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In industrial safety, engulfing pool fires can cause damages and collapse of process vessels with catastrophic consequences. This work investigates the ethoxylation of 1-dodecanol as a case-study with a multiscale approach able to analyse scenarios of runaway triggered by a pool fire engulfing the reactor. The aim is to understand whether and when the cooling power of the external heat exchanger can prevent dangerous temperature build-up in the chemical reactor. [ABSTRACT FROM AUTHOR]

Compact evaporators like plate heat exchangers can play a significant role in reducing the investment cost of low cooling power sorption systems. If water is used as refrigerant, their design remains mainly empirical. The objective of this paper is thus to investigate the specific characteristics of water pool boiling in narrow channel at subatmospheric pressure in order to acquire the fundamental knowledge needed to improve the design of compact evaporators in these sorption systems. An experimental test setup was thus designed and built to study water pool boiling in narrow channel at subatmospheric pressure (from 5 to 1.2 kPa) on a vertical heated copper disk. The influence of the thickness of the narrow channel and of the pressure on the heat transfer is discussed. As the pressure and the channel thickness decrease the occurrence of a specific subatmospheric pool boiling regime is observed, degrading heat transfer coefficient. Nevertheless, the general trends of evolution are in agreement with those generally observed in the literature: heat transfer is enhanced as the thickness of the narrow channel decreases but, depending on the pressure, decreasing too much the channel thickness could lead to a deterioration of the heat transfer coefficient. A particle image velocity (PIV) device was implemented to the experimental setup in order to highlight the effect of the wake-induced flow on the heat transfer. [ABSTRACT FROM AUTHOR]

Condensation in microchannels and minichannels is widely used in small devices such as air-cooled condensers for the air-conditioning and automotive industry, in heat pipes, thermosyphons and other applications for system thermal control. Currently, many research centers all over the world are dealing with the structure and operation of compact refrigerating devices. This is in line with the trend of 21st century that is moving towards the use of energy-saving and environmentally friendly technical equipment. In the present study, a critical review on condensation heat transfer in microchannels and minichannels is presented. This review include a wide range of different parameters such as the channel diameter (d), the saturation temperature (Ts), the mass flux (G), the vapor quality (x), different working fluids like steam, CO2 or R744, FC72, R22, R410A, and R407C, various shapes such as circular and noncircular, different orientations like horizontal and vertical, and systems consist o f either single or multiple channels. At the end, recommendations for future studies will be given. As a result, this paper cannot only be used as the starting point for the researcher interested in condensation heat transfer in microchannels and minichannels, but it also includes recommendations for future studies on condensation heat transfer in microchannels and minichannels. [ABSTRACT FROM AUTHOR]

The dynamic simulation of a sub-scale ITER Central Solenoid (CS)/STRucture (STR) cooling loop has been performed to investigate the cryogenic control strategies against pulsating heat loads. HELIOS facility has been modified for this particular study, which consists of a Liquid Helium (LHe) reservoir with two immersed heat exchangers, a circulation pump and an approximately 130 m long piping with three evenly distributed heated sections. The setup provides the equivalent thermo-hydraulic configuration of the ITER CS/STR, cooled by the forced-flow Supercritical Helium (SHe). The dynamic simulator, C-PREST, has been utilized to model the HELIOS test loop and to compare the results with the experimental data sets. This paper presents the dynamic simulation results and discusses the control strategy to minimize the cooling power requirements, to have high reliability. [ABSTRACT FROM PUBLISHER]

