Temperature Difference Ratio Research Articles

Investigation on the natural convection in horizontal concentric annulus using the variable property-based lattice Boltzmann flux solver

The natural convection in horizontal concentric annulus with isothermal walls is studied numerically by using the recently-proposed variable property-based lattice Boltzmann flux solver (VPLBFS). The widely-concerned constant property solution (CPS) and the real solution (VPS) in which the total variation in fluid properties is considered, are obtained by using the simplified version and the standard version of the VPLBFS, respectively. The integral effect of the total variation in fluid properties on flow patterns and heat transfer rates is discussed, and the deviation of the CPS from the real solution is quantified in a wide range of temperature difference ratio. Then, several commonly-reported solutions with partial variation in fluid properties (P-VPSs) are obtained by using various simplified versions of the VPLBFS. The individual effects of partial variation in fluid properties are discussed through the comparison between the P-VPSs and the CPS. It is found that the individual effects depend on individuals, but none of which can be regarded as a good approximation to the integral effect of the total variation in fluid properties as a large temperature difference ratio is imposed. The present work gives the real solution for the natural convection heat transfer in horizontal concentric annulus and demonstrates the necessity of considering the total variation in fluid properties in the study about thermal flow problems in which the Boussinesq approximation is invalid.

온도차이비율과 열관류율 평가를 통한 공동주택 결로방지 설계기준 지역 I 용 복층유리 이중창의 설계 개선안 도출

온도차이비율과 열관류율 평가를 통한 공동주택 결로방지 설계기준 지역 I 용 복층유리 이중창의 설계 개선안 도출

An experimental study of nozzle number on Ranque Hilsch counter-flow vortex tube

The present study investigates the effects of the orifice nozzle number and the inlet pressure experimentally on the cooling performance of the counter flow type vortex tube. The energy generation has been conducted using a generator of type stream–tek generator model GNMD-KIT with the number of nozzles (2, 3, and 6), and aspect ratio 1.6 and, an inner diameter of 7.5mm. In the experiments, for each of the orifices, inlet pressures have been adjusted from 200kPa to 600kPa. The energy separation to be investigated here focuses on the cold temperature difference and coefficient of performance for cooling. The experimental results concluded in this paper proved that the higher effect of nozzle number is for nozzle number three and hence that nozzle number could affect the energy separation efficiently. A comparison of the present experiments with other published works has been conducted. An analytical study of the characteristics equation has been carried out to evaluate the best correlation of the ratio of cold temperature difference to the inlet temperature as a function of pressure, cold mass fraction and nozzle numbers. The goodness of fit of the regression model is inspected using the analysis of variance and t-test. The values of R2 are adjusted close to 97% which show a very good agreement between the experimental and predicted values.

Experimental Investigation of Thermal Behaviors in Window Systems by Monitoring of Surface Condensation Using Full-Scale Measurements and Simulation Tools

The aim of the present study was to investigate the thermal performance of window systems using full-scale measurements and simulation tools. A chamber was installed on the balcony of an apartment to control the temperatures which can create condensation on the interior surfaces of window systems. The condensation process on the window was carefully scrutinized when outdoor and indoor temperature and indoor relative humidity ranged from −15 °C to −20 °C, 23 °C to 24 °C, and 50% to 65%, respectively. The results of these investigations were analyzed to determine how the moisture is influenced by changing temperatures. It appears that the glass-edge was highly susceptible to the temperature variations and the lowest temperature on the glass edge was caused by the heat transfer through the spacer, between the two glass panels of the window. The results from the simulation used in this study confirm that the thermal performance of window systems can be improved the use of super insulated or thermally broken spacers. If the values of the indoor humidity and temperature are given, then the outdoor temperature when condensation forms can be obtained by using Temperature Difference Ratio (TDR). This methodology can be employed to predict the possible occurrence of condensation.

The Temperature Profile for The Innovative Design of the Perforated Fin

The development of the perforated fin had proposed in many studies to enhance the heat transfer from electronic pieces. This paper presents a novel derivative method to find the temperature distribution of the new design (inclined perforated) of the pin fin. Perforated with rectangular section and different angles of inclination was considered. Signum Function is used for modeling the variable heat transfer area. Set of parameters to handle the conduction and convection area were calculated. Degenerate Hypergeometric Equation (DHE) was used for modeling the Complex energy differential equation and then solved by Kummer’s series. In the validation process, Ansys 16.0-Steady State Thermal was used. Two geometric models were considered. The big reliability of the presented model comes from the high agreement of the validation results about (0.25%). The results show the increase of the inclination leads to the enhancement of the temperature difference and heat transfer ratio. Improved of Heat transfer ratio is ranging from 13% to 50%.Article History: Received June 12th 2016; Received in revised form August 6th 2016; Accepted August 24th 2016; Available onlineHow to Cite This Article: Jasim, H.H and Soylemez, M.S. (2016). The temperature profile for the innovative design of the perforated fin. Int. Journal of Renewable Energy Development, 5(3), 259-266http://dx.doi.org/10.14710/ijred.5.3.259-266

