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Heat flux sensor

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temperature during one cycle of a combustion engine, all types of industrial applications, and research-oriented work where the registration of highly transient temperatures is of importance. The response time of the gauges has been proven to be in the range of a few microseconds. The output of all gauges represents the time-dependent temperature of its measuring part which in this case may significantly deviate from the temperature of the gauge-surrounding heating or cooling environment. For example, in a piston engine a flush wall-mounted temperature gauge registers with its typical response time the variation of the cylinder wall temperature and not the variation of the average gas temperature within the cylinder. The measured time-dependent surface temperature of the gauge and its known thermal properties allow to recalculate the time-dependent heat flux from the heating environment onto the gauge which caused the temperature change of the gauge. This is accomplished by the theory of heat conduction into a semi-infinite body. The design of the gauges is such that during a typical time period of about 10 ms, the requirements of a body of semi-infinite thickness are fulfilled. The direction of the deduced heat flux is perpendicular to the measuring surface of the gauge.
962: 726: 60: 29: 1140:. Generally, heat flux sensors are quite slow and will need several minutes to reach 95% response. This is the reason why one prefers to work with values that are integrated over a long period; during this period the sensor signal will go up and down. The assumption is that errors due to long response times will cancel. The upgoing signal will give an error, the downgoing signal will produce an equally large error with a different sign. This will be valid only if periods with stable heat flow prevail. 20: 1417: 756: 399: 817:. The sensitivity is primarily determined by the sensor construction and operation temperatures, but also by the geometry and material properties of the object that is measured. Therefore, the sensor should be calibrated under conditions that are close to the conditions of the intended application. The calibration set-up should also be properly shielded to limit external influences. 992: 970:
While heat flux sensors are typically supplied with a sensitivity by the manufacturer, there are times and situations that call for a re-calibration of the sensor. Especially in building walls or envelopes the heat flux sensors cannot be removed after the initial installation or may be very difficult
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Summarizing: The intrinsic specifications that can be attributed to heat flux sensors are thermal conductivity, total thermal resistance, heat capacity, response time, non-linearity, stability, temperature dependence of sensitivity, uniformity of sensitivity and sensitivity to lateral fluxes. For the
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To do a calibration measurement, one needs a voltmeter or datalogger with resolution of ±2μV or better. One should avoid air gaps between layers in the test stack. These can be filled with filling materials, like toothpaste, caulk or putty. If need be, thermally conductive gel can be used to improve
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It is difficult to quantify non-uniformity and sensitivity to lateral fluxes. Some sensors are equipped with an extra electrical lead, splitting the sensor into two parts. If during application, there is non-uniform behavior of the sensor or the flux, this will result in different outputs of the two
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Another factor that determines heat flux sensor behavior, is the construction of the sensor. In particular some designs have a strongly nonuniform sensitivity. Others even exhibit a sensitivity to lateral fluxes. The sensor schematically given in the above figure would for example also be sensitive
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must measure convection perpendicular to the face of the sensor to be accurate due to the circular-foil construction, while the wire-wound geometry of the Schmidt-Boelter gauge can measure both perpendicular and parallel flows. In this case the sensor is mounted on a water-cooled body. Such sensors
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Other parameters that are determining sensor properties are the electrical characteristics of the thermocouple. The temperature dependence of the thermocouple causes the temperature dependence and the non-linearity of the heat flux sensor. The non-linearity at a certain temperature is in fact the
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The measurement of heat flux in walls is comparable to that in soil in many respects. Two major differences however are the fact that the thermal properties of a wall generally do not change (provided its moisture content does not change) and that it is not always possible to insert the heat flux
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FHF04SC is a self-calibrating version of the flexible FHF04 heat flux sensor. Sensors that are embedded in construction can sometimes be very troublesome to remove if they need to be re-calibrated (in a lab). Some sensors incorporate heaters in order to be able to leave the sensor in place while
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Special heat flux solutions are used in highly transient temperatures changes. These gauges called Thermocouple MCT, allow the measurement of highly transient surface temperatures. For example, they are typical for testing wind tunnel models in impulse facilities, the change of the cylinder wall
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In a world ever more concerned with saving energy, studying the thermal properties of buildings has become a growing field of interest. One of the starting points in these studies is the mounting of heat flux sensors on walls in existing buildings or structures built especially for this type of
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connected in series called thermopiles are used. General advantages of thermopiles are their stability, low ohmic value (which implies little pickup of electromagnetic disturbances), good signal-noise ratio and the fact that zero input gives zero output. Disadvantageous is the low sensitivity.
