Abstract This study conducted an investigation on the heat transfer process of helix ground heat exchanger (HGHE) by numerical simulation and experiment. The concept of thermal interference index was proposed, and the thermal interference index in the soil around HGHE was investigated under different soil type conditions. The results showed that with the progress of the heat transfer process of the HGHE, the thermal interference of the soil around the HGHE gradually increases. Therefore, the transient heat transfer coefficient and efficiency coefficient of the HGHE decrease, which weakens the heat exchange between the HGHE and the soil to a certain extent. When burying the HGHE, priority should be given to the soil type with excellent thermal conductivity, which is conducive to the outward diffusion of heat emission from the heat exchanger. In this way, it can effectively reduce the thermal interference index of the soil around the HGHE and can indirectly improve the heat transfer performance of the heat exchanger. For example, in sandy loam soil type condition, the thermal interference at the middle of the busbar position is 2.14 (m·°C)/W, which is 83.3% of the clay loam soil type condition. Therefore, the heat flux of HGHE under sandy loam condition is about 20.7% higher than that under clay loam condition.

Inverse Estimation of Swirl Cooling Heat Transfer Coefficient

A transient formulation of entropy and heat transfer coefficients of Newton's cooling law with the unifying entropy potential difference in compressible flows

Enhanced heat transfer in microgravity from asymmetric sawtooth microstructure with engineered cavities

Characteristics of the transient heat transfer of impinging flames and correlation analysis using a new characteristic velocity under CI engine-like conditions

Reconstruction of transient convective heat transfer coefficients in heat transfer of gun barrels with variable coefficients

Stagewise melting heat transfer characteristics of phase change material in a vertically placed rectangular enclosure

The recovery of low-temperature steam is of great significance to the effective utilization of energy. Direct contact condensation (DCC) technology is an effective heat recovery method with a low initial investment. An evaluation of the direct contact condensation heat transfer technology of water droplets and low-temperature saturated steam (at an absolute pressure of 7.3–19.9 kPa) was performed using both experimental and computational approaches. In the experiment, an experimental device based on the weighing method was set up, and the direct contact heat transfer process between droplets with a normalized diameter of less than 21.7 and saturated pure steam at 40–60 °C was experimentally investigated. The transient condensation efficiency and heat transfer coefficient were calculated by the real-time mass variation. The rapid condensation stage was classified to discuss the effects of initial droplet diameter, pressure, temperature, and mass flow rate on the heat transfer process. A two-dimensional model was developed using computational fluid dynamics techniques and verified by experimental results. The results indicated that when the normalized diameter of the droplet is less than two, 1.6 is the optimal value for DCC. For droplets with a normalized diameter greater than two, the optimal droplet temperature and mass flow rate are 15 °C and 10 g/s, respectively.

Experimental investigation on flow boiling characteristics in offset strip fin channels under different sloshing conditions

Experimental study on transient heat transfer characteristics during the dropping of containment pressure

Experiments have examined the phenomenon of direct contact condensation when steam is injected vertically into the subcooled water pool. The investigation is carried out by varying the steam mass flow rate and submergence depth of the steam injection pipe in the range of 10–50 kg/h and 1–13 cm, respectively. The behavior of the bubble that appeared at the pipe outlet, transient heat transfer coefficient, pressure variation in the steam injection pipe, and its associated frequency have been analyzed. The images captured by high-speed camera showed different bubble shapes. The overall cycle time of bubble evolution has decreased with an increase in the mass flow rate and increased with an increase in the pipe submergence depth. The time-averaged heat transfer coefficient increased with an increase in the mass flow rate and decreased with the rise of the pipe submergence depth. The pressure drop within the steam injection pipe shows the parabolic variation with an increase in the mass flow rate and is slightly influenced by the submergence depth due to changes in interfacial structures within the pipe. The peak frequency associated with the pressure has increased with an increase in the mass flow rate and decreased with an increase in the pipe submergence depth at higher mass flow rates. The fast Fourier transform of interfacial area of the larger bubble at the pipe outlet shows that the first peak frequency lies between 0.5 and 5 Hz, and the second peak frequency lies in the range of 25–30 Hz.

