The use of Plate Heat Exchanger (PHE) as condensers and evaporators increases every year. The easy and modular construction and the high thermal performance at very compact size make the PHE to an ideal heat exchanger for a wide range of applications. Due to the missing of authoritative models for the design of PHEs used as condensers or as evaporators they will typically be constructed larger than needed. For a physically based model more detailed knowledge is needed to take into account the flow and heat interactions during the condensation or evaporation process inside a PHE. In this work the two-phase flow in a PHE is analysed. For this purpose one gap of a PHE was built with two transparent polyurethane plates with the same geometrical parameter than the stainless steel plates of a commercial used PHE. Demineralized-water and air are used to define an exact 2-phase-flow. Measurements of the contact angles and surface energies of the stainless steel plates and the transparent polyurethane plates with different working fluids have been made to show the relation between the wettability and the surface energies of the plates. These measurements show a significant influence of the surface energies on the wettability of the steel and polyurethane plates and therefore it is necassary to take into account the plate material properties for the visualization experiments. A flow pattern map is developed and the typical flow patterns are presented and explained. The defined flow regimes converge with comparable data from the literature. The flow pattern of bubbly flow, irregular bubbly flow, film flow and slug flow can be identified. The film flow occurs over the whole range of the air flow rate and at superficial liquid velocities below 0.1 m/s. Above this limit at low flow rates of the gaseous phase a bubbly flow occurs and with increasing air flow rate the flow pattern changes at a superficial air velocity of 1.5 m/s to an irregular bubbly flow. With further rising of the gas phase fraction the irregular bubbly flow shifts at gas velocities nearly 4 m/s into a transition regime, which is marked by the mixed behaviour of the irregular bubbly and the slug flow regime. Slug flow can be identified when the superficial velocity of the air rises up to 7 m/s.

New generation supercomputers with three dimensional stacked chip architectures pose a major challenge with respect to removal of dissipated heat which can reach currently as high as 250 W/cm 2 in multilayer chip stacks of less than 0.3 cm 3 volume. Interlayer integrated water cooling [1] is a very promising approach for such high heat flux removal due to much larger thermal capacity and conductivity of water compared to air, the traditional cooling fluid. In the current work, a multiscale conjugate heat transfer model is developed for integrated water cooling of chip layers and validated with experimental measurements on a specially designed thermal test vehicle that simulates a four tier chip stack with a footprint of 1 cm 2 . The cooling heat transfer structure, which consists of microchannels with cylindrical pin fins, is conceived in such a way that it can be directly integrated with the device layout in multilayer chips. Every composite layer is cooled by water flow in microchannels (height: 100 μm), which are arranged in 2 port water inlet-outlet configuration. The total power removed in the stack is 390 W at a temperature gradient budget of 60 K from liquid inlet to maximal junction temperature, corresponding to about 1.3 kW/cm 3 volumetric heat flow. The computational cost and complexity of detailed CFD modeling of heat transfer in stacked chips with integrated cooling can be prohibitive. Therefore, the heat transfer structure is modeled using a porous medium approach, where the model parameters of heat transfer and hydrodynamic resistance are derived from averaging the results of the detailed 3D-CFD simulations of a single stream-wise row of fins. The modeling results indicate that an isotropic porous medium model does not accurately predict the measured temperature fields. The variation of material properties due to temperature gradients are found to be large, therefore variable properties are used in the model. It is also shown that the modeling of the heat transfer in the cooling sublayers requires the implementation of a porous medium approach with a local thermal non-equilibrium as well as orthotropic heat conduction and hydrodynamic resistance. The improved model reproduces the temperatures measured in the stack within 10%. The model is used to predict the behavior of multilayer stacks mimicking the change of heat fluxes resulting from variations in the computational load of the chips during their operation.

Almost all technical devices in use today are assemblies of individual pieces. For all force-based assembly methods, such as bolting or press-fitting, the thermal behavior is influenced by the contact resistance at the joint surface. For metal pieces in contact with each other, the authors have developed a measurement method and analysis tools enabling the determination of the contact heat transfer coefficient. Previously published results [1, 2, 3] have shown the dependence of the contact heat transfer coefficient on surface structure, contact pressure and material properties. The present work provides experimental and analytical data for the contact heat transfer coefficient and also proposes a model for calculating the real contact area of two surfaces which are placed under different contact pressures. Experiments were conducted for two material combinations with three different surface structures, while varying the contact pressures from 7 MPa to 230 MPa. When selecting average surface roughness (R z ) as a characterizing parameter for surface structure, the results did not show a consistent trend. Thus, in this paper R z was replaced by the real contact area between the two surfaces of interest. This area was determined by applying a refined method based on surface roughness measurements. The experimental data show a better consistency, when plotting the contact heat transfer coefficient relative to real contact area (F k ) rather than the previously used R z –values.

