Search

An active regenerative solar still with an area of 1.03 m 2 , enabling one to reuse the latent heat of condensation and sensible heat of brine, is constructed and tested indoors, using a solar simulator for irradiation. In this still, a considerable fraction of the latent and sensible heat is successfully recycled and utilized for preheating the feedstock and recycling air via a falling film evaporator–condenser. The forced thin layer evaporation and film condensation, which are the efficient enhanced processes for heat transfer, are applied in this unit. As a result, the performance ratio of the unit is about two to three times greater than that of a conventional basin-type solar still (single-effect).

The stability of the thin liquid film in a capillary is important to the phase-change heat transfer process in miniature or micro structures. From the basic equations for motion and heat transfer at the interface of the film, its stability is theoretically studied. With evaluation of the effects and relative magnitudes of various driving forces and with the use of long-wave theory in addition to linear stability analysis, the controlling equations are simplified and an evolution equation for the film’s thickness is obtained. Detailed analysis on the evolution equation shows that instability occurs first in the meniscus region and the instability condition varies with boundary conditions, geometrical scales and thermal properties. The numerical results agree well with earlier ones with some favorable extensions and improvements.

In this paper, the preparation of a form-stable phase change material (form-stable PCM)–polyethylene–paraffin compound (PPC) is described. This kind of form-stable PCM is a compound which consists of a paraffin as a dispersed phase change material and a high density polyethylene (HDPE) as a supporting material. Several kinds of HDPEs and paraffins are evaluated as candidate materials for PPC as a form-stable PCM. The structure of the prepared PPC is analyzed by using scanning electronic microscope (SEM) and its latent heat is given by DSC method.

The thermal performance of two different schemes of solar-assisted heat-pump systems has been theoretically studied. In first scheme, the evaporator of the heat pump is taken directly as the solar collecting plate and always maintained at the ambient temperature. As there is no heat loss from the collecting plate, the thermal efficiency of the collector is high and equals the solar absorptivity of the collecting plate. As suggested, the heat-pump evaporator of the second scheme is placed in a novel fresh water solar pond/tank with high efficiency. Since the evaporator operates at a relatively high temperature, the COP of the heat pump can be increased. The calculated results show that the COP of a solar-assisted heat pump using the second scheme is considerably higher than that of the first scheme.

A technique for preparing single heat mirror films with high quality is described. We also present an improved method for evaluating its optical and thermal radiative properties in the infrared region (2.5

Heat transfer in the evacuated collector tube is a three-dimensional laminar natural convection problem driven by buoyancy. Because of its complexity, no effective theoretical model is available despite of limited experimental work which is confined to one aspect. The present work aims to depict the convective heat transfer inside a two-ended inclined tube with East-West symmetric heat input using numerical methods. Based on reasonable assumptions, governing equations of the inside fluid are established. The corresponding discretizated equations are solved by employing numerical methods. The calculated results are displayed for velocity and temperature profiles on different cross-sectional planes, which present the flow pattern characterized by upflow and downflow along the axial direction and adherent flow along the peripheral direction, and the heat transfer process from the wall to the center. Furthermore, the transient Nusselt number and average temperature level are shown and discussed. Finally, the parametric effects of the tube radius and the heat input on the flow and heat transfer are also given.

It is believed that the use of transparent insulation materials (TIM) is prospective in the fields of solar energy and architecture engineering. Semi-transparent films are the basic constituents of some TIM, e.g., honeycomb structure. Two most important characteristics of semi-transparent films are their transmittance for solar radiation and emittance for long wave thermal radiation. In this paper, a technique for determining the optical constants of these films is presented. The thermal radiation properties of several semi-transparent films are reported.

Some interrelated parameters of heat and mass transfer in two phases of pressure rise and constant pressure are obtained by studying the desorption processes of two kinds of cylindrical adsorbent beds, with fins and without fins. Moreover, the effects of equivalent thermal conductivity of adsorbent beds, contact thermal transfer coefficient, heat transfer of fins, condensation temperature, uncondensable gas in the adsorber are analyzed, finally, enhancement of heat and mass transfer has been attained

The traditional hot-probe method, which is developed from the transient hot-wire method, can only be applied to determine thermal conductivity. This kind of method is based on the idealized 'one-dimensional radial heat flow' model. As a matter of fact, the finite length influence of a hot probe on measurement is remarkable when the hot probe is not sufficiently long. The corrected term of finite length for a hot probe is nonlinearly dependent on the thermal diffusivity of the measured sample and the length of the hot probe. In this work the long/short hot-probe method (LSHPM) is developed which can simultaneously determine the thermal conductivity, thermal diffusivity and specific heat of the measured sample. The basic principle of the LSHPM is analysed, the measurement procedure is described, and the relative differences of the measurement results are compared with the values recommended by the Thermophysical Properties Research Center, which are 0.7%, 1.3% and 2.0% for thermal conductivity, thermal diffusivity and specific heat respectively.

This paper presents a new method (the relative transmission fringe depth (RTFD) method) of determining the optical constants and the thickness of semitransparent thin films. It has the following distinctive features: high precision, simplicity, and a self-examining function for the measured results. In order to meet the needs of application and engineering design, the n-F diagram (F is a new parameter which expresses the relative transmission fringe depth) is drawn. From it, n, k and d of films can be determined conveniently and precisely. With this method, the constants and thicknesses of SnO2:I heat mirror coatings, plastic films used in agriculture, and micasheets were determined. The results are in complete agreement with those obtained using a polarimetric meter. Also, the calculated T- lambda curves agree well with the T- lambda curves obtained using a spectrophotometer.

For predicting the thermal performance of integrated and plastic bag solar water heaters, it is important to know the convective heat transfer coefficients (CHTC) between the absorber plate and water. Based on different empirical relations published in heat transfer literature, CHTC from the absorber plate to water are calculated and compared for different cases encountered with integrated and plastic bag solar water heaters. On the basis of comparison, the appropriate empirical relations for the different cases are recommended.