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### Research Papers: Bio-Heat and Mass Transfer

Singh Sonam, Bhargava R. Simulation of Phase Transition During Cryosurgical Treatment of a Tumor Tissue Loaded With Nanoparticles Using Meshfree Approach J. Heat Transfer 136, 121101 (2014) (10 pages);   Paper No: HT-13-1430;   doi:10.1115/1.4028730

In medical world, the minimally invasive freezing therapy or cryosurgery is an efficacious treatment for complete and controlled eradication of tumor cells. Many difficulties are encountered in cryosurgery process such as inappropriate freezing may not completely destroy the target tumor tissue and excessive freezing may harm the surrounding healthy tissues due to release of high amount of cold from the freezing probe. In present study, the target tumor tissue is loaded with nanoparticles in order to improve the freezing capacity of probe and to regulate the orientation and size of ice-ball formed during cryosurgery. In this process, phase transformation occurs in the undesired tumor tissues. For simulation of phase transition in bio heat transfer equation, the fixed-domain, heat capacity method is used to take into account the latent heat of phase change. In this study, a meshfree numerical technique known as element free Galerkin method (EFGM) is employed to simulate the phase transition and temperature field for a biological tissue subjected to nanocryosurgery. The latest nanofluid model which includes the effects of particles size, concentration, and the interfacial layer at the particle/liquid interface is utilized and their impact on freezing process is investigated in detail.

### Research Papers: Evaporation, Boiling, and Condensation

Mendoza Hector, Beaini Sara, Carey Van P. An Exploration of Transport Within Microdroplet and Nanodroplet Clusters During Dropwise Condensation of Water on Nanostructured Surfaces J. Heat Transfer 136, 121501 (2014) (9 pages);   Paper No: HT-12-1069;   doi:10.1115/1.4026167

Experimental studies of dropwise condensation have generally indicated that higher heat transfer coefficients correspond to smaller mean sizes for droplets growing through condensation on the surface. Recent investigations of dropwise condensation on nanostructured surfaces suggest that optimizing the design of such surfaces can push mean droplet sizes down to smaller values and significantly enhance heat transfer. This paper summarizes a theoretical exploration of the limits of heat transfer enhancement that can be achieved by pushing mean droplet size to progressively smaller sizes. A model analysis is developed that predicts transport near clusters of water droplets undergoing dropwise condensation. The model accounts for interfacial tension effects on thermodynamic equilibrium and noncontinuum transport effects, which become increasingly important as droplet size becomes progressively smaller. In this investigation, the variation of condensing heat transfer coefficient for droplet clusters of different sizes was explored for droplet diameters ranging from hundreds of microns to tens of nanometers. The model predictions indicate that the larger droplet transport trend of increasing heat transfer coefficient with decreasing mean droplet size breaks down as droplet size becomes smaller. The model further predicts that as drop size becomes smaller, a peak heat transfer coefficient is reached, beyond which the coefficient drops as the size continues to diminish. This maximum heat transfer coefficient results from the increasing importance of surface tension effects and noncontinuum effects as droplet size becomes smaller. The impact of these predictions on the interpretation of dropwise condensation heat transfer data, and the implications for design of nanostructured surfaces to enhance dropwise condensation are discussed in detail.

### Research Papers: Forced Convection

Xing Yunfei, Zhong Fengquan, Zhang Xinyu. Numerical Study of Turbulent Flow and Convective Heat Transfer Characteristics in Helical Rectangular Ducts J. Heat Transfer 136, 121701 (2014) (6 pages);   Paper No: HT-14-1036;   doi:10.1115/1.4028583

Three-dimensional turbulent forced convective heat transfer and its flow characteristics in helical rectangular ducts are simulated using SST k–ω turbulence model. The velocity field and temperature field at different axial locations along the axial direction are analyzed for different inlet Reynolds numbers, different curvatures, and torsions. The causes of heat transfer differences between the inner and outer wall of the helical rectangular ducts are discussed as well as the differences between helical and straight duct. A secondary flow is generated due to the centrifugal effect between the inner and outer walls. For the present study, the flow and thermal field become periodic after the first turn. It is found that Reynolds number can enhance the overall heat transfer. Instead, torsion and curvature change the overall heat transfer slightly. But the aspect ratio of the rectangular cross section can significantly affect heat transfer coefficient.

### Research Papers: Heat and Mass Transfer

Nandkeolyar Raj, Kameswaran Peri K., Shaw Sachin, et al. Heat Transfer on Nanofluid Flow With Homogeneous–Heterogeneous Reactions and Internal Heat Generation J. Heat Transfer 136, 122001 (2014) (8 pages);   Paper No: HT-13-1179;   doi:10.1115/1.4028644

We investigated heat and mass transfer on water based nanofluid due to the combined effects of homogeneous–heterogeneous reactions, an external magnetic field and internal heat generation. The flow is generated by the movement of a linearly stretched surface, and the nanofluid contains nanoparticles of copper and gold. Exact solutions of the transformed model equations were obtained in terms of hypergeometric functions. To gain more insights regarding subtle impact of fluid and material parameters on the heat and mass transfer characteristics, and the fluid properties, the equations were further solved numerically using the matlab bvp4c solver. The similarities and differences in the behavior, including the heat and mass transfer characteristics, of the copper–water and gold–water nanofluids with respect to changes in the flow parameters were investigated. Finally, we obtained the numerical values of the skin friction and heat transfer coefficients.

