Construction and Operation of a Compact Fine-Wire Psychrometer (Classic Reprint)

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Excerpt from Construction and Operation of a Compact Fine-Wire PsychrometerThe principal difficulty encountered in using unaspirated psychrometric instruments is the need for providing an optimum quantity of water to the wet element while allowing for maximum evaporative cooling of the sensor. In addition, the evaporation process and the resultant cool ing of the air immediately adjacent to the wet element must not in¿uence the response of the dry element. During measurements, it is assumed: that a steady state of relative humidity exists, that the heat required to vaporize water from the wet element is supplied by the air flowing over the sensor, and that the rate of evaporation is a function of the vapor pressure gradient between the sensor and the air. Therefore, for an unaspirated wet sensor to achieve maximum cooling for any given vapor pressure deficit, convective heat transfer must be sufficient to maintain the vapor pressure gradient, hence, maximum evaporation. These criteria can be met by using sufficiently small sensing elements wherein convective heat loss increases with a decrease in element size. A second advantage of very small elements is that the error due to absorption of shortwave radiation decreases with a reduction in size. The theoretical aspects of sensor size and convective transfer of heat, together with design criteria, are discussed in greater detail by Platt and Griffiths (1964) and Powell (1936)About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.