Heat Addition Research Articles

End Effects on H2-Forced Convection in Rectangular Ducts of Large Aspect Ratios

The H2-forced convection in a rectangular duct of large aspect ratio (>10) is studied. It is found that the short ends have non-negligible effects on the Nusselt number and the temperature distribution. Even at infinite aspect ratios, the Nusselt number depends on the net heat addition from the ends, but not how they are distributed.

Diffuse emission of CO2 and convective heat release at Nisyros caldera (Greece)

The diffuse emission of CO2 from the south east sector of Nisyros caldera (Lakki plain) has been measured during a detailed survey (~1400 soil CO2 flux measurements) performed in October 2018. The gas emissions are fed by hydrothermal sources and, in minor part, by the soil biogenic activity whose mean CO2 flux (4 g m−2 d−1) is here estimated for the first time. The total amount of hydrothermal CO2 reaches 92 ± 8 t/d, a value that is slightly higher than that estimated with the same method between 1999 and 2001 (74 ± 7 t/d). The gas is emitted by different diffuse degassing structures (DDSs), including volcanic-hydrothermal structures (craters and domes) and NE-SW and NW-SE-trending tectonic lineaments.Even if the total CO2 emission is not particularly high at Nisyros (close to the median of CO2 emissions measured in volcanoes worldwide), the process is very energetic. The thermal energy associated with the shallow condensation of the steam in the DDSs reaches ~60 MW, while we estimate at 134–270 MW the total amount of thermal energy involved in the convective rising of the deep geothermal liquids that transport the gas from the depth toward the surface. This large flux of energy could dramatically increase during future earthquakes by addition of heat and mass from a deep hydrothermal reservoir, potentially triggering hydrothermal explosions, as it happened several times in the past few centuries.

Performance maximization of a solar aided power generation (SAPG) plant with a direct air-cooled condenser in power-boosting mode

Solar aided (coal-fired) power generation (SAPG) technology has been approved to be an efficient way to use solar energy for power generation. However, most solar-rich areas are often short of cooling water supply, especially in China. The air-cooled condenser could alleviate this issue effectively for power plants in these areas. In this paper, a solar aided power generation with direct air-cool condenser (SAPG + ACC) plant is studied and optimized to maximize its performance. Due to the addition of solar heat in an SAPG plant, the exhaust steam flow rate leaving the turbine changes, especially in power-boost mode, which affects the turbine exit pressure and deviates the condenser from its designed operating condition. To achieve maximum net power output, the correlation among the optimum (turbine) exit pressure (OEP), the solar heat input and the ambient temperature, is obtained in this study. The annual plant's performances with four proposed operating strategies of the air-cooled condenser are compared and analyzed. The results show that for an SAPG + ACC plant, the operating Strategy.3, i.e. operated with the hourly OEP is the optimal one, resulting the plant has annual solar-to-electricity efficiency (SEE) of 17.82% and its levelized cost of electricity (LCOE) is of 0.09 $/kWh.

