Transient Hot-wire Technique Research Articles

Design and development of a system based on transient hot wire technique to determine dry rubber content in natural rubber latex

Design and development of a system based on transient hot wire technique to determine dry rubber content in natural rubber latex

Deterioration of equivalent thermal conductivity of granite subjected to heating-cooling treatment

Understanding the thermal conductivity of granite is critical for many geological and deep engineering applications. The heated granite was subjected to air-, water-, and liquid nitrogen (LN2-) coolings in this context. The transient hot-wire technique was used to determine the equivalent thermal conductivity (ETC) of the granite before and after treatment. The deterioration mechanism of ETC is analyzed from the meso-perspective. Finally, the numerical model is used to quantitatively study the impact of cooling rate on the microcrack propagation and heat conduction characteristics of granite. The results show that the ETC of granite is not only related to the heating temperature, but also affected by the cooling rate. The ETC of granite decreases nonlinearly with increasing heating temperature. A faster cooling rate causes a greater decrease in ETC at the same heating temperature. The higher the heating temperature, the stronger the influence of cooling rate on ETC. The main explanation for the decrease in ETC of granite is the increase in porosity and microcrack density produced by the formation and propagation of pore structure and microcracks during heating and cooling. Further analysis displays that the damage of granite at the heating stage is induced by the difference in thermal expansion and elastic properties of mineral particles. At the cooling stage, the faster cooling rate causes a higher temperature gradient, which in turn produces greater thermal stress. As a result, it not only causes new cracks in the granite, but also aggravates the damage at the heating stage, which induces a further decrease in the heat conduction performance of granite, and this scenario is more obvious at higher temperatures.

Development of a data-driven subsurface thermal probing technique for lunar exploration

Conducting in-situ measurements of planetary environments is a key scientific goal in the geoscience field for the extraterrestrial exploration, such as the Moon or Mars. Among these measurements, determining the thermal properties of regolith is particularly challenging due to the material’s inhomogeneities. In this paper, an active thermal probing technique is proposed, utilizing a transient hot-wire technique with a needle-like probe structure integrated with temperature sensors and a heater. It is capable of measuring in-situ temperature variations and inner heat flux without disturbing the surrounding regolith. In addition, a machine-learning-based method is proposed for inverting in-situ thermophysical properties, including density, thermal conductivity, and heat capacity. An embedded artificial neural network model has been developed and trained with data sets from both finite element simulations and experiments. This machine learning model is capable of efficiently predicting temperature responses for different lunar regolith simulants. For total 12 parameters, the errors of ten cases are less than 10%, and other two cases are 12.23% and 13.17%. Finally, the proposed method is verified by heat measurement experiments under normal pressure and vacuum, and the variation of thermal properties with different compactness is obtained. The proposed probing technique provides novel ideas to measure the in-situ thermal properties of extraterrestrial regolith.

Measurement of Thermal Conductivity and Thermal Diffusivity of Porcine and Bovine Kidney Tissues at Supraphysiological Temperatures up to 93 °C.

This experimental study aimed to characterize the thermal properties of ex vivo porcine and bovine kidney tissues in steady-state heat transfer conditions in a wider thermal interval (23.2-92.8 °C) compared to previous investigations limited to 45 °C. Thermal properties, namely thermal conductivity (k) and thermal diffusivity (α), were measured in a temperature-controlled environment using a dual-needle probe connected to a commercial thermal property analyzer, using the transient hot-wire technique. The estimation of measurement uncertainty was performed along with the assessment of regression models describing the trend of measured quantities as a function of temperature to be used in simulations involving heat transfer in kidney tissue. A direct comparison of the thermal properties of the same tissue from two different species, i.e., porcine and bovine kidney tissues, with the same experimental transient hot-wire technique, was conducted to provide indications on the possible inter-species variabilities of k and α at different selected temperatures. Exponential fitting curves were selected to interpolate the measured values for both porcine and bovine kidney tissues, for both k and α. The results show that the k and α values of the tissues remained rather constant from room temperature up to the onset of water evaporation, and a more marked increase was observed afterward. Indeed, at the highest investigated temperatures, i.e., 90.0-92.8 °C, the average k values were subject to 1.2- and 1.3-fold increases, compared to their nominal values at room temperature, in porcine and bovine kidney tissue, respectively. Moreover, at 90.0-92.8 °C, 1.4- and 1.2-fold increases in the average values of α, compared to baseline values, were observed for porcine and bovine kidney tissue, respectively. No statistically significant differences were found between the thermal properties of porcine and bovine kidney tissues at the same selected tissue temperatures despite their anatomical and structural differences. The provided quantitative values and best-fit regression models can be used to enhance the accuracy of the prediction capability of numerical models of thermal therapies. Furthermore, this study may provide insights into the refinement of protocols for the realization of tissue-mimicking phantoms and the choice of tissue models for bioheat transfer studies in experimental laboratories.

