Air Heater Research Articles

Energetic and economic analysis of a novel concentrating solar air heater using linear Fresnel collector for industrial process heat

Industrial processes share a relevant portion of global energy consumption. A large variety of high energy-demanding industrial processes need hot air in the medium temperature range, provided by natural gas combustion or by electricity. Hot air is used as a medium in a large variety of processes such as drying, curing, and thermal treatments of several products and materials. Heat can be provided by solar thermal technologies aimed at the sustainable industry. Non-concentrating flat plate type solar collectors can directly heat air up to 100 °C while higher temperatures can be achieved using linear concentrating technology. In this study an innovative system using linear Fresnel collectors directly provides hot air for the industry up to 350 °C, avoiding the need for liquid heat transfer fluids. Accordingly, the installation is simplified, and lower installation and maintenance requirements are expected compared to other solar technologies. The present studies provide an energetic and economic analysis of the concentrating solar air heater, considering a medium-scale benchmark as a reference case in representative European locations. The results indicate that the solar technology here presented can be economically competitive with conventional natural gas heating, having a huge potential for fossil fuel source replacement in hot air based industrial processes.

Weaknesses of steady state analysis when used for selecting solar air heaters

The paper highlights the constrains faced by the user when choosing the most appropriate solar collector from a set of collectors belonging to the same category. Two basic kinds of one porous and one non-porous with single flow/pass flat solar air heaters were tested. The collectors have the same size but different internal shapes and absorber materials. The two collectors were tested and a shading procedure was implemented in order to emphasize several aspects related to the thermal inertia of the collectors. Comparison has been made between the efficiency values obtained experimentally. The shade test shows a faster decrease of the outlet air temperature for V-porous absorber collector in comparison with the U-corrugated absorber collector i.e. 6 °C and –3.5 °C respectively in a time interval of 74 s. Exposing the collectors on a fresh heating cycle under a low stability radiative regime (450–750 W/m2) one observe that 60% of the first 180 s the corrugated collector outperforms the porous collector; after that interval of time the porous collector becomes more effective. The low thermal inertia of the solar air collectors yields high variation of the thermal efficiency in days with low stability of the radiative regime. In such days, using measured series of solar irradiance data with long sampling period between two successive measurements does not allow a proper choice of the most appropriate solar collector type.

Experimental Study of the Effect of Porous Media on the Performance of Single-Pass Solar Air Heater

Solar energy is harnessed to heat the air, which is then utilised for warming greenhouses and drying crops. Solar air heaters may readily increase their performance using an absorbent plate design with a front pass of steel wools. This kind of SAH has been investigated and compared to a conventional flat absorbent plate. Steel wool, a cost-effective and permeable substance, possesses excellent heat conductivity, and it can be utilised in ongoing initiatives to enhance convection and thermal efficiency. The analysis in this research is based on data from experiments, focusing on the single-pass SAH technique and considering two scenarios: traditional system and porous system, with air mass flow rates of 0.015 Kg/s and 0.035 Kg/s. The experimental findings show that employing porous materials increases the exhaust temp by 12.28% and 21.32 % form of air 0.015 and 0.035 Kg/s, respectively. Moreover, the solar radiation readings for non-porous and porous medium SAHs were recorded as 905.32-912.92 and 979.04-945.6 W/m2, respectively, at 1:30 p.m. Furthermore, thermal efficiency is between 33.29 % and 64.36 % in the porous scenarios and between 30.12% and 57.36% for non-porous cases. Porous media increases the thermal efficiency by 10 % and mass flow rate by 14 %.

