Heat Output Rate Research Articles

Experimental investigation of the effects of add-on fan radiators on heat output and indoor air temperature

Conventional panel radiators are widely used to satisfy indoor heating demands thanks to the heat transfer from the radiator by natural convection and radiation. To increase the heat output from an existing radiator without increasing the supply temperature or replacing the radiator with bigger ones, fans can be mounted below the radiator and this installation carries out heat transfer from the radiator by forced convection. The heat output increases and the changes in the rates of heat transfer mechanisms of these radiators, which are called add-on fan radiators, were experimentally investigated under different supply temperature and fan speed conditions. In addition, the effects of add-on fan radiators on the air temperature values in the test room were also examined. The results show that the addition of the fan unit increased the heat output from the radiator considerably. Also, more enhancement was observed at lower supply temperature conditions. It was also concluded that although the rate of heat output by natural convection and radiation decreased in add-on fan radiators, the total heat output from the radiator was higher than the conventional radiators due to the heat output arising from forced convection prevent this decrease.

Experimental Investigation of Absorber Design on the Performance of a Solar Tracking Distillation System

The problem of water scarcity, especially in North Africa and Libya, has been reviewed. A distillation apparatus has been proposed that uses solar energy as a source of unlimited energy. It should be noted that most countries in North Africa to a relatively favourable area between 35° north latitude and 37° south latitude. Because of this, they can rely on sunlight as an unwavering source of fresh water. The setup used in the experiment uses a solar parabolic concentrator, which collects solar radiation and concentrates it on an evaporator. The parabolic reflector increases the amount of incoming solar radiation and its concentration on the evaporator, thereby increasing the heat output and production rate of the solar still, thereby increasing the efficiency of the solar still. The suggested distillation unit-body consists of a parabolic reflector, an evaporator (Tube absorber) which was placed on the focal line of the parabolic reflector, and a pyramidal glass frame that acts as a condenser. Motors and electronics that expose the reflector to the sun's rays throughout the day from sunrise to sunset. The results show that increases in solar intensity, ambient temperature, and evaporation area increase specific productivity. Using the tracking system as an automatic control unit to make the reflector the sun rays all over the day from sunrise to sunset.

Combining a new baseboard radiator with a fan coil system for improving heating performance and reduce energy consumption

AbstractIn the present work, the heating performance of a new system combined with a new modified baseboard radiator and fan coil is investigated. Using longitudinal fins with special geometry and also forced airflow at the end of the system causes that at the lower inlet water temperature compared with the conventional models, higher heat output rate be obtained. The heat output rate of the new modified system is obtained by experimental metrology based on the European Standard No. EN‐442. Temperature and velocity distribution in the room space is done by simulation of the modified system in the Flovent software. Computational fluid dynamics (CFD) results are validated against experimental results and there is a good agreement between them. Also, the energy consumption of the system during the winter season is calculated in TRANSYS software. Experimental results show that the heat output rate of a new modified heating system with inlet water temperature in the range of 45–55°C is on average 4.17 times higher compared with the conventional model. CFD simulation also showed that the combined system provides good thermal comfort conditions. Energy consumption of the new system reduced about 13% compared with conventional models.

Heat production in quiescent cardiac muscle is length, velocity and muscle dependent: Implications for active heat measurement.

What is the central question of this study? Intracellular energetic processes in quiescent cardiac muscle release 'basal' heat; during contraction, a much larger amount of 'active' heat is also produced. Previously, measurement challenges have constrained researchers to assume that basal heat rate remains constant during contraction and shortening. Is this assumption correct? What is the main finding and its importance? We show that basal heat rate is modulated by the extent and velocity of muscle shortening. Their relative contributions are muscle specific. We apply a method with which researchers can now disentangle, for each experiment, changes in basal heat from active heat production, providing more precise measures of the individual energetic processes underlying cardiac muscle contraction. Separating the variations in cardiac basal heat rate from variations in active heat rate is necessary to determine cardiac muscle energy consumption accurately during the performance of active work. By developing a model of cardiac muscle basal heat rate, we aimed to investigate changes in basal heat rate when cardiac muscle performs work. Experiments were conducted on 10 isolated rat cardiac trabeculae subjected to both active (work-loops) and quiescent (length-change and velocity) interventions. Muscle force, length and heat output rate were measured simultaneously in a flow-through work-loop calorimeter. Quiescent muscle characteristics were used to parameterize muscle-specific models of change in basal heat rate, thereby to predict dynamic changes in basal heat rate during active work-loop contraction. Our data showed that the quiescent heat characteristics of cardiac muscle varied between samples, displaying dependence on both the extent and the rate of change in muscle length. We found a moderate correlation between muscle dimensions (cross-sectional area and volume) and the length-dependent basal heat parameter (P=0.0330 and P=0.0242, respectively), but no correlation with the velocity-dependent parameter. These findings lead us to conclude that the heat output of cardiac muscle at quiescence varies with both the extent and the velocity of shortening, to an extent that is muscle specific, and that this variation must be measured and accounted for in each specimen when assessing active energetics.

