Condenser Plates Research Articles

Air gap membrane distillation unit operated by thermoelectric module

Membrane Distillation (MD) is a promising and evolving technology with substantial potential for efficient freshwater production. However, most of the traditional MD systems typically incorporate several components, including a coolant chamber, coolant stream, coolant pump, chiller, and coolant lines. Eliminating these key components offers numerous benefits to MD systems. Therefore, this work presents an experimental investigation of a novel hybrid air gap membrane distillation (AGMD) unit coupled with thermoelectric modules (TEMs). The thermoelectric module acts as a heat pump by simultaneously providing both the heating and the cooling demands of the air gap membrane distillation unit. In the TEM-AGMD prototype, the hot surface of the TEM is deployed to heat the feed stream to be treated, while the cold side of the TEM is in close contact with the AGMD condensation plate, thereby eliminating the need for the cooling stream, coolant line, coolant pump, chiller, and coolant chamber. Thus, the investigated system exhibited fewer components and needed no pumping power for the cooling stream, resulting in a compact and an energy efficient membrane distillation (MD) system. Results from the experiment indicate that optimal system performance can be achieved by increasing the number of thermoelectric modules, implementing multi-stage membrane distillation, and intensifying the circulating feed flowrate. Furthermore, operating the thermoelectric modules at high power input boosts unit productivity but worsens the unit's specific energy consumption. Moreover, the proposed TEM-AGMD unit can achieve a minimal specific energy consumption of 962 kWh/m3. The proposed prototype boasts an easy design that enables outstanding water desalination with exceptional salt rejection and minimal power consumption. The combination of thermoelectric module with membrane distillation, capitalizing on recent advancements in MD technology, holds great promise for developing a hybrid system for decentralized water treatment and desalination.

Primarily experimental study of the energy performances of a humidification-dehumidification seawater desalination system coupled with a heat pump

The study presented in this article explores a comprehensive analysis of a humidification-dehumidification (HDH) seawater desalination system integrating a heat pump for heating seawater intended for distillation, and incorporates additional condensation plates supplied with cold seawater. This system was the subject of an experimental investigation to simultaneously evaluate the energy performance of the heat pump and the thermal behavior of the desalination unit, focusing on seawater and condensation wall temperatures, as well as the stratification of temperatures of humid air inside the unit compared to the evaporation surface. Experimental results showed an average daily production of distilled water of approximately 32.75 kg/m² per day, with an electrical consumption of 37.68 kWh/day, which was reduced to 26.72 kWh/day through the integration of photovoltaic solar energy. Based on heat and mass balance equations of all the system’s components, the study used a detailed thermodynamic model. The system's energy performance was analyzed by calculating the coefficient of performance (COP), the specific energy consumption (SEEC), and the gain output ratio (GOR), reflecting the overall energy efficiency of the HDH system coupled with the heat pump, as well as the recovery ratio (RR), indicating the proportion of the recovered water compared to the input water.

SENSITIVITY ANALYSIS ON HEAT EXCHANGERS SELECTION AND ITS INFLUENCE ON THE EFFICIENCY OF A TRANSCRITICAL CO2 CYCLE WITH INDIRECT DEDICATED MECHANICAL SUBCOOLING

This work evaluates through numerical modeling, the efficiency of an air-to-water heat pump that operates using a transcritical CO2 cycle assisted by an indirect dedicated mechanical subcooling (IDMS) cycle, with R1234ze(E) as the refrigerant. The research aims to analyze how the size of the heat exchangers used as the evaporator and the condenser for the IDMS cycle affects the overall efficiency of the system. A numerical model previously developed in Matlab® is used to modify the refrigerant and compressor of the IDMS cycle and to determine the optimal number of evaporator and condenser plates that maximize the efficiency of the whole system. The compressor model is derived from manufacturer correlations, whereas the models for the heat exchangers are obtained through a parametric study developed using IMST-ART® to characterize their operating parameters based on their number of plates and the inlet conditions of water and refrigerant. Once the models are developed, they are integrated into the model of the overall system to find the heat exchanger sizes that maximize the efficiency of the system.

