Heat sources in proton exchange membrane (PEM) fuel cells

The reduction in size of modern electronic components and the accompanying reduction in size of computer casings requires optimized thermal designs for reliable electronic systems. Cooling problems related to electronic systems can be divided into the cooling of components mounted on heat sinks, components mounted on boards and environmental-level analysis. This paper will concentrate on the cooling of components with heat sinks using a finite difference simulation of the heat transfer in typical heat sink configurations. Various heat sinks were simulated to obtain the effect of the influencing parameters on the heat transfer at the boundaries. The simulated results were compared with experimental values over a range of heat dissipation in each type of heat sink. From the experiments, improved heat transfer models were developed at the boundaries to compensate for the influencing parameters such as heat sink orientation relative to gravity and by-pass air flow. It can be concluded from the results that three-dimensional simulations have distinct advantages over traditional design graphs to analyze the performance of heat sinks and should be common practice for the electronics design engineer.

Equivalent heat source approach in a 3D transient heat transfer simulation of full-penetration high power laser beam welding of thick metal plates

One of the major concerns in the operability of power generation systems is their susceptibility to combustion instabilities. In this work, we aim to examine the effective use of heat exchangers, an integral component in any power generation system, to passively control combustion instability. The combustor is modelled as a quarter-wave resonator (1-D, open at one end, closed at the other) with a compact heat source within, which follows time lag law for heat release. The heat exchanger (hex) is modelled as an array of tubes with bias flow and is placed near the closed end of the resonator, causing it to behave like a cavity-backed slit plate: an effective acoustic absorber. For simplicity and ease of analysis, we treat the physical processes of heat transfer and acoustic scattering occurring at the hex as two individual processes separated by an infinitesimal distance. The aeroacoustic response of the tube array is modelled using a quasi-steady approach and the heat transfer across the hex is modelled by assuming it to be a heat sink. Unsteady numerical simulations were carried out to obtain the heat exchanger transfer function (HTF), which is the response of the heat transfer at hex to upstream velocity perturbations. Combining the aeroacoustic response and the HTF, in the limit of the infinitesimal distance between these processes tending to zero, gives the net influence of the hex. Other parameters of interest are the heat source location and the cavity length (the distance between the tube array and the closed end). We then construct stability maps for the first resonant mode of the aforementioned combustor configuration, for various parameter combinations. Preliminary observations show that stability can be achieved for a wide range of parameters.

The effect of geometrical parameters on heat transfer characteristics of microchannels heat sink with different shapes

The drive for small and compact electronic components with higher processing capabilities is limited by their ability to dissipate the associated heat generated during operations, and hence, more advanced heat sink designs are required. Recently, the emergence of additive manufacturing techniques facilitated the fabrication of complex structures and overcame the limitation of traditional techniques such as milling, drilling, and casting. Therefore, complex heat sink designs are now easily realizable. In this study, we propose a design procedure for mathematically realizable architected heat sinks and investigate their performance using the computational fluid dynamics (CFD) approach. The proposed heat sinks are mathematically designed with topologies based on triply periodic minimal surfaces (TPMSs). Three-dimensional CFD models are developed using the starccm+ platform for uniform heat sinks and topologically graded heat sinks to study the heat transfer performance in forced convection domains. The overall heat transfer coefficient, surface temperature, and pressure drop versus the input heat sources as well as the Reynolds number are used to evaluate the heat sink performance. Moreover, temperature contours and velocity streamlines were examined to analyze the fluid flow behavior within the heat sinks. Results showed that the tortuosity and channel complexity of the Diamond solid-networks heat sink result in a 32% increase in convective heat transfer coefficient compared with the Gyroid solid-network heat sink which has the comparable surface area under the examined flow conditions. This increase is at the expense of increased pressure drops which increases by the same percentage. In addition, it was found that expanding channel size along flow direction using the porosity grading approach results in significant pressure drop (27.6%), while the corresponding drop in convective heat transfer is less significant (15.7%). These results show the importance of employing functional grading in the design of heat sinks. Also, the manufacturability of the proposed designs was assessed using computerized tomography (CT) scan and scanning electron microscopy (SEM) imaging performed on metallic samples fabricated using powder bed fusion techniques. A visible number of internal manufacturing defects can affect the performance of the proposed heat sinks.

