Numerical and CFD Design of Heat Exchanger Used to Biomass Combustion

The article describes the design of a heat exchanger used for biomass combustion. The design takes into account simple maintenance of the exchanger, low input costs of construction and the highest possible efficiency. In the design is used the tubular type of heat exchanger. The construction consists of a tubular part - flue gas part, inter-tube space - heat transfer medium space. The output of the numerical model, CFD model is the heat transfer coefficient, heat exchanger power and final comparison of CFD and numerical model outputs.

TO THE QUESTION OF HYDRAULIC COMPATIBILITY OF REPAIR MATERIALS IN FREE-FLOW PIPES IN TRENCHLESS RENOVATION

Experimental studies were conducted in order to determine hydraulic compatibility of repair materials in trenchless renovation of free-flow water outlet pipelines, experimental unit for liquid flow regime investigation during free-flow motion for definition of flow hydraulic element were developed and introduced. It was shown that results of experimental studies allows to receive calculated values of coefficients of relative roughness for three types of polymeric pipes, which can be used as repair materials for pulling in old pipelines. It was observed that during pipelines renewal in such way, it is necessary backfilling of tube space, eliminating formation of polymeric pipelines waviness because of temperature drops and exclusive negative consequences of hydraulics and structural strength

Effects of Tube Space on the Thermal Performance of Water-in-Glass Evacuated Tube Solar Water Heaters

In the present specification of domestic solar water heating systems (GB/T19141), regardless of the type of collectors used in the systems, Q17, the daily heat gain corresponding to the daily radiation of 17MJ/m2 on the collector surface, is a key indication to rate the thermal performance of a domestic solar water heaters. In this work, an attempt was made to investigate effect of the distance between two adjacent tubes in solar tube collectors of a water-in-glass evacuated tube solar water heater (ETSWH) on by theoretical calculations and experimental measurements. Results obtained by simulations and experimental test showed that the tube space had a significant effect on of the ETSWH, the shorter the tube distance, the higher the Q17, thus better the ETSWH performs. However, the actual situation is the case, the shorter the tube distance, the lower the real daily solar gain of the system, thus worse it performs. This implied that Q17 as the indication of thermal performance of the ETSWH is not reasonable, and specifying the tube distance in solar tube collectors of the ETSWH in the technical specification of GB/T19141 is advisable so as to eliminate effect of the tube distance on Q17.

Application of Transparent Enclosure Theory to Solar Energy Absorption by Cylindrical Tubes in Sunspaces

A general matrix formulation for beam and diffuse radiative solar transfer is presented for an enclosure containing partially transparent walls. The general theory is used to study the absorption of radiant solar energy in a building sunspace having a south-facing window and a row of opaque vertical cylindrical-tube solar absorbers. A two-dimensional model is formulated for the sunspace in which a typical cylindrical absorber tube is subdivided into a number of uniform elements and the window and sunspace surfaces are each represented as single elements. The matrix expressions are evaluated for incident solar flux conditions typical for a south vertical window on a clear winter day. The results are presented as dimensionless ratios of absorbed-to-incident solar flux as a function of the tube spacing to radius ratio. The spatial distribution of absorbed solar flux is presented at discrete time interals for the cylindrical tube. Space and time-averaged values of absorbed solar flux are also presented for the cylinder, the window, and the room. The potential application of these results for thermal modeling in passive solar applications is discussed.