Condensation Heat Research Articles

Condensation heat transfer of zeotropic refrigerant mixtures R407C and R448A in a horizontal smooth tube

Zeotropic refrigerant blends have attracted wide interest due to their promises to reduce global warming potential as well as their potential ability to improve the performance of heat pumps and air conditioners. The complex phenomenon of non-isothermal phase change complicates condensation of zeotropic refrigerant mixtures and merits extensive investigation to better understand their performance profiles. The present work experimentally studied condensation heat transfer of R407C and R448A – two R134a-based zeotropic refrigerant mixtures – in a horizontal smooth tube, condensed by counter-current water cooling. Measurements for mass flux were in the range of 120 to 320 kg m−2s−1 and saturation temperature in the range of 42 to 64 °C. Variation in refrigerant temperature and composition shift during condensation were quantitatively presented. The experimental data showed the effects of mass flux and saturation temperature on the heat transfer coefficients of R407C and R448A in different vapor quality regions. The analysis of heat and mass transfer resistances related to the flow regimes and refrigerant thermophysical properties provides a deep understanding of the condensation heat transfer of zeotropic refrigerant mixtures. The experimental data presented in this work are of value for the design of condensers.

Heat Transfer and Thermal Efficiency in Oxy-Fuel Retrofit of 0.5 MW Fire Tube Gas Boiler

Industrial boilers cause significant energy wastage that could be mitigated with oxy-fuel combustion versus traditional air combustion. Despite several feasibility studies on oxy-fuel burners, they are widely avoided in industry due to major infrastructural challenges. This study measured the performance and heat transfer characteristics of each component in a 0.5 MW fire tube gas boiler after retrofitting it with an oxy-fuel burner. Comparisons were drawn across three combustion modes—air combustion, oxy-fuel combustion, and oxy-fuel flue gas recirculation (FGR). The Dittus–Boelter equation was employed to predict heat transfer in the fire tube for all combustion modes at full load (100%). Heat transfer in the latent heat section of the economizer was measured and compared with predictions using the Zukauskas equation. With this retrofit, oxy-fuel combustion improved the thermal efficiency by about 3–4%. In oxy-fuel combustion, the flow rate of exhaust gas decreased. When integrated into an existing fire tube boiler, the fire tube’s heat transfer contribution diminished greatly, suggesting the economic viability of a redesigned, reduced fire tube section. Additionally, a new design could address the notable increase in gas radiation from the fire tube in oxy-fuel and FGR, as well as aid in the efficient recovery of condensation heat from exhaust gases.

A novel strategy to enhance heavy oil Recovery: Condensation heat transfer calculation and 2-D visualized physical simulation

High carbon emissions and low efficiency in thermal utilization are pivotal challenges in heavy oil development. Addressing the urgent need to enhance heavy oil production, this paper introduces an innovative approach in which aerogel and flue gas serve as supplementary additives in steam thermal recovery. To investigate the mechanisms behind the improved heat transfer and oil recovery facilitated by the combination of aerogel and flue gas, condensation heat transfer experiments and 2-D visual oil displacement experiments were carried out. The condensation heat transfer coefficient, oil displacement performance, and heat utilization efficiency were analyzed and compared. The results showed the porous structure of the aerogel enhances its thermal insulation properties by adsorbing flue gas, thereby reducing the steam-to-cold object condensation heat transfer coefficient by 60.6%. The cementation between aerogel nanoparticles (NPs) retained in the formation and rock particles formed an insulating layer that impedes the upward propagation of steam heat. Combined with efficacy of flue gas foam in improving fluid flow, this promoted the horizontal expansion of the steam chamber, resulting in an 8.2% and 3.4% increase in the steam chamber’s extent compared to using steam and a combination of steam with aerogels, respectively. Moreover, the profile control and thermal insulation impacted following the NPs, lowering the water cut in the produced fluid and enhancing the oil recovery by 7.9%. Upon the application of flue gas, this enhancement in recovery extended to 9.3%.

Numerical Investigation of Air-Steam Condensation in a Vertically Enhanced Tube with Concave and Convex Surfaces

Condensation heat transfer enhancement technology is an important problem for heat exchangers. The air-steam condensation inside a vertically enhanced tube with concave and convex surfaces is analyzed numerically, and the effects of relevant parameters on thermohydraulic performance are discussed. The numerical results show that the drop in steam and temperature between the inlet and outlet is improved by 53.8% and 96.8%, respectively, compared with smooth tubes. In the condensation process, the noncondensable gas accumulates near the wall, which leads to the deterioration of condensation. The structures of concave and convex surfaces disrupt the boundary layer flow and noncondensable gas film and promote flow mixing, leading to enhanced condensation heat transfer. All the numerical results provide guidance values for heat transfer enhancement technology in the applications of condensers.

