Evaporative Heat Research Articles

VARIABLE CAPACITY ABSORPTION COOLING SYSTEM PERFORMANCE FOR BUILDING APPLICATION

The increasing energy costs and environmental awareness call for a shift towards some interesting energy alternatives preferably the use of renewable energy. The present study investigates the impact of varying cooling capacity and other operating parameters in a single-effect absorption refrigeration system, using the concept of energy and exergy as a building heating/cooling alternative. The solar heat is used as an input to the generator of absorption refrigeration system. The results obtained from investigation revealed that variation in cooling capacity influences coefficient of performance (COP), exergy loss in different components as well as exergy efficiency. The values of COPcooling and COPheating lies in the range of 0.71-0.89 and 1.71-1.89 respectively for variations in cooling capacities ranging from 1 TR to 20 TR at maximum generator temperature of 80oC. However, exergy efficiency of the system lies in the range of 0.32-0.41 for same variation in cooling capacities. It has also been established that an increase in evaporator temperature and at maximum cooling capacity both COPcooling and COPheating shows an increasing trend. The exergy efficiency also shows maximum value at the highest cooling capacity at a particular evaporator temperature which further with an increase in evaporator temperature shows a decreasing trend. The irreversibility behavior in all the components i.e., solution heat exchanger, absorber, generator, evaporator and condenser shows an expected trend with the variation in cooling capacity. Hence, use of the above mentioned system as a heating and/or cooling alternative for buildings is suggested.

Energo- and exergo-technical assessment of ground-source heat pump systems for geothermal energy production from underground mines

ABSTRACTThe objective of this study is to perform the energy and exergy analysis of an integrated ground-source heat pump (GSHP) system, along with technical assessment, for geothermal energy production by deployment of Engineering Equation Solver (EES). The system comprises heat pump cycle and ground heat exchanger for extracting geothermal energy from underground mine water. A simultaneous energy and exergy analysis of the system is brought off. These analyses provided persuasive outcomes due to the use of an economic and green source of energy. The energetic coefficient of performance (COP) of the entire system is 2.33 and the exergy efficiency of the system is 28.6%. The exergetic efficiencies of the compressor, ground heat exchanger, evaporator, expansion valve, condenser and fan are computed to be 38%, 42%, 53%, 55%, 60% and 64%, respectively. In the numerical investigation, different alteration such as changing the temperature and pressure of the condenser show promising potential for further application of GSHPs. The outcomes of this research can be used for developing and designing novel coupled heat and power systems.

High-temperature evaporation of water emulsion droplets used in thermal fluid treatment

High-temperature (over 500 K) evaporation of water, emulsions, slurries and solutions has been extensively studied over the recent years due to a number of prospective applications. Some of these are, for example, the evaporation or burnout of impurities in the course of for thermal wastewater treatment, gasification, as well as flue gas waste heat recovery by intermixing them with water and water vapor to create a new generation of heat transfer agents. Further development of these technologies is constrained by the fact that the approaches used so far are mostly empirical. Obtaining reliable experimental data on evaporation characteristics (vaporization rate and lifetime) of water emulsion droplets in the course of thermal evaporation and burnout of impurities is a pressing task. It is also desirable to experimentally cover all the temperature ranges, droplet sizes, and component concentrations, typical of advanced water treatment. In this research, we use high-speed hardware-and-software system to track the free surface of a droplet. We determine the dependence of heating and complete evaporation time as well as heating and vaporization rate on the gas environment temperature, droplet size, and emulsion component concentration. We then derive the approximating equations for the dependences determined. The difference in evaporation conditions and characteristics is also defined for droplets of water and emulsions with different additive types and concentrations. Finally, we outline different modes of evaporation as well as the required conditions for monotonous evaporation or explosive breakup (pulverization).

In-Situ Evolution of Heat and Mass Transfer Phenomena and Evaporative Water Losses of Three Agro-Waste Evaporative Cooling Pads: An Experimental and Modeling Study

