Review of heat transport properties of solar heat transfer fluids

The present article reviews the test techniques for some of the important heat transport properties of oils such as viscosity, density, specific heat capacity and thermal conductivity mainly used for characterization of heat transfer fluids. It can be seen that while density of oils can be tested at higher temperatures, the other heat transport properties of oils like viscosity, specific heat capacity and thermal conductivity have a limitation of being tested at low temperatures below 100–150 °C. While quite a few number of researchers have reported evaluation of heat transfer properties like specific heat capacity and thermal conductivity of oils by different methods, there remains a huge scope of debate and discussions on the repeatability and reproducibility of such tests, especially in case of oils used in high-temperature applications. A lot of insight has been gathered with respect to testing of thermal conductivity of oils, and several common test methods have been compared with each other. Lastly, two mathematical models, reported in the literature in open domain, have been reviewed and compared with each other. If the oils are to be used at elevated temperatures, like heat transfer fluids used in concentrated solar power generation where temperatures go as high as 400 °C and beyond, there is an urgent need to standardize a laboratory test method for performance evaluation of heat transport properties, which can help in formulating new generation oils based on novel chemistries and technologies like nanofluids, synthetic oils of novel chemistries, molten salts and molten metals.     

Turbulent heat transfer in tubular heat exchangers with twisted tape

Journal of Thermal Analysis and Calorimetry - Enhancing heat transfer in heat exchangers has gained attention of researchers for many years because of reduction in costs of generating heat...     

Determination of heat of mixing and heat of vaporization with a differential scanning calorimeter

A simple method is presented for measuring the heat of mixing and the heat of vaporization of volatile liquids at temperatures below their boiling point. It consists in introducing liquids by a microsyringe into a nearly closed cell of the DSC. The relative standard deviation for 4 to 5 runs is ca. 5% for heat of mixing and ca. 2% for heat of vaporization.     

A method for the determination of the specific heat and heat of decomposition of composite materials

A method has been developed to determine the specific heat of a material during thermal decomposition using a combination of DSC and TGA data obtained at the same heating rate. The heat of decomposition is calculated simultaneously using the same data. This technique was used to determine the specific heat and heat of decomposition of a widely used fiberglass-filled phenol—formaldehyde resin and a fiberglass-filled acrylonitrile—butadiene (AB) copolymer. Experimental data are presented for the specific heat of both the virgin and char components for temperatures between 60 and 730°C. The calculated specific heat of the mixture during decomposition for both materials is also presented.     

The specific heat of surface layers

Summary The well-known relation ofW. Thomson for the latent heat of surface expansion was obtained by applying the second law to a cyclic surface expansion and heating process. A simple derivation of an expression for the excess heat capacity of the surface layer is obtained by applying the first law to the same cyclic process.If we do not include the amount of potential energy converted to heat,A /TdT in the definition of the excess heat capacity, the resultant relation between the specific heat of the surface layers and their excess heat capacity is of the same form as that expressing the latent heat of vaporization in terms of the differential heat capacities of the liquid and vapor phases.Numerical calculation shows that the excess heat capacity for the surface layer of water amounts to 24 percent of the heat capacity of the molecular layer in the bulk liquid phase.     

Limiting efficiency of adsorption heat pump

Based on the concept of unrecoverable energy losses in small-scale dissipative structures, the upper limit of the heat pump efficiency has been estimated. This limiting efficiency is achieved in the absence of energy losses due to heat exchange with the heat carrier but when nonequilibrium nonisothermal vapor transfer is taken into account. The limiting efficiency is smaller than the thermodynamically equilibrium efficiency and serves a better reference point in the search for optimal process layout.     

Thermodynamic evaluation of heat recovery through a Canopus heat exchanger for vapor compression refrigeration (VCR) system

This communication deals with the waste heat recovery from the industrial refrigeration and air-conditioning system by introducing Canopus heat exchanger. There is a considerable amount of low-grade heat available in large-capacity systems. To recover this low-grade heat, a Canopus heat exchanger is introduced between compressor and condenser components. The system feasibility is studied with various operating parameters and its effect on heat recovery factor and overall COP of the system. The parametric results obtained for different eco-friendly working fluids, such as R-134a and R-507a, have been presented. It is found that, in general, overall COP of the system is improved without affecting the actual performance of the system. The potential of low-grade heat availability is increased with increasing cooling capacity.     

