Temperature oscillation of a dual compensation chamber loop heat pipe under acceleration conditions

Loop heat pipe has a wide application in the fields of airborne electronics cooling and thermal management. However, the pertinent temperature oscillation of the loop heat pipe could lead to adverse effects on the electronics. In the current study, an ammonia-stainless steel dual compensation chamber loop heat pipe was developed to experimentally investigate the temperature oscillation under different acceleration conditions. The impact of several control parameters such as different heat loads, loading modes, acceleration directions and magnitudes on the operational performance of the loop heat pipe was analyzed in a systematic manner. The heat load applied on the evaporator ranged from 25 W to 300 W. The acceleration magnitude varied from 1 g to 9 g and four different acceleration direction, i.e. configurations A, B, C and D, were taken into account. Two different loading modes were applied with different heat load and acceleration force. Experimental results show that (i) the loop temperature will change and oscillate as the acceleration force was applied under all test conditions. It can be easily found that the temperature oscillation occurred at both heat loads of 250 W and 300 W. (ii) for the case of the first loading mode, periodic temperature oscillation is observed on the liquid line, whereas for the second loading mode, periodic temperature oscillation can be easily appeared on the entire loop. (iii) the loop temperature under both configurations A and B with acceleration of 7 g does not oscillate at heat load of 150 W, 200 W and 250 W when the first loading mode is applied. Especially under configuration B, the acceleration could contribute to repress the temperature oscillation. Under the current heat loads for almost all cases, the temperature oscillation can be observed for configurations A, C and D with acceleration of 5 g. (iv) the amplitude of evaporator at heat load of 300 W under configuration C are 0.6 °C, 0.3 °C, 0.2 °C and 0.3 °C with acceleration of 3 g, 5 g, 7 g and 9 g. The corresponding period is 66 s, 36 s, 34 s and 36 s, respectively

A data driven deep neural network model for predicting boiling heat transfer in helical coils under high gravity

In this article, a deep artificial neural network (ANN) model has been proposed to predict the boiling heat transfer in helical coils under high gravity conditions, which is compared with experimental data. A test rig is set up to provide high gravity up to 11 g with a heat flux up to 15100 W/m 2 and the mass velocity range from 40 to 2000 kg m −2 s −1. In the current work, a total 531 data samples have been used in the ANN model. The proposed model was developed in a Python Keras environment with Feed-forward Back-propagation (FFBP) Multi-layer Perceptron (MLP) using eight features (mass flow rate, thermal power, inlet temperature, inlet pressure, direction, acceleration, tube inner surface area, helical coil diameter) as the inputs and two features (wall temperature, heat transfer coefficient) as the outputs. The deep ANN model composed of three hidden layers with a total number of 1098 neurons and 300,266 trainable parameters has been found as optimal according to statistical error analysis. Performance evaluation is conducted based on six verification statistic metrics (R 2, MSE, MAE, MAPE, RMSE and cosine proximity) between the experimental data and predicted values. The results demonstrate that a 8-512-512-64-2 neural network has the best performance in predicting the helical coil characteristics with (R 2=0.853, MSE=0.018, MAE=0.074, MAPE=1.110, RMSE=0.136, cosine proximity=1.000) in the testing stage. It is indicated that with the utilisation of deep learning, the proposed model is able to successfully predict the heat transfer performance in helical coils, and especially achieved excellent performance in predicting outputs that have a very large range of value differences

Thermal performance of a mine refuge chamber with human body heat sources under ventilation

This paper investigated the dynamic coupling heat transfer characteristics of rock and air in a Mine Refuge Chamber (MRC) under ventilation. In the current work, a comprehensive fifty-person MRC model combining human-body heat sources and ventilation is established, the proposed model is validated against available experimental data with deviation less than 4%. Furthermore, sensitivity analysis is performed to investigate the influence of several control parameters such as heating rate, ventilation and wall area in a MRC through using numerical simulation. Results indicated that: (i) the heat transfer process in a MRC will reach a stage of air temperature slow increase (ATSI) in less than 0.5 h. The air temperature rises linearly with the square root of time during the ATSI stage; (ii) for a MRC built in a sandstone seam with an initial rock temperature of less than 27 °C, the average air temperature will not exceed 35 °C in 96 h when the ventilation volume rate is 0.3 m 3/min per person; (iii) the rate of temperature rise in MRC is proportional to the rate of heat generation, but it is inversely proportional to the thermal conductivity, density and thermal capacity of the rock, as well as the ventilation volume rate and the wall area; (iv) an empirical correlation for the MRC average air temperature is developed while the supply air temperature equals to the initial rock temperature

Thermal Performance Analysis of an Underground Closed Chamber with Human Body Heat Sources under Natural Convection

