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Enhancement of energy delivery of a carbon dioxide (CO2) Brayton cycle without compression work liability is achievable using low grade heat for thermal compression. The limitation of the expansion ratios of a single stage adsorption thermal compression is obviated by opting for pressure build up in two stages. Despite the use of a large number of adsorbers, it is shown that, specific work output can be augmented substantially with no undue penalty on the overall cycle efficiency albeit with a marginal shortfall in work output per unit mass of adsorbent. These features are elucidated through an activated carbon based thermal compression of CO2 yet limiting high side pressures to 80 bar and the principal heat source at a temperature equal to or less than 300 degrees C in tandem with another low grade source at 100 degrees C for thermal compression. The net outcome is a substantial reduction in the size of the power block and heat exchangers resulting from enhancement of the expansion ratio and reduction in the mass flow rate in the circuit.

Dynamic performance of a single-stage, two-bed, silica gel + water adsorption chiller operating in Bangalore, India is studied. Driving thermal energy is provided directly by an evacuated tube solar collector field. System dynamics are evaluated in the absence of thermal storage, which causes intra-day fluctuations in heat source and evaporator temperatures, which in turn influence the system performance. These dynamics are demonstrated for representative days in the months of April (summer) and December (winter). The focus is on the effect of variation of the collector area and the adsorption cycle time on the system performance. The maximum temperature of heat transfer fluid (water) is limited to 95 degrees C. The cyclic and daily averages of solar coefficient of performance (DACOPsoi) and cooling capacity (DACC) are used as key performance indicators. One of the key aspects of the this study is to show that both of them can be maximized by suitably choosing the collector area and cycle time. Further, it is demonstrated that the solar driven adsorption chiller described here is ideally suited for cascading with an air-cooled R-134a vapour compression refrigeration system (VCRS). The variable throughput obtained from the solar adsorption chiller can help in liquid sub-cooling and hence to cover the deficit in cooling capacity of the VCRS arising due to high ambient temperature. (C) 2016 Elsevier Ltd. All rights reserved.

After a substantial impact on refrigeration, carbon dioxide (CO2) is gaining considerable attention as a working fluid for thermal power generation. This can be attributed mainly to its excellent heat transfer properties and compactness of components arising from its high density. It has the merit of being amenable to operation in sub-, trans- or super-critical Brayton cycle modes. However, inhibiting factors are high pressures needed when operated in trans- or supercritical cycles and the work of compression eroding most of the work of expansion in sub-critical cycle operation. Some of the lacunae of CO2 such as high work of compression can be alleviated by using non-mechanical means such as thermal compression using the adsorption technique either for partial compression in high pressure Brayton cycles or for total compression in low pressure cycles. CO2 has also been proposed as an additive to flammable hydrocarbons such that their flammability can be suppressed and yet retaining their other desirable thermodynamic qualities. This review explores the potential and limitations of thermodynamic cycles where either CO2 is used alone or as a component in mixture of working fluids. Inter alia, it also highlights the issues of regulation of load management using the efficiency-specific power output plane. When used as a blending component, pinch point in the regenerators affects the cycle performance. The objective is to identify research and developmental challenges involving CO2 as a working fluid specifically for solar power generation. (C) 2016 Elsevier Ltd. All rights reserved.

Solar, thermal power generation by and large uses Rankine cycles with organic working fluids or steam when highly concentrated solar source is used. Brayton cycle is seldom used because the work of compression forms a major fraction of turbine output. We investigate removal of this lacuna by adopting thermal compression using the adsorption route. Here we propose a two source operated cycle with the low temperature source used for thermal compression and the high temperature source to increase the inlet temperature of the working fluid to the turbine. We adopt carbon dioxide as the working fluid in view of its excellent heat transfer properties and environmentally friendly disposition. Activated carbon is used as the adsorbent in the thermal compression process. It is shown that, though the First law thermal efficiency does not show the real merit of the cycle, the exergetic efficiency is substantially high even for low side operating pressures in the range of 15-25 bar. In particular, where the waste heat is available around 100 degrees C and concentrated solar power is available even at 200-300 degrees C, exergetic efficiencies in excess of 25% can be realised. When other advantages such as dispensing with one whole segment of moving parts (compressor) are taken into account, the running costs of such a cycle can be so low that it would be, a viable proposition. However, we appreciate that, large scale use of adsorption compression is associated with huge technological problems for which we propose some remedies. (C) 2016 Elsevier Ltd. All rights reserved.