Utilization of evaporative cooling to condition rooms for increased productivity of farm animals is very common. The major challenge in adopting this technology in sub-Saharan Africa is the availability of cheap and effective cooling pads to provide the desired room condition. In this research, prediction of heat and mass transfer coefficient and evaporation losses of three agro based evaporative cooling pads based on mass density difference of the process fluid and binary diffusivity coefficient at the exit air temperature was established. The study was performed for wood charcoal, jut and palm fruit fiber as evaporative cooling pad materials. The dynamic performance of these three agro based cooling pads was also investigated in real time under a very fluid dry environment with a constantly intruding moist wind from southern Atlantic Ocean. The experimental results showed that mass transfer coefficient for the three products varied from 1.969 × 10−2 to 1.503 × 10−1 m/s depending on the product and the applied air flow rate. Similarly, the heat transfer coefficient ranged from 19.79 to 151.1 W/m2 K. Periodic variation in evaporative effectiveness was observed with highest value occurring at the lowest inlet air velocity of 1.13 m/s for jute fiber. Comparison of the modeling results between Halasz, and the indicative rule of thumb used by Baltimore Aircoil was favorable to Halasz model with a coefficient of variation ranging from 0 to 3.06 × 10−7 and a correlation coefficient of about 0.98. the second model has shown a deviation from experimental results that can reach 45% under particular conditions.

Heat transfer of aqueous salt solution layers

Heat transfer and evaporation of layers of water and aqueous solutions of salts on a heated horizontal wall were studied experimentally. Aqueous solutions of salts can be divided into two characteristic groups. For the first group of salts, the evaporation rates and heat transfer coefficients increase with time. For the second group, the rate of evaporation falls sharply with increasing salt concentration and with decreasing liquid layer height. This difference in salts’ behavior is determined by the difference in equilibrium curves and in physical and chemical properties of salts. The heat transfer coefficient for water and salt solutions increases when the layer height becomes less than 1.2–1.5 mm. With increasing concentration of salt and when approaching the crystallization point the role of free convection in the liquid phase decreases sharply, and the Nusselt number approaches 1. For salt solutions (LiBr, CaCl2 and LiCl), a significant excess of convection (α) over the conductive heat transfer (λ) is observed for the layer height δ over 1.8–2.0 mm. For pure water, convective and conductive components are comparable even for δ = 3 mm. This difference for salts is associated with substantial intensification of heat transfer, which is probably caused by the concentration flow of Marangoni MaC. Strong influence of MaC on heat and mass transfer in a thin layer and at high temperatures is detected for the first time and is extremely important for accurate modeling in unsteady and non-isothermal processes. Experimental data show a surprising result. The free liquid convection for salt solutions significantly exceeds the convection in the water layer for the most part of the evaporation time.

Effect of different bulking agents on water variation and thermal balance and their respective contribution to bio-generated heat during long-term storage sludge biodrying process.

Biodrying was first used for the post-treatment of long-term storage sludge with vinasse as bulking agents. The effect of different bulking agents on water and heat variation and their respective contributions to bio-generated heat during storage sludge biodrying were investigated. Three different bulking agents (beer lees and distillers grains, with conventional straw used for comparison) were mixed with storage sludge for biodrying for an 18-day period. The results revealed the treatment with beer lees as bulking agent achieved the best performance with the highest water removal capacity (658gkg-1 initial water). The extent of organic degradation in the mixture was related to the degradation ability of the bulking agents. The degradation of C- and H-containing materials (e.g., carboxylic acid) accounted for volatile solids (VS) loss. Water and thermal analyses showed that evaporation was the main way of water loss (accounting for 90%), while evaporation heat was the main component of heat consumption (accounting for 56.67-60.62%).The biodegradation of bulking agents contributed a high proportion of the bio-generated heat consumed by water evaporation (82.35-86.67%).

Temporal Instability of a Confined Liquid Film with Heat and Mass Transfer

The Kelvin–Helmholtz instability of the cylindrical interface between the vapor and liquid phases of a fluid has been investigated when the vapor is hotter than the liquid and the physical model is a free-swirling annular liquid layer confined in a tube with the gas phase in the center. A stability analysis that includes the effect of swirl along with mass and heat transfer is presented. In this paper, the ratio between conduction heat flux and evaporation heat flux characterizes the heat transfer at the interface. This work examines the effect of various nondimensional parameters on the instability of the flow. When the ratio of the conduction heat flux to the evaporation heat flux increases, the growth rate increases and the wave number remains unchanged. Although the confinement increases, the stability of the liquid varies from its condition without heat and mass transfer.

