Flow Thermal Parameters Research Articles

Dynamic performance prediction and experimental analysis of wet clutch actuator considering thermal flow characteristics

The hydraulic actuator system (HAS) for wet clutches in heavy-duty vehicle transmissions is required to have a fast response and high precision in the pressure regulation procedure. Conventional pressure control valves for HAS are almost slide spool structures, which perform a large flow force at a high flow rate. An open-center spool structure is designed and developed in this paper, which is a combination of a traditional slide spool and a valve sleeve. It has an orifice-groove combination throttling orifice, which can take into account the large through-flow capacity and small flow force. Firstly, to deeply understand the mechanism of pressure variation in the clutch chamber, a high-fidelity dynamic characteristic mathematical model of HAS considering the oil temperature is proposed. Secondly, the functional relationship between the oil temperature on the medium physical property parameters and the orifice thermal flow parameters in the model is deduced in detail. An experimental bench to measure the pressure valve dynamic performance and actuator pressure regulation characteristics in a wide temperature domain is then designed and implemented to validate the accuracy of the simulation model. Finally, the mechanisms of oil temperature and system pressure on pressure impact and pressure response are quantitatively analyzed in association with a supervised learning algorithm. The feasible domains of the two adjustable variables are also explored. This study provides a new perspective on dynamic control and energy saving of HAS pressure valves and a new method for the prediction of HAS performance under complicated operating conditions.

Thermal and Visualisation Study of the HFE7100 Refrigerant Condensation Process

Abstract Technological advances are contributing to the search for highly efficient energy designs, and increasing interest in compact heat exchangers. Indeed, small channel diameters determine large heat transfer coefficients and condition a significant heat transfer area about the overall volume of the heat exchanger, as well as a smaller amount of refrigerant flowing in the system. Nevertheless, the operating stability and energy efficiency of compact heat exchangers are influenced by two-phase flow structures, which depend on thermal flow parameters. Knowledge of the structures formed during the condensation process is therefore essential for optimising the operation of refrigeration and air-conditioning equipment. This article presents the results from experimental studies of the HFE7100 refrigerant, from the hydrofluorocarbon group, condensation process in mini-channels with hydraulic diameters dh = 2.0 mm, 1.2 mm, 0.8 mm and 0.5 mm. Thermal flow characteristics were determined, and the forming structures of two-phase flow were recorded. The results of visualisation were subjected to morphological image analysis, based on a special algorithm written in MATLAB software. The algorithm makes it possible to determine the void fraction, which is necessary for calculating the vapour quality, as well as the area of vapour bubbles and their number, directionality and length along the x- and y-axes.

Simple analytical considerations on a thermal-flow operating parameters of a heat storage tank

A heat storage tank (HST), described in this paper, may be applied to numerous systems used for thermal energy generation and storage. Working principle and heat-flow processes of the HST remain the same and are independent of the systems in which the HST is being used. This paper presents a thermal-flow analysis of a heat storage tank (HST) operating in an air compressor heat pump (ACHP) and a dry cooler (DC) combined cycle. The HST is operated under transient conditions for four different ACHP steady states. The HST was analysed using lumped capacitance method. The heating power of a single coil varied from 2.2 to 3.2 kW. 50% increase in mass flow rate of heating water in the coils increased the HST water mean temperature by 5.6 °C. A differential equation for the HST water temperature variation was solved analytically and it was presented with the use of dimensionless numbers. The presented solution is of a general form. An important parameter such as number of the coils may be varied easily. Additionally, a Mathcad computational program was proposed for the estimation of HST-ACHP-DC system thermodynamic and thermal-flow parameters. System dynamics was studied using MATLAB/Simulink. An optimal operating parameters of the HST were found and are presented in the paper. The aforementioned parameters are as follows: mass flow rates of heating and cooling media in all three coils, mass flow rate of freshwater supplying the HST, number of loops in coils and resulting heat transfer area, diameter of the loops of the coils, diameter of the coils, time after which water in the HST reaches a steady value, time period within which the HST may fulfil demand for central heating and domestic hot water (DHW) preparation without being charged simultaneously. The presented analytical model was validated based on the available data in the field literature and a high compliance was reached. For this purpose theoretical model results were compared to results of HST computational fluid dynamics (CFD) simulations. The temperature calculated using the presented model differed from the one obtained by the CFD analysis by 2.96 K.