Several operational aspects for thermal power plants in general are non-intuitive and involve simultaneous optimization of a number of operational parameters. In the case of solar operated power plants, it is even more difficult due to varying heat source temperatures induced by variability in insolation levels. This paper introduces a quantitative methodology for load regulation of a CO2 based Brayton cycle power plant using the `thermal efficiency and specific work output' coordinate system. The analysis shows that a transcritical CO2 cycle offers more flexibility under part load performance than the supercritical cycle in case of non-solar power plants. However, for concentrated solar power, where efficiency is important, supercritical CO2 cycle fares better than transcritical CO2 cycle. A number of empirical equations relating heat source temperature, high side pressure with efficiency and specific work output are proposed which could assist in generating control algorithms. (C) 2015 Elsevier B.V. All rights reserved.

The paper presents a simulation study of loose cylindrically shaped particles packed within a copper plate and aluminum fins. The model presented solves coupled heat and mass transfer equations using the finite volume method based on ANSY S FLUENT medium. Three different arrangements of cylindrical particles are considered. The model is validated with experimental data. It is found that the arrangements which represented monolayer configurations are only marginally better in heat transfer and uptake efficiency than the tri-layer configuration in the presence of fins. However, there is an appreciable difference in the uptake curve between monoand tri-layer configurations in the absence of fins. Finally, it is found that the fin pitch also plays an important role in determining the time constant for the adsorber design.

Collisions at left-turn intersections are among the most prevalent types of serious crashes involving teen drivers, and inadequate surveillance is a key factor. The Risk Awareness and Perception Training (RAPT) program has been shown to be effective in improving anticipation of latent hazards. The goal of this study was to determine whether RAPT Version 3 (RAPT-3) improved the intersection turning behaviors of novice teen drivers when the hazards were not latent and frequent glancing to multiple locations at the intersection was needed. Teens drivers age 16 to 18 years with ≤ 180 days of licensure were randomly assigned to (a) an intervention group that received RAPT-3 training (trained group, n = 18) or (b) a control group that received no training (untrained group, n = 19). Both groups completed the RAPT-3 baseline assessment, and the trained group completed the RAPT-3 training and the RAPT-3 post-assessment. Training effects were evaluated in a driving simulator. Simulator (gap selection errors and collisions) and eye tracker (traffic check errors) metrics from six left-turn stop sign–controlled intersections in the Simulated Driving Assessment (SDA) were analyzed. The trained group scored significantly higher in the RAPT-3 postassessment than in the RAPT-3 baseline assessment (p < .0001). There were no significant differences between the trained and untrained teens in the SDA in either traffic check and gap selection errors or collisions. Although trained teens learned about hazard anticipation related to latent hazards, learning did not translate to performance differences in left-turn stop sign–controlled intersections at which the hazards were not latent. The findings point to a need for further research to better understand teens' challenges with left-turn intersections.

High temperature, high pressure transcritical condensing CO2 cycle (TC-CO2) is compared with transcritical steam (TC-steam) cycle. Performance indicators such as thermal efficiency, volumetric flow rates and entropy generation are used to analyze the power cycle wherein, irreversibilities in turbo-machinery and heat exchangers are taken into account. Although, both cycles yield comparable thermal efficiencies under identical operating conditions, TC-CO2 plant is significantly compact compared to a TC-steam plant. Large specific volume of steam is responsible for a bulky system. It is also found that the performance of a TC-CO2 cycle is less sensitive to source temperature variations, which is an important requirement of a solar thermal system. In addition, issues like wet expansion in turbine and vacuum in condenser are absent in case of a TC-CO2 cycle. External heat addition to working fluid is assumed to take place through a heat transfer fluid (HTF) which receives heat from a solar receiver. A TC-CO2 system receives heat though a single HTF loop, whereas, for TC-steam cycle two HTF loops in series are proposed to avoid high temperature differential between the steam and HTF. (C) 2013 P. Garg. Published by Elsevier Ltd.

Desalination is one of the most traditional processes to generate potable water. With the rise in demand for potable water and paucity of fresh water resources, this process has gained special importance. Conventional thermal desalination processes involves evaporative methods such as multi-stage flash and solar distils, which are found to be energy intensive, whereas reverse osmosis based systems have high operating and maintenance costs. The present work describes the Adsorption Desalination (AD) system, which is an emerging process of thermal desalination cum refrigeration capable of utilizing low grade heat easily obtainable from even non-concentrating type solar collectors. The system employs a combination of flash evaporation and thermal compression to generate cooling and desalinated water. The current study analyses the system dynamics of a 4-bed single stage silica-gel plus water based AD system. A lumped model is developed using conservation of energy and mass coupled with the kinetics of adsorption/desorption process. The constitutive equations for the system components viz. evaporator, adsorber and condenser, are solved and the performance of the system is evaluated for a single stage AD system at various condenser temperatures and cycle times to determine optimum operating conditions required for desalination and cooling. (C) 2013 P. Dutta. Published by Elsevier Ltd.