Characterization of the Optical and Thermal Properties of Cardiac Tissue as a Function of Temperature.

In this work, we devised the first characterization of the optical and thermal properties of ex vivo cardiac tissue as a function of different selected temperatures, ranging from room temperature to hyperthermic and ablative temperatures. The broadband (i.e., from 650 nm to 1100 nm) estimation of the optical properties, i.e., absorption coefficient (μa) and reduced scattering coefficient $({\mu ^{\prime}}_s)$, was performed by means of time-domain diffuse optics. Besides, the measurement of the thermal properties was based on the transient hot-wire technique, employing a dual-needle probe to estimate the tissue thermal conductivity (k), thermal diffusivity (α), and volumetric heat capacity (Cv). Increasing the tissue temperature led to variations in the spectral characteristics of μa (e.g., the redshift of the 780 nm peak, the rise of a new peak at 840 nm, and the formation of a valley at 900 nm). Moreover, an increase in the values of ${\mu ^{\prime}}_s$ was assessed as tissue temperature raised (e.g., for 800 nm, at 25 °C ${\mu ^{\prime}}_s = 9.8{\text{ c}}{{\text{m}}^{{\text{ - 1}}}}$, while at 77 °C ${\mu ^{\prime}}_s = 29.1{\text{ c}}{{\text{m}}^{{\text{ - 1}}}}$). Concerning the thermal properties characterization, k was almost constant in the selected temperature interval. Conversely, α and Cv were subjected to an increase and a decrease with temperature, respectively; thus, they registered values of 0.190 mm2/s and 3.03 MJ/(m3•K) at the maximum investigated temperature (79 °C), accordingly.Clinical Relevance- The experimentally obtained optical and thermal properties of cardiac tissue are useful to improve the accuracy of simulation-based tools for thermal therapy planning. Furthermore, the measured properties can serve as a reference for the realization of tissue-mimicking phantoms for medical training and testing of medical instruments.

Thermal properties of AlN (nano) filled LDPE composites

Abstract The thermal properties of aluminium nitride nano-particles (n-AlN) filled into low-density polyethylene (LDPE) are discussed. Cylindrical specimens were prepared using a melt mixing process. X-ray diffraction was performed to characterize the structural properties of the pellets under investigation. The X-ray diffraction analysis confirms the change in secondary structure, such as crystallinity, of the LDPE due to the dispersion of n-AlN powder. The thermal stability of pure and n-AlN filled LDPE was checked by performing thermo-gravimetric analysis. The analysis confirms an improvement in the thermal stability of LDPE due to n-AlN addition. The thermal conductivity of the samples was measured using a KD2 Pro device (based on the transient hot wire technique of thermal conductivity measurement) at room temperature. Our finding reveals ∼1.36 fold enhancement in the effective thermal conductivity of LDPE due to the addition of 15 vol.% of n-AlN. The room-temperature thermal conductivity data of the investigated pellets were analyzed as a function of n-AlN concentration in the light of available theoretical models and correlations. The variation in thermal conductivity data of LDPE with n-AlN concentration is well explained by the semi-empirical model proposed by Agari and Uno.

Thermophysical characterization of mustard husk (MSH) and MSH char synthesized by the microwave pyrolysis of MSH

