Effect of mass recovery evaporator temperature and condenser temperature on the performance of a solar adsorption-based desalination plant

Water scarcity increases alarmingly as the population increases. Over the years, a number of salt water desalination techniques have been proposed and reached limitations. The requirement of minimum energy is very well satisfied by an adsorption system, since it can operate with low-grade energy and waste heat exhaust from most industries. The first part of this work discusses the effect of condenser and evaporator temperatures on the performance of silica-gel adsorption cycle mathematically. The second part discusses the performance variations due to mass recovery in the two-bed adsorption system mathematically. It was found that the reduction in condenser temperature and increase in the evaporator temperature both increase the fresh water productivity and cooling capacity of a plant. A desalination plant with mass recovery assistance is superior in performance than the conventional plant. Portable water productivity of 8?m³/day/ton is achieved with the condenser temperature of 15°C and the evaporator temperature of 30°C.     

Effect of temperature on the anaerobic thermophilic conversion of volatile fatty acids by dispersed and granular sludge

The effect of temperature on the rate of volatile fatty acid (VFA) conversion by thermophilic methanogenic sludge, cultivated at 55°C, was studied using both batch activity tests and continuous flow experiments. The temperature dependence of acetate conversion in the range between 37–70°C could be described by an Arrhenius derived model when dispersed sludge with a low specific activity was used. For this sludge the optimum acetate conversion rate was found at 65°C. However, the maximum acetate utilization rate was not affected by temperature in the range between 50°C to 65°C when granular sludge with a high specific methanogenic activity was used. Crushing the granules led to a 2 to 3 fold increase in the maximum activity at 60–65°C, indicating that the conversion rate was very likely limited by the diffusion rate of acetate into the granules. Similar results were obtained with butyrate as the substrate. The temperature dependence of the crushed granules was similar to that of the less active dispersed sludge. In contrast, the thermophilic propionate oxidation rate was highest with the intact granular sludge while a similar temperature dependence was found for both the granular and dispersed sludges. The affinity for VFA increased with decreasing temperature. This phenomenon was most pronounced for the granular sludge. The thermophilic treatment of a VFA-mixture in a UASB reactor appeared to be only slightly affected by temperature when moderately low loading rates were applied, i.e. 20 kg COD·m⁻³·d⁻¹. However, temperature had a strong effect applying loading rates of 40–90 kg COD·m⁻³·d⁻¹ accompanied with high effluent VFA concentrations. The results reveal a high thermostability of the thermophilic wastewater treatment process in the range 45–60°C if “high-rate” reactors with a granular sludge bed are used.     

Experiments on rockburst proneness of pre-heated granite at different temperatures: Insights from energy storage,dissipation and surplus

Many underground engineering projects show that rockburst can occur in rocks at great depth and high temperature, and temperature is a critical factor affecting the intensity of rockburst. In general, temperature can affect the energy storage, dissipation, and surplus in rock. To explore the influence of temperature on the energy storage and dissipation characteristics and rockburst proneness, the present study has carried out a range of the uniaxial compression(UC) and single-cyclic loading-unl...     

Experimental Study on Downslope Fire Spread over a Pine Needle Fuel Bed

The downslope fire represents a percentage of wildland fireline while the heat transfer mechanism of this process is poorly understood. In this study, the experiments were carried out in a fuel bed of dead pine needles with the slopes of ??30°, ??20°, ??10° and 0° for 0.4 and 0.8 kg/m² fuel loads. Flame length, flame angle, temperatures over the fuel bed, flow speed at the fuel bed surface, radiation heat flux near the end of the fuel bed were measured. The rate of spread shows a parabolic shape which decreases firstly and then increases from 0° to ??30°. The combustion interface, reconstructed from the temperature histories of two vertical thermocouples, was perpendicular to the fuel bed under all slope conditions for two fuel loads. The measured radiation heat flux is higher at ??30° slope than level ground, which is attributed to higher flame emissivity. A quasi-physical model was developed to describe the heat transfer mechanism of downslope fire spread. The calculation results show that the flame radiation dominated the downslope fire spread process and the combustion zone radiation should not be neglected in the near flame region.     

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.     