Supercritical carbon dioxide based Brayton cycle for possible concentrated solar power applications is investigated and compared with trans- and sub-critical operations of the same fluid. Thermal efficiency, specific work output and magnitude of irreversibility generation are used as some of the performance indicators. While the thermal efficiency increases almost linearly with low side pressure in the sub- and trans-critical cycles, it attains a maximum in the supercritical regime at 85 bar after which there are diminishing returns on increasing the low side pressure. It is also found that supercritical cycle is capable of producing power with a thermal efficiency of >30% even at a lower source temperature (820K) and accounting for foreseeable non-idealities albeit with a higher turbine inlet pressure (similar to 300 bar) which is not matched by a conventional sub-critical cycle even with a high source temperature of 978K. The reasons for lower efficiency than in an ideal cycle are extracted from an irreversibility analysis of components, namely, compressor, regenerator, turbine and gas cooler. Low sensitivity to the source temperature and extremely small volumetric flow rates in the supercritical cycle could offset the drawback of high pressures through a compact system.

Low grade thermal energy from sources such as solar, geothermal and industrial waste heat in the temperature range of 380-425 K can be converted to electrical energy with reasonable efficiency using isopentane and R-245fa. While the former is flammable and the latter has considerable global warming potential, their mixture in 0.7/0.3 mole fraction is shown to obviate these disadvantages and yet retain dominant merits of each fluid. A realistic thermodynamic analysis is carried out wherein the possible sources of irreversibilities such as isentropic efficiencies of the expander and the pump and entropy generation in the regenerator, boiler and condenser are accounted for. The performance of the system in the chosen range of heat source temperatures is evaluated. A technique of identifying the required source temperature for a given output of the plant and the maximum operating temperature of the working fluid is developed. This is based on the pinch point occurrence in the boiler and entropy generation in the boiling and superheating regions of the boiler. It is shown that cycle efficiencies of 10-13% can be obtained in the range investigated at an optimal expansion ratio of 7-10. (C) 2012 Elsevier Ltd. All rights reserved.

A two-stage 4-bed/stage silica-gel + water adsorption system is developed for combined cooling and desalination, which adopts air cooled heat rejection obviating the disadvantages of cooling towers. Each stage has four adsorbers: three beds with identical design and one bed having a marginally different design. The present paper describes the design features and constructional details of the various components of this system. The results presented herein focus only on the performance of the identical beds. The start-up transience of various components namely, the evaporator, the adsorber beds and the condenser, is presented in detail. The cyclic steady state characteristics of the adsorption system in 2- and 3-bed modes of operation are compared. Near identical specific throughput from the system is observed irrespective of the mode of operation. (C) 2015 Elsevier Ltd and IIR. All rights reserved.

The heat of adsorption of methane, ethane, carbon dioxide, R-507a and R-134a on several specimens of microporous activated carbons is derived from experimental adsorption data fitted to the Dubinin-Astakhov equation. These adsorption results are compared with literature data obtained from calorimetric measurements and from the pressure-temperature relation during isosteric heating/cooling. Because the adsorbed phase volume plays an important role, its dependence on temperature and pressure needs to be correctly assessed. In addition, for super-critical gas adsorption, the evaluation of the pseudo-saturation pressure also needs a judicious treatment. Based on the evaluation of carbon dioxide adsorption, it can be seen that sub-critical and super-critical adsorption show different temperature dependences of the isosteric heat of adsorption. The temperature and loading dependence of this property needs to be taken into account while designing practical systems. Some practical implications of these findings are enumerated.

There exists a minimum in the Waring function, psi(T) = -d(ln p)/d(1/T), and in the Riedel function, alpha(T) = d(ln p)/d(In T), in the liquid-vapor coexistence curve for most fluids. By analyzing National Institute of Standards and Technology data for the molar enthalpy of vaporization and the compressibility variation at the liquid-vapor phase change of 105 fluids, we find that the temperatures of these minima are linearly correlated with the critical temperature, T-c. Using reduced coordinates, we also demonstrate that the minima are well-correlated with the acentric factor. These correlations are used for testing four well-known vapor pressure equations in the Pitzer corresponding states scheme.