Investigating condensation from humid air under mixed convection regime

A wide range of industrial applications rely heavily on heat transfer during vapor condensation from a mixture of water vapor and noncondensable gases (NCG). For a vertically-mounted condenser plate, the vapor-diffusion boundary-layer thickness is influenced by the interplay of the thermogravitational and forced flow fields, eliciting classical mixed convection scenario. This thickness in turn dictates the condensation heat and mass transfer rates. While condensation in presence of NCG under free and forced convection scenarios are well-characterized in the literature, its counterpart in the mixed convection regime is relatively uncharted. Herein, condensation from an upward stream of humid air over a vertically mounted mild steel condenser surface is characterized under different flow velocities. The free-stream flow is thus directed opposite to the thermogravitational flow induced next to the plate. We observe that with increasing the magnitude of the upward flow velocity of the free stream, the condensation heat transfer coefficient (CHTC) initially decreases until it reaches a minimum at 0.4 m/s, beyond which the CHTC rises again with the flow velocity. Using the Nusselt analogy for mixed convection for the relevant flow regimes we substantiate our experimental findings and extend the observation for predicting condensation behavior under different experimental ambient conditions.

Flow boiling characteristics in a microchannel heat sink with a condensing cover plate

Flow patterns and heat transfer characteristics during flow boiling in a microchannel heat sink with a condensing cover plate have been numerically investigated. The phase-field model is used to analyze the effects of different thermal conditions of the condensing cover plate on the bubble dynamics and heat transfer characteristics. Further, the effects of the wettabilities of the cover plate and the heating surface on the bubble evolution have been studied for different values of coolant mass flux. The condensing cover plate maintained at 50 °C significantly improves heat transfer performance with an enhancement of 23.97 % compared to the condenser plate maintained at 80 °C and a 27.35 % improvement compared to an insulated cover plate. The hydrophobicity of the condensing cover plate facilitates vapor bubble evacuation from nucleation sites, producing maximum heat transfer at a contact angle of 130°. Heat transfer performance decreases beyond the 130° contact angle due to the bubble attachment to the condensing cover plate and impeding subsequent nucleation from the cavity. The maximum heat transfer is observed for the heating surface with a contact angle of 60°. The heat transfer in the microchannel is deteriorated below and above this contact angle. At low coolant mass flux, the heat transfer is controlled by bubble nucleation. After reaching a steady state, the combined effects of bubble nucleation and liquid inertia affect the bubble generation frequency and heat transfer in the microchannel.

Development and application of a thermal model for the improved stepped solar still with a built-in passive condenser

Recently, the author proposed, fabricated, and experimentally tested an improved stepped solar still (ISS) with a built-in passive condenser, which exhibited significantly better performance than the standard version. Therefore, this paper presents a detailed transient thermal (theoretical) model for the ISS. The model is based on mass and energy balance equations for various components of the solar still, including the absorber, saline water, glass cover, insulation layer, backplate, condenser plate, and humid air in both the evaporator and condenser chambers. The model was programmed and solved using the MATLAB software. In contrast to previous studies that confined their model validation to a single day and specific conditions, this investigation rigorously validated the developed model using a comprehensive range of experimental data collected under diverse operational and meteorological conditions. Results show that, for all the conditions considered, there is very good agreement between the theoretical and experimental observations. The model has a maximum relative error of 3.7% in the estimation of daily freshwater yields, and it has a root-mean-square error (RMSE) of 4.7, 2.9, and 2.7 0C in the estimation of glass cover, absorber, and brine water temperatures, respectively. Finally, the model is used to predict and theoretically investigate the impact of meteorological design and operating parameters on the performance of the ISS. The analysis showed that a 20% increase/decrease in solar intensity would cause a corresponding increase/decrease in daily production by approximately the same amount.

Effect of vibration of the condensation plate on the heat transfer during the dropwise condensation on a hybrid hydrophilic-hydrophobic plate using electrostatic spray

ABSTRACT This research addressed the effect of dynamic stimulation and vibration at different frequencies on the heat transfer in a condensation substrate coated by Danphobix commercial coating containing aluminum particles while using deionized water as functioning fluid. The required vibrations were generated by a DC motor and measured by evaluating the rate of the DC vibration motor using a laser tachometer. Data collection was conducted in each frequency for different temperature differences. After the calculations, the heat transfer coefficient (HTC) and the heat flux were determined for each frequency and a definite temperature difference. A comparison of the results indicated an improvement in the condensation heat transfer coefficient and heat flux of these coatings under various frequencies. Such an improvement reached 22.3% around 120 Hz (compared to the vibration-free case) by increasing the vibration frequency for a fixed motor, followed by a decline. Potential applications of this research’s outcome can be in improving the performance of heat exchangers.

Research and Application of Photothermal Photovoltaic Integrated Cookware

The integrated solar thermal photovoltaic cooker utilizes slot type high-temperaturecondensing technology to heat the food inside the vacuum tube, solving the problem of food heating when going out. The photoelectric conversion and energy storage are used to reduce dependence on conventional energy, realize electric energy heating, and solve outdoor power consumption problems. This structure includes an arc-shaped parabolic condenser plate, which is located at the lower part of the vacuum tube. The upper end of the solar vacuum tube is equipped with a steamer, which is normally heated by the heat stored in the solar vacuum tube. The inclined bottom of the steamer is equipped with an electric heating wire, which provides power through a solar cell module to heat the food inside the vacuum tube.

