Evaporative Heat Research Articles

Physicochemical characteristics and rheological behaviour of some fruit juices and their concentrates

Fruit juices and their concentrates are popular drinks consumed by people of all ages for their sensory and nutritional qualities. In this paper, the physicochemical and rheological properties of african star apple, apple, apricot, banana, cherry, goldenberry, grape, guava, mango, medlar, orange, peach, pear, plum, pomegranate and pomelo juices, and their concentrates were reviewed. The selection of cultivars is a critical factor for the production of juices rich in healthy compounds and the quality of fruit juice strongly depends on processing technology. In summary, carbohydrates (fructose, glucose, sorbitol and sucrose), organic acids (ascorbic, citric, malic and shikimic acids), amino acids (asparagine, proline, glycine, serine, methionine and alanine) and phenolic compounds (catechin, chlorogenic acid and rutin) are among the significant constituents of fruit juices, and their concentrates. Also, the content of organic acids in fruit juices not only influence their taste and flavour but also their nutrition, stability, acceptability and keeping quality. Understanding of rheological properties of fruit juice is essential for quality control, process engineering application (designing and selection of proper equipment including heat exchangers, transport systems, evaporators and pumps), calculating energy usage and power requirement for mixing. The rheological behaviour of fruit juices and concentrates can be described by different rheological models depending on the nature of the juices. Several investigators used and suggested the Newtonian and Herschel-Bulkley models describe the rheological behaviour of various fruit juices. The apparent viscosity of fruit juice decreased considerably at higher temperatures. The effect of temperature on the apparent viscosity is generally expressed by the Arrhenius relationship and the activation energy (Ea) for fruit juices flow increased with the concentration of the juices. Higher activation energy means that the apparent viscosity is relatively more sensitive to temperature change.

Performance optimization of a heat pump driven liquid desiccant dehumidification system using exergy analysis

Liquid desiccant dehumidification system driven by heat pump is recognized as an efficient approach for humidity control in the air-conditioning system. The liquid desiccant dehumidification system is optimized by exergy destruction analysis method in the present research. According to the exergy destruction theory, the exergy destruction of a liquid desiccant dehumidification system is divided into exergy destructions arising from heat pump cycle, evaporators, condensers, heat and mass transfer modules and various mixing processes, respectively. The heat and mass transfer process uniformity coefficients γt and γω are proposed to describe the uniformity of the heat and mass transfer driving forces along the whole system. It’s indicated γt and γω of the basic cross-flow system are as high as 1.4 and 1.2. Then reducing the exergy destruction is chosen as the guideline to optimize the system. On the basis of the basic cross-flow system, the improved cross-flow system and the improved counter-flow system are further proposed. γt (γω) of the improved systems are reduced to 1.12(1.12) and 1.04(1.01), respectively. Owing to the system optimization, the exergy efficiency increases from 20.1% of the basic cross-flow system to 21% and 25% respectively, COPsys increases from 5.7 to 6.0 and 7.4 respectively. The exergy analysis method is effective for an optimized scenario of a heat-pump driven liquid desiccant process.

Thermodynamic and economic analysis of a micro-combined polygeneration system coupled with solar energy and fuels for distributed applications

A novel micro-combined polygeneration system based on solar energy and fuels is designed with aim to simultaneously satisfy energy demands of electricity, heating and cooling in distributed areas. Integration solar radiation with conventional natural gas-fired power systems is conceived to eliminate existing disadvantages of low efficiency and high cost for fuel-only and solar-only plants. Thermodynamic and economic analyses are evaluated to explore performance of proposed systems with three working fluids. Energetic and exergic efficiencies are individually 0.839 and 0.4536, 0.8721 and 0.5852, and 0.8656 and 0.5825 for N2-, He- and Ar-based micro-combined systems under specified power capacity of 100 kW. Solar collector field, compressor, turbine and combustion chamber exhibit four largest exergy destruction, followed orderly by heat exchanger, generator, condenser, evaporator, throttling valve and pump. Preliminary economic analysis indicates that levelized electricity costs of N2-, He- and Ar-based micro-combined systems are 0.112, 0.103 and 0.101 $ kWh−1 with corresponding payback periods of 4.563, 5.090 and 5.138 years. Parametric analysis reveals that five operating parameters (compression ratio, turbine inlet temperature, solar collector field outlet temperature, generator outlet temperature and split ratio) exert noticeable influence on thermal efficiency of micro-combined systems. In conclusion, proposed micro-combined polygeneration system achieves efficient conversation of thermal energy into electricity, heating and cooling at a rational energy utilization for distributed areas.

