Latent Heat Of Vaporization Research Articles

FITTINGS OF ADSORPTION ISOTHERM MODELS AND THERMODYNAMIC PROPERTIES OF URUNDAY SEEDS

ABSTRACT This study aimed to obtain and evaluate thermodynamic properties and hygroscopic equilibrium isotherms of urunday seeds as a function of air relative humidity and temperature, as well as identify the best-fitted mathematical models for adsorption phenomenon. A static-gravimetric method was used to obtain hygroscopic equilibrium moisture content. Seeds were placed in airtight containers with different saturated saline solutions for relative humidity control. These were then kept in BOD incubator chambers at 10, 20, 30, and 40 °C. Hygroscopic equilibrium moisture content decreased as temperature increased, for the same water activity. The Sigma-Copace model best-fitted seed adsorption data for equilibrium water activity intervals between 0.1129 and 0.8232 (dry basis). Both vaporization latent-heat and differential sorption entropy increased with decreasing hygroscopic equilibrium moisture content. Adsorption process in urunday seeds was controlled by enthalpy.

Explaining the Zonal Asymmetry in the Air‐Sea Net Heat Flux Climatology Over the Antarctic Circumpolar Current

AbstractSurface heating occurs over the streamline of the Antarctic Circumpolar Current (ACC) and balances the heat transport associated with the global meridional overturning circulation. With a combination of ocean assimilation model output, objectively analyzed products, and atmospheric reanalysis, this paper investigates the mechanism of climatological surface cooling in the Pacific sector with zonal asymmetry. The poleward shift of the ACC path in the Pacific with barotropic potential vorticity conservation was found to account for this cooling. The southward transport of warm/wet surface waters encounters relatively cold/dry air at high latitudes, causing strong turbulent heat fluxes. Sensible heat flux related to the sea‐air heat convection plays an equivalent role alongside the sea surface evaporative latent heat flux, both of which dominate the surface cooling in the Pacific sector. Solar radiation decreases with a poleward meandering of the ACC, which aggravates the cooling process. A significant seasonal cycle of the ensemble mean net surface heat flux (Qnet) is demonstrated, that is, approximately half‐year heating (cooling) during austral warm (cool) seasons. The estimated magnitude of Qnet over the ACC is approximately 20 W m−2 by averaging 10 heat flux climatologies and 4 W m−2 in an ocean state estimate model. However, efforts are still needed to reduce the excess heat flux over the sea surface in the Southern Ocean for the heat flux products.

Performance evaluations of an adsorption-based power and cooling cogeneration system under different operative conditions and working fluids

In order to harvest low-grade waste heat below 80 °C, we present an alternative adsorption-based power and cooling cogeneration system, which consists of an adsorption-based desalination system for generating concentrated and diluted salt solutions as well as providing cooling power, and a pressure retarded osmosis system for converting the produced salinity gradient energy into electricity. Effects of operation conditions, adsorbents, salt types and solvents are systematically investigated to evaluate the coefficient of performance (COP), electric efficiency, and exergy efficiency of the hybrid system. Results reveal that there exists an optimal desorption temperature leading to the maximum COP and electric efficiency. Larger salt concentration results in upgraded electrical efficiency and exergy efficiency, and degraded COP. Adsorbents with larger relative pressure where the adsorbent achieves half of the maximum absorption uptake and moderate adsorption enthalpy are more appealing. Solvents with high vaporization latent heat and specific heat capacity contribute to COP, however, decrease electrical efficiency and exergy efficiency. Salts rendering a larger osmotic coefficient improve electric and exergy efficiencies, however degrade the COP. When operating at a desorption temperature of 50 °C, the maximum exergy efficiency can reach 33.9%, meanwhile the electric efficiency and COP are 1.63% and 0.87, respectively.

