Matrix method of solution is applied to determine generalized thermoelastic wave propagation in an unbounded medium due to periodically varying heat source under the influence of magnetic field. Green–Lindsay (GL) model of generalized thermoelasticity for finite wave propagation is considered along with a magnetic field for a rotating medium with uniform velocity. Basic equations are solved by eigenvalue approach method after compiling in a form of vector–matrix linear differential equation in Laplace transform domain. Finally inverting the perturbed magnetic field and other field variables by a suitable numerical method, the results are analyzed by depicting several graphs in space–time domain.

Flat plate oscillating heat pipe (FP-OHP) is a new heat transfer device and considered as a promising candidate for effective heat transfer device in electronics industries. A number of theoretical studies and experimental investigations have been carried out on FP-OHP in the past decades after its invention. However, due to the operational characteristics of FP-OHP, the effect of various parameters on the thermal performance FP-OHP has not been completely revealed so far. This paper attempted to discuss the effect of operational parameters on the thermal performance of FP-OHP. In the present study, the FP-OHP was investigated with different charge ratio, orientation, working fluid and heat load from 10 W to 150 W. In order to investigate the effect, 18 parallel square channels of 2 x 2 mm2 are machined onto pure copper plate (93 x 70 x 8 mm3) to form FP-OHP. DI water, ethanol, methanol, acetone, and FC-72 are investigated. The measured thermal resistance was strongly depended by operational parameters. The optimum performance was observed by acetone with a charge ratio of 70% in the vertical orientation. The lowest thermal resistance of 0.39 °C/W is achieved using acetone as a working fluid at 100 W.

The present paper discusses about the effect of tube geometry and liquid feeder height on the heat transfer performance of falling film evaporation over the horizontal heated plain tubes. To investigate this, a two dimensional CFD model was developed, compared and validated with published data available in the literature. A numerical simulation was carried out for varying liquid load, tube diameter; liquid feeder height and corresponding changes in the heat transfer co-efficient was recorded and analysed. An attempt was also made to measure the thickness of the film around the tubes from the simulation model. Mechanisms that control the factors such as heat transfer co-efficient and film thickness were numerically investigated and discussed in the present work. Numerical results indicated that low value of liquid film thickness appears approximately at the angular position of the range between 90-125o. Also the numerical investigation revealed that liquid film thickness decreases and heat transfer co-efficient increases with the increase of feeder height. No remarkable change in film thickness was observed with increase in the tube diameter.

A loop heat pipe (LHP) is an efficient passive, two-phase heat transfer device which can transport heat up to large distances (over ∼ 5 m) even in the anti-gravity mode. It is necessary to miniaturize the LHPs to make them suitable for space-constrained avionics applications. However, before incorporating these devices under high-vibrational environmental conditions such as those encountered in avionics applications, it is imperative to study their thermal performance under such loads. With the aim of understanding the effect of acceleration and frequency of imposed vibration on thermal performance of miniature LHP (mLHP), a contextual experimental study has been reported here using an ammonia charged mLHP (8 mm evaporator diameter; titanium wick) in the horizontal orientation for two cases: (a) without vibration and (b) with the transverse and longitudinal harmonic vibrations (1–4g, frequencies 15–45 Hz, and sine sweep 15–45 Hz in 1 s). With start-up loads between 5 W and 8 W, the LHP can transfer heat load of about 120 W at safe evaporation temperature of 70 °C. Results show that for the transverse vibration, acceleration rate and frequency of imposed vibrations do not affect the thermal performance of mLHP. For the longitudinal vibration, the device performance gets noticeably enhanced with increased acceleration. The decisive role of heat leak (from evaporator to the compensation chamber (CC)) with imposed vibrations is clearly observed, and its link to the internal fluid distribution can be discerned from data trends.

The linear stability of a rotating doubly diffusive couple stress fluid layer is examined. Numerical calculations reveal that the system is capable of supporting many exceptional departures from those of singly and doubly diffusive couple stress fluid systems. Contrary to its stabilizing effect, the presence of couple stresses hasten the stationary onset depending the rotational strength. Moreover, disconnected closed oscillatory neutral curves are established to happen underneath sure conditions suggesting the necessity of three decisive thermal Rayleigh numbers to identify the linear stability criteria rather than the standard single value. The prevailing results are obtained as limiting cases from the current study.

