Phase Change Material Heat Research Articles

B132 熱輸送システムの熱回収性能に関する研究(分散エネルギーシステムにおける要素技術とその集積化3)

Effective utilization of waste heat from biomass power plants has become very important to reduce CO_2 emissions. However, it is difficult to use waste heat on site or very near by. This is so that there is too much waste heat to use as heating and cooling applications on the site. We need a method to transport waste heat to heating and cooling applications of other sites. Kobe Steel Ltd. and Kobelco Eco-Solutions Co., Ltd are developing latent thermal energy storage equipment for this transport system. The erythritol of phase change material (PCM) and direct contact heat transfer technology are being used for this equipment. Direct contact heat transfer technology is a thermal energy storage method of contacting heat medium to PCM directly. The advantages are high performances of heat input and heat output and light weight equipment without heat exchanger. Therefore, in this paper, we report on a study of a new model of thermal storage cassette, for the target performance of maintaining fixed heat output at a temperature of 90℃ for 8 hours, and performing 90% or more of heat recovery.

05/00819 The main constructional characteristics of contemporary urban residential buildings in Greece

Recently, multi-split air source heat pumps (ASHPs) have been used increasingly for space heating in cold winter. When it operates in frosting environment, periodic defrosting is necessary to maintain a high system performance. However, researches on its defrosting were few due to its high capital and complicated controls. To solve its fundamental problem of insufficient heat available during defrosting, a novel reverse-cycle defrosting (NRCD) method based on the phase change thermal storage has been developed. In this paper, comparative experiments using both standard reverse-cycle defrosting (SRCD) method and NRCD method were carried out on a multi-split ASHP unit with a phase change material heat exchanger (PCM-HE) acting as energy accumulator during heating operation and heat source during defrosting operation. Experimental results suggested that when using the NRCD method, the system performances, such as suction pressure and temperature, defrosting and heat-resumption durations, COP during defrosting operation can be effectively improved.

G152 熱輸送システムと吸収式冷温水機を用いた冷房システムの開発(一般セッション 熱機関・システムII)

Effective utilization of waste heat from municipal solid waste incineration plants and biomass power plants has become very important to reduce CO_2 emissions. But it is difficult to use waste heat on site or very near by. Because waste heat from municipal solid waste incineration plants is too many value to use for heating and cooling applications on site. We need the method to transport waste heat to heating and cooling applications of other site. Kobe Steel Ltd. is developing latent thermal energy storage equipment for this transport system. The erythritol of phase change material (PCM) and direct contact heat transfer technology are being used for this equipment. Direct contact heat transfer technology is thermal energy storage method of contacting heat medium to PCM directly. The advantages are high performances of heat input and heat output, light weight equipment by no heat exchanger. This time, in order to study the applicability as a heat source to the absorption refrigerator of this system, the experiment which used thermal energy storage cassette and absorption refrigerator was carried out. As a result, stable operation of this system and the effect of fuel consumption reduction were obtained.

Performance of a natural circulation solar air heating system with phase change material energy storage

The design, construction and performance evaluation of a passive solar powered air heating system is presented. The system, which has potential applications in crop drying and poultry egg incubation, consists of a single-glazed flat plate solar collector integrated with a phase change material (PCM) heat storage system. The PCM is prepared in modules, with the modules equispaced across the absorber plate. The spaces between the module pairs serve as the air heating channels, the channels being connected to common air inlet and discharge headers. The system was tested experimentally under daytime no-load conditions at Nsukka, Nigeria, over the ambient temperature range of 19–41 °C, and a daily global irradiation range of 4.9–19.9 MJ m −2. Peak temperature rise of the heated air was about 15 K, while the maximum airflow rate and peak cumulative useful efficiency were about 0.058 kg s −1 and 22%, respectively. These results show that the system can be operated successfully for crop drying applications. With suitable valves to control the working chamber temperature, it can also operate as a poultry egg incubator.

Experiments on Contact Melting Under Vibration Within Rectangular Enclosures

Nomenclature A = amplitude of vibration AR = aspect ratio, H/W a = maximum acceleration of vibration, (27r/)A Cp = specific heat Fo = Fourier number, at/HW Fr = Froude number, alg f = frequency of vibration Gr = Grashof number, gfi(Tw Tf)H/v g = gravitational acceleration H = height of test cell k = thermal conductivity Ste = Stefan number, CP(TV Tf)/&hf T = temperature t = time W = width of test cell a = thermal diffusivity j8 = thermal expansion coefficient A/I/ = latent heat of phase change material

A simple method, the -history method, of determining the heat of fusion, specific heat and thermal conductivity of phase-change materials

A simple method of determining the melting point, heat of fusion, specific heat and thermal conductivity of phase-change materials (PCMs) is presented. Compared with other methods, such as conventional calorimetric methods, differential thermal analysis and differential scanning calorimetry methods, it has the following salient features: the experimental unit is simple, able to measure the heat of fusion, specific heat and thermal conductivity of several samples of PCMs simultaneously and allows one to observe the phase-change process of each PCM sample. Using the method, the thermophysical properties of various salt hydrates, paraffin and some PCMs developed by us were measured. For the PCMs whose thermophysical properties are available in the literature, our results gave fairly good agreement. The method is especially useful for the selection of lots of candidate PCMs used for the purpose of engineering and for preparing new PCMs.

