Relativistic heat conduction

The hyperbolic heat conduction equation (HHCE), which acknowledges the finite speed of heat propagation, is based on microscopic evidence from the kinetic theory and statistical mechanics. However, it was argued that the HHCE could violate the second law of thermodynamics. This paper shows that a HHCE-like equation (RHCE) can be derived directly from the theory of relativity, as a direct consequence of space-time duality, without any consideration of the microstructure of the heat-conducting medium. This approach results in an alternative expression for the heat flux vector that is more compatible with the second law. Therefore, the RHCE brings the classical field theory of heat conduction into agreement with other branches of modern physics.     

An Analytical Solution of Melting around a Moving Elliptical Heat Source

ＡｎＡｎａｌｙｔｉｃａｌＳｏｌｕｔｉｏｎｏｆＭｅｌｔｉｎｇａｒｏｕｎｄａＭｏｖｉｎｇＥｌｌｉｐｔｉｃａｌＨｅａｔＳｏｕｒｃｅ￥Ｗ．Ｚ．Ｃｈｅｎ；Ｓ．Ｍ．Ｃｈｅｎｇ；Ｚ．Ｌｕｏ；Ｈ．Ｑ．Ｚｈｕ（ＨｕａｚｈｏｎｇＵｎｉｖｅｒｓｉｔｙｏｆＳｃｉｅｎｃｅａｎ...     

Non-Fourier heat conduction in a hollow sphere with periodic surface heat flux

Presented is the analysis of non-Fourier effect in a hollow sphere exposed to a periodic boundary heat flux. The problem is studied by deriving an analytical solution of the hyperbolic heat conduction equation. Using the obtained analytical expression, the temperature profiles at outer and inner surfaces of the sphere are evaluated for various thermal relaxation times. By comparing the results of non-Fourier model with those obtained from Fourier heat conduction equation, the transition process from parabolic model to hyperbolic one is shown. The phase difference and amplitude ratio of boundary surfaces are calculated as functions of the thermal relaxation time and the results are depicted graphically.     

水源热泵空调的特点和应用

简述了水源热泵空调的特点及节能应用     

Falkner-Skan problem for a static and moving wedge with prescribed surface heat flux in a nanofluid

An analysis is carried out to study the problem of the steady flow and heat transfer over a static or moving wedge with a prescribed surface heat flux in a nanofluid. The governing partial differential equations are transformed into a set of nonlinear ordinary differential equations using similarity transformation, before being solved numerically by the Keller box method and the Runge-Kutta-Fehlberg method with shooting technique. The features of the flow and heat transfer characteristics are analyzed and discussed. Three different types of nanoparticles are considered, namely copper Cu, alumina Al₂O₃ and titania TiO₂ with water as the base fluid. It is found that the skin friction coefficient and the heat transfer rate at the surface are highest for copper-water nanofluid compared to the alumina-water and titania-water nanofluids. Moreover, the heat transfer rate at the surface increases with the Falkner-Skan power law parameter m.     

Potential of ground heat source systems

This paper presents a historical background of ground source heat pump technology, followed by a review of its current shortcomings. Based on these observations the author assesses the R&D needs and recommendations for future research.     

A moving finite line source model to simulate borehole heat exchangers with groundwater advection

Available analytical models for the thermal analysis of ground source heat pumps (GSHPs) either neglect groundwater flow or axial effects. In the present study a new analytical approach which considers both effects is developed. Comparison with existing analytical solutions based on the finite and infinite line source theory is carried out. This study shows that in general the heat transfer at the borehole heat exchanger (BHE) is affected by groundwater flow and axial effects. The latter is even more important for long simulation times and short borehole lengths. At the borehole wall the influence of the axial effect is restricted to Peclet numbers lower than 10, assuming the BHE length as characteristic length. Moreover, the influence of groundwater flow is negligible for Peclet numbers lower than 1.2. As a result for Peclet numbers between 1.2 and 10 the combined effect of groundwater flow and axial effects has to be accounted for when evaluating the temperature response of a BHE at the borehole wall and thus the use of the moving finite line source model is required.     

