The purpose of this study is developing a latent heat storage system that uses waste heat from factories in the temperature range 100–200ºC as a heat source. Mannitol and a mixture of mannitol and erythritol, which are sugar alcohols, were used as phase change materials (PCMs). We also studied a direct contact heat exchange method with lower thermal resistance.
The solidification behavior was examined in detail using a test section consisting of a Pyrex glass tube with one nozzle hole for injecting heat transfer oil. The tube had an inner diameter of 87 mm and height of 300 mm. There was a nozzle plate with one hole that had a diameter of 2 mm in the lower part of the test section, and heat was transferred to the PCM by injecting heat transfer oil from the hole.
The findings were the following. The heat transfer oil droplets from the hole start to solidify on the upper surface of the heat storage material. As time elapses, solidification starts near the nozzle plate. The oil droplet diameter increases with increasing flow rate. The diameter of the liquid column increases owing to solidification near the nozzle plate. The initial solidification shape of the mannitol–erythritol mixture (70% mannitol and 30% erythritol) is different from that of the mannitol. In addition, the observed solidification has a different shape depending on the flow rate.
Utilization of the solid phase transformation heat of the iron-based alloy as well as its sensible heat was proposed as a Heat Storage Materials, HSM, for the rapid carbonization and pulverization process of biomass. Aluminizing of the HSM is a promising way to improve focused to improve its high temperature oxidation resistance. In this study, behavior of solid phase transformation and high temperature oxidation behavior, and wear and impact resistances of the oxide layer are examined for Fe-Mn-C alloy as a candidate of HSM.
Latent heats and transformation temperatures were evaluated using a DSC. Mass change ratio of the samples were measured using a TG. Then, DSC measurements were carried out with the oxidized samples. Spherical segment samples were charged into lab-scale rotary kiln type furnace to evaluate wear and impact resistance of oxide layer formed during high temperature oxidation.
Endo- and exo-thermic heats of Fe-2%Mn-0.7%C showed similar with Fe-0.77%C alloy. Endo- and exo-thermic temperatures deceased with increase in Mn concentration. Fe-Mn-C alloy did not show sufficient oxidation resistance at high temperature, whereas the aluminized sample showed a superior oxidation resistance due to the formation of continuous Al2O3 layer. Thinner Al2O3 layer is formed on the alloy sample by the aluminizing with lower Al concentration and shorter time and its latent heat become larger. The Al2O3 layer of the aluminized and oxidized samples were not peeled and significant weight change did not also occur after the experiment using the rotary kiln type furnace.
Waste heat recovery is important in steel making industry. Intermittency of waste heat from batch processes is a barrier to applying heat recovery systems to steel plant. Latent heat storage using Phase Change Material (PCM) is attractive technique to solve this problem. Moreover, effective thermal energy recovery can be achieved by the combination of waste heat utilization and endothermic reaction. In this paper, Ni/Latent-heat-storage grain was fabricated and catalytic performance about ethanol steam reforming was analyzed. The fabricated grains exhibited latent heat of 69.9 kJ kg–1 and the latent heat of product didn’t change after catalytic performance test. In the performance test, all of the ethanol was cracked and the maximum concentration of H2 in outlet gas flow was 62%. The result of the catalytic test indicated side reaction occurred in the experiment. Heat supply from PCM mitigated temperature change and the mitigation helped to stop decreasing H2 yield in the catalytic reaction.
In hot strip rolling, the work roll (WR) shifting method is widely used to disperse thermal crown and work roll wear. The low WR surface temperature and “insensitivity” to temperature changes not only enable more precise control in the WR shifting method, but also contribute to resource and energy savings.
In this paper, we proposed a WR with temperature buffering function in which hollow roll is filled with phase change material (PCM), and verified its effect with a simple numerical model. In spite of the low volume fraction of 16%, the proposed roll obtained a decrease in roll surface temperature that greatly exceeded the temperature estimated from the amount of heat stored in PCM. This is because the decrease in surface temperature is due not only to the heat storage effect of PCM but also to the temperature leveling effect accompanying the increase in effective thermal conductivity of molten PCM. Therefore, it was suggested that the proposed roll contributes to the refinement of control by the WR shifting method and to resource saving and energy saving.
This research focuses on dehydration / hydration of magnesium hydroxide as a chemical heat storage material. Previous studies have reported that the use of additives in magnesium hydroxide improved the dehydration / hydration reactivity. However, additives used in previous studies have had problems in terms of environmental impact and cost. Therefore, the purpose of this study is to search for safe and inexpensive additives. We have selected citrate compounds as an inexpensive and safe additive. The effect of the additive was verified by measuring the dehydration / hydration reaction of magnesium hydroxide using a thermogravimetric instrument. Furthermore, XRD was used for sample characterization. As a result, the most improved reactivity was confirmed in the sample using sodium citrate as an additive. SC5 (molar ratio, magnesium hydroxide: sodium citrate dihydrate = 100: 5) decreased the dehydration peak temperature by about 31ºC compared to pure magnesium hydroxide. Sodium citrate dihydrate was found to undergo thermal degradation during sample heating. Then, when the repeated reaction test was implemented, the improvement of the dehydration rate after the 2nd time was confirmed. These results indicate that the product of thermal decomposition of sodium citrate dihydrate is effective as an additive.