Cooling control effect of water mist on thermal runaway propagation in lithium ion battery modules

Thermal runaway (TR) and its propagation in lithium ion batteries (LIBs) are potential risks during usage, and the likelihood therein is increasing owing to the widespread utilization of LIBs. However, the prevention of LIB thermal hazards remains a technical barrier. In this study, a novel control strategy with water mist (WM) was proposed and investigated through a series of experiments. To comprehensively understand the control mechanisms, the WM cooling effect was discussed by changing the application time and duration. The results showed that WM exhibited excellent cooling capacity with the consumption of 1.95 × 10−4 kg Wh−1 water and TR propagation in the battery module could be easily prevented. During WM application, the maximum cooling rate of LIB exceeded 100 K s−1 and the surface temperature decreased to 373.15 K in a few seconds. Meanwhile, TR propagation hazard could be controlled under much severer condition, where four out of five LIBs in the module were triggered into TR. The cooling process mainly depended on the WM evaporation latent heat and the cooling power for a single battery reached 40.71 W. The critical temperature, Tc1, could be used to forecast the control effect before WM application. And the cooling factor was proposed to determine the cooling effect during hazard control. Thermal hazard could be considered successfully prevented, when LIBs surface temperature reduced below 373.15 K. This work provides fundamental understanding of WM cooling control strategy, indicating the possibility of using this strategy in real cases.

Investigation of the Heat Budget of the Tropical Indian Ocean During Indian Ocean Dipole Events Occurring After ENSO

The Indian Ocean Dipole (IOD) is an important natural mode of the tropical Indian Ocean (TIO). Sea surface temperature anomaly (SSTA) variations in the TIO are an essential focus of the study of the IOD. Monthly variations of air-sea heat flux, rate of change of heat content and oceanic thermal advection in positive/negative IOD events (pIODs/nIODs) occurring after El Nino/La Nina were investigated, using long-series authoritative data, including sea surface wind, sea surface flux, ocean current, etc. It was found that the zonal wind anomaly induced by the initial SSTA gradient is the main trigger of IODs occurring after ENSOs. In pIODs, SSTA evolution in the TIO is primarily determined by the local surface heat flux anomaly, while in nIODs, it is controlled by anomalous oceanic thermal advection. The anomalous southwestern anticyclonic circulation in pIODs enhances regional differences in evaporative capacity and latent heat, and in nIODs, it augments the east-west difference in the advective thermal budget. Further, the meridional anomaly mechanism is also non-negligible during the development of nIODs. As the SWA moves eastward, the meridional SWA prevails near 60°E and the corresponding meridional anomalous current appears. The corresponding maximum meridional thermal advection anomaly reaches 200 W m −2 in September.

Analysis of Performance and Stability Factors of Vehicle Ethanol Gasoline for Motor Vehicle

Ethanol gasoline is a new type of clean energy which is formed by mixing fuel ethanol and ordinary gasoline in a certain proportion. The use of ethanol gasoline in motor vehicles can reduce the emissions of exhaust pollutants and improve the engine performance, but there are also problems such as low combustion calorific value, strong corrosion and easy stratification. Based on the comparison of physical and chemical properties of ethanol and gasoline, the octane number, calorific value, oxygen content, latent heat of vaporization and ignition limit of ethanol gasoline were analyzed. The main problems are discussed in this paper, and the factors affecting the stability of ethanol gasoline are analyzed from three aspects of temperature, water content and ethanol content.

Experimental and theoretical evaluation of thermophysical properties for moist air within solar still by using different algorithms of artificial neural network

In this research article, an attempt has been made to predict the thermophysical properties of moist air in a solar still cavity with the help of Artificial Neural Network (ANN) modelling. Six training algorithms have been used to train, test, and validate the ANN model (viz. OSS, CGP, CGF, RP, SCG, and LM). Water and inner glass cover temperatures were selected as the input parameters whereas, the model output are: thermal conductivity, partial vapour pressure at water & glass surface, thermal conductivity, volumetric expansivity, specific heat, latent heat of vaporization, and dynamic viscosity. The findings have revealed that the proposed ANN model can be used to predict the thermophysical properties of moist air with excellent accuracy. The results of ANN model were tested against the well-established relations of Tsilingiris. Out of all the training algorithms used LM was found to be the best in all the stages of ANN modelling, as the results are well within an accuracy level of more than 95%. Hence, the developed LM algorithm-based ANN model is one of the most suitable algorithm for the prediction of the thermophysical properties of moist air.

