Thermal Performance of a Low-Temperature Heat Exchanger Using a Micro Heat Pipe Array

Abstract

Domestic heat exchangers, even though widely used in industry, are not adequate for studies on low-temperature flue-gas use technologies. Despite spite their limitations, very few theoretical models have been investigated based on practical applications. Moreover, most of the existing studies on heat exchangers have focused particularly on one-dimensional and two-dimensional heat transfer models, while limited studies focus on three-dimensional ones. Therefore, this study aims at investigating the thermal performance of a low-temperature flue-gas heat recovery unit in the cold regions. Specifically, this study was conducted in the context of Changchun of Jilin Province, China, a city with the mean ambient temperature of −14 °C and mean diurnal temperature of −10 °C during winter. Experimental results showed that the thermal efficiency of the heat exchanger was higher than 60%. Through assessing the heat exchange coefficient and heat exchange efficiency of the heat exchanger, it is found that the thermal efficiency had been improved up to 0.77–0.83. Furthermore, the ICEPAK software and the standard k-ε RNG turbulence model were used to carry out simulations. The velocity and outlet temperature of fresh airflow and polluted airflow were simulated through setting different inlet temperatures of fresh air and polluted air inlet. Numerical results further indicated that the flow state was laminar flow. The micro heat pipe array side had small eddies and the heat transfer was significantly improved due to the flow of air along the surface of the micro heat pipe.

Numerical Model of Heat Pipes as an Optimization Method of Heat Exchangers

“…In turn, Zhang and co-authors in [11] proposed an innovative design with dense ribs of less thickness in the upper layer and relatively low ribs of greater thickness in the lower layer to further improve the overall thermal efficiency of a two-layer microchannel heat exchanger; the numerical model was based on similar equations presented in this publication. In the works on numerical modeling [12][13][14][15], the authors use numerical models to optimize heat exchangers, both traditional and heat pipes, and obtain results similar to the results obtained in this publication. Rossome and Ochman, together with their co-authors in [16,17], study numerical processes of heat exchange in thermal energy stores.…”

Review of Recent Applications of Heat Pipe Heat Exchanger Use for Waste Heat Recovery

“…HVAC systems [46,47], heat recovery in the cold regions [48], industrial equipment [49], oil fume heat recovery [50] / HPHXs are constructed based on HPs and typically consist of multiple HPs connected in parallel to achieve larger-scale heat exchange, as shown in Figure 1. In an HPHX, the evaporator end of the HP is placed in a high-temperature heat source, while the condenser end is located in a cooler environment.…”

“…The micro-heat pipe represents a novel class of flat-plate heat pipes, usually with a very small diameter and complex structure, which has the advantages of a rapid thermal response, expansive specific surface area, superior heat transfer capabilities, and low cost. In order to solve the problem of freezing the internal working medium of the heat exchanger in cold regions, Yang et al [48] investigated the structure and characteristics of micro-heat pipe arrays and applied them to low-temperature flue gas heat recovery in cold regions. Furthermore, Yang et al [49] proposed a gas-water heat exchanger utilizing micro-heat pipe technology for waste heat recovery and experimentally analyzed the effects of different inlet temperatures and wind speeds on the heat exchanger.…”

Experimental investigation and optimization of heat pipe heat exchanger performance under two distinct heat transport mediums through TOPSIS approach

“…Yang Jingang et al [22] studied the performance of a gas-water heat exchanger based on micro-heat technology. The work evaluated the effects of various wind speeds and inlet temperatures on the heat transfer output, and from the results, maximum heat transfer was attained for the flue gas inlet temperature of 190 °C.…”