Immersing cooling of large spherical produces: Thermal parameters

This article presents a combined experimental and modelling study for determining the thermal parameters of spherical produces in immersing cooling. In experiments, large spherically shaped water melons were selected as test samples, and cooled in water at surrounding temperatures of 0·5°C, 1·0°C, and 1·5°C. Inside temperatures of the produces were recorded at these water temperatures. In the analytical part, the models were introduced to determine the thermal parameters involved in the process, such as cooling coefficients, lag factors, heat transfer coefficients, thermal conductivities, thermal diffusivities, Biot numbers as well as the cooling times in terms of half cooling and seven-eighths cooling times. The results indicate that the cooling coefficient, the heat transfer coefficient, the Biot number, and the thermal diffusivity of the produce decreased by 3·2%, 0·42%, 0·42%, and 3%, respectively, with increasing cooling medium temperature. The lag factor increased by 9·3%. The half cooling time and the seven-eights cooling time indicating the cooling rates of the produce increased by respectively 15·01% and 7·56%. One can conclude that the present technique is a useful, simple and effective tool for determining thermal parameters for produces cooled in a fluid medium.     

Generalized volumetric behaviour of refrigerants based on a new four-parameter corresponding states correlation

The generalized volumetric behaviour of polar and non-polar refrigerants has been correlated using a new four-parameter corresponding states method. This method results in an accurate representation of the PVT surface for reduced temperatures from 0·55 to 1·62 and for reduced pressures up to 23·5, which covers almost all the range of importance for refrigerant applications. Input parameters required are critical temperature, critical pressure, the acentric factor and a pseudo-polarity factor calculated from the compressibility factor of a saturated liquid at a reduced temperature of 0·7. Three reference fluids are used to evaluate the compressibility factors. Comparison between experimental and calculated volumetric properties shows that highly accurate results are obtained by the new method for 20 polar of non-polar substances that are mainly used as working fluids in refrigeration systems and heat pumps. Average errors in the calculation of compressibility factors are 0·63, 2·24 and 0·53% for the gaseous, critical and liquid regions, respectively. Overall average error is 0·91% for the entire region studied.     

Thermal performance of a south facing wall as solar collector storage system

This paper illustrates an analysis of the performance of a solar wall as a collector storage system. the south facing wall consists of a mass of concrete/brick whose one surface is blackened and glazed, and a network of pipes (metallic or plastic) is laid in a plane from which heat can be extracted by flow of fluid in such a manner that the temperature of the plane of heat retrieval keeps constant. the collection efficiency of the system is found to be 80·0 and 60·7 per cent for collection temperatures 20 and 25°C respectively on the surface; the maxima/minima of the rate of heat retrieval (Q(t)) occurs about 12 h after the maxima/minima of solar temperature at a depth of the plane of heat retrieval = π/α1, with a maximum efficiency of 21·47.     

Heat exchanger design: Thermal performances of rectangular fins protruding from vertical or horizontal rectangular bases

An experimental investigation of the steady-state rates of heat transfer from an array of vertical rectangular fins of 3 mm thickness and 250 mm length, protruding 60 mm perpendicularly upwards from a 250 mm × 190 mm horizontal rectangular base, is reported. For constant (to ±0·1°C) base temperatures between 40°C and 80°C, in an ambient environment of 20±0·2°C, the optimal separation of the parallel fins, corresponding to the maximum rate of heat loss, is 10·5±1·0 mm.The effects of the extent of the fin protrusions on the thermal performances of such vertical fins, on the same base, which was arranged to be either vertical or horizontal, have been studied. The experiments were performed with three different fin protrusions, namely 32 mm, 60 mm and 90 mm, for a base temperature of 40°C above that of the ambient environment. The steady-state rate of heat dissipation from the fin array increased slightly less than linearly with the fin protrusion for both orientations, but the relationship became closer to linear as the fin spacing was increased.A comparison of the abilities to dissipate heat to the room air from the same geometrical configuration having a rectangular fin array but positioned with vertical fins on a vertical base, vertical fins protruding upwards from a horizontal base, or horizontal fins on a vertical base, has been made. The orientation with vertical fins protruding upwards from the horizontal base, is the preferred option because of the relatively high rates of heat transfer that can then be achieved.     