Simulation of condensation unit in ASPEN PLUS

The article discusses the scheme of deep utilization of the heat of flue gases. It has been established that in boiler units operating on natural gas, the only way to significantly improve the use of fuel is to deeply cool the combustion products to a temperature at which it is possible to condense the maximum possible portion of the fumes contained in the gases. To analyze the main energy indicators of the condensing unit and optimize its operating modes, a priority scheme was simulated in Aspen Plus. In this scheme, there are tees, heat exchangers and a reactor (boiler furnace). The configuration of tees (mixers) is carried out by setting the costs or fractions of two flows entering or leaving the element. The boiler furnace is modeled as a Gibbs reactor, which calculates the chemical and thermodynamic equilibrium by minimizing the difference in the Gibbs energy of the products and the starting materials. Using the Aspen Plus computer program, the condensation unit circuit was simulated at the PTVM-100 boiler unit with the specification of the optimal operating parameters of material flows and heat exchange equipment. The calculations show that when using a condensing boiler, a triple energy effect is achieved: the physical heat of the flue gases is used; the latent heat of vaporization released during condensation is used; the condensate released from the flue gases is used.

Development of a CPU/GPU portable software library for Lagrangian–Eulerian simulations of liquid sprays

The Lagrangian–Eulerian method is widely used for simulations of fuel sprays in turbulent combustion because of the advantage of treating the spray droplets as discrete points. One challenge of the Lagrangian–Eulerian method is the intense computational requirement when tracking the large number of Lagrangian particles needed for high fidelity. We have developed a performance-portable library, Grit, to track the Lagrangian particles in parallel on central processing unit (CPU) and graphics processing unit (GPU) accelerated high performance computing (HPC) architectures. Grit is a C++ library which employs Message Passing Interface (MPI) for distributed memory parallelism and Kokkos programming model for on-node shared memory parallelism with performance portability across different architectures of GPUs and multi-core/manycore CPUs. The parallel algorithms, key parallel kernels, and their performances on the pre-exascale supercomputer, Summit, are presented. Grit is coupled with a direct numerical simulation (DNS) solver, S3D, for multiphase simulations. A conservative formulation has been developed and implemented in Grit for phase coupling with thermodynamic consistency. The formulation separates the conservation of mass, momentum and energy from the physical models to prevent accidental violation of conservation laws due to inconsistent models. The formulation also enforces consistent definitions of enthalpies of the fuel for both phases and the latent heat of evaporation. Simulations of turbulent particle-laden flow and the evaporation of dilute turbulent spray jet are performed to verify the software implementation, and to demonstrate the scalability of Grit for large-scale multiphase simulations.

Experimental study on the effect of the liquid/surface thermal properties on droplet impact

Droplet impact on hot surfaces is widely encountered in industry and engineering applications. In the present paper we investigate the effect of the combination of the droplet liquid type and the solid surface type and their effect on droplet impact dynamics. We test three surfaces, copper 110, aluminum 1199, and stainless steel 304, and two liquids, water and ethanol. These surfaces and liquids are characterized by high and low thermophysical properties. The three surfaces are tested with water to investigate the effect of the surface on the droplet dynamics. After that, we test both liquids with aluminum. Our findings showed that the Leidenfrost temperature does not always correlate with the surface thermal proper-ties as reported in the literature. Some surfaces can undergo changes because of the heating and this reduces their initial thermal properties. For this reason, such surfaces are capable to show two Leidenfrost temperatures because of the thermophysical properties reduction during heating. Our findings also revealed that the Leidenfrost temperature of liquids with low thermophysical properties including surface tension, evaporation latent heat and density show trivial effect by the droplet impact velocity; i.e. the Leidenfrost temperature show trivial increase by increasing the droplet impact velocity. Liquids with high thermophysical proper-ties show significant Leidenfrost temperature increase by increasing the impacting velocity.