The effect of using forced airflow on the thermal performance of the skirting board heating system

The heating performance of two new modified hydronic skirting board heating systems with air supply is investigated in the present work. In the modified system indoor airflow is forced through the system. The main aim of the present work is to achieve a system with higher heating efficiency and lower energy consumption than the conventional cases. The heat output rate of the system is evaluated experimentally for different water flow rates and inlet water temperatures based on standard No. En-442. Comparison of the results between the new system and the conventional model with air supply shows that heating performance improved about 40%. Thermal comfort conditions in the room are analyzed numerically according to Fanger’s method. Also to CFD validation, the temperature distribution of the simulation is compared with experimental data and obtained results show that there is a good agreement between them. Based on the obtained results, people dissatisfied (PDD) in the different parts of the room is less than 30%.

Thermal performance and energy saving investigation in a modified baseboard radiator and compare it with conventional heating systems—Experimental and CFD approach

AbstractIn the present work, thermal performance of a new modified baseboard radiator is investigated experimentally based on the European Standard EN‐442. Temperature distribution and thermal comfort conditions of the floor heating system and panel radiator is compared with the present system numerically. To validation of the simulation results, a comparison has been made between the simulation and the experimental obtained results. Comparison shows that there is a good agreement between them. The heat output rate of the new system increased about 46.06% compared with conventional baseboard radiant model and also the baseboard heating system is capable of providing better thermal comfort conditions than two other systems. Energy consumption in three systems is investigated experimentally by smart temperature control mechanism. Results show that energy consumption in the baseboard radiant is 83.03% and 55.96% lower than floor heating system and panel radiator, respectively.

Research on heating performance of heating radiator at low temperature

This paper investigates the heating performance of radiators at low temperature based on the laboratory test data, and studies the deviation of heat output obtained by the standard characteristic formula and the actual laboratory test value. The results show that the deviation between the predicted value and the actual test value is less than 5%, meeting the need of engineering calculation accuracy. According to this result, this paper studies the low-temperature heating performance of various typical types of radiators, and obtains the attenuation rate of heat output at different excess temperatures relative to the heat output under standard conditions. The number correction coefficient table for radiators in the selection period was given by statistical analysis method, which could be directly used by the designer. This paper used the scenario comparison method to study the heating effect of radiator heating and floor radiant heating. A TRNSYS computing platform was built, using an air source heat pump as a heat source, to simulate the heating effect of two indoor heating methods. The results show that under the same heat source condition, the heating effect of the radiator heating after pieces number correction is similar with floor radiant heating, which proves that the result of the radiators number correction at low temperature is reasonable.

Evaluation of the Environmental Sustainability of a Stirling Cycle-Based Heat Pump Using LCA

Heat pumps are increasingly seen as efficient and cost-effective heating systems also in industrial applications. They can drastically reduce the carbon footprint of heating by utilizing waste heat and renewable electricity. Recent research on Stirling cycle-based very high temperature heat pumps is motivated by their promising role in addressing global environmental and energy-related challenges. Evaluating the environmental footprint of a heat pump is not easy, and the impacts of Stirling cycle-based heat pumps, with a relatively high temperature lift have received little attention. In this work, the environmental footprint of a Stirling cycle-based very high temperature heat pump is evaluated using a “cradle to grave” LCA approach. The results for 15 years of use (including manufacturing phase, operation phase, and decommissioning) of a 500-kW heat output rate system are compared with those of natural gas- and oil-fired boilers. It is found that, for the Stirling cycle-based HP, the global warming potential after of 15 years of use is nearly −5000 kg CO2 equivalent. The Stirling cycle-based HP offers an environmental impact reduction of at least 10% up to over 40% in the categories climate change, photochemical ozone formation, and ozone depletion when compared to gas- and oil-fired boilers, respectively.

