Determining parameters of heat exchangers for heat recovery in a Cu–Cl thermochemical hydrogen production cycle

A heat exchanger is a device built for efficient heat transfer from one medium to another. Shell and tube heat exchangers are separated wall heat exchangers and are commonly used in the nuclear and process industry. The CuCl cycle is used to thermally crack water in to H₂ and O₂. The present study presents the heat exchanger thermal design using analysis of variance for heat recovery from oxygen at 500 °C, coming from the molten salt reactor. Polynomial regressions in terms of the amount of chlorine in the oxygen, the mass flow rate on the tube side, and the shell's outlet temperature are estimated for various exchanger parameters and the results are compared with the bell Delaware method. Based on energy and exergy analysis, this study also discusses the best possible path for the recovered heat from oxygen. Optimal heat exchanger parameters are estimated by Design-Expert^® Stat-Ease for most effective heat recovery.     

Study on a new ejection–absorption heat transformer

Based on the performance analysis of the single stage, the two-stage and the double absorption heat transformer, a new ejection–absorption heat transformer is presented and analyzed in this paper. The results show that it has a simpler configuration than the double absorption heat transformer and two-stage heat transformer. The delivered useful temperature in the ejection–absorption heat transformer is higher than for a single stage heat transformer and simultaneously its system performance is raised.     

Study on a silica gel–water adsorption chiller integrated with a closed wet cooling tower

A silica gel–water adsorption chiller integrated with a closed wet cooling tower is proposed. This adsorption chiller consists of two vacuum chambers, each with one adsorber, one condenser and one evaporator. Vacuum valves were not adopted in this chiller in order to enhance the reliability. A novel heat recovery process was carried out after a mass recovery-like process to improve the coefficient of performance (COP). Integration of the closed wet cooling tower into the chiller could ensure the cleanliness of cooling water circulating in the chiller and also promote the convenient setup of the chiller. A transient one-dimensional mathematical model was adopted to study this adsorption chiller. The simulated results showed that the cooling power and COP were 10.76 kW and 0.51 respectively when the hot water inlet temperature, the chilled water inlet temperature, the air inlet wet bulb temperature and dry bulb temperature were 85, 15, 28 and 30 °C respectively.     

Novel thermoelectric generator heat exchanger for indirect heat recovery from molten CuCl in the thermochemical Cu–Cl cycle of hydrogen production

The looming threat of global warming has elicited efforts to develop reliable sustainable energy resources. Hydrogen as a clean fuel is deemed a potential solution to the problem of storage of power from renewable energy technologies. Among current thermochemical hydrogen generation methods, the thermochemical copper-chlorine (Cu–Cl) cycle is of high interest owing to lower temperature requirements. Present study investigates a novel heat exchanger comprising a thermoelectric generator (TEG) to recover heat from high temperature molten CuCl exiting the thermolysis reactor. Employing casting/extrusion method, the performance of the proposed heat exchanger is numerically examined using COMSOL Multiphysics. Results indicate that maximum generated power could exceed 40 W at the matching current of 4.5 A. Maximum energy conversion efficiency yields to 7.1%. Results demonstrate that TEG performance boosts with increasing the inlet Re number, particularly at the hot end. For the molten CuCl chamber, findings denote that there is a 36% discrepancy between highest and lowest Re numbers. Similarly, the highest efficiency value pertains to the case with the highest inlet velocity. Moreover, the highest temperature difference between inlet and outlet of the cooling water is about 28 °C and 10 °C for the lowest and highest inlet Re numbers, respectively. Average deviation from anticipated friction factor and Nusselt number are 0.31% and 12.62%, respectively.     