Comparative Analysis of Effect of Diesel and N-Butanol Blend Properties on Combustion Process and Hydrocarbon Emission at Various Oxygen-Intake Concentrations

AbstractThe effects of the cetane number (CN) and latent heat of vaporization (LHV) of diesel/n-butanol fuel on the hydrocarbon (HC) emission and combustion process at various oxygen intake concent...

Temporal-Spatial Analysis of the Warming Effect of Different Cultivated Land Urbanization of Metropolitan Area in China

The regional warming effect is different when different cultivated land types are converted into urban construction land, while its temporal and spatial changes are unclear. We studied the temporal and spatial changes in the warming effect when dry land was converted to urban land (DL2UBL), and irrigated land to urban land (IL2UBL) in Yangtze River Delta (CSJ), Beijing-Tianjin- Hebei (JJJ) and Chengdu-Chongqing (CY) metropolitan areas from 2000 to 2015. The average warming effect of the three metropolitan areas was more intensive in DL2UBL than in IL2UBL in winter, and opposite occurred in summer. The diurnal warming changes between them were small during the day, but obvious at night, which corresponds to the diurnal change of the latent heat of evaporation. Due to the difference in the spatial distribution of humidity, to the north of 34°N, the warming effect of DL2UBL was stronger than that of IL2UBL, and to the south of 34°N, it was stronger for IL2UBL, while from west to east, the warming trend of DL2UBL and IL2UBL keep pace and decline slightly. The influence in planetary boundary layer was also analyzed. We hope that our findings provide scientific support for future metropolitan land use decisions associated with tradeoffs.

Numerical investigation of modified cavitation model with thermodynamic effect in water and liquid nitrogen

In this paper, three different cavitation models were employed and coupled with thermodynamic effect to simulate the cavitation flow in water and liquid nitrogen. The water cavitating flows around a NACA0015 hydrofoil and liquid nitrogen cavitating flows around a tapered hydrofoil were investigated numerically. The three-dimensional computations were compared and validated with the cavitation experiments. The applicability of the numerical solutions of cavitating regarding to the cavitation model was studied. The change of saturated vapor pressure caused by latent heat of vaporization and the change of local vaporization pressure caused by turbulent kinetic energy were taken into consideration. The numerical result of the modified Merkle cavitation model shows good agreement with the experimental result, indicating that the modified Merkle cavitation model could be employed to simulation the cavitation flows in water and liquid nitrogen. Additionally, corresponding of the thermodynamic effect in water and liquid nitrogen cavitation were discussed.

Rigorous Tritium Wet Scrubber Column Modeling and Design

The rigorous steady-state equilibrium stage Tritium Wet Scrubber Column model has been developed. The model includes the six water isotopologues H2O, HDO, HTO, D2O, DTO, and T2O; heat balance; and packing pressure drop. Heat balance is particularly important in wet scrubber calculations due to evaporative cooling of air with less than 100% relative humidity. Evaporative cooling is generally beneficial, but freezing is possible with very cold dry air, making it important to understand operating limits. The pros and cons of precooling and saturation of the airstream are discussed. The Tritium Wet Scrubber Column model has been applied to scrubbing airstreams containing tritiated light water vapor and for tritiated heavy water vapor in CANDU® heavy water applications. Deuterium and tritium are recovered at slightly different efficiencies, and because of differences in the latent heat of vaporization for H2O and D2O, liquid and vapor compositions affect the column heat balance. Case studies are presented for tritiated light water vapor air detritiation and also for tritiated heavy water vapor air detritiation to provide guidance for design. Further, practical aspects of the wet scrubber column construction and operation are discussed.

