This paper presents an advanced desalination cycle that hybridizes a conventional multi-effect distillation (MED) and an emerging yet low-energy adsorption cycle (AD). The hybridization of these cycles, known as MED + AD or MEDAD in short, extends the limited temperature range of the MED, typically from 65 degrees C at top-brine temperature (TBT) to a low-brine temperature (LBT) of 40 degrees C to a lower LBT of 5 degrees C, whilst the TBT remains the same. The integration of cycles is achieved by having vapor uptake by the adsorbent in AD cycle, extracting from the vapor emanating from last effect of MED. By increasing the range of temperature difference (DT) of a MEDAD, its design can accommodate additional condensation-evaporation stages that capitalize further the energy transfer potential of expanding steam. Numerical model for the proposed MEDAD cycle is presented and compared with the water production rates of conventional and hybridized MEDs. The improved MEDAD design permits the latter stages of MED to operate below the ambient temperature, scavenging heat from the ambient air. The increase recovery of water from the seawater feed may lead to higher solution concentration within the latter stages, but the lower saturation temperatures of these stages mitigate the scaling and fouling effects. (C) 2014 Elsevier Ltd. All rights reserved.

This paper describes the successful operation of an adsorption cycle in a miniaturized adsorption chiller (AD). The experiments show that the bench-scale pressurized adsorption chiller (PAC) has been successfully designed, commissioned, and tested. Experimental results at various heat fluxes, half-cycle operation time intervals, and a cooling load of up to 24 W are also presented. A COP ranging from 0.05 to 0.15 is achieved depending on the parameters of the experimental conditions. Most importantly, the cooling performance of the PAC is achieved at a low encasement temperature that is below ambient. Besides having a high cooling density, the PAC has almost no major moving parts except for the fan of the condenser and it permits quiet operation as compared to other active coolers.

This paper discusses the analysis of an adsorption (AD) chiller using system entropy generation as a thermodynamic framework for evaluating total dissipative losses that occurred in a batch-operated AD cycle. The study focuses on an adsorption cycle operating at heat source temperatures ranging from 60 to 85°C, whilst the chilled water inlet temperature is fixed at 12.5°C, – a temperature of chilled water deemed useful for dehumidification and cooling. The total entropy generation model examines the processes of key components of the AD chiller such as the heat and mass transfer, flushing and de-superheating of liquid refrigerant. The following key findings are observed: (i) The cycle entropy generation increases with the increase in the heat source temperature (10.8 to 46.2W/K) and the largest share of entropy generation or rate of energy dissipation occurs at the adsorption process, (ii) the second highest energy rate dissipation is the desorption process, (iii) the remaining energy dissipation rates are the evaporation and condensation processes, respectively. Some of the noteworthy highlights from the study are the inevitable but significant dissipative losses found in switching processes of adsorption-desorption and vice versa, as well as the de-superheating of warm condensate that is refluxed at non-thermal equilibrium conditions from the condenser to the evaporator for the completion of the refrigeration cycle.

This paper describes the development of a simple hybrid desalination system of a Multi-Effect Distillation (MED) and an adsorption (AD) cycle operating at sub-atmospheric pressures and temperatures. By hybridizing the conventional MED with an AD cycle, there is a symbiotic enhancement of performances of both cycles. The performance enhancement is attributed to (i) the cascade of adsorbent's regeneration temperature and this extended the usage of thermal energy emanating from the brine heater and (ii) the vapor extraction from the last MED stage by AD cycle which provides the effect of lowering saturation temperatures of all MED stages to the extent of 5 degrees C, resulting in scavenging of heat leaks into the MED stages from the ambient. The combined effects of the hybrid cycles increase the water production capacity of the desalination plant by nearly twofolds.In this paper, we demonstrate a hybrid cycle by simulating an 8-stage MED cycle which is coupled to an adsorption cycle for direct vapor extraction from the last MED stage. The sorption properties of silica gel is utilized (acting as a mechanical vapor compressor) to reduce the saturation temperatures of MED stages. The modeling utilizes the adsorption isotherms and kinetics of the adsorbent + adsorbate (silica-gel + water) pair along with the governing equations of mass, energy and concentration. For a 8-stage MED and AD cycles operating at assorted temperatures of 65-90 degrees C, the results show that the water production rate increases from 60% to twofolds when compared to the MED alone. The performance ratio (PR) and gain output ratio (GOR) also improve significantly. (C) 2012 Elsevier Ltd. All rights reserved.