Integrated battery thermal management and CO2 control in electric buses using recirculated air and waste heat recovery

In recent years, electric vehicles (EVs) have significantly progressed due to their environmental protection and energy-saving advantages. However, maintaining indoor thermal comfort and effective battery thermal management are critical considerations for EVs. Unlike conventional vehicles, EVs cannot use waste heat and depend on heat pump systems for winter heating and summer cooling. This research proposes a novel system to reduce the energy consumption of heat pump systems by using recirculated air while addressing the challenges of battery temperature management and maintaining safe CO2 concentrations in the cabin. The primary objectives of this research are threefold: first, to ensure passenger comfort through an integrated approach that includes cabin CO2 concentration safety; second, to recover heat from recirculated cabin air to save energy and control battery temperature; and third, to comprehensively analyze the performance of the Electric Vehicle Thermal Management System (EVTMS) using precise Computational Fluid Dynamics (CFD) analysis and mathematical modeling. This study will significantly enhance the understanding of energy consumption related to CO2 concentration control; an aspect previously overlooked in the literature. It will develop a battery temperature management strategy that leverages bus exhaust heat. These contributions will aid in achieving both passenger comfort and battery stability in electric buses, providing practical insights for the design and optimization of thermal management systems for future electric buses.

Determination of Turbulent Prandtl Number for Thermal Fluid Dynamics Simulation of HVAC Unit by Data Assimilation

Abstract Regarding high-precision temperature field prediction of a heating ventilation and air conditioning (HVAC) unit using thermal fluid dynamics simulation, the determination of the turbulent Prandtl number (Prt) was a key issue. In this study, we present an attempt to improve the accuracy of thermal fluid dynamics simulations in HVAC units by adjusting the Prt using data assimilation techniques. First, we simultaneously measured the velocity and temperature in the hot and cold air mixing zone of a simple HVAC model using particle image velocimetry and thermocouples. Second, we coupled data assimilation to the thermal fluid simulation model to determine the Prt in the mixing field. Finally, we proposed two functions of the Prt for high velocity and low velocity regions using multidimensional analysis. In the future, we believe that the Prt functions can be applied to thermal fluid simulations of actual HVAC unit to accurately predict performance without conducting prototype experiments, thereby contributing to reducing development cost and time of HVAC unit.

Progressive Dies for L-hanger Ducting (L-HD) Utilizing Low-Carbon Steel SPCC-SD Material: An Experimental and Numerical Analysis

Industrial developments, especially in the manufacturing and construction sectors, recognize L-hanger ducting as a critical component in HVAC (heating ventilation and air conditioning) ducting systems, which play a role in supporting and stabilizing air ducts. The L-Hanger ducting manufacturing process involves a series of stages, such as shearing, blanking, piercing, trimming, and bending processes. This research focuses on the design and simulation of dies and punches for piercing, blanking, and bending processes using 1.6 mm-thick SPCC-SD material. The aim of this research is to design and analyze progressive dies in order to increase the efficiency of the production process. A comprehensive calculation of the forces involved in the shearing, blanking, piercing, trimming, and bending processes is required in order to predict press machine tonnage requirements to support the production process. This research applies theoretical and numerical validation approaches. Theoretical analysis is used to calculate the overall forces, which are then compared with numerical results and verified through an experimental approach. By understanding and optimizing the design of progressive dies, it is hoped that we can increase the production efficiency of L-hanger Ducting and expand knowledge in the field of metal forming, contributing to the metal forming industry and supporting the development of science.

Solar air heater energy and exergy enhancement using a v-corrugated wire mesh absorber: An experimental comparison

In this paper, the energy and exergy performance of a double-pass solar air heater (SAH) using a novel model of a v-corrugated wire mesh absorber (CM-SAH) is investigated experimentally. The v-corrugated wires are adjacent to each other in one layer along the airflow direction to reduce the hydraulic resistance. Simultaneously, this arrangement increases the surface absorptance rate of solar radiation and expands the heat exchange area. To evaluate the performance of CM-SAH, a standard SAH having a v-corrugated absorber plate (CP-SAH) and the same configuration dimensions is compared with CM-SAH. The comparison is achieved under the same operating conditions and using different air mass flow rates of (0.01, 0.02, and 0.03 kg/s). The results show that the CM-SAH outperformed the CP-SAH in terms of thermal efficiency, exergy efficiency, and output air temperature. The maximum thermal efficiencies reach 87.3 % and 65.1 %, while the maximum exergy efficiencies reach 4.4 % and 3.4 %, for CM-SAH and CP-SAH, respectively. In addition, the thermal efficiency of CP-SAH decreased after midday while that of CM-SAH continuously increased.

