Dehumidification Capacity Research Articles

Determination of Dehumidification Capacity of Water Wall with Controlled Water Temperature: Experimental Verification under Laboratory Conditions

Water elements with flowing water on the surface are common in buildings as a form of indoor decoration, and they are most often perceived as passive humidifiers. However, by controlling water temperature, they can be also used for air dehumidification. The dehumidification capacity of indoor water elements was investigated experimentally under laboratory conditions. For the experimental verification of dehumidification capacity, a water wall prototype with an effective area of falling water film of 1 m2 and a measuring system were designed and developed. A total of 15 measurements were carried out with air temperatures ranging from 22.1 °C to 32.5 °C and relative humidity from 58.9% to 85.6%. The observed dehumidification capacity varied in the range of 21.99–315.36 g/h for the tested measurements. The results show that the condensation rate is a dynamic process, and the dehumidification capacity of a water wall strongly depends on indoor air parameters (air humidity and temperature). To determine the dehumidification capacity of a water wall for any boundary conditions, the equations were determined based on measured data, and two methods were used: the linear dependence between humidity ratio and condensation rate, and nonlinear surface fitting based on the dependence between the condensation rate, air temperature, and relative humidity.

Thermal-hydraulic performance investigation of an aluminium plate heat exchanger and a 3D-printed polymer plate heat exchanger

• A novel polymer plate heat exchanger is fabricated using a 3D-printing method. • Domestic scale polymer and aluminium heat exchangers fabricated and tested. • Both heat exchangers display very similar dry surface performance. • Polymer heat exchanger demonstrates good dehumidification performance. • Dehumidification capacity is 25% less in polymer heat exchanger compared to metal. Polymer heat exchangers have gained interest due to their favourable qualities over metal heat exchangers, including being lightweight, low cost, and having reduced fouling and corrosion. In this work, two identical prototype, counter-flow, air-to-air, plate heat exchangers were fabricated, one from aluminium and the other from thermoplastic using a fused filament fabrication 3D printer. The results have shown that under dry operating conditions, typical of certain domestic appliances, both heat exchangers demonstrate similar thermal characteristics where the thermal effectiveness is greater than or equal to 0.50. Under wet conditions, the aluminium heat exchanger out performs the polymer heat exchanger, and this effect increases with an increasing temperature difference between the heat exchanger’s hot-side inlet and cold-side inlet. In terms of both thermal and dehumidification capacity, the aluminium heat exchanger can outperform the polymer heat exchanger by as much as 22% and 38%, respectively. Despite the lower performance of the polymer heat exchanger, the absolute capacity and dehumidification rate are still reasonable and show promise for the use of polymer heat exchangers as a good alternative to metal heat exchangers in heat recovery applications in domestic appliances, for example, in clothes dryers or dehumidifiers, where operation takes place under both dry and wet operating conditions.

Study on heat transfer and dehumidification performance of desiccant coated microchannel heat exchanger

The desiccant coated heat exchanger is capable of dealing with sensible load and latent load of hot and humid air. The heat and moisture transfer coefficients of the desiccant coated microchannel heat exchanger (DMHE) are derived theoretically and increase with the airflow velocity in the heat exchanger. The microchannel structure optimization is implemented. It is found that the smaller the fin pitch and flat tube pitch are, the greater the heat and moisture transfer coefficients are. The thicker the desiccant coating, the larger the moisture transfer coefficient, the smaller the heat transfer coefficient. The experimental results show that the dehumidification capacity and the thermal performance coefficient of DMHE are 1.59 kgh−1 and 2.09 respectively with the regeneration hot water at 60 °C. The Taguchi method is employed to evaluate the influence of cooling water temperature, airflow velocity, and water flow rate on the dehumidification performance of DMHE. The airflow velocity is the main factor affecting the dehumidification capacity, where lower cooling water temperatures and faster the airflow velocity increases the dehumidification performance.

