, Miftah"'

1. Modelling and optimisation of heat exchanger integrated in fan coil unit

Author

Altwieb, Miftah Omar and Mishra, Rakesh

Subjects
TA Engineering (General). Civil engineering (General)
Abstract

The Fan Coil Unit (FCU) is an integral part of heating, ventilation and air conditioning systems used in residential and commercial buildings. One main component of this device is a multi-tube and fin heat exchanger. Improvement of thermal performance in such heat exchangers is vital for improved performance of FCU. Performance improvements in the FCUs are mainly limited by available technology, manufacturing capabilities and overall cost effectiveness of the design. Better thermal performance usually comes at a cost of higher pressure drop or more expensive materials and manufacturing costs. In this thesis, a global framework for design and optimisation was developed taking into account overall costs of design, manufacturing and operation. Full 3D CFD models of multi-tube and fins heat exchanger were developed to investigate complex and non-uniform flow on water and air sides of the device. The CFD models were developed to enable local heat transfer analysis within the FCU. Experimental setup to evaluate performance of the heat exchanger has been designed and built. Different configurations of heat exchanger were tested experimentally and numerically, including the baseline configuration, so called plain fins. More efficient design of louvre fins and and fins with vortex generating mechanism (perforation in the fin surfaces) were also investigated. Best thermal performance was found to be for the perforated louvre fins. CFD model was validated against experimental results and obtained data was used to create a novel semi-analytical prediction model for Fanning friction factor (f) and Colburn factor (j). Appropriate costs calculation model was also developed and employed for total costs estimation of the FCU over the period of 15 years. The framework proposed in this thesis for optimised design and development strategy of heat exchangers resulted in development of a novel design which offers significant improvements in comparison to the current design. This new optimised design of the heat exchanger (with perforation in louvre fins) increased thermal performance by additional 10% while the total costs increased by only 6%.

Published
2018

3. Experimental and Numerical Investigations on the Response of a Multi Tubes and Fins Heat Exchanger under Steady State Operating Conditions

Author

Altwieb, Miftah Omar and Mishra, Rakesh

Subjects
TJ
Abstract

In this study, experimental and numerical investigations on the response a multi tubes and fins heat exchanger under steady state operating conditions have been carried out. A test setup has been developed in order to study the heat transfer and pressure drop characteristics of this heat exchanger. In accordance with the heat exchanger used for experiments, an identical geometry numerical 3D model has been created. The numerically calculated results have been validated against experimental data in terms of air outlet temperature and pressure drop measured across airside. Moreover, two novel design equations have been developed to predict the heat transfer rate and the pressure drop across the airside, after conducting a comparative numerical study on the airside performance of the multi tubes and fins heat exchanger having plain, louvre and semi-dimple vortex generator (VG).

4. Modelling and Optimisation of Heat Exchanger Integrated in Fan Coil Unit

Author

Altwieb, Miftah Omar

Subjects
TA
Abstract

The Fan Coil Unit (FCU) is an integral part of heating, ventilation and air conditioning systems used in residential and commercial buildings. One main component of this device is a multi-tube and fin heat exchanger. Improvement of thermal performance in such heat exchangers is vital for improved performance of FCU. Performance improvements in the FCUs are mainly limited by available technology, manufacturing capabilities and overall cost effectiveness of the design. Better thermal performance usually comes at a cost of higher pressure drop or more expensive materials and manufacturing costs.\ud \ud \ud In this thesis, a global framework for design and optimisation was developed taking into account overall costs of design, manufacturing and operation. Full 3D CFD models of multi-tube and fins heat exchanger were developed to investigate complex and non-uniform flow on water and air sides of the device. The CFD models were developed to enable local heat transfer analysis within the FCU.\ud \ud \ud Experimental setup to evaluate performance of the heat exchanger has been designed and built. Different configurations of heat exchanger were tested experimentally and numerically, including the baseline configuration, so called plain fins. More efficient design of louvre fins and and fins with vortex generating mechanism (perforation in the fin surfaces) were also investigated. Best thermal performance was found to be for the perforated louvre fins.\ud \ud \ud CFD model was validated against experimental results and obtained data was used to create a novel semi-analytical prediction model for Fanning friction factor (f) and Colburn factor (j). Appropriate costs calculation model was also developed and employed for total costs estimation of the FCU over the period of 15 years.\ud \ud \ud The framework proposed in this thesis for optimised design and development strategy of heat exchangers resulted in development of a novel design which offers significant improvements in comparison to the current design.\ud \ud \ud This new optimised design of the heat exchanger (with perforation in louvre fins) increased thermal performance by additional 10% while the total costs increased by only 6%.

