Showing papers on "Subcooling published in 2023"

Experimental study of liquid immersion cooling for different cylindrical lithium-ion batteries under rapid charging conditions

Abstract: In this study, the liquid immersion cooling scheme based on SF33 has been proposed and tested for cooling the six different types of cylindrical lithium-ion batteries (LIBs) under fast charging conditions. Firstly, the voltage and temperature responses of LIBs under fast charging conditions with natural convection and SF33 immersion cooling were explored. It is found that the SF33 immersion cooling has a significant advantage over natural convection on controlling the battery temperature, thus ensuring the stability and safety of LIBs in the fast charging process. Subsequently, the high-speed photography was used to observe the bubble behaviors in the cooling process of SF33, and the heat transfer mechanism in the two-phase heat transfer process corresponding to immersion cooling of LIB was preliminary analyzed and discussed. It can be concluded that when the charging current is higher, the phenomenon of subcooled boiling as well as saturation boiling is generated in the SF33. The transition from single-phase convective heat transfer to boiling heat transfer greatly increases the heat transfer coefficient.

Heat Transfer Calculations during Flow in Mini-Channels with Estimation of Temperature Uncertainty Measurements

Abstract: The main aim of this work was to provide heat transfer calculations of flow boiling in mini-channels with an application for the Trefftz functions. The test section comprised five parallel mini-channels with a depth of 1 mm, with a common heated wall. For the estimation of the temperature uncertainty, during the experiment the temperature measurement was performed with the use of K-type thermoelements and an infrared camera in two mini-channels simultaneously. According to the Guide to the Expression of Uncertainty in Measurement, the Monte Carlo method is a practical alternative to the GUM uncertainty framework. Since the uncertainty components are not approximately the same magnitude, the Monte Carlo method was indicated to estimate the uncertainty of the surface temperature measurement. The results obtained from this simulation method were compared with the results of the computation related to the uncertainty propagation method. The results of both methods of temperature measurement were found to be consistent. The results of the statistical analysis were used to describe heat transfer calculations. The heat transfer investigations concerning the subcooled boiling region were performed during the other experiment. The local heat transfer coefficients on the contact surface between the working fluid and the heated wall were calculated from the Robin boundary condition. The mathematical model described by the heat equation in the mini-channel wall and by the Fourier-Kirchhoff equation in a flowing fluid leads to an inverse heat transfer problem. This problem was solved using the FEM with the Trefftz-type basis functions. The estimation of temperature uncertainty measurements due to the Monte Carlo method was included in the final results of the heat transfer coefficient.

Experimental study on flow patterns in narrow rectangular channels

Abstract: Plate fuel elements are commonly used in compact nuclear reactors due to the advantages of high fuel consumption. In this paper, the two-phase flow pattern in the coolant channel of plate fuel elements, i.e. the rectangular narrow channel was studied. Visualization flow pattern experiments of upward steam-water two-phase flow in narrow rectangular channels, 745 mm long and 67 mm wide with gap widths of 1.3 mm and 1.9 mm, were investigated. The experiments were performed in the conditions of pressure ranging from 1 to 2 MPa, mass flow rate ranging from 200 to 1500kg/(m2⋅s), inlet subcooling ranging from 20–100 °C and tilt angle ranging from 0 to 45°. Three flow patterns, consisting of bubble flow, churn flow and annular flow, were obtained in a wide range of thermal parameters. Flow patterns maps were plotted and the influences of pressure, mass flow rate, inlet subcooling, channel gap and tilt angle on the flow pattern transformation of narrow rectangular channel were studied. This study is of great significance for investigating the subsequent heat transfer process of two-phase flow in compact nuclear reactors.

A review of phase change materials in multi-designed tubes and buildings: Testing methods, applications, and heat transfer enhancement

Abstract: Phase change materials (PCMs) can be used as a latent heat storage system which is a very cost-efficient and affordable method for conserving thermal energy for future use. They are capable to store and release a vast amount of energy. In the past decade, PCMs are used widely for thermal insulation in buildings. A literature search revealed that various reviews have been conducted in recent years, although most of them have focused on PCM applications in a specific field, such as thermal comfort and building energy efficiency. Very few of them investigated PCMs in tubes with multiple designs and their testing methods simultaneously. This study thus investigates the recent development of thermal energy storage systems incorporating PCMs in multi-designed tubes and buildings, as well as their testing methods, other applications and heat transfer improvement. The melting point of PCM varies depending on the type. For instance, the RT23 PCM has a melting point of only 23o C, making it an excellent choice for home insulation. A 31-finned tube shows the maximum energy efficiency for commercial paraffin and reduces the PCM melting time by 65 %. However, the expansion of PCM applications is typically restricted by the reliability, efficiency, overall cost, and performance of the technology. A significant improvement is still needed in the phase transition, thermal conductivity, and compatibility of the materials. When dealing with inorganic PCMs, it is very important to take steps to prevent subcooling, supercooling, and phase separation by adding nucleating agents.

