Applied Heat Load Research Articles

Investigation on the dynamic thermal response of jet evaporators to short-term thermal excitation

This study investigates the dynamic thermal response of a jet evaporator under short-term thermal excitation in a mechanically pumped two-phase loop (MPTL) with a special focus on the temperature response characteristics of the jet evaporator under different flow and heat flux conditions. Two dimensionless numbers, Ja and Re, were proposed to characterize the thermal response. In addition, the time constant and transient time were introduced to evaluate the temperature response rate, whereas thermal stability was characterized by the temperature overshot amplitude. The results indicate that the gradual response mode, single-jump overshoot response mode, and twice-jump overshoot response mode can be sequentially obtained with an increase in the applied heat load, that is, an increase in Ja. The Re number influences the threshold value of the Jacob number for the response-mode transition. Elevating the heat load accelerates the thermal response rate of the jet evaporator and reduces its time constants, whereas increasing the flow rate enhances the thermal capacity and anti-interference ability. Furthermore, as the flow rate increased, the thermal capacity and anti-interference ability of the MPTL were enhanced, leading to an increase in the time constant and transient time. Notably, the twice-jump overshoot response exhibited a smaller temperature overshoot than the single-jump overshoot response, suggesting improved thermal stability.

Advanced Dynamic Thermal Vibration of Laminated FGM Plates with Simply Homogeneous Equation by Using TSDT and Nonlinear Varied Shear Coefficient

The effects of advanced nonlinear varied shear coefficient and third-order shear deformation theory (TSDT) on the dynamic responses of thick functionally graded material (FGM) plates under thermal vibration are investigated. The nonlinear coefficient of the displacement field of TSDT is used to obtain the expression of advanced varied shear coefficient for the thick FGM plates. The dynamic displacements, shear rotations and stresses in numerical results under sinusoidal applied heat loads are obtained and investigated. Two parametric effects of environment temperature and FGM power law index on the dynamic responses of thermal stress and center deflection of thick FGM plates are also investigated. The transient responses of center deflection are found for the cases of simply homogeneous equation and fully homogeneous equation. Also, the transient responses of center deflection are found for cases of nonlinear and linear varied-modified coefficient of shear correction.

Thermal control of temperature-sensitive electronic components using a vapor chamber integrated with a straight fins heat sink: An experimental investigation

Cooling temperature-sensitive appliances, such as electronic components, has recently become essential in their design and development to reduce the negative effect of excessive temperature rise on performance. The current experiment focuses on passive cooling of electronic devices utilizing an innovative vapor chamber with a cylindrical cross-section that is integrated with a straight fins heat sink. Therefore, a fabricated system is attached to an electric heater to imitate the heat dissipation from electronic devices. Several experiments are conducted to investigate the effect of two working fluids (Ethyl alcohol and water), seven varied charge ratios (ranging from 20% to 65%), different system orientations (ranging from 0° to 180° in 45° intervals), and seven distinct heat load values on overall system performance. The performance of the integrated vapor chamber-straight fins (VC-SF) heat sink is then compared to those of two conventional heat sinks, a straight fins (SF) heat sink and a solid copper plate (SCP) heat sink. The results reveal that using the integrated vapor chamber-straight fins (VC-SF) heat sink significantly reduces the average front wall temperature associated with the electronic component when compared to other heat sinks, and this effect holds true throughout all operating scenarios. Furthermore, when compared to other working fluids and charging ratios, the system filled with pure water as the working fluid and a charge ratio of 25% performs better for all operating conditions. Finally, at an inclination angle of 0°, the minimal hot wall temperature associated with the electronic component's operating temperature can be reached, resulting in the greatest performance. In contrast, the highest hot wall temperature is attained at an inclination angle of 180°, regardless of the applied heat load or charging ratio.