Condenser operating conditions effects on dielectric liquid boiling and condensation heat transfer in closed systems

Localized boiling and enclosed condensation of a dielectric liquid in a thermosyphon can be used as an alternative to traditional air cooling for high performance microprocessors. A small quantity of dielectric fluid boils at the surface of the microprocessor and is condensed by a heat exchanger, which removes the heat from the system. Here, the heat exchanger was a water-fed cold plate cooling a round fins heat sink. Such a thermosyphon can remove large heat fluxes and increase the energy efficiency of data centers.An experimental setup was built to measure the impact of various operating parameters on the thermal resistances of the thermosyphon. The thermal resistances that were considered were the boiling resistance between the heater and the dielectric fluid, the condensation resistance between the dielectric fluid and the cold water feeding the cold plate, and their sum (the total thermal resistance). The operating parameters tested were the cold plate inlet flow rate (0.2 L/min and 1 L/min), the cold plate inlet temperature (15 °C and 24 °C) and the filling ratio of the enclosure (33 %, 66 % and 88 %).It was observed that changing the filling ratio did not have a significant impact on the thermal resistances of the thermosyphon. Increasing the cold plate inlet flow rate from 0.2 L/min to 1 L/min and decreasing the cold plate inlet temperature from 24 °C to 15 °C both led to significantly lower total thermal resistance. However, increasing the flow rate lowered the rate at which the pressure increased with the amount of heat removed from the system, while this rate did not change when decreasing the cold plate inlet temperature.These observations could be properly explained by a simple analytical model, with a single free parameter (increasing the thermal resistance of the heat sink for the lowest cold plate flow rates). With the free parameter adjusted to the data, the model had a root-mean square error of 1.8 °C and a maximum error of 6 °C, over all measured conditions.This study demonstrates how changing the filling ratio or the cold plate inlet temperature and flow rate have an impact on the pressure, the temperature and the thermal resistances inside the thermosyphon. This is a first step in evaluating the energetic and economic efficiency of the thermosyphon solution for its future integration in data centers.

Influence of Aqueous‐Phase Chemistry on the Concentrations of PM2.5 and Hydrometers During the Development of Convective Clouds Over the Yellow Sea in July of 2017

AbstractMeteorological processes are investigated during the development of deep convective clouds over the Yellow Sea inside a quasi‐stationary rainy front in the East Asian region. WRF‐Chem simulations were conducted to assess the effects of aqueous‐phase chemistry on the concentrations of PM2.5 and hydrometers in deep convective clouds and the associated precipitation. A reduction in the south‐north air temperature gradient induced an inactive quasi‐stationary rainy front with nonlinear zonal clouds during the Changma period in the East Asian region in 2017, causing intensified surface heating due to solar radiation. A mesoscale cyclone was formed near the Shantung Peninsula inside the inactive quasi‐stationary rainy front, extending the eastward tongue of the troughs across the Yellow Sea. Deep convective clouds (CC16 on July 16, CC17 on July 17, and CC18 on July 18) formed in a severe mode on the east side of the mesoscale cyclone over the Yellow Sea at midnight as the warm type, as the warm and humid south‐southwesterly winds present at that time produced convection energy. PM2.5 from eastern China flowed into warm‐type CC16, CC17, and CC18 areas, producing more cloud droplets below 500 hPa via activation. In contrast, the release of additional condensation heat amplifies updrafts within convective clouds during efficient nighttime environmental cooling, thereby enhancing the production of cold‐type ice, reaching altitudes of up to 15 km. The WRF‐Chem PM2.5 outcomes indicate a significant increase in heavy rainfall, exceeding 10 mm hr−1, particularly in the context of the development of cold‐type convective clouds.

