The effect of internal particle heat conduction on heat transfer analysis of turbulent gas–particle flow in a dilute state

In many cases the conduction mechanism inside a particle can not be ignored (large particles, low thermal conductivity and high porosity) during turbulent gas–particle flows. However, the accurate solution might be difficult to apply. Therefore, we first develop here the ability to conduct accurate solution and then we define the criterion for which the internal conductivity might be ignored. A combination between commercial C.F.D. code and user defined programs was developed to predict numerically the gas–particle velocity and temperature profiles. The selected criterion (defined at the outlet of the pipe’s cross-section), referred to the relation between the computational desirable average temperature difference without ignoring internal heat conductivity and the average particles temperature by ignoring internal heat conductivity, determines whether to consider the heat conduction mechanism in numerical simulations or to ignore it. It was found that the average particles temperature for T _p =  f(r) is lower than the case when T _p =  constant. Also, it was found that the non-dimensional temperature difference criterion is a continuous function of [Bi ×  (d _p/D)] for a specific geometry, various pipe and particle diameters, various particles’ thermal conductivities, constant heat flux and Re number. The numerical code enables to extend the classical criterion for Bi number of solids to various gas–particle systems and different operational conditions.     

What dominates heat transfer performance of hybrid nanofluid in single pass shell and tube heat exchanger?

Influence of nanoparticle volume concentration and proportion on heat transfer performance (HTP) of Al₂O₃ – Cu/water hybrid nanofluid in a single pass shell and tube heat exchanger is analyzed. Multiphase mixture model is adopted to model the flow. Three-dimensional governing equations and associated boundary conditions are solved using finite volume method. The numerical results are validated with the experimental results. Results indicate that optimized nanoparticle volume concentration and proportion dominate HTP of hybrid nanofluid. Heat transfer coefficient and Nusselt number are monotonic increase functions of nanoparticle volume concentration and proportion. The percentage increase in heat transfer coefficient of hybrid nanofluid is 139% than water and 25% than Cu/water nanofluid. At higher Reynolds number, the increment in Number of Transfer Units (NTU) between water and hybrid nanofluid is close to 75%. Maximum enhancement in Nusselt number for hybrid nanofluid exceeds 90% when compared to nanofluid (Al₂O₃/Water nanofluid). Consequently, highest heat transfer performance is attained for hybrid nanofluid systems. Effectiveness of heat exchanger increases almost to 124% when hybrid nanofluid is employed. We show that it is higher than water as well (conventional coolant). Results are expected to be helpful in further industrial-scale deployment of nanofluids, which is an area that is currently relevant for ongoing academia-industry partnership efforts worldwide.     

Effect of β heat treatment on phase transformations of TC21 during rolling

Phase transformations during hot rolling is determined for the forged and β heat treated TC21 titanium alloys. The results show that β heat treatment has a great effect on phase constitution. Three types of precipitates, namely, α₂, ω and (Ti, Zr)₅Si₃ phase is observed in the rolled forged materials, whereas the rolled β heat treated materials exhibites the presence of lamellar α and type 2α precipitate. The influence of β heat treatment on the phase transformations has been discussed on the basis of alloying elements, and β heat treatment can eliminate or decrease elemental segregation.     

Development of microstructure during heat treatment of high carbon Cr–Mo steel

Abstract

Stainless steels containing enhanced chromium and carbon contents are particularly attractive for applications requiring improved wear and corrosion resistance. The as cast microstructure of such steels is composed mainly of ferritic matrix along with a network of interdendritic primary carbides. It has been shown that heat treatment of these steels results in microstructures that contain more than one type of carbide. A selective dissolution technique has been employed to isolate carbides from the matrix. Scanning electron microscope and X-ray diffraction studies of the as cast steels have shown that the primary carbides are essentially of M₇C₃ type, whereas in heat treated specimens both M₇C₃ (primary) and M₂₃C₆ (secondary) type carbides have been observed. The relative amounts of these carbides are found to be dependent on the heat treatment temperature. In addition, nucleation of austenite occurs above 950°C and at ～1250°C the matrix transforms entirely to austenite, which is retained completely on quenching to room temperature.     

Investigation of two-phase heat transfer coefficients of argon–freon cryogenic mixed refrigerants

Mixed refrigerant Joule Thomson refrigerators are widely used in various kinds of cryogenic systems these days. Although heat transfer coefficient estimation for a multi-phase and multi-component fluid in the cryogenic temperature range is necessarily required in the heat exchanger design of mixed refrigerant Joule Thomson refrigerators, it has been rarely discussed so far. In this paper, condensation and evaporation heat transfer coefficients of argon–freon mixed refrigerant are measured in a microchannel heat exchanger. A Printed Circuit Heat Exchanger (PCHE) with 340 μm hydraulic diameter has been developed as a compact microchannel heat exchanger and utilized in the experiment. Several two-phase heat transfer coefficient correlations are examined to discuss the experimental measurement results. The result of this paper shows that cryogenic two-phase mixed refrigerant heat transfer coefficients can be estimated by conventional two-phase heat transfer coefficient correlations.     