Effective waste heat recovery from engine exhaust using fin prolonged heat exchanger with graphene oxide nanoparticles

Waste heat recovery is an important alternative to reduce the energy consumption in industrial processes. Heat Exchangers are used effectively for heat recovery. Thus, the role of heat exchangers for waste heat recovery system is crucial. The exclusive of heat transmission of a heat exchanger can be improved by many methods such as by modifying the geometries and using nano-additives of different concentration. In this continuation, a modified geometry of finned heat exchanger is developed with CFD analysis. Modified heat exchanger includes the fins in the internal pipe to improve heat transfer. Nanoparticles of graphene oxide with various concentrations are introduced in working fluid. A steady numerical study is performed by using ANSYS Fluent with k-omega turbulence model for exhaust flow. Variation at inlet velocities of exhaust gas and water, particles concentration and internal fin geometry are considered. The reduction in hot fluid temperature from 6 m/s to 2 m/s enhanced the effectiveness by approximately 33.3%. The decrease in hot fluid velocity to 2 m/s and 6 m/s can reduce its outlet temperature by 100 K and 14 K at 0.03 m/s cold fluid temperature. The inclusion of nanoparticles at 0.1% can enhance the effectiveness by maximum of 7%.     

A review on heat transfer characteristics of cryogenic heat pipes

Journal of Thermal Analysis and Calorimetry - Heat pipes are broadly applied for thermal management of devices with high heat flux. Due to the dependency of their efficient operating range on the...     

Waste heat driven solid sorption coolers containing heat pipes for thermo control

This paper provides a focus on the R&D of solid sorption coolers and heat pumps made in the Luikov Heat & Mass Transfer Institute (CIS Countries Association Heat Pipes) under Thermacore, Inc. Agreement.Commercial and space applications of sorbent systems offer an attractive alternative to compression systems and liquid sorption systems for cooling, heating and air conditioning.MgA zeolites solid sorption systems are analyzed. Some new results are presented.Solid sorption heat pump technology utilizing heat pipe heat recovery with a condensing/evaporating refrigerant holds considerable promise for bivariant (space and domestic) applications due to the variable temperature and variable load capabilities of such machines.     

Electrochemical heat flow calorimeter

A device designed for research of heat phenomena occurring in chemical power sources (CPS) is described. The device includes two functional blocks: electrochemical and calorimetrical, operating under single control, which allows simultaneously performing electrochemical and calorimetric measurements. The calorimetric block is a heat flow calorimeter. The calorimetric chamber design provides the possibility of studying thermal processes in laboratory electrochemical cells and CPS of planar, disk, and prismatic design. The absolute measurement error of the heat flow is ±50 μW at the resolution of 1 μW. The operating temperature range of the calorimetric chamber is 0–90°C. The basis of the electrochemical block is a module of a four–range potentiostat–galvanostat. The maximum polarizing current of the potentiostat is ±200 mA at the maximum voltage on the auxiliary electrode of ±10 V. Multiuser remote access from the user computers over Ethernet to the device is provided for control and treatment of experimental data. Digital deconvolution filters allowing to compensate the response rate of the heat flow meter are used for processing primary data of calorimetric measurements.     

灰污热流探针模拟锅炉受热面灰沉积的研究

基于傅里叶导热定律,设计了一简单实用的灰污热流探针,以神木煤、黄陵煤、新汶水煤浆和新汶黑液水煤浆为研究对象,在0.25MW热态实验炉上用灰污热流探针模拟了灰沉积过程,研究了四种燃料灰沉积过程中的热流变化特性和灰沉积机理。结果表明,灰污探针能很好地模拟不同燃料的灰污形成过程,模拟结果与实际情况相吻合;灰粒的沉积速率和吸收热流的衰减速率主要取决于燃料本身特性,同时也受烟气温度的影响;通过对探针上灰污的表观物理特性、微观结构、元素构成和矿物相的分析,发现四种燃料的灰沉积机理是不同的,黑液水煤浆灰污中Na、K含量较高,主要物相为熔融温度很低的富Na霞石和无水芒硝,黄陵煤灰污含有较高的Fe、Ca、S,而水煤浆燃烧时Fe的沉积和富集是灰污形成的主要因素;四种实验燃料中,黑液水煤浆和黄陵煤的结渣趋势强于神木煤和水煤浆。     

Generalized solvation heat capacities

The partial molar heat capacity associated with a constant-pressure solvation process is extended to define a total of six generalized solvation heat capacities, each of which contain unique physical information. These arise from all the possible cross derivatives of the reversible heat of solvation (with respect to T and N), each evaluated at either constant pressure or constant volume. The resulting quantities may be interconverted using expressions that depend on the solvent equation of state and the solute partial molar volume. Moreover, contributions to each of the solvation heat capacities arising from the temperature dependence of the solute-solvent interaction energy and the solvent-reorganization energy (at either constant pressure or constant volume) are formally identified. For the self-solvation of a molecule in its own pure fluid, the latter quantities may be extracted directly from experimental data, while for more general solvation processes additional input is required, either from computer simulation or from theoretical approximations. The results are used to experimentally quantify the generalized heat capacities pertaining to the self-solvation of xenon, difluoromethane, n-hexane, and water, as well as the hydration of xenon, cyclohexane, and three hard sphere solutes (of about the same size as water, xenon, and cyclohexane).     