Enthalpies of Hydrate Formation from Hydrate Formers Dissolved in Water

The international interest in the energy potential related to the huge amounts of methane trapped in the form of hydrates is rapidly increasing. Unlike conventional hydrocarbon sources these natural gas hydrate deposits are widely spread around the world. This includes countries which have limited or no conventional hydrocarbon sources, like for instance Japan. A variety of possible production methods have been proposed during the latest four decades. The pressure reduction method has been dominant in terms of research efforts and associated investments in large scale pilot test studies. Common to any feasible method for producing methane from hydrates is the need for transfer of heat. In the pressure reduction method necessary heat is normally expected to be supplied from the surrounding formation. It still remain, however, unverified whether the capacity, and heat transport capabilities of surrounding formation, will be sufficient to supply enough heat for a commercial production based on reduction in pressure. Adding heat is very costly. Addition of limited heat in critical areas (regions of potential freezing down) might be economically feasible. This requires knowledge about enthalpies of hydrate dissociation under various conditions of temperature and pressure. When hydrate is present in the pores then it is the most stable phase for water. Hydrate can then grow in the concentration range in between liquid controlled solubility concentrations, and the minimum concentration of hydrate in water needed to keep the hydrate stable. Every concentration in that range off concentrations results unique free energy and enthalpy of the formed hydrate. Similarly for hydrate dissociation towards water containing less hydrate former than the stability limit. Every outside liquid water concentration results in unique enthalpy changes for hydrate dissociation. There are presently no other available calculation approaches for enthalpy changes related to these hydrate phase transitions. The interest of using CO2 for safe storage in the form of hydrate, and associated CH4 release, is also increasing. The only feasible mechanism in this method involves the formation of new CO2 hydrate, and associated release of heat which assist in dissociating the in situ CH4 hydrate. Very limited experimental data is available for heats of formation (and dissociation), even for CH4. And most experimental data are incomplete in the sense that associated water/hydrate former rate are often missing or guessed. Thermodynamic conditions are frequently not precisely defined. Although measured hydrate equilibrium pressure versus temperature curves can be used there is still a need for additional models for volume changes, and ways to find other information needed. In this work we propose a simple and fairly direct scheme of calculating enthalpies of formation and dissociation using residual thermodynamics. This is feasible since also hydrate can be described by residual thermodynamics though molecular dynamics simulations. The concept is derived and explained in detail and also compared to experimental data. For enthalpy changes related to hydrate formation from water and dissolved hydrate formers we have not found experimental data to compare with. To our knowledge there are no other alternative methods available for calculating enthalpy changes for these types of hydrate phase transitions. And there are no limits in the theory for which hydrate phase transitions that can be described as long as chemical potentials for water and hydrate formers in the relevant phases are available from theoretical modeling and/or experimental information.

Thermal energy analysis on liquid desiccant air conditioning system at different desiccant solution parameters

Selection of suitable liquid desiccant operating parameters plays a significant role in the design of energy efficient liquid desiccant air conditioning system. To achieve same dehumidification rate from ambient air, different combinations of solution parameters (heat capacity ratio, concentration, and vapor pressure) could be employed in the system. Considering dehumidifier air inlet condition and dehumidification rates are fixed, an analytical study is carried out on the thermal energy analysis of the system at different solution operating parameters. Operating parameters considered in this study are solution concentrations ( Cs = 0.25, 0.3, 0.35 and 0.40) and heat capacity ratios ([Formula: see text] = 2.5, 3, 4 and 5). Control volume which includes a pair of air and solution channels (half width channels) of full scale liquid-to-air membrane energy exchangers (LAMEE) has been chosen to analyze the energy transfer between air and solution. The results indicate system requires lesser chiller load ( Qchiller) at high concentration and low heat capacity ratio ( Cs = 0.40 and [Formula: see text] = 2.5) which is 0.29 kW to achieve 0.61 kW cooling load. This is 99% lesser than the Qchiller at high concentration and high heat capacity ratio ( Cs = 0.40 and [Formula: see text] = 5) and 30% lesser than the Qchiller at low concentration and low heat capacity ratio ( Cs = 0.25 and [Formula: see text] = 2.5). Solution heat addition rate ( Qadd) per kW cooling capacity ( Qcc) at this solution condition is found as 0.85 kW.

Experimental Study of Operating Conditions and Integration of Thermoelectric Materials in Facade Systems

