Search

The measurements for the short-wave solar reflectivity of a Reflective Coating Material (RCM) with various cleaning operations that were obtained in a previous study were used in this study to conduct numerical simulations in order to assess the moisture and energy performance of cool and black roofs when they were subjected to the weather conditions of Saudi Eastern Province and Kuwait City. The results of the numerical simulations showed that black roofs always work with less moisture than cool roofs. Because the highest relative humidity in the different components of the black and cool roofs was well below 80%, there was no risk of condensation and mold growth in these roofs. For both weather conditions of Saudi Eastern Province and Kuwait City, the results showed that installing cool roofs have resulted in increasing the heating energy loads in relation to black roofs. Conversely, the results showed that the decrease in the cooling energy loads due to installing cool roofs were typically much greater than the increase in the heating energy loads. As such, cool roofs have resulted in net energy savings in relation to black roofs. Replacing black roof by cool roof in Saudi climate, the results showed that the annual energy savings in the total energy load was 25% and 34% as a result of installing cool roof with RCM at no cleaning and weekly homemade cleaning, respectively. Additionally, replacing black roof by cool roof in Kuwaiti climate, the results showed that the annual energy savings in the total energy load was 23% and 31% a result of installing cool roof with RCM at no cleaning and weekly homemade cleaning, respectively.

Cool roofs use reflective materials or coatings to reflect a portion of the incident solar radiation. This results in a lowering the surface temperature of the cool roof compared to black roofs, and thus helps reduce the cooling energy loads during the summer season. The research reported in this paper was conducted to assess experimentally and numerically the performance of cool and black roofs that were subjected to the hot, humid and dusty climate of Jubail Industrial City (JIC). This paper focused on characterizing one of the important properties of reflective coating material (RCM), which is its solar reflectivity. In this study, the effect of dust/dirt accumulation on the solar reflectivity of the RCM was investigated at different exposure times to the natural weathering conditions of JIC. The test results showed that dust and dirt can significantly contribute in reducing the solar reflectivity of the RCM. As such, a number of cleaning processes were conducted on the surface of the RCM so as to increase its solar reflectivity. The effect of each cleaning process on the solar reflectivity of the RCM was investigated. Finally, this paper provides a test protocol and procedure for characterizing the dust concentration/intensity on the surfaces of the RCM and cleaning this material after different exposure times to a natural and polluted climate.

Considerable energy is used for cooling buildings in hot climates like those found in Gulf Cooperation Council (GCC) countries. Designing building envelopes for the purpose of saving energy can necessarily help reduce the building's operating expenses and therefore energy demand over time. For roofing systems, a research project was recently conducted to assess experimentally and numerically the performance of the roofing systems. This paper presents the experimental results of this project. Cool/reflective/white roofs use reflective materials or coatings to reflect a portion of the incident solar radiation. This results in lowering the surface temperature of the cool roofs compared to black roofing systems. As such, cool roofs help reduce the cooling loads during the summer season. This paper presents the test results of characterizing the short-wave solar reflectivity of a reflective roofing material that can be used in cool roofs of Saudi buildings. A Reflective Coating Material (RCM) that is commercially available in the GCC markets was used in this study. Also, the reduction in the solar reflectivity due to dust and dirt accumulations on the surface of the RCM was investigated in this study when this coating was exposed to a dusty and polluted climate of Jubail Industrial City (JIC). As well, the effect of applying different cleaning operations on the solar reflectivity of the RCM was investigated. The test results showed that dust/dirt can significantly contribute in reducing the short-wave solar reflectivity of the RCM. For the RCM subjected to the natural weathering conditions at different exposures times, the results showed that a maximum enhancement of 5% in the short-wave solar reflectivity was achieved, as a result of conducting air plowing process that simulates the wind action. Additionally, a maximum enhancement of 45% in the short-wave solar reflectivity was achieved as results of conducting water cleaning/rinsing process that simulates the rain action and as well conducting washing with dishwashing detergent that simulates homemade cleaning. Furthermore, conducting professional cleaning has resulted in insignificant enhancement in the short-wave solar reflectivity compared to conducting homemade cleaning. Finally, this paper provides a test procedure for characterizing the dust concentration/intensity on the surface of the RCM at different exposure times to the natural and polluted climate. This test procedure can easily be applied on different types of reflective roofing materials and membranes that can be used in cool roofs.