Soil–atmosphere interaction in the overburden of a short-lived low and intermediate level nuclear waste (LLW/ILW) disposal facility

Abstract The long-term safety of shallow disposal facility for short-lived low and intermediate level nuclear waste (LLW/ILW) relies on the performance of engineered barriers (caps and liners). Soil-atmosphere interaction may affect the capping material at shallow depths, due to changes of its coupled hydro-thermal-mechanical behavior under the effect of atmospheric conditions. This study aims to investigate the soil-atmosphere interaction at different time scales in the overburden of an LLW/ILW disposal facility, located in middle France. Actual meteorological data from Valencia El Saler station in Spain, including solar radiation, air temperature, latent heat, rainfall, and actual evaporation, at four different time scales (30 min, daily, weekly and monthly), were applied as the future climate conditions of the studied area based on climate analogues. A numerical approach combining a coupled hydro-thermal model and a soil-atmosphere interaction model was employed. Results show that the employment of meteorological data at a short time scale (30 min) can increase the simulation accuracy by capturing the rainfall events and accelerating the soil-atmosphere interactions. Furthermore, the effect of future climate conditions in the long-term (7 years) on soil hydro-thermal behavior was examined. This study allows a further detailed inspection of the climate’s role in the LLW/ILW storage system.

Experimental investigation on the heat transfer performance and evaporation temperature fluctuation of a new-type metal foam multichannel heat pipe

Recent electronic industry developments require a variety of compact and high-performance heat sinks for the heat dissipation of electronic devices. In this paper, on the basis of a new type of heat pipe called the metal foam multichannel heat pipe (metal foam MCHP) proposed by our team, an experimental apparatus on its heat transfer characteristics was built. The heat transfer characteristics of the metal foam MCHP with the distilled water as the working fluid were experimentally investigated in a heat flux range of (18750-112500) W/m2, a filling ratio range of 0.1–0.6 and single-sided/double-sided heating modes. The experimental results showed that the working fluid could flow up and down in the metal foam MCHP, and thus the heat was transferred from the evaporation section to the condensation section during the operation. The thermal resistance of the metal foam MCHP decreased with the increase of the heat flux. When the heat flux was up to 112500 W/m2, the thermal resistance decreased to 0.142 °C/W. The optimal filling ratio of the metal foam MCHP charging with the distilled water was 0.2. During the experiment, the temperature fluctuations of each measuring point in the evaporation section were almost within 2 °C and the temperature differences of different measuring points in the evaporation section were within 8 °C. The thermal resistances of the metal foam MCHP under the single-side heating mode and the double-sided heating mode were compared, and the thermal resistance of the metal foam MCHP was found to be higher under the single-sided heating mode. In addition, compared with the traditional PHPs, the metal foam MCHP showed better heat transfer performance and better stability and uniformity of the evaporation temperature.

Numerical calculation based on mass and energy balance of waste incineration in the fixed bed reactor

To evaluate the waste process incineration, a mass, and energy balance is employed to investigate the waste incineration process in a fixed bed. Thermodynamics equilibrium is implemented to describe the incineration process. The complete combustion is only products CO2, H2O, SO2, ash, and excess O2 considered. The mass balance calculates the total mass flow in and out incinerator. Energy balance includes input heat, evaporating heat, chemical heat, radiation, and convection. The input heat is calculated by considering the heat capacity, temperature, heating value, and total mass flow. Evaporation heat is calculated based on the water content, mass flow of each aqueous, and evaporation hot water flow. The result shows that efficiency energy of waste incinerator up to 79,33%. It means the incinerator is included in the good category.

