Amount Of Sensible Heat Research Articles

Energy saving potential of latent heat exchanger-integrated dual core energy recovery ventilator

High-efficiency energy recovery ventilators (ERVs) have a significant impact on the conservation of building energy. In particular, the importance of the latent cooling performance of ERV which used in hot, humid climates has been growing. To enhance the latent heat recovery performance of the existing ERVs and attain satisfactory sensible heat recovery performance as well, a dual-core energy recovery ventilation unit combining a hollow fiber membrane-based latent heat exchanger (M-LHX) and a sensible heat exchanger (SHX) was proposed in a previous work. This study evaluated the energy saving potential of the proposed ventilation unit integrated air-conditioning system via a series of building energy simulation. As the reference system, a conventional ERV with a flat-plate membrane enthalpy exchanger was chosen. The M-LHX and SHX in the proposed ventilation unit enable decoupled sensible and latent heat recovery of outdoor air. Energy simulations were conducted for a single-story office building located in South Korea, which is one of the humid regions during the summer. The simulation results showed that the proposed ventilation unit could reduce 15.9, 14.4, and 14.1% of building air-conditioning loads in summer, intermediate season, and winter, respectively, compared with the reference ERV. This is because the proposed ventilation unit provided energy benefits by recovering more latent heat from the M-LHX and comparable amount of sensible heat from the SHX than the reference system. Accordingly, the proposed system presented the annual primary energy savings of 10.6% over the reference system, although the proposed system consumed more fan energy.

Multifunctional microcapsules based on ZnO and n-octadecane: From thermal energy storage to photocatalytic activity

Energy management is one of the most important issues to be addressed in the near future in many fields, one of which is buildings. In this sense, new phase change materials (PCM) are being widely studied for storing energy. Encapsulating PCM is a good way to incorporate these materials into different applications in which energy storage is useful. In this study, microcapsules based on ZnO containing n-octadecane as a phase change material were synthesized and characterized with regard to their structural, morphological and optical properties according to several synthesis parameters, such as the proportion of precursors, stirring rate and ageing time. The microcapsules were characterized using x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and UV–Vis spectroscopy in diffuse reflectance mode. The presence of n-octadecane inside the capsules was confirmed. Their thermal behaviour was analysed by means of differential scanning calorimetry. Heating/cooling cycles were performed, after which the microcapsules presented good stability. Furthermore, the encapsulation efficiency was estimated from melting and crystallization enthalpy values, reaching a value of 23.1%. Moreover, the isobaric specific heat of the microcapsules is higher than that of ZnO, which means that substituting ZnO with microcapsules in buildings leads to an important increase in the amount of sensible heat stored. Finally, the photocatalytic activity of the microcapsules was analysed by studying the photodegradation of Crystal Violet dye. The degradation rate increased when the microcapsules were present, so the photocatalytic activity of the microcapsules was confirmed under UV and visible irradiation, which is of interest because they can be used to remove organic pollutants from buildings.

Climate adaptive optimization of green roofs and natural night ventilation for lifespan energy performance improvement in office buildings

Green roofs and natural night ventilation are highly coupled and complementary techniques to improve building energy efficiency, but previous studies have not fully explored the synergetic benefits of combining two technologies. Furthermore, the traditional method of design optimization using Typical Meteorological Year (TMY) weather data falls short of providing climate-adaptive designs for new buildings that react differently to weather changes, as well as capturing the applicability and uncertainty of yearly weather variations. Therefore, building long-term performance in practice often deviates significantly from its design expectation. To quantitatively assess the energy savings when integrating green roofs and night ventilation (GR-NV) while taking future long-term weather impacts into account, this study proposes a systematic approach that integrates field testing, sensitivity analysis, building energy simulation, and climate adaptive optimization. The proposed approach is validated and demonstrated in an office building in Chongqing, China. The results show that Chongqing's annual mean air temperature in 2050 would climb by 2.4 °C in comparison to that of TMY. With the global warming effects, the annual night ventilation hours and the amount of sensible heat dissipated by NV increased by 78 h (13.2%) and 15.8 MJ/m2 (18.7%) from 1991 to 2050. The choice of plant species in the GR-NV system would also be impacted by global warming. The optimal design alternative based on FMY could reduce annual energy use by up to 5.07 kWh/m2 (12.2%) in new buildings.