Multi-effect distillation (MED) systems are proven and energy efficient thermally-driven desalination systems for handling harsh seawater feed in the Gulf region. The high cycle efficiency is markedly achieved by latent energy re-use with minimal stage temperature-difference across the condensing steam and the evaporating saline seawater in each stage. The efficacies of MED system are (i) its low stage-temperature-difference between top brine temperature (TBT) and final condensing temperature, (ii) its robustness to varying salinity and ability to handle harmful algae Blooming (HABs) and (iii) its compact foot-print per unit water output. The practical TBT of MED systems, hitherto, is around 65 degrees C for controllable scaling and fouling with the ambient-limited final condenser temperature, usually from 30 to 45 degrees C.The adsorption (ADC) cycles utilize low-temperature heat sources (typically below 90 degrees C) to produce useful cooling power and potable water. Hybridizing MED with AD cycles, they synergistically improve the water production rates at the same energy input whilst the AD cycle is driven by the recovered waste heat. We present a practical AD + MED combination that can be retrofitted to existing MEDs: The cooling energy of AD cycle through the water vapor uptake by the adsorbent is recycled internally, providing lower temperature condensing environment in the effects whilst the final condensing temperature of MED is as low as 5-10 degrees C, which is below ambient. The increase in the temperature difference between TBT and final condensing temperature accommodates additional MED stages. A detailed numerical model is presented to capture the transient behaviors of heat and mass interactions in the combined AD + MED cycles and the results are presented in terms of key variables. It is observed that the water production rates of the combined cycle increase to give a GOR of 8.8 from an initial value of 5.9. (C) 2013 Elsevier Ltd. All rights reserved.

This paper presents an investigation of heat transfer correlation in a falling-film evaporator working with saline water at sub-atmospheric pressures. The experiments are conducted at different salinity levels ranging from 15000 to 90000 ppm, and the pressures were maintained between 0.92 to 2.81 kPa (corresponds to saturation temperatures of 5.9 - 23 C-0). The effect of salinity, saturation pressures and chilled water temperatures on the heat transfer coefficient are accounted in the modified film evaporation correlations. The results are fitted to the Han & Fletcher's and Chun & Seban's falling-film correlations which are used in desalination industry. We modify the said correlations by adding salinity and saturation temperature corrections with respective indices to give a better agreement to our measured data.

In falling film evaporators, the overall heat transfer coefficient is controlled by film thickness, velocity, liquid properties and the temperature differential across the film layer. This article presents the heat transfer behavior for evaporative film boiling on horizontal tubes, but working at low pressures of 0.93-3.60 kPa (corresponding solution saturation temperatures of 279-300 K) as well as seawater salinity of 15,000 to 90,000 mg/l or ppm. Owing to a dearth of literature on film-boiling at these conditions, the article is motivated by the importance of evaporative film boiling in the desalination processes such as the multi-effect distillation (MED) or multi-stage flashing (MSF): It is observed that in addition to the above-mentioned parameters, evaporative heat transfer of seawater is affected by the emergence of micro-bubbles within the thin film layer, particularly when the liquid saturation temperatures drop below 298 K (3.1 kPa). Such micro bubbles are generated near to the tube wall surfaces and they enhanced the heat transfer by two or more folds when compared with the predictions of conventional evaporative film boiling. The appearance of micro-bubbles is attributed to the rapid increase in the specific volume of vapor, i.e., dv/dT, at low saturation temperature conditions. A new correlation is thus proposed in this article and it shows good agreement to the measured data with an experimental uncertainty of 8% and regression RMSE of 3.5%. (C) 2012 Elsevier Ltd. All rights reserved.

This paper features the adsorption equilibria of refrigerants R134a, R290, R410a, and R507a on microporous activated carbon samples at temperatures between 278 K and 338 K with pressures up to 1.4 MPa. The adsorption isotherm data are obtained by utilizing the constant-volume-variable-pressure (CVVP) approach and analyzed using the Dubinin-Ashtakov (DA) model. The regressed adsorption parameters acquired by using this model produces isotherm curves that agree within 5 % of the experimental results. The concentration- and temperature-dependent enthalpies of adsorption of these pairs are evaluated and presented.

This paper presents performance analysis of absorption refrigeration system (ARS) using an entropy generation analysis. A numerical model predicts the performance of absorption cycle operating under transient conditions along with the entropy generation computation at assorted heat source temperatures, and it captures also the dynamic changes of lithium bromide solution properties such as concentration, density, vapor pressure and overall heat transfer coefficients. An optimization tool, namely the genetic algorithm (GA), is used as to locate the system minima for all defined domain of heat source and cooling water temperatures. The analysis shows that minimization of entropy generation the in absorption cycle leads to the maximization of the COP.

The usage of adsorbed natural gas (ANG) storage is hindered by the thermal management during the adsorption and desorption processes. An effective thermal enhancement is thus essential for the development of the ANG technology and the motivation for this study is the investigation of a gas storage system with internal thermal control. We employed a fin-tube type heat exchanger that is placed in a pressurized cylinder. A distributed-parameter model is used for the theoretical modeling and simulations are conducted at assorted charging and discharging conditions. These studies included the transient thermal behaviours of the elements within the ANG-charged cylinder and parameters such as pressure and temperature profiles of adsorbent have been obtained during charge and discharge cycles, and results are compared with a conventional compressed methane vessel.

