Experimental study of cooling water pipe circuits by theoretical and numerical analysis in a reactor vault

Our aim is to study the heat transfer processes in a cooling circuit. In this project, a mild steel plate of 1.1 m?×?1.1 m?×?6 mm dimensions is used. Square pipes are embedded in a liner plate, through which the water is circulated to remove heat from the reactor vault. To improve the contact between the pipes and the liner, the pipes are welded to the liner throughout their length. A heater plate simulating main vessel was placed, and the electrical heaters were laid all over the inner surface of main vessel. The square pipes were made to let the water flow through them, and the flow rate is set using a flow meter and this water is heated by convection and it is condensed by passing through a heat exchanger. Thermocouples are fixed at different locations of cooling pipes, the liner and the water inlet/outlet.     

A decade’s (2014–2024) perspective on cassava’s (Manihot esculenta Crantz) contribution to the global hydrogen cyanide load in the environment

In recent years, developing countries have increased their cassava (Manihot esculenta) production for food security. Cassava contains cyanogen glycosides, mainly as linamarin, which through bio-catalysis, i.e. enzyme hydrolysis, results in hydrogen cyanide (HCN). HCN is released into the environment through numerous ways with subsequent volatilisation. Thus, the HCN released during the period 2002–2013 was estimated between 0.025?×?10^?3 to 6.71 ppq (African), 0.012?×?10^?3 to 1.01 ppq (Asian) and 0.007?×?10^?3 to 0.920?×?10^?3 ppq (South American). Furthermore, a decade’s (2014–2024) projection of HCN volatilisation displays increases of 60.5% (Africa), 57.7% (Asia) and 50.5% (South America) when compared with the current production. Furthermore, gas released during cassava plants’ growth, i.e. HCN, NH₃, and NO₂, was quantified in healthy plants. Varying concentrations of HCN were released. These further indicated the presence of a pseudo-halogenic gas in the environment – a contributor to climate change.     

Enhancing heat transfer rate in a car radiator by using Al2O3 nanofluid as a coolant

Conventional fluids such as water, ethylene glycol and mineral oils are normally used as heat transfer fluids. Various techniques are applied to enhance the heat transfer. Heat exchange of the coolant moving through the vehicle radiators is of incredible significance for the advancement of fuel utilisation. In this experiment, the heat transfer performance of the automobile radiator is evaluated experimentally. For this we have taken two different combinations of nanoparticles. Aluminium oxide (Al₂O₃) and magnesium oxide (MgO) nanoparticles are added to the base fluid (80% water?+?20% ethylene glycol) at two concentrations 0.12% and 0.4% volume concentration considering the best pH for longer stability. Similarly, another combination with aluminium oxide (Al₂O₃) and titanium oxide (TiO₂) at the same volume concentrations of 0.12% and 0.4% in the base fluid is also prepared. Furthermore, this increases nanoparticle concentration, air velocity and nanofluid velocity and enhances the overall heat transfer coefficient.     

Innovative low-energy evaporative cooling system for buildings: study of the porous evaporator wall

To face the current increase of building cooling demand and the concerns related to climate changes, an energy-efficient evaporative cooling system using porous material has been developed. This article presents the innovative cooling system and a detailed hygrothermal analysis of its main element: the porous evaporator. A mathematical model and an experimental set-up are presented, which enable to determine the suitable material properties for the evaporator and its impact on the overall cooling system performance, focusing on the optimal use of both energy and water. A good agreement is observed between numerical and experimental results, and the evaporative cooling power is estimated from 12 to 72?W/m² of evaporator wall, depending on the evaporator characteristics. A parametric analysis is conducted to select the best material for the evaporative cooling system. An intrinsic permeability of the material of 4?×?10^?17?m² is recommended for this new cooling system.     

Experimental studies on flow and heat transfer characteristics of secondary refrigerant-based CNT nanofluids for cooling applications

ABSTRACT

The aim of the research work is to explore the convective heat transfer coefficient characteristics of propanol-based nanofluids for cooling applications. The stable suspension of the nanofluid with volume fractions of 0.15 and 0.3 is prepared and characterised. The measurement on the density shows that there is only a negligible increase in the density of the nanofluid and the specific heat of the nanofluid increases with the volumetric concentration of nanofluids. Furthermore, there is an enhancement in the convective heat transfer coefficient of 70% for the nanofluid containing 0.3% of CNT.