Abstract Thermophysical properties are calculated to determine performance parameters comprising specific heat capacity, thermal conductivity, thermal diffusivity and they are directly related to the dynamics of the material at atomic level and for thermal treatment of mustard husk (MSH) and MSH char, they play a vital role. Temperature dependence of thermophysical properties of MSH and MSH char have been investigated within the temperature range between 30 and 110 °C. MSH char is synthesized by the microwave pyrolysis of MSH. Thermogravimetric analysis of MSH and MSH char confirmed that MSH is more thermally stable as compared to MSH char. Moreover, it gave information about the degradation behaviour of MSH and MSH char. Thermophysical properties are measured by thermal analyser, based on the transient hot wire technique which is suitable to measure the thermal conductivity at elevated temperatures. At room temperature, thermal conductivity and thermal diffusivity of MSH are 0.187 W m−1 K−1 and 0.132 mm2 s−1, respectively. Specific heat capacity of MSH and MSH char are found to be almost same (1.349 kJ kg−1 K−1 for MSH and 1.310 kJ kg−1 K−1 for MSH char). Thermal conductivity and thermal diffusivity values are decreasing on increasing the temperature while specific heat capacity is increasing linearly on increasing the temperature. Low thermal conductivity and thermal diffusivity values of MSH imply that the conventional conductive heating is less effective and inefficient for the thermal treatment of MSH.

Viscosity, thermal conductivity, and interfacial tension study of CO2 + difluoromethane (R32)

Reliable understanding of viscosity (η), thermal conductivity (λ), and interfacial tension (γ) are demanded in the refrigeration process, especially in the heat, mass and momentum transfer calculations. In this work, measurements of these thermophysical properties for (CO2 + R32) have been conducted by vibrating wire viscometry, transient hot-wire technique, and differential capillary rise approach. The experimental condition ranges from (208.4 to 344.4) K and pressures up to 7.58 MPa at x(CO2) = 0.7, 0.8 and 0.9, including those in the single-phase and near the melting curves. The standard uncertainties (k = 1) are between (0.21 and 6.80) μPa·s, (0.00012 and 0.00290) W·m–1·K–1, and (0.13 and 0.67) mN·m–1 for viscosity, thermal conductivity, and interfacial tension, respectively. The achieved results and the literature data (if applicable) were utilised to regress the extended corresponding states correlation and Parachor approach implemented in REFPROP 10.0. With the regressed models, most viscosity and thermal conductivity results can be described within 4%. The determined data and improved model provided here should contribute significantly to the design margin minimisation in the refrigeration cycle.

Correct Use of the Transient Hot-Wire Technique for Thermal Conductivity Measurements on Fluids

The paper summarizes the conditions that are necessary to secure accurate measurements of the thermal conductivity of fluids using the transient hot-wire technique. The paper draws upon the development of the method over five decades to produce a prescription for its use. The purpose is to provide guidance on the implementation of the method to those who wish to make use of it for the first time. It is shown that instruments of the transient hot-wire type can produce measurements of the thermal conductivity with the smallest uncertainty yet achieved (± 0.2%). This can be achieved either when a finite element method (FEM) is employed to solve the relevant heat transfer equations for the instrument or when an approximate analytic solution is used to describe it over a limited range of experimental times from 0.1 s to 1 s. As well as establishing the constraints for the proper operation of the instrument we consider the means that should be employed to demonstrate that the experiment operates in accordance with the theoretical model of it. If the constraints are all satisfied then an uncertainty in thermal conductivity measurements of as little as ± 0.2–0.5% can be obtained for gases and liquids over a wide range of thermodynamic state from 0.1 MPa to 700 MPa and temperatures from 70 K to 500 K with the exception of near critical conditions. It is observed that many applications of the transient hot-wire technique do not conform to the constraints set out here and therefore may be burdened with very much greater uncertainties, sometimes large enough to render the results meaningless.

Accurate Measurements of the Thermal Conductivity of n-Docosane, n-Tetracosane, 1,6-Hexanediol, and 1,8-Octanediol in the Solid and Liquid Phases

New measurements of the thermal conductivity of n-docosane, n-tetracosane, 1,6-hexanediol, and 1,8-octanediol, in the solid and liquid phase, are presented. The technique employed is the transient hot-wire technique, based on a full theoretical model. The technique is absolute and is characterized by an uncertainty of 1%. At the 95% confidence level, the standard deviations of the thermal conductivity measurements of n-docosane, are 0.40% for the solid phase (267 K to 308 K), and 0.60% for the liquid phase (330 K to 360 K); of n-tetracosane, 0.60% for the solid phase (265 K to 306 K), and 0.30% for the liquid phase (339 K to 363 K); of 1,6-hexanediol, 0.70% for the solid phase (263 K to 296 K), and 0.40% for the liquid phase (327 K to 351 K); and of 1,8-octanediol 1.1% for the solid phase (265 K to 312 K), and 0.50% for the liquid phase (344 K to 356 K), respectively.

