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The bio-based materials have experienced in recent years a relevant evolution in construction and for many building applications. Despite the efforts to develop new solutions to achieve the objectives of numerical characterizations, a few researches in this area have been carried out using a heterogeneous wood-cement composite. This study is based on a constructive approach using the finite volume method in order to generate a numerical model capable of reproducing the equivalent transfer properties of a wood-cement composite. The challenge is to understand, design, and control this multiphase inhomogeneous structure and predict transfers and flows within the community in order to achieve an optimal functionality. Experimental measurements and microscopic characterization using X-ray microtomography were performed to compare and demonstrate the method validation. The comparative results demonstrate a less than 10% deviation between the measurements and the simulations of the equivalent thermal properties. Thus, thermal conductivity and permeability, under different medium configurations, were characterized. Therefore, it was observed that these properties depend strongly on the porosity and the pore distribution in the continuous phase. Moreover, these two parameters are highly dependent on cement percentages in the structure. [ABSTRACT FROM AUTHOR]

This paper studies the heat-shielding performance of a beetle forewing to explore how it has excellent thermal protective properties. With an experimental setup of a self-developed heating environment, the heat transfer characteristics of the beetle forewing were tested at 50°C under steady state conditions. Two types of the forewings are considered: cut wing and live wing. The heat transfer results show that the live forewing provides a good heat-shielding performance with the heat-shielding index stabilizing at around 22.1%, which is 60% higher than that of the cut wing. Based on scanning electron microscope images of the microstructure of the cross section of the beetle forewing, a simplified finite element analysis is performed to numerically calculate the heat transfer properties of the forewing. The numerical simulations reveal that the proposed structure of the forewing is good for the design of an effective thermal protection system. In addition, the uncertainty analysis is performed to evaluate the quality of experimental data. These results provide a foundational understanding of the heat transfer characteristics of beetle forewing, which will inspire a promising candidate for an actively cooled thermal protection systems. [ABSTRACT FROM AUTHOR]

The theoretical analysis of different concentrating photovoltaic and thermal systems (CPV/T) is presented in this paper; it allows to evaluate the cooling fluid temperature in different working conditions. In particular, two CPV/T systems with different optics, line-focus and point-focus, are studied and compared theoretically by means of a model developed in ANSYS-CFX able to evaluate the theoretical temperature values of the fluid that flows in the cooling circuit, designed with the Solidworks software. The comparison in terms of the thermal performances between the point-focus and line-focus configurations of a CPV/T system has been realized considering different working conditions. As model input the uniform cell temperature has been set to different values, included between 323 K and 363 K, or determined experimentally referring to the point-focus configuration. In particular, the outlet temperatures of the cooling fluid, the fluid and cells temperatures difference at the outlet section, the time necessary to reach a steady-state condition, the fluid temperature trend in different parts of the tube and along the circuit, have been evaluated. Moreover, the fluid temperature trend has been studied varying the fluid velocity, its mass flow rate, and the insulation thickness. Finally, the point-focus CPV/T system thermal performances have been also evaluated adopting some experimental measurements as input data; the fluid temperature trend has been tested under a variable cell temperature during different hours of a sunny and a cloudy day. [ABSTRACT FROM AUTHOR]

The determination of local convective heat transfer coefficients in microfluidics is a very hard task. Due to the small dimensions of channels and walls, the use of conventional measurement techniques is only partially suitable in microfluidics. For this reason, a strong effort has been made during the last decades in order to propose innovative techniques which use internal (to microdevices) sensors of reduced dimensions and/or external conventional sensors. In this paper a review of the main experimental techniques proposed for the determination of the local near-wall fluid temperature, the local wall temperature, and the local fluid bulk temperature will be given by putting in evidence for each technique's positive and negative aspects as well as their actual limitations with the aim to stimulate and address the research on this topic in the near future. The problems and the limitations existing nowadays for the accurate measurements of the local thermal properties of a convective microflow demonstrate that for the analysis of microconvection experimental data have to be always integrated by a numerical modeling of the observed system. [ABSTRACT FROM AUTHOR]

