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Results demonstrate that the onset of nucleate boiling and active nucleation site density are dependent on different subcooled flow boiling parameters. Models presented incorporate the influence of static contact angle on liquids-surface pairs, such as refrigerants.

Results show a linear increase in local bubble velocity for both R134a and R600a chlorofluorocarbon (CFC) materials, which are used as substitutes for CFC-12 in refrigeration and air-conditioning plants. Data indicate that bubble dynamics are dependent on the heat flux for both materials.

Research describes the computation of the total exchange area in emitting, absorbing and anisotropic scattering semi-transparent medium as a function of the radiative properties, the geometry of the medium, and its boundaries using a matrix relation approach. A zone method is proposed to express direct exchange area and indirect exchange area.

Mass recovery can play an important role to better the performance of adsorption refrigeration cycles. Cooling capacity can be significantly increased with mass recovery process. The coefficient of performance (COP) of the activated carbon/ammonia adsorption refrigeration cycle might be increased or decreased with mass recovery process due to different working conditions. The advantage is that its COP is not sensitive to the variation of heat capacity of adsorber metal and condensing and evaporating temperature. The cycle with mass and heat recovery has a relatively high COP. [DOI: 10.1115/1.1487883] Keywords: Activated Carbon, Ammonia, Mass Recovery, Heat Recovery, Adsorption, Refrigeration Cycle

This paper investigates the technical feasibility of using a compact, air-cooled, solar-assisted, absorption air conditioning system in Puerto Rico and similar regions. Computer simulations were conducted to evaluate the system's performance when subjected to dynamic cooling loads. Within the computer model heat and mass balances are conducted on each component of the system, including the solar collectors, thermal storage tank, the air-cooled condenser, and the air-cooled absorber. Guidance on component design and insight into the effects of such operating factors as ambient air temperature were gained from exercizing the simulation model. Comparisons are made with an absorption air conditioning system that uses a cooling tower instead of air-cooled components. The particular absorption system of study is one that uses lithium bromide and water as the absorbent and refrigerant, respectively. The heat input to the absorption system generator is provided by an array of flat plate collectors that are coupled to a thermal storage tank. Systems having nominal cooling capacities of 10.5, 14, and 17.5 kW were considered. Useful information about the number of collectors needed, storage tank volume, and efficiency of the overall system is presented. [DOI: 10.1115/1.1487885]

A window in a room within a domestic environment in a structure with aluminum siding is analyzed with respect to its radiating properties. The window is modeled as a rectangular aperture, which diffracts the distant horizontally polarized signal from a DTV transmitting antenna into the environment of the room. The diffraction signal, also horizontally-polarized, is combined with the distant signal, which penetrates the aluminum siding at some loss, and thereby a field distribution within the room is created. The window-diffracted signal is almost entirely a near field (Fresnel Zone) within the room while the distant field is a far field (Fraunhofer Zone) within the room. Various locations within the room are examined with respect to echoes, with and without scattering (human) bodies. A receiving antenna is positioned at the locations examined. Index Terms--Dielectric scattering, diffraction, DTV (Digital Television), Fraunhafer zone, Fresnel zone, indoor electromagnetic propagation, indoor TV reception, reflection, refraction, VSB (vestigial sideband modulation).

Two-phase forced convective flow in microchannels is promising for the cooling of integrated circuits. There has been limited research on boiling flow in channels with dimensions below 100 [micro]m, in which bubble formation and flow regimes can differ from those in larger channels. This work develops single and multichannel experimental structures using plasma-etched silicon with pyrex glass cover, which allow uniform heating and spatially-resolved thermometry and provide optical access for visualization of boiling regimes. Boiling was observed with less than 5 [degrees] C of superheating in rectangular channels with hydraulic diameters between 25 and 60 [micro]m. The channel wall widths are below 350 [micro]m, which minimizes solid conduction and reduces variations in the heat flux boundary condition. Pressure drop and wall temperature distribution data are consistent with predictions accounting for solid conduction and homogeneous two-phase convection. [651] Index Terms--Heat exchanger, microchannel, two-phase cooling.

In this paper mechanical aspects of cracking during single- and multi-spot welding of AA5754 was investigated by both experimental and analytical approaches. The impact of mechanical loading on crack initiation and propagation was studied with the consideration of various process parameters including the loading imposed by electrodes, the formation of liquid nugget, and constraining factors during and after welding. Tensile properties of AA5754 and their dependence on the temperature were tested at room and up to solidus temperatures, in order to provide a reference of cracking stress. Thermal-mechanical analysis was conducted based on the temperature field around the nugget and the state of stress encountered during welding. This analysis revealed that tensile stress might build up in the vicinity of the nugget during cooling, as explained in the experimental observation. General guidelines for suppressing cracking were proposed, i.e., to provide sufficient constraint around the weld spot during and after welding. [DOI: 10.1115/1.1418693]

