Theoretical Study Of Heat Transfer Research Articles

Active cooling of a photovoltaic module in hot-ambient temperatures: theory versus experiment

Abstract The performance improvement of a PV-module is investigated theoretically and experimentally in a long-term research-plan via module cooling by different approaches including passive, active, and evaporative cooling as well as water cooling for the same module. In the present paper, the investigation is conducted to decide on the suitability of active-cooling of the module in hot-ambient temperatures. A module without cooling is used as a base case for comparison against cooled modules with and without fins attached to the module’s rear-surface and extended down in an air-cooling duct underneath the module. At first, a theoretical study of heat transfer through the module is conducted to investigate how the calculated cell temperature and module output power are influenced by the air velocity from a blower, ambient temperature and solar irradiation. The results showed a decrease of cell temperature by about 7–10 °C with a subsequent increase of electrical efficiency. The cell temperature decreases significantly with the increase of duct height and with the increase of the number and length of fins, the same as in passive cooling. The cell temperature decreases by more than 3 °C at duct height of 0.2 m. The calculated values of cell temperature, open-circuit voltage and short-circuit current of the module with and without active cooling agreed reasonably with the present measured values over the day hours of two successive days in summer season. At air velocity of 1.5 m/s, the increase of electrical efficiency by active cooling was found 0.67–0.80 %. Further increase of air-flow velocity or duct-height in active cooling seeking higher efficiency is not recommended due to increase of consumed electric power by air-blower and limited decrease of cell temperature. This concludes that air cooling is not effective in regions of hot ambient temperatures. For a non-cooled module, the cell temperature is related to the ambient temperature in terms of the solar radiation and NOCT, the datasheet value of normal-operating-cell-temperature. The relationship is modified in the present paper to account for air-flow through the duct seeking its extension for application to air-cooled modules.

ОБҐРУНТУВАННЯ ПАРАМЕТРІВ СПОСОБУ ВИКОРИСТАННЯ ГЕОТЕРМАЛЬНОЇ ЕНЕРГІЇ ДЛЯ ЦІЛОРІЧНОГО ЗАБЕЗПЕЧЕННЯ ВОДОЮ БЕТОНОВИРОБНИХ ПІДПРИЄМСТВ

Purpose: Substantiating the parameters of the method of using alternative energy sources for the year-round supply of thermostabilized water to enterprises producing concrete, due to establishing the regularities of the functioning of the geothermal heat exchanger. Methodology: a comprehensive approach, which includes theoretical studies of heat transfer from the massif to the geothermal heat exchanger, calculation and analytical method for determining the main parameters of the geothermal heat exchanger. Results: a subsurface thermal energy extraction installation was developed, due to the use of a geothermal heat exchanger, which will allow year-round production of thermostabilized water from shallow non-potable reservoirs. Scientific novelty: the study of heat transfer from the massif to the geothermal heat exchanger made it possible to determine the dependence of the length of the geothermal heat exchanger on its diameter. Water heating to 8°С in winter and water cooling to 20°С in summer will be provided by a geothermal heat exchanger with a length of 28 m and a pipe diameter of 0.5 m. Further increase in the diameter of the pipes will lead to a decrease in the efficiency of the TRP. Practical significance: obtaining thermostabilized water throughout the year will create conditions for year-round operation of concrete-making enterprises for the intensive restoration of Donbass.

Theoretical study of heat transfer across biphenylene/h-BN superlattice nanoribbons

Controlling thermal conductivity of nanostructures is a key element in manufacturing tailor-made nanodevices for thermoelectric applications. Moreover, superlattice nanostructures have been demonstrated to be useful in achieving minimal thermal conductivity for the employed nanomaterials. In this work, we model two-dimensional biphenylene, a recently-synthesized sp2-hybridized allotrope of carbon atoms, for the implementation of a biphenylene/hexagonal Boron-Nitride (biphenylene/h-BN) superlattice nanoribbons. The effects of the length of ribbon and its superlattice period (lp) on the thermal conductivity are explored using molecular dynamics simulations. We calculated the length-independent intrinsic thermal conductivity (Kα) of the superlattice nanostructure, which was approximately 68% and 55% lower than the thermal conductivity of pristine h-BN and biphenylene nanosheets, respectively. The superlattice period largely determines the minimum thermal conductivity, which was at 64.1 W m−1k−1 for a period value of lp = 2.51 nm. This work opens a new window to tune and/or minimize thermal conductivity in nanoribbons when designing thermoelectric and thermal insulation materials for favorable applications.

