The shortest period of coal spontaneous combustion on the basis of oxidative heat release intensity

It’s necessary to forecast the shortest spontaneous combustion period for preventing and controlling the coal spontaneous combustion.During the experimental process,a calculating model of the SSCP is established on the basis of the oxidative heat release intensity and thermal capacity at different temperatures.According to the basic parameters of spontaneous combustion,heat of water evaporation and gas desorption,the SSCPs of different coals are further predicted.Finally,this study analyzed the relationships of the SSCP and the judging indexes of the self-ignite tendency.The result shows that the SSCP non-linearly increases with the decrease of dynamic oxygen adsorption and increase of activation energy.Compared with the practical fire situation of mine,this reliable method can meet the actual requirement of mine production.

Novel Coil Winding Method to Realize Pot Heated Evenly

To solve the problem about the inhomogeneous thermal effect of pot heated by coils along the circumference, a novel coil winding method is proposed and compared with the general winding method in the paper. First, based on the Biot-Savart law and Ampere＇s rule, the magnetic induction generated by a straight current carrying conductor and a current loop is discussed, respectively. Then the novel coil winding method is developed by adjusting the location of inhomogeneous joints. The joints are periodically scattered along the circumferential direction and symmetrically designed around the central axis.Numerical results show that the quite non-uniform temperature in the base of pot at the circular direction is effectively improved by using the proposed winding method. The potential danger produced by high temperature at some region of coils plate is minimized.It is energy-efficient and safe for residential appliances.

Effect of Sinusoidal Heating on Natural Convection Coupled to Thermal Radiation in a Square Cavity Subjected to Cross Temperature Gradients

Coupled natural convection and surface radiation within a square cavity, filled with air and submitted to discrete heating and cooling from all its walls, is studied numerically. The thermally active elements are centrally located on the walls of the cavity. Two heating modes, called SB and SV, are considered. They correspond to bottom and vertical left elements sinusoidally heated in time, respectively, while the top and vertical right ones are constantly cooled. The remaining portions of all the walls are considered adiabatic. The parameters governing the problem are the amplitude and the period of the temporally sinusoidal temperature, the emissivity of the walls , the relative lengths of the active elements and the Rayleigh number . The effect of such parameters on flow and thermal fields and the resulting heat transfer is examined. It is shown that, during a flow cycle, the flow structure can present complex behavior, depending on the emissivity and the amplitude and period of the exciting temperature. The rate of heat transfer is generally enhanced in the case of sinusoidal heating. Also, the resonance phenomenon existence, characterized by maximum fluctuations in flow intensity and heat transfer, is proved in this study.

Effects of Viscous Dissipation and Periodic Heat Flux on MHD Free Convection Channel FlowwithHeat Generation

This study investigates the influence of periodic heat flux and viscous dissipation on magnetohydrodynamic(MHD)flow through a vertical channel with heat generation.A theoretical approach is employed.The channel is exposed to a perpendicular magnetic field,while one side experiences a periodic heat flow,and the other side undergoes a periodic temperature variation.Numerical solutions for the governing partial differential equations are obtained using a finite difference approach,complemented by an eigenfunction expansion method for analytical solutions.Visualizations and discussions illustrate how different variables affect the flow velocity and temperature fields.This offers comprehensive insights into MHD flow behavior and its interactions with the magnetic field,heat flux,viscous dissipation,and heat generation.The findings hold significance for engineering applications concerning fluid dynamics and heat transfer,offering valuable knowledge in this field.The study concludes that the transient velocity and temperature profiles exhibit periodic patterns under periodic heat flow conditions.A temperature reduction is observed with an increase in the wall temperature phase angle.In contrast,an increase in the heat flux phase angle values raises the temperature values.