In this research, an experimental evaluation is conducted on the hydrothermal behavior of water-based manganese ferrite nanofluid flowing in a metal foam tube. For this purpose, manganese ferrite nanoparticles are synthesized, and X-ray diffraction and scanning electron microscopy are implemented to specify the samples for determination of phase and size of nanoparticles. The effects of Reynolds number, Prandtl number, and presence of MnFe2O4 nanoparticles inside the water on the Nusselt number and friction factor have been studied. The experimental analysis shows that the increment of Reynolds number, Prandtl number, and nanoparticles concentration improve the heat transfer performance. The maximum of 19.1% and 10.5% increase in Nusselt number and friction factor have been achieved respectively by dispersion of 2 wt% manganese ferrite nanoparticles inside the deionized water at Reynolds number of 1,000. A hydrothermal index is proposed to consider the thermal and hydrodynamic characteristics of the nanofluid, and it is attained that the convection heat transfer improvement dominates the pressure drop in this work. According to the experimental results, the Nusselt number and friction factor of the nanofluid is modeled as a function of Reynolds number, Prandtl number, and nanoparticles concentration using artificial neural network with an acceptable precision. [ABSTRACT FROM AUTHOR]

This study investigates the performance of an adsorption chiller driven by thermal heat collected from solar collectors’ panels with heat storage. The heat is reserved in a storage tank and the reserved heat is used to drive the adsorption chiller. The investigation was carried on the climatic conditions of Dhaka, Bangladesh. Heat transfer fluid goes from the collectors to the adsorption cooling unit, then from the adsorption cooling unit to the storage tank. It is seen that heat storage is more effective than direct solar coupling; however, it requires more collectors, depending on the size of the storage tank. The analysis shows that cycle time is one of the most influential parameters for the solar-driven adsorption cooling system. It is seen that the size of the collector can be reduced if the proper cycle time is adjusted. The analysis also revealed that the system with 22 collectors (each of 2.415 m2) along with 1000 s cycle time provides better performance for the base run conditions. It is also seen that the solar-driven adsorption chiller with heat storage works well beyond the sunset time. [ABSTRACT FROM AUTHOR]

The objective of this study is to clarify physical mechanisms involved in the evaporation of small (a few microliters) sessile drops. We aim to understand the relation between local thermal information at the solid–liquid interface and overall evaporation. An infrared (IR) camera and a charge-coupled device (CCD) camera were used to determine the temperature and heat flux distribution at the solid–liquid interface and the profile of the evaporating drop, respectively. The temperature distribution at the solid–liquid interface was determined using a multilayer substrate consisting of a silicon wafer coated with a thin thermal insulator that is partially transparent to IR. The liquids used were water and FC-72. The evaporation rate of water drops was found to occur mostly at the contact line. However, the heat transfer distribution at the liquid–solid interface was relatively uniform, indicating the heat transferred from the wall must be transported within the drop to the contact line. The mechanisms by which this occurs have yet to be determined. In contrast, the evaporation rate of FC-72 drops where hydrothermal waves were present was found to be proportional to the liquid–vapor interface area rather than the circumference of the drop, indicating a more uniform distribution of evaporation. [ABSTRACT FROM AUTHOR]

For the development of industrial heat pump systems supplying a high-temperature heat source over 130°C, experiments were carried out on cooling heat transfer of supercritical pressure fluids flowing in a plate heat exchanger (PHE). Using two refrigerants of HFC134a and HCFC22 as the test fluids, heat transfer coefficient data were obtained at different pressure, flow rate, and heat load conditions. The heat transfer coefficient generally had a maximum in the vicinity of the pseudocritical point and showed seven- to ninefold values compared with tube flow. Based on the measurements, characteristics of cooling heat transfer of supercritical pressure fluids in the PHE were clarified and a correlation of heat transfer coefficient was developed. [ABSTRACT FROM AUTHOR]

