Luai M. Al-Hadhrami

Heat Transfer in Rotating Rectangular Cooling Channels (AR=4) With Angled Ribs

An investigation into determining the effect of rotation on heat transfer in a rib-roughened rectangular channel with aspect ratio of 4:1 is detailed in this paper. A broad range of flow parameters have been selected including Reynolds number (Re=5000-40000), rotation number (Ro=0.04-0.3) and coolant to wall density ratio at the inlet (Δρ/ρ) i =0. 122. The rib turbulators, attached to the leading and trailing surface, are oriented at an angle (α=45 deg) to the direction of flow. The effect of channel orientations of β=90 deg and 135 deg with respect to the plane of rotation is also investigated. Results show that the narrow rectangular passage exhibits a much higher heat transfer enhancement for the ribbed surface than the square and 2:1 duct previously investigated. Also, duct orientation significantly affects the leading and side surfaces, yet does not have much affect on the trailing surfaces for both smooth and ribbed surfaces. Furthermore, spanwise heat transfer distributions exist across the leading and trailing surfaces and are accentuated by the use of angled ribs. The smooth and ribbed case trailing surfaces and smooth case side surfaces exhibited a strong dependence on rotation number

Effect of rotation on heat transfer in two-pass square channels with five different orientations of 45° angled rib turbulators

Abstract The effect of various 45° angled rib turbulator arrangements on the Nusselt number ratio in a rotating, two-pass, square channel is investigated for three Reynolds numbers (5000, 10,000, 25,000), with rotation number up to 0.11, and two channel orientations with respect to the axis of rotation ( β =90° and 135°). Five different arrangements of rib turbulators are placed on the leading and trailing surfaces at an angle of +45° or −45° to the main stream flow. The rib height-to-hydraulic diameter ratio ( e / D ) is 0.125; the rib pitch-to-height ratio ( P / e ) is 10; and the inlet coolant-to-wall density ratio (Δ ρ / ρ ) is maintained around 0.11. The results show that the rotating ribbed surface Nusselt number ratios increase by a factor of 2 compared to the rotating smooth surface results. The results also show that the heat transfer enhancement depends on the rib-angle orientation (+45° or −45°) to the main stream flow in the first or second pass of the channel for both rotating and non-rotating conditions. Overall, the parallel rib cases show better heat transfer enhancement than the crossed rib case for both rotating and non-rotating conditions. The 90° channel orientation with respect to the axis of rotation produces greater rotating effect on heat transfer over the 135° channel orientation.

Heat Transfer in Rotating Rectangular Cooling Channels (AR=4) With Dimples

As the world of research seeks ways of improving the efficiency of turhomachinery, attention has recently focused on a relatively new type of internal cooling channel geometry, the dimple. Preliminary investigations have shown that the dimple enhances heat transfer with minimal pressure loss. An investigation into determining the effect of rotation on heat transfer in a rectangular channel (aspect ratio=4:1) with dimples is detailed in this paper. The range of flow parameters includes Reynolds number (Re =5000-40000), rotation number (Ro=0.04-0.3) and inlet coolant-to-wall density ratio (Δρ/ρ =0.122). Two different surface configurations are explored, including a smooth duct and dimpled duct with dimple depth-to-print diameter (δ/D ρ ) ratio of 0.3. A dimple surface density of 10.9 dimples/in 2 was used for each of the principal surfaces (leading and trailing) with a total of 131 equally spaced hemispherical dimples per surface; the side surfaces are smooth. Two channel orientations of β=90 and 135 deg with respect to the plane of rotation are explored to determine channel orientation effect. Results show a definite channel orientation effect, with the trailing-edge channel enhancing heat transfer more than the orthogonal channel. Also, the dimpled channel behaves somewhat like a 45 deg angled rib channel, but with less spanwise variations in heat transfer.

Techno-Economic Potential of Retrofitting Diesel Power Systems with Hybrid Wind-Photovoltaic-Diesel Systems for Off-Grid Electrification of Remote Villages of Saudi Arabia

Recent climatic anomalies such as hot summers, cold winters, hurricanes, and cyclones are all reflections of global warming due to burning of fossil fuels. To combat unprecedented global warming and to mitigate future energy challenges, there is worldwide interest in utilization of renewable sources of energy such as solar-photovoltaic (solar-PV) and wind energy. Other driving forces paving avenue for renewable energy include rapid escalation in oil prices, growing concerns regarding depletion of oil/gas reserves, etc. Retrofitting of diesel systems with hybrid wind-PV-diesel systems is being widely disseminated to reduce diesel fuel consumption and to minimize atmospheric degradation. One of the potential market for deployment of hybrid systems is in remote locations which are driven by diesel generators. The Kingdom of Saudi Arabia (KSA) has a number of remote villages scattered all over the Kingdom. The aim of this study is to analyze wind speed and solar radiation data of Rafha, KSA, and to assess the technical and economic potential of hybrid wind-PV-diesel power systems to meet the load requirements of a typical remote village Rawdhat Bin Habbas (RBH) with annual electrical energy demand of 15,943 MWh. Rafha is located near RBH. The monthly average wind speeds range from 2.99 m/s to 4.84 m/s at 10 m height. The monthly average daily global solar radiation ranges from 3.04 to 7.3 kWh/sq.m. The hybrid systems simulated consist of different combinations of 600 kW wind machines, PV panels, supplemented by diesel generators. National Renewable Energy Laboratorys (NREL) Hybrid Optimization Model for Electric Renewables (HOMER) software has been used to perform the techno-economic study. The simulation results indicate that for a hybrid system comprising of 1.2 MW wind farm capacity (two 600 kW units, 50 m hub-height) and 1.2 MW of PV capacity together with 4.5 MW diesel system (three 1.5 MW units), the renewable energy fraction with 0% annual capacity shortage is 24% (10% wind + 14% PV). The cost of generating energy (COE) from this hybrid wind-PV-diesel system has been found to be 0.118