"Theoretical Study of Heat Transfer in Straight Round Pipes with Periodically Arranged Surface Flow Turbulators of Semicircular Cross-Section Depending on the Prandtl Number for Various Geometric and Mode Parameters"

"Theoretical Study of Heat Transfer in Straight Round Pipes with Periodically Arranged Surface Flow Turbulators of Semicircular Cross-Section Depending on the Prandtl Number for Various Geometric and Mode Parameters"

A Theoretical Study of Heat Transfer in Non-conducting Materials in Both the Regions

A Theoretical Study of Heat Transfer in Non-conducting Materials in Both the Regions

Mathematical Simulation of Forest Fire Impact on Industrial Facilities and Wood-Based Buildings

The present work is devoted to the theoretical study of heat transfer in the enclosing structures of a wooden building exposed to the front of a forest fire. In the general case, the following effects could be distinguished: The direct effect of a forest fire flame, the effect of convective and radiant heat flux, and the removal of firebrands from the front of a forest fire. In this paper, only building enclosures were considered to be exposed to radiant heat flux from the front of a forest fire. The scenarios of the impacts of low- and high-intensity surface forest fires and crown forest fires were considered, taking into account the parameterized structure of the fire front, as well as various cladding materials and the time of the forest fire. As a result of mathematical modeling, temperature distributions over the surface and thickness of the cladding material were obtained, and ignition conditions were determined based on experimental data. The proposed simplified mathematical model and the obtained results can be used in the practice of protecting industrial facilities or rural settlements from forest fires. Particular attention should be paid to the potential use of the results in the Information System for Remote Monitoring of Forest Fires, ISDM-Rosleskhoz, in conjunction with geo-information technologies and methods of remote monitoring.

Investigation of Forced Convective Heat Transfer in Nanofluids

The present paper concerns a theoretical study of heat transfer of the laminar two dimensional flows of various nanofluids taking into account the dissipation due to viscous term past a 2-D flat plate had a different temperatures. The steady incompressible flow equations were used and transformed to a nonlinear Ordinary Differential Equation (ODE) using a similarity variable. These equations were solved numerically using implicit finite difference method in which the partial derivatives were replaced by appropriate central differences patterns and using Newton’s method to linearize the resulting algebraic equations. Finally, the block-tridiagonal-elimination technique was used to solve that linear system. Three types of nanoparticles namely, Cu-water, Al2O3-water, and TiO2-water in the base flow of water were considered. The symbolic software Mathematica was used in the present study. Different types of nanoparticles, different values of, nanoparticle volume fraction, Eckart and Prandtl number were tested and analyzed at different wall temperature. The effect of these parameters on the flow behaviour, the local skin friction coefficient, Nusselt number, the velocity and the temperature profiles were presented and investigated. It is concluded that these parameters affect the fluid flow behaviour and heat transfer parameters especially nanoparticle concentration. The presence of nanoparticles showed an enhancement in the heat transfer rate moreover its type has a significant effect on heat transfer enhancement.

Mathematical Modelling Time Dependent for Heat Transfer Process in Homogenous Composite ZnO/Activated CNF

A theoretical study of heat transfer on composite Zinc Oxide (ZnO)/Activated Carbon Nanofibers (CNF) by using mathematical model from diffusion equation for stationary composite with various heating time was studied. The equation and boundary conditions are interpreted by using Taylor series expansion to obtain a steady-state numerical solution from the Jacobi iteration algorithm. The composites where put inside the furnace model by filaments on the two sides of the walls as the source of heat (general model for furnace). By using this model, the position of sample to receive the homogeneous temperature determined. We compared the steady-state and unsteady-state conditions to identify the temperature distribution at real-time. The results show that the heat distribution will reach an asymptotic state by performing a numerical analysis is 200 K and 300 K for 25 minute time of heating. In this study, shows the efficient way for annealing homogenous materials to identify the position inside the furnace which can be used as a guide to receive the homogenous temperature during the annealing processes.

