Coupledheat and watertransfer in soil has been long recognized. The coupledtransfer of heat and water near the soil surface and the temperature fluctuations and water contents that result are important for all biological, chemical, and physical processes that occur near the soil surface. Although advancements have been made in understanding coupledheat and watertransfer processes in soil, deficiencies in our understanding continue to persist. The lack of soil water retention measurements at the dry end of the soil water retention curve (SWRC) limits our ability to accurately predict and simulate water movement at and near the soil surface. Furthermore, most studies neglect the effect of soil wettability and solutes on coupledheat and watertransfer in soil. The overall purpose of this work is to improve our understanding of the effects of soil wettability and salinity on soil water retention and coupledheat and mass transfer in soil. The following three objectives were designed to accomplish this: (1) Measure soil water sorption including hysteresis at the dry end of the SWRC as it relates to soil wettability for two different soils; (2) Determine the effect of soil wettability on coupledheat and watertransfer in response to thermal gradients; and (3) Determine the combined effects of soil wettability and soil salinity on coupledheat and mass transfer. The effect of soil wettability on soil water sorption, including relatively dry soil conditions, was measured. The effect of wettability was most noticeable at the driest end of the SWRCs for the silt loam and sand soils that were studied. Hysteresis was also found to exist in both relatively dry wettable and hydrophobic soils. Wettability and hysteresis should be considered when studying dynamics involved in water adsorption and desorption in
that the freezing process induces the movement of both heat and mass from warm to cold regions, inducing the moisture content in the unfrozen soil zone to decrease sharply toward the freezing front. Soil texture and initial moisture conditions seem to be crucial in affecting the availability and mobility of water. Guymon and Luthin (1974) describe a one-dimensional model for freeze- thaw processes based on an equivalent quasi-linear variational functional for the Richards equation and the heat conduction equation including convective components. Fuchs et al. (1978) develop a theory of soil freezing applicable to unsaturated conditions with solute presence in the soil. They state that solutes tend to depress the freezing point temperature and modify the relationship be- tween temperature, moisture content and apparent thermal properties of the soil. Phase change is taken into account in the apparent heat capacity formulation, and the water flow contribution is accounted for in the apparent thermal conductivity, thus the simultaneous heat and water transport equations result in a merged single differential equation for heat. Jame and Norum (1980) further develop the model of Harlan (1973) and highlight that the effect of mass transfer on the thermal state of soil is an important factor to be considered. Newman and Wilson (1997) propose a theoret- ical formulation for unsaturated soils using soil-freezing and soil-water characteristic curve data to combine the heat and mass transfer relationships into a single equation for freezing or frozen regions of the soil. Christoffersen and Tulaczyk (2003) have constructed a high-resolution numer- ical model of heat, water, and solute flows in sub-ice stream till subjected to basal freeze-on. They propose a formulation of the equilibrium relation without assuming p i = 0 through the full version
The spatial distribution of concentration (expressed as salt mass per unit mass of water to fa- cilitate the analysis of mass transfer processes) is noteworthy. Salinity is extremely high at the surface, where the water content is negligible, reaching salt solubility and producing precipitates. This high concentration zone grows with time, advancing in depth with the evaporation front. Immediately below, salinity drops sharply to values underneath the initial concentration. The min- imum concentration is always located immediately below the evaporation front. Further down, salinity rises slightly with depth, but is still more diluted than the initial conditions. A di fference between the experimental data and the numerical model is observed: the minimum in the simulated concentration is smaller than the measured one. The water content and temperature profiles do co- incide with what might be expected (drier and warmer conditions at the surface than at depth) unlike the concentration profile. Most traditional models (e.g. Huinink et al. (2002)) predict a maximum concentration at the evaporation front and a smooth monotonic reduction downwards toward initial concentration, caused by downwards diffusion. The radically different behaviour observed in our concentration profiles can be attributed to vapor fluxes. Actually, the time evolu- tion of cumulative evaporation (Figure 2 of Gran et al. (2011)) evolves according to the traditional model (e.g. Sghaier et al. (2007)), but the evolution of salt concentration profile does not.
An experimental study of the flow pattern and heattransfer associated with a single vapour bubble sliding on a downward facing heated surface was presented by Qiu & Dhir . Holographic interferometry was used to measure the fluid temperature in a plane parallel to the bubble flow direction and perpendicular to the heater surface. This highly detailed study into the bubble wake demonstrated that vortical structures in the wake can enhance heattransfer from the wall by bringing cooler liquid in from the bulk. Bayazit et al.  also postulated that small-scale vortices shed from the extremes of the bubble were the main contribution to heattransfer. Delaur´ e et al.  performed a simultaneous PIV and heattransfer study of a single air bubble interacting with natural convection from a copper block at various angles. The heattransfer coefficient was found to respond closely to changes in flow velocity and fluctuations in the fluid temperature, both caused by the bubble’s motion.