Analysis of melting around a moving heat source

This paper presents an analysis for simulating melting heat transfer around a moving, horizontal, cylindrical heat source. Motivated by the experimental observations, the melt domain is divided into two regions, namely, the close-contact region and the melt pool region. Two mathematical models are formulated and solution procedures are developed accordingly. The temperature and the flow fields in the two regions are calculated for a constant surface temperature heat source and the resulting velocity of the source and motion and shape of the interface are determined. The effects of the prescribed surface temperature of the source and its density, as well as influence of natural convection in the melt pool, are investigated and reported. The predicted melt flow structure and the motion and shape of the solid-liquid interface are found to be in good agreement with the experimental observations when natural convection in the melt is included in the model.     

An assessment of sand source heat pump systems

Two small scale heat pumps have been built to extract heat from warm dry sand. the earlier unit uses R12B1 as the working fluid and the later one R11. the experimental data demonstrate the possibility of providing sterilized water in remote areas using warm dry sand as a heat source. Unsteady state heat transfer rates were measured using an electrically heated tube installed axially in a cylinder of sand. the results agree closely with those predicted by theory. Heat extraction data also obtained by passing cold water through the ground coil of the heat pump.     

Periodic temperature distribution around an underground sphere with a periodic heat source

The paper addresses the problem of the estimation of ground losses from underground structures. Existing work has been limited to the cylinder and the sphere for steady state conditions. The numerical solution of the three-dimensional equations for time-dependent conditions requires a prohibitive amount of computing time. The present paper analyses a spherical underground structure with a periodic source at its centre and with periodic ground surface temperature.     

Performance of a solar air composite heat source heat pump system

For the shortcoming of air source heat pump in heating condition, a composite heat exchanger was designed which integrates fin tube and tube heat exchanger, and it can achieve synchronous and composite heat exchange in one heat exchanger between working fluids, gaseous and liquid heat source. With the above composite heat exchanger as the core component, the Solar Air Composite Heat Source Heat Pump System (SACHP) was developed which has three working modes, including single solar heat source mode, single air heat source mode and solar air dual heat sources mode. A SACHP experiment table was established and conducted a comprehensive experimental study of three working modes of this system in the standard enthalpy difference laboratory. The results show that when the ambient temperature was −15 °C, compared to the single air heat source mode, the dual heat source mode increased 62% in heat capacity and 59% in COP; when the temperature difference of combined heat transfer was 5 °C, compared to the single air heat source mode, the dual heat source mode increased 51% in heat capacity and 49% in COP. Experimental results demonstrate that the application of the solar air composite heat pump technology can accelerate the application process of the solar heat pump in air conditioners for buildings.     

The boundary element method applied to forced convection heat problems

An integral equation formulation for steady flow of a viscous fluid is presented based on the boundary element method. The continuity, Navier–Stokes and energy equations are used for calculation of the flow and temperature fields. The governing differential equations, in terms of primitive variables, are derived using velocity–pressure–temperature parameters. The calculation of fundamental solutions and solutions tensor is shown. Applications to simple flow cases, such as driven cavity, forward facing step, deep cavity and channel are presented. Convergence difficulties are indicated, which have limited the applications to flows of low Reynolds numbers.     

Analytic model for transient heat exchanger response

The temperature transient response of a single-phase fluid and a wall in a heat exchanger is investigated for when the other constant temperature fluid is subjected to a step change in temperature or when the single-phase fluid is subjected to a step change in mass flow rate. The dynamic behavior of the heat exchanger is approximated by an integral method assuming that the single-phase fluid temperature distribution can be expressed by a combination of the initial and final temperature distributions and a determined time function. The results are validated by comparison against numerical simulations. Excellent agreement is obtained.     