This paper presents a highly effective desiccant rotor that can be regenerated at a temperature between 20 and 30°C, corresponding to return air exhausted from conditioned spaces. The desiccant rotor consists of a honeycomb structure, which is coated with organic polymer desiccant materials. For a specific operating condition, the desiccant rotor functions as a rotary total heat exchanger. Desiccant rotors with thickness of 0.2 m and more lead to both higher dehumidification and temperature efficiencies compared to conventional total rotary heat exchangers in different states of the inlet process and regeneration airflows. Both the dehumidification and temperature efficiencies achieve 100% at a thickness of 0.4 m, and at rotational speeds between 100 and 300 rph. Dehumidification, together with cooling, is very effective. For the desiccant rotor with a thickness of 0.4 m, the humidity change of the process air corresponds closely to isothermal dehumidification. In terms of the dehumidification and cooling functions, the performance of the desiccant rotor with thickness of 0.2 m and more is very advantageous compared to conventional desiccant rotors and rotary total heat exchangers. [ABSTRACT FROM AUTHOR]

This paper concerns the further testing of a new double calorimeter. We earlier reported initial development of the calorimeter and thereafter inferred rates coefficients for adsorption of moisture under a “large pressure jump.” (The test materials were silica gel type A and water.) The paper presents a further check on the calorimeter by demonstrating that measured desorption and adsorption rates were compatible. A disappointing aspect was an unintended near step change in condenser pressure at the start of the experiment. The condenser design was deficient, and better drainage is needed in the future to maintain vapor in immediate contact with cold surfaces. Notwithstanding the lower than intended pressure driving force, the heat addition to the silica gel was measurable, following an exponential pattern against time with regression coefficient better than 99%. The rate coefficients that fitted each data set were broadly in line with coefficients reported for adsorption (within the limits of experimental error). [ABSTRACT FROM AUTHOR]

The commercial success of sorption refrigeration and heat pump systems depends on a good heat and mass transfer in the adsorbent bed, which allows higher coefficients of performance and greater specific heating or cooling power that reduce capital costs. In this study the thermal conductivity and thermal contact resistance of vibrated and compressed granular active carbon and binary mixtures of active carbon are investigated using two types of conductivity measurements: a steady-state measurement between flat plates and a transient hot tube measurement. With these results is possible to draw conclusions on how the wall geometry, particle size distribution, and bulk density affect the overall thermal performance. Results show that using binary mixtures of grains and powder gives results superior to those of either grains or powder alone. The conductivity of the binary mixtures increases roughly linearly with bulk density and the 2/3 grain mixture achieves the highest densities. The method used to achieve compaction (vibration or compression) did not seem to affect the result. Thermal contact resistances reduce with increasing density but do vary with the mixture ratio, also appearing to be best with a 2/3 grain–1/3 powder mixture. [ABSTRACT FROM AUTHOR]

Thermal energy storage is critical for reducing the discrepancy between energy supply and energy demand, as well as for improving the efficiency of solar thermal energy systems. Among the different types of thermal energy storage, phase-change materials (PCM) thermal energy storage has gained significant attention recently because of its high energy density per unit mass/volume at nearly constant temperature. This study experimentally investigates the using of a triplex tube heat exchanger (TTHX) with PCM in the middle tube as the thermal energy storage to power a liquid desiccant air-conditioning system. Four longitudinal fins were welded to each of the inner and middle tubes as a heat transfer enhancement in the TTHX to improve the thermal performance of the thermal energy storage. The average temperature of the PCM during the melting process in the TTHX with and without fins was compared. The PCM temperature gradients in the angular direction were analyzed to study the effect of the natural convection in the melting process of the thermal storage. The energy storage efficiency of the TTHX was determined. Results indicated that there was a considerable enhancement in the melting rate by using fins in the TTHX thermal storage. The PCM melting time is reduced to 86% by increasing of the inlet heat transfer fluid. The average heat storage efficiency calculated from experimental data for all the PCMs is 71.8%, meaning that 28.2% of the heat actually was lost. [ABSTRACT FROM AUTHOR]

