Thermal Resistance

— The purpose of this project is to develop a procedure to numerically model airflow over wing using hypermesh and FLUENT. Three dimensional models for the airfoil 2412 were created, drawn and meshed in hypermesh using geometry data gathered by the National Advisory Committee for Aeronautics. Those models were read into FLUENT where boundary conditions flows were applied and the discretized Navier-Stokes equations were solved numerically. Numerical prediction of incompressible turbulent flow has been performed on a 3-D wing moving with a velocity of 50 m/s. CATIA, 3D modeling software was used to model 3D surface modeling of the wing. FLUENT, the computational fluid dynamics code, which incorporate k-ε turbulence model and segregated implicit solver was used to perform computation. The aerodynamic analysis was performed to study the flow behavior of the air over the wing. The analysis includes the contours of pressure and velocity that impacts the wing followed by an evaluation of the coefficient of lift.

... The thermoelectric module is clamped between a cooling jacket and a heater block. The heater block is made from aluminum. ... To control the hot-end temperature T H , the coolant flow through the cooling jacket is turned on and off by two control valves installed in the flow lines. ...

Heat pipes are very flexible systems with regard to effective thermal control. They can easily be implemented as heat exchangers inside sorption and vapour-compression heat pumps, refrigerators and other types of heat transfer devices. Their heat transfer coefficient in the evaporator and condenser zones is 10 3 -10 5 W/m 2 K, heat pipe thermal resistance is 0.01-0.03 K/W, therefore leading to smaller area and mass of heat exchangers. Miniature and micro heat pipes are welcomed for electronic components cooling and space two-phase thermal control systems. Loop heat pipes, pulsating heat pipes and sorption heat pipes are the novelty for modern heat exchangers. Heat pipe air preheaters are used in thermal power plants to preheat the secondary-primary air required for combustion of fuel in the boiler using the energy available in exhaust gases. Heat pipe solar collectors are promising for domestic use. This paper reviews mainly heat pipe developments in the Former Soviet Union Countries. Some new results obtained in USA and Europe are also included.

Background, aim, and scope The interest in polyethylene terephthalate (PET) recycling is quite recent, but it has been growing steadily over the past few years. In this context, the aim of this paper is to assess the eco-profile, the energy savings and the environmental benefits of the use of recycled raw materials to manufacture products for thermal insulation of buildings in Italy (i.e., PET bottles post-consumer). Materials and methods The life cycle analysis is developed according to ISO 14040/44. In this paper, based on the LCA, the main types of environmental impact of a thermal insulation product have been outlined. This study is specifically focused on polyester nonwovens, produced by a company located in Italy. The cradle-to-gate life cycle inventory is performed for the mass of product needed to give a thermal resistance R of 1 (m2 K/W). The calculation of the impacts is done with SimaPro software. With an environmental product declaration-oriented approach, a set of impact categories is used for the classification and characterisation of the life cycle impact assessment. Results The results of the impact assessment for 1m2 K/W of thermal insulation panels made with recycled PET are then compared with similar products made with virgin PET. The lower impact associated with the recycled PET for each category is underlined: the percentage reduction is around 46% in the GWP category. In the production process, the fiber-spinning phase results as the most relevant in terms of energy consumption. In addition, the energy saved when applying the thermal insulation in a building is estimated at 87 MJ/m2 per unit area per year in Rome. All the energy used during the production of a thermal insulation panel is recovered in about 2 years. Conclusions The product shows significantly low environmental impacts thanks to the use of non-virgin PET, thus maintaining high mechanical and physical properties. If the recovery of PET from separate waste collection in Italy increases, this would reduce the share of waste PET purchased from foreign countries and would therefore reduce further the impact of transports for the production of the thermal insulation panel under investigation.

This paper presents the thermal properties of different knitted fabric structures made from cotton, regenerated bamboo and cotton-bamboo blended yarns. Three blends of fibres (100% cotton, 50:50 cotton: bamboo and 100% bamboo) were used to produce three yarn counts (30 tex, 24 tex and 20 tex). Each of these yarns was used to manufacture three types of knitted structures namely plain, rib and interlock. It was found that the thermal conductivity of knitted fabrics generally reduces as the proportion of bamboo fibre increases. For the same fibre blend proportion, the thermal conductivity was lower for fabrics made from finer yarns. The thermal conductivity and thermal resistance values of interlock fabric was the maximum followed by the rib and plain fabrics. The water vapour permeability and air permeability of knitted fabrics increase as the proportion of bamboo fibre increases. The air permeability and water vapour permeability values were higher for plain fabric as compared to those values of rib and interlock fabrics.