The long-term performance in respect to moisture management within any wood frame wall assembly depends on the hygrothermal response of the wall to local climate moisture loads. Estimating the wood moisture content, temperature, and time of exposure to conditions suitable for the onset, growth, and propagation of mold or rot are critical parameters when assessing the longevity of wood frame structures. A number of approaches for assessing the vulnerability of wood frame structures to deterioration have been developed in recent years; one of which has been used by NRC-Construction for evaluating the performance of wall assemblies based on the results from hygrothermal simulation. In this paper, an example of the use of this approach for the assessment of a stucco-clad wall incorporating drainage cavities is described as is the use of a mold index to capture the risk of the formation of mold in walls. An example is given in assessing the moisture management of a stucco-clad wood frame wall incorporating vented and ventilated drainage cavities for three Canadian locations., Symposium on Advances in Hygrothermal Performance of Building Envelopes: Materials, Systems and Simulations, 26-27 October, 2016, Orlando, FL. USA, Series: Selected Technical Papers; no. STP1599

Field monitorings of thermal performance of residential 2 x 6 wood-frame wall systems that had been retrofitted using vacuum insulation panels (VIPs) and extruded polystyrene foam (XPS) panels were undertaken in May 2011 – May 2012 at the Field Exposure of Walls Facility (FEWF) of NRC-Construction. The main objective of this research was to measure the steady-state and transient thermal performance of three wall assemblies (4 ft x 6 ft), two of which incorporated VIPs within an XPS Tongue and Groove (T&G) configuration and VIPs within an XPS Clip-On (C-O) configuration, and a third assembly incorporating only XPS. The three wall assemblies were installed in the FEWF for 1-year cycle of exposure to outdoor natural weather conditions. The hygIRC-C model was used in this study. The results of the model calculations were in good agreement with the experimental data. Given that the VIPs could be punctured during the installation process or could fail during normal operating conditions, additional model calculations were used to predict the thermal resistance in cases where one or more VIPs failed. The model was also used to predict the yearly cumulative heat losses across these wall systems. It is important to point out that the aging effect and the effect of the thermal bridging due to envelope (i.e. skin) of the VIPs are not accounted for in this study. However, sensitivity analysis of the thickness and thermal conductivity of the VIP envelope was conducted to investigate the effect of these parameters on the effective thermal resistance of VIP.

A table is provided in the 2009 ASHRAE Handbook of Fundamentals (Chapter 26) that contains the thermal resistances (R-values) of enclosed airspaces. The ASHRAE table provides the R-values for enclosed airspaces of different thicknesses, effective emittances, mean airspace temperatures, and temperature differences across the airspaces. This table is extensively used by modelers, architects and building designers in the design for the R-values of building enclosures. The effect of the airspace aspect ratio (length/thickness) on the R-value is not accounted for in the ASHRAE table. However, previous studies showed that the aspect ratio of the airspace can affect its R-value. In this paper, the previous studies that focused on determining the R-values for vertical enclosed airspaces and horizontal enclosed airspaces with upward and downward heat flow are extended to investigate the effect of the aspect ratio on the R-values of 45° sloped enclosed airspaces under downward heat flow for different airspace thicknesses and having a wide range of values for the effective emittance, mean temperature, and temperature differences across the airspaces. The predicted R-values are compared with those provided in the ASHRAE table. Considerations are also given to investigate the potential increase in the R-values of enclosed airspaces when a thin sheet is placed in the middle of the airspace and whose surfaces have different values of emissivity. Thereafter, practical correlation is developed for determining the R-values of 45° sloped enclosed airspaces for future use by modelers, architects and building designers. The simplicity of this correlation for the sloped enclosed airspaces along with those that were previously developed for vertical and horizontal airspaces suggests that these correlations could be included in the ASHRAE Handbook of Fundamentals.