Investigation of dropwise condensation of water through an efficient individual-based model

In recent years, researchers have directed their studies towards solutions aimed at enhancing heat exchangers effectiveness. In this context, dropwise condensation (DWC) has been identified among the most promising solutions to increase the condensation heat transfer coefficient (HTC). In fact, DWC provides heat transfer coefficients up to ten times higher than those achievable during filmwise condensation (FWC), resulting in both economic and energy benefits. The DWC phenomenon is usually modelled by combining the heat exchanged through a single droplet and the drop-size distribution. The latter can be divided into a distribution of large droplets N(r), determinable analytically by semi-empirical models, and a distribution of small droplets n(r), typically determined through statistical approaches called population-based models. Another possibility for the determination of the droplet-size density is to simulate the DWC process by an individual-based model (IBM). In this case, each drop is tracked throughout its entire life cycle (nucleation, growth, coalescence, sliding), and the drop-size distribution is obtained as a result. In this paper, a new IBM for the simulation of DWC of steam is proposed. The developed model allows for the simulation of more than 10 million droplets while keeping an acceptable simulation time thanks to the implementation of parallel computing. The predictions obtained from the model, in terms of drop-size distribution and condensation heat flux, are compared against both PBM results and experimental data.

Experimental investigation of condensation heat transfer on vertically inclined grooved aluminium surfaces

This study details the experimental investigation of surface condensation heat transfer on vertically inclined aluminium surfaces with simple modifications. A bespoke experimental apparatus was constructed to control the saturation conditions inside the condensation chamber where the test surface is located. The degree of subcooling of the test surface was precisely controlled by an external heat exchanger. The meter bar technique was used to evaluate the condensation heat flux. Using distilled water as the working fluid and a plane aluminium test surface as the baseline case, the experimental apparatus was validated by comparison of the determined heat transfer coefficient with Nusselt’s model of filmwise condensation on a vertical plane surface, where an excellent agreement was obtained. 7 different aluminium test surfaces were subsequently investigated, each one modified with grooves measuring 0.5mm by 0.5mm (height and width), with a consistent spacing of 0.5mm between them. Groove angles relative to the vertical axis of 0° (180°), 30°, 45°, 60°, 90°, 120°, and 150° were investigated, where grooves were symmetrically mirrored at the centre of each test surface. Results highlighted a significant influence of groove angle on the heat transfer coefficient, with the best-performing sample (150˚) producing a maximum enhancement of 45% and an average enhancement of 34% compared to the baseline test surface over the respective range of subcooling.

Measuring liquid film thickness during downflow condensation in a minichannel

The availability of experimental liquid film thickness data during in-tube condensation heat transfer is fundamental for the development of reliable correlations for the design of condensers. During annular flow condensation, the heat transfer is directly linked to the liquid film thickness, as the main thermal resistance is due to thermal conduction through the film of condensate. Therefore, understanding the liquid film characteristics is paramount for modelling two-phase annular flows. Although several prediction methods for liquid film thickness are available in the literature, they are mainly related to air-water adiabatic experiments. More liquid film thickness data are required for a better understanding of the condensation phenomena and for the development of more accurate models. In this work, the liquid film thickness characteristics of R245fa, R134a and HFE-7000 have been investigated during condensation inside a vertical channel with 3.38 mm inner diameter. Shadowgraphy and chromatic confocal imaging were used to detect the evolution of the liquid film thickness with high temporal resolution. The experimental data were useful to address the existence of a dependence of the liquid film thickness on dimensionless numbers. The combination of two dimensionless numbers, specifically the vapor Weber number and the Reynolds number of the liquid phase, allows to better catch the liquid film thickness trends with the varying operating conditions.

An Experimental Investigation of R600a Condensation in a Multiport Microchannel.

This study aims to provide condensation heat transfer coefficients of R600a (isobutane) refrigerant under mass fluxes between 50 and 98 kg/m2·s at saturation temperatures of 35 °C, 40 °C and 45 °C. Additionally, experiments are conducted with varying inlet vapour quality to understand its effect on the condensation heat transfer measurement. An aluminium multiport microchannel with a hydraulic diameter (Dh) of 0.399 mm is used, where a plexiglass cover is mounted on the top of the microchannels to observe the flow conditions. A 1D heat transfer through the aluminium block is assumed, and heat flux through the refrigerant to the coolant is measured to obtain condensation heat transfer coefficients of R600a. The results showed that decreasing saturation temperature and increasing vapour quality increase the condensation heat transfer coefficient. Increasing refrigerant mass flux increases the heat transfer coefficient up to a specific mass flux. It is observed that the effect of inlet vapour quality becomes significant as introduced quality decreases due to increasing fluctuation.

Grooved hybrid copper surfaces for condensation heat transfer.