Abbreviations: CNT: carbon nanotubes; IPA: isopropyl alcohol; MWCNT: multi-walled carbon nanotubes; SDBS: sodium dodecyl benzene sulphate     

Modified expression of Kozeny–Carman equation based on semilog–sigmoid function

A modified Kozeny–Carman (KC) equation is presented based on a semilog–sigmoid (SS) function of a soil’s particle size distribution (PSD). The KC equation is widely used to estimate soil permeability. However, a more effective use of the equation requires the accurate measurement of the specific surface area of the soil per unit volume. In this study, it is demonstrated that the specific surface area can be derived from the SS function, which simply but accurately represents the soil’s PSD. The modified KC equation is also extended in terms of uniformity and sorting coefficients for its potential use in geotechnical applications. The applicability of the modified KC equation is confirmed through a comparison of the theoretical results of over 50 permeability tests that yielded values ranging from 1?×?10^?5 to 1?×?10^?1?m/s.     

Reliability-based load factors for airblast and structural reliability of reinforced concrete columns for protective structures

Reliability-based design allows the decision-maker to select the level of reliability for a specific explosive blast loading scenario. Important to this is an understanding of airblast and resistance uncertainty. Reliability-based load factors are calculated and are dependent on the variability of model error, explosive mass and range. Reliability-based design load factors (RBDFs) are estimated for explosive ordnance, terrorism, weaponeering and other scenarios. The effect of RBDFs on structural reliabilities for reinforced concrete (RC) columns is then calculated where resistance and loading are random variables, and compared to target values. It was found, for realistic combinations of range and explosive mass variabilities, that RC columns designed to existing standards have a significant margin of safety with a probability of failure of 1?×?10^?3 to 1?×?10^?5. However, if there is large airblast variability, then the application of RBDFs is necessary to ensure that safety levels are acceptable according to international standards.     

Impacts of land use/cover changes on carbon storage in Beijing 1990–2010

According to the data sets of land use/land cover (LULC) in 1990, 1995, 2000, 2005 and 2010, and carbon pools of each LULC category, we estimated the carbon storage of Beijing and each district from 1990 to 2010 by InVEST model. The results indicate that the carbon storage of Beijing ranged from 1.29?×?10⁸ t C to 1.23?×?10⁸ t C over the last 20 years, and decreased 5.6?×?10⁶ t C. The carbon storage is mainly located in suburbs. The cropland turned into construction land causes the continual depletion of carbon storage, which is accompanied by continual urbanization.     

Numerical Simulation of Fire Exposed Façades Using LEPIR II Testing Facility

The fire behavior of external wall insulation system on façades is assessed during LEPIR II testing. This facility involves a 600 kg wood crib fire in a 30 m³ lower compartment of a two levels high concrete structure. External flames develop in front of the façade from the fire compartment through windows with dimensions 1?×?1.5 m (W?×?H). In order to predict the fire exposure of a façade during the test, CFD simulations were carried out with the computational fluid dynamics code Fire Dynamics Simulator (FDS) for two full-scale experiments. The main objective of this study was to evaluate the ability of FDS to reproduce quantitative results in terms of gas temperatures and heat fluxes close to the tested façade. This is an important step before the fire performances of any insulation system can be predicted by numerical tools. A good repeatability was observed in terms of measured gas temperatures for experiments. Maximum heat release rate of the fire, close to 5 MW, was achieved after 5 min of test. When experimental results were compared with numerical calculations, good agreement was found for every quantity. The most critical zone on the facade is located above the fire room and is directly impacted by external flame outgoing from the fire compartment. Temperatures up to 500°C were observed in this zone. For the thermocouples located up to the second level opening, these probes were not located directly in the flames, but rather in the hot gases above the fire plume. The maximum temperature achieved was thus close to 400°C. The proposed model gives correct thermal loads and flames shape near the façade during calibration tests and can be used for further evaluation of combustible material on façade.     

Experimental investigation on adsorption capacity of ACF–methanol pairs for cooling application

Solar cooling technology is very popular among other conventional cooling technologies due to increment in global warming effects. In solar cooling technology, solar-powered adsorption refrigeration system has potential to compete with other non-conventional cooling technologies, that is, Absorption, PV-based, Waste-heat-driven and Biogas cooling. The main objective of this research work was to investigate the adsorption capacity of methanol onto activated carbon fibre in the temperature range of 15–80°C during an isobaric adsorption process. To correlate adsorption characteristics’ data of the experiment, the Dubinin–Astakhov equation is used. From a series of experiments, the maximum adsorption capacity was found to be 0.44?kg/kg of ACF by maintaining packing density of bed at 110?kg/m³. The effect of heat generator temperature on adsorption capacity is also studied in this investigation.     