An investigation on effect of EDL on heat transfer of micro heat pipe with square and triangular cross section

Electronic industries have always been trying to improve the efficiency of electronic devices with small dimensions through thermal management of this equipment, thus increasing the use of small thermal sinks. In this study micro heat pipes with triangular and square cross sections have been manufactured and tested. One of the main objectives is to obtain an understanding of micro heat pipes and their role in energy transmission with electrical double layer (EDL). Micro heat pipes are highly efficient heat transfer devices, which use the continuous evaporation/condensation of a suitable working fluid for two-phase heat transport in a closed system. Since the latent heat of vaporization is very large, heat pipes transport heat at small temperature difference, with high rates. Because of variety of advantage features these devices have found a number of applications both in space and terrestrial technologies. The theory of operation micro heat pipes with EDL is described and the micro heat pipe has been studied. The temperature distribution have achieved through five thermocouples installed on the body. Water and different solution mixture of water and ethanol have used to investigate effect of the electric double layer heat transfer. It was noticed that the electric double layer of ionized fluid has caused reduction of heat transfer.

Design, fabrication and performance evaluation of pulsating heat pipe assisted tool holder

Pulsating heat pipe is a kind of highly efficient heat conductor in which the latent heat of evaporation is used to transport great amounts of heat in the presence of only small differences in temperature. The pulsating heat pipe assisted tool holder was designed and fabricated. Dry turning of Ti-6Al-4V alloy was carried out with the pulsating heat pipe assisted tool holder as well as the conventional one for comparison. FEM simulations were also carried out to investigate the influence of the pulsating heat pipe assisted cooling on the cutting performance. Results show that the highest cutting temperatures of the PHP assisted tool holder could be reduced by 10 % as so compared to that of the conventional one. The pulsating heat pipe assisted cooling can also reduce the wear of the cutting tools and improve their lives by 20∼30 %. The FEM simulations show a good agreement with the cutting experiment, as a result, validate the potential value of the pulsating heat pipe assisted cooling in dry cutting operations.

Ledinegg instability analysis on direct vapor generation inside solar collectors

Compared with direct steam generation (DSG), direct vapor generation (DVG) system based on organic working fluid has better application potential in low and medium temperature distributed system. However, there is a lack of understanding of the two-phase flow instability that commonly occurs in DVG systems and can cause fatal damage to the system. In this paper, Ledinegg instability is considered as a common flow instability, and its occurrence characteristics and avoidance strategies are presented. First, a theoretical model was established to study Ledinegg instability of organic working fluid. Then, the effects of heat flux q, inlet subcooling Tc, length-to-diameter ratio L/D and fluid properties are analyzed. Particularly, a characteristic parameter RL representing the possibility of Ledinegg instability is proposed for the first time in performance evaluation of Ledinegg instability. The results show that as L/D decreases from 200 to 100, RL reduces from 0.88 to 0.25. As q increases from 10 kW/m2 to 30 kW/m2, RL increases from 0.54 to 1.03. When Tc is less than 3 °C, RL approaches 0 and Ledinegg instability disappears. With the increase of surface tension σ and the latent heat of vaporization r, the decreases of vapor-liquid density ratio ρsv/ρsl and the decreases of vapor-liquid viscosity ratio μsv/μsl, RL increases. The physical equation describing RL of Ledinegg instability is helpful to guide DVG system to reduce or avoid Ledinegg instability in design and operation.

Cryogenic Energy for Indirect Freeze Desalination—Numerical and Experimental Investigation