Performance Analysis of Hybrid Desiccant Cooling System with Enhanced Dehumidification Capability Using TRNSYS

In a field test of a hybrid desiccant cooling system (HDCS) linked to a gas engine cogeneration system (the latter system is hereafter referred to as the combined heat and power (CHP) system), in the cooling operation mode, the exhaust heat remained and the latent heat removal was insufficient. In this study, the performance of an HDCS was simulated at a humidity ratio of 10 g/kg in conditioned spaces and for an increasing dehumidification capacity of the desiccant rotor. Simulation models of the HDCS linked to the CHP system were based on a transient system simulation tool (TRNSYS). Furthermore, TRNBuild (the TRNSYS Building Model) was used to simulate the three-dimensional structure of cooling spaces and solar lighting conditions. According to the simulation results, when the desiccant capacity increased, the thermal comfort conditions in all three conditioned spaces were sufficiently good. The higher the ambient temperature, the higher the evaporative cooling performance was. The variation in the regeneration heat with the outdoor conditions was the most dominant factor that determined the coefficient of performance (COP). Therefore, the COP was higher under high temperature and dry conditions, resulting in less regeneration heat being required. According to the prediction results, when the dehumidification capacity is sufficiently increased for using more exhaust heat, the overall efficiency of the CHP can be increased while ensuring suitable thermal comfort conditions in the cooling space.

Field synergy analysis on heat and moisture transfer processes of desiccant coated heat exchanger

The theoretical analysis of the field synergy is tried to apply to desiccant coated heat exchangers (DCHEs) to clarify its coupled heat and moisture transfer characteristics and the way to enhance the characteristics. In this paper, the heat and moisture transfer model of DFHE is established and verified by comparison with experimental data. Three field synergy angles between temperature gradient, velocity vectorand moisture gradient are introduced and calculated for different types of DFHEs with different air velocities. Through the analysis, the field synergy method is proved available for analysing the coupled heat and mass transfer process of DCHE. Different heat and mass transfer performance index of different structure sizes of DFHEs are analysed. By comparing the sensible heating capacity, dehumidification capacity, Re and field synergy angles of them, the optimization design direction of structure size is obtained. The DFHE with higher ratio between total transfer area and total volume is proved to display better performances. So by optimazing the types of DCHE, DMHE is introduced, and the superiority of DMHE is proved. And the reason why DMHE presents higher heat and mass transfer capacity is illustrated.

Design Of Hvac System For Beverage Industry

The objective of this project is to design HVAC system for beverage industry. Firstly, the requirements and Design Basic Report (DBR) of the HVAC system are defined. DBR gives a clear picture of filtration level, required conditions, Cost-effectiveness, Energy conservation, Fire safety, Indoor air quality (IAQ) and Ease of maintenance. Air Flow diagram makes you understand the Air Handling Unit (AHU) zoning for the HVAC system. Beverage industry zoning areas include pulp cutting, blending and homogenizer, filler, anteroom, CIP room and pasteurization. Design calculation provides the data for recirculation and 100% fresh air supply and return system. Processing line is having sequence process rooms and each room have its own individual cooling load calculations. Design calculation gives the value of Tonnage of refrigerant, CFM and Dehumidification capacity of the system. Ducting layout issue the best routing for the site installation to distribute the air from the supply and return system. It includes the details of Damper, Ducting, Duct Insulation and Instrumentation to use in the facility. Supply and return system placement are also covered in this layout drawing and the Bill of Quantity is prepared.

Research on falling film dehumidification performance of microencapsulated phase change materials slurry

