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A three-dimensional laminar flow model was used for 37 Reynolds numbers (0.1, 0.2…1, 2…10, 20…100, and 200…1000) through six rectangular microchannels (aspect ratios: 1, 0.75, 0.5, 0.25, 0.2, and 0.125) to develop correlations for hydrodynamic entrance length. The majority of the Reynolds numbers are in the low regime (Re

The objective of this study is to experimentally characterize and compare the performance of a nanofluid comprised of Al2O3 nanoparticles with 1% volumetric concentration in a 60% ethylene glycol/40% water (60% EG) solution to that of 60%EG in a liquid to air heat exchanger. The test bed used in the experiment was built to simulate a small air handling system typical of that used in HVAC applications. Previously established empirical correlations for thermophysical properties of fluids were used to determine the values of various parameters (e.g. Nusselt number, Reynolds number, and Prandtl number). The testing shows that the 1% Al2O3 nanofluid generates a marginally higher rate of heat transfer than the 60% EG under certain conditions. At Re = 3000, the nanofluid produced a rate of heat transfer that was 2% higher than that of the 60% EG. The empirically determined Nusselt number associated with the convection in the coil tubing for the nanofluid follows the behavior predicted by the Dittus-Boelter correlation (R2 = 0.97), while the empirically determined Nusselt number for the 60% EG follows the Petukhov correlation similarly (R2 = 0.97). Pressure loss and hydraulic power for the nanofluid were higher than for the base fluid over the range of conditions tested. The exergy destroyed in the heat exchange and fluid flow processes were between 9% and 12% lower for the nanofluid than the base fluid over the tested range of Reynolds numbers.

Experimental study has been carried out to determine the thermal conductivity of five different nanofluids containing aluminum oxide, copper oxide, zinc oxide, silicon dioxide and titanium dioxide nanoparticles dispersed in a base fluid of 60:40 (by mass) propylene glycol and water mixture. The effect of particle volumetric concentration up to 6% was studied with temperatures ranging from −30° to 90 °C. Experiments showed an increase in thermal conductivity of nanofluids with increasing concentration and temperature. The thermal conductivity of nanofluids showed a strong dependence on particle volumetric concentration, particle size, properties of particles and the base fluid and temperature. Several existing theoretical models for thermal conductivity of nanofluids were compared with the experimental data, but they all showed disagreement. From comparisons, the most agreeable model was selected and a curve-fit constant was derived to match the data of propylene glycol nanofluids. This model expresses the thermal conductivity of nanofluids as a function of Brownian motion, Biot number, fluid temperature, particle volumetric concentration, and the properties of the nanoparticles and the base fluid. This model provided good agreement with 600 experimental data points obtained from five different nanofluids with an average absolute deviation of 1.79 percent. Because of the enhanced thermal conductivity with increasing temperature, nanofluids should be more beneficial at higher temperature applications.

This paper presents the specific heat measurements of five different nanofluids containing aluminum oxide (Al2O3), zinc oxide (ZnO), copper oxide (CuO), titanium oxide (TiO2) and silicon dioxide (SiO2) nanoparticles dispersed in a base fluid of 60% propylene glycol and 40% water by mass (60:40 PG/W). The measurements were carried out over a temperature range of −30 to 90 °C, for nanoparticle volumetric concentrations of 0.5% to 6% and for average particle sizes ranging from 15 to 76 nm to evaluate their effects on the specific heat. From comparison, it was found that the existing specific heat correlations were not able to predict the measured experimental values. Therefore, a new correlation was developed to predict the specific heat of measured nanofluids. This new correlation is in good agreement with 610 experimental data points of the five nanofluids with a maximum deviation of −5% exhibited by the Al2O3 nanofluid and an average deviation of −0.094%, considering all five nanofluids.

Surface tension measurements were performed on four nanofluids containing aluminum oxide (Al 2 O 3 ), zinc oxide (ZnO), titanium dioxide (TiO 2 ) and silicon dioxide (SiO 2 ) nanoparticles suspended in a base fluid of 60% propylene glycol and 40% water by mass (60:40 PG/W). First, benchmark tests for the surface tension of water were performed, for which accurate data are available in the published literature. Measured data agreed well with the published data confirming the accuracy of the apparatus, as well as the experimental procedure. Following the benchmark tests, measurements were performed on nanofluids over a temperature range of 30 °C to 70 °C for particle volumetric concentrations ranging from 0 to 6 % and particle sizes in the range of 15–50 nm. From the experimental data, it was observed that the surface tension of nanofluids decreased with an increase in temperature. At a constant temperature, an increase in the particle volumetric concentration of a nanofluid caused a decrease in the surface tension. For nanofluids at fixed volumetric concentration and temperature, the surface tension was found to be lower for smaller particle sizes except the ZnO nanofluid. A statistical analysis performed on the experimental data yielded a single correlation valid for all the nanofluids tested. This surface tension correlation is a function of temperature, volumetric concentration and the size of the nanoparticles, which predicts results successfully with an average deviation of 2.6% from the measured values.

