Heat Transfer Coefficient Of Air Research Articles

NUMERICAL INVESTIGATION OF A TEST BOX FOR RADIATIVE COOLING MATERIALS

Radiative cooling (RC) has emerged as a promising technology for passive cooling applications, offering a sustainable and energy-efficient solution to alleviate the increasing demand for air conditioning. This study focuses on a numerical investigation aimed at understanding and optimizing the test box used to evaluate the thermal performance of samples of radiative cooling materials. The numerical simulations employ advanced computational models to analyze key factors influencing the thermal behavior of the test box under varying several boundary conditions. The study also explores the thermal interaction between the test box and its surroundings, considering the effects of ambient temperature and air heat transfer coefficient. The numerical simulations provide valuable insights into the dynamic thermal behavior of the test box, aiding in the development of optimized designs that minimize parasitic heat gains, which may hide the actual cooling performance of the RC sample under real conditions. The outcomes of this numerical investigation contribute to the ongoing efforts in the field of radiative cooling, and the development of a test box for radiative cooling materials

Numerical and experimental investigation of a solar air heater duct with circular detached ribs to improve its efficiency

A solar air heater duct (SAH-duct) SAH-duct has low thermal performance due to the low heat transfer coefficient of air which is the working fluid. Proper mixing of relatively hot and cold air with respect to the hot absorber plate of the SAH-duct can enhance heat transfer. It can be achieved by placing suitable hindrances in the path of airflow like detached ribs. This study presents the numerical investigation of an asymmetrically heated 2D rectangular SAH-duct with in-line arranged circular detached ribs. In the geometrical configurations of the detached ribs; blockage ratio d/H, clearance ratio c/d, and relative longitudinal pitch ratio P/d are varied as 0.04–0.48, 0.1–1.2, and 05–50 respectively at Reynolds number Re 3000–15000 to study their effect on the thermal-hydraulic performance of the SAH-duct. Local and space-averaged thermal-fluid properties like heat transfer coefficient, and friction factor, Nusselt number, pressure coefficient, etc. are discussed through the graphical illustrations and contour plots. The various dimensions of the ribs are varied to find the optimum geometrical configuration of the detached ribs.

Patterns of air temperature changes in air ducts of non-contact air heating or cooling systems

The article is devoted to the study of the patterns of changes in air temperature during its movement in a sheet steel air duct during the operation of non-contact air heating systems, when the temperature of the moving air through the duct is higher than the room air temperature, as well as in the process of non-contact air cooling, when the temperature of the moving air in the duct below the room temperature. Based on the mathematical model of the ongoing physical processes developed in the article, an analytical formula is derived that allows, taking into account the presence of a heat-insulating layer or without it, to determine the patterns of changes in the temperature of moving air through the air duct at a given distance, depending on the thickness of the wall of the air duct and the speed of its movement. A dependence is given that determines the value of the heat transfer coefficient of air moving inside the duct to the inner surface of the duct on the speed, which at a constant flow rate is presented as a dependence of heat transfer on the open cross-sectional area of the duct. An analysis was carried out of the change in temperature of the moving volume of air inside the duct as a result of heat exchange with the surrounding air. A comparative calculation of the change in temperature of air moving in a thermally insulated air duct and in an air duct without thermal insulation was performed. The necessity of carrying out a calculation to determine the patterns of changes in the temperature of moving air inside the air duct when designing air heating systems or air conditioning systems is substantiated. It is concluded that it is necessary to conduct a technical and economic analysis on the feasibility of installing thermal insulation of air ducts made of thin sheet steel.

Numerical investigation on the heat transfer of air/helium precooler for air-breathing pre-cooled engine

Installing a precooler behind the intake is an effective approach for hypersonic air-breathing pre-cooled engine to cool the hot incoming air. Synergetic air-breathing rocket engine is a revolutionary hypersonic air-breathing pre-cooled engine with complex thermodynamic cycle i.e. air cycle, helium cycle. Air/helium precooler is a key component and its configuration and operating condition have great effect on the performance characteristics of air-breathing pre-cooled engine. Thus, the minimum periodic flow and heat transfer model of the precooler are established. The effects of key parameters on the heat transfer performance of precooler are numerically studied. The results indicate that: when the tube row number increases from 7 to 15, the average heat transfer coefficient of air side decreases by 57%, the heat exchange rate increases by 19%, and effectiveness increases by 18.4%. The tube transverse pitch can enhance the heat transfer coefficient of air and helium side, while the heat exchange rate decreases by 33 % when the tube transverse pitch increases from 1.5 to 3.5. The helium inlet velocity can improve the heat transfer performance of precooler and reduce the flow resistance of air side.