Experimental investigation of the effect of nozzle numbers on Ranque–Hilsch vortex tube performance

The present study investigates the effects of the orifice nozzle number and the inlet pressure experimentally on the cooling performance of the counter flow-type vortex tube. The energy generation has been conducted using a stream-tek generator (model GNMD-KIT) with different numbers of nozzles (2, 3, and 6), an aspect ratio of 1:6, and an inner diameter of 7.5 mm. In the experiments, for each of the orifices, inlet pressures have been adjusted from 200–600 kPa. The energy separation investigated here focuses on the cold temperature difference and coefficient of performance for cooling. The experimental results concluded in this article prove that the greatest effect of nozzle number is for three nozzles, and hence, that nozzle number could affect the energy separation efficiently. A comparison of the present experiments with other published works has been conducted. An analytical study of the characteristics equation has been carried out to evaluate the best correlation of the ratio of cold temperature difference to the inlet temperature as a function of pressure, cold mass fraction, and nozzle number.

A Systematic Comparison of Stagewise/Interval-Based Superstructure Approaches for the Optimal Synthesis of Heat Exchange Networks

This article describes a study in which the various stagewise and interval-based superstructures for the mixed integer non-linear programming (MINLP) optimisation of heat exchanger networks were systematically compared, using exactly the same basis. The effect of using different logarithmic mean temperature difference (LMTD) approximations on the Total Annual Cost of the network and the network structure were examined. The accuracy of the approximations was also analyzed over a wide range of temperature difference ratios. It is concluded that the best approximation, which is the Underwood-Chen approximation, should be used in future mathematical optimisation of Heat Exchanger Network Synthesis problems.

Optimizations of the waste heat recovery system for a large marine diesel engine based on transcritical Rankine cycle

The aim of this study is to investigate the economic performance of the waste heat recovery (WHR) system for a marine diesel engine. Four waste heat sources, which are exhaust gas, cylinder cooling water, scavenge air cooling water and lubricating oil of a marine diesel engine, are first applied to drive the transcritical Rankine cycle (TRC). R1234yf, R1234ze, R134a, R152a, R236fa and R290 are employed in the system as working fluids. The effects of expander inlet pressure and temperature on net power output, thermal efficiency, total cost, mass flow rate, and available efficiency of the WHR system are analyzed. The levelized energy cost is used to evaluate the economic optimizations and their corresponding optimal parameters in the WHR system. The results show that the optimal levelized energy cost of R236fa is the most excellent and is lower than that of R1234ze, R134a, R152a, R1234yf or R290 by 5.07%, 6.25%, 7.42%, 9.77% or 12.11%, respectively. The payback period, fuel oil saving, and CO2 emission reduction are applied to assess the suitability of these working fluids. Furthermore, the economic optimization correlations in terms of dimensionless optimal pressures and temperature difference ratios are proposed for the system design of the optimal operating conditions.

내표면 온도차 비율(TDRi) 분석을 통한 현대 신한옥 외벽 모서리 부위 단열성능 평가

Recently, many New Han-oks have been constructing in all over the country to popularize as a type of green house. But, achievement of thermal performance of external wall is still the very important issue to become popular. Purpose: The purpose of this study is to verify the thermal performance level of modern New Han-ok through Temperature Difference Ratio inside(TDRi) analysis at corners of the external wall in Han-ok. Method: To achieve this goal, measurements were carried out in 12 Han-oks(experimental mock-up(1), exhibition Han-ok(1), happy village Han-oks(10)) by taking a infra-red thermography using thermal video system. Following are analysis items about connection joint between wall and wood columns of external wall conditions; the part between external wall and external wall(2D), external wall and ceiling(or floor)(2D), 2 external walls and ceiling(or floor)(3D) and so on. Result: It was analyzed that the probability of condensation at most of connection joint appear high and TDRi of 3D corners is higher than that of 2D corners in general. It means that the development of construction techniques about connection joint between wood columns and external wall is still required. The results of this study may be used to improve the construction technology of new Han-ok and as a basis for the specifying the desired thermal comfort environment of dwelling.