Study on Feeding Effect of Different Levels of Protein and Energy on Production Performance of Pregnant Mother and Neo-Natal Calves

The present study was undertaken to assess feeding effect on productive and reproductive performances of pre-natal and post-natal Red Chittagong Cattle （RCC） cows under on-station condition. A total of 16 pregnant RCC cows having pregnancy 6-7 months and between 1-3 parities was selected for the study and was allocated randomly into four dietary treatment groups. There are four type diets, i.e., To （standard diet according to National Research Council （NRC）, 1995）, T1 （5% below standard diet）, T2 （5% above standard diet）, T3 （10% above standard diet） and a control treatment T4 （maintained as farm practice）. The energy and protein requirements of experimental cows were determined as per standard developed by NRC. The results revealed that crude protein （CP） and metabolizable energy （ME, MJ/day） requirements among cows of different dietary groups were not significantly different, although CP requirements between T1 and T3 differed significantly. Total dry mater （DM） and ME intake differed significantly （P 〈 0.001） among cows of different dietary groups, but DM intake was significantly lower for cows in farm practice group Z4 compared to the cows of other dietary groups. The total CP intake had no significant variation （P 〉 0.05） among cows of all dietary groups, but CP intake from roughage varied significantly （P 〈 0.001）. Final live weight and total live weight gain had no significant variation for cows of all groups, but there were significant （P 〈 0.05） variation for daily weight gain. Daily weight gain of cows for first four dietary groups were significantly （P 〈 0.05） higher than cows of farm practice groups T4. Weight of calf from birth to 90 days and daily weight gain calves under different dietary groups showed that there were no significant （P 〉 0.05） variation of calf birth weights for all dietary groups, although lower birth weight was found in farm practice groups T4. Gestation length and postpartum heat period of cows of different dietary treatment groups revealed that there was no significant （P 〉 0.05） variation for those traits among cows of different dietary treatment groups, although there seems to be shorter postpartum heat for cows in dietary group T2 and longer period in farm practice group T4. Total and daily milk yield up to 30 days and 90 days of cows had no significant （P 〉 0.05） effect for different dietary treatment groups, although there seems to be slightly better milk production performance for dietary T2 and To, respectively for 30 days and 90 days total and daily milk yield. There were no significant （P 〉 0.05） changes of total and daily weight gain of cows for all dietary groups, however cows of standard dietary group To performed slightly better than those of cows of other dietary groups. Milk composition of cows of different dietary treatment groups showed that there was no significant （P 〉 0.05） variation on milk composition for cows of different dietary groups. Post-natal body condition score （BCS） for the 1st, 3rd and 4th months differed significantly （P 〈 0.05） among different dietary groups, while not found significant difference on the 2nd month. Therefore, it may be concluded that pre-natal feeding has significant effect on body weight gain, birth weight of calves and milk production of dairy cows. Hence, it is suggested that better nutrition may be provided during pre-natal period to harvest good quality of calves and higher milk yield from post-natal period.

Numerical analysis on phase change material melting process of a conical spiral tube energy storage tank

Spiral tube heat exchangers have been widely used in phase change energy storage due to the compact structure and large heat transfer area.Therefore,this study numerically analyzes the effects of spiral tube diameter,number of rotations,and unsteady heat source on the melting process in conical spiral tube energy storage tanks using Fluent software.The results indicate that when the tube diameter is increased from 8 to 11 mm and the number of rotations is increased from 5 to 8,the melting time is extended by 15.74%and 17.83%,respectively.The energy storage capacity increases by 0.64%and 1.83%,respectively.The average energy storage rate decreases by 13.05%and 13.58%,respectively.Furthermore,the sinusoidal wave heat source with small heat source periods has little effect on the melting process,while large heat source periods can significantly accelerate the melting.And the influence of amplitudes on the thermal storage performance under large heat source periods is more obvious.When the heat source period is increased from 2 to 160 min and the amplitude is increased from 5 to 20 K,the melting time is reduced by 24.50%and 17.20%,respectively.The total energy storage capacity decreases by 6.36%and increases by 1.62%,respectively.The average energy storage rate increases by 24.03%and 22.74%,respectively.The study provides guidance for the performance optimization of spiral tube phase change systems.