Contact angle measurements were performed on deionized water, propylene glycol and mixture of 60% propylene glycol and 40% water by mass (60:40 PG/W), over a temperature range of 25 °C to 40 °C. All measurements were performed on the surface of a glass slide at the solid–fluid–air-interface. After confirming the contact angle value of water with the data of other researchers, the same procedure was applied to four nanofluids (nanoscale particles dispersed in a base fluid) containing aluminum oxide (Al2O3), zinc oxide (ZnO), titanium dioxide (TiO2) and silicon dioxide (SiO2) nanoparticles dispersed in 60:40 PG/W. For the nanofluids, the particle volumetric concentrations were varied from 0 to 6% and the average particle sizes ranged from 15 to 50 nm. From the experimental data, it was observed that the contact angles of three single phase liquids and four nanofluids were less than 90°, indicating that all these fluids were wetting to the glass surface. The contact angles of all tested fluids exhibited a continuous decrement with an increase in temperature, and a linear equation for contact angle with temperature matched the data well. For the nanofluids, an increase in the particle volumetric concentration caused a decrease in the contact angle at a constant temperature. The variation of the contact angle followed a second order polynomial relation with the volumetric concentration. For nanofluids at the same volumetric concentration and the same temperature, the contact angles were observed to be lower for larger particle sizes, except for the ZnO nanofluid. A statistical analysis performed on the experimental data yielded a correlation suitable to represent all the nanofluids tested. This contact angle correlation is a function of temperature, volumetric concentration and the size of the nanoparticles, which predicts results successfully with an average deviation of 6.3% from the measured values.

A three-dimensional turbulent flow and heat transfer of two different nanofluids, containing aluminum oxide (Al2O3) and copper oxide (CuO) nanoparticles, dispersed in ethylene glycol and water mixture (EG/W) in the flat tubes of an automotive radiator have been numerically studied to evaluate their performance. Computations have been carried out for nanoparticles volumetric concentrations up to 6% and over a Reynolds number range typically encountered in automobile radiators. Appropriate correlations for density, viscosity, specific heat and thermal conductivity of nanofluids as a function of particle volume concentration and temperature, developed from experiments have been used in this study. Numerical results have been first validated for the flow of single phase liquids, such as water and EG/W by comparing the computed values of Nusselt number and friction factor with those given by accurate correlations available in the literature. Inside the flat tube continuous reductions in the local heat transfer coefficient and wall shear stress are observed around the periphery of the flat tube, starting from the mid-point of the flat-wall and proceeding to the center of the curved wall. For the same Reynolds number, computations with nanofluids show an increase of friction factor and heat transfer coefficient with an increase in the particle volume concentration. The study reveals that under the basis of equal pumping power, Al2O3 and CuO nanofluids up to 3% and 2% particle volumetric concentrations respectively provide higher heat transfer coefficients than that of the base fluid. From the present study, several new correlations to determine the Nusselt number and friction factor for the nanofluids flowing in the flat tubes of a radiator have been proposed for the entrance as well as the fully developed regions.

In this study the pH levels of aluminum oxide (Al2O3), silicon dioxide (SiO2), and zinc oxide (ZnO) nanoparticles dispersed in propylene glycol and water mixture were measured in the temperature range of 0°C to 90°C. The volumetric concentration of nanoparticles in these fluids ranged from 0 to 10% for different nanofluids. The average particle sizes (APS) considered were from 10 nm to 70 nm. The pH measuring apparatus and the measurement procedure were validated by measuring the pH of a calibration fluid, whose properties are known accurately. The measured pH values agreed within less than ±0.5% with the published data reported by the manufacturer. Following the validation, the pH values of different nanofluids were measured. The measurements showed that pH of nanofluids decreased with an increase in temperature and increased with an increase in particle volumetric concentration. For the same nanofluid at a fixed volumetric concentration, the pH was found to be higher for larger particle sizes. From the ...

Three nanofluids comprising of aluminum oxide, copper oxide and silicon dioxide nanoparticles in ethylene glycol and water mixture have been studied theoretically to compare their performance in a compact minichannel plate heat exchanger (PHE). The study shows that for a dilute particle volumetric concentration of 1%, all the nanofluids show improvements in their performance over the base fluid. Comparisons have been made on the basis of three important parameters; equal mass flow rate, equal heat transfer rate and equal pumping power in the PHE. For each of these cases, all three nanofluids exhibit increase in convective heat transfer coefficient, reduction in the volumetric flow rate and reduction in the pumping power requirement for the same amount of heat transfer in the PHE. On the cold fluid side of the heat exchanger, a coolant, HFE-7000, has been studied, which has the potential for application in extremely low temperatures, but has not been investigated widely in the literature. Experimental data measured from a minichannel PHE in a test loop using water as the base fluid have validated the test apparatus with excellent agreement of predicted heat transfer rate and the overall heat transfer coefficient with the experimental values. From experiments on a 0.5% aluminum oxide nanofluid, preliminary correlations for the Nusselt number and the friction factor for nanofluid flow in a PHE has been derived. This apparatus will be useful to test different kinds of nanofluids to ultimately determine the effects of parameters such as: volumetric concentration, particle size and base fluid properties on thermal and fluid dynamic performance of nanofluids in compact heat exchangers.