The heat capacity of NdPO4

The heat capacity of neodymium orthophosphate has been measured in the temperature range (0.6 to 1570) K. From the results the excess (electronic) heat capacity has been derived by subtracting the lattice heat capacity derived from the heat capacity of the isostructural LaPO₄ and GdPO₄, reported earlier. The calculated excess heat capacity thus obtained is in reasonable agreement with that calculated from the crystal field energies.     

Temperature Modulated Differential Scanning Calorimetry Part IV. Effect of heat transfer on the measurement of heat capacity using quasi-isothermal ADSC

An analysis developed in previous work has been further refined in order to study the effect of heat transfer on the heat capacity and phase angle measurements by TMDSC. In the present model, a temperature gradient within the sample has been taken into account by allowing for heat transfer by thermal conduction within the sample. The influence of the properties of the sensors, the heat transfer conditions between the sensor and sample,and the properties of the sample have been investigated by varying each parameter in turn. The results show that heat capacity measurements are reliable only within a restricted frequency range, for which the experimental conditions are such that the heat transfer phase angle depends linearly on the modulation frequency. This revised version was published online in July 2006 with corrections to the Cover Date.     

Aspects of thermal conductivity relative to heat flow

Summary The various techniques and methodologies of thermal conductivity measurement have been conventionally based on the determination of the rate of directional heat flow through a material having a unit temperature differential between its opposing faces. The constancy of this rate depends on the material density, its thermal resistance and the heat flow path itself. The last of these variables contributes most significantly to the true value of steady-state axial and radial heat dissipation depending on the magnitude of transient thermal diffusivity along these directions. The purpose of this paper is to exemplify the above features by defined parameters of heat flow measurement by existing methodologies. No new method is proposed here. Importantly, the relationship between the rate of heat transfer, total heat transferred and thermal conductivity at a given temperature under steady-state conditions for a fixed heat flow path will be illustrated.     

Single run heat capacity measurements

An outline for the data analysis of single-run heat capacity measurments by dual sample DSC is presented with the following features: 1. Heat flow correction by subtracting the contribution due to the sample pan, including correction for mismatched pan masses. 2. Heat flow and temperature correction with a nonlinear temperature calibration, temperature lag correction, and heating rate correction. 3. Calculation of the cell constants for both cell positions and evaluation of the asymmetry factor between cell positions A and B. 4. Heat capacity calibration and calculation with slope and asymmetry correction. 5. Calculation of heat capacity for multiple runs. 6. Data curve fitting for heat capacity.This work was supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 8818412 and the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc. Thanks are given to TA Instruments, Inc. (New Castle, DE) for providing the commercial heat capacity software and helping with the acquisition of the calorimeter.     

Low-temperature heat capacity of diglycylglycine

Heat capacity of tripeptide diglycylglycine was measured in a temperature range from 6.5 to 304 K. The results were compared with those for glycine and glycylglycine. Peptide bonding was found not to change C _P(T) virtually above 70 K, where heat capacity does not obey the Debye model. Comparison with literature data allows one to expect a significant difference in the heat capacity for enantiomorph and racemic species of valine and leucine, like it was found recently for D-and DL-serine.     

Systematic errors in the measurement of heat by flow microcalorimetry

It is shown that a number of systematic errors must be considered when performing heat measurements by flow microcalorimetry because the nature of the flow technique is such that substantial heat loss can be incurred. The conventional procedure of electrical calibration is found to be an inadequate correction parameter. Equations to account for the effects of thermal disequilibrium are derived from the basic principles incorporated in the Tian equation. The predicted relationships are tested by simple experiments and shown to be correct. The various correction parameters are measured for a wide range of flow rate and heat input conditions. A composite equation is presented which allows for the correction of heat loss while deconvoluting electrical heat from a heat of reaction. The total heat output rate from a flow calorimeter can be calculated for most experimental conditions by reference to this equation and to the tabulated correction values.     

Calculation of heat regimes in pipeline systems of petrochemical industry

A computation technique for dynamics of heat regimes in pipeline systems that accounts for the heat exchange with environment and changes of thermophysical characteristics of a pumped medium and heat transfer coefficient caused by difference in temperatures of the pumped medium and a pipeline wall was offered.