Inertia of measurements with “auxiliary-wall” type heat meters

The article examines the problem of thermal inertia on the basis of an auxiliary-wall type heat meter, it demonstrates the boundaries of applicability of the approximate relationship for calculating non-steady-state heat fluxes.Notation q() non-steady-state heat flux through the heat meter - _i,a _i thermal conductivity, thermal diffusivity, and thickness of the heat meter, respectively - ₂,a ₂ thermal conductivity and thermal diffusivity, respectively, of the base of the heat meter - t() temperature gradient over the thickness of the heat meter - index of thermal inertia - time - s parameter of Laplace transform - t₁ (x, ) temperature of the heat meter at point x - t₂(x, ) temperature of the base - t_c ambient temperature - Y_q(s) transfer function from the heat flux q() to the temperature gradient t() Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 2, pp. 298–305, August, 1980.     

Experimental investigation of heat transfer enhancement in helical coil heat exchangers using water based CuO nanofluid

The present work deals with the study of heat transfer enhancement using water based CuO nanofluids in the helical coil heat exchanger. Nanofluids were prepared using two-step method by using wet chemical method. Nanofluids with various volume percentage between 0 and 0.5 of CuO nanoparticles and their flow rate between 30 and 80 LPH (Reynolds number ranging from 812 to 1895, Laminar flow regime) were considered in the present study. The setup consists of a test section (helical coil), cooler, reservoir, pump, flow meter, thermocouples and flow controlling system. The temperature measurements were carried out with the help of thermocouples. The investigation was carried out to study the effect of particle loading and flow rate on heat transfer coefficient and Nusselt number. It has been found that the increase in the loading of CuO nanoparticles in base fluid shows a significant enhancement in the heat transfer coefficient of nanofluid. In the present study, at 0.1 vol% concentration of CuO nanoparticles in nanofluid, enhancement in heat transfer coefficient was 37.3% as compared to base fluid while at 0.5 vol%, it is as high as 77.7%. Also with the increase in the flow rate of the CuO nanofluid, significant increase in heat transfer coefficient was observed.     

Effect of heat treatment on morphology of Fe-rich intermetallics in Al–Cu alloys

The iron-rich intermetallics are considered to be stable in aluminium alloys and usually hard to dissolve into the matrix during solution heat treatment (SHT). Nevertheless, solid-state transformations between Fe-rich intermetallics may happen and will play a great role in breaking-up of the large Fe-rich intermetallics particle during hot deformation process. In this study, the solid-state phase transformation of the iron-rich intermetallics from Al_mFe to β-Fe (Al₇Cu₂Fe) has been studied using SEM, XRD and deep-etched technique in a 2xxx Al–Cu cast alloy during SHT. The mechanism of solid-state transformation for the Fe-rich intermetallics was discussed, including the solid-state reaction, nucleation and growth of iron-rich intermetallics and Al phases.     

Investigation of the heat conductivity of niobium in the temperature range 0.05–23 K

We report thermal conductivity measurements on a single-crystal niobium specimen of resistivity ratio 33,000 over the temperature range 0.05–23 K in the superconducting state and above 9.1 K in the normal state. The axis of the niobium rod was [110] oriented. The surface roughness was varied by sandblasting of the sample. The values of the thermal conductivity in the range from the lowest temperatures up to the maximal value covered a range of six orders of magnitude (=2×10^–5 W cm^–1 K^–1 at 50 mK to =22 W cm^–1 K^–1 at 9 K). Above 2 K the results for the untreated and the sandblasted sample are in accord, whereas below 2 K the influence of the sample surface is discernible. The various conduction and scattering mechanisms are discussed.     

Influence of heat treatment on creep of a Mn–N stabilised austenitic stainless steel

Creep at 700 °C/196 MPa and 900 or 925 °C/27.4 MPa of 21Cr–4Ni–9Mn austenitic stainless steel is determined as a function of the heat treatment. The heat treatment variation involves altering the solution heat treatment cooling rate from water quenching to cooling at 6 or 4 °C/min causing: serrated grain boundaries versus planar grain boundaries, coarser intergranular carbides, and discontinuous precipitation of grain boundary reaction zones. Water quenching causes improved creep resistance. Creep fracture and cracking is intergranular. Coarse intergranular carbides and grain boundary reaction zones cause premature void formation and cracking, this damage leading to an accelerating creep rate and lowering creep resistance of the more slowly cooled conditions. During creep, grain boundary serrations, which may otherwise contribute to improved creep, are eliminated. Determining the individual influence of grain boundary serrations on creep requires a detailed investigation of various heat treatment parameters to prevent concurrent formation of grain boundary reaction zones and serrations.     

“Averaging” method in problems of convective mass and heat transfer

An approximate method is proposed for the solution of nonlinear boundary problems of convective heat and mass transfer; the method is based on the procedure of averaging equations or boundary conditions.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 2, pp. 205–215, August, 1984.     