Density measurements were performed on several nanofluids containing nanoscale particles of aluminum oxide (Al2O3), zinc oxide (ZnO), copper oxide (CuO), titanium oxide (TiO2), and silicon dioxide (SiO2). These particles were individually dispersed in a base fluid of 60:40 propylene glycol and water (PG/W) by volume. Additionally, carbon nanotubes (CNTs) dispersed in de-ionized water (DI) was also tested. Initially, a benchmark test was performed on the density of the base fluid in the temperature range of 0–90 °C. The measured data agreed within a maximum error of 1.6% with the values presented in the handbook of American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). After this validation run, the density measurements of various nanofluids with nanoparticle volumetric concentrations from 0 to 6% and nanoparticle sizes ranging from 10 to 76 nm were performed. The temperature range of the measurements was from 0 to 90 °C. These results were compared with the values predicted by a currently acceptable theoretical equation for nanofluids. The experimental results showed good agreement with the theoretical equation with a maximum deviation of −3.8% for copper oxide nanofluid and average deviation of −0.1% for all the nanofluids tested.

The Prandtl number, Reynolds number and Nusselt number are functions of thermophysical properties of nanofluids and these numbers strongly influence the convective heat transfer coefficient. The pressure loss and the required pumping power for a given amount of heat transfer depend on the Reynolds number of flow. The thermophysical properties vary with temperature and volumetric concentration of nanofluids. Therefore, a comprehensive analysis has been performed to evaluate the effects on the performance of nanofluids due to variations of density, specific heat, thermal conductivity and viscosity, which are functions of nanoparticle volume concentration and temperature. Two metallic oxides, aluminum oxide (Al2O3), copper oxide (CuO) and one nonmetallic oxide silicon dioxide (SiO2), dispersed in an ethylene glycol and water mixture (60:40 by weight) as the base fluid have been studied.

This paper presents new correlations for the convective heat transfer and the friction factor developed from the experiments of nanoparticles comprised of aluminum oxide, copper oxide and silicon dioxide dispersed in 60% ethylene glycol and 40% water by mass. The experimental measurements were carried out in the fully developed turbulent regime for the aforementioned three different nanofluids at various particle volumetric concentrations. First, the rheological and the thermophysical properties such as viscosity, density, specific heat and thermal conductivity were measured at different temperatures for varying particle volume concentrations. Next, these properties were used to develop the heat transfer coefficient correlation from experiments, as a function of these properties and the particle volumetric concentration. The pressure loss was also measured and a new correlation was developed to represent the friction factor for nanofluids.

A three-dimensional laminar flow and heat transfer with two different nanofluids, Al 2 O 3 and CuO, in an ethylene glycol and water mixture circulating through the flat tubes of an automobile radiator have been numerically studied to evaluate their superiority over the base fluid. New correlations for viscosity and thermal conductivity of nanofluids as a function of particle volumetric concentration and temperature developed from the experiments have been used in this paper. Numerical results from the present simulation were first validated for the flow of water by comparing the friction factor and the Nusselt number in flat tubes, for which accurate results are available in the literature. Next, the model was applied to study the peripheral variations of shear stress and convective heat transfer coefficient, both showing higher magnitudes in the flat regions of the tube. Convective heat transfer coefficient in the developing and developed regions along the flat tubes with the nanofluid flow showed marked improvement over the base fluid. Results for the local and the average friction factor and convective heat transfer coefficient show an increase with increasing particle volumetric concentration of the nanofluids. Quantitative results of the increase of the heat transfer coefficient and the friction factor with increasing volumetric concentrations of nanofluids at various Reynolds numbers are presented. The pressure loss increases with increasing particle volumetric concentrations of nanofluids; however, due to the reduced volumetric flow needed for the same amount of heat transfer, the required pumping power diminishes.

Theoretical investigations on the application of nanofluids in the hydronic heating system of buildings have been presented in this paper. Realistic fluid velocities and temperatures employed in heat exchange equipment were used to compare the convective heat transfer coefficient and the pumping power requirement of nanofluids of various particle volume concentrations. The base fluid used in the analyses as a basis for comparison was a solution comprised of 60% ethylene glycol and 40% water (by weight). The thermophysical and heat transfer performance of the base fluid have been compared with copper oxide nanoparticles dispersed in the same base fluid with volumetric particle concentration ranging up to 4%. First, the variations of thermophysical properties such as viscosity, thermal conductivity, specific heat and density have been evaluated for different concentrations. Using these properties, several plots have been developed for quantitatively determining the enhancement of convective heat transfer coefficient as a function of flow velocity, Reynolds number and the nanoparticle volumetric concentration. For constant Reynolds number for flow in tubes, the Nusselt number and convective heat transfer coefficient increases as nanoparticle volume concentration increases. As the properties of nanofluids and the base fluid are temperature dependent, we have performed calculations for two fluid temperatures (323 K and 360 K). The results show that a higher convective heat transfer coefficient is achieved at higher temperatures for a nanofluid of equal concentration circulating at equal velocity. Frictional pressure loss and pumping power increases relative to the base fluid with particle volume concentration, but decreases with mean fluid temperature.