Experimental study on adsorption capacity of an activated carbon-based adsorption water chiller

The objective of this study was to evaluate the adsorption capacity of a working pair for an adsorption water chiller. Activated carbon fibre–methanol, activated carbon fibre–ethanol and activated carbon pallet–ethanol were used as an adsorbent–adsorbate pair in this study. The experiment was conducted using a stainless steel adsorber, 110?mm diameter by 150?mm height, filled with adsorbent and transparent plastic evaporator, 100?ml capacity, filled with adsorbate. The experiment was performed by isobaric adsorption in the temperature range of 10–100°C at the evaporator temperature of 20°C (water chiller). An experimental investigation showed that the activated carbon fibre–methanol pair has the highest adsorption capacity (0.44?kg/kg) compared to the activated carbon fibre–ethanol and activated carbon pallet–ethanol pairs. The finding revealed that uniform structure and large surface area of adsorbent as well as low boiling point and large latent heat of adsorbate had highly significant effects on adsorption capacity. The effect of time and adsorber temperature on adsorption capacity is also discussed in this study.     

Engineered geothermal power systems for Singapore

Singapore has a high geothermal gradient (～35°C/km) as evidenced by hot springs (70°C) and high heat flow (estimated to be about 130 mW/m²). In this study, ground water models are presented based on AUTOUGH–2 computer modelling. The models show a freshwater lens up to 4.8 km depth under Singapore's land area, whose temperature increases with depth up to 192°C. Three geothermal prospects are identified: an engineered geothermal system (EGS) in hot, wet granite on the main island; an EGS in hot, wet volcanics or granite on Pulau Tekong and hot sedimentary aquifers (HSAs) in the Jurong Formation, both on and off-shore. Geothermal water at 150°C could be used for electricity generation, industrial process heating and desalination. A cost estimate exercise for a district cooling system (DCS) powered by 90°C geothermal water shows that there are significant economic advantages. A feasibility study is required.     

Transmission Through and Breakage of Multi-Pane Glazing Due to Radiant Exposure

A series of small and large-scale tests were performed to measure the radiant transmission of energy and the window breakage characteristics of seven different multi-plane glazing samples. The samples tested included both double and triple-pane glazing specimens with a laminate interlayer between panes for additional strength. These test series were designed to provide the information necessary to assess the hazard from radiant energy to building occupants and contents due to a large fire in close proximity to a structure with a large amount of exterior windows. For incident heat fluxes 30 kW/m² or lower, the triple-pane glazing samples had a total transmittance less than 10% of the incident heat flux, back-side surface temperatures did not exceed 100°C, and the back-side heat flux did not exceed 4 kW/m². For double-pane laminates, the total transmittance was less than 25% of the incident heat flux, the back-side temperature did not exceed 220°C, and the back-side heat flux did not exceed 5 kW/m². For incident heat fluxes greater than 30 kW/m², the glazing samples degraded very quickly, generally buckling and losing integrity. The time for the first pane to crack decreased with increasing incident flux level. A number of tests included a water deluge system, which served to maintain sample integrity for extended exposures. In these cases, the total transmittance was less than 6% of the incident heat flux, back-side surface temperatures did not exceed 45°C, and the back-side heat flux did not exceed 1 kW/m².     

Modeling temperature distribution and thermal property of asphalt concrete for laboratory testing applications

Material characterization from laboratory tests on asphalt concrete or predictions of pavement performance are meaningful only if temperature of the material is well taken into account. This paper discusses an analytical model to predict the transient temperature distribution within asphalt concrete and to determine its thermal properties. The paper also presents the laboratory test program designed to validate the model. Temperature measurements were carried out on a cylindrical specimen at different times after the specimen with a steady-state low temperature (3.5 °C) was placed inside an environmental chamber in a steady-state high temperature (36 °C). The temperature magnitude at different positions and its variation with time was recorded at a sampling rate of 1 min⁻¹. The analytical temperature models based on the classical planar wall and long cylinder were established to approximate the temperature distribution of asphalt concrete specimens with the geometry of a short cylinder or a beam. Thermal diffusivity as a function of thermal conductivity and heat convection is solved from the models, and then back-calculation was conducted to achieve the thermal properties using curve fitting. It was found that the analytical model could predict the measured temperatures reliably. For the materials used in this research, a thermal conductivity of 2.88 W/m °C and diffusivity of 1.42 × 10⁻⁶ m²/s were attained from the back-calculation. The time–temperature relationship, as determined from the prediction model, was found to be very sensitive to the geometric size and thermal properties of asphalt concrete.     

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.     