Numerical analysis of vapor condensation process in a condensation dome of a patent-based solar-vacuum desalination plant

Water-desalination process using renewable energy sources have become more and more popular as they can produce drinking water without negative effect to the environment. The present study examines the condensation dome of a vacuum-based water desalination plant using transient 3D finite volume method. The whole system is under semi-vacuum condition (to reduce the boiling temperature of the saltwater) and the water vapor is condensed in the mentioned condensation dome. The objective of the current research is to evaluate the performance of the proposed condensation dome in a patent-based desalination plant under various novel possible geometric and operational conditions which have not been investigated before. First, four different scenarios of the fins are examined for a given time step. Then the best selected fin arrangement is simulated under a wide range of ambient air conditions in the same time step. Finally, the condensation process is simulated for the selected geometric and ambient conditions under various time steps between 1 and 60 s. The results revealed that, adding only external fins, and then considering both internal and external fins can boost the water condensation rate around 24 % and 62 % respectively compared to that for the base dome without any fin. Besides, when both internal and external fins are in the same direction, the condensation performance is 5 % higher than that for case 3 in which any internal fin is located between every pair of external fins. However, condensation rate is less sensitive for fin configuration when ambient air becomes warmer. Furthermore, higher level of ambient air heat transfer coefficient (higher wind speed) boosts the water condensation rate as well. The general outcome for the tested size of the dome is promising with around 2000 gr condensed water after 60s in the best selected conditions.

Thermal and hydraulic characteristics of an air heater with modified delta flow obstructions

Air heaters are extensively used for various applications like space heating, drying of agricultural products etc. Air heaters are low efficient due to poor heat transfer properties of air. Flow obstructions enhances the heat transfer coefficient of air by disturbing the formation of the laminar sub-layer. In this work, the effect of a modified inclined delta obstruction (inclined in the direction of flow (α) and in the direction perpendicular to flow (β) on the thermal and hydraulic performance parameters of an air heater (Nusselt number-Nu, friction factor-f and Thermal Enhancement Factor-TEF). In this study initially, performance parameters of a smooth air heater (size: 30 mm × 50 mm × 300 mm, constant heat flux: 800 W/m2) are analysed using Computational Fluid Dynamics (CFD) at different air flow rates (Re = 5000,10,000,15,000 and 20,000). In the second stage, experiments are conducted on a bench-scale setup using the same conditions to validate the results obtained from CFD. Results from the CFD study were also validated by using empirical correlations (Dittus – Boelter equation and Modified Blasius equation). In third stage, the effect of orientation (α: orientation in the direction of flow, β: orientation in the direction perpendicular to flow) of the modified delta flow obstructions was studied using CFD. From the present study, it is observed that the thermo-hydraulic performance of modified delta obstruction is found to be superior to conventional delta flow obstructions. Modified delta obstructions enhance Nu by 4 to 6 times and increase pressure drop by 6 to 10 times in comparison to the air heater without obstruction. From the numerical study, it was observed that the modified delta flow obstruction improves the performance of the air heater in comparison with conventional delta obstruction and the maximum TEF of 1.99 was obtained at Re =5000, α = 300 and β = -450.

CFD analysis of a flat tube with semi‐circular fins using graphene nanofluid and to compare performance with square type of fins

AbstractCFD analysis on a flat tube with semi‐circular fins under laminar flow conditions was performed with graphene‐based nanofluids considering the nanofluids as incompressible. Different simulations were performed at four different concentrations of nanofluids (0.01%, 0.1%, 0.2%, and 0.4%) and at different volume flow rates (4, 6, 8, and 10 LPM) and at four different forced convective heat transfer coefficients at different wind velocities at 300 K (50, 100, 150, and 200 W/m2 K). It was observed that with an increase in the concentration of nanoparticles in nanofluids, the thermal conductivity of base fluid water was increased (at 353 K the nanofluid of 0.4% volume concentration, the thermal conductivity of nanofluid increased by 200% with respect to base fluid). Graphene‐based nanofluids have higher effectiveness than most nanofluids hence it is considered for the analysis, at 0.4% concentration of nanofluid the effectiveness observed was 36.84% at 4 LPM, and for water, the effectiveness was 28.22% under similar conditions. The effect of flow rate on temperature drop was significant. At 4 LPM and at 0.4% of nanofluid, an outlet coolant temperature of 333 K was observed whereas the water outlet temperature at 10 LPM is 346.13 K. The effect of forced convective air heat transfer coefficient was significantly high. At h = 50 W/m2 K the outlet temperature of 0.4% nanofluid at 4 LPM was 345.25 K and at h = 200 W/m2 K, the outlet coolant temperature was 333.47 K. A single tube of the radiator was considered for the analysis whereas the original radiator consists of 50 tubes due to problems of Ansys in meshing.

