Effects of dilution with carbon dioxide on the laminar burning velocity and flame stability of H2–CO mixtures at atmospheric condition

The objective of this investigation was to study the effect of dilution with CO₂ on the laminar burning velocity and flame stability of syngas fuel (50% H₂–50% CO by volume). Constant pressure spherically expanding flames generated in a 40 l chamber were used for determining unstretched burning velocity. Experimental and numerical studies were carried out at 0.1 MPa, 302 ± 3 K and ? = 0.6–3.0 using fuel-diluent and mixture-diluent approaches. For H₂–CO–CO₂–O₂–N₂ mixtures, the peak burning velocity shifts from ? = 2.0 for 0% CO₂ in fuel to ? = 1.6 for 30% CO₂ in fuel. For H₂–CO–O₂–CO₂ mixtures, the peak burning velocity occurred at ? = 1.0 unaffected by proportion of CO₂ in the mixture. If the mole fraction of combustibles in H₂–CO–O₂–CO₂ mixtures is less than 32%, then such mixtures are supporting unstable flames with respect to preferential diffusion. The analysis of measured unstretched laminar burning velocities of H₂–CO–O₂–CO₂ and H₂–CO–O₂–N₂ mixtures suggested that CO₂ has a stronger inhibiting effect on the laminar burning velocity than nitrogen. The enhanced dilution effect of CO₂ could be due to the active participation of CO₂ in the chemical reactions through the following intermediate reaction CO + OH ? CO₂ + H.     

Cooling performance investigation of electronics cooling system using Al2O3–H2O nanofluid

In this study, the cooling performance of Al₂O₃–H₂O nanofluid was experimentally investigated as a much better developed alternative for the conventional coolant. For this purpose the nanofluid was passed through the custom-made copper minichannel heat sink which is normally attached with the electronic heat source. The thermal performance of the Al₂O₃–H₂O nanofluid was evaluated at different volume fraction of the nanoparticle as well as at different volume flow rate of the nanofluid. The volume fraction of the nanoparticle varied from 0.05 vol.% to 0.2 vol.% whereas the volume flow rate was increased from 0.50 L/min to 1.25 L/min. The experimental results showed that the nanofluid successfully has minimized the heat sink temperature compared to the conventional coolant. It was noticed also that the thermal entropy generation rate was reduced via using nanofluid instead of the normal water. Among the other functions of the nanofluid are to increase the frictional entropy generation rate and to drop the pressure which are insignificant compared to the normal coolant. Given the improved performance of the nanofluid, especially for high heat transportation capacity and low thermal entropy generation rate, it could be used as a better alternative coolant for the electronic cooling system instead of conventional pure water.     

Steam condensing – liquid CO2 boiling heat transfer in a steam condenser for a new heat recovery system

In a new waste heat recovery system, waste heat is recovered from steam condensers through cooling by liquid CO₂ instead of seawater, taking advantage of effective boiling heat transfer performance; the heat is subsequently used for local heat supply. The steam condensing – liquid CO₂ boiling heat transfer performance in a steam condenser with a shell and a helical coil non-fin tube was studied both numerically and experimentally. A heat transfer numerical model was constructed from two models developed for steam condensation and for liquid CO₂ boiling. Experiments were performed to verify the model at a steam pressure range of 3.2–5 kPa and a CO₂ saturation pressure range of 5–6 MPa. Overall heat transfer coefficients obtained from the numerical model agree with the experimental data within ±5%. The numerical estimations show that the boiling local heat transfer coefficient reaches a maximum value of 26 kW/m² K. This value is almost one order higher than that of a conventional water-cooled condenser.     

Theoretical analysis and experimental research on transcritical CO2 two stage compression cycle with two gas coolers (TSCC + TG) and the cycle with intercooler (TSCC + IC)