Transient heat transfer characteristics of submerged heat source under seismic excitation

Numerical study on the condensation characteristics of various refrigerants outside a horizontal plain tube at low temperatures

In this study, a mathematical model is developed for analyzing the time-dependent magneto-convective flow and heat transfer characteristics of an electrically conducting (functional) third-grade Reiner-Rivlin non-Newtonian nanofluid from a moving or stationary hot cylinder in the presence of magnetic field and thermal radiation. A well-tested convergent Crank–Nicolson type finite difference algorithm is employed to solve the transformed, nonlinear boundary value problem. The Tiwari-Das nanofluid volume fraction model is adopted for nanoscale effects and the Rosseland algebraic flux model for radiative heat flux effects. It has been shown that the shape of nanoparticles remarkably contributes to the enhancement of heat transfer. Several metallic nanoparticle types such as Al2O3, Cu, and TiO2 are examined. It is found from the investigation that the viscoelastic nanofluid with TiO2 nanoparticles results in more heat transfer than the other nanoparticles. Lower velocity and higher temperature values are computed at transient conditions with a higher third-grade fluid parameter for the flow of nanofluid (Al2O3-SA). The plots of transient friction and heat transfer coefficients are visualized at the surface of a hot cylinder. The tabulated heat transfer coefficient is comparatively more for the moving cylinder than the stationary cylinder. Detailed validation of results of the numerical scheme with previous studies is included. The simulations find applications in coating deposition (enrobing) of magnetic nanomaterial at high temperatures, functional nanomaterial synthesis, etc.

Experimental investigation of lithium-ion cells ageing under isothermal conditions for optimal lifetime performance

Transient experimental investigation of airside heat transfer in a crossflow heat exchanger

A modified sequential gradient-based method for the inverse estimation of transient heat transfer coefficients in non-linear one-dimensional heat conduction problems

The valves of an internal combustion engine play an essential role in the automobiles and their surroundings significantly affect their thermo-mechanical behavior. The work aims to assess numerically the effect of the real thermo-mechanical boundary conditions on the valves by considering the actual complex surrounding. For this purpose, we have subdivided the valve into seven adequate zones. We have evaluated the average values of the transient heat transfer coefficient, the adiabatic wall temperature and the mechanical load at each subdivision are during the opening and the closing periods. A transient Finite Element Model under ANSYS APDL software is developed and simulations are carried out until reaching the steady state. The temperature distribution and the thermal stresses at each valve position is obtained and then analyzed. The main findings show that the stress intensity distribution is developed in the zones labelled stem guide port and seat local of large temperature gradients, which causes high thermal stresses responsible of cracks or thermal fatigue damage. In addition, knowing the temperature map, the thermal gradient and stress under actual conditions will surely help manufacturers to better design exhaust valve, avoid early failure and enhance the durability of valves.

A drop impingement on a hot surface is known as an effective way for heat removal. The present work uses a VOF (volume of fluid) model to simulate the flow behavior and temperature distribution on a 50 °C heated plate while relatively cold water drop is impinging. The temperature distribution at the impingement zone is used to examine the transient heat transfer coefficients using a single drop and double drops conditions. The spreading factor is tested in both cases. A test rig is built to verify the temperature distribution and a heat balance method is introduced to find the experimental heat coefficients on the heated. The CFD solution and its flow results gives a good agreement for single drop previous results. The results for the double drop condition show a high tendency for rebound and splash of the drop leaving the central zone without water drop coverage which way causes a burn out in case of high heat fluxes. The single drop condition show a symmetrical temperature and heat transfer coefficients distribution while the double drop impingement gives lower value of coefficients with non-uniform and unsymmetrical distribution specially at the bigger drop to plate distances. The experimental average heat coefficients gives relatively low error of only 5% in case of double drop when compared to the single drop values.

Determining transient heat transfer coefficient for dropwise condensation in the presence of an air flow