Precise modelling of thermoelastic cracks remains challenging due to the fact that both of heat flux and stress fields have singularity issue. In the previous studies, the first author proposed different types of symplectic analytical singular element (SASE) for thermal conduction and stress analysis of cracks. It has been demonstrated that these crack-tip elements of which the interior fields are defined by analytical solutions are highly accurate and efficient. However, the thermal mechanical coupling problem of crack cannot be treated with the existing SASEs. The main difficulty is that the analytical solution of the crack problem considering arbitrary temperature distribution is not available. Approximate solution may lead to significant numerical instabilities. Moreover, the construction of a crack-tip singular element for both thermal conduction and stress analysis is complicated and requires more efforts. In this study, the governing symplectic dual equation of thermoelastic crack is restudied. The analytical solution considering arbitrary temperature distribution is obtained in close form which, to the best of the authors' knowledge, has not been found before. Then, the finite element formulation of a new SASE for thermal-mechanical fracture analysis is derived analytically through a variational approach. A two-step analysis procedure is proposed to calculate the mixed mode thermal stress intensity factors (TSIFs)) and the analytis can be done on a fixed finite element mesh. Mesh refinement around the crack tip is unnecessary, and the mixed-mode TSIFs can be solved accurately without any post-processing.

Viscoelastic materials are a kind of representative passive vibration control materials with many applications in civil engineering for earthquake mitigation in building structures, and these materials often serve in a thermo-elastic coupling environment. In this work, a one-dimensional magneto-thermoviscoelastic problem of a single-layer viscoelastic plate is investigated with memory-dependent derivative and nonlocal effect in the context of generalized thermo-elasticity. The plate is placed in a magnetic field, and the upper surface is subjected to a thermal shock. The governing equations for the single-layer plate are formulated considering the time delay and the kernel function of the memory-dependent derivative, nonlocal effect, temperature-dependent properties, and magnetic field. The Laplace transform and its numerical inversion are employed to solve this problem. The nondimensional temperature, displacement, and stress are calculated and presented graphically. Based on the numerical results, the influence of time delay and kernel function of the memory-dependent derivative, nonlocal effect parameters, temperature-dependent properties, and magnetic field parameters on the distributions of the nondimensional temperature, displacement, and stress are discussed.

The governing equations of two-temperature generalized magneto-thermoelasticity with hydrostatic initial stress are specialized in two dimensions and are solved for surface wave solutions. The appropriate solutions in a half-space are obtained which satisfy relevant radiation condition and boundary conditions at thermally insulated as well as isothermal surface. The frequency equation of Rayleigh wave is obtained. The frequency equation is also reduced for limiting cases of small thermal coupling and small reduced frequency. Velocity of propagation and amplitude-attenuation factor of Rayleigh wave are computed for a numerical example. To illustrate the dependence of velocity and amplitude-attenuation factor upon two-temperature parameter, initial stress parameter thermal relaxation time and magnetic field, the numerical results are shown graphically.

Cracking control is very important for laser drilling of yttria-stabilized zirconia (YSZ). In this paper, a thermomechanical model is presented to investigate what will be happened in the trepan drilling of YSZ by a picosecond pulsed laser. The thermal model is developed for describing the interaction between laser and YSZ material to obtain the transient temperature. The mechanical model is developed to calculate the stress distribution caused by the phase transformation based on the temperature results. The goal of the present study is to explore the intrinsic mechanism of cracking around the drilled hole from the aspect of the phase transformation in laser drilling of YSZ.

In this paper, a non-Fourier model of heat conduction and moisture diffusion coupling is proposed. We study a hygrothermal elastic problem within the framework of time-fractional calculus theory for a centrally symmetric sphere subjected to physical heat and moisture flux at its surface. Analytic expressions for transient response of temperature change, moisture distribution, displacement, and stress components in the sphere are obtained for heat/moisture flux pulse and constant heat/moisture flux at the sphere's surface, respectively, by using the integral transform method. Numerical results are calculated and the effects of fractional order on temperature field, moisture distribution, and hygrothermal stress components are illustrated graphically. Subdiffusive and super-diffusive transport coupling behavior as well as wave-like behavior are shown. When fractional-order derivative reduces to first-order derivative, the usual heat and moisture coupling is recovered, which obeys Fourier heat conduction and Fick's moisture diffusion.

Hot wire anemometer (HWA) measurements of turbulent gas flow have been performed in upward forced convection experiments at pressures ranging from 0.6 MPa to 6.3 MPa and fluid temperatures ranging from 293 K to 673 K. The results are relevant to deteriorated turbulent heat transfer (DTHT) and flow laminarization in strongly heated gas flows which could occur in gas-cooled very high temperature reactors (VHTRs). 2 The HWA signals were analyzed to directly confirm the occurrence of flow laminarization phenomenon due to strong heating. An X-probe was used to collect radial and axial velocity fluctuation data for pressurized air and pure nitrogen flowing through a circular 16.8 mm diameter flow channel in a 2.7 m long graphite test section for local Reynolds numbers varying from 500 to 22,000. Analyses of the Reynolds stresses and turbulence frequency spectra were carried out and used as indicators of laminar, transition, or fully turbulent flow conditions. Low Reynolds stresses indicated the existence of laminar or transitional flow until the local Reynolds number reached a large value, ∼11,000 to 16,000, much higher than the conventional Re = 4000–5000 for transition to fully turbulent flow encountered in pipe flows. The critical Reynolds number indicating the completion of transition approximately doubled as the pressure was increased from 0.6 MPa to 2.8 MPa.