During the past decades, formalisms have been established empirically or half-empirically based on observations in the aforementioned diverse disciplines, among which are mutual information (Vastano and Swinney (1988)), Granger causality (Barnett (2009), Granger (1980)) and transfer entropy (Kaiser and Schreiber (2002), Schreiber (2000)). Particularly, transfer entropy is established with an emphasis of the above transfer asymmetry between the source and receiver, so as to have the causal relation represented; it has been successfully applied in many real problem studies. These formalisms, when carefully analyzed, can be approximately understood as dealing with the change of marginal entropy in the Shannon sense, and how this change may be altered in the presence of information flow (see San Liang and Kleeman (2007), section 4). This motivates our research on the possibility of a rigorous formalism when the dynamics of the system is known.
Available Online at www.ijpret.com 96 compared to PHT, this suggests that salicylate ions is more stable as compared to phthalic acid. The positive value of K i.e. compressibility of solvent molecule is due to weak electrostatic forces in the vicinity of ions. It may be concluded that solute-solute interaction in solution is due to linking of dicarboxylic ions by water molecules.
(2) For the phase transition zone the hysteresis type behavior of the soil is in agreement with the results found by P.J. W i l l i a m s ^ for clay soils and are of approximately the same magnitude, see Fig.3-7. An exact comparison is not possible since the soils are not identical.
Three problems arise in this approach. (i) The size of soil thin sections does not allow studying greater system of gravitational pores and fractions as it is possible using the CT, MRI and dye tracer techniques. However, as was shown by Kodešová et al. (2008), the gravitational pores may not have a signiﬁcant impact on the water ﬂow and solute transport under the natural ﬁeld conditions. (ii) Scanning of the soil thin sections provides only the two-dimensional (2D) images of the soil porous systems. Analysis of the soil thin section sequence and following recon- struction of the 3D image may partly improve the discussed method. (iii) Soil micromorphological images taken using the optical microscope cannot be used to evaluate pores smaller than 40 µm. The electron microscope scanning and image analyses presented by Rösslerová-Kodešová and Kodeš (1999) may be applied to obtain this information.
crimped spiral fins. They show that a good predictive ability against the test data . Elliptic tubes were investigated and compared with conventional circular ones for heattransfer. It has been reported that elliptic tubes enhance heattransfer by 13% . Investigations for flow inside of the tube have also been performed. Smith et al. presented the experimental results for tubes fitted with helical screw tape and stated that the increase of average Nusselt number was 230% and 340%, respectively for with and without core-rod inserted, compared to conventional plain tube .Further experiments on the twisted tape, inserted into the tube, in clockwise and counterclockwise had been carried out with the different twist ration and angles . Segmental baffles in heat exchanger can guide the flow across the tube bundle and prevent the tubes from vibrating and sagging. 3D simulations on the middle-overlapped helical baffles were carried out with different helical angles .
69 Future Directions:
Based on this work, there are a number of avenues of research that still need to be performed, both in terms of experimental and simulation studies. For future experimentation studies, the results from this work and others suggest that the use of nanofluids in laminar flow will results in higher levels of heattransfer enhancement. Changing the geometry of the particle from the spherical 40 nm particles used in this work could lead to some additional insights into the heattransfer process in these systems. As an example, based on previous work, decreasing particle size can lead to larger enhancements possibly due to the increased surface area of the particle contacting the fluid. Additionally, changing particle shape to that of a rod or a plate will allow the particle to interact with the laminar flow field differently than a spherical particle. This will possibly introduce different mixing effects and surface area enhancement effects to the system. Particle material is also of interest as heattransfer enhancement is seemingly tied to the thermal conductivity of the particles. Working with higher thermal conductivity materials, such as Al and Cu could lead to additional enhancements beyond those observed in this work. As the research space is still very large, it is strongly suggested that a design of experiments be completed before performing these experiments so as to limit the time needed to acquire statistically significant data based on the large number of experimental variables that are present within this system.
Abdul gave Ola (2002), the initial simulation engine four ignition times. It has been used to fire the formula Wiebe Predicting the pressure cylinder which was used to determine the specific work. The transfer of heattransfer losses and cylinder friction and pumping into account to predict the mean effective pressure, breaking the thermal efficiency and fuel consumption break. It has been studied more of the parameters that can affect engine ignition four times as parity ratio performance, ignition timing and the rate of heat release, the compression ratio, compression and expansion rate . Using actual combustion has a profound impact on the size of the similarity of personal pressure to that observed in the actual engine curve. The modeling process is getting closer to reality, obviously, now worth as an aid in the design.