This article discusses the application of thermoelectric (TE) materials in building facade systems, which can be used to create active exterior enclosures. TEs are semiconductors that have the ability to produce a temperature gradient when electricity is applied, exploiting the Peltier effect, or to generate a voltage when exposed to a temperature gradient, utilizing the Seebeck effect. TEs can be used for heating, cooling, or electricity generation. In this research, heating and cooling applications of these novel systems were explored. We designed and constructed two prototypes, where one prototype was used to study integration of TE modules (TEMs) as stand-alone elements in the facade, and one prototype was used to explore integration of TEMs and heat sinks in facade assemblies. Both prototypes were tested for heating and cooling potential, using a thermal chamber to represent four different exterior environmental conditions (-18°C, -1°C, 16°C and 32°C). The interior ambient conditions were kept constant at room temperature. The supplied voltage to facade-integrated TEMs varied from 1 to 8 V. We measured temperature outputs of TEMs for all investigated thermal conditions using thermal imaging, which are discussed in this article. The results indicate that while stand-alone facade-integrated TEMs are not stable, addition of heat sinks improves their performance drastically. Facade-integrated TEMs with heatsinks showed that they would operate well in heating and cooling modes under varying exterior environmental conditions.

Supersonic combustion of hydrogen using an improved strut injection scheme

Numerical investigation of mixing is performed at Mach 2.0 model Scramjet combustor employing parallel strut injection schemes for fuel. In the present investigation, basic strut injector is modified in such a way to produce additional vortices in streamwise direction and improve fuel-air mixing. Air is injected at Mach 2.0 at the combustor inlet and fuel is injected at sonic speed from the blunt end of the strut. The flow field involving high-speed turbulent mixing and heat addition was modeled by three-dimensional Reynolds averaged Navier-Stokes equations. A realizable k-ε model was chosen to close the turbulence problem with the default model constants. Non-premixed combustion of hydrogen and air is modeled using the mixture fraction β-pdf framework. Turbulence-chemistry interactions are handled by a strained flamelet model. Comparisons of numerical results with experimental results have demonstrated the accuracy and applicability of computational grid and a numerical scheme for hot and cold flow solutions. The shock-shear layer interaction present within the combustor increases the local turbulent intensity and has a positive effect on mixing. The mixing efficiency obtained with improved strut injector is compared with the basic strut. Improved strut injection scheme showed a mixing efficiency of >95% with a 45% reduction in length. Further combustion efficiency is calculated in the streamwise direction and plot follows the similar trend as the mixing efficiency. The proposed modification of strut geometry showed improved mixing and combustion performance.

A preliminary experimental study on a lab-scale Linear Joule Engine prototype

Abstract A lab-scale prototype of Linear Joule Engine has been developed with the optimized design parameters from previous studies. The Linear Joule Engine applies free-pistons in double acting cylinders and Joule Cycle with an external combustor or heater as heat addition component in the cycle. It offers an alternative prime mover technology using different low carbon or zero carbon fuels, e.g. hydrogen, bio-methanol, ammonia, etc. in the energy transition period. A series of preliminary experiments was conducted to reveal the relationships between moving mass, valve timing, supply pressure and dynamic equilibrium. The experiment results were also used to provide guidance on the prototype design of linear alternator and heat addition component. A scaled-up and modularized Linear Joule Engine system integrated with linear alternator would have an exciting potential to be used as ship main engine, range extender of hybrid vehicles, etc.

Effective efficiency and power density analysis for WiDE as a fuel in diesel engine performance

AbstractA comparative theoretical performance analysis for diesel, 5% water in diesel emulsion (WiDE), and 10% WiDE as fuels in a single‐cylinder diesel engine is presented here. Variations in engine performance parameters such as effective power density (EPD), effective power (EP), and effective efficiency (EE), along with compression ratio and equivalence ratio, have been analyzed on the basis of isobaric heat addition and isochoric heat rejection assumptions. Also, friction loss, exhaust loss, and total loss occurring in engines with the above‐mentioned fuels have been discussed. Theoretical analysis revealed that in a diesel engine with compression ratio 18, the EP and power density increased by 28.6% and 30.45%, respectively, for diesel fuel compared with 10% WiDE fuel. The optimum cycle temperature ratio, EP, and power density were obtained with an equivalence ratio of 1.2 and the optimum EE with an equivalence ratio of 0.89 for diesel, 5% WiDE, and 10% WiDE fuels. However, the maximum exhaust loss and the minimum incomplete combustion losses were obtained with an equivalence ratio of 1.2 and 0.8, respectively. At an equivalence ratio of 1.2, diesel fuel had a higher exhaust loss of 9.25% and 27.21% and heat loss of 5.39% and 11.8%, respectively, compared with 5% WiDE and 10% WiDE fuels. Thus, the fuel consumption rate with diesel as fuel was higher, followed by 5% WiDE and 10% WiDE fuels for diesel engine performance.