An intensive study has been performed to understand and tune deep reactive ion etch (DRIE) processes for optimum results with respect to the silicon etch rate, etch profile and mask etch selectivity (in order of priority) using state-of-the-art dual power source DRIE equipment. The research compares pulsed-mode DRIE processes (e.g. Bosch technique) and mixed-mode DRIE processes (e.g. cryostat technique). In both techniques, an inhibitor is added to fluorine-based plasma to achieve directional etching, which is formed out of an oxide-forming (O2) or a fluorocarbon (FC) gas (C4F8 or CHF3). The inhibitor can be introduced together with the etch gas, which is named a mixed-mode DRIE process, or the inhibitor can be added in a time-multiplexed manner, which will be termed a pulsed-mode DRIE process. Next, the most convenient mode of operation found in this study is highlighted including some remarks to ensure proper etching (i.e. step synchronization in pulsed-mode operation and heat control of the wafer). First of all, for the fabrication of directional profiles, pulsed-mode DRIE is far easier to handle, is more robust with respect to the pattern layout and has the potential of achieving much higher mask etch selectivity, whereas in a mixed-mode the etch rate is higher and sidewall scalloping is prohibited. It is found that both pulsed-mode CHF3 and C4F8 are perfectly suited to perform high speed directional etching, although they have the drawback of leaving the FC residue at the sidewalls of etched structures. They show an identical result when the flow of CHF3 is roughly 30 times the flow of C4F8, and the amount of gas needed for a comparable result decreases rapidly while lowering the temperature from room down to cryogenic (and increasing the etch rate). Moreover, lowering the temperature lowers the mask erosion rate substantially (and so the mask selectivity improves). The pulsed-mode O2 is FC-free but shows only tolerable anisotropic results at -120 °C. The downside of needing liquid nitrogen to perform cryogenic etching can be improved by using a new approach in which both the pulsed and mixed modes are combined into the so-called puffed mode. Alternatively, the use of tetra-ethyl-ortho-silicate (TEOS) as a silicon oxide precursor is proposed to enable sufficient inhibiting strength and improved profile control up to room temperature. Pulsed-mode processing, the second important aspect, is commonly performed in a cycle using two separate steps: etch and deposition. Sometimes, a three-step cycle is adopted using a separate step to clean the bottom of etching features. This study highlights an issue, known by the authors but not discussed before in the literature: the need for proper synchronization between gas and bias pulses to explore the benefit of three steps. The transport of gas from the mass flow controller towards the wafer takes time, whereas the application of bias to the wafer is relatively instantaneous. This delay causes a problem with respect to synchronization when decreasing the step time towards a value close to the gas residence time. It is proposed to upgrade the software with a delay time module for the bias pulses to be in pace with the gas pulses. If properly designed, the delay module makes it possible to switch on the bias exactly during the arrival of the gas for the bottom removal step and so it will minimize the ionic impact because now etch and deposition steps can be performed virtually without bias. This will increase the mask etch selectivity and lower the heat impact significantly. Moreover, the extra bottom removal step can be performed at (also synchronized!) low pressure and therefore opens a window for improved aspect ratios. The temperature control of the wafer, a third aspect of this study, at a higher etch rate and longer etch time, needs critical attention, because it drastically limits the DRIE performance. It is stressed that the exothermic reaction (high silicon loading) and ionic impact (due to metallic masks and/or exposed silicon) are the main sources of heat that might raise the wafer temperature uncontrollably, and they show the weakness of the helium backside technique using mechanical clamping. Electrostatic clamping, an alternative technique, should minimize this problem because it is less susceptible to heat transfer when its thermal resistance and the gap of the helium backside cavity are minimized; however, it is not a subject of the current study. Because oxygen-growth-based etch processes (due to their ultra thin inhibiting layer) rely more heavily on a constant wafer temperature than fluorocarbon-based processes, oxygen etches are more affected by temperature fluctuations and drifts during the etching. The fourth outcome of this review is a phenomenological model, which explains and predicts many features with respect to loading, flow and pressure behaviour in DRIE equipment including a diffusion zone. The model is a reshape of the flow model constructed by Mogab, who studied the loading effect in plasma etching. Despite the downside of needing a cryostat, it is shown that—when selecting proper conditions—a cryogenic two-step pulsed mode can be used as a successful technique to achieve high speed and selective plasma etching with an etch rate around 25 µm min-1 (<1% silicon load) with nearly vertical walls and resist etch selectivity beyond 1000. With the model in hand, it can be predicted that the etch rate can be doubled (50 µm min-1 at an efficiency of 33% for the fluorine generation from the SF6 feed gas) by minimizing the time the free radicals need to pass the diffusion zone. It is anticipated that this residence time can be reduced sufficiently by a proper inductive coupled plasma (ICP) source design (e.g. plasma shower head and concentrator). In order to preserve the correct profile at such high etch rates, the pressure during the bottom removal step should be minimized and, therefore, the synchronized three-step pulsed mode is believed to be essential to reach such high etch rates with sufficient profile control. In order to improve the etch rate even further, the ICP power should be enhanced; the upgrading of the turbopump seems not yet to be relevant because the throttle valve in the current study had to be used to restrict the turbo efficiency. In order to have a versatile list of state-of-the-art references, it has been decided to arrange it in subjects. The categories concerning plasma physics and applications are, for example, books, reviews, general topics, fluorine-based plasmas, plasma mixtures with oxygen at room temperature, wafer heat transfer and high aspect ratio trench (HART) etching. For readers 'new' to this field, it is advisable to study at least one (but rather more than one) of the reviews concerning plasma as found in the first 30 references. In many cases, a paper can be classified into more than one category. In such cases, the paper is directed to the subject most suited for the discussion of the current review. For example, many papers on heat transfer also treat cryogenic conditions and all the references dealing with highly anisotropic behaviour have been directed to the category HARTs. Additional pointers could get around this problem but have the disadvantage of creating a kind of written spaghetti. I hope that the adapted organization structure will help to have a quick look at and understanding of current developments in high aspect ratio plasma etching. Enjoy reading... Henri Jansen 18 June 2008

A double-pipe helical heat exchanger was numerically modeled for laminar fluid flow and heat transfer characteristics under different fluid flow rates and tube sizes. Two different tube diameters were used. The overall heat transfer coefficients were calculated for both parallel flow and counterflow. Validation of the simulations was conducted by comparing the Nusselt numbers in the inner tube with those found in literature; the results fell within the range found in the literature. The greatest thermal resistance was found in the annular region. The annulus Nusselt number was correlated with a modified Dean number, and showed a strong linear relationship.