Method for estimating change over time of the amount of heat stored in a semi-infinite phase-change material with a broad phase-change-temperature range

In this paper, equations are proposed that can predict the change over time of the amount of heat stored in a semi-infinite phase-change material (PCM) that has a broad phase-change-temperature range and apparent specific heat that can be approximated by a Gaussian distribution. The proposed equations can be applied under the condition that the initial temperature distribution is uniform below Tc-3σ and the surface temperature is maintained warmer than Tc+3σ. Here, Tc is the central temperature of the apparent specific heat when the apparent specific heat is approximated by a Gaussian distribution and σ is the standard deviation. The change over time of the amount of sensible heat in the semi-infinite PCM is approximately expressed using equations obtained by integrating the temperature distributions. In addition, the distribution of the latent heat is approximated from the temperature distribution, and the change over time of the amount of latent heat in the semi-infinite PCM is derived by integrating the distribution of the latent heat. Therefore, the change over time of the total amount of heat in a semi-infinite PCM is expressed as the sum of the change over time of the amounts of sensible heat and latent heat in the semi-infinite PCM.

A robust physics-based model framework of the dew point evaporative cooler: From fundamentals to applications

Owing to its great energy efficiency, dew point evaporative cooling is an ideal solution for cooling of electronics, data centers and electric vehicles, where a large amount of sensible heat is generated. To promote the application of dew point evaporative coolers, a common research gap between theoretical and experimental studies is addressed, i.e., how fundamental understanding can be turned into practical applications? In this paper, a coupled scaling and regression analysis is proposed as the key approach to linking the physics-based model to fast data-driven optimization. Accordingly, a complete model framework is developed for the dew point evaporative cooler by establishing a core regression model with its governing dimensionless numbers. The model is integrated with a robust multi-objective optimization algorithm for real applications. Instant predictions of product air temperature and maximum pressure drop can be obtained from the regression model, while it still retains some physical insights into how the cooling performance is affected by the dominant factors. A few optimization studies are carried out to navigate the optimal design and control strategies of the dew point evaporative cooler under assorted ambient conditions. It is noted that the regression model can accurately predict the experimental data of two coolers within ± 5.0% maximum discrepancy, and subsequent optimization suggests improved cooler designs with 30%–60% enhancement in energy efficiency, compared to an existing cooler prototype.

Systematic Mass and Energy Evaluation of Biomass Staged Gasification System Based on Thermodynamic and Kinetic Equilibrium Approaches

In this work, a typical three-staged gasification system was studied using Aspen Plus. Two models, namely thermodynamic and kinetic equilibrium models were built and compared. Results show that the kinetic equilibrium model could predict the syngas yield quite accurately than thermodynamic equilibrium model. Pyrolysis stage and reduction stage were endothermic, while the partial oxidation stage was exothermic. The heat load of pyrolysis and reduction stage was -17.632kW and -14.368kW. The oxidation of volatiles released large amount of heat and formed high temperature zone around 1100°C. The hot flue gas contained large amount of sensible heat that provide the heat for pyrolsis and reduction stage. Based on the energy balance calcualtion, autothermal operation could be achieved for this three-staged gasification. And extra heat in hot flue gas could be used for household heat supply. Based on the model, the influence of operation parameters, including reduction temperature, air equivalence ratio, steam flow rate and oxygen concentration on gasification performance was investigated.