A comprehensive review of rectangular duct solar air heaters featuring artificial roughness

Abstract Solar air heaters (SAHs) are widely used solar thermal systems with applications in diverse sectors. However, its effectiveness is restrained by low convective heat transfer (HT) coefficients at the absorber plate, leading to inefficient HT, and the elevated temperature of the absorber plate causes significant heat losses, reducing thermal efficiency. This study addresses these challenges by introducing ribs or roughness on the absorber plate creating turbulence in the airflow, resulting in significant improvements. The research investigates various rib configurations, the influence of rib parameters, performance methods, and arrangements to evaluate their HT and friction characteristics. Among these rib configurations, a comparative analysis is done on various factors such as the Nusselt number ratio, thermal enhancement factor, friction factor ratio, and thermal efficiency to optimize distinct roughness parameters and rib arrangement patterns. This study also provides valuable recommendations from existing literature, offering insights into the effective design, prospects, and implementation of SAH systems.

Thermal Performance of a Cylindrical Li[Ni0.6Co0.2Mn0.2]O2/Graphite Battery based on the Electrochemical-Thermal Coupling Model

The thermal safety of lithium-ion batteries has garnered significant attention due to its pivotal role in the field of new energy. In this work, a three-dimensional electrochemical-thermal coupling model based on the P2D model was established for predicting the thermal performance. The charge-discharge and temperature rise experiments via 18650 cylindrical Li[Ni0.6Co0.2Mn0.2]O2 / graphite batteries are designed to confirm the rationality of the model. The simulation results show that the highest temperature of the battery surface during discharging at 1 C and 4 C are 42.85 °C and 61.25 °C, and the experimental results are 42.50 °C and 62.85 °C, respectively. The electrode heat generation mainly comes from the reaction heat of cathode and anode during 1 C charge process, the maximum power is 1.2 W and 0.6 W, respectively. In the discharge process, the cathode dominates the reaction contribution of 1.02 W and the reaction heat power from the anode is only 0.016 W. The capacity of heat dissipation can be increased by enhancing the convective heat transfer coefficient and air velocity within a reasonable range. The proposed electrochemical-thermal coupling model is valuable to evaluate the heat behavior and promote the battery development.

Numerical and experimental investigations of thermohydraulic performance enhancement of triangular duct solar air heaters using circular wing vortex generators

AbstractThis study presents the thermohydraulic performance enhancement in a triangular duct solar air heater (TSAH) using circular wing vortex generators (CWVGs) on the absorber plate using computational fluid dynamics (CFD) methodology for the Reynolds number (Re) range of 6000–21,000. The use of wing vortex generators offers relatively lower interference with the core flow region, while the circular geometry offers a smooth curved edge, which reduces multiple vortex interactions in the wake region, thereby limiting the pressure drop. This study explores the impact of flow attack angle, longitudinal pitch, transverse pitch, and diameter of CWVG on the thermohydraulic performance of TSAH. The results reveal that a lower flow attack angle exhibits enhanced heat transfer with a lower friction factor penalty. The nondimensional diameter greater than d/Dh = 0.325 tends to limit heat transfer and exhibits an increased friction factor. The transverse pitch parameter also exhibits a similar trend where the threshold nondimensional pitch is found to be 1.5. The highest improvement in Nu is 4.37 times that of smooth duct for d/Dh = 0.433, Pl/d = 1, Pt/d = 1.5 and α = 20° at Re = 6000. The highest rise in friction factor is about 10.23 times that of smooth duct for d/Dh = 0.433, Pl/d = 1.0, Pt/d = 1.5, and α = 20° at Re = 21,000. The highest thermohydraulic performance parameter (THPP) value is about 2.23 at Re = 6000, with THPP values ranging from 1.69 to 2.23 across different CWVG configurations. Finally, mathematical correlations are developed for Nu and friction factors which are in close agreement with CFD results, with deviations averaging 5.03% and 3.69%, respectively.

