Guarded Hot Plate Apparatus Research Articles

Thermal conductivity of insulating materials using a peltier cell based cooling system

Abstract In this work we have built and evaluated a system that allows us to determine the thermal conductivity of insulating materials. We use this system to study the thermal properties of suitable for building materials, typical of high altitude Andean regions. The equipment’s setup is of a Guarded Hot Plate Apparatus (GHPA), the equipment’s central part has a circular hot plate and a concentric crown shaped disc (guard), which are not in contact each other. Two circular samples are placed on both sides of the hot plate and then the square cold plates are mounted at the lower and upper sides of the samples. The cold plates are refrigerated by mean of liquid which flows through an spiral coil embedded in it. The liquid is cooled by Peltier cells whose hot sides are in contact with air radiators. The temperature’s gradient is measured between the hot plate and the guard with a Type E thermocouple and to measure the temperature of the cold plates Type K thermocouples are used. To show the equipment’s performance, some thermal conductivity tests were carried out on the following materials: sugar cane bagasse, adobe with Stipa ichu, ashlar and glass.

Measuring the Specific Heat Capacity of Thermal Insulation Materials Used in Buildings by Means of a Guarded Hot Plate Apparatus

The specific heat capacity of building insulation materials is rather difficult to be determined using the conventional calorimetric methods. This is due to the small samples required for these methods which are not representative of the insulation material. Larger samples would not fulfill the requirements of the lumped system. Methods based on the transient heat transfer using heating wires or planes are commonly quick but less accurate measurements as they only consider the volume near the surface of the sample and need additional corrections and calibrations. The present investigation is based on a transient temperature control procedure using a common guarded hot plate device, which is normally used to determine the thermal conductivity of insulation materials. The procedure was performed on two different materials: one wood-based (wood fiber) and one mineral-based (expanded perlite). The results show a value of about 1200 J·kg−1·K−1 for the former and 600 J·Kg−1·K−1 for the latter. This method can also be extended to other thermal insulation materials for building application.

Uncertainty of thermal conductivity measurement at high temperatures using guarded hot plate apparatus

The guarded hot plate (GHP) is a primary method to measure the thermal conductivity (λ) of low-to-medium λ materials. Precision measurement of λ using the GHP method is challenging because the deviations from the basic assumptions in the principles of the method should be minimized, and the effect of such deviations on λ measurements must be quantified for uncertainty assessment. In the present study, the measurement uncertainty in λ of insulation materials when using a GHP apparatus was assessed at high temperatures of up to 700 °C. Both high-temperature environment and low-λ specimen make the measurement of λ difficult compared to the near-room-temperature environment or medium-λ specimen; thus, the assessed uncertainty tends to be large. A simple model that accommodates stray heat flow was described in this study and subsequently validated by measurements in various thermal configurations around the specimen. To reduce the stray heat flow, a new set of thermocouples at various parts in the GHP apparatus was specifically calibrated to accurately measure the temperature difference across the air gap before their installation, and proper auxiliary set temperatures were found in a systematic search. By employing all of these techniques, the relative expanded uncertainty (with a coverage factor of 2) in λ measurements at 200–700 °C was assessed to be 4.6%–6.8%. The present work provided a complete procedure from the measurement of λ and its uncertainty assessment for low-λ material at high temperature, where the precision measurement and uncertainty assessment of λ have been considered problematic.

Development and Performance Evaluation of Locally Fabricated Thermal Conductivity Apparatus

This paper presents the design and construction of a Guarded Hot Plate (GHP) apparatus for the accurate assessment of thermal conductivities of some Nigerian local building materials. The GHP apparatus is a steady-state measurement device. This apparatus is designed to measure the thermal conductivities of masonry building materials of different compositions. The design features included hot and cold plates fabricated with aluminum plates of 6 mm thickness and varying dimensions; the guard plates also made of aluminum, but of 6.35 mm thickness, forms a rigid enclosure for the specimen all encased in a mild steel housing. The operating measuring temperature range is from -20 for varying specimen thickness up to 60mm. Results are presented for concrete, laterite, and a mixture of cement with laterite, clay, and sand respectively, and it covers a range of thermal conductivities of 0.77W/mK to 1.80 W/mK. Moisture effect on concrete was recorded for the lightweight concrete as the thermal conductivity value reduced from 1.80W/m.K to 1.32W/m.K for the oven-dried concrete sample over a 1.5% (by weight) reduction in water content. The performance evaluation of the locally fabricated GHP apparatus showed a 3.03% percentage difference over ASHRAE’s published data on oven-baked concrete thermal conductivities

