M.A. Alsaad

The use of hydrocarbon mixtures as refrigerants in domestic refrigerators

Abstract This paper reports on an experimental study carried out for evaluating the performance parameters of a domestic refrigerator when four ratios of propane, butane and isobutane are used as possible alternative replacements to the traditional R-12 refrigerant. The proposed alternative refrigerants have the advantage of being locally available, cheap and of an environmentally friendly nature. An unmodified R-12 domestic refrigerator was charged and tested with each of the four hydrocarbon mixtures that consist of 100% propane, 75% propane–19.1% butane–5.9% isobutane, 50% propane–38.3% butane–11.7% isobutane and 25% propane–57.5% butane–17.5% isobutane. The parameters investigated are the evaporator capacity, the compressor power, the coefficient of performance (COP) and the cooling rate characteristics. The present work shows that the hydrocarbon mixture with 50% propane–38.3% butane–11.7% isobutane is the most suitable alternative refrigerant with the best performance among all other hydrocarbon mixtures investigated. When this hydrocarbon mixture was used the evaporator temperature reached −16°C with COP of 3.7 at condenser temperature of 27°C as compared to COP=3.6 for the traditional R-12 refrigerant at the same temperatures. The refrigerator worked satisfactorily with the proposed alternative refrigerant without the need for any modification or adjustment.

Characteristic distribution of global solar radiation for Amman, Jordan

Abstract Hourly global solar radiation data measured on a horizontal surface in Amman, Jordan, available for the period 1983–1987, have been studied and analysed. Average values of daily, monthly and yearly global radiation, as well as maximum and minimum radiation values, were determined. The average monthly mean daily global radiation ranged from 8.001 to 2.653 kWh m −2 per day. Over the 1983–1987 period, the annual daily mean of global radiation was 5.302 kWh m −2 per day. The maximum monthly mean daily global radiation varied between 8.295 and 3.611 kWh m −2 per day whereas that of the minimum monthly mean daily radiation varied between 7.590 and 1.680 kWh m −2 per day. The calculated monthly mean daily global solar radiation data were employed to develop linear correlations between the sunshine hours and each of the average, maximum and minimum global radiation for Amman, using regression technique. The accuracy of the derived correlations was tested using measured radiation data for Amman. The results show that the developed correlations are adequate to predict monthly mean daily global radiation within a maximum error ranging between 6.6 and 9.6%. The average error incurred in predicting global radiation does not exceed 0.3%.

Parametric study of a box-type solar cooker

Abstract This paper presents the theoretical analysis and performance investigation of a single, as well as double, glazed box-type solar cooker with or without reflectors. The mathematical model is developed using the heat balance analysis of the various components of the cooker. In the present analysis, the properties of cooking materials and the value of the overall heat loss coefficient are allowed to vary as a function of the absorber plate and food temperatures. The obtained thermal equations are solved on the computer using a stepwise solution which enabled the temperatures of the various elements of the cooker to be predicted. An optimization parametric study has been performed using several important parameters of the cooker. The effect of those parameters on the cooker performance was studied. The results of the theoretical investigation are compared with the experimental results available. The experimental results conform reasonably with the predicted values.

Solar radiation map for Jordan

Abstract In the present paper, a study is made to present the global radiation data available for 24 locations spreading all over Jordan. To achieve this objective, correlations between clearness index and fraction of bright sunshine hours, derived for 10 Jordanian stations, are utilized as measured data of global radiation and bright sunshine hours are only available for those locations. The derived linear regression correlations are used to estimate global radiation for the other 14 stations where only records of bright sunshine hours are available. The results for all stations are presented in the form of monthly global radiation table and annual solar radiation map.

Development and testing of concrete solar collectors

This paper investigates the development and performance of three types of concrete solar collectors made from locally available materials. The only difference between these collectors was the flow passage materials. These passages were made from locally manufactured Galvanized Steel Pipes (GSP). Propyleneglycol (Thermopipe) and Polyvinyl Chloride (PVC) pipes. It was found that concrete solar collector with galvanized steel pipes was as good as local metallic conventional collectors with a daily efficiency as high as 40% compared with 45% for the local metallic conventional one. The time constants for concrete collectors investigated are much higher than metallic collectors, with the value as high as 37.4 minutes.

