Heat Flow Rate Measurements Research Articles

Temperature and Heat Flow Rate Calibration of a Calvet Calorimeter from $$0\,{^{\circ }}\hbox {C}$$ 0 ∘ C to $$190 \,{^{\circ }}\hbox {C}$$ 190 ∘ C

This study describes the temperature and heat flow rate calibrations of a Calvet calorimeter (SETARAM, BT2.15) in the temperature range of 0–190 $${^{\circ }}\hbox {C}$$ . Temperature calibration is carried out using three reference materials, namely water, gallium, and indium, as specified in the International Temperature Scale of 1990 (ITS-90). The sample temperature of the Calvet calorimeter is corrected by the obtained mean value, $$-0.489 \,{^{\circ }}\hbox {C}$$ , of the measured extrapolated peak onset temperature ( $$T_{e})$$ when the heating rate ( $$\upbeta )$$ is zero ( $$\Delta T_\mathrm{corr }(\upbeta ~=~0$$ )). The heat flow rate is calibrated using a reference material with a known heat capacity, namely SRM 720 $$\alpha $$ - $$\hbox {Al}_{2}\hbox {O}_{3}$$ (synthetic sapphire), which is traceable to the National Institute of Standards and Technology. From the heat flow rate measurements of the blank baseline and SRM 720, the proportional calibration factor, $$\hbox {K}_{\Phi }$$ , in the 0–190 $$ \,{^{\circ }}\hbox {C}$$ temperature range was determined. The specific heat capacity of copper was measured with the obtained calibration values, and the measured data show consistency with the reference value.

The influence of cellulose nanocrystal additions on the performance of cement paste

The influence of cellulose nanocrystals (CNCs) addition on the performance of cement paste was investigated. Our mechanical tests show an increase in the flexural strength of approximately 30% with only 0.2% volume of CNCs with respect to cement. Isothermal calorimetry (IC) and thermogravimetric analysis (TGA) show that the degree of hydration (DOH) of the cement paste is increased when CNCs are used. The first mechanism that may explain the increased hydration is the steric stabilization, which is the same mechanism by which many water reducing agents (WRAs) disperse the cement particles. Rheological, heat flow rate measurements, and microscopic imaging support this mechanism. A second mechanism also appears to support the increased hydration. The second mechanism that is proposed is referred to as short circuit diffusion. Short circuit diffusion appears to increase cement hydration by increasing the transport of water from outside the hydration product shell (i.e., through the high density CSH) on a cement grain to the unhydrated cement cores. The DOH and flexural strength were measured for cement paste with WRA and CNC to evaluate this hypothesis. Our results indicate that short circuit diffusion is more dominant than steric stabilization.

Round-Robin Test of Heat Flux Sensors

The first intercomparison on the density of heat flow-rate measurements has been organized by MKEH (Hungarian Trade Licensing Office, Metrology Division) within the framework of EUROMET (Project No. 426). This round-robin test gives evidence about the measurement capabilities of the local realizations of a density of a heat flow-rate scale up to 100 W • m -2. Two types of heat flux plate sensors differing in their size were circulated among partner laboratories. Each one of the six partners calibrated the sensors using its own calibration system, a guarded hot plate or a heat flow meter apparatus. This article compares all the results of the round-robin test and gives the mutual differences among the partners. The participants could benefit from the measurement results by improving, in case of need, their calibration methods and procedures and by reducing their uncertainties. The impact of this comparison will go directly to the users in industry. © 2011 Springer Science+Business Media, LLC.

Experimental study on single bubble growth under subcooled, saturated, and superheated nucleate pool boiling

Nucleate pool boiling experiments with constant wall temperature were performed using pure R113 for subcooled, saturated, and superheated pool conditions. A microscale heater array and Wheatstone bridge circuits were used to maintain the constant wall temperature and to measure the instantaneous heat flow rate accurately with high temporal and spatial resolutions. Images of bubble growth were taken at 5,000 frames per second using a high-speed CCD camera synchronized with the heat flow rate measurements. The bubble geometry was obtained from the captured bubble images. The effect of the pool conditions on the bubble growth behavior was analyzed using dimensionless parameters for the initial and thermal growth regions. The effect of the pool conditions on the heat flow rate behavior was also examined. This study will provide good experimental data with precise constant wall temperature boundary condition for such works.

