Phase change , energy

Lim, J.S., Bejan, A., and Kim, J.H., 1992, Thermodynamic optimization of phase change energy storage using two or more materials, ASME J. Energy Res. Technol. 114 84—90. 

During a solid to liquid phase change, energy is ... 

Farid, M.M. Khudhair, A.M. Razack, S.A.K. Al-Hallaj, S. A review on phase change energy storage Materials and applications. Energ Corners Manage 45 (2004) 1597—1615. 

When the sample holder assembly is heated at a programmed rate, the temperatures of both the sample and the reference material increase uniformly. The furnace temperature is recorded as a function of time. If the sample undergoes a phase change, energy is absorbed or emitted, and a temperature difference between the sample and the reference (AT) is detected. The minimum temperature difference which can be measured by DTA is 0.01 K. 

Farid MM, Khudhair AM, Razack SAK, Al-HaUaj S (2004) A review on phase change energy storage materials and applications. Energy Convers Manage 45(9-10) 1597-1615. doi 10.1016/j.enconman.2003.09.015... 

Kaygusuz K (2003) Phase change energy storage for solar heating systems. Energy Source 25(8) 791-807. doi 10.1080/00908310390207837... 

Above 81.5 K the C(2x 1) structure becomes the more stable. Two important points are, first, that a change from one surface structure to another can occur without any bulk phase change being required and, second, that the energy difference between dtemative surface structures may not be very large, and the free energy difference can be quite temperature-dependent. 

Calorimetry is the basic experimental method employed in thennochemistry and thennal physics which enables the measurement of the difference in the energy U or enthalpy //of a system as a result of some process being done on the system. The instrument that is used to measure this energy or enthalpy difference (At/ or AH) is called a calorimeter. In the first section the relationships between the thennodynamic fiinctions and calorunetry are established. The second section gives a general classification of calorimeters in tenns of the principle of operation. The third section describes selected calorimeters used to measure thennodynamic properties such as heat capacity, enthalpies of phase change, reaction, solution and adsorption. 

In addition to the reduction in performance, flow maldistribution may result in increased corrosion, erosion, wear, fouling, fatigue, and material failure, particularly for Hquid flows. This problem is even more pronounced for multiphase or phase change flows as compared to single-phase flows. Flow distribution problems exist for almost all types of exchangers and can have a significant impact on energy, environment, material, and cost in most industries. 

Fig. 16. Maximum achievable signal-to-noise ratio (SNR) on read-out of different writable optical data storage systems as a function of the writing energy (laser power) (121). SQS = Organic dye system (WORM) PC = phase change system (TeSeSb) MO = magnetooptical system (GbTbFe). See text.

Desalination. Desalination of seawater and brackish water has been and, as of the mid-1990s, is the primary use of RO. Driven by a need for potable water in areas of the world where there is a shortage, this industry has developed. Desalination involves the reduction of the total dissolved soHds (IDS) concentration to less than 200 mg/L. RO offers several advantages over other possible desalination processes such as distillation (qv), evaporation (qv), and electro dialysis. The primary advantage of RO over the traditionally used method of distillation is the energy savings that is afforded by the lack of a phase change in RO. 

Advantages to Membrane Separation This subsertion covers the commercially important membrane applications. AU except electrodialysis are pressure driven. All except pervaporation involve no phase change. All tend to be inherently low-energy consumers in the-oiy if not in practice. They operate by a different mechanism than do other separation methods, so they have a unique profile of strengths and weaknesses. In some cases they provide unusual sharpness of separation, but in most cases they perform a separation at lower cost, provide more valuable products, and do so with fewer undesirable side effects than older separations methods. The membrane interposes a new phase between feed and product. It controls the transfer of mass between feed and product. It is a kinetic, not an equihbrium process. In a separation, a membrane will be selective because it passes some components much more rapidly than others. Many membranes are veiy selective. Membrane separations are often simpler than the alternatives. 

---