Numerical simulation of the melting of a NePCM for cooling of electronic components

In this paper, a numerical study is carried out to investigate the melting process of a nano-enhanced phase change material (NePCM) in a latent heat thermal energy storage unit (LHTESU) with insertion of Cu nanoparticles. The use of such a strategy provides passive cooling of a protruding electronic component attached to a substrate. The governing equations of heat transfer are solved using the enthalpy-porosity technique and the finite volume method based using a personal FORTRAN code. An investigation of the effect of the PCM quantity is carried out taking into account three different values of the characteristic length lo (0.06 m, 0.08 m and 0.10 m) which represents the PCM quantity. The effect of nanoparticle characteristics, including volume fraction and shape factor on melting rate, are also discussed. The results showed that the maximum operating temperature of the electronic component decreases by 2.9 °C with an insertion of a nanoparticles fraction of 0.04 and a characteristic length of 0.08 m. For the same characteristic length, the melting time is 8630 s, 8460 s and 8290 s with nanoparticles fraction of 0.00, 0.02 and 0.04, respectively. With the nanoparticles fraction of 0.04, the amount of sensible heat stored within the PCM increases by 1.3% and the latent heat decreases by 1.1%. In addition, the insertion of nanoparticles with a shape factor of 16.1 reduces the maximum operating temperature of the electronic component by 2.5 °C. Correlations, giving the electronic component maximum working time and the plateau temperature, were developed using the asymptotic computational fluid dynamics technique (ACFD).

Analyzing the applicability of in situ heating methods in the gas production from natural gas hydrate-bearing sediment with field scale numerical study

For natural gas hydrate (NGH) exploitation, the in-situ electrical heating has been proved as a promising production method in laboratory experimental scale. But the results in this scale are difficult to reliably reflect field trials due to limitations in the size of the reactor. So, by TOUGH+HYDRATE software, this paper stimulates hydrate exploitation in field scale by in situ electrical heating. In addition, depressurization is applied as a comparison. Based on the analysis of several parameters like reservoir temperature and hydrate distribution, results show that although a larger heating power can result in a faster move of the decomposition front, the fast free gas production takes a large amount of sensible heat out of the reservoir. Also, the electrical heating effect is limited by the heat conductivity of formation in the field scale, so the heat promoting distance of the heating method is less than 10 m after five years production even with 1000 W/m of electrical heating power. A large amount of heat loss and the shortage of heating injection make the energy efficiency of it decreased significantly with the production time. So, large heating power cannot always remain fast gas and water production rates. Furthermore, the higher heating power does not mean a better exploitation effect. Thus, it is vital to choose a reasonable heating power in the field exploitation. Under the NGH reservoir and production parameters set in this paper, the most optimal electrical heating power should be 500 W/m with comprehensive consideration of gas production rate, NGH front promoting velocity and energy efficiency.

Study of the Cooling Performance of a Mist-Type Regenerative Evaporative Cooler Under Different Feed Water Temperature

In hot and humid climates, evaporative cooler is coupled with desiccant dehumidifier to obtain effective cooling. To realize the M-cycle-based cooler which combines liquid desiccant regeneration and evaporative cooling in a single apparatus, the effect of different feed water temperature on cooling performance is investigated in this paper. It was observed that wetting water film layer of conventional regenerative evaporative cooler (REC) carries a significant amount of sensible heat from the hot water/solution which reduced the wet-bulb effectiveness of the cooler. To enhance its effectiveness, an ultrasonic atomization mist REC was proposed. The influence of different intake conditions on cooling performance was studied and found that mist REC performed better than conventional cooler for higher feed water temperature. The wet-bulb effectiveness of the cooler ranged from 0.56 to 1.15 with maximum cooling capacity of 580[Formula: see text]W, which is comparable to the previous studies. This prototype can be further developed to an ultrasonic liquid desiccant waterless evaporative cooler.