Evaporation of a single emulsion fuel droplet in elevated temperature and pressure conditions

The evaporation characteristics of water/n-decane emulsion droplet at various temperatures and pressures were experimentally observed. Emulsion fuel was made by adding pure water to the base n-decane fuel with a volume ratio of 0.2. Span 80 was used as a surfactant, and ultrasonification was conducted for the mixing process. The temporal variation of the droplet diameter was optically observed by using a high-speed camera, and the changes in droplet temperature were also measured. The evaporation process of emulsion droplets was divided into three stages, namely, droplet heating, inflation/puffing, and pure evaporation. As the ambient temperature increased, the behavior of droplet inflation shifted to puffing during the inflation/puffing stage. A decline in the inflation/puffing incidence rate was noted at high-pressure conditions. The evaporation rate during the pure evaporation stage and the overall droplet lifetime were affected by the ambient temperature but not by the ambient pressure. The inflation of the droplet mostly occurred at relatively lower temperature and pressure conditions; it changed to puffing, however, at higher temperature and pressure conditions.

Westward mountain-gap wind jets of the northern Red Sea as seen by QuikSCAT

We analyse ten years of QuikSCAT satellite surface winds to statistically characterize the spatio-temporal variability of the westward mountain-gap wind jets over the northern Red Sea. These wind jets bring relatively cold and dry air from the Arabian Desert, increasing heat loss and evaporation over the region similar to cold-air outbreaks from mid and subpolar latitudes. QuikSCAT captures the spatial structure of the wind jets and agrees well with in situ observations from a heavily instrumented mooring in the northern Red Sea. The local linear correlations between QuikSCAT and in situ winds are 0.96 (speed) and 0.85 (direction). QuikSCAT also reveals that cross-axis winds such as the mountain-gap wind jets are a major component of the regional wind variability. The cross-axis wind pattern appears as the second (or third) mode in the four vector Empirical Orthogonal Function analyses we performed, explaining between 6% to 11% of the wind variance. Westward wind jets are typical in winter, especially in December and January, but with strong interannual variability. Several jets can occur simultaneously and cover a large latitudinal range of the northern Red Sea, which we call large-scale westward events. QuikSCAT recorded 18 large-scale events over ten years, with duration between 3 to 8 days and strengths varying from 3–4 to 9–10 m/s. These events cause large changes in the wind stress curl pattern, imposing a remarkable sequence of positive and negative curl along the Red Sea main axis, which might be a wind forcing mechanism for the oceanic mesoscale circulation.

Carbon coating nanostructured-LiNi1/3Co1/3Mn1/3O2 cathode material synthesized by chemical vapor deposition method for high performance lithium-ion batteries

Efficient energy storage of lithium-ion batteries plays a significant role across lots of sectors including consumer electronics, electric and hybrid electric vehicles and a smart grid accommodating intermittent renewable energy sources. Nanostructured cathode materials present fascinating opportunities for high-performance lithium-ion batteries, but intrinsic problems linked with the high surface area to volume ratios in the nanometer-range have restricted their adoption for practical applications. We demonstrate processing platform that realize high-performance nanostructured-LiNi1/3Co1/3Mn1/3O2 (NCM) layer cathode with carbon coating as a conductive additive. In this paper, we first presented a green, novel, economic and controllable chemical vapor deposition (CVD) method with sucrose as carbon source to coating NCM. Sol-gel synthesized NCM of carbon coated with optimized thickness by this formula are shown to have outstanding rate performance and robust cycle lifetime. The thickness - optimized sample of discharge capacity is as high as 104.5 mAh g−1 for 10 C (6s). High capacity retentions of 94.29% and 94.78% after 100 cycles for 0.1 C, respectively. Compared with the heat evaporation method, with the CVD method has better uniformity and higher quality. This approach further improves evidently the NCM of electrochemical performance and thus promotes lithium-ion battery development technology into unprecedented regimes of operation.

Modelling of liquid nitrogen spray cooling in an electronic equipment cabin under low pressure

Timely and effective cooling is essential for the performance of electronic equipment. For spacecraft, however, the severe aerodynamic heating and low-pressure environment have posed a serious challenge to the heat removal of the high-power electronic equipment. Spray cooling is considered to be an appropriate way to maintain the temperature of the electronic devices within acceptable limits. This paper considers the heat balance in spray cooling using a First Law of Thermodynamics modelling approach as well as a thermal control strategy for a semi-enclosed electronic equipment cabin. Theoretical analysis and numerical results are presented to show the applicability of the developed model and strategy. Characteristics of liquid nitrogen droplet heating, boiling and flash evaporation as well as spray patterns are discussed in detail. Furthermore, the control method of the spray nozzles switching and the interaction mechanism between pressure and temperature within the electronic equipment cabin during spray cooling are also addressed. The thermal control strategy and the model predictions presented in this work can help researchers and designers to ascertain optimum operational conditions of spraying cooling, including the spray mass flow rate, the spray length and the distribution of the sprayed droplets.

