Analysis and calculating for preheat temperature and average convection heat change coefficient in the continue annealing furnace

The aim of the thesis is to utilize essential theory of heat transfer,to use correlative expressions to calculate average convection heat change coefficient and heating temperature of strip in Jet Preheat Furnace (JPF),make the calculating results accordant with production data,and make the calculation to be used the process of production.The method is to collect:entry temperature and speed of strip,temperature and speed of N_2 - H_2,to analyse heat transfer according to length and thickness of strip,jet hole and mutual position of jet piping in JPF,to analyse heat transfer and built the physical model.In mathematic model, Martin correlative expressions are tried to calculate using the data from production,and are modified in part properly.At the same time,heat boundary condition is analysed with theory of impact jet and production data.The conclusion is obtained that boundary condition is rarely average numerical value of temperature of strip and N_2 - H_2 with impact jet condition,instead of a relation of function of temperature of strip, temperature and speed of N_2- H_2,array of jet holes,diameter of hole,distance between hole and strip,and acquired a calculating expression.In calculation of examples,the thesis collected and calculated 15 kinds of strips.The thickness of strips are 2=0.51~1.41 mm,material DQ - IF、DDQ,EDDQ,SEDDQ and 340DDQ.Main assess numerical value is temperature value after strip is heated with certain speed and within section of time.Maximum error in 9 groups of numerical value in the thesis is 3.36%comparing with production data.The correlative expressions can be used in production to adjust temperature of strip through changing speed and temperature of N_2 - H_2 and speed of strip.The correlative expressions are compiled computer process.The process can be applied in on line control of production by rapid calculating speed.

Exact analytical solution to three-dimensional phase change heat transfer problems in biological tissues subject to freezing

Analytically solving a three-dimensional （3-D） bioheat transfer problem with phase change during a freezing process is extremely difficult but theoretically important. The moving heat source model and the Green function method are introduced to deal with the cryopreservation process of in vitro biomaterials. Exact solutions for the 3-D temperature transients of tissues under various boundary conditions, such as totally convective cooling, totally fixed temperature cooling and a hybrid between them on tissue surfaces, are obtained. Furthermore, the cryosurgical process in living tissues subject to freezing by a single or multiple cryoprobes is also analytically solved. A closed-form analytical solution to the bioheat phase change process is derived by considering contributions from blood perfusion heat transfer, metabolic heat generation, and heat sink of a cryoprobe. The present method is expected to have significant value for analytically solving complex bioheat transfer problems with phase change.

Shaped Insulating Refractory Products——Determination of Permanent Linear Change on Heating

1 Scope This standard covers the definition, technical requirement, apparatus, specimen, test procedure, calculation and test report on permanent linear change of shaped insulating refractory products.

Heat Transfer Performance and Structural Optimization of a Novel Micro-channel Heat Sink

With the advent of the 5G era,the design of electronic equipment is developing towards thinness,intelligence and multi-function,which requires higher cooling performance of the equipment.Micro-channel heat sink is promising for the heat dissipation of super-thin electronic equipment.In this study,thermal resistance theoretical model of the micro-channel heat sink was first established.Then,fabrication process of the micro-channel heat sink was introduced.Subsequently,heat transfer performance of the fabricated micro-channel heat sink was tested through the developed testing platform.Results show that the developed micro-channel heat sink has more superior heat dissipation performance over conventional metal solid heat sink and it is well suited for high power LEDs application.Moreover,the micro-channel structures in the heat sink were optimized by orthogonal test.Based on the orthogonal optimization,heat dissipation performance of the micro-channel radiator was further improved.

Enhanced Phase Change Heat Storage of Layered Backfill Body under Different Boundary Conditions

In view of the high temperature problem faced by mining activities,the coordinated mining of ore deposit and geothermal energy is a solution in line with the concept of green mining.The layered backfill body with finned double-pipe heat exchanger continuously exchanges heat with the surrounding thermal environment,which plays an effective role in gathering geothermal energy.In this paper,the heat storage process of each layered backfill body under different boundary conditions is simulated by Fluent.The results show the heat storage characteristic of layered backfill body can be significantly improved by adding fins to the double-pipe heat exchanger.On the whole,the heat storage effect of bottom layer backfill body(BLBB)is the best.The total heat storage capacity of top layer backfill body(TLBB),middle layer backfill body(MLBB)and BLBB with the finned double-pipe heat exchanger is 666.3 kJ,662.2 kJ,1003.0 kJ;1639.0 kJ,1760.8 kJ,1911.2 kJ and 1731.1 kJ,1953.3 kJ,1962.8 kJ respectively at 1 h,8 h and 24 h.This study explores the law of heat storage of layered backfill body under different boundary conditions and also expands the idea for layered backfill body to efficiently accumulate geothermal energy.