Performance of a greenhouse heating system with a phase change material

A greenhouse with a phase change material (PCM) heat storage system containing a quasi-eutectic mixture was tested with a classical lettuce-tomato rotation. Measurements on the greenhouse microclimate and assessment of the thermal storage performances were carried out during two heating seasons, with special attention paid to evapo-condensatioe processes. It is concluded that such a heat storage system, when used in the South of France, can keep a greenhouse roughly 10°C higher than outside during typical nights of March or April. It appears however that the present phase change storage medium, with a transition point as high as 22°C, is not adequate for periods with low solar gains (January or February). On the other hand, when the greenhouse temperature exceeds the melting point of the PCM (in late winter), the present (1.6 MJ m −2) storage capacity was found to be too low to cope with actual solar gains. Humidity measurements showed the positive effect of condensation on the storage. At night, as most of the condensates are drained away, the purely convective and weaker heat transfers from the storage contribute to keep the greenhouse humidity below saturation and preserve the crops from fungal diseases.

Modeling of Arbitrary-Shaped Specific and Latent Heat Curves in Phase-Change Storage Simulation Routines

In solar heat storage, use is often made of the latent heat of phase-change materials (PCM) with a wide temperature transition range. In this paper the heat withdrawal of a slab of such a phase-change material after a step-wise change in wall temperature, and as a function of the shape of the specific and latent heat curve, has been studied with a computer simulation. It will be outlined that various shaped curves show the same heat withdrawal character as an equivalent rectangular-shaped specific heat curve. A procedure to obtain this equivalent curve will be given.

Fluoride Salts as Phase Change Materials for Thermal Energy Storage in the Temperature Range 1000–1400 K: Thermal Analysis and Heat of Fusion Measurements

Eutectic compositions and congruently melting intermediate compounds in binary and ternary fluoride salt systems were characterized for potential use as latent heat of fusion phase change materials to store thermal energy in the temperature range 1000–1400 K. The melting points and eutectic compositions for many systems with published phase diagrams were experimentally verified and new eutectic compositions having melting points between 1000 and 1400 K were identified. Heats of fusion of several binary and ternary eutectics and congruently melting compounds were experimentally measured by differential scanning calorimetry. For a few systems in which heats of mixing in the melts have been measured, heats of fusion of the eutectics were calculated from thermodynamic considerations and good agreement was obtained between the measured and calculated values. Several combinations of salts with high heats of fusion per unit mass (>0.7 kJ/g) have been identified for possible use as phase change materials in advanced solar dynamic space power applications.

Thermal energy store for a heat-pumped, domestic, central-heating system

A computer model describing the effect of the presence of thermal energy storage upon the performance of a conventional heat-pumped domestic central-heating system was developed. To validate this model and to discover what problems would exist in a real system, an experimental test rig was built: it incorporated a phase-change material heat store in the heat-load circuit of a heat-pumped heating system. The performance of each component of the system was determined, and the overall performance of the system compared with that predicted by the computer model. The improvements in the performance of the heating system as a result of this investigation included: higher heat output potential; less frequent on/off cycling; and reduced running costs.

New low-cost storage in air conditioning

SYNOPSIS This paper describes the development of a new low-cost phase-change material packaging concept for air conditioning systems. The realization of the promise of storage assisted air conditioning for saving oil and money is dependent upon the successful development of a low-cost storage subsystem and the adoption of time-of-day electricity rates. Time-of-day rates are currently under consideration or have been adopted in 27 different states and consideration of these rates has been required by federal legislation. The adoption of this low-cost thermal energy storage technology for storage assisted air conditioning and other storage assisted heat pump applications has the potential of saving 100 million barrels of oil over the next ten years and 12 million barrels of oil per year by 1985. These savings would accrue from a change in the summer air conditioning peak electricity load from oil and gas-fired peak electrical generators to the base load electrical generators fired by coal, nuclear and hydroelectric. This low-cost air conditioning storage concept is based on hydrated salt phase change material, specifically a mixture based on sodium sulphate decahydrate and a new low-cost packaging technology which uses a film laminate as the phase change material mixture's package and heat exchanger. In this paper. the relative economics of various technological options for air conditioning storage are compared. It is demonstrated that this economic analysis leads to the necessity to develop a low-cost film package and heat exchanger. An analysis of savings to homeowners based on current and planned off-peak rates is included. Since this is the first product developed utilizing this new low-cost material as a packaging film, it is anticipated that major improvements in both cost and performance specifically related to individual systems will be developed and implemented over the next ten years, with significant improvements coming in the next several years.