Excess heat evolution from nanocomposite samples under exposure to hydrogen isotope gases

Anomalous heat effect by interaction of hydrogen isotope gas and metal nanocomposites supported by zirconia or by silica has been examined. Observed absorption and heat evolution at RT were not too large to be explained by some chemical processes. At elevated temperatures of 200–300 °C, most samples with binary metal nanocomposites produced excess power of 3–24 W lasting for up to several weeks. The excess power was observed not only in the D-Pd·Ni system but also in the HPd·Ni system and HCu·Ni system, while single-element nanoparticle samples produced no excess power. The Pd/Ni ratio is one of the keys to increase the excess power. The maximum phase-averaged excess heat energy exceeded 270 keV/D, and the integrated excess heat energy reached 100 MJ/mol-M or 90 MJ/mol-H. It is impossible to attribute the excess heat energy to any chemical reaction; it is possibly due to radiation-free nuclear process.     

Performance investigation of a two-stage sorption hydrogen compressor

Metal hydrides (MH) are widely investigated for several thermodynamic applications; sorption hydrogen compressor (SHC) is one among them. In this study, the thermodynamic performance and heat – mass transfer behaviour of a two-stage sorption hydrogen compressor (TSSHC) are investigated with the employment of La_0·9Ce_0·1Ni₅ and MmNi_4.8Al_0.2 alloys in series. The hydrogen supply and the discharge temperatures are chosen as 20 °C and 80 °C, respectively. The thermodynamic performance data, i.e. compressor work and efficiency, are evaluated using the experimentally measured pressure-concentration-isotherm (PCI) and thermodynamic properties. In contrast, the heat and mass transfer behaviour is predicted by solving governing equations through the finite volume method (FVM). The numerical model is validated with experimental PCIs, and the results are in close agreement. The predicted cycle time is 75 min, comprising hydrogen supply, sensible heating and cooling, and hydrogen delivery. The TSSHC possessed a compression ratio of 9.5 and a cycle efficiency of 11.4% in which the hydrogen supply pressure is 9 bar using 0.5 kg of each alloy. Later, the influence of mass transfer on overall compressor work, heat input and efficiency is also presented.     

Measurement of the specific heat capacity of plastic waste/fly ash recycled composite using a differential scanning calorimeter

This paper deals with measurements of the specific heat capacity of plastic waste/fly ash recycled composite and its components using both a differential scanning calorimeter and sapphire disks as standard reference material. The measurement is carried out at temperatures below the melting point of the plastic component. The constant heating rates are set at 2, 5, and 10 K·min^?1. The specific heat capacity of the recycled composite increases from 1.3 to 1.6 kJ·kg^?1·K^?1 with increasing the temperature from 305 to 360 K, when the heating rates are set at 2 and 5 K·min^?1. In addition, the deviation in the data is within ±3%. However, the data for 10 K·min^?1 are about 2% lower than those for 2 K·min^?1. The specific heat capacity is independent of the shape and mass of the recycled composite sample. The uncertainty for the specific heat capacity data of the recycled composite is estimated to be within ±4%. The specific heat capacity of the fire retardant is as large as that of the fly ash. In addition, the specific heat capacity of the recycled composite depends largely on the content of the plastic waste. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(7): 435–448, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20164     

Estimation of metal temperature of MCrAlY coated IN738 components based on interdiffusion behaviour