### Research Papers: Micro/Nanoscale Heat Transfer

Guo Liang, Xu Xianfan. Ultrafast Spectroscopy of Electron-Phonon Coupling in Gold J. Heat Transfer 136, 122401 (2014) (6 pages);   Paper No: HT-14-1429;   doi:10.1115/1.4028543

Transient reflectance of gold was measured using ultrafast spectroscopy by varying the wavelength of the probe laser beam in the visible range. Based on the band structure of gold, the influence of the probe beam wavelength on the signal trend is analyzed in terms of sensitivity, effect of nonthermalized electrons, and relaxation rate. It is found that probing around 490 nm renders the best sensitivity and a simple linear relation between the transient reflectance and the electron temperature. The two-temperature model (TTM) is applied to calculate the electron-phonon coupling factor by fitting the transient reflectance signal. This work clarifies the ultrafast energy transfer dynamics in gold and the importance of using proper probe laser wavelength for modeling the transient heat transfer process in metal.

### Research Papers: Natural and Mixed Convection

Agarwal Shilpi, Rana Puneet, Bhadauria B. S. Rayleigh–Bénard Convection in a Nanofluid Layer Using a Thermal Nonequilibrium Model J. Heat Transfer 136, 122501 (2014) (14 pages);   Paper No: HT-13-1634;   doi:10.1115/1.4028491

This paper studies the effect of local thermal nonequilibrium (LTNE) on the thermal instability in a horizontal layer of a Newtonian nanofluid. The nanofluid layer incorporates the effect of Brownian motion along with thermophoresis. A two temperature model has been used for the effect of LTNE among the particle and fluid phases. The boundary condition involved assumes that the nano-concentration flux is zero thereat, including the effect of thermophoresis. The linear stability is based on normal mode technique and for nonlinear analysis, a minimal representation of the truncated Fourier series analysis involving only two terms has been used. The effect of various parameters on Rayleigh number has been presented graphically. A weak nonlinear theory based on the truncated representation of Fourier series method has been used to obtain the thermal Nusselt number, whose variation with respect to various parameters has been depicted graphically.

### Research Papers: Max Jacob Award Paper

Chermiti Imen, Hidouri Nejib, Ben Brahim Ammar. Entropy Generation Analysis of a Chemical Absorption Process Where Carbon Dioxide is Absorbed by Falling Monoethanolamine Solution Film J. Heat Transfer 136, 123001 (2014) (10 pages);   Paper No: HT-13-1658;   doi:10.1115/1.4028114

The present paper reports a study about entropy generation analysis for the case of chemical absorption of a gas into laminar falling liquid film. The CO2 absorption into monoethanolamine (MEA) aqueous solutions has been considered. Temperature and concentration expressions are determined by using Laplace transform and used for the entropy generation calculation. The effects of irreversibilities due to heat transfer, mass transfer, viscous effects, coupling effects between heat and mass transfer, and chemical reaction on the total entropy generation of the considered system are derived. The obtained results show that entropy generation is mainly due to chemical reaction irreversibility at the gas–liquid interface. Between this interface and the reaction film thickness (where the reaction take place), entropy generation is due to both chemical reaction and mass transfer irreversibilities. More details concerning the contribution of each kind of irreversibility to entropy generation through the falling film are graphically presented and discussed.

### Technical Brief

Easter J., Jarrett C., Pespisa C., et al. An Area-Average Correlation for Oil-Jet Cooling of Automotive Pistons J. Heat Transfer 136, 124501 (2014) (4 pages);   Paper No: HT-12-1125;   doi:10.1115/1.4027835

Laboratory tests were performed to measure cooling rates of an impinging oil-jet on the underside of an automotive piston as functions of oil nozzle-to-piston surface spacing, oil pressure, oil temperature, and piston temperature. Based on these results, area-average Nusselt number correlations were derived for a Reynolds number range of 100–4500, a Prandtl number range of 90–750, and a nozzle-to-piston surface spacing range over 73–160 mm, which are within the ranges expected for oil-jet cooling of automotive pistons.

You Xiang-Cheng, Xu Hang, Pop Ioan. Analysis of Fully Developed Opposing Mixed Convection Flow in an Inclined Channel Filled by a Nanofluid J. Heat Transfer 136, 124502 (2014) (5 pages);   Paper No: HT-13-1235;   doi:10.1115/1.4028564

In this paper, an analysis is made on the convective heat transfer of a nanofluid between two inclined parallel plates with a uniform heat flux boundary condition. The analytical solutions are obtained explicitly for the velocity, temperature, and pressure distributions, which are dependent on two parameters P1 and P2. By alerting their values, four different regimes for flow reversal are found. On the other hand, it is found that the nanoparticle volume fraction $φ$ has a significant influence on the flow reversal. Physically important quantities such as wall friction and Nusselt number are in detail discussed for the TiO2-water nanofluid.