Evaporative Cooling Applied in Thermal Power Plants:A Review of the State-ofthe-Art and Typical Case Studies

A review is conducted about the application of the evaporative cooling technology in thermal power plants.Different case studies are considered,namely,evaporative air conditioners,evaporative cooling in direct air-cooled systems,gas turbine inlet cooling,wet cooling towers,and hybrid cooling towers with a crosswind effect.Some effort is provided to describe the advantages related to direct evaporative cooling when it is applied in thermal power plants and illustrate the research gaps,which have not been filled yet.In particular,typical case studies are intentionally used to compare the cooling performances when direct evaporative cooling is implemented in different types of cooling towers,including the natural draft wet cooling tower(NDWCT)and the pre-cooled natural draft dry cooling tower(NDDCT).It is shown that the NDWCT provides the best cooling performance in terms of power station cooling,followed by the pre-cooled NDDCT,and the NDDCT;moreover,the evaporative pre-cooling is able to enhance the cooling performance of NDDCT.Besides,on a yearly basis,better NDDCT cooling performances can be obtained by means of a spray-based pre-cooling approach with respect to wet media pre-cooling.Therefore,the use of nozzle spray is suggested for improvement in the performance of indirect/direct air-cooling systems with controlled water consumption.

Stark-potential evaporative cooling of polar molecules in a novel optical-access opened electrostatic trap

We propose a novel optical-access opened electrostatic trap to study the Stark-potential evaporative cooling of polar molecules by using two charged disk electrodes with a central hole of radius r0 = 1.5 mm, and derive a set of new analytical equations to calculate the spatial distributions of the electrostatic field in the above charged-disk layout. Afterwards, we calculate the electric-field distributions of our electrostatic trap and the Stark potential for cold ND3 molecules, and analyze the dependences of both the electric field and the Stark potential on the geometric parameters of our charged-disk scheme, and find an optimal condition to form a desirable trap with the same trap depth in the x, y, and z directions. Also, we propose a desirable scheme to realize an efficient loading of cold polar molecules in the weak-field-seeking states, and investigate the dependences of the loading efficiency on both the initial forward velocity of the incident molecular beam and the loading time by Monte Carlo simulations. Our study shows that the maximal loading efficiency of our trap scheme can reach about 95%, and the corresponding temperature of the trapped cold molecules is about 28.8 inK. Finally, we study the Stark-potential evaporative cooling for cold polar molecules in our trap by the Monte Carlo method, and find that our simulated evaporative cooling results are consistent with our developed analytical model based on trapping-potential evaporative cooling.

Surface-induced evaporative cooling

The effects of surface-induced evaporative cooling on an atom chip are investigated. The evolutions of temperature, number and phase-space density of the atom cloud are measured when the atom cloud is brought close to the surface. Rapid decrease of the temperature and number of the atoms is found when the atom-surface distance is 〈 100 ttm. A gain of about a factor of five on the phase-space density is obtained. It is found that the efficiency of the surface-induced evaporative cooling depends on the atom-surface distance and the shape of the evaporative trap. When the atoms are moved very close to the surface, severe heating is observed, which dominates when the holding time is 〉 8 ms. It is important that the surface-induced evaporative cooling offers novel possibilities for the realization of a continuous condensation, where a spatially varying evaporative cooling is required.

Light-induced evaporative cooling in a magneto-optical trap

This paper presents an experimental demonstration of light-induced evaporative cooling in a magneto-optical trap. An additional laser is used to interact with atoms at the edge of the atomic cloud in the trap. These atoms get an additional force and evaporated away from the trap by both the magnetic field and laser fields. The remaining atoms have lower kinetic energy and thus are cooled. It reports the measurements on the temperature and atomic number after the evaporative cooling with different parameters including the distance between the laser and the centre of the atomic cloud, the detuning, the intensity. The results show that the light-induced evaporative cooling is a way to generate an ultra-cold atom source.