This article presents the design and the heat transfer study in a novel adsorbent bed with compound parabolic concentrator (CPC) for solar adsorption chillers. The objectives of the study were to investigate the heat transfer in the adsorbent bed experimentally, and to verify the fins layout through finite-element analysis (FEA) simulation. CPCs with different concentration ratios were experimentally tested and an appropriate design of CPC was selected for a prototype. The prototype was designed with the objective of improving the heat and mass transfer ability of the adsorbent bed. Fins were placed in the transverse direction under the receiver area of each CPC. Spaces were provided from three sides of the adsorbent for easy movement of the refrigerant. FEA software was used to study the effect of the fins layout and fins pitch. The experimental results showed that the heat was efficiently transferring up to the end and extended parts of the bed. Simulation results indicated that the present strategy of placing the fins in a transverse direction gives uniform heat distribution compared to a fins layout with fins placed in a longitudinal direction. The proposed design scheme will be helpful to improve the system performance by increasing the heat and mass transfer ability of an adsorbent bed. [ABSTRACT FROM AUTHOR]

For the development of a high-performance heat exchanger using small channels or minichannels for air-conditioning systems, it is necessary to clarify the characteristics of vapor‐liquid two-phase flow and heat transfer of refrigerants in small-diameter tubes. In this keynote paper, the related research works that have already been performed by the author and coworkers are introduced. Based on the observations and experiments of R410A flowing in small-diameter circular and noncircular tubes with hydraulic diameter of about 1 mm, the characteristics of vapor‐liquid two-phase flow pattern and boiling heat transfer were clarified. In low quality or mass flux and low heat flux condition, in which the flow was mainly slug, the “liquid film conduction evaporation” heat transfer peculiar to small-diameter tubes prevailed and exhibited considerably good heat transfer compared to nucleate boiling and forced convection evaporation heat transfer. The effects of the tube cross-sectional shape and flow direction on the heat transfer primarily appeared in the region of the “liquid film conduction evaporation” heat transfer. A new heat transfer correlation considering all of three contributions has been developed for small circular tubes. [ABSTRACT FROM AUTHOR]

Case Studies Editor's Note:We at theJournal of Heat Transfer Engineering (HTE)are happy to announce the introduction of a new section entitled “Case Studies.” The first case study was published in vol. 37(3–4). This is the second case study in the series. We are asking authors to contribute their practical experiences in the form of real-world case studies.  The goal is to disseminate practical information especially to young engineers who are stepping into the real world. The format of such articles will be a full-length paper or a short brief.  It does not have to entail a typical research-type paper format with details about measurement accuracies, references, and so on.  The article could have a brief introduction with the problem description, remedy, lessons learned, and recommendations.  The review process will be simple and less involved than with typical research papers.  The goal is not to discredit a person or a company but to share experiences.  We all make mistakes; however, we also find solutions, and it is the solution part that is rewarding and that should be shared for the betterment of the society. Zahid Ayub HTECase Studies Editor [ABSTRACT FROM AUTHOR]

In this study, experiments were performed to examine characteristics of flow boiling heat transfer and pressure drop of a low global warming potential refrigerant R32 flowing in a horizontal copper circular tube with 1.0 mm inside diameter for the development of a high-performance heat exchanger using small-diameter tubes or minichannels for air conditioning systems. Axially local heat transfer coefficients were measured in the range of mass fluxes from 30 to 400 kg/(m2·s), qualities from 0.05 to 1.0, and heat fluxes from 2 to 24 kW/m2at the saturation temperature of 10°C. Pressure drops were also measured in the rage of mass fluxes from 30 to 400 kg/(m2·s) and qualities from 0.05 to 0.9 at the saturation temperature of 10°C under adiabatic condition. In addition, two-phase flow patterns were observed through a sight glass fixed at the tube exit with a digital camera. The characteristics of boiling heat transfer and pressure drop were clarified based on the measurements and the comparison with data of R410A obtained previously. Also, measured heat transfer coefficients were compared with two existing correlations. [ABSTRACT FROM AUTHOR]