The thermal resistance ( R -value) of an enclosed airspace depends on the emissivity of all surfaces that bound the airspace, the size and orientation of the airspace, the direction of heat transfer through the airspace, and the respective temperatures of all surfaces that define the airspace. A table is provided in the 2009 ASHRAE Handbook of Fundamentals (Chapter 26) that contains the R -values of enclosed airspaces. The ASHRAE table is extensively used by modellers, architects and building designers in the design for thermal resistance of building enclosures. This table provides R -values for enclosed airspaces for different values of airspace thickness, effective emittance, mean airspace temperature, and temperature differences across the airspace. The effect of the airspace aspect ratio (length/thickness) on the R-value is not accounted for in the ASHRAE table. However, in previous studies, it was shown that the aspect ratio of the airspace can affect its R-value. In this paper, previous studies undertaken by the author that focused on determining the R -value for vertical enclosed airspaces and horizontal enclosed airspaces with downward heat flow are extended to investigate the effect of the aspect ratio on the R -value of horizontal enclosed airspaces under an upward heat flow condition for different airspace thicknesses and having a wide range of values for effective emittance, mean temperature, and temperature differences across the horizontal airspaces. The R -values predicted from numerical simulation are compared with those provided in the ASHRAE table. Considerations were also given to investigate the potential increase in the R -values of enclosed airspaces when a thin sheet is placed horizontally in the middle of the airspace and whose surfaces have different values of emissivity. Thereafter, practical correlations are developed for determining the R -values of horizontal enclosed airspaces for future use by modellers, architects and building designers. The simplicity of these correlations for horizontal airspaces with upward heat flow along with those that were previously developed for vertical airspaces and horizontal airspaces with downward heat flow suggests that these correlations could be included in the ASHRAE Handbook of Fundamentals.

Reflective insulations are being used in home attics, flat roofs, sloped roofs and wall systems of building envelopes. The present model, hygIRC-C, was used to investigate the contribution of the reflective insulations to the thermal resistance of specimens. The predictions of the present model were compared with test data of different sample stacks with different types of reflective insulations. In a previous study, the present model was benchmarked using test data obtained from a Guarded Hot Box (GHB) in accordance with the ASTM C-1363 test method. In this study, the test data was obtained from a different test method based on the heat flow meter in accordance of ASTM C-518 in the case of horizontal sample stacks with reflective insulations. Results showed that the predicted heat fluxes on the same area and same location of Heat Flux Transducers (HFTs) on the top and bottom surfaces of the sample stacks are in good agreement with the measured heat fluxes (within ±1%). The derived R-values using these heat fluxes are also in good agreements. Due to the combined effect of heat transfer by convection and radiation in the airspace (facing the reflective surface), these predicted and measured heat fluxes are greater than the area-weighted average heat flux of whole sample stack, which is needed to determine the effective R-value of the sample. As such, the derived R-value from the test data resulted in underestimation of the effective R-value of the sample stack. After gaining confidence in the present model, it was used to conduct parametric study in order to quantify the contribution of reflective insulations to the effective R-value for a sample stack with different inclination angles, different directions of heat flow (upward and downward) and for a wide range of foil emissivity. Furthermore, the present model was used to compare the predicted R-values with the listed R-values in the 2009 ASHRAE Handbook [22] for enclosed air cavity (20 mm thick) of different effective emittance, inclinations and directions of heat flow.

A 3D numerical model was developed to investigate the effect of foil emissivity on the effective thermal resistance of an above-grade wall assembly with foil bonded to wood fibreboard in a furred assembly having airspace next to the foil. This model solved simultaneously the energy equation in the various material layers, the surface-to-surface radiation equation in the furred airspace assembly, Navier–Stokes equation for the airspace, and Darcy and the Brinkman equations for the porous material layers. In this work, the furring was installed horizontally. In the first phase, the present model was benchmarked against the experimental data generated by a commercial laboratory for an above-grade wall assembly. The wall consists of a conventional wood frame structure sheathed with fibreboard and covered on the interior side with a low emissivity material bonded to wood fibreboard that is adjacent to a furred airspace assembly. The results showed that the predicted R -value was in good agreement with the measured one. After gaining confidence in the present model, it was used to predict the effective thermal resistance of the same above-mentioned wall but having Oriented Strand Board (OSB) sheathing in lieu of wood fibreboard sheathing. In the second phase, the model was used to quantify the contribution on the wall R -value by having a low foil emissivity. The results showed that a low foil emissivity of 0.04 can increase the R -value of this wall to as much as ∼9%. This is on-going research. The present model is being used to investigate the transient thermal response of foundation wall systems with furring installed horizontally and vertically, and subjected to different Canadian climate conditions.