The radiation element method by ray emission method, [REM.sup.2], has been formulated to predict radiative heat transfer in three-dimensional arbitrary participating media with nongray and anisotropically scattering properties surrounded by opaque surfaces. To validate the method, benchmark comparisons were conducted against the existing several radiation methods in a rectangular three-dimensional media composed of a gas mixture of carbon dioxide and nitrogen and suspended carbon particles. Good agreements between the present method and the Monte Carlo method were found with several particle density variations, in which participating media of optical thin, medium, and thick were included. As a numerical example, the present method is applied to predict radiative heat transfer in a boiler model with nonisothermal combustion gas and carbon particles and diffuse surface wall. Elsasser narrow-band model as well as exponential wide-band model is adopted to consider the spectral character of C[O.sub.2] and [H.sub.2]O gases. The distributions of heat flux and heat flux divergence in the boiler furnace are obtained. The difference of results between narrow-band and wide-band models is discussed. The effects of gas model particle density, and anisotropic scattering are scrutinized. [DOI: 10.1115/1.1388235]

A model is presented for the prediction of radiation heat transfer between fluidizing particles and a heat transfer surface. Data show that in a gas-solid fluidized bed, between fluidizing particles and a cooled surface, cooled fluidizinf particles suppress the radiation heat transfer between the surface and high temperature particles of the bed.

This review endeavors to explain optical phenomena such as birefringence, polarization, and intensity fluctuation encountered in electromagnetic propagation by discussing radiative transfer in anisotropic media and nematic liquid crystals.

The purpose of this paper is to review the status of research into one of the most challenging and important problems facing physics today: how does the atmosphere moderate the radiative energy balance that determines the Earth's climate? Behind this question lies the whole basis for understanding the greenhouse effect, including coupled feedback processes. This understanding has consequences for major issues of public concern, climate change and global warming. Following an introduction to the basic physics of the energy balance and the greenhouse effect, a discussion is given of how the spectrum of outgoing thermal radiation (by which the planet cools to space) depends on internal parameters such as surface temperature and atmospheric humidity. This includes a discussion of the sign and magnitude of the water vapour-climate feedback, and the 'super greenhouse effect'. It is shown that the role of cloud in the energy balance is extremely important, although poorly understood. Recent work to exploit the information contained in the resolved spectrum of outgoing longwave radiation (OLR) is described, including a new technique to search for the 'signal' of climate change within the 'noise' of natural climate fluctuations. Finally, some comments are offered on the problem of the predictability of future climate changes.

A two-dimensional, steady-state finite-element model was developed to simulate the thermal effects of the application of an attic radiant barrier system (ARBS) inside a ventilated residential attic. The attic is ventilated using the exhaust air from an evaporative cooler. The study uses a (kappa)-(epsilon) turbulent model to describe the velocity and temperature distributions in the attic. The ambient temperature and solar isolation densities on the outside inclined attic surfaces are used as driving functions for the model. The model also included the appropriate heat exchange modes of convection and radiation on these outside surfaces. Several recirculation zones were visually observed in the attic flow pattern. Also, the use of the ARBS seems to lower the heat transfer through the ceiling by 25-30%, but this effect decreases significantly as the outside ventilation rates are increased through the attic space. The 2D model revealed some interesting temperature distributions along the attic surfaces that could not have been predicted by the one-dimensional models. The lower emissivity ARBS seems to raise the temperature of the inclined attic surfaces as well as the temperature of the exhausted ventilation air.

A simple expression has been found for transferred radiative intensity as a function of refractive indices of and distance separating the black body and the object. The expression has been interpreted in terms of the specific black body modes evanescent in the space between the black body and the object and which make the greatest contribution to the transmission of radiation. The black body, the gap region and the object are modeled as lossless dielectrics. A physical model can be used to understand the increase of the heat transferred from the black body beyond the amount expected from the free space Planck distribution.

A new study uses z-scan measurement to investigate the nonlinear absorption of thin gold films deposited onto surface-modified quartz substrates.

Mathematical formulation and theoretical analysis demonstrate that flame-history and extinction of droplet combustion depend on fuel and oxidizer Lewis numbers, stoichiometric-ratio, heat release, and the nondimensional emissivity parameters.

A new method for estimating heat transfer between solid material and fluid gas in porous media has been developed. The method gives the longitudinal characteristics of the heat transfer in a porous medium. Local Nusselt numbers on the heated wall of a flow passage are obtained numerically in advance in the first stage. Experimental Nusselt numbers on the wall are obtained by measurement of wall temperatures and heat flux in the next stage.

Radiative heat transfer in arbitrary configurations with nongray absorbing, emitting, and anisotropic scattering media. Thermal radiation is a combustion chamber is very difficult where spectral absorption and anisotropic scattering are in the medium. the ray emission model, REM(super.2), is developed to take in the spectral dependence of radiation properties with the narrow band model and assuming anisotropic scattering.