Condensation is commonly utilized in numerous thermal management applications and has two modes termed filmwise and dropwise, the latter providing superior heat transfer performance. However dropwise condensation is usually limited by its dependence on gravitational shedding of condensate. To combat this, hybrid surfaces consisting of regions of different wettability have emerged as a promising solution. Of such designs, hybrid grooved surfaces consisting of grooves with varying wettability in the groove valleys and ridge tops are of current interest. To date, most such surfaces have been silicon-based and over flat substrates. In this work, condensation experiments are performed on a copper tube with fabricated grooved hybrid surfaces. The aim is to take advantage of anisotropic wetting due to the presence of grooves and condensate drainage from higher wettability regions. The experimental results quantify the heat transfer with the degree of subcooling. At the same time, droplet dynamics were studied on the hydrophobic-hydrophilic surfaces, showing several droplet growth and departure mechanisms leading to effective heat transfer.

Deep Learning Enabled Comprehensive Evaluation of Jumping-Droplet Condensation and Frosting.

Superhydrophobicity-enabled jumping-droplet condensation and frosting have great potential in various engineering applications, ranging from heat transfer processes to antifog/frost techniques. However, monitoring such droplets is challenging due to the high frequency of droplet behaviors, cross-scale distribution of droplet sizes, and diversity of surface morphologies. Leveraging deep learning, we develop a semisupervised framework that monitors the optical observable process of condensation and frosting. This system is adept at identifying transient droplet distributions and dynamic activities, such as droplet coalescence, jumping, and frosting, on a variety of superhydrophobic surfaces. Utilizing this transient and dynamic information, various physical properties, such as heat flux, jumping characteristics, and frosting rate, can be further quantified, conveying the heat transfer and antifrost performances of each surface perceptually and comprehensively. Furthermore, this framework relies on only a small amount of annotated data and can efficiently adapt to new condensation conditions with varying surface morphologies and illumination techniques. This adaptability is beneficial for optimizing surface designs to enhance condensation heat transfer and antifrosting performance.

Wettability patterning of titanium surfaces through pulsed laser melting for enhanced condensation heat transfer

Wettability engineering of different surfaces has been in the spotlight for the last few decades for enhanced condensation heat transfer in various applications. In this study, we experimentally investigated the water vapor condensation on a wettability-tailored Titanium-based (Ti-6Al-4V) grade 5 alloy. We utilize the microsecond laser to texture the surface by melting at various scanning speeds to realize a wide range of scalable surface structures. We further render these surfaces hydrophobic through chemical vapor deposition of silane at atmospheric pressure. Further water vapor condensation experiments are performed on these surfaces. The results show that the increased surface roughness due to laser-based melting altered the surface wettability of the Ti-surface and made it hydrophilic, exhibiting water drop contact angles ranging between 18° and 56° for the scan speeds between 25mm/s and 50 mm/s, respectively. The vapor deposition of silane on laser-melted Ti-surfaces lowered its surface energy and made them hydrophobic, showing contact angles of water drop up to ~106° specifically at lower scan speeds (~ 25 mm/s). Finally, the vapor condensation experiments showed an enhanced amount of condensed water collection with dropwise mode compared to the bare Ti surface due to a change in the wetting nature altered by laser melting.

Numerical simulation-based design of optimized surfaces for condensation heat transfer

Heat transfer enhancement is a well-established research topic due to its industrial relevance. The advent of 3D printing, also known as additive manufacturing, has opened up the pathway for the design of compact heat exchangers with innovative shapes, complex geometries and smaller size. In particular, additive manufacturing technologies speed up the transition from CAD models to physical prototypes and thus numerical simulation tools for two-phase heat transfer are expected in the future to play a key role for the design of heat exchangers. With regard to filmwise condensation, numerical methods capable to account for all the main forces involved (such as gravity, surface tension, vapor shear stress) must be considered for the optimization of the condensing surfaces. The present study is focused on the preliminary design of innovative shapes for enhancing the condensation heat transfer in a grooved wick heat pipe. Most of the condensation heat transfer studies available in the literature deal with vapor condensing inside tubes or over cylindrical/plain surfaces, while the condensation process occurring inside heat pipes has been less investigated. The grooved wick surfaces must be designed with the aim to promote the drainage of the condensate and minimize the thickness of the liquid film forming over the wick structures. In the present work, the behaviour of different surfaces is studied during condensation of refrigerants by performing Volume of Fluid (VOF) 2D numerical simulations with Ansys®Fluent. The numerical results allow to determine the liquid film thickness and the heat flux distribution along the grooves.

Numerical Investigation of Heat Transfer and Development in Spherical Condensation Droplets.