DOE-2 energy simulation program was used to determine the effects of rooftop garden on the annual energy consumption, cooling load and roof thermal transfer value (RTTV) of a ®ve-story hypothetical commercial building in Singapore. The thermal resistances (R-values) of tur®ng, shrubs and trees were estimated using data from site measurements, and the effects on the building energy consumption of a rooftop garden with these three types of plants were simulated. Two soil types with different soil thickness on the building roof were also simulated. The results showed that the installation of rooftop garden on the ®ve-story commercial building can result in a saving of 0.6±14.5% in the annual energy consumption, and shrubs was found to be most effective in reducing building energy consumption. The results also revealed that the increase of soil thickness would further reduce the building energy consumption and the moisture content of soil can affect the outcome quite substantially. #

Several researches have been conducted to determine the fresh and hardened properties of crumb rubber concrete (CRC), concrete containing crumb rubber as partial replacement to fine aggregate. The benefits of outlined from these works include low density, good thermal resistivity, better sound absorption, increase slump values and toughness, and better impact resistivity of the resulting concrete. Reduction in strength, increase in water absorption and are some of the adverse effect of utilizing crumb rubber in concrete. The study reported in this paper is a development of crumb rubber hollow concrete block (CRHCB). For the purpose of this work, sixty-four trial mixes were prepared to produce hollow concrete blocks of dimension 390 mm × 190 mm × 190 mm using 0%, 10%, 25% and 50% crumb rubber (CR) as replacement of fine aggregate. Tests conducted on the hardened concrete include compressive strength, thermal conductivity, electrical resistivity, acoustic absorption and transmission loss, and electrical resistivity. It has been found that CRHCB can be produced as load-bearing hollow blocks as well as lightweight hollow blocks. The CRHCB also has better thermal, acoustic and electrical properties in comparison with conventional hollow block.

Selection and determination of optimum thickness of insulation is of prime interest for many engineering applications. In this study, a simple method is developed to estimate the thickness of thermal insulation required to arrive at a desired heat flow or surface temperature for flat surfaces, ducts and pipes. The proposed simple method covers the temperature difference between ambient and outside temperatures up to 250°C and the temperature drop through insulation up to 1000°C. The proposed correlation calculates the thermal thickness up to 250 mm for flat surfaces and estimates the thermal thickness for ducts and pipes with outside diameters up to 2400 mm. The accuracy of the proposed method was found to be in excellent agreement with the reported data for wide range of conditions where the average absolute deviation between reported data and the proposed method is around 3.25%. The method is based on basic fundamentals of heat transfer and reliable data. Therefore the formulated simple-to-use expression is justified and applicable to any industrial application.

A multi-objective thermal design optimization and comparative study of electronics cooling technologies is presented. The cooling technologies considered are: continuous parallel micro-channel heat sinks, inline and staggered circular pin-fin heat sinks, offset strip fin heat sinks, and single and multiple submerged impinging jet(s). Using water and HFE-7000 as coolants, Matlab's multi-objective genetic algorithm functions were utilized to determine the optimal thermal design of each technology based on the total thermal resistance and pumping power consumption under constant pressure drop and heat source base area of 100 mm 2 . Plots of the Pareto front indicate a trade-off between the total thermal resistance and pumping power consumption. In general, the offset strip fin heat sink outperforms the other cooling technologies.

A lumped-parameter thermal model of a cylindrical LiFePO 4 /graphite lithium-ion battery is developed. Heat transfer coefficients and heat capacity are determined from simultaneous measurements of the surface temperature and the internal temperature of the battery while applying 2 Hz current pulses of different magnitudes. For internal temperature measurements, a thermocouple is introduced into the battery under inert atmosphere. Heat transfer coefficients (thermal resistances in the model) inside and outside the battery are obtained from thermal steady state temperature measurements, whereas the heat capacity (thermal capacitance in the model) is determined from the transient part. The accuracy of the estimation of internal temperature from surface temperature measurements using the model is validated on current-pulse experiments and a complete charge/discharge of the battery and is within 1.5 • C. Furthermore, the model allows for simulating the internal temperature directly from the measured current and voltage of the battery. The model is simple enough to be implemented in battery management systems for electric vehicles.