Turbulence-radiation interactions (TRI) are discussed as they relate to nonreactive flow of combustion gases. A numerical study has been carried out. The role of TRI depends to a great degree on how the temperature fluctuations correlate with concentration fluctuations. In most cases of interest in the real world the fluctuations are uncorrelated so there is almost negligible TRI effect on wall heat loads.

Power absorption characteristics of an inductively coupled discharge are investigated experimentally and compared with a two-dimensional inductive heating theory in a planar single turn antenna at high frequency (18 MHz) and low pressure ([less than or equal to]50 mtorr) conditions. We measure the resistance R, which consists of vacuum resistance [R.sub.v] and the plasma resistance [R.sub.p] for a given RF power of [Mathematical Expression Omitted], where [I.sub.c] is the coil current. The vacuum resistance is determined to be 0.44 [Omega] in our case. The plasma resistance increases as the gas pressure increases in a pressure range of 2 to 50 mtorr. Also, it increases with power. In a highpressure range near 50 mtorr, however, it has a nearly constant value of about 0.6 [Omega]. Index Terms - Inductively coupled plasma (ICP), plasma resistance.

A study on the effective cooling of electric components using micro heat pipes presents a mathematical model to predict temperature variations and heat transport capacity that contribute to the overall axial temperature drop as a function of heat transfer. Results obtained from this model show that the temperature drop occurring in the evaporator is considerably larger than those occurring in the condenser. Both temperature drops increase with increases in the input power.

This paper examines the bulk aerodynamic method and proposes an alternative algorithm for estimating evapotranspiration from radiative temperature over unstressed full-canopy cover crops. Both approaches are studied using calibration and validation datasets over four complete different canopies: grass, wheat, alfalfa, and maize. The former method gives acceptable results for grass, wheat, and alfalfa crops but is very discouraging for maize. The parameter [(k[B.sub.-1]).sub.s] is evaluated to adjust the bulk aerodynamic method. Different expressions for [(k[B.sup.-1]).sub.s] over homogeneous crops are tested. The latent heat flux estimations do not improve significantly for the different [(k[B-1]).sub.s] values studied for the four crops. A simple and more accurate semiempirical method is proposed. The new approach, based on the Bowen ratio energy balance method, introduces the relation between the radiative Bowen ratio and the traditional Bowen ratio. A linear relationship is found between the two Bowen ratios over grass, wheat, alfalfa, and maize crops. Errors under 10% are achieved for latent heat flux estimations. When such small accuracies are not required and input data are available, the bulk aerodynamic approach is preferred for grass, wheat, and alfalfa because it can be applied without any empirical adjustment. The major advantage of this regression-based approach is that no a priori assumptions concerning the resistances are required. The results are promising for remote sensing applications, although they need further verification in other climatological conditions.

A measurement of ultra-low absorption of microwave radiation in dielectrics is reported. Two Fabry-Perot resonators with [greater than or equal to] 600 000 quality factors, fully general-purpose interface bus programmable millimeter-wave frequency synthesizer with 10-15-mW continuous wave (CW) power level, 100-Hz frequency resolution from 78 to 118 GHz, and corresponding hardware and software for signal processing were used. The [+ or -]500-Hz accuracy of resonance curve width measurements was reached. This high accuracy allowed loss tangent measurement as small as 10[.sup.-6] -10[.sup.-7] in dielectric samples with a thickness of [approximately]0.5 mm. A convenient method of measurements of almost arbitrary plane parallel samples has been developed and described. Practical applications such as development and control of thin low-loss resonant windows of powerful ([approximately]1-MW CW) gyrotrons used in thermonuclear experiments, precise reflection coefficient of metals measurements, as well as other applications are discussed. The existence of such technique up to frequencies exceeding 1 THz makes measurements described at the whole millimeter and submillimeter-wave bands affordable. Index Terms - Backward wave oscillators, dielectric losses, Fabry-Perot resonators, millimeter- and submillimeter-wave spectroscopy, millimeter-wave measurements, submillimeter-wave measurements.

Green's functions of the external force boundary value problem for an infinite plane with an arbitrary shaped hole, that is subjected to heat, under adiabatic and isothermal boundary conditions are obtained for two cases. The first case has the heat source and heat sink located within the plane while the other case has the heat source located within the plane but has the heat sink at infinity. The two cases are studied by using complex stress functions, temperature function, a rational mapping function and the thermal dislocation method.

Research is conducted to examine the radiation effects on laminar mixed convection in an inclined square duct. The vorticity-velocity technique is used to solve the three-dimensional parabolic governing equation while the discrete ordinates method is used to solve the radiative transfer equation. The impact of the modified Rayleigh number, mixed convection parameter, optical thickness and conduction-to-radiation parameter on fluid flow and heat transfer properties is also investigated.