This study establishes thermodynamic assumptions regarding the growth of condensation droplets and a mathematical formulation of droplet energy functionals. A model of the gas-liquid interface condensation rate based on kinetic theory is derived to clarify the relationship between condensation conditions and intermediate variables. The energy functional of a droplet, derived using the principle of least action, partially elucidates the inherent self-organizing growth laws of condensed droplets, enabling predictive modeling of the droplet's growth. Considering the effects of the condensation environment and droplet heat transfer mechanisms on droplet growth dynamics, we divide the process into three distinct stages, marked by critical thresholds of 105 nm3 and 1010 nm3. Our model effectively explains why the observed contact angle fails to reach the expected Wenzel contact angle. This research presents a detailed analysis of the factors affecting surface condensation and heat transfer. The predictions of our model have an error rate of less than 3% error compared to baseline experiments. Consequently, these insights can significantly contribute to and improve the design of condensation heat transfer surfaces for the phase-change heat sinks in microprocessor chips.

An Active Strategy Based on Different Droplet Removal Modes on Polydimethylsiloxane Magnetic Microstructures.

The efficient removal of droplets on solid surfaces holds significant importance in the field of fog collection, condensation heat transfer, and so on. However, on current typical surfaces, droplets are characterized by a passive and single removal mode, contingent on the traction force (e.g., capillary force, Laplace pressure, etc.) generated by the surface's physics and chemistry design, posing challenges for enhancing the efficiency of droplet removal. In this paper, an effective active strategy based on different removal modes is demonstrated on magnetic responsive polydimethylsiloxane (PDMS) superhydrophobic microplates (RM-MPSM). By regulating the parameters of microplates and droplet volume, different effective departure modes (top jumping and side departure) can be induced to facilitate the removal of droplets. Moreover, the removal volume of droplets through the side departure mode exhibits a significant reduction compared to that observed in the top jumping mode. The exceptional removal ability of RM-MPSM demonstrates adaptability to diverse functional applications: efficient fog collection, removal of condensation droplets and micro-particles. The efficient modes of droplet removal demonstrated in this work hold significant implications for broadening its application in many fields, such as droplet collection, heat transfer, and anti-icing.

Condensation heat transfer performance of R290 in a plate heat exchanger for electric vehicle heat pumps

In the continuous improvement of electric vehicles driving range, a heat pump system with low-global warming potential (GWP) refrigerant is a promising solution. In the present work, the condensation heat transfer coefficient (HTC) and frictional pressure drop (FPD) were experimentally evaluated in an offset strip fins embedded plate heat exchanger (PHE), using an eco-friendly, low-GWP refrigerant R290 as the working fluid. A Modified Wilson Plot Method was used to predict the heat transfer of the coolant side (water/ethylene glycol; 50/50 %). The main focus of the present study revolves around the R290-to-coolant condensation experiment, wherein we analyzed the influence of mass flux (G = 20–50 kg m−2 s−1), heat flux (q = 3–12 kW m−2), and saturation temperature (Tsat = 40–55 °C) on HTC and FPD within the PHE while variable mean vapor quality (xm). According to the results, all experimental conditions were fall in the forced-convection condensation regime. The results state that HTC increases with a rise in q, G, and xm, but decreases with a surge in Tsat. Conversely, FPD increases with a rise in G and xm, and decreases with a escalation in Tsat, while q has no significant impact. Correlations were developed to predict the Nusselt number and friction factor values of R290 with mean absolute errors of 10.6 % and 11.2 %, respectively. These correlations are compared to previous research findings, signifying their efficacy in predicting the heat transfer characteristics of R290 within PHEs.

A Predictive Machine Learning-Based Analysis for In-Tube Co-current Steam Condensation Heat Transfer in the Presence of Non-condensable Gases

