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Volume 18 (2001)
- Issue 4 Pages 365-
- Issue 3 Pages 203-
- Issue 2 Pages 105-
- Issue 1 Pages 1-
Volume 18, Issue 2
Displaying 1-10 of 10 articles from this issue
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Papers
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Atsushi SOBUE, Koichi WATANABE2001 Volume 18 Issue 2 Pages 105-113
Published: 2001
Released on J-STAGE: October 11, 2011
JOURNAL FREE ACCESSIn the present study, we have quantitatively evaluated the global warming impact by household refrigerator and air-conditioning systems on the basis of reliable TEWI information. In TEWI evaluation of household refrigerators, the percentage of the impact by refrigerant released to the atmosphere (direct effect) is less than 18.6% in TEWI. In case of room air-conditioners, however, the percentage of direct effect is less than 5.4% in TEWI. Therefore, it was confirmed that impact by CO2 released as a result of the energy consumed to drive the refrigeration or air-conditioning systems throughout their lifetime (indirect effect) is far larger than direct effect by the entire system. A reduction of indirect effect by energy saving is the most effective measure in reducing the global warming impact by refrigeration and air-conditioning systems, For a realization of the energy saving, not only the advanced improvement in energy efficiency by household appliance manufacturers but also the improvement of consumer's mind in selecting the systems and a way of using are concluded important.View full abstractDownload PDF (601K) -
Atsushi SOBUE, Koichi WATANABE2001 Volume 18 Issue 2 Pages 115-126
Published: 2001
Released on J-STAGE: October 11, 2011
JOURNAL FREE ACCESSIn the present study, we quantitatively evaluated the global warming impact by refrigeration and air-conditioning systems in office buildings on the basis of reliable TEWI information. This paper proposes an improved TEWI evaluation procedure by considering regional heat demands and part load of air-conditioning systems. In the TEWI evaluation of commercial chillers, a percentage of the impact by refrigerant released to the atmosphere (direct effect) is less than 19.9% in TEWI values. Therefore, a reduction of the impact by CO2 released as a result of the energy consumed to drive the refrigeration or air-conditioning systems through out their lifetime (indirect effect) is the most effective measure in reducing the global warming impact. On the other hand, we have also pointed out energy loss that might be generated by an excess investment to the equipment. We have also showed a usefulness in dividing the heating / cooling system into several small-capacity units so as to improve the energy utilization efficiency.View full abstractDownload PDF (811K) -
Yoshio UTAKA, Shixue WANG2001 Volume 18 Issue 2 Pages 127-134
Published: 2001
Released on J-STAGE: October 11, 2011
JOURNAL FREE ACCESSThe condensation heat transfer characteristic curves for binary mixture of water and ethanol vapors in the range of relatively small concentration of ethanol vapor, i.e., mass fraction of 0, 0.0002∼0.20, were measured by using the leak-tight experimental apparatus. The variations of the several characteristic points representing the characteristic curves were discussed. It was also shown that the excellent heat transfer characteristics were achieved in the low ethanol concentration because the surface subcooling region of the diffusion resistance is narrow and the variation of the surface tension is large in this domain. Especially the maximum heat flux was revealed at about the mass fraction of 0.06 and the maximum heat transfer coefficient appeared at about the mass fraction of 0.02 under very low concentration of non -condensable gas (about 10 ppm).View full abstractDownload PDF (528K) -
(Condensation and Absorption Experiment of CO2)Akira TAKIMOTO, Hirotsugu KOHIGASHI, Osamu MATSUDA2001 Volume 18 Issue 2 Pages 135-142
Published: 2001
Released on J-STAGE: October 11, 2011
JOURNAL FREE ACCESSHigh efficiency of gas absorption may be one of the important techniques for protection of global environment. A new concept of gas absorption by utilizing condensation process was proposed which is called "condensate film method", and its proof experiment was conducted with regard to the condensation heat transfer in vertical cooling tube. Theoretical analysis was performed on the critical condition of mist formation in the cooling tube flow and the falling liquid film under the same mass flow rate condition. Comparing between the both analytical results and experimental data, the concept proposed in this paper was identified and the mechanism of the gas absorption through the condensate and the mist droplets was clarified.View full abstractDownload PDF (534K) -
Chaobin DANG, Hirofumi DAIGUJI, Eiji HIHARA, Masahide TOKUNAGA2001 Volume 18 Issue 2 Pages 143-151
Published: 2001
Released on J-STAGE: October 11, 2011
JOURNAL FREE ACCESSThe performance of fined small tube heat exchangers was investigated both experimentally and theoretically. The Inner diameters of tubes were 1.0mm, 2.1mm and 4.0mm. Exchanged heat and pressure drop obtained from numerical simulation agreed well with the experimental ones. Calculation results show that the volume of a 2.0mm tube heat exchanger can be reduced to 33% of that of a 4mm tube heat exchanger with the same capacity. In addition the distribution of two-phase flow in a branching unit was investigated by measuring downstream temperature distribution. The flow distribution in a branching unit strongly affects the exchanged heat.View full abstractDownload PDF (501K) -
H.S WANG, Hiroshi HONDA2001 Volume 18 Issue 2 Pages 153-161
Published: 2001
Released on J-STAGE: October 11, 2011