As one of the natural refrigerants, CO₂ is a potential substitute for synthesized refrigerants with favorable environmental properties. In order to improve the performance of the CO₂ transcritical compression cycle, the performance of the two stage compression cycle with two gas coolers (TSCC + TG) and the two stage compression cycle with intercooler (TSCC + IC) were analyzed, respectively. Under the given calculation condition, the optimum intermediate pressure of the cycle TSCC + TG and the TSCC + IC are 7.09 MPa and 5.89 MPa, and the maximal COP are 2.77 and 3.08, respectively. Range of the given evaporating temperature and outlet temperature of gas cooler, the experimental testing shows that the performance of cycle TSCC + IC are 11.88% and 10.87% better than that of the cycle TSCC + TG, respectively. Range of the given inlet temperature and cooling water volume flow of gas cooler, the refrigeration COP (COP_c) and heat COP (COP_h) of the cycle TSCC + IC are average 10.97% and 4.39% higher than that of the cycle TSCC + TG. Range of the given inlet temperature and chilled water volume flow of evaporator, the refrigeration COP (COP_c) and heat COP (COP_h) of the cycle TSCC + IC are average 10.71% and 3.67% higher than that of the cycle TSCC + TG, respectively. The error between theoretical calculation and experimental testing is not exceeds 20%.     

The effect of CO2/H2O on the formation of soot particles in the homogeneous environment of a rapid compression facility

Previous investigations show that soot particle volume fraction and number density were significantly reduced by exhaust gas recirculation (EGR) diluents CO₂ and H₂O. However, these investigations were often convoluted by their experimental flame configurations and primarily focused on soot volume fraction rather than soot inception. To isolate the effects on soot inception and the corresponding chemistry, the current study measured the reactivity of CO₂ (up to 9.5% volume fraction) for both C₂H₂ (1.00% volume fraction) and CH₄ (1.85% volume fraction) fuels in homogeneous mixtures. Computed effect of H₂O on these and other fuels are also presented. Experiments were performed at high temperature (1640 K and 1770 K) and high equivalence ratios (Φ = 55 and 75) to understand the effect of CO₂ on polycyclic aromatic hydrocarbons (PAH) and formation of nascent soot particles with negligible oxygen influence. Experimental results show that CO₂ enhanced the soot inception rate when added to C₂H₂ but had an undetectable affect on CH₄. Gas chromatography confirmed that CO₂ increases CO mole fraction and reduces C₂H₂ fuel concentration. Chemical kinetic simulations showed that the C₂H₂ was being converted to soot precursors. CO₂ enhanced the soot inception rate for C₂H₂ by producing OH radicals. Images of nascent soot particles produced in the presence of CO₂ were used to determine the size of PAH molecules in the particles and particle morphology. Both attributes were similar to particles formed without CO₂. CO₂ had little impact on the long reaction pathway from CH₄ to PAH molecules because H and CH₃ radicals propagated these reactions more readily than OH radicals.     

Novel heat transfer fluids for direct immersion phase change cooling of electronic systems

We describe the use of computer-aided molecular design (CAMD) and figure of merit (FOM) analysis to identify new heat transfer fluids for direct immersion cooling of electronic systems. Thirty-five new fluids, with thermophysical properties in the range 320 K < T_b < 370 K, k > 0.09 W m^?1 K^?1 and H_vap > 35 kJ mol^?1, were identified via a CAMD approach. Further analysis of these 35 fluids led to the selection of 1,1,1-trifluoro-3-methylpentane (C₆H₁₁F₃) for experimental evaluation. C₆H₁₁F₃ was synthesized from commercially available precursors, and its thermophysical properties were measured to verify its FOM. Next, the pool boiling performance of a mixture of 7 wt.% C₆H₁₁F₃ + 93 wt.% HFE 7200 was determined using a 10 mm × 10 mm grooved Si thermal test chip coated with copper. An improvement of 7% in the critical heat flux (CHF) was obtained, suggesting that C₆H₁₁F₃ is worth further examination as a candidate for direct immersion phase change cooling applications.     

Cooling of microprocessors using flow boiling of CO2 in a micro-evaporator: Preliminary analysis and performance comparison

