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The primary heat rejection cycle, which is critical for the stability and integrity of the metal production process and equipment, involves the transfer of heat from flue gas to a fluid circulated through a gas-cooler. The rate of heat transfer from the flue gas is influenced by several parameters, including the temperature of the cooling fluid. Heat transfer rates that are too high or too low can negatively impact equipment's life, emphasising the need for a temperature operational envelope in the cooling fluid prior to entering the gas-cooler. Rejected heat is used for power generation, transferred to the environment, or both. This study examines the impact of control philosophies on both temperature and power generation, while maintaining the exit temperature within the desired range as the highest priority. A more advanced philosophy that combines bypass control with feedforward parameters can maintain temperatures within safe operating limits at all times, while improving the power generation, compared to a typical works approach which is used as a baseline. This study presents a formulation that increased power generation from an average of 6.11 MW for a typical works philosophy to 10.68 MW, while maintaining the temperature within the operating temperature envelope. [ABSTRACT FROM AUTHOR]

Several cities in the Kingdom of Saudi Arabia often receive very hot water (46°C) from the water distribution network, which is supplied by a thermal desalination plant. In this work, an effort has been made to find suitable techno-economic solutions to cool hot distillate produced from thermal desalination before being sent to the water distribution network. The main constraints considered in the study were a cooled distillate temperature of 38°C when air temperatures reach 45°C and relative humidity reaches 70%. Several options, such as once-through seawater cooling, distillate flashing and condensing, and cooling towers have been evaluated. Wet cooling towers were able to reduce the temperature to 38°C most of the time, with the cooled temperature exceeding 40°C only 7.5% of the time. However, when seawater cooling was used, about 10% of the time the seawater temperature exceeded 35°C, which limited the cooling to 3.57°C only, that is cooled water temperature was only 40.43°C because of the constraints on the amount of seawater that could be supplied. After giving due consideration to the climatic factors, field/plant constraints and their impact on the efficiency of the solutions proposed, cooling towers were found to be the most suitable option. [ABSTRACT FROM AUTHOR]

The primary heat rejection cycle, which is critical for the stability and integrity of the metal production process and equipment, involves the transfer of heat from flue gas to a fluid circulated through a gas-cooler. The rate of heat transfer from the flue gas is influenced by several parameters, including the temperature of the cooling fluid. Heat transfer rates that are too high or too low can negatively impact equipment’s life, emphasising the need for a temperature operational envelope in the cooling fluid prior to entering the gas-cooler. Rejected heat is used for power generation, transferred to the environment, or both. This study examines the impact of control philosophies on both temperature and power generation, while maintaining the exit temperature within the desired range as the highest priority. A more advanced philosophy that combines bypass control with feedforward parameters can maintain temperatures within safe operating limits at all times, while improving the power generation, compared to a typical works approach which is used as a baseline. This study presents a formulation that increased power generation from an average of 6.11 MW for a typical works philosophy to 10.68 MW, while maintaining the temperature within the operating temperature envelope.

The Megawatt Implementation of a NuclEar ReActor using Low-enrichment uranium (MINERAL) is designed to deliver 2 MW(electric) of steady-state electricity to a colony established on the surface of Mars with a minimum lifetime of 10 years. The main challenge associated with a low-enrichment uranium fission surface power system is reducing the total mass, which will be higher than that of an equivalent high-enrichment uranium system. Optimizing the mass of the system is crucial to limit the amount of Earth-Mars cargo needed to deploy a MINERAL unit. The use of yttrium hydride as a moderator has shown promise in reducing the overall mass of the reactor. An in-house Python framework evaluates the neutronic, thermal-hydraulic, and heat rejection performance throughout the design process. The final design iteration uses a CO2 Brayton cycle cooled by a passive heat rejection system consisting of six panels with a total surface area of 4752 m2. The cylindrical core is fueled with low-enrichment uranium monocarbide with 0.83 wt% of pure 157Gd moderated with yttrium hydride and surrounded by a beryllium oxide reflector. The reactivity is controlled by ten control drums and a central control rod, which provide enough margin to operate the reactor and ensure its subcriticality in case of a submersion accident. The mass of the core with the reflector, reactivity control system, and shield is 7.2 tonnes. [ABSTRACT FROM AUTHOR]

