Numerical and Experimental Study of Heat Transfer in a BIPV-Thermal System

Numerical analysis on enhanced performance of new coaxial cross twisted tapes for laminar convective heat transfer

Numerical Study of Conjugate Heat Transfer in a BIPV-Thermal System

Local and overall convective heat transfer coefficients for human body with air ventilation clothing: Parametric study and correlations

Experimental assessment of the gap width effect on turbulent flow and forced convective heat transfer around a single rod suspended in a channel

Jet impingement heat transfer has gained attention of the researchers due to its very high rate of convective heat transfer. The objective of this study is to establish an analytical technique to predict the convective heat transfer coefficient and the reference temperature over a surface being impinged. This technique is based on the fundamental mathematical concept of Green’s function. A code in MATLAB is developed to predict both local convective heat transfer coefficient and reference temperature over the impinging surface, which requires the transient temperature data at both faces of the impinging plate as input. Radiation correction is also considered to incorporate radiation losses in high-temperature applications. This code works on the principle of one-dimensional heat transfer across the impinging plate, for known dimensions, thermal diffusivity, and surface emissivity. A numerical simulation of hot jet at Reynolds number equal to 1000, over a cold plate of thickness 10 mm, is carried out for a given set of spatially varying convective heat transfer coefficient and reference temperature values, along the impinging surface. The impinging plate is considered to be orthotropic to ensure one-dimensional heat conduction across the plate thickness. Transient temperature at both the faces for a duration of 10 s with an interval of one second was recorded and used as input to the code to validate the proposed technique. Local heat transfer coefficient and the reference temperature predicted are in good agreement with those input values for numerical analysis using ANSYS, having a maximum deviation of 2 and 10%, respectively. Further, it is observed that estimated values of convective heat flux at a given location on the impinging surface varies linearly with temperature at the same location, which confirms Newton’s law of cooling.

This paper presents a numerical study on the heat transfer performance of U-shaped double-pipe heat exchanger for the concentrated solar power system. The effects of the mass flow rate, temperature and pressure of inlet super-critical CO2 are evaluated. The results show that due to the effect of centrifugal force, temperature and flow velocity distribution divergences happen in the elbow part of the double-pipe. That can enhance the heat transfer performance. With the inlet super-critical CO2 mass flow rate increased, the convection heat transfer coefficient and Nusselt number of the super-critical CO2 both increase. When the inlet super-critical CO2 mass flow rate increases to 0.6 kg s−1, the maximum local average convection heat transfer coefficient and Nusselt number of the super-critical CO2 are 7120.0 W m−2K−1 and 1892.7. By increasing the inlet super-critical CO2 temperature or pressure, the convection heat transfer coefficient of the S–CO2 can be increased. With the inlet super-critical CO2 temperature increased from 700.0 K to 780.0 K, the maximum local average convection heat transfer coefficient of super-critical CO2 increases from 5034.5 W m−2K−1 to 5149.1 W m−2K−1. Compared with the other two parameters, the effect of inlet super-critical CO2 pressure on the heat transfer performance is relatively smaller.

The objective of the present study was to understand the fundamental mechanism of the enhancement of the convective heat transfer coefficient as well as the thermal capacity of a working fluid by using the latent heat of the solid-liquid phase change of particles. Tests were performed with water flowing turbulently in a long heating test section (i.e., 627 diameters) with a uniform heat flux boundary condition. Three effects influence the local friction and heat transfer coefficients: (1) the developing effect, (2) the radial viscosity change effect, and (3) the axial viscosity change effect. A new analysis method to obtain fully developed friction factor and Nusselt number is proposed. The Blasius equation, f = 0.079 Re-0.25, was found to yield a good prediction of the turbulent friction coefficient with a 2.1% error. It would make a better prediction if the proportionality constant 0.079 in the equation was replaced with a new constant: 0.081. The power factor, m, in a general Nusselt number correlation, Nu = C Rem Pr0.4, was found to be 0.979, which was greater than the widely used value of 0.8 used in the Dittus-Boelter correlation. Tests were also conducted with a phase-change-material (PCM) slurry that was a suspension of PCM particles in a carrier fluid, water. A new method to generate very fine PCM particles using an emulsifier was introduced. With such fine PCM particles, the flow loop did not clog. Local pressure drops and local heat transfer coefficients were measured along the test section. Significant decreases in pressure drop occurred where the PCM particles in the slurry melted. The local convective heat transfer coefficient was found to vary significantly (up to 200%) when the particles melted. This made it difficult to directly apply the LMTD method or the effective thermal capacity method, which had been used in previous researches, to the heat transfer analysis of the PCM slurry flow. A new three-region melting model is proposed, and an explanation of the physical mechanism of the convective heat transfer enhancement due to the PCM particles is provided.