AbstractThe primary objective of this study is to develop a predictive model that accurately estimates the condensation heat transfer coefficient (HTC) in the context of in-tube co-current flow condensation, with specific consideration given to the influence of non-condensable gases (NCGs). The need to find useful models and/or correlations that can accurately predict how well a passive condenser in the Economic Simplified Boiling Water Reactor will transfer heat during condensation is greatly warranted. This innovative cooling system utilizes gravity to condense water vapor, effectively dissipating heat from the containment vessel in the event of an accident and transferring the heat into the secondary cooling system. For the development of the forecasting model, we employed Multi-Gens Genetic Programming implemented in MATLAB. This approach possesses the capability of enabling visualization and articulating a transparent mathematical expression that directly establishes the connection between inputs and outputs. This model was specifically developed for forecasting the HTC during the condensation process, considering two distinct types of NCG: air, helium, and a mixture of air and helium, in addition to data for pure steam. The model was trained using a dataset comprising 2913 data points gathered from five experimental references. The model's input comprises a varied range of parameters, including local location ($$z$$ z ), temperature of the steam/NCG mixture ($${T}_{mix}$$ T mix ), condenser wall temperature ($${T}_{wall}$$ T wall ), coolant flow rate ($$\beta_{c}$$ β c ), total pressure ($${P}_{tot}$$ P tot ), condenser inner diameter ($${D}_{1}$$ D 1 ), condenser outer diameter ($${D}_{2}$$ D 2 ), molecular weight (MM), NCG mass fraction ($${w}_{NCG}$$ w NCG ), and mixture Reynolds number ($${Re}_{mix}$$ Re mix ). The output of our model corresponds to the condensation HTC ($$h$$ h ). Four specific correlations were examined with the third correlation attaining the highest anticipated values within a deviation range of ± 30, reaching 90.9%, exhibiting good performance in terms of both performance index and coefficient of determination. This correlation was validated, and its accuracy assessed by employing an unused training dataset that included nitrogen as a NCG. The outcomes showed that 92.94% of the predicted data fell within a deviation range of ± 30%. The findings of this study signify a notable advancement in the analysis of datasets obtained from experiments. Particularly, it delves into the impact of NCGs by considering their molecular weight and mass fraction.

Steam Condensation Heat Transfer in the Presence of Noncondensable Gases (NCGs) in Nuclear Power Plants (NPPs): A Comprehensive Review of Fundamentals, Current Status, and Prospects for Future Research

Efficient steam condensation is crucial for safe nuclear power plant (NPP) operations, preventing pressure buildup, overheating, and the release of radioactive materials. However, the presence of noncondensable gases (NCGs), such as air, nitrogen, hydrogen, or helium, can hinder the condensation process by creating a thermal resistance layer that impedes steam diffusion and condensation on the system’s surface. Maximizing the efficiency of steam condensation requires a thorough grasp of the fundamental processes, theories, advancements, and technical hurdles. Therefore, this work thoroughly addresses these needs, with a particular emphasis on addressing the challenges posed by NCGs by dividing the work into four thematic areas. The first theme relates to a comprehensive examination of pure steam condensation phenomena, which includes an exploration of familiar condensation scenarios and various film condensation types. The second theme examines condensation in the presence of NCGs, their mixture properties, and related theories and modelling of heat and mass transfer. The third theme investigates condensation in NPP by exploring passive cooling systems and condensation phenomena under both natural and forced convection conditions during nuclear accidents, the origin of NCGs in NPP and their transportation aspects. This is followed by experimental work related to condensation scenarios and scale. Finally, the last theme looks upon the recent advancements in computational fluid dynamics (CFD) modelling of wall condensation, system analysis codes coupling with CFD, and the implementation of machine learning (ML) for predicting the condensation HTC. By bridging the gap between fundamental knowledge and practical applications, the four thematic areas presented in this work are aimed at providing a comprehensive foundation for researchers and experts in the field of steam condensation when NCGs are involved. The ultimate objective is to bolster the safety and efficacy of NPP operations by understanding the heat and mass transfer mechanisms while mitigating the risk of catastrophic events.

A phase-change-material-assisted absorption thermal battery for space heating under low ambient temperatures

Solar-driven Absorption Thermal Battery (ATB) is a promising technology for space heating. However, providing heating under low ambient temperatures seriously degrades the storage performance of ATB, which is still a major challenge. Therefore, this study proposed a Phase-Change-Material (PCM)-assisted ATB to recover and store the condensation heat in the charging process. Then, the recovered heat is used to heat the evaporator to strengthen the evaporation-absorption process. This study investigates two different PCMs: organic paraffin and inorganic hydrated salt. The dynamic behaviors and cycle performance of the basic and two PCM-assisted ATBs are compared. Then, parametric studies are conducted for a better system design. Results indicate that the PCM-assisted ATB can significantly enhance the Energy Storage Density (ESD) and slightly improve the Energy Storage Efficiency (ESE). The hydrated-salt-assisted ATB yields the best storage performance with an ESD of 141.5 kWh/m3 and an ESE of 0.78. In contrast, the basic ATB only obtains an ESD of 70.7 kWh/m3 and an ESE of 0.73. The discharging process is strengthened with the increase of phase change temperature, but the charging process is weakened. The maximum ESD of 160.1 kWh/m3 is achieved at the phase change temperature of 28 °C.