The performance of hydronic finned-tube heating units with nanofluids is compared to their performance with a conventional heat transfer fluid comprised of 60% ethylene glycol and 40% water, by mass (60% EG) using a mathematical model. The nanofluids modeled are comprised of either CuO or Al2O3 nanoparticles dispersed in the 60% EG solution. The finned tube configuration modeled is similar to that commonly found in building heating systems. The model employs correlations for nanoparticle thermophysical properties and heat transfer that have been previously documented in the literature. The analyses indicate that finned tube heating performance is enhanced by employing nanofluids as a heat transfer medium. The model predicts an 11.6% increase in finned-tube heating output under certain conditions with the 4% Al2O3/60% EG nanofluid and an 8.7% increase with the 4% CuO/60% EG nanofluid compared to heating output with the base fluid. The model predicts that pumping power required for a given heating output with a given finned tube geometry is reduced with both the Al2O3/60% EG and the CuO/60% EG nanofluids compared to the base fluid. The finned tube with 4% Al2O3/60% EG has the lowest liquid pumping power at a given heating output of all the fluids modeled.

This paper presents nanofluid convective heat transfer and viscosity measurements, and evaluates how they perform heating buildings in cold regions. Nanofluids contain suspended metallic nanoparticles, which increases the thermal conductivity of the base fluid by a substantial amount. The heat transfer coefficient of nanofluids increases with volume concentration. To determine how nanofluid heat transfer characteristics enhance as volume concentration is increased; experiments were performed on copper oxide, aluminum oxide and silicon dioxide nanofluids, each in an ethylene glycol and water mixture. Calculations were performed for conventional finned-tube heat exchangers used in buildings in cold regions. The analysis shows that using nanofluids in heat exchangers could reduce volumetric and mass flow rates, and result in an overall pumping power savings. Nanofluids necessitate smaller heating systems, which are capable of delivering the same amount of thermal energy as larger heating systems using base fluids, but are less expensive; this lowers the initial equipment cost excluding nanofluid cost. This will also reduce environmental pollutants because smaller heating units use less power, and the heat transfer unit has less liquid and material waste to discard at the end of its life cycle.

Experimental investigations have been carried out to study the rheological behavior of aluminum oxide nanofluid. Nanoparticles with average particle size of 53 nm were dispersed in a base fluid of 60% (by mass) of ethylene glycol and water. Nanofluids of volumetric concentrations 1 to 10% were tested for determining the viscous properties. It was found that this nanofluid behaved as non-Newtonian at lower temperatures (-35°C to 0°C) and Newtonian at higher temperatures (0°C to 90°C). The data showed that the viscosity increases with an increase in concentration and decreases with increase in temperature. Two new correlations were developed expressing viscosity as a function of temperature and concentration.

Experimental investigations have been carried out for determining the thermal conductivity of three nanofluids containing aluminum oxide, copper oxide and zinc oxide nanoparticles dispersed in a base fluid of 60:40 (by mass) ethylene glycol and water mixture. Particle volumetric concentration tested was up to 10% and the temperature range of the experiments was from 298 to 363 K. The results show an increase in the thermal conductivity of nanofluids compared to the base fluids with an increasing volumetric concentration of nanoparticles. The thermal conductivity also increases substantially with an increase in temperature. Several existing models for thermal conductivity were compared with the experimental data obtained from these nanofluids, and they do not exhibit good agreement. Therefore, a model was developed, which is a refinement of an existing model, which incorporates the classical Maxwell model and the Brownian motion effect to account for the thermal conductivity of nanofluids as a function of temperature, particle volumetric concentration, the properties of nanoparticles, and the base fluid, which agrees well with the experimental data.

Density measurements were performed on three different nanofluids containing aluminum oxide (Al2O3), antimony-tin oxide (Sb2O5:SnO2), and zinc oxide (ZnO) nanoparticles in a base fluid of 60:40 ethylene glycol/water by mass. First, a benchmark test for the density of the base fluid is presented showing excellent agreement with the data presented in the handbook of the American Society of Heating, Refrigerating, and Air Conditioning Engineers. Next, density measurements of the above-mentioned nanofluids over a temperature range of 0°C to 50°C for several particle volume concentrations are presented. These measured results were compared with a widely used theoretical equation and good agreements between the theoretical equation and measurements were obtained for the Al2O3 and Sb2O5:SnO2 nanofluids. However, the deviation was observed to be higher with the ZnO nanofluid and it increased with particle volume concentration.

Turbulent flow and heat transfer of three different nanofluids (CuO, Al2O3 and SiO2) in an ethylene glycol and water mixture flowing through a circular tube under constant heat flux condition have been numerically analyzed. New correlations for viscosity up to 10% volume concentration for these nanofluids as a function of volume concentration and temperature are developed from the experiments and are summarized in the present paper. In our numerical study, all the thermophysical properties of nanofluids are temperature dependent. Computed results are validated with existing well established correlations. Nusselt number prediction for nanofluids agrees well with Gnielinski correlation. It is found that nanofluids containing smaller diameter nanoparticles have higher viscosity and Nusselt number. Comparison of convective heat transfer coefficient of CuO, Al2O3 and SiO2 nanofluids have been presented. At a constant Reynolds number, Nusselt number increases by 35% for 6% CuO nanofluids over the base fluid.

