Evaporative Heat Research Articles

Assembling ultra-thick and crack-free colloidal crystals via an isothermal heating evaporation induced self-assembly method

Ultra-thick and crack-free colloidal crystals have many advantages in a number of existing and emerging applications. In this work, such systems are fabricated by a simple and reproducible method based on assembly of monodisperse silica particles by a crystalline layer assembly technique (CLAT). We find that high quality of colloidal crystals is obtained by using two simple processes: sintering of silica particles and thermal treatment of colloidal crystals. The crack-free colloidal crystal with a thickness of 100μm is fabricated. The morphologies and microstructures of colloidal crystals are identified by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The reflection spectra are measured by UV-VIS spectrum measurement. The reflection spectra of the colloidal crystal with different thicknesses are calculated by using multiple scattering methods. When the thickness of the colloidal crystal is smaller than 60μm, the reflection spectra of experimental measurements agree very well with that of theoretical calculations.

Effect of filler materials on the performance of gas tungsten arc welded AISI 304 and Monel 400

Dissimilar metal welding involving AISI 304 and Monel 400 finds widespread use in marine and offshore environments for the fabrication of heat exchangers, evaporators, piping and vessels in petrochemical and power generation industries. However studies on the performance of such weldments are scantly found in the literature even though the individual metals have higher corrosion resistance and strength. This paper reports the work carried out on welding of AISI 304 and Monel 400 using Gas Tungsten Arc Welding (GTAW) technique to examine the weldability, mechanical and metallurgical properties. Investigations have been carried out on the hot corrosion behavior of these joints subjected to cyclic air oxidation and K2SO4+NaCl (60%) molten salt environment at 600°C. A comparative analysis was carried out on these weldments for two different filler metals such as E309L and ENiCu-7. The oxide scales formed on the various zones of the weldment have been characterized systematically using surface analytical techniques. Weld zone was found to be more susceptible to degradation than base metals used. The effect of filler materials on the hot corrosion is discussed. The studies reported in this paper would be beneficial for fabricators embracing this type of dissimilar weldments in the petrochemical and power generation industries.

Cortisol and Interleukin-6 Responses During Intermittent Exercise in Two Different Hot Environments with Equivalent WBGT

Blood marker concentrations such as cortisol (COR) and interleukin (IL)-6 are commonly used to evaluate the physiological strain associated with work in the heat. It is unclear, however, if hot environments of an equivalent thermal stress, as defined by a similar wet bulb globe temperature (WBGT), result in similar response patterns. This study examined markers of neuroendocrine (COR) and immune (IL-6) responses, as well as the cardiovascular and thermal responses, relative to changes in body heat content measured by whole-body direct calorimetry during work in two different hot environments with equivalent WBGT. Eight males performed a 2-hr heavy intermittent exercise protocol (six 15-min bouts of cycling at a constant rate of metabolic heat production (360W) interspersed by 5-min rest periods) in Hot/Dry (46°C, 10% relative humidity [RH]) and Warm/Humid (33°C, 60% RH) conditions (WBGT ∼ 29°C). Whole-body evaporative and dry heat exchange, change in body heat content (ΔHb), rectal temperature (Tre), and heart rate were measured continuously. Venous blood was obtained at rest (PRE) and the end of each exercise bout for the measurement of changes in plasma volume (PV), plasma protein (an estimate of plasma water changes), COR, and IL-6. Ratings of perceived exertion and thermal sensation were measured during the last minute of each exercise bout. No differences existed for ΔHb, heart rate, Tre,%ΔPV, plasma protein concentration, perceptual strain (thermal sensation, perceived exertion), and COR between the Hot/Dry and Warm/Humid conditions. IL-6 exhibited an interaction effect (p = 0.041), such that greater increases were observed in the Hot/Dry (Δ = 1.61 pg·mL−1) compared with the Warm/Humid (Δ = 0.64 pg·mL−1) environment. These findings indicate that work performed in two different hot environments with equivalent WBGT resulted in similar levels of thermal, cardiovascular, and perceptual strain, which support the use of the WBGT stress index. However, the greater IL-6 response in the Hot/Dry requires further research to elucidate the effects of different hot environments and work intensities.