Study on flow and heat transfer characteristics of heat pipe with axial “Ω”-shaped microgrooves

A theoretical model of fluid flow and heat transfer in a heat pipe with axial “Ω”-shaped grooves has been conducted to study the maximum heat transport capability of these types of heat pipes. The influence of variations in the capillary radius, liquid–vapor interfacial shear stress and the contact angle are all considered and analyzed. The effect of vapor core and wick structure on the fluid flow characteristics and the effect of the heat load on the capillary radius at the evaporator end cap, as well as the effect of the wick structure on the heat transfer performance are all analyzed numerically and discussed. The axial distribution of the capillary radius, fluid pressure and mean velocity are obtained. In addition, the calculated maximum heat transport capability of the heat pipe at different working temperatures is compared with that obtained from a traditional capillary pressure balance model, in which the interfacial shear stress is neglected. The accuracy of the present model is verified by experimental data obtained in this paper.     

Study on a lab-scale hydrogen production by closed cycle thermo-chemical iodine–sulfur process

The Iodine–Sulfur (IS) thermo-chemical process for the production of hydrogen is one of the most promising approaches for use of the high temperature process heat supplied by high temperature reactor, which was developed in the Institute of nuclear and new energy technology (INET) of Tsinghua University, China, and INET initiated the fundamental studies on IS cycle since 2005. Based on the experiment results obtained by fundamental researches, a lab-scaled closed cycle loop (IS-10), which featured in electro-electrodialysis (EED) for hydriodic acid (HI) concentration, was designed and built at INET. The loop was composed of three sections, i.e., Bunsen section, HI section and sulfuric acid section. The closed cycle experiment on the loop was successfully carried out recently. In HI section, HI_x produced by Bunsen reaction was continuously purified through reverse Bunsen reaction, concentrated by EED, and then HI solution was obtained by distillation. Finally HI was catalytically decomposed to H₂ and I₂ with the conversion of 20%. In sulfuric acid section, sulfuric acid was continuously purified, concentrated by distillation, and catalytically decomposed to SO₂, O₂ and H₂O with the conversion of 75%. In Bunsen section, water, including recycled water, reacted with I₂ and SO₂ recycled from HI section and sulfuric acid section to form two separated acids phases, thus to form a closed cycle. The closed cycle experiment lasted for 7 h with the hydrogen production rate of 10 NL/h, with Pt loaded on activated carbon and copper chromite used as the catalysts for HI and sulfuric acid decomposition, respectively. This paper summarizes the main features of IS-10 and the main results of the closed cycle experiment. So far IS-10 is the second reported facility on which closed experiment was carried out, and the first one with EED embedded to perform a closed cycle operation.     

Coupling of copper–chloride hybrid thermochemical water splitting cycle with a desalination plant for hydrogen production from nuclear energy

Energy and environmental concerns have motivated research on clean energy resources. Nuclear energy has the potential to provide a significant share of energy supply without contributing to environmental emissions and climate change. Nuclear energy has been used mainly for electric power generation, but hydrogen production via thermochemical water decomposition provides another pathway for the utilization of nuclear thermal energy. One option for nuclear-based hydrogen production via thermochemical water decomposition uses a copper–chloride (Cu–Cl) cycle. Another societal concern relates to supplies of fresh water. Thus, to avoid causing one problem while solving another, hydrogen could be produced from seawater rather than limited fresh water sources. In this study we analyze a coupling of the Cu–Cl cycle with a desalination plant for hydrogen production from nuclear energy and seawater. Desalination technologies are reviewed comprehensively to determine the most appropriate option for the Cu–Cl cycle and a thermodynamic analysis and several parametric studies of this coupled system are presented for various configurations.     