An analytical model is developed to investigate the effects of applying thin metallic coatings on the legs of skutterudite based thermoelectric unicouples and to calculate the impact on the dimensions and the performance parameters of the unicouple. These coatings suppress the sublimation of antimony from the legs near the hot junction (∼973 K) and, hence, minimize the degradation in the unicouple performance with operation time. Coating materials investigated are: tantalum (Ta), titanium (Ti), molybdenum (Mo) and vanadium (V), which have different thermal conductivities, electrical resistivities, coefficients of thermal expansion (CTE) and vapor pressures. Detailed comparison of these coating materials was necessary since none clearly satisfies both a minimal decrease in the performance of the unicouple and ease of fabrication and long life. The former favors low thermal conductivity and high electrical resistivity, while the latter favors low CTE and low vapor pressure. The lengths of the coatings of both the n- and p-legs, which were found to be different for best unicouple performance, are determined as functions of the antimony vapor pressure off the exposed portions of the legs, which varied from 1.0 to 1000 mPa, and the thickness of the applied metallic coating (1–9 μm). Results indicated that increasing the coating thickness decreases the conversion efficiency but increases the load electrical power of the unicouple. Despite their high CTE, Ti or V coatings are best in terms of the effect on the unicouple performance when a coating thickness >1 μm in needed. They cause the smallest decreases, while Ta or Mo coating with lower CTEs, result in the largest decreases in the conversion efficiency. With thin coatings (⩽1 μm), however, the effects on conversion efficiency and electrical power of the unicouple are significantly small. In this case, a Mo coating would be best since it has the smallest CTE and low vapor pressure.

Tests were performed of skutterudite based unicouples with (MAY-04) and without (MAR-03) metallic coating on the legs near the hot junction to quantify the effect on reducing performance degradation with operation time. The p-legs in the unicouples were made of CeFe3.5Co0.5Sb12 and the n-legs of CoSb3. The MAY-04 test was performed in vacuum (∼9 × 10−7 torr) for ∼2000 h at hot and cold junction temperatures of 892.1 ± 11.9 K and 316.1 ± 5.5 K, respectively, while the MAR-03 test was performed in argon cover gas (0.051–0.068 MPa) at 972.61 ± 10.0 K and 301.1 ± 5.1 K, respectively. The argon cover gas decreased antimony loss from the legs in the MAR-03 test, but marked degradation in performance occurred over time. Conversely, the metallic coating in the MAY-04 test was very effective in reducing performance degradation of the unicouple. Because the cross sectional areas of the legs in MAY-04 were larger than those in MAR-03, the measured electrical power of the former is much higher than that of the latter, but the Beginning of Test (BOT) open circuit voltages, Voc (204.2 mV) for both unicouples were almost the same. The peak electrical power of the MAY-04 unicouple decreased 12.35% from 1.62We at BOT to 1.42We after ∼2000 h of testing, while that of the MAR-03 unicouple decreased 25.37% from 0.67 to 0.5We after 261 h of testing at the above temperatures. The estimated peak efficiency of the MAY-04 unicouple, shortly after BOT (10.65%), was only ∼0.37% points lower than the theoretical value, calculated assuming zero side heat losses and zero contact resistance per leg.

Thermal analysis is performed of radioisotope power systems (RPSs) in which skutterudite based thermoelectric arrays (SKTAs) of 2 × 7 and 4 × 7 unicouples are thermally coupled to general purpose heat sources (GPHSs). The SKTAs are separated from the GPHS bricks by a thin graphite sleeve to ensure a hot junction temperature of 973 K and minimal or no increase in the 238 PuO 2 fuel temperature. They are connected electrically in series, and the performance parameters of the RPSs are calculated as functions of load voltage from 24 to 38 VDC. The cold junction temperature of the SKTAs and the radiator base temperature are determined from coupling the unicouples performance optimization model and the radiator thermal analysis model for sizing the aluminum fins. Calculated peak specific powers of the RPSs at the beginning of mission (BOM) are compared with those calculated at the peak electric power at different load voltages. The load voltage strongly affects the performance of the RPSs. The peak specific powers and those corresponding to the peak electrical powers increase with increasing load voltage up to certain values then drop with further increase in load voltage. The highest BOM specific powers of ∼6.859–6.973 W e /kg, are ∼43.3–45.7% higher than that of the heritage RTG (4.786 W e /kg) with 7 GPHS bricks and SiGe unicouples. Such specific powers for the RPSs with SKTAs are attainable with 28.6% less 238 PuO 2 fuel and at 2.85–11.62% more BOM electrical power (122 W e ) than those of the heritage RTG (105 W e ).