[Display omitted] • TEC refrigeration system integrated with MCHSs is employed for electronic chips. • The study examines various TiO 2 /water nanofluid concentrations and flow rates. • Nanofluid usage enhances thermal characteristics compared to pure water. • The best improvement in Q ̇ c and COP is at high concentration and low flow rate. Advances in chip technology lead to increased energy consumption due to larger chip capacities and, as a result, intense heat flux generation, resulting in the need for more robust cooling solutions. These solutions include fan-only systems, fan-conventional heat sink (HS) integrated systems, and fan-conventional HS-heat pipe (HP) integrated systems. While thermoelectric couples (TECs) offer benefits like compactness and noise-free operation, they alone cannot sufficiently cool sophisticated chips. Combining TECs with microchannel heat sinks (MCHS) and superior fluid utilization is essential for faster and more efficient cooling. Notably, this study is the first to explore a TEC integrated with two MCHSs, using a TiO 2 /water nanofluid to optimize the performance of this miniature refrigeration system. Herein, an experimental study was carried out to evaluate the thermal performance of the proposed cooling system at various volume flow rates using both TiO 2 -water nanofluid and pure water for comparative purposes. The results were interpreted in terms of Reynolds number, Prandtl number, heat transfer rate, Nusselt number (Nu), total thermal resistance, and the coefficient of performance (COP). In both MCHSs, the Nu exhibited an upward trend as the flow rate increased from 9 × 10−5 m3/s to 16 × 10−5 m3/s, independent of concentration. At 16 × 10−5 m3/s, the highest flow rate investigated, it was observed that as φ increased from 0 % to 0.03 %, the Nu for the first control volume increased from 47.17 to 47.32, while the Nu for the second control volume decreased from 46.43 to 46.23. Additionally, as φ increased from 0 % to 0.03 %, accompanied by a reduction in flow rate from 16 × 10−5 m3/s to 9 × 10−5 m3/s, the experimental COP rose from 0.325 to 0.853. The results indicate that the proposed refrigeration system in this study is promising for electronic circuit cooling applications, particularly at low flow rates and high nanoparticle volume concentrations. [ABSTRACT FROM AUTHOR]

In this paper, an enhanced calculation method of a heat rejection system operating on the moon is presented. This was taken into consideration in the developed calculation method and in the propagation of heat fluxes with the radiation of the removed heat. The developed method made it possible to effectively evaluate the capabilities of various refrigerants and choose the radiator parameters and the refrigerant flow regime in a less time-consuming process and with minimal deviations (<5%) compared to the previously developed two-dimensional radiator model by the authors. A comparative analysis was carried out for two refrigerants: helium and liquid ammonia. It has been established that when using liquid ammonia, there are more possibilities for varying the geometric parameters of the radiator. The use of liquid ammonia as a refrigerant made it possible to reduce the power spent on pumping the refrigerant through the radiator. Using helium, the power for pumping the refrigerant was N R = 5.1 W during a turbulent flow Re = 4500. On the other hand, the power for pumping liquid ammonia was N R = 0.27 W. In addition, using liquid ammonia increased the heat flux radiated by the radiator pipe by 3.9 times, which made it to possible to increase the fin width and reduce the length of the radiator pipe. [ABSTRACT FROM AUTHOR]

In this paper, an enhanced calculation method of a heat rejection system operating on the moon is presented. This was taken into consideration in the developed calculation method and in the propagation of heat fluxes with the radiation of the removed heat. The developed method made it possible to effectively evaluate the capabilities of various refrigerants and choose the radiator parameters and the refrigerant flow regime in a less time-consuming process and with minimal deviations (NR= 5.1 W during a turbulent flow Re = 4500. On the other hand, the power for pumping liquid ammonia was NR= 0.27 W. In addition, using liquid ammonia increased the heat flux radiated by the radiator pipe by 3.9 times, which made it to possible to increase the fin width and reduce the length of the radiator pipe.