Impinging jets for convective cooling are used in several technical applications. Piston cooling with impinging oil jets is one key application. To improve the heat transfer between the surface of the piston and the oil film it is necessary to understand the underlying mechanisms of heat transfer at the boundary face. For this reason it is important to analyze the oil flow and to identify and evaluate the influence of the parameters governing film formation. Also the oil jet is investigated, because the film formation can be influenced by the jet. In the experiments the oil temperature is set to 30 °C or 60 °C and the pressure at the nozzle inlet is varied between 1.6 bar and 4.2 bar. The minimal Reynolds number is 125 and the maximum is 1924. The liquid Weber number varies between 2.2 × 10 −2 and 52.9 × 10 −2 . The results of the visualization measurements reveal the influence of the exit velocity, oil temperature and the related material properties on the film formation process. On the one hand the results show the macroscopic relation between Reynolds number and the level of instability. On the other hand the relation between Weber number and the break-up at the surface of the jet and accordingly of the film surface can be demonstrated.

It has been a common practice to use cooling passages in gas turbine blade in order to keep the blade temperatures within the operating range. Insufficiently cooled blades are subject to oxidation, to cause creep rupture, and even to cause melting of the material. To design better cooling passages, better understanding of the flow patterns within the complicated flow channels is essential. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. Power output and the efficiency of turbine are completely related to gas firing temperature from chamber. The increment of gas firing temperature is limited by the blade material properties. Advancements in the cooling technology resulted in high firing temperatures with acceptable material temperatures. To better design the cooling channels and to improve the heat transfer, many researchers are studying the flow patterns inside the cooling channels both experimentally and computationally. In this paper, the authors present the performance of three turbulence models using TEACH software code in comparison with the experimental values. To test the performance, a square duct with rectangular ribs oriented at 90° and 45° degree and placed at regular intervals. The channel also has bleed holes. The normalized Nusselt number obtained from simulation are validated with that of experiment. The Reynolds number is set at 10,000 for both the simulation and experiment. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. The three-dimensional turbulent flows and heat transfer are numerically studied by using several different turbulence models, such as non-linear low-Reynolds number k-omega and Reynolds Stress (RSM) models. In k-omega model the cubic terms are included to represent the effects of extra strain-rates such as streamline curvature and three-dimensionality on both turbulence normal and shear stresses. The finite volume difference method incorporated with the higher-order bounded interpolation scheme has been employed in the present study. The outcome of this study will help determine the best suitable turbulence model for future studies.

Heat transfer in the rotary kiln is a complex phenomenon due to the different modes of heat transfer. In the first part of this study, the local heat transfer coefficients are analysed theoretically, to describe the heat transfer mechanisms in the cross section of the rotary kiln. Furthermore, the axial solid motion along the length of the kiln is considered in the local surfaces which exchanges the heat. A pilot plant drum of length 0.45 m and internal diameter of 0.6 m has been designed and fabricated to measure the contact heat transfer coefficient from the kiln wall to the covered solid bed. The cylinder is heated continuously by means of three electrical heaters fixed externally around the cylinder at various positions. K-type thermocouples have been used to measure the wall and solid bed temperature along the circumferential and the radial direction. Experiments are performed with various materials such as Quartz sand and Copper pellets of different size, shape and thermal conductivity. The effect of the material properties, the rotational speed (1–6 rpm) and the filling degree (10–20%) on the contact heat transfer have been studied thoroughly.

Open cell metal foam offers an interesting combination of materials properties from a heat exchanger point of view such as a high specific surface area, tortuous flow paths for flow mixing and low weight. A heat exchanger design with metal foams is studied in this work, aimed at low airside pressure drop. It consists of a single row of Al tubes covered with thin layers (4–8 mm) of metal foam. Through wind tunnel testing the impact of various parameters on the thermo-hydraulic performance was considered, including the Reynolds number, the tube spacing, the foam height and the type of foam. The results indicated that if a good metallic bonding between the foam and the tubes can be achieved, metal foam covered tubes with a small tube spacing, small foam heights and made of foam with a high specific surface area potentially offer strong benefits at higher air velocities (> 4 m/s) compared to helically finned tubes. The bonding was done by conductive epoxy glue and was found to have a strong impact on the final results, showing a strong need for a cost-effective and efficient brazing process to connect metal foams to the tube surfaces.