A series of field tests of hybrid desiccant cooling systems was conducted during July and August 2012. The temperature and humidity of supply and return air and power and heat consumption were monitored, and data were transferred in real time through the internet. The performance of the cooling system (i.e., cooling capacity and the coefficient of performance [COP]) was evaluated from measured data and variations with regard to outdoor conditions were analyzed. The cooling capacity decreased with an increase of outdoor temperature, while it increased as outdoor humidity increased. The COP also increased with an increase in outdoor humidity. However, the dependence of the COP on outdoor temperature was rather weak. [ABSTRACT FROM AUTHOR]

This study investigated the cycle optimization of four-bed, silica gel–water adsorption with reheat cycle, where the desorber (upper bed) and adsorber (lower bed) always interact with the condenser and evaporator, to exploit a low heat-source temperature. In a previous study, the performance of a reheat cycle with chilled water outlet temperature fixed at 9°C was observed without considering the cycle optimization. Maintaining a constant chilled water outlet temperature is also of equal importance to improve the conversion efficiency so that maximum cooling capacity can be derived. In this paper, a simulation model of reheat adsorption cycles is developed to analyze the optimization of the cycle time, including adsorption/desorption time, mass recovery time, and preheating/precooling time, with chilled water outlet temperature fixed. The reheat working principle is also introduced. The proposed cycle is compared with the four-bed versison without reheat cycle in terms of coefficient of performance (COP) and cooling capacity. The result shows that the performance of a reheat cycle is superior to that of four-bed version without reheat, especially for low heat-source temperature. For low heat-source temperature (55–65°C) both COP and cooling capacity of the reheat cycle with optimization were raised significantly compared to the high heat-source temperature (70–80°C). [ABSTRACT FROM AUTHOR]

Several mathematical models are available for estimation of effective thermal conductivity of nonreactive packed beds. Keeping in view the salient differences between metal hydride beds in which chemisorption of hydrogen takes place and conventional nonreactive packed beds, modified models are proposed here to predict the effective thermal conductivity. Variation in properties such as solid thermal conductivity and porosity during hydrogen absorption and desorption processes are incorporated. These extended models have been applied to simulate the effective thermal conductivity of the MmNi4.5Al0.5hydride bed and are compared with the experimental results. Applicability of the extended models for estimation of the effective thermal conductivity at different operating conditions such as pressure, temperature, and hydrogen concentration is discussed. [ABSTRACT FROM AUTHOR]

The effective use of marine biomass has recently been identified as a feasible method of renewable energy production. Therefore, to facilitate the effective use of algae biomass, it is essential to develop techniques for the mass production of algal cultures. It is also important to develop artificial culture techniques that are not affected by natural phenomena such as weather. This study utilized a newly developed culture technology that uses seawater with high concentrations of dissolved CO2(CO2seawater). The experiments in this study were conducted to test the effects of CO2seawater on algal growth. In addition to experimental conditions that were previously investigated in industrial algae farming scenarios, it is also necessary to consider the effects of new parameters associated with increased CO2concentrations. The following four conditions were experimentally investigated: (1) the tolerance of algae to changes in pH, (2) the effect of CO2seawater on long-term culture growth, (3) the effect of continuous culture experiments, and (4) the effect of water flow rate on cultured algae. The results in terms of having excelled especially indicate that a 1-month long-term algae culture period in seawater with CO2concentration of 1.0% led to growth that was approximately 4.5 times faster than growth in seawater without the CO2additive. Furthermore, the results also provided useful information regarding the proper flow rate needed to enhance algal growth. [ABSTRACT FROM AUTHOR]