Monitoring the energy-use effects of cool roofs on California commercial buildings

Solar-reflective roofs stay cooler in the sun than solar-absorptive roofs. Such “cool” roofs achieve lower surface temperatures that reduce heat conduction into the building and the building's cooling load. We monitored the effects of cool roofs on energy use and environmental parameters in six California buildings at three different sites: a retail store in Sacramento; an elementary school in San Marcos (near San Diego); and a four-building cold storage facility in Reedley (near Fresno). The latter included a cold storage building, a conditioning and fruit-palletizing area, a conditioned packing area, and two unconditioned packing areas.Results showed that installing a cool roof reduced the daily peak roof surface temperature of each building by 33–42 K. In the retail store building in Sacramento, for the monitored period of 8 August–30 September 2002, the estimated savings in average air conditioning energy use was about 72 Wh/m²/day (52%). On hot days when the afternoon temperature exceeded 38 °C, the measured savings in average peak demand for peak hours (noon–5 p.m.) was about 10 W/m² of conditioned area. In the school building in San Marcos, for the monitored period of 8 July–20 August 2002, the estimated savings in average air conditioning energy use was about 42–48 Wh/m²/day (17–18%). On hot days, when the afternoon temperature exceeded 32 °C, the measured savings in average peak demand for hours 10 a.m.–4 p.m. was about 5 W/m² of conditioned area. In the cold storage facility in Reedley, for the monitored period of 11 July–14 September 2002, and 11 July–18 August 2003, the estimated savings in average chiller energy use was about 57–81 Wh/m²/day (3–4%). On hot days when the afternoon temperature exceeded 38 °C, the measured savings in average peak-period demand (average cooling-power demand during peak demand hours, typically noon–6 p.m.) was about 5–6 W/m² of conditioned area.Using the measured data and calibrated simulations, we estimated savings for similar buildings installing cool roofs in retrofit applications for all 16 California climate zones. For similar retail stores in climate zones 2 and 4–16, installing a cool roof can save about 6–15 kWh/m²/year of conditioned area. In climate zones 2–16, estimates of average peak demand savings for hours noon–5 p.m. range from 2.9 to 5.8 W/m². For similar school buildings in climate zones 2–16, installing a cool roof can save from 3 to 6 kWh/m²/year of conditioned roof area. For all 16 climate zones estimates of average peak demand savings for hours noon–5 p.m. range from 2.6 to 3.8 W/m². In similar cold storage buildings in all 16 climate zones, installing a cool roof can save about 4.5–7.4 kWh/m²/year of conditioned roof area. In all 16 climate zones, estimates of average peak demand savings for hours noon–5 p.m. range from 3.9 to 6.6 W/m².     

Characteristic parameters of a hypocaust construction

Hypocaust, an ancient Roman concept for keeping the inside of buildings warm, has been explained with a survey of a few modern buildings based on these concepts and using solar heat employing a number of design variations. Results expressed in terms of energy requirements per m² of floor area per degree day comes out to be minimum (15.4 kJ m⁻² per DD per annum) for a solar chimney and maximum for solar air collectors (128.4 kJ m⁻² per DD per annum). The basic parameters that determine the performance of a hypocaust construction are size of the cavity determining the heat transfer between the flowing fluid and the building component and the storage capacity of the hypocaust element. The optimum width of the cavity comes out to be between 50 mm and 100 mm. Heat storage capacity of the building element used as hypocaust corresponds to 0.125°K temperature rise per hour in relation to the building heat load.     

Ignition,Heat Release Rate and Suppression of Elastomeric Materials

The focus of this paper is to determine flammability characteristics of rubber materials that are common to vehicle tires, conveyor belts, and electrical power cable insulation and to compare the thermal magnitude of cargo quantities of these materials to other fuels that are publicly transported. Although a literature review was performed, very little data was found on this topic. Standard flammability test procedures were used to measure the critical flux for ignition, critical ignition temperature, and heat release rates (HRR) of rubber compounds common to tire tread materials and conveyor belt covers. Both the intermediate scale calorimeter: ISO 14696, ASTM E-1623 (ICAL) and the cone calorimeter: ISO E-5660, ASTM 1354 (Cone) provided the bulk of the data. Critical ignition flux and vertical flame spread data for rubber based electrical insulations were determined using a radiant panel from a modified ASTM flame spread apparatus: ASTM E-162. thermogravimetric analysis was also used to evaluate thermal decomposition progression of selected test materials. Further, suppression tests were conducted on tire piles to evaluate agents to extinguish and control tire fires. Also, the HRR of the tire piles were measured and compared to work performed by others. Results confirm that the area heat release rate of rubber materials is directly proportional to exposure flux intensity. The critical exposure flux for ignition of a variety of rubber-based materials is approximately 20 kW/m² to 30 kW/m² and the critical temperature for piloted and non-piloted ignition were independent of exposure intensity at ~400°C and ~600°C respectively. In large quantities, rubber tire loads have total HRR comparable to the heat released from similar areas of liquid hydrocarbon spills.     

