Cooling Performance Improvement of the Heat Driven Type Metal Hydride Refrigerator-Heat Transfer Enhancement Influence of Metal Hydride Sheet Loading Into a Metal Hydride Particle Bed

In the refrigeration and air conditioning fields, the demands of energy conservation and renewable energy have been increased recently. In this study, we aim at the development of the heat driven type metal hydride (abbr., MH) that can be driven by the low temperature exhaust or solar heat under 100ᵒC. In order to use this system commercially, heat transfer enhancement of MH particle bed, activation characteric improvement and production cost reduction of MH must be achieved. In this study, we use the two heat transfer enhancement methods for improving the low effective thermal conductivity of MH particle bed. One is the MH sheet and another is the brush type carbon fiber. MH sheet is inserted into MH layer. And, by this method, we aim not only to enhance the heat transfer of MH particle bed but also to achieve the temperature uniformity of MH particle one. The cooling performance of our MH refrigeration system is estimated by measurement and calculation

Study On Energy Conservation And Carbon Dioxide Emission Reduction Of Commercial Display Refrigerator Of Supermarket Utilizing The Exhaust Heat From The Novel Environment-Friendly Dispersed Power

Since the nuclear disaster was caused by the Great East Japan Earthquake in 2011, Japanese energy generation system has been expected to prioritize safety and trustworthiness. To meet this requirement, distributed power supply systems, such as gas engine, fuel cell, photovoltaic system, and solar heat, are considered to be one of solutions. By producing electricity, these systems generate thermal energy as a byproduct, and by using exhaust heat as thermal energy, we can help to minimize the CO2 emissions. In this study, we aimed energy-conservation and carbon dioxide emission reduction of supermarket which introduced a novel environment-friendly dispersed power. At first, we divided the energy consumption devices of the supermarket into the groups of illumination, air conditioning, refrigeration, hot water supply by using purpose and measured the time changes of its energy consumption in each seasons. And we verified the outside and the indoor air conditions, and the operation characteristics of individual energy consumption devices. The supermarket we measured is located in Isesaki-city, the northern Kanto region in Japan. From this measurement, we understood that the annual energy consumption of the refrigeration section was about 60-70% of the whole one of supermarket. It means that the energy reduction of the refrigeration section greatly contributes to energy conservation of supermarket. Most of the energy consumption apparatus of the refrigeration section of the supermarket are refrigerated cabinets and its power consumption highly depended on the indoor air enthalpy and the outside air temperature. When we are going to introduce dispersed power into a certain facility, the biggest problem that should be solved is annual utilization rate increase in exhaust heat. Because the annual utilization rate increment of the exhaust heat was not guaranteed by using only to heating, we built the demonstration supermarket which equipped environmental friendly dispersed power (gas engine, solar cell, solar heat), and utilized this supermarket for waste heat helpful use. In this study, we tried to increment the condenser exit supercooling of the refrigerated cabinet which had had the biggest energy consumption in a supermarket and, validated its energy conservation effect and carbon dioxide emission reduction one. The cold temperature that used for supercooling was manufactured by adsorption type refrigerator. The energy conservation effect of supercooling is about from 10 to 25% during the summertime and intermediate time. However there is no effect of supercooling in the winter because the outside temperature is low. At last we found that when the outside temperature is about 15? or more, supercooling effect appears. In addition, since energy consumption of the refrigerated cabinet is influenced by the indoor enthalpy, we adjusted the indoor air temperature and humidity by introducing the desiccant system and validated its effect

Heat Transfer Enhancement by Using Fin for MH Hydrogen Storage Tank - Discuss on the Geometrical Optimization of Fin -

The expectation for renewable energy is rising from the viewpoints of recent environmental problems and energy problems. The reason why renewable energy is not widespread is that there are temporal and spatial restrictions on real application. There is an increasing interest in hydrogen energy as energy that compensates for such weaknesses of renewable energy.　Hydrogen can easily converted to be thermal energy, mechanical energy, electric energy and used. It is important to establish effective saving techniques for effective development of hydrogen energy systems. Three methods of liquification, pressurization and metal hydride (on briefly, referred to as MH) are the major hydrogen energy storage methods. In this study, we focus on the hydrogen storage by using the metal hydride. MH can storage hydrogen with high density, and it can be used at low temperature and low pressure, but has the disadvantage that the release rate of hydrogen due to the low effective thermal conductivity of the MH alloy layer. In this study, the heat transfer enhancement effects of several fins on metal hydride particle layer are estimated by experiment and simulation. The unsteady state heat conduction calculation of MH alloy layer with and without fins was conducted with the Solidworks simulation soft and, the experimental and the calculation parameters are charging volume ratio of fins, and the shapes of fin like as cross fin and circular cross fin. Another estimation parameter is the diameter of storage tank. One storage tankhas an outer diameter of 80 mm, an inner diameter of 78 mm, the other has an outer diameter of 25 mm and an inner diameter of 23.5 mm. The number of fins was increased until the charging volume ratio of the fin, 25 volume %, we estimated the heat transfer enhancement influence of the fins on the MH ally layer. According to our calculation results, the effective thermal conductivity is increased with increasing of charging volume ratio of fin, but this heat transfer enhancing effect is saturated at over 10 volume % of it. In oursimulation model of a circle cross fin, the tank which have an outer diameter of 52 mm and an inner diameter of 50 mmwas used. In the simulation results of using circle cross fins cases, the highest heat transfer enhancement effect was obtained when circular diameter of circular cross fin was 24 mm. Compared with cross fins (which has a heat transfer enhancing effect of 4.68 times compared with without fins), the volume content of circular cross fin was 1.4% higher than that of cross fin. However, the heat transfer enhancement effect of circular cross fin was 2.46 times higher than that of cross fin. And, it is confirmed that circle cross fin which have charging volume ratio, under 10% can achieve a high heat transfer enhancing effect and is suitable to heat transfer enhancing of MH particle layer