Phase Change and Heat Transfer Analysis of Different Refrigerants During Condensation in Minichannel Using a Novel Numerical Approach

Abstract This paper analyses the condensation heat transfer phenomena in minichannel using acetone, ammonia, propylene, and R134a as the working fluids used in new-age space applications. A novel numerical model is developed considering the changes in local vapor pressure in the channel established due to shrinking in the flow passage by the gradual formation of the liquid layer. The present developed numerical model is compared with the available numerical and experimental results. The impacts of different inlet mass fluxes (250, 500, and 750 kg/m2 s), channel heights (1, 4, 6, and 8 mm), applied heat loads (10, 100, 250, and 500 W), and channel orientations (0 deg, 30 deg, 45 deg, 60 deg, and 90 deg) on the performance of the condensation heat transfer process are investigated. The formation of the thin liquid film layers and evaluation of the liquid–vapor interface profiles are examined. The study reveals that the channel orientation has a marginal influence on the flow pattern for the considered channel length of 20 mm. The maximum change in pressure loss is found at the channel orientation of 45 deg, and the average heat transfer coefficient is almost the same for all the considered orientations. The flow pattern is affected by the increase in mass flux resulting in the delay of heat transfer coefficient fluctuations. The average heat transfer coefficient decreases with increasing heat load, and the minimum average heat transfer coefficient is obtained for heat load, Q = 500 W.

Effects of surfactants on subcooled pool boiling characteristics: An experimental study

Surfactants are often used as additives to stabilize the dispersed phase of the water-based multicomponent fluids (such as non-azeotropic emulsion) for enhancing the boiling process, but their effects on the boiling heat transfer of water are still not clear. In this paper, a pool boiling experiment is designed to investigate the specific effects of surfactants (Tween20 (Polysorbate 20), Span20 (Arlasel 20), and Tween20-Span20 mixture) on the subcooled boiling heat transfer characteristics of pure water. The experimental results are analyzed by considering the influences of addition type and concentration of surfactant as well as the applied heat loads. It is found that: (1) Tween20 can achieve excellent boiling enhancing performance (decreasing the wall superheat by up to 10.4 °C and raising the boiling heat transfer coefficient by up to 13.4%) by increasing the number of nucleation sites. And the enhancement is improved with the increase of concentration when the heat flux is below a certain level, while it is weakened at high heat flux for Tween20 with a high concentration (1 mL L-1). The reason is that high concentration Tween20 results in an excessive increase of nucleation sites which prevents the return of working fluid and weakens the enhancement of heat transfer. (2) Span20 shows a boiling enhancement only when its concentration is 0.05 mL L-1 (lower than the CMC) among the test ones. Further increment in Span20 concentration (exceeding the CMC) leads to a large increase of wall superheat because it increases the viscosity of working fluid and deteriorates the heat transfer performance. (3) Tween20-Span20 mixture significantly aggravates the aforementioned boiling deterioration effect of Span20 (due to the reduced CMC for the mixture of Tween20 and Span20, weakening the heat transfer), and thus is not suitable for preparing boiling-heat-transfer-enhancing fluids. These results can provide a better understanding of surfactants and guide the practical preparation of multicomponent fluids for boiling heat transfer enhancement.

Experimental investigation on the start-up performance of a novel flat loop heat pipe with dual evaporators

Thermal management for multiple heat sources has been becoming increasingly important, especially under high heat flux conditions. As a passive heat transfer device, loop heat pipes (LHP) with multiple evaporators does not consume extra energy, demonstrating a great potential in thermal management. This paper proposed a flat plate LHP with dual evaporators for the first time. Two flat plate evaporators were adopted, and both of them had their own porous wick, compensation chamber (CC) and vapor line. The condensed liquid converged, then moved along the main liquid line. The CC of two evaporators was joined by a tube, which can ensure the sharing of the returning liquid. To verify the performance of novel flat plate LHP, the start-up test was investigated under different heat load arrangements, involving only a single evaporate was applied heat load, two evaporators were applied with the equal or unequal heat load. Meanwhile, the operation stability was determined by testing the performance with the successionally variable heat load. This system has been shown to operate successfully at heating source temperature below 100 °C with heat load ranging from 10 W–10 W to 130 W–130 W (corresponding to the maximum heat flux of 13.52 W/cm2).