A Reduced Radiator Model for Simplification of ONAN Transformer CFD Simulation

In this paper, a reduced computational fluid dynamics (CFD) model is proposed for determining the total heat dissipation and the oil temperature distribution of transformer radiators in oil natural air natural (ONAN) cooling mode. In the reduced radiator CFD model, the air flow simulation is replaced with an optimized air heat transfer coefficient ( <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>h</i><i>_air</i></b> ) equation. An experimentally verified full radiator CFD model, which includes the air flow simulation, has been introduced as a benchmark model for evaluating the validity of the reduced model. It was found that one <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{h}}_{{\boldsymbol{air}}}}$</tex-math></inline-formula> can provide sufficient accuracy in simulating the air convection effect of transformer radiators. An <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{h}}_{{\boldsymbol{air}}}}$</tex-math></inline-formula> equation was derived through a parametric study using the full radiator CFD model. The performance of the proposed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{h}}_{{\boldsymbol{air}}}}$</tex-math></inline-formula> equation was compared with the existing empirical equations, and its validities for different insulating liquids and different ambient temperatures were proven by additional CFD modelling. This <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{h}}_{{\boldsymbol{air}}}}$</tex-math></inline-formula> equation can be transformed into a dimensionless form to help the radiator design and facilitate the complete-cooling-loop (CCL) based transformer CFD modelling.

Experimental investigation of presence of air on performance of steam heating process

A Presence of air and other non-condensable gasses poses a serious nuisance for the steam network in a process industry. From a reduction in the process throughput to an acceleration in corrosion effects, presence of air & non-condensable can hamper the productivity as well as life of a process plant. For instance, the thermal conductivity (in W/mk) of air is 0.000049; in contrast with 0.002 for water, 0.20 for iron, and 0.96 for copper. Thus, even a thin layer of air can increase the resistance to heat flow significantly. Even the convective heat transfer coefficient for air is quite low (∼15 W/m2K) as compared to condensing steam (∼2000 W/m2K); so that even if the air convicts heat, it is likely to do so poorly.The objective of this paper is to show experimentally, how air affects the heat transfer process. We investigate the heat transfer performance in terms of the rate of temperature rise (ΔT/Δt) for a water-bath-type indirect heat exchanger. The bath is filled with 100 Litre of water each time and heated with steam; where an air vent is bypassed or taken in-line alternatively, while maintaining the initial conditions constant as far as feasible. The water bath is heated from 25 to 30℃ (room temperature) to 90-95℃ and the time taken for heating is noted in each case. The experimental set-up is equipped with electronic sensors for various temperatures, pressures, steam flow rates etc. Over a set of 10 such experiments, we have found that the presence of the air vent in the steam line consistently improves the rate of temperature rise (ΔT/Δt) with uniform heating in all sections of the heat exchanger. Furthermore, when the air vent is bypassed, the different sections of the heat exchanger are heated at different rates leading to distinct hot & cold spots in the heat exchanger sections.

Experimental determination of the convection heat transfer coefficient in an eccentric annular duct

The use of bayonet tube heat exchangers and heaters is widespread in many industrial applications and an improvement in the heat transfer coefficient may provide benefits over other technologies. This work presents novel experimental results about the turbulent convection heat transfer coefficient of air in the annular section of a bayonet tube for two different configurations: concentric and eccentric tubes. For both configurations, the convection heat transfer coefficient was obtained at different air flow rates, therefore, at different Reynolds numbers. In the case of the eccentric configuration, the angular position of the inner tube was varied to determine the circumferential distribution of the local convective heat transfer coefficient. An increase of the convection coefficient was observed for both configurations at higher Reynolds numbers. Concerning the angular position with regard the inner tube, the largest local convective heat transfer coefficient was obtained at the angular position where the distance between the inner and outer tubes was maximum, yielding a value 22.3% higher than in the case of a concentric annular section. All these experimental results were used to propose a new correlation for the local convective heat transfer coefficient as a function of the Prandtl and Reynolds numbers, the eccentricity, and the angular position of the inner tube, with a maximum discrepancy between correlation and experimental data below 10%.