Abstract

Interdiffusion at the interface between a Co–36·5Ni–17·5Cr–8Al–0·5Y, MCrAlY coating and the underlying IN738 superalloy was studied in a large matrix of specimens isothermally heat treated up to 12 000 h at temperatures 875, 925 or 950°C. Microstructural investigations and calculated phase fraction diagrams show that a precipitate free zone forms between the coating and superalloy and grows with time. The width of the growing zone was estimated on the basis of average intensity profiles obtained from experimental X-ray maps measured using energy dispersive spectroscopy (EDS) in a scanning electron microscope (SEM). A simple parabolic growth model was set up for estimating the metal temperature near the coating/substrate interface based on the growth kinetics of the precipitate free zone. Parameters for the model were extracted from measurements of the width of the growing precipitate free zone with time. The developed model was used to estimate metal temperatures for a service exposed, first stage gas turbine blade.     

Axial and radial heat transfer studies in a circulating fluidized bed

The axial and radial variation of the heat transfer coefficient in a circulating fluidized bed riser column, and the effect of operating parameters thereon, are investigated. The experimental set-up consists of a riser column of 102 mm×102 mm in bed cross-section, 5·25 m in height with a return leg of the same dimensions. The unit is fabricated with plexiglass columns of 0·6 m in length which are interchangeable with one another. Two axial heat transfer test sections of 102 mm×102 mm in cross-section, 500 mm in height, and made of mild steel, are employed for the axial heat transfer study and one horizontal tube section of 22·5 mm OD made of mild steel is employed for the radial heat transfer study. The primary air velocity is varied between 4·21 and 7·30 m s⁻¹. Local sand of mean size (d_p) 248 μm is used as the bed material. One empirical model with the help of dimensional analysis has been proposed to predict the heat transfer coefficient to a bare horizontal tube in a CFB riser column and the model results are validated with the experimental data; good agreement has been observed. © 1997 John Wiley & Sons, Ltd.     

Heat transfer to a horizontal tube bundle located in the freeboard of a bubbling fluidized bed combustor

The characteristics of heat transfer from bubbling gas-fired fluidized bed to a horizontal staggered water-tube bundle located in the freeboard region is experimentally investigated. The purpose is to demonstrate the effect of bed temperature on the coefficients of heat transfer by the different modes to each of the four rows of the bundle, which experiences heat transfer by convection from flue gases, luminous radiation from bed material and non-luminous radiation from gases. The bed temperature itself is varied and controlled through the fuel–air mass ratio. Sixteen runs have been conducted with bed temperature ranging from 1114 to 1429 K, resulting in an overall heat transfer coefficient in the range 74·0–105·0 W m⁻² K⁻¹ for the first row and 58·0–65·0 W m⁻² K⁻¹ for the last. An overall convective heat transfer coefficient from gases, and possible carried over sand particles, to the bundle is formulated. © 1997 by John Wiley & Sons, Ltd.     

BN type inclusions formed in high Cr ferritic heat resistant steel

Abstract

Scanning electron microscopy observations of fractured steel rod samples were made to clarify the formation and dissolution behaviour of boron nitrides in high Cr ferritic heat resistant steels during heat treatment at high temperature. A large number of coarse size BN type inclusions of 2 to 5 μm were distributed at the bottom of the dimples. They did not dissolve during annealing at 1150°C. However, they had a tendency to begin dissolving and reducing its particle size with time at 1200°C and dissolved completely in a short time at 1250°C. From the chemical analyses of boron and nitrogen in many high Cr heat resistant steels and SEM observations of their fractured samples, critical boron and nitrogen concentrations for the formation of coarse size BN type inclusions of 0·001%B and 0·015%N were found, and the solubility limit of BN was represented as log [%B]=?2·45log [%N]?6·81 at 1150°C.     

