Description

An experimental and numerical study of fluid flow and heat transfer in residential electric hot water tanks with sidewall inlets is presented in this paper. The semi-empirical model proposed here divides the tank into two distinct regions: a piston-type flow region, where the axial flow velocity is uniform, and a fully mixed uniform temperature region at the bottom of the tank near the cold water inlet. The piston-type region is treated numerically using a quasi-one-dimensional model, while the height of the fully mixed region is based on an experimentally derived correlation.

A full-size transparent tank is used to visualize fluid motion in the fully mixed region. Results of these flow visualization studies, combined with temperature measurements, have led to the development of an empirical correlation relating the rate of growth of the height of the mixed region to the entrance Richardson (Ri) number and a dimensionless time parameter representing the percentage of tank discharge. The results obtained in this study confirm that the effects of mixing cannot be neglected. The semi-empirical model is validated against experimental data for constant and varying inlet Ri

The results for constant Ri agree favorably with the experimental data except at the beginning of the discharge process, where the presence of a small stratification zone cannot be predicted by the model. The results also show that the thermocline and the outlet temperature predictions have a high level of agreement with experimental results. The proposed model is also checked for varying Ri conditions. In this case, the proposed model was able to capture accurately the successive formation of two different fully mixed regions separated by an intermediate thermocline.

Relative humidity sensors are common components in building heating, ventilating, and air-conditioning (HVAC) systems, and their performance can significantly impact energy use in these systems. Therefore, a study was undertaken to test and evaluate the most commonly used relative humidity sensors in HVAC systems, namely, the capacitive and resistive types. The procedures presented here provide a methodology to test and evaluate duct-mounted relative humidity sensors for accuracy, linearity, hysteresis, and repeatability. The test and evaluation procedures presented in this paper are all inclusive in that they range from procuring the humidity sensors to comparing the accuracy of humidity sensors. Specifically, a procedure is presented to both procure humidity sensors from the manufacturers and to maintain quality control by controlling the storage, handling, and movement of the sensor while documenting time and date at each step. Further, it describes the apparatus and instrumentation, along with test conditions, used to perform experiments on humidity sensors. Additionally, it outlines a detailed experimental procedure to evaluate the accuracy of humidity sensors. Finally, a discussion is presented on analyzing and comparing the accuracy of humidity sensors by using test data. The results of the accuracy test and evaluation of the humidity sensors and the results of the linearity, repeatability, and hysteresis evaluation will be presented later.

Units: SI

Citation: ASHRAE Transactions, vol. 111, pt. 1, Orlando 2005

Product Details

Published:

2005

Number of Pages:

7

File Size:

1 file , 540 KB

Product Code(s):

D-25646