Several researches have been conducted to determine the fresh and hardened properties of crumb rubber concrete (CRC), concrete containing crumb rubber as partial replacement to fine aggregate. The benefits of outlined from these works include low density, good thermal resistivity, better sound absorption, increase slump values and toughness, and better impact resistivity of the resulting concrete. Reduction in strength, increase in water absorption and are some of the adverse effect of utilizing crumb rubber in concrete. The study reported in this paper is a development of crumb rubber hollow concrete block (CRHCB). For the purpose of this work, sixty-four trial mixes were prepared to produce hollow concrete blocks of dimension 390 mm  190 mm  190 mm using 0%, 10%, 25% and 50% crumb rubber (CR) as replacement of fine aggregate. Tests conducted on the hardened concrete include compressive strength, thermal conductivity, electrical resistivity, acoustic absorption and transmission loss, and electrical resistivity. It has been found that CRHCB can be produced as load-bearing hollow blocks as well as lightweight hollow blocks. The CRHCB also has better thermal, acoustic and electrical properties in comparison with conventional hollow block.

DOE-2 energy simulation program was used to determine the effects of rooftop garden on the annual energy consumption, cooling load and roof thermal transfer value (RTTV) of a five-story hypothetical commercial building in Singapore. The thermal resistances (R-values) of turfing, shrubs and trees were estimated using data from site measurements, and the effects on the building energy consumption of a rooftop garden with these three types of plants were simulated. Two soil types with different soil thickness on the building roof were also simulated. The results showed that the installation of rooftop garden on the five-story commercial building can result in a saving of 0.6–14.5% in the annual energy consumption, and shrubs was found to be most effective in reducing building energy consumption. The results also revealed that the increase of soil thickness would further reduce the building energy consumption and the moisture content of soil can affect the outcome quite substantially.

Romania's inclusion in the European transport network and implementation of Aeolian turbines in massive groups imply increases in the transport capacity of some lines, required to transport or evacuate high powers over the existing capacities.

Phase change materials (PCMs) can store large amounts of heat or cooling in a small amount of material, they potentially have less weight and volume compared with other thermal energy storage materials. Thermal energy storage applications such as solar hot water systems and off peak refrigeration systems are able to use PCMs to store heat or cooling. However, research has shown that the effectiveness of these systems heavily depends on the arrangement of the PCM system, which affects both the storage density and the thermal resistance to heat transfer. However, specifying as well as determining an effective PCM system has been difficult in the past because it involves using numerical modelling which is time consuming. This paper presents the results of an experimental investigation carried out on a tube-in-tank design filled with PCM for cold storage applications. The PCMs used are salt hydrate with phase change temperature of À27°C and water. From the experimental measurements, the average heat exchange effectiveness of the storage tank was determined and a characteristic design curve has been developed as a function of the measured average NTU.

Because of concerns over the construction industry's heavy use of cement and the general dissatisfaction with the performance of building envelopes with respect to durability, there is a growing demand for a novel class of "green" binders. Geopolymer binders have re-emerged as binders that can be used as a replacement for Portland cement given their numerous advantages over the latter including lower carbon dioxide emissions, greater chemical and thermal resistance, combined with enhanced mechanical properties at both normal and extreme exposure conditions. The paper focuses on the use of geopolymer binders in building applications. It discusses the various options for starting materials and describes key engineering properties associated with geopolymer compositions that are ideal for structural applications. Specific properties, such as compressive strength, density, pore size distribution, cumulative water absorption, and acid resistance, are comparable to the specifications for structures incorporating conventional binders. This paper presents geopolymer binders, with their three dimensional microstructure, as material for structural elements that can be used to advance the realization of sustainable building systems.

An experimental study was carried out on a scraped surface heat exchanger used for freezing of waterethanol mixture and aqueous sucrose solution. The influence of various parameters on heat transfer intensity was established: product type and composition, flow rate, blade rotation speed, distance between blades and wall. During starting (transient period) the solution is first supercooled, then ice crystals appear on the scraped surface (heterogeneous nucleation) and no more supercooling is observed. It seems that, when blades are 3 mm far from the surface, a constant ice layer is formed having this thickness and acting as a thermal resistance. But when the blades rotate at 1 mm from the surface, periodically all the ice layer is removed despite the surface is not really scraped. This could simplify ice generator technology. An internal heat transfer coefficient was defined; it depends mainly on rotation speed. Correlations were proposed for its prediction, which could be applied, at least as a first approach, for the most common freezing applications of scraped surface heat exchanger i.e. ice creams (which are derived from sucrose solutions) and two-phase secondary refrigerants (which are principally ethanol solutions).

This paper describes the stress distribution of the SRM University FSAE Car brake rotor by using FEA. The finite element analysis is performed by using computer aided design (CAD) software. The main objective is to investigate and analyze the thermal and structural stress distribution of brake rotor at the real time condition during braking process and then comparing it with a modified rotor having ceramic coating. The paper describes the mesh optimization with using finite element analysis technique to predict the higher stress and critical region on the component. The optimization is carried out to reduce the stress concentration and material on the surface of the rotor. With using computer aided design (CAD), SOLIDWORKS software the structural model of a brake rotor is developed. Furthermore, the finite element analysis performed with using software ANSYS.

