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[en] Research highlights: → Combined absorption heat pump - methanol steam reforming system. → Determine optimum absorption heat pump (AHP) step number. → Decrease of GHSV caused increase of feasibility criterion up to AHP step number 3. → Increase of S/C shifted feasibility criterion peak from AHP step number 3 to 2. -- Abstract: This paper presents an evaluation of combined absorption heat pump (AHP) and methanol steam reforming (MSR) system. To measure the effectiveness of this combined system, a feasibility criterion was proposed, which measured the ratio between net energy gain obtained by MSR reaction over energy required by AHP system. By using the proposed feasibility criterion, optimum AHP step number could be determined. Other parameters pertaining to both AHP and MSR system were also determined and calculated. In particular, discussions would focus on the effects of steam-carbon molar ratio (S/C) and gas hourly space velocity (GHSV) of experimental MSR upon feasibility criterion of combined system. It was shown that the decrease of GHSV caused the increase of feasibility criterion up to the AHP step number 3; meanwhile, the increase of S/C resulted in the shifting of feasibility criterion peak from AHP step number 3 to 2.
[en] Highlights: ► We analyze double effect absorption refrigeration systems exergoeconomically. ► We study the effect of operating conditions on thermoeconomic parameters of the systems. ► We calculate the heat transfer coefficients in different components of the systems. ► In the systems the evaporator and the absorber are the most expensive components. - Abstract: Exergoeconomic analyses are reported for three classes of double effect LiBr/water absorption refrigeration systems in order to investigate the influence of various operating parameters on investment costs of the overall systems and product cost flow rates. In addition, the contributions of component costs to the overall costs are obtained for each system and the results of the exergoeconomic analyses of the systems are described. The results reveal the advantages and disadvantages of different configurations of double effect LiBr/water absorption refrigeration systems from an exergoeconomic point of view and are expected to be useful in the selection, design and modification of the structure and operating parameters of such systems.
[en] Highlights: • The CO_2 solubility of 30 aqueous amine solutions was measured at 30 wt% and 313.15 K. • The CO_2 loading of HMD is the highest, and that of TEA is the lowest. • 2DMAE, 3DMA1P, 1DMA2P, MDEA, TMPAD and 2EAE have a low heat of absorption with CO_2. • 2EAE can be used as an alternative to MEA in the CO_2 capture process. - Abstract: This article presents a thermodynamic and kinetic characterization of CO_2 absorption by 30 aqueous amine solutions. A solvent screening setup (S.S.S.) was used to find the CO_2 loading (α) for 30 different aqueous amine solutions (30 wt%) at a pressure of 1 bar with feed gas containing 15 vol% CO_2 and 85 vol% N_2 at 313.15 K to provide reliable absorber parameters. The structures of various amines (linear, non-linear, polyamines, sterically hindered, etc.) were tested and the S.S.S. results showed that hexamethylenediamine (HMD) has higher CO_2 loading at 1.35 moles of CO_2/mole of amine, and triethanolamine (TEA) has the lowest at 0.39 mole of CO_2/mole of amine. The heat of absorption indicates that MDEA has the lowest and HMD has the highest at −52.51 kJ/mole of CO_2 and −98.39 kJ/mole of CO_2, respectively. The combined data for the CO_2 loading and the absorption heat generated 6 amines that have good properties for the post-combustion CO_2 capture process in comparison with that of MEA. These amines are made up of one secondary amine (2-ethylaminoethanol, 2EAE) and 5 tertiary amines (N-methyldiethanolamine, MDEA, 1-dimethylamino-2-propanol, 1DMA2P, 2-dimethylaminoethanol, 2DMAE, 3-dimethylamino-1-propanol, 3DMA1P and N,N,N′,N′-tetramethyl-1,3-propanediamine, TMPDA). In comparison with the amine reference MEA (ΔH = −85.13 kJ/mole of CO_2 and α = 0.58 mole CO_2/mole of amine), the 6 amines have heats of absorption that are between −68.95 kJ/mole of CO_2 and −52.51 kJ/mole of CO_2, and their CO_2 loading is between 0.52 and 1.16 mole of CO_2/mole amine. The third important parameter, namely the reaction kinetics between aqueous amine solutions and CO_2, was studied by using stopped-flow equipment to measure the pseudo-first order reaction (k_0, s"−"1) at different amine concentrations. A determination of the second order rate constants (k_2, m"3 mole"−"1 s"−"1) at 298.15, 303.15, 308.15 and 313.15 K was performed by using the proposed reaction mechanisms. The base catalysis mechanism was used to correlate the experimental data of the tertiary amines and the zwitterion mechanism was used to correlate the experimental data of the primary/secondary amines. The kinetics results show that 2EAE, a secondary amine, was very high in comparison with MDEA, 1DMA2P, 2DMAE, 3DMA1P and TMPDA, all of which are tertiary amines that are very close to MEA, which is the reference case. This result shows that 2EAE is a good candidate for CO_2 capture as an alternative to MEA because it has good CO_2 absorption, a low heat of absorption and high kinetic reaction with CO_2. Moreover, the outcomes for the thermodynamic and kinetic properties indicate that the following 5 amine blends have emerged from this study: 2EAE/MDEA, 2EAE/1DMA2P, 2EAE/2DMAE, 2EAE/3DMA1P and 2EAE/TMPDA.