Enhancement of photovoltaic system performance via passive cooling: Theory versus experiment

Passive cooling of a photovoltaic module via fins attached to the rear surface of the module is investigated. A solar module with no air cooling was used as a base model for comparison against modules cooled by the attached fins, which serve as a heat sink. The modules with fins are cooled by still air and ventilation air. A theoretical study of heat transfer through PV modules with and without fins was conducted to investigate how the calculated cell temperature and module output power are influenced by the ambient temperature and solar irradiation. The results showed a drop of module temperature and increase of electrical efficiency due to fins cooling. The electrical efficiency of the module increases significantly with the increase of fins height and number. The calculated values of cell temperature, open-circuit voltage and short-circuit current of the module with and without fins agreed reasonably with those measured experimentally over the day hours. The output power over the day hours increases at first from sunrise until noon time followed by a decrease until sunset. On the contrary, the electrical efficiency decreases from sunrise until noon time followed by an increase until sunset in agreement with previous findings in the literature.

Theoretical Study of Heat Transfer on Peristaltic Transport of Non-Newtonian Fluid Flowing in a Channel: Rabinowitsch Fluid Model

The present investigation is concerned with the problem of heat transfer and peristaltic flow of non-Newtonian fluid using Rabinowitsch fluid model through a channel under long wavelength and low Reynolds number approximation. Expressions for velocity, pressure gradient, pressure rise, friction force and temperature have been obtained. The effect of different parameters on velocity, pressure gradient, pressure rise, streamlines, friction force and temperature have been discussed through graphs.

Theoretical study of heat transfer in straight circular pipes with periodically arranged surface flow turbulence semicircular cross-section for the flow of liquid metal to various geometrical and operating parameters

Theoretical study of heat transfer in straight circular pipes with periodically arranged surface flow turbulence semicircular cross-section for the flow of liquid metal to various geometrical and operating parameters

Experimental and Theoretical Studies of Heat Transfer in Graphene/Agar under Laser Irradiation

Experimental and Theoretical Studies of Heat Transfer in Graphene/Agar under Laser Irradiation

Theoretical Study of Heat Transfer through a Sun Space Filled with a Porous Medium

A theoretical study had been conducted to detect the effect of using a porous medium in sunspace to reduce heating load and overcoming coldness of winter in the cold regions. In this work, the heat transferred and stored in the storage wall was investigated. The mathematical model was unsteady, heat conduction equation with nonlinear boundary conditions was solved by using finite difference method and the solution technique of heat conduction had based on the Crank Nicholson method. The results had adopted on the aspect ratio (H/L=30), Darcy number (Da=10-3), porosity (φ=0.35) and particle to fluid thermal conductivity ratio (kp/kf=38.5). The results showed that using the porous medium had enhanced the heat transferred and stored in the storage wall. For the outside storage wall temperature, an increase of 19.7% was achieved by using the porous medium instead of the air, while it was 20.3% for the inside storage wall temperature.

Theoretical Study of Heat Transfer through a Sun Space Filled with a Porous Medium

A theoretical study had been conducted to detect the effect of using a porous medium in sunspace to reduce heating load and overcoming coldness of winter in the cold regions. In this work, the heat transferred and stored in the storage wall was investigated. The mathematical model was unsteady, heat conduction equation with nonlinear boundary conditions was solved by using finite difference method and the solution technique of heat conduction had based on the Crank Nicholson method. The results had adopted on the aspect ratio (H/L=30), Darcy number (Da=10-3), porosity (φ=0.35) and particle to fluid thermal conductivity ratio (kp/kf=38.5). The results showed that using the porous medium had enhanced the heat transferred and stored in the storage wall. For the outside storage wall temperature, an increase of 19.7% was achieved by using the porous medium instead of the air, while it was 20.3% for the inside storage wall temperature.

Thermographic phosphor thermometry in transient combustion: A theoretical study of heat transfer and accuracy

Thermographic phosphors (TPs) are used in combustion environments to study wall surface temperatures and heat fluxes. Recently they are also applied in unsteady environments like internal combustion engines to study the heat transfer to walls. The present study investigates theoretically some related effects leading to limitations of the method and thus trying to help experimenters to choose proper conditions for their experiments. The influence of absorptivity and film thickness is studied first. Then the unsteady heat flux of a surrounding gas phase is investigated as a function of film thickness and conductivity, including the effect on the temperatures which would be measured using TPs. The errors in temperature measurements and time resolution are investigated for typical cases. Finally the relation between the surface temperature and film thickness is investigated for combinations of two base materials (quartz and steel) coated with layers of Mg2SiO4 or SiO2, as representatives for TP host materials. It is seen that the maximum surface temperature is influenced in unsteady heat transfer processes even by relatively thin layers.