Thermo-hydraulic analysis of a solar cogeneration air-heater

The requirement of energy becomes utmost essential for sustainability of modern societies and for future growth of economy and industries. The ever-increased demand of energy has put tremendous pressure on conventional energy resources which are already been stretched to its limit. The renewable energy resources especially solar energy being a viable and sustainable source of energy has acclaimed a wide attention as prominent substitute to conventional energy sources. Among these, the utility of solar air heater is yet to be explored fully. SAH has a number of applications namely drying of aquatic products, drying of crops, room heating and other industrial applications. However, the drawbacks of SAH are weather and time dependency, need of large heat transfer area and a large volume flow of air due to depressing heat transfer coefficient of air. To mitigate the aforementioned problems, a double-glazed double-pass SAH system is proposed and tested theoretically. The focus of the recommended system is to minimize the factors which reduce the performance of the conventional SAH. A comparative study is done between the double-glazed DPSAH system with and without roughness.

Thermomagnetic mix convection heat transfer of air in the influence of the magnetic field of permanent magnet

Due to their various applications in both cooling and heating, fins have received a lot of attention from researchers. Several methods in thermal enhancement of fins such as shape analysis, etc. have been investigated. In this paper, the effect of magnetic field on heat transfer coefficient of air in the rotated enclosure has been investigated which Neodymium–Iron–Boron fin is used as a magnetic field source. Oxygen atoms due to their paramagnetic properties are affected by the magnetic field. The heat transfer mechanism in the enclosure, because of the existence of Kelvin body force, is forced convection. The effect of Rayleigh number, cavity degree, and residual magnetic flux density has been studied (The range of the studied parameters is as follows: Br (0–5) T, Ra (1 ×105–5 ×105) ∝(0−60) Degree.) and the results are represented as a streamline, temperature contours and profiles, velocity, and Nusselt number profiles. Results show that with increasing of fins magnetic power up to Br = 5 T, Nusselt number improved by 5.422%. Eventually, the optimum state occurred in Rayleigh 5×105 at an angle of 15° and Br = 5.0T which had 9.68% heat transfer enhancement.

Analytical and experimental investigation on heat transfer and flow parameters of Multichannel louvered fin cross flow heat exchanger using iterative LMTD and ∊-NTU method

Automotive Heat exchangers plays vital role by ensuring human comfort in cabin by maintaining optimum temperature and maintains operating temperature of Internal Combustion(IC) engine within permissible limits. In this work, iteration based mathematical model to solve for analytical thermo-hydraulic performance estimation of a typical heat exchanger is adopted with Log Mean Temperature Difference (LMTD) method by incorporating the variation in properties of fluids during each iteration, since the overall thermal resistance ratio between targeted & calculated Heat Rejection Rate (HRR) has to be converged to unity to solve for the actual thermal performance of the heat exchanger. This condition ensures convergence and there is no deviation between the two adjacent iterations in terms of HRR value. Additionally, the above condition ensures that deviation between analytical value calculated by Effectiveness-NTU (∊-NTU) method and experimental data will be reduced significantly due to the proposed iterative LMTD approach adopted in this work. Along with iterative LMTD methodology, ∊-NTU method is adopted for last iteration to cross-verify the obtained value of the HRR for same operating conditions. In order to evaluate heat transfer coefficients for air and coolant side, standard correlations are used from well-established and validated literature data. For coolant side pressure drop calculations, network solution methodology is adopted where fluid flow behavior in each segment of heat exchanger is studied in detail and analytical relationships are used to predict net pressure drop in entire heat exchanger. In our mathematical model, louvered fin effects on heat transfer is taken into account by adopting colburn approach and the geometrical effects of internal fins on flow channels is also included. Experimental validations tests are carried out to compare with the analytical results of HRR, Coolant Side Pressure Drop (CSPD) and Air Side Pressure Drop (ASPD) across heat exchanger. A good agreement is found between experimental and analytical results which validates the accuracy of present mathematical model and methodology, the maximum deviation for HRC is 4% on higher side, for CSPD and ASPD it is 15.4%,8.7% on higher side respectively.