[en] This paper presents the theoretical performance of solar energy operated/assisted continuous absorption air conditioning machines while operating under local climatic conditions. The two most commonly used pairs of working fluids i.e. LiBr-H/sub 2/O and NH/sub 3/ -H /sub 2/O have been employed in the study the thermodynamic analysis of the two absorption machines has been reported while operating in air conditioning mode and deriving input heat for the vapor generator from a flat plate solar collector. The COP, the relative solution circulation ratio and the energy transfer at various points in the system are also reported for both LiBr-H/sub 2/O and NH/sub 3/-H/sub 2/O absorption machines. The monthly average daily solar energy collected to drive the absorption machines and utilizability of solar energy while operating the hot water solar collector at the temperature of generation have been discussed. The collector aperture area required per TR (ton of refrigeration has been estimated for both the absorption machines. Monthly average daily collector efficiencies are also reported for the three summer months. Finally, the operating cost of VCS, gas operated VAS and solar energy operated VAS have been reported and conclusions have been made. (author)
[en] Proceeding from problems at the absorption of the laser radiation and from the solution of thermal conduction models the authors report on selected investigations about the boring, the cutting and the scribing of thin films. Several typical experimental results are given. (author)
[en] This paper is connected with laser welding of 2.5 mm thick and 300-500 mm long SW7M and NCV1 steel sheets using the 2.5 kw CO2 lasers of continuous and pulse operation. There are discussed results of investigations on metallographic, heat resistance of welds, the welding micro deformations and investigations of influence of front surface state of welded elements on quality of welds. (author). 3 refs, 3 figs, 2 tabs
[en] The absorption heat pump (AHP) was studied with thermodynamics. A four reservoirs model of absorption heat pump was established considering the heat resistance, heat leak and the internal irreversibility. The reasonable working regions, the performance effects of irreversibility, heat leak and the correlation of four components were studied. When studying the effects of internal irreversibility, two internal irreversibility parameters (Ihe for generator-absorber assembly and Ire for evaporator-condenser assembly) were introduced to distinguish the different effects. When studying the heat transfer relations of four components, a universal relationship between the main parameters were deduced. The results which have more realized meaning show that, the reduction of the friction, heat loss, and internal dissipations of the evaporator-condenser assembly are more important than its reduction of generator-absorber assembly, and lessening the heat leak of generator are more important than its reduction of other components to improve the AHP performance.
[en] Air-cooled geothermal plants suffer substantial decreases in generating capacity at increased ambient temperatures. As the ambient temperature rises by 50 F above a design value of 50 F, at low brine-resource temperatures, the decrease in generating capacity can be more than 50%. This decrease is caused primarily by increased condenser pressure. Using mixed-working fluids has recently drawn considerable attention for use in power cycles. Such cycles are more readily amenable to use of absorption ''heat pumps.'' For a system that uses ammonia and water as the mixed-working fluid, this paper evaluates using an absorption heat pump to reduce condenser backpressure. At high ambient temperatures, part of the turbine exhaust vapor is absorbed into a circulating mixed stream in an absorber in series with the main condenser. This steam is pumped up to a higher pressure and heated to strip the excess vapor, which is recondensed using an additional air-cooled condenser. The operating conditions are chosen to reconstitute this condensate back to the same concentration as drawn from the original system. We analyzed two power plants of nominal 1-megawatt capacity. The design resource temperatures were 250 F and 300 F. Ambient temperature was allowed to rise from a design value of 50 F to 100 F. The analyses indicate that using an absorption heat pump is feasible. For the 300 F resource, an increased brine flow of 30% resulted in a net power increase of 21%. For the 250 F resource, the increase was smaller. However, these results are highly plant- and equipment-specific because evaluations must be carried out at off-design conditions for the condenser. Such studies should be carried out for specific power plants that suffer most from increased ambient temperatures
[en] In this paper, an experimental study of the absorption process of water vapor into lithium bromide solution is reported. For the purpose of developing high performance absorption chiller/heater utilizing lithium bromide solutions as working fluid, it brings the largest contribution to improve the performance of the absorber which normally requires the largest surface area among the four heat exchangers of the system. The performance of four types of absorber tubes; bare tube, bumping bare tube, floral tube and twisted floral tube, have been experimentally evaluated. The results show that the floral tube and the twisted floral tube show about 40% higher heat and mass transfer performance than the bare tube which is conventionally used in absorbers