Performance enhancement of the double-layered micro-channel heat sink by use of tapered channels

In this paper performance of a double-layered micro-channel heat sink with tapered lower and upper channels (TDL-MCHS) is investigated numerically. Initially, numerical results were validated with results available in the literature and then uniformity of bottom wall temperature, thermal resistance and pressure drop for TDL-MCHS was evaluated for different flow rates of coolant and convergence angles. The results showed that by increasing the flow rate of coolant and the convergence angle of channels, thermal resistance ratio (λR) and maximum bottom wall temperature difference ratio (λΔT) are reduced. Whereas, pressure drop is increased. In addition, increasing the volumetric flow rate of coolant and convergence angle of channels, reduced the temperature gradient in bottom wall of the heat sink. Thermal performance was improved through increasing the channels convergence angle, although more pressure drop occurred and therefore increased pumping power was required. The convergence angle for optimal temperature distribution and thermal resistance ratio in terms of pumping power, was angle of 4°. Maintaining constant overall volume for the micro-channel heat sink, and changing the channel angles caused improvements in its thermal performance. This new design of micro-channel heat sink have the potential to be employed for developing new generations of heat sinks with higher heat rejection capabilities for microelectronic devices.

Condensation Resistance Evaluation of a Double-sliding Window System for Apartment Buildings

In a cold climate such as Korea, the condensation risk is high for window systems. Condensation can lead to mold or mildew problems, thereby causing discomfort for building occupants. To evaluate the risk of condensation for residential apartment buildings, the most commonly used double-sliding window system with double glazing on a four-track polyvinyl chloride (PVC) frame was examined as a reference model. A variety of different frame profile options has been proposed as alternatives to existing window systems. The condensation risk from the reference model was compared to that of the alternatives using two-dimensional steady-state heat transfer simulations. The temperature difference ratio (TDR) was calculated for each case using the inside surface temperature determined at the evaluation locations by the simulation results. Then, these TDRs were compared to determine the most improved alternative.

Performances of thermoelectric module under solar Fresnel concentration

Using Fresnel concentration to collect solar irradiation, the hot-end temperature of the semiconductor thermoelectric generator is enhanced, and the cold end is cooled through a radiator in air. For studying the performance of thermoelectric module under solar Fresnel concentration, a theoretical model of thermoelectric generator under steady condition is built from the perspective of energy flux. The model neglects the convection and radiation heat transfer between the cold and hot end and between the arms, and simplifies the heat conduction only along the arm. Utilizing this model, the temperature gradient on thermoelectric generator (dT/dx), the output current (I), the output voltage (V), and the output power (P) of thermoelectric generator are derived, and the influences of the resistance ratio a(=R/RH2) and the temperature difference ratio b(=T/TH2) on generator output performance under a certain structure parameters of thermoelectric generator are discussed. The results show that with the increase of resistance ratio (a), the output current (I) decreases, however the output power (P) and the conversion efficiency (he) first increase, then decreases. When the resistance ratio a=1, the output power (P) and the conversion efficiency (he) reach their maximum values. When the resistance ratio (a) is smaller, the output power (P) increases rapidly with the increase of the resistance ratio (a). When the resistance ratio (a) is larger, the output power (P) decreases slowly with the increase of the resistance ratio (a). With the increase of temperature difference ratio (b), the output power (P) and the conversion efficiency (he) increase, no matter what the value of the resistance ratio (a) is. It verifies the sensitivity of the output power (P) to the temperature difference. Therefore, with a certain figure of merit, the appropriate adjustment of temperature difference ratio (b) may improve the output power (P) and the conversion efficiency (he). Besides, the load residence should be larger than the internal residence for keeping the high output performance. A Fresnel concentration thermoelectric module, including 6 thermoelectric generators, is employed to experimentally explore its output performances. In experiment, the energy flux density on the surface of the thermoelectric generator is not uniform as desired. The uneven hot-end temperature will degrade the conversion efficiency, and even excessive local temperature may damage the semiconductor thermoelectric generator. A deviation of the thermoelectric generator from the focal plane of Fresnel lens will help to improve the energy flux uniformity and achieve an optimized output characteristics. The required output voltage and output power can be obtained through series/parallel connection of these thermoelectric generators. With the series connection of the thermoelectric generators, the output current is increased. With the parallel connection of the thermoelectric generators, the output voltage is increased.

NATURAL CONVECTION AROUND A HEAT CONDUCTING AND GENERATING SOLID BODY INSIDE A SQUARE ENCLOSURE WITH DIFFERENT THERMAL BOUNDARIES

Two-dimensional steady laminar natural convection around a heat conducting and generating solid body inside a square enclosure with different thermal boundaries is performed. The mathematical model is governed by the coupled equation of mass, momentum and energy. These equations are discretized by finite volume method with power-law scheme and solved numerically by SIMPLE algorithm with under-relaxation technique. Effect of Rayleigh number, temperature difference ratio of solid-fluid, aspect ratio of solid-enclosure and the thermal conductivity ratio of solid-fluid are investigated numerically for Pr = 0:7. The flow and heat transfer aspects are demonstrated in the form of streamlines and isotherms respectively.

