psychrometric properties

04142018, 12:45 PM
Post: #1




psychrometric properties
For those interested in a compact & concise formulation for the Numerical Calculation of psychrometric properties on a calculator, I suggest a perusal of Numerical Calculation of psychrometric properties on a calculator by A.K. Singha, Harpal Singha, S.P. Singh & R.L. Sawhney from PERGAMON at Elsevier Science Ltd (Building and Environment 37 (2002) 415 – 419).
Abstract Simple and precise equations for calculation of saturation vapour pressure in three different temperature ranges are presented in the paper. Input parameters required for calculation of psychrometric properties are wet and drybulb temperatures, dew point and drybulb temperatures and relative humidity and drybulb temperature. In this paper, the equations used for computing saturation vapour pressure may also be used for determining dew point temperature for the entire pressure range. © 2002 Published by Elsevier Science Ltd. Keywords: Drybulb temperature; Wetbulb temperature; Dew point temperature; Humidity ratio; Specifc volume and relative humidity explanatory excerpt: … equations from (1) to (13) are used for the determination of psychrometric properties, if any two psychrometric properties of an air–water mixture are known. (see Table 1) [attachment=5833] (1) Dry and wetbulb temperature, or (2) drybulb and dew point temperature, or (3) drybulb temperature and relative humidity. Thus, Case(1): When Ta and Tw are known: Case(2): When Ta and γ are known: Case(3): When Ta and Tdp are known: … The paper presents three equations for the calculation of saturation vapour pressure in three different temperature ranges 0°C to −40°C, 0°C to 63°C and 63°C to 110°C. The same equations also calculate dew point temperature. The relationships proposed here are valid from −40°C to 110°C. Outside the stated limits, the equations need to be reformulated. The paper also defines various physical and thermodynamic properties of air–water mixture and determines their values by direct calculations. If you are interested & can neither find &/nor download the document, feel free to PM & I'll do my best to facilitate. BEST! SlideRule 

04152018, 06:05 AM
Post: #2




RE: psychrometric properties  
04152018, 11:49 AM
(This post was last modified: 04162018 11:35 AM by SlideRule.)
Post: #3




RE: psychrometric properties
I hope my post on ©Numerical Calculation of psychrometric properties on a calculator is taken as value added to the member(s) on the topic. The material, in my assessment, only offers a different perspective on the material without claim to being simpler, more accurate, more complete etc. I proffer NO such critique of the comprehensive posting(s) by other members on the attendant subject but rather another historical reference on the same, hence the title of the web site, the Museum … Calculators. I would post the ©article in its' entirety except the ©article is still available from ®Elsevier. Perhaps a more seasoned and senior member will PM an alternative from individual downloads to an open post in this forum.
BEST! SlideRule ps: I do reply to PM's (+2) 

04162018, 04:56 AM
(This post was last modified: 04162018 04:57 AM by Ángel Martin.)
Post: #4




RE: psychrometric properties
(04152018 11:49 AM)SlideRule Wrote: I hope my post on ©Numerical Calculation of psychrometric properties on a calculator is taken as value added to the member(s) on the topic. The material, in my assessment, only offers a different perspective on the material without claim to being simpler, more accurate, more complete etc. I proffer NO such critique of the comprehensive posting(s) by other members on the attendant subject but rather another historical reference on the same, hence the title of the web site, the Museum … Calculators. I would post the ©article in its' entirety except the ©article is still available from ®Elsevier. Perhaps a more seasoned and senior member will PM an alternative from individual downloads to an open post in this forum. Yes I agree it's a value added and provides perspective to the same subject. Comparing approaches is always an excellent way to learn! Thanks for posting the references. "To live or die by your own sword one must first learn to wield it aptly." 

04162018, 10:27 PM
Post: #5




RE: psychrometric properties
I've worked in water damage mitigation for over a decade and have used all kinds of psychrometric calculators over the years. I believe specialized nomographs and slide rules were also made but I haven't laid hands or eyes on these myself.
This link explains the use of a pyschrometric chart, which I was taught how to use, but I've only ever used electronic calculators for the task. The one I used most often was sold by the DriEaz company and they called it the "Digital Pyschrometric Calculator." It was made in Taiwan. Notably, it takes about one full second to run grain/specific humidity calculations. I don't remember the exact price but they were surprisingly expensive, over $40 apiece. Below are some pictures: There are a couple of free apps floating around which also perform pyschrometric calculations. 

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