Observation of Atomic Dynamic Behaviors in the Evaporative Cooling by In-Situ Imaging the Plugged Hole of Ultracold Atoms

We experimentally observe the dynamic evolution of atoms in the evaporative cooling, by in-situ imaging the plugged hole of ultracold atoms. Ultracold rubidium atoms confined in a magnetic trap are plugged using a blue-detuned laser beam with a waist of 20 m at a wavelength of 767 nm. We probe the variation of the atomic temperature and width versus the radio frequency in the evaporative cooling. Both the behaviors are in good agreement with the calculation of the trapping potential dressed by the rf signal above the threshold temperature,while deviating from the calculation near the phase transition. To accurately obtain the atomic width, we use the plugged hole as the reference to optimize the optical imaging system by precisely minimizing the artificial structures due to the defocus effect.

Radiative-coupled evaporative cooling:Fundamentals,development,and applications

As global energy demand continues to rise and climate change accelerates,the need for sustainable and energy-efficient cooling solutions has reached a critical level.Conventional air conditioning systems heavily rely on energy-intensive mechanical cooling,which significantly contributes to both electricity demand and greenhouse gas emissions.Passive cooling strategies,particularly radiative cooling(RC)and evaporative cooling(EC),present an alternative approach by harnessing natural processes for temperature regulation.While standalone RC can be affected by weather conditions and EC relies on water availability,Radiative-coupled EC(REC)offers a versatile and sustainable cooling solution suitable for various applications.Here we summarize an overview of the theoretical foundations and mathematical models of REC,encompassing REC by bulk water(REC-BW),REC by perspiration(REC-P),and REC by sorbed water(REC-SW).Moreover,we explore a range of applications,spanning from industrial processes to personal thermal management,and examine the advantages and challenges associated with each REC approach.The significance of REC lies in its potential to revolutionize cooling technology,reduce energy consumption,and minimize the environmental impact.REC-BW can conserve water resources in industrial cooling processes,while REC-P offers innovative solutions for wearable electronics and textiles.REC-SW’s adaptability makes it suitable for food preservation and future potable cooling devices.By addressing the challenges posed by REC,including water consumption,textile design,and optimization of bilayer structures,we can unlock the transformative potential of REC and contribute to sustainable cooling technologies in a warming world.

Research status and development trends of evaporative cooling air-conditioning technology in data centers

This paper systematically describes the technical principles,evaluation indicators,system forms and research progress of air-side evaporative cooling air conditioning systems,water-side evaporative cooling air conditioning systems and freon-side evaporative cold coagulation heat air conditioning systems of Data center.In order to reduce the energy consumption of the refrigeration and air-conditioning system in the Data center,the applica-tion conditions and scenarios of the different forms of evaporative cooling air-conditioning systems should be considered comprehensively.Therefore,it is very important that the renewable energy-dry air can be used to the greatest extent.These efforts would contribute to China’s 2030"Carbon Peak"and 2060"Carbon Neutral."

“Phase Diagram” of Surface Temperature Distribution of Sessile Droplets and the Effects of Evaporative Cooling

The temperature distribution along the surface of evaporating droplets can affect significantly the flow field inside the liquid and consequently the deposition pattern on the substrate. Although a “phase diagram” for the temperature distribution along the droplet surface was revealed by the numerical simulations, its experimental verification has still not been reported. In this paper, the surface temperature of evaporating droplets has been observed by using an infrared (IR) camera. The experimental observations show that three different patterns of temperature distribution along the droplet surface occur in succession with the change of the contact angle during the evaporation process, which is in good agreement with the theoretical predictions by the “phase diagram” of the surface temperature distribution. Furthermore, the effects of evaporative cooling on the “phase diagram” of sessile droplets have been explored. The numerical results indicate that the evaporative cooling effect can alter the size of the phase regions in the “phase diagram”. These results may provide a better understanding of the evaporation process of drying sessile droplets.