Cold heat generation system using chemical reaction from unused thermal energy is investigated. In this study, water/urea system is particularly studied. While dissolution of urea in water is endothermic process, deposition of urea from water solution is exothermic process. Therefore, endothermic dissolution of urea in water is utilized for generation of cold heat. On the other hand, thermal energy can be released by the exothermic deposition of urea from water solution. This is the advantage of the system because total thermal energy required to evaporate the water can be reduced by the exothermic deposition of urea. The cyclic operation of dissolution and deposition of urea is experimentally studied. As a result, cold heat generated by the dissolution can be estimated from the energy balance and enthalpy of dissolution. Based on the experimental results, a numerical model to estimate temperature of water/urea solution and performance of the system is developed. From the numerical results, heat exchange rate of the deposition (concentration) process is essential especially for the improvement of the performance of the system.
In this experimental study, a prototype system for transporting heat rapidly from a heat source. The system was a device combined with phase change material (PCM) and heat pipes. The prototype system was originally developed for an abnormal heat generation incident such as thermal runaway, of lithium-ion battery (LiB) in electric vehicles when the battery temperature exceeds 80ºC. In the study, one cell or two cells of A4-sized LiB cells were actually short circuited in the prototype system, and the performance of the system was evaluated by measuring the cell temperature. Two kinds of PCM were tested in the experiments. The melting point of one of the PCMs was 50ºC, and that of another PCM was 35ºC. Moreover, to enhance heat transport inside the PCM itself, SiC powders were added to PCM to have larger thermal conductivities. From those experiments, it was understood that PCM played an important role for receiving rapid and large heat source in the initial period, and that heat pipes and heat sink devices became well activated after the initial period. The PCM with lower melting temperature was better in cooling the LiB cell. Moreover, the effect of increasing thermal conductivity of the PCM was remarkable after the LiB cell reached the maximum temperature. These fundamental results of the prototype system combined with PCM and heat pipes would be helpful when this idea is applied to other practical purposes.
Recently, many countries have become increasingly interested in unused but possibly useful energy resources. Among these unused resources, the thermal energy produced around us can be used as a potential energy source for heating, cooling and power generation. This thermal energy is relatively stable on the supply side as waste heat in the industrial field. Heat transport devices are one of the important technology for the effective use of unused heat energy. This paper conducts basic research on devices that effectively transport heat below 200ºC. A pulsating heat pipe (PHP) is an excellent heat transport device based on the phase change of a working fluid. Experiments are performed to investigate the thermal performance of a PHP using different working fluids. The PHP consists of 20 parallel channels made of a copper capillary tube with an internal diameter of 1.8 mm. The PHP is filled with deionized water and an aqueous solution of 1-butanol as working fluids, with different filling ratios (FRs) in the range 50-60 vol.%. The 1-butanol aqueous solution is known as a self-rewetting fluid. The experimental results indicate that, in the case of self-rewetting fluid, stable oscillating motion in the PHP arises at the heat load regime lower than that with water. In addition, the effective thermal conductivity of the PHP with the highest concentration of self-rewetting fluid is higher than that with other fluids in the high heat load regime.
For industrial effective use of low-density energy such as factory exhaust heat or solar heat utilization, development of large heat storage with fast heat exchange technology is required. Especially in cold regions such as in Hokkaido, the demand for heat in winter is large, and attempts to use large-scale, high-temperature unused waste heat from steel manufacturers and pulp factories to medium temperature zones such as hot water supply and air conditioning will become increasingly important in near future. Also, in automobiles and factories, the heat engine needs to be cooled during operation and must operate within a certain temperature range. However, if the heat engine is cooled down after it is stopped, it must be heated again as it restarts. Therefore the technology to suppress the temperature drop of the system by the application of heat storage and regeneration technology is expected. Previously, water or aqueous liquids were used for heat storage with heat exchange to suppress temperature drop of the system, however, only the sensible heat can be used for heat storage. For else, polymer phase change substances are used instead. However, high heat transfer characteristics could not be obtained as for their poor fluidity. This paper reports on the thermal properties of phase change emulsions as functional fluid that have both heat storage and fluidity for heat exchanging, moreover, basic characteristics of heat sinks modelled by metal powder additive manufacturing using a copper alloy with high thermal conductivity for the system application.