Dimensional analysis and empirical correlations for heat transfer and pressure drop in condensation and evaporation processes of flow inside micropipes: case study with carbon dioxide (CO2)

In this paper, the experimental results of the convection heat transfer coefficient and pressure drop values during condensation and evaporation of CO2 were obtained at different operating conditions for flow inside micropipes. Reynolds number (ReD) ranged between 2000 and 15000. The dimensional analysis technique was utilized to develop correlations for Nusselt numbers and pressure drops. A comparison between experimental and correlated results was carried out. The results showed that for the condensation process, the bias errors were 5.25% and 0.4% for pressure drops and Nusselt number respectively. Consequently, Average Standard Deviation (ASD) values reached 17.94% and 4.62% for both respectively. On the other hand, for the evaporation process, the Nusselt number error was 3.8% with an ASD of 4.14%. The correlations presented in the present work can be used in calculating pressure drops and heat transfer coefficients for phase change flows in mini and micro tubes. It helps to enhance design calculations of heat exchangers, condensers and evaporators

Effect of undiluted bioethanol on combustion and emissions reduction in a SI engine at various charge air conditions

This paper investigates the effects of neat bioethanol combustion on the performance and emission reduction characteristics of a spark ignition (SI) engine at various air temperature conditions. The experiments were carried out for different intake air temperatures and various operating conditions, and the results were compared to those for conventional gasoline fuel. The investigated results show that as intake ambient air temperatures is decreased, the intake flow rates is increased by the increased density of the intake air. The ethanol fuel has a higher volumetric efficiency than gasoline for all engine speeds and ambient temperature conditions. The cylinder pressures are increased with the improvement of volumetric efficiency due to the decrease of intake temperature. In addition, ethanol combustion creates higher combustion pressures than that of gasoline due to the high latent heat evaporation rate and low boiling point. The coefficients of variation of maximum pressure show slightly decreasing trends as the ambient air temperature increases. The concentration of NOx emissions tends to increase proportionally with the increase of ambient air temperature and engine speed for all test conditions. However, the HC, and CO emissions from ethanol combustion are improved than those of gasoline combustion.

Improvement of efficiency and temperature control of induction heating vapor source on electron cyclotron resonance ion source

An electron cyclotron resonance ion source (ECRIS) is used to generate multicharged ions for many kinds of the fields. We have developed an evaporator by using induction heating method that can generate pure vapor from solid state materials in ECRIS. We develop the new matching and protecting circuit by which we can precisely control the temperature of the induction heating evaporator. We can control the temperature within ±15 °C around 1400 °C under the operation pressure about 10(-4) Pa. We are able to use this evaporator for experiment of synthesizing process to need pure vapor under enough low pressure, e.g., experiment of generation of endohedral Fe-fullerene at the ECRIS.

Analysis of Local Air–Sea Interaction in East Asia Using a Regional Air–Sea Coupled Model

Abstract A regional air–sea coupled climate model based on the third regional climate model (RegCM3) and the regional oceanic model [the Princeton Ocean Model (POM)] is used to analyze the local air–sea interaction over East Asia in this study. The results indicate that the simulated sea surface temperature (SST) of the coupled model RegCM3–POM is reasonably accurate, and that the spatial pattern and temporal variation are consistent with that of the Global Sea Ice and Sea Surface Temperature dataset (GISST). The correlation between the SST and the atmospheric variables shows that the uncoupled model RegCM3 forced by the given SST cannot reproduce the real-time and SST lag correlation between SST and precipitation, and between SST and surface wind speed, whereas the relationship in the coupled model RegCM3–POM is reasonably accurate. RegCM3–POM reflects the air–sea interaction in the South China Sea and western Pacific Ocean, where the SST lead correlation is the inverse of the SST lag correlation between SST and precipitation, and strong winds bring warm water to the midlatitudes, so the correlation between wind speed and SST is negative in low latitudes and positive in the Kuroshio area. The uncoupled model fails to reproduce the effect of the atmosphere on the ocean. The further study on air–sea interaction in the South China Sea indicates that the earlier warm seawater corresponds to strong sensible heat flux, evaporation, precipitation, and weak net solar radiation, and the early strong sensible heat flux, evaporation, wind at the 10-m level, and weak net solar radiation cause the cold SST.

The effect of three-phase contact line speed on local evaporative heat transfer: Experimental and numerical investigations

In pool boiling or flow boiling devices or e.g. during meniscus evaporation within capillary structures the local heat flux and evaporation rate at the position where the liquid–vapor interface meets the solid wall can be extremely high. This three-phase contact line region is characterized by a thin liquid film with a very low heat resistance. Depending on the application the contact line can move with velocities of several meters per second, either in receding (dewetting) or in advancing (wetting) direction. In this paper, experimental and numerical results on the influence of three-phase contact line speed on the local heat transfer in the contact line region during pool boiling and during meniscus evaporation are presented and analyzed. It is shown that the local heat flux can be one or more orders of magnitude higher than the mean heat flux supplied to the system. This local heat transfer peak is almost independent of the contact line speed in the case of a receding contact line while it significantly increases with contact line speed for an advancing contact line. This behavior could be observed in different evaporation configurations and with different fluids. Experimental and numerical results agree well and allow a characterization of the transient heat transfer phenomena in the contact line region during evaporation.