Progress of international program on hydrogen production with the copper–chlorine cycle

This paper highlights and discusses the recent advances in thermochemical hydrogen production with the copper–chlorine (Cu–Cl) cycle. Extended operation of HCl/CuCl electrolysis is achieved, and its performance assessment is conducted. Advances in the development of improved electrodes are presented for various electrode materials. Experimental studies for a 300 cm² electrolytic cell show a stable current density and production at 98% of the theoretical hydrogen production rate. Long term testing of the electrolyzer for over 1600 h also shows a stable cell voltage. Different systems to address integration challenges are also examined for the integration of electrolysis/hydrolysis and thermolysis/electrolysis processes. New results from experiments for CuCl–HCl–H₂O and CuCl₂–HCl–H₂O ternary systems are presented along with solubility data for CuCl in HCl–H₂O mixtures between 298 and 363 K. A parametric study of multi-generation energy systems incorporating the Cu–Cl cycle is presented with an overall energy efficiency as high as 57% and exergy efficiency of hydrogen production up to 90%.     

Study on China's low carbon development in an Economy–Energy–Electricity–Environment framework

Emissions mitigation is a major challenge for China's sustainable development. We summarize China's successful experiences on energy efficiency in past 30 years as the contributions of Energy Usage Management and Integrated Resource Strategic Planning, which are essential for low-carbon economy. In an Economy–Energy–Electricity–Environment (E4) framework, the paper studies the low-carbon development of China and gives an outlook of China's economy growth, energy–electricity demand, renewable power generation and energy conservation and emissions mitigation until 2030. A business-as-usual scenario is projected as baseline for comparison while low carbon energy and electricity development path is studied. It is defined as low carbon energy/electricity when an economy body manages to realize its potential economic growth fueled by less energy/electricity consumption, which can be characterized by indexes of energy/electricity intensity and emissions per-unit of energy consumption (electricity generation). Results show that, with EUM, China, could save energy by 4.38 billion ton oil equivalences (toes) and reduce CO₂ emission by 16.55 billion tons; with IRSP, China, could save energy by 1.5 Btoes and reduce CO₂ emission by 5.7 Btons, during 2010–2030. To realize the massive potential, China has to reshape its economic structure and rely much on technology innovation in the future.     

Effects of Cattaneo–Christov heat flux analysis on heat and mass transport of Casson nanoliquid past an accelerating penetrable plate with thermal radiation and Soret–Dufour mechanism

In this analysis, the effect of Catteneo–Christov model on heat alongside mass transport magnetohydrodynamics of a Casson nanoliquid with thermal radiation and Soret–Dufour mechanism is considered. The fluid flow is considered through porous media as the thermophysical attributes such as viscosity along with thermal conductivity are considered to be constant. Suitable similarity transformations were employed on the governing coupled flow equation to yield total differential equations (ODE). An accurate and newly developed spectral method called spectral homotopy analysis method (SHAM) was employed to provide solution to the simplified equations. The numerical method of homotopy analysis method (HAM) is SHAM. SHAM portrays the division of nonlinear equations into linear as well as nonlinear parts. The findings in this study show that an increment in the Casson parameter is seen to elevate the velocity plot at the wall and lessen the velocity far away from the plate. An increase in the Brownian motion and thermophoresis term is observed to speed up the local skin friction coefficient.     

Study on fluid–solid coupling heat transfer in fractal porous medium by lattice Boltzmann method

A lattice Boltzmann model is applied to simulate fluid–solid coupling heat transfer in fractal porous medium. The numerical simulation is conducted to investigate the influences of pressure drop and porosity on fluid flows and the effect of thermal conductivity ratio of solid matrix to fluid on heat transfer. The simulation results indicate that fluid flows still obey Darcy’s Law in the range of flow and pressure level in this paper, and that both velocity field and temperature evolution conform to the local structural characteristics of porous medium. The comparison of temperature results from lattice Boltzmann model against those from the finite-volume method (FVM, one of the conventional CFD methods) is also presented to demonstrate the reliability of LBM. The present results agree well with those from FVM, All these indicate the feasibility and the reliability for the lattice Boltzmann model to be used to reveal the phenomenon and rules of fluid–solid coupling heat transfer in complex porous structures.     

