Chaudhry H.N.,Heriot - Watt University Dubai
Applied Thermal Engineering | Year: 2016
The way in which heat pipes are arranged plays an important role on the overall effectiveness of this sustainable thermal system. A numerical and experimental analysis into determining the optimum heat pipe streamwise distance for providing passive airside cooling in ventilation airstreams was carried out. The airflow and temperature profiles were numerically predicted using Computational Fluid Dynamics (CFD), the findings of which were quantitatively validated using wind tunnel experimentation. Using the heat pipe diameter (D) of 20 mm, the spanwise thicknesses were varied from 44 mm (St/D ratio of 2.2) to 52 mm (St/D ratio of 2.6). In order to ensure sustainable operation of the system, water was used as the heat pipe working fluid. Keeping the boundary conditions constant for all modes (inlet velocity of 2.3 m/s and inlet temperature of 314K), the rate of heat transfer was found to be directly proportional to the temperature difference between inlet and outlet interface. The findings determined that the spanwise thickness of 50 mm (St/D ratio of 2.5) provided the highest heat transfer in comparison to the other analysed models at 768 W. The overall effectiveness of the system was found to decrease from 5.6% to 4.7% when the spanwise thickness reduced from 50 mm to 44 mm. A good agreement was obtained between the numerical and experimental findings with a maximum error of 1.6% for temperature and 14.6% for velocity parameters. The investigation successfully evaluated the performance of heat pipes under varying geometrical arrangement, when utilised for the purpose of pre-cooling ventilation airstreams for a sustainable built environment. © 2015 Elsevier Ltd. All rights reserved.
Chaudhry H.N.,Heriot - Watt University Dubai |
Hughes B.R.,University of Leeds
Applied Energy | Year: 2014
A detailed investigation into determining the passive airside cooling capability of heat pipes in response to gradually varying external temperatures was carried out. The city of Doha, Qatar was taken as the location of case-study and the climatic data for June 21st, 2012 was incorporated in the transient thermal modelling. The physical domain comprised of 19 cylindrical heat pipes arranged in a staggered grid subjected to varying source temperatures. Wind tunnel testing was carried out for the duration of 24. h in order to establish a relationship between the source temperatures and their effect on the climate responsive behaviour of heat pipes. Infrared thermal imaging was used to capture the surface temperature formations at regular intervals of time during the test. The findings from the study showed that under a low Reynolds Number airstream, the cooling capacity of heat pipes increases by 0.1. °C for every 1. °C rise in external source temperature. Conversely, the investigation showed that the thermal response of heat pipes reduces by 0.3. °C when subjected to decreasing source temperature gradients of 1. °C, thus indicating a low effectiveness. The highest temperature reduction was recorded at 2.3. °C indicating a convective heat transfer of 1546. W and a heat pipe effectiveness of 8.5%. The test confirmed that in general, the heat pipes performed better during the day-time when external temperatures reached over 40. °C in comparison to night-time operation when external temperatures dropped below 35. °C. The present work successfully characterised the sustainable operation of heat pipes in reducing air temperatures without the requirement of any mechanical intervention. © 2014 Elsevier Ltd.
Adeloye A.J.,Heriot - Watt University |
Rustum R.,Heriot - Watt University Dubai
Hydrology Research | Year: 2012
Water resources assessment activities in inadequately gauged basins are often significantly constrained due to the insufficiency or total lack of hydro-meteorological data, resulting in huge uncertainties and ineffectual performance of water management schemes. In this study, a new methodology of rainfall-runoff modelling using the powerful clustering capability of the self-organising map (SOM), unsupervised artificial neural networks, is proposed as a viable approach for harnessing the multivariate correlation between the typically long record rainfall and short record runoff in such basins. The methodology was applied to the inadequately gauged Osun basin in southwest Nigeria for the sole purpose of extending the available runoff records and, through that, reducing water resources planning uncertainty associated with the use of short runoff data records. The extended runoff records were then analysed to determine possible abstractions from the main river source at different exceedance probabilities. This study demonstrates the successful use of emerging tools to overcome practical problems in sparsely gauged basins. © 2012 IWA Publishing.
Soori P.K.,Heriot - Watt University Dubai |
Vishwas M.,Lead Systems Specialist
Energy and Buildings | Year: 2013
Lighting is the highest consumer of electrical energy in office buildings and it is one of the areas that offer many opportunities for improving the energy efficiency thereby reducing the energy consumption. This paper presents control strategy for energy efficient office lighting system design. The energy efficiency of a typical office building lighting system in Dubai is examined in this paper. The impact of use of natural lighting and artificial lighting on the HVAC system is assessed and highlighted. Lighting control algorithm is developed with the ultimate goal of achieving energy efficiency and health aspects of occupants into consideration. It is simulated using control systems simulation software functional explorer (FX) tools and recommendations are forwarded. The proposed control algorithm can be used as a reference to other new buildings to be built in Dubai or Middle East in general. © 2013 Elsevier B.V. All rights reserved.
Hughes B.R.,Heriot - Watt University Dubai |
Mak C.M.,Hong Kong Polytechnic University
Energy and Buildings | Year: 2011
Commercial wind towers have been the focus of intensive research in terms of their design and performance. There are two main forces which drive the flow through these devices, external wind and buoyancy due to temperature difference. This study examines the relationship between these two forces and the indoor ventilation rate achieved. The work uses computational fluid dynamics (CFD) modeling to isolate and investigate the two forces and draw comparisons. The study found that as expected the external driving wind is the primary driving force providing 76% more internal ventilation than buoyancy driven flow, which is deemed secondary. Moreover the study found that the effect of buoyancy is insignificant without an external airflow passage other than the wind tower itself. The addition of an external airflow passage such as a window in combination with buoyancy force increased the indoor ventilation by 47%. Therefore the careful positioning of windows in conjunction with internal heat source has the potential to overcome the lack of external wind driven forces in dense urban environments. © 2011 Elsevier B.V. All rights reserved.