Reaction Calorimetry in Microreactor Environments—Measuring Heat of Reaction by Isothermal Heat Flux Calorimetry

2017 ◽  
Vol 21 (5) ◽  
pp. 763-770 ◽  
Author(s):  
Gabriel Glotz ◽  
Donald J. Knoechel ◽  
Philip Podmore ◽  
Heidrun Gruber-Woelfler ◽  
C. Oliver Kappe
Keyword(s):  
Heat Flux ◽  
Reaction Calorimetry ◽  
Heat Of Reaction

Mixing Time Scale Measurement With Fast Exothermic Reactions Using Microchannel Reaction Calorimetry

2018 ◽  
Author(s):  
Felix Reichmann ◽  
Yannick Jirmann ◽  
Norbert Kockmann
Keyword(s):  
Heat Flux ◽  
Time Scale ◽  
Mixing Time ◽  
Main Reaction ◽  
Reaction Calorimetry ◽  
Flow Rates ◽  
Exothermic Reactions ◽  
Reaction Progress ◽  
Reaction Calorimeter ◽  
Mixing Time Scale

Continuous reaction calorimetry in microreactors is a powerful technology for the investigation of fast and exothermic reactions regarding thermokinetic data. A Seebeck element based reaction calorimeter has been designed, manufactured, and its performance has been shown in previous works using neutralization reaction in a microreactor made from PVDF-foils [1]. The Seebeck elements allow for spatial and temporal resolution of heat flux profiles across the reactor. Therefore, hot spots and regions of main reaction progress are detected. Finally, heat of reaction has been determined in good agreement with literature data [1]. However, more information can be retrieved related to chemical transformations using the continuously operated reaction calorimeter. In this work, mixing time scale is determined for instantaneous and exothermic reactions. Volumetric flow rate is varied and the region of main reaction progress is shifted within the microreactor. The reaction occurs near the reactor outlet for low flow rates. Here, mixing is dominated by diffusion. However, the reaction and hot spot are shifted towards the reactor inlet for high flow rates as convective mixing regime is reached and secondary flow profile with Dean vortices develop due to curvature of the reaction channel. Finally, mixing time scales can be derived from the location of heat flux peaks. Results display a decrease in mixing time at increased flow rates. Additionally, passive micromixers can be evaluated regarding their efficiency and comparison can be drawn. Moreover, pumps can be characterized and evaluated regarding low-pulsation dosing using the Seebeck element based reaction calorimeter.

Towards Improved Reaction Runaway Assessment Methods I. Simple Calorimetric Method Of Evaluation Of Heat Transfer Coefficient And Reactor Thermal Mass

2003 ◽  
Vol 1 (1) ◽  
Author(s):  
Maria Papadaki ◽  
Hosadu Parameswara Nawada
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Balance ◽  
Reaction Calorimetry ◽  
Small Scale ◽  
Heat Of Reaction ◽  
Overall Heat Transfer Coefficient ◽  
Reaction Calorimeter ◽  
Method Of Evaluation

The use of reaction calorimetry in the chemical industry is constantly growing. Its use aims at the assessment and subsequent reductions of the risks arising from reaction thermal runaways in the event of cooling system malfunction or agitation failure and at optimum process design.A reaction calorimeter is a small-scale automated jacketed reactor equipped with a precise temperature controller, which is capable of heat balancing. The reactor contents may be heated or cooled by heat-transfer oil and they are continuously agitated. A powerful thermostatic bath allows rapid adjustment of jacket temperature to maintain the desired reactor temperature-profile. The reactor and jacket temperatures as well as a number of other quantities are continuously measured. A heat balance, based on a number of assumptions, is used for the evaluation of the heat of reaction and its global kinetics. The evaluation of the overall heat transfer coefficient and the accumulated heat are achieved by means of calibrations. Their measurement is, in the main, long. Also it is very often lacking sufficient accuracy.In the present approach, a simple method for the accurate evaluation of the overall heat transfer coefficient is presented. It is also shown how the analysis of the heat-balance equations in different stages can be used for the simultaneous evaluation of a number of quantities and constants of the reaction calorimeter using a single set of calibration experiments.

Seebeck Calorimeter for the Characterization of Highly Exothermic Reactions in a Microreactor Made From PVDF-Foils

2017 ◽  
Author(s):  
Felix Reichmann ◽  
Stefan Millhoff ◽  
Yannick Jirmann ◽  
Norbert Kockmann
Keyword(s):  
Heat Flux ◽  
Reaction Calorimetry ◽  
Acid Base ◽  
Chemical Reactors ◽  
Exothermic Reactions ◽  
Thermoelectric Voltage ◽  
Calibration Methods ◽  
Transfer Measurement ◽  
Color Indicator

Reaction calorimetry is one of the most important steps in designing chemical reactors. This contribution describes a continuously operated micro calorimeter using Seebeck elements for microreactors made of PVDF-foils. Seebeck elements allow for local and temporal resolution of heat flux profiles. Various calibration methods for the Seebeck effect based heat flux sensors are presented. Here, the direct correlation between measured thermoelectric voltage and heat flux is found to be the most promising one. Commissioning of the calorimeter and validation of its performance are done by means of heat transfer measurement of warm water and an acid base reaction. Obtained reaction enthalpy values of the neutralization reaction of acetic acid and sodium hydroxide agree very well with literature data. The progression of the reaction can be followed optically using phenolphthalein as color indicator and can be compared to measured data. Heat profiles over the course of the microreactor were shown and checked for consistency. Consequently, this approach helps to characterize reactors and aids reactor development.