Effect of coal mine organic aerosol on the methane/air lower explosive limit

Organic aerosol is formed in coal mines due to heat release and evaporation of organics from coal during the longwall operation. This frictional heating occurs when a metallic cutting bit strikes a rock. Thus formed organic aerosol can contribute significantly to the explosivity of methane/air atmosphere in coal mines. In this paper, the flammable limits for the methane–air mixtures with organic aerosol are determined. For this purpose, organic aerosol is synthesizes from the coal-tar pitch in a laboratory evaporation–nucleation flow chamber. Aerosol particles synthesized under laboratory conditions are aggregates consisting of small primary particles with the fractal-like dimension Df = 2.0 ± 0.1, which is close to Df = 2.1 ± 0.1 of coal mine aerosol. It is shown that the flammability of organic aerosol/methane mixture in air is in good agreement with the Le Chatelier additive principle. The lower ignition limit for the pure organic aerosol in air is 44 g/m3.

Comparison of three microphysics parameterization schemes in the WRF model for an extreme rainfall event in the coastal metropolitan City of Guangzhou, China

Abstract An extreme rainfall event in the coastal metropolitan city of Guangzhou, China is simulated by the Weather Research and Forecasting (WRF) model using three bulk microphysics schemes to explore the capability to reproduce the observed precipitation features by these schemes and their differences. The detailed comparison among the three runs in terms of radar reflectivity, precipitation, thermodynamic fields and microphysical processes are conducted. Results show that all the simulations can reproduce the two main heavy rainfall centers in Guangzhou and the first convection initiation. The accumulated precipitation in the simulation using the WSM6 scheme performs better than the others in terms of intensity and distribution compared to observations. The weaker accumulated precipitation in the second heavy rainfall center in the simulations using the Thompson and Morrison schemes result from their more dispersed precipitation distributions dominated by the cold pool intensity and distribution. The latent heating from the water vapor condensation dominates the convection initiation and storm development. The latent cooling from the rain water evaporation dominates the cold pool intensity and distribution, which influences the storm moving and subsequent convection propagation, and finally the intensity and distribution of surface precipitation. Sensitivity experiments of the latent heat confirm the dominant roles of latent heating/cooling, especially the water vapor condensation heating and rain water evaporation cooling, in the differences of the thermodynamic fields, storm development, convection propagation and surface precipitation among the three simulations.

Optimization Method for Grooved Surface Structures Regarding the Evaporation Heat Transfer of Ultrathin Liquid Films at the Nanoscale.

Rough nanostructured surfaces can enhance evaporation heat transfer. Most studies artificially optimized the geometry and size during the design of nanostructured surfaces. Instead of the empirical design of nanostructured surfaces, this paper proposes a mathematical optimization method of the grooved nanostructured surface design. This method is inspired by the molecular dynamics simulations of grooved nanostructured surfaces. The results show that the heat transfer performance exhibits a positive correlation with the defined sectional area of the grooved nanostructured surface; thus, this method is developed to convert the maximum heat transfer and evaporation rate to a mathematical conditional extremum solution. The mathematical description of the optimization method is to solve the surface structure with the maximum sectional area when the heat transfer area is constant. Comparing the molecular dynamics (MD) simulation results of the optimal surface and the existing ones under the same simulation conditions indicates that the optimal surface has the best heat transfer performance compared with the other ones. Additionally, discussions on the types of grooved nanostructured surfaces, the materials of solid and liquid, and the wettability of grooved surfaces verify the generality of the calculation results and the optimization method. The explanation of the method is that different nanostructured surfaces have a similar potential energy per liquid atom, which affects the latent heat of the evaporation process. However, the maximum sectional area corresponds to the minimum interfacial thermal resistance and the maximum interaction energy per unit area, which will enhance the heat transfer at the solid-liquid interface. Moreover, a nanostructured surface with the maximum sectional area also obtains the maximum area of the liquid-vapor interface and thus enhances the evaporation heat transfer process.