In this paper, we consider theoretically conditions for forming crystals of positively charged dust, when the dust is heated by a laser or by a strong infrared source and emits electrons thermionically. We discuss parameters for grains dispersed in an inert gas at pressure of a few mbar. We briefly discuss levitation by forces associated with gas flow or photon flux. A possible experimental scheme for achieving such a crystal is briefly outlined. Index Terms - Coulomb crystals, dusty plasmas.

The results of applying stochastic spectral theory to the temperature distribution and thermal radio emission of a half-space medium are presented. Analytic closed-form expressions for the covariance functions of the temperature profile and the brightness temperature, represented as one-dimensional (1-D) integrals of the spectrum of the surface temperature, have been obtained. Index Terms - Covariance functions, radiobrightness, random boundary conditions, stochastic processes, temperature distribution.

A cone concentrator combined with a solar cavity receiver is presented and its performance compared to a single cavity receiver. For both cases the available heat sink within the receiver is calculated. The cone concentrator suffers from a high amount of rejected rays if the exit aperture is made too small. A larger exit aperture on the other hand increases the thermal losses of the cavity. The optimum cone geometry therefore has to be found taking also into account a model of the cavity. Different operating temperatures and different values of absorption coefficients of the cavity walls are considered. A cone concentrator was built and tested at the solar furnace in Cologne. It transmits 97 percent of the rays entering the entrance aperture, which is in exact agreement with the theoretical predictions.

The mechanism of melting of a subcooled powder bed consisting of a mixture of two powders with markedly different melting points under a moving Gaussian heat source was investigated using a numerical model. The model takes into account the shrinkage induced by the density change on the melting process. Experimental results showed that the effect of surface heat loss caused by convection and radiation is not negligible even if the shrinkage phenomenon is not considered in the model.

The mechanism of weakly ionized plasma arc heat transfer between electrodes with dissimilar geometric configurations was investigated using an orthogonal body-fitted coordinate system. To this end, a set of self-consistent conservation equations for the charged particle densities and the temperatures in the plasma were numerically solved. Results for the heat transfer as well as the electron number density and temperature variation in the discharge gap were considered for a thin cylindrical anode together with a planar cathode.

The radiative cooling of a semitransparent molten glass jet with temperature-dependent viscosity was investigated using a mathematical model. Numerical simulations were utilized to determine the axial velocity and jet diameter variations along the length of the jet, the centerline-to-surface glass temperature distributions and the axial bulk mean temperature distributions. The results were compared with predictions for an opaque medium.

The application of shape memory alloy (SMA) thin films in optical devices is introduced and explored for the first time. Physical and optical properties of titanium-nickel (TiNi) SMA thin films change as these films undergo phase transformation on heating. An optical beam can be modulated either mechanically with a TiNi actuator or by the changes that occur in TiNi's optical properties upon heating and phase transformation. Reflection coefficients of TiNi films were measured in their so-called martensitic (room-temperature) and austenitic (elevated-temperature) phases. The reflection coefficients of the austenitic phase were higher than those of the martensitic phase by more than 45% in the wavelength range between 550 and 850 nm. Also, a microfabricated TiNi diaphragm with a 0.26-mm-diameter hole was used as a prototype light valve. The intensity of the transmitted light through the hole was reduced by 10%-17% when the diaphragm was heated. A novel TiNi light valve fabricated by using silicon micro-machining techniques is also proposed and discussed. We present both optical data and structural data obtained by using transmission electron microscopies.

A two-node model of a room has been implemented in a computer program, WinSim, developed for evaluation of thermal performance of windows in new buildings and in case of retrofitting. The program calculates the annual heating demand and the number of hours with indoor temperatures higher than a user defined limit. WinSim is characterised by the limited amount of required input data. Guidelines for calculation of the effective thermal capacity of the room are given, and results obtained with WinSim have been compared to results from an advanced building simulation program. Good agreement has been found between the two programs with respect to calculated annual heating demand and energy savings due to window exchange, and also the calculated number of hours with overtemperature is similar. Based on the limited examples used for the comparison, it can be concluded that WinSim is well suited for a quick but realistic evaluation of thermal performance of windows.

The Monte Carlo (MC) method is an effective way of solving radiative heat transfer problems involving realistic geometries and properties. A new method to track the reflected paths of energy bundles, referred to as Discrete Function Monte Carlo, is presented. The method is faster than traditional ray-tracing approaches. Predictions from DFMC and MC methods were in close agreement.

A time-dependent and two-dimensional thermal model describing heat transfer in multispan sandwich rectangular plates is presented. The boundary conditions on the faces of the plate are considered and the radiative and nonuniform convective exchange are taken into account. Experimental results are in good agreement with the numerical simulation.