Study on heat transfer of process intensification in moving bed reactor based on the discrete element method

Blast furnace slag is a typical main by-product of iron making and possesses a large amount of sensible heat from the blast furnace, which accounts for nearly 30 % of the total energy consumption of the steel industry. The waste heat recovery is of great significance for energy savings and emissions reduction for the iron and steel industry. The moving bed reactor is the most effective dry waste heat recovery device, and plays a key heat recovery role in industries across the world. Further, achieving higher recovery rates with the moving bed reactor is persistently being pursued. In this study, the flow pattern of the granulated slag and heat transfer were numerically simulated by the discrete element method. The effects of initial granulated slag temperature, number of heat exchange tubes, and tube arrangement in flow and heat transfer are analyzed in detail. The results clearly demonstrate that heat transfer process is intensified as the initial temperature of the slag decreases and the number of heat exchange tube increases. Moreover, when the heat exchange tubes are staggered, the intensified heat transfer effect is more effective.

Convex parameter estimator for grey-box models, applied to characterise heat flows in greenhouses

An algorithm is presented to identify model parameters in grey-box models. The solver is convex, so the global optimum is guaranteed. The method is applied to estimate bulk transfer coefficients in greenhouses from easily monitored data. This model covers the most important processes, such as conduction losses to the environment, heat exchange with neighbouring compartments, heating from the sun and lighting installations, and ventilation losses. Screen positions are also included in the model. Each process is parameterised, so that the specific situation of each greenhouse can be identified. Greenhouse experiments are often repeated in the same greenhouse or performed in parallel. If some model parameters are assumed to remain identical in these experiments, this can be incorporated in the optimiser making it more robust. The estimator is exemplified using measurements from two compartments in a greenhouse; one equipped with LED lighting, the other equipped with HPS lighting. It showed that effective conduction parameters for the greenhouse and screens were similar to values found in literature (5.8 and 5 W m−2 K−1, respectively). The model also predicted that both lighting systems provide the same amount of sensible heat at the height of the plants, despite the HPS system consuming 43% more energy. A vertical temperature measurement confirmed that both lighting systems produced the same amount of heat at the height of the plants. The LED system dispersed heat more evenly over height, while the HPS system heated the upper layers more.

Numerical study on heat transfer and thermal stress of the upper cone membrane wall in radiant syngas cooler

The high temperature syngas induced from the entrained-flow gasifier contains a large amount of sensible heat, which can be efficiently recovered by radiant syngas cooler (RSC). In this work, the membrane wall models of the upper cone section in the RSC are established. The heat transfer characteristics between membrane wall and syngas are explored by numerical simulation under different operating conditions, and the thermal stress distribution on the membrane wall surface is calculated by the fluid-structure coupling method. The results show that the inner surface of the fin is partially overheated and the maximum stress exceeds the allowable stress of the material when there is no protection for the membrane wall. The increase of inlet syngas temperature and flow rate will enhance heat transfer of the upper cone membrane wall, and the effect of the inlet syngas temperature is more obvious. After the application of the silicon carbide refractory, the surface temperature of the membrane wall, especially the temperature of the wide fin parts, is greatly reduced. Moreover, the membrane wall is slightly deformed and warped due to the temperature difference between the two sides of the membrane wall.

24-Hour Microclimate Conditions in Livestock Building

Abstract The size of all sensible heat balance components in livestock building varies in time, because it depends on time-varying weather factors. On the example of two buildings, sensible heat balance was shown on a daily basis. Measurements carried out in winter and spring in two livestock buildings with usable attics included measurements of air temperature and humidity inside and outside, air velocity in ventilation channels, and wind speed. Measuring devices were designed to record the results of measurements at intervals of 300s. During each such time interval, sensible heat losses by ventilation, heat losses by permeation through the barrier construction, and the amount of sensible heat produced by the animals were calculated. The results of measurements were shown in graphs. The study is important for the development of animal livestock building.