Microwave ovens are used extensively for heating a variety of not-ready-to-eat food products. Non-uniform heating of foods in microwave ovens is a major concern in assuring microbiological safety of such products. The non-uniform heating of foods is attributed by complex interaction of microwaves with foods. To understand this complex interaction, a comprehensive model was developed to solve coupled electromagnetic and heattransfer equations using finite-dif- ference time-domain based commercial software. The simulation parameters, cell size, heating time step, and number of iterations for steady state electromagnetic field were optimized. The model was validated by 30 s heating profile of a cylindrical model food (1% gellan gel) in a 700 W microwave oven. The model was validated qualitatively by compar- ing the simulated temperature profiles on three planes in the gel and compared them to the corresponding thermal im- ages. Quantitative validation was performed by comparing simulated temperature of the gel at 12 locations with exper- imental temperature acquired at those points using fiber optic sensors. Simulated spatial temperature profiles agreed well with the thermal image profiles. The root mean square error values ranged from 0.53 to 4.52 °C, with an average value of 2.02 °C. This study laid a framework for selecting the required model parameters which are critical for better temperature prediction. The developed model can be effectively used to identify hot and cold spots in food products, thereby helping in microwaveable food product development to achieve better cooking performance in terms of heat- ing uniformity, food quality and safety. The model can also be used to identify the best product, package and cavity parameters to achieve better heating uniformity and electromagnetic distribution inside the cavity.
The present problem addresses double diffusive free convection in an inclined square cavity ﬁlled with ﬂuid saturated porous medium under the inﬂuence of Soret and Dufour effects. The inclined cavity makes an angle with the horizontal plane. At the two horizontal walls of the cavity the heat and solute transverse gradients are applied and lateral walls of the cavity are being regarded insulated and impermeable. Using the appropriate dimensionless quantities, the governing equations with boundary conditions are transformed to non-dimensional form. The governing partial differential equations are solved by Finite element method of Galerkin weighted residual scheme. Numerical results are obtained for different values of the Rayleigh number, Lewis number, buoyancy ratio, Soret Number and Dufour number. The overall investigation of variation of streamlines, isotherms, iso-concentration, Nusselt number and Sherwood numbers are presented graphically. To examine the accuracy, the present results are compared with the available results.
II How to control the lysimeter bottom boundary to investigate the effect of climate change on soil processes?
locations where these nonlocal controls on the soil water balance are important. The separation of the lysimeter from its surroundings also introduces an artificial boundary at the bottom that may affect the soil water balance of the lysimeter. The classically used bottom boundary of a lysimeter is a seepage-face boundary through which water can only leave when the soil is saturated and through which no upward inflow is possible. Disconnecting the capillary connection with deeper soil affects the drainage and prevents capillary rise. Several studies have shown that upward directed water fluxes from shallow groundwater tables and deeper soil layers serve as an additional water supply for ET processes (Schwaerzel and Bohl 2003; Yang et al. 2007; Luo and Sophocleous 2010; Karimov et al. 2014). A seepage-face boundary condition may lead to a bias in the drainage (Stenitzer and Fank 2007) and in the solute transport processes (Abdou and Flury 2004; Boesten 2007) so that lysimeter observations are not directly transferable to field-scale conditions (Vereecken and Dust 1998; Flury et al. 1999). However, methods have been developed to control the bottom boundary of a lysimeter so that the water balance and moisture profiles in the lysimeter correspond closely with those that would prevail in the undisturbed soil profile (Fank and Unold 2007). The lysimeters in SOILCan have a controlled bottom boundary condition using a rake of suction candles that enables upward and downward flow of water from and to a weighted leachate tank. To ensure the lysimeter waterdynamics are according to the field dynamics, the matric potential at the bottom is controlled and adjusted to measured matric potentials in an undisturbed soil profile next to the location where the lysimeter is installed and at the same depth as the bottom of the lysimeter. An adjustable control algorithm takes into account different soils and conductivities, allowing the bidirectional pumping system to control the water flow direction across the lysimeter bottom to minimize matric potential differences between the field and the lysimeter.