This paper lists the values of slope properties of entropy, enthalpy and exergy along isotherms, isochors, isobars and isentropes in terms of properties that can be primarily measured, namely pressure, volume, temperature, their slopes derivable from equations of state and one of the specific heats in the ideal gas state. It is also shown that all these slopes can be expressed in terms of a coefficient of thermal expansion and isothermal compressibility as well. These could be useful as an educational tool in chemical and mechanical engineering.

The winding of web materials is a subject of economic import that has resulted in mechanics analysis and model development. Many materials are wound into rolls for storage and subsequent processing. Winding is an accretive process in which the internal stresses within each layer of the wound roll are affected by the web layers that have been most recently added. As rolls wind, the edges take the approximate shape of an Archimedean spiral. All analyses and models to date have imposed the assumption that this spiral form can be replaced by a series of concentric web layers that are added one by one to the exterior of the model of the winding roll. It was also assumed that the bending stresses and strains associated with winding a flat web into a wound roll are negligible, an assumption with a validity that is highly dependent on web thickness. In this investigation, the web will be attached to a core and wound in a spiral form from the start to the completion of the wound roll. It will be shown that modeling the spiral geometry of the web in a wound roll can be beneficial in understanding stress concentrations in the vicinity of the starting position of the web on the core and for understanding how nip rollers can affect the web tension in the outer layer of a winding roll.

Results of performance measurement of a small cooling capacity laboratory model of an adsorption refrigeration system for thermal management of electronics are compiled. This adsorption cooler was built with activated carbon as the adsorbent and HFC 134a as the refrigerant to produce a cooling capacity under 5 W using waste heat up to 90 degrees C. The thermal compression process is obtained from an ensemble of four solid sorption compressors. Parametric study was conducted with cycle times of 16 and 20 min, heat source temperatures from 73 to 87 degrees C and cooling loads from 3 to 4.9W. Overall system performance is analyzed using two indicators, namely, cooling effectiveness and normalized exergetic efficiency. (C) 2011 Elsevier Ltd. All rights reserved.

This paper presents the results of an investigation on the performance of combined adsorption refrigeration cycles. The novel combined cycle amalgamates the activated carbon (AC)-R507A as the bottoming cycle and AC-R134a cycle as the topping cycle and deliver refrigeration load at as low as −10 °C at the bottoming cycle. The cycle simulation is based on the experimentally confirmed adsorption isotherms, kinetics and isosteric heat of adsorption data for R134a and R507A on highly porous based activated carbon of type Maxsorb III. The optimum cooling capacity, coefficient of performance (COP) and chiller efficiency are calculated in terms of cycle time, switching time, regeneration and brine inlet temperatures. Results show that the combined adsorption cycles are feasible even when low-temperature heat source is available.

It is well known that the choice of upper pressure limit in a transcritical CO2 refrigeration cycle is independent of the gas cooler approach temperature. This is in contrast to sub-critical cycles, where the condensing pressure is invariably governed by the ambient conditions. The criteria used for limiting the upper pressure limit in a transcritical cycle are the state of maximum COP for a given set of evaporating and gas cooler exit temperatures. The latter is governed by the local ambient conditions and the possible approach. This paper provides a thermodynamic basis for the evaluation of this pressure for the case of ideal compression and with some compressors available in the market. In addition, it also provides an additional criterion that minimizes the cycle irreversibility which is predominantly due to gas throttling. This paper evaluates the pressure limits for these two criteria for some typical evaporating temperatures and ambient conditions. The possible compressor discharge temperatures in each case are calculated and criteria for two-stage compression are identified.

This paper presents the results of an investigation on the efficacy of hybrid compression process for refrigerant HFC 134a in cooling applications. The conventional mechanical compression is supplemented by thermal compression using a string of adsorption compressors. Activated carbon is the adsorbent for the thermal compression segment. The alternatives of bottoming either mechanical or thermal compression stages are investigated. It is shown that almost 40% energy saving is realizable by carrying out a part of the compression in a thermal compressor compared to the case when the entire compression is carried out in a single-stage mechanical compressor. The hybrid compression is feasible even when low grade heat is available. Some performance indictors are defined and evaluated for various configurations.

This paper presents some of the results derived from extensive experimentation on display cases for supermarkets and derives some possible improvements to augment temperature uniformity and energy performance. The effect of the perforation pattern of the rear duct on the distribution of airflow between these and the front curtain is brought out. The critical component is air infiltration across the curtain, which is governed by internal air distribution and curtain characteristics. It is observed that a 70-30 distribution of flow between the curtain and the rear duct perforations yields a performance that satisfies the standards. Further, a judicious distribution of perforations on the rear duct at various levels and across is necessary. Correlations available in the literature are useful in making a qualitative assessment of the results.