Heat recovery process modelling of semi-molten blast furnace slag in a moving bed using XDEM

As a valuable byproduct of the iron-making process, blast furnace slag with temperature up to 1450–1650°C contains a tremendous amount of sensible heat. Dry granulation and waste heat recovery via a moving bed is an attractive alternative to the conventional water quenching method due to energy-savings and the reduction in water consumption. In this study, the extended discrete element method (XDEM) as a numerical simulation method is adopted to investigate the heat transfer characteristics of semi-molten slag particles in a moving bed. The solidification and cooling processes inside the particles are described using one-dimensional (1D) and transient energy conservation equations and the enthalpy method is used to describe the release of latent heat. The result is compared with a case in which the temperature inside the particles is considered to be uniform. The numerical results indicate that the convective and radiative heat transfer rate and the released sensible and latent heat are all higher when the initial semi-molten state of particles is considered, but the waste heat recovery rate of a particle won't make much difference. The results of this research provide a theoretical basis for the accurate industrial simulation of the heat transfer in a moving bed.

The role of sensible heat in a concentrated solar power plant with thermochemical energy storage

Abstract The calcium looping process is one of the most prospective candidates for thermochemical energy storage system owing to its high energy density, widespread availability and low cost. This paper aims to explore the effect of sensible heat on storage efficiency in the system of thermochemical energy storage based on calcium looping process. Three storage efficiencies in the charging process, discharging process, and total system are defined to quantify the role of sensible heat. The obtained results indicate that the maximum storage efficiencies in the charging process, discharging process, and total system are limited by the amount of sensible heat. Their values can be increased by 45.1%, 32.1%, and 61.59% when the sensible heat is taken full advantage in the charging process, discharging process, and total system, as compared to those without sensible heat. In addition, a sensitivity analysis on the amount of sensible heat is also performed, which demonstrates the amount of sensible heat is determined by different operation conditions. A positive effect is observed on the amount of sensible heat from several dominant parameters including reactor size, reaction temperature, molar flow of calcium carbonate and split ratio, except for carbonation pressure and carbon dioxide storage pressure. Besides, the optimal amount of sensible heat is in the range of 15–40% carbon dioxide percentage of the gas phase under the discharging pressure from 3 to 7 bar. These valuable results can deepen our understanding of the importance of heat recovery in the systems of thermochemical energy storage. More importantly, some meaningful descriptors are established to efficiently assess storage efficiencies for all gas-solid systems of thermochemical energy storage with heat recovery.

Sensible heat discharging from pavements with varying thermophysical properties

A large portion of the solar absorption of traditional pavements is discharged as sensible heat to the above air and contributes to the formation of urban heat island. The amount of the sensible heat depends on pavement surface-layer thermophysical properties including thermal conductivity, density, heat capacity, surface’s emissivity, and albedo. To sort out the influences of these factors in order, this study develops a new simplified theoretical formula to estimate the instantaneous sensible heat flux and the daily accumulative sensible heat from pavements with varying thermal properties. Both the theoretical formula and the numerical results reveal that raising the thermal conductivity, density, or heat capacity of the pavement or increasing them simultaneously decreases the sensible heat but the decreasing rate is negligibly small compared to the amount of the sensible heat. A greater amount of pavement-rejecting sensible heat could be reduced by increasing the surface-layer emissivity. But most traditional pavements have a high emissivity of 0.80–0.95 already so there is a tiny space to vary the pavement’s emissivity for curbing the sensible heat. The most effective way to curtailing the pavement-rejected sensible heat is to make the pavement surface highly reflective.

Experimental study of sensible heat storage/retrieval in/from a nanofluid enclosed between concentric annular tubes

In this work, an experimental study has been carried out to quantify an amount of sensible heat storage/recovery in a specific nanofluid (distilled water +Titanium dioxide). The experimental results show, especially, the influence of nanoparticles mass concentration on the heat storage/recovery performance for a fixed mass flow rate (Γ= 300 kg/ℎ) of heat transfer fluid (HTF). This parameter contributes to the improvement of the heat transfer and therefore the enhancement of the sensible heat storage/retrieval.