Comparison of the Evaporation and Condensation Heat Transfer Coefficients on the External Surface of Tubes in the Annulus of a Tube-in-Tube Heat Exchanger

An experimental study was carried out to explore the heat transfer characteristics on the outside of smooth and enhanced tubes, during evaporation and condensation of R134A in the annulus of a tube-in-tube heat exchanger. The three-dimensional enhanced surface tube consisted of primary enhancement patterns and secondary patterns; results were compared to the performance of an equivalent smooth tube. The equivalent external diameter of the inside horizontal copper tubes used in this study was 19.05 mm, while the outer tube varied in size, allowing a comparison of heat transfer for different annulus dimensions. Tests were conducted with a fixed inlet/outlet vapor quality and a constant saturation temperature for varied mass velocities in the range of 30 to 100 kg/(m2∙s). For condensation, the ratio of heat transfer coefficient enhancement (enhanced tube/ smooth tube) was up to 1.78; this can be attributed to the turbulence increase, as well as liquid film re-distribution, produced from the dimples. Furthermore, the condensation heat transfer coefficient increased rapidly with increasing mass flux. For flow boiling in the annulus between the 1EHT tube and outer tube, the heat transfer coefficient during boiling was 11–36% higher when compared to the smooth tube at xave = 0.35, while the performance of the 1EHT tube was not as good as the smooth tube at xave = 0.5. The heat transfer deterioration can be explained by decreased effective nucleate flow boiling heat transfer area and the flow pattern transition between a slug/wavy-stratified flow to wavy-stratified flow.

Bat thermoregulation in the heat: Limits to evaporative cooling capacity in three southern African bats.

High environmental temperatures pose significant physiological challenges related to energy and water balance for small endotherms. Although there is a growing literature on the effect of high temperatures on birds, comparable data are scarcer for bats. Those data that do exist suggest that roost microsite may predict tolerance of high air temperatures. To examine this possibility further, we quantified the upper limits to heat tolerance and evaporative cooling capacity in three southern African bat species inhabiting the same hot environment but using different roost types (crevice, foliage or cave). We used flow-through respirometry and compared heat tolerance limits (highest air temperature (Ta) tolerated before the onset of severe hyperthermia), body temperature (Tb), evaporative water loss, metabolic rate, and maximum cooling capacity (i.e., evaporative heat loss/metabolic heat production). Heat tolerance limits for the two bats roosting in more exposed sites, Taphozous mauritianus (foliage-roosting) and Eptesicus hottentotus (crevice-roosting), were Ta=~44°C and those individuals defended maximum Tb between 41°C and 43°C. The heat tolerance limit for the bat roosting in a more buffered site, Rousettus aegyptiacus (cave-roosting), was Ta=~38°C with a corresponding Tb of ~38°C. These interspecific differences, together with a similar trend for higher evaporative cooling efficiency in species occupying warmer roost microsites, add further support to the notion that ecological factors like roost choice may have profound influences on physiological traits related to thermoregulation.

Preparation and performance of fast-response ITO/Li-NiO/Li-WO3/ITO all-solid-state electrochromic devices by evaporation method

In this study, all-solid-state electrochromic device (ECD) with a novel four-layered structure of glass/ITO/Li-NiO/Li-WO3/ITO was prepared by e-beam and resistive heating evaporation. Tungsten oxide (WO3), nickel oxide (NiO) and indium tin oxide (ITO) were used as electrochromic layer, complementary layer and electrode layer, respectively. Lithium was used as electrolyte ion and evaporated on the complementary layer directly, replacing the normally used independent electrolyte layer. Since the lithium ions can transfer between WO3 and NiO layer directly during the electrochromic process, the ECD shows a fast response speed with coloring and bleaching time of 8.6 s and 1.7 s, respectively, due to the reduction of the overall resistance of the device. The unique structure of ECD may further advance the development in the practical applications.

