Mohammad O. Hamdan

Enhancing heat transfer in parallel-plate channels by using porous inserts

Abstract In the present work, transient forced convection in the developing region of parallel-plate ducts is numerically investigated. A high-thermal conductivity porous substrate is attached to the inner wall of one plate in order to enhance the heat transfer characteristics of the flow under consideration. The Darcy–Brinkman–Forchheimer model is used to model the flow inside the porous domain. The present study reports the effect of several operating parameters on the flow hydrodynamics and thermal characteristics. Mainly, the current study demonstrates the effects of porous layer thickness, Darcy number, thermal conductivity ratio, and microscopic inertial coefficient on the thermal performance of the present flow. It is found that the highest Nusselt Number is achieved at fully porous duct. Results show that for Darcy number less than 10−4, the effect of microscopic inertial coefficient can be eliminated while for large microscopic inertial coefficient, higher than 103, the effect of Darcy number is observed to be insignificant. Heat transfer can be enhanced by: (1) using high thermal conductivity inserts, (2) decreasing Darcy number, and (3) increasing microscopic inertial coefficient. Also, the study shows that in the developing region, Darcy number and microscopic inertial coefficient have higher effect on the thermal and hydrodynamic behavior of the flow than that in the fully developed region.

Enhancing forced convection by inserting porous substrate in the core of a parallel‐plate channel

Investigates numerically the mechanism of enhancing heat transfer by using porous substrate. The numerical investigation is carried out for transient forced convection in the developing region of a parallel‐plate channel partially filled with a porous medium. A porous substrate is inserted in the channel core in order to reduce the boundary layer thickness and hence, enhance heat transfer. Darcy‐Brinkman‐Forchheimer model is used to simulate the physical problem. Results of the current model show that the existence of the porous substrate may improve the Nusselt number at the fully developed region by a factor of four and even higher depending on the value of Darcy number. It is found that the maximum Nusselt number is achieved at an optimum thickness. Also, the study shows that partially filled channels have better thermal performance than the totally filled ones. However, there is an optimum thickness of porous substrate, beyond it the Nusselt number starts to decline.

Measurement and Modeling of Confined Jet Discharged Tangentially on a Concave Semicylindrical Hot Surface

The paper investigates experimentally and numerically the heat transfer augmentation from a semicircular heated surface due to confined slot-jet impingement. For different Reynolds numbers, the average and local Nusselt numbers are calculated by reporting the heater thermal image obtained by an infrared camera, the inlet and outlet flow temperature via thermocouples, the flow rate via rotameter, and the pressure drop across the inlet and outlet flow via pressure transducers. The single enclosed jet flow is used to create a single cyclone inside the internal semicircular channel to promote the heat transfer at different jet Reynolds numbers (Rejet = 1000–5000). Three turbulence models, namely, the standard k – ɛ, k – ω and the Reynolds stress model (RSM) have been investigated in the present paper by comparing Nusselt number and normalized pressure drop distribution against the experimental data, helping ascertain on the relative merits of the adopted models. The computational fluid dynamics results show that the RSM turbulent model reasonably forecast the experimental data.

Diesel Engine Performance and Emission Under Hydrogen Supplement

This experimental study reports the behavior of diesel engine while being supported by hydrogen supplement. Hydrogen supplement is added through the air intake manifold at the atmosphere condition (0 °C and 101.325 kPa). The study reports the hydrogen supplement effect on the combustion characteristics, engine performance, emission and fuel consumption. The hydrogen supplement is varied by increment of 2 LPM while keeping the engine under fixed output power condition (torque of 14.7 N-m and speed of 1,100 rpm). In order to keep the engine output power fixed, the diesel fuel consumption is reduced and the hydrogen fuel consumption e hydrogen flow rate. For same power condition (torque and speed), the study shows that hydrogen can be used to reduce diesel fuel consumption however this comes on the expense of increasing of NOx emission. The main finding of this study is that compression engine with hydrogen supplement and diesel as the primary fuel starts knocking when hydrogen form 34 % the output power contribution (or 19 % as mass ratio between hydrogen to diesel).