This paper provides a review of thcrmoclectric cooling and its application to the cooling of electronic equipment. A background discussion of thermoelectric cooling is provided bricfly citing early history, current developments, and thc defining thertnoclcctric hcat pumping equations. Scvcral examples arc provided of early IBM applications of thcrmoclectric cooling. An analysis to asscss thcrmoclcctric cooling enhancement in terms of increases in allowable powcr dissipation or chip tcmpcrature reduction is dcscribcd along U ith rcsults. 0-7803-5916-W00/$10.00 02000 IEEE 1 Sixteenth IEEE SEMI-THERMm Symposium

The thermal degradation and fire resistance of different natural fibre composites were studied. Unsaturated polyester (UP) and modified acrylic resins (Modar) were used as matrix composites. The smoke emission of the materials was also analysed, as well as, the performance against the fire of the biocomposites and glass reinforced composites was compared. Thermal degradation indicated that the Modar matrix composites were more resistant to temperature than the composites with UP matrix. Flax fibre, due to their low lignin content, exhibit the best thermal resistance among the natural fibres studied.

A computer's CPU may perform millions of calculations every second .As the Processor continues to work at a rapid pace, it begins to generate heat. If this heat is not kept in check, the processor could overheat and eventually destroy itself. Fortunately, CPUs include a heat sink, which dissipates the heat from the processor, preventing it from overheating with the increase in heat dissipation from microelectronic devices and the reduction in overall form factors, thermal management becomes a more and more important element of electronic product design. Both the performance reliability and life expectancy of electronic equipment are inversely related to the component temperature of the equipment. The relationship between the reliability and the operating temperature of a typical silicon semiconductor device shows that a reduction in the temperature corresponds to an exponential increase in the reliability and life expectancy of the device. Therefore, long life and reliable performance of a component may be achieved by effectively controlling the device operating temperature within the limits set by the device design engineers.

Romania's inclusion in the European transport network and implementation of Aeolian turbines in massive groups imply increases in the transport capacity of some lines, required to transport or evacuate high powers over the existing capacities.

We report on the design, fabrication, and evaluation of large-aperture, oxide-confined 850 nm vertical cavity surface emitting lasers (VCSELs) with high modulation bandwidth at low current densities. We also compare the use of InGaAs and GaAs quantum wells (QWs) in the active region. Both VCSELs reach an output power of 9 mW at room temperature, with a thermal resistance of 1.9 • C/mW. The use of InGaAs QWs improves the high-speed performance and enables a small-signal modulation bandwidth of 20 GHz at 25 • C and 15 GHz at 85 • C. At a constant bias current density of only 11 kA/cm 2 , we generate open eyes under large-signal modulation at bit rates up to 25 Gbit/s at 85 • C and 30 Gbit/s at 55 • C.

Heat pipe is a special type of heat exchanger that transfers large amount of heat due to the effect of capillary action and phase change heat transfer principle. Recent development in the heat pipe includes high thermal conductivity fluids like nanofluids, sealed inside to extract the maximum heat. This paper reviews, influence of various factors such as heat pipe tilt angle, charged amount of working fluid, nanoparticles type, size, and mass/volume fraction and its effect on the improvement of thermal efficiency, heat transfer capacity and reduction in thermal resistance. The nanofluid preparation and the analysis of its thermal characteristics also have been reviewed.

This paper reports the optimal geometry of an array of fins that minimizes the thermal resistance between the substrate and the flow forced through the fins. The flow regime is laminar. Two fin types are considered: round pin fins, and staggered parallel-plate fins. The optimization of each array proceeds in two steps: The optimal fin thickness is selected in the first step, and the optimal thickness of the fluid channel is selected in the second. The pin-fin array is modeled as a Darcy-flow porous medium. The flow past each plate fin is in the boundary layer regime. The optimal design of each array is described in terms of dimensionless groups. It is shown that the minimum thermal resistance of plate-fin arrays is approximately half of the minimum thermal resistance of heat sinks with continuous fins and fully developed laminar flow in the channels.

The thermal conductivity of aluminum matrix composites having a high volume fraction of SiC particles is investigated by comparing data for composites fabricated by infiltrating liquid aluminum into preforms made either from a single particle size, or by mixing and packing SiC particles of two largely different average sizes (170 and 16 m). For composites based on powders with a monomodal size distribution, the thermal conductivity increases steadily from 151 W/m K for particles of average diameter 8 m to 216 W/m K for 170 m particles. For the bimodal particle mixtures the thermal conductivity increases with increasing volume fraction of coarse particles and reaches a roughly constant value of 220 W/m K for mixtures with 40 or more vol.% of coarse particles. It is shown that all present data can be accounted for by the differential effective medium (DEM) scheme taking into account a finite interfacial thermal resistance.

Light emitting diodes, LEDs, historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors have led to a movement towards general illumination. The increased electrical currents used to drive the LEDs have focused more attention on the thermal paths in the developments of LED power packaging. The luminous efficiency of LEDs is soon expected to reach over 80 lumens/W, this is approximately 6 times the efficiency of a conventional incandescent tungsten bulb. Thermal management for the solid-state lighting applications is a key design parameter for both package and system level. Package and system level thermal management is discussed in separate sections. Effect of chip packages on junction to board thermal resistance was compared for both SiC and Sapphire chips. The higher thermal conductivity of the SiC chip provided about 2 times better thermal performance than the latter, while the under-filled Sapphire chip package can only catch the SiC chip performance. Later, system level thermal management was studied based on established numerical models for a conceptual solid-state lighting system. A conceptual LED illumination system was chosen and CFD models were created to determine the availability and limitations of passive air-cooling.

