Effectiveness-mass transfer units (ε-MTU) model of a reverse osmosis membrane mass exchanger

A strong analogy exists between heat exchangers and osmotic mass exchangers. The effectiveness-number of transfer units (ε-NTU) method is well-known for the sizing and rating of heat exchangers. A similar method, called the effectiveness-mass transfer units (ε-MTU) method, is developed for reverse osmosis (RO) mass exchangers. Governing equations for an RO mass exchanger are nondimensionalized assuming ideal membrane characteristics and a linearized form of the osmotic pressure function for seawater. A closed form solution is found which relates three dimensionless groups: the number of mass transfer units, which is an effective size of the exchanger; a pressure ratio, which relates osmotic and hydraulic pressures; and the recovery ratio, which is the ratio of permeate to inlet feed flow rates. A novel performance parameter, the effectiveness of an RO exchanger, is defined as a ratio of the recovery ratio to the maximum recovery ratio. A one-dimensional numerical model is developed to correct for the effects of feed-side external concentration polarization and nonlinearities in osmotic pressure as a function of salinity. A comparison of model results to experimental data found in the literature resulted in an average error of less than 7.8%. The analytical ε-MTU model can be used for design or performance evaluation of RO membrane mass exchangers.Center for Clean Water and Clean Energy at MIT and KFUPMNational Science Foundation (U.S.). Graduate Research Fellowship (Grant 1122374

Formulation of Seawater Flow Exergy Using Accurate Thermodynamic Data

Seawater is a complex electrolyte solution of water and salts with sodium chloride as the major constituent. However, the thermodynamic properties of seawater are considerably different from those of aqueous sodium chloride solution. In the literature, exergy analyses of seawater desalination systems have sometimes modeled seawater by sodium chloride solutions of equivalent salt content or salinity; however, such matching does not bring all important properties of the two solutions into agreement. Furthermore, some published studies attempt to represent sodium chloride solutions as a specific model for an ideal mixture of liquid water and solid sodium chloride, which is shown to have serious shortcomings. In this paper, the most up-to-date thermodynamic properties of seawater are compared with those of aqueous sodium chloride solution as well as the ideal mixture model. The flow exergy is calculated using various models and the results are compared. In addition, the minimum work required to desalinate a unit mass of fresh water from seawater of varying salinity is calculated using these models. The flow exergy calculated using the ideal mixture model in question is about 50% less than that of seawater. Accordingly, the minimum desalination work is underpredicted by about 50% when calculating it using that ideal mixture model. This consequently shows that exergy analysis and the second law efficiency calculations performed using the ideal mixture model is comparatively far from the actual values.Center for Clean Water and Clean Energy at MIT and KFUP

Thermal Performance Evaluation of Seawater Cooling Towers

Seawater has been used for long time as a cooling fluid in heat exchangers to reduce fresh water usage in industry and power plants. The thermophysical properties of seawater are different from those of fresh water due to the salt content or salinity. This difference is sufficient to affect the heat and mass transfer processes which in turn change the thermal performance. Thermal design of fresh water cooling towers is described in detail in many textbooks and handbooks. However, only a rule of thumb is frequently used for designing of seawater cooling towers. This rule recommends degrading the tower performance by approximately 1% for every 10,000 ppm of salts in the feed water. In this paper, the thermal performance of seawater cooling towers is presented using a detailed model of counterflow wet cooling towers which takes into consideration the coupled simultaneous heat and mass transfer processes and uses state-of-the-art seawater properties from the literature. The model governing equations are solved numerically and the validity of this model is checked using new experimental data that has been measured using a bench top counterflow seawater cooling tower. The effect of the variation of seawater salinity as well as other operating conditions on the effectiveness and Merkel number is investigated.Center for Clean Water and Clean Energy at MIT and KFUP

Heat shock protein 60 and chromatin assembly factor-1 mRNA levels in hepatitis C virus-related hepatocellular carcinoma and clinical significance

Background: Hepatocellular carcinoma (HCC) is the third cause of cancer-related death worldwide. Heat Shock protein 60 (HSP60), a mitochondrial chaperone, is overexpressed in diverse malignant cells. Chromatin Assembly Factor-1 (CAF-1), a histone chaperone, is down-regulated in quiescent non-proliferating human cells. We aimed to clarify the role of HSP60 and CAF-1 mRNA expression in diagnosis of HCC post-HCV infection.Methods: HSP60 and CAF-1 mRNA levels in urine and blood were quantified by Taqman real-time PCR in 49 subjects; 25 cirrhotic with HCV-related HCC, 12 cirrhotic without HCC and 12 healthy controls.Results: HSP60 and CAF-1 mRNA levels in urine and blood were significantly higher in HCC versus cirrhosis and controls, and in cirrhosis versus controls. Their levels in HCC were significantly increased by advancement of HCC BCLC staging system. HSP60 in urine had 85% sensitivity and 66% specificity at cut off 258354 RU and 85% sensitivity and 60 % specificity at cut off 37576 RU in blood for HCC diagnosis. CAF-1 in urine had 81% sensitivity and 66% specificity at cut off 137756 RU and 77% sensitivity and 64% specificity at cut off 49726 RU in blood for HCC diagnosis. HSP60/CAF-1 sensitivity and specificity in urine and blood were better than either marker alone, with better results in urine (91% and 73%, respectively) than blood (88% and 66%, respectively).Conclusions: HSP60 and CAF-1 in urine and blood may be useful HCC diagnostic markers that were correlated with advancement of HCC with better combined marker sensitivity and specificity than either marker alone especially for urine