Energy-Economic Analysis of Plate Evaporator using Brine-based Hybrid Nanofluids as Secondary Refrigerant

Energy and economic analyses of corrugated plate evaporator have been performed in this study by using brine-based hybrid nanofluids as secondary refrigerant for low temperature applications (milk chilling, ice making and fish freezing). Various hybrid nanofluids containing alumina with different nanoparticles (copper, silver and multi walled carbon nanotube) dispersed in ethylene glycol/water, propylene glycol/water, calcium chloride/water and potassium acetate/water brines have been considered. A comparison has been made based on overall heat transfer coefficient, evaporator size (heat transfer area), pump work, COP, annual cost and payback period. The maximum reduction in heat transfer area has been observed for PG brine-based alumina–silver hybrid nanofluid. Whereas, the maximum reduction in pump work and augmentation in COP have been obtained for PG brine-based alumina–MWCNT hybrid nanofluid. EG brine-based Alumina–Cu hybrid nanofluid yields minimum annual cost. Most of the nanofluids (except PG brine-based Al2O3–Ag nanofluid) seem to be not beneficial for practical use due to comparatively long payback period; however, that can be significantly reduced in future by decreasing nanoparticle cost and increasing nanofluid stability. The present study reveals that the brine-based hybrid nanofluids may be the potential option as next generation secondary refrigerants for low temperature applications.

Forced thermal ignition of a polydisperse fuel spray

ABSTRACTA new mathematical model is presented for determining critical conditions for forced thermal ignition of an arbitrary polydisperse fuel spray/oxidant mixture. An asymptotic analysis is used to ascertain both the necessary initial applied temperature as well as the time needed to accumulate enough fuel vapor through droplet evaporation in order that thermal runaway, indicating ignition, should occur. The influence of the combined effect of heat loss due to evaporation and volumetric heat loss on critical ignition conditions is accounted for. The quenching distance is analyzed and found to match the expression used in the literature. It is demonstrated that, for practical purposes, even when volumetric heat loss alone does not prevent ignition, the presence of the fuel droplets can do so. The impact of liquid fuel-related parameters on ignition conditions is discussed in detail.

Performance and thermo-sustainability analysis of non-hybrid organic Rankine cycles (ORCs) at varying heat source and evaporator conditions

The performance and thermo-sustainability indicators (TSI) of non-hybrid organic Rankine cycles (ORCs) are considered at varying evaporator pressure (EVP) and heat source temperature (HST). The ORCs structures include the ORC-basic, ORC-internal heat exchanger (ORC-IHE), ORC-turbine bleeding and ORC-turbine bleeding/regeneration. The TSI considered exergy efficiency, waste exergy ratio (WER), exergetic sustainability index (ESI) and environmental effect factor (EEF). The calculated overall exergy efficiency varies from 35.35 to 47.23 for evaporator pressure between 2 and 3 MPa and 49.02 to 52.71 for HST between 500 and 650 K. Additionally, WER, ESI and EEF were found to vary from 0.253 to 0.278, 1.15 to 1.87 and 0.547 to 0.82, respectively while ESI decreases for all variants of HST. The results indicate high ESI and low WER in ORC-IHE and the ORC-turbine bleeding /regeneration for all variations in EVP and HST.

Improved Satellite Estimation of Near‐Surface Humidity Using Vertical Water Vapor Profile Information

AbstractNear‐surface air‐specific humidity is a key variable in the estimation of air‐sea latent heat flux and evaporation from the ocean surface. An accurate estimation over the global ocean is required for studies on global climate, air‐sea interactions, and water cycles. Current remote sensing techniques are problematic and a major source of errors for flux and evaporation. Here we propose a new method to estimate surface humidity using satellite microwave radiometer instruments, based on a new finding about the relationship between multichannel brightness temperatures measured by satellite sensors, surface humidity, and vertical moisture structure. Satellite estimations using the new method were compared with in situ observations to evaluate this method, confirming that it could significantly improve satellite estimations with high impact on satellite estimation of latent heat flux. We recommend the adoption of this method for any satellite microwave radiometer observations.