Transient experimental investigation of airside heat transfer in a crossflow heat exchanger

• Experimental analysis is performed to study the dynamic response of a heat exchanger. • Residence time is found to have a significant effect on the response time. • Transient air heat transfer coefficient is obtained by energy balance on the wall. • An empirical correlation of airside Nusselt number is developed. • The response time of both fluids was not instantaneous to the step imposed. The increase in energy consumption and the demand for effective thermal management systems necessitate the search for enhanced heat exchangers with high thermal performance, lower weight, and compact size. Crossflow heat exchangers are a key component in the thermal management system of many industries such as HVAC, automotive, etc. Transient analysis helps predict the behavior of heat exchangers when they experience variations in their operational conditions in terms of flow rate or temperature. This work experimentally studies the dynamic response of a cross flow heat exchanger to overcome the data scarcity in transient airside and presents the results for various cases of step changes in air mass flow rate. The effect of the step change on heat transfer is investigated and presented by airside Nu, fluids dimensionless temperature, airside Re, heat transfer rates, and Colburn j factor. Results show that the two fluids do not respond instantaneously to the step imposed. The magnitude of the step change has a dissimilar effect on the response time of each fluid. The response time increases with the increase in the step change. A generalized empirical correlation is obtained to predict the airside Nu. This study advances the control of heat exchangers by exploring their transient response due to step changes in one of the fluids inlet condition.

Analysis of increase in efficiency of air-cooled heat exchangers due to intensification of heat exchange

Currently, the issues of improving the heat transfer processes in air-cooled heat exchangers play a huge role in terms of increasing the cooling efficiency and thus reducing the size of heat exchangers. This significantly saves resources. There are several basic methods for increasing the heat transfer of fluids in air coolers, for example, such as: finning of tubes and heat exchange intensification with the help of tube inserts. The purpose of the study is to analyze the efficiency of different fin types and the use of tube inserts, as well as changes in the heat transfer coefficients of air and natural gas, depending on the changes in the types of fins and tube inserts, and their geometry. The application software is Xchanger Suite provided by the company HTRI to ITMO University. The result is the optimally selected geometry of the heat exchange intensifiers based on the analysis, what allows reducing the dimensions of the air- cooled heat exchangers, while providing the necessary heat load, the heat exchange surface reserve coefficient and the heat transfer coefficients.

Heat Transfer Scale Effect Analysis and Parameter Measurement of an Electrothermal Microgripper.

An electrothermal microgripper is an important actuator in microelectromechanical and micro-operating systems, and its temperature field analysis is the core problem in research and design. Because of the small size of an electrothermal microgripper, its microscale heat transfer characteristics are different from those of the macrostate. At present, only a few studies on the heat transfer scale effect in electrothermal microgrippers have been conducted, and the heat transfer analysis method under the macrostate is often used directly. The temperature field analysed and simulated is different from the actual situation. In the present study, the heat transfer mechanism of an electrothermal microgripper in the microscale was analysed. The temperature field of a series of microscale heating devices was measured using microthermal imaging equipment, and the heat transfer parameters of the microscale were fitted. Results show that the natural convective heat transfer coefficient of air on the microscale can reach 60–300 times that on the macroscale, which is an important heat transfer mode affecting the temperature field distribution of the electrothermal microgripper. Combined with the finite element simulation software, the temperature field of the electrothermal microgripper could be accurately simulated using the experimental microscale heat transfer parameters measured. This study provides an important theoretical basis and data support for the optimal design of the temperature controller of the electrothermal microgripper.

Thermal characteristics of a flat plate solar collector: Influence of air mass flow rate and correlation analysis among process parameters