Modelling and experimental studies of alternative heat treatments in Steel 92 to optimise long term stress rupture properties

Abstract

The desire for power plant to give increased generating efficiency and decreased CO₂ emission has led to considerable effort over the last 10–15 years, to develop ferritic–martensitic steels which can be used for steam temperatures up to about 650°C. Examples are the addition of boron and increasing chromium content to 10–12 wt-%. However, high chromium levels have led to problems with long term precipitate stability. One approach which has not been widely explored, is the use of novel heat treatments to optimise the preservice microstructure to give the best long term creep rupture strength. Increased austenitising temperatures and lower tempering temperatures have been examined in Steel 92 (9Cr–0·5Mo–2W) and have produced significant improvements in creep rupture strength at temperatures up to 650°C compared with material given a conventional heat treatment. This has been achieved without any loss in ductility compared with conventional heat treatments. Test data for durations in excess of 40 000 h are presented. Modelling of microstructure evolution based on Monte Carlo simulations has shown important differences especially in the stability of grain boundary M₂₃C₆ and intragranular MX particles, between material with conventional and modified heat treatments. The model predictions are in good agreement with metallographic observations made on material before and after stress rupture testing. Continuum creep damage mechanics modelling based on the microstructural evolution has also been applied to predict creep life of Steel 92 and satisfactory agreement with creep rupture tests has been obtained.     

Effect of lubricating oil contamination on evaporation in refrigerants R12 and R22

An investigation has been made into the effect of oil concentration on evaporation heat transfer coefficients in refrigerant-oil mixtures flowing in a horizontal tube. A new correlation is presented for heat transfer coefficients in convective evaporation of refrigerant-oil mixtures that predicts the results of the present study within approximately ±20%. The paper reports measurements of evaporation heat transfer coefficients in refrigerants R12 and R22, both oil-free and with two concentrations of Shell Clavus 32 oil. A 1·8 m long ⅜ in O/D copper tube (8·05 mm I/D) was used, at evaporation temperatures of −5°C, 0°C and +5°C. Heat flux and mixture mass velocity were kept constant at 2500 W m⁻² and 155 kg m⁻² s⁻¹, respectively, and measured coefficients were in the range of 1400 to 3900 W m⁻² K⁻¹. The results showed that, for a complete evaporator, 2% oil may be expected to increase the heat transfer coefficient by 12%, but 10% oil returns the coefficient to oil-free values.     

Transient temperature distributions in canned products during heat sterilization and cooling

This reseach was performed using experimental temperature data and a simple analytical model to estimate the temperature distributions at the centres of cylindrically canned products (diameter/thickness ratio = 4/1) during heat sterilization and cooling under continuous flow conditions for two retort temperatures (115 and 121°C). The recorded experimental temperature data for an individual can for two different retort temperatures were then used to construct the dimensionless experimental centre temperature curves. In order to predict dimensionless centre temperature profiles with a mathematical model, the convection boundary condition (i.e. 0·1 < Bi < 100) in transient heat transfer was considered. The predicted temperature profiles were compared with the experimental centre temperature measurements for two cases—heat sterilization and cooling. The experimental temperature values were in very good agreement with the theoretical predictions. The results of this study show that the present technique is a reasonable tool for estimating in a simple and accurate form the temperature distributions of a cylindrically canned product subject to both heat sterilization and cooling.     

Development of Ni based single crystal superalloys for power generation gas turbine blades

Abstract

In advanced industrial gas turbine systems, there has been a great demand for new single crystal (SC) superalloys with an excellent combination of high temperature creep strength, hot corrosion resistance and oxidation resistance. In the present study, twelve nickel based SC superalloys were designed with the aid of the d-electrons concept. Their chemical compositions were in the range 1·2–1·5%Ti, 3·8–6·5%Cr, 11%Co, 0–1·4%Mo, 0–3·0%Ru, 6·5–7·4%Ta, 5·0–6·4%W, 3·6–5·4%Re, 5·1–5·5%Al, 0·12–0·14%Hf and balanced Ni in wt-%. A series of experiments such as creep rupture tests, burner rig tests and cyclic oxidation tests were conducted with the heat treated SC specimens of these alloys. Almost all the designed alloys were found to be superior in creep rupture life to a second generation superalloy currently used in the world. In the hot corrosion resistance estimated from the burner rig tests, any designed alloys were similar or even superior to a second generation superalloy. The oxidation resistance was very different among the designed alloys, but some of them showed better resistance than the second generation superalloy. Thus the SC alloys containing about 4–5 wt-%Re had ～30°C or more higher temperature capability than the second generation superalloy, while exhibiting excellent hot corrosion resistance and good oxidation resistance.     

