Experimental study on titanium heat exchanger used in a gas fired water heater for latent heat recovery

Hot-water supply has high percentage of energy consumption in Japanese civilian sector. Gas water heaters are used in most cases. Therefore, improvement in thermal efficiency of a gas water heater is an important issue for energy saving. In order to improve thermal efficiency of a gas water heater, an additional heat exchanger is required for latent heat recovery from exhaust humid combustion. The purpose of this study is to develop a compact latent heat recovery heat exchanger with a simple configuration. It is necessary for compactness to reduce the gap between the heat transfer tubes. However, the narrow gap will cause stagnation of condensed water. In order to remove the condensed water from horizontal tube bank, three kinds of tubes with different surface treatments, polished tubes, unpolished tube, and smooth tube with circular micro-grooves, were examined. As the result, condensed water was easily removed by the groove with the 0.7mm depth, to avoid the formation of water bridges between tubes. The effect could lead to no deterioration in the heat transfer performance by decreasing the tube clearance to 1.0mm.

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Water heater with heat exchanger of latent heat recovery type

Fuel and Energy Abstracts ◽

10.1016/s0140-6701(03)90791-0 ◽

2003 ◽

Vol 44 (2) ◽

pp. 103

Keyword(s):

Heat Exchanger ◽

Latent Heat ◽

Heat Recovery ◽

Water Heater

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Prediction and Performance of Compact Latent Heat Recovery Heat Exchanger With Small Diameter Tubes

ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference, Volume 2 ◽

10.1115/ht2007-32071 ◽

2007 ◽

Cited By ~ 1

Author(s):

Masahiro Osakabe

Keyword(s):

Heat Exchanger ◽

Power System ◽

Latent Heat ◽

Heat Recovery ◽

Small Diameter ◽

Cooling Water ◽

Prediction Method ◽

Outer Diameter ◽

Exhaust Gas ◽

And Performance

The most part of energy losses in power system such as fuel cells is due to the heat released by the exhaust gas to atmosphere. The exhaust gas consists of non-condensable gas and steam with sensible and latent heat. As a lot of latent heat is included in the exhaust gas, its recovery is very important to improve the power system efficiency. Based on the previous basic studies, a thermal hydraulic prediction method for latent heat recovery exchangers was proposed. For the condensation of steam on heat transfer tubes, the modified Sherwood number taking account of the mass absorption effect on the wall was used. Two kinds of compact heat exchanger with staggered banks of bare tubes of 10.5 or 4mm in outer diameter was designed with the prediction method. The more compactness was obtained with the smaller tubes at a designed heat recovery. The thermal hydraulic behavior in the compact heat exchangers was experimentally studied with air-steam mixture gas. In the parametric experiments varying the steam mass concentration, the temperature distributions of cooling water and mixture gas were measured. The experimental results agreed well with the prediction proposed in this study and the more compactness with the smaller tubes was proved.

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EFFECT OF CONDENSATION ON THE EFFICIENCY OF HEAT RECOVERY VENTILATORS FOR BROILER HOUSES

International Journal of Air-Conditioning and Refrigeration ◽

10.1142/s2010132513500090 ◽

2013 ◽

Vol 21 (02) ◽

pp. 1350009 ◽

Cited By ~ 3

Author(s):

HWATAIK HAN ◽

SANG-HOON NAM ◽

GEON-SOO HAN

Keyword(s):

Heat Exchanger ◽

Relative Humidity ◽

Latent Heat ◽

Heat Recovery ◽

Harsh Environments ◽

Sensible Heat ◽

Outdoor Temperature ◽

Toxic Gases ◽

Temperature Efficiency ◽

Plate Type

This study experimentally investigates the effect of internal condensation on the performance of a heat recovery ventilator. Experiments were performed using a plate-type sensible heat exchanger element that was designed for very humid and dusty environments such as chicken broiler houses. The results of these experiments show that the temperature efficiency considering condensation is always greater than that without considering latent heat. As outdoor temperature decreases or indoor relative humidity increases, temperature efficiency increases owing to an increase in the rate of condensation. The present polypropylene-based sensible heat exchanger element could be a solution for harsh environments because it can discharge condensate water by gravity and is resistant to moisture and other toxic gases.

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