Sodium-to-air heat exchangers (AHX) are used in fast breeder reactors for removal of decay heat generated in the core after a reactor shutdown. The AHX is an important component of the safety-grade decay heat removal system in a fast reactor. Decay heat removal critically depends on the performance of the AHX, which is essentially a cross-flow heat exchanger with liquid sodium flowing on the tube side and air flowing across finned tubes in the cross-flow mode. In this paper, a three-dimensional numerical study is carried out to investigate the flow and heat transfer characteristics when air flows over a representative bank of finned tubes in an AHX. The computational model has been validated against published experimental benchmarks. Based on parametric studies, appropriate correlations for the Nusselt number and fin effectiveness are derived. A computationally efficient porous body model is then developed and an integrated thermal hydraulics study of AHX is carried out using the derived heat transfer correlation. The numerical predictions of the porous body model are compared with the results of an experimental AHX tested at the Indira Gandhi Centre for Atomic Research; Kalpakkam, India. A good agreement between the results is seen. [ABSTRACT FROM PUBLISHER]

In this paper, a conjugate forced convection heat transfer from a good conducting plate with temperature-dependent thermal conductivity is studied. The semi-analytical solution for the nonlinear integro-differential equation occurring in the problem is handled easily and accurately by implementing the differential transform method (DTM). The horizontal plate is heated with uniform heat flux at the lower surface while being cooled at the upper surface under laminar forced convection flow. A numerical approach is also performed via a finite-volume method to examine the validity of the results obtained by DTM. The results of DTM show closer agreement with the results of the numerical method than the results obtained by the perturbation method existing in the literature. It is concluded that for a good conducting plate with a finite thickness the distribution of the conjugate heat flux at the upper surface is significantly affected by the plate thickness. Moreover, we conclude that in the conjugate heat transfer case the temperature distribution of the plate is flatter than the one in the nonconjugate case. [ABSTRACT FROM AUTHOR]

This work deals with the analysis of forced convection in single-phase laminar flow of liquid through microsized circular geometry with a diameter of 100 × 10−6 m. The problem with hydrodynamically and thermally developing flow in the entrance region with no-slip, no-temperature jump and constant wall heat flux boundary condition is numerically studied. Two-dimensional (with axisymmetry) simulation is carried out to understand the effect of fluid property variations on flow development and heat transfer. Pure continuum-based governing equations are solved to predict the significance of momentum and energy transport due to temperature-dependent viscosity and thermal conductivity variation, respectively. The radial inward flow is induced due to temperature-dependent density variation that sharpens the axial velocity profile. The investigation also analyzes the change in Nusselt number with locations in the channel for Graetz problem with uniform heating condition. The flattening of axial velocity profile, radial temperature profile, and inward radial flow influences the heat flow characteristics. The investigations in computational domain show that Nusselt number in thermal entrance region deviates from constant properties solution due to scaling effects. [ABSTRACT FROM AUTHOR]

In many engineering applications and natural phenomena, thermal radiation interacts with complex media composed of dispersed phases that may be of different type: solid/solid, solid/gas, or liquid/gas. Most of them are semitransparent media that emit, absorb, and scatter thermal radiation. Heat transfer by combined radiation with conduction or convection in such media is a problem of high practical importance, mostly in situations where radiation is a dominant mode. Improvement of thermal performance of such materials or of the manufacturing processes that involve these media requires the availability of efficient methods (i) for radiative transfer modeling, and (ii) to predict and to experimentally determine the thermophysical properties intended to feed the models. This paper is focused on radiative properties assessment. After a brief overview of the materials and properties of interest, the emphasis is put on methodology of property investigation combining both theoretical prediction and experimental identification. Examples related to different particulate media are presented, showing recent advances and needs for further investigation. [ABSTRACT FROM AUTHOR]