Performance improvement of solar bakery unit by integrating with metal hydride based solar thermal energy storage reactor

Storage of solar thermal energy is an effective way to overcome the issue of incompatibility between the solar system and its users. This paper proposed a novel perception by integrating a metal hydride based thermochemical energy storage (MH-TES) system with a solar bakery unit (SBU). A numerical simulation was performed by using COMSOL MULTIPHYSIS 5.3a to assess the dynamic behavior of the reactor. The results showed that the high-temperature metal hydride (HTMH) reactor during the discharging process has a high improvement potential rate (0.195 kW), a high exergetic factor (59.97%) and low exergy efficiency (30.25%) as compared to HTMH reactor during the heat charging process. The overall exergy efficiency of the HTMH reactor was estimated as 34.03%. The maximum value of energy output (Qout), exergy output (Exout), gravimetric exergy output rate (GEOR) and gravimetric efficient heat output rate (GEHOR) during discharging period was calculated as 1560 W, 174 W, 7.4 W/kg and 66 W/kg, respectively. The energy efficiency of SBU is improved from 6% to 42.89% by integrating with the MH-TES system. This paper presents a comprehensive approach for thermal analysis of HTMH for the solar bakery system, which contributes to system optimization for efficient solar energy storage.

Thermochemical storage performance of a packed bed of calcium hydroxide composite with a silicon-based ceramic honeycomb support

The thermal decomposition of calcium hydroxide (Ca(OH)2) into calcium oxide (CaO) and water vapor has been suggested as a reversible gas–solid reaction suitable for thermochemical energy storage. This study aims to develop a composite material to enhance the heat transfer in a reaction bed. We focus on a novel material using CaO/Ca(OH)2 and a ceramic honeycomb support composed of silicon carbide and silicon. A laboratory-scale evaluation of the thermochemical storage performance of the composite using honeycomb support has not been sufficiently reported in the literature. In this study, a 100 W-scale packed bed reactor was used to evaluate the performance of the composite. We found that the composite had a volumetric energy density of 0.76 MJ L-bed−1 and exhibited a heat output rate of 1.6 kW L-bed−1 (for the first 5 min at the highest hydration pressure of 85 kPa), which was 1.8 times higher than the heat output rate previously reported for a pure Ca(OH)2 pellet bed. The composite also retained its high reactivity during repetitive reactions. Therefore, it was concluded that the composite using the ceramic honeycomb support is practically more useful for thermochemical energy storage than conventional pure CaO/Ca(OH)2 materials.

Performance of thermochemical energy storage of a packed bed of calcium hydroxide pellets

AbstractThermochemical energy storage (TCES) using reversible gas‐solid reactions is a promising technology owing to the high energy density and capability of long‐term storage. TCES using a calcium oxide/calcium hydroxide/water (CaO/Ca(OH)2/H2O) reaction system has attracted considerable attention because of the low material cost and environmental friendliness of the reactants. Previous experimental studies have focused on the TCES performances of packed beds of calcium oxide/calcium hydroxide powder. However, pelleted materials can be more favorable than powdered materials from a practical viewpoint. The aim of this study is to evaluate the performance of TCES of a packed bed of calcium oxide/calcium hydroxide pellets. In this work, a total of 60 g of calcium hydroxide pellets (diameter of 1.9 mm and length of 2‐10 mm) was evaluated using a 100‐W scale packed bed reactor. The heat storage density of the bed was 1.0 MJ L‐bed−1, and an average heat output rate of 0.71 kW L‐bed−1 was observed for the first 10 minutes under a hydration pressure of 84.6 kPa. The stability of the reaction conversion of the bed was demonstrated during 17 cycles of experiments.

Composite material for high‐temperature thermochemical energy storage using calcium hydroxide and ceramic foam

AbstractThermochemical energy storage using a calcium oxide/calcium hydroxide/water (CaO/Ca(OH)2/H2O) reaction system is a promising technology for thermal energy storage at high‐temperatures (400°C‐600°C). The purpose of this study is to develop a practical composite material by enhancing heat transfer through the reaction bed and mitigating problems of pure CaO/Ca(OH)2 materials, such as formation of centimeter‐scale agglomerates and change in the bulk volume during repetitive reactions. The present study focused on a novel composite material using a silicon carbide/silicon (SiC/Si) foam. In the literature, performance of thermochemical energy storage of the composite using the ceramic foam remains unclear. In this study, we evaluated the performance of the composite material (~63 g) by a 100‐W‐scale packed bed reactor. The volumetric heat output rate (for the first 5 minutes, under maximum hydration pressure) of the composite was 1.3 kW L‐bed−1, which was 1.4 times higher than that previously reported for a bed of pure Ca(OH)2 pellets. The composite material, in which the CaO/Ca(OH)2 samples were subdivided inside pores with a mean diameter of 400 μm, retained high reactivity during cycle reactions, and maintained its bulk volume. Therefore, the composite material developed in this study shows promising application for high‐temperature thermochemical energy storage.