The flow pattern based flow boiling heat transfer and two-phase pressure drop models for CO₂, recently developed by Cheng et al. [L. Cheng, G. Ribatski, J. Moreno Quibén, J.R. Thome, New prediction methods for CO₂ evaporation inside tubes: Part I – A two-phase flow pattern map and a flow pattern based phenomenological model for two-phase flow frictional pressure drops, Int. J. Heat Mass transfer 51 (2008) 111–124; L. Cheng, G. Ribatski, J.R. Thome, New prediction methods for CO₂ evaporation inside tubes: Part II – An updated general flow boiling heat transfer model based on flow patterns, Int. J. Heat Mass transfer 51 (2008) 125–135], have been used to predict the thermal performance of CO₂ in a silicon multi-microchannel evaporator (67 parallel channels with a width of 0.223 mm, a height of 0.68 mm and a length of 20 mm) for cooling of a microprocessor. First, some simulation results of CO₂ flow boiling heat transfer and two-phase pressure drops in microscale channels are presented. The effects of channel diameter, mass flux, saturation temperature and heat flux on flow boiling heat transfer coefficients and two-phase pressure drops are next addressed. Then, simulations of the base temperatures of the silicon multi-microchannel evaporator using R236fa and CO₂ were performed for the following conditions: base heat fluxes from 20 to 100 W/cm², a mass flux of 987.6 kg/m²s and a saturation temperature of 25 °C. These show that the base temperatures using CO₂ are much lower than those using R236fa. Compared to R236fa, CO₂ has much higher heat transfer coefficients and lower pressure drops in the multi-microchannel evaporator. However, the operation pressure of CO₂ is much higher than that of R236fa. Based on the analysis and comparison, CO₂ appears to be a promising coolant for microprocessors at low operating temperatures but also presents a great technological challenge like other new cooling technologies.     

Sintered porous heat sink for cooling of high-powered microprocessors for server applications

This paper experimentally investigates the sintered porous heat sink for the cooling of the high-powered compact microprocessors for server applications. Heat sink cold plate consisted of rectangular channel with sintered porous copper insert of 40% porosity and 1.44 × 10^?11 m² permeability. Forced convection heat transfer and pressure drop through the porous structure were studied at Re ? 408 with water as the coolant medium. In the study, heat fluxes of up to 2.9 MW/m² were successfully removed at the source with the coolant pressure drop of 34 kPa across the porous sample while maintaining the heater junction temperature below the permissible limit of 100 ± 5 °C for chipsets. The minimum value of 0.48 °C/W for cold plate thermal resistance (R_cp) was achieved at maximum flow rate of 4.2 cm³/s in the experiment. For the designed heat sink, different components of the cold plate thermal resistance (R_cp) from the thermal footprint of source to the coolant were identified and it was found that contact resistance at the interface of source and cold plate makes up 44% of R_cp and proved to be the main component. Convection resistance from heated channel wall with porous insert to coolant accounts for 37% of the R_cp. With forced convection of water at Re = 408 through porous copper media, maximum values of 20 kW/m² K for heat transfer coefficient and 126 for Nusselt number were recorded. The measured effective thermal conductivity of the water saturated porous copper was as high as 32 W/m K that supported the superior heat augmentation characteristics of the copper–water based sintered porous heat sink. The present investigation helps to classify the sintered porous heat sink as a potential thermal management device for high-end microprocessors.     

Transpiration cooling of a nose cone by various foreign gases

The transpiration cooling mechanisms used for thermal protection of a nose cone was investigated experimentally and numerically for various cooling gases. The effects of injection rates, model geometry, inlet temperature and Reynolds number of the main stream were studied for air, nitrogen, argon, carbon dioxide and helium. The experiments used a hot gas wind tunnel with T_∞ = 375 K and 425 K and Re_∞ = 4630–10,000. The experimental results indicated that even a small amount of coolant injection drastically reduced the heat transfer from the hot gases with the cooling effectiveness increasing with increasing injection rate, although the increases became smaller as the gas injection rate was further increased. The temperature and cooling effectiveness distribution along the transpiration surface of the nose cone model exhibited similar tendencies for all the coolants employed in present experimental research. The temperature decreased from the stagnation point towards the downstream region, then increased because of the non-uniform mass flow distribution of the coolant and thermal conduction from the metal backplane, whereas the cooling effectiveness variation was the reverse. The local cooling effectivenesses and thermal capacities were found to depend on the coolant thermophysical properties. Two-dimensional numerical simulations using the RNG κ?ε turbulence model for the main stream flow and the Darcy–Brinkman–Forchheimer momentum equations and thermal equilibrium model for the porous zone compared well with the general features in the experiments.     