Appropriate conditions for determining the temperature difference ratio via infrared camera

The temperature difference ratio is used to measure the thermal performance of a building envelope. Calculation of temperature difference ratio requires temperature differences between indoor and outdoor environments and wall surface temperatures, obtained here using an infrared camera. This approach performs well when the temperature differential between indoor and outdoor environments is greater than 10℃ and when wind speed is less than 3.0 m/s. We identify periods suitable for accurate evaluation of thermal insulation performance with an infrared camera, based on eight cities in Korea. The number of measureable hours ranges between 3183 and 1317 annually. Optimum periods for measurement are between November and March, specifically between 01:00 and 09:00 h. Measurements obtained during these periods can therefore be regarded as relatively accurate. Practical application: A thermal imaging camera provides an easy method for checking the insulation performance and construction conditions of a building. Conventionally, this would be checked experimentally, but thermal imaging allows easy visualization of conditions.

FLOW REVERSAL OF FULLY DEVELOPED MIXED CONVECTION OF NANOFLUIDS IN A VERTICAL CHANNEL FILLED WITH POROUS MEDIUM

The present analysis is concerning the criteria for the onset of flow reversal of the fully developed flow mixed convection of nanofluids in a vertical channel filled with porous medium. The governing equations and the critical values of the buoyancy force are solved and calculated numerically via dsolve package in MAPLE. It was found that the critical values of mixed con- vection parameter for the occurrence of reversed flow decreases with increasing temperature difference ratio and increases with increasing nanoparticles mass flux.

Entropy generation in a condenser and related correlations

Abstract The paper presents an analysis of relations describing entropy generation in a condenser of a steam unit. Connections between entropy generation, condenser ratio, and heat exchanger effectiveness, as well as relations implied by them are shown. Theoretical considerations allowed to determine limits of individual parameters which describe the condenser operation. Various relations for average temperature of the cold fluid were compared. All the proposed relations were verified against data obtained using a simulator and actual measurement data from a 200 MW unit condenser. Based on data from a simulator it was examined how the sum of entropy rates, steam condenser effectiveness, terminal temperature difference and condenser ratio vary with the change in the inlet cooling water temperature, mass flow rate of steam and the cooling water mass flow rate.

Analysis of thermal mixing in circle shaped body inserted inclined channel

In this study, thermal mixing (TM) phenomena in a rectangle channel with adiabatic circle shaped body are investigated experimentally. Two parallel jets in different temperatures are located in the channel which has a circular exit hole to supply continuity of mass. Experiments are carried out for different inclination angle (0°, 30°, 60° and 90°) of the channel. Also, effects of ratio of flow rate, jets diameters, and temperature difference between hot and cold jets were analyzed. A circle shaped passive element with low thermal conductivity is located into channel to control thermal mixing. Thermal mixing index is calculated from measured temperatures. Experimental results showed that thermal mixing of fluid is effected from geometric parameters, drastically. It is found that TM is function of the temperature difference of inlet jets.

Natural Convection in a Tilted Square Enclosure Having Heat Generating Solid Body and with Various Thermal Boundaries

Steady laminar natural convection around a heat conducting and generating solid body inside a two-dimensional tilted square enclosure with different thermal boundaries are investigated numerically. The mathematical model is governed by the coupled equation of mass, momentum and energy. These equations are solved using SIMPLE algorithm by means of the finite-volume method together with under-relaxation technique. Effect of angle of inclination of enclosure, aspect ratio of solid-enclosure, temperature difference ratio of solid-fluid and the thermal conductivity ratio of solid-fluid are analyzed. The fluid circulation and the corresponding heat transport inside the enclosure are represented in terms of streamlines and isotherms respectively.

공동주택 창호 타입에 따른 창호 결로 성능 평가 : TDR(Temperature Difference Ratio, 온도차이비율)을 중심으로

공동주택 창호 타입에 따른 창호 결로 성능 평가 : TDR(Temperature Difference Ratio, 온도차이비율)을 중심으로

Experimental Investigation of Temperature Difference Ratio of Trailing Edge Film Cooling Downstream of Pressure Side Split with Internal Spacer Arrays

This paper investigates experimentally the effects of spacer geometry on temperature difference ratio downstream of pressure side split of trailing edge film cooling. The internal pin fins arrayed staggered and pin fins in the last row face to the cooling hole one by one. The geometric parameters include relative length of trailing edge l/b, ratio of length to span of split a/c, ratio of length to width a/b, angle of split α. And the effects of blowing ratio and Reynolds number are also researched specially. The correlation of temperature difference ratio vs. Reynolds number, blowing ratio, and geometric parameters respectively was induced.