Thermal conductivity and thermal diffusivity of fullerene-based nanofluids

Owing to their outstanding characteristics, carbon based nanofluids (CbNFs) have been applied to various advanced heat transfer and cooling technologies. It was claimed that these CbNFs can considerably improve the properties of the base working fluids. Among all the thermal characteristics, the thermal conductivity (λ) is regarded as the primary parameter to be considered for the application of nanofluids (NFs). In the present research study we measured for the first time both λ and thermal diffusivity (aT) of very stable fullerene (C60)-based NFs in liquid phase (1,2,3,4-tetrahydronaphthalene and 1,2-dicholorobenzene) by the transient multi-current hot wire technique at atmospheric pressure in a wide range of temperature (254–323 K). Similar to the base liquids (BLs), we observed a slight decrease in λ with an increase in temperature. Additionally, compared to the BLs λ was reduced upon the addition of C60. The results were compared with the predicted ones using different theoretical models. Not much variation in aT was observed between the C60 NFs and the corresponding BLs due partly to the small variation of λ with the addition of C60.

Measurement of kinematic viscosity and thermal conductivity of 3,3,4,4,5,5-HFCPE in liquid and vapor phases

1H, 2H-hexafluorocyclopentene (3,3,4,4,5,5-HFCPE) is being expected as a suitable alternative working fluid for organic Rankine cycles and high-temperature heat pumps due to the attractive environmentally friendly properties, particularly for the low GWP value. The key objectives are to measure the kinematic viscosity and thermal conductivity of 3,3,4,4,5,5-HFCPE in both liquid and vapor phases, as well as to establish simple correlations at saturation conditions. In this study, the kinematic viscosity measurements were performed by the tandem capillary tubes method over the pressures up to 4.0 MPa and temperatures from 332 to 494 K for the liquid phase and from 413 to 514 K for the vapor phase. The measurement uncertainties were calculated using the propagation law of uncertainties by the GUM guideline, where the expanded uncertainties were estimated at 2.2% for the liquid phase and 2.9% for the vapor phase with k = 2 and a 95% confidence level. On the other hand, the thermal conductivity measurements were performed by the transient hot-wire technique at pressures up to 4.0 MPa and temperatures from 333 to 473 K for the liquid phase, and from 393 to 473 K for the vapor phase. The expanded uncertainties were calculated as 3.0% and 3.5% for liquid and vapor phases with k = 2 and a 95% confidence level, respectively. Also, simple correlations were developed to predict the kinematic viscosity and thermal conductivity at saturated conditions.

Thermal conductivity measurements and correlations of pure R1243zf and binary mixtures of R32 + R1243zf and R32 + R1234yf

Thermal conductivity measurements of pure R1243zf and binary mixtures of R32 + R1243zf and R32 + R1234yf were conducted in the homogeneous liquid and vapour phases with a transient hot-wire technique. The mole fractions of R32 are 0.25, 0.50, and 0.75 in both binary systems. The temperature range of the measurements was from (264.1 to 405.6) K with pressures ranging between (0.9 and 6.1) MPa. The transient hot-wire apparatus was validated with measurements of pure CO2 in both the liquid and vapour regions. The relative combined expanded uncertainty (k = 2) in the experimental thermal conductivity was approximately 2.0 %. The relative deviations of the measured thermal conductivities from those calculated using the extended corresponding states (ECS) model as implemented in the software REFPROP 10 were between (−13 and 10) % in the vapour phase, and between (−14 and 1) % in the liquid phase. Additionally, the performance of a new approach to predicting fluid transport properties, the residual entropy scaling model incorporating the cubic-plus-association equation of state (RES-CPA model) was tested for these mixtures by first determining the scaling parameter of pure R1243zf. The RES-CPA model was then able to predict the mixture thermal conductivities generally within 10 %, which is similar to the ECS model; however no additional parameters were introduced to the RES-CPA model to describe binary interactions.