In the process of liquid desiccant dehumidification, the temperature-rise of the desiccant solution caused by moisture absorption will seriously affect the dehumidification capacity and performance. It is expected that the temperature rise of solution can be restrained by adding microencapsulated phase change materials (MicroPCMs) into the liquid desiccant solution. In this paper, based on computational fluid dynamics (CFD) method, two-dimensional models of flat plate and corrugated plate falling film dehumidification of the microencapsulated phase change material slurry (MPCMS) were developed and validated. The dynamic boundary method was used to determine the interfacial mass transfer coefficient. The influences of several factors on the dehumidification performance, including the concentration of MicroPCMs, the inlet temperature of the MPCMS and the falling film plate configuration, were investigated. The results show that, adding MicroPCMs into the liquid desiccant solution is beneficial to the dehumidification performance improvement. The inlet temperature of MPCMS is a very critical variable. When the inlet temperature of the slurry is in the phase transformation temperature range of MicroPCMs, with the adding of the microcapsule, the temperature rise in dehumidification process can be restrained, and the moisture removal performance can be improved significantly. When the MPCMS inlet temperature is at the phase transformation onset point, and the concentration of MicroPCMs is 5%, the water condensation rate is 14.2% higher than that of the base solution. Moreover, it’s not that the more microcapsules added, the larger mass transfer coefficient is. There is an optimum concentration of MicroPCMs to achieve the maximum interfacial mass transfer coefficient. The corrugated plate configuration is more conducive to the dehumidification enhancement by the MPCMS.

Optimization of operational parameters of a liquid desiccant system integrated with a heat recovery unit

The liquid desiccant system can make a contribution to a sustainable path for maintaining healthy and comfortable indoor environments. The liquid desiccant system has two major subsystems, dehumidification and regeneration. Cold energy recovery was achieved by passing the indoor exhaust air through an air hose to import and dehumidify the inlet air prior to the precooling stage/phase. Heat energy recovery was effected by a heat exchanger. The system simply recycles the heat energy without any moisture transfer in the air, preheating the inlet air to the regeneration subsystem. Furthermore, based on the dehumidification capacity, regeneration capacity and the personal comfort criteria, the optimal match of air volume was selected. The results show the condition with the dehumidification airflow of 2600 CMH and the return air ratio in the range from 75% to 80% range was suitable for personal comfort. In this case, the matching regeneration airflow was 1600 CMH without heat recovery, so that the air flow rates for dehumidification and regeneration are optimal.

Experimental Investigation of Desiccant Dehumidification Cooling System for Climatic Conditions of Multan (Pakistan)

In this study, experimental apparatus of desiccant dehumidification was developed at lab-scale, using silica gel as a desiccant material. Experimental data were obtained at various ambient air conditions, while focusing the climatic conditions of Multan (Pakistan). A steady-state analysis approach for the desiccant dehumidification process was used, and thereby the slope of desiccant dehumidification line on psychrometric chart (ϕ*) was determined. It has been found that ϕ* = 0.22 in case of silica gel which is lower than the hydrophilic polymeric sorbent, i.e., ϕ* = 0.31. The study proposed two kinds of systems, i.e., (i) standalone desiccant air-conditioning (DAC) and (ii) Maisotsenko-cycle-assisted desiccant air-conditioning (M-DAC) systems. In addition, two kinds of desiccant material (i.e., silica gel and hydrophilic polymeric sorbent) were investigated from the thermodynamic point of view for both system types, using the experimental data and associated results. The study aimed to determine the optimum air-conditioning (AC) system type, as well as adsorbent material for building AC application. In this regard, perspectives of dehumidification capacity, cooling capacity, and thermal coefficient of performance (COP) are taken into consideration. According to the results, hydrophilic polymeric sorbent gave a higher performance, as compared to silica gel. In case of both systems, the performance was improved with the addition of Maisotsenko cycle evaporative cooling unit. The maximum thermal COP was achieved by using a polymer-based M-DAC system, i.e., 0.47 at 70 °C regeneration temperature.

