Numerical investigation of conjugated heat transfer in a channel with a moving depositing front

This article presents numerical simulations of conjugated heat transfer in a fouled channel with a moving depositing front. The depositing front separating the fluid and the deposit layer is captured using the level-set method. Fluid flow is modeled by the incompressible Navier–Stokes equations. Numerical solution is performed on a fixed mesh using the finite volume method. The effects of Reynolds number and thermal conductivity ratio between the deposit layer and the fluid on local Nusselt number as well as length-averaged Nusselt number are investigated. It is found that heat transfer performance, represented by the local and length-averaged Nusselt number reduces significantly in a fouled channel compared with that in a clean channel. Heat transfer performance decreases with the growth of the deposit layer. Increases in Reynolds, Prandtl numbers both enhance heat transfer. Besides, heat transfer is enhanced when the thermal conductivity ratio between the deposit layer and the fluid is lower than 20 but it decreases when the thermal conductivity ratio is larger than 2

Thermal Technology)

Cross flow heat exchangers having crimped spiral fin and inline arrangement configurations under dehumidification are studied. The effect of tube diameter, fin spacing, fin height, transverse tube pitch are examined. From the experiment, it is found that the heat transfer and the frictional characteristics of the heat exchanger under dehumidification is close to that of the non-dehumidifying process. However, the air stream pressure drop and the heat transfer coefficient of the wet surface heat exchanger are higher and lower than those of the dry surface respectively. Moreover, equations are developed for predicting the f and the j factors of a tested heat exchanger. Results from the developed equations agree well with the experimental data

Performance testing of cross flow heat exchanger operating in the atmosphere of flue gas particulate with vapor condensation

Performance testing of a cross flow heat exchanger operating under the atmosphere of flue gas particulate from combustion was carried out in this work. This heat exchanger exchanges heat between flue gas from the fuel oil combustion and cold water. The heat exchanger is composed of a spiral finned tube bank having 3 rows and 8 tubes per row with a staggered arrangement. The fin spacings considered are 2.85 and 6.10 mm. The theories of thermodynamics and heat transfer are used for analyzing the performance of this system.In this experiment, the flue gas temperature of 200ºC from combustion having 0.35 kg/s mass flow rate flows along outside surface of the heat exchanger and transfers heat to the 25ºC cooling water having 0.15 kg/s mass flow rate flowing in the tube side. Each experiment uses 750 hr for testing. During the testing, part of flue gas condenses on the heat transfer surface.From the experiment, it was found that the heat transfer rate of both heat exchangers tended to decrease with time while the airside pressure drop increased. These results come from the fouling on the heat transfer surface. Moreover, it is found that the heat exchanger having 2.85 mm fin spacing has an approximately 4 times higher fouling resistance than that of the 6.10 mm fin spacing.In this work a model for calculating the fouling resistance is also developed as a the function of time. The model is developed from that of Kern and Seaton and the mean deviation of the model is 0.789

Performance analysis of solar water heater combined with heat pump using refrigerant mixture

In the research presented in this paper the thermal performance of a solar water heater combined with a heat pump is studied. A solar collector was modified from corrugated metal roofing with a copper tube attached beneath. The performance of the solar water heater was tested, and models for the collector efficiency and storage tank were developed and used for the evaluation of their performance when combined with a heat pump system. The performance of the combined solar water heater and heat pump was investigated using a simulation program. In this analysis, a model for a heat pump using the refrigerant mixture R22/R124/R152a was selected. From the simulation program, the results show that the highest performance occurred at a mass fraction of R22 = 20%, R124 = 57% and R152a = 23%, a compressor speed of 20 rps, and mass flow rate of refrigerant at 0.01 kg/s. The coefficient of performance (COP) of this system is between 2.5 and 5.0. Moreover, economic analysis shows that the suitable mass of hot water in the storage tank is 400 kg and that the payback period for this system is 2.3 years.Solar heat pump Solar collector Simulation program Corrugated metal sheet Refrigerant mixture