Feasibility of Vortex Tube Air-Conditioning System

This paper investigates the feasibility of using vortex tube as air-conditioning device. Series of experiments are conducted to evaluate the design parameters and calculate the performances of counter-flow Ranque–Hilsch vortex tube (RHVT). The study is conducted for different inlet pressures conditions, number of nozzle inlets, vortex chamber depth and thermal insulation condition. The vortex tube performance is investigated by measuring temperatures, pressures and mass flow rates for the inlet and hot/cold exits. It is found that vortex tube has very coefficient of performance which make it inadequate to compete with conventional air conditioning system.Copyright

Analytical Thermal Analysis of Solar Chimney Power Plant

An analytical model and a thermodynamics study of the steady airflow inside a solar chimney are performed in this paper. A simplified Bernoulli equation combined with fluid dynamics and ideal gas equation are modeled and solved using EES solver to predict the performance of a solar chimney power plant. The analytical model is validated against an experimental and numerical data available in the literature. The developed analytical model is used to evaluate the effect of geometric parameters on the solar plant power generation. The analysis is showing that the height and diameter of the tower are the most important physical variables for the solar chimney design. The collector area has minimal effect on second-law efficiency but strong effect on harvested energy. The second law efficiency has non-monotonic relation with the turbine head.Copyright

Solar air-conditioning: Case study of solar absorption versus photovoltaic vapor compression systems

Due to recent research and development activities in solar-based air-conditioning systems, the GCC engineering community has been investigating alternative solutions to assess the feasibility towards adopting solar absorption refrigeration as a sustainable air-conditioning approach in hot environments. This study investigates the feasibility of two solar air-conditioning technologies, namely solar thermal absorption refrigeration and photovoltaic vapor compression technologies. Based on commercially available efficiencies of solar collectors and photovoltaic panels, this case study indicates that photovoltaic vapor compression air-conditioning systems have higher coefficient of performance and require smaller surface area when compared to solar thermal absorption refrigeration systems.

Numerical and experimental analysis of a heat-pipe-embedded printed circuit board for solid state lighting applications

ABSTRACT Thermal management is one of the main issues for electronics cooling especially for tightly packaged PCBs that experience local heat generation. Thus, theoretical and experimental investigations have been conducted to predict thermal performance of a novel heat-pipe-embedded-PCB. First, plain heat-pipe is experimentally tested under various inclination angles and validated by theoretical and numerical calculations. Flattened heat-pipes have been embedded into PCB prototypes made of polymer and aluminum and have been tested for similar experimental parameters; they have shown a decrease in compared with conventional heat pipe. Accordingly, reduction of approximately 50% is achieved for both embedded PCB prototypes.

Numerical Investigation of Solar Chimney Power Plant in UAE

This paper presents a numerical simulation results for a steady air flow inside a solar chimney power plant. A standard k-epsilon turbulence model is used to model a prototype solar chimney that was built in Al Ain in UAE. The chimney tower has height of 8.25 m and 24 cm diameter which is used to draw air from a solar collector that cover 100 m2 area. The CFD analysis is used to determine the location of the turbine using available power quantity. The CFD data shows that the collector height and chimney size is highly affecting each other. In the current design, the small chimney size has produced a stagnant zone inside the collector which has reduced the air flow rate inside the solar chimney. Also the CFD simulation shows that installing a nozzle at the entrance of the chimney is crucial parameter that affects the performance of the solar chimney and evidently reduces the pressure loss.

The Potential of Using Raw Jojoba Oil as Fuel in Furnaces

There is a constant need for coming up with new and alternative energy sources that are sustainable and at the same time environment friendly. Many research studies have already been conducted to fulfill the above target and addressed the use of plants-based oils in internal combustion engines. Less emphasis however was directed to the use of such oils in open combustion systems such as furnaces and boilers. The present study considers the potential of using green energy sources such as raw jojoba oil with minimal pretreatment as a sole fuel or alternatively as fuel supplements for furnaces. Blends of raw jojoba oil and diesel, with different proportions were burned in a small cylindrical furnace under different air flow conditions. The studied range of the jojoba oil proportions (on mass basis) in the liquid blends is from 20 to 60 %. More jojoba in the liquid mixture showed difficulty in sustaining a self-supporting flame due to the low volatility and high viscosity of raw jojoba oil. Moreover, the performance of the furnace with 20 % jojoba in the liquid fuel mix shows only small difference from performance on Diesel only. This suggests that about 20 % of Diesel can be replaced with raw jojoba with no significant loss of the thermal performance. More unburned species are emitted as the jojoba content in the fuel blend increases.