Design and optimization of simple atmospheric water generator using thermoelectric module

Atmospheric water generator (AWG) is a device for producing water from humid air. The water is produced by cooling the air until below its dew point temperature. This study presents the optimization of a simple thermoelectric AWG device (S-TEAWG) for emergency purposes. The designed S-TEAWG consists of a thermoelectric module and condensation plate as a cooler and condensation surface, respectively. The plate is attached to the cold side of the thermoelectric module to enhance the contact surface area with the ambient air. The thermoelectric module with the dimension of 4 cm × 4 cm is operated at 12 V of voltage and 50 oC of hot side temperature. The device is installed vertically thus the condensates flow down naturally due to gravity. Various surface areas of vertical plates, from 0.01 m2 to 0.09 m2, are evaluated theoretically to obtain the maximum water production. The results show that the lower temperature of the vertical plate is achieved at a smaller surface area. However, the optimum surface area is obtained at 0.03 m2 with 60.9 ml/d of water production.

Internal feed preheating necessary for energy-efficient modular multi-effect membrane distillation

Multi-effect membrane distillation (MEMD) systems achieve a high product recovery ratio by effectively utilizing the heat of condensation for further vaporization within the module. In this study, a novel internal feed-preheating design for improving the energy efficiency of modular MEMD systems is proposed and evaluated using a 2D CFD model. Custom user-defined functions are implemented to account for water vapor and associated energy transport across the membrane in an MEMD design with serpentine flow across various effects. Preheat channels embedded into the condensation plates help increase the temperature of feed entering the first effect by ∼25 K, close to heater plate temperature. As a result, high-grade external heat input is not used for sensible heating, instead being utilized towards evaporation and pure water production, resulting in ∼32 % improvement in energy efficiency. However, the added thermal resistance of the preheat channels results in lower average flux and hence recovery, which can be ameliorated by increasing the effective conductivity of the preheat channels. Increasing the thermal conductivity of preheat channels results in ∼23.5 % rise in recovery ratio. Such preheat designs are necessary to reap energy efficiency improvements by increasing the total number of effects in multi-effect vacuum and gap MD systems.

Performance enhancement of a diffusion-type solar still: Wettability and flowability of condensation surface

Several studies have been conducted to enhance the production of solar stills. However, studies focusing on the augmentation of condensation are still insufficient compared with those focusing on production improvement by enhancing evaporation. This study evaluates the effect of contact and sliding angles of condensation surfaces, which are criteria for determining wettability and flowability on the production of solar stills. Single-effect diffusion solar still was fabricated, and glass specimens with various wettability properties were prepared as condensation plates of the still to compare the performances. Experiments were performed by changing the condensation plates of the solar still. Meanwhile, the condensation process and droplet forms were observed as a function of wettability. The experimental results showed that the production rate increased by 45% with a decrease in the sliding angle; it also increased as the surface became superhydrophilic or superhydrophobic, but the sliding angle was a better indicator. Therefore, the material to be used for the condensation surface should be selected based on the sliding angle preferentially.

Optimisation of geometry and surface wettability for enhanced efficiency of the solar still-based desalination unit

Evaporative solar desalination systems offer an economical method to produce pure water from brine solutions. In the present study, the effects of geometry (top surface inclination) and the surface wettability of the condensation plate on the performance of the basin-type solar desalination unit was investigated through the route of CFD (computational fluid dynamics) simulations. It was observed that inclination angle and surface patterning influence the overall rate of condensation. With the 26o top surface inclination, the rate of water production was 33.33% more than that of the 15o and 35o top surface inclinations. Surface wettability influences the production rate of pure water. A novel patterned condensation surface has been proposed, which can enhance the rate of condensation by 12.8% to produce more purified water. The patterned surface was obtained by placing alternate patches of hydrophilic and hydrophobic layers.