dividing surface in the true system in comparison to the classical TST estimate. Figure 3.3 presents the thermal reaction rates for System A3 calculated using KC-RPMD (red), the Zusman expression for ET (black), and numerically exact quantum dynamics methods (blue) as a function of the friction of the bath. 20 For intermediate values of the friction coefficient, log(γ/m s ω s ) > −1, all three sets of ET rates are observed to be independent of the strength of the friction coefficient corresponding to the Marcus regime of ET. However, the magnitude of the dynamical recrossing factor in the plateau region is larger for the exact quantum results due to an increase in the ET rate associated with nuclear tunneling. 20 For the weakly dissipative regime when log(γ/m s ω s ) < −1, both the rates calculated using KC-RPMD and the exact quantum dynamics method, in comparison to the Zusman expression, show strong friction dependence, though with distinctly different qualitative behavior. In the weakly dissipative regime, the time-scale for relaxation of the solvent-coordinate is long, such that the solvent-coordinate is able to pass through configurations associated with the crossing of the diabats numerous times; these multiple crossing events allow for multiple transitions between electronic states to occur, a phenomenon not captured by the Zusman expression for ET. When the solvent is treated classically, as in the KC-RPMD simulations, the multiple electronic transitions lead to a decorrelation between the initial and final electronic state causing a decrease in the ET rate; as observed in Fig. 3.3 the KC-RPMD simulations are able to properly capture the physics governing this regime of ET. When the solvent is treated quantum mechanically, as in the exact quantum dynamics simulations, 20 the nuclear wavepackets are able to constructively interfere during each pass of the crossing of the diabatic states, leading to an enhancement of the ET rate. 20,34 Like all dynamics methods based on the imaginary-time formulation of statistical mechanics, 3 KC-RPMD is unable to capture such coherence effects due to the loss of phase-information in the approximate dynamics. However, Fig. 3.3 provides a promising result, illustrating that the KC-RPMD method is able to appropriately capture the competition between the time-scale for solvent relaxation and the probability of transitioning between electronic states.
exchanger and experiments performed on it to analyses pressure drop and temperature change in hot and cold fluid on shell side and tube side. The research was carried out by Yoo Geun-jong et. al on fluid flow and heattransfer characteristics of spiral coiled tube and effects of Reynolds number and curvature ratio .They performed a numerical analysis and studied flow and heattransfer characteristics in spiral coiled tube heat exchanger. They increased gradually increased radius of curvature of spiral coiled tube till total rotating angle of 12 Π is reached. They concluded that cross sectional velocity distribution of the main flow and secondary flow shows similarity for both spiral and helical coiled tubes. They also concluded that friction factor and Nu increases in sane proportion with Re and square root of dean number in both coiled tubes. They finally concluded that Re had stronger effect as compared to curvature ratio. The research was carried out by Naphon and Wongwises on study of the heattransfer characteristics of a compact spiral coil heat exchanger under wet-surface conditions . The main focus of their work was to find the heattransfer characteristics and the performance of a spiral coil heat exchanger under cooling and humidifying conditions. They used air and water as working fluids. They developed a mathematical model based on mass and energy conservation and solved by using the Newton– Raphson iterative method to determine the heattransfer characteristics. They found out that enthalpy, effectiveness and the humidity effectiveness decreased with increasing air mass flow rate for a given inlet- water temperature, inlet-air humidity ratio and water mass flow rate. The increase in the outlet enthalpy and outlet humidity ratio of air was larger than those of the enthalpy of saturated air and humidity ratio of saturated air. Therefore, the enthalpy effectiveness and humidity effectiveness tend to decrease with increasing air mass flow rate. They also observed that the effect of inlet-air temperature on the tube surface temperature. At a specific inlet-air temperature, the tube surface temperature generally increases with
transfer in the system. Convective heattransfer coefficient also plays an important role in evaluating heattransfer capability of an automotive radiator. In the forced flow system (such as in engine cooling by radiator) the coolant is pumped through the radiator, introducing convective heattransfer mechanisms and pumping power penalties. Heris, Esfahany, and Etemad, 2006 investigated convective heattransfer of CuO/water based nanofluids under laminar flow conditions under constant wall temperature. They observed that the heattransfer coefficient increases with the Peclet number as well as the nanofluid concentrations or the volume fractions of the nanoparticles. Similar findings were indicated by Zamzamian et al (2011) in their experimental investigation of the forced convection heattransfer of Al2O3/EG and CuO/EG nanofluids, although their work focused on turbulent flow in a double-pipe and plate heat exchangers.
The optimum roll temperature range was 160−250 °C for the rolling process of magnesium alloy. The time (t) and the pressure difference (ΔP) between the import and export (when the roll was heated from room tempera- ture to 200 °C under different velocities) are shown in Table 5. The trend of the change is shown in Figure 10. The fluid velocity changed from 0.3 to 1.1 m/s, t reduced from 34.4 to 15.5 minutes, the pressure increased from 0.03 to 0.32 MPa, the heating time shortened, and the velocity increased to a certain value. Further, the heattransfer increase rate decreased, but the pressure became larger and the flow resistance increased. The relation- ships between velocity (v), time (t), and the pressure dif- ference (ΔP) between the import and exports were fitted as in Eqs. (21) and (22). In the actual production, the best velocity was selected according to the required heating time, and whether different equipment could withstand the pressure.