Environmental simulation and refrigeration demand analysis for shield tunnel construction in hot summer and cold winter regions

The thermal hazards generated during the tunnel boring machine construction process significantly impact the physical and mental health of personnel. A field test was conducted on the tunnel of Metro Line 1 in Changsha, China, where the average temperature in the work zone reached up to 33.16 °C, and the air velocity was generally below 0.2 m/s. These conditions were unfavorable for ventilation and heat dissipation. In this paper, a full-scale CFD simulation model was established to simulate the construction environment and analyze the cooling demand. The results indicated that increasing the fresh air velocity could lower the temperature in the work zone; however, this effect was limited. When the fresh air temperature exceeded a certain threshold, it actually raised the average temperature of the work zone. Consequently, there is a need for supplementary cooling of the fresh air during the hot summer months. At a fresh air velocity of 15 m/s, the maximum temperature in the work zone was recorded at 27.8 °C when the fresh air was cooled down to 22.5 °C through auxiliary cooling measures. This approach effectively controlled the temperature in the work zone, reduced flow dead zones, and significantly improved air distribution and heat dissipation. Additionally, it ensured the physical and mental well-being of the construction workers and the safe operation of the equipment. This study provides valuable guidance for managing thermal environments in underground tunnel construction.

An Integrated Quantitative Method of Risk Analysis and Decision Making for Safety Manipulation of a Forest Firefighting Aircraft by Using Physical Models of Multi-Hazard Factors

Although firefighting aircrafts are effective for fighting forest fires, they are affected by a variety of risks related to forest fires during flight operations such as thermal radiation, temperature rise, decrease in air density, and changes in updraft aerodynamics. However, quantifying these influences poses a challenge. Our research reveals that safety standards predominantly hinge on technical indicators like flight height, speed, and angle of attack, which makes it possible to quantify the above effects. A general method framework for analysing firefighting flight safety criteria was constructed in this thesis. Using relevant physical models, such as heat radiation, temperature, air density, and updraft in a forest fire environment, safety criteria with an analytical form were established. The corresponding safety constraints of each criterion were calculated quantitatively, and the most stringent constraint was determined based on multiple factors to obtain a comprehensive safety constraint boundary composed of the critical altitude, stall speed, and critical angle of attack. Finally, the effectiveness of the method is verified in a simulation case. The research results show that the constrained boundary calculation method proposed in this study can provide a scientific basis for the formulation of technical specifications for forest aviation fire safety and aviation fire task planning.

Enhanced heat transfer technology for solar air heaters

Abstract Solar air heaters (SAHs) exhibited low thermal performance due to air thermal properties. To optimize the convective heat transfer between air and the absorber plate, researchers designed plenty of enhanced structures based on experimental and numerical analysis. This article reviewed the improvement methods of SAHs and emphasized the crucial role of thermodynamic models and evaluation criteria. Current research focuses on improving the convective heat transfer coefficient. In terms of enhanced structures, using flow deflectors, flow disruptors, corrugated absorber plates, and porous media improved collection efficiency. This result showed these enhanced structures could effectively further the performance of SAHs and provide new ways for sustainable energy utilization.