Siphon Flows in Stratified Coronal Loops

1994 ◽  
Vol 144 ◽  
pp. 185-187
Author(s):  
S. Orlando ◽  
G. Peres ◽  
S. Serio
Keyword(s):  
Heat Flux ◽  
Scaling Laws ◽  
Flow Model ◽  
Supersonic Flows ◽  
Coronal Loops ◽  
Characteristic Parameters

AbstractWe have developed a detailed siphon flow model for coronal loops. We find scaling laws relating the characteristic parameters of the loop, explore systematically the space of solutions and show that supersonic flows are impossible for realistic values of heat flux at the base of the upflowing leg.

Rate of Sublimation of Ice by Radiative Heating in Freeze-Etching

1980 ◽  
Vol 38 ◽  
pp. 618-619
Author(s):  
Yeshayahu Talmon
Keyword(s):  
Heat Flux ◽  
Freeze Fracture ◽  
Constant Heat Flux ◽  
Radiative Heating ◽  
Constant Heat ◽  
Entire Sample ◽  
Simplified Method ◽  
Freeze Etching ◽  
Sublimation Rates ◽  
Fractured Surface

To bring out details in the fractured surface of a frozen sample in the freeze fracture/freeze-etch technique,the sample or part of it is warmed to enhance water sublimation.One way to do this is to raise the temperature of the entire sample to about -100°C to -90°C. In this case sublimation rates can be calculated by using plots such as Fig.1 (Talmon and Thomas),or by simplified formulae such as that given by Menold and Liittge. To achieve higher rates of sublimation without heating the entire sample a radiative heater can be used (Echlin et al.). In the present paper a simplified method for the calculation of the rates of sublimation under a constant heat flux F [W/m2] at the surface of the sample from a heater placed directly above the sample is described.

Numerical analysis of local heat flux and thin-slab solidification in a CSP funnel-type mold with electromagnetic braking

2020 ◽  
Vol 117 (6) ◽  
pp. 602
Author(s):  
Heping Liu ◽  
Jianjun Zhang ◽  
Hongbiao Tao ◽  
Hui Zhang
Keyword(s):  
Heat Flux ◽  
Casting Speed ◽  
Shell Growth ◽  
Local Heat ◽  
Operating Conditions ◽  
Thin Slab ◽  
Wide Face ◽  
Slab Width ◽  
Steel Grades ◽  
Local Heat Flux

In this article, based on the actual monitored temperature data from mold copper plate with a dense thermocouple layout and the measured magnetic flux density values in a CSP thin-slab mold, the local heat flux and thin-slab solidification features in the funnel-type mold with electromagnetic braking are analyzed. The differences of local heat flux, fluid flow and solidified shell growth features between two steel grades of Q235B with carbon content of 0.19%C and DC01 of 0.03%C under varying operation conditions are discussed. The results show the maximum transverse local heat flux is near the meniscus region of over 0.3 m away from the center of the wide face, which corresponds to the upper flow circulation and the large turbulent kinetic energy in a CSP funnel-type mold. The increased slab width and low casting speed can reduce the fluctuation of the transverse local heat flux near the meniscus. There is a decreased transverse local heat flux in the center of the wide face after the solidified shell is pulled through the transition zone from the funnel-curve to the parallel-cure zone. In order to achieve similar metallurgical effects, the braking strength should increase with the increase of casting speed and slab width. Using the strong EMBr field in a lower casting speed might reverse the desired effects. There exist some differences of solidified shell thinning features for different steel grades in the range of the funnel opening region under the measured operating conditions, which may affect the optimization of the casting process in a CSP caster.

Analysis of significant measures for thermal conductivity

2020 ◽  
pp. 35-42
Author(s):  
Yuri P. Zarichnyak ◽  
Vyacheslav P. Khodunkov
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Heat Flux Density ◽  
Measurement Method ◽  
Conductivity Measurement ◽  
Surface Heat ◽  
Measuring Instrument ◽  
New Class ◽  
Achievable Accuracy

The analysis of a new class of measuring instrument for heat quantities based on the use of multi-valued measures of heat conductivity of solids. For example, measuring thermal conductivity of solids shown the fallacy of the proposed approach and the illegality of the use of the principle of ambiguity to intensive thermal quantities. As a proof of the error of the approach, the relations for the thermal conductivities of the component elements of a heat pump that implements a multi-valued measure of thermal conductivity are given, and the limiting cases are considered. In two ways, it is established that the thermal conductivity of the specified measure does not depend on the value of the supplied heat flow. It is shown that the declared accuracy of the thermal conductivity measurement method does not correspond to the actual achievable accuracy values and the standard for the unit of surface heat flux density GET 172-2016. The estimation of the currently achievable accuracy of measuring the thermal conductivity of solids is given. The directions of further research and possible solutions to the problem are given.

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