Heat flow vs. temperature

The sample (typically 1 mg) is sealed in a glass container (capillary or ampoule) in a nitrogen or air atmosphere. The reference material is typically an empty sealed container. The sample and reference are heated in an oven at a constant temperature rate (typically 10 °C per minute) from ambient to 400 °C. Energy flow to the sample is measured as a slight deviation in its local temperature. Data are presented in terms of plot of heat flow vs. temperature. Processes (phase changes, reactions) total enthalpies are determined by integration of the heat rate curve. 

Figure 2. Heat flow vs. temperature obtained with a high pressure differential scanning calorimeter for two samples of YBa2Cu307 x.

In a DSC scan, the difference of energy input (heat flow) into a sample and into a reference material is plotted as a function of temperature. In a plot of heat flow vs. temperature, endothermic minima correspond to desolvation of solvates or phase transitions of polymorphs, and exothermic maxima correspond to crystallization or decomposition. Integration over the area of a transition feature yields the associated transition enthalpy. 

Fig. 2 Schematic five types of SMPs depicted as a function of their thermal behavior. Plotted is the heat flow vs temperature as measured in a differential scanning calorimetry (DSC) experiment (a) Cat. A-1, chemically crosslinked tunorphous polymer network (Tirans = 7g) (b) Cat. A-11, chemically ciossfinked semicrystaUine polymer networks (Taims = 7m)> ( ) Cat. B-1, physically crosslinked thermoplastic with Tirans = T (d) Cat. B-11, physically crosslinked thermoplastic (Tams = I m) and (e) liquid crystalline polymer (Tlrans = T -n)...

Thermal Event Ejfect on plot of heat flow vs temperature... 

A typical reaction calorimeter consists of a jacketed reactor, addition device, temperature transducer(s) and calibration heaters. There are a number of devices within Dow ranging from the commercially available Mettler RC-1 (1-2 L volume) to smaller, in-house reactors (10-50 ml). While each of these devices has their unique attributes (e.g., in-situ spectrometry, quick turn-around, ability to reflux, etc.), all of the calorimeters will produce a signal of heat flow vs. time. The heat flow is usually produced in response to the addition of a reagent or an increase in temperature. Volume of gas or pressure generated may also be measured. 

Convection should create curvature in the measured temperature-depth profiles in the sediments, but because of the relatively large thermal diffusion coefficient the curvature is slight, and at the time of the first heat flow measurements it could not be detected. As thermistors improved, detailed temperature vs. depth measurements in sediments near active ridge crest areas indicated non-linearity caused by convection with both concave upward profiles indicating upwelling and concave dovraward profiles caused by dovmwelling of water in the sediments. 

FIGURE 4.13 Modulate heat flow rate and sample temperature plotted vs. time for n-pen-tacontane by quasi-isothermal MTDSC. (From Pak, J., Boiler, A., Moon, I., Pyda, M., and Wunderlich, B., Thermochim. Acta, 357-358, 259, 2000. With permission.)... 

IS A one-shell pass and multiple-of-two-tube-passes heat exchanger will be designed. Water flows at the rate of 360,000 kg/hr (Vc = 3 m/s) in the tubes (2 cm ID, 2.5 cm OD, k = 20 W/m-K). The inlet and outlet temperature of the water are Ta- = 10 "C and Tc0 = 65 °C, respectively. Ethylene glycol flows (Vs = 1.5 m/s) through the shell at the rate of 720,000 kg/hr [cp = 2 kJ/kg-K), and its temperature decreases from Tki = 180 C Evaluate the shell-side heat transfer coefficient on the basis of cross flow, (a) Calculate the heat transfer area, (b) Recalculate the exit temperatures after reducing the water flow rate to 240,000 kg/hr. 

Temperature vs. heat flow rate in countercurrent flow. 

In DSC, differences in heat flow into a reference and sample are measured vs. the temperature of the sample. The difference in heat flow is a difference in energy DSC is a calorimetric technique, and results in more accurate measurement of changes in enthalpy and heat capacity than that obtained by DTA. 

In addition to the total area A, at least 10-20 sets of heat flow rates dH/dt and partial areas at different temperatures should be tabulated for a single DSC curve, and calculating the differences between two neighboring points, E and n can be obtained from the slope and intercept of the A ln(dH/df)/(A ln(A - a) vs A (1/T)/A ln(A - a) plot. 

DSC measurements of the energy during melting of aqueous polymer solutions and gels yield heats of mixing, and sorption [89] has been used to study the heat changes occurring in a polymer as it is cooled (plots of temperatures vs. heat flow (measured in mW)). 

It is often difficult to determine the glass transition temperature of semicrystalline polymers from DSC curves the glass transition can be very broad and smeared out, and long term experience is needed to see the glass transition on such DSC curves. In these cases, the derivative signal dQdT vs. T or dCp/dT vs. T) (where Q is the heat flow) can help, because the heat capacity increase will be replaced by a broad peak. However, calculation of the ACp at Tg is still often difficult. Care must be taken when reporting Tg from these DSC curves, because the peak temperature on the (dQdT)-T curve corresponds to the inflection point and not the half-height heat capacity increase of the Cp-T (or Q-T) curves. The precision of the Tg determination in these DSC curves is much worse than for amorphous polymers in the best case it is 1°C. 

In a typical experiment where the temperature is raised from Ti to T2, a plot of heat flow (mW) vs temperature is obtained. Generally, the change in enthalpy AH is related to the area A under the curve ... 

Fig.. 1-171 CdS. Thermal conductivity vs. temperature for c axis parallel and perpendicular to the heat flow A T [ 1.145, 146]...

Non-isothermal crystallization kinetics for nylon-6 and nanocomposite samples were studied. The onset of the crystallization, crystallization temperature and the heat of the crystallization were noted during the cooling cycle. Using Universal Analysis software, running integration function was performed for crystallization peak in heat flow (J/g) vs. time (minutes) plot to get the values of relative crystallinity X, for different values of time t. The time required for the sample to crystallize 50% ti/2) was noted for the nylon-6 and nanocomposite samples. Then the chart of In [-In (1 - Xj)] vs. In t was plotted. The Avrami equation was used to determine values of n and k from the slopes and the interception of the best fit (Equation 14.4). 

Counter Flow Heat Exchanger Actual Temperatures vs. RELAP5-3D Temperatures... 

The phenomenon of flow instability is a result of interaction between pressure drop and coolant flow in heated channels. For the heated channels, the pressure drop as a function of mass flow deviates from m -dependency at low flow rates and shows a minimum. Before the minimum, any decrease in the flow rate results in an increase of the pressure drop with the consequence of low local pressure and saturation temperature. The minimum in the pressure drop/mass flow kurve depends on flow characteristics and heat flux. The determination of critical heat flux at the onset of flow instability has been experimentally inverstigated by whittle and Forgan /6/ for the coolant chaimels conditions exiting in MTR. They measured the mass flow, exit temperature and pressure drop corresponding to minima in the pressure drop -vs- flow rate kurve for subcooled water flowing (upward and downward) in norrow heated channels (width 2.54 cm, thickness 0.14 to 0.32 cm, and length 40 to 61 cm) under the followong conditions ... 

We now address the thermod5mamic experimental evidences for the solid solution outside of the miscibility gap. Microcalorimetry can directly measure entropy changes vs. x at fixed temperature T during the electrochemical reaction. Observed heat flow P is related to entropy change A5 by P = -ITAS/nF, where / is the input current and F is the Faraday constant The classical entropy of mixing 5rf(x) can be calculated for a fully disordered lattice of lithium atoms and vacant sites, and heat flow varies linearty with = kBln[l/x],... 

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