Present research focuses on the analysis of temperature profile, heat transfer characteristics and thermal efficiency of a flat plate solar air collector (FPSAC) at different air mass flow rates. Further, the interrelationship among several variables was also investigated using multivariate analysis. Experiments were performed with FPSAC at non-load conditions in the outdoor environment at natural convection (NC) and forced convection (FC) conditions. Air with mass flow rate (ṁ) of 0.01, 0.015 and 0.02 kg/s exhibited 30.73%, 57.88% and 96.40% enhanced convective heat transfer coefficient (hc,p-a) than 0.006 kg/s. Moreover, increase of ṁ from 0.006 kg/s to 0.02 kg/s augmented the thermal efficiency (ηth) from 22.53 to 32.3%. With regard to 0.006 kg/s, air mass flow rate of 0.02 kg/s produced 8.6% and 4.3% reduced heat transfer coefficient from absorber plate to glass due to convection (hc,p-g) and radiation (hr,p-g). Pearson correlation analysis indicated a strong positive effect of solar intensity on the temperature of absorber plate, glass cover and outlet air of collector, but a weak correlation with collector inlet air temperature, useful heat gain, ηth, and hc,p-a. Further, a positive correlation of solar intensity with hc,p-g and hr,p-g was also noticed. Principal component analysis enabled the visualization of association among solar intensity, temperature of different components of collector, heat transfer coefficients, thermal efficiency and time of the day. The analysis indicated that useful heat gain, heat transfer coefficient of air and thermal efficiency of the collector were not highly influenced by solar intensity.

Heat augmented due to array of protrusions on absorber plate in solar heat exchanger

The low heat transfer coefficient of air causes poor performance of solar heat exchanger. Protrusion shaped roughness has been considered in the present investigation to enhance the performance of solar heat exchanger. The heat-exchanger designed has triangular cross-sectional flow passage and it is embedded with heater assembly for creating required solar intensity over absorber plate to create exact same condition at in-house setup. The protrusions are in rectangular fashion on absorber plate and distance between them is non-dimensionalized as relative-distance-along-duct-width (w/e) and relative-distance-along-duct-length (l/e). Protrusions results better hydraulic and thermal performance through the solar heat exchange. In comparison to smooth solar heat exchanger, the Nusselt number enhanced by 245% in protruded heat exchanger at w/e = 11, and l/e = 11. But, use of protrusions also causes adverse effects in the flow field which resulted higher pressure drop or frictional penalty. Beside this, the heat transfer dominated the frictional penalty and improves the thermohydraulic performance index by 187% as that of smooth solar heat-exchanger.

Numerical investigation of heat transfer characteristics of high-speed and high-temperature air cooled open-cycle reactor

The nuclear aircraft is one important type in the application of near space. The high-speed and high-temperature air flows through the open-cycle reactor of the aircraft engine differs from typical reactors. The heat transfer characteristics of high-speed air flow have great effects on the reactor performance. Therefore, the simulation of the air flow in the reactor coolant channel is conducted. Firstly, the numerical methods are validated against experiments. Subsequently, the effects of the distribution of the heat flux, inlet velocity, temperature and pressure on the heat transfer performance of the coolant channel are investigated. The results reveal that the heat transfer correlations evaluated at average bulk temperature are more appropriate compared to that evaluated at the average film or wall temperature. The heat flux influences the heat transfer coefficient indirectly due to the varied air properties. The higher inlet air temperature means the larger thermal conductivity, which leads to the higher heat transfer coefficient. The heat transfer coefficient of air under high-pressure conditions can be equivalent to that of water under the forced circulation conditions. The research can lay basis for the analysis of the flow and heat transfer characteristics of the air flow in the open-cycle reactor.

A Comparative Study of Solar Heat Transfer on Roof-Top Water Storage Tank Orientations in Saudi Arabia

The effect of tank orientation on heat transfer of a typical roof-top water storage tank is examined in this paper. The theoretical study is based on scale analysis of the governing equation that is used to evaluate the comfort time of both vertical and horizontal water storage tanks. The scale analysis is validated numerically by solving the resulting energy equation using an explicit numerical technique based on two programs written in the MATLAB software for each tank orientation. Different water tank capacities are examined for both horizontal and vertical orientations. Data for commercially available water storage tanks are used in the calculations. Three parameters play an important role in the evaluation process of the comfort time ratio. These are (1) the tank capacity, (2) the tank characteristic length, and (3) the tank surface area. It is shown that the heat transfer coefficient associated with water inside the tank is much higher than the outside air heat transfer coefficient around the body of the tank. The simplicity of the proposed method will allow the user in quick decision making as to which water storage tank orientation would provide longer comfort time. For example, in a vertical tank with a capacity of 1000 L, the water will heat up slowly and from 11:00 AM onwards, it will approximately need 3.7 h to reach the temperature of the environment. On the other hand, in a horizontal tank of the same capacity, the water will heat up much quickly and it will take only about 0.9 h for water to reach the surrounding environment temperature. Eventually, this work will contribute to less water evaporation from these tanks, thus saving water that is essential to water starved desert climates such as in the Kingdom of Saudi Arabia.