Numerical simulation of thermal flows and entropy generation of magnetized hybrid nanomaterials filled in a hexagonal cavity

The current study addresses the features of entropy generation and thermal flows regarding magnetized hybrid nanofluid in the presence of a cylinder in a closed hexagonal domain. The hexagonal cavity comprises two heated horizontal walls, and two are insulated while the other walls are cold. The whole system has been modeled as coupled non-linear partial differential equations. Also, normalized the governing coupled equation by utilizing a proper pair of variables and are computed with a finite element approach. For the approximation of velocity profiles, a finite element space involving the quadratic polynomial (P2) is selected whereas the pressure and temperature estimation is accomplished through a space of linear polynomial (P1). An analogy is handed with published findings at confining instance. The degree of freedom and grid convergence test is considered for the kinetic energy (KE) and Bejan number (Be). The study reveals a major role in enhancing the heat transfer rate due to hybrid nano-particles. The results show that the increase of magnetic field effect considers the reduction of the heat transfer because the conduction motion occupies the motion of the fluid flow. When the Hartmann number is increased, the magnetic entropy is raised, too. For intensified the Hartmann numbers, the highest ratio of heat transfer occurs for the case of the hybrid nanoparticles, and then MgO-water, followed by the Ag-water. The nature of thermal flow parameters has been scrutinized.

External Condensation of HFE 7000 and HFE 7100 Refrigerants in Shell and Tube Heat Exchangers.

The paper describes the results of experimental studies of media as an intermediary in heat exchange taking place in low volume conditions. Their properties predestine them both as a future-proof for transporting and storing heat materials. The paper concerns the current topic related to the miniaturization of cooling heat exchangers. There are many studies in the literature on the phase transition of refrigerants in the flow in pipe minichannels. However, there is a lack of studies devoted to the condensation process in a small volume on the surface of pipe minichannels. The authors proposed a design of a small heat exchanger with a shell-and-tube structure, where the refrigerant condenses on the outer surface of the pipe minichannels cooled from the inside with water. It is a response to the global trend of building highly efficient, miniaturized structures for cooling and air conditioning heat exchangers. Two future-proof, ecological replacements of the CFC refrigerants still present in the installations were used for the experimental research. These are low-pressure fluids HFE 7000 and HFE 7100. The tests were carried out in a wide range of changes in thermal-flow parameters: G = 20–700 kg·m−2s−1, q = 3000–60,000 W·m−2, ts = 40–80 °C.

Experimental analysis applied to an evacuated tube solar collector equipped with parabolic concentrator using multilayer graphene-based nanofluids

Solar collectors are essential to enable the direct use of solar energy. Graphene nanoparticles stand out among other nanoparticles because it presents high thermal conductivity. The aim of this study is to evaluate the thermal efficiency increase achieved applying multilayer graphene (MLG) in low volumetric fractions dispersed in water. An evacuated tube solar collector equipped with parabolic concentrator was herein used in a closed circuit. Thermal efficiency was evaluated considering different recirculating flow rates (6, 24, 42 and 60 L h−1), two volumetric fractions of MLG (0.00045% and 0.00068%) with and without concentrator. A semi-empirical equation was developed to estimate thermal efficiency based on hydraulic- and thermal-flow parameters. In relation to the flow rate the best performance was obtained at 42 L h−1. Furthermore, the use of the parabolic concentrator increased by approximately 298% the thermal efficiency in comparison to the collector without concentrator. An excellent fit (R2 = 0.970) was obtained between efficiencies estimated through the semi-empirical equation and those estimated through measurements performed in the current study. MLG nanofluid in concentrations of 0.00045 vol% and 0.00068 vol% increased the thermal efficiency of the solar collector by 31% and 76%, respectively in comparison to the base fluid.