Review of research and application of evaporative cooling in preservation of fresh agricultural produce

Extensive review of evaporative coolers for the preservation of fresh agricultural produce in some countries was presented.Most of the designs employ mainly direct evaporative cooling methods which are simple but with lower thermal performance,and can only be used for short term storage of agricultural produce with moderate respiratory rates.Researches into novel technologies in evaporative cooling systems which can improve the cooling performances,such as membrane air treatments,dew point type and heat pipe type heat exchanger in indirect/direct evaporative cooling application,and their feasibilities in agricultural storage are either absent or scarce.Some kinds of materials especially agricultural residues have been used for air water contact in evaporative cooling in different climates,but most of the analyses focused on effect of air flow rate and pad thickness on the cooling effectiveness,and the energy efficiency and evaporation loss of these materials in most cases were not evaluated or presented.The paper highlights the prospects and constraints of commercialization and marketing of evaporative coolers in some developing countries,and the general weakness in researches and the ways forward in new area of research and development are concluded.

A techno-economic assessment for viability of some waste as cooling pads in evaporative cooling system

The viability of some waste as cooling pads for evaporative cooling application in South-Western Nigeria was experimentally assessed.This is to ascertain their effectiveness as a substitute for costly imported pads in a low income environment.Also presented was the feasibility of utilizing standalone evaporative coolers for storage and selling of fruits in South-Western Nigeria.Natural ambient air was forced through the various pads at three different fan speeds and constant cooling pad thickness of 30 mm.Performance characteristics were considered based on daily analysis using temperature and humidity data measured from morning to evening at location co-ordinates latitude 7°10′N and longitude 5°05′E for 6 weeks.The daily temperature T and humidity h ranged between 26℃≤T≤45℃ and 28%≤h_(2)≤80%.Temperature differenceDT and humidity differenceDh of 0.6℃≤ΔT≤18.3℃ and 1.0%≤Δh≤53%was achieved for the four cooling pad materials tested at three fan speeds.HighestDT andDh was recorded at fan speed of 4 m/s with shredded latex foam and jute sack respectively.The cooling efficiency(η)calculated for all the pads under the three speeds ranged from 17.3%≤η≤98.8%.Payback period(PBP)analysis indicated the considered EVC is economically feasible and investors will break even in 1.75 years.

Evaporative cooling of ^(87)Rb atoms into Bose-Einstein condensate in an optical dipole trap

We create a Bose-Einstein condensate （BEC） of 87Rb atoms by runaway evaporative cooling in an optical trap. Two crossed infrared laser beams with a wavelength of 1064 nm are used to form an optical dipole trap. After precooling the atom samples in a quadrupole-Ioffe configuration （QUIC） trap under 1.5 #K by radio-frequency （RF） evaporative cooling, the samples are transferred into the center of the glass cell, then loaded into the optical dipole trap with 800 ms. The pure condensate with up to 1.5× 10^5 atoms is obtained over 1.17 s by lowering the power of the trap beams.

Numerical Study and Optimization of a Combined Thermoelectric Assisted Indirect Evaporative Cooling System

This paper numerically investigates the performance of a novel combined cross-regenerative cross flow(C-RC)thermoelectric assisted indirect evaporative cooling(TIEC)system.This C-RC TIEC system combines the indirect evaporative cooling and thermoelectric cooling technologies.A heat and mass transfer model is developed to perform the performance analysis and optimization of this novel system.Performance comparison between the novel C-RC TIEC system and a regenerative cross flow TIEC system is conducted under various operating conditions.It is found that the novel system provides better performance with higher coefficient of performance(C O P)and higher dew point effectiveness than the regenerative cross flow TIEC system,especially under smaller working current and smaller number of thermoelectric cooling modules.The performance optimization of the novel system is also made by investigating the influences of primary air parameters,three different mass flow rate ratios,as well as the length ratio of the left wet channel to the whole wet channel.The results show that there exist optimal mass flow rate ratios and wet channel length ratio resulting in the maximum C O P.