The purpose of this paper is to provide empirical correlations for isosteric heats of adsorption on carbon based adsorbents for two refrigerants namely ethanol and HFC 134a. A non-dimensional correlation which partitions the contributions of the concentration and temperature dependence is proposed. The correlation is tested out against data obtained from experimental isotherms of ethanol adsorption on activated carbon fibers [ACF (A-20) and ACF (A-15)] and HFC 134a on two specimens of activated carbon powders and one specimen of carbon granules. It is expected that the suggested correlation will be useful for designers of adsorption chillers where indenting heat inventories fulcrums on the magnitude of isosteric heat of adsorption.

Motor vehicle crashes remain the leading cause of death of teens in the United States. Newly licensed drivers are the group most at risk for such crashes. The driving skills of teen drivers are new and still often untested; therefore, their ability to react properly in an emergency situation remains a subject for research. Because it is not possible to expose human subjects to critical life-threatening driving scenarios, researchers increasingly have been using driving simulators to assess driving skills. This paper summarizes the results of a driving scenario in a study that compared the driving performance of novice teen drivers ( n = 21) 16 to 17 years old with 90 days of provisional licensure with that of experienced adult drivers ( n = 17) 25 to 50 years old with at least 5 years of Pennsylvania licensure who drove at least 100 mi per week and had experienced no self-reported collisions in the previous 3 years. As part of a 30 to 35 mph simulated drive that encompassed the most common scenarios that result in serious crashes, participants were exposed to a sudden car event. As the participant drove on a suburban road, a car surged from a driveway hidden by a fence on the right-hand side of the road. To avoid the crash the participant had to brake hard and demonstrate dynamic control over both attentional and motor resources. The results showed significant differences between the experienced adult and the novice teen drivers in the amount of brake pressure applied. When placed in the same situation, the novice teens decelerated on average 50% less than the experienced adults ( p < .01).

The first objective of this paper is to show that a single-stage adsorption based cooling-cum-desalination system cannot be used if air cooled heat rejection is used under tropical conditions. This objective is achieved by operating a silica gel + water adsorption chiller first in a single-stage mode and then in a 2-stage mode with 2 beds/stage in each case. The second objective is to improve upon the simulation results obtained earlier by way of empirically describing the thermal wave phenomena during switching of operation of beds between adsorption and desorption and vice versa. Performance indicators, namely, cooling capacity, coefficient of performance and desalinated water output are extracted for various evaporator pressures and half cycle times. The improved simulation model is found to interpret experimental results more closely than the earlier one. Reasons for decline in performance indicators between theoretical and actual scenarios are appraised. (C) 2015 Elsevier Ltd and IIR. All rights reserved.

This paper presents the instrumentation and control architecture for a laboratory based two-stage 4-bed silica gel + water adsorption system. The system consists of primarily two fluids: refrigerant (water vapour) and heat transfer fluid (water) flowing through various components. Heat input to the system is simulated using multiple heaters and ambient air is used as the heat sink. The laboratory setup incorporates a real time National Instruments (NI) controller to control several digital and analog valves, heaters, pumps and fans along with simultaneous data acquisition from various flow, pressure and temperature sensors. The paper also presents in detail the various automated and manual tasks required for successful operation of the system. Finally the system pressure and temperature dynamics are reported and its performance evaluated for various cycle times. (C) 2015 Elsevier Ltd. All rights reserved.

This paper describes the techniques adopted for visualization of Rayleigh-Benard convection during solidification of eutectic, hypo- and hyper-eutectic salt solutions. Neutrally buoyant hollow glass spheres were inducted in the body of the solidifying salt solution. The convection currents were captured by scattering of a laser beam by these beads. The apparatus has two components, namely: (i) measurement of interface/mushy region movement and temperature distribution and (ii) flow visualization with laser beam scattered by hollow glass spheres. The distinct nature of convection cells in the eutectic and hypo eutectic region is brought out.

We have used transmission electron microscopy to observe the structural changes that have occurred in multi-walled carbon nanotubes (MWCNTs) because of acid treatment. After a thiolation reaction of the acid-treated MWCNTs using P4S10 in refluxing toluene, we have also used electron energy loss spectroscopy to characterize the changes on the nanotubes from sidewall functionalization. We have determined that the sulfur content bonded to the nanotubes is 0.6% in terms of the atomic content of the samples. Raman spectroscopy was used to examine the vibrational changes that occurred to the nanotubes as well as identifying new vibrational modes around 500 cm−1 characteristic of carbon-sulfur bonds.