The Optimization Model of Effective Thermal Conductivity for Metal Hydride Heat Pump of Refrigeration Cycle

Answering the call for the eco-friendly energy development, the thermally driven metal hydride heat pump (MHHP) is one of the feasible approaches for its great potential in the recovery of low-grade heat without greenhouse-gas emissions, making it a leading contender among different alternate fuels. The main challenge for the practical application of MHHP is the relatively poor system performance, which is mainly considered due to the low effective thermal conductivity (ETC) of metal hydride reaction bed. Therefore, aiming for improving heat transfer performance, previous researches have proved that inserting high-conductivity sheet such as Metal Hydride (MH) sheet and Aluminum Foam (AF) sheet into the reactor is one of the most practical methods. However,there is no significant improvement of system performance when enhancing the effective thermal conductivity (E.T.C) of reaction bed. Thus for the purpose of improving the system performance of MHHP, this paper first identifies the relationship between the ETC of metal hydride reaction bed and the system in terms of two performance indicators: COP and cooling power (kW/kg) with a numerical model. By adjusting the cycle time, it is shown that when cycle time increasing, the available hydrogen capacity increases, and thus the heat output increases, resulting in a better coefficient of performance. However, once a certain cycle time has been reached it has less effect on the hydrogen capacity. In addition, the heat loss caused by the system’s heat capacity is proportional to cycle time, and the average flow rate of hydrogen would be decreased when cycle time increasing, allowing COP to reduce. Therefore, there existed an optimal cycle time. As an important factor affecting cycle time, the ETC is related mathematically to find out the optimal value for a better performance of MHHP. The experimental confirmation is conducted eventually, and the comparison of results shows a reasonable agreement with an acceptable error range. To sum up, the optimization of the ETC based on the relationship with the system performance is proposed in this paper, which can help to find the optimal value overall situation toward to a more efficiency system of MHHP

IHTC14-22317 THE DEVELOPMENT OF PEFORMANCE PREDICTION METHODS FOR AN AUTOMOTIVE CO 2 AIR CONDITIONING CYCLE

ABSTRACT In previous researches, we have been focusing on the performance of the each element heat transfer and hydraulic performance of refrigeration cycle. Experimental investigations have been repeated several times and, finally, we have substantial data base including the effect of lubricant oil. Moreover, the mal-distribution of two-phase in an evaporator can be also predicted from the experimental data base. Under these circumstances, this study is intended to effectively put the construction of an automotive CO 2 air conditioning system into practical design use through the simulation using the abovementioned data base. This paper describes the refrigeration cycle performance prediction of each element (e.g. an evaporator, a gas-cooler, and so on) by a simulation using substantial data base and various available correlations proposed by us and several other researchers. In the performance prediction model of heat exchangers, local heat transfer and flow characteristics are considered and in addition, the effects of lubricant oil on heat transfer and pressure drop are duly considered. The comparison is also made between simulation results and bench test results using a real automotive air conditioning system. Finally, the developed simulation method can predict the cooling ability successfully within ±5%. By incorporating the lubricant oil effect, the simulation results are improved to ±5% and ±15% for the cooling ability and pressure drop respectively. INTRODUCION Due to the increasing environmental concern, the reduction of greenhouse effect gas, particularly, CO 2 emission and the direct leak of HCFC and HFC's have been considered to be among most important subjects in the field of refrigeration and airconditioning system. At present, the demand for the higher efficiency of a refrigeration system (COP) increases. More recently, the possibility of global warming potential (GWP) is extremely large, and the conventional refrigerant can go ahead through the policy that does not recognize a chlorofluorocarbon alternative to the refrigerant for car air-conditioners positively in EU particular, and the interest for natural refrigerant increases. Among various candidates of natural refrigerants, CO 2 is environmentally safe, being not toxic and non-flammable, so CO 2 has advantages for practical reasons. Moreover, CO 2 possesses a low viscosity, high specific heat, and high thermal conductivity. In general, it has excellent thermodynamic and transport properties as a refrigerant. On the other hand, however, since CO 2 has high critical pressure and its critical temperature is low, it becomes a transcritical cycle and the COP becomes low when compared with conventional refrigerants. Therefore, the high efficiency of heat exchangers is inevitable and it is necessary to grasp the plenary heat transfer coefficients and the basic characteristics of pressure drop in an evaporator and in a gas cooler. Moreover, it presents other problems; for example, the performance deteriorates because the lubricant oil contaminates into the refrigerant in a real working system. So various efforts have been made to investigate these aspects. Although a lot of evaporation heat transfer data are available in literature (Koyama 2004 (1) , Yamada 2004 (2) , Katsuta 2006 (3) ) and it is recognized that the evaporation heat transfer is very sensitive for lubricant oil concentration rate (OCR), few investigations have addressed to the effect of OCR and its prediction. The objective of this research, therefore, is to investigate the effect of oil mixing rate on the thermal and hydraulic characteristics using CO 2 as working refrigerant. In previous researches, we have been focusing on the performance of the each element heat transfer and hydraulic performance. Experimental investigations have been repeated several times and, finally, we have substantial data bas