Unsteady two-dimensional analytical model for a thermal time-of-flight flow sensor

A thermal time-of-flight sensor consists of a resistive element that periodically delivers heat to a flow and two downstream thermocouples that detect the temperature change due to this heat addition. This study presents an analytical solution to the two-dimensional advection diffusion equation in cylindrical coordinates for an axially semi-infinite domain subjected to a time-dependent Neumann boundary condition. The results describe the propagation of heat in the thermal time-of-flight sensor. The finite Hankel transformation and the generalized integral technique are used to solve the governing equation. The analytical temperature profile shows dependence on the Peclet number and on the tube diameter. The derived temperature distribution is compared with measured data from an experimental setup using R134a as the working fluid. The model demonstrates good agreement with the experimental data, with an average relative error of <9%.

Inert and Reactive Oxide Particles for High-Temperature Thermal Energy Capture and Storage for Concentrating Solar Power

Oxide particles have potential as robust heat transfer and thermal energy storage (TES) media for concentrating solar power (CSP). Particles of low-cost, inert oxides such as alumina and/or silica offer an effective, noncorrosive means of storing sensible energy at temperatures above 1000 °C. However, for TES subsystems coupled to high-efficiency, supercritical-CO2 cycles with low temperature differences for heat addition, the limited specific TES (in kJ kg−1) of inert oxides requires large mass flow rates for capture and total mass for storage. Alternatively, reactive oxides may provide higher specific energy storage (approaching 2 or more times the inert oxides) through adding endothermic reduction. Chemical energy storage through reduction can benefit from low oxygen partial pressures (PO2) sweep-gas flows that add complexity, cost, and balance of plant loads to the TES subsystem. This paper compares reactive oxides, with a focus on Sr-doped CaMnO3–δ perovskites, to low-cost alumina-silica particles for energy capture and storage media in CSP applications. For solar energy capture, an indirect particle receiver based on a narrow-channel, counterflow fluidized bed provides a framework for comparing the inert and reactive particles as a heat transfer media. Low-PO2 sweep gas flows for promoting reduction impact the techno-economic viability of TES subsystems based on reactive perovskites relative to those using inert oxide particles. This paper provides insights as to when reactive perovskites may be advantageous for TES subsystems in next-generation CSP plants.

The relationship of sea level changes to climatic change in northeast Asia and northern North America during the last 75 ka B.P.

The Arctic air mass is the cold, dry body of air slowly moving eastwards around the North Pole in the northern hemisphere. Its southern boundary consists of four planetary waves known as the Rossby waves that mark the interface with subtropical air bringing heat polewards. The Arctic air mass is constantly being modified by the addition of heat and moisture over the oceans, as well as by winter cooling over the land masses due to limited incoming solar radiation and constant reradiation of heat into the atmosphere. The coldest air in winter is located over northeastern Siberia and moves east, cooling Canada. Warm ocean currents add large quantities of heat to the air mass moving over them, but without this addition of heat, the Arctic air mass becomes significantly colder. Research in Tibet and Northeast Asia on depression of sea level shows that during the Late Wisconsin cold event (65–10 ka B.P.), vast quantities of sea water were sequestered on land primarily as ice sheets, exposing the sea bed in the Bering Strait from 50–10 ka B.P. together with the bottom of the South China Sea between 30–20 ka B.P.. The East China Monsoon failed to reach Tibet and much of Northeast China, resulting in severe cooling of northeast Siberia and northern Tibet. This, in turn, caused severe cooling in eastern Canada together with the development of a vast, predominantly cold-based ice sheet. As the sea levels started to rise (about 19 ka B.P.), the East China Monsoon slowly redeveloped and a gradual warming took place on both continents. However, along the west side of the North American Cordillera, the Late Wisconsin glaciation only began in 29 ka B.P. but continued along the west coast until about 10 ka B.P. This paper explores the relationship of the Late Wisconsin history on the two continents, together with the mechanisms causing the landforms and climatic differences. Finally, the probable effects of these climatic changes on the early peopling of North America are discussed.