A new physical quantity, E h ¼ 1 2 Q vh T , has been identified as a basis for optimizing heat transfer processes in terms of the analogy between heat and electrical conduction. This quantity, which will be referred to as entransy, corresponds to the electric energy stored in a capacitor. Heat transfer analyses show that the entransy of an object describes its heat transfer ability, as the electrical energy in a capacitor describes its charge transfer ability. Entransy dissipation occurs during heat transfer processes as a measure of the heat transfer irreversibility. The concepts of entransy and entransy dissipation were used to develop the extremum principle of entransy dissipation for heat transfer optimization. For a fixed boundary heat flux, the conduction process is optimized when the entransy dissipation is minimized, while for a fixed boundary temperature the conduction is optimized when the entransy dissipation is maximized. An equivalent thermal resistance for multi-dimensional conduction problems is defined based on the entransy dissipation, so that the extremum principle of entransy dissipation can be related to the minimum thermal resistance principle to optimize conduction. For examples, the optimum thermal conductivity distribution was obtained based on the extremum principle of entransy dissipation for the volume-to-point conduction problem. The domain temperature is substantially reduced relative to the uniform conductivity case. Finally, a brief introduction on the application of the extremum principle of entransy dissipation to heat convection is also provided.

This paper introduces a comparison of different measuring methods of buildings fabric thermal resistance, including the test wall measuring points arrangements and measurement results, conducted in a test chamber in Cagliari (Italy) in summer 2009. Two methods and their measurement uncertainties are presented and compared by the compatibility of measurement study.

A field study, conducted in 189 dwellings in winter and 205 dwellings in summer, included measurement of hygro-thermal conditions and documentation of occupant responses and behavior patterns. Both samples included both passive and actively space-conditioned dwellings. Predicted mean votes (PMV) computed using Fanger's model yielded significantly lower-than-reported thermal sensation (TS) values, especially for the winter heated and summer air-conditioned groups. The basic model assumption of a proportional relationship between thermal response and thermal load proved to be inadequate, with actual thermal comfort achieved at substantially lower loads than predicted. Survey results also refuted the model's second assumption that symmetrical responses in the negative and positive directions of the scale represent similar comfort levels. Results showed that the model's curve of predicted percentage of dissatisfied (PPD) substantially overestimated the actual percentage of dissatisfied within the partial group of respondents who voted TS > 0 in winter as well as within the partial group of respondents who voted TS < 0 in summer. Analyses of sensitivity to possible survey-related inaccuracy factors (metabolic rate, clothing thermal resistance) did not explain the systematic discrepancies. These discrepancies highlight the role of contextual variables (local climate, expectations, available control) in thermal adaptation in actual settings. Collected data was analyzed statistically to establish baseline data for local standardized thermal and energy calculations. A 90% satisfaction criterion yielded 19.5 C and 26 C as limit values for passive winter and summer design conditions, respectively, while during active conditioning periods, set-point temperatures of 21.5 C and 23 C should be assumed for winter and summer, respectively.

The vacuum insulation panel (VIP) is a high performance thermal insulation component recently introduced into building technology. Its high thermal resistivity provides new solutions for slim but still energy efficient building envelopes. One of the key issues for building application is to minimize failure in service and to ensure a service life in the order of several decades under typical stress conditions especially thermal and hygric effects. However, little experience exists up to now on the long-term properties and the durability of VIPs. This article describes aging mechanisms and reports experimental results for different temperature and humidity induced deteriorations. A functional representation of the measured data at steady state conditions is introduced. For specific VIP applications the internal pressure increase is calculated on the basis of a dynamic thermal model. End-of-life criteria and respective service life estimates are discussed as well. #

Thermo-physiological comfort aspects of compression athletic wear have been studied. Core-spun elastane-cotton blended yarns with different elastane proportion, elastane stretch and twist multiplier have been spun and single jersey knitted fabrics are prepared. A three-level three-variable factorial design technique proposed by Box and Behnken has been used to study the interaction effects of the variables on the characteristics of fabrics. The influence of these variables on physical and comfort properties of fabric is studied, the response surface equations for all the properties are derived and the design variables are optimized for various fabric properties. The fabrics become heavier and thicker, and show improved thermal resistance, lower air and water permeability and poor moisture management properties, with the increase in proportion of elastane and level of elastane stretch. Higher twist results in better air and water vapour permeability but lower thermal resistance and wicking.

The new European energy regulation now considers a high standard of thermal protection in buildings with reasonable energy consumption, satisfactory thermal comfort conditions and low operational costs. A series of significant restrictions on the disposal of used tires in landfills, stockpiles, or illegal dumping grounds are also imposed in recent European Union directives. The potential use of crumb rubber-concrete combination, in favor of these arrangements, for producing a low cost and lightweight composite brick with improved thermal resistance is examined here. The physico-mechanical and thermal insulation performances of these rubber-added bricks are investigated. The obtained compressive strength, flexural strength, splitting strength, freezing-thawing resistance, unit weight and water absorption values satisfy with the relevant international standards. The experimental observations reveal that high level replacement of crumb rubber with conventional sand aggregate does not exhibit a sudden brittle fracture even beyond the failure loads, indicates high energy absorption capacity, reduces the unit weight dramatically and introduces smoother surface compared to the current concrete bricks in the market. Thermal insulation performance is improved by introducing various amount of crumb rubber into the ordinary cementitious mixes. The percentage-wise improvements in thermal insulation performance have varied nearly between 5 and 11%, depending on the amount of crumb rubber used.