Comparison of heat output and CO<sub>2</sub> respiration to assess soil microbial activity: a case of ultisol soil

Glucose-induced microcalorimetry and carbon dioxide (CO<sub>2</sub>) production are two widely applied methods to assess microbial activity in soil. However, the links among them, microbial communities and soil chemical properties based on large number of soil samples are still not fully understood. Seventy-two soil samples of different land uses were collected from an ultisol soil area in south China. The best correlation between the rate of heat output and the rate of CO<sub>2</sub> respiration occurred in 8–16 h reaction (R<sup>2</sup> = 0.64), followed by 0–8 h (R<sup>2</sup> = 0.50) (P < 0.001). However, the correlations decreased sharply after 16 h. The heat output per biomass unit (Q<sub>T</sub>/MBC) was well correlated with the total phospholipid fatty acids (PLFAs) (R<sup>2</sup> = 0.56) and bacterial PLFAs (R<sup>2</sup> = 0.53) (P < 0.001). In contrast, these links were not apparent between soil respiratory quotient (qCO<sub>2</sub>) and the total PLFAs and microbial communities. Redundancy analysis further confirmed that Q<sub>T</sub>/MBC was a more comprehensive indicator to assess soil microbial activity and soil quality than qCO<sub>2</sub>, showing a good negative correlation to soil organic carbon, total nitrogen (N) and mineral N, and pH. This work is very helpful to better guide the application of calorimetry and CO<sub>2</sub> respiration in assessing microbial activity in soils.

Thermochemical performance of carbon nanotubes based hybrid materials for MgO/H2O/Mg(OH)2 chemical heat pumps

Newly developed hybrid materials made of magnesium hydroxide and carbon nanotubes were proposed as heat storage medium for MgO/H2O/Mg(OH)2 chemical heat pumps. Samples were synthesized by deposition-precipitation method varying the Mg(OH)2 load (32–52wt.%) and the type of carbon nanotubes, pristine or functionalized. The performances of the synthesized materials were evaluated by thermogravimetric analysis, which simulates the chemical heat pump cycle. The presence of the carbonaceous material positively affected the reaction performances, so that the hybrid materials showed improved heat storage/output capacity and faster heat output rate compared to pure Mg(OH)2. The functionalization treatment and a proper Mg(OH)2 load were fundamental to better the dispersibility of Mg(OH)2 into the carbon nanotubes bundles which in turn enhanced the thermochemical performance of the active material, fully exploiting for the first time its maximum potential heat storage capacity, that is ∼1300kJ/kgMg(OH)2, thus bringing the development of this technology to a level closer to its industrial application.

Long-term fertilization of P coupled with N greatly improved microbial activities in a paddy soil ecosystem derived from infertile land

Microcalorimetry was used to study the effects of long-term (20 years) fertilization regimes on microbial activities in a paddy soil in southern China derived from infertile land. Managements of phosphorus fertilizer coupled with nitrogen fertilizer significantly promoted the contents of total and available P, mineral N and microbial biomass C (MBC) (P < 0.05). Both principal component analysis (PCA) of calorimetric indices and metabolic quotient of heat (QT/MBC) showed that fertilization of P coupled with N, P-deficient fertilization and non-fertilized control significantly separated from each other. Redundancy analysis plot showed that rate of heat output (QT/t), peak power (Pmax) and constant of growth rate (k) were significantly correlated with soil total and available P, total and mineral N, which were greatly increased by the P fertilizer coupled with N fertilizer. In contrast, QT/MBC and peak time (tmax) were greatly increased by the P-deficient treatments. In addition, QT/t as a new introduced parameter was negatively correlated well with QT/MBC (R2 = 0.93, P < 0.01). Accordingly, integrating microcalorimetric result analyzed by PCA as well as sensitive indicators of QT/MBC, QT/t and tmax are useful to assess soil microbial activity. The higher QT/t, lower QT/MBC and tmax indicate higher microbial activity and soil quality. In conclusion, long-term fertilization of P coupled with N, especially combined organic fertilizer greatly improved soil fertility and microbial activity; in contrast, deficiency of soil P had lower microbial activity in the paddy soil derived from infertile land.

Recent advances in telemetry for estimating the energy metabolism of wild fishes.