Hot Corrosion Studies on Bimetallic Combinations of Monel 400 and AISI 304 Subjected to Molten Salt Environment

Dissimilar joints of Monel 400 and AISI 304 are used widely in marine and offshore environments for the fabrication of heat exchangers, evaporators, piping and vessels as well as in the chemical, petrochemical, and power generation industries. An attempt was made to weld Monel 400 and AISI 304 by gas tungsten arc welding using ENiCu-7 and E309L filler wires. A comparative analysis was carried out on these weldments so as to examine the weldability, mechanical and metallurgical properties of the weldment. In addition, corrosion behavior of these weldments has been carried out on the dissimilar weldments in K2SO4 + NaCl (60%) molten salt environment at 600°C under cyclic conditions. The oxide scales formed on the various zones of the weldment have been characterized systematically using surface analytical techniques. Weld zone was found to be more susceptible to degradation than in base metals.

Modelling and theoretical analysis of a high temperature heat pump system with two-stage centrifugal compressor

A high temperature heat pump system utilising produced water, which is a main byproduct in oil fields, is presented, and its steady state simulation model is established. This is an alternative to water boil in the field of district heating. The model includes submodels for key components, such as two-stage centrifugal compressor with one economiser, shell and tube condenser, expansion valve, flooded evaporator and suction line heat exchanger. By combining a modular method with a dimidiate method, the simulation algorithm is developed with the objective of requiring only input parameters that are readily available to the design engineer and negating any additional constraint on system operation. The simulation results indicate that the high temperature heat pump with the coefficient of performance of 3·18 would save over 15% energy compared with traditional boil.

Application of kinetic Monte Carlo method to equilibrium systems: Vapour–liquid equilibria

Kinetic Monte Carlo (kMC) simulations were carried out to describe the vapour–liquid equilibria of argon at various temperatures. This paper aims to demonstrate the potential of the kMC technique in the analysis of equilibrium systems and its advantages over the traditional Monte Carlo method, which is based on the Metropolis algorithm. The key feature of the kMC is the absence of discarded trial moves of molecules, which ensures larger number of configurations that are collected for time averaging. Consequently, the kMC technique results in significantly fewer errors for the same number of Monte Carlo steps, especially when the fluid is rarefied. An additional advantage of the kMC is that the relative displacement probability of molecules is significantly larger in rarefied regions, which results in a more efficient sampling. This provides a more reliable determination of the vapour phase pressure and density in case of non-uniform density distributions, such as the vapour–liquid interface or a fluid adsorbed on an open surface. We performed kMC simulations in a canonical ensemble, with a liquid slab in the middle of the simulation box to model two vapour–liquid interfaces. A number of thermodynamic properties such as the pressure, density, heat of evaporation and the surface tension were reliably determined as time averages.

Development of compact CW-IR laser deposition system for high-throughput growth of organic single crystals

We developed a compact continuous-wave infrared (CW-IR) laser deposition system for the high-throughput growth of organic single crystals. In this system, two CW-IR lasers are used for the sample heating and thermal evaporation of materials. The CW-IR laser heating is simple and allows good control of the deposition rate and growth temperature, in response to the on/off laser switching. Six samples can be loaded simultaneously in a chamber, which allows one-by-one sequential deposition for high-throughput experiments, without breaking the vacuum. Using this setup, we studied the effect of ionic liquids on the growth of C60 crystals in vacuum.

Analysis of Heat Island Intensity in Urban Blocks Using Coupled Simulation

In this paper, a building canopy model is coupled with CFD for the analysis of microclimates within urban blocks under different urban and architectural planning. This model considers radiant heat exchange in the building canopy, water evaporation of vegetations and heat released from the air conditioning systems. Using this model, thermal environment of a real urban block is analyzed. The simulation results show that heat released from the air conditioning systems is one of the most important factors affecting outdoor thermal environment. Temperature of vegetation is significantly lower than that of road surfaces. However, air temperature difference is not great between zones with vegetation and other zones at 1.5m height.

Intermittent Drying: Energy Expenditure and Product Quality

AbstractSeveral issues pertinent to intermittent drying of clay‐like materials were analyzed with respect to energy consumption, quality of dried products, and drying time. Experimental tests were performed on the cylindrically‐shaped kaolin samples for batch convective drying realized with both periodically alternated temperature and humidity of the drying air. To assess the benefits from intermittent drying, a series of tests were carried out at both parameters kept constant. The net energy necessary for material heating and moisture evaporation was numerically calculated based on the authors' model of drying kinetics, and related to the experimentally measured total electric energy consumption to evaluate the effectiveness of intermittent drying. The quality of dried samples was quantified in terms of crack intensity and magnitude. It was found that intermittent drying permits much better product quality with comparable drying time and energy consumption when drying occurs under constant conditions.