Natural convective flow and heat transfer of supercritical CO2 in a rectangular circulation loop

Fluid dynamics and heat transfer of supercritical CO₂ natural convection are important for nuclear engineering and new energy system design etc. In this paper, in order to study the flow and heat transfer behavior of supercritical CO₂ natural circulation system, a computational simulation on a closed natural circulation loop (NCL) model has been carried out. The fluid temperature in the loop varies between 298.15 K and 323.15 K, which is across the CO₂ critical temperature, and the density is found to be in the range of 250–800 kg/m³. The results show a small temperature difference of 25 °C between heating and cooling sources can induce a mass flow with the Reynolds number up to 6 × 10⁴ using supercritical CO₂ fluid. A periodic reversal flow pattern is found and presented in this paper. Enhanced heat transfer phenomenon is also found for the supercritical CO₂ natural convective flow. The mechanisms to this enhancement and the heating effect on the flow are also discussed in detail in the present study.     

Effects of operating parameters on the performance of a CO2 air conditioning system for vehicles

This paper deals with the effects of the operating parameters on the cooling performance that can be applied for a transcritical CO₂ automotive air conditioning system. The experimental conditions of the performance tests for a CO₂ system and components such as a gas cooler and an evaporator were suggested to compare with the performance of each at the standardized test conditions. This research presents experimental results for the performance characteristics of a CO₂ automotive air conditioning system with various operating conditions such as different gas cooler inlet pressures, compressor speeds and frontal air temperatures/flow rates passing through the evaporator and the gas cooler. Experimental results show that the cooling capacity was more than 4.9 kW and coefficient of performance (COP) was more than 2.4, at each optimum pressure of gas cooler inlet during idling condition. Also, the cooling capacity was about 7.5 kW and COP was about 1.7 at the optimum pressure of gas cooler inlet during driving condition when air inlet temperatures of gas cooler and evaporator were 45 °C and 35 °C, respectively. Therefore, we concluded that the automotive air conditioning system using CO₂ refrigerant has good performance. This paper also deals with the development of optimum high pressure control algorithm for the transcritical CO₂ cycle to achieve the maximum COP.     

An experimental and kinetic modeling study of three butene isomers pyrolysis at low pressure

Pyrolysis of three butene isomers (C₄H₈) including 1-butene (1-C₄H₈), 2-butene (2-C₄H₈) and i-butene (iC₄H₈) were studied from 900 to 1900 K at low pressure. Synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry with molecular-beam sampling technique was used for isomeric identification of products and intermediates and also for concentration measurement. Based on the experimental results, a kinetic model consisting of 76 species and 232 reactions was developed to simulate mole fractions of species. The mole fraction profiles of pyrolysis species predicted by the model are in good agreement with the experimental measurements. The decomposition pathways of C₄H₈ are illustrated according to the reaction flux analysis. Our analysis demonstrates that reaction sequences 1-C₄H₈ → aC₃H₅ → aC₃H₄ → pC₃H₄ → C₂H₂, 2-C₄H₈ → saxC₄H₇ → 1,3-C₄H₆ → C₂H₃ → C₂H₂ and iC₄H₈ → iC₄H₇ → aC₃H₄ → pC₃H₄ → C₂H₂ are the major decomposition pathways of 1-butene, 2-butene and i-butene, respectively.     

Flow pattern transition instability in a microchannel with CO2 bubbles produced by chemical reactions

The present study investigates experimentally the two-phase flow in a rectangular microchannel with CO₂ bubbles generated by chemical reactions of sulfuric acid (H₂SO₄) and sodium bicarbonate (NaHCO₃). The microchannel with a hydraulic diameter of 132.7 μm is prepared using bulk micromachining and anodic bonding process. Evolution of two-phase flow patterns in the microchannel was observed using a high speed video camera and the corresponding pressure drop was investigated. It is found that the inlet concentration and flow rate of reactants have a significant effect on the evolution of two-phase flow characteristics and slug flow is the dominant flow pattern. The flow pattern transition instability between bubbly-slug and slug flow takes place for the cases with highest inlet concentration, i.e., C = 0.8 mol/L, and low flow rates of this study. The oscillation frequency is from 0.024 to 0.041 Hz and the magnitude of oscillation in pressure drop is from 10 to 15 kPa. A mechanism based on the flow circulation in the liquid slug may reasonably explain the flow pattern transition instability. Small amplitude, high frequency oscillations with a frequency of about 45 Hz are superimposed on the low frequency flow pattern transition as well as prevail for other cases without the flow pattern transition instability. The two-phase flow pressure drop increases with increase in both flow rate and inlet concentration.     