Influence of sea-ice anomalies on Antarctic precipitation using source attribution in the Community Earth System Model

Abstract. We conduct sensitivity experiments using a general circulation model that has an explicit water source tagging capability forced by prescribed composites of pre-industrial sea-ice concentrations (SICs) and corresponding sea surface temperatures (SSTs) to understand the impact of sea-ice anomalies on regional evaporation, moisture transport and source–receptor relationships for Antarctic precipitation in the absence of anthropogenic forcing. Surface sensible heat fluxes, evaporation and column-integrated water vapor are larger over Southern Ocean (SO) areas with lower SICs. Changes in Antarctic precipitation and its source attribution with SICs have a strong spatial variability. Among the tagged source regions, the Southern Ocean (south of 50∘ S) contributes the most (40 %) to the Antarctic total precipitation, followed by more northerly ocean basins, most notably the South Pacific Ocean (27%), southern Indian Ocean (16 %) and South Atlantic Ocean (11 %). Comparing two experiments prescribed with high and low pre-industrial SICs, respectively, the annual mean Antarctic precipitation is about 150 Gt yr−1 (or 6 %) more in the lower SIC case than in the higher SIC case. This difference is larger than the model-simulated interannual variability in Antarctic precipitation (99 Gt yr−1). The contrast in contribution from the Southern Ocean, 102 Gt yr−1, is even more significant compared to the interannual variability of 35 Gt yr−1 in Antarctic precipitation that originates from the Southern Ocean. The horizontal transport pathways from individual vapor source regions to Antarctica are largely determined by large-scale atmospheric circulation patterns. Vapor from lower-latitude source regions takes elevated pathways to Antarctica. In contrast, vapor from the Southern Ocean moves southward within the lower troposphere to the Antarctic continent along moist isentropes that are largely shaped by local ambient conditions and coastal topography. This study also highlights the importance of atmospheric dynamics in affecting the thermodynamic impact of sea-ice anomalies associated with natural variability on Antarctic precipitation. Our analyses of the seasonal contrast in changes of basin-scale evaporation, moisture flux and precipitation suggest that the impact of SIC anomalies on regional Antarctic precipitation depends on dynamic changes that arise from SIC–SST perturbations along with internal variability. The latter appears to have a more significant effect on the moisture transport in austral winter than in summer.

Assessment of Power Harvesting in Electronic Modules Using Phase Change Material with Null Electricity: An Experimental Study

In this work, the assessment of power harvesting in electronic modules during its operation is experimentally investigated. The phase change material (PCM) based natural cooling is analyzed with a developed model using different circulating fluids such as DI water, ethanol, and methyl acetate respectively. The experiments are conducted to evaluate the power harvesting by PCM for circulating fluids at the different heat input between 60 and 110 W. Result implies that (i) highest percentage of waste heat extraction is about 98.7% for methyl acetate because of low boiling point and heat of evaporation at high heat input (ii) thermal resistance of methyl acetate is less of about 0.237 K/W owing to high vapour flow rate and less subcooling effect (iii) the maximum power harvested by PCM with the effect of vapourized methyl acetate is found as 9.41 W owing to less time to reach the steady-state temperature (SST) of PCM at 110 W.

ELECTRON-BEAM MELTING OF INGOTS OF TiAl SYSTEM INTERMETALLICS

Performance of scientific-technical researches at the E. O. Paton Electric Welding Institute of the NAS of Ukraine have been directed on development of technology for manufacture of titanium aluminide –based alloys using the method of electron-beam melting (EBM). The mathematical models of heat state and evaporation of alloying elements in EBM were developed. The results of calculations of heat state using the mathematical model allowed determining a dependence of depth of liquid pool on different melting rates. The mathematical models of processes of evaporation in EBM of titanium aluminide ingots were used for plotting the nomograms, which help to determine the necessary content of alloying element of the alloy in the initial charge for acquiring the necessary concentration of this element in ingot at set technological parameters of melting. In scopes of designed mathematical models there were investigated different technological modes of electron-beam melting of ingots based on titanium aluminide. The optimum EBM modes, at which a solidification front approaches to flat, were determined. At that, more uniform distribution of the additives on ingot section and volume is provided as well as level of stressed state is reduced. The works were carried out on manufacture of titanium aluminide based-ingots with addition of refractory as well as volatile alloying elements. Composition and structure of produced ingots were examined. It is shown that electron-beam melting allows getting chemically homogeneous ingots based on titanium aluminide and is a perspective method for production of such class materials.