Hybridized high concentration photovoltaic unit with enhanced performance air gap membrane distillation unit via depositing reduced graphene oxide layer upon the condensation plate using electrophoretic deposition technique

Amongst the membrane distillation techniques, the air gap configurations showed an outstanding thermal efficiency, while a decline in productivity was recorded due to the additional thermal and mass resistances. The current study proposes minimizing the additional thermal and mass resistances by altering the condensation process to dropwise condensation. Depositing a layer of reduced graphene oxide using the electrophoretic deposition technique on the copper condensation plate was investigated to obtain a hydrophobic nature and attain dropwise condensation. Moreover, different operating conditions were examined for the optimum conditions, which were 45 V, 30 s, 1 cm, and 0.5 mg/ml, for the applied voltage, deposition time, distance between electrodes, and concentration, respectively. This modified condensation plate was investigated experimentally on the lab-scale test rig and showed an improvement in the productivity of 12.5% and 28.5% at the minimum and maximum feed temperatures, respectively. On the other hand, solar energy was utilized to eliminate the heating source required for the membrane distillation unit. A high concentration photovoltaic (HCPV) unit was introduced numerically in the current work with 36 multijunction cells. Furthermore, a microchannel heat sink was successfully designed to keep the cells from thermal degradation. The numerical results showed that the HCPV system could supply hot water up to 55 °C and produce electric power up to 230 W.

Influence of surface wettability on the transient characteristics of vapor condensation from humid air

ABSTRACT The initial transient behavior of condensation of water vapor from humid air plays vital roles in a large variety of engineering applications. Although such influences on the steady-state attributes of dropwise and filmwise condensations have been widely investigated in the literature, description of their initial transient behaviors is rather limited. Herein we have characterized the initial transient regimes of condensation from humid air under varying NCG fractions on condenser plates of four different wettability. Results of the experiments provide the droplet size distribution on the condensing surface, condensate collection rate, and transient life of condensation for selected parametric conditions.

Thermal performance of a two-phase flat thermosyphon with surface wettability modifications

• A two-phase flat thermosyphon with surface wettability modifications is studied. • Superhydrophobic condenser surface reduces the thermal resistance by 43.74 %. • Superhydrophilic evaporator surface deteriorates the thermal performance. • Appropriate wettability modifications improve thermal performance significantly. In the present work, surface wettability modifications were utilized to enhance the phase change heat transfer in a water-charged two-phase flat thermosyphon. A flat thermosyphon's thermal performance with various surface wettability modifications on evaporator and condenser plates was investigated for various heat inputs and filling ratios in the horizontal orientation. The evaporator and condenser's surface wettabilities were varied to superhydrophilic (contact angle of 0-1°) and superhydrophobic (contact angle of 155.4 ± 3°). Changing the evaporator's surface wettability to superhydrophilic nature increased the thermal resistance of thermosyphon due to the high superheat requirement and delay during bubble nucleation. A 43.74% decrease in the thermal resistance was observed for a thermosyphon with a superhydrophobic condenser due to the dropwise condensation and faster condensate return to the evaporator compared to the bare one. A lumped parameter model was used to predict the thermal resistance of flat thermosyphon with a superhydrophobic condenser and hydrophilic evaporator, which is in good agreement with the experimental results. The experimental results encourage research on a two-phase flat thermosyphon with a superbiphilic evaporator and superhydrophobic condenser as it can further improve thermal performance.

Volatilization behavior of impurities in molybdenum concentrate through vacuum distillation

A method for separation of metal sulfides in molybdenum concentrate by vacuum distillation has been developed. The feasibility for separation was mainly dependent on the differences in saturated vapor pressure between impurity sulfides and molybdenum disulfide, which was determined by theoretical calculation. The main factors including distilling temperature and heating duration were studied by experiments. The volatiles enriched on the graphite condensation plates were also investigated by scanning electron microscope and X-ray diffraction and according to that the volatilization behavior of impurities was analyzed. Multiple impurity sulfides could be removed through one-step vacuum distillation on the premise that MoS2 did not decompose. It's turned out that the contents of impurity elements were efficiently decreased by this method without breaking crystal and layered structure of MoS2.

Improving Heat Transfer from Peltier Devices Used in an Atmospheric Water Generation

Present Atmospheric Water Generation (AWG) systems are useful for providing water in areas with limited water supplies. Many industrial AWG systems use VCR (vapor-compression refrigeration) to achieve a large amount of cooling to extract liquid water out of the air. These systems require large amounts of energy to operate, usually in the form of diesel or AC-powered generators. The systems also have many moving parts that require maintenance and use refrigerants that can leak and cause problems with the environment. An alternative AWG solution is to use DC-powered Peltier devices (thermoelectric coolers) to reduce the temperature of condensation plates to extract water from the air. This solution eliminates the issues with traditional industrial AWG systems since the Peltier devices are solid-state, have very long mean-time between failure (MTBF) performance, and can be powered by solar panels that eliminate the need to burn hydrocarbon-based fuels or have access to a reliable power grid. Also eliminated is the need to use chlorofluorocarbon (CFC) or hydrochlorofluorocarbons (HCFC) refrigerants that have been shown to deplete the ozone layer. This paper will present methods to improve the efficiency of the thermoelectric coolers by more efficiently extracting heat from the hot side of the device. This efficiency will be quantified by evaluating the coefficient of performance (COP) of the thermoelectric cooler under the various operating conditions. Different combinations of conductive heat transfer using aluminium heatsinks, convection heat transfer using forced airflow, and phase change heat transfer using copper heat pipes filled with distilled water will be investigated and evaluated.