5. A new three-dimensional CFD model for efficiency optimisation of fluid-to-air multi-fin heat exchanger

Author

Altwieb, Miftah, Kubiak, Krzysztof J., Aliyu, Aliyu M., Mishra, Rakesh, Altwieb, Miftah, Kubiak, Krzysztof J., Aliyu, Aliyu M., and Mishra, Rakesh

Abstract

New simulation and experimental results have been obtained and are presented for a multi-tube fin heat exchanger unit, from which semi-analytical correlations for the Fanning friction and Colburn factors were developed. The multi-tube and fin heat exchanger represents the main component of the Fan Coil Unit, an essential component of HVAC systems used for domestic and commercial heating and cooling. Improving the efficiency of the heat exchanger typically comes at the expense of higher pressure drops or costlier materials and production costs. Here, an experimental setup was designed and constructed to evaluate the thermal performance of such a heat exchanger. Geometrical modifications were explored for thermal performance enhancement. Furthermore, full three-dimensional CFD case studies of the heat exchanger were investigated to examine the effect of the geometrical features on the air side of the heat exchanger to study the effect of fin spacing, transverse and longitudinal pitches. The CFD model developed was first globally validated against experimental results. The model results were used to predict the Fanning and Colburn factors and the local fin efficiency based on the carefully selected geometric parameters. The data obtained was utilised to develop two new semi-analytical models for the Fanning and Colburn friction factors which were well within ±10% error bands and showed strong correlation coefficients of more than 98 and 97% respectively.

6. Heat Transfer Enhancement by Perforated and Louvred Fin Heat Exchangers

Author

Altwieb, Miftah, Mishra, Rakesh, Aliyu, Aliyu M., Kubiak, Krzysztof J., Altwieb, Miftah, Mishra, Rakesh, Aliyu, Aliyu M., and Kubiak, Krzysztof J.

Abstract

Multi-tube multi-fin heat exchangers are extensively used in various industries. In the current work, detailed experimental investigations were carried out to establish the flow/heat transfer characteristics in three distinct heat exchanger geometries. A novel perforated plain fin design was developed, and its performance was evaluated against standard plain and louvred fins designs. Experimental setups were designed, and the tests were carefully carried out which enabled quantification of the heat transfer and pressure drop characteristics. In the experiments the average velocity of air was varied in the range of 0.7 m/s to 4 m/s corresponding to Reynolds numbers of 600 to 2650. The water side flow rates in the tubes were kept at 0.12, 0.18, 0.24, 0.3, and 0.36 m3/h corresponding to Reynolds numbers between 6000 and 30,000. It was found that the louvred fins produced the highest heat transfer rate due to the availability of higher surface area, but it also produced the highest pressure drops. Conversely, while the new perforated design produced a slightly higher pressure drop than the plain fin design, it gave a higher value of heat transfer rate than the plain fin especially at the lower liquid flow rates. Specifically, the louvred fin gave consistently high pressure drops, up to 3 to 4 times more than the plain and perforated models at 4 m/s air flow, however, the heat transfer enhancement was only about 11% and 13% over the perforated and plain fin models, respectively. The mean heat transfer rate and pressure drops were used to calculate the Colburn and Fanning friction factors. Two novel semiempirical relationships were derived for the heat exchanger’s Fanning and Colburn factors as functions of the non-dimensional fin surface area and the Reynolds number. It was demonstrated that the Colburn and Fanning factors were predicted by the new correlations to within ±15% of the experiments.

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