Latent Heat Of Water Vapor Research Articles

Experimental Study on the Performance of an Air Conditioning Unit with a Baffled Indirect Evaporative Cooler

Indirect evaporative coolers (IECs) use the latent heat of water evaporation to cool air. This system has the advantage of operating at low power without a compressor and does not increase the absolute humidity of the air. However, an IEC is difficult to use on its own because its cooling capacity is limited by the theoretical constraint of the wet-bulb temperature of the ambient air. Therefore, an air conditioning unit (ACU) was integrated with an IEC and experimentally evaluated in this study. The dry and wet channels of the IEC were integrated with an ACU evaporator and a condenser, unlike previous studies where IECs were integrated solely with either an evaporator or a condenser. This reduced the cooling load on the evaporator and helped the condenser to dissipate heat to improve the performance of the existing ACU. In addition, the IEC was equipped with baffles to improve its performance. To assess the extent of the performance improvement due to integration with the IEC, comparisons were also performed under the same experimental conditions with an ACU only. The results showed that under conditions with an indoor temperature of 32 °C, integrating the IEC with the ACU increased the average cooling capacity by 13.1% and decreased the average power consumption by 8.60% during the test period, compared to using only the ACU. Consequently, the average coefficient of performance (COP) increased by 19.5% compared to using only the ACU under the same conditions.

Application of Biomass Smoldering for Rural Building Heating in China: Strengths and Challenges.

Biomass smoldering for rural building heating could be a potential choice for bioenergy utilization in China to reduce the pollution caused by agroresidues open burning and to satisfy the increased demand of rural building heating. Its strengths include low pretreatment, transportation, and storage fees of fuel; ease of operation; good fertilizer characteristics of ash; use of latent heat of water vapor; pollution reduction; reduction of pests, weeds, and plant diseases on the farm; etc. However, controls of the burn rate and the gas emission are two challenges of the application, and related solutions of these challenges are discussed.

Daytime air–water harvesting based on super hygroscopic porous gels with simultaneous adsorption–desorption

In recent years, solar-powered, passive adsorption-based air–water harvesting has shown tremendous potential in addressing freshwater shortages in arid regions. Although remarkable progress has been witnessed in unlocking the potential of new adsorbents in the laboratory, the productivity of freshwater is still limited by the slow adsorption kinetic, the large latent heat of water evaporation, and the efficiency of condensation. In this work, superhygroscopic porous gels consisting of titanium nitride, hydroxypropyl methylcellulose, and LiCl (THL) were developed and demonstrated to have a unique high water uptake of 1.18–6.43 gwatergsorbent−1 at 25 °C and 15%–90% relative humidity. To validate the feasibility of THL for moisture extraction, reasonable energy management of the water harvester was carried out, and the potential daytime outdoor water collection in summer and winter reached 3.82 and 2.98 lwater kgsorbent−1 day−1, respectively, at relative humidity of ∼60% and ∼30%. The implementation strategy proposed in this paper provides a reliable path for solar-driven AWH, confirming the adaptability and possibility of achieving high yield freshwater production in real scenarios of practical significance.

Personal Thermoregulation by Moisture-Engineered Materials.

Personal thermal management can effectively manage the skin microenvironment, improve human comfort, and reduce energy consumption. In personal thermal-management technology, owing to the high latent heat of water evaporation in wet-response textiles, heat- and moisture-transfer coexist and interact with each other. In the last few years, with rapid advances in materials science and innovative polymers, humidity-sensitive textiles have been developed for personal thermal management. However, a large gap exists between the conceptual laboratory-scale design and actual textile. Here, moisture-responsive textiles based on flap opening and closing, those based on yarn/fiber deformation, and sweat-evaporation regulation based on textile design for personal thermoregulation are reviewed, and the corresponding mechanisms and research progress are discussed. Finally, the existing engineering and scientific limitations and future developments are considered to resolve the existing issues and accelerate the practical application of moisture-responsive textiles and related technologies.