Uncertainty of Thermal Conductivity Measurement at High Temperatures Using Guarded Hot Plate Apparatus

Uncertainty of Thermal Conductivity Measurement at High Temperatures Using Guarded Hot Plate Apparatus

Verification and validation of an advanced guardedhot plate for determination of thermal conductivity

The guarded hot plate (GHP) method is a widely used technique to measure thermal conductivity of thermal insulation specimens in steady-state conditions. In this paper, an advance of GHP has been developed in the Laboratory for Thermal Technique and Fire Protection in Institute IMS. The innovative GHP has been applied for measuring thermal conductivity using additional heat flux meters. The design of this GHP is similar to the design of the plate for GHP apparatus, however, it has different design: smaller width of thermal barrier, which is filled with insulation glue. Heaters inside hot and guard plates are built from wire for thermocouples, which is a unique type of heater. Geometry of heater has been optimized inside plates to achieve uniform temperature distribution along the specimen surface. Temperature uniformity of GHP and energy balance were experimentally determined. The verification and validation results of improved GHP have been shown. The test method was validated comparing test results of thermal conductivity with results of the round-robin test. Four national companies participated in the round-robin comparison on thermal conductivity measurement by GHP method. The measurement was performed on the same specimen of thermal insulation material (expanded polystyrene) according to SRPS EN 12667 at temperatures ranging between 10-40?C. The measured thermal conductivity of all participants in the round-robin test was input data for statistical processing according to SRPS ISO 5725-2 and ISO 13528. To evaluate the performance of the participants, the ?z? score has been used. Measurements were conducted successively for all participants. Since 2020, the Accreditation Body of Serbia also approved this test method.

Development of thermal insulation sandwich panels containing end-of-life vehicle (ELV) headlamp and seat waste

Recycling automotive waste has increasingly become an alternative solution towards producing sustainable materials given the rising issue of raw material shortages and waste management challenges at global level. The improper end-of-life vehicle (ELV) waste management poses detrimental impacts on the environment. This paper proposes a novel method to develop thermal insulation sandwich panels using ELV waste, motivated by the critical needs of creating high-performance thermal insulation for buildings. Six sandwich panels (P1-P6) of different weight and ratio of shredded ELV particles were manufactured. The sandwich panels structure was made of three layers: a core, and a glass face sheet bonded to each side. The core structure composed of Polycarbonate (PC) from headlamp lenses and polyurethane (PU) from seat, bonded using resin casting approach. Thermal conductivity of the samples was measured using guarded hot-plate apparatus. Results corroborated that thermal conductivity of ELV-based sandwich panels reduced remarkably compared to panel without ELVs, recorded at 15.51% reduction. Composition gives the best thermal performance was made of mixed ELV core materials of ratio 50%PC:50%PU, it has a thermal conductivity value of 0.1776 W/mK. The transparency data were obtained using Haze-gard plus haze meter. The best luminous transmittance value was exhibited by P2 (100% PC), 67.47%. The best clarity value and haze value were shown by P6 (25% PC: 75% PU), 55.13% and 52.6% respectively. ELV waste can be recycled to develop useful sustainable thermal insulation to improve thermal and optical transparency performance of buildings as a substitute for conventional materials which have a relevance for future façade concepts.

Thermal Resistance of Air-Filled Mattresses: Measurement Repeatability and the Effect of Selected Test Parameters

Abstract There is no standardized test method specifically for determining the thermal resistance (R-value) of air-filled mattresses. Unacceptable inter- and intra-laboratory variations in round-robin testing have been attributed to differences in the test apparatus and test parameters used. To identify relevant sources of variation, the repeatability of the guarded hotplate apparatus (in a double plate configuration) was first characterized, and then the effect of modifying selected test parameters on mattress thickness and thermal resistance was investigated. Two mattress types, in two different sizes, were examined: one contained air only while the other contained air plus a nonwoven polyester fill. It was found that repeatable outcomes could be attained when using the guarded hotplate apparatus (95 % repeatability limit of less than 0.08 m2K/W for all mattresses tested). The modification of test parameters had significant effects on mattress thickness or R-value, or both. External pressure, the temperature difference across the specimen, supplementary insulation, mattress size, and environmental conditions affected both the thickness and R-value of the test mattresses. Inflation pressure, over the range tested, did not have a significant effect on the R-value but did influence mattress thickness. This work highlights the need for the standardization of the test apparatus and test parameters and will aid in the development of a standardized test method.