浅议混合地源热泵系统(HGSHPS)

随着GSHP技术的进一步发展，针对夏冬季节冷热负荷不平衡地区的混合地源热泵系统（HGSHPS）应运而生，为进一步扩大GSHP的适用地域范围创造了有利条件。文中分别介绍了适用于南方及北方气候特点的两种HGSHPS，并对其结构、原理、主要技术优点以及控制策略作了详尽的分析，指出了其研究中的核心问题，展望了其应用前景。     

Application of a heat pump system using untreated urban sewage as a heat source

Untreated urban sewage contains large amounts of thermal energy; and its temperature is suitable as a heat source in heat pumps for the heating and cooling of buildings. However, it is not widely used in heat pump systems due to the problem of filth. This paper presents an untreated sewage source heat pump (USSHP) system in which auto-avoiding-clogging equipment is used to continuously capture suspended solids in the sewage. Thus, the block problems caused by filtration and fouling in the heat exchanger tubes can be efficiently resolved in this system. In an actual engineering application, the characteristic parameters of USSHP system are tested under typical operating conditions for heating status. Based on the test results, the performances of the USSHP system are examined. The results indicate that the thermal resistance of the convective heat transfer and fouling on the sewage side in the sewage exchanger is 80% of its total thermal resistance. The COP of the heat pump unit and the COP of the USSHP system are 4.3 and 3.6, respectively.     

Temperature variations near pipes used as a soil source for heat pumps

Calculations have been made to determine the variation with time of the temperature distribution around pipes buried 15 m below the soil surface, assuming the latter to be held at a constant temperature. For a fixed rate of heat extraction it is found that the soil temperatures reach quasi-static conditions in, at most, a few days after extraction commences, implying that simpler theories for steady-state temperatures are applicable. Calculations on the effects of grouping pipes together indicate that the pipes can be considered to be effectively isolated from one another if their separation is not less than 1 m.     

吉林地区地下水地源热泵探析

介绍了地下水地源热泵的工作原理,分析其在吉林市城区使用的可行性,剖析了现已投入使用的吉林地区某市政府办公楼地下水地源热泵机组,并将此机组运行情况与常规锅炉供热方式进行比较,展现了地下水热泵高效、节能、环保的优势。对该热泵机组不合理处提出改造方案,最后分析讨论了地下水地源热泵在吉林地区的发展趋势及应用前景。     

Dimensionless temperatures at the wall of an infinitely long,variable-rate,cylindrical heat source

In geothermal applications the thermal conductivity of rocks is needed, for example, to determine terrestrial heat flow, to evaluate heat losses to the surrounding formations in wells and to design borehole heat exchangers. Cylindrical probes (heaters) with a constant heat flow rate are used in boreholes or in the laboratory to obtain the thermal conductivity of formations and of cementing systems in geothermal wells. A new technique to calculate the temperature at the wall of an infinitely long, cylindrical, time-dependent heat source is presented.     

Temperature distribution in a rectangular plate heated by a moving heat source

In this paper, a solution to the problem of heat conduction in a rectangular plate subjected to the activity of a moving heat source is presented. The temperature of the plate changes because a limited area on the plate surface is heated by a heat source. The heat source moves along an elliptical trajectory which always remains within the plate area. An exact solution to the problem in an analytical form is obtained by applying the Green’s function method. Exemplary results of numerical calculations to determine the temperature distribution in the plate are presented.     

Flow and heat transfer over an unsteady stretching surface with non-uniform heat source

The non-uniform heat source/sink effect on the flow and heat transfer from an unsteady stretching sheet through a quiescent fluid medium extending to infinity is studied. The boundary layer equations are transformed by using similarity analysis to be a set of ordinary differential equations containing three parameters: unsteadiness parameter (S), space-dependent parameter (A?) and temperature-dependent parameter (B?) for heat source/sink. The velocity and temperature fields are solved using the Chebyshev finite difference method (ChFD). Results showed that the heat transfer rate, − θ′(0) and the skin friction, − f″(0) increase as the unsteadiness parameter increases whereas decrease as the space-dependent and temperature-dependent parameters for heat source/sink increase.