Analysis of microstructure in AlSi7Mg0.3 cast alloy with different content of Fe.

Abstract The use of recycled alloys brings potential energy savings, and generates less CO2 emission compared to primary aluminum production, but it is necessary to take into account their specifics properties. The properties of the secondary aluminum alloys are comparable to primary alloys, but important attention must be paid due to the higher iron content. Iron with the presence of other elements in the alloy creates intermetallic compounds which have negative influence especially on the mechanical properties. It is impossible to remove iron from melt by standard operations. Some elements eliminates iron by changing iron intermetallic phase morphology, decreasing its extent and by improving alloy properties. Therefore, the effects of different content of Iron (Fe) on the microstructure and the morphology of the intermetallic iron phases of AlSi7Mg0.3 alloy casted in to the sand molds were investigated. For influencing their morphology formation the heat treatment T6 (according standards) and addition of Manganese (Mn) were used in some bars. 2D and 3D metallographic and image analysis have been performed to measure the microstructural changes occurring at different Fe, Mn levels and heat treatment conditions. The study confirms that T6 have influence on to size of Fe-rich phases (especially in needles form), but the increasing length of Fe-needles intermetallic phases with increasing content of Fe did not by confirmed.

Tragic Aftermath of Californian Jungle Fire and Hawaiian Volcano Outburst, a Warning about Persistently Rising Global Warming, Resulting into High Rated Disaster’s Chain

Earthglobe is almost at flash point with respect to global heat contents and temperature and any sizeable further addition of heat to its environment will result into huge disaster of life, property and infrastructure at multiple locations on the globe. The recent example of this is the aftermath of Cali-fornian forest fires (2017-2018) and Hawaii volcano eruption as elaborated in this treatise. This has resulted into 7 main catastrophic events over the Earth globe in its first round, while in 2nd round, all the previous same 7 or similar event in the same or an area close to it are repeated with one more event added in the list. These wildfires add large quantity of heat directly to the globe and even more through abstraction of out going global heat radiation by their generated green house gasses, pollution and soot. The 2nd round is perhaps also supported by Hawaii volcanic eruption. The 3rd round has mainly completed and few expected events are yet in pipe line, but California jungle fire of November 2018 has strengthened its attacks again. The mechanics and tracks of its attacks with pulled in of its allies has been elaborated in this work with role of this wildfire and its all children; heat, soot, pollution and green house gasses in possible boast of global heat contents and temperature. It is observed that disastrous aftermath from all such heating events in the north are contained mainly in Northern Hemisphere, while contrary to this; some of such events in the south have hard strikes on the North. It is requested that Global heat contents rise, jungle fire and volcanic eruptions must be completely stopped by all means because this causes widespread disaster mainly over the tropical regions of Globe as experienced from Californian Jungle Fire.