Forced convection heat transfer with phase-change-material slurries: Turbulent flow in a circular tube

Experimental transient natural convection heat transfer from a vertical cylindrical tank

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

The determination of local convection heat transfer coefficients of pipe flow using pulsed laser heating (PLH) from a combination of experimental and numerical study is presented in this paper. The method is advantageous because it is fluid-independent, contact-free and high in spatial and temporal resolution. For simplicity, the experiment used water at different temperatures and flow rates inside two long circular tubes which were subject to radiation heating using a finite size (20 mm in diameter) pulsed laser beam. An infrared camera was used to image and measure its surface temperatures. Two correlations for convection heat transfer coefficient in the thermal/combined entry length region were used in this paper for comparison with the experimental results. The experimental results using the thermal circuit method processed by MATLAB® agree well with both correlations. To gain better insight and quantify the uncertainty, a 3-D conjugated heat transfer simulation was carried out using Fluent CFD. The implication of the accuracy and limitation of the PLH method on the determination of local heat transfer coefficients are also discussed in the analysis.

The main aim of the research is to support the development of the commercial vehicle electric parking brake. Though nowadays widely used on passenger cars, electric parking brake applications on commercial vehicles present completely different challenges. With the brake mass, thermal capacity and required clamp forces an order of magnitude higher, safe parking demands much more attention. In the first instance, the priority is placed upon predicting heat dissipation from the brake disc only. The research is presented in two parts; part one (presented here) focuses on analytical modelling and experimental verification of predicted disc temperatures over long cooling periods, with part two investigating the air flow, velocities and convective heat transfer coefficients using computational fluid dynamics modelling, also followed by experimental validations. To begin the analytical analysis, a study was conducted into the variance in mean local convective heat transfer coefficients over a simplified brake disc friction surface, by investigating typical dimensionless air properties. A nonlinear equation was derived for the average surface convective heat transfer coefficient ([Formula: see text]) variability with temperature drop for the entire cooling phase. Starting from fundamental principles, first-order differential equations were developed to predict the bulk disc temperature. By including variation of the convective and radiative heat dissipation throughout the cooling period, a good correlation was achieved with measured values, to within 10%. Experiments were conducted on a specifically designed thermal rig which uses 15 kW induction heater to heat the disc. Numerous experiments proved the results are very repeatable, throughout the cooling period. It was established, for the grey cast iron brake disc with a fully oxidised surface, the emissivity value are practically constant at ɛ = 0.92. Although the research is being conducted on a brake disc, the results have generic application to any disc geometry, whatever the application.

Convective heat transfer of falling film around the horizontal half-oval tube with reverse airflow in an evaporative condenser

Local and average convective heat transfer coefficients were measured for arrays of widely spaced impinging air jets and correlated in terms of system geometry, air flow, and fluid properties. The configurations were square arrays of circular turbulent jets (spaced from 10–25 diameters apart) incident upon a flat isothermal target surface. Independent parameters were varied over ranges generally corresponding to gas turbine cooling applications. Local heat transfer coefficients were influenced by interference from neighboring jets only when the target plate and the jet orifice plate were less than five jet diameters apart. Average heat transfer coefficients were nearly equal for all the arrays tested as long as the coolant flow per unit area of target surface was held constant. In fact, there was a tendency for the more widely spaced configurations to produce slightly higher average heat transfer under such conditions.

Experimental study of convective heat transfer from the surface of a gyratory lantern