N.H. Shuaib

Numerical Study of Fluid Dynamic and Heat Transfer in a Compact Heat Exchanger Using Nanofluids

Compact heat exchangers (CHEs) are characterized by a high surface area per unit volume, which can result in a higher efficiency than conventional heat exchangers. They are widely used in various applications in thermal fluid systems including automotive thermal fluid systems such as radiators for engine cooling systems. Recent development of nanotechnology brings out a new heat transfer coolant called “nanofluids,” which exhibit larger thermal properties than conventional coolants due to the presence of suspended nanosized composite particles in a base fluid. In this study, a numerical investigation using different types of nanoparticles in ethylene glycol-base fluid namely copper (Cu), diamond (DM), and silicon dioxide (SiO2) on automobile flat tube plate-fin cross-flow CHE is explored. The nanoparticles volume fraction of 2% is considered for all types of nanofluids examined in this study. The three-dimensional (3D) governing equations for both liquid flow and heat transfer are solved using a standard finite volume method (FVM) for the range of Reynolds number between 4000 and 7000. The standard 𝜅-𝜀 turbulence model with wall function is employed. The computational model is used to study the variations of shear stress, skin friction, and convective heat transfer coefficient. All parameters are found to yield higher magnitudes in the developing and developed regions along the flat tubes with the nanofluid flow than base fluid. The pressure drop is slightly larger for nanofluids but insignificant at outlet region of the tube. Hence, the usage of nanofluids in CHEs transfers more energy in a cost-effective manner than using conventional coolants.

The Effect of Geometrical Parameters on Heat Transfer Characteristics of Compact Heat Exchanger with Louvered Fins

Compact heat exchangers (CHEs) have been widely used in various applications in thermal fluid systems including automotive thermal management systems. Among the different types of heat exchangers for engine cooling applications, cross-flow CHEs with louvered fins are of special interest because of their higher heat rejection capability with the lower flow resistance. In this study, the effects of geometrical parameters such as louver angle and fin pitch on air flow and heat transfer characteristics on CHEs are numerically investigated. Numerical investigations using five different cases with increased and decreased louver angles (

Thermal and hydrodynamic performance analysis of circular microchannel heat exchanger utilizing nanofluids

Purpose – The purpose of this paper is to investigate numerically the thermal and hydrodynamics performance of circular microchannel heat exchanger (CMCHE) using various nanofluids.Design/methodology/approach – The three‐dimensional steady, laminar developing flow and conjugate heat transfer governing equations of a balanced MCHE are solved using finite volume method.Findings – The results are shown in terms of temperature profile, heat transfer coefficient, pressure drop, wall shear stress, pumping power, effectiveness and performance index. The addition of nanoparticles increased the heat transfer rate of the base fluids. The temperature profiles of the fluids have revealed that higher average bulk temperatures were obtained by the nanofluids compared to water. The addition of nanoparticles also increased the pressure drop along the channels slightly. The increase in nanoparticle concentrations yielded better heat transfer rate while the increase in Reynolds number decreased the heat transfer rate.Resea...

Impact of tangential burner firing angle on combustion characteristics of large scale coal-fired boiler

Combustion characteristics in large scale boilers are influenced by a number of factors such as coal properties and burner operating conditions. Burner firing angle for example, will affect the fireball size and locations of heat release which affect the formation of ash slagging in a tangentially fired furnace. In this study, a computational fluid dynamics (CFD) simulation of coal combustion in a tangentially fired 700 MW power plant was developed to investigate the impact of burner firing angles on the flame profile in the furnace. The model was developed based on the two-phase flow model, coal devolatilization, char burnout model, discrete particle tracking and radiation heat transfer. The firing angles were changed by ±5° from the base angle of 43° and 55°. The study shows that firing angles have significant effect on the size of the flame fireball and the concentric fireball arrangement. Increasing the firing angle resulted in a larger fireball size with a region of low temperature at the core of the fireball. The simulation also shows that the flow profile becomes more stable with increasing firing angle, regardless of burner elevations. The results presented in this paper may enhance the understanding the complex relation between burner operating condition such as firing angle on flow patterns and combustion processes in a tangentially fired boilers.