Experimental investigation of heat transfer enhancement in straight and U-bend double-pipe heat exchanger with wire insert

In this paper, the possibility of heat transfer enhancement in the U-bend exchanger was presented. Experimental research has been carried out for four individual heat exchanger constructions i.e. plain tube in tube, turbulized tube in tube, plain U-bend and U-bend with turbulator. Also, heat transfer experiments for various boundary conditions were performed to obtain reference values. In case of U-bend exchanger with and without turbulator, tests were conducted based on the water-water system. The study covered a wide measuring range, i.e. Re = 800–9000 - on the jacket side, Pel = 500–1400 W (for reference) cold water temperature of 9°C and hot water of 50°C. The exchangers were made from a copper pipe with an external diameter of 10 mm and 18 mm and wall thickness of 1 mm. The helicoidal vortex generator was made from brass wire with a diameter of 2.4 mm, coil diameter 13 mm and pitch 11 mm. For these geometries, the values of pressure drop and rate of heat transfer were determined. The comparison of heat transfer efficiency was performed based on NTU-ε method. For the same thermal-flow parameters, wire inserts provide up to 280% heat transfer enhancement and 85% higher heat transfer rate.

Experimental investigations on heat transfer enhancement in shell coil heat exchanger with variable baffles geometry

The paper presents the possibility of using passive intensification of heat transfer in the form of baffles to increase the energy efficiency of the shell and coil heat exchanger. The experiment was carried out by using a modular coil heat exchanger in the form of an electric heater. Water was used as a working fluid with constant thermal-flow parameters at the inlet of the module. It should be noted that experiments were made for a large range of power i.e. from 200 W to 1200 W and with mass flow rates from 0.01 kg−1 to 0.03 kg−1. For this flow range, Reynolds numbers were obtained in the field 150 < Re < 450. Consequently, all experiments were carried out for laminar flow conditions. This work shows, that due to the presence of mixed convection, natural convection has a significant effect on small values of Reynolds numbers and large values of Richard’ number. Also, the baffles location has a significant influence on HX performance. The proposed solution of the shell coil exchanger with a baffle is characterized by better heat transfer efficiency on the shell side, but rather for lower values of Reynolds (Re < 150) numbers and high values of heat fluxes. For all configurations is noticeable the influence of the supplied heat flux value on the rate of heat transfer. The paper presents new experimental Nusselt numbers correlation on the shell side of the heat exchanger with core-baffles. This correlation depends on Grashoff and Dean numbers as well as dimensionless shell diameter (C/D0), the correlation also includes Prandtl number. Experimental data were compared with selected correlations from literature as well as with own correlation. It was shown that only own semi-empirical correlation has satisfactory compliance with experimental results within 35% error band and with less than 8% of absolute deviation. The considered construction has markedly better heat transfer efficiency on the shell side for small Reynolds numbers (Re<150) comparing to the tube-in-tube exchanger with wire coil turbulator(over 20%).

유체 구조 상호작용 문제를 가진 다공성 촉매 담체에서 실동경계조건의 역문제 해석을 위한 최적화 기법

이 논문은 촉매 담체에서 열유동 및 구조해석의 실동경계조건에 대한 역문제 해법을 나타낸다. 촉매 담체의 배기가스 정화효율은 열유동 매개변수와 촉매 성분 등에 영향을 받고 열유동 균일도에 의해 평가된다. 역문제의 정식화-열유동 매개변수(입구 온도, 속도, 반응열, 대류열전달계수)를 얻고-와 직접 문제-주어진 출구 온도 분포로부터 평가-를 설명하였다. 실험계획법과 반응표면 최적화 기법은 제안된 역문제 해결을 위해 이용하였다. 촉매 담체의 온도 분포는 예측된 열유동 매개변수에 대한 열유동 해석에 의해 얻었다. 열응력과 내구성 평가는 이 온도 분포에 기반해서 수행하였다. 역문제 접근 방법의 유효성과 정확성은 반응표면모델과 측정된 실차 시험과 좋은 일치를 달성함으로써 설명하였다.<BR>