The colonization of the Moon and building permanent lunar outposts in the near future has become a main objective for most space agencies around the world. Future lunar outpost with a permanent human presence would have high power requirements to support such activities as scientific experimentation, in situ mining and processing, astronomical observation, and surface exploration. Several challenges are associated with the habitation of the lunar surface, such as, choosing an appropriate power generation unit. Stirling engines are one of the attractive power generation options which were implemented in space missions before, and are most likely to be used in future space exploration missions. In this paper, a detailed calculation methodology of a radiator design in a lunar power plant is developed. A brief research on some of the challenges that are associated with the habitation of the Moon and an overview of a lunar power plant consisting of a free piston Stirling engine (FPSE) are presented. A program code based on the developed calculation methodology consisting of two algorithms (one- and two-dimensional cases) was developed, and the results of both algorithms were compared and presented. Moreover, three different radiator design options having helium as a refrigerant circulating in them were considered and their results were analyzed. Finally, the conclusions and future directions of this work are provided. • Stirling engines are an effective power generation option on the moon. • Solar and Nuclear power should be considered as an energy source on the moon. • A suitable location on the moon should have stable temperature ranges. • Thermophysical properties of the refrigerant affects the work of the radiator. • Hydraulic resistance in the pipes affects the dimensions of the radiator. [ABSTRACT FROM AUTHOR]

The present work aims to investigate the potential advantages in using a novel wet and dry configuration for heat rejection units in ORC power plants. The reference case is a geothermal power plant that exploits a low temperature brine and uses a closed loop of cooling water to release the condensation heat to the ambient. In the calculations, the off-design operation of the whole plant is optimized from a techno-economic point of view with a realistic part-load behavior of the ORC and the use of experimentally validated correlations for the heat rejection section. The performance attainable with the novel LU-VE Emeritus® unit equipped with a water spray system and adiabatic panels is compared with those achievable with the same unit in dry operation. Final results show a marked increase of electricity production as well as of revenues with Emeritus® units with respect to a dry unit. • We studied the off-design behavior of different geothermal ORC. • We compared the novel Emeritus heat rejection units and conventional dry air coolers. • We optimized the whole system from a techno-economic point of view. • We highlighted the advantages in adopting wet and dry heat rejection units. • We analyzed the impact of perforation cost on system optimal design. [ABSTRACT FROM AUTHOR]

This paper presents a detailed thermodynamical exergy analysis of an optimized MSF distillation plant based on the latest published thermodynamics properties of water and seawater software of the Massachusetts Institute of Technology by using design and optimized plant operation data. Exergy flow rates are evaluated throughout the plant and the exergy flow diagram is prepared in both cases. The rates of exergy destruction and their percentages are indicated on the diagram so that the locations of each exergy destruction can easily be identified. The study concludes that as a result of an optimization, making the MSFD unit once-through cooling system to recirculating type by using cooling tower system, the unit's exergy destruction pattern changes meaningfully. Besides, in the three exist thermal desalination plants up to 53 percent of feed water, i.e.; 667 m3/h and the same amount of reject water can be conserved. Though, with this modification, the unit steam consumption has been increased up to 13 ton/h, about 50 percent of design. Moreover, the detail of the study showed that the exergy destruction can be reduced more than 39% in the pumps, and 30% in blowdown and around 29% in distillate streams. For brine heater, an enhance as small as 0.37% is also achieved. In the other hand, the rate of destruction of exergy increased around 25% in the cooling process and above 5% in the evaporators.

• Circulating water redistribution among various sectors is proposed for anti-freezing. • Water flow rate of the frontal sector increases with increasing the wind speed. • At low wind speeds, water flow should not decrease more for middle and rear sectors. • Middle and rear sectors cannot freeze with low water flow rates at high wind speeds. In extremely cold days, the freezing risk of air-cooled heat exchanger has been a great concern for natural draft dry cooling system in power plants. In this work, the circulating water redistribution among various sectors is proposed and analyzed at different wind speeds against the equal water flow distribution mode, by which both the anti-freezing and energy-efficient operation demands of natural draft dry cooling system are satisfied. The results show that at the low wind speed of 4 m/s, the water flow rates of the middle and middle rear sectors should not decrease too much in case of the unexpected freezing risks. However, at the high wind speeds of 12 m/s and 16 m/s, they face no freezing risks due to the extremely low cooling capacity of ambient air. As a result, these two air-cooled sectors can be dismissed at high wind speeds for a better energy efficiency. By directing the circulating water of the middle and middle rear sectors to others, not only the serious freezing risks of the sectors can be avoided, but the economic operation of natural draft dry cooling system can also be achieved. [ABSTRACT FROM AUTHOR]