Thermodynamic evaluation of methanol steam reforming for hydrogen production

Thermodynamic equilibrium of methanol steam reforming (MeOH SR) was studied by Gibbs free minimization for hydrogen production as a function of steam-to-carbon ratio (S/C = 0–10), reforming temperature (25–1000 °C), pressure (0.5–3 atm), and product species. The chemical species considered were methanol, water, hydrogen, carbon dioxide, carbon monoxide, carbon (graphite), methane, ethane, propane, i-butane, n-butane, ethanol, propanol, i-butanol, n-butanol, and dimethyl ether (DME). Coke-formed and coke-free regions were also determined as a function of S/C ratio.Based upon a compound basis set MeOH, CO₂, CO, H₂ and H₂O, complete conversion of MeOH was attained at S/C = 1 when the temperature was higher than 200 °C at atmospheric pressure. The concentration and yield of hydrogen could be achieved at almost 75% on a dry basis and 100%, respectively. From the reforming efficiency, the operating condition was optimized for the temperature range of 100–225 °C, S/C range of 1.5–3, and pressure at 1 atm. The calculation indicated that the reforming condition required from sufficient CO concentration (<10 ppm) for polymer electrolyte fuel cell application is too severe for the existing catalysts (T_r = 50 °C and S/C = 4–5). Only methane and coke thermodynamically coexist with H₂O, H₂, CO, and CO₂, while C₂H₆, C₃H₈, i-C₄H₁₀, n-C₄H₁₀, CH₃OH, C₂H₅OH, C₃H₇OH, i-C₄H₉OH, n-C₄H₉OH, and C₂H₆O were suppressed at essentially zero. The temperatures for coke-free region decreased with increase in S/C ratios. The impact of pressure was negligible upon the complete conversion of MeOH.     

Convection heat and mass transfer along a vertical heated plate with film evaporation in a non-Darcian porous medium

A numerical analysis has been carried about to study the heat and mass transfer of forced convection flow with liquid film evaporation in a saturated non-Darcian porous medium. Parametric analyses were conducted concerning the effects of the porosity ε, inlet liquid Reynolds number Re_l, inlet air Reynolds number Re_a on the heat and mass transfer performance. The results conclude that better heat and mass transfer performances are noticed for the system having a higher Re_a, a lower Re_l, and a higher ε. Re_l plays a more important role on the heat and mass transfer performance than Re_a and ε. For the case of ε = 0.4 and Re_a = 10,000, the increases of Nu and Sh for Re_l = 50 are about by 33.9% and 35.3% relative to the values for Re_l = 250.     

100 t/a-Scale demonstration of direct dimethyl ether synthesis from corncob-derived syngas

Direct conversion of biomass-derived syngas (bio-syngas) to dimethyl ether (DME) at pilot-scale (100 t/a) was carried out via pyrolysis/gasification of corncob. The yield rate of raw bio-syngas was 40–45 Nm³/h with less than 20 mg/Nm³ of tar content when the feedrate of dried corncob was 45–50 kg/h. After absorption of O₂, S, Cl by a series of absorbers and partial removal of CO₂ by the pressure-swing adsorption (PSA) unit sequentially, the obtained bio-syngas (H₂/CO≈1) was directly synthesized to DME over Cu/Zn/Al/HZSM-5 catalyst in the fixed-bed tubular reactor. CO conversion and DME space-time yield (STY) were 67.7% and 281.2 kg/m_cat³/h respectively at 260 °C, 4.3 MPa and 3000 h^?1(GHSV, syngas hourly space velocity). Synthesis performance would be increased if the tail gas (H₂/CO > 2) was recycled to the reactor when GHSV was 650–3000 h^?1.     