Performance evaluation of an integrated solar water heater as an option for building energy conservation

Since a majority of residential and industrial building hot water needs are around 50 °C, an integrated solar water heater could provide a bulk source that blends collection and storage into one unit. This paper describes the design, construction and performance test results of one such water-heating device. The test unit has an absorber area of 1.3 m² and can hold 170 l of water, of which extractable volume per day is 100 l. Its performance was evaluated under various typical operating conditions. Every morning at about 7:00 a.m., 100 l of hot water were drawn from the sump and replaced with cold water from the mains. Although, during most of the days, the peak temperatures of water obtained are between 50 and 60 °C, the next morning temperatures were lower at 45–50 °C. Daytime collection efficiencies of about 60% and overall efficiencies of about 40% were obtained. Tests were conducted with and without stratification. Night radiation losses were reduced by use of a screen insulation.     

高原地区太阳能热风采暖系统中岩石床的性能研究

鉴于高原地区自然环境特点,以太阳能热风采暖系统中岩石床为研究对象,建立岩石床的数学模型。从蓄热特性和阻力压降2个方面,模拟分析岩石容积比热容、空气入口温度以及不同海拔高度下空气密度对岩石床性能的影响。结果表明:在一定条件下,海拔每升高1 000 m,空气密度减小约10%,岩石床的平均蓄热功率降低约5%,阻力压降下降约10%,为达到设计的蓄热要求,应增加风机的风量和风压;空气入口温度越低,岩石床阻力压降越大;考虑到蓄热量与热扩散系数两方面因素,建议选取导热系数小,容积比热容大于1 800 k J/(m3·K)的岩石作为蓄热材料。     

Desiccant honey dehydrator

A desiccant honey dehydrator has been designed, developed and tested. It heats and dehumidifies air to dehydrate honey. Re-circulation has been employed to prolong use-period of the desiccant bed. The dehydration was done with dehumidified or ambient air at 35°C and 45°C. The honey was also dehydrated in open for reference purposes. The maximum moisture evaporation rates in the case of a desiccant honey dehydrator using dehumidified air, ambient air and open dehydrating at 45°C were 132, 78.7 and 52?g/h?m², respectively.     

Performance characteristics of a two-stage transcritical N2O refrigeration cycle with vortex tube

ABSTRACT

The thermodynamic analysis has been presented in this article using nitrous oxide as the refrigerant in a two-stage transcritical cycle with the vortex tube (TSTCVT) instead of the expansion valve and its results are compared with the two-stage transcritical cycle with the expansion valve (TSTCEV). The evaporator and the gas cooler temperature ranges in both the cycles have been considered between ?55°C to 5°C and 35°C to 60°C for the analysis. Gas cooler and intercooler pressures are simultaneously optimised to obtain the maximum cooling coefficient of performance (COP). The COP of the TSTCVT improves by 1.97–27.19% in comparison to TSTCEV. A decrease in evaporator temperature and an increase in gas cooler exit temperature reduce the COP of TSTCVT. The comparison of refrigerants N₂O and CO₂ in TSTCVT shows that N₂O exhibits higher cooling COP, higher second law of efficiency and lower optimum gas cooler pressure under the considered operating conditions.     

Fitting conduction transfer function method to low Fourier numbers: application to ground-coupled floors

This paper proposes a practical solution to the problems arising when the conduction transfer function (CTF) method is applied to solve the 1D transient component of heat transfer in the internal zone of ground-coupled floors. The lower boundary condition for these problems must be imposed at a depth of several metres. The proposed method is based on the division of the ground domain into a number of layers that allows calculation of transfer function coefficients while keeping the first cross coefficient negligible. A mathematical expression is proposed for the proper layer thickness that assures the applicability of the CTF method to thick ground domains. A numerical validation for a slab-on-grade configuration has been carried out showing maximum errors of 0.09°C (0.42%) and 0.73?W/m² (2.24%) for temperature and heat flow rates on the floor surface, respectively.     

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.     

Experimental Study on the Combustion Characteristics of Primary Lithium Batteries Fire

The use of lithium batteries requires understanding their fire and explosion hazards. In this paper, a report is given on an experimental study of the combustion characteristics of primary lithium batteries. Burning tests of single and bundles of primary lithium batteries were conducted in a calorimeter to measure their heat release rates when exposed to an irradiance of 20 kW m^?2. Several variables including time to ignition, mass loss, heat release rate and plume temperature were measured to evaluate the ignition and combustion characteristics. The burning batteries were observed to have flame temperatures in excess of 1,200°C and to release corrosive compounds. The experimental results show that the combustion efficiency, carbon dioxide yield and mass loss are proportional to the number of batteries in the bundle. The total heat released by battery bundles was deduced empirically to be proportional to the number of batteries with a power of 1.26. The results provide experimental basis for the development of fire protection measures during the use, storage and distribution of primary lithium batteries.