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A difficulty during this measurement is that the human skin is not particularly suitable for the mounting of heat flux sensors. Also, the sensor has to be thin: the skin essentially is a constant temperature heat sink, so added thermal resistance has to be avoided. Another problem is that test
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The interpretation of measurement results of heat flux sensors is often done assuming that the phenomenon that is studied, is quasi-static and taking place in a direction transversal to the sensor surface. Dynamic effects and lateral fluxes are possible error sources.
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to reach. In order to calibrate the sensor, some come with an integrated heater with specified characteristics. By applying a known voltage on and current through the heater, a controlled heat flux is provided which can be used to calculate the new sensitivity.
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Heat flux sensors are used for a variety of applications. Common applications are studies of building envelope thermal resistance, studies of the effect of fire and flames or laser power measurements. More exotic applications include estimation of fouling on
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Usually, the thermal resistance and the thermal capacity of the entire heat flux sensor are equal to those of the filling material. Stretching the analogy with the electric circuit further, one arrives at the following expression for the response time:
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To promote uniformity of sensitivity, a so-called sandwich construction as shown in the figure to the left can be used. The purpose of the plates, which have a high conductivity, is to promote the transport of heat across the whole sensitive surface.
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The calibration is done by applying a controlled heat flux through the sensor. By varying the hot and cold sides of the stack, and measuring the voltages of the heat flux sensor and temperature sensor, the correct sensitivity can be determined with:
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The case that the heat flux sensor is used as a radiation detector (see figure to the left) will serve to illustrate the effect of changing fluxes. Assuming that the cold joints of the sensor are at a constant temperature, and an energy flows from
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Another possibility to minimize the temperature dependence of a heat flux sensor, is to use a resistance network with an incorporated thermistor. The temperature dependence of the thermistor will balance the temperature dependence of the
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Typical heat flux plate, HFP01. This sensor is typically used in the measurement of the thermal resistance of and heat flux on building envelopes (walls, roofs). Also, this sensor type can be dug in to measure soil heat flux. Diameter 80
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persons might be moving. The contact between the test person and the sensor can be lost. For this reason, whenever a high level of quality assurance of the measurement is required, it can be recommended to use a self-calibrating sensor.
722:. From this formula one can conclude that material properties of the filling material and dimensions are determining the response time. As a rule of thumb, the response time is proportional to the thickness to the power of two. 742:
As a first possibility, the thermal dependence of conductivity of the filling material and of the thermocouple material can be used to counterbalance the temperature dependence of the voltage that is generated by the
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Gardon or Schmidt Boelter gauge showing the instrument main components: metal body, black sensor, water cooling pipe in and out, mounting flange, and cable. Dimensions: diameter housing is 25mm. Photo shows model
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research. Heat flux sensors mounted to building walls or envelope component can monitor the amount of heat energy loss/gain through that component and/or can be used to measure the envelope thermal resistance,
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can be measured. Heat flux sensors are known under different names, such as heat flux transducers, heat flux gauges, or heat flux plates. Some instruments are actually single-purpose heat flux sensors, like
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Typically, two or three sensors are buried in the ground around a meteorological station at a depth of around 4 cm below the surface. The problems that are encountered in soil are threefold:
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Heat flux sensor mounted on a window. Heat flux sensors can be used like this to determine the R-value or U-value of building envelope materials while they are still installed in buildings.
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sensor in the wall, so that it has to be mounted on its inner or outer surface. When the heat flux sensor has to be mounted on the surface of the wall, one has to take care that the added
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If the sensor is mounted onto a surface and is exposed to convection and radiation during the expected applications, the same conditions should be taken into account during calibration.
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The third aspect of soil is that by the constant process of wetting and drying and by the animals living on the soil, the quality of the contact between sensor and soil is not known.
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The result of all this is the quality of the data in soil heat flux measurement is not under control; the measurement of soil heat flux is considered to be extremely difficult.
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The sensor response time equation above holds as long as the cold joints are at a constant temperature. An unexpected result shows when the temperature of the sensor changes.
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As shown before in the figure to the left, heat flux sensors generally have the shape of a flat plate and a sensitivity in the direction perpendicular to the sensor surface.
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A heat flux sensor should measure the local heat flux density in one direction. The result is expressed in watts per square meter. The calculation is done according to:
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Soil heat flux is a most important parameter in agro-meteorological studies, since it allows one to study the amount of energy stored in the soil as a function of time.