Heat Transfer Enhancement and Friction factor Analysis in Solar Air Heater Duct with Ribbed Absorber Plate

Heat Transfer Enhancement and Friction factor Analysis in Solar Air Heater Duct with Ribbed Absorber Plate

Implementation and validation of optimal start control strategy for air conditioners and heat pumps

Commercial buildings are responsible for approximately 20 % of the total energy consumption and greenhouse gas emissions in the United States. Over 85 % of these buildings lack building automation systems, and many are small (<50,000 square feet), underserved, and use rooftop units (RTUs) for heating, ventilation, and air-conditioning needs. Because these buildings lack proper energy management systems, several operational deficiencies lead to excess energy consumption. Studies have shown that managing the RTUs’ heating and cooling set points, schedules, setbacks, and optimal start can result in a 20 % to 25 % reduction in electricity consumption in small commercial buildings. These buildings typically use fixed schedules to start the RTUs 60 to 120 min before occupancy begins, which results in excess energy consumption. This paper presents research that demonstrates and evaluates the performance of four optimal start methods, which utilize data-based modeling as a key element in facilitating adaptive control in response to time-varying inputs while requiring minimal sensor inputs. The evaluation found energy savings in two commercial buildings equipped with RTUs by periodically alternating four different optimal start models during the cooling and heating season. The resulting energy savings are positive for all models and range from 2 to 5 kWh/day/unit. The units on the east side of the building showed higher savings, while interior units showed greater variability in savings due to the differences in capacities and room sizes. Savings were considerably greater during the heating season compared to the cooling season. The performance of all four models on Mondays was poor; models suggested a shorter optimal start time, which resulted in relatively larger errors. The future work will look at using a different model for the days after weekends and holidays.

Fluid Flow and Thermal Characteristics of an Obtuse-Angled Trapezoidal Solar Air Heater Channel With Corner Modifications and Ribs on Absorber Plates

Fluid Flow and Thermal Characteristics of an Obtuse-Angled Trapezoidal Solar Air Heater Channel With Corner Modifications and Ribs on Absorber Plates

Influence of grazing management strategy and data time scales on estimates of sensible heat flux in grasslands

Study regionInner Mongolia Autonomous Region, North China Study focusSensible heat flux (H) quantifies the intensity of water evapotranspiration, making the factors influencing H pivotal to water consumption. North China's semi-arid grasslands are characterized by widespread grazing and strong wind conditions. Grazing strategy modifies surface air heat transfer resistance via vegetation and consequently alters H. Nevertheless, the majority of studies overlook the impact of the observed variables' time scale on H estimation. This paper employs a "big-leaf" model to estimate H, incorporating both grazing management strategy and data time scale, validated using the Bowen ratio, and attempted to analyze the factors that affect H. New hydrological insights for the regionAerodynamic characteristics estimated from daily data typically exceed estimates derived from hourly data. The influence of surface radiative temperature and air temperature on H outweighs that of aerodynamic resistance, whereas aerodynamic resistance accounts for the disparity in estimating H between daily and hourly data. In grazing-prohibited grasslands, the daily H values estimated by the Big Leaf model closely match those obtained from the Bowen ratio. When estimating the hourly H value for grazing prohibited and grazing grasslands, the increase was 25.95 w/m2 and 52.27 w/m2 compared to the daily scale, respectively. For the estimation of water and heat fluxes across different regions, the temporal scale of input data is a pivotal factor.

Prediction of thermal efficiency of double pass solar air heater having discrete multi V and staggered ribs

AbstractThis manuscript endeavors to elucidate a comprehensive analysis for the assessment of thermal efficiency in double pass solar air collectors augmented with fabricated roughness, instrumental in the generation of heated air for applications in heating and drying. The analytical procedure delineates comparisons between a smooth and a double‐sided, roughened absorber, characterized by discrete, multi V and staggered configurations of roughness. The analysis was performed for different roughness parameters including relative roughness width (W/w) from 4 to 8 and relative staggered rib size (r/e) from 1 to 4 and relative rib pitch (p′/p) from 0.2 to 0.8 while other parameters were kept constant. The research scrutinizes the impact of a constellation of parameters: the temperature rise coefficient (ΔT/I, varying between 0.002 and 0.02 K‐m²/W), Reynolds number (Re, spanning 2000–20,000), solar irradiance (I, ranging from 600 to 1000 W/m²), and the geometric variables of the artificial roughness, on both the thermal efficiency and efficiency enhancement factor of the collector. The study revealed that the roughened collector exhibits higher thermal efficiency compared to smooth collector for a similar condition. The extreme enhancement in thermal efficiency of the collector with roughness has been found to be 56.75% more than nonroughened collector for Re = 2000. A further observation was made that thermal efficiency has increased sharply for lower flow rate (Re &lt; 10,000) whereas for higher flow rates (Re &gt; 10,000), this increase becomes nearly asymptotic. In addition, the efficiency enhancement factor has also been found to increase with an increase in ΔT/I. A peak value of 2.321 has been found to be obtained for the efficiency enhancement factor for ΔT/I = 0.02 K‐m2/W and I = 1000 W/m2 as a result of the studies conducted.