A Review on the Utilization of Guarded Hot Plate Apparatus for Obtaining Thermal Conductivity

The current paper addresses a brief overview of various works carried out to obtain the thermal conductivity of engineering materials by using a guarded hot plate apparatus. There are various types of operators for measurement of thermal conductivities and are available in different designs and varied ranges of thermal conductivities and temperatures. Guarded hot plate apparatus is one of the apparatus which is successfully employed for measurement of thermal conductivity in which there is a heating plate sandwich in the middle of the material that is heating plate will remain in the middle of a material having same directions and the material is kept on its top and bottom side. The underlying principle of this apparatus is Fourier’s Law of heat conduction. Overall it was observed and depicted that various researches have used this apparatus as it is capable of measuring the thermal conductivity of a wide range of materials like insulators having very low thermal conductivity and good conductors having very high thermal conductivity values. How to cite this article: Singh S, Singh N, Saini A. A Review on the Utilization of Guarded Hot Plate Apparatus for Obtaining Thermal Conductivity. J Adv Res Mech Engi Tech 2020; 7(1&2): 26-29. DOI: https://doi.org/10.24321/2454.8650.202002

Influence of Thermal Contact Resistance on Thermal Conductivity Measurement with a High-Temperature Guarded Hot Plate Apparatus

A high-temperature guarded hot plate (GHP) apparatus was developed by the Shandong Nonmetallic Materials Institute for the thermal conductivity of insulations. To investigate the influence of the thermal contact resistance of this apparatus under high-temperature test condition on the measurement results, the mullite specimen was measured under different pressures and temperatures before and after the surface treatment. The result indicated that the influence of thermal contact resistance on measurement results was remarkable only under the low-pressure, low-temperature condition with the surface untreated, and could be ignored under routine testing condition. To further confirm this conclusion, the specimen was ground to different thicknesses and then measured with a pressure 2.0 kPa at different temperatures. The measurement results showed that the thermal contact resistance of this high-temperature GHP apparatus was assumed to be sufficiently small at this pressure, especially at higher temperature.

Rice husk incorporated foam concrete wall panels as a thermal insulating material in buildings

The major segment for energy consumption is found in industry, transport, agricultural, residential and commercial sector. The main part of the energy consumption in residential and commercial buildings is due to the use of mechanical devices to maintain a comfortable indoor environment. Thermal conductivity of building materials is one of the factors which influence the heat transfer in buildings. Thermal conductivity can be reduced by the use of materials with low density. The present paper reports the development of a sustainable thermal insulating external wall panel and its mechanical, thermal and durability properties. The wall panel was prepared using foam concrete and rice husk and replacing the cement by fly ash. Strength of panel was tested by conducting in plane bending test and compressive strength test. Thermal conductivity was tested using guarded hot plate apparatus. Durability properties were tested by conducting water absorption test, drying shrinkage and acid resistance test. The test results showed that the rice husk and fly ash content had a major influence on the thermal conductivity and durability properties of the developed wall panels.

Construction and preliminary testing of a guarded hot plate apparatus for thermal conductivity measurements at high temperatures

We constructed a guarded hot plate (GHP) apparatus that can be used for thermal conductivity measurements from 100 °C to 1000 °C. The apparatus measures the effective thermal conductivity of square-shaped thermal insulation materials of 300 mm per side in a controlled gas environment. As a preliminary test for the high temperature GHP apparatus, we first measured the amount of electrical power required for heaters at various locations to maintain the temperature at up to 900 °C. After this, two specimens of thermal insulation material whose thermal conductivities are ≈0.044 W·m–1 K–1 and ≈0.025 W m–1 K–1 at room temperature were tested at a thermally steady state with unilateral heat flow at temperatures between 100 °C and 800 °C. We applied an offset to the guard plate to actively compensate for the lateral heat flow across the air gap. The measurements showed that the linearity between the temperature difference on the two sides of the specimen and the power dissipated across the specimen was extremely good (with a standard deviation of 0.1%). After some modifications suggested from the preliminary test, we expect that the high temperature GHP will work within the technical specification CEN/TS 15548-1:2014 in the range up to 800 °C, but rigorous uncertainty assessment is yet to be performed after such modifications.