• Discharge of seasonal sorption storage was studied as a pressure-driven process. • The useful heat and average power during this process were experimentally measured. • Three adsorbents were compared at different temperatures and flow rates. • Useful heat is lower than adsorption heat mainly because of the sensible heat lost. Interest towards adsorption heat storage, especially for long-term (seasonal) applications, is growing. The previous studies have always treated the heat storage cycle as a fully temperature-initiated process, similarly to common adsorption cooling and heating cycles. However, in long term storage applications, the discharge stage of the cycle is initiated by a jump of pressure rather than by a traditional drop of temperature. This requires specific investigations on the useful heat recoverable as well as on the adsorption dynamics. In the present paper, an appropriate experimental methodology was applied for studying the heat discharge stage. Three well known adsorbents (Mitsubishi AQSOA FAM-Z02, silica Siogel and composite LiCl/silica) were experimentally tested in a lab-scale heat storage unit, evaluating the effect of cycle operating parameters. The results, elaborated in terms of useful heat recoverable from the charged adsorbent, highlighted that the evaporation temperature and the flow rate of heat transfer fluid have a great influence on the adsorption dynamics and the useful heat. For the silica gel and FAM Z02, the maximum heat storage capacity 450 kJ/kg is reached at the evaporation temperature of 25 °C. The composite performs better at low evaporation temperatures, allowing heat upgrade even at 5 °C. The flow rate of the heat transfer fluid has a more significant effect on FAM Z02 than on the other adsorbents, for which an optimal flow rate of 1.2 kg/min was found. [ABSTRACT FROM AUTHOR]

Abstract Permeability damage due to fines migration will impair the well productivity, which ultimately ruin the well life and creates economic loss. In clay bearing oil and gas fields, fine particles that resting on the rock surface are under the regime of the four forces, namely, electrostatic, gravity, drag, and lift. Former two forces keep the fines attached to the rock surface, while the latter two forces contribute in the detachment of fine particle from rock surface/pore wall. Fines are also detached and migrated due to permeating fluid that are strained in the pore throat during suspension transport. Thereby, declining the permeability level and reducing the oil and gas flow, and water-cut. In reservoir engineering viewpoint, thermal conduction is the transfer of heat from the source or surrounding rock to reservoir rock or it is an ability of porous rock to pass and distribute the heat to pore walls. In contrast, heat rejection is the liberation of heat energy from the porous surface to the pore space or surroundings due to invasion of external fluid to pore wall that in turn detaches the fines from pore wall and lead to a suspension flow in the interspace of the porous rocks. This type of modelling should be applied against fines displacement in oil reservoirs during waterflooding. Hence, this paper presents classical heat and mass transfer theory based analytical modelling to investigate the effects of waterflooding on migration of fine particles in oil reservoirs. Additionally, experiments were conducted to validate these fines behaviors against the analytical cum thermodynamic models, and it showed good correlation. Highlights • A thermodynamic based analytical model was developed for fines migration in oil reservoirs. • The enthalpy and entropy of oil bearing sandstone rocks was modelled. • There is a mathematical observation of high amount heat liberation from reservoir rocks to porous interspace. [ABSTRACT FROM AUTHOR]