Evaporation-induced gas-phase flows at selective laser melting

Selective laser melting is the method for 3D printing from metals. A solid part is built from powder layer-by-layer. A continuum-wave laser beam scans every powder layer to fuse powder. The process is studied with a high-speed CCD camera at the frame rate of 104 fps and the resolution up to 5 µm per pixel. Heat transfer and evaporation in the laser-interaction zone are numerically modeled. Droplets are ejected from the melt pool in the direction around the normal to the melt surface and the powder particles move in the horizontal plane toward the melt pool. A vapor jet is observed in the direction of the normal to the melt surface. The velocities of the droplets, the powder particles, and the jet flow and the mass loss due to evaporation are measured. The gas flow around the vapor jet is calculated by Landau’s model of submerged jet. The measured velocities of vapor, droplets, and powder particles correlate with the calculated flow field. The obtained results show the importance of evaporation and the flow of the vapor and the ambient gas. These gas-dynamic phenomena can explain the formation of the denudated zones and the instability at high-energy input.

Molecular dynamics simulation on the effect of nanoparticles on the heat transfer characteristics of pool boiling

ABSTRACTMolecular dynamics simulation was performed to investigate pool boiling of nanofluids on the metal wall. Nanoparticles were placed near the wall. Results showed that with the addition of nanoparticles the fluid temperature, net evaporation number and heat flux were increased, indicating that the boiling heat transfer was enhanced. In addition, the nanoparticles were able to move around the wall disorderly but did not move with the fluid. The effects of heated temperature and nanoparticle size on the boiling heat transfer were also investigated. By increasing heated temperature and nanoparticle size, the boiling heat transfer enhancement increased.

Solar-radiant heat reducing effect by heat of water evaporation of a moss-greening material with ceramic containing waste silica.

Solar-radiant heat reducing effect by heat of water evaporation of a moss-greening material with ceramic containing waste silica.

Evaluation of the Effect ofBiofield Energy Treatment on Physicochemical and Thermal Properties of Hydroxypropyl β-Cyclodextrin

Hydroxypropyl β-Cyclodextrin (HPBCD) has many applications in the foods, nutraceuticals, and pharmaceuticals industries. The primary objective of this study was to evaluate the influence of the Trivedi Effect® on the physicochemical and thermal properties of HPBCD using modern analytical techniques. The HPBCD test sample was divided into two parts. One part did not receive the Biofield Energy Treatment and was called as a control sample, whereas, the other part received the Biofield Energy Treatment remotely by a renowned Biofield Energy Healer, Alice Branton and was called as a treated sample. The particle size values of the treated HPBCD were decreased by 5.32%, 1.51%, 0.36%, and 1.12% at d10, d50, d90, and D (4,3), respectively compared with the control sample. Thus, the surface area of the treated HPBCD was significantly increased by 6.67% compared with the control sample. The evaporation and melting temperature of the treated HPBCD were increased by 4.76% and 1.92%, respectively compared with the control sample. However, the latent heat of evaporation and latent heat of fusion of the treated HPBCD were significantly decreased by 7.95% and 33.85%, respectively compared to the control sample. The total weight loss in the treated HPBCD sample was decreased by 1.83% compared with the control sample. But, the residue amount was 40.55% more in the case of the treated HPBCD compared to the control sample. The Trivedi Effect®-Consciousness Energy Healing Treatment introduced a new form of HPBCD which may show better stability, solubility, dissolution rate, absorption, and bioavailability compared to the control sample. The treated would be more useful for the improvement of solubility of the lipophilic drug, stabilize volatile and unstable compounds, preparation of cholesterol free food products, weight loss supplements, and other anti-obesity medication, and also for the industry using it as a raw material.

F-Gas regulation-Possible solutions for the retrofit dead end

The EU F-gas regulation of 2006 and the recast of 2014 are forcing the market to reduce the use of refrigerants with high global warming potential (GWP). As a result, the production of hydrofluorocarbon (HFC) refrigerants with higher GWP decreased, making the prices of all HFC gases to increase. Any maintenance problem in a refrigeration system asks to evaluate the retrofitting of the gas making necessary to know the expected behaviour of the system. This paper aims to discuss the gases that can substitute the now-a-days HFCs, and the impact the retrofit will cause in a real air-conditioning systems. Many studies on retrofit address the behaviour of the refrigeration cycle, but usually, do not take into account the behaviour of the system as a whole. This paper models a water-to-water air-conditioning system taking into consideration the evaporator and condenser heat exchangers, the refrigeration cycle, the air-conditioning loop and the heat exchanger to the acclimatized area. Moreover, the paper studies the performance of the system when subjected to high condensing temperatures. The paper concludes that all possible retrofit solutions need to use flammable gases that make the refrigeration power of the equipment to reduce.