Analysis of the process characteristics of an absorption heat transformer with compact heat exchangers and the mixture TFE–E181

In the project described in this paper an experimental rig for a one-stage absorption heat transformer was designed and constructed. One aim of the project was to reduce the investment costs for the apparatus. This incorporates new and less expensive compact brazed plate heat exchangers for generator, evaporator, condenser and solution heat exchanger. The absorber was designed as a helical coil pipe absorber, where the weak solution trickles down as a falling film outside of the coil. The tests of the equipment involved measurements using a mixture of trifluorethanol (TFE) and tetraethyleneglycoldimethylether (E181). The process characteristics were investigated for different temperatures of the rich solution leaving the absorber. Experimental results are presented and compared with the results of a computer simulation model. Additionally the model was used to compare the COP of the heat transformation process with the mixtures lithium bromide–water (LiBr–H₂O) and ammonia–water (NH₃–H₂O). Furthermore, the overall heat and mass transfer coefficients for the plate heat exchangers and the falling film absorber were evaluated and compared with those of shell and tube heat exchangers.     

Thermodynamic analysis of an SOFC–GT–ORC integrated power system with liquefied natural gas as heat sink

To recover the waste heat from solid oxide fuel cell (SOFC) and improve the overall electrical efficiency, a new integrated power system driven by SOFC is proposed to achieve the cascade energy utilization. This system integrates an SOFC–GT system with an organic Rankine cycle (ORC) using liquefied natural gas (LNG) as heat sink to recover the cryogenic energy of LNG. Based on the mathematical model, a parametric analysis is conducted to examine the effects of some key thermodynamic parameters on the system performance. The results indicate that the overall electrical efficiency of 67% can be easily achieved for the current system, which can be further improved with parametric optimization. An increase in fuel flow rate of SOFC can raise the net power output, but it has a negative effect on SOFC and overall electrical efficiency. The compressor pressure ratio contributes to an increase in SOFC and overall electrical efficiency, which are contrary to the effects of air flow rate and steam-to-carbon ratio. Under the given conditions, compared with the Kalina sub-system, the ORC sub-system produces 12.6% more power output by utilizing the cryogenic energy of LNG with simple configuration.     

Study on a compact silica gel–water adsorption chiller without vacuum valves: Design and experimental study

A compact silica gel–water adsorption chiller without vacuum valves was manufactured and experimentally studied. This chiller contains two adsorption/desorption chambers and one chilled water tank. Each adsorption/desorption chamber consists of one adsorber, one condenser and one evaporator. The chilled water tank is adopted to mitigate the variation of the chilled water outlet temperature. A mass recovery-like process, which is a heat recovery process between the two evaporators, was carried out in this chiller. A novel heat recovery process was also fulfilled after the mass recovery-like process to improve the coefficient of performance (COP). The cooling power and COP were 9.60 kW and 0.49 respectively when the average hot water inlet temperature, cooling water inlet temperature, and chilled water outlet temperature were 82.0, 31.6 and 12.3 °C, respectively.     

Thermodynamic analysis of a novel fossil-fuel–free energy storage system with a trans-critical carbon dioxide cycle and heat pump

This paper presents and analyzes a novel fossil-fuel–free trans-critical energy storage system that uses CO₂ as the working fluid in a closed loop shuttled between two saline aquifers or caverns at different depths: one a low-pressure reservoir and the other a high-pressure reservoir. Thermal energy storage and a heat pump are adopted to eliminate the need for external natural gas for heating the CO₂ entering the energy recovery turbines. We carefully analyze the energy storage and recovery processes to reveal the actual efficiency of the system. We also highlight thermodynamic and sensitivity analyses of the performance of this fossil-fuel–free trans-critical energy storage system based on a steady-state mathematical method. It is found that the fossil-fuel–free trans-critical CO₂ energy storage system has good comprehensive thermodynamic performance. The exergy efficiency, round-trip efficiency, and energy storage efficiency are 67.89%, 66%, and 58.41%, and the energy generated of per unit storage volume is 2.12 kW·h/m³, and the main contribution to exergy destruction is the turbine reheater, from which we can quantify how performance can be improved. Moreover, with a higher energy storage and recovery pressure and lower pressure in the low-pressure reservoir, this novel system shows promising performance.     