Highlights • Design of a hybrid heat rejection system for Shand Power Station to maintain Zero Liquid Discharge while integrating CO 2 capture and storage. • Evaluation of the effect of annual variations in dry bulb and wet bulb temperatures on the heat load by using Thermoflex. • The yearly average power consumption of the hybrid system was calculated and compared with those of the design case. Abstract The integration of CCS to a coal-fired power plant not only results in the increase in water consumption and cooling duty, but also additional water discharge especially from cooling the flue gas to the much lower temperature required for the CO 2 capture process. This paper presents the design of a heat rejection system for the Shand Power Station that maintains a neutral liquid impact on the existing plant while adding SO 2 and CO 2 capture processes. Moreover, the effect of temperatures throughout the year on heat rejection load and power consumption is investigated. The heat rejection systems were designed and optimized by using Aspen HYSYS and Aspen EDR to accommodate 245 MWth which is the additional heat rejection required for the CO 2 capture process, assuming that flue gas pre-cooling is accomplished from an external source. In the case of this study, the flue gas cooler heat integration, and a quench system serviced by cooling duty which is offset from the existing unit condenser due to the integration steam source provides the required flue gas pre-cooling. The hybrid heat rejection system, which uses a dry cooler in series with a wet cooler, cools the CO 2 capture plants circulating water loop from 44.5 °C to 25 °C. The wet cooling is by a Wet Surface Air Cooler (WSAC), in order to provide a second layer of protection to ensure that none of the CO 2 capture chemicals will be inadvertently released to the environment. The design dry bulb and wet bulb temperatures are based on the 85 percentiles of the Estevan's weather data for 26 years from 1991 to 2017, and are 18 °C and 13.7 °C respectively. Water produced by the capture process was utilized as the primary source for the wet cooling in order to avoid increasing the overall water draw of the facility. Using the dry cooler for rejecting the higher grade heat, and the WSAC for the lower grade heat improves cooling water temperature, while also maintaining Zero Liquid Discharge (ZLD) status. The heat load on the dry cooling and wet cooling is 156.5 and 81.8 MWth which corresponds to 67 and 33% of the total heat respectively. The effect of annual variations in dry bulb and wet bulb temperatures on the heat load of the hybrid cooling system was investigated by using Thermoflex. It was noted that the annual average heat rejection load shifted toward wet cooling system due to the lower temperature and the need to evaporate water available from the CO 2 capture process with the percentage of 58% for dry cooling and 42% for wet cooling. This resulted in reduction of fan power requirements. The average fan power consumption throughout a year is 2.58 MW which is only 52% of the design case (4.96 MW). [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Green cooling towers, or thermal green-walls, recirculate hot water flowing through a living plant and porous material. Through convective and evaporative heat and mass transfer they can actively cool a building or an industrial heat waste. Thus they can provide an alternative cooling technology. Thermal green-walls use wetland plant species in highly constructed wetlands selected for their heat tolerance. In addition, they offer such co-benefits as carbon capture and control of local microclimates. Optimal heat rejection (HR) requires the plant rhizosphere to be completely inundated at temperatures much higher than the ambient air temperature, potentially inducing thermal physiological stress. To study the viability of specific plants within a HR system, we exposed three macrophytes, Iris versicolor , Scirpus cyperinus and Carex lurida , to hydroponic recirculating water at three different temperatures (25 °C, 35 °C, and 40 °C). We assessed the plant responses over a period of eight weeks by measuring photochemical efficiency, leaf temperature, stomatal conductance, G s and biomass output. Plant biomass was highest at 35 °C (particularly in I. versicolor), even higher than ambient water temperature at 25 °C. We observed a general homeothermic-like response in G s over a 5-week time period, but the response was species-specific with respect to temperature. Results suggests a possible leaf-level physiological acclimation mechanism as well as high maintenance of tissue moisture that allows macrophytes to tolerate hydro-thermal stress, and support their suitability to perform in HR systems at input temperature, T win = 35 °C. [ABSTRACT FROM AUTHOR]

The purpose of this research is to propose a simple and fast method to evaluate the effect of heat rejection of split-type air conditioner on the thermal environment surrounding the building and the building cooling demand to provide guidance for architectural design in the urban planning stage. In this paper, we first determined the factors that affect or are affected by heat rejection as heat dissipation, wind speed, and ambient air temperature, which as inputs to the CFD to build the regression model of the temperature rise. Then, the regression model is coupled with the energy consumption simulation software EnergyPlus to estimate the building cooling increase. The result of taking a typical residential building as a reference show that the maximum temperature rise and cooling demand increase with the values of 1.86°C and 17%.