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The measurement of the heat exchange of human beings is of importance for medical studies, and when designing clothing, immersion suits and sleeping bags.
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C.T. Kidd and C.G. Nelson, "How the Schmidt-Boelter gage really works," Proc. 41st Int. Instrum. Symp., Research Triangle Park, NC: ISA, 1995, 347-368
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Heat flux sensors are also used in industrial environments, where temperature and heat flux may be much higher. Examples of these environments are
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However, a well-designed sensor may have a lower temperature dependence and better linearity than expected. There are two ways of achieving this:
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to heat flows from left to right. This type of behavior will not cause problems as long as fluxes are uniform and in one direction only.
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is not too large. Also, the spectral properties should be matching those of the wall as closely as possible. If the sensor is exposed to
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For better understanding of heat flux sensor behavior, it can be modeled as a simple electrical circuit consisting of a resistance,
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First is the fact that the thermal properties of the soil are constantly changing by absorption and subsequent evaporation of water.
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R.Gardon, "An instrument for the direct measurement of intense thermal radiation", Rev. Sci. Instrum., 24, 366-370, 1953.
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contact between layers. A temperature sensor should be placed on or near the sensor and connected to a readout device.
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Doing measurements at different temperatures allows for determining sensitivity as a function of the temperature.
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are used in fire resistance testing to put the fire to which samples are exposed to the right intensity level.
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part. Depending on the application, one might want to measure all three of these quantities or single one out.
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The assumption that conditions are quasi-static should be related to the response time of the detector.
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This shows that one should expect a false reading during a period that equals several response times,
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In order to do in-situ measurements, the user must be provided with the correct calibration constant
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Second, the flow of water through the soil also represents a flow of energy, going together with a
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In order to avoid errors caused by long response times, one should use sensors with low value of
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An example of measurement of conductive heat flux is a heat flux plate incorporated into a wall.
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There are various examples of sensors that internally use heat flux sensors examples are
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Assuming that the sensor temperature starts changing at the cold joints, at a rate of
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An example of a sensor sensitive to radiative as well as convective heat flux is a
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T.E. Diller, Advances in Heat Transfer, Vol. 23, p.297-298, Academic Press, 1993.
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ASTM C1130-17 Standard Practice for Calibration of Thin Heat Flux Transducers
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latter two specifications, a good method for quantification is not known.
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Silicon encased heat flux sensor for measurements on rugged surfaces
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We will discuss three large fields of application in what follows.
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or Schmidt–Boelter gauge, used for studies of fire and flames. The
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for solar radiation measurement. Other heat flux sensors include
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surfaces, temperature measurement of moving foil material, etc.
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derivative of the temperature dependence at that temperature.
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An example of measurement of radiative heat flux density is a
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that generates an electrical signal proportional to the total
1369:"GreenTEG | Heat transfer coefficient of fabrics |" 775: 1347: 182:, which often is misinterpreted by conventional sensors. 67:
The heat flux can have different origins; in principle
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is the sensor response time, the reaction to this is:
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is the calibration constant, specific for the sensor.