The aim of this investigation is to estimate the theory of generalized magneto-thermoelasticity to solve the problems of two-dimensional (2D) half-space under thermal shock, initial stress, and two temperatures. The governing equations are solved by using Lame's potentials method in the context of classical dynamical (CD) and Lord-Şhulman (LS) theories. The boundary conditions are as follows (i) the total normal stresses in the boundary equivalent to the initial stress; (ii) the shear stresses are vanished at the boundary; and (iii) the incidence boundary is thermal insulated. The reflection coefficients have been obtained for two incident p - and SV-waves. The results obtained for the incident waves calculated numerically by using appropriate metal and presented graphically. Comparisons have been made with the results obtained from the presence and absence of magnetic field and initial stress.

Within the framework of scale resolving simulation techniques, this paper considers the application of the stress-blended eddy simulation (SBES) model to pressure side (PS) film cooling in a high-pressure turbine nozzle guide vane. The cooling geometry exhibits two rows of film cooling holes and a trailing edge cutback, fed by the same plenum chamber. The blowing conditions investigated were in the range of coolant-to-mainstream mass flow ratio (MFR) from 1% to 2%. The flow regime resembles that in a real engine (exit isentropic Mach number of Ma 2is = 0.6), but also low speed conditions (Ma 2is = 0.2) were considered for comparison purposes. The predicted results were validated with measurements of surface adiabatic effectiveness and instantaneous off-wall visualizations of the flow field downstream of cooling holes and cutback slot. The focus is on SBES ability of developing shear layer structures, because of their strong influence on velocity field, entrainment mechanisms and, thus, vane surface temperature. Special attention has been paid to the development and dynamics of coherent unsteadiness, since measured values of shedding frequency were also available for validation. SBES provided significant improvement in capturing the unsteady physics of cooling jet-mainstream interaction. The effects of changes in flow regime and blowing conditions on vortex structures were well predicted along the cutback surface. As regards the cooling holes, the high speed condition made it difficult to match the experimental Kelvin–Helmholtz breakdown in the shear layer, in the case of high velocity jets.

A vector–matrix differential equation is formulated using normal mode analysis from the governing equations of a three-dimensional anisotropic half space in presence of heat source and gravity. The corresponding solution is obtained with the help of eigenvalue approach. Numerical computations for displacement, thermal strain and stress component, temperature distribution are evaluated and presented graphically.

Convective heat transfer in a channel partially filled with porous medium has received a lot of attention due to its wide engineering applications. However, most researches focused on a channel partially filled with single layer porous medium. In this paper, we will analyze the heat transfer and entropy generation inside a channel partially filled with N-layer porous media. The flow and the heat transfer in the porous region are described by the Darcy–Brinkman model and the local thermal nonequilibrium model, respectively. At the porous-free fluid interface, the momentum and the heat transfer are described by the stress jump boundary condition and the heat flux jump boundary condition, respectively; while at the interface between two different porous layers, the momentum and the heat transfer are described by the stress continuity boundary condition and the heat flux continuity boundary condition, respectively. The analytical solutions for the velocity and temperature in the channel are derived and used to calculate the overall Nusselt number, the total entropy generation rate, the Bejan number, and the friction factor. Furthermore, the performances of the flow and heat transfer of a channel partially filled with third-layer porous media are studied.

Both experimental and numerical studies of a turbulent flow in a bifurcating channel are performed to characterize the dynamical behavior of the flow and its impact on the convective heat transfer on the sides of the branch. This configuration corresponds to the radial vents placed in the stator vertically to the rotor–stator air gap in the electrical machines. Indeed, our analysis focuses on the local convective heat transfer on the vents internal surface under a turbulent mass flow rate. The flow field measurements were carried out with two components particle image velocimetry (PIV) system, and the local heat transfer on the sides of the bifurcation branch was measured using an infrared thermography device. The convective heat transfer and the flow dynamics through the geometry are investigated numerically considering a three-dimensional (3D) flow. The closure system of the Navier–Stokes equations for steady and incompressible flow is based on the low-Reynolds numbers Reynolds stress model (RSM) (RSM-stress- ω ). The comparison of the 3D computed results with the measurements in the xy symmetry plane is satisfactory in the vertical and horizontal channels. The numerical prediction of the secondary flow in the vertical branch was analyzed and complements the experimental results. It was particularly noticed that the accelerated flow observed at the right side of the branch's inlet allows more pronounced heat transfer comparatively to the left side. Beyond approximately 7 hydraulic diameters from the entrance of the branch, the Nusselt number curves on the two sides of the branch tend to be the same developed Nusselt number, Nud.

