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In the present work, a study on convective heat, mass transfer coefficients and evaporative heat transfer coefficient of the thin layer drying process of ivy gourd is performed. The experiment was conducted in three drying modes such as natural, forced convection solar dryer and open sun drying. The hourly data for the rate of moisture removal, sample temperature, relative humidity inside and outside the solar and ambient air temperature for complete drying have been recorded. The drying air temperature varied from 55, 65, 70 and 75 °C, and the air velocity was 1, 1.5 and 2 m/s. All the drying experiments had shown a falling rate period. The data obtained from experimentation have been used to evaluate the experimental constant values of C and n by simple regression analysis. Based on the values of “ C ” and “ n ”, convective and evaporative heat transfer coefficients for ivy gourd were determined. The average convective heat and mass transfer coefficients varied between 2.64 and 8.30 W/m 2 °C and 0.0025 to 0.0076 m/s for temperature ranges, at the different air velocities, respectively. The average evaporative heat transfer coefficient for ivy gourd varied from 181.89 to 421.84 W/m 2 °C. It was observed that convective and evaporative heat transfer coefficients increase with the increase in drying air temperature. The rate of increment of evaporative heat transfer coefficient is higher than the convective heat transfer coefficient. The intensity of heat and mass transfer during solar drying depends on the drying air temperature and velocity. Graphical abstract

The convective and radiative heat transfer coefficients of clothing are important parameters for human thermoregulation and comfort models. Many researchers have studied convective and radiative heat transfer coefficients of the naked human body. However, there is limited information on convective and radiative heat transfer coefficients for the clothed human body. Therefore, this study aims to confirm whether the convective and radiative heat transfer coefficients vary with different clothing ensembles in addition to clarifying how the difference in clothing heat transfer coefficients affects the prediction of thermal comfort index, such as the predicted mean vote (PMV) index. The convective and radiative heat transfer coefficients for eight sets of clothing ensembles were measured through a manikin experiment. The results demonstrated that (1) the largest difference between convective heat transfer coefficients for various clothing ensembles was 32%, and (2) PMV values differed between the clothing ensembles with the largest value being approximately 0.2, which corresponds nearly 1 °C change in the indoor temperature. Therefore, it is necessary to consider the actual clothing convective heat transfer coefficient for the precise prediction of thermal comfort.

The heat transfer coefficient, including interfacial heat transfer coefficient (IHTC) and convective heat transfer coefficient (CHTC), plays a pivotal role in the thermal dynamics of hot gas forming processes. This parameter can determine the temperature field, thereby affecting the deformation and mechanical properties of the material to improve productivity. In this paper, we present an innovative experimental apparatus designed to measure the temperature evolutions of the aluminum specimen and the die during the hot gas forming processes. This apparatus is capable of simultaneously measuring IHTC and CHTC. Using the inverse finite element method, the simulated temperature histories are matched with empirical data and the best-fit values are adopted as indicative of IHTC and CHTC. This study identified the effects of contact pressure and die temperature on IHTC, as well as the impact of gas pressure on CHTC. In addition, a predictive model was developed to forecast the IHTC and CHTC at varying contact pressures and die temperatures with a prediction accuracy surpassing 0.95. By leveraging the predictive model presented in this paper, users can modulate contact pressure and die temperature based on specific production needs to achieve a targeted temperature profile. This method offers enhanced precision in managing the temperature field of the workpiece during hot gas forming experiments, thereby refining the temperature distribution. Moreover, it optimizes the formability and microstructural attributes of the material, ultimately leading to improved mechanical characteristics.