Nanofluids comprised of silicon dioxide (SiO2) nanoparticles suspended in a 60:40 (% by weight) ethylene glycol and water (EG/water) mixture were investigated for their heat transfer and fluid dynamic performance. First, the rheological properties of different volume percents of SiO2 nanofluids were investigated at varying temperatures. The effect of particle diameter (20 nm, 50 nm, 100 nm) on the viscosity of the fluid was investigated. Subsequent experiments were performed to investigate the convective heat transfer enhancement of nanofluids in the turbulent regime by using the viscosity values measured. The experimental system was first tested with EG/water mixture to establish agreement with the Dittus-Boelter equation for Nusselt number and with Blasius equation for friction factor. The increase in heat transfer coefficient due to nanofluids for various volume concentrations has been presented. Pressure loss was observed to increase with nanoparticle volume concentration. It was observed that an incr...

This paper presents a study on nanofluids applications, such as a coolant in a diesel electric generator (DEG). Specific heat measurements of aluminum oxide nanofluid with various particle concentrations have been presented demonstrating a reduction in their values with an increase in the particle concentration and an increase with temperature. Experiments were performed on the DEG to assess the effect of nanofluids on cogeneration efficiency. The investigation showed that applying nanofluids resulted in a reduction of cogeneration efficiency. This is due to the decrease in specific heat, which influences the waste heat recovery from the engine. However, it was found that the efficiency of waste heat recovery heat exchanger increased for nanofluid, due to its superior convective heat transfer coefficient.

In this study, theoretical analyses have been performed to determine the feasibility of transporting gas-to-liquid (GTL) products through the Trans-Alaska Pipeline System (TAPS) using a non-Newtonian fluid flow approach. Due to heat loss, the fluid temperature decreases in the direction of flow, and this affects the fluid properties, which in turn influence the convection coefficient and pumping power requirements. This article presents fluid temperature and heat loss along the pipeline at different locations. Furthermore, this study includes calculations on the power required to pump GTL and crude oil/GTL mix. Parametric studies had been performed varying two parameters: wind velocity, to vary convection over the pipeline, and snow depth. Ambient air velocities of 0.45 m/s (1 mph), 4.47 m/s (10 mph), and 8.94 m/s (20 mph) have been considered. Snow depths of 0 m (0 ft), 0.305 m (1 ft), and 0.61 m (2 ft) have also been taken into account. These results show that the pumping power and heat loss fo...

Nanofluids are new kinds of fluids engineered by dispersing nanoparticles in base fluids. This paper presents an experimental investigation of rheological properties of copper oxide nanoparticles suspended in 60:40 (by weight) ethylene glycol and water mixture. Nanofluids of particle volume percentage ranging from 0% to 6.12% were tested. The experiments were carried over temperatures ranging from −35 °C to 50 °C to demonstrate their applicability in cold regions. For the particle volume concentrations tested, nanofluids exhibited Newtonian behavior. An experimental correlation was developed based on the data, which relates viscosity with particle volume percent and the nanofluid temperature.

There are many locations in the world where natural gas is abundant, but isolated from the transportation infrastructure. Research is currently underway to develop methods to convert the gas to liquid (GTL) and transport it to the market. For safe and efficient transportation of this GTL, researchers and engineers must know its properties. This article presents several correlations for viscosity, specific heat, and thermal conductivity of this GTL. Researchers are also considering transportation of GTL commingled with crude oil. Therefore, the properties of this commingled mixture are presented here as well. Data on how these properties vary with temperature is also presented in graphs; this information would be very useful for designing a method of transportation in extremely cold regions.

Measurements have been carried out for determining the viscosity of several nanofluids, in which different nanoparticles were dispersed in a base fluid of 60% propylene glycol (PG) and 40% water by mass. The nanoparticles were aluminum oxide (Al2O3), copper oxide (CuO), silicon dioxide (SiO2), titanium oxide (TiO2), and zinc oxide (ZnO) with different average particle diameters. Measurements were conducted for particle volume concentrations of up to 6% and over a temperature range of 243 K–363 K. All the nanofluids exhibited a Bingham plastic behavior at lower temperatures of 243 K–273 K and a Newtonian behavior in the temperature range of 273 K–363 K. Comparisons of the experimental data with several existing models show that they do not exhibit good agreement. Therefore, a new model has been developed for the viscosity of nanofluids as a function of temperature, particle volume concentration, particle diameter, the properties of nanoparticles, and those of the base fluid. Measurements were also conducted for single walled, bamboolike structured, and hollow structured multiwalled carbon nanotubes (MWCNT) dispersed in a base fluid of 20% PG and 80% water by mass. Measurements of these carbon nanotubes (CNT) nanofluids were conducted for a particle volume concentration of 0.229% and over a temperature range of 273 K–363 K, which exhibited a non-Newtonian behavior. The effect of ultrasonication time on the viscosity of CNT nanofluids was investigated. From the experimental data of CNT nanofluids, a new correlation was developed which relates the viscosity to temperature and the Péclet number.

A finite element scheme is presented to model the dissociation of gas hydrates in porous media by hot water injection. We show a complete derivation of the finite element formulation, including the associated mass and energy conservation equations capable of performing transient analysis of both conductive and convective heat transfer for gas and liquid flow in porous media. The scheme also includes the latent heat effect to accommodate the change of phase due to melting of hydrate. In the companion paper, Part II, this method is successfully applied to hydrate reservoirs.