The purpose of this article is to report the experience of design and testing of orifice plate-based flow measuring systems for evaluation of air leakages in components of air conditioning systems. Two of the flow measuring stations were designed with a beta value of 0.405 and 0.418. The third was a dual path unit with orifice plates of beta value 0.613 and 0.525. The flow rates covered with all the four were from 4-94 l/s and the range of Reynolds numbers is from 5600 to 76,000. The coefficients of discharge were evaluated and compared with the Stolz equation. Measured C-d values are generally higher than those obtained from the equation, the deviations being larger in the low Reynolds number region. Further, it is observed that a second-degree polynomial is inadequate to relate the pressure drop and flow rate. The lower Reynolds number limits set by standards appear to be somewhat conservative.

Batteries play a vital role in solar photovoltaic refrigeration systems. Despite breakthroughs in operational characteristics of various components of such systems, leadacidbatteries continue to be the only viable electrical energy storage devices as of date. The purpose of this paper is to report the results of characterization of a leadacidbattery system as a component of a small capacity uninterruptedrefrigeration system. The charging characteristics on solar energy, mains anda generator set poweredby an internal combustion engine are presented. It is shown that through a judicious choice of capacity and load matching, the maximum power point tracker can be eliminated.

The purpose of this paper is to present exergy charts for carbon dioxide (CO2) based on the new fundamental equation of state and the results of a thermodynamic analysis of conventional and trans-critical vapour compression refrigeration cycles using the data thereof. The calculation scheme is anchored on the Mathematica platform. There exist upper and lower bounds for the high cycle pressure for a given set of evaporating and pre-throttling temperatures. The maximum possible exergetic efficiency for each case was determined. Empirical correlations for exergetic efficiency and COP, valid in the range of temperatures studied here, are obtained. The exergy losses have been quantified. (C) 2003 Elsevier Ltd. All rights reserved.

In this paper, a detailed thermodynamic performance analysis of a transcritical condensing (TC) cycle is performed with pure CO2 and a blend of 48.5 % propane with 51.5 % CO2 as working fluids. A realistic thermodynamic model is used incorporating irreversibilities in turbo-machineries and heat exchangers. The Key finding is that the addition of propane elevates the heat rejection temperature, but does not impair any of the performance indicators. Such a fluid may be useful for power generation in concentrated solar power applications by using which a hike of up to 2 % can be realized in the thermal efficiency of a power plant.

We investigate the isentropic index along the saturated vapor line as a correlating parameter with quantities both in the saturated liquid phase and the saturated vapor phase. The relation is established via temperatures such as T-hgmax and T* where the saturated vapor enthalpy and the product of saturation temperature and saturated liquid density attain a maximum, respectively. We obtain that the saturated vapor isentropic index is correlated with these temperatures but also with the saturated liquid Gruneisen parameters at T-hgmax. and T*.

The present study simulates a two-stage silica gel + water adsorption desalination (AD) and chiller system. The adsorber system thermally compresses the low pressure steam generated in the evaporator to the condenser pressure in two stages. Unlike a standalone adsorption chiller unit which operates in a closed cycle the present system is an open cycle wherein the condensed desalinated water is not fed back to the evaporator. The mathematical relations formulated in the current study are based on conservation of mass and energy along with isotherm relation and kinetics for RD-type silica gel + water pair. Various constitutive relations for each component namely the evaporator, adsorber and condenser are integrated in the model. The dynamics of heat exchanger are modeled using LMTD method, and LDF model is used to predict the dynamic characteristic of the adsorber bed. The system performance indicators namely, specific cooling capacity (SCC), specific daily water production (SDWP) and coefficient of performance (COP) are used as objective functions to optimize the system. The novelty of the present work is in introduction of inter-stage pressure as a new parameter for optimizing the two-stage operation of AD chiller system. (C) 2014 Elsevier Ltd. All rights reserved.

This paper presents adsorption isotherms for HFC-134a on activated charcoal, in the temperature range of 273-353 K and for pressures up to 0.65 MPa, measured using the volumetric method. Three samples of charcoals with widely varying surface areas were chosen. The shapes of the isotherms,obtained from the experimental data were similar in all cases and comparable to those reported in the literature. Adsorption parameters were evaluated from the isotherms using the Dubinin-Astakhov (DA) equation. The concentration dependence of the isosteric enthalpies of adsorption is extracted from the data.

Heat and moisture transport in 2-5 mm coarse grade monolithic cork slabs was studied at near ambient temperature conditions with various concentrations of moisture in them. It is observed that the apparent thermal conductivity increases by approximately 60% compared to dry state when the cork is saturated with water. For the sample chosen, the saturation moisture content is 42.5% on dry mass basis and the void volume is 9.6%. An empirical correlation is proposed for the evaluation of the thermal conductivity under various mass and volume fractions of moisture based on the mixing rules for thermal conductivity of dry cork and that of liquid water.