Thermal conductivity modeling of monodispersed microspheres using discrete element method

Particle beds are widely used in various systems and processes, such as particle heat exchangers, granular flow reactors, and additive manufacturing. Accurate modeling of the thermal conductivity of particle beds and understanding of their heat transfer mechanisms are important. However, previous models were based on simple cubic packing of particles, which could not accurately represent the actual heat transfer processes under certain conditions. Here, we examine the effect of the packing structure on the thermal conductivity of particle beds. We use monodispersed silica microspheres with average particle sizes ranging from 23 to 330 μm as a model material. We employ a transient hot-wire technique to measure the thermal conductivity of the particle beds with packing density of 43%–57% within a temperature range of room temperature to 500 °C and under N2 gaseous pressures of 20–760 Torr. We then use a discrete element method (DEM) to obtain the realistic packing structure of the particles, which is then fed into a finite-element model (FEM) to calculate the thermal conductivity, with the consideration of solid conduction, gas conduction, and radiation heat transfer. Our results show that the thermal conductivity model based on the more realistic random packing structure derived from the DEM shows better agreement with the experimental data compared to that based on the simple cubic-packing structure. The combined DEM and FEM methodology can serve as a useful tool to predict the effective thermal conductivity of particle beds and to quantify different heat transfer mechanisms under various conditions.

Simultaneous measurement of effective thermal conductivity and effective thermal diffusivity of Li2TiO3 pebble bed using transient hot-wire technique

Lithium-based ceramics in the form of pebble beds have been considered for tritium breeder material in the fusion reactor's breeder blanket. It is essential to study the thermal characteristics of these ceramic pebble beds subjected to fusion relevant conditions. Effective thermal conductivity (k), effective thermal diffusivity (α) and effective specific heat (cp) of a packed bed are some of the crucial parameters for the design of breeder blanket module. In the present study, the transient hot-wire technique was used to measurek, α and cp of lithium metatitanate (Li2TiO3) pebble bed fabricated at Institute for Plasma Research, India. Thermal properties of Li2TiO3 pebble bed (1 ± 0.15 mm pebble diameter and ∼63% packing fraction) are measured within the temperature range of 45 °C to 800 °C in stagnant helium gas environment. The filling gas pressure variation effect on the Li2TiO3 pebble bed's thermal properties for the pressure range of 0.105 MPa to 0.4 MPa has also been studied. Equations are suggested for k and α of Li2TiO3 pebble bed as a function of temperature at different pressure in the helium gas environment.

Analysis of Heat Transfer Characteristics of a GnP Aqueous Nanofluid through a Double-Tube Heat Exchanger.

The thermal properties of graphene have proved to be exceptional and are partly maintained in its multi-layered form, graphene nanoplatelets (GnP). Since these carbon-based nanostructures are hydrophobic, functionalization is needed in order to assess their long-term stability in aqueous suspensions. In this study, the convective heat transfer performance of a polycarboxylate chemically modified GnP dispersion in water at 0.50 wt% is experimentally analyzed. After designing the nanofluid, dynamic viscosity, thermal conductivity, isobaric heat capacity and density are measured using rotational rheometry, the transient hot-wire technique, differential scanning calorimetry and vibrating U-tube methods, respectively, in a wide temperature range. The whole analysis of thermophysical and rheological properties is validated by two laboratories. Afterward, an experimental facility is used to evaluate the heat transfer performance in a turbulent regime. Convective heat transfer coefficients are obtained using the thermal resistances method, reaching enhancements for the nanofluid of up to 13%. The reported improvements are achieved without clear enhancements in the nanofluid thermal conductivity. Finally, dimensionless analyses are carried out by employing the Nusselt and Péclet numbers and Darcy friction factor.

Liquid thermal conductivity of three biodiesel compounds: Methyl myristate, methyl laurate and methyl caprate

In order to provide the basic thermophysical property data for the research of alternative clean fuels, the liquid thermal conductivity of methyl myristate, methyl laurate and methyl caprate which are considered as the main compounds of biodiesel was reported. The measurements of three fatty acid esters, covering a temperature range from (292 to 372) K and pressure up to 15 MPa, have been performed by a transient hot-wire technique with a bare platinum hot wire. The relative uncertainty of the experimental results was estimated to be ± 2.0% (in the 0.95 confidence level). The present thermal conductivity data were correlated as a polynomial function of temperature and pressure for the purpose of interpolation.