Solar steam-driven membrane filtration for high flux water purification

In recent years, interfacial solar steam generation has shown great potential for desalination with high solar-to-steam conversion efficiency. However, the freshwater production rate is still limited by the substantial latent heat of water evaporation and condensation efficiency. Here we designed an interfacial solar steam-driven reverse osmosis/nanofiltration device that generates high pressure that pushes water molecules through a filtration membrane to achieve separation from ions. The solar steam-driven reverse osmosis device reaches a water production rate as high as 81 kg m−2 h−1 under 12 sun illumination. Moreover, a theoretical model indicates that there still exists attractive room to further improve the freshwater output by optimizing the thermal insulation and expansion ratio of the device. This work paves a new way to design highly efficient miniaturized or decentralized drinking water devices. Reverse osmosis of seawater is a popular though energy demanding process to produce freshwater. Interfacing reverse osmosis membranes with solar steam generation shows potential for a more efficient desalination process.

Energy-saving and emission reduction system of data center heat pipe based on latent heat of water evaporation

To address the current problem of high energy consumption in data centers, this paper proposes a data center heat pipe air-conditioning system based on the latent heat of water evaporation, which uses the latent heat of water evaporation for cooling by creating a low pressure environment to evaporate large amounts of water. In order to verify the effect of the system, a heat pipe test bench based on the latent heat of water evaporation was designed and built. Compared with the traditional heat pipe in the data center for heat dissipation, the performance and economy of the water evaporation latent heat pipe system designed in this paper are analyzed experimentally. A multi-physics coupled model of water evaporation latent heat pipe air-conditioning based on COMSOL Multiphysics was established to simulate and study the temperature field and velocity field distribution of water evaporation latent heat pipe air-conditioning system in data centers. The research shows that: - Under the designed test conditions, compared with the traditional heat pipe system, the water evaporation latent heat pipe air conditioner can conduct 2540 kJ more heat in one day in an outdoor environment of 24?C. - At an ambient temperature of 35?C and an indoor temperature of 25.8 ?C, the cooling capacity of the heat pipe in the data center water evaporation latent heat pipe air-conditioning system is twice the cooling capacity of the air conditioner, and the heat pipe can work efficiently regardless of the outdoor ambient temperature. - The energy-saving effect of the latent heat pipe of water evaporation in the data center has a significant effect on air conditioners with an energy efficiency rating (EER) lower than 2.5-4.4. It can improve the energy efficiency of level 5 with an EER of 2.5 to level 2 with an EER of 3.22, greatly reducing the power consumption of the data center air-conditioning system. When the EER of the air conditioner exceeds 4.4, the coefficient of performance of the data center water evaporation latent heat pipe air-conditioning system will be lower than that of the air conditioner itself.

Rational Heat Schemes Using Condensing Boilers in Local Heat Supply Systems

Within the framework of this publication, thermal diagrams of autonomous heat supply systems using condensing heat generators are considered. The insignificant Russian experience of using small condensation boilers in residential construction shows that it is often used to simply replace traditional equipment with condensation technology in existing (or traditionally used) heat schemes, for example, with protection of the boiler from “cold return” by recirculating heat carrier or installing a hydraulic regulator. The consequence of this is almost completely lost the effect of the use of condensing boilers. At the same time, even using the heating temperature schedule of quality regulation 80-60°C and applying water heating to the DHW target up to 45°C you can achieve the effect of the boiler operation in the condensation mode, depending on the construction area, up to 75% of the total working time per year, generating about 70% of thermal energy in the annual cycle. However, it must be borne in mind that the efficiency of the condensing boiler is determined by the part of the latent heat of water vapor in the combustion products, which can be obtained with partial condensation. If this part is small, for example, when cooling the flue gases to 50-45°C (on gas), then the efficiency gain is only 1-3%.

Experimental Study on a Ceramic Membrane Condenser with Air Medium for Water and Waste Heat Recovery from Flue Gas.