This paper compares the performance of SiGe (Si 0.8 Ge 0.2 ) and skutterudite segmented thermoelectric unicouples (STUs) at a hot side temperature of 973 K and cold side temperatures of 300, 573 and 673 K and for the same total length and cross sectional dimensions of the p-leg. The area of the n-leg and lengths of and the interfacial temperatures between segments of various materials in the STU legs are determined using a global optimization methodology. Results indicate that the STUs could potentially achieve peak efficiencies of 7.8% and 14.7% when operated at a cold side temperature of 573 K, typical of that in current radioisotope thermoelectric generators (RTGs), and 300 K, respectively. These efficiencies are 55% and 99% higher, respectively, than for SiGe at the same temperatures. However, due to the higher density of skutterudite, the electrical power densities corresponding to the peak efficiencies of the STUs are 39 and 109 W e /kg versus 92 and 232 W e /kg for SiGe at cold side temperatures of 573 K and 300 K, respectively. On the other hand, the heat inputs and heat rejection powers for the STUs are 42–55% and 39–53%, respectively, of those for SiGe at the peak efficiency and 70–75% and 67–77% of those of SiGe, respectively, at the peak electric power density. Therefore, when used in RTGs, STUs could halve the 238 PuO 2 fuel mass and the radiator area, while operating at >45% higher electrical power density (>7 W e /kg) than SiGe in current RTGs (∼5.5 W e /kg).

The 2009 ASHRAE Handbook - Fundamentals (Chapter 26) provided a table that contains the thermal resistances (R-values) of vertical, horizontal, and high-sloped (45°) enclosed airspaces. This table is extensively used by modelers, architects, and building designers in the design for the R-values of building enclosures. The effect of the airspace aspect ratio and the inclination angle (θ) of 30° on the R-values are not accounted for in the ASHRAE table. However, previous studies showed that the aspect ratio of the airspace can affect its R-value. In this article, the previous studies that focused on determining the R-values for vertical, horizontal, and high-sloped enclosed airspaces are extended to investigate the effect of the aspect ratio on the R-values of low-sloped (θ = 30°) enclosed airspaces under downward heat flow for different airspace thicknesses and having a wide range of values for the effective emittance, mean temperature, and temperature differences across the airspaces. Thereafter, practical correlation is developed for determining the R-values of low-sloped enclosed airspaces for future use by modelers, architects, and building designers.

Many parts of the building envelope contain enclosed airspaces. The thermal resistance (R-value) of an enclosed airspace depends on the emissivity of all surfaces that bound the airspace, the size and orientation of the airspace, the direction of heat transfer through the airspace, and the respective temperatures of all surfaces that define the airspace. The 2009 ASHRAE Handbook of Fundamentals (Chapter 26) provides a table that contains the R-values for an enclosed airspace. The ASHRAE table is extensively used by modelers, architects and building designers in the design of building enclosures. This table provides R-values for enclosed airspaces for different values of the thickness of the airspace, effective emittance, mean airspace temperature, and temperature differences across the airspace. The effect of the airspace aspect ratio (height/thickness of airspace) on the R-value is not included in the ASHRAE table. However, in a recent study on the R-value of reflective insulations using a numerical simulation model, it was shown that the aspect ratio of the airspace can affect the R-value of the enclosed airspace. The numerical simulation model used in this study had been benchmarked against experimental data obtained using two standard test methods: ASTM C-518 and ASTM C-1363. In this paper, a numerical simulation study was conducted, that was based on previous work focused on enclosed airspaces, to investigate the effect of the aspect ratio on the R-value of vertical enclosed airspaces of different thicknesses and having a wide range of values for effective emittance, mean temperature, and temperature differences across the airspace. The R-values predicted from numerical simulation are compared with those provided in the ASHRAE table. Considerations were also given to investigating the potential increase in R-values of enclosed airspaces when a thin sheet is placed vertically in the middle of the airspace and whose surfaces have different values of emissivity. Finally, practical correlations are developed for determining the R-values of an enclosed airspace for future use by modelers, architects and building designers. The simplicity of these correlations suggests that these could be included in the ASHRAE Handbook of Fundamentals.