JOURNAL FREE ACCESSA theoretical study has been made on the effects of tube diameter and tubeside fin geometry on the heat transfer performance of air-cooled condensers. Extensive numerical calculations of overall heat transfer from refrigerant R410A flowing inside a horizontal microfin tube to ambient air were conducted for a typical operating condition of the air-cooled condenser. The tubeside heat transfer coefficient was calculated by applying a modified stratified flow model developed by Wang et al.8). The numerical results show that the effects of tube diameter, fin height, fin number and helix angle of groove are significant, whereas those of the width of flat portion at the fin tip, the radius of round corner at the fin tip and the fin half tip angle are small.View full abstractDownload PDF (534K) -
Hideyuki OKAMOTO, Masao MASUDA, Yoshiyuki KOZAWA2001 Volume 18 Issue 2 Pages 163-171
Published: 2001
Released on J-STAGE: October 11, 2011
JOURNAL FREE ACCESSlt is recognized that COP of heat driven heat pump system using metal hydride is 0.3-0.4 in general. In order to rise COP, we have proposed two kinds of specific operation control; the control of cycle change time according to cold heat load and the control of cooling water temperature according to outside air wet-bulb temperature. The characteristics of the heat pump system using metal hydride have grasped by various experiments and simulations. The validity of the simulation model has been confirmed by comparing with experimental results. As results of the simulations programmed for the actual operation control month by month, yearly COP has risen till 0.5-0.6 for practical scale air-conditioning system without regard for the building use. By the operation control hour by hour, yearly COP has risen till 0.6-0.65. Moreover, in the office building case added 40% sensible heat recovery, yearly COP has risen more than 0.8.View full abstractDownload PDF (602K) -
Takahiko MIYAZAKI, Atsushi AKISAWA, Takao KASHIWAGI2001 Volume 18 Issue 2 Pages 173-183
Published: 2001
Released on J-STAGE: October 11, 2011
JOURNAL FREE ACCESSWaste heat utilization is a fundamental approach to end-use energy savings. Medium or low temperature waste heat is not usable unless its temperature level matches the demand. From this standpoint, power generation from medium or low temperature waste heat is beneficial because it improves the availability of the energy by converting waste heat into electricity or mechanical work.
Conventional waste heat driven power generation cycles, such as the Kalina cycle, attain relatively low thermal efficiencies because of the low exergy in medium or low temperature heat. This paper proposes a three-stage combined power cycle using cold energy for power generation from medium temperature (≅200°C)waste heat. The system consists of an ammonia-water Rankine cycle, an ethane-propane Rankine cycle and a liquefied natural gas direct expansion cycle.
A cycle simulation of the system is executed, and the operating conditions where the exergetic efficiency is maximized are presented in this article. It is found that the exergetic efficiency reaches 31% under these operating conditions.View full abstractDownload PDF (592K) -
Part1 : Analysis of Performance Characteristics of GHP ChillerToshihiko FUJITA, Nobuhiro MITA, Tadashi MORIYAMA, Norimasa HOSHINO, Y ...2001 Volume 18 Issue 2 Pages 185-192
Published: 2001
Released on J-STAGE: October 11, 2011
JOURNAL FREE ACCESSA gas engine-driven heat pump (GHP) uses a natural gas-or LPG-powered engine to drive the compressor in a vapor-compression refrigeration cycle. The GHP has the benefits of being able to use the fuel energy effectively by recovering waste heat from the engine jacket coolant and exhaust gas and also to keep high efficiency even at part-load operation by varying the engine speed with relative ease. Hence, energy-efficient heat source systems for air-conditioning and hot water supply may be constructed with GHP chillers in place of conventional electrical-driven heat pump chillers. GHPs will necessarily contribute to the peak shaving of electrical demand in summer.
In this study, the performance characteristics of a 457kW GHP chiller have been investigated by a simulation model analysis, for both cooling and heating modes. From the results of the analysis, it has been found that the part-load characteristics of the GHP chiller are fairly well. The evaluation of the heat source systems using GHP chillers will be described in Part 2.View full abstractDownload PDF (394K) -
Part2 :Simulation Evaluating GHP Chiller Heat Source Systems for Air-Conditioning and Hot Water SupplyToshihiko FUJITA, Nobuhiro MITA, Tadashi MORIYAMA, Norimasa HOSHINO, Y ...2001 Volume 18 Issue 2 Pages 193-202
Published: 2001
Released on J-STAGE: October 11, 2011
JOURNAL FREE ACCESSIn Part 1 of this study, the performance characteristics of a 457kW gas engine-driven heat pump (GHP) chiller have been obtained from a simulation model analysis for both cooling and heating modes and it has been found that the part-load characteristics of the GHP chiller are fairly well.
On the back of Part 1, a computer simulation program has been developed for the evaluation of GHP chiller systems to compare with the other types of heat source systems for air-conditioning and hot water supply applications. The simulation program can be used to estimate annual energy consumption, annual CO2 emission, etc. of the systems with the data of monthly and hourly thermal loads on various buildings, outdoor air conditions, and characteristics of various components comprising the systems. By applying this to some cases of medium-scale hotel, office, shop, and hospital buildings, it has been found that the GHP chiller systems have advantages particularly in the cases of hotels and hospitals where a lot of hot water demand exists. It has also been found that the combination of a GHP chiller and a direct-fired absorption water chiller boiler (hot and chilled water generator) appears promising.View full abstractDownload PDF (641K)
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