Calibration Method and Uncertainty Assessment of a High-Temperature GHP Apparatus

In this research, a calibration method of a high-temperature guarded hot plate (GHP) apparatus was proposed in order to improve the measurement accuracy of thermal conductivity. The measurement uncertainties of this GHP apparatus were assessed to validate the reliability of this calibration method. The temperature difference across the guarded gap was set as the bias value to eliminate the heat exchange over the guarded gap. The effects of the thermal expansion and pressure of the apparatus on thickness were investigated to revise the measurement results of in-situ thickness and meter area, respectively. The assessed uncertainty indicated that the related expanded uncertainty approximately increased with the increase in testing temperature and the calibration method should be valid in the temperature range. The contribution of each factor on the combined uncertainty showed that the temperature distribution in plane direction was the main factor in influencing the measurement of thermal conductivity.

Experimental measurements and evaluation of the expanded water repellent perlite used for the cargo containment system of LNG carrier

To minimize the water absorption and to improve the thermal insulated properties of the insulation materials used for the cargo containment systems (CCSs) of LNG carrier, a kind of expanded water-repellent perlite has been developed by coating hydrophobic membrane onto the outer surface of the expanded perlite to change its physical and chemical characteristics. Considering the CCSs operated in a wide temperature range from environmental temperature to cryogenic temperature, the thermal analysis has been conducted to quantitatively determine the thermal insulted properties of the insulation materials. Furthermore, a double-sided guarded hot plate apparatus (GHP) is specifically designed and fabricated for the measurement of the thermal conductivities of the insulation specimens operated down to liquid nitrogen temperature. The breakage ratio associated with the water absorption and the thermal conductivity of the expanded water-repellent perlite is firstly proposed, and then a series of experiments are carried out to determine the thermal conductivity of the expanded water-repellent perlite ranging from room temperature to cryogenic temperature based on the different breakage ratios.

Development of guarded hot plate apparatus utilizing Peltier module for precise thermal conductivity measurement of insulation materials

In this paper, a guarded hot plate (GHP) apparatus utilizing a Peltier module is proposed and developed to precisely measure the thermal conductivity of insulation material. The Peltier module is used to detect a temperature difference with high sensitivity and to precisely measure heat flux. To develop the GHP apparatus, a two-dimensional axisymmetric heat conduction analysis and calibration experiments of thermistors and Peltier module were conducted. In addition, to assess the reliability of the developed apparatus, thermal conductivity measurements for a high-density glass wool and vacuum insulation panel (VIP) were conducted. Based on the results, the expanded uncertainties of the measurements were estimated. Therefore, the apparatus was found to be reliable for conducting precise thermal conductivity measurements not only for conventional insulation materials but also for a VIP.

Experimental investigations into thermal transport phenomena in vacuum insulation panels (VIPs) using fumed silica cores

This paper reports the experimental and theoretical evaluation of various heat exchange phenomena that occur in a vacuum insulation panel (VIP). Fumed silica and a range of IR-opacifiers were mixed in different proportions to identify the best composition that yields minimum thermal conductivity value at ambient and evacuated conditions. Three variants of carbon black (CB) and one each of silicon carbide (SiC) and titania (TiO2) were employed as opacifiers. Of all tested, CB was found to be the best opacifier based on the detailed experimental FTIR investigations performed whereby specific extinction was measured for each composition. To demonstrate the performance of the optimised samples of core materials developed four VIPs were manufactured which achieved a significantly low overall VIP thermal conductivity of <4mWm−1K−1 (R-value>36.03ft2̊Fh/BTUin.) measured using guarded hot plate apparatus. With these thermal conductivity values the samples perform much better than most state of the art commercially offered VIPs.