Photothermal conversion in a solar collector with tilted walls

This paper presents a performance analysis of a solar air collector with tilted side faces. The northern side wall is tilted at an angle of 38° and other walls are tilted at an angle of 9° relative to the vertical. All these walls are covered with a thin reflective aluminium film. The device may be used as drier, sterilizer or cooker in rural areas. The prototype collector was designed and produced in the Study and Research Center on Renewable Energies of Cheikh Anta Diop University of Dakar. A theoretical study of heat transfer allows us to formulate the partial differential equations that govern the operation of the collector. These equations were solved numerically using a finite differences method. The agreement between the computed and experimental results for the daily global solar energy and the temperature inside the collector validate the theoretical model. The discrepancy between theory and experiment is less than 2% for the global solar radiation and there is also satisfactory agreement for the absorber temperature. Key words: Solar collector improvement, global solar radiation, numerical modeling, heating system.

Theoretical study of heat transfer with moving phase-change interface in thawing of frozen food

A theoretical solution was obtained for a transient phase-change heat transfer problem in thawing of frozen food. In the physical model, a sphere originally at a uniform temperature below the phase-change temperature is suddenly immersed in a fluid at a temperature above the phase-change temperature. As the body temperature increases, the phase-change interface will be first formed on the surface. Subsequently, the interface will absorb the latent heat and move towards the centre until the whole body undergoes complete phase change. In the mathematical formulation, the nonhomogeneous problem arises from the moving phase-change interface. The solution in terms of the time-dependent temperature field was obtained by use of Green's function. A one-step Newton–Raphson method was specially designed to solve for the position of the moving interface to satisfy the interface condition. The theoretical results were compared with numerical results generated by a finite difference model and experimental measurements collected from a cold water thawing process. As a good agreement was found, the theoretical solution developed in this study was verified numerically and experimentally. Besides thawing of frozen food, there are many other practical applications of the theoretical solution, such as food freezing, soil freezing/thawing, metal casting and bath quenching heat treatment, among others.

Theoretical study of heat transfer by radiation conduction and convection in a semi-transparent porous medium in a cylindrical enclosure

In this paper, numerical solutions are presented for the radiation effect on heat transfer by simultaneous convection conduction and radiation about a semi-transparent cylindrical porous medium. The set of differential equations are solved using a fourth-order finite difference method. Various results are obtained for the dimensionless temperature profiles in the solid and fluid phases of the radiative and total heat fluxes. The effects of some radiative properties of the medium on the heat transfer rate are examined.

Heat transfer at thin molten layer crystallization I. Molten layer cooling stage

The paper presents a theoretical study of heat transfer at the cooling stage of the crystallization process of a horizontal molten layer. The obtained mathematical model, based on a physical model and on the differential equation for temperature, enabled to study the influence of some parameters (the global heat transfer coefficient between the molten layer and the cooling agent and the thickness of the layer) on the temperature distribution inside on urea1 molten layer.

Rapid isothermal processing

The physics and technology of a relatively new, short-time, thermal processing technique, namely rapid isothermal processing (RIP), based on incoherent sources of light for the fabrication of semiconductor devices and circuits, are reviewed in this paper. Low-cost, minimum overall thermal budget, low-power consumption, and high throughput are some of the attractive features of RIP. The discussion of RIP, in the context of other thermal processes, history, operating principles, different types of RIP systems, various applications of RIP using single processing steps, and novel applications of RIP, including in situ processing and multistep processing, is described in detail. Current trends are in the direction of RIP-dominated silicon integrated circuit fabrication technology that can lead to the development of the most advanced three-dimensional integrated circuits suitable for applications such as parallel processing and radiation hardening. RIP is not only a superior alternative to furnace processing, but it is also the only way to perform certain crucial steps in the processing of compound semiconductor devices such as high-mobility transistors, resonant tunneling devices, and high-efficiency solar cells. Development of more accurate temperature measurement techniques and theoretical studies of heat transfer and other fundamental processes are needed. Dedicated equipment designed for a specific task coupled with in situ processing capabilities will dominate the future direction of RIP.