Sample calorimeter

In the twin calorimeter, first developed by Joule177 [72], the sample is placed in one calorimeter, while a reference compound of known thermal properties is placed in a second calorimeter matched as closely as possible to the sample calorimeter. This has been very useful in studying rapid reactions, or for measurements of very small heats or slow reactions. 

Abstract An iron sampling calorimeter with warm-liquid ionization chambers has been tested at the CERN SPS in order to study the signal development and to verify the energy calibration of the hadron calorimeter in the KASCADE-Grande air shower experiment. The signal calibration of the detectors is discussed. First results of the analysis of the longitudinal shower development in the calorimeter are presented and compared with results from simulations based on the GEANT/ FLUKA code. 

The detector Engler et al. 1999 is an iron sampling calorimeter with the lateral dimensions 16 x 20 m2. It consists of 9 layers of ionization chambers and a layer of plastic scintillation counters to provide fast trigger signals interspaced... 

DO 42,000 L Ar Fermilab EM and hadronic sampling calorimeter Electrons, photons, and hadrons 1991... 

The main measured quantity discussed in this paper is the reversing heat flow. It is proportional to the temperature difference between reference calorimeter (empty) and sample calorimeter (AT T, Representing the instantaneous heat flow as a Fourio series with v representing an integer running from 1 to oo and p ... 

The heat-flow rate of the sample calorimeter, consisting of a pan and the sample, and the reference calorimeter, consisting usually of an empty pan, is governed by the rate of temperature change, q (in K min ), and the heat capacity, Cp (in 1K ). The heat capacity measured at constant pressure, p, and composition, n, can then be represented by Cp = (8H/8T)p , with H being the enthalpy and T, the temperature. The overall heat capacity of the sample calorimeter is written as = (mCp + Q), where m... 

Mathematically this simation without a AT loop is expressed by the upper three boxed equations in Fig. 4.60, where dQs/dt and dQs/dt are the heat-flow rates into the reference and sample calorimeters, respectively. The measured and true temperatures are represented by T and T. For simplicity, one can assume that the proportionality constant K is the same for the sample and reference calorimeters. Differences are assessed by calibration. Both bottom equations are then equal to the power input from the average temperature amplifier. Wav (ill W or J s ). 

One additional point needs to be considered. The commercial DSC is constructed in a slightly different fashion. Instead of letting the differential amplifier correct only the temperature of the sample calorimeter by adding power, only half is added, and an equal amount of power is subtracted from the reference calorimeter. This is accomplished by properly phasing the power input of the two amplifiers. A check of the derivations shows that the result does not change with this modification. 

The mathematical treatment of calorimetry is complicated since there are no prefect insulators for heat. Even a vacuum is no barrier since radiation can transport heat, particularly at elevated temperatures. For this reason one uses differential techniques where reference and sample calorimeters are placed in symmetrical environments with... 

In the sketch A of Fig. A.l 1.2 the equivalent electrical circuit for a conventional DSC measurement is drawn. The heat-flow rate into the sample calorimeter (pan + sample) is represented by and is the heat-flow rate into the empty pan which is the reference calorimeter. The heat-flow rate into the sample itself should then be = and matches Eq. (3) of Fig. 4.69 when assuming the thermal resistances... 

The second and third terms express the imbalance of the thermal resistances and heat capacities outside the calorimeters. The fourth term, the effect of different heating rates between reference and sample calorimeter. This last term is of importance when a transition occurs in the sample and does not follow the assumptions made for Figs. 4.71 and 4.72 [3]. (Note the differences to [2] from changed symbols and signs, 4> = q, at = - AT, ATb = AT , q = dT /dt, as well as from expanded subscripts). 

Calorimeters measure the heat produced by a sample of nuclear material, whereby the heat originates primarily from the a-decay of the isotopes making up the nuclear material. Calorimeters have traditionally been fabricated using a sensor of nickel wire wound around a measurement chamber (Bracken et al. 2002). The nickel wire provides a temperature-sensitive resistance leading to highly accurate and precise electrical measurements of the power produced by a sample. Calorimeters are calibrated with Pu heat somces or plutonium samples with known mass and isotopic composition. Calorimetric assay is the most precise and accmate NDA measmement method for plutonium products (>100 grams). 

D Furnace, sample, calorimeter substance Figure 7.13 Drop calorimeter. 

Before the DSC experiment is started, the two calorimeters (i.e., the sample and reference pods, since they are separate calorimeters with one heater) are in equilibrium, they are at the same temperature Tu = T = where is the block temperature, is the sample temperature and T, is the reference temperature. When the operator starts the heating experiment, the block will be heated at a linear rate therefore the sample and the reference calorimeters will also be heated. They will lag behind the block temperature, but to a different extent since the heat capacity of the sample calorimeter is higher because of the additional mass of the sample as compared with an empty pan for the reference. The sample temperature will lag behind T,. Assuming the pan masses are identical, the Th - and Th - temperature differences will be proportional to the heat capacity of the sample and reference calorimeters, respectively. The temperatures Th, T, and T, are measured by thermocouples. 

One additional point needs to be considered. The commercial DSC is constructed in a slightly different fashion than that just described. Rather than letting the differential amplifier loop correct only the temperature of the sample, an equal amount of power is subtracted from or added to the power delivered to the reference by the average temperature amplifier. This is accomplished by proper phasing of the power input of the differential temperature amplifier. In reality, thus, one-half of is added to the sample calorimeter in addition to the full power from the average temperature loop, while one-half of IFp is at the same time subtracted from the power going into the reference calorimeter. This results in a total additional power to the sample that is equal to IV, as required by our calculations. The performance of the DSC is thus still described by Eqs. (1), (4), (5), (10), and (11). 

Recently it became possible to measure heat capacity in a single run by using a DSC with three calorimeter positions (Du Pont 912 Dual Sample DSC, as shown in Fig. 4.4, top, expanded to three positions). One position is used to carry the sample calorimeter, another, the empty calorimeter, and the last, the calorimeter filled with the AI2O3 standard. The precision achieved, after correction for asymmetry, was 1%. Improvements in instrument design could easily develop this method into the standard DSC. 

Multiple. sample capabilities. Plant studies routinely require examination of many. samples, particularly when the objectives of the study include identification of phenotypes with desired growth, stability, or yield characteristics. Screening large populations for individuals with desired metabolic characteristics is impossible in single-sample calorimeters. Current commercial multiwell calorimeters allow up to three samples to be run simultaneously. A calorimeter with as many as 100 sample wells could be effectively employed for plant studies. 

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