The 2009 ASHRAE Handbook of Fundamentals (Chapter 26) provides a table that contains the thermal resistances (R-values) of enclosed airspaces for different values of airspace thickness, effective emittance, mean airspace temperature, and temperature differences across the airspace. This table is extensively used by modelers, architects, and building designers in the design for thermal resistance of building enclosures. The effect of the airspace aspect ratio (length/thickness) on the R-value is not accounted for in the ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) table. However, in previous studies, it was shown that the aspect ratio of the airspace can affect its R-value. In this article, the previous studies by the author who focused on determining the R-value for vertical enclosed airspaces and horizontal enclosed airspace under upward heat flow condition are extended to investigate the effect of the aspect ratio on the R-value of horizontal enclosed airspaces under a downward heat flow condition for different airspace thicknesses and having a wide range of values for effective emittance, mean temperature, and temperature differences across the airspaces. The R-values predicted from numerical simulation are compared with those provided in the ASHRAE table. Considerations were also given to investigate the potential increase in the R-values of enclosed airspaces when a thin sheet is placed horizontally in the middle of the airspace and whose surfaces have different values of emissivity. Thereafter, practical correlation was developed for determining the R-values of horizontal enclosed airspaces for future use by modelers, architects, and building designers. The simplicity of this correlation derived for horizontal airspaces under downward heat flow condition together with those that were previously developed for vertical airspaces and horizontal airspaces under upward heat flow condition suggests that these correlations could be included in the ASHRAE Handbook of Fundamentals.

The phenomenon of dezincification of α-brass in 4% NACl solution (synthetic sea water) following polarization at various potentials was studied using XPS and AES surface analytical techniques. The electrolyte was simultaneously analyzed by atomic absorption. At potentials more negative than the steady state open-circuit potential (E st ) of brass, dissolution of both copper and zinc was restricted by the values of the solubilities of Cu 2 O and ZnO. At potentials more positive than E st dissolution of α-brass occurred with 100% current efficiency with a rate two orders of magnitude higher than that measured at negative potentials. XPS analysis of the alloy surface following polarization proved the formation of CuCl and two forms of ZnO. Dissolution of copper is assumed to occur through CuCl 2 - where that of zinc is suspected to occur through HZnO 2 . The two metals go into solution in a ratio comparable to that of the alloy. Following prolonged polarization, xps spectra indicated the redeposition of metallic copper from solution on top of the CuCl precipitate.

In order to evaluate the effectiveness of in-place emergency ventilation strategies to control smoke spread in the event of a fire in a section of a roadway tunnel, both numerical and experimental studies were performed. The experimental study was conducted to provide the necessary initial and boundary conditions for the numerical phase of the investigation. A fire heat release rate of 1 MW was used in all fire tests. This fire heat release rate was selected to minimize the risk of damage to the tunnel and its associated systems while producing reliable data for visualizing the smoke movement in the tunnel. The numerical study used Computational Fluid Dynamics, Fire Dynamic Simulator version 4.0 to investigate smoke removal in the tunnel for large fire of 30 MW (bus or truck on fire). In total, four field fire tests and seven numerical simulations were conducted. Based on the study results, recommendations were made to optimize the ventilation scenarios in the tunnel section. This article presents the details of the study as well as the recommendations made.

This paper presents the results of a survey of floor areas and combustible contents in multi-family dwellings such as semi-detached houses, town houses and low-rise apartments. The survey was primarily based on measurements and photographic information obtained from real-estate websites. This is a novel method, which reduces the effort required to conduct fire load surveys in residential buildings. In addition to quantifying combustible contents, an important objective of the survey was to determine the similarities in combustible contents and configurations of these dwellings, which could be used in designing fire experiments. The survey provided an insight into the types and quantity of combustible contents found in the dwellings, as well as the types of floor configurations and other information that are pertinent to fire issues. Typical furnishings that constituted a significant portion of the movable fire load were identified and possible values of fire load densities were calculated for rooms such as: kitchens, dining rooms, living rooms and bedrooms. The average fire load densities in various rooms were estimated to be: kitchens—807 MJ/m2; dining rooms—393 MJ/m2; living rooms—412 MJ/m2; basement living rooms—288 MJ/m2; primary bedrooms—534 MJ/m2; and, secondary bedrooms—594 MJ/m2. Although kitchens had the highest fire load densities the actual fire load (heat content) was found to be lower than bedrooms, which have a higher fire load due to the presence of mattresses, clothing and carpeting.

