Temperature modulated

For low-temperature heating systems using natural convective or radiant appliances the normal design water flow temperature to the system is 83°C (see also Table 27.8). Boost temperatures may be used on modulated-temperature systems because of the changes in heat output characteristics with varying temperatures. Additionally, comfort aspects must be borne in mind, as forced convective emitters operating on modulated temperature systems can deliver air streams at unacceptably low temperatures. 

ASTM E1952, 2001. Standard test method for thermal conductivity and thermal diffusivity by modulated temperature differential scanning calorimetry. 

The power output of solar modules is expressed in terms of their "peak" power output (Wp). This is the amount of electric power that a module generates when it receives 1.0 kW/m2 of vertical solar irradiation at 25°C module temperature (also called one sun). Therefore, a 10% efficient module receiving one sun, will produce 100 Wp/m2. If this solar irradiation exists for 8 hours per day, this module will generate 0.8 kWh/m2/day. Naturally both the number of sunny hours of the day and the intensity of insolation vary (see Figures 1.29 and 1.30 and www.bpsolar.com). In addition the angle of irradiation and/or cell temperature can also be less than optimum. 

The operation of a photovoltaic system is governed by the current-voltage characteristic curves of the photovoltaic module. Such a set of curves, for different values of the incident solar irradiance and constant photovoltaic module temperature, is shown in Figure 2.4. The curves consist of two parts. In the first part the photovoltaic module behaves as a constant-current source, with amplitude proportional to the solar irradiance level. In the rest of the curve, current decays... 

Manufacturers provide operating characteristics of photovoltaic modules in standard conditions, which are defined by a solar irradiance value equal to 1000 W/m2 and a photovoltaic module temperature equal to 25°C. The most important of them is the maximum power that can be obtained at these conditions and is used for the determination of the photovoltaic module nominal power. However, in a considered site, solar irradiance changes during the day. In addition, depending on the environmental conditions, due to the internal thermal losses of the photovoltaic module, its temperature also varies. As a result, the maximum extracted power is usually lower than that provided by the manufacturers. 

For the characterization of solar resource, measured irradiance data as well as site-specific parameters are needed. These include geographic information (site latitude and longitude) for the calculation of the solar angle that also varies during the day, as well as ambient temperature for the estimation of the photovoltaic module temperature (Manwell, 1998). 

More complex temperature programmes are sometimes useful. These might combine periods of variable heating and cooling rates with isothermal periods. For example, stepwise heating can be used to detect the onset of melting under quasi-isothermal conditions (Laye, 2002). Modulated temperature DSC (MTDSC), in which the linear temperature scan is perturbed by a sinusoidal, square or saw-tooth wave, or other modulation of temperature, has a number of potential advantages over the conventional linear scan. These include increased sensitivity and resolution, and the ability to separate multiple thermal events (Laye, 2002). 

Bottom, R. (1999). The role of modulated temperature differential scanning calorimetry in the characterisation of a drug molecule exhibiting polymorphic and glass forming tendencies. Int. J. Pharm., 192,47-53. [251]... 

A comparative study of different poliovirus capsid structures revealed a hydrophobic pocket that contained sites for cellular lipid interaction (Hogle et al, 1985 Filman et al, 1989). This lipid component, which is termed the pocket factor, may be sphingosine. Amino acids that modulate temperature sensitivity of poliovirus infectivity map to the interfaces between capsid protomers and are adjacent to the site of lipid binding. A similar lipid molecule appears to be present in some but not all... 

MODULATED TEMPERATURE DIFFERENTIAL SCANNING CALORIMETRY/DYNAMIC DIFFERENTIAL SCANNING CALORIMETRY... 

Reading M. Hourston DJ. Modulated Temperature Differential Scanning Calorimetry. Theory and Practical Applications in Polymer Characterisation. Dordrecht, Holland Springer, 2006. 

Coleman NJ, Craig DQM. Modulated temperature differential scanning calorimetry A novel approach to pharmaceutical thermal analysis. Ini J Pharm 1996 135 13-29. 

Differential Scanning Calorimetry. DSC scans were made at 20°C min"1 on a Mettler TA300O system equipped with a DSC-30 low temperature module. Temperature calibration was done with a multiple Indium-lead-nickel standard. An indium standard was used for heat flow calibration. Thin shavings (ca. 0.5 mm thick) were cut with a razor blade from the cross-sectional edge of a plaque. These sections contained both surface and center portions. 

The aim of this entry is to discuss the primary thermal analysis technique, TGA, in terms of the associated instrumentation, calibration procedures, and application range. Related techniques, such as TGA-DTA, EGA, SCTA, and modulated temperature TGA, are also discussed, as these reflect the significant developments of the TGA family of techniques that have occurred over the last decade. 

Such a differential heating program leads to increased sensitivity and resolution in TGA but also to a much increased time-frame for the analysis. Dynamic rate TG appears to have addressed both of these features and hence has much potential as a high resolution/ rapid thermal analysis system, which, unlike SCTA, can be applied for rapid and reproducible thermal analysis of a wide range of complex materials. Finally, modulated temperature thermogravimetrie analysis has enhanced potential for the kinetic analysis of thermal decomposition reactions over conventional TGA because of its greater resolution of thermal events. 

He R, Craig DQM. An investigation into the thermal behaviour of an amorphous drug using low frequency dielectric spectroscopy and modulated temperature differential scanning calorimetry. J Pharm Pharmacol 2001 53 41-48. 

Temperature modulated DSC (MDSC)2°2-204 jg another technique that has proved useful in the study of the glass transition " - where, it has been claimed, the approach is capable of providing better resolution and sensitivity than conventional DSC.2° In this, a modulated temperature programme is superimposed upon the conventional heating ramp and the resulting heat flows are interpreted in terms of two heat capacities an in-phase storage heat capacity and an out-of-phase kinetic heat capacity. Various theoretical procedures have been proposed for this and there is little doubt that the approach can provide information that is complementary to conventional DSC.2 ° However, the technique does involve slow temperature scans (cf. high-speed DSC above) and the authors feel that there are areas where the additional data are not, at present, easy to interpret. 

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