Thermal conductivity measurements of refrigerant mixtures containing hydrofluorocarbons (HFC-32, HFC-125, HFC-134a), hydrofluoroolefins (HFO-1234yf), and carbon dioxide (CO2)

Thermal conductivity measurements of eight binary refrigerant mixtures were conducted in the homogeneous liquid and vapour phases with the transient hot-wire technique. The temperature range of the measurements spanned from (224.3 to 386.6)K with pressures ranging between (1.0 and 6.5)MPa. The binary mixtures were equimolar (R125 + R32), (R32 + R134a), (R32 + CO2), (R125 + R134a), (R125 + CO2), (R134a + R1234yf), (R134a + CO2) and (R1234yf + CO2). Additionally, two multi-component mixtures, (R32 + R1234yf + CO2) and (R32 + R1234yf + R134a + R125 + CO2), were investigated. The transient hot-wire apparatus was validated with measurements of pure CO2 in the liquid and vapour regions. The relative combined expanded uncertainty (k = 2) in the experimental thermal conductivity was on the order of 2.0%. The relative deviations of the measured thermal conductivities in the vapour phase from those calculated using the extended corresponding states (ECS) model with default binary interaction parameters (BIPs), as implemented in the software REFPROP 10, were between (−12 and +8)%, while those in the liquid phase were between (−15 and +4)%. The new experimental data were used to tune the BIPs in the ECS model. Significant improvements were observed especially in the liquid phase of the five-component mixture, with the root-mean-square of the relative difference between the experimental data and the model estimation reduced by a factor of nearly three.

Improved Thermophysical Properties and Energy Efficiency of Aqueous Ionic Liquid/MXene Nanofluid in a Hybrid PV/T Solar System.

In recent years, solar energy technologies have developed an emerging edge. The incessant research to develop a power source alternative to fossil fuel because of its scarcity and detrimental effects on the environment is the main driving force. In addition, nanofluids have gained immense interest as superior heat transfer fluid in solar technologies for the last decades. In this research, a binary solution of ionic liquid (IL) + water based ionanofluids is formulated successfully with two dimensional MXene (Ti3C2) nano additives at three distinct concentrations of 0.05, 0.10, and 0.20 wt % and the optimum concentration is used to check the performance of a hybrid solar PV/T system. The layered structure of MXene and high absorbance of prepared nanofluids have been perceived by SEM and UV–vis respectively. Rheometer and DSC are used to assess the viscosity and heat capacity respectively while transient hot wire technique is engaged for thermal conductivity measurement. A maximum improvement of 47% in thermal conductivity is observed for 0.20 wt % loading of MXene. Furthermore, the viscosity is found to rise insignificantly with addition of Ti3C2 by different concentrations. Conversely, viscosity decreases substantially as the temperature increases from 20 °C to 60 °C. However, based on their thermophysical properties, 0.20 wt % is found to be the optimum concentration. A comparative analysis in terms of heat transfer performance with three different nanofluids in PV/T system shows that, IL+ water/MXene ionanofluid exhibits highest thermal, electrical, and overall heat transfer efficiency compared to water/alumina, palm oil/MXene, and water alone. Maximum electrical efficiency and thermal efficiency are recorded as 13.95% and 81.15% respectively using IL + water/MXene, besides that, heat transfer coefficients are also noticed to increase by 12.6% and 2% when compared to water/alumina and palm oil/MXene respectively. In conclusion, it can be demonstrated that MXene dispersed ionanofluid might be great a prospect in the field of heat transfer applications since they can augment the heat transfer rate considerably which improves system efficiency.

Measurement of effective thermal conductivity of lithium metatitanate pebble bed by transient hot-wire technique

Abstract In future fusion reactor lithium metatitanate (Li2TiO3) as a functional material in the form of packed pebble beds have been selected in breeding blanket concepts to generate and release tritium. The effective thermal conductivity (keff) of Li2TiO3 pebble beds are needed to be well characterized for the design and analysis of breeding blankets under fusion relevant conditions. The transient hot-wire technique based experimental system has been fabricated, tested and installed for keff measurement of Li2TiO3 pebble beds. Finite element method (FEM) simulations have been performed to optimize the dimension of an experimental setup with the intention of minimizing the uncertainty in keff measurements. The experiments have been performed on 1 ± 0.15 mm diameter Li2TiO3 pebble bed with a packing fraction of 63 %. The influences of temperature (35–800 °C), gas environment (helium and air) and gas pressure (0.105−0.4 MPa (abs.)) have been investigated on keff of Li2TiO3 pebble beds. Reduction in keff was found with a decrease in helium gas pressure while the reduction in keff was not significant with a decrease in air pressure. The measured keff results of Li2TiO3 pebble beds have been compared and agreed well with the literature experimental results. The empirical correlations are also proposed for keff of Li2TiO3 pebble beds in helium and in air environment at 0.105−0.4 MPa and as a function of temperature.