Performance study of dual-phase CO[formula omitted] cooling on the example of the ATLAS ITk strip end-cap detector

The technique of evaporative CO2 cooling is one of the standard cooling options for high-energy particle detectors, such as the new ATLAS Inner Tracker (ITk) for the planned high-luminosity upgrade of the LHC by 2026. The advantages of CO2 are a high latent heat transfer at reasonable flow parameters, a low viscosity which allows to use small diameter cooling pipes with a low pressure drops, a well-suited temperature range for detector cooling between ＋25 and −40 °C and being an environment friendly alternative to many other currently used coolants. When comparing with a monophase coolant, the operation in the dual-phase regime comes with several parameters influencing the cooling performance.This paper contains the results of experimental studies performed to understand these influencing factors. For this, prototype structures from the ITk strip detector end-cap were used, like bare local support structures (‘cores’) or fully loaded structures (‘petals’). Here, the design is optimized to guarantee a good heat transfer between the silicon strip modules glued on the surface and the embedded titanium cooling pipe with the CO2 coolant. Systematic investigations on the thermal performance using infrared thermography are used to study the influence of dual-phase CO2 cooling parameters such as the orientation of CO2 flow. Moreover, the dependence of the pressure drop as a key parameter for the cooling performance on the applied heat load or the selected mass flow rate is investigated.

Fluid flow and heat transfer of porous TPMS architected heat sinks in free convection environment

Heat dissipation in electronic devices is challenging due its limited size and cooling space constraint. Implementing Triply Periodic Minimal Surfaces (TPMS)-based cellular structures could enhance the thermal exchange mechanism due to their novel architected, interconnected, and inter wind porous topologies and high surface area to volume ratio. In this study, three novel mathematically-driven TPMS heatsink structures were investigated using computational fluid dynamics (CFD) based models. TPMS heat sinks consisting of seven triply periodic unit cells were examined to investigate their thermal performance and fluid flow behavior in free convection air environment. The thermal performance indicators as convection heat transfer coefficient and surface temperature under parametric variation of applied heat load, fluid enclosure boundary condition, and TPMS structure orientation were determined. Enclosure boundary conditions found to have a significant effect on the thermal behavior of each heat sink structure; including radiation contribution was found to account for approximately 23% of the overall heat transfer in due to the complex TPMS internal structure. Three empirical Nusslet number correlations were then derived for the investigated TPMS structures. The results showed that TPMS-based heat sinks outperform conventional heat sinks by 48–61% owing to the random perturbations of flow and high packing density. This work shows the potential of TPMS porous architectures as very promising heat sinks.

Experimental Investigations on Performance Analysis of a Wickless Thermosiphon Heat Pipe With Two Heat Sources and Multiple Branches

Abstract In an electronic circuit of laptops, supercomputers with multiple central processing units, spacecraft etc., it is required to arrange the cooling system for multiple heat loads in the smallest possible space in view of power-saving opportunities. In the present study, the experimental investigations are carried out on a wickless multi-branch heat pipe in gravity-assisted mode with two evaporators and one condenser on each of the individual branches. The start-up and dynamic characteristics were studied with different filling ratios (range, 40–70%), with equal heat loads (range, 0–200 W) and unequal heat loads (range, 0–100 W) on evaporators. The results are analyzed in terms of temperature variation in axial direction, thermal resistance, and heat transfer coefficient for a multi-branch thermosiphon heat pipe (MBTHP). It was found that the optimal filling ratio depends on the applied heat load under tested conditions. In a thermosiphon mode, the heat pipe was capable of transporting a maximum heat load of 210 W and maximum heat flux of 20.31 W/cm2 with the maximum evaporator temperature lower than 100 °C. The minimum wickless thermal resistance of heat pipe was found to be 0.21 °C/W at 50% filling ratio and 160 W and maximum total heat transfer coefficient was found as 6.33 k W/m2 °C.

Implementation of Soft Computing Technique for Recovery of Impulsive Heat Loads

The knowledge of surface heat flux over aerodynamic surfaces is highly desirable for high-speed applications. Impulse test facilities like shock tubes and shock tunnels are invariantly employed for this where the aerodynamic test models experience step/ramp heat loads. Contrary to conventional methods, the usage of an advanced soft computing technique through an adaptive neuro-fuzzy inference system (ANFIS), for recovery of such surface heat loads, is theme of this paper. A coaxial thermal sensor is fabricated in house from chromel and constantan alloy. This E-type thermal probe is subjected to known heat flux (2–3.5 W) of laser light in an exclusive experimental setup, and the temperature responses are recorded. The simulations are also performed to get the temperature history for these heat loads. The experimental and computational results, either separately or together, are used to train the ANFIS network. The time-averaged values of heat flux obtained from ANFIS-based recovery shows excellent agreement in trend and magnitude (uncertainty band of ) with the applied heat load. The present studies demonstrate the possible use of a soft computing technique for heat flux recovery in short-duration experiments within a desired accuracy level by using training data obtained experimentally or computationally or both.