Effects of heat treatment and addition of small amounts of Cu and Mg on the microstructure and mechanical properties of Al-Si-Cu and Al-Si-Mg cast alloys

The present study investigates the effects of heat treatment on the microstructures and mechanical properties of Al-Si-Cu and Al-Si-Mg alloys containing small amounts of added copper and magnesium, with the aim of obtaining the maximum alloy hardness via the adjustment of the solution heat treatment and aging. The solution heat treatment was performed at 500 °C and 525 °C for the Al-Si-Cu alloy and at 525 °C for the Al-Si-Mg alloy. The samples of both alloys were solution treated for various times between 5 min and 16 h, followed by quenching and finally an artificial aging was performed at 210 °C for a time ranging from 10 min to 50 h. The microstructures of the as-cast alloys and heat-treated samples were studied using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and hardness tests. The results show that the solution treatment time significantly affects the coarseness of the microstructure, causes the dissolution of the intermetallic phases, and homogenizes the distribution of copper and magnesium in the matrix. The peak-aged Al-Si-Cu alloy was obtained after a solution heat treatment at 525 °C for 15 min followed by 2 h of aging. The peak-aged Al-Si-Mg alloy was obtained after 8 h of solution heat treatment at 525 °C followed by 40 min of aging. The Al-Si-Mg alloy with the 0.6 wt% Mg addition displayed an age-hardening response that was approximately 34% higher than that of the Al-Si-Cu alloy with a 0.3 wt% Cu addition.

Design and operating considerations for a shell-and-plate, moving packed-bed, particle-to-sCO2 heat exchanger

An efficient modeling methodology for simulating moving packed-bed heat exchangers for the application of particle-to-sCO2 heat transfer in next-generation concentrating solar power (CSP) plants is presented. Moving packed-bed heat exchangers have application to power-cycle heat addition for particle-based CSP plants and indirect energy storage for direct sCO2 CSP receivers. Further development of moving packed-bed heat exchangers for application to commercial CSP systems requires numerical simulation tools for the design and evaluation of particle-to-sCO2 heat transfer. In this paper, a steady-state reduced-order model of a shell-and-plate moving packed-bed heat exchanger is presented and used to investigate design considerations and performance limitations. The model appropriately captures the flow configuration of a multi-bank shell-and-plate design where the local cross-flow and global counter-flow configurations are addressed. This allows for the design tradeoffs in heat exchanger geometry and particle properties to be explored on the heat exchanger conductance and sCO2 pressure drop. Overall heat transfer coefficients for the particle-to-sCO2 heat exchanger at CSP operating temperature (500–800 °C) can approach 400 W m−2 K−1 using particle channel dimensions of 4 mm with particle diameters of 200 µm. The sensitivity of particle thermophysical properties was also explored to identify important parameters for improving the overall heat transfer coefficient that can be leveraged in the development of alternative particles. Packed bed void fraction and solid thermal conductivity were identified to be areas for potential improvement of sintered bauxite particles, which could increase the overall heat transfer coefficient by up to 60 W m−2 K−1. To achieve DOE cost targets (<$150 kWt−1) for sCO2 power cycle heat addition, diffusion bonded plates containing sCO2 microchannels must be produced at less than $2400 m−2 for the moving packed-bed heat exchanger to become commercially viable.

Removal of ochratoxin A by a carboxypeptidase and peptides present in liquid cultures ofBacillus subtilis CW14

Ochratoxin A (OTA) is an important mycotoxin that contaminates a variety of agricultural products. The cell-free supernatant ofBacillus subtilis CW14 liquid cultures were reported previously to be capable of removing OTA efficiently. In this work, we examined several substances that are probably involved in this removal of OTA usingin vitro experiments. The strain CW14 culture supernatant that was separated by ultrafiltration showed that the fractions collected at &gt;10 kDa and &lt;3 kDa had a significant ability to reduce OTA (84.9 and 74.8%, respectively) when incubated with 6 μg/ml OTA at 37 °C for 24 h. A putative metalloenzyme was responsible for the activity of the &gt;10-kDa fraction, which was confirmed by the detrimental effects of heat treatments or addition of SDS, proteinase K, or EDTA. Subsequently, a carboxypeptidase (CP) gene that was likely related to the enzymatic conversion of OTA by the &gt;10-kDa fraction was cloned from theB.subtilis CW14 genome, and over-expressed inEscherichia coli. The recombinant CP degraded 71.3% of OTA at 37 °C for 24 h, and ochratoxin α (OTα) was confirmed as a degradation product. From the &lt;3-kDa fraction, some small peptides (1.7 kDa &gt;Mw &gt;0.7 kDa) were purified and decreased OTA by 45.0% under the same conditions, but no product was detected. These peptides were presumed to be capable of binding OTA due to their affinity with the OTA molecule, and the OTA-peptide complexes escaped from the extraction procedures for OTA quantification. These results indicated there was a probable synergistic effect that was involved in removal of OTA by the strain CW14 culture supernatant, which included enzymatic degradation by a CP and physical adsorption by some small peptides.