A finite element model has been applied to the dissociation of gas hydrates in porous media by hot water injection. In the first step, it was applied to calculate the temperature and saturation profiles for a two-phase convective heat transfer case. The second step involved hydrate thawing calculations with release of water and gas. Realistic results were obtained in predicting the temperature, pressure, and water saturation profiles in the hydrate medium with respect to time, when subjected to hot water injection at high pressure in a wellbore. Furthermore, the thaw front progression calculated by this scheme exhibits stable and satisfactory behavior with respect to time.

Thermal models for cooling microscale electronic processor chips through forced and natural convection heat sinks are presented in this paper. This research is an extension of an earlier study where extensive analyses were done to develop necessary heat transfer equations for the heat sink of a Pentium III chip. Once the prediction of these model equations closely matched the performance of Pentium III heat sink, we applied them to a processor chip of micrometer scale. This led to the design of a miniaturized heat sink based upon a scaling procedure. In this heat sink, airflow was found to be in micron-size channels. Therefore, calculation of the Knudsen number was necessary to verify that the continuum theory still held for our designed microchannels. Analysis showed that heat dissipated from the heat sink, based upon forced convection over the fins, was 204 mW. We also considered radiation heat transfer from the sink, which gave a smaller value of 0.8 mW based upon an emissivity of 0.07. All analyses to this point were based upon analytical relations. Next we refined our analysis using the computational fluid dynamics code Fluent to obtain improved results. This yielded refined velocities, heat transfer coefficients and a total heat dissipation of 268 mW from microsize fins.

A finite-element scheme has been formulated, which is capable of solving transient analysis of both conductive and convective heat transfers due to fluid flow in porous media. The model also includes the latent heat effect to consider the phase change aspect of a frozen medium. To test the validity of the model, it was applied to six cases for which analytical solutions are available. The test cases cover (i) single-phase fluid flow through porous media, (ii) radial conduction with and without phase change, (iii) conductive and convective heat transfer in an aquifer, and (iv) two-phase immiscible flow in porous media. In all these cases, good agreement with analytical solutions are observed validating the computational scheme. This computational scheme should be useful in solving frozen ground problems, thermal stimulation technique for natural gas recovery from hydrates, and single-phase and two-phase convective heat transfer problems in enhanced oil recovery scheme in petroleum engineering.

An inner-variable integral theory was derived for solving incompressible two-dimensional turbulent boundary layers. This new derivation incorporated major improvements to the earlier inner-variable approach of White (1974) and Das and White (1986) by including a better wake function and a superior pressure gradient-wake correlation. Initially, the derivation from the first principle led to three nonlinear ordinary differential equations that must be solved simultaneously to yield important boundary layer parameters. Subsequently, to simplify the theory, it was systematically reduced in two steps: first to a two-equation method, and next to a one-equation method. Then comparisons were carried out among the three methods using well-established experimental data from a wide range of flows. The two-equation method gave the best overall performance and was selected as the standard method. Finally, it was tested against additional experiments, giving reliable predictions against eleven different experimental flows under diverse flow conditions.

Small hybrid rocket motors using solid propellant and gaseous oxidizer are becoming increasingly popular as a propulsion device. This paper describes the development of a one‐dimensional flow model for the design of a small rocket motor. Combustion of polyethylene as solid propellant with oxygen is used as a candidate hybrid fuel to test and evaluate the performance of this hybrid system. To assess the performance under different operating conditions, a computer program has been developed, which facilitates inputs to be varied and effects assessed. A system of governing equations is summarized in the main body of this paper and is numerically solved by the computer program. The results of the modelling are then used to design and build a small low‐cost rocket motor for experimental verification. Therefore, the materials presented herein could be used in the future design of hybrid rocket motors.

Gas-to-liquids (GTL) technology involves the conversion of natural gas to liquid hydrocarbons. In this article, theoretical studies have been presented to determine the feasibility of transporting GTL products through the Trans-Alaska Pipeline System (TAPS). To successfully transport GTL through TAPS, heat loss along the route must be carefully determined. This study presents heat transfer and fluid dynamic calculations to evaluate this feasibility. Because of heat loss, the fluid temperature decreases in the direction of flow and this affects the fluid properties, which in turn influence convection coefficient and pumping power requirements. The temperature and heat loss distribution along the pipeline at different locations have been calculated. Fairly good agreement with measured oil temperatures is observed. The powers required to pump crude oil and GTL individually, against various losses have been calculated. Two GTL transportation modes have been considered; one as a pure stream of GTL and...

This study compares the performance of three different nanofluids containing aluminum oxide, copper oxide, and silicon dioxide nanoparticles dispersed in the same base fluid, 60:40 ethylene glycol and water by mass, as coolant in automobile radiators. The computational scheme adopted here is the effectiveness-number of transfer unit (ε − NTU) method encoded in matlab. Appropriate correlations of thermophysical properties for these nanofluids developed from measurements are summarized in this paper. The computational scheme has been validated by comparing the results of pumping power, convective heat transfer coefficients on the air and coolant side, overall heat transfer coefficient, effectiveness and NTU, reported by other researchers. Then the scheme was adopted to compute the performance of nanofluids. Results show that a dilute 1% volumetric concentration of nanoparticles performs better than higher concentration. It is proven that at optimal conditions of operation of the radiator, under the same heat transfer basis, a reduction of 35.3% in pumping power or 7.4% of the surface area can be achieved by using the Al2O3 nanofluid. The CuO nanofluid showed slightly lower magnitudes than the Al2O3 nanofluid, with 33.1% and 7.2% reduction for pumping power or surface area respectively. The SiO2 nanofluid showed the least performance gain of the three nanofluids, but still could reduce the pumping power or area by 26.2% or 5.2%. The analysis presented in this paper was used for an automotive radiator but can be extended to any liquid to gas heat exchanger.