In this article, a general definition of the process average temperature has been developed, and the impact of the various dissipative mechanisms on 1/COP of the chiller evaluated. The present component-by-component black box analysis removes the assumptions regarding the generator outlet temperature(s) and the component effective thermal conductances. Mass transfer resistance is also incorporated into the absorber analysis to arrive at a more realistic upper limit to the cooling capacity. Finally, the theoretical foundation for the absorption chiller T-s diagram is derived. This diagrammatic approach only requires the inlet and outlet conditions of the chiller components and can be employed as a practical tool for system analysis and comparison. (C) 2000 Elsevier Science Ltd and IIR. All rights reserved.

This article presents a thermodynamically consistent set of specific enthalpy, entropy, and heat capacity fields for LiBr-$H_2O$ solution. The temperatures span from 0 to $190^oC$, while the concentrations span from 0 to 75 wt%. The work is based on the empirical inputs of Duhring's gradient and intercept, specific heat capacity data at a reference concentration of 50 wt% and density data. These properties have been evaluated using most of the experimental data available in the literature. The present approach circumvents the issue of negative dew point at low temperatures and high concentrations. The information provided in this article could be useful for designers of absorption chillers.

This paper presents the cool-down, warm-up and steady state performance of a 100 W AC operated domestic refrigerator powered by a field of photovoltaic panels, a battery bank and an inverter. It is shown that there is no degradation in the performance when a non-sinusoidal waveform AC source is used to operate the refrigerator although it may involve only a slight additional heating of the hermetic compressor. Thermal mapping of the temperatures at various points on the refrigerator is provided for steady state, cool-down, warm-up, periodic opening of the door and ice making. An energy flow diagram is given for a steady state sunny day operation. Major sources of losses are identified.

The objective of this paper is to describe salient features of a small refrigerator powered by a field of photovoltaic panels backed up by a petrol-start, kerosene-run portable generator set. Such units find applications in medical shops, veterinary applications and storage of vaccines in primary health centers. The modular arrangement allows use of certain components as a part of an uninterrupted power supply system for such refrigerators. Some preliminary results on temperature distributions and performance data are also presented.

This paper presents results of experimental investigations on a field of 8 photovoltaic panels assembled 2 in series and 4 such parallel combinations. The diurnal and environmental effects have been characterized systematically. The usage conditions are clean and dusty states of panels, the centers of each series combinations shorted and unshorted. It is observed that the curvature at the maximum power point of the I-V curve could be an indicator of the panel characteristics. The temperature effects on the voltage at the maximum power point are also discussed. It is brought out that field evaluation is essential and often maximum power point tracking can be dispensed if a known load exists and a judicious choice of battery bank capacity is made.

The exergy-enthalpy and temperature-exergy diagrams have been generated in the range 0.1-10 MPa and from the triple point to 500 K. These diagrams on the International Temperature Scale (ITS-90) have been generated using a calculation scheme proposed by Jacobsen et al. A computer program is developed for calculating the thermodynamic properties of nitrogen, including exergy as a property, from the triple point to 800 K at pressures up to 30 MPa. These exergy based thermodynamic property charts can be useful in the energy efficiency analyses of cryorefrigeration cycles involving nitrogen as a working medium. A sample analysis is included.

The main theme of this paper is to study the flammability suppression of hydrocarbons by blending with carbon dioxide, and to evaluate these mixtures as possible working fluids in organic Rankine cycle for medium temperature concentrated solar power applications. The analysis takes into account inevitable irreversibilities in the turbine, the pump, and heat exchangers. While the isopentane + CO2 mixture suffers from high irreversibility mainly in the regenerator owing to a large temperature glide, the propane + CO2 mixture performs more or less the same as pure propane albeit with high cycle pressures. In general, large temperature glides at condensing pressures extend the heat recovery into the two-phase dome, which is an advantage. However, at the same time, the shift of the pinch point towards the warm end of the regenerator is found to be a major cause of irreversibility. In fact, as the number of carbon atoms in alkanes decreases, their blend with CO2 moves the pinch point to the colder end of the regenerator. This results in lower entropy generation in the regenerator and improved cycle efficiency of propane + CO2 mixtures. With this mixture, real cycle efficiencies of 15-18% are achievable at a moderate source temperature of 573 K. Applicability for a wide range of source temperatures is found to be an added advantage of this mixture.