Chemical Heat Storage Using an SiC Honeycomb Packed with CaCl<sub>2</sub> Powder

Chemical heat storage is a promising technology for improving thermal energy efficiency. In this study, CaCl2 and H2O were selected as a reaction system for utilization of low-grade exhaust heat that is cooler than 200°C. Heat discharging and charging were conducted through the CaCl2 hydration reaction. A silicon carbide honeycomb was adopted to improve heat transfer in the CaCl2 packed bed. The heat storage, condenser, and evaporator temperature were set at 150°C, 30°C and 90°C respectively. Repeated trials and experiments are time consuming for optimizing design of the equipment. Therefore, in this research, we constructed a simulation that can predict the performance of the device. A numerical simulation model was utilized in preparation for the design of the heat storage module. The consistency of both the simulation and the experimental results was confirmed by comparing them.

Effect of phase change materials on heat dissipation of a multiple heat source system

Abstract This paper experimentally investigates heat dissipation of a heat pipe with phase change materials (PCMs) cooling in a multiple heat source system. Two heat sources are fixed at one end of the heat pipe. Considering that a heat sink cannot dissipate all the heat generated by two heat sources, various PCMs are used due to a large latent heat. Different materials in a container are wrapped outside of the middle heat pipe to take away the heat from the evaporation section. The experimental tests obtain temperature data of heat source, evaporation section, and energy storage characteristics of PCMs are also determined under constant and dynamic values of the heat source powers. It is found that under this multiple heat source system structure, the phase change material RT35 maintains temperature variations of the evaporation section at a lower temperature and shortens the required time to reach the equilibrium temperature under a heating power of 20 W.

Numerical Study of Transient Bio-Heat Transfer Model With Heat Transfer Coefficient and Conduction Effect in Cylindrical Living Tissue

The human thermal comfort is affected by the body’s heat exchange mechanism conduction, convection, radiation, and evaporation. The mode of heat transfer between the body and environment depends upon the human internal physiological phenomena, together with the boundary conditions. The present paper provides the comprehensive overview of the thermoregulatory system of human body and studies the numerical solution of unsteady-state one dimensional Pennes bio-heat equation with appropriate boundary conditions. The solution is used to observe the temperature profiles at different thermal conductivities, and different heat transfer coefficients in the living tissue at the various time steps. Various physical and physiological factors across the cylindrical living tissue have been incorporated in the model.

Systematization of the Critical Parameters of Substances due to Their Connection with Heat of Evaporation and Boyle Temperature

We show that a variety of the critical parameters of substances can be systematized by relating them to the corresponding Boyle values and heat of vaporization under normal conditions. We have found new relationship for the critical parameters of substances obtained by processing the NIST database and other various sources. According to new relationship, the sum of the ratios of the critical and Boyle temperatures and the critical temperature to the heat of vaporization practically remains constant. The previous one (Apfelbaum and Vorob’ev in J Phys Chem B 113:3521, 2009) states that the sum of the critical temperature and density reduced to the corresponding Boyle values is also constant. Check for 70 substances from the NIST database and calculations for Mie m-6 potential confirmed these regularities within few percent accuracy.

Using Large-Aperture Scintillometer to Estimate Lake-Water Evaporation and Heat Fluxes in the Badain Jaran Desert, China

Accurate estimation of evaporation (E0) over open water bodies in arid regions (e.g., lakes in the desert) is of great importance for local water resource management. Due to the ability to accurately determine sensible (H) and latent (LE) heat fluxes over scales of hundreds to thousands of meters, scintillometers are more and more appreciated. In this study, a scintillometer was installed on both sides of the shore over the Sumu Barun Jaran Lake in the Badain Jaran Desert and was applied to estimate the sensible and latent heat fluxes and evaporation to be compared with the data of an evaporation pan and an aerodynamic model. Based on the field data, we further analyzed the seasonal differences in the flux evaluation using water temperature at different depths at half-hour and daily time scales, respectively. The results showed that in cold seasons, values of H were barely affected by the changes of shallow water temperature, whereas in hot seasons, the values were changed by 20%–30% at the half-hour time scale and 6.2%–18.3% at the daily time scale. In different seasons, shallow water temperature at different depths caused changes in the range of 0%–20% of LE (E0). This study contributes to a better understanding of uncertainties in measurements by large-aperture scintillometers in open-water environments.