Conjugate Heat Transfer Analysis for Cooling of a Conductive Panel by Combined Utilization of Nanoimpinging Jets and Double Rotating Cylinders

Abstract: In this work, double rotating active cylinders and slot nanojet impingement are considered for the cooling system of a conductive panel. Colder surface temperatures of the cylinders are used, while different rotational speeds are assigned for each of the cylinders. The impacts of cylinder rotational speeds, size and distance between them on the cooling performance are evaluated. The rotational effects and size of the cylinders are found to be very effective on the overall thermal performance. At the highest rotational speeds of the cylinders, the average Nusselt number (Nu) rises by about 30.8%, while the panel temperature drops by about 5.84 °C. When increasing the cylinder sizes, temperature drops become 7 °C, while they are only 1.75 °C when varying the distance between the cylinders. Subcooling and nanofluid utilization contributes positively to the cooling performance, while 1.25 °C and 10 °C temperature drops are found by varying the subcooled temperature and solid volume fraction. An artificial neural network is used for the estimation of maximum and average panel temperatures when double cylinder parameters are used as the input.

Solidification of phase change materials in horizontal annuli

Abstract: This paper presents experimental results on solidification of n-octadecane and dodecanoic acid in horizontal annuli with 18-, 27-, and 36-mm center tubes and a 127-mm outer cylinder. Dodecanoic acid was superheated to 2.5 °C above the solidification temperature and n-octadecane was superheated by 2.5 or 37.5 °C. Dodecanoic acid was solidified from the center tubes at temperatures 8.44, 21.1, or 33.8 °C below the solidification temperature; these temperatures for n-octadecane were 8.44 or 21.1 °C. Additionally, the solidification of dodecanoic acid was studied under the conditions of consecutive melting and solidification, where it was subcooled by 2.5 °C and the superheating was dictated by the melting conditions. For these cases, the melting/solidification temperature differentials were 16.9 or 33.8 °C above/below the melting/solidification temperature. A comparative study of melting and solidification of n-octadecane was also done. For the melting experiments, n-octadecane was subcooled by 2.5 °C and melted at 21.1 °C above the melting temperature, which was compared to the respective solidification experiments. The volumes of solid/liquid PCMs per unit length of the enclosures and the positions of solid-liquid interfaces were obtained photographically. The results show that the solidification rates can be enhanced by using a larger center tube, solidifying the PCM at a lower temperature, and using PCMs initially liquid close to the solidification temperature. The effects of these parameters are greater on the solidification of n-octadecane than dodecanoic acid. The effects of PCMs on the solidification process depend on how strong the conductive heat transfer is. The results also show that up to 30 % (if not more) of solidification can be contributed by natural convection in the early stages of the solidification process.

Effect of gravity, wall superheat, and liquid subcooling on bubble dynamics during nucleate boiling

Abstract: Dynamics of a vapor bubble formed on a single nucleation site has been studied in this work numerically. The effect of level of gravity, wall superheat and liquid subcooling has been studied parametrically. The numerical simulation has been carried out by solving under the condition of axisymmetry, the mass, momentum, and energy equations for the vapor and the liquid phases. In the model the contribution of micro-layer has been included and instantaneous shape of the evolving vapor-liquid interface is determined :from the analysis. It is found that effect of reduced gravity is to stretch the growth period and bubble diameter at departure. Increase in wall superheat results in reduction in the growth period with a slight increase in the bubble diameter at departure. The effect of liquid subcooling on bubble departure substantially increased. In subcooled boiling both evaporation and condensation have been shown to occur simultaneously on the vapor-liquid interface of the bubble. The predictions from the model are found to be generally in good agreement with the data obtained at earth normal gravity and in low gravity environment of KC-135 aircraft.