Soft Computing—A Way Ahead to Recover Heat Flux for Short Duration Experiments

Abstract The present investigations provide a pathway for implementation of soft computing-based Adaptive Neuro-Fuzzy Inference System (ANFIS) technique for prediction of surface heat flux from short duration temperature measurement in shock tubes or shock tunnels. Computational modeling of a coaxial thermal probe (CTP) is carried out to get the necessary temperature-time histories for different temporal variations of applied heat loads. Different possible inputs are assessed while defining the most suitable ANFIS structure for the recovery of step or ramp heat loads. This proposition is then tested for recovery of heat flux in a given range or of given time history. In each case, the uncertainty band is found to be in the acceptable range. The final assessment of this novel methodology is performed for recovery of heat flux signal from temperature measurement in a shock tube-based experiment. An in-house fabricated fast response CTP, prepared from chromel (3.25 mm diameter and 10 mm length) and constantan (0.91 mm diameter and 15 mm length) is used for these experiments. The surface heat flux recovered from the experimental signal using ANFIS is seen to have excellent agreement with the conventional analytical method in terms of both trend and magnitude, within an uncertainty band of ± 2%. Therefore, present investigations advocate the use of soft computing technique for heat flux recovery in a short duration temperature measurement due to its accuracy of prediction, lesser complexities in mathematical modeling, and being less computationally intensive.

Semi-analytical solution for temperature rise in a heterogeneous half plane containing arbitrarily shaped inhomogeneities subjected to surface heating

Temperature rise caused by surface heating is responsible for thermal-related failures of heterogeneous material, such as composites and alloys, in manufacturing processes and tribology. This study presents a semi-analytical method (SAM) for temperature rise in a half plane involving dispersed inhomogeneities of arbitrary shape undergoing external heat load. Green functions and frequency response functions (FRFs) for subsurface heat flux induced by the applied heat load, as well as a set of formulas for influence coefficients correlating disturbed temperature rise and uniform eigen-temperature gradients inside a rectangular inclusion in a full plane, are derived. The rectangular inclusion solution in a full plane is treated as an elementary solution to solve disturbed temperature rise in a heterogeneous half plane involving arbitrarily shaped inhomogeneities, through implementing the equivalent inclusion method (EIM), the method of images and discretizing the total computation area into a good many rectangular elements with the same size. Results obtained by the SAM are consistent with those of the finite element method (FEM). Effects of inhomogeneity numbers, material properties, volume fractions, and velocities of the moving heat load on temperature rise are discussed in detail. HIGHLIGHTS Green functions and frequency response functions for heat flux in a half plane subjected to surface heating are obtained. Influence coefficients relating disturbed temperature rise and uniform rectangular inclusion in a full plane are derived. The elementary rectangular inclusion method is utilized to cope with problems for inhomogeneities of arbitrary shapes and distributions. Effects of inhomogeneity numbers, material properties, volume fractions, and velocities of the moving heat load on temperature rise are discussed.

On the contribution of malt quality and the malting process to the formation of beer staling aldehydes: a review

Despite decades of extensive research, beer flavour instability remains a challenge for both brewing and malting industries. Malt impacts the brewing process as well as the quality of the final beer. It also affects the stability of beer flavour, as it delivers to the brewing process various compounds with the potential to compromise the desired flavour characteristics of beer. These include staling aldehydes and their precursors, such as amino acids, reducing sugars, α-dicarbonyls and bound-state aldehydes. In general, the content of these compounds depends on barley variety and quality, the malting regime and final malt quality. Malt that represents a low potential for beer staling, i.e. that has low values of Kolbach Index, heat load, colour, LOX activity, Strecker aldehydes, transition metal ions and high antioxidative activity, leads to beer with enhanced flavour stability. However, the consistent production of malt with the desired quality remains challenging. Approaches to achieve this include adjustment of steeping and germination conditions, allowing control of grain modification and thus, the reservoir of aldehydes precursors. Also, the application of alternative kilning technologies may reduce the applied heat load, responsible for the formation of staling aldehydes and triggering development of the oxidising free radical species. This review provides an evaluation of current knowledge on the contribution of the malting process and malt quality to the formation of beer staling aldehydes. © 2021 The Authors. Journal of the Institute of Brewing published by John Wiley & Sons Ltd on behalf of The Institute of Brewing & Distilling.