최적화 기법을 이용한 삼원촉매변환기의 열유동 경계조건의 동정

한국에서 삼원촉매 내구성은 1988년에 5년/80,000 km 이지만 2002년 이후로 10년/120,000 km이 요구된다. 국내의 삼원촉매는 배출가스 정화효율이나 압력강하 등이 만족하지만 열적 내구성은 만족시키지 못하고 있다. 삼원촉매는 내부에서 높은 온도를 유지하지만 외부 표면에서는 낮은 온도를 유지한다. 본 연구는 열유동과 구조해석 및 다음과 같은 과정에 의해서 열적 내구성을 평가하였다. 열유동 매개변수 범위는 차량시험과 열유동 해석에 의해 결정하였다. 후면 촉매 온도에 대한 반응 표면은 열유동 매개변수에 대한 실험계획법을 이용해 구성되었다. 차량시험에서 후면 촉매 온도에 대한 열유동 매개변수는 만족도 함수에 의해 예측하였다. 삼원촉매의 온도분포는 예측된 열유동 매개변수에 대한 열유동 해석에 의해 평가하였다. 【Three-way catalyst durability in the Korea requires 5 years/80,000km in 1988 but require 10 years/120,000km after 2002. Domestic three-way catalyst satisfies exhaust gas conversion efficiency or pressure drop etc. but don't satisfy thermal durability. Three-way catalyst maintains high temperature in interior domain but maintain low temperature on outside surface. This study evaluated thermal durability of three-way catalyst by thermal flow and structure analysis and the procedure is as followings. Thermal flow parameters ranges were determined by vehicle test and basic thermal flow analysis. Response surface for rear catalyst temperature was constructed using the design of experiment (DOE) for thermal flow parameters. Thermal flow parameters for rear catalyst temperature in vehicles examination were predicted by desirability function. Temperature distribution of three-way catalyst was estimated by thermal flow analysis for predicted thermal flow parameters.】

97/01386 The use of ‘combustion additives’ to improve heat transfer and reduce combustion emissions in package boilers

The combined cycle power island consists of three major components: the gas turbine (GT), the heat recovery steam generator (HRSG), and the steam turbine (ST). The cleaned syngas is sent to the GT to produce electric power. The exhaust of the GT is used to generate steam through the HRSG. The steam is used to drive a steam turbine to generate more electric power. Since GTs are very special high-tech products, they are designed and manufactured with specific operating conditions in mind. Selection of GTs must be made from the existing commercially available models with their specific ratings; whereas, STs and HRSGs can be scaled up and manufactured to match the power required by the plant designers. Similarly, almost all of the other components in the rest of an integrated gasification combined cycle plant—such as air separation units, gasifiers, gas cleanup systems, etc.—can be scaled and custom-made to match the flow rates and fuel qualities needed for the GTs. Therefore, all of the thermal-flow parameters are typically designed around the GT’s specifications.In this chapter, the fundamental thermodynamics of Brayton and Rankine cycles are presented. Specifications of commercial gas turbines are then introduced, followed by discussions of the working principles of each component in gas turbines, including aerodynamics in compressors, turbines, and the reverse-flow combustor and dump diffuser assembly, turbine airfoil cooling, and combustion mechanisms. Various schemes to enhance work output and cycle efficiencies are introduced, including regeneration, reheat, intercooling, steam injection, inlet fogging/overspray. Examples of case studies of simple and combined cycles with various power and efficiency enhancement schemes are presented.