Performance Study of a Hybrid Heat Pump Dryer based on Numerical Analysis and Experimental Set-up

Seafood, especially sea cucumbers and oysters are an expensive delicacy in several Asian countries. Traditional sun-drying of these products takes 3 to 4 days and fetches a lower market price. Modern industrial drying machines used for seafood drying are unable to dry sea cucumbers and oysters without texture and color degradation as they are delicate, temperature-sensitive and have longer drying time. An economical drying system that does not cause texture or color degradation is the heat pump drying system and is commonly applied for agriculture and fabric drying. In this study, the heat pump technology is applied to develop two hybrid dryer models (bottom discharge and front discharge) to dry shellfish and sea cucumbers in large scale for storage and transportation. Each model is tested in a laboratory-scale with wet sponges as input material for its dehumidification capacity and the power consumed to attain the target dryness. The front discharge model is found to have rapid drying capability and economy. Computational fluid dynamic tools are used to study the hot air flow behavior and flow uniformity inside the drying chamber. The front discharge model showed smooth uniform flow over the trays with fewer losses in the flow velocity. The front discharge model with higher drying rate, lower power consumption and uniform airflow distribution over the trays is chosen for the industrial-scale design.

A modeling study on a direct expansion based air conditioner having a two-sectioned cooling coil

In small- to medium- scale buildings such as residences and retails located in hot and humid regions, direct expansion based air conditioning systems are widely used for the control of indoor thermal environment. However, to simultaneously control indoor air temperature and humidity using direct expansion air conditioning systems, additional and costly provisions/installation spaces are usually required. Therefore, to address the inadequacies encountered in previous related studies, based on multi-evaporator technology, a novel direct expansion based air conditioning system having a two-sectioned evaporator or cooling coil (TS-DXAC) was proposed to provide variable dehumidification capacity and improved indoor air distribution. In this paper, the development of a steady-state physics-based mathematical model for the novel TS-DXAC system is presented. The model was developed by referring to the existing sub-models for the key system components, such as a compressor, a condenser and an evaporator, which were currently available in open literature. The developed model was experimentally validated using a purposely established prototype experimental TS-DXAC system, with the differences between experimental and predicted results of less than 6%. Using the validated TS-DXAC model, a follow-up modeling study was carried out on optimizing the sizes of the two sections. The simulation results suggested that a lower surface area ratio for the two sections (Rs) can lead to a larger variation ranges of both output total cooling load (TCC) and equipment sensible heat ratio (E SHR). For example, at the inlet state of 26 °C and 50% relative humidity, when Rs was altered from 1:1 to 1:3, the variation range for TCC was increased by 33%, and that for E SHR by 51%, which was beneficial to better dehumidification.

Study on the uneven distribution of vertical space humidity in a rocket testing workshop

In view of the problem of inconsistent air-conditioning delivery and uneven distribution of vertical space humidity in a rocket testworkshop at a coastal launch site, this paper analyzes the cause and mechanism of the problem based on the characteristics of high space air distribution, test plant structure and air-conditioning system. And puts forward the specific measures such as adjusting high-rise space air delivery target, optimizing the air-conditioning control strategy and improving the unit’s dehumidification capacity. These measures provide support for the solution of the problem and the optimal design and transformation of air-conditioning.

Performance evaluation of a hybrid solar powered rotary desiccant wheel air conditioning system for low latitude isolated islands

Low latitude isolated islands have the climate characteristic of high temperature and high humidity, but in short of conventional energy. This study proposes a novel hybrid solar powered rotary desiccant wheel air conditioning (SRDAC) system to improve the indoor temperature of buildings on low latitude isolated islands. The SRDAC system combines photovoltaic power generation, solar thermal collector, vapor compressed cooling system and a two stage rotary desiccant wheel system. In this study, mathematical models of the subsystems of the SRDAC system are established firstly. MATLAB was used to analyze the performance of the SRDAC system, which includes the dehumidification capacity, cooling capacity, condensation heat quantity and thermodynamic performance coefficient. Then, the photovoltaic area and solar thermal collector area of the SRDAC system were matched and optimized based on meteorological parameters of low latitude isolated islands. Finally, the SRDAC system’s economic performance was analyzed. The results show that, for every 10 ℃ increase in regeneration temperature, the dehumidification capacity and cooling capacity increase by 0.9 g/kg-2.7 g/kg and 0.4 kW-1.9 kW, respectively. For every 1 g/kg increase of outdoor air moisture content, the total installed area increased by 2.2%-2.3%. The SRDAC system shows a good operating performance, can better adapt to the climate characteristics of low latitude isolated islands, and effectively reduces the temperature and moisture content of the air. This study serves as a reference for the application of SRDAC system in extremely hot and humid climates.