Development of the thermal performance model using temperature gradient analysis for optimized design of steam surface condenser

This paper presents a new method of evaluating the thermal performance of a steam condenser based on the temperature gradient between steam and cooling water. With reference to the experimental results, the pressure transition temperature (PTT), defined as the limiting cooling water temperature initiating insufficient heat removal over the applied heat load, was identified. An analytical methodology was developed to estimate the PTT for given geometrical and thermal-hydraulic conditions of the condenser system. The methodology was extended to a temperature gradient analysis (TGA) model for the performance evaluation of power plant-scale condensers by considering the effects of condensate inundation, tube loading pattern, steam shear, and fouling resistance. The assessment results of the TGA model showed good agreement with existing numerical and lumped-volume models, as well as measurement data of existing power-plant condenser systems. Its simplicity and strong capability to elucidate most of the design variables of the condenser make the TGA model suitable for executing many iterative calculations required when designing and optimizing the new condenser system.

Analysis of thermal response of new diagnostic probe in TCV

• Thermal response of the new probe head during triple plunge into the TCV tokamak has been analysed numerically. • The applied heat load corresponds to the heat flux distribution in the Scrape-Off-Layer. • Thermal resistance between shroud cap and the shroud cylinder determines the probe’s thermal behaviour. • The predicted temperatures show that the critical values are not exceeded in any of the probe components. • The results demonstrated suitability of the probe’s design for the measurements in TCV. Thermal response of the new multi-purpose diagnostic probe inside the TCV (Tokamak à Configuration Variable) tokamak is studied. The New Probe Head (NPH) was constructed at the University of Innsbruck and developed in collaboration with various European laboratories within EUROfusion program. The NPH can be used in different MST devices by applying corresponding adapters. Its design, followed by the prototype, has to go through a number of tests (numerical and experimental), before it can be used in the tokamak environment, where it has to withstand repeated exposure to the Scrape-Off-Layer (SOL) plasma. Presented numerical analyses of the NPH thermal response inside the TCV tokamak are performed by the Jožef Stefan Institute.

Fracture behavior of tungsten-based composites exposed to steady-state/transient hydrogen plasma

The fracture behavior of plasma-facing components (PFCs) under extreme plasma-material interaction conditions is of great concern to ITER and future fusion reactors. This was explored in the current study by exposing pure tungsten (W), W-1%TiC and W-2%Y2O3 composites to a combined steady-state/transient hydrogen plasma up to a base surface temperature of ~2220 K, and up to 5000 transient pulses for 1000 s using the linear plasma generator Magnum-PSI. The applied heat loads were characterized by combining sheath physics, thermographic information and finite element analyses, with which the thermal stress was evaluated. Combining microstructural investigation and thermo-mechanical numerical analyses, a physical picture of fracture is developed. The transient heat loads drive surface crack initiation, whose depth can be estimated by a simple analytical model for pure tungsten, while the cooling period following the steady-state heat load induces tensile stresses, opening existing surface cracks deeper. The fracture process is mediated by the microstructure whereby the ceramic particles stabilize the microstructure but promote surface crack initiation due to suppressed plasticity at the grain boundaries and the particle-matrix interfaces. The surface cracks relieve the subsequent cycles of transient thermal stress but intensify the steady-state thermal stress, therefore, promoting deep crack propagation. These results help to understand failure mechanisms in PFCs under extreme operation conditions which are valuable for developing advanced PFCs.

Acute Heat Exposure Alters Autophagy Signaling in C2C12 Myotubes.