Highlights • Heat rejection control strategies that increase chillers efficiency are presented. • Different cooling towers sequencing approaches are investigated theoretically. • A cooling water set-point as a function of the wet-bulb temperature is proposed. • Both simulation and monitoring results show up to 15% electricity savings. Abstract Energy efficient cooling systems are urgently required in order to face the increasing cooling demand of the building and industry sectors and comply with the ambitious EU target of greenhouse gas emission reductions. The present work aims to show that simple heat rejection control strategies can lead to significant energy savings. Different approaches of sequencing the operation of several cooling towers and a method to adapt the cooling water temperature set-point to the actual ambient conditions are proposed. These strategies are first investigated theoretically for an existing chilled-water plant of 13.7 MW installed cooling capacity. Up to 20% energy savings are theoretically possible depending on the used control strategy and the weather conditions. A variable cooling water set-point as a function of the wet bulb temperature allows for the most significant savings. After implementation of this measure in the existing cooling plant, 2 years monitoring results show that the overall system efficiency of the chilled water plant could be increased by 15% compared to the initial status confirming the results of the theoretical study. [ABSTRACT FROM AUTHOR]

This study is motivated by global directions towards reducing carbon emissions. LNG is a very energy intensive industry and improving its efficiency is an essential area of study. LNG process is sensitive to cooling media, so conventional air cooling is replaced by proposed water cooling with a cooling tower. Aspen Hysys V11 is used for simulating the base and proposed systems in this study. The proposed water-cooling system is simulated and compared with the conventional air-cooling system in Alexandria, Egypt as the base location of the study, at a single simulation point. For more data refinement, hourly temperature records are used for simulation and total annual performance is calculated based on 8784 simulation points, which achieved a total year improvement of 3.98% reduction in SPC, fuel gas and CO 2 emissions and 7.21% reduction in annual propane consumption. To assess the suitability of the system in different climates, four different locations are assessed: Nigeria, Qatar, Egypt, and Russia. Performance is measured throughout the year on hourly calculations. Results revealed that power reduction up to 4.26% can be achieved based on total year performance. The power reduction achieved is 1.24%, 1.6%, 3.98%, and 4.26% for Russia, Nigeria, Egypt, and Qatar, respectively. • Comparing water and air cooling based on hourly data. • Annual performance assessment of LNG Cascade Cycle. • Total annual performance improvement up to 4.26%. • Assessing different locations with different climate conditions. • Locations with lower RH% achieving higher performance. [ABSTRACT FROM AUTHOR]

The fission heat in a lunar surface nuclear reactor power system transported to the Stirling engine could not be fully converted into electrical power and the exhaust heat was released to the heat rejection system. Based on the technology feasibility, a mechanical pumped cooling loop was proposed for heat rejection system, composed mainly of mechanical pumps, cooling loops and radiator plates. A heat rejection model with the convective and radiative heat transfer was developed. The convective heat transfer coefficient was larger than the radiative heat transfer coefficient by two orders of magnitude and the radiative heat transfer was the primary step controlling the heat rejection process. The radiator size and mass of the heat rejection system were calculated by the model and they were greatly affected by the cooling temperature. Increasing cooling temperature could reduce the required radiator size and mass of the heat rejection system, since higher cooling temperature could increase the heat rejection driving force. Considering the thermal efficiency of the nuclear power system, the reasonable cooling temperature would be in the range of 480 K–520 K, with the lowest specific mass of the lunar surface nuclear power system being 66 kg/kWe achieved in this range. [ABSTRACT FROM AUTHOR]

The evaporative condensers operate at lower condensing temperatures compared with dry heat transfer units when connected to the same refrigeration system, as well as involve less water and reduce the pumping power associated to cooling towers. These characteristics are strictly correlated with the evaporation process. For these reasons they are conveniently used for heat rejection in big industrial plants and recent technological developments have made it possible to exploit their higher efficiency even in smaller air conditioning systems. In this work a test rig for the evaporative condensers performance analysis and the relevant experimental activities are presented. The combined effect of the dry bulb temperature and relative humidity on the system performance has been investigated. The maximum reduction of the heat transfer rate, due to an increase of 6 % of the initial value of relative humidity, results of 30 % for the highest dry bulb temperature. The air processes plot in a psychrometric chart show that the latent to sensible heat transfer ratio decreases with relative humidity. [ABSTRACT FROM AUTHOR]