Experimental study of pool temperature effects on nucleate pool boiling

Nucleate pool boiling experiments with constant wall temperature were performed using pure R113 for subcooled, saturated, and superheated pool conditions. A microscale heater array and Wheatstone bridge circuits were used to maintain the constant wall temperature and to measure the instantaneous heat flow rate accurately with high temporal and spatial resolutions. Images of bubble growth were taken at 5000 frames per second using a high-speed CCD camera synchronized with the heat flow rate measurements. The bubble geometry was obtained from the captured bubble images. The effect of the pool conditions on the bubble growth behavior was analyzed using dimensionless parameters for the initial and thermal growth regions. The effect of the pool conditions on the heat flow rate behavior was also examined. The bubble growth behaviors during subcooled, saturated, and superheated pool boiling were analyzed using a modified Jakob number that we newly defined. Dimensionless time and bubble radius parameters with the modified Jakob number characterized the bubble growth behavior well. These phenomena require further analysis for various pool temperature conditions, and this study will provide good experimental data with precise constant wall temperature boundary condition for such works.

냉매 이성분 혼합물의 포화 풀핵비등 특성에 관한 연구

Saturated nucleate pool boiling experiments for binary mixtures, which are consisted of refrigerant R11 and R113, were performed with constant wall temperature condition. Results for binary mixtures were also compared with pure fluids. A microscale heater array and Wheatstone bridge circuits were used to maintain the constant temperature of the heating surface and to obtain heat flow rate measurements with high temporal and spatial resolutions. Bubble growth images were captured using a high speed CCD camera synchronized with the heat flow rate measurements. The departure time for binary mixtures was longer than that for pure fluids, and binary mixtures had a higher onset of nucleate boiling (ONB) temperature than pure fluids. In the asymptotic growth region, the bubble growth rate was proportional to a value between and . The bubble growth behavior was analyzed to permit comparisons with binary mixtures and pure fluids at the same scale using dimensionless parameters. There was no discernable difference in the bubble growth behavior between binary mixtures and pure fluids for a given ONB temperature. And the departure radius and time were well predicted within a error. The minimum heat transfer coefficient of binary mixtures occurred near the maximum value, and the average required heat flux during bubble growth did not depend on the mass fraction of R11 as more volatile component in binary mixtures. Finally, the results showed that for binary mixtures, a higher ONB temperature had the greatest effect on reducing the heat transfer coefficient.

포화상태 풀비등시 단일기포의 성장에 관한 연구

Nucleate boiling experiments on heating surface of constant wall temperature were performed using R113 for almost saturated pool boiling conditions. A microscale heater army and Wheatstone bridge circuits were used to maintain a constant wall temperature condition of heating surface and to measure the heat flow rate With high temporal and spatial resolutions Bubble images during the bubble growth were taken as 5000 frames per second using a high-speed CCD camera synchronized With the heat flow rate measurements The bubble growth behavior was analyzed using the new dimensionless parameters for each growth regions to permit comparisons With previous experimental results at the same scale. We found that the new dimensionless parameters can describe the whole growth region as initial and later (thermal) respectively The comparisons showed good agreement in the initial and thermal growth regions. In the initial growth region<br/> including surface tension controlled, transition and inertia controlled regions as divided by Robinson and Judd,<br/> the bubble growth rate showed that the bubble radius was proportional to t2/3 regardless of working fluids and heating conditions. And ill the thermal growth region as also called asymptotic region, the bubble showed a growth rate that was proportional to t1/5, also. Those growth rates were slower than the growth rates proposed ill previous analytical analyses The requited heat flow rate for the volume change of the observed bubble was estimated to be larger than the heat flow rate measured at the wall. Heat, which is different from the Instantaneous heat supplied through the heating wall, can be estimated as being transferred through the interface between bubble and liquid even With saturated pool condition. Tins phenomenon under a saturated pool condition needs to be analyzed and the data from this study can supply the good experimental data With the precise boundary condition (constant wall temperature).<br/>

Radioisotope-based technology for problem solving in industrial process plants in Ghana

Radioisotope-based Technology (RBT) has been used to diagnose malfunctions of industrial processing plants without interruption of overall production. In Ghana, RBT has been applied mainly for monitoring conditions in distillation columns and level/interfaces measurements in the petroleum refinery. The techniques used for on- line diagnoses of anomalies in industrial plants are highlighted and the results of experiments carried out using the technology in Tema Oil Refinery are also presented. Future prospects for RBT applications in residence time distribution measurements in mineral ore processing plants, leak detection in heat exchangers and flow rate measurements of liquids in pipelines are also discussed. Journal of Applied Science and Technology (JAST), Vol. 7, Nos. 1 & 2, 2002, pp. 27 - 36