In this article, a combined experimental and numerical study has been performed to investigate the thermal performance of a mine refuge chamber (MRC) under natural convection. In the current study, a 20-hour heating experiment is carried out in a fifty-person MRC laboratory and the heat lamps are utilized to simulate the human heat loss. A new analytical model is proposed to predict the air temperature and validated against the experimental data. Sensitivity analysis is performed to further investigate the effects of the thermal parameters of the rock. Results indicated that: (1) two different air temperature increase stages, rapid and slow increase stages, are observed in the MRC; (2) A new analytical method for predicting the air temperature in MRC under natural convection is proposed, it shows that the air temperature increasing trend becomes slow with the increase of the thermal conductivity, density and specific heat capacity of the rock; (3) the surface heat transfer coefficient on the vertical walls reaches the largest and it increases linearly with air temperature

Air Quality Control in Mine Refuge Chamber with Ventilation through Pressure Air Pipeline

A combined experimental and numerical study was performed to improve the performance of the ventilation system in a mine refuge chamber (MRC). In the experiment, CO2 cylinders and dispersion pipes were used to simulate the CO2 release of 50 people, and 0.1 L/min per person of fresh air was provided by an air compressor. A new analytical model for a 50-person MRC was proposed and validated against the experimental data. Sensitivity analysis was carried out to investigate the effects of several control factors. The results indicated the following: (1) The ventilation system layout has a significant influence on the CO2 concentration distribution in an MRC, while the uniformity of the CO2 concentration distribution in the MRC may not be effective with increased number of air inlets. (2) Under a well-arranged ventilation system in the 50-person MRC, the average CO2 concentration can be controlled at less than 0.5 % with a ventilation rate of 0.1 m3/min per person, and less than 0.2 % with a ventilation rate of 0.3 m3/min per person. (3) A quantitative correlation exists between the CO2 concentration and ventilation volume rate, as well as the CO2 release rate, for an MRC under a well-arranged ventilation system

Brueckner Rearrangement Effects in Λ5^5_\LambdaHe and ΛΛ6^6_{\Lambda\Lambda}He

Rearrangement effects in light hypernuclei are investigated in the framework of the Brueckner theory. We can estimate without detailed numerical calculations that the energy of the $\alpha$-core is reduced by more than 2.5 MeV when the $\Lambda$ adheres to $^4$He to form $^5_\Lambda$He. Similar assessment of rearrangement contributions is essential to deduce the strength of $\Lambda\Lambda$ interaction from experimentally observed $\Delta B_{\Lambda\Lambda}$. The recently observed experimental value of $\sim$ 1 MeV for the $\Delta B_{\Lambda\Lambda}$ of \hll suggests that the matrix element of $$ in \hll is around -2 MeV.Comment: 7 pages, to appear in Phys. Rev.

A Novel Approach to Highly Substituted β‐Carbolines via Reductive Ring Transformation of 2‐Acyl‐3‐isoxazolylindoles

We have worked out a new approach to 1,3,4‐trisubstituted β‐carbolines of pharmaceutical interest. As central building blocks we used 2‐acylindoles, which are readily available from indole‐2‐Weinreb amides. Bromination at C‐3, followed by Suzuki–Miyaura cross‐coupling with isoxazole‐4‐boronates gives 2‐acyl‐3‐isoxazolylindoles. Ring closure to the β‐carbolines was accomplished by reductive ring transformation upon catalytic hydrogenation in the presence of Cs2CO3

Prediction of the release process of the nitrogen-extinguishant binary mixture considering surface tension

Nitrogen used for pressurization in the extinguisher can be partially dissolved in the fire extinguishing agent. Consequently, the evolution of the dissolved nitrogen has a significant effect on the release behavior of the fire extinguishing agent in a rapid process. In this article, a new model was developed to predict the critical pressure of the nitrogen evolution and the release process of the fire extinguishing agent was described in detail. According to the Peng-Robinson (PR) equation of state and van der Waals mixing rule, the effect of the dissolved nitrogen on the surface tension of the fire extinguishant was analyzed by considering surface phase and fugacity coefficient. A method to calculate the surface tension of the liquid agent dissolved with nitrogen was proposed. The results showed that the proposed model can determine the accurate critical pressure of the evolution of the dissolved nitrogen and further evaluated whether nitrogen escapes. At different initial filling pressure, in addition, the release process of the nitrogen-extinguishant such as CF3I, FC218 (C3F8), HFC125 (C2HF5), and Halon1301 (CF3Br) was well predicted by the fluid release model when taking the surface tension and adiabatic index of the mixture into account. Compared with the previously obtained experimental data, the predictions obtained indicated that the present model can adequately describe the liquid and the gas mixture release stage in the release process of the nitrogen-extinguishant