Thermal transport at the interface between Lennard-Jones crystals is explored via non-equilibrium molecular dynamics simulations. The vibrational properties of each crystal are varied by changing the atomic mass of the crystal. By applying a constant thermal flux across the two-crystal composite system, a steady-state temperature gradient is established and thermal boundary conductance at the interface between the crystals is calculated via Fourier’s law. With the material properties of the two crystals fixed, thermal boundary conductance can be affected by an intermediate layer inserted between the two crystals. It is found that when the interstitial layer atomic mass is between those values of the crystals comprising the interface, interfacial transport is enhanced. This layer helps bridge the gap between the different vibrational spectra of the two materials, thus enhancing thermal transport, which is maximized when the interstitial layer atomic mass approaches the average mass of the two fixed crystals. The degree of enhancement depends on the vibrational mismatch between the interstitial layer and the crystals comprising the interface, and we report an increase in thermal boundary conductance of up to 50%.

Electron beam interaction with thin films is a critical phenomenon in applications such as nanostructure fabrication, surface treatment and curing, surface sterilization, scanning electron microscopy, and electron beam lithography. Unlike bulk solids, thin films whose thickness is on the same order of magnitude as the penetration depth require consideration of interface effects: namely resistance to heat transfer and more electron scattering. In such cases, the energy deposition profile, the location of interfaces and the associated change in material properties must be accounted for. In this paper we describe the thermal simulation of a thin copper film (0.5 μm, 1 μm, 2μm) on a Si substrate irradiated by an electron beam (10 keV, 20 keV, 40 keV). We explore the effect of the interface position relative to the electron range and the local heating effects associated with continuous or long pulse beams.

The main purpose of this study was to confirm operability and effectiveness of the complex methods developed for theoretical prediction and experimental-computational determining some properties of modern highly porous materials, used as thermal protection shields in objects of space engineering, power engineering, etc. Them concern Fibrous Materials (FM), Open-Cell Reticulated Foams (OCRF) etc . The basis for the method proposed is in the combination of Direct Mathematical Simulation (DMS) for global structure of the complex irregular systems, which have the property of local regularity and Inverse Heat Transfer Problem (IHTP) methods. This approach makes possible to obtain and to predict such properties as radiation and molecular thermal conductivities, energy accommodation coefficient, complex refractive index, scattering indicatrix, scattering and absorption factors, etc. Such problems are of great practical importance in the study of material properties.

Solar collectors with surface receivers have low overall energy conversion efficiencies due to large emissive losses at high temperatures. Alternatively, volumetric receivers promise increased performance because solar radiation can be transferred into a fluid medium, which subsequently reduces the concentrated heat at the surface. Nanofluid-based direct solar receivers, where nanoparticles in a liquid medium can scatter and absorb solar radiation, have recently received interest to efficiently distribute and store the thermal energy. We present a combined modeling and experimental study to investigate the efficiency of fluid-based solar receivers seeded with carbon-coated absorbing nanoparticles. A simple one-dimensional transient heat transfer model was developed to compare idealized surface receivers to idealized volumetric receivers. In the limit of idealized behavior, volumetric receivers were shown to be more efficient than selective-surfaces for high concentration levels ( C > 100) and/or tall receiver designs ( H > 10 cm). Furthermore, volumetric receivers allowed the working range of the fluid to be extended to higher temperatures while maintaining relatively high receiver efficiency. We also designed and custom built a cylindrical receiver to experimentally demonstrate the concept of nanofluid-based receivers and validate the modeling efforts. We explored the effect of particle characteristics such as size, distribution, and material properties, as well as collector parameters such as absorbing depth and level of solar concentration. The work offers design guidelines for the development of efficient volumetric receivers for future solar thermal energy conversion systems.

The development of high performance thermal management strategies offers opportunities to increase energy conversion efficiencies for solar thermoelectric systems. In particular, heat pipes and two-phase thermosyphons have received increased interest due to their ability to passively and efficiently transport heat using liquid phase-change. However, the high manufacturing and materials costs limit the broad utilization of such cooling solutions. In this work, we investigate heat pipe designs using glass where the manufacturing methods can be inexpensive for solar thermoelectric systems. We developed an analytical model based on dimensionless thermal resistances that determines how material properties, geometry, scaling and solar concentration affect heat transfer performance. We simultaneously investigated the feasibility of three realistic heat pipe solar thermoelectric systems. The results from the work offer design guidelines for the development of high performance, low cost heat pipes for solar thermoelectric systems.

Relative to solar water heaters, solar air heaters have received relatively little investigation and have resulted in few commercial products. However, in the context of a Humidification-Dehumidification (HDH) Desalination cycle, air heating accounts for advantages in cycle performance. Solar collectors can be over 40% of an air-heated HDH system’s cost, thus design optimization is crucial. Best design practices and sensitivity to material properties for solar air heaters are investigated, and absorber solar absorptivity and glazing transmissivity are found to have the strongest effect on performance. Wind speed is also found to have an impact on performance. Additionally a well designed, and likely low cost, collector includes a double glazing and roughened absorber plates for superior heat transfer to the airstream. A collector in this configuration performs better than current collectors with an efficiency of 58% at a normalized gain of 0.06 K m 2 /W.