Application of adaptive control in a refrigeration system to improve performance

This paper reports an experimental investigation using adaptive control in a refrigeration system. This system is composed basically of a semi-hermetic compressor, concentric tubes heat exchangers, the condenser and evaporator, and thermostatic expansion valve (TXV). The refrigerant used in the refrigeration system was the HCFC-22 and also an AC frequency inverter was used to control the speed of the compressor. The temperatures were measured by PT-100 sensors and the pressures using piezoresistive pressure transducers. Data acquisition was implemented using the Labview software. An electronic card with analogical signal output was also used. These analogical signals were converted into digital through a Programmable Logic Controller (PLC) and then sent to the computer through a PC serial port. Tests were performed with a variable speed compressor in the range from 30 to 70 Hz and the experimental results showed that the highest performance (COP) was attained by working in the range of 50 Hz, using adaptive fuzzy control.

Contribution of H-bond vibrations to heat capacity of water

The origin of the anomalously large value of the heat capacity of liquid water is discussed. Comparing the temperature dependence of the heat capacities for water with those for argon and hydrogen sulfide, we separate contributions of the translational and rotational degrees of freedom. The residual part is considered as being caused by the specific contributions of the transversal vibrations of H-bonds. The estimate for the number of H-bonds per molecule is obtained from the analysis of this contribution. This estimate is in quite good agreement with the estimates which follow from the analysis of the specific volume, heat of evaporation, and kinematic shear viscosity.

Numerical study on the evaporative and condensational dissipation of phosphoric acid in PAFC

In phosphoric acid fuel cell (PAFC) stack, reduction of the phosphoric acid that is impregnated in the cell is a major factor to restrict the operating life. In this paper, the phosphoric acid reduction by the evaporative and condensational dissipation was evaluated by numerical analysis. The calculations that include the behavior of heat transfer, gas flow, and evaporation and condensation of phosphoric acid were conducted for the model cell with conditions that correspond to an on site stack. The phosphoric acid was considered as a composite of phosphorus pentoxide and water, and the evaporation and condensation rates were derived based on the nucleation theory for a two components system. The phosphoric acid distributions in the vapor phase and liquid phase at the process gas and electrode were calculated for the duration of 3300h, and as a result of those, the exhausting and remaining amount of phosphoric acid for the cell were evaluated. The analysis results were compared with the experimental results for the model cell.

Calculation of heat balance in burning HMX

Temperature dependences are calculated for a number of physicochemical properties of HMX: the heat capacity of the liquid phase, change in the enthalpy due to heating of the condensed phase to a predetermined temperature, heat of evaporation, saturated vapor pressure, and the vapor diffusion coefficient in low-molecular-weight gases. The data obtained are used to calculate the amount of heat needed to heat the condensed phase to the burning surface temperature in the range of 560–900 K at various degrees of decomposition. The heat of decomposition of HMX under combustion conditions is calculated from the known composition of the reaction products at a pressure of 1 bar. The results of experimental determination of the thermal effects of HMX decomposition by differential scanning calorimetry are presented. The results of the calculations and experiments suggest that at a degree of decomposition ⩾0.6, heat release in the condensed phase can provide heating and evaporation of HMX without heat input from the gas phase. It is shown that the calculated saturation vapor pressures of HMX, which are higher than those presented in the literature, are in better agreement with available experimental data on the HMX vapor concentration profile near the burning surface.

Energy-saving Optimization of Crude Benzol Pretreating in Hydrotreating Process

The article mainly analyses energy consumption in raw material pretreatment craft question of crude benzol hydrotreating process, with available energy analytic method. By calculating the available energy of heat exchangers and evaporators of K-K process, find the energy consumption situation during crude benzene refinement production, and then give some suggestions in Energy-saving Optimization measure.

A novel passive feeding method for methanol steam reformers

This work presents a simple novel feeding method for a methanol steam reformer. Using a single heat source, a fixed ratio of water and methanol vapor can be fed into the reformer in a passive way. By adjusting the thermal resistances of the two separate heat paths, different amounts of heat, related to the stoichiometric ratio and heats of evaporation, are conducted to two separate evaporators to vaporize the liquid fuels. Compared with the conventional practice that feeding ratio of the two fuels are actively controlled with two pumps, no pump is needed in this novel feeding system. Thus, the controlling system can be simplified and the auxiliary power consumption can be minimized. Experiments were conducted to verify the feasibility of this novel fuel-feeding method. With increasing reaction temperature, the product composition varied from 61% H 2, 20% CO 2 and 0.7% CO to 72% H 2, 22% CO 2 and 2% CO.