Numerical study of geometrical effects on the performance of an H-type cylindrical resonant photoacoustic cell

We have numerically studied the geometrical effects on the performance of an H-type cylindrical resonant photoacoustic cell, composed of one resonator and two symmetrical buffer cylinders, by performing simulations on the generation of acoustic waves in the cell. Here, the acoustic response (pressure), resonance frequency and quality factor are calculated for the cell performance, while the lengths and diameters of both resonator and buffer cylinders are considered for the geometrical parameters or dimensions. Our calculation solves linearized forms of the continuity equation, Navier-Stokes equation, energy equation, and equation of state using a finite element method under an assumption that the heat addition due to the laser passage and thus the variations in the velocity, pressure and temperature fields inside the cell are small enough. First, we performed a statistical analysis using a design of experiment method to evaluate the relative impacts of the cell dimensions on the acoustic response. Subsequently, we performed a parametric study to quantify the cell performance with the dimensional variations. Our results, along with the response surface methodology, provide guidance for a systematic design optimization of the cell for the best acoustic response. The approach in this study may be applied to the design of various types of resonant photoacoustic spectroscopy devices.

Study on desiccant solution control strategies for efficient liquid desiccant air conditioning system control performance

Frequent change in ambient conditions requires precise control of the desiccant solution operating parameters to suit the required conditioned space load. Either of the two control strategies shall be adopted for this, which are the dehumidifier solution inlet temperature (DSIT) control strategy and the dehumidifier solution inlet mass flow rate (DSIM) control strategy. This article aims to study the efficient control strategy selection approach for a specific air conditioning application since it leads to energy savings as well as thermal comfort. Initially, the optimum desiccant mass flow rate will be found for the liquid desiccant air conditioning system at peak ambient conditions. And the effect of the control strategies on system performance has been analytically investigated at different ambient conditions. A significant reduction in the solution heat addition rate has been observed with both control strategies with the addition of an air-solution heat exchanger. It has also been seen that the required chiller load is nearly same with both control strategies but a little drop (3%–14.5% variation) was observed with the DSIT strategy at low ambient conditions. However, a considerable drop in solution pumping power due to the significant reduction in solution mass flow rate and its pressure drop with the DSIM strategy suggests that it is an energy-efficient control strategy.

On increasing the thermal mass of a salinity gradient solar pond with external heat addition: A transient study

In salinity gradient solar ponds (SGSPs) solar thermal energy is mainly stored in the lower-convective zone (LCZ) the volume of which defines the thermal mass of storage. The present study explores the provision of increasing the heat storage in a SGSP by increasing the thermal mass of it. It also addresses the method of enhancing the thermal performance of a SGSP by increasing the thermal mass, while adding heat from external sources. Earlier studies have proved that adding external heat to the SGSP for storage enhances the thermal performance of it significantly. This study aims to prove that increasing the thermal mass of storage further increases the energy efficiency of a SGSP when external heat is added to it. A hybrid system of a SGSP coupled with evacuated tube solar collectors (ETSCs) is used in this study. Several parameters like storage temperature in LCZ, heat addition flux and heat addition efficiency of ETSC, instantaneous efficiency of SGSP, heat extraction from SGSP are studied in this paper for different cases of with and without heat addition and with normal and enhanced thermal mass. It is found that increasing thermal mass can significantly enhance the thermal performance and efficiency of a SGSP.