The effect of nanoparticle coating on the performance of a miniature loop heat pipe (mLHP) is experimentally investigated for heat inputs of 20–380 W using distilled water as the working fluid. Applications include the cooling of electronic devices such as circuit breaker in low voltage switch board and insulated gate bipolar transistor. Physical vapor deposition method is used to coat the nanoparticles on the evaporator surface for different coating thicknesses of 100 nm, 200 nm, 300 nm, 400 nm, and 500 nm, respectively. An optimum filling ratio (FR) of 30% is chosen for the analysis. Experimental findings show that the nanoparticle coating gives a remarkable improvement in heat transfer of the heat pipe. An average reduction of 6.7%, 11.9%, 17.2%, and 22.6% in thermal resistance is observed with coating thicknesses of 100 nm, 200 nm, 300 nm, and 400 nm, respectively. Similarly, enhancements in evaporator heat transfer coefficients of 47%, 63.5%, 73.5%, and 86% are noted for the same coating thicknesses, respectively. Evaporator wall temperature decreased by 15.4 °C for 380 W with a coating thickness of 400 nm. The repeatability test ensures the repeatability of experiments and the stability of coatings in the long run.

A dynamic, partially permeable crack model for orthotropic materials is established with the crack full of thermal medium. Besides external thermal and elastic loadings, the heat flux generated by the crack interior full of a medium also contributes to the crack boundary conditions, which is dependent on the crack opening displacement. Thus, the heat conduction is dependent on elastic field. First, the heat conduction equation is solved exactly in terms of unknown heat flux of the crack interior. Then, the elastic field is presented for real or complex eigenvalue cases on the basis of the operator theory. Finally, the thermal and elastic fields are presented analytically, and the heat flux of the crack interior is determined explicitly. Numerical results are offered to show the influences of the thermal conductivity coefficient, normal and shear loadings and crack velocity on the distributions of the heat flux, temperature difference across the crack surfaces, and thermal stress intensity factor. Figures illustrate that increasing the crack velocity leads to a more thermally impermeable crack and produces a bigger temperature difference across the crack surfaces.

Presented here are the results of an experimental investigation of two ultrathin miniature loop heat pipes (mLHPs) with different internal wicking structures: one with a primary wicking structure in the evaporator and a secondary wicking structure in the liquid line, and the other only with the same primary wicking structure in the evaporator, but no secondary wick. The systematic experimental investigation was conducted using natural convection as the cooling mechanism in order to study the heat transfer performance of the two mLHPs and fully examine the effects of the secondary wick. The results indicated that both of the test articles could effectively dissipate 12 W at all test orientations with a minimum total thermal resistances of 6.38 °C/W and 6.39 °C/W, respectively. However, the results indicated that the presence of the secondary wicking structure in the liquid line at low power loads resulted in more stable startup characteristics and a weaker dependence on the different orientations. Moreover, it was demonstrated that the steady-state evaporator temperatures of the test article with the secondary wicking structure in the liquid line were much lower than those observed for a 1-mm thick copper plate with the same geometric dimensions for all heat loads in the horizontal orientation, showing a higher thermal performance.

Design of effective microcooling systems to address the challenges of ever increasing heat flux from microdevices requires deep examination of real-time problems and has been tackled in depth. The most common (and apparently misleading) assumption while designing microcooling systems is that the heat flux generated by the device is uniform, but the reality is far from this. Detailed simulations have been performed by considering nonuniform heat load employing the configurations U, I, and Z for parallel microchannel systems with water and nanofluids as the coolants. An Intel ® Core ™ i7-4770 3.40 GHz quad core processor has been mimicked using heat load data retrieved from a real microprocessor with nonuniform core activity. This study clearly demonstrates that there is a nonuniform thermal load induced temperature maldistribution along with the already existent flow maldistribution induced temperature maldistribution. The suitable configuration(s) for maximum possible overall heat removal for a hot zone while maximizing the uniformity of cooling have been tabulated. An Eulerian–Lagrangian model of the nanofluids shows that such “smart” coolants not only reduce the hot spot core temperature but also the hot spot core region and thermal slip mechanisms of Brownian diffusion and thermophoresis are at the crux of this. The present work conclusively shows that high flow maldistribution leads to high thermal maldistribution, as the common prevalent notion is no longer valid and existing maldistribution can be effectively utilized to tackle specific hot spot location, making the present study important to the field.