Weibull Parameters Estimation Using Four Different Methods and Most Energy-Carrying Wind Speed Analysis

/kWh (“assuming diesel fuel price of 0.1

Wind Speed Characteristics and Resource Assessment Using Weibull Parameters

/l”). The study exhibits that for a given hybrid configuration, the number of operational hours of diesel generators decreases with increase in wind farm and PV capacity. Attention has also been focused on wind/PV penetration, unmet load, excess electricity generation, percentage of fuel savings and reduction in carbon emissions (relative to diesel-only situation) of different hybrid systems, cost breakdown of wind-PV-diesel systems, COE of different hybrid systems, etc.

Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=2) With Five Different Orientations of 45 Deg V-Shaped Rib Turbulators

The study presents the analysis of wind speed data from seven stations in Saudi Arabia, measured at 20, 30, and 40 m height above ground level (AGL) over a period varying from 2 to 5 years. Specifically, Weibull parameters were calculated using five different methods, four of them based on the statistical analysis of the collected data and a fifth one based on WAsP algorithm used in WindoGrapher software. The calculated values using the five different methods were found to be in good agreement at all the measurement heights. The correlation between the monthly mean values of Weibull scale parameter and the measured wind speed values was found to be linear for all the sites. The linear coefficient ‘a’ was found to be sites characteristic value and independent of the height AGL for most of the locations. Moreover, linearity has been substantiated between the monthly mean wind power density (WPD) and the corresponding measured wind speed for all the stations, with linear coefficients ‘a’ directly proportional to height AGL. Finally, the values of Weibull shape parameter (k) were found to be independent of height AGL, while that of scale parameter (c) varying with height.

HYBRID SOLAR AIR-CONDITIONING SYSTEM

The study utilized wind speed measurements made at three heights and the Weibull parameters to study the wind speed characteristics and assess the wind power potential of seven sites in Saudi Arabia. Weibull shape and scale parameters were estimated using maximum likelihood method. These parameters were found to fit the actual wind frequency distributions with acceptable coefficient of determination (>0.95) for all the sites considered in this study. The annual mean wind speed varied between 4.30 m/s and 5.9 m/s at 40 m above ground level corresponding to Gassim and Dhulom data collection stations. The local wind shear exponent calculated using measured wind speed values at 20, 30, and 40 m and the power law were established for future use and were found to vary from 0.06 to 0.34 corresponding to Gassim and Yanbo, respectively. The Weibull shape and scale parameters increased more at 30 m compared to at 40 m with increase in height from 20 to 30 m and 30 to 40 m. No regular monthly trends could be detected whereas monthly mean wind speed, shape, and scale parameters, most probable wind speed, and maximum energy carrying wind speed was concerned. The most windy sites (Dhulom, Arar, Juaymah, Rawdat Ben-Habbas, and Dhahran) were suggested for wind power development in Saudi Arabia.

Wind power potential assessment for seven buoys data collection stations in Aegean Sea using Weibull distribution function

An experimental study was made to obtain heat transfer data for a two-pass rectangular channel (aspect ratio=2:1) with smooth and ribbed surfaces for two channel orientations (90 deg and 135 deg with respect to the plane of rotation). The V-shaped ribs are placed on the leading and trailing surfaces. Five different arrangements of 45 deg V-shaped ribs are studied. The Reynolds number and rotation number ranges are 5000-40000, and 0.0-0.21, respectively. The rib height to hydraulic diameter ratio (e/D) is 0.094; the rib pitch-to-height ratio (P/e) is 10; and the inlet coolant-to-wall density ratio (Δρ/ρ) is maintained around 0.115 for every test

Assessment of wind power, wind exponent, local air density and air turbulence intensity for an isolated site

The hybrid solar air-conditioning system includes an air intake having an air drying system that uses a liquid desiccant to dry ambient air, a desiccant regeneration system that uses a heat exchanger having oil heated by solar energy to remove water from the desiccant, an indirect evaporative air conditioner that uses an air-air heat exchanger to cool the dried air indirectly with evaporatively cooled air, a distilled water recovery system to recover water from the desiccant and from the evaporatively cooled air in the form of distilled water, and a microprocessor-based controller to control room temperature and relative humidity, and to regulate air intake and the flow of desiccant and oil in the system. The hybrid system enables the use of evaporative cooling in regions having high humidity.