The three indicators of isentropic lines, namely, the isentropic index, the ratio of pressure and density p/rho and the derivative (partial derivative p/partial derivative rho)s are investigated for all of the fluids in the RefProp 9.0 program. The behaviour of these three entities is evaluated along the saturated vapour line as well as in the superheated vapour region. There is a distinct demarcation of fluids whose isentropic indices can be less than 1 and others for which this behaviour is absent. The critical molar volume is found to be the characterizing feature. Several other interesting features of those three thermodynamic properties are also highlighted. It is observed that most practical engineering compression and expansion processes occur along the decreasing direction of the sound speed.

Experimental adsorption data of difluoromethane (HFC-32) on activated carbon in powder (ACP) and fiber (ACF) forms over a range of (25 to 75) degrees C and pressures up to 1400 kPa are reported. The data are fitted to Toth and Dubinin-Astakhov isotherm equations. Adsorbed phase volume is derived from the data. Isosteric heats of adsorption are extracted, and their dependence on relative loading and relative pressure is analyzed.

For most fluids, there exist a maximum and a minimum in the curvature of the reduced vapor pressure curve, p(r) = p(r)(T-r) (with p(r) = p/p(c) and T-r = T/T-c, p(c) and T-c being the pressure and temperature at the critical point). By analyzing National Institute of Standards and Technology (NIST) data on the liquid-vapor coexistence curve for 105 fluids, we find that the maximum occurs in the reduced temperature range 0.5

A low thermal diffusivity of adsorption beds induces a large thermal gradient across cylindrical adsorbers used in adsorption cooling cycles. This reduces the concentration difference across which a thermal compressor operates. Slow adsorption kinetics in conjunction with the void volume effect further diminishes throughputs from those adsorption thermal compressors. The problem can be partially alleviated by increasing the desorption temperatures. The theme of this paper is the determination the minimum desorption temperature required for a given set of evaporating/condensing temperatures for an activated carbon + HFC 134a adsorption cooler. The calculation scheme is validated from experimental data. Results from a parametric analysis covering a range of evaporating/condensing/desorption temperatures are presented. It is found that the overall uptake efficiency and Carnot COP characterize these bounds. A design methodology for adsorber sizing is evolved. (c) 2012 Elsevier Ltd. All rights reserved.

We propose a new method for evaluating the adsorbed phase volume during physisorption of several gases on activated carbon specimens. We treat the adsorbed phase as another equilibrium phase which satisfies the Gibbs equation and hence assume that the law of rectilinear diameters is applicable. Since invariably the bulk gas phase densities are known along measured isotherms, the constants of the adsorbed phase volume can be regressed from the experimental data. We take the Dubinin-Astakhov isotherm as the model for verifying our hypothesis since it is one of the few equations that accounts for adsorbed phase volume changes. In addition, the pseudo-saturation pressure in the supercritical region is calculated by letting the index of the temperature term in Dubinin's equation to be temperature dependent. Based on over 50 combinations of activated carbons and adsorbates (nitrogen, oxygen, argon, carbon dioxide, hydrocarbons and halocarbon refrigerants) it is observed that the proposed changes fit experimental data quite well.

A laboratory model of a thermally driven adsorption refrigeration system with activated carbon as the adsorbent and 1,1,1,2-tetrafluoroethane (HFC 134a) as the refrigerant was developed. The single stage compression system has an ensemble of four adsorbers packed with Maxsorb II specimen of activated carbon that provide a near continuous flow which caters to a cooling load of up to 5W in the 5-18 degrees C region. The objective was to utilise the low grade thermal energy to drive a refrigeration system that can be used to cool some critical electronic components. The laboratory model was tested for it performance at various cooling loads with the heat source temperature from 73 to 93 degrees C. The pressure transients during heating and cooling phases were traced. The cyclic steady state and transient performance data are presented. (C) 2010 Elsevier Ltd. All rights reserved.

This article examines, through a molecular perspective, the ‘ozone-friendly’ refrigerants R-134a and R-123 vis-à-vis R-12 and R-11, which are targeted to be phased out under the Montreal Protocol on Substances that Deplete the Ozone Layer, Final Act (1987). It appears that the molecular weight, size parameter, and dipole moment, of R-134a and R-123, may induce a pronounced effect on the chemical equilibrium of ice particles in the polar stratospheric clouds and subsequently influence the photochemical reactions therein.Non-polar, high-molecular-weight perfluoropropane (R-218), could be a better substitute for R-12, while R-134, which is a non-polar HFC of the ethane family, could also be a candidate although its molecular weight is lower than that of R-12. The search for a good substitute for R-11, however, must continue.