Abstract: This paper presents the operational characteristics of a double-stage double-effect metal hydride heat pump (DSDE-MHHP) working with LaNi4.1Al0.52Mn0.38/LmNi4.91Sn0.15/Ti0.99Zr0.01V0.43Fe0.09Cr0.05Mn1.5 as high/medium/low temperature alloys. The performances of the DSDE-MHHP are predicted by solving the transient, two-dimensional, conjugate heat and mass transfer characteristics between the paired metal hydride reactors of cylindrical configuration using the finite volume method (FVM). The designed operating temperatures chosen for the present analysis are 568, 361, 296, and 289K as heat driven (T D), heat rejection (T H), heat sink (T M) and refrigeration (T C) temperatures, respectively. The variations in hydrogen concentrations, hydride equilibrium pressures, and temperatures within the hydride beds, and the heat exchange between the hydride beds with the heat transfer fluids are presented for a complete cycle. The operating cycle of a DSDE-MHHP is explained on dynamic pressure–concentration–temperature (PCT) plot. The variation of temperatures in the reactors during hydriding and dehydriding processes is compared with experimental data and a good agreement was observed between them. For given operating temperatures of 568/361/296/289K, the average coefficient of performance (COP) and the specific cooling power (SCP) of the system are found to be 0.471 and 28.4W/kg of total hydride mass, respectively. [Copyright &y& Elsevier]

Abstract: Vibration-free miniature Joule–Thomson (JT) coolers are of interest for cooling a wide variety of devices, including low-noise amplifiers, semiconducting and superconducting electronics, and small optical detectors used in space applications. For cooling such devices, coolers are needed which have operating temperatures within a wide temperature range of 2–250K. In this paper, the optimization of the working fluid in JT cold stages is described that operate at different temperatures within that range. For each temperature, the most suitable working fluid is selected on the basis of the coefficient of performance of the cold stage, which is defined as the ratio of the gross cooling power to the change in Gibbs free energy of the fluid during compression. In addition, a figure of merit of the heat exchange in the counter-flow heat exchanger is evaluated that depends only on the properties of the working fluid. [Copyright &y& Elsevier]

A cryocooler that consists of a two-stage Gifford-McMahon (GM) mechanical refrigerator and a Joule-Thomson (JT) expansion circuit is developed for use in resistance thermometer calibration. The cryocooler is designed to attain a lower temperature rather than to produce a higher cooling power. A simple but high-performance counterflow heat exchanger is developed for the cryocooler. The heat exchanger has a high flow conductance while maintaining a high heat exchange efficiency. It is an improved type of counterflow heat exchanger composed of a spiral capillary and a thin-wall straight outer tube. The developed cryocooler uses a single counterflow heat exchanger not like a conventional GM/JT cryocooler, which usually has two or three counterflow heat exchangers. 4He is used as the working fluid for the JT expansion circuit. The pot where the condensed 4He collects after the JT expansion can reach 1.3 K in the continuous operation mode and 1.0 K in the single-cycle operation mode. The cooling power of the cryocooler is 580 μW at 1.34 K with a molar flow rate of 300 μmol/s. Temperature control of the pot was demonstrated from 1.4 to 12 K using two control methods. One method involves controlling the evacuation speed in the JT circuit and the other involves controlling the heat input from a heater to the pot. The temperature of the pot is controlled within the order of magnitude of 2 mK from peak to peak with either method. [ABSTRACT FROM AUTHOR]

The control of cryogenic temperatures is usually accomplished by a passive stage, exploiting the combined effect of a thermal mass connected to a thermal resistance; by an active control, often of a PID type, based on the combination of a dedicated sensor, a heater and a controller; or by a combination of the two. Such a system typically uses a controlled stage that is isolated from the source of the fluctuations by a thermal isolator. Controlled insertion of heat into this stage counters the temperature fluctuations reaching the stage. Inherent to this type of system is the insertion of heat into the controlled stage that eventually reaches the cold end of the cooler, reducing the net heat lift available. The larger the thermal isolation, the smaller the reduction of the net heat lift, but with the attendant increase in the interface temperature. Any scheme that can reduce the penalty associated with the loss of heat lift or the temperature offset would be attractive in terms of cooler performance. If the cooler system has a recuperative heat exchanger between the coldest heat sink and a higher temperature precooler, a different approach can be used. In this paper we describe a novel control approach capable of passively damping low frequency fluctuations, requiring minimal reduction of cooler heat lift and minimal temperature increase of the cold end interface. This alternative scheme is based on the idea of controlling the temperature of a section of the recuperative heat exchanger between the coldest precooler and the cold end of the cooler and it has been tested on a 20 K hydrogen sorption JT cooler. [Copyright &y& Elsevier]