Insulating Materials for Energy Saving in Buildings

Insulation is considered one of the effective solutions to achieve energy savings in buidings. Better insulation having low thermal conductivity contributes significantly to new construction and retrofitting existing buildings. The Energy Conservation Building Code and National Building Code of India define the prescriptive and mandatory requirements for the U-factor and R-values for different climates but the way to achieve these values is left to the designers. As none of the walling and roofing assemblies in buildings fulfill the criteria for overall thermal transmittance, the study deals with determining the thermal conductivity of sustainable walling materials and prefab roofing technologies as well as insulating materials using Guarded Hot-Plate Apparatus. The MATLAB program is developed for computing the U-values and for predicting the desired retrofit insulation thicknesses to make different materials and roofing assembly combinations comply the Code requirements in different climatic regions of India. The results of the study are used for computing the performance with and without insulation using DesgnBuilder software for improving energy efficinecy of the buildings in composite climate in India.

Thermal conductivity and contact resistance of mesoporous silica gel adsorbents bound with polyvinylpyrrolidone in contact with a metallic substrate for adsorption cooling system applications

Silica gel bound with polyvinylpyrrolidone (PVP) is a new composite adsorbent with promising uptake rate designed for adsorption cooling systems. In this study, the thermal conductivity of silica gel-PVP and its thermal contact resistance (TCR) with a metallic substrate are measured using the guarded-hot plate apparatus under vacuum pressure. This study sheds light on the importance of TCR at the interface between the adsorbent and substrate, which has been overlooked in most studies in the literature. The measurements show that the thermal conductivity of silica gel-PVP adsorbent is 0.26 W/m/K which is 78.6% higher than that of dry silica gel packed bed. Also, the analysis indicates that the TCR between the adsorbent and metallic substrate is between 1.29–3.80 K/W which is equivalent to 0.20–0.69 mm of adsorbent thickness. Finally, the results indicate that the ratio of total TCR between the adsorbent and metallic substrate is up to 26% of the adsorbent-metallic substrate bulk resistance.

Development of the random simulation model for estimating the effective thermal conductivity of insulation materials

This paper developed a new random model to simulate the microstructures and the effective thermal conductivities (ke) of the insulation materials based on the assumption of either two phases or multiphase. To support the validity of the proposed approach, comparisons with experiments were made. These experiments can be divided into two kinds: the first one is the foamed concretes (FC) with a range of bulk densities from 354 kg/m3 to 1341 kg/m3, which are manufactured by the pre-foaming type; and the second one is the lightweight concretes (LWC) with densities ranging from 526 kg/m3 to 1895 kg/m3, which are made up of Portland cement (PC) and expanded perlite (EP). For the comparison with the simulation results, the ke was measured by a guarded hot plate apparatus (GHP). The results indicated that the simulation results of ke by the present model are in good agreement with the experiment values. For each sample, ke increases with the increase of the bulk density of the sample. Moreover, the degree of ke decrease becomes small in the lower bulk densities. In addition, the present model gives a detailed description of the heat transfer behavior in the insulation material.

Experimental evaluation of insulation materials for walls and roofs and their impact on indoor thermal comfort under composite climate

Better insulation having low thermal conductivity is a significant contributor for new construction and retrofitting existing buildings, when the emphasis is on energy efficiency. The objective of the study is to determine the impact of the thermal insulation materials in buildings enabling effective energy savings with minimal occupation of space. Although, the Energy Conservation Building Code (ECBC), India defines the prescriptive and mandatory requirements for the U-factor and R-value but the way to achieve these values is left to the designer and there is no published data on these values. To accomplish these objectives, the experiments for computation of thermal resistance and over all heat transfer coefficients have been carried out by measuring the thermal conductivity of the various types of materials available in the Indian market having different thicknesses by Automatic Guarded Hot Plate Apparatus. One hundred and twelve combinations of wall and roof sections have been computed and compared with different thicknesses of insulating materials for determining U-factor and R-value to satisfy ECBC requirements. The results of the study show that 50 mm thick Elastospray with conventional roof and wall satisfy the ECBC requirements whereas, other insulation materials require higher thickness to fulfill the recommended values. To validate the results, two prototype buildings are constructed at CSIR–CBRI campus; one with conventional burnt clay brick wall, reinforced cement concrete roof and 50 mm thick outside thermal insulation and the other without insulation. The results of the winter and summer season for six months are presented.