Single bubble growth in saturated pool boiling of binary mixtures

Nucleate pool boiling experiments for binary mixtures, which are consisted of R11 and R113, were performed with constant wall temperature condition. Results for binary mixtures were also compared with pure fluids. A microscale heater array and Wheatstone bridge circuits were used to maintain the constant temperature of the heating surface and to obtain heat flow rate measurements with high temporal and spatial resolutions. Bubble growth images were captured using a high-speed CCD camera synchronized with the heat flow rate measurements. The departure time for binary mixtures was longer than that for pure fluids, and binary mixtures had a higher onset of nucleate boiling (ONB) temperature than pure fluids. In the asymptotic growth region, the bubble growth rate was proportional to a value between t 1/6 and t 1/4. The bubble growth behavior was analyzed to permit comparisons with binary mixtures and pure fluids at the same scale using dimensionless parameters. There was no discernible difference in the bubble growth behavior between binary mixtures and pure fluids for a given ONB temperature. And the departure radius and time were well predicted within a ±30% error. The minimum heat transfer coefficient of binary mixtures occurred near the maximum | y− x| value, and the average required heat flux during bubble growth did not depend on the mass fraction of R11 as more volatile component in binary mixtures. Finally, the results showed that for binary mixtures, a higher ONB temperature had the greatest effect on reducing the heat transfer coefficient.

Single bubble growth in saturated pool boiling on a constant wall temperature surface

Nucleate pool boiling experiments with constant wall temperatures were performed using R11 and R113 for saturated pool boiling conditions. A microscale heater array and Wheatstone bridge circuits were used to maintain a constant wall temperature condition and to obtain measurements with high temporal and spatial resolution. Accurate heat flow rate data were obtained from microscale heater array by controlling the surface conditions at a high temporal resolution. Images of the bubble growth were captured using a high-speed CCD camera synchronized with the heat flow rate measurements. The geometry of the bubble was obtained from the images. In the asymptotic growth region, the bubble showed a growth rate that was proportional to t 1/5, which was slower than the growth rate proposed in previous analytical analyses. The bubble growth behavior was analyzed using a new dimensionless parameter to permit comparisons with previous results at the same scale. The comparisons showed good agreement in the asymptotic growth region. A non-dimensional correlation for the bubble radius that can predict the bubble growth and the heat flow rate simultaneously, was suggested. The required heat flow rate for the volume change of the observed bubble was estimated to be larger than the instantaneous heat flow rate measured from the wall. Heat, other than the instantaneous heat supplied from the wall, is estimated to be transferred through the interface between bubble and liquid, even with saturated pool conditions. This phenomenon under a saturated pool condition needs to be analyzed and the data from this study can supply the good experimental data with the precise boundary condition (constant wall temperature).

New modulated DSC measurement technique

The introduction of modulated DSC (MDSC) increased the utility of DSC by adding the ability to separate the sample heat flows resulting from time dependent and time independent processes. The time independent sample heat flow rate is just that which is due to the sample heat capacity. MDSC is based on conventional DSC where the measured signal is the temperature difference between the sample and reference positions of the sensing apparatus. The measured heat flow rates display significant dependence on the period of the modulation, as demonstrated by the well-known decrease of measured heat capacity with decreasing modulation period. To reduce the frequency dependence, MDSC experiments are usually performed using rather long periods, typically 60 s or more, or various calibration or correction techniques may be applied. Long periods require low average heating rates and result in rather lengthy experiments that reduce the productivity of the DSC. A new MDSC heat flow measuring technique has been developed that greatly reduces the frequency dependence of the heat flow measurement. It includes three components: (1) a new DSC cell that has independent sample and reference calorimeters and includes two differential temperature measurements, (2) a new DSC heat flow measurement method that is based upon independent sample and reference heat flow rates and (3) a new MDSC heat flow calculation method that uses the independent sample and reference heat flow rate measurements. MDSC experiments using this new technique display greatly reduced period dependence, allowing modulation periods as short as 20 s to be used. Higher average heating rates may be used and productivity of the DSC is increased as much as threefold or more. 1 Patents applied for. 1

Superposition of thermal loads model for measuring thermal diffusivity in solids

A new method for the measurement of the thermal diffusivity in solids using transient conditions is demonstrated. This method utilizes the principle of superposition of thermal loads. Only time measurements are required, and no accurate temperature and heat flow rate measurements are needed. The method utilizes the Seebeck effect for the measurement of the time dependence of the temperature. A solution of the heat transfer equation for the model pertinent to the described method is derived, and results obtained for several materials are presented.

A New Method for Thermal Diffusivity Measurements in Metals Utilizing the Thermo-Electric Effect

ABSTRACTA new method for the measurement of the thermal diffusivity in metals, using transient conditions, is demonstrated. This method is using the principle of superposition of thermal loads. Only time measurements are required, and no accurate temperature and heat flow rate measurements are needed. The method utilizes the Seebeck effect for the measurement of the time dependence of the temperature. A solution of the heat transfer equation for the model pertinent to the described method is derived, and results obtained for several materials are presented.