Renewed interest in freeze desalination has emerged due to its advantages over other desalination technologies. A major advantage of the freeze desalination process over evaporative methods is its lower energy consumption (latent heat of freezing is 333.5 kJ/kg and latent heat of evaporation is 2256.7 kJ/kg). Cryogenic fluids like LN2/LAir are emerging as an effective energy storage medium to maximise utilisation of intermittent renewable energy sources. The recovery of this stored cold energy has the potential to be used for freeze desalination. Computational Fluid Dynamics (CFD) modelling was developed to simulate the evaporation of liquid nitrogen to simultaneously conduct freeze desalination to investigate the feasibility of using cryogenic energy for freeze desalination. This integrated CFD model was validated using experimental heat exchanger test facility constructed, to evaporate liquid nitrogen to supply the cooling required for freezing. Parametric study on the LN2 flow rate to observe the volume of ice obtained was also examined using CFD, where increasing the velocity of LN2 by 6 times, increased the volume of ice obtained by 4.3 times. A number of freezing stages were required in order to reduce the ice salinity from 1.5% down to 0.1% as regarded by the World Health Organisation (WHO) as safe to drink. In the cryogenic desalination test rig, approximately 1.35 L of liquid nitrogen was required to reduce the ice salinity from 1.5% to less than 0.1%. Furthermore, the above results illustrate the potential of using the cold energy of cryogenic fluids such as Liquified Natural Gas (LNG) and LN2/LAir for freeze desalination applications as most cold energy during LNG regasification has been unexploited today.

Novel low-cost parabolic trough solar collector with TPCT heat pipe and solar tracker: Performance and comparing with commercial flat-plate and evacuated tube solar collectors

This work presents a novel low-cost parabolic trough solar collector in which a two-phase closed thermosiphon (TPCT) heat pipe made of stainless steel and composed of evaporation and condensation parts with a total length of 285 cm has been utilized to capture solar heat. The evaporation part with the length of 240 cm positioned in the center of the collector’s reflector has been coated with selective coating and is insulated from environment using twin wall evacuated glass tube. The condensation part with the length of 45 cm located inside a cylindrical manifold thermally insulated using glass wool transfers the vaporization latent heat of vapor existing inside the condensation part to heat transfer fluid (HTF) flowing inside the manifold, and heats it. CuO-H2Onanofluid prepared by mixing distilled water and copper oxide nonopowder with 1% weight concentration has been utilized as the working fluid of the TPCT heat pipe. The collector has been installed on a low-priced sensorless dual-axis solar tracker operating using offline data obtained from solar map equations. The tracker has been chosen as dual-axis to guarantee continuously keeping the reflector’s aperture perpendicular to the sun ray. The proposed parabolic trough solar collector has been built, and comparative experimental measurements obtained from the operation of the built solar collector, a state-of-the-art evacuated tube solar collector (commercial high-efficient evacuated tube solar collector ETC-20) and a state-of-the-art flat-plate solar collector (commercial high-efficient flat-plate solar collector FPC-A26) under identical realistic conditions are given. Experimental measurements and comparison prove the following points which are the novelties and contributions of this research work:•The novel parabolic trough solar collector presented in this study provides higher thermal efficiency compared to the state of the art of both evacuated tube solar collectors (ETC-20) and flat-plate solar collectors (FPC-A26) available in the market.•It provides flatter thermal efficiency curve.•It provides higher power production density (ratio of peak output power to aperture area).•It has lower construction cost and a reasonable ratio of price to power production.

Cool Steam Method for Desalinating Seawater

Cool steam is an innovative distillation technology based on low-temperature thermal distillation (LTTD), which allows obtaining fresh water from non-safe water sources with substantially low energy consumption. LTTD consists of distilling at low temperatures by lowering the working pressure and making the most of low-grade heat sources (either natural or artificial) to evaporate water and then condensate it at a cooler heat sink. To perform the process, an external heat source is needed that provides the latent heat of evaporation and a temperature gradient to maintain the distillation cycle. Depending on the available temperature gradient, several stages can be implemented, leading to a multi-stage device. The cool steam device can thus be single or multi-stage, being raw water fed to every stage from the top and evaporated in contact with the warmer surface within the said stage. Acting as a heat carrier, the water vapor travels to the cooler surface and condensates in contact with it. The latent heat of condensation is then conducted through the conductive wall to the next stage. Net heat flux is then established from the heat source until the heat sink, allowing distilling water inside every parallel stage.