Proceeding of Compact Heat Exchangers and Enhancement Technology for the Process Industries - 2003最新文献

Operation of the total heat exchangers (THXs) discussed in this article is based on thin fibrous paper, permeable to moisture but highly impermeable to air, capable of recovering both sensible and latent heat from air. The efficiencies of these exchangers are heavily influenced by air leakage from exhaust air channel to supply air channel, which renders traditional efficiency definitions of heat exchangers ambiguous. A concept of effective fresh air efficiency defined on the basis of per-unit-effective-fresh-air is proposed and the leakage effect on the efficiency is examined with experiments. Experimental results indicate that there might exist a best leakage rate (~12%) in so far as the energy saving is concerned, beyond which the performance of the total heat exchanger is highly unstable. Below the threshold leakage rate, within the experiments conducted in this study, the energy saving ratio of total heat exchanger increases with the leakage rate. INDEX TERMS Total heat exchangers, Energy savings, Heat exchanger efficiency INTRODUCTION The total heat exchangers (THXs) discussed in this article are air-to-air heat exchangers where the heat transfer is through a process of simultaneous heat and mass transfer, containing the latent heat of moisture transfer in addition to sensible heat transfer. Installation of the THXs in ventilation systems helps saving air-conditioning energy by exchanging the total heat between exhaust air and fresh outdoor air. This study focused on the stationary cross-flow type THX, which is constructed by interlacing and stacking moisture-permeable paper (also called functional paper), forming separate flow channels for the outdoor air and the exhaust air while allowing them to exchange heat and moisture across the paper. A typical configuration of the stationary cross-flow THXs is shown in Figure 1. To prevent the air leakage from the exhaust air channel to the fresh air channel, which impairs the ventilation effects, a perfect functional paper should be permeable to moisture but impermeable to air molecules. In real situation, however, the air leakage always exists as long as there is pressure and/or concentration difference between the two sides of the functional paper. The amount of the leakage depends on the material of the paper as well as on the value of the pressure difference. The latter is in turn affected by the flow rates and the configuration of the THXs. In addition to the reduction of the effective ventilation to the conditioned space, the leakage airflow may largely influence the heat transfer process of a THX. This article presents an analysis of the appropriate performance indicators and the characteristics of THXs under the effect of leakage. The analysis is an improvement over the past industrial standards (JRA, 2000) that defined the performance parameters and test methods for the THXs without covering the leakage effects in the definitions of heat exchanger efficiency. ∗ Contact author email: msjeng

本文讨论的全热交换器(THXs)的运行是基于薄纤维纸，透湿，但高度不透气，能够从空气中回收显热和潜热。这些换热器的效率受到从排风道到送风道的空气泄漏的严重影响，这使得传统的热交换器效率定义模糊不清。提出了以单位有效新风为基础的有效新风效率概念，并通过实验验证了泄漏对效率的影响。实验结果表明，在节能方面，总换热器可能存在最佳泄漏率(~12%)，超过该值，总换热器的性能将极不稳定。在泄漏率阈值以下，本研究实验范围内，总换热器节能率随泄漏率的增大而增大。总热交换器(THXs)本文讨论的总热交换器(THXs)是空气-空气热交换器，其传热是通过同时传热和传质过程进行的，除显热传递外，还包含水分传递的潜热。在通风系统中安装thx，通过在排风和室外新鲜空气之间交换总热量，有助于节省空调能源。本研究的重点是固定的横流型THX，它是由透湿纸(也称为功能纸)交错堆叠而成，使室外空气和排风形成独立的流动通道，同时使它们在纸上交换热量和水分。图1所示为固定式横流thx的典型配置。为了防止空气从排风道泄漏到新风道，影响通风效果，完美的功能纸应该是透湿而不透空气分子的。但在实际情况下，只要功能纸的两侧存在压力和/或浓度差，就会存在漏风现象。泄漏量取决于纸张的材质以及压差的值。后者又受到流量和thx配置的影响。泄漏气流除了减少调节空间的有效通风量外，还会对THX的换热过程产生很大的影响。本文分析了泄漏影响下THXs的性能指标和特性。该分析是对过去工业标准(JRA, 2000)的改进，该标准定义了thx的性能参数和测试方法，但没有涵盖热交换器效率定义中的泄漏影响。*联系作者电子邮件:msjeng@itri.org.tw Proceedings: Indoor Air 2002

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引用次数: 0

EXPERIMENTAL AND THEORETICAL INVESTIGATIONS OF A PILOT COMPACT HEAT EXCHANGER FOR HEAT RECOVERY AT THE HAMBURGER ALUMINIUM WERK GMBH 汉堡铝厂热回收中试紧凑型换热器的实验与理论研究

Proceeding of Compact Heat Exchangers and Enhancement Technology for the Process Industries - 2003

Pub Date : 1900-01-01 DOI: 10.1615/978-1-56700-195-2.340

引用次数: 1

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