Characteristics of an air source heat pump with novel photoelectric sensors during periodic frost–defrost cycles

To avoid mal-defrost phenomenon, an innovative photoelectric sensor is developed and presented in this paper. It is referred to as “Tube Encircled Photoelectric Sensor” (TEPS). Experiments are carried out in a controlled environmental chamber under standard frosting conditions. Ten TEPSs in 4 different models are tested on a commercial size air source heat pump with the nominal heating capacity of 60 kW. The characteristics of the air source heat pump, together with the performance of the TEPSs are investigated during 9 periodic frost–defrost cycles. Compared with the original defrosting control strategy equipped by the manufacturer, the proposed TEPS sensor reveals its potential ability to accurately control the defrosting process. Experimental results demonstrate that TEPSs can substantially prolong defrost intervals from 28.8 min to 52 min under the experimental conditions, and the number of defrost cycles can be reduced from 9 to 5. The performance improvement is found to be 6% to the heating efficiency, and 5% to the COP.     

Significance of exponential space-based heat source and inclined magnetic field on heat transfer of hybrid nanoliquid with homogeneous–heterogeneous chemical reactions

Many chemical reactive methods, like combustion, catalysis, and biochemical involve homogeneous–heterogeneous chemical reaction (HHCR). The collaboration among the heterogeneous and homogeneous reactions is exceedingly multifarious, including the creation and depletion both within the liquid and catalytic surfaces. Here, we observe the influences of Cu and Al₂O₃ nanoparticles past an elongating sheet under HHCR. An inclined magnetic field with an acute angle is applied to the direction of the flow. Further, radiative heat, temperature, and exponential space-based heat source aspects are modifying the thermal equation. The governing nonlinear equations are deciphered by utilizing the Runge–Kutta-based shooting method. It is found that HHCR reduces the solute layer thickness, whereas the increase in the angle of inclination of applied magnetism thickens momentum layer thickness.     

Plant sizing and evaluation of hydrogen production costs from advanced processes coupled to a nuclear heat source. Part I: Sulphur–iodine cycle

Hydrogen demand is already strong. It should significantly increase in the next few years due to the refinery industry's growing needs and new applications such as synthetic fuel or biofuel production. To meet the demand, advanced processes are being developed throughout the world in a sustainability context. Among the most studied ones are thermochemical cycles: the sulphur–iodine and hybrid-sulphur cycles.     

Experimental study and development of an improved sulfur–iodine cycle integrated with HI electrolysis for hydrogen production

The sulfur–iodine (SI or IS) thermochemical cycle assembled with solar or nuclear energy has been proposed as a large-scale, clean and renewable hydrogen production method. In present work, an improved SI cycle integrated with HI electrolysis for hydrogen production was developed according to experiments and simulation. The mathematical models of HI electrolysis using proton exchange membrane (PEM) electrolytic cell was developed, and then the user-defined module of HI electrolysis was set up through Aspen Plus and verified by experimental data. After designing and simulating the new flowsheet of the SI cycle based on HI electrolysis, 10 L/h of H₂ and 5 L/h of O₂ were obtained. The theoretic thermal efficiency of flowsheet reached 25–42% in terms of the utilization of waste heat. An ideal thermal efficiency of 33.3% through the proper internal heat exchange in the flowsheet was determined. Sensitivity analyses of parameters in the system were conducted. Increasing proton transfer number of PEM electrolytic cell in HI section improved the thermal efficiency of SI cycle. The ratio of distillate to feed rate and the plate number of distillation column in H₂SO₄ section were the most sensitive factors to the heat duty of overall SI cycle. The proposed new flowsheet for SI cycle is competitive to the flowsheets previously proposed in the field of flowsheet simplification.