The performance and specific electrical powers of Radioisotope Power Systems (RPSs) with Skutterudite‐based Thermoelectric Arrays (SKTAs) of 2×7 and 4×7 unicouples connected electrically in series are calculated as functions of load voltage from 24 to 38 VDC. The p‐legs of the unicouples are made of CeFe3.5Co0.5Sb12 and the n‐legs are made of CoSb3, and the optimized cross‐section areas of these legs for maximum efficiency operation are calculated as functions of the RPS terminal voltage. The RPS employs five General Purpose Heat Source (GPHS) bricks, generating 1250 Wth at BOM, and 40 SKTAs, which are connected in series in two or four parallel strings. The peak electrical power and peak conversion efficiency of the SKTAs (20 mm long) occurs at the same electrical current because the unicouples operate at constant hot junction temperature (973 K) and constant input thermal power. The cold junction temperature of the unicouples and the radiator base temperature are determined from coupling the unicouples performance optimization model with a detailed radiation thermal analysis for sizing the aluminum fins for rejecting waste heat into space. The calculated peak specific powers and the corresponding electrical powers of the RPSs at Beginning‐Of Mission (BOM) are compared with those calculated at the peak electric power at different load voltages. Results indicated that the value of the load voltage strongly affects the performance of the RPS. Both the RPS peak specific powers and those corresponding to the peak conversion efficiency / peak electrical power increase with increasing the load voltage up to certain values then drop with further increasing that voltage. The highest BOM specific powers of the RPS is ∼ 6.859 –6.973 We/kg, ∼ 43.3% and 45.7% higher than that of the RTG (4.786 We/kg) with 7 GPHS brick and SiGe unicouples. Such specific electrical powers of the RPS with SKTAs are attainable with 28.6% less 238PuO2 fuel and 2.85% to 11.62% more BOM electrical power (122 We) than the RTG (105 We).

Conceptual designs of Advanced Radioisotope Power System (ARPS) with Cascaded Thermoelectric Converters (CTCs) are developed and optimized for maximum efficiency operation for End‐Of Mission (EOM) electrical power of at least 100 We. These power systems each employs four General Purpose Heat Source (GPHS) bricks generating 1000 Wth at Beginning‐of‐Life (BOL) and 32 Cascaded Thermoelectric Modules (CTMs). Each CTM consists of a top and a bottom array of thermoelectric unicouples, which are thermally, but not electrically, coupled. The top and bottom arrays of the CTMs are connected electrically in series in two parallel strings with the same nominal voltage of > 28 VDC. The SiGe unicouples in the top array of the CTMs are optimized for nominal hot shoe temperature of 1273 K and constant cold shoe temperature of either 780 K or 980 K, depending on the thermoelectric materials of the unicouples in the bottom array. For a SiGe cold junction temperature of 780 K, the unicouples in the bottom array have p‐legs ...

This paper presents a one-dimensional, optimization model of Segmented Thermoelectric Unicouples (STUs). The model predictions are compared with some results of experiments performed at the Jet Propulsion Laboratory to measure the performance parameters of a number of STUs made of n-type Bi2Te3 and CoSb3 based alloys and p-type Bi2Te3 and CeFe4Sb12 based alloys. In addition to determining the input and rejected thermal power of the STUs and the axial temperature distributions in the n- and p-legs, the present model optimizes the lengths and/or the interfacial temperatures of the various segments for either optimum conversion efficiency or optimum electrical power density. Results indicate that well-insulated STUs could have a conversion efficiency of ∼12%, when operated at Tc=305–316 K and Th=872–885 K and the total interfacial resistance per leg is ∼50 μΩ-cm2. However, due to the high total interfacial resistances of ∼690 and 146 μΩ-cm2 and the side heat losses of 1.83 W and 3.7 W, respectively, in the experiments, the peak conversion efficiency is ∼5.5% and 4.6% for uni8 and uni12, respectively. Model predictions show that, for a total interfacial resistance of ∼50 μΩ-cm2 per leg and zero side heat losses, skutterudite STUs have the potential of achieving a conversion efficiency of 15% when operated at hot and cold side temperatures of 973 K and 300 K, respectively.

For the past 25 years, unicouples made of Silicon Germanium alloys (Si0.8Ge0.2 and Si0.63Ge0.38) have been used in the majority of the spacecraft powered by Radioisotope Thermoelectric Generators (RTGs) to explore various planets of the solar system as well as the sun. These unicouples operate typically at hot and cold side temperatures of 1175–1273 K and 573 K, respectively, converting the heat produced in the General Purpose Heat Source (GPHS) modules to electricity at efficiencies