Novel power generation models integrated supercritical water gasification of coal and parallel partial chemical heat recovery

Supercritical water gasification (SCWG) of coal is a promising clean coal technology. Supercritical water can effectively and cleanly convert coal to hydrogen-rich syngas. Three power generation models integrated SCWG of coal are proposed and compared in this article. The gasification products have a large amount of sensible heat. Efficient use of the sensible heat can improve the model performance. Compared to the models with total and without chemical heat recovery, the model with partial chemical heat recovery has the advantages of much less exhausted energy and relative small amount of fuel coal used to heat the water to the supercritical state. The efficiency of the model with partial chemical heat recovery is higher than that of other models, and increases with increasing coal-water slurry concentration (CWSC). The efficiencies of the models with partial chemical heat recovery, without chemical heat recovery, and with total chemical heat recovery are 46.60%, 37.56%, and 42.17% when CWSC is 11.3%, respectively. The thermal efficiency of the PCHR model is higher than most conventional coal-fired power plants and coal-based IGCC projects.

Performance analysis of temperature swing adsorption for CO2 capture using thermodynamic properties of adsorbed phase

The present work describes the theoretical research frameworks mainly for the thermodynamic properties of adsorbed phase, which is applied in the field of temperature swing adsorption (TSA) for CO2 capture. The heat of adsorption and specific heat capacity of the adsorbed phase are quantitatively analyzed based on the adsorption isotherm data of CO2 on activated carbon at the temperature ranging from 273K to 358K. Employing such thermodynamic properties of adsorbed CO2, the effect of four cyclic parameters on the energy-efficiency performance of 4-step TSA processes is evaluated based on the thermodynamic carbon pump theory including the minimum separation work and the second-law efficiency. The results show that the regeneration heat has been increased with considering adsorbed phase, and the amount of sensible heat for the adsorbed phase accounts for approximately one-sixth to one-fourth of the total thermal energy consumption. However, the corresponding second-law efficiencies just drop 1.43–7.21%. Although the total thermal energy consumption is higher than the traditional absorption technologies, the second-law efficiencies are slightly higher due to lower heating requirements and auxiliary power.

A Lagrangian Climatology of Wintertime Cold Air Outbreaks in the Irminger and Nordic Seas and Their Role in Shaping Air–Sea Heat Fluxes

Understanding the climatological characteristics of marine cold air outbreaks (CAOs) is of critical importance to constrain the processes determining the heat flux forcing of the high-latitude oceans. In this study, a comprehensive multidecadal climatology of wintertime CAO air masses is presented for the Irminger Sea and Nordic seas. To investigate the origin, transport pathways, and thermodynamic evolution of CAO air masses, a novel methodology based on kinematic trajectories is introduced. The major conclusions are as follows: (i) The most intense CAOs occur as a result of Arctic outflows following Greenland’s eastern coast from the Fram Strait southward and west of Novaya Zemlya. Weak CAOs also originate in flow across the SST gradient associated with the Arctic Front separating the Greenland and Iceland Seas from the Norwegian Sea. A substantial fraction of Irminger CAO air masses originate in the Canadian Arctic and overflow southern Greenland. (ii) CAOs account for 60%–80% of the wintertime oceanic heat loss associated with few intense CAOs west of Svalbard and in the Greenland, Iceland, and Barents Seas and frequent weak CAOs in the Norwegian and Irminger Seas. (iii) The amount of sensible heat extracted by CAO air masses is set by their intensity and their pathway over the underlying SST distribution, whereas the amount of latent heat is additionally capped by the SST. (iv) Among all CAO air masses, those in the Greenland and Iceland Seas extract the most sensible heat from the ocean and undergo the most intense diabatic warming. Irminger Sea CAO air masses experience only moderate diabatic warming but pick up more moisture than the other CAO air masses.