Effects of Volume Changes on the Thermal Performance of PCM Layers Subjected to Oscillations of the Ambient Temperature: Transient and Steady Periodic Regimes.

The Stefan problem regarding the formation of several liquid-solid interfaces produced by the oscillations of the ambient temperature around the melting point of a phase change material has been addressed by several authors. Numerical and semi-analytical methods have been used to find the thermal response of a phase change material under these type of boundary conditions. However, volume changes produced by the moving fronts and their effects on the thermal performance of phase change materials have not been addressed. In this work, volume changes are incorporated through an additional equation of motion for the thickness of the system. The thickness of the phase change material becomes a dynamic variable of motion by imposing total mass conservation. The modified equation of motion for each interface is obtained by coupling mass conservation with a local energy-mass balance at each front. The dynamics of liquid-solid interface configurations is analyzed in the transient and steady periodic regimes. Finite element and heat balance integral methods are used to verify the consistency of the solutions to the proposed model. The heat balance integral method is modified and adapted to find approximate solutions when two fronts collide, and the temperature profiles are not smooth. Volumetric corrections to the sensible and latent heat released (absorbed) are introduced during front formation, annihilation, and in the presence of two fronts. Finally, the thermal energy released by the interior surface is estimated through the proposed model and compared with the solutions obtained through models proposed by other authors.

The role of endoscopy in the management of GERD.

We recommend that uncomplicated GERD be diagnosed on the basis of typical symptoms without the use of diagnostic testing, including EGD. We recommend EGD for patients who have symptoms suggesting complicated GERD or alarm symptoms. We recommend that EGD not be routinely performed solely for the assessment of extraesophageal GERD symptoms. We recommend that endoscopic findings of reflux esophagitis be classified according to an accepted grading scale or described in detail. We suggest that repeat EGD be performed in patients with severe erosive esophagitis after at least an 8-week course of PPI therapy to exclude underlying BE or dysplasia. 44BB We recommend against obtaining tissue samples from endoscopically normal tissue to diagnose GERD or exclude BE in adults. We suggest that endoscopy be considered in patients with multiple risk factors for Barrett's esophagus. We recommend that tissue samples be obtained to confirm endoscopically suspected Barrett's esophagus. We suggest that endoscopic antireflux therapy be considered for selected patients with uncomplicated GERD after careful discussion with the patient regarding potential adverse effects, benefits, and other available therapeutic options.