Optimization and evaluation of thermo-hydraulic performance of solar air heaters equipped with different roughness geometries

Solar air heaters have poor thermal efficiency. Applying artificial roughness elements is a common approach to enhance thermal performance of a solar air heater. In this study, fluid flow and heat transfer characteristics of solar air heaters equipped with six different roughness geometries, including inline cubical elements, staggered cubical elements, rectangular baffles, square ribs, V-shaped baffles, and V-shaped ribs, were assessed. First, parameters of each roughness geometry were optimized and then thermo-hydraulic performance of solar air heaters having optimum roughness geometries was compared. For each roughness geometry, two design parameters were selected and 25 numerical experiments were designed based on the full factorial design of experiment approach. The thermo-hydraulic performance parameter (THPP) was set out as the objective function and its relationship with roughness parameters was defined using the non-parametric regression response surface method. Finally, the optimum values of roughness parameters were determined using the nonlinear programming by quadratic Lagrangian (NPQL) technique. Comparing the performance of solar air heaters having optimum roughness geometries showed that rectangular baffles led to the largest and inline cubical elements brought about the smallest THPP at almost all Reynolds numbers. The maximum THPP of rectangular baffles was 2.28 at the Reynolds number of 25,000.

Finite difference analysis for entropy optimized nanomaterial Darcy-Forchheimer flow with homogeneous and heterogeneous reactions

Hybrid nanoliquids are not underestimated for their involvement in microelectronics, transportation, coolant processes, ships, biological processes and power generation. Hence motivation for current work is to examine homogeneous-heterogeneous reactions in entropy optimized flow by curved sheet stretched with nonlinear velocity. Trihybrid nanoliquid is synthesized through 2 % of ferrous oxides(Fe3O4), 2 % of silver(Ag) and 2 % of copper(Cu). Kerosene oil is employed as the base fluid. These specific kinds of nanoparticles are taken into consideration because of their numerous applications in heat dissipation, air filters, dynamic sealing, biosensors and catalysts process. Kerosene oil may have applications in many different domains such as energy storage, cleaning agent, portable heaters, fuel additive and industrial lubricants. Darcy-Forchheimer model is employed. Analysis in presence of radiation, dissipation, Ohmic heating, entropy generation and heat generation/absorption are organized. Unlike the previous considerations, the thermal expression here consists of impacts through Darcy-Forchheimer relation. Adequate transformations are implemented. Computations have been arranged by applying finite difference technique (FDM) using MATLAB. Quantities for physical interest are addressed. The presented analysis may have relevance for solar systems, chemical reacting processes, cooling towers and polymer data processes. The conclusions are also organized for important key findings. It is noticed that trihybrid nanomaterial has more entropy rate when compared with hybrid and classical nanoliquids when volume fraction is chosen as 2 % for trihybrid fluid. It is proposed that the ability to transfer heat is enhanced when nanoparticles are added to conventional fluids. Decay in concentration is noticed for both homogeneous and heterogeneous parameters. Reduction for Bejan number is noticed through homogeneous diffusion factor. Comparison with previous study is also presented and found great consensus between them.