Turbulent forced convection effectiveness of alumina–water nanofluid in a circular tube with elevated inlet fluid temperatures: An experimental study

The present study aims to explore experimentally the influence of elevated inlet fluid temperature on the turbulent forced convective heat transfer effectiveness of using alumina–water nanofluid over pure water in an iso-flux heated horizontal circular tube at a fixed heating power. A copper circular pipe of inner diameter 3.4 mm was used in the forced convection experiments undertaken for the pertinent parameters in the following ranges: the inlet fluid temperature, T_in = 25 °C, 37 °C and 50 °C; the Reynolds number, Re_bf = 3000–13,000; the mass fraction of the alumina nanoparticles in the water-based nanofluid formulated, ω_np = 0, 2, 5, and 10 wt.%; and the heating flux, q_o^″ = 57.8–63.1 kW/m². The experimental results clearly indicate that the turbulent forced convection heat transfer effectiveness of the alumina–water nanofluid over that of the pure water can be further uplifted by elevating its inlet temperature entering the circular tube well above the ambient, thereby manifesting its potential as an effective warm functional coolant. Specifically, an increase in the averaged heat transfer enhancement of more than 44% arises for the nanofluid of ω_np = 2 wt.% as the inlet fluid temperature is increased from 25 °C to 50 °C.     

Numerical study of confined slot jet impinging on porous metallic foam heat sink

This study numerically investigates the impinging cooling of porous metallic foam heat sink. The analyzed parameters ranges comprise ε = 0.93/10 PPI Aluminum foam, L/W = 20, Pr = 0.7, H/W = 2–8, and Re = 100–40,000. The simulation results exhibit that when the Re is low (such as Re = 100), the Nu_max occurs at the stagnation point (i.e. X = 0). However, when the Reynolds number increases, the Nu_max would move downwards, i.e. the narrowest part between the recirculation zone and the heating surface. Besides, the extent to which the inlet thermal boundary condition influences the prediction accuracy of the Nusselt number increases with a decreasing H/W and forced convective effect. The application ranges of H/W and Re that the effect of the inlet thermal boundary condition can be neglected are proposed. Lastly, comparing our results with those in other studies reveals that the heat transfer performance of the Aluminum foam heat sink is 2–3 times as large as that without it. The thermal resistance is also 30% less than that of the plate fin heat sink for the same volumetric flow rate and the 5.3 mm jet nozzle width. Therefore, the porous Aluminum foam heat sink enhances the heat transfer performance of impinging cooling.     

Thermodynamic and transport properties of gases for use in solid oxide fuel cell modelling

Data are provided and estimation methods presented for the calculation of specific heat capacities, viscosities, thermal conductivities and diffusion coefficients for both pure components and mixtures of C₃H₈, C₂H₆, CH₄, H₂O, CO₂, CO, H₂, N₂, O₂ and Ar over the temperature range 273–1473 K at ambient pressure. Pure component data is assembled from various data compilations supplemented by validated estimation techniques. Fourteen estimation methods for mixture properties have been compared with each other and with over 1400 experimental data points to facilitate the choice of methods best suited to this application. A statistical analysis of the data (including expected accuracy) is presented and recommendations are made for practical use.     

Subcooled flow boiling heat transfer and associated bubble characteristics of FC-72 on a heated micro-pin-finned silicon chip

Experiments are conducted here to investigate subcooled flow boiling heat transfer and associated bubble characteristics of FC-72 on a heated micro-pin-finned silicon chip flush-mounted on the bottom of a horizontal rectangular channel. In the experiments the mass flux is varied from 287 to 431 kg/m² s, coolant inlet subcooling from 2.3 to 4.3 °C, and imposed heat flux from 1 to 10 W/cm². Besides, the silicon chips contain three different geometries of micro-structures, namely, the smooth, pin-finned 200 and pin-finned 100 surfaces. The pin-finned 200 and 100 surfaces, respectively, contain micro-pin-fins of size 200 μm × 200 μm × 70 μm (width × length × height) and 100 μm × 100 μm × 70 μm. The measured data show that the subcooled flow boiling heat transfer coefficient is reduced at increasing inlet liquid subcooling but is little affected by the coolant mass flux. Besides, adding the micro-pin-fin structures to the chip surface can effectively raise the single-phase convection and flow boiling heat transfer coefficients. Moreover, the mean bubble departure diameter and active nucleation site density are reduced for rises in the FC-72 mass flux and inlet liquid subcooling. Increasing coolant mass flux or reducing inlet liquid subcooling results in a higher mean bubble departure frequency. Furthermore, larger bubble departure diameter, higher bubble departure frequency, and higher active nucleation site density are observed as the imposed heat flux is increased. Finally, empirical correlations for the present data for the heat transfer and bubble characteristics in the FC-72 subcooled flow boiling are proposed.