Evaporative cooling rubidium atoms with microwave radiation

We report the experimental achievement of ^（87）Rb Bose-Einstein condensation in a magnetic trap with microwave and radio frequency（RF） induced evaporation.Evaporative cooling is realized by using 6.8 GHz microwave radiation driving the ^（87）Rb atoms to transit from the ground-state hyperfine state ｜F=2,m_F= 2〉to ｜F=l,m_F=1〉.Compared with RF-induced evaporation,^（87）Rb atoms are hardly to achieve pure condensate by microwave evaporation cooling due to the effect of atoms in the ｜F=1,m_F=1〉state being pumped back into the trapping ｜F=2,m_F=1〉state.

Experimental investigation of evaporative cooling systems for agricultural storage and livestock air-conditioning in Pakistan

Evaporative cooling(EC)is an ancient technique that is usually suitable for hot and dry climatic conditions due to the potential of water vapor evaporation.In this study,three kinds of evaporative cooling systems such as direct EC(DEC),indirect EC(IEC),and Maisotsenko cycle EC(MEC)were locally developed at lab-scale.The performance of the systems was evaluated and compared for agricultural storage and livestock air-conditioning application in Pakistan.The experiments were performed for climatic conditions of Multan city(Pakistan)and the data were collected for hourly and daily basis.According to the results,it was observed that the DEC system has the ability to reduce the temperature of ambient air to an average of 8.5℃.Whilst IEC and MEC systems were able to drop the temperature of ambient air to an average of 6.8℃and 8.9℃,respectively.As per the results,the DEC system remained behind to provide desired conditions for livestock and agricultural product storage applications due to excessive humidity.On the other hand,the IEC and MEC systems can achieve the desired conditions for livestock application,but could not provide feasible conditions for various fruits and vegetable storage.The study concludes that hybrid EC systems can be developed to provide desired conditions for a wide range of applications under varying climatic conditions.

Heat and mass transfer model optimization and annual energy efficiency analysis for energy recovery indirect evaporative cooling

Indirect evaporative cooling(IEC)is a kind of high efficiency,energy-saving and environmental protection cooling technology,which has been widely used in data centers and other fields in recent years.In this paper,the optimized two-dimensional non-condensation state model of indirect evaporative cooling was proposed.Meanwhile the computer program was updated to solve the developed mathematical model under variable fresh air conditions.The optimized model was verified by the experimental data,and the maximum deviation was only 4.6%.Based on the modified model and the annual hourly meteorological parameters in Tianjin,China,it was analyzed the optimal heat transfer area of IEC used as fresh air pre-cooling unit under various air volumes to provide references for system design and equipment selection.Finally,taking an IEC-primary return air conditioning system of a gymnasium as an example,the hourly energy-saving effect of whole year was simulated by the developed IEC model.The simulation results showed that IEC could control the fresh air temperature below 27℃ and the moisture content below 18 g/kg throughout the year,and undertook 102.6% of the total fresh air cooling load.The findings are useful in future system optimization and design of IEC equipment.

The effects of exhaust air vent location on thermal comfort inside a residential building equipped with an evaporative cooling system

The location of exhaust air vents of an evaporative cooling system can have significant effects on providing thermal comfort and controlling humidity, temperature and air distribution in buildings. In the current study, four different strategies have been evaluated for exhaust air vent locations to provide the optimum thermal comfort inside a typical residential house. This study provides a numerical solution for temperature and relative humidity profiles in the residential house and within the living space in each room typically at a height of 1.8 m or less. By evaluating different exhaust air vent locations in a room, the best strategy(ies) to provide more appropriate thermal comfort condition and obtained and as a conclusion, the exhaust vents should be located on furthest wall away from the entrance of the room and in the middle. The results provided in the current study can eventually be applied in the design of evaporative cooler exhaust vent systems in residential buildings and lead to improve the performance of these systems.

Experimental Study on the Thermal Performances of a Tube-Type Indirect Evaporative Cooler

The so-called indirect evaporative cooling technology is widely used in air conditioning applications.The thermal characterization of tube-type indirect evaporative coolers,however,still presents challenges which need to be addressed to make this technology more reliable and easy to implement.This experimental study deals with the performances of a tube-type indirect evaporative cooler based on an aluminum tube with a 10 mm diameter.In particular,the required tests were carried out considering a range of dry-bulb temperatures between 16℃ and 18℃ and a temperature difference between the wet-bulb and dry-bulb temperature of 2℃∼4℃.The integrated convective heat transfer coefficient inside the tube in the drenching condition has been found to lie in the range between 36.10 and 437.4(W/(m^(2)⋅K)).

Evaporative/radiative electrospun membrane for personal cooling

Functional textiles that promote daily comfort and productivity must efficiently release body sweats and transmit radiative heat through sweat evaporation and mid-infrared radiation(MIR)(8–13μm).However,most of the traditional clothing cannot provide simultaneous sweat evaporation and mid-infrared radiation transmission efficiently,leading to a poor design of personal cooling wearables.Herein,an evaporative/radiative integrated functional fibrous electrospun membrane is meticulously designed and controllably fabricated via facile electrospinning technology for personal cooling management.The developed membrane can be applied as a smart wearable with distinct personal thermal management applications.The promising temperature and humidity responsive vapor transmission of the membrane grants 1.2 times of evaporative cooling than that of traditional cotton.Besides,based on its high mid-infrared radiation transmission(53%)property in the range of 8–13μm,the as-spun membrane provides extra cooling of 1.5°C than that of cotton.Moreover,the building energy saving performances demonstrated that 47.1%annual building cooling can be achieved using the developed electrospun membrane.In general,the evaporative/radiative electrospun membrane creates a passive cooling microclimate for the human body,meeting the growing demand of wearable for personal cooling.

Mixed-field effect at the hyperfine level of^(127)I^(79)Br in its rovibronic ground state:Toward field manipulation of cold molecules

The mixed-field effect at the hyperfine level of the rovibronic ground state of the^(127)I^(79)Br(X^(1)Σ,v=0,J=0)molecule is computed on the J-I uncoupled basis of|JM_(J)I_(1)M_(1)I_(2)M_(2)>,where J is the molecular total angular momentum excluding nuclear spin,M_J is the projection number of J,I_(1) and I_(2) are the nuclear spins of the iodine and bromine atoms,and M_(1) and M_(2) are the projection numbers of I_(1) and I_(2),respectively.When the two applied electric and magnetic fields are parallel,the perturbations are rare and only one perturbation is observed in a relatively large field regime in our computation range.However,when the two fields are off-parallel,the perturbations increase significantly and some sublevels show the Feshbach-like resonance phenomenon.Therefore,such sublevels transit between weak-field seeking and strong-field seeking repeatedly,which can be utilized to enhance or suppress cold molecular collision and chemical reaction rates.Such behavior of the molecular hyperfine structure in the mixed off-parallel fields may also be utilized to construct an electric-field-assisted anti-Helmholtz magnetic trap for cold molecules and to realize evaporative cooling of cold molecules(sub-mK)into the ultracold regime(μK).

Bright-white hydrogels for on-demand passive cooling

Passive cooling permits thermal management of near-zero energy consumption and low CO_(2)emissions.Despite significant progress of passive radiative coolers,comfortable and steady temperatures can hardly be achieved due to their inadequate daytime cooling power(below 0.2 k W m^(-2))yet over-cooling at night.Here,we provide a bright-white hydrogel that enables ondemand passive cooling by virtue of adaptive water evaporation and high solar reflectance up to 86.1%.Notably,theoretical cooling power determined by the evaporating rate can reach 1.25 k W m^(-2)in daytime but decreases dramatically at night.Hence sub-ambient temperature reduction of 11-13℃at noon yet nearly none at night are realized,with the diurnal temperature difference narrowed significantly.Moreover,effective cooling using colored hydrogels,and transition from evaporative cooling to solar heating have been demonstrated.This novel evaporative cooling approach will pave the way for smart passive coolers of high efficiency,colorful appearance,and low cost.