Detailed experimental analysis of the energy performance of a desiccant wheel activated at low temperature

Desiccant dehumidification systems, such as those using desiccant wheels (DW), are an interesting alternative to conventional dehumidification systems based on vapor-compression cycles. The aim of this work was to obtain experimentally the performance of a DW activated at low temperature along the heat and mass transfer surface under different working conditions. The air temperature and humidity were measured at 32 different points, in order to analyse the performance of the DW at different circular sectors of the rotor.The results showed that the surface temperatures of the desiccant material on the process side decreased when the rotation speed decreased. Conversely, the surface temperatures of the desiccant material on the regeneration side increased when the rotation speed decreased.The minimum outlet process air temperatures and the maximum process air dehumidification were obtained in the circular sector closest to the regeneration side. In this circular sector the highest efficiency values were obtained. The number of circular sectors where the highest efficiency values were obtained increased when the rotation speed or air flow rates increased. Using these data, the wheel control strategy could be designed to increase the dehumidification capacity.

Experimental investigation of the dehumidification performance of a metal-organic framework MIL-101(Cr)/ ceramic fibre paper for use as a desiccant wheel

Abstract To improve the dehumidification performance and perform regeneration of desiccant wheels at low temperatures, various MIL-101(Cr)/ceramic fibre paper (MIL-101/CFP) samples, as dehumidification materials, were developed through a brush-coating method using ceramic fibre paper as the carrier. The dehumidification materials were then characterized and analysed by nitrogen adsorption-desorption, scanning electron microscopy (SEM), powder X-ray diffraction (PXRD) and thermal gravimetric analysis. The dynamic dehumidification performance and dehumidification-regeneration cycles of the materials were studied. The results show that MIL-101/CFP has high purity and satisfactory thermal and hydrothermal stability. The dehumidification experiment confirms that MIL-101/CFP with a coating ratio C of 70% maintains a high equilibrium dehumidification capacity and presents a dehumidification capacity that is 100 mg/g higher compared to that of commercially available desiccant wheel materials.

Dehumidification assessment for desiccant coated heat exchanger systems in different buildings and climates: Fast choice of desiccants

Energy conservation and emission reduction have become a global consensus. As a novel promising energy-saving dehumidification technology, desiccant coated heat exchanger (DCHE)-based air conditioning systems have attracted immense attention recently. This paper provides a quick and reasonable selection of desiccant materials for DCHE systems using water as the cooling medium in different buildings and climates. By the theoretical calculation of moisture needed to be removed in three types of buildings (offices, residential buildings and restaurants) and the analysis of the dehumidification capacity of desiccants in DCHEs reported in the literature, optimal desiccants for different building types and ambient air conditions under given parameters are recommended. Salt-supported porous composite desiccants possess flexible dehumidification performance and can be utilized in most climates and building types, except for extremely humid indoor environments with high requirement for fresh air. Zeolites are especially suitable for return air states, American Air-Conditioning and Refrigeration Institute (ARI) summer and ARI humid climates in buildings with moderate indoor moisture gain, such as offices or residential buildings. Polyelectrolytes can be applied in humid climates and buildings with high indoor wet loads, such as restaurants. This paper offers a promising route to the applications of desiccant materials in novel energy-saving air conditioning technologies.

Simulation analysis and optimization research on cooling and dehumidifying effects for evaporator

The improvement performance of refrigerating dehumidification system was theoretically discusses based on a dehumidification model. The influence of evaporator inlet wind speed, dry bulb temperature and relative humidity on dehumidification were analysed by the model. The results show that, when inlet air temperature and humidity were kept constant, the dehumidification capacity increased first and then decreased with increase of the wind speed. When the moisture content and the wind speed of the inlet air were kept constant, the dehumidification capacity gradually decreased with increase of the inlet air dry bulb temperature. The inlet air dry bulb temperature was between 21-36?C and the relative humidity was between 40% and 85%, the difference between the inlet air wet bulb temperature and the evaporation temperature at the optimum COP was about 10?C. There was a nearly linear relationship between the corresponding evaporation temperature at the optimal COP and the evaporation temperature with the maximum dehumidification capacity, compared with the test value, the error was less than 10%.