Performance study of a double-absorption water/calcium chloride heat transformer

In order to increase the temperature lift and efficiency of single-absorption heat transformers there are other possible arrangements. Double-absorption heat transformers have a relatively simple design and smaller size compared to two-stage heat transformers. In this work, the thermodynamic performance of the water/calcium chloride system was modelled for a double-absorption heat transformer. Results indicate that temperature lifts of up to 40°C are possible with coefficients of performance close to 0·3. © 1998 John Wiley & Sons, Ltd.     

Experimental and numerical study of the isotherms and determination of physicochemical parameters of the hydrogen absorption/desorption process by the metal hydrides

In this work, absorption/desorption isotherms of the LaNi_3·6Mn_0·3Al_0·4Co_0.7 alloy, have been determined from the experimental data at three temperatures (T_Fluid = 298 K, T_Fluid = 303 K, and T_Fluid = 313 K). However, the experimental isotherms are compared with a proposed theoretical model. The physicochemical parameters of the proposed model are determined from the experimental data. Using these parameters, the absorption and desorption processes of hydrogen by the LaNi_3·6Mn_0·3Al_0·4Co_0.7 alloy can be compared. During the absorption/desorption process, the behaviors of each parameter are studied under the effect of temperature and pressure. In addition, internal energy, entropy, and enthalpy are calculated by using the proposed model. On the other hand, the temperature and pressure effects on the variation of these functions have been studied. The calculated physicochemical parameters suggested that the hydrogen absorption/desorption process in the LaNi_3·6Mn_0·3Al_0·4Co_0.7 alloy was feasible, spontaneous and exothermic in nature.     

Weather data for building energy cost-benefit analysis

This paper deals with European TRY weather data processing for climatic indexes generation, useful for HVAC energy and cost simplified evaluation. For nine Italian locations are presented: 99 and 2·5% dry bulb temperatures, 2·5% wet bulb temperatures, heating and cooling degree days, latent enthalpy days, unitary sensible and latent loads. TRY psychrometric data were processed according to a bin method that preserves the correlation between dry bulb temperature and moisture content, and then reduced by an averaging technique. An example is worked out in order to present an engineering shorthand for energy and cost evaluation of HVAC system. © 1998 John Wiley & Sons, Ltd.     

NATURAL CONVECTION-RADIATION INTERACTIONS IN A CUBE FILLED WITH A NONGRAY GAS

A three-dimensional numerical study was performed on interactions of natural convection and radiation in a cubical enclosure filled with carbon dioxide gas. The enclosure was heated differentially by two opposing vertical walls. Gas radiation was analyzed by the P₁ differential approximation method and the weighted sum of gray gas model. Computations were carried out over a range of the Rayleigh number, Ra, between 10⁵ and 10⁹. The Prandtl number and the overheat ratio were held fixed at 0·68 and 1·0, respectively. Unsteady transitional flows were computed by a direct simulation method, without using any explicit turbulence models. From the predictions, a mean heat transfer correlation has been proposed as Nu = 0·323 Ra^0·342 in the surface/gas radiation mode, where Nu is the time and spatially averaged Nusselt number at the isothermal walls.     

Efficiency of fresnel lenses with respect to thermal losses

Experimental observations and heat loss calculations for a Fresnel lens under forced and natural convection have both been obtained. A lens with a 2·0 mm step width and 325·99 cm² area when exposed to solar radiation and kept normal to solar radiation with an intensity of 43·116 cal/cm²/h has given a steady-state temperature of 187·5°C at its focus.