Metabolic rate is a critical factor in animal biology and ecology, providing an objective measure that can be used in attributing a cost to different activities and to assessing what animals do against some optimal behaviour. Ideally, metabolic rate would be estimated directly by measuring heat output but, until recently, this has not been easily tractable with fishes so instead metabolic rate is usually estimated using indirect methods. In the laboratory, oxygen consumption rate is the indirect method most frequently used for estimating metabolic rate, but technical requirements preclude the measurement of either heat output or oxygen consumption rate in free-ranging fishes. There are other field methods for estimating metabolic rate that can be used with mammals and birds but, again, these cannot be used with fishes. Here, the use of electronic devices that record body acceleration in three dimensions (accelerometry) is considered. Accelerometry is a comparatively new telemetric method for assessing energy metabolism in animals. Correlations between dynamic body acceleration (DBA) and oxygen consumption rate demonstrate that this will be a useful proxy for estimating activity-specific energy expenditure from fishes in mesocosm or field studies over extended periods where other methods (e.g. oxygen consumption rate) are not feasible. DBA therefore has potential as a valuable tool for attributing cost to different activities. This could help in gaining a full picture of how fishes make energy-based trade-offs between different levels of activity when faced with conflicting or competing demands arising from increased and combined environmental stressors.

Efficiency improvement of heat storage materials for MgO/H2O/Mg(OH)2 chemical heat pumps

MgO/H2O/Mg(OH)2 chemical heat storage of waste energy from industrial processes is a promising technology in view of a more efficient use and saving of primary energy sources. A new approach was used to develop a hybrid heat storage material made of magnesium hydroxide (Mg(OH)2) and exfoliated graphite (which is used to improve the heat transfer with its high thermal conductivity). Mg(OH)2 nanoplatelets were directly grown on graphite surface via a deposition–precipitation method to increase the compatibility between the two materials. The material thus obtained, named DP-MG, was experimentally tested to determine its heat storage and output capacities. An improvement of the material efficiency was obtained with a higher storage capacity at lower reaction temperature and a higher heat output rate.

Calcium bromide hydration for heat storage systems

AbstractA chemical reaction is a common and simple way to produce heat for a heat storage system. The reaction produces heat energy without the use of electricity or fuel. The goal of this study was to develop a heat storage system for use in automobiles, which is able to provide heat rapidly via a hydration reaction. A heat storage system without an evaporator stores high-density heat and has a high heat output rate since the solid–liquid product that is formed is transferred as a heat medium to the object that requires heat. The exothermic heat produced from the solid–liquid reaction was measured, and the relationship between the equivalence ratio and the reaction heat was evaluated. The heat output and heat recovered by the heat storage system, which comprised a reaction vessel and a heat exchanger, were measured. We selected solid CaBr2 because it was the best metal halide for a hydration reaction and had a high heat yield from the dissolution reaction. With this system, we were able to achieve a heat...

Early-age heat development in GGBS concrete structures

China accounts for approximately half of global steel production and more than 80 Mt of blast-furnace slag is generated every year as a by-product. About 80% of blast-furnace slag is recycled in China and the majority of this is used as an additive in low-grade composite cement or ‘blast-furnace cement’. This paper discusses the technical feasibility of using ground granulated blast-furnace slag (GGBS) in structural concrete for high-value applications in China. The effects of the slag on concrete compressive strengths are investigated experimentally at different curing temperatures. The influence of partial replacement of CEM I with GGBS on the heat development of concrete is investigated through isothermal calorimetry tests. The presence of slag contributes to a reduced heat output rate. The results obtained from the isothermal calorimetry tests are also used to simulate the heat liberation process in suspended concrete slabs using finite-element software. Finite-element modelling results, validated by semi-adiabatic calorimetry tests, indicate that partial replacement of CEM I cement with GGBS contributes to a reduced peak hydration temperature and this has a beneficial effect in hot-weather concreting.

The suitability of a supersulfated cement for nuclear waste immobilisation

Composite cements based on ordinary Portland cement are used in the UK as immobilisation matrices for low and intermediate level nuclear wastes. However, the high pore solution pH causes corrosion of some metallic wastes and undesirable expansive reactions, which has led to alternative cementing systems being examined. We have investigated the physical, chemical and microstructural properties of a supersulfated cement in order to determine its applicability for use in nuclear waste encapsulation. The hardened supersulfated cement paste appeared to have properties desirable for use in producing encapsulation matrices, but the high powder specific surface resulted in a matrix with high porosity. Ettringite and calcium silicate hydrate were the main phases formed in the hardened cement paste and anhydrite was present in excess. The maximum rate of heat output during hydration of the supersulfated cement paste was slightly higher than that of a 9:1 blastfurnace slag:ordinary Portland cement paste commonly used by the UK nuclear waste processing industry, although the total heat output of the supersulfated cement paste was lower. The pH was also significantly lower in the supersulfated cement paste. Aluminium hydroxide was formed on the surface of aluminium metal encapsulated in the cement paste and ettringite was detected between the aluminium hydroxide and the hardened cement paste.