Optimal way for choosing parameters of spacecraft’s screen-vacuum heat insulation

The heat transfer in multiple plate sandwiches of spacecraft’s screen-vacuum heat insulation is simulated for determining the characteristics of heat shielding against long-term solar heat flux. To choose optimal characteristics of heat shielding, it is necessary to determine precisely the number of plates and their peculiarities. The new, absolutely stable method for solving numerically heat transfer problems is presented. We obtain results showing that the screen-vacuum insulation is characterized by low heating-up inertance that is unacceptable. To remove this effect, the inertial heat shielding is used on the internal surface of the heat shielding and its state is examined.     

Radiative heat transfer of ultra‐fine powder insulation in nonplanar geometry

Abstract

The purpose of this work is to study the radiation heat transfer through some typical ultra‐fine powder insulations. The spectral extinction coefficients for these powders have been measured via infrared transmission measurements. The experimental results are compared with both the dependent and independent scattering and absorption theoretical calculations. The radiative transport process is modeled by the diffusion approximation method. Based on the experimental data, the radiant thermal conductivity between two concentric cylinders and spheres was calculated. The results show that the radiant thermal conductivity between two concentric spheres is about 50 percent higher than that between two cylinders.     

Specific heat capacity of molybdenum chalcogenides. III. Measurements of the heat capacity of Sn1 − x Ga x Mo5S6. An investigation of the singularities at low temperatures

The heat capacity of molybdenum chalcogenides with different Sn/Ga content was measured at temperatures of T 60 K. The occurrence of two phases of the chalcogenides studied could clearly be seen for higher Ga concentrations. In the miscibility gap there coexists a superconducting phase (T _c= 12.5 K) SnGa_0.25Mo₅S₆ with the ferromagnetic GaMo₅S₆ phase (T _curie = 19 K). As for the pure ternary compound GaMo₅S₆, a singularity of the heat capacity could also be observed in the range of the structural change (T = 45 K). All the singularities are discussed.     

An investigation on effects of heat treatment on corrosion properties of Ni–P electroless nano-coatings

Electroless Ni–P coatings are recognized for their excellent properties. In the present investigation electroless Ni–P nano-crystalline coatings were prepared. X-ray diffraction technique (XRD), scanning electron microscopy (SEM), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were utilized to study prior and post-deposition vacuum heat treatment effects on corrosion resistance together with the physical properties of the applied coatings.     

The specific heat of samarium metal (80–400 K)

We have measured the specific heat of several high purity polycrystalline specimens of samarium metal over the temperature range 80 K to 400 K. A broad peak is observed at T_Nh ~106K, the temperature at which antiferromagnetic ordering first sets in with ordering of the moments on hexagonal sites. This behaviour contrasts with the sharp peak observed by previous workers on samarium samples of lower purity.     

Analysis of the temperature field in the capillary structure of an “antigravity” heat pipe

The authors analyze the influence of the geometric parameters and the technical and physical properties of the capillary structure on the operating temperature of the antigravity heat pipe.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 2, pp. 203–207, August, 1986.     

Effect of solution heat treatments on superalloys Part 1 – alloy 718

Abstract

The hot ductility as measured by Gleeble testing of Alloy 718 at four different solution heat treatments (954°C/15 h, 954°C/1 h, 982°C/1 h and 1050°C/3 h+954°C/1 h) has been investigated. It is concluded that constitutional liquation of NbC assisted by δ phase takes place and deteriorates the ductility. Parameters established by analysing the ductility dependence on temperature indicate a reduced weldability of the material in the coarse grain size state (ASTM 3) while indicating an increased weldability when containing a large amount of δ phase due to a grain boundary pinning effect. The accumulation of trace elements during grain growth at the highest temperature is believed to be the cause for the observed reduced on-cooling ductility.     

Effects of rejuvenation heat treatment on microstructure and creep property of a Ni-based single crystal superalloy

Both surface and internal microstructures of a second-generation Ni-based single crystal(SX) superalloy were studied after creep and rejuvenation heat treatment(RHT).It is indicated that the microstructures,such as the dislocation network,the γ phase and the γ' phase,can be recovered to those after the standard heat treatment(SHT).It is found that RHT affected zone(RAZ) formed at the surface is composed of theγ'-free layer,the transition layer and the recrystallization(RX),which are less than 20 μm in depth totally.Such depth of the RAZ doesn't affect the properties of the superalloy.The morphology of γ' phase at the RAZ is related to the composition of the elements.The average creep life after RHT is close to the average life after SHT.It is concluded that RHT could effectively repair SX parts and increase the total life of the sample after a damage by creep.     

Specific heat capacity of solids under pressure from measurements of (∂T/∂P)s

A procedure is described for calculating specific heat capacity under pressure, c _p (T, P), from data for c _p (T, 0) and adiabatic (T/P) _s. The main advantage is that (T/P)_s can be readily measured under high-pressure conditions.