The external surface heat transfer coefficient of building envelope is one of the important parameters necessary for building energy saving design, but the basic data in high-altitude area are scarce. Therefore, the authors propose a modified measurement method based on the heat balance of a model building, and use the same model building to measure its external surface heat transfer coefficient under outdoor conditions in Chengdu city, China at an altitude of 520 m and Daocheng city at an altitude of 3750 m respectively. The results show that the total heat transfer coefficient ( h t ) of building surface in high-altitude area is reduced by 34.48%. The influence of outdoor wind speed on the convective heat transfer coefficient ( h c ) in high-altitude area is not as significant as that in low-altitude area. The fitting relation between convection heat transfer coefficient and outdoor wind speed is also obtained. Under the same heating power, the average temperature rise of indoor and outdoor air at high-altitude is 41.9% higher than that at low altitude, and the average temperature rise of inner wall is 25.8% higher than that at low altitude. It shows that high-altitude area can create a more comfortable indoor thermal environment than low-altitude area under the same energy consumption condition. It is not appropriate to use the heat transfer characteristics of the exterior surface of buildings in low-altitude area for building energy saving design and related heating equipment selection and system terminal matching design in high-altitude area.

The local heat transfer coefficient (LHTC) can be an effective indicator to describe the local heat transfer characteristics of fractures but has rarely been employed to investigate the local heat exchange properties of a hot dry rock fracture compared to the overall heat transfer coefficient (OHTC). The aim of this paper is to investigate the LHTC of water flowing through a single fracture within a cylindrical granite specimen under confining pressure by combining the numerical modeling approach and the experimental results. A numerical model was successfully developed and verified by the test data. It is found that the local heat transfer coefficient is obviously closely related to the fluctuation of the fracture morphology. Within a certain range of aperture, narrower fracture has higher local heat transfer ability. Increasing the flow rate did not significantly improve the local heat transfer ability in the flat area of the fracture for a fixed fracture aperture. However, at the rougher areas, the flow rate has a higher effect, and the sunken positions at the fracture surface have much larger LHTC. A correlated model was developed to describe the relationship between waviness and LHTC. In addition, a comparison between the LHTCs and the OHTCs shows that the definition-based method presents the smallest values of the OHTCs, which are the closest to the arithmetic mean values of the corresponding LHTCs.

Surface turbulent heat fluxes are crucial for monitoring drought, heat waves, urban heat islands, agricultural water management, and other hydrological applications. Energy Balance Models (EBMs) are widely used to simulate surface heat fluxes from a combination of remote sensing-derived variables and meteorological data. Single-source EBMs, in particular, are preferred in mapping surface turbulent heat fluxes due to their relative simplicity. However, most single-source EBMs suffer from uncertainties inherent to the parameter kB−1, which is used to account for differences in the source of heat and the sink of momentum when representing aerodynamic resistance in single-source EBMs. For instance, the parameterization of kB−1 in the commonly used single-source Surface Energy Balance System (SEBS) model uses a constant value of the foliage heat transfer coefficient (Ct), in the parameterization of the vegetation component of kB−1 (kBv−1). Thus, SEBS ignores the effect of turbulence on canopy heat transfer. As a result, SEBS has been found to greatly underestimate sensible heat flux in tall forest canopies, where turbulence is a key contributor to canopy heat transfer. This study presents a revised parameterization of kBv−1 for the SEBS model. A physically based formulation of Ct, which considers the effect of turbulence on Ct, is used in deriving the revised parameterization. Simulation results across 15 eddy covariance (EC) flux tower sites show that the revised parameterization significantly reduces the underestimation of sensible heat flux compared to the original parameterization under tall forest canopies. The revised parameterization is relatively simple and does not require additional information on canopy structure compared to some more complex parameterizations proposed in the literature. As such, the revised parameterization is suitable for mapping surface turbulent heat fluxes, especially under tall forest canopies.

Nanofluid as a coolant has potential for use in the heat transfer field because of its augmentation in thermal properties that offers advantages in heat transfer. Research on various working temperatures is still ongoing in the nanofluid field. This study focused on the effect of temperature on heat transfer behavior using titanium dioxide or TiO2 nanofluid as the working fluid in forced convection. The heat transfer coefficient was determined for flow in a circular tube under constant heat flux boundary conditions. The experiment was conducted with a Reynolds number less than 25000 with concentrations of TiO2 nanofluid at 0.5%, 1.0% and 1.5%. At 30oC, the maximum enhancement of 9.72% for 1.5% volume concentration was observed. Enhancements of 22.75% and 28.92% were found at 50oC and 70oC, respectively under similar nanofluid concentrations. The nanofluid performance was significantly influenced by working temperature. The heat transfer enhancement of TiO2 nanofluid was considerably improved at higher working temperature and high concentration because of the improvement of thermal properties.  