This paper presents the results of an investigation on the efficacy of a silica gel–water based advanced adsorption desalination (AD) cycle with internal heat recovery between the condenser and the evaporator. A mathematical model of the AD cycle was developed and the performance data were compared with the experimental results. The advanced AD cycle is able to produce the specific daily water production (SDWP) of 9.24m3/tonne of silica gel per day at 70°C hot water inlet temperature while the corresponding performance ratio (PR) is comparatively high at 0.77. It is found that the cycle can be operational at 50°C hot water temperature with SDWP 4.3. The SDWP of the advanced cycle is almost twice that of the conventional AD cycle.

This paper presents the thermo-economic analysis of the adsorption desalination (AD) cycle that is driven by low-temperature waste heat from exhaust of industrial processes or renewable sources. The AD cycle uses an adsorbent such as the silica gel to desalt the sea or brackish water. Based on an experimental prototype AD plant, the life-cycle cost analysis of AD plants of assorted water production capacities has been simulated and these predictions are translated into unit cost of water production. Our results show that the specific energy consumption of the AD cycle is 1.38 kWh/m(3) which is the lowest ever reported. For a plant capacity of 1000 m(3)/d, the AD cycle offers a unit cost of $0.457/m(3) as compared to more than $0.9 for the average RO plants. Besides being cost-effective, the AD cycle is also environment-friendly as it emits less CO2 emission per m(3) generated, typically 85% less, by comparison to an RO process.

An evacuated tubular solar collector was fabricated from acrylics for improved resistance to shattering. A plasmatron was employed to apply a thin gas-barrier coating to the surfaces of the plastic tube to prevent/alleviate gas infiltration. Experiments were conducted to investigate the effect of vacuum level on the performance of the non-glass vacuum-tube solar collector. Inserted in the evacuated tube was a finned heat pipe for solar energy collection and heat transfer to a water tank. Time variations of temperatures on the heat pipe surface and in the water tank were recorded and analyzed for different degrees of vacuum in the collector. The steady-state temperature of the non-glass collector was compared to that of a commercial glass vacuum-tube collector to assess the feasibility of the use of evacuated plastic tubes for solar energy collection. A simple analytical model was also developed to assist in understanding and analyzing the transient behavior and heat losses of the vacuum-tube solar collector. (C) 2009 Elsevier Ltd. All rights reserved.

This paper presents the experimentally measured adsorption isotherm data for methane onto the pitch-based activated carbon type Maxsorb III for temperatures ranging from (120 to 220) K and pressures up to 1.4 MPa. These data are useful to study adsorbed natural gas (ANG) storage systems when the low temperature natural gas regasified from the liquid phase is considered to charge in the storage chamber. Adsorption parameters were evaluated from the isotherm data using the T6th and Dubinin-Astakhov models. The isosteric heat of adsorption, which is concentration- and temperature-dependent, is extracted from the data. The Henry's law coefficients for the methane/Maxsorb III pairs are evaluated at various temperatures.

This paper discusses the performance analysis of adsorption desalination cycles with different configurations. The salient features of the AD cycle are the ability to the utilization of low temperature waste heat (typically less than 85°C), the deployment of environmentally friendly adsorbent/adsorbate pair (silica gel/water pair) and no major moving parts. The advanced AD cycle that incorporates the internal heat recovery between the condenser and evaporator by a heat recovery circuit is compared with conventional two-bed and four-bed AD cycles. Mathematical models to investigate the performance of the cycles are also presented. Extensive experiments have been conducted to explore the performance of such systems and are analysed in terms of key performance indicators namely the specific daily water production (SDWP) and the performance ratio (PR). Based on the experimental data, it is found that the SDWP of the advanced AD cycle with the condenser-evaporator heat recovery circuit is about 15 m3 of potable water per tonne of silica gel which is nearly two times that of the conventional AD cycles. Moreover, it is also found that the advanced AD cycle can be operational at 50°C hot water temperature with SDWP 4.3.

The adsorption isotherm of an adsorbate-adsorbent pair is the key information for storage capacity and thermal management of adsorptive gas storage system. This article presents the adsorption isotherm of methane, which is the major component of natural gas, on pitch-based activated carbon type Maxsorb III for a wide range of temperature (120 to 350) K and pressure up to 2.5 MPa. The uptake values have been experimentally measured using volumetric technique. Since the Maxsorb III sample is highly microporous and heterogeneous in surface structure, the popular Toth isotherm model is used to fit the data due its accountability of the heterogeneity parameter. The measured uptake data are useful to estimate the charge pressure of adsorbed natural gas storage system at different adsorbent temperature for constant adsorption capacity.

This article presents the transient modeling and performance of waste heat driven pressurized adsorption chillers for refrigeration at subzero applications. This innovative adsorption chiller employs pitch-based activated carbon of type Maxsorb III (adsorbent) with refrigerant R134a as the adsorbent-adsorbate pair. It consists of an evaporator, a condenser and two adsorber/desorber beds, and it utilizes a low-grade heat source to power the batch-operated cycle. The ranges of heat source temperatures are between 55 to 90 °C whilst the cooling water temperature needed to reject heat is at 30 °C. A parametric analysis is presented in the study where the effects of inlet temperature, adsorption/desorption cycle time and switching time on the system performance are reported in terms of cooling capacity and coefficient of performance.