Chemical characteristics and source apportionment of atmospheric particles during heating period in Harbin, China

Atmospheric particles（total suspended particles（TSPs）; particulate matter（PM） with particle size below 10 μm, PM10; particulate matter with particle size below 2.5 μm, PM2.5）were collected and analyzed during heating and non-heating periods in Harbin. The sources of PM10 and PM2.5were identified by the chemical mass balance（CMB） receptor model.Results indicated that PM2.5/TSP was the most prevalent and PM2.5was the main component of PM210, while the presence of PM10–100was relatively weak. SO-4and NO-3concentrations were more significant than other ions during the heating period. As compared with the non-heating period, Mn, Ni, Pb, S, Si, Ti, Zn, As, Ba, Cd, Cr, Fe and K were relatively higher during the heating period. In particular, Mn, Ni, S, Si, Ti, Zn and As in PM2.5were obviously higher during the heating period. Organic carbon（OC） in the heating period was 2–5 times higher than in the non-heating period. Elemental carbon（EC） did not change much. OC/EC ratios were 8–11 during the heating period, which was much higher than in other Chinese cities（OC/EC： 4–6）. Results from the CMB indicated that 11 pollution sources were identified, of which traffic, coal combustion, secondary sulfate, secondary nitrate, and secondary organic carbon made the greatest contribution. Before the heating period, dust and petrochemical industry made a larger contribution. In the heating period, coal combustion and secondary sulfate were higher. After the heating period, dust and petrochemical industry were higher. Some hazardous components in PM2.5were higher than in PM10, because PM2.5has a higher ability to absorb toxic substances. Thus PM2.5pollution is more significant regarding human health effects in the heating period.

CHARACTERISTICS OF THE SURFACE AND ATMOSPHERIC HEATING FIELDS OVER QINGHAI-XIZANG PLATEAU FOR THE PERIOD FROM AUGUST 1982 TO JULY 1983

The surface and atmospheric heating fields over the Qinghai-Xizang Plateau are computed by using the observational data of solar radiation during 1982—1983.The mian results are as follows:The central and northern parts of the Plateau act as heat sinks in winter from November to January.Both eastern and south- ern parts of the Plateau are of heat sources.In summer,the main part of the Plateau acts as a strong heat source,and the center of the heating field is in the southeastern Plateau.However the main part of the Plateau acts as a heat sink for the atmospheric heating fields from October to March.The maximum intensity of the atmospheric heat sink over the central Plateau appears in December and January.From April to September,the main part of the Plateau acts as a heat source for the atmospheric heating fields.

The periodic unfolding method for the heat equation in perforated domains

We study the heat equation with non-periodic coefficients in periodically perforated domains with a homogeneous Neumann condition on the holes. Using the time-dependent unfolding method, we obtain some homogenization and corrector results which generalize those by Donato and Nabil(2001).

MHD Flow and Heat Transfer of a Generalized Burgers' Fluid due to a Periodic Oscillating and Periodic Heating Plate

This paper investigates the MHD flow and heat transfer of the incompressible generalized Burgers＇ fluid due to a periodic oscillating plate with the effects of the second order slip and periodic heating plate. The momentum equation is formulated with multi-term fractional derivatives, and by means of viscous dissipation, the fractional derivative is considered in the energy equation. A finite difference scheme is established based on the Gl-algorithm, whose convergence is confirmed by the comparison with the analytical solution in an example. Meanwhile the numerical solutions of velocity, temperature and shear stress are obtained. The effects of involved parameters on velocity and temperature fields are presented graphically and analyzed in detail. Increasing the fractional derivative parameter a, the velocity and temperature have a decreasing trend, while the influences of fractional derivative parameter ,8 on the velocity and temperature behave conversely. Increasing the absolute value of the first order slip parameter and the second order slip parameter both cause a decrease of velocity. Furthermore, with the decreasing of the magnetic parameter, the shear stress decreases.