A number of fire ventilation scenarios were investigated in order to identify the proper ventilation scheme for conducting design fire tests in a medium-sized residential room of a size of 4.2 m long, 3.8 m wide and 2.4 m high. The ventilation schemes were based on using a window, door, or both with different sizes. The fuel package that was used in all scenarios consisted of a mock-up sofa made of polyurethane foam and two wood cribs underneath it. The selection of this fuel package is supported by fire statistics that many fatal residential fires begin with an item of upholstered furniture. The CFD technique was used to conduct the numerical simulations for eleven ventilation scenarios using the Fire Dynamics Simulator (FDS) version 5. The effect of window and door sizes, and fire load location on the heat release rate, burning rate, temperature during the period of fully-developed fire (post-flashover), and the onset of post-flashover and its duration were investigated.Copyright © 2008 by ASME

This paper presents the results of a 3‐D performance analysis of Skutterudite‐Based Segmented Unicouple (SKU) with nine μm thick Molybdenum (Mo) coatings on n‐ and p‐legs near the hot junction. The analysis performed at hot and cold junction temperatures of 973 K and 300 K investigated the effect of the coating on lateral distributions of the electric current, voltage, and temperatures in the legs and the conversion efficiency and electric power generated by the unicouple. The p‐ and n‐legs are 20 mm long and have hot and cold segments of CeFe3.5Co0.5Sb12 and Bi0.4Sb1.6Te3, and of CoSb3 and Bi2Te2.95Se0.05, respectively. The cross‐section area of the p‐leg is 11 mm2. The cross sectional area of the n‐leg and the lengths of the Mo coatings and of various segments of the legs are determined for maximum conversion efficiency using a 1‐D optimization model. The 3‐D analysis performed with ANSYS finite element commercial software used the dimension determined by the 1‐D model. Results show that the electric currents near the outer surface of the Mo coatings flow in the opposite direction to those in the n‐ and p‐legs. In very thin parts of legs near the interface with the coatings, electric currents flow in the same direction as in the coatings, but decrease rapidly with inward distance from the interface, eventually becoming zero, then flowing in the same direction as the electric current in the legs. Such current circulation increases joules losses in the coated parts of the hot segments of the legs, decreasing the conversion efficiency. The increased heat flow from the hot shoe through the metallic coatings contributes to decreasing the conversion efficiency, but increasing the electric power generated by SKU.

Skutterudite‐based thermoelectric unicouples are currently being considered for use in next generation Radioisotope Power Systems (RPSs) to reduce the amount of 238PuO2 fuel and the mission’s cost and increase the system specific power. In these unicouples, typically operateing at a hot junction temperature of 973K, the loss of the volatile antimony from the n‐ and p‐legs near the hot junction, if not suppressed, could gradually degrade their performance. Recently, it has been shown that such a loss of antimony could be effectively suppressed by applying a thin metallic coating on the legs near the hot junction. However, to minimize the impact on the conversion efficiency, the thickness and the length of the coating need to be optimized. An analytical model for coated skutterudite‐based segmented unicouples is developed and used to optimize the length and thickness of the coating and quantity its effect on the conversion efficiency and load electrical power. Several coating materials are investigated: Tantalum (Ta), Titanium (Ti), Molybdenum (Mo), and Vanadium (V). The required coating length for maintaining the antimony vapor pressure off the exposed portions of the legs ⩽ 10−3 Pa depends on its thickness, which varied from 1.0 to 9 μm. Results indicated that increasing the coating thickness decreases the conversion efficiency, but increases the load electrical power. The smallest decrease in the conversion efficiency occurs when using Ti or V coating, while using Ta or Mo coating results in a large decrease in the conversion efficiency.

A performance test of a Skutterudite‐based unicouple (MAY‐04) with a metallic coating to suppress the sublimation of antimony from the legs near the hot junction is performed in vacuum (∼ 9 ×10−7 torr) for ∼ 2,000 hours at hot and cold junction temperatures of 892.1 ± 11.9 K and 316.1 ± 5.5 K, respectively. The p‐leg is made of CeFe3.5Co0.5Sb12 and the n‐leg is made of CoSb3. Presented are the measured voltage‐current characteristics, electrical power, open‐circuit voltage, and the Seebeck coefficients of the legs as functions of cumulative test time. Also presented is the estimate of the conversion efficiency, ∼ 96 hrs after the start of test. To demonstrate the effectiveness of the metallic coating, the measurements for MAY‐04 are compared with those of two uncoated unicouples of the same leg materials (MAR‐03 and JUN‐03), which had been tested earlier. The cross‐sectional areas of the legs in MAY‐04 are larger than those in MAR‐03 and JUN‐03, tested in argon cover gas at ∼ 0.051–0.068 MPa for 450 and 1...