This paper presents an experimental investigation on a copper miniature loop heat pipe (mLHP) with a flat disk shaped evaporator, 30 mm in diameter and 10-mm thick, designed for thermal control of computer microprocessors. Tests were conducted with water as the heat transfer fluid. The device was capable of transferring a heat load of 70 W through a distance up to 150 mm using 2-mm diameter transport lines. For a range of power applied to the evaporator, the system demonstrated very reliable startup and was able to achieve steady state without any symptoms of wick dry-out. Unlike cylindrical evaporators, flat evaporators are easy to attach to the heat source without need of any cylinder-to-plane reducer material at the interface and thus offer very low thermal resistance to the heat acquisition process. In the horizontal configuration, under air cooling, the minimum value for the mLHP thermal resistance is 0.17 C/W with the corresponding evaporator thermal resistance of 0.06 C/W. It is concluded from the outcomes of the current study that a mLHP with flat evaporator geometry can be effectively used for the thermal control of electronic equipment including notebooks with limited space and high heat flux chipsets. The results also confirm the superior heat transfer characteristics of the copper-water configuration in mLHPs.

This paper presents the thermal properties of different knitted fabric structures made from cotton, regenerated bamboo and cotton-bamboo blended yarns. Three blends of fibres (100% cotton, 50:50 cotton: bamboo and 100% bamboo) were used to produce three yarn counts (30 tex, 24 tex and 20 tex). Each of these yarns was used to manufacture three types of knitted structures namely plain, rib and interlock. It was found that the thermal conductivity of knitted fabrics generally reduces as the proportion of bamboo fibre increases. For the same fibre blend proportion, the thermal conductivity was lower for fabrics made from finer yarns. The thermal conductivity and thermal resistance values of interlock fabric was the maximum followed by the rib and plain fabrics. The water vapour permeability and air permeability of knitted fabrics increase as the proportion of bamboo fibre increases. The air permeability and water vapour permeability values were higher for plain fabric as compared to those values of rib and interlock fabrics.

Heat pipes are very flexible systems with regard to effective thermal control. They can easily be implemented as heat exchangers inside sorption and vapour-compression heat pumps, refrigerators and other types of heat transfer devices. Their heat transfer coefficient in the evaporator and condenser zones is 10 3 -10 5 W/m 2 K, heat pipe thermal resistance is 0.01-0.03 K/W, therefore leading to smaller area and mass of heat exchangers. Miniature and micro heat pipes are welcomed for electronic components cooling and space two-phase thermal control systems. Loop heat pipes, pulsating heat pipes and sorption heat pipes are the novelty for modern heat exchangers. Heat pipe air preheaters are used in thermal power plants to preheat the secondary-primary air required for combustion of fuel in the boiler using the energy available in exhaust gases. Heat pipe solar collectors are promising for domestic use. This paper reviews mainly heat pipe developments in the Former Soviet Union Countries. Some new results obtained in USA and Europe are also included.

This paper specifically addresses the thermal characteristics of the miniature Loop Heat Pipe (mLHP) with the flat disk shaped evaporator, 10 mm thick and 30 mm in diameter, for the thermal control of the compact electronic equipments. The loop was made of copper with nickel wick and water as the working fluid. Detailed study was conducted on the start-up reliability of the mLHP at high as well as low heat loads. It was found that the device was able to start-up at input power as low as 5 W, however the start-up time was very high at such heat loads. During the testing of mLHP under step and random power cycles, the thermal response presented by the loop to achieve steady state was very short. At low heat loads, thermal and hydraulic oscillations were observed throughout the loop. The amplitudes of these fluctuations were very high at condenser inlet and liquid line exit. It is expected that the extent and nature of the oscillations occurrence is dependent on the thermal and hydrodynamic conditions inside the compensation chamber. Overall, the effect of these oscillations on the thermal performance of the mLHP was not very significant. In the horizontal orientation, the device was able to transfer maximum heat load of 70 W with evaporator temperature below 100 ± 5 • C limit. The thermal resistance (R mLHP ) of the mLHP lies between 0.17 to 5.66 • C/W.

Background: Wickless heat pipe is a simple but effective heat transfer device working on two phase change of working fluid inside. In such device, the heat transport efficiency increases due to the occurrence of phase change of working fluid. Self rewetting fluids which are diluted aqueous alcoholic solutions having more than four numbers of carbon atoms are used because they have positive surface tension gradient with the temperature in the operating temperature region. Anomalous increase in the surface tension with rise in temperature is observed in the wickless heat pipe filled with self rewetting fluids. Objective: To study and compare the performance of two copper wickless heat pipes filled with self rewetting fluids namely aqueous solution of n-Butanol and aqueous solution of n-Pentanol with the wickless heat pipe of copper material filled with De Ionised (DI) water. The self rewetting fluids are prepared by adding n-Butanol and n-Pentanol at a concentration of 0.001 moles per litre to the DI water. Results: The performance of wickless heat pipe filled with self rewetting fluids is compared with the heat pipe filled with DI water for the thermal efficiency, resistance, overall heat transfer coefficient. From the experimental results it has been found that the maximum thermal efficiency is obtained for wickless heat pipe filled with aqueous solution of n-Pentanol for 90° orientation. On the other hand, the thermal resistance is high for low heat input but the overall heat transfer coefficient of wickless heat pipe increases with increase of heat input. Conclusion: Best performance is obtained for the wickless heat pipe filled with aqueous solution of n-Pentanol.