满足运载火箭测控需求的Ka频段CTDRSS终端技术

To meet the application requirements for a Ka-band space-based TT&C terminal for a launch vehicle,this paper proposes the implementation scheme of a space-based TT&C terminal,analyzes and solves the miniaturized design of equipment and the key technology for high-efficiency heat dissipation.The phased array antenna test shows that without external heat dissipation measures,the phased array antenna can work for a long time to meet the working requirements of launch vehicle,which has been verified in the LM-8 mission,and has wide engineering application prospects.

Giant isothermal entropy change In(111)-oriented PMN-PT thin film

An isothermal entropy change of 240 nm(111)-oriented PMN–PT 65/35 film near the ferroelectric Curie temperature,relative cooling power(RCP)and change of heat capacity have been investigated.The extracted data characterized giant isothermal entropy change of more than 16 J/kgK in electric field shift△E of 455 kV cm^(-1),which is nearly twice than that found for PbZr_(0.9)5Ti_(0.05)O_(3)thin film at 492 kV cm^(-1)near the Curie point.Furthermore,the RCP≈700 J/kg and change of heat capacity≈233 J/kgK in electric field shift△E of 747 kV cm^(-1).

The effect of differential temperatures on the latent heat in the nucleation of CdSe quantum dots

This work studied the effect of differential temperatures on the latent heat in the nucleation of CdSe quantum dots（QDs）.The result showed that,by the formula of phase change,with increasing the reaction temperature,the latent heat in the nucleation of QDs reduced.CdSe QDs with the size-dispersion from 2.7 to 3.6 nm were synthesized via oleic acid-paraffin liquid system by controlling the reaction temperature from 180 to 220℃.Synthesized QDs were characterized by UV-vis absorption spectra and X-ray diffraction（XRD）.The result of UV-vis absorption spectra showed that with increasing of reaction temperature,the first absorption peak was red-shifted and the size of QD increased.The result of XRD showed that the synthesized QDs were zinc-blende structure.

Study of ZrO_2 nanopowders based stearic acid phase change materials

ZrO2 nanopowders based stearic acid phase change materials （PCMS） were prepareo oy mgn-energy milling. The concept of heat capacity factor （HCF） was used to analyze the thermal properties of the materials. The heat storage property of PCMs, containing the same content of stearic acid （23~ by mass） in the starting materials but synthesized by different technical processes, was investigated by using HCE It was found that there were vast influences of different dispersants on the heat capacity. The samples orelaared with chloroform provided the best heat storage ability in all samples tested.

Theoretical work on magnetocaloric effect in La_(0.75)Ca_(0.25)MnO_(3)

In this work,a phenomenological model is applied to describe the magnetocaloric effect for the La_(0.75)Ca_(0.25)MnO_(3)system near a second-order phase transition from a ferromagnetic to a paramagnetic state.Based on this model,it can predict the values of the magnetocaloric properties from calculation of magnetization as a function of temperature under different external magnetic fields.The magnetic entropy change reaches a peak of about 5.39 J/(kg·K)at 257 K upon 4 T applied field variation.TheΔSM distribution is much more uniform than that of gadolinium,which is desirable for an Ericson-cycle magnetic refrigerator.

Theoretical investigations on electrocaloric properties of(111)-oriented PbMg_(1/3)Nb_(2)/3O_(3) single crystal

The electrocaloric(EC)effect accompanied with the ferroelectric to paraelectric phase transition in(111)-oriented PbMg_(1/3)Nb_(2)/3O_(3)(PMN)is investigated.It is shown that the largest change TDis 0.37 K in 3 kV/cm electric field shift near the Curie temperature of 221 K;that is,the cooling TDper unit field(MV/m)is 1.23×10^(-6) m·K/V.This value is significantly larger,and comparable with the value of 0.254×10^(-6) m·K/V for PbZr_(0.95)Ti_(0.05)O_(3)thin film under larger electric field shift ED=30 kV/cm.Thus,the EC effect of(111)PMN single crystal provides cooling solutions at low temperatures,and opens more opportunities for practical application in cooling systems.

Electrocaloric properties of Zr-modified Pb(Mg_(1/3)Nb_(2/3))O_(3) polycrystalline ceramics

In this work,electrocaloric properties of Pb(Mg_(1/3)Zr_(2x/3)Nb_(2(1-x)3))O_(3-x/3) polycrystalline ceramics for different stoichiometric compositions have been investigated.The results show that largest changes(ΔT)are in range of 1.07 to 4.84 K in 10 kV cm^(-1) electric field change.These values are significantly large,and are comparable with values of other lead-containing ceramics under the same or larger electric field shift.The conclusion is that these materials are excellent candidates for working materials in refrigeration and liquefaction devices in a wide temperature range.