Pressure drop and friction factor for different shapes of microchannels

A numerical investigation has been performed on the pressure drop and friction factor of water flow in three different shapes of microchannel heat sinks which are rectangular, trapezoidal, and triangular for Reynolds number range of 100–1000. The three-dimensional steady, laminar flow and heat transfer governing equations are solved using the finite volume method. It is found that the values of Poiseuille number and friction factor depend greatly on different geometrical parameters. It is also inferred that the heat sink having the smallest hydraulic diameter for each type of shapes under consideration has better performance among the other heat sinks studied. The values of Poiseuille number and friction factor increase with the increase of width-height ratio (Wc/Hc) for rectangular microchannels. For trapezoidal microchannels, the Poiseuille number and friction factor increase with the increase of bottom-to-top width ratio (b/a), increase with the decrease of height-to-top width ratio (h/a), increase with the decrease of length-to-hydraulic diameter ratio (L/Dh). While for triangular microchannels, the Poiseuille number and friction factor increase with the increase of its tip angle (β). It is identified that the transition Reynolds number from laminar flow to turbulent flow is occurred at 1100.

Heat Transfer Enhancement in Microchannel Heat Sink Using Nanofluids

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Experimental performance evaluation of short duration high speed flow shock tunnel

This paper describes the experimental procedure to evaluate the performance of short duration high speed flow shock tunnel located at the Universiti Tenaga Nasional “UNITEN”. The experimental work includes measurements of pressure, peak pressure, shock strength and shock speed. Physical description of the facility along with the principle of operation is presented. The pressure history of flow process was captured using fast response pressure transducer mounted at three stations located at the end of the facility. The measurements were performed using two different driver/driven gas combination. The first one is Air-Air while the second one was Helium-Air. The results of two combinations were compared and analyzed. The results show that the facilitys performance is highly influenced the gas combination. The results provide very good estimate for the above mentioned parameters obtained after diaphragm rupture and also provide better understanding of the parameters that affect the performance of the facility.

Numerical Investigation on the Nanofluid Flow and Heat Transfer in a Wavy Channel

In this article, laminar convective heat transfer of copper-water nanofluid in isothermally heated wavy -wall channel is numerically investigated. The governing continuity, momentum and energy equations in body-fitted coordinates are discretized using finite volume approach and solved iteratively using SIMPLE algorithm. The study covers Reynolds number and nanoparticle volume concentration in the ranges of 100–800 and 0–5 % respectively. The effects of nanoparticles volume concentration and Reynolds number on velocity and temperature profiles, the local Nusselt number, the local skin-friction coefficient, average Nusselt number, pumping power and heat transfer enhancement are presented and analyzed. Results show that there is a significant enhancement in heat transfer by addition of nanoparticles. This enhancement increase with concentration of particles but the required pumping power also increases. The present results display a good agreement with the literature.

Experimental Analysis and FEM Simulation of Novel Finned Loop Heat Pipe

Experiments are conducted to investigate heat transfer characteristics of finned loop heat pipe (FLHP) for heat input range from 20 W to 100 W. The experiments are carried out by manufacturing the FLHP, which the setup consists of a water tank with pump, a flat evaporator, condenser installed with two pieces of fans and air flow fins, two transportation lines (vapor and liquid lines), copper pipe sections for attachment of the thermocouples and power supply. The unique of the current experimental setup is the vapor and liquid lines of FLHP are made of transparent plastic tube to visualize the fluid flow patterns. In this study, the total thermal resistance (Rt) is estimated for both natural and forced convection modes under steady state condition, by varying the air velocity from 2 m/s to 10 m/s. The coolant velocity and heat input to achieve minimum Rtare found out and the corresponding effective thermal conductivity is calculated. The transient temperature distribution in the FLHP is also observed. The experimental observations are verified by simulation using Finite Element Method (FEM). The results reveal that the air velocity and power input have significant effects on the performance of FLHP. As the heat input and air velocity increase, total thermal resistance decreases.

Flow and heat distribution analysis of different transformer sub-stations

This paper describes CFD investigation on the flow and heat transfer in transformers at different sub-station buildings. The analysis aimed to determine the cooling capability of the existing transformer building employing natural ventilation system to dissipate heat sufficiently when new dry-type transformer operating under full load condition is used. The transformer and building models were developed based on the actual transformer configuration in operation at three different locations in Malaysia. The calculation was carried out on three different types of sub-stations namely stand-alone, attach-to-building and underground. The effect of natural ventilation speed and building volume on the transformer surfaces temperature are also investigated. It was predicted that the existing sub-station configuration is able to dissipate heat produced from the dry type transformer by using its natural ventilation system regardless of the sub-station types. However, the smallest building case shows relatively high surrounding temperature.