This study has been undertaken to generate objective data regarding the thermo physiological comfort characteristics of fabrics used in the manufacturing of inner and outer layer fabrics worn by uniformed personnel in North India. Effect of layering fabrics with and without air gaps between them has been assessed to simulate the effect of a multilayered garment assembly. Results show that thermal insulation increases markedly when an inner layer is paired with an outer layer of fabric, although breathability is not affected much. Proposed equations can be used to accurately predict the comfort properties of layers, if the comfort properties of individual fabrics are known. Thermal resistance of a garment assembly can be controlled by regulating the air gap between fabric layers. This data can be used to engineer uniform fabrics, so as to maximize the thermal comfort of wearers during hot weather conditions.

In this work, a two-dimensional analysis is used to study the thermal performance of a cylindrical heat pipe utilizing nanofluids. Three of the most common nanoparticles, namely Al 2 O 3 , CuO, and TiO 2 are considered as the working fluid. A substantial change in the heat pipe thermal resistance, temperature distribution, and maximum capillary heat transfer of the heat pipe is observed when using a nanofluid. The nanoparticles within the liquid enhance the thermal performance of the heat pipe by reducing the thermal resistance while enhancing the maximum heat load it can carry. The existence of an optimum mass concentration for nanoparticles in maximizing the heat transfer limit is established. The effect of particle size on the thermal performance of the heat pipe is also investigated. It is found that smaller particles have a more pronounced effect on the temperature gradient along the heat pipe.

This paper derives and discusses an improved method for estimating the temperature of solar cells operating under high concentration conditions. The accuracy of this method was certified over a broad range of sunlight concentrations and operating temperatures using available experimental data related to multi-junction solar cells. This method provided more accurate estimations of cell temperature under high concentrations than the conventional V oc -I sc method. On-sun solar cell tests were carried out under high concentrations. The experimental data showed that the solar cell temperature, which was calculated by the improved method, increased almost linearly with the concentration ratio. A heat transfer model was established for comparison with the method. The results from both methods were in agreement. Furthermore, the thermal resistances of the solar-cell heat-sink system were also estimated using this method.

The knowledge of soil electrical and thermal resistivities is essential for several engineering projects such as laying of high voltage buried power cables, nuclear waste disposal, design of fluidized thermal beds, ground modification techniques etc. This necessitates precise determination of these resistivities, and relationship between them, which mainly depend on the soil type, its origin, compaction density and saturation. Such a relationship would also be helpful for determining one of these resistivities, if the other one is known. With this in view, efforts were made to develop artificial neural network (ANN) models that can be employed for estimating the soil electrical resistivity based on its soil thermal resistivity and the degree of saturation. To achieve this, measurements of electrical and thermal resistivities were carried out on different types soils compacted at different densities and moisture contents. These models were validated by comparing the predicted results vis-à-vis those obtained from experiments. The efficiency of these ANN models in predicting the soil electrical resistivity has been demonstrated, if its thermal resistivity is known. These ANN models are found to yield better results as compared to the generalized relationships proposed by the earlier researchers.

The inhibitory action of tea polyphenols towards the development and growth of bacterial spores was examined. Among the tested Bacillus bacteria, tea polyphenols showed antibacterial effects towards Bacillus stearothermophilus, which is a thermophilic spore-forming bacterium. The heat resistance of B. stearothermophilus spores was reduced by the addition of tea polyphenols. Clostridium thermoaceticum, an anaerobic spore-forming bacterium, also exhibited reduced heat resistance of its spores in the presence of tea polyphenols. (-)-Epigallocatechin gallate, which is the main component of tea polyphenols, showed strong activity against both B. stearothermophilus and C. thermoaceticum. The heat resistance of these bacterial spores was more rapidly decreased by the addition of tea polyphenols at high temperatures.

An experimental investigation has been explore in order to study the flow of fluid and heat transfer characteristics on a Rectangular Wavy microchannel heat sink. Various applications are envisaged for the use of microchannel heat sink in electrical and electronic power generation and distribution. The Heat sink with microchannel is designed on an Aluminium specimen with Rectangular Wavy configuration with a channel cross section of 1mm x 0.5mm.To improve the heat transfer performance of the cooling system is achieved by using nanoparticles in the fluid passing through the microchannel heat sink. Results are presented by using different concentration (with 1% to 3%) of Nano fluids in water for the heat sink. Various cooling characteristics including thermal resistance, temperature drop and pressure drop across the microchannel heat sink are analysed for different volume concentrations, different volumetric flow rates and Reynolds number. Other significant characteristics for the measurement of heat transfer characteristics across this microchannel heat sink are also analysed and presented in this experiment.