龙口市浅层地温能潜力评价及经济环境效益分析

浅层地温能作为绿色新能源,近年来在越来越多的地区得到开发与应用,通过对龙口市主城区展开水文地质调查、地温场调查、现场热响应试验及热物性试验等工作,查明了工作区浅层地温能的赋存条件,得到了地埋管型地源热泵的开发利用潜力分区,并通过等效计算获得浅层地温能开发利用经济、环境效益价值。根据调查与计算分析可知:考虑土地利用系数时,(1)工作区地下水换热系统夏季可制冷面积1082.00×10⁴ m²,冬季可供暖688.55×10⁴ m²;地埋管换热系统夏季可制冷面积1573.43×10⁴ m²,冬季可供暖1677.81×10⁴ m²。(2)浅层地温能开发利用总能量为755.79×10⁴ GJ/a,折合标准煤15.06×10⁴ t/a,节煤量43.04×10⁴ t/a,热资源价值10543.51万元/a。(3)可减少排放氮氧化物、二氧化硫、二氧化碳、悬浮质粉尘、生成煤灰碴等总计37.91×10⁴ t/a,节省污染治理费4249.03万元/a。     

Solar stills for production of distilled water

Solar stills have been designed to produce water for use in teaching and research laboratories. Various designs and configurations have been constructed and tested over the past 10 years. The original double-surfaced cascade stills (stills A and B) were constructed in aluminium and were rather expensive. Later models termed Series D and E were of galvanised mild steel with stainless steel distillate drains and safety overflow drains. These galvanised steel units suffered from severe corrosion after a few years of operation. The latest design series F, is built in aluminium with stainless steel distillate drains and automatic feed valves. All of the stills produce very pure distilled water (conductance ～1.5 × 10^?6 Ω^?1 cm^?1; pH 6.8–7.4) at a cost which is below that of conventional electrically heated stills.     

Experimental analysis of thermal performance of evacuated tube solar air collector with phase change material for sunshine and off-sunshine hours

An experimental investigation of an evacuated tube solar air collector coupled to a latent thermal energy store for generating hot air when no solar radiation is incident was undertaken. Acetamide was used as a phase change material (PCM). The latent thermal energy store was integrated with the manifold of the solar collector and water was used as the working fluid transferring solar gain to the air being heated. The maximum measured temperature differential between the heated air and the ambient air was 37°C and 20.2°C during conditions of incident and non-incident solar radiation, respectively. This occurred using a circular fin configuration at a flow rate of 0.018?kg?s^?1. The efficiency at low (0.018?kg?s^?1) air flow rates was 0.05–0.50 times less as compared to high (0.035?kg?s^?1) air flow rates. This system has advantages over systems using sensible storage as it can be used after sunset due to better heat storing capacity of the PCM.     

Suspended timber ground floors: measured heat loss compared with models

ABSTRACT

There are approximately 6.6 million dwellings in the UK built before 1919, predominantly constructed with suspended timber ground floors whose thermal performance has not been extensively investigated. The results are presented from an in-situ heat-flow measuring campaign conducted at 27 locations on a suspended timber ground floor, and the estimated whole-floor U-value compared with modelled results. Findings highlight a significant variability in heat flow, with increased heat loss near the external perimeter. In-situ measured-point U-values ranged from 0.54?±?0.09?Wm^?2 K^?1, when away from the external wall perimeter, to nearly four times as high (2.04?±?0.21?Wm^?2 K^?1) when near the perimeter. The results highlight the fact that observing only a few measurements is likely to bias any attempts to derive a whole-floor U-value, which was estimated to be 1.04?±?0.12?Wm^?2 K^?1 and nearly twice that derived from current models. This raises questions about the validity of using such models in housing stock models to inform retrofit decision-making and space-heating-reduction interventions. If this disparity between models and measurements exists in the wider stock, a reappraisal of the performance of suspended timber ground floors and heat-loss-reduction potential through this element will be required to support the UK’s carbon-emission-reduction targets.     

Predicting the Fire Dynamics of Exposed Timber Surfaces in Compartments Using a Two-Zone Model

There is an increasing desire to use more engineered timber products in buildings, due to the perceived aesthetics of timber and desire for more sustainable architecture. However, there are concerns about fire performance of these products especially in taller buildings. This has led to renewed research to understand the behaviour of timber surfaces in compartments exposed to fire. This paper describes a two-zone calculation model for determining the fire environment within a compartment constructed from timber products where varying amounts of timber are exposed on the walls and ceiling. A set of eight full-scale compartment experiments previously reported in the literature are used to assess the capability of the model. The fire load energy density in the experiments ranged from 92 MJ/m² to 366 MJ/m² comprising either wood cribs or bedroom furniture with the largest compartment having dimensions 4.5?×?3.5?×?2.5 m high with an opening 1.069 m wide?×?2.0 m high. The experiments were ventilation-controlled. It is shown that the model can be used to provide conservative predictions of the fire temperatures for compartments with timber exposed on the walls and/or ceiling as part of an engineering analysis. There are several limitations that are discussed including the need to consider the debonding of layers in the case of cross-laminated timber. It is recommended that further benchmarking of the model be done for different ventilation conditions and with engineered timber products where debonding does not occur. This will test the model under a wider range of conditions than examined in this paper.     