Simple hourly global solar radiation prediction models

Three simple prediction models of hourly global radiation, namely, a normal distribution model (ND), a half-sine wave model (HW), and a polynomial model (PO), are tested using data for a period of five years of the area of Amman, Jordan. The results show that none of these models alone can adequately represent the tested data. Specifically, the results show that PO model represents the data in about 42% of the hours of the year, the ND model about 32%, and the HW model about 34%. Thus a new model which is a combination of the three simple models developed to provide a comprehensive representation of the tested data. This model is given as follows: rg = Φp(i, h) [a0+a1h+a2h2+a3h3+a4h4]+Φs(i,h) b0 +b1sinπh15 + π2 + Φn(i, h) 1σ2πexp−h22σ2 where h is the hour of the day, i the month of the year, and Φp, Φs, and Φn have 0, 0.5 or 1 values depending on i and h. It is found that this model represents the data in about 74% of the time.

Light-Scattering Study of the Glass Transition in Lubricants

The sound velocity of four lubricants has been measured as a function of temperature and pressure using Brillouin scattering. A change in slope of the velocity as a function of temperature or pressure allowed the determination of the glass transition temperature and pressure. The glass transition data were used to construct a phase diagram for each lubricant. The data indicate that the glass transition temperature increased with pressure at a rate which ranged from 120 to 200 C/GPa. The maximum pressure attained was 0.69 GPa and the temperature range was from 25 to 100 C.

Computational evaluation of solar heating systems using concrete solar collectors

Abstract This paper uses the F -chart technique to evaluate three types of solar heating systems, namely; space solar heating and domestic hot water system (SHDHW), domestic hot water system (DHW) and solar swimming pool heating system (SPHS), using three types of concrete solar collectors, models A, B, and C, and one conventional metallic solar collector. The economical analysis of SHDHW system revealed that the concrete collectors provided about 49 and 63% of the annual load when the collecting area of the solar panel increased from 55 to 88 M 2 (25 to 40% of the building roof area). The corresponding solar contributions when conventional metallic collectors were used are 41 and 53%, respectively. This represents an improvement of the annual solar fraction of about 19% when concrete collectors are used instead of the metallic collectors. It was found that solar heating systems with concrete solar collector models gave higher solar fractions and total life cycle savings than the conventional solar metallic collector.

A GENERAL MODEL FOR THE PREDICTION OF HOURLY DIFFUSE SOLAR RADIATION

A general computer simulation model, ψ, for predicting average hourly diffuse solar radiation, developed and tested for Amman, Jordan, is presented in this paper. This model is based on three simple components with a control function ψ that can be switched on ( ψ = 1) or off ( ψ = 0) or set at half way position between on and off ( ψ = 0.5), The three components which constitute the ψ model are a normal distribution, a half-sine wave, and a polynomial of the fourth degree. These are individually tested as separate models. It is determined that none of them is alone adequately acceptable for the tested data. It is found that for an error of 1% or less, the polynomial model - although it is the best of the three - represents the data for only 18 hours of the year or 10% of the time while the ψ model represents 53 hours or about 29% of the time. The acceptability of the three models increases with an increase of the upper limit of error. If the error is 10% or less the polynomial model represents the data fo...

The applicability of hourly solar radiation models to Amman, Jordan

Abstract Hourly and daily global and diffuse solar radiation data measured on a horizontal surface during the period 1983–1987 for Amman, Jordan are studied and analyzed. The observed ratios between monthly mean hourly to daily global and diffuse radiation are determined. The applicability of various radiation models for the estimation of hourly global and diffuse radiation from daily values of global and diffuse radiation, respectively, for Amman is tested against measured data. The normal distribution curve suggested by Jain [ Solar Wind Technol. 5 , 7 (1988)] is found suitable for predicting hourly global radiation for Amman and it has shown excellent agreement with the observed values amobgst all other models used. The classical equation of Liu and Jordan [ Solar Energy 4 , 1 (1960)] produced satisfactory results of hourly diffuse radiation which are much closer to the observed values as compared to that obtained using other suggested models. Comparison between results obtained using various radiation models is made by calculating the root mean squared error, RMSE, for each model used.