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This constant is also called 698:the specific heat capacity and 222:Applications in medical studies 1361: 1324: 1315: 1306: 913:{\displaystyle V_{\text{sen}}} 820: 504:{\displaystyle C_{\text{sen}}} 477:{\displaystyle R_{\text{sen}}} 388:{\displaystyle E_{\text{sen}}} 361:{\displaystyle V_{\text{sen}}} 92:, and Schmidt-Boelter gauges. 48:applied to the surface of the 1: 1300: 278: 966:performing a re-calibration. 829: 202:, or thermal transmittance, 7: 1283: 10: 1459: 1026:, the sensor response is: 940:{\displaystyle \phi _{q}} 920:is the sensor output and 651:is the sensor thickness, 511:and also a response time 368:is the sensor output and 711:{\displaystyle \lambda } 234:Applications in industry 95: 806:{\displaystyle E_{sen}} 1274: 1247: 1221: 1174: 1134: 1105: 1020: 1019:{\displaystyle t>0} 996: 967: 941: 914: 885: 807: 760: 731: 712: 692: 665: 645: 623: 532: 505: 478: 451: 431: 403: 389: 362: 333: 64: 33: 25: 1275: 1248: 1222: 1175: 1135: 1106: 1021: 994: 964: 942: 915: 886: 808: 759:Sandwich construction 758: 728: 713: 693: 691:{\displaystyle C_{p}} 666: 664:{\displaystyle \rho } 646: 624: 533: 506: 484:, a thermal capacity 479: 452: 432: 409:Usually, a number of 401: 390: 363: 334: 62: 31: 22: 1424:at Wikimedia Commons 1257: 1231: 1190: 1147: 1117: 1032: 1004: 924: 897: 841: 784: 720:thermal conductivity 702: 675: 655: 635: 548: 515: 488: 461: 441: 421: 372: 345: 289: 1246:{\displaystyle t=0} 957:In-situ calibration 437:, and a capacitor, 244:solar concentrators 130:for measurement of 1389:ASTM International 1270: 1243: 1217: 1170: 1130: 1101: 1016: 997: 968: 937: 910: 881: 803: 761: 732: 708: 688: 661: 641: 619: 528: 501: 474: 447: 427: 404: 385: 358: 329: 248:coal fired boilers 240:aluminium smelting 212:thermal resistance 151:laser power meters 65: 34: 26: 1420:Media related to 1267: 1215: 1167: 1157: 1127: 1092: 1089: 1055: 1042: 907: 879: 866: 851: 644:{\displaystyle d} 617: 581: 571: 558: 525: 498: 471: 450:{\displaystyle C} 430:{\displaystyle R} 382: 355: 327: 324: 314: 1450: 1422:Heat flux sensor 1419: 1404: 1403: 1401: 1400: 1387:(1.0 ed.). 1379: 1373: 1372: 1365: 1359: 1358: 1351: 1345: 1344: 1337: 1331: 1328: 1322: 1319: 1313: 1310: 1295:Thermocouple MCT 1279: 1277: 1276: 1271: 1269: 1268: 1265: 1252: 1250: 1249: 1244: 1226: 1224: 1223: 1218: 1216: 1214: 1210: 1204: 1200: 1194: 1179: 1177: 1176: 1171: 1169: 1168: 1165: 1159: 1158: 1155: 1139: 1137: 1136: 1131: 1129: 1128: 1125: 1110: 1108: 1107: 1102: 1100: 1096: 1095: 1094: 1093: 1091: 1090: 1087: 1078: 1057: 1056: 1053: 1044: 1043: 1040: 1025: 1023: 1022: 1017: 946: 944: 943: 938: 936: 935: 919: 917: 916: 911: 909: 908: 905: 890: 888: 887: 882: 880: 878: 877: 868: 867: 864: 858: 853: 852: 849: 812: 810: 809: 804: 802: 801: 717: 715: 714: 709: 697: 695: 694: 689: 687: 686: 670: 668: 667: 662: 650: 648: 647: 642: 628: 626: 625: 620: 618: 613: 612: 611: 599: 598: 588: 583: 582: 579: 573: 572: 569: 560: 559: 556: 537: 535: 534: 529: 527: 526: 523: 510: 508: 507: 502: 500: 499: 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589: 587: 578: 574: 568: 564: 555: 551: 549: 546: 545: 538:to the sensor. 