This paper presents an analytical optimization of a remote power system for a hypothetical Alaskan village. The analysis considers the potential of generating renewable energy (e.g., wind and solar), along with the possibility of using energy storage to take full advantage of the intermittent renewable sources available to these villages. Storage in the form of either compressed hydrogen or zinc pellets can then provide electricity from hydrogen or zinc–air fuel cells whenever wind or sunlight are low. The renewable system is added on to the existing generation system, which is based on diesel engines. Results indicate that significant reductions in fossil fuel consumption in these remote communities are cost effective using renewable energy combined with advanced energy storage devices. A hybrid energy system for the hypothetical village can reduce consumption of diesel fuel by about 50% with annual cost savings of about 30% by adding wind turbines to the existing diesel generators. Adding energy storage devices can further reduce fuel use, and depending on the economic conditions potentially reduce life-cycle costs. With optimized energy storage, use of the diesel gensets can be reduced to almost zero, with the existing equipment only maintained for added reliability. However, about one quarter of the original fuel is still used for heating purposes.

Rural Alaskan communities have special challenges to supply dependable heat and electric power while preserving environmental quality. To help address these issues in a coherent fashion, we have established an energy center at the University of Alaska Fairbanks. Initially, we will evaluate fuel cells and reformers in a test chamber, looking at both performance and reliability. Later, we will study the integration of the electric and other utilities and focus on arctic engineering issues. In designing the test chamber, we were confronted with a number of conflicting heat balance issues related to (1) additional heat for freeze protection and (2) removal of heat generated by people and equipment. This paper discusses some of the details of how we addressed these issues.

Experimental investigations were carried out for the determination of thermal conductivity of silicon dioxide (SiO2) nanoparticles dispersed in 60% ethylene glycol and 40% water by mass. Experiments conducted in a temperature range of 20 C to 90 C and for several particle volumetric concentrations up to 10% showed that the ratio of thermal conductivity of nanofluid to that of the base fluid increased with an increase in temperature and volumetric concentration. As an example, as much as a 20% enhancement in thermal conductivity was evidenced for a particle volumetric concentration of 10% at 87 C. Comparison of experimental results of this nonmetallic nanoparticles suspension with the well-known model developed by Hamilton and Crosser for microparticles suspensions, exhibits that this model underpredicts the thermal conductivity of nanofluids. Therefore, a new correlation has been derived following recent models developed for metallic nanoparticles suspensions, which is a combination of the Hamilton–Crosser model plus a term due to the Brownian motion. This new correlation expresses the thermal conductivity of silicon dioxide nanofluid as a function of temperature, volumetric concentration and the properties of the base fluid and the nanoparticles. [DOI: 10.1115/1.4024003]

In this study the electrical conductivity of aluminum oxide (Al2O3), silicon dioxide (SiO2) and zinc oxide (ZnO) nanoparticles dispersed in propylene glycol and water mixture were measured in the temperature range of 0 degrees C to 90 degrees C. The volumetric concentration of nanoparticles in these fluids ranged from 0 to 10% for different nanofluids. The particle sizes considered were from 20 nm to 70 nm. The electrical conductivity measuring apparatus and the measurement procedure were validated by measuring the electrical conductivity of a calibration fluid, whose properties are known accurately. The measured electrical conductivity values agreed within +/- 1% with the published data reported by the manufacturer. Following the validation, the electrical conductivities of different nanofluids were measured. The measurements showed that electrical conductivity of nanofluids increased with an increase in temperature and also with an increase in particle volumetric concentration. For the same nanofluid at a fixed volumetric concentration, the electrical conductivity was found to be higher for smaller particle sizes. From the experimental data, empirical models were developed for three nanofluids to express the electrical conductivity as functions of temperature, volumetric concentration and the size of the nanoparticles.

In situ gas hydrates have been found abundantly in the Arctic regions of the United States, Canada, and Russia. Gas recovery from such a hydrate reservoir under permafrost conditions is described in the present paper. The technique is based upon a finite‐element transient heat‐conduction model that includes the ability to handle phase change. That model is applied to field data available from the North Slope of Alaska for predicting natural‐gas production. Parametric studies have also been conducted to explore the effects of hydrate zone thickness, wellbore temperature, wellbore radius, porosity, etc., on the gas production rate. Comparisons of temperature distributions throughout the medium, and the propagation of the moving dissociation front with respect to time predicted by the present scheme and a finite‐difference scheme, show good agreement. The data generated in the present study may be useful in deciding on the most optimal technique for gas recovery from hydrates. Additionally, it may provide dr...

