Specific heat capacity determining

The systematic errors associated with the delivery of energy via electric leads in the course of specific heat capacity determinations can be eliminated by the application of a contactless energy supply. But here the exact determination of the energy introduced brings new problems and error sources. Moreover, this approach does not eliminate the errors caused by heat leakage associated with the sample mount and with the measurement of the sample temperature. 

Several factors are involved in determining the cooking times required for foods in a microwave oven. One of these factors is specific heat capacity. Determine the approximate time required to warm 250 mL of chicken broth from 4 °C (a typical refrigerator temperature) to 50 °C in a 700 W microwave oven. Assume that the density of chicken broth is about 1 g/mL and that its specific heat capacity is approximately 4.2 J g ... 

Because the specific heat capacity of the water vapor is different from that of the dry air, the true dry-bulb mixed-stream air temperature can be determined only by means of a heat balance. 

Assuming that radiation losses amount to 20 kJ/kg of dry air used, determine the mass flow of dry air supplied to the dryer and the humidity of the outlet air. The latent heat of water vapour at 295 K = 2449 kJ/kg, the specific heat capacity of dried material = 0.88 kJ/kg K, the specific heat capacity of dry air = 1.00 kJ/kg K, and the specific heat capacity of water vapour = 2.01 kJ/kg K. 

The specific heat capacity commonly has units of J/g-K. The specific heat capacity of water is 4.18 J/g-K. If we have the specific heat capacity, the mass, and the change of temperature, it is possible to determine the amount of energy absorbed or released (q). 

A triple-effect evaporator is fed with 5 kg/s of a liquor containing 15 per cent solids. The concentration in the last effect, which operates at 13.5 kN/m2, is 60 per cent solids. If the overall heat transfer coefficients are 2.5, 2.0 and 1.1 kW/m2 K, respectively, and the steam is fed at 388 K to the first effect, determine the temperature distribution and the area of heating surface required in each effect, assuming the calandrias are identical. What is the economy and what is the heat load on the condenser The feed temperature is 294 K and the specific heat capacity of all liquors is 4.18 kJ/kg K... 

You can use the specific heat capacity of a substance to calculate the amount of energy that is needed to heat a given mass a certain number of degrees. You can also use the specific heat capacity to determine the amount of heat that is released when the temperature of a given mass decreases. The specific heat capacity of liquid water, as shown in Table 5.2, is 4.184 J/g °C. This relatively large value indicates that a considerable amount of energy is needed to raise or lower the temperature of water. 

Specific Heat Three different values for specific heat can be determined and are described as the specific heat capacity, specific heat of fusion, and specific heat of evaporation. These values are described as follows ... 

Calorimetry experimental technique used to determine the specific heat capacity of a substance or various heats of chemical reactions... 

Determining the Approximate Value of the Atomic Mass of Lead from Its Specific Heat Capacity. To determine the specific heat capacity of a metal, use a calorimeter and a device for heating the metal. A very simple calorimeter can be made from several beakers inserted one into another (Fig. 38). The inner beaker should have a volume of 100 ml, the middle one—300-400 ml, and the outer one—500 ml. Water is poured into the small beaker, while the others are needed to produce an air thermal-insulating layer. 

Fig. 38. A device for determining the atomic mass of a metal from its specific heat capacity...

To determine the amount of heat absorbed by the glass of the calorimeter beaker, mark the level of the water in the beaker when running the experiment. Use the data obtained to approximately determine the mass of the glass heated by the water. Consider that the mass of the thermometer glass immersed in the liquid is about 2 g. Use the found specific heat capacity to calculate the atomic mass of lead by the Dulong and Petit law. 

ASTM E1269, 2004. Standard test method for determining specific heat capacity by differential scanning calorimetry. 

The Nemst calorimeter is a calorimeter for the measurement of specific heat capacities at low temperatures. The sample to be measured is suspended in a glass or metal envelope that car be evacuated. The sample is heated by means of a platinum wire located in a bore inside the sample. The wire also serves as a resistance thermometer. The specific heat capacity is determined by recording the temperainre rise in the sample for a given delivery of energy. 

Determine the temperature change when 10.0 g of (a) KCl (b) MgBr2 (c) KN03 (d) NaOH dissolves in 100.0 g of water Assume that the specific heat capacity of the solution is 4.18 J-K, -g 1 and that the enthalpies of solution in Table 8.6 are applicable. 

In order to obtain accurate results, this function should be accounted for when the temperature of a reaction mass tends to vary over a wider range. However, in the condensed phase the variation of heat capacity with temperature is small. Moreover, in case of doubt and for safety purposes, the specific heat capacity should be approximated by lower values. Thus, the effect of temperature can be ignored and generally the heat capacity determined at a (lower) process temperature is used for the calculation of the adiabatic temperature rise. 

A substance, metallic in nature, is to be identified, and heat capacity is one of the clues to its identity. A block of the metal weighing 150g required 38.5 cal to raise its temperature from 22.8°C to 26.4°C. Calculate the specific heat capacity of the metal and determine if it is the correct alloy, which has a specific heat capacity of 0.0713 cal/g K. 

While the procedure for this experiment is provided with a fair amount of detail, students can have input into the design of the calorimeter and, although a list of materials is provided, different materials can be made available and they can choose the ones they think would be most effective. The inquiry aspect of this experiment lies primarily in the detailed analysis of their results required to suggest an appropriate interstitial material and the need to assess sources of error. If, for example, students have a large error in the determination of the specific heat capacity of copper, they must decide what could contribute to the error and then try to redesign their calorimeter or their technique in order to limit the error. 

This would not be problematic if standardized, reliable, reproducible, and inexpensive laboratory tests were available to estimate each of the required properties. Although several specialized laboratory tests are available to measure some properties (e.g., specific heat capacity can be determined by differential scanning calorimetry [DSC]), many of these tests are still research tools and standard procedures to develop material properties for fire modeling have not yet been developed. Even if standard procedures were available, it would likely be so expensive to conduct 5+ different specialized laboratory tests for each material so that practicing engineers would be unable to apply this approach to real-world projects in an economically viable way. Furthermore, there is no guarantee that properties measured independently from multiple laboratory tests will provide accurate predictions of pyrolysis behavior in a slab pyrolysis/combustion experiment such as the Cone Calorimeter or Fire Propagation Apparatus. 

If the total heat capacities of the empty sample and reference containers were perfectly matched, then the empty sample container versus empty reference container trace should appear as a flat baseline of zero value during the entire scan. This is rarely the case (due to asymmetries in instrument construction) and is actually not necessary for this calculation. The temperature deviation from this line for the other traces is a result of the extra thermal mass on the sample side, causing it to lag the reference in temperature during the heating ramp. Defining cp as the specific heat (J/g-K), the sample specific heat is determined by the ratio ... 

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