522: 518: 516: 513: 512: 495: 491: 489: 486: 485: 468: 464: 462: 459: 458: 442: 439: 438: 422: 419: 418: 379: 375: 373: 370: 369: 352: 348: 346: 343: 342: 321: 317: 311: 307: 305: 296: 292: 290: 287: 286: 281: 272: 236: 224: 216:solar radiation 195: 166: 132:solar radiation 98: 77:conductive heat 17: 12: 11: 5: 1456: 1446: 1445: 1440: 1426: 1425: 1411: 1410:External links 1408: 1406: 1405: 1374: 1360: 1346: 1332: 1323: 1314: 1304: 1302: 1299: 1298: 1297: 1292: 1285: 1282: 1263: 1242: 1239: 1236: 1227:, starting at 1213: 1209: 1203: 1199: 1163: 1153: 1123: 1099: 1085: 1081: 1076: 1072: 1068: 1065: 1061: 1051: 1047: 1038: 1015: 1012: 1009: 985: 982: 976: 973: 958: 955: 934: 930: 903: 876: 872: 862: 856: 847: 831: 828: 822: 819: 800: 797: 794: 790: 777: 774: 749: 748: 744: 707: 685: 681: 660: 640: 616: 610: 606: 602: 597: 593: 586: 577: 567: 563: 554: 521: 494: 467: 446: 426: 378: 351: 320: 310: 304: 299: 295: 280: 277: 271: 268: 260:fluidized beds 252:blast furnaces 235: 232: 223: 220: 194: 191: 187: 186: 183: 176: 165: 162: 97: 94: 15: 9: 6: 4: 3: 2: 1455: 1444: 1441: 1439: 1436: 1435: 1433: 1423: 1418: 1414: 1413: 1394: 1390: 1386: 1385: 1378: 1370: 1364: 1356: 1350: 1342: 1336: 1327: 1318: 1309: 1305: 1296: 1293: 1291: 1288: 1287: 1281: 1261: 1240: 1237: 1234: 1211: 1201: 1184: 1181: 1161: 1151: 1141: 1121: 1111: 1097: 1083: 1079: 1074: 1070: 1066: 1063: 1059: 1049: 1045: 1036: 1027: 1013: 1010: 1007: 993: 989: 981: 975:Error sources 972: 963: 954: 951: 948: 932: 928: 901: 891: 874: 870: 860: 854: 845: 836: 827: 818: 816: 798: 795: 792: 788: 773: 769: 765: 757: 753: 745: 741: 740: 739: 736: 727: 723: 721: 705: 683: 679: 671:the density, 658: 638: 629: 614: 608: 604: 600: 595: 591: 584: 575: 565: 561: 552: 543: 539: 519: 492: 465: 444: 424: 415: 412: 411:thermocouples 407: 400: 396: 376: 349: 339: 318: 308: 302: 297: 293: 284: 276: 267: 265: 261: 257: 256:flare systems 253: 249: 245: 241: 231: 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Retrieved 1383: 1377: 1363: 1349: 1335: 1326: 1317: 1308: 1290:Gardon gauge 1185: 1182: 1142: 1112: 1028: 998: 987: 978: 969: 952: 949: 892: 837: 833: 824: 814: 779: 770: 766: 762: 750: 737: 733: 630: 544: 540: 416: 408: 405: 340: 285: 282: 273: 237: 228: 225: 208: 196: 188: 179: 170: 167: 159: 155:pyranometers 148: 136: 125: 122: 107: 99: 82:pyranometers 66: 37: 35: 821:Preparation 815:sensitivity 747:thermopile. 743:thermopile. 128:pyranometer 90:thermopiles 75:as well as 1432:Categories 1399:2018-05-30 1301:References 279:Properties 114:convective 110:conductive 69:convective 42:transducer 1262:τ 1122:τ 1084:τ 1075:− 1067:− 929:ϕ 871:ϕ 830:Measuring 706:λ 659:ρ 631:In which 615:λ 601:ρ 553:τ 520:τ 294:ϕ 118:radiative 73:radiative 54:heat flux 46:heat rate 1393:Archived 1284:See also 1438:Sensors 768:parts. 204:U-value 200:R-value 157:, etc. 893:where 730:SBG01. 341:Where 264:cokers 143:Gardon 139:Gardon 103:boiler 50:sensor 266:,... 96:Usage 40:is a 1011:> 718:the 116:and 1266:sen 1166:sen 1156:sen 1126:sen 1088:sen 1054:sen 1041:sen 906:sen 865:sen 850:sen 580:sen 570:sen 557:sen 524:sen 497:sen 470:sen 381:sen 354:sen 323:sen 313:sen 1434:: 1253:, 262:, 258:, 254:, 250:, 246:, 242:, 206:. 153:, 134:. 112:, 71:, 56:. 36:A 24:mm 1402:. 1371:. 1357:. 1343:. 1241:0 1238:= 1235:t 1212:t 1208:d 1202:T 1198:d 1162:C 1152:R 1098:) 1080:t 1071:e 1064:1 1060:( 1050:E 1046:= 1037:V 1014:0 1008:t 933:q 902:V 875:q 861:V 855:= 846:E 799:n 796:e 793:s 789:E 684:p 680:C 639:d 609:p 605:C 596:2 592:d 585:= 576:C 566:R 562:= 493:C 466:R 445:C 425:R 377:E 350:V 319:E 309:V 303:= 298:q

Index



transducer
heat rate
sensor
heat flux

convective
radiative
conductive heat
pyranometers
Gardon gauges
thermopiles
boiler
conductive
convective
radiative
pyranometer
solar radiation
Gardon
Gardon
laser power meters
pyranometers
R-value
U-value
thermal resistance
solar radiation
aluminium smelting
solar concentrators
coal fired boilers

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