Mobility of Cr(VI) anions in the phase of the amphoteric inorganic ion exchanger

The method of impedance spectroscopy has been used to investigate hydrogel and xerogel of hydrated zirconium dioxide containing Cr(VI) obtained from cation-and anion-substituted forms of an ion exchanger. It is shown that a complex composition of the amphoteric inorganic ion exchanger as well as protonization of its functional groups producing a substantial impact on the value of its electrical conductivity do not make it possible to assess mobility of sorbed ions. Nonetheless, the effective values of internal diffusion mobility of Cr(VI) may be obtained by the kinetic method: diffusion coefficients corresponding to the Cr(VI) → OH constitute 8.57 × 10^?12?6.85 × 10^?11 m²/s or hydrogel and 3.33 × 10^?13?5.45 × 10^?12 m²/s for xerogel depending on the sorbate concentration.     

Contributions from coal and industrial materials to mercury in air,rainwater and snow

The mean mercury level in some British coals was 0.97 (range 0.13–2.28) ppm. Mean values of 0.01–3.3 ppm have been reported for coals elsewhere in the world with maxima up to 300 ppm. Release of mercury from coal used all over the world lies in the range 0.14?2.72 × 10⁹ g yr^?1 depending on mean mercury concentrations in the coal and amount of mercury trapped by precipitators before release from chimney stacks. The amount released from cement manufacture is estimated to be 2.5 × 10⁸ g yr^?1. Iron ores had 0.09 (range 0.02–0.28) ppm, minerals 0.31 (range 0.01–0.73) ppm, the ingredients used in cement contained between 0.03–0.46 ppm, rainwater 16.7 (range 6–30) ng 1^?1, snow 13 (range 4–21) ng 1^?1 and air levels were 18.9 (range 1–66) ng m^?3. Proposals to burn more coal for energy are discussed in relation to (i) the mercury released from it, (ii) the mercury already present in the environment which is constantly being revaporized and redistributed, and (iii) the mercury washed out of the atmosphere into permanent sinks such as marine sediments.     

A comparative performance analysis of solar heat exchangers for solar hot water application under controlled laboratory conditions

The paper presents the experimental performance evaluation of a novel retrofit heat exchanger (‘SolaPlug’) developed for solar hot water storage applications. The performance of this system was compared with a traditional dual-coil (‘Coil’) solar cylinder under controlled operating conditions. The tests were conducted under different solar-simulated conditions with a 30 and 20 evacuated tube collector. The results showed that after a 6-h test period, the average water temperatures within the store for the ‘SolaPlug’ system were 58.8°C and 40.5°C at 860 and 459?W?m^?2, respectively, and for the ‘Coil’ system were 60.5°C and 40.6°C when a 30 tube collector was used. The performance of the ‘SolaPlug’ system was marginally better than the ‘Coil’ system under the low solar input condition. Under high insolation condition, the overall ‘SolaPlug’ system efficiency was found to be 4.3% lower than that of the ‘Coil’ system. The ‘SolaPlug’ heat exchanger rating was 222?W?K^?1.     

Solar cells sensitised by push–pull azo dyes: dependence of photovoltaic performance on electronic structure,geometry and conformation of the sensitizer

Novel Azo dyes possessing varying conjugation lengths and different extents of electron cloud delocalisation were synthesised and characterised and explored as sensitizers for dye-sensitised solar cells (DSSC). The envisaged azo dyes comprising of electron withdrawing and electron-donating moieties which are linked through conjugation bridges of varying lengths facilitated the prevalence of push–pull mechanism in the molecules. Optimisation of the geometry were performed for the synthesised compounds using B3LYP/ 6-31?+?G (d,p) level of density functional theory and their computed optical absorption and band gaps were validated with experimental results. The dyes exhibited molar extinction coefficients in the range of 3.2?×?10⁴ to 4.2?×?10⁴?mol^?1?Lcm^?1. The highest occupied molecular orbital (HOMO) was located between ?5.53 and ?5.03?eV for the various sensitizers synthesised and their lowest unoccupied molecular orbital (LUMO) was located between ?2.86 and ?3.08?eV. HOMO–LUMO gaps were in the range of 2.02–2.67?eV. Fill factor of the cells varied from 28% to 32% and the power conversion efficiencies ranged from 0.4% to 2.7%. This is the first time reporting of a systematic investigation, correlating the influence of nature and position of substituent, extending of conjugation and geometry of sensitizers on the photo physical properties of the sensitizers and the photovoltaic performance of corresponding DSSC.

Highlights

• The article focuses on push–pull azo dyes and were explored as promising candidate sensitizers for low cost dye-sensitised solar cells (DSSC).

• The effect of chemical structure, extend of conjugation and geometry of the sensitizer on the photo physical properties of the sensitizers and the photovoltaic performance of DSSC were analysed.