This article documents some of the factors that influence the heat transfer through polysynthetic thermal compounds at the central processing unit (CPU)/heat sink interface. First, special attention is paid to assessing the effect of mechanical and thermal properties of the contacting bodies, applied contact pressures, and surface roughness characteristics, as well as the use of different thermal interface materials on the maximum temperature experienced by the CPU. Second, it can be appreciated that good wetting of the mating surfaces and the retention of asperity micro-contacts can become critical elements in effectively removing the heat generated by the CPU. This study uses the Holman model for calculating the heat transfer, indicating the role of thermal contact resistance. The mathematical results clearly indicate that any strain in the interface material leads to a change in thermal contact resistance, with an effect on CPU overheating. Experimentally obtained images with an atomic force microscope clearly revealed that eliminating micro-gaps using thermal interface materials can facilitate the heat transfer by significantly lowering the thermal contact resistance of the CPU/heat sink assembly. This effect is amplified by the plastic deformation of micro-contacts due to high contact pressures and lower micro-hardness levels. [ABSTRACT FROM AUTHOR]

This study provides a detailed literature review and an assessment of results of the research and development work forming the current status of nanofluid technology for heat transfer applications. Nanofluid technology is a relatively new field, and as such, the supporting studies are not extensive. Specifically, experimental results were reviewed in this study regarding the enhancement of the thermal conductivity and convective heat transfer of nanofluids relative to conventional heat transfer fluids, and assessments were made as to the state-of-the-art of verified parametric trends and magnitudes. Pertinent parameters of particle volume concentration, particle material, particle size, particle shape, base fluid material, temperature, additive, and acidity were considered individually, and experimental results from multiple research groups were used together when assessing results. To this end, published research results from many studies were recast using a common parameter to facilitate comparisons of data among research groups and to identify thermal property and heat transfer trends. The current state of knowledge is presented as well as areas where the data are presently inconclusive or conflicting. Heat transfer enhancement for available nanofluids is shown to be in the 15-40% range, with a few situations resulting in orders of magnitude enhancement. [ABSTRACT FROM AUTHOR]

Fouling is an important and complex problem that affects a variety of industries. Surface fouling takes place as a result of the complex reactions that cause deposits to form on process surfaces. A number of parameters influence fouling development, including flow velocity, surface temperature, surface material/finish, surface geometry, and fluid properties. It is a transient process that begins with a clean process surface and may progress until the surface can no longer be used effectively. The event sequence of the fouling process appears in general to be universal, beginning when fluid comes into contact with a process surface. During this induction period, a conditioning film forms, and the heat transfer efficiencies do not change significantly. Conditioning film appearance may occur in weeks, days, or minutes. This stage is followed by a rapid accumulation of deposit growth. It is during this growth phase that the heat transfer across the process surface starts to dramatically change. Finally, a pseudo-steady-state period is arrived at when accumulation is almost constant. This accumulation causes heat transfer to significantly decrease and a complete cleaning of the surfaces may be required. Included here is a discussion on process surface materials used in applications where fouling may be a concern. Previous work in this area has prompted this study in order to provide better information for designs involving fouling. Conclusions and observations regarding the materials/surfaces that are commonly used in designs where fouling may be a concern are presented here. Photographs are presented of frontal surfaces and edges. Finally, transient surface roughness values are given for several materials. [ABSTRACT FROM AUTHOR]

Heat transmission through a layered compound material consisting of carbon steel backing and insulation (either aluminized silver or fiberglass) was examined to determine thermal properties. The heat flux impinged on the insulation material side of this simulated "firewall." A heat transfer model was developed that could, in principle, be used to predict the heat transfer through layered compound materials using techniques of thermal property parameter estimation. The parameter estimates are based on thermocouple measurements of surface temperatures during heating on both sides of the material. The experiment analyzed in this article involved a vertical plate exposed on the insulation side to a transient step-applied radiant heat flux. The transient temperature measurements were fitted to heat transfer models. Thermal diffusivity and Biot number were estimated using ordinary least-squares nonlinear regression. [ABSTRACT FROM AUTHOR]