Edward K. Summers

Entropy Generation Analysis of Desalination Technologies

Increasing global demand for fresh water is driving the development and implementation of a wide variety of seawater desalination technologies. Entropy generation analysis, and specifically, Second Law efficiency, is an important tool for illustrating the influence of irreversibilities within a system on the required energy input. When defining Second Law efficiency, the useful exergy output of the system must be properly defined. For desalination systems, this is the minimum least work of separation required to extract a unit of water from a feed stream of a given salinity. In order to evaluate the Second Law efficiency, entropy generation mechanisms present in a wide range of desalination processes are analyzed. In particular, entropy generated in the run down to equilibrium of discharge streams must be considered. Physical models are applied to estimate the magnitude of entropy generation by component and individual processes. These formulations are applied to calculate the total entropy generation in several desalination systems including multiple effect distillation, multistage flash, membrane distillation, mechanical vapor compression, reverse osmosis, and humidification-dehumidification. Within each technology, the relative importance of each source of entropy generation is discussed in order to determine which should be the target of entropy generation minimization. As given here, the correct application of Second Law efficiency shows which systems operate closest to the reversible limit and helps to indicate which systems have the greatest potential for improvement.

Technical evaluation of stand-alone solar powered membrane distillation systems

Abstract Economic evaluation was carried out to understand the main contributors to water production cost in solar-powered membrane distillation (SP-MD) systems. Three SP-MD systems (Direct Contact (DCMD), Air Gap (AGMD), and Vacuum (VMD)) were modeled and economically analyzed. A parametric study was conducted on the AGMD, the most frequently used SP-MD configuration, to understand the relationships between various design and operation parameters and water production cost. The parametric study results show that, in the AGMD system, increasing the feed inlet temperature had a significant effect in lowering the cost while higher feed flow rate resulted in increased water production cost. This study also shows that higher effective membrane length and lower air gap width and feed channel depth reduce the cost of water. Finally, the choice of MD configuration (AGMD, VMD, DCMD) in SP-MD systems will impact the final water cost.

A novel solar-driven air gap membrane distillation system

Abstract Membrane distillation (MD) is a thermal-based membrane technology that is capable of treating highly concentrated or contaminated brines, including use as part of a zero liquid discharge desalination system. The low temperatures of operation of MD make it ideal to be used with solar energy as a heat source. However, current solar powered MD systems show poor performance and operate at low temperature compared to other thermal desalination systems. This paper describes a novel configuration of air gap MD which employs direct heating of the MD membrane by solar energy. The configuration provides a more uniform temperature profile over the membrane in the flow direction thereby enhancing vapor production. Heat transfer process modeling of the system shows that it can achieve a thermal efficiency that is nearly twice that of current solar powered MD systems.

Air-Heating Solar Collectors for Humidification-Dehumidification Desalination Systems

Relative to solar water heaters, solar air heaters have received relatively little investigation and have resulted in few commercial products. However, in the context of a Humidification-Dehumidification (HDH) Desalination cycle, air heating accounts for advantages in cycle performance. Solar collectors can be over 40% of an air-heated HDH system’s cost, thus design optimization is crucial. Best design practices and sensitivity to material properties for solar air heaters are investigated, and absorber solar absorptivity and glazing transmissivity are found to have the strongest effect on performance. Wind speed is also found to have an impact on performance. Additionally a well designed, and likely low cost, collector includes a double glazing and roughened absorber plates for superior heat transfer to the airstream. A collector in this configuration performs better than current collectors with an efficiency of 58% at a normalized gain of 0.06 K m2 /W.Copyright

Evaluation of a minimally invasive renal cooling device using heat transfer analysis and an in vivo porcine model

Partial nephrectomy is the gold standard treatment for renal cell carcinoma. This procedure requires temporary occlusion of the renal artery, which can cause irreversible damage due to warm ischemia after 30 min. Open surgical procedures use crushed ice to induce a mild hypothermia of 20°C in the kidney, which can increase allowable ischemia time up to 2.5 h. The Kidney Cooler device was developed previously by the authors to achieve renal cooling using a minimally invasive approach. In the present study an analytical model of kidney cooling in situ was developed using heat transfer equations to determine the effect of kidney thickness on cooling time. In vivo porcine testing was conducted to evaluate the cooling performance of this device and to identify opportunities for improved surgical handling. Renal temperature was measured continuously at 6 points using probes placed orthogonally to each other within the kidney. Results showed that the device can cool the core of the kidney to 20°C in 10-20 min. Design enhancements were made based on surgeon feedback; it was determined that the addition of an insulating air layer below the device increased difficulty of positioning the device around the kidney and did not significantly enhance cooling performance. The Kidney Cooler has been shown to effectively induce mild renal hypothermia of 20°C in an in vivo porcine model.

Renal Cooling Device for Use in Minimally Invasive Surgery

Over 58,000 patients suffer from renal cell carcinoma annually in the U.S. Treatment for this cancer often requires surgical removal of the cancerous tissue in a partial nephrectomy procedure. In open renal surgery, the kidney is placed on ice to increase allowable ischemia time; however, there is no widely accepted method for reducing kidney temperature during minimally invasive surgery. A device has been designed, prototyped, and evaluated to perform effective renal cooling during minimally invasive kidney surgery to reduce damage due to extended ischemia. The device is a fluid-containing bag with foldable cooling surfaces that wrap around the organ. It is deployed through a 15 mm trocar, wrapped around the kidney, and secured using bulldog clamps. The device then fills with an ice slurry and remains on the kidney for up to 20 min. The ice slurry is then removed from the device and the device is retracted from the body. Modeling results and tests of the prototype in a simulated lab environment show that the device successfully cools porcine kidneys from 37°C to 20°C in 6–20 min.

Innovative Renal Cooling Device for Use in Minimally Invasive Surgery

Over 58,000 patients suffer from renal cell carcinoma annually in the US. Treatment for this cancer often requires surgical removal of the cancerous tissue in a partial nephrectomy procedure. In open renal surgery, the kidney is placed on ice to increase allowable ischemia time; however there is no widely accepted method for reducing kidney temperature during minimally invasive surgery. A novel device has been designed, prototyped, and evaluated to perform effective renal cooling during minimally invasive kidney surgery to reduce damage due to extended ischemia. The device is a fluid-containing bag with foldable cooling surfaces that wrap around the organ like a taco shell. It is deployed through a 12mm trocar, wrapped around the kidney and secured using bulldog clamps. The device then fills with an ice slurry and remains on the kidney for up to 20 minutes. The ice slurry is then removed from the device and the device is retracted from the body. Tests of the prototype show that the device successfully cools porcine kidneys from 37 � C to 20 � C in under 5 minutes.