An integral method is presented for computing separated and reattached turbulent boundary layers for incompressible two-dimensional flows. This method is a substantial improvement over the inner-variable approach of Das and White (1986), which was based on a direct boundary layer scheme that had several shortcomings. In this new approach, the integral equations have been completely reformulated so that the theory now proceeds in an inverse mode using displacement thickness as input. This new formulation eliminates the need for the second derivative of velocity distribution, which in the past has always been a source of error in all previous inner-variable approaches. Other significant additions are: (a) a single pressure gradient-wake correlation from a large amount of experimental data; and (b) replacement of the wake parameter from the final equations with a more stable parameter, wake velocity. Derivations of integral equations and their final working expressions, in both dimensional and nondimensional forms, are presented in detail. Predictions by this theory for skin friction, freestream velocity, momentum thickness, velocity profile and separation, and reattachment points agree well with experimental data. Sensitivity studies display that the theory is stable against variations in initial conditions, input distributions, and the pressure gradient-wake correlation.

Obtaining deep ice cores from glaciers and the world's ice caps and rock samples from beneath the ice requires a new approach in coring technology that permits quick access to sampling zones. A combination of mechanical drilling coupled with water as a drilling and hydraulic fluid shows promise in providing quick access to interesting sample areas, as well as the ability to obtain good quality rock or ice core samples. The system consists of a deep well pump to circulate drilling water from within the ice, a triplex pump to provide hydraulic power, heaters, specially designed instrumented hoses, and a down-hole mud motor to drive the drill. The system is described in detail and thermal models of its effect on cores presented.

This paper presents the specific heat measurements of three nanofluids containing aluminum oxide, zinc oxide, and silicon dioxide nanoparticles. The first two are dispersed in a base fluid of 60:40 by mass of ethylene glycol and water (60:40 EG/W) and the last one in deionized water. Measurements were conducted over a temperature range of 315–363 K, which is the normal range of operation of automobile coolants and building heating fluids in cold regions. The nanoparticle volumetric concentrations tested were up to 10%. The measured values were compared with existing equations for the specific heat of nanofluids. A close agreement with the experimental data was not observed. Therefore, a new general correlation was developed for the specific heat as functions of particle volumetric concentration, temperature, and the specific heat of both the particle and the base fluid from the present set of measurements. The correlation predicts the specific heat values of each nanofluid within an average error of about 2.7%.

The performance of hydronic heating coils with nanoparticle enhanced heat transfer fluids (nanofluids) is evaluated and compared with their performance with a conventional heat transfer fluid comprised of 60% ethylene glycol (EG) and 40% water, by mass (60% EG). The nanofluids analyzed are comprised of either CuO or Al2O3 nanoparticles dispersed in the 60% EG solution. The heating coil has a finned tube configuration commonly used in commercial air handling and ventilating systems. Coil performance is modeled using methods that have been previously developed and validated. The methods are modified by incorporating Nusselt number correlations for nanofluids that have been previously documented in the literature. Similarly, correlations for nanoparticle thermophysical properties that have been documented in the literature are employed. The analyses show that heating coil performance may be enhanced considerably by employing these nanofluid solutions as a heat transfer medium. The model predicts a 16.6% increase in coil heating capacity under certain conditions with the 4% Al2O3/60% EG nanofluid, and a 7.4% increase with the 2% CuO/60% EG nanofluid compared with heating capacity with the base fluid. The model predicts that, for a coil with the Al2O3/60% EG nanofluid, liquid pumping power at a given heating output is reduced when compared with a coil with the base fluid.

An integral method is presented for calculating two-dimensional incompressible turbulent boundary layers using the inner-variable theory of White with several refinements. White formulated the problem through a linear wake function for flows proceeding under pressure gradients. We use a polynomial wake that is superior to the linear wake

This paper reports on experimental investigation of the rheological behavior of copper oxide nanoparticles dispersed in a 60:40 propylene glycol and water mixture. Nanofluids of a particle volume concentration from 0 to 6% have been tested in this study. The experiments were conducted over a temperature range of -35 degrees C to 50 degrees C to establish their behavior for use as a heat transfer fluid in cold climates. The experiments reveal that this nanofluid in the range of particle volume percentage tested exhibits a Newtonian behavior. A new exponential correlation has been developed from the experimental data, which expresses the viscosity as a function of particle volume percent and the temperature of the nanofluid. The slope of relative viscosity curve was found to be higher at lower temperatures.

A nanofluid is the dispersion of metallic solid particles of nanometer size in a base fluid such as water or ethylene glycol. The presence of these nanoparticles affects the physical properties of a nanofluid via various factors including shear stress, particle loading, and temperature. In this paper the rheological behavior of copper oxide (CuO) nanoparticles of 29 nm average diameter dispersed in deionized (DI) water is investigated over a range of volumetric solids concentrations of 5 to 15% and various temperatures varying from 278-323 degrees K. These experiments showed that these nanofluids exhibited time-independent pseudoplastic and shear-thinning behavior. The suspension viscosities of nanofluids decrease exponentially with respect to the shear rate. Suspension viscosity follows the correlation in the form ln(mus) = A(1/T)-B, where constants A and B are the functions of volumetric concentrations. The calculated viscosities from the developed correlations and experimental values were found to be within +/- 10% of their values.