Autophagy is a major intracellular degradation process that is essential for the clearance of unnecessary proteins/organelles and the maintenance of cellular homeostasis. The inhibition of autophagy results in cellular consequences associated with many skeletal muscle pathologies, and therapies designed to elevate autophagic activity may provide protection from such pathologies. Acute exposure to low levels of heat has therapeutic effects; however, the impact of heat on skeletal muscle autophagy remains unclear. In the present study, C2C12 myotubes were maintained at 37°C thermoneutral (TN) or heated at 40°C heat treatment (HT) for 1 h. Myotubes were harvested immediately after heating, or returned to 37°C for recovery of 2 or 24 h. HT resulted in an elevation in pAMPK (T172), Beclin-1, and LC3 II, a marker for autophagosome formation, but no change in p62. In the context of autophagy inhibition with Bafilomycin A1, HT resulted in lower LC3 II compared to TN. The applied heat load induced the heat shock response, as evidenced by immediate upregulation of HSF1 and Hsp70. Hsp70 continued to increase during recovery, whereas pHsp27 was downregulated acutely in response to HT, but retuned to TN levels by 2 h of recovery. HT also reduced the phosphorylation of the MAP-kinases p38 and JNK. These findings suggest that an acute, short bout of mild heat may be beneficial to skeletal muscle by increasing AMPK activity, markers of autophagasome formation, and the heat shock response.

Application of a two-phase thermosyphon loop calculation method to a cold neutron source

A new method for thermodynamic calculations of a two-phase cryogenic hydrogen thermosyphon loop is verified by means of process responses and neutronic performance measurements on the JEEP-II cold neutron source. The method is based on a one-dimensional finite element division, where each time-step is split up in a change of enthalpy and a change in entropy. The method is used to simulate the pressure during cooling from room temperature down to cryogenic temperatures. The simulated void fraction is compared with the neutronic performance of the moderator during the cool down process. The method is also applied for the simulation of the process step responses when the temperature set point is varied and when the applied heat load is changed. Comparisons of the simulated results with actual measurements show that the method can give an accurate representation of the pressure response and resulting void fractions. The method and results presented here should be useful for the optimization of cold sources where accurate control of pressure and knowledge of void fraction are important for efficient operation.

Heat transfer performance of a compact loop heat pipe with alumina and silver nanofluid

The heat transfer performance and entropy analysis are done in a compact loop heat pipe (CLHP) with Al2O3/water and Ag/water nanofluid. A compact loop heat pipe having a flat square evaporator with dimensions of 34 mm (L) × 34 mm (W) × 19 mm (H) has been fabricated and tested for the heat load ranging from 30 to 500 W. The experimental tests are conducted by keeping the CLHP in the vertical orientation with distilled water, silver (Ag)/water and aluminium oxide (Al2O3)/water nanofluid having low volume concentrations of (0.09% and 0.12%). The effect of wall and vapour temperature, evaporator and condenser heat transfer coefficient, thermal resistance on the applied heat loads is experimentally investigated and compared. The experimental results showed that the evaporator thermal resistance is reduced by 34.70% and 20.21%, respectively, for 0.12 vol% of Ag, Al2O3 nanoparticles when compared with that of the distilled water. For the same volume concentrations of Ag, Al2O3 nanoparticles, an enhancement of 34.52%, 23.7%, 39.27% and 30.8%, respectively, observed for the convective heat transfer coefficients at the evaporator and condenser. The entropy is also reduced by 19.08% and 11.58% when Ag and Al2O3 nanofluids are used as the operating fluid. From the experimental tests, it is found that the addition of small amount of Ag nanoparticles in the working fluid enhanced the operating range by 15% when compared with that of Al2O3/water nanofluid without the occurrence of any dry-out conditions.

Optimal Integration of Cascade Thermoelectric Cooler into Electronic Housing

Integration of thermoelectric cooler (TEC) into electronic housing is a real issue due to specific restrictions imposed on the TEC parameters under such application. Typically, the TEC must be optimized to achieving necessary cooling with minimal input power. The last is proportional to the heat gains on the TEC cold side. Hence, for optimal integration of the TEC into electronic housing, the corresponding heat load must be predetermined.In this study, the experimental approach to the definition of the heat load on the TEC inside electronic housing is proposed. The method is based on application of a special metering TEC with calibrated dependence of temperature difference ΔT on the applied heat load. The heat gains from the header body are defined by direct measurement of ΔT value generated by this specimen inside the header. Studied is TO8 header which is widely used for incorporating thermoelectrically cooled temperature sensitive optoelectronic components. Defined are heat gains in vacuum and in a gas atmosphere as a function of residual pressure. Obtained results are used for design and implementation of cascade TECs optimized for receiving temperature