Determination of cost-efficient cooling power range for improving the performance of internally cooled ultrasonic atomization liquid desiccant dehumidifiers

Liquid desiccant dehumidifiers (LDDs) can be improved by adding internal cooling. However, the addition of excessive cooling power may deteriorate the system‘s cost-efficiency, whereas the addition of insufficient cooling power leads to negligible performance improvements. The objective of this study is to determine the suitable cost-efficient cooling power range for improving the performance of internally cooled LDDs (IC-LDDs). A novel method and a set of criteria related to the moisture removal rate, cooling-power efficiency ( ηc) and coefficient of dehumidification performance from cooling power ( DCOPcooling) were proposed to determine cost-efficient cooling power. The internally cooled ultrasonic atomization liquid desiccant system (IC-UADS), together with a well-validated model based on the conservation laws of mass and energy and the sensible heat balance, was adopted to demonstrate the analysis. The results showed that, although the dehumidification performance improves with increasing cooling power, the improvement rate decreases, while ηcand DCOPcoolingdecline quickly (by 87.9%). For cost-efficient improvement, the necessary power proportion of internal cooling to the system‘s target dehumidification capacity tends to be stable, which was about 29% for the IC-UADS, and independent of the operating conditions. The results may help to determine the reasonable cooling power range for cost-efficient improvement of IC-LDDs.

Performance characteristics of a novel internally-cooled plate membrane liquid desiccant air dehumidification system

An air dehumidification system with internally-cooled plate membrane-based liquid desiccant dehumidifier is presented. The novel system can effectively dehumidify the ambient air by the internally-cooled dehumidifier. On the other hand, the dehumidifier and regenerator are in independent operation due to the separate solution passage, which makes the system more flexible and energy saving. In this research, heat and mass transfer processes in the dehumidifier, the regenerator, the air-cooled water chiller, and other key components are modeled in detail. Based on these sub-models, the whole system model is established and solved. An experiment is carried out to validate the theoretical model and the calculated results agree with the experimental data well. The impacts of main operating parameters on the system performance (e.g. specific dehumidification power, coefficient of performance and dehumidification) are investigated numerically. The results show that the specific dehumidification power of the system at design condition reaches 263 g h−1 m−2, which indicates that the system gets strong dehumidification capacity. The COP of the whole system is in the range of 0.46–0.62 and energy consumption for regeneration occupies above 60% of total energy input.

Synthesis and Characterization of Alginate–Silica Gel Composites for Adsorption Dehumidification

Desiccant coated heat exchanger (DCHE)-based adsorption dehumidification systems have great potential for energy conservation and emission reduction. The selection of desiccant materials can greatly impact the overall performance of DCHE systems. However, the unsatisfied adsorption quantity of widely used silica gel at middle relative humidity range and the possible corrosion problem of salt-supported silica gel are bottlenecks for the engineering application. A strategy for synthesizing novel alginate–silica gel composites that have fair adsorption quantity without corrosion is demonstrated. Textural properties suggested that silica gel particles can be well distributed in the surface of composite samples with the liquid–solid mixing and post cross-linking method. Dynamic water adsorption test showed that the composite with a sodium alginate-to-silica gel mass ratio of 5:1 possessed the best water adsorption kinetics. Water adsorption quantity difference of the composite between a typical adsorption condition (80% RH) and a regeneration condition (30% RH) is more than twice that of silica gel. Dehumidification capacities of the composite-coated DCHE were 34–60% higher than those of a silica gel-coated DCHE under set simulation conditions. This method offers a promising way of material synthesis for researchers who are interested in the area of coatings, separations, dehumidification, etc.