OpenPNM: A Pore Network Modeling Package

Pore network modeling is a widely used technique for simulating multiphase transport in porous materials, but there are very few software options available. This work outlines the OpenPNM package that was jointly developed by several porous media research groups to help address this gap. OpenPNM is written in Python using NumPy and SciPy for most mathematical operations, thus combining Python's ease of use with the performance necessary to perform large simulations. The package assists the user with managing and interacting with all the topological, geometrical, and thermophysical data. It also includes a suite of commonly used algorithms for simulating percolation and performing transport calculations on pore networks. Most importantly, it was designed to be highly flexible to suit any application and be easily customized to include user-specified pore-scale physics models. The framework is fast, powerful, and concise. An illustrative example is included that determines the effective diffusivity through a partially water-saturated porous material with just 29 lines of code

Prognosis of Component Degradation Under Uncertainty: A Method for Early Stage Design of a Complex Engineering System

This paper proposes a method that dynamically improves a statistical model of system degradation by incorporating uncertainty. The method is illustrated by a case example of fouling, or degradation, in a heat exchanger in a cogeneration desalination plant. The goal of the proposed method is to select the best model from several representative condenser fouling models including linear, falling rate, and asymptotic fouling, and to validate and improve model parameters over the duration of operation. Maximum likelihood estimation (MLE) was applied to obtain a stochastic distribution of condenser fouling. Akaike’s Information Criterion (AIC) and the Bayesian Information Criterion (BIC) were then computed at time intervals to assess the accuracy of the MLE results. The degradation model was further evaluated by estimating future prognoses and then cross-validating with real world fouling data. The results show the accuracy of a prognosis can be improved substantially by continuously updating fouling model parameters. The proposed method is a step toward facilitating prognosis of engineering systems in the early design stages by improving the prediction of future component degradation.Center for Clean Water and Clean Energy at MIT and KFUPMNatural Sciences and Engineering Research Council of Canad

Comparisons between ground and air source heat pumps in hot/dry climates : Saudi Arabia as a case study

The use of ground source heat pump (GSHP) systems in cold climates, such as those in parts of North America, Scandinavian countries and China has been discussed for decades. However, hot and dry climates are encountered in vast regions across the globe but, unfortunately, not much data exists in terms of the GSHP systems. This paper aims to investigate the feasibility of using GSHP systems in hot and dry regions and Saudi Arabia is a case study by comparison between using a ground source heat pump and the conventional air source heat pump (ASHP) systems based on Saudi Arabia climates conditions. In order to compare the economics of geothermal heat pump systems to other HVAC alternatives, a direct capital costs comparison is made between GSHP and ASHP. Based on the length of the ground loop, which was calculated using the ASHRAE method, the initial installation cost for GSHP leads to an increase in the investment costs of GSHP because of the extra expensive drilling costs for the ground loop heat exchanger and piping. However, over the period of approximately 22 years there is a 19.6% total cost savings using GSHP compared to ASHP and the GSHP is more feasible with a long payback period. Also, the CO2 emission decrease by about 34%

Net community production in the North Atlantic Ocean derived from Volunteer Observing Ship data

The magnitude of marine plankton net community production (NCP) is indicative of both the biologically driven exchange of carbon dioxide between the atmosphere and the surface ocean and the export of organic carbon from the surface ocean to the ocean interior. In this study the seasonal variability in the NCP of five biogeochemical regions in the North Atlantic was determined from measurements of surface water dissolved oxygen and dissolved inorganic carbon (DIC) sampled from a Volunteer Observing Ship (VOS). The magnitude of NCP derived from dissolved oxygen measurements (NCPinline image) was consistent with previous geochemical estimates of NCP in the North Atlantic, with an average annual NCPinline image of 9.5 ± 6.5 mmol O2 m−2 d−1. Annual NCPinline image did not vary significantly over 35° of latitude and was not significantly different from NCP derived from DIC measurements (NCPDIC). The relatively simple method described here is applicable to any VOS route on which surface water dissolved oxygen concentrations can be accurately measured, thus providing estimates of NCP at higher spatial and temporal resolution than currently achieved

Bubble columns for condensation at high concentrations of noncondensable gas: Heat-transfer model and experiments

Carrier gas based thermodynamic cycles are common in water desalination applications. These cycles often require condensation of water vapor out of the carrier gas stream. As the carrier gas is most likely a noncondensable gas present in very high concentrations (60–95%), a large additional resistance to heat transfer is present. It is proposed to reduce the aforementioned thermal resistance by condensing the vapor–gas mixture in a column of cold liquid rather than on a cold surface using a bubble column heat exchanger. A theoretical predictive model for estimating the heat-transfer rates and new experimental data to validate this model are described. The model is purely physics based without the need for any adjustable parameters, and it is shown to predict heat rates within 0 to −20% of the experimental values. The experiments demonstrate that heat-transfer rates in the proposed device are up to an order magnitude higher than those achieved in existing state-of-the-art dehumidifiers.Center for Clean Water and Clean Energy at MIT and KFUP

ENERGY EFFECTIVENESS OF SIMULTANEOUS HEAT AND MASS EXCHANGE DEVICES

Simultaneous heat and mass exchange devices such as cooling towers, humidifiers and dehumidifiers are widely used in the power generation, desalination, air conditioning, and refrigeration industries. For design and rating of these components it is useful to define their performance by an effectiveness. In this paper, several different effectiveness definitions that have been used in literature are critically reviewed and an energy based effectiveness which can be applied to all types of heat and mass exchangers is defined. The validity and the limitations of the various effectiveness definitions are demonstrated by way of several examples including direct and indirect contact, parallel and counterflow heat and mass exchangers. The limiting case of a simple heat exchanger is also discussed. The importance of thermal balancing in minimizing entropy production and its implications for optimization and design of these devices is dealt with in detail. The application of the energy effectiveness to heat-exchanger-like "-NTU correlations is also examined using a detailed numerical model.King Fahd University of Petroleum and Mineral