Decadal–centennial-scale solar-linked climate variations and millennial-scale internal oscillations during the Early Cretaceous

Understanding climate variability and stability under extremely warm ‘greenhouse’ conditions in the past is essential for future climate predictions. However, information on millennial-scale (and shorter) climate variability during such periods is scarce, owing to a lack of suitable high-resolution, deep-time archives. Here we present a continuous record of decadal- to orbital-scale continental climate variability from annually laminated lacustrine deposits formed during the late Early Cretaceous (123–120 Ma: late Barremian–early Aptian) in southeastern Mongolia. Inter-annual changes in lake algal productivity for a 1091-year interval reveal a pronounced solar influence on decadal- to centennial-scale climatic variations (including the ~ 11-year Schwabe cycle). Decadally-resolved Ca/Ti ratios (proxy for evaporation/precipitation changes) for a ~ 355-kyr long interval further indicate millennial-scale (~ 1000–2000-yr) extreme drought events in inner-continental areas of mid-latitude palaeo-Asia during the Cretaceous. Millennial-scale oscillations in Ca/Ti ratio show distinct amplitude modulation (AM) induced by the precession, obliquity and short eccentricity cycles. Similar millennial-scale AM by Milankovitch cycle band was also previously observed in the abrupt climatic oscillations (known as Dansgaard–Oeschger events) in the ‘intermediate glacial’ state of the late Pleistocene, and in their potential analogues in the Jurassic ‘greenhouse’. Our findings indicate that external solar activity forcing was effective on decadal–centennial timescales, whilst the millennial-scale variations were likely amplified by internal process such as changes in deep-water formation strength, even during the Cretaceous ‘greenhouse’ period

Massive higher spin fields in curved spacetime and necessity of non-minimal couplings

Free massive higher spin fields in weak background gravitational fields are discussed. Contrary to the spin one case, higher spin fields should have nontrivial non-minimal couplings to the curvature. A precise analysis is given for the spin 2 case, and it is shown that two conditions should be satisfied among five non-minimal coupling constants, which we derive both in the Hamiltonian and Lagrangian formalisms. It is checked that the linearized limit of the massive gravity theory indeed has the non-minimal couplings that satisfy the conditions. We also discuss the form of the non-minimal couplings for the spin 3 case.Comment: 19 pages; discussion on spin 3 added, references added (v2); footnote 9 corrected (v3

Experimental Study on Thermoacoustic Cooling System with Two Stacks in a Straight Resonator Tube

National audienceIt has been done an experimental study of the use of two stacks 1 and 2 in a straight resonance tube of a thermoacoustic cooling system. We used a half-wavelength straight resonance tube at which the one end is closed by rigid plug and the other end is closed by a plastic diaphragm which can vibrate axially due to sound wave produced by a loudspeaker facing to it. The tube is PVC pipe and filled by free air at atmospheric pressure and has 112 cm of length so it gives a calculated operating frequency around 152 Hz. The stacks are parallel plates type, which have plates thickness of 0.3 mm, and the plates spacing of 0.85 mm which is around four times of the thermal penetration depth. The diameter of stack is the same as the inner diameter of the tube, i.e. 46 mm, while the length of stack is 100 mm. We varied the sound frequency in the range of 130 - 160 Hz, the input electric power of loudspeaker from 40 W until 160 W, and stacks center position in the range of 8 - 25 cm measured from each end of the tube, to investigate the their influences to the temperature decrease which can be achieved. It is found that the temperature decreases of the two cooling points 1 and 2 reached maximum at sound frequency of 147 Hz and when the two stacks were placed near to the ends of the tube. It is also found that a higher electric power tends to produce a larger temperature decrease. At 90 W of the input electric power, the maximum temperature decrease around 9.8 ↓C was obtained at cooling point 1 when the center of the stack 1 was placed at 80 mm from the rigid closed end of the tube