Experimental performance analysis of a novel ultra-low charge ammonia air condensed chiller

• A novel design of an Ultra-Low-Charge ammonia chiller is proposed and experimentally tested. • The chiller includes semi-hermetic compressor, micro-channel condenser and dry-expansion plates heat exchanger. • The miscible lubricant allows the use of a single-stage oil-separator while ensuring a proper oil return. • The optimized system achieved a charge 40% lower than the current systems in the market with up to 20% extra COP. • The package technology assessed simplifies the installations thanks to the use of secondary fluids. Environmental restrictions on the use of fluorinated refrigerants are turning the attention to natural solutions. Ammonia is historically proven as a refrigerant that requires low purchasing costs, has superior thermodynamic properties, and exhibits great values of coefficient of performance. Therefore, considering ammonia safety issues, solutions able to prevent leakages and minimize the charge of refrigerant are kind of welcomed. This paper conducts an investigation focused on the experimental analysis of the refrigerant charge and performance of a novel ultra-low charge air-cooled packaged chiller for medium temperature industrial applications. The unit is developed using emerging technology to reduce the amount of ammonia charge, such as the microchannel condenser, semi-hermetic screw compressor, miscible lubricant, single-stage oil separator, and dry-expansion plates heat exchanger. In doing so, the empirical adjustment of the ammonia charge revealed that there is an optimum that maximizes the coefficient of performance and the cooling capacity of the system. A charge capacity ratio of 75 g/kW was achieved for a unit with a rated cooling capacity of 230 kW and a gross coefficient of performance of 2.3, i.e, a reduction of 50% in the specific charge and an improvement of 20% in the performance, with regard to the systems in the market. Moreover, the system performance, such as operating temperatures, evaporator effectiveness, and oil return, are assessed for a wide range of conditions and compressor rotational speeds.

Filmwise Condensation From Humid Air on a Vertical Superhydrophilic Surface: Explicit Roles of the Humidity Ratio Difference and the Degree of Subcooling

Abstract The process involving heat and mass transfer during filmwise condensation (FWC) in the presence of noncondensable gases (NCG) has great significance in a large variety of engineering applications. Traditionally, the condensation heat transfer is expressed in the literature as a function of the degree of subcooling—reckoned as the difference between the ambient dry bulb temperature and the condenser wall temperature. However, in the presence of NCG, there exists a finite gradient of vapor mass fraction near the condenser plate, which directly influences the vapor mass flux to the condenser surface, thus limiting the condensation rate. The effects of both these influencing thermodynamic parameters, i.e., the degree of subcooling and the difference of humidity ratio (between the freestream environment and on the condenser plate), have been characterized in this work both experimentally and through a mechanistic model. The vapor mass flux during condensation on a subcooled vertical superhydrophilic surface under free convection regime is experimentally measured in a controlled environment (temperature and humidity) chamber. The mechanistic model, based on the similarity of energy and species transports, is formulated for the thermogravitational boundary layer over the condenser plate and tuned against the experimental results. Further, the model is used to obtain comprehensive data of the condensate mass flux and condensation heat transfer coefficient (CHTC) as functions of the salient thermal operating conditions over a wide parametric range. Results indicate that humidity ratio difference has a more pronounced influence on the condensation mass transfer rather than the degree of subcooling. Regime maps of condensate flux and CHTC show how these can be explicitly identified in terms of the degree of subcooling and humidity ratio difference, regardless of the prevailing thermal and humidity conditions at the freestream and the condenser plate. The mechanistic model thus lends to the development of empirical correlations of condensate mass flux and CHTC as explicit functions of these two parameters for easy use in practical FWC configurations.

Effect of Cone Shape Condenser Plate Tilt Angle on Solar Still Productivity

The demand for fresh water continues to increase and it is crucial for sustaining life. One approach to meet this demand is through desalination of sea water. Solar desalination is a low cost technique to produce fresh water with a simple working process. The still’s design parameters such as the cover angle and material can impact the yield. This research aspires to examine the influence of cone condenser plate tilt angle on the solar still throughput. Results showed that the utmost amount of fresh water produced is from the still with the tilt angle of 50 degrees.