Due to its low global warming potential (GWP) and good environmental properties, CF3I can be a suitable component of refrigerant mixtures in the field of refrigeration and air conditioning. In this work, the local condensation heat transfer characteristics of CF3I were experimentally investigated in a plate heat exchanger (PHE). The condensation heat transfer experiments were carried out under conditions of vapor qualities from 1.0 to 0.0, at saturation temperatures of 25–30 °C, mass fluxes of 20–50 kg/m2s, and heat fluxes of 10.4–13.7 kW/m2. Local heat transfer coefficients were found to vary in both the horizontal and vertical directions of the plate heat exchanger showing similar trends in all mass fluxes. In addition, the characteristics of local heat flux and wall temperature distribution as a function of distance from the inlet to the outlet of the refrigerant channel were explored in detail. The comparison of the experimental data of CF3I with that of R1234yf in the same test facility showed that the heat transfer coefficients of CF3I were comparable to R1234yf at a low vapor quality and a mass flux of 20 kg/m2s. However, R1234yf exhibited a transfer coefficient about 1.5 times higher at all vapor qualities and a mass flux of 50 kg/m2s. The newly developed correlation predicts well the experimentally obtained data for both CF3I and R1234yf within ±30%.

This study aimed to develop a model using experimentally obtained convective heat and mass transfer coefficients to predict the effect of temperature, humidity, and drying rate on wood drying. Tangential wood samples of Eucalyptus nitens (H. Deane & Maiden) were used in the investigation. The experimental design consisted of two temperature levels (40 °C and 55 °C), two relative humidity levels (55% and 75%), and two air velocity settings (2 m·s−1 and 3 m·s−1). The experiments were conducted under a constant evaporation rate, spanning the maximum and critical moisture content in the wood. A statistical model using multivariate regression was created to predict the convective heat and mass transfer coefficients. The results indicated that the experimental data and empirical correlations exhibited an error margin of 37.77% and 37.86%, respectively. A significant positive correlation was found between the convective heat transfer coefficient and air velocity, temperature, and relative humidity, while the convective mass transfer coefficient showed a significant positive correlation only with air velocity and temperature. The model predicted the convective heat and mass transfer coefficients with high accuracy and statistical significance. Using the proposed method, we successfully obtained both convective coefficients, which enable accurate description of heat and mass flow during the convective drying of Eucalyptus nitens wood.

Grinding is a crucial process in machining workpieces because it plays a vital role in achieving the desired precision and surface quality. However, a significant technical challenge in grinding is the potential increase in temperature due to high specific energy, which can lead to surface thermal damage. Therefore, ensuring control over the surface integrity of workpieces during grinding becomes a critical concern. This necessitates the development of temperature field models that consider various parameters, such as workpiece materials, grinding wheels, grinding parameters, cooling methods, and media, to guide industrial production. This study thoroughly analyzes and summarizes grinding temperature field models. First, the theory of the grinding temperature field is investigated, classifying it into traditional models based on a continuous belt heat source and those based on a discrete heat source, depending on whether the heat source is uniform and continuous. Through this examination, a more accurate grinding temperature model that closely aligns with practical grinding conditions is derived. Subsequently, various grinding thermal models are summarized, including models for the heat source distribution, energy distribution proportional coefficient, and convective heat transfer coefficient. Through comprehensive research, the most widely recognized, utilized, and accurate model for each category is identified. The application of these grinding thermal models is reviewed, shedding light on the governing laws that dictate the influence of the heat source distribution, heat distribution, and convective heat transfer in the grinding arc zone on the grinding temperature field. Finally, considering the current issues in the field of grinding temperature, potential future research directions are proposed. The aim of this study is to provide theoretical guidance and technical support for predicting workpiece temperature and improving surface integrity. The temperature field is divided into uniform continuous segment and nonuniform discontinuous counterpart. The heat source distribution model is summarized for different cutting depths. The energy proportional coefficient and convective heat transfer coefficient models are summarized. The application and implementation of temperature field and grinding thermal mode are summarized.