This paper describes the use of CFD and mathematical optimization to minimise heat sink mass given a maximum allowable heat sink temperature, a constant cooling fan power and heat source. Heat sink designers have to consider a number of conflicting parameters. Heat transfer is influenced by, amongst others, heat sink properties (such as surface area), airflow bypass and the location of heat sources, whilst size and/or mass of the heat sink needs to be minimized. This multiparameter problem lends itself naturally to optimization techniques. In this study a commercial CFD code, STAR-CD, is linked to the DYNAMIC-Q method of Snyman. Five design variables are considered for three heat source cases. Optimal designs are obtained within six design iterations. The paper illustrates how mathematical optimization can be used to design compact heat sinks for different types of electronic enclosures.

This study aims to identify the thermodynamic cycle that produces the maximum possible power output from a heat source and sink with finite heat capacities. Earlier efforts used sequential Carnot cycles governed by heat transfer rate equations to determine the maximum power cycle. In this paper, a hypothesis is proposed where the heat capacities of the heat addition and rejection processes of the proposed maximum power cycle are assumed to match the heat source and sink, respectively. The result is a simple thermodynamic model that approximately defines the performance and shape of the proposed maximum power cycle, which are compared and verified with the shape and performance of optimized sequential Carnot cycles with closely matching results.

Optimal design of heat pump integrated low-grade heat utilization systems

Cooling of electronic circuits is a necessity to ensure their reliability and optimum working conditions. In this work different types of pin fin based bio-inspired flow fields are analyzed. The flow fields are of differently shaped pin fin arrays, with leaf-type branching secondary channels, having a porosity range of 0.520.78. The number of inlet and outlet pairs for the models analyzed varies from one to four, to cater to the increased heat flux inputs. The simulation of the heat sink models is done using COMSOL. The coupling between heat transfer and laminar fluid flow is done using conjugate heat transfer analysis. The heat sinks are subjected to a constant heat flux input and tested for the laminar Re range of 10002300. The square pin fin model is validated at a porosity of 0.52 and aspect ratio-8.6, for test conditions specified in reference work. Validation of simulation results is done by comparing the mixing cup temperature with that obtained by applying the heat balance equation. The results prove that, the thermal and hydraulic resistance of bio-inspired pin fin models studied in this investigation is lower than that of traditional pin fin array models, leading to a higher Nu for similar pressure drops. The four-inlet heat sink models show a thermal resistance of 0.130.15 C/W at an inlet Re of 2300 with a calculated pumping power of 0.081-0.132 W for the flow field. The reduced porosity square pin fin model has a thermal resistance of 0.0673 C/W at pumping power of 3.44 W.

Study on spray cooling characteristics of dry ice particles for IGBT in high-speed trains{fr}Etude des caractéristiques de refroidissement par pulvérisation des particules de glace sèche pour l'igbt dans le train à grande vitesse

Experimental research on reverse flow phenomenon in an equal-height-difference natural circulation system at low pressure

The research on the heat source characteristics and the equivalent heat source of the arc in gaps

Differing from land-based systems, conventional passive residual heat removal systems (PRHRSs) in nuclear-powered ships encounter challenges for use as safety systems due to limited space and difficulties in adopting safety aids. To resolve this problem, the authors have previously suggested a compact and long-term-operable PRHRS that uses air cooling and seawater cooling in tandem, and its feasibility was confirmed through a design study and transient analysis. Nevertheless, the system performance depends on various parameters, and their sensitivities have yet to be analyzed. The purpose of the current study is to conduct a parametric analysis of the system focusing on four parameters: filling ratio, thermal center difference between heat source and sink, heeling angle, and heat source temperature. The Multi-dimensional Analysis of Reactor Safety (MARS-KS) code was used for the parametric analysis. The results show that the parameters are highly interrelated with each other, and consequently, the system exhibits significantly different behavior depending on the parameter conditions. In particular, the filling ratio determines the overall trends of the system. It was also found that the presence of two heat sinks with a single heat source in the natural circulation loop of the system complicate the natural circulation behavior. Based on the results, we conclude that a thorough examination and careful control of the parameters are necessary to implement the proposed system. The highlights are as follows: 1. Parametric analysis of compact and long-term-operable PRHRS is conducted. 2. Analysis reveals that the filling ratio is the most dominant parameter for system performance. 3. The unique behavior of the natural circulation loop with two heat sinks and a single heat source is analyzed.

Heat transfer and pressure drop characteristics of R134a flow boiling in the parallel/tandem microchannel heat sinks

In order to investigate the heat transfer of different types of heat sinks under non-uniform heating condition, both plate-fin heat sinks and pin-fin heat sinks were tested with a square heat source having length of 45 mm, 10 mm and 4 mm at various frontal air velocities in this study. The results showed that heat sinks with larger heater size yielded higher heat transfer coefficient for both heat sinks. Besides, the increase of heat transfer coefficient was more rapid for heat sink with a larger heater size as the frontal velocity increased.