Ceramic membrane condensers that are used for water and waste heat recovery from flue gas have the dual effects of saving water resources and improving energy efficiency. However, most ceramic membrane condensers use water as the cooling medium, which can obtain a higher water recovery flux, but the waste heat temperature is lower, which is difficult to use. This paper proposes to use the secondary boiler air as the cooling medium, build a ceramic membrane condenser with negative pressure air to recover water and waste heat from the flue gas, and analyze the transfer characteristics of flue gas water and waste heat in the membrane condenser. Based on the experimental results, it is technically feasible for the ceramic membrane condenser to use negative pressure air as the cooling medium. The flue gas temperature has the most obvious influence on the water and heat transfer characteristics. The waste heat recovery is dominated by latent heat of water vapor, accounting for 80% or above. The negative pressure air outlet temperature of the ceramic membrane condenser can reach 50.5 °C, and it is in a supersaturated state. The research content of this article provides a new idea for the water and waste heat recovery from flue gas.

Relationship of Lagrangian microscopic energy efficiency of a gas parcel in a thermoacoustic engine to macroscopic one

As suggested by much smaller microscopic Carnot efficiency of a transversely oscillating gas-parcel in a thermoacoustic engine than macroscopic Carnot efficiency of the whole stack, the Lagrangian microscopic energy efficiency of a gas parcel is different from the macroscopic energy efficiency of the whole stack. The relationship of the former to the latter is theoretically discussed. Furthermore, it is numerically shown that the microscopic energy efficiency in a wet stack is considerably lower than that in a dry stack due to both heat loss by latent heat of water evaporation and more heat influx associated with evaporation.

Theoretical Analysis of A Nozzle Condensation-Drying Cycle.(Dept.M)

The energy required for industrial drying processes consumed by a conventional dryers are essentially thrown away without the ability to recover the latent heat of water vapor in the air, significant reductions in dryer energy usage cannot be made. In an attempt to recover the latent heat of the water vapor, a closed drying cycle is proposed, which uses a nozzle as the means to recover this energy from moist-saturated air. This nozzle condensation drying cycle (NCDC) is composed of the following components: dryer, nozzle, diffuser, air water separator, heat exchanger and compressor. Analysis of this drying cycle shows that ideally this cycle requires lower energy compared with an ideal open cycle heated dryer or a heat pump dehumidification cycle. However, which equipment isentropic efficiencies are included, the energy costs are approximately a third of the cost of the ideal open cycle healed dryer. The cycle can be operated at varying conditions, allowing for a single design to be utilized for various ap plications. Other advantages are in applications that require drying of hazardous liquids from a product.

Raising of fuel utilization efficiency in the contact heat exchange boilers

The relevance of the study is due to low effective utilization of heat of fuel combustion in existing heat generators, in particular, boiler units intended for heat supply to industrial enterprises and residential buildings. Another important research area of the study is the ascertaining ability of a boiler to operate on raw water, which hasn’t undergone a process of preliminary reduction of hardness. The article reveals the use of latent heat of water vapor contained in the exhaust gases in all models of existing boiler units. The authors proposed and described a method for the effective utilization of the latent heat by means of contact heating of the coolant.

Realization of Low Latent Heat of a Solar Evaporator via Regulating the Water State in Wood Channels.

Solar-driven interfacial evaporation with heat localization is an efficient method for large-scale water purification. However, due to the high latent heat of water evaporation and dilute solar flux (1 kW m-2), the solar steam productivity is low. Here, the latent heat of water evaporation was reduced because of the capillary water state in wood channels. We constructed a wood-based 3D solar evaporator via regulating the hydrophilicity of a surface of burnt wood and adjusting the height of the wood above a water surface. Capillary water was formed in the light absorption layer, resulting in the latent heat decrease from 2444 to 1769 J g-1. A high evaporation rate of 1.93 kg m-2 h-1 under one sun irradiation (1 kW m-2) was achieved. Together with the environmental energy-harvesting ability, the evaporation rate reached 3.91 kg m-2 h-1 (per occupied area), which is among the best values ever reported. More importantly, the 3D solar evaporator works efficiently in a water collection device, yielding 2.2 times more water than that of a common interfacial evaporator.

Demonstration of 99% CO2 Removal from Coal Flue Gas by Amine Scrubbing

Abstract A post-combustion CO2 capture campaign was conducted at the National Carbon Capture Center (NCCC) with 5 m PZ (piperazine) using the advanced flash stripper configuration. 68 steady-state runs were identified and 90% or to 99.1% CO2 removal was achieved with a 12 m of packing in the absorber. A 20% increase in solvent rate enhanced CO2 removal from 90% to 99% and the rich loading decreased from 0.40 to 0.38 mol CO2/mol alkalinity. With high removal, the temperature profile from modeling indicated there was a mass transfer pinch in the absorber, which means 12 m packing is more than needed even for 99% removal. The rich loading did not decrease significantly at high CO2 removal, therefore the energy cost for regeneration remained practically unchanged. The material balance around the absorber based on CO2 loaded calculated from density and viscosity closed within 2.3%. The rate-based Aspen Plus® model under-predicted the number of transfer units in the absorber by an average of 16%. This was caused by the difference between CO2 concentration measured by titration and calculated from density and viscosity. With the advanced flash stripper (AFS), the process heat duty was between 1.9 and 2.5 GJ/t CO2 and did not increase more than 5% at higher CO2 removal. Due to the fast reaction kinetics of PZ, the 12 m absorber was overdesigned for 99% CO2 removal and the rich loading was unchanged at high removal. Further, the superior design of the AFS recovered the latent heat of water vapor and minimized the energy consumption for solvent regeneration. Therefore, it is feasible to capture 99% of the CO2 from coal-fired flue gas with PZ scrubbing at a reasonable energy cost.

Demonstration of 99% CO2 removal from coal flue gas by amine scrubbing

A post-combustion CO2 capture campaign was conducted at the National Carbon Capture Center (NCCC) with 5 m PZ (piperazine) using the advanced flash stripper configuration. 68 steady-state runs were identified and 90% or to 99.1% CO2 removal was achieved with a 12 m of packing in the absorber. A 20% increase in solvent rate enhanced CO2 removal from 90% to 99% and the rich loading decreased from 0.40 to 0.38 mol CO2/mol alkalinity. With high removal, the temperature profile from modeling indicated there was a mass transfer pinch in the absorber, which means 12 m packing is more than needed even for 99% removal. The rich loading did not decrease significantly at high CO2 removal, therefore the energy cost for regeneration remained practically unchanged.The material balance around the absorber based on CO2 loaded calculated from density and viscosity closed within 2.3%. The rate-based Aspen Plus® model under-predicted the number of transfer units in the absorber by an average of 16%. This was caused by the difference between CO2 concentration measured by titration and calculated from density and viscosity.With the advanced flash stripper (AFS), the process heat duty was between 1.9 and 2.5 GJ/t CO2 and did not increase more than 5% at higher CO2 removal. Due to the fast reaction kinetics of PZ, the 12 m absorber was overdesigned for 99% CO2 removal and the rich loading was unchanged at high removal. Further, the superior design of the AFS recovered the latent heat of water vapor and minimized the energy consumption for solvent regeneration. Therefore, it is feasible to capture 99% of the CO2 from coal-fired flue gas with PZ scrubbing at a reasonable energy cost.

Highly efficient solar vapour generation via hierarchically nanostructured gels.

Solar vapour generation is an efficient way of harvesting solar energy for the purification of polluted or saline water. However, water evaporation suffers from either inefficient utilization of solar energy or relies on complex and expensive light-concentration accessories. Here, we demonstrate a hierarchically nanostructured gel (HNG) based on polyvinyl alcohol (PVA) and polypyrrole (PPy) that serves as an independent solar vapour generator. The converted energy can be utilized in situ to power the vaporization of water contained in the molecular meshes of the PVA network, where water evaporation is facilitated by the skeleton of the hydrogel. A floating HNG sample evaporated water with a record high rate of 3.2 kg m-2 h-1 via 94% solar energy from 1 sun irradiation, and 18-23 litres of water per square metre of HNG was delivered daily when purifying brine water. These values were achievable due to the reduced latent heat of water evaporation in the molecular mesh under natural sunlight.

6-3.水分蒸発を利用したクーラー室外機の排熱抑制に関する研究((1)省エネルギー機器開発,Session 6 省エネルギー)

6-3.水分蒸発を利用したクーラー室外機の排熱抑制に関する研究((1)省エネルギー機器開発,Session 6 省エネルギー)

A self-sustaining pyroelectric nanogenerator driven by water vapor

Energy harvesting via pyroelectric nanogenerators (PNGs) is emerging as an attractive way to utilize waste heat. However, most of current PNGs need mechanical or electrical alternating devices to achieve the fast temperature oscillation, which is the key for PNGs to work. Herein we report a self-sustaining polymeric PNG driven by water vapor, without any energy-consuming alternating devices. Due to the high latent heat of water vapor, a fast temperature oscillation up to 23°C/s was achieved by automatic water condensation and evaporation on the surface of the PNG. Thus, the PNG based on commercial polyvinylidene difluoride polymer was able to output an open-circuit voltage of 145V and a short-circuit current of 0.12μA/cm2. The peak power density was 1.47mW/cm3 by volume and 4.12μW/cm2 by area, which is comparable to previously reported PNGs relying on alternating devices. Our PNG could provide uninterrupted electricity to drive a low-power electronic device (such as a digital watch) to work continuously. The electricity could also be stored in a capacitor for high-power tasks, such as flashing multiple blue LED lights once per minute. The self-sustaining PNG driven by water vapor provides a new strategy for efficiently recovering energy from hot water vapor that are wasted in industry and in our daily life.

Using thermal balance model to determine optimal reactor volume and insulation material needed in a laboratory-scale composting reactor

A comprehensive model of thermal balance and degradation kinetics was developed to determine the optimal reactor volume and insulation material. Biological heat production and five channels of heat loss were considered in the thermal balance model for a representative reactor. Degradation kinetics was developed to make the model applicable to different types of substrates. Simulation of the model showed that the internal energy accumulation of compost was the significant heat loss channel, following by heat loss through reactor wall, and latent heat of water evaporation. Lower proportion of heat loss occurred through the reactor wall when the reactor volume was larger. Insulating materials with low densities and low conductive coefficients were more desirable for building small reactor systems. Model developed could be used to determine the optimal reactor volume and insulation material needed before the fabrication of a lab-scale composting system.

Cloud-scale simulation study on the evolution of latent heat processes of mesoscale convective system accompanying heavy rainfall: The Hainan case

This paper investigates the structure of latent heat budgets and dynamical structure of mesoscale convective systems (MCS) accompanying heavy rain using a cloud-scale model WRF simulation for the Hainan case. Results show that: (1) according to the fractions skill score and HK scores, the WDM6 scheme is more suitable to predict the rainfall than other microphysical schemes. (2) During the lifetime of MCSs, the top two heating microphysical processes are water vapor condensed into cloud water and water vapor condensed into rainwater. The total latent heat is closely related to the top two heating processes. However, the change of latent heat released by some microphysical processes is not identical with the different rainfall processes. (3) The total latent heat of MCS1 increases during the short life, while the total latent heat of MCS2 and MCS3 reach maximum during the mature stage. The difference is mainly caused by the latent heat of water vapor condensed into cloud water and rainwater. The total latent heat released by cond and rcond of MCS1 is smallest during the mature stage, while it is largest during the mature stage of MCS2 and MCS3. (4) The vertical motions are different with different MCSs. The descending motion of the short-lived process (MCS1) is strongest during the mature stage. It caused the smallest latent heat released by water vapor condensed into cloud water and rainwater at the same period. Besides, there are some differences in the change of latent heat released by microphysical processes of MCS2 and MCS3, which are closely related to the drag force of the vertical motion.

Study on LiBr-Liquid Desiccant System Driven by Heat Pump

Humidity is one of the most important factors for human thermal comfort, and the liquid desiccant system is an effective dehumidification mode, especially for renewable energy such as solar energy or waste heat acting as the driving heat. The whole system performance is depended on high absorption (or desorption) of water vapor in absorption (or desorption) process. Moreover, the cooling and heating energy should apply to absorption and desorption process respectively since the latent heat of water vapor transferred between air and liquid desiccant solution. However, in a real system, cooling and heating energy are always independent and matching imperfectly. In this study, heat pump is applied in a liquid desiccant system as the cooling and heating energy which can use thoroughly. Moreover, lithium bromide is acted as the working solution which is focused on experimentally test